A review of the physical oceanography of the seas around New Zealand 1982

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1 New Zealand Journal of Marine and Freshwater Research ISSN: (Print) (Online) Journal homepage: A review of the physical oceanography of the seas around New Zealand 98 R. A. Heath To cite this article: R. A. Heath (985) A review of the physical oceanography of the seas around New Zealand 98, New Zealand Journal of Marine and Freshwater Research, 9:, 79-4, DOI: 0.080/ To link to this article: Published online: 9 Mar 00. Submit your article to this journal Article views: 360 Citing articles: 38 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9: /85/ $.50/0 Crown copyright A review of the physical oceanography of the seas around New Zealand 98 R. A. HEATH New Zealand Oceanographic Institute Division of Marine and Freshwater Science Department of Scientific and Industrial Research P. O. Box -346, Wellington New Zealand Abstract The paper reviews the physical oceanography of the seas around New Zealand as known up to 98 and includes: deep-ocean water characteristics and mean flow; fronts, tides, and coastal and continental shelf oceanography; and waves and tsunamis. Keywords New Zealand; physical oceanography; currents; tides; temperature; salinity; coastal; waves; tsunamis; flow CONTENTS INTRODUCTION DEEP-OCEAN CHARACTERISTICS AROUND NEW ZEALAND Spatial variations of temperature and salinity Surface temperature and salinity distribution Mid-shelf temperatures Bottom temperatures and salinities Water masses Subtropical and Subantarctic Surface Water Antarctic Intermediate Water Pacific Deep Water Bottom Water Oceanic Fronts Subantarctic Front Subtropical Convergence Tasman Front Mean oceanic circulation Oceanic flow in the Tasman Sea Flow around New Zealand Received 7 October 983; accepted 0 August 984 TIDES The South-west Pacific Semi-diurnal Tide Internal tides Diurnal tidal Continental-Shelf waves Coastal tidal influences Tides in Cook Strait, Marlborough Sounds, and Tasman Bay COASTAL AND CONTINENTAL SHELF OCEANOGRAPHY Coastal harbours and estuaries Short-residence-time coastal inlets Residence time Resonant period Entrance cross-sectional areas Heat budget Tidal asymmetry Tidal energy dissipation Storm events Long-residence-time coastal inlets Fiords, sounds Southern fiords Pelorus Sound Coastal embayments Hawke Bay Tasman Bay Continental Shelf The Maui Development Environmental Study West Coast Project physical oceanography WIND WAVES TSUNAMIS RECENT DEVELOPMENTS ACKNOWLEDGMENTS REFERENCES INTRODUCTION In 973 a summary of the oceanic circulation around New Zealand was presented (Heath 973a). This summary followed the completion of an investigation designed to define the geostrophic circulation around New Zealand (e.g., Garner 969b). The programme, conducted by the New Zealand Oceanographic Institute (NZOI) through the successive summers of the 960s, consisted of occupation of temperature/salinity-with-depth stations out to 00 km offshore from New Zealand in waters over 000 m deep on a km ( latitude)

3 80 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 grid. Under the guidance of D. M. Garner, the surveys built on the pioneering studies of Brodie (960), Garner (96, 96), and Garner & Ridgway (965). A decade has passed since the 973 summary and sufficient progress has been made in further understanding of the physical oceanography to warrant an updated more comprehensive review. In the past decade, studies of the mean circulation have concentrated on areas which appeared particularly complex in the 960s block-survey data. However, direct current observations from around New Zealand indicate that generally the strongest water-movement signal is that associated with the tides (Heath 973b). Consequently, in the natural development of physical oceanography through the 970s and early 980s, there has also been considerable emphasis on tidal studies. In addition, early 970s current observations from the continental shelf of New Zealand's western coast revealed that the non-tidal flow is dominated by local meteorological forces. This has led to studies of the meteorological/ocean coupling both within the Maui Environmental Project (Kibblewhite et al. 98), based at the University of Auckland, and in the West Coast Project, based primarily at the NZOI. Both of these latter studies emphasise the recent trend into integrated multi-disciplinary research. The Maui Environmental Study has also rekindled interest in wind-wave research. This multi-disciplinary approach has also been applied in coastal waters, highlighted by the Pauatahanui Environmental Project (e.g., Healy 980), the Upper Waitemata Harbour Study (Williams & Rutherford 983), studies in the Avon-Heathcote Estuary (Knox & Kilner 973), and the Auckland Combined Cycle Power Station sites investigations (Hydrology c Working Group 980). This review deals first with the broad-scale circulation and distribution of properties and then moves down in an either spatial or temporal scale through tides, continental shelf, coastal embayments, fiord studies, multi-disciplinary studies, tsunamis, and wind waves. It is written mainly with those workers in mind whose fields of interest have some dependence on the physical environment. Each topic goes from the broad to the specific. All the details of specific studies cannot obviously be given. This is especially true for studies of coastal embayments where a compromise has been reached by giving only the overlying principles (one of the major reasons for the studies). The reader is led to the details on each embayment via the bibliography. The zonal limits of the area under discussion are south of the Tropical Convergence (30 S) and north of the Polar Front (60 S). A schematic diagram of the mean ocean circulation around New Zealand and a location of oceanic fronts is given in Fig. ; location of seafloor features referred to in the text are given in Fig.. DEEP-OCEAN CHARACTERISTICS AROUND NEW ZEALAND The overall movement of water in the ocean is not random but, at any one time and place it is made up of movements associated with identifiable physical mechanisms. In shallow water, the most readily recognised flows are those associated with the tides and the direct influence of the wind. Rather more difficult to recognise is the steady-state mean flow, that is, the flow that over a long time gives rise to a nett water movement. In addition, there are repetitive motions, other than the tidal flow, each with a definite cycle time, or period, which depend on the local seafloor topography. An example of this latter movement is seiching within a harbour, the period of the motion depending on the water depth and size of the harbour. Major mean water movements in the ocean are produced by surface winds and the thermohaline forces, resulting from different rates of evaporation/precipitation and heating/cooling. There are strong interactions involved between the water and air, the temperature of the near-surface waters having a strong influence on the overlying air temperature and hence the prevailing wind. In turn, solar heating and evaporation has a major influence on the oceanic water properties. Oceanic waters acquire distinctive properties at their area of origin and retain these properties for considerable periods of time and, therefore, over considerable distances. Observation of the temperature and salinity structure with depth (T/S/D) in the ocean provides a means of monitoring the water characteristics, and therefore the mean oceanic circulation. The T/S/D observations are also the basis of possibly the most widely used technique for measuring ocean currents, the geostrophic method. The use of this method is the prime motivation for taking extensive T/S/D observations of which the NZOI block survey data (Garner 967a, b, 970; Ridgway 970; Heath 975a; Ridgway & Heath 975) is one example. The geostrophic method relies on the fact that in the ocean there is a general balance between the Coriolis Acceleration and the horizontal pressure force (or at the sea surface the gravitational force associated with the slope of the sea surface relative to the horizontal). Wind blowing over the sea tends to drag the water along with it; the resulting surface water speed is usually -% of the wind speed. Under the influence of the Coriolis Acceleration, the water, driven

4 Heath Review of the physical oceanography of the seas around NZ 8 Temperature ( C) Salinity (XCT3)Salinity(X0" 3 ) Salinity (X0" 3 ) Fig. Plots of temperature ( C) and salinity (X Kh 3 ) against depth (m) and salinity against temperature for hydrological stations occupied by the Danish Oceanographic Vessel Dana in December 98 north-east of New Zealand at position latitude 3 35' S, longitude 76 5' W. Fig., Heath 973a. Reprinted from: Tuatara 0:5-40. by the wind, tends to pile up in certain regions, producing a sloping sea surface. The slope (relative to the geoid) is small, the largest difference is c. m with the highest sea level near Japan and the lowest near Antarctica the sea level at North Cape is about c. 0.3 m higher than at Stewart Island (see Fig. 7). The slope of the sea surface (or equally the horizontal pressure force) can be calculated from the density of the sea water, which in turn is calculated from the observed temperature and salinity. Spatial variations of temperature and salinity Surface temperatures and salinity distributions The distribution of surface temperature and salinity around New Zealand in February/March, drawn from data collected in a series of NZOI block surveys, is shown in Fig. 3 and 4 respectively. Charts of these water properties have been produced by Ridgway et al. (975), they cover the latitudes 8-50 S. The surface temperature and salinity range from 5 C and 35.8 X 0 3 in the north to 0 C and 34. X 0 3 in the south. The seasonal range of surface temperatures around New Zealand is about 6-7 C in Subtropical Water and the seasonal salinity range is about X 0 3, (the seasonal temperature range has a minimum on the west coast of the South Island), the maximum values occur in February and the minimum values in August (Ridgway pers. comm.). Seasonal changes in the subsurface temperature structure of the water are illustrated by the differences between the temperature distribution on the continental shelf for summer and winter as found by Garner (969a). Mid-shelf temperatures Garner (969a) made temperature observations around the entire New Zealand mainland in the summer and winter of 967 in water of an average depth of 00 m. In summer he found the isotherms were near horizontal with a well-defined seasonal thermocline developed north of Castlepoint on the eastern coast and Hokitika on the western coast of New Zealand. The surface temperature ranged from 0 C in the north to 3 C in the south. In winter the isotherms were predominantly vertical, and the surface temperature ranged from 6 C in the north to 9.5 C on the northern Canterbury coast. However, in some areas of the South Island west coast, temperatures near the bottom were warmer in winter than summer indicating that advective effects associated with inflow of water derived from the East Australian Current may over-ride the seasonal cycle of warming and cooling. Bottom temperatures and salinities Ridgway (969) has contoured the distribution of bottom temperature and salinity in the area bounded by latitudes 4 S, 57 30' S, longitudes 57 E, 67 W with bottom depths greater than 500 m from extrapolated values from hydrological stations. The bottom salinity within this region was found to vary little from 34.7 X 0 3 below about 3000 m depth. Temperatures less than VC were found below depths of 5000 m south of 35 S and 4000 m south of 45 S; these temperatures are characteristic of Bottom Water. Between these depths and 000 m, bottom temperatures ranged from - C, which is characteristic of Pacific Deep Water.

5 8 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 i D'URVILLE \ CURREN WESTLAND ^CURRENT/ 50 S W 80 c 70 E Fig. General circulation and position of fronts in the South-west Pacific ocean. Above 000 m the bottom temperature range is temperature and salinity other than those at the relatively large and is characteristic of Antarctic actual depth where the specimens are found. Intermediate Water from m and surface water above 500 m. The marked difference between Water these bottom temperatures and salinities compared masses to the surface values and their lack of appreciable Around New Zealand there are 5 main water seasonal variation emphasises the need for caution masses, the surface Subtropical and Subantarctic in correlating biological distribution with values of Waters, and from the surface down, Antarctic

6 Heath Review of the physical oceanography of the seas around NZ 60 E S 50 - { V at the seas u rface aroun d New Zealand contoured from data collected by the NZOI in a series

7 84 New Zealand Journal of Marine and Freshwater Research, 985, Vol W 65 _70 75! W >. ^ = ^ \ Fie 4 Isohaline (X 0~ 3 ) at the sea surface around New Zealand contoured from data collected by the NZOI in a series of Wock hydrological surveys, which in total encompass New Zealand conducted in March of the successive years from Fig. 4, Heath 973a. Reprinted from : Tuatara 0: 5-40.

8 Heath Review of the physical oceanography of the seas around NZ Latitude (Subantarctic Front) S " Ql ' 600' ' 0- Subtropical Latitude 40 convergence I ' ' 700' 800- Fig. 5 Meridional profile of temperature ( C) and salinity (x 0 3 ) along longitude 60 E from Eltanin 6 ( , February 965) and Eltanin 6 (60-658, December to February 966) data. Fig., Heath 98a. Reprinted from : Deep-sea Research 8A(6) : Intermediate Water, Deep Water, and Antarctic Bottom Water. These water characteristics are illustrated by curves of temperature and salinity with depth, and the salinity at a given temperature, for a station immediately north of New Zealand (Fig. ). The surface water masses are separated from each other by oceanic fronts (Fig. ) which are characterised by rapid spatial changes in water properties. Subtropical and Subantarctic Surface Water Subtropical Water, characterised by high salinity and temperature, has its origin in the central Pacific Ocean. The Subtropical Water around New Zealand is derived mainly from the southwards flow on the eastern coast of Australia, the East Australian Current, which is in turn fed by the westwards flowing South Equatorial Current. There may also be some direct entry from the north-east of New Zealand. Subantarctic Water, which is characterised by relatively low salinity and temperature, is driven north in the West Wind Drift within the Circumpolar Current south of New Zealand. The region where these water masses meet is called the Subtropical Convergence (Fig. -6). Antarctic Intermediate Water (AAIW) Antarctic Intermediate Water is thought historically to be derived from low-salinity surface water south of the Antarctic Convergence (Polar Front) (55-60 S) which sinks at the Convergence and travels northwards. The subsurface salinity minimum which is characteristic of the AAIW (Fig. ) has a salinity of about X 0~ 3, located at a depth of about 700 m south of the Subtropical Convergence and 000 m north of the Convergence around New Zealand (Heath 97a).

9 86 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 North Subtropical Convergence South Fig. 6a Schematic representation of the classical open-ocean meridional circulation near the Subtropical Convergence (after Gordon 967, fig. 3). Isolines are of salinity (X 0" 3 ). 500 Q_ <U Q 00 - Subtropical Water ~ D65 D6 D604 D608 D605 Fig. 6b Schematic representation of the meridional circulation near the Subtropical Convergence over the Chatham Rise as deduced from simple diffusive-advective model studies (Heath 976a). Contours are of salinity (X 0 3 ) at longitude 77 40' E (after Heath 976a, fig. ). Fig. 8a, b, Heath 98e. Reprinted from: NZOI summary 8: 5 p km Recently McCartney (977) has suggested the name Subantarctic Mode Water (SAMW) for the thick, subsurface layer of nearly isothermal water (called a thermostad) lying in a circumpolar band immediately north of the Subantarctic Front (Fig. 3 and 5). The Subantarctic Front separates Aust- ralian Subantarctic Water and Circumpolar Subantarctic Water and is located north of the Polar Front. The SAMW formed in the South-east Pacific Ocean and Scotia Sea is, however, identical in temperature and salinity to the AAIW found in the South Pacific and South Atlantic (McCartney 977); the connection between AAIW and SAMW is presently a subject of discussion. The temperature of the SAMW decreases towards the east from about 37 W (south-east of South America). It has a temperature of 8-9 C south of the Tasman Sea but decreases rapidly to about 7 C east of the Chatham Rise (McCartney 977). The relatively weak thermal structure of the Australasian Subantarctic Water over the Campbell Plateau south-east of New Zealand is conducive to the pro-

10 Heath Review of the physical oceanography of the seas around NZ 87 duction of SAMW and probably leads to the sharp decrease in temperature of the Subantarctic Mode thermostad from west to east past New Zealand (Heath 98a). Pacific Deep Water Pacific Deep Water, which is found below the Antarctic Intermediate Water, originates at the surface in the North Atlantic Ocean with some addition from the Mediterranean Sea. It travels southwards in the Atlantic Ocean, eastwards in the Circumpolar Current (where it is modified to form Circumpolar Deep Water), then northwards in the South-west Pacific Ocean; it is characterised by a salinity maximum of about X 0~ 3 at a depth of c m around New Zealand (Warren 970). Bottom Water Bottom Water, which is found below the Pacific Deep Water, is thought to originate mainly through winter cooling and sinking of the water around the Antarctic continental margin, mainly in the Weddell and Ross Seas (e.g., Warren 98). These water masses do not, however, exist in a static situation. They are transported in the ocean currents and at the same time are modified both by mixing and by the external meteorological environment to produce the observed horizontal distribution of the hydrological parameters. OCEANIC FRONTS Between latitudes 30 and 60 S in the South-west Pacific there are 3 major oceanic fronts. From south to north, these are the Subantarctic Front, the Subtropical Convergence, and the Tasman Front (Fig. ). Subantarctic Front This front separates Australasian Subantarctic Water (ASW) from Circumpolar Subantarctic Water (CSW) and has a surface temperature near its northern edge of 8 C and a salinity of 34.5 X 0 ~3 (see, e.g., Emery 977). It is the northern or subantarctic boundary of the Antarctic Polar Front Zone and in the Australasian region was initially described by Burling (96) and called the Australian Subantarctic Front. However, it is now thought to be a circumpolar feature. It is generally located near 50 S but south of New Zealand it is deflected south to lie along the continental slope of the Campbell Plateau (Fig. and ). Subtropical Convergence This front separates Subtropical Water (STW) in the north from Subantarctic Water (SAW) (Fig. - 6). In the New Zealand region it approximately follows the 5 C surface isotherm in summer, the 0 C surface isotherm in winter, and the X 0 'surface-salinity isopleth (Garner 959a). The Subtropical Convergence (Fig. ) is continuous around southern New Zealand, passing from south-west of New Zealand north-eastwards through the Snares Depression (300 km south of Stewart Island) along the continental shelf of the eastern coast of South Island and through the Mernoo Saddle (at 43 40' S). On the eastern coast of South Island the front which in the open ocean is called the Subtropical Convergence is called the Southland Front. The position of the Southland Front north of the Mernoo Saddle is variable depending on the circulation. It may extend towards Kaikoura (Fig. ) or as far north as the eastern coast of North Island before turning south to join with the Subtropical Convergence along the Chatham Rise (Fig. and 6) (Heath 97a, 975b; Robertson et al. 978; Gilmour & Cole 979). East of the Chatham Rise the Subtropical Convergence generally projects southwards as a tongue-like feature (Heath 98a). Analytical models of the meridional flow at the Subtropical Convergence over the Chatham Rise (Heath 976a) suggest that the meridional flow component is towards the north near the surface, decreases with depth, and is towards the south near the bottom (Fig. 6) this differs from that of the classical open-ocean meridional circulation (Fig. 6). Recent current-meter observations agree with the analytical model results, although not too much significance should be placed on these current measurements which extended over only 34 days (Heath 983a). Tasman Front The Tasman Front (Stanton 969, 973a, 975, 976a, 979, 98; Stanton & Hill 97) extends across the northern Tasman Sea from the East Australian Current (Fig. ). It was formerly called the Mid-Tasman Convergence (Stanton 979) because it was thought to be the boundary between water that moved directly across the Tasman Sea from the East Australian Current and that which took a more circuitous route further south in the Tasman Sea. Accumulated data from the Tasman Sea (Denham & Crooks 976; Stanton 979, 98; Andrews et al. 980) show the Tasman Front as marking the position of a zonal jet needed to connect the western boundary current off the eastern coast of Australia (the East Australian Current) to the flow east of New Zealand (see below). Unlike

11 88 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 the other fronts in the New Zealand region it is not a water-mass boundary but is associated with the dynamics of the flow. The surface temperatures change by - C across the Front and salinity by X 0 3. Meanders in the Tasman Front's position are probably related to the variability of the East Australian Current system as well as the influence on the flow of the Tasman Sea ridge system, the Lord Howe Rise, and Norfolk Ridge. Mean oceanic circulation If the extensive New Zealand submarine platform (Fig. ) did not exist the flow in the position of New Zealand would be dominantly zonal. The presence of New Zealand has a strong influence on the flow not only through the obvious physical barrier it presents but also through the dynamic control of the rugged seafloor topography (Bye et al. 979). Oceanic flow in the Tasman Sea The circulation on the West Coast of New Zealand is closely connected with the southwards circulation along the eastern coast of Australia, the East Australian Current. Godfrey et al. (980), in reviewing all the available data, found that the East Australian Current system differs either side of a line lying roughly south-south-east from the Australian coast at 3 0' S. Near this latitude on the east Australian coast there is a sharp change in the orientation of the coast. North and east of this line the circulation appears to consist of large eddies elongated meridionally or open to the north, whereas south of this line the circulation consists of small near-circular eddies. An eastwards flow leaves this current system (along 58 E at 3 S in Stanton's 979 data (Stanton 98)) and meanders towards the east over the Lord Howe Rise and Norfolk Ridge (Fig. and ) and north-west of New Zealand. The associated baroclinic structure in this flow, identified by the slope of the temperature and salinity isopleths in vertical sections, and sharp surface gradients, is termed the Tasman Front. Stanton (98) gives typical values of volume transports of 5 X 0 6 m 3 s ' in the Tasman Front compared with 35 X 0 6 m 3 s~' in the East Australian Current, i.e., about half of the flow in the East Australian Current recirculates. The presence of an intense flow directed mainly zonally across the Tasman Sea supports Warren's (970) proposal that the flow of water in the East Australian Current system might be connected to the flow east of New Zealand by a zonal jet across the Tasman Sea north of the northern tip of New Zealand. The zonal jet was proposed because meridional velocities (u) in the Tasman Sea were specified to be small by the wind-stress curl 7 X x: (i.e., V X t = 5f u where B = 5y f the Coriolis parameter, y the co-ordinate positive towards the north), and an eastern boundary current off the western coast of New Zealand would violate vorticity requirements. This then has been proposed as the large-scale constraint which the circulation is required to meet with the details depending on the smaller topography (Godfrey et al. 980; Stanton 98). Admitting a variable-depth ocean, however, there is the possibility of the vorticity balance in an eastern boundary current being achieved by transport across isobaths on the continental slope (Heath 980a). Observations of the geostrophic flow west of New Zealand indicate that, over the latitudinal extent of New Zealand, well offshore there is significant zonal flow (Fig. 7; Heath 980a). Indeed, flow along the southern flank of the Challenger Plateau, and some of the flow from north of the Challenger Plateau, turns southwards along the south-western coast of South Island (Stanton 976b) to contribute to the northwards-flowing Southland Current (Heath 97b, 975a) on the eastern coast of the South Island continental slope and shelf. There is, however, a pronounced increase in of the current speed north-west of New Zealand over the Norfolk Ridge (Fig. 3 and 0; Garner 970; Stanton 979) with which the Tasman Front is associated. The fact that there is considerable zonal volume transport in the Tasman Sea over the latitudinal range of New Zealand, with associated meridional currents on the New Zealand west coast (Stanton 976b), would suggest that the influence of the bottom topography is important. The zonal volume transport towards the east, relative to a reference depth of 500 m over the Norfolk Ridge (Stations ; Fig. 8, 0, and ), is 9. X lomr whereas that along the Challenger Plateau (Stations ; Fig. 8, 0, and ) is 7.6 X 0 m s'. That Warren's (970) proposal also appears to have observational support might suggest that the baroclinic shear may be sufficiently strong to diminish influence of the bathymetry. A close examination of this suggestion, which would involve detailed analysis of baroclinicity of the flow in the Tasman Sea, has not as yet been completed. However, evidence supporting the suggestion is provided by the available information on current shear (Heath in press). Comparison of the horizontal current shear between pairs of stations in the Tasman Sea shows that, in the East Australian Current and over the Lord Howe Rise and Norfolk Ridge, currents decrease rapidly with depth to 0-0% of their surface values in the upper 500 m whereas, over the

12 Heath Review of the physical oceanography of the seas around NZ 89 Latitude ( S) Lord Howe Rise Challenger Plateau Fig. 7 Dynamic height anomalies (dynamic metres) between indicated depths along c. 66 E meridian from latitudes 7-48 S west of New Zealand (from data collected by Garner (967b, 970). Fig. 6, Heath 980a. Reprinted from : New Zealand Journal of Marine and Freshwater Research 4(): 69-8

13 90 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 al-000 Geopotential (m s ') 0 0- Fig. 8 Geopotential depth profiles for pairs of stations in a line approximating the 65 E meridian west of New Zealand. Station positions are shown in Fig. 0. Fig. 6 of Heath in press. Reprinted from : Australian Journal of Marine and Freshwater Research- New Caledonia Trough and in the Tasman Basin, the near-surface shear is less (e.g., Fig. 9, 0, and ). The zonal "Scorpio" (Stommel et al. 973) sections of properties across the Pacific Ocean and Tasman Sea at 8 and 43 S clearly show that the deep water below about 500 m in the New Caledonia Trough (Fig. ) is not connected to that south and west of the Lord Howe Rise in the Tasman and East Australian Basins. For example, the salinity below 500 m depth in the New Caledonia Trough does not appear to be influenced by the salinity maximum of the Pacific Deep Water evident in the Tasman and East Australian Basins. These facts suggest that although the currents over the shallow ridges respond to the bottom topography, the baroclinic shear severely reduces the influence of the ridges. The picture that emerges then (in terms of the mean situation) is that the baroclinic structure of the East Australian Current is largely determined by the source waters in the northern Tasman and Coral Seas. In turn, these waters are derived from the Equatorial Pacific where the current shear in the upper 500 m is large and the shear below 500 m is small (cf. Wyrtki 974, fig. 3 and 6). The slope of the isopycnals which give rise to this current shear is consistent with thermocline model solutions (see e.g., Veronis 969) which are forced by the vertical Ekman suction attributable to the oceanic-scale winds. Meridional isopycnal plots along the central Pacific Ocean show the current shear in the upper 500 m weakening towards the south between 30 and 50 S before strongly increasing in the Circumpolar Current (see, e.g., Reid 965). The weakening in the shear is evident in thermocline models (see, e.g., Veronis 98) but is also attributable to the presence of relatively uniform Subantarctic Mode Water (McCartney 977) formed immediately north of the Subantarctic Front; formation of this water is not included in the thermocline solutions. The eastwards baroclinic zonal flow across the northern Tasman Sea is relatively weak compared to that in the East Australian Current eddies except where it is forced over the shallow topography of the Lord Howe Rise and Norfolk Ridge. The increased vertical shear over the shallower bottom topography is associated with the increased flow which is needed to maintain continuity. This increased vertical shear is also evident in the flow near the Kermadec Ridge north-east of New Zealand (Fig. 9, 0, and ) but is not present over the intervening deep regions (Heath in press). A complimentary explanation of the difference in current shear can be given in terms of the modal structure of Rossby Waves (long waves associated with the latitudinal variation in the Coriolis Parameter). In middle latitudes in the Pacific Ocean only the barotropic and first baroclinic-mode Rossby Waves are sufficiently fast to propagate against the mean eastwards zonal flow. Therefore, the baroclinic current structure off the New Zealand east coast would be expected to be that of the first baroclinic mode (i.e., with little shear as observed). The deep western boundary of the South Pacific Ocean is the Kermadec Ridge. Rossby Waves cannot propagate unhindered over this ridge (Heath 975c; Huthnance 98). However, a baroclinic Rossby Wave may adjust by shifting the node in the vertical structure of horizontal currents to near the top of the ridge (see, e.g., Veronis 98) giving rise to strong baroclinic shear over the ridge. In terms of Rossby Waves the strong shear in the East Australian Current may be produced by baroclinic Rossby Waves (mainly the first 3 baroclinic modes) which propagate and are advected into the area immediately south of the equator or

14 Heath Review of the physical oceanography of the seas around NZ 9 from the topographically modified first baroclinicmode wave propagating from the east over the ridge systems north-west and north-east of New Zealand. Geopotential (m s ) Flow around New Zealand The flow out of the Tasman Sea north of New Zealand gives rise to the East Auckland Current which flows south-eastwards along the eastern coast of North Island, between North Cape and East Cape (Barker & Kibblewhite 965; Heath 980a). Near East Cape the main flow of the East Auckland Current turns north (i.e., that part north of c. 37 S) and the rest turns in a clockwise direction around East Cape giving rise to the southwards flowing East Cape Current (Fig. ). A warm, saline tongue of water extends southwards from East Cape (Heath 975b) the western side of which is the East Cape Current. Within the southern end of this tongue an eddy is located at about 4 S, 78 E. This eddy is evident in all the hydrographic surveys collected to date and is thought to be a permanent feature (Sdubhundhit & Gilmour 964; Garner 967a; Heath 968, 97a, 975b) the question of how much re-circulation there is on this coast of water within the East Cape Current system and the variability of the flow input around East Cape has not been addressed (plans are in hand to answer this question using remote-sensing techniques and satellite-tracked buoys). Satellite thermal imagery indicates that further south (4 S, 76" E) there is another permanent eddy which has been evident in hydrographic surveys but was previously thought to be a transient feature (E. J. Barnes, NZOI, pers. comm.). Water flowing along the southern flank of the Challenger Plateau and along the continental slope on the south-west coast of South Island flows eastwards through Foveaux Strait (Fig. ). Low-salinity Subtropical Water (STW) also flows on to the Snares Shelf from the west and is separated from the less saline cooler water over the Campbell Plateau by the Southland Front (Fig. ), which passes through the Snares Depression (Fig. and ). The Southland Front is most strongly developed over the continental slope on the eastern coast of South Island and is associated with the northwards-flowing Southland Current (Burling 96; Jillett 969; Heath 97b, 975a). It is, therefore, considerably diluted and mixed STW and Subantarctic Surface Water (ASW) that is continuous with the water on the western side of the Southland Front off the eastern coast of South Island. The Southland Current flows northwards along the continental shelf off the eastern coast of South Island (Heath 97b, 975a, b, 976b) and through the Mernoo Saddle (Fig. and ). This Saddle has East Australian Current X Fig. 9 Geopotential-versus-depth profiles in the East Australia Current (EAC), (from fig. 5.3 Andrews 979, not to the same scale as those near New Zealand), from the flow near topographic highs north-west (Stations ) and north-east (Stations ) of New Zealand and east (Stations 63-67) of New Zealand. Station positions are shown in Fig. 0.

15 9 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 I , \ , ^ 0 65 Fig. 0 Dynamic topography (dynamic metres) of sea surface relative to 500 dbar around New Zealand contoured from summer data collected in February-March (Garner 967a, b, 970; Barker & Kibblewhite 969; Ridgway 970, 975; Heath 975a; Ridgway & Heath 975). Fig. 7, Heath 980a. Reprinted from: New Zealand Journal of Marine and Freshwater Research 4() : a maximum depth of 580 m and separates the New Zealand continental slope from the Chatham Rise, which extends 000 km eastwards from South Island (Fig. ). Water from deeper than 580 m on the continental slope south of the Mernoo Saddle is forced upwards through the saddle. Only water deeper than about 800 m does not pass through and flows eastwards. In the horizontal plane a cool, low-salinity tongue protrudes north from the Mernoo Saddle; the western side of the tongue is the Southland Front and the eastern side the Subtropical Convergence (Heath 97b). One component of the Southland Current turns offshore near Kaikoura, and the other can extend as far north as 40 S close inshore (Fig. ). Most of the water in the latter component sweeps across the southern end of Cook Strait around Cape Campbell. The mean circulation in Cook Strait has been deduced from drift-card records (Brodie 960; Heath 969) and changes in water characteristics (Garner 953, 954, 959a, b, 96; Heath 97).

16 Heath Review of the physical oceanography of the seas around NZ 93 Fig. Bathymetry around New Zealand (m) (from Carter 980) showing the major topographic features.

17 94 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Warm saline Subtropical Water in the D'Urville Current sweeps into Cook Strait from the northwest (Brodie 960; Heath 969) this current is derived from the Westland Current flowing northwards along the western coast of South Island. The water of the Southland Current in Cook Strait mixes with water from the D'Urville Current flowing in from the north, and with water over the Cook Strait Canyon derived from the East Cape Current. Water from the Southland Current may extend across the head of the Marlborough Sounds at the northern end of the South Island. Mixed water derived from all three currents travels eastwards across Cook Strait and around Cape Palliser to meet the water of the Southland Current, that has diverged seawards between Kaikoura and Cook Strait. There is evidence that the non-tidal surface flow in Cook Strait may be strongly influenced by meteorological conditions (Bowman et al. 983a, b) a particular example is provided by drogued radiotracked buoys moving rapidly south-eastwards through Cook Strait under south-eastwards-directed wind conditions (Bowman et al. 983a, b; Kibblewhite et al. 98). Other current measurements in the Strait exhibit a slow mean flow towards the north-west (Heath 980b). The Southland Current turns eastwards and back southwards south of Hawke Bay (usually near Cape Turnagain) combining with the East Cape Current. The combined Southland Current and East Cape Current water, after flowing south to about the latitude of Cape Palliser, turns east then north to form the outer arm of the East Cape Current System. Recent satellite imagery indicates that this flow on the east coast of New Zealand is highly variable and complex (E. J. Barnes, NZOI, pers. comm.). TIDES The rhythmic tidal rise and fall of sea level in coastal embayments is familiar to New Zealanders. These tides are produced by the gravitational attraction of the moon and sun on the waters of the earth; the attraction is greatest on the water directly below the moon or sun and least on the opposite side of the earth furthest away from the moon or sun. At both of these points the attractive force away from the earth is larger than at the centre of the earth. With the earth rotating one revolution each 4 hours relative to the sun (a solar day) and 4.8 h relative to the moon (a lunar day), any location on the earth (except at the north and south geographic poles) will experience a rhythmic rise and fall in gravitational attraction with maxima and minima each day. This gravitational attraction induces tidal currents which in turn, because of their variability from place to place at any one Table Time interval between new or full moon and the occurrence of spring tide (from Bye & Heath 975). Location A. West Coast Norfolk Island Kawhia New Plymouth Westport Greymouth B. Cook Strait/Tasman Bay Nelson Porirua C. North-east Coast Russell Auckland Tauranga D. East Coast Gisborne Napier Wellington Lyttelton Timaru Bluff Campbell Island Time interval (hours) time, lead to the observed rise and fall in seasurface elevation. With a few exceptions (namely on the Fiordland coast) the tidal currents on New Zealand's continental shelf are sufficiently large that over a tidal cycle the observed water flow changes in direction as well as speed, that is the tidal currents are stronger than any other flow component. On the New Zealand coast, the tidal currents are at a maximum and are directed anti-clockwise around New Zealand at high tide, and clockwise at low tide (Bye & Heath 975). In enclosed waters the maximum inflow generally occurs c. 3 h before high tide and the maximum outflow 3 h after high water. Because of the dynamic effects associated with these tidal currents (e.g., friction and the Coriolis Acceleration) and the restraining influence of the land, the lunar and solar tidal distributions are more complicated than that of the equilibrium tide, where the high tide occurs when the moon or sun is on the same meridian or at its antipode. In fact, only in Foveaux Strait does high lunar tide occur when the moon is on the same meridian, and only near Greymouth does high solar tide occur when the sun is on the same meridian. The New Zealand tidal regime is most interesting in that the phase of the main lunar and solar tides embraces the complete range of phases from degrees (Fig. and 3). Stated another way,

18 Heath Review of the physical oceanography of the seas around NZ 95 Fig. Contours of the observed phase of the principal lunar semi-diurnal tidal constituent (M ) around New Zealand. The observed values of the amplitude (m) and phase ( ) are also shown. Fig., Heath 977a. Reprinted from : New Zealand Journal of Marine and Freshwater Research () : this means that at any particular time there is a high tide somewhere on the New Zealand coast. When the times of maximum solar and lunar tidal elevation coincide we have the condition known as spring tide when the reinforcing tides give rise to a maximum in the range of the sea-surface elevation between low and high tides. Conversely, when the solar and lunar tides are opposed to each other (i.e., 80 out of phase) the tidal range is smallest and the condition is known as neap tide. In general, spring tide on the New Zealand coast occurs several hours to several days after new or full moon (Table ). In some constricted areas the time of high tide changes very rapidly from place to place, namely in Cook Strait (where high tide at Porirua occurs c. 4h after that at Wellington (Heath 974a, 978a)), through Foveaux Strait, and around the northern tip of New Zealand. As a consequence, strong tidal flows are encountered in these regions. The South-west Pacific semi-diurnal tide As mentioned above, the semi-diurnal tides exhibit a full range of phases around the New Zealand coast from Bye & Heath (975) have shown that

19 96 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Fig. 3 Contours of the observed phase of the principal solar semi-diurnal tidal constituent (S ) around New Zealand. The observed values of the amplitude (m) and phase ( ) are also shown. Inaccuracies in the phase estimates for the small S tide on the central east coast of New Zealand preclude specification of contours of equal phase. Fig. 4, Heath 977a. Reprinted from : New Zealand Journal of Marine and Freshwater Research () : the observed M -tidal elevations around New Zealand are consistent with topographic trapping by the New Zealand continental shelf and slope of a wave incident from the north-east. Their solution also has an amphidrome south-east of New Zealand in approximately the same position as evident in world-scale numerical tidal models (see, e.g., Hendershott 97; Accad & Pekeris 978). Tidal admittances in the semi-diurnal band around New Zealand, decrease sharply for those constituents with periods of less than. hours, that is, the admittances are appreciably smaller for the T, S, and K constituents than for U, N, M, and L. This decrease is more pronounced on the eastern coast of New Zealand than on the western coast. An explanation for the change in admittance has been given (Heath 98b) based on analysis of the two largest serni-diurnal constituents lying either side of the break in the admittances, the M tide with a period of.4 h and the S tide with a period of h. He concluded that the M, tide around New Zealand has a dominant progressivewave component, which is trapped by the New Zealand continental shelf and slope, and only a

20 Heath Review of the physical oceanography of the seas around NZ 97 s. X) 3l/J C e bee 43 u o c g Z T3 C rou c 3UI3. easui S rrent 3 o tuent ( sti c o "3 rnal 3 -di c 3 jor e para dal s.depi H 8 itatioi o rreni eter 3 U Ofi c 8 Reteren a llipticity LU H (cm s ; to "^ "B. c B a S PQ o d oo a! o ON! d o 8 cd o o X) 'a ^^SS.S 8 x> O Obse 00 OS ot o - g xj u E 8 Xi O q d [ " H ON*i t [ *-->i ^ O t-i O r^. y-, CJ -*5 Q) --H 5 P - o i- o i- >ri oo i4_ o ^- o ^ - - o o S ^ # x) ^ xi -^ Tf ON I "7 00 QO 4 o - 4 o ^ o 4 tn tn c small standing-wave contribution. In contrast to the M tide, the S, tide has a dominant standing-wave component on the western coast of New Zealand and only a weak trapped progressive-wave component. Differences in the relative strength of the progressive and standing waves arise from the relative strength of the tidal energy incident from different directions which initially result from spatial differences in the tidal distribution of the semidiurnal constituents in the North Pacific Ocean (Heath 98c). Little of the standing-wave component is transmitted around southern New Zealand from the western to the eastern coast (Heath 979a, 98b) and as a result the observed S -tidal admittances are small. Essentially, the eastern coast of New Zealand lies in the shadow of the semi-diurnal wave which is incident approximately perpendicular to the western coast (and produces the standing wave there), whereas the progressive-wave components are trapped on the continental shelf and slope and pass with little loss around southern New Zealand. Only recently have long-term current observations been made which allow further testing of the above analysis which is based on tidal elevational amplitudes and phases. To date there have been 4 major sets of current observations made offshore near New Zealand which have been subject to tidal analysis; in the South-west Pacific Basin, on the Subantarctic slope bordering the eastern side of the Campbell Plateau, on the Chatham Rise, and off the western coast of South Island. (Details of the analyses are given in Table.) All 4 sets indicate that the main tide is in the form of an M barotropic progressive wave with an anti-clockwiserotating-ellipse with small ellipticity. The observations from the South-west Pacific Basin have an S tide consistent with a free wave. This agrees with the analysis based on the tidal elevation alone (Heath 98a). These current observations have revealed other interesting features of the tides, namely strong internal tides, and stronger-thanexpected diurnal tidal flows. BUI 3 tor tl a g. hpse ] lysis. 3 c atio 3 (^ o ra c/) PQ oo M o<» o E w Ov u 43 Internal tides Internal (baroclinic) tides are associated with the vertical movement of the density surfaces within the water column as opposed to the familiar barotiropic tide which is associated with the movement of the sea surface itself. Internal tides may be broken down into a series of vertical modes, each with its own distinct vertical distribution of horizontal currents. Each baroclinic mode has the same frequency as the corresponding barotropic tide (the mode which has no change in current with depth) but a different wavelength which is less than that

21 98 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 of the barotropic tide. The observations from the South-west Pacific Basin indicate that in the eastwest M flow components, 6% of the variance is in the first baroclinic-mode internal tide and 7% is in the barotropic tide. In contrast, the respective values for the north-south component are 7 and 83%. Whereas the barotropic tidal ellipse has an ellipticity of 0.06 and is oriented (3 T) approximately parallel to the New Zealand land mass (00 km distant), the first baroclinic mode ellipse has an ellipticity of 0. and is oriented approximately perpendicular (7 T) to the most likely generation site, the Subantarctic Slope, which is 650 km distant (Fig. ). The first baroclinic mode appears to be phase-coherent with the barotropic tide (and hence the tide-generating force) which is remarkable, for its wavelength is only 7 km (Heath 983b). On the Chatham Rise the variance of the first baroclinic mode in the north-south and east-west directions of the M tide is 5 and % respectively compared to 70 and 69% in the barotropic tide (Heath 983a). An analysis of the current observations from off the western coast of South Island suggests that the amplitude of the M internal tide is about the same as that of the barotropic tide (3-4 cm s~') whereas the S internal tide is substantially larger than the S, barotropic tide (Heath 984). One reason for the strong internal tide on the western coast is that the standing-wave tidal components are larger there than on the eastern coast and the associated (and observed) flow component directed up the bottom slope is conducive to the production of internal tides. This strong internal tide with its associated substantial variation in depth of the isopleths and water flow over a tidal cycle (Stanton 978a) could have a strong influence on the movement of sediment and upwards mixing of nutrients. Diurnal tidal Continental-Shelf waves In the current observations from the Subantarctic Slope bordering the eastern side of the Campbell Plateau and from the Chatham Rise, the diurnal tidal flows are unusually large. For example, the admittance of the K,-tidal currents relative to the admittance of the M -tidal current changes from c. 0.4 to 3.5 over the 000 km westwards from the flat South-west Pacific Basin to the Subantarctic Slope. In the Chatham Rise observations, the ratio of the observed flow to elevational (at Lyttelton) amplitudes is 0. for the M tide and 0.9 for the K, tide. These stronger-than-expected diurnal tidal flows are consistent with the generation of continental shelf waves (Heath 983a, b) trapped waves which are non-divergent and therefore may have associated large currents with only small expression in terms of tidal elevation. As with the internal tides, the currents associated with these continental shelf waves are likely to influence sedimentation and mixing. Coastal tidal influences The presence of a complete phase range around New Zealand in the semi-diurnal tides leads to abnormally strong tidal currents where the phase changes rapidly around the Northland Peninsula, in Foveaux Strait, and in Cook Strait (Fig. and 4). In these areas the flows are large enough to transport sediment (elsewhere on the coast, except in shallow water, other flow components superimposed on the tides are needed before sediment is transported (Carter & Heath 975)). However, present current observations indicate that only around northernmost New Zealand does the tidal asymmetry dominate the time-averaged mean flow and therefore determine the direction of peak flow and therefore the direction of sediment transport (Heath 98 Id). Cook Strait is the only opening in the main New Zealand landmass. The semi-diurnal tide progressing anti-clockwise around New Zealand is c. 50 out of phase (Fig. 4) at the latitude of Cook Strait. Therefore interesting effects arise both in Cook Strait and in the adjacent Marlborough Sounds and Tasman Bay. Tides in Cook Strait, Marlborough Sounds, and Tasman Bay Out-of-phase semi-diurnal tidal progressive waves enter the Narrows of Cook Strait from the western and eastern coasts and each reflects, where the Strait widens out, after passing through the Narrows (Heath 974a, 976c, 978a). Each wave reflects, with an open-mouth reflection, conditions whereby the tidal elevation is zero. That is, the observed small tidal elevation (Q, rapid change in phase of the tidal elevations (Fig. 4 and 5), and fast tidal currents (u) in Cook Strait are adequately represented by: L, = A cos cot sin kx + B cos (cot <(>) sin k (L-x) u = yjgh [ A sin cot cos kx + B sin (cot - (}>) cos k (L - x)] where the x co-ordinate is directed through Cook Strait positive towards the south, x = 0 where the wave advancing from the south-east (with amplitude A/) reflects as the Narrows of Cook Strait widens towards the north-west, L = distance through Cook Strait, x = L where the wave advancing from the north-west (with amplitude B/)

22 Heath Review of the physical oceanography of the seas around NZ 99 Fig. 4 Lines of equal phase of the lunar (M ) and solar (S ) semi-diurnal tidal constituents in Cook Strait contoured from the data shown (after Heath 977b.) reflects as the Narrows of Cook Strait widens towards the south-east, (j> the phase lag of the wave advancing from the north-west at x = 0 relative to that advancing from the south-east at x = L, g the acceleration of gravity, h the water depth, and co and the angular frequency of the M tide with wavenumber k. Currents in Cook Strait have been measured using log ships (Hydrographic Branch 960) and by fitting relative tidal flow harmonic constants, analysed from electric potential measurements made by Gilmour (960), to the tidal amplitude evident from trajectories of Cook Strait swimmers (Heath 980b). Mean flows appear to be small ( m s~') (Heath 980b), although Bowman et al. (980) have estimated the tidal residual flow generated by a non-linear M -tidal numerical model of the greater Cook' Strait region to be 0.3 ms towards the south. It would appear likely that the day-to-day mean flow would be highly variable in Cook Strait depending on meteorological conditions both in Cook Strait and its surrounds the drogue measurements of Bowman et al. (983a) indicate that the mean flow can be large when winds blow from the north-west. The unusual and interesting tides in the Narrows of Cook Strait lead to unusual influences in adjacent water. An analysis of the possible generation of overtides by non-linear effects in the semi-diurnal tides indicates that the largest overtides (the main overtides generally have periods half of those of the tide from which they are derived (e.g., the M 4 tide derived from the M has a period of 6. h)) are generated by the influence of the constriction on the flow (Heath 98d). This analysis indicates that the flows associated with the overtides (M 4 )

23 Table 3 Physical characteristics of 3 New Zealand inlets (from Heath 976d). Inlet name Moutere Avon-Heathcote Aotea Waimea Whanganui Parengarenga Nelson Tauranga Kawhia Porirua- Pauatahanui Rangaunu Raglan Whangarei Bluff Otago Hokianga Manukau Whangaruru Lyttelton Firth of Thames Kaipara Whangaroa Akaroa Doubtless Bay Paterson Inlet Tasman Bay Poverty Bay Pelorus Sound Bay of Islands Wellington Harbour Queen Charlotte Sound Hawke Bay Surface area at high tide (0 6 m ) Mudflat area at low tide (0 6 m ) Cross-sectional area entrance Low tide Mid tide spring spring (0 3 m ) (0 3 m ) 0.4 _ _ Tidal Spring tides (m) i range Neap tides (m) ; Tidal compartment Spring tides (0 6 m 3 ) Neap tides (0 6 m 3 ) Volume at low water spring (0 6 m 3 ) X X0 5 Catchment area including surface area (0 3 km ) to West Head 7. Perimeter (km) Width at entrance W (km) Maximum length L (km) Source of data H6 Knox et al. 973 H535 H6.L Sheet S0 L Sheet S3, H6 H5. LSh. N IN H A H64 H54i H73 Irwin 978 H53 H44 H53 H67, L Sheets S8,S8 H66 H4 H434 H5 H63 H533 H43 HI 09 H634 H55 H5 H6 H65 H65 H5 H4633 NZ65 H56 o ip" 3 < O C 3 P_ O s pd n P Q. 3 <J> P - Q

24 Heath Review of the physical oceanography of the seas around NZ 0 x observed -00 Wellington Fig. 5 The phase (, lower curves) and amplitude (m) in Cook Strait Narrows given by two standing waves. The x's give the observed values at Wellington, Oteranga Bay, Makara, and Titahi Bay. The solid curves are for x = 0 at Makara, the dashed curves for x = 0 at Titahi Bay. Fig. of Heath 974a. Reprinted from: Deutsche Hydrographische Zeitschrift 7(5&6): 4-4. are small (supported by the hydrographic observations mentioned above but really requiring extensive current observations to evaluate) but the M 4 elevation, relative to the fundamental (M ) tides is substantial. A consequence of this relatively large M 4 /M tidal elevational ratio is that there is a large tidal-flow asymmetry in the Marlborough Sounds whose entrance opens into Cook Strait this accounts for the observed large M 4 -tidal elevations at Picton (within Queen Charlotte Sound) and the observed large asymmetry in the tidal flow in Pelorus Sound (Heath 98Id). The small M -tidal elevations in the Narrows of Cook Strait lead to unusual currents in adjacent Tasman Bay (Fig. 6; Heath 979b). Current observations from the centre of the mouth of Tasman Bay demonstrated a strong quarter-diurnal tidalcurrent signal and had strong sixth- and eighthdiurnal tidal signals as well as the semi-diurnal tidal signal (Fig. 5 and 7). The amplitudes of these overtides are stronger at the time of spring than at neap tides with the quarter- and eighth-diurnal overtides directed mainly along the T axis, the rather weak sixth-diurnal overtide along 90-0 T and the strongest semi-diurnal component directed along 00-0 T (Heath 979b). An explanation for these unusually strong overtidal flows has been given in terms of the large change in semidiurnal tidal elevation across western Cook Strait; i.e., between the small elevations in the Narrows of Cook Strait, as indicated above, to the large tidal elevations in the adjacent Tasman Bay (the largest anywhere in New Zealand) which result from solidwall reflection of the tide evident from the north. This rapid change in elevation gives rise to large non-linear field acceleration near D'Urville Island, at the north-eastern entrance to Tasman Bay, and consequently significant overtides. The bathymetry of Tasman Bay is such that the periods of quarterand half-wavelength oscillations across and along Tasman Bay are near those of the overtide periods and provide a resonance for the components initially generated near D'Urville Island (Heath 979b). COASTAL AND CONTINENTAL SHELF OCEANOGRAPHY New Zealand has many coastal embayments and an extensive submarine platform. Early studies of the physical regime of many of the embayments and segments of the shelf have been made as background to biological, geological, or engineering studies. More recently a multi-disciplinary approach has been used in some studies. Coastal harbours and estuaries Any summary of localised hydrological or circulation studies of coastal harbours and estuaries should include the limitations that the original author placed on the data. For this reason the reader is best referred to the original papers. Bibliographies of published papers on the New Zealand coast have been compiled by Spencer (964) on coastal geomorphology and submarine morphology ; Anderson & Grange (976) for Manukau Harbour; Estcourt (976) for mainland estuaries, harbours etc.; Gordon & Ballantine (977) for the Cape Rodney to Okakari Point Marine Reserve; Bardsley (977) for Kaipara Harbour; Anderson (977) for Wairau Lagoons and the surrounding coastal region; Carrig & Spence (977) of coastal planning to 975; Marshall (977) for Northland; Pickrill (979) on wind waves; Hume

25 0 New Zealand Journal of Marine and Freshwater Research, 985, Vol I, J LLJ 0 :\I \4 4 6 _8 0', ^ "~~ North South West South Fig. 6a Components of the unfiltered hourly mean current velocities positive to the east (solid line) and north (dashed line) under spring (upper) and neap tidal (lower) conditions at a depth of 30 m in 36 m of water at latitude 40"43' S, 73 36' E in Tasman Bay (Fresne in Fig. 6b). The observed tidal elevation at Tarakohe (Fig. 6b) is shown for the spring tidal conditions. Fig. 3 of Heath 979b. Reprinted from : Estuarine and Coastal Marine Science 8: (980) for selected areas of Waitemata and Manukau Harbours; and Hume & Harris (98) for Northland-Auckland area. Variations of surface temperatures within many New Zealand harbours have been recorded in association with biological studies and reference to a few of these is listed below: in Wellington by Ralph & Hurley (95), Skerman (958), and Booth (975); Otago by Skerman (958), Hurley (959), Hurley and Burling (960), and Westerskov (980); and in Auckland, Lyttelton, Timaru, and Bluff by Skerman (958). Since 977, daily water temperatures and weekly salinities have been obtained (as part of a coastal climate programme under the guidance of N. M. Ridgway of NZOI) from Wellington, New Plymouth, Napier, Tauranga, Auckland, and Leigh in North Island and, since 978, from Nelson, Kaikoura, Lyttelton, Timaru, Bluff, Anita Bay (Milford Sound), Westport, and Farewell Spit in South Island. This extends Paul's (978) analyses of historical trends in New Zealand's sea temperatures and the extensive temperature records from the marine biological laboratories such as those collected at Leigh by W. Ballantine (e.g., Evans & Ballantine 983). Localised hydrological studies of the Hauraki Gulf have been made by Cassie (956, 960), Slinn (968), Paul (968), Jillett (97), and Crossland (980), of Port Fitzroy by Hickman (979), of Otago Harbour by Slinn (968) and Quinn (978), of Aotea and Raglan Harbours and Port Waikato by Heath & Shakespeare (977), and of the Bay of Islands by Booth (974). The circulation in Lyttelton Harbour has been analysed by Garner & Ridgway (955) and in Wellington Harbour by Brodie (958). The last decade has seen an upsurge in interest in man's effect on his environment and the perceived need for an understanding of how the marine system operates as a whole. With limited resources in New Zealand for research into marine systems it is not possible to study all New Zealand's coastal inlets within a finite period. With this in mind a loose plan was mounted at the NZOI to classify the major New Zealand inlets into groups of similar type and then, as resources permit, study or inlets in each group. The idea was that not only would these studies provide essential background information but would also allow principles to be established which would act as a guide for any 'firefighting' studies in similar inlets.

26 Heath Review of the physical oceanography of the seas around NZ 03 Fig. 6b Current-meter sites in western Cook Strait and Tasman Bay. Fig. of Heath 979b. Reprinted from: Estuarine and Coastal Marine Science 8 : A classification of 3 main coastal inlets (Fig. 8), based essentially on a collation of their physical parameters, led to a major subdivision. In one group tidal flow dominates, and in the other, different types of driving forces may also be important the latter group was subdivided into six subgroups (Heath 976d). Lists of the physical characteristics are given in Tables 3 and 4. Studies included, to date, within this programme include Manukau Harbour (Heath et al. 978), Tasman Bay (Heath 976e), and Pelorus Sound (Heath 974b, 976f, 98a; Carter 976). The environmental upsurge in the past decade has led logically to several major multi-disciplinary multi-institutional coastal projects in harbours and estuaries including the Pauatahanui Environmental Project (e.g., Healy 980) in Pauatahanui Inlet, the Upper Waitemata Harbour Study (Williams & Rutherford 983) which is still in progress, and the pioneering, mainly biological, study of the Avon-Heathcote Estuary (Knox & Kilner 973). In summarising the recent studies, the lead has been taken from the broad classification of inlet types. Only those inlets where the residence time is greater than several days have been treated specifically. For the other inlets where the residence time is only a few days the overall aspects of the inlet studies will be given the original intention of the studies was to provide a basis (a recipe) for study of other inlets. Short-residence-time coastal inlets Residence time The residence time of a parcel of water in an inlet is the time that parcel of water remains in the inlet. It ; s different for different parcels of water and therefore is difficult to measure directly. A variety of methods is nevertheless available to give estimates of the residence time in different sections of an inlet. Estimates arising from the tidal prism method (see, e.g., Bowden 967) formed part of the basis of the original classification (Table 4). Subsequent calculations have been made from the time needed to replace the fresh water (calculated from the salinity defect) within the harbour. These available estimates are given in Table 4. In Pauatahanui Inlet, the residence time has also been estimated from the change in relative salinity across the entrance front between the inlet and offshore coastal water as it enters and leaves the inlet the estimate of four days compares well with that based on the salinity defect (Heath & Grange unpub. data).

27 04 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Table 4 Freshwater runoff and ratios of physical characteristics of 3 New Zealand inlets (from Heath 976d). Residence time Inlet Average annual runoff (m 3 s -< ) Average Perimeter runoff + surface January Tuly area (m 3 s-') (km- ) Surface area + maximum length (km) Total volume + spring tidal compartment P (Tidal periods) Volume at low water -r average runoff (Days) Total volume + spring tidal compartment + average runoff (Days) Moutere Avon-Heathcote Aotea Waimea Whanganui Parengarenga Nelson Tauranga Kawhia Porirua- Pauatahanui Ranganunu Raglan Whangarei Bluff Otago Hokianga Manukau Whangaruru Lyttelton Firth of Thames Kaipara Whangaroa Akaroa Doubtless Bay Paterson Inlet Tasman Bay Poverty Bay Pelorus Sound Bay of Islands Wellington Harbour Queen Charlotte Sound Hawke Bay _ , Resonant period The response of inlets to forcing either by long waves (e.g., tides, tsunamis) or local winds is largely determined by the inlet bathymetry. Available calculations of the likely resonant periods and those observed in response to tsunamis or local winds is given in Table 5. Also given are the decay times of the response. Of special interest is Lyttelton Harbour. Surface elevational records from Lyttelton Harbour frequently exhibit short-period oscillations (-3 h) superimposed on the semi-diurnal tide (Fig. 9). These oscillations were particularly strong in response to both the 960 Chilean and the 964 Alaskan tsunamis. The large response appears to be a consequence of the Chatham Rise, which extends 000 km perpendicular to the eastern coast of South Island adjacent to Lyttelton Harbour and acts as a three-quarter-wavelength aerial to doublesided edge waves (Heath 98c).

28 Heath Review of the physical oceanography of the seas around NZ 05 Fig. 7 Line spectra of the unfiltered hourly mean current components positive to the east (solid line) and north (dashed line) computed using the Extra Fast Fourier Transform with 8 data points from the latter portion of the record shown in Fig. 6a. The periods of the more prominent lines are indicated. Fig. of Heath 979b. Reprinted from: Estuarine and Coastal Marine Science 8: ' 004" JE mplitude < h j jj JN i I] i I 6-40 h 6-74 h/! / k hr4'3n ' 98 A * ' il V^v~V \ East-West Component JNorth-South Component h ;', Harmonic number Entrance cross-sectional areas Furkert (947) showed that in many inlets around New Zealand the entrance cross-sectional area (A) is linearly related to the tidal compartment (a). Subsequent analysis indicates that for 6 inlets (Whangaroa, Whangarei, Bluff, Raglan, Kaipara, Manukau, Hokianga, Kawhia, Tauranga, Rangaunu, Parengarenga, Otago, Nelson, and Aotea Harbours, Whanganui and Moutere Inlets) the relationship is a = A 098 X 0 47 with a correlation coefficient (r) of 0.95 (Heath 975d). The Waimea Inlet, the Avon-Heathcote Estuary, and Porirua- Pauatahanui Inlets also fit closely to this relationship. These inlets have bars or banks that protect them from severe swell and act as bypasses to the littoral drift of sediment. Frequent occurrences of swell in the entrance to Wellington, Lyttelton, and Aotea Harbours, coupled with the small littoral drift of sediment on adjacent rocky coastlines, appear to promote development of larger entrances than those associated with tidal control in unconsolidated sediment (Heath 976g). This relationship, between the entrance cross-sectional area and the tidal compartment, has been interpreted as indicating that the entrance cross-sectional area is near equilibrium with the bottom stress. However, observation of only a minimal change in cross-sectional area of the entrance to Rangaunu Harbour under spring- and neap-tidal conditions indicates the equilibrium condition is established on a longer time-scale than that of the spring-neap-tidal cycle (Heath et al. 983). This is interpreted as indicating that the transport of sediment through the harbour entrance is not sufficiently large to maintain equilibrium with the changing tidal variation on the time-scale of the neap-spring tidal cycle. Heat budget Many of New Zealand's coastal inlets have extensive mudflats which is indicative of a large change in surface area from low to high tide. This changing surface area on a period of c..4 h (the dominant tidal period) coupled with a solar heat input on a daily (4 h) cycle leads to a variable heat input. Also, many of the inlets are sufficiently shallow that their waters are warmer in summer and cooler in winter than the adjacent deeper coastal waters with which they are exchanged. A variation in inlet water temperature is expected therefore to occur on a variety of time scales superimposed on the general seasonal trend. Observations of the temperatures in Pauatahanui Inlet over a short period exhibit differences from one tide to the next. Subsequent analysis based on the calculated heat budget indicates that variations would be expected, with periods of 4.75-day beat frequency, between the tidal and solar interaction, the variable diurnal inequality, and many high-frequency components (Heath 977b). Study has not been made of the heat balance in other New Zealand inlets but it is suggested that the variability may have important biological implications.

29 06 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Tidal asymmetry In many shallow inlets the main semi-diurnal tide (the M, tide) is distorted such that whereas in the open ocean the tidal elevational curve is symmetrical, in shallow inlets the time from high to low tide may differ from that from low to high tide formally the curve can be broken down into symmetrical sinusoids with frequencies of the fundamental semi-diurnal tide and of its overtides. The overtides have frequencies which are integer multiples of the frequency of the fundamental. There is a variety of mechanisms for producing this asymmetry including: the fact that the tidal elevation is an appreciable fraction of the mean water depth and therefore the speeds of the tidal wave and frictional dissipation, which depend on the depth, vary over the tidal cycle; changes in the water speed from place to place; and the fact that the speed of the water movement also depends on the water depth. This tidal asymmetry in the tidal elevation has an associated tidal-flow asymmetry and therefore the peak of the flood tide may be different in speed from that of the peak ebb tide. This can have a significant influence on processes such as the transport of bedload sediment. Although the net water movement over a tidal cycle is zero, the transport of bedload sediment (which depends nonlinearly on the water speed and has a speed threshold of operation) may have a non-zero mean when averaged over a tidal cycle. An analysis of these effects in Rangaunu Harbour has been found to be important in determining the net sediment movement (R. A. Pickrill, NZOI, pers. comm.; Heath et al. 983). Tidal energy dissipation The time of high tide is generally delayed with distances from the entrance of a tidal inlet. This delay is associated with the energy loss from the tides, and provides a means of estimating the overall listed energy dissipation in the inlet. There is a need to supply the energy from the tide external to the inlet. This energy is provided by the pressureforcing term in the energy balance associated with a small net progressive-wave input of tidal energy (see, e.g., Jeffreys 970; Garrett 975). Observationally, this is evident by the peak of the tidal flow being delayed, that is, the peak flow occurs later than in a frictionless system (for a frictionless system the peak flow would precede the peak elevation by a quarter of a tidal period; with friction, the tidal flow is delayed to be less than a quarter of a tidal period before the tidal elevational peak). Part of the tidal energy loss can go into mixing of fresh and salt water within the inlet. The ratio of the tidal energy loss to the buoyancy input by the freshwater inflow (because of its difference in salinity from the coastal waters), can be used to give some measure of the potential stratification of an inlet. This ratio, the stratification parameter, defined by Ippen and Harleman (96), is related to the estuarine Richardson number. Calculations of this type have been made for Rangaunu Harbour and indicate that (as observed) the harbour would be expected to be well mixed (Heath et al. 983). Storm events Results from the Pauatahanui Environmental Project have emphasised the importance of storm events to the annual budget of nutrient input to estuaries. Of the several nutrient elements required for plant growth, the two that are usually in shortest supply, and therefore place a limit on growth, are nitrogen and phosphorus. Input of reactive nitrogen into Pauatahanui Inlet has a larger seasonal variation than that for reactive phosphorus with both having a winter maximum and a summer minimum. This winter increase is mainly attributable to inputs associated with storm events (Healy 980). Long-residence-time coastal inlets Fiords, Sounds Southern Fiords The New Zealand fiords comprise 4 inlets located over a 00 km stretch of the south-western coast of South Island. They are drowned glacial valleys. Stanton & Pickard (98) have described the physical oceanography of these fiords based on observations made in December 977 from RV Tangaroa. Their description builds on the earlier studies made in specific fiords (e.g., Milford Sound (Garner 964; Stanton 978b); Caswell Sound (Stanton 978b); Nancy Sound (Stanton 978b); Doubtful Sound (Batham 965), and Dusky Sound (Jillett & Mitchell 973)). More recently Stanton (984) has extended the work of Stanton & Pickard (98). The New Zealand fiords are typically narrow and steep-sided with one or more submarine entrance sills (30-45 m deep) separating relatively deep basins (up to 40 m deep) from the open ocean. The coast on which they are located is extremely mountainous, with a resulting high precipitation leading to large freshwater inflow into the fiords. Stanton & Pickard (98) found that the New Zealand fiords have a relatively low-salinity upper layer (s = X 0 3, temperature -7 C)

30 Heath Review of the physical oceanography of the seas around NZ E ISO 40 3arengarenga Harbour \V,Rangaunu Harbour yw^^vswhangaroa Harboar Harbour Hokianga Harbour-V^ \, r^ngaruri. \ "Ti.Whangare Harbour 35 - Whanganui n ^ \ ". Quc on f ^HJTasman $ C^a otte ' Estuary Hafcur Vs und / / Kaipara Harbour*/? p J Avon- Heathcote Es uary ^, hf Thames /.Port Lyttelion Manukau Harbour-^Si A y Raglan Harbour ~\p nga Harbour ^"^ karoa Harbour Aotea Harbour-w Kawhia Harbour-^ J < / /Hawke Bay r 7p^Poverty Bay 40-S - A Bluff Harbour J =3 / <&^-~ / / /, otago Harbou - /^T Pauatahanui Inlets/ / y fi^--- Patterson Fig. 8 Location maps of the coastal inlets considered in broad classification. Fig. of Heath 976a. Reprinted from : Deep-sea Research 3 : separated by a halocline at 5-0 m depth from a subsurface high-salinity layer with a salinity maximum (s = X 0 3 ). This salinity maximum was found at about 00 m depth in the northern fiords and near the bottom in the southern fiords. Stanton and Pickard's (98) survey and previous surveys found high dissolved-oxygen values in the deep water of the New Zealand fiords, indicating that the main basins are adequately ventilated. Pelorus Sound Pelorus Sound is a drowned river valley about 50 km long with an extensive delta at its head (8 km ) formed by the sediment output from the Kaituna and Pelorus Rivers. Within the broad classification of inlet types (Heath 976d) it is linked with Lyttelton and Akaroa Harbours, Paterson Inlet, and Queen Charlotte Sound. Originally it was chosen for study because, with the adjacent Queen Charlotte Sound, it presents an the opportunity to evaluate the influence of freshwater inflow in a control situation; Pelorus Sound has much more freshwater inflow than Queen Charlotte Sound. In effect, the limited observational effort has gone into evaluating the complex changes with time of the flow and density field in Pelorus Sound. Between 973 and 976, four separate sets of oeeanographic observations were made in Pelorus Sound. Each of the data sets includes salinity observations and most, but not all, include temperature, seston, and current observations. Each of the observational periods was limited to a maximum of 6 days and consequently the evaluation between the changing density field and circulation could not be traced continuously through a cycle. Rather, an understanding of how the sound operates has been built up piece-meal from individual data sets. Results have been presented in Carter (976) and Heath (974b, 976f, 98c). In brief, the picture that emerges is that with the onset of high-freshwater inflow, turbid low-salinity water moves quickly down the Sound. Salinity and seston observations, made in June 975 (Fig. 9) during heavy rainfall, revealed a thin (< m) surface layer of turbid, low-salinity water moving seawards at m s (Carter 976). Subsequently this low-salinity water mixed downwards with the isohalines sloping downwards towards the head of the Sound (Fig. 9). This stage of development may be accompanied by the generation of an

31 08 New Zealand Journal of Marine and Freshwater Research, 985, Vol Pelorus Sound seston 60 Fig. 9a Salinity (X O 3 ) and seston concentration (mg / - ') with depth along the main axis of Pelorus and Kenepuru Sounds, 8 October 976. Fig. 3 of Heath 98a. Reprinted from : New Zealand Journal of Marine and Freshwater Research 6(): internal tide with associated larger water movement and enhanced mixing. Kenepuru Sound, a side arm to Pelorus Sound, acts as a damper on the change in the salinity field in Pelorus Sound, providing a large reservoir of saline water with which the less-saline water in the Havelock Arm of Pelorus Sound must mix on an outgoing tide. The final stage of development that prevails under low-freshwater inflow conditions is that of isohalines in the outer Sound (Fig. 9) being nearly vertical with an area of rapid change in salinity developed near the confluence of Pelorus and Kenepuru Sounds. There is strong tidal asymmetry in Pelorus Sound caused primarily by the co-oscillating overtide generated outside the Sound by non-linear effects on the fundamental.4 h tide in Cook Strait (see above). Variations in the phase of the tidal flow with depth result both from frictional energy dissipation of the flow on the shallow area near the head of Pelorus Sound and from internal tides. Seiching has been observed in Kenepuru Sound the periods of and h are consistent with the periods of the half- and quarter-wavelength barotropic seiche in Kenepuru Sound, and its generation is possibly connected to the phase difference between the surface and bottom flows near the confluence of Kenepuru and Pelorus Sounds. Salt transport during periods when the sound has a clear vertical structure is mainly by advection; an extreme example occurs with peak freshwater inflow. After sustained periods of low freshwater inflow, the isohalines are nearly vertical in the outer sound and horizontal diffusion becomes important.

32 Heath Review of the physical oceanography of the seas around NZ Havelock Conniston Koutuwai Portage f Water g Lytton Water Tawero Pt West Entry Pt HAVELOCK ARM KENEPURU ARM 8-7 L Fig. 9b Surface salinity (X 0 3 ) in Pelorus Sound at different times under different freshwater inflow conditions. Fig. 9 of Heath 976f. Reprinted from : New Zealand Journal of Marine and Freshwater Research 0() :

33 0 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Table 5 Resonant period of several New Zealand harbours. The methods of calculation were: Numerical one-dimensional integration without end corrections. a Observed response to 960 Chilean tsunami. b Observed response to 964 Alaskan tsunami. 3 Observed response to meteorological forcing. 4 Helmholtz period calculated from simple representation of harbour. Harbour Resonant period (h) Mode Method of calculation adissipation rates Q t Reference Lyttelton Wellington Otago Entrance to Halfway Is Tauranga Whangarei Akaroa , P.,.3.3.0, , X/4 X/4 X/ 3X/4 In association with Chatham Rise Helmholtz X/4 X/4 XII X/ 3X/4 X/4 X/ 3X/4 X/4 X/ 3X/4 X/4 X/ 3X/4 X/4 X/ 3X/4 a, b a, b, 3 4 a a, 3 a a a a a a X 0-' 3.5 X 0-4 Heath 976h Heath 976h Heath 98c Heath 97e Heath 976h Heath 976h Heath 976h Heath 974d Heath 974c Heath 974c Heath 974c Heath 976h Heath 976h Heath 976h Heath 976h Heath 976h Heath 976h Heath 976h Heath 976h Heath 976h 6E O t x = linear factional coefficient. PFirst number includes full width of harbour second (lesser) number includes section of width between m isobaths. The overall residence time of the water in Pelorus Sound has been estimated at about days. Coastal embayments In the classification of New Zealand coastal embayments, Hawke Bay, Tasman Bay, Doubtless Bay, the Firth of Thames, and the Bay of Islands are classified as possibly being subjected to boundary forcing with both vertical and horizontal twodimensional wind-derived motion. Of these bays, the first two have been studied in some detail numerical tidal study of the Hauraki Gulf (Bowman & Chiswell 98) includes the Firth of Thames, and Booth (974) analysed drift-card records from the Bay of Islands.

34 Heath Review of the physical oceanography of the seas around NZ Hawke Bay Drift-card investigations of the surface circulation in Hawke Bay were made by Ridgway (960, 96). More recently, Ridgway and Stanton (969) occupied a dense grid of hydrological stations in the bay which enabled them to observe the circulation from the salinity distribution, and Bradford et al. (980) investigated the physical oceanography as part of a biological productivity investigation. The early hydrologic and drift-card studies indicate that water moves westwards into Hawke Bay along its mid-line and bifurcates to produce alongshore flows towards the north and south, with water leaving the bay at its southern and northern extremities. This situation is consistent with the biological distribution (Bradford et al. 980). The circulation appears to be controlled by the current outside the bay, the northwards wind-derived surface flow of the Southland Current and the southwards-flowing East Cape Current further offshore (Ridgway 960). Saline water entering the bay is modified by freshwater run-off and this generally lowers the salinity within the bay by c. 0.4 X 0 3. Estimates of the residence time of the waters of Tasman Bay have been made by a variety of methods each, of course, with its own severe limitations. The tidal-prism method is not appropriate in Tasman Bay (Heath 976c). However, modifying the tidal-prism method to take into account only the amount of water entering the bay each tidal cycle gives a residence time of 37 days. The residence time calculated using the mean circulation within the bay, based on measurements presented on the hydrographic chart (Hydrographic Branch 963), gives a residence time of 94 days or, based on drift-card observations, a residence time of 7 days (Heath 973c). Other estimates based on the Ekman Transport, calculated indirectly from the drift-card trajectories, give residence times of 67 days for a wind blowing across the entrance at 8 m s H or 6 days for a wind of 6ms. Based on current observations from the centre of the entrance Jo Tasman Bay (Heath 978b) gives an estimate of the residence time of 8 days. In reality, the residence time would appear to be from -3 months. Tasman Bay Investigations of the circulation in Tasman Bay have been made from drift-card observations (Heath 969, 973c; Baker 97), from hydrological observations and current measurements (Heath 976e; Ridgway 977), and numerical model studies of the wind-derived (Heath 976c) and tidal (Heath 974a, 976c; Bowman et al. 980) flows. The drift-card observations indicate that the surface flow in Tasman Bay is highly wind-dependent with surface flow towards the head of the bay during northerly winds, which are most frequent from October to March, and out of the bay when the winds are from the southerly quarter, which is most frequent from April to August. The mean flow, however, appears to consist of a clockwise circulation in Golden Bay, an anti-clockwise circulation in the main part of Tasman Bay, with an additional southwards flow on the eastern side of Tasman Elay. The numerical model of the circulation in the bay resulting from specification of the flow outside the bay and a wind of 5 knots from the west (Heath 976e) and other direct current measurements (Heath 976e; Ridgway 977) support the circulation pattern. In summer, the temperature increases towards the head of Tasman Bay and the seasonal thermocline is stronger inside the bay than outside, both effects result from solar heating. The greatest amount of coastal dilution occurs in the western part of Golden Bay. Continental Shelf With the upsurge in fishing interests on the continental shelf and the discovery and development of the Maui gas field, there has been a need for more intense oceanographic research on the continental shelf. This need fits into the natural development of the science in New Zealand. The pioneering research on the New Zealand continental shelf was made by Garner (96) when he observed the seasonal change in the temperature and salinity structure along several sections situated across the shelf around New Zealand and observed the mean surface flow using drift cards. Further progress was made in the detailed study of the temperature and salinity field across the continental shelf and slope off the Otago coast by Jillett (969) and Robertson (980) as a component of their plankton research, and north of Auckland by the Defence Scientific Establishment (then Navy Research Laboratory) as a component of their defence underwater sound research (e.g., Barker & Kibblewhite 965; Barker & Denham 970; see also Webber 974), and off the western coast of North Island by Roberts & Paul (978). More recently Booth (pers. comm.) has been occupying sections off the east coast of North Island as a component of his rock-lobster research. There have been extensive temperature and salinity observations made as part of fisheries-related programmes off the north-eastern North Island (Mercer 979; Grassland 980; Habib et al. 980, 98), off the

35 New Zealand Journal of Marine and Freshwater Research, 985, Vol I I I I I I I I I I I I I I I I I I I i I I I 9th March 964 Scale 0.5 Wellinqton (m) I I I I I I I I I I I I I I I st April I I I I I I Fig. 0a Sea-surface elevation at Lyttelton () and Wellington () Harbours, showing the response to the 964 Alaskan tsunami. Fig. 5 of Heath 979c. Reprinted from : Marine Geodesy (4) :

36 Heath Review of the physical oceanography of the seas around NZ 3 0-6th April 970 /^ C -5-,.- - \, \ \ - 4 \ 0-5- \ n Time (h) li I f CD 0-5- II 8 0 i l Time(h) l I 4 Fig. 0b Sea-surface elevation at Lyttelton () and Wellington () Harbours, 9 April 970 and these together with Timaru (3) Harbour on 6 April 970. Fig. of Heath 979c. Reprinted from : Marine Geodesy (4): eastern coast of North Island (York 969; Lesser 978; Roberts 980), and around the complete North Island (JAMARC Report 98). Two major multi-disciplinary projects have been mounted, the Maui Environmental Project guided by the University of Auckland and involved primarily with western Cook Strait, the site of the Maui Field, and the West Coast Project guided by the NZOI and involved primarily with the western coast of South Island. The geographic proximity of the projects has led to considerable overlapping as the localised research is placed into a broad geographical context. The Maui Environmental Project, started in 974, is now into its third phase. The results of the first phases are summarised in Kibblewhite et al. (98) as well as in the numerous specialised reports and papers. The West Coast Project, though conceived in 978, has gained increasing momentum only since about 980. The Maui Development Environmental Study The Maui Development Environmental Study of the marine environment in the region bounded in the north by Albatross Point (38 06' S, immediately south of Kawhia Harbour) on the western

37 4 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 coast of North Island and in the south by Cook Strait, was undertaken by the University of Auckland at the request of Shell BP and Todd Oil Services Limited. Phase I (974) involved essentially a literature review. Based on this review a Phase II programme of active field work in physical oceanography, coastal geology, and marine biology commenced in 977. Results of this Phase II study are presented in Kibblewhite et al. (98) and the reader is referred to that publication for a comprehensive account. Tidal studies included tide-gauge and currentmeter observations and development of an M -tidal numerical model. The tidal model has been used as a tool to indicate tidal mixing and the likely location of tidal fronts (Bowman etal. 980, 983a). Subsequent to the development of the tidal model, three oceanographic cruises (October 978, January 980, and January 98) in greater Cook Strait have been conducted by scientists from a range of disciplines and institutions (e.g., Bowman et al. 983a, b). On each cruise, sea-surface temperature, conductivity, nutrients (nitrate, phosphate, silicate), and chlorophyll a were mapped continuously and similar observations with depth were made at frequent stations. These cruise observations revealed tidal mixing fronts in Cook Strait and off Cape Farewell. The observations under strong southwards-directed wind conditions revealed a plume of high-nutrient water extending eastwards from Cook Strait the presence of an associated strong flow was confirmed by drogued radio buoys. Much of the more recent oceanographic emphasis in this Maui study has centred on the upwelling region at the north-western corner of South Island near Cape Farewell. This area has been known for a considerable time to be a centre of upwelling (e.g., Stanton 97, 976b) but not until a multidisciplinary approach was adopted with physical, chemical, and biological observations was the significance of the upwelling realised. The upwelling supplies a plume of nutrient-rich water which extends into western Cook Strait this plume may sometimes have eddies embedded in it (Bowman et al. 983c). The high nutrients enhance phytoplankton production and possible subsequent zooplankton growth and aggregation. Squid-fishing boats fish along the edge of this plume (Bowman et al. 983c). The present thrust in research related to this plume involves investigation of the flow over a bump in the bottom topography as a possible mechanism for generation of eddies within the plume using numerical models (S. M. Chiswell, State University of New York, Stony Brook, USA) and field investigations of the physics of the system and the rate of transfer of nutrients within the system (by the Division of Marine and Freshwater Science, Department of Scientific and Industrial Research). West Coast Project physical oceanography The natural development of physical oceanographic studies in New Zealand has led from the block-survey, deep-ocean data collection of the 960s (e.g., Garner 969b) through the study of the dominant tidal-current signal in the 970s, to the present recent studies of other aspects of the temporal variability on the continental shelf. The area chosen for initial study of this latter aspect was the western coast of South Island. This choice was guided both by the perceived need within the West Coast Project with its multi-disciplinary approach to studying the complete system, and hopefully less complex circulation compared with elsewhere on the New Zealand continental shelf. Historically, the mean flow on the western coast continental shelf was defined from mariners' reports and drift-card evidence (e.g., Brodie 960). More recently, water properties (Stanton 97, 973b, 976b; Ridgway 980) and current-drogue and meters (Heath 973b, 978b; Sanderson 979) have been used to define the circulation (e.g., Fig. ). The picture that emerges from these studies is of a weak mean flow on the continental shelf, northwards on the western coast of South Island (the Westland Current) towards Cape Egmont, with at least part of this flow contributing to the D'Urville Current which flows eastwards into Cook Strait. The direction of flow on the continental shelf north of Cape Egmont is not all clear. On the basis of driftcard evidence, Brodie (960) indicated a converging of the current towards about latitude 37 S, with southwards-directed currents north of 37 S (the West Auckland Current) and northwards-directed currents south of 37 S (an extension of the Westland Current). However, current-meter observations at 38 ' S, under calm atmospheric conditions, indicate a mean southwards flow (Heath 978b). Current-meter observations (Heath 978b) and radio-tracked drogue studies (Sanderson 979) indicate that the day-to-day flow is dominated by a response to atmospheric forcing. This response consists of both a direct wind-induced near-surface flow and a barotropic flow resulting from change in the sea-surface slope induced by blockage of the direct wind-induced Ekman Transport by the coastal boundaries. To understand further the circulation on the western coast it is necessary to determine the influence of the three most probable driving mechanisms

38 Heath Review of the physical oceanography of the seas around NZ T (m s" ) T 030 Time (d) Fig. Directional components of the.33 h means of the current-meter records at depths of 8 and 68 m at Tasman (40 8' S, 73 ' E) (Fig. 6b), -3 March 970, with the atmospheric pressure and mean sea level at New Plymouth (continuous curve) and Wanganui (dashed curve). Arrows show the wind condition.

39 6 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 boundary, atmospheric, and thermocline forcing. A programme of direct current and sea-surface elevational observations on the western coast of South Island is now in effect to study these mechanisms by essentially evaluating the dominant periods of the variability on this coast before mounting a combined current-observation hydrographic programme. An estimate of the relative magnitude of the driving mechanisms has been made from model studies. A linearised model of Csanady (976) for the time-averaged mean flow on a continental shelf has been applied to the New Zealand western coast continental shelf (Heath 98b). The means are time averages over time scales that are long relative to that of local atmospheric forcing. Forcing of the flow is via the seasurface elevation (specified from deep-ocean steric levelling with adjustment for boundary effects), mean winds, and thermohaline forcing (specified by observations and determined by the strong fluctuating flow, the time average of which is the weaker mean flow). The main flow components are found generally to be caused by forcing by the sea-surface elevation and local winds. North of latitude 4 30' S the mean sea surface slopes down towards the south, with an associated southwards-directed flow component; south of 4 30' S it slopes down towards the north with an associated northwardsdirected flow component. On the north-western coast of South Island the predominant north-eastwards-directed wind produces a north-eastwards alongshore flow component. On the western coast of North Island north of Cape Egmont, the predominant onshore wind produces a flow towards the north. Thermohaline forcing leads to a southwards alongshore flow decreasing to zero near the seafloor. WIND WAVES Through the 950s there was an active group of New Zealand scientists at the forefront of wave theory research (e.g., Watters 953; Barber 954, 958, 959; Barber and Doyle 956; Burling 959a, b). However, not until the 970s was there a concerted effort to characterise the wave climate in specific locations around New Zealand. The necessity for these studies came from coastal-erosion research (e.g., Kirk 97) and as input for possible engineering design associated with offshore hydrocarbon recovery (see, e.g., Kibblewhite et al. 98). A bibliography of wind waves in New Zealand has been compiled by Pickrill (979). The available wave information from around New Zealand is listed by the Marine Information Advisory Service (MIAS) located at the Institute of Oceanographic Sciences, Wormley, England (MIAS 98; see also Pickrill 979). The wave data available up to 978 were used by Pickrill and Mitchell (979) to characterise the New Zealand wave climate. They found that the New Zealand wave environment is dominated by swell originating from the west and south-west of New Zealand and storm waves generated north of New Zealand. Thus, the western and southern coasts of New Zealand are directly exposed to the dominant swell and, as a consequence, are a highenergy environment. The prevailing deep-water waves south of New Zealand are m high with 0- s periods with a slight increase in wave height in winter. On the western coast there is a mixture of swell from the south and south-west and locally generated eastwards- and northwards-directed storm waves. The prevailing waves have a height of m and a period of 4-8 s. There is no strong seasonal variation but there is a short-period cycle of wave height of about five days associated with a similar quasi-rhythmic cycle in the weather. The eastern coast of New Zealand receives swell from the south and locally generated southerly and northerly storm waves. The prevailing waves have a height of m and a period of 7- s. There is a quasi-rhythmic short-period weather-generated cycle superimposed on a weak seasonal cycle (Pickrill & Mitchell 979). The northern coast of New Zealand between North and East Capes is not exposed to swells of southern origin. The prevailing waves are from the north-east and have a height of m and a period of 5-7 s (Pickrill & Mitchell 979). Harris & Hughes (98) have analysed the wave climate on the north-east coast of New Zealand in some detail based largely on waverider records collected off Hicks Bay. They show that the typical situation is that of waves generated by enclosed meteorological systems, either mid-latitude or Tasman depressions moving from west to east. The wave heights are dependent on the time taken to generate them and therefore on the speed with which the systems move. Frequently the systems do not persist long enough to produce a "fully arisen sea" with the spectra more in accord with the JON- SWAP spectrum than that of Pierson and Moscowitz for a fully arisen sea. With this system of nearlocal generation (as opposed to distantly generated swell) the wave height can increase rapidly with time (see also Harris et al. 983). As an important part of the Maui Development Environmental Study (see, e.g., Kibblewhite et al. 98) the wave climate at the site of the Maui gas field has been analysed in considerable detail. Based

40 Heath Review of the physical oceanography of the seas around NZ 7 on an extensive ongoing waverider-buoy time series of sea-surface elevations extending back to 976, a number of theses and papers have been published on the wave spectra (Chiswell 977; Chiswell & Ewans 978; Chiswell & Kibblewhite 980, 98) and wave generation and forecasting (Chiswell 979). In summary, based on 5 years of data, the researchers at the University of Auckland, New Zealand have found that the greatest significant wave height was 0.5 m, the highest wave was 9.5 m, the average significant wave height was - 3 m with wave heights less than m for 35.7% of the time and greater than 4 m for 0.4% of the time. The average period is 6-7 s with a persistent swell from the south-west with an average period of s. The mean form of the spectra for the fully developed sea at Maui is similar to the JONSWAP form observed in the North Atlantic apart from a small peak enhancement at Maui which is thought to be a characteristic of the site (Kibblewhite et al. 98). TSUNAMIS Tsunamis are waves which propagate away from an area where the sea surface has been subjected to a short-duration disturbance. They are usually generated by sub-sea earthquakes and rapidly radiate outwards from the area of initial disturbance. The Pacific Ocean with its seismically active margins has many tsunamis. Laing (954) and more recently Ridgway (984) has listed the specific tsunamis, either locally or distantly generated, which have been observed in New Zealand. Locally generated tsunamis appear to produce short-period waves locally whereas distantly generated tsunamis appear to produce longer-period harbour and continental shelf oscillations. Notable amongst the latter Pacific-wide tsunamis felt in New Zealand were the 960 Chilean (Heath 976h) and 964 Alaskan tsunamis. Both of these tsunamis produced a response in New Zealand east-coast harbours. The largest-amplitude oscillations occurred in Lyttelton Harbour with maximum peak-to-trough ranges of 5.5 m for the 960 Chilean tsunami and.5 m for the 964 Alaskan tsunami (Fig. 0). Periods of the dominant observed oscillations are given in Table 5. The main harbour response to tsunamis is generally that of the quarter-wavelength resonance (depending on the harbour dimensions), although at Lyttelton and possibly other east-coast ports, a continental edge-wave response is evident this latter response possibly involves the Chatham Rise, extending 000 km perpendicular to the east coast of South Island, acting as a three-quarter wavelength aerial (Heath 98c). The open coast most likely to be subjected to locally-generated tsunamis is the Bay of Plenty with White Island, an active volcano located 44 km offshore, and the Kermadec Trench (a plate boundary) further towards the north-east. This situation has led to recent studies of potential tsunami impact on this coast (de Lange 983). RECENT DEVELOPMENTS At the time of writing there are several new developments taking place in New Zealand's physical oceanography. Prime amongst these is the increasing insight being provided by remotesensing techniques. In Auckland, Professor R. Cochrane and his students have for some time been studying the movement of river-channel sediment (e.g., Cochrane & Male 977). The use of satellite imagery to indicate the transport of suspended sediment has also been used by Carter & Herzer (979) in their study of the east coast South Island sediments. More recently Professor B. Foster has been using satellite imagery to study the presence of a plume of cool upwelled water which sweeps into western Cook Strait from its source near Cape Farewell (see, e.g., Kibblewhite et al. 98). In Otago, Zeldis & Jillett (98), using aerial photographic surveys, have gained new insight into the physical/biological interaction in south-eastern New Zealand continental shelf waters where the galatheid crab Munida gregaria is found to aggregate at river plumes and headland points and in mid-shelf internal waves. The co-operative use of satellite imagery between the New Zealand Meteorological Service and the Physics and Engineering Laboratory and Division of Marine and Freshwater Science both of DSIR has already provided a better insight into the eastern-coast North Island circulation (see, e.g., Barnes 985, fig. 3) and the circulation in western Cook Strait. The use of satellite imagery, satellite-tracked buoys, current meters, and shipboard operations should, in the near future, show us how limited is our present understanding of the oceans around New Zealand, or, on a more optimistic note, will allow further expansion of the increased insight that is emerging of the processes off the east coast of North Island, the west coast of South Island, western Cook Strait, and off the Otago coast. ACKNOWLEDGMENTS I thank John Booth, Sandy Harris, Dennis Gordon, John Jillett, and Norman Ridgway for critically reading the manuscript and leading me to additional information, and Rose-Marie Thompson for typing the manuscript.

41 8 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 REFERENCES Accad, Y.; Pekeris, C. L. 978: Solution of the tidal equations for the M and S tides in the world's oceans from a knowledge of the tidal potential alone. Philosophical transactions of the Royal Society, London A90(368): Anderson, P. W. 977: Bibliography of scientific studies of the Wairau Lagoons and surrounding coastal region, South Island, New Zealand. New Zealand Oceanographic Institute miscellaneous publication 8: 6 p. Anderson, P. W.; Grange, K. R. 976: Bibliography of scientific studies of Manukau Harbour, Auckland. New Zealand Oceanographic Institute miscellaneous publication 74: 6 p. Andrews, J. C. 979: Eddy structures and the West and East Australian Currents. Research report. Flinders Institute for Atmospheric and Marine Science 30: 7 p. Andrews, J. C; Lawrence, M. W.; Nilsson, C. S. 980: Observations of the Tasman Front. Journal of physical oceanography 0: Baker, A. N. 97: Reproduction, early life history and age-growth relationships of the New Zealand pilchard Sardinops neopilchardus (Steindachner). Fisheries research bulletin, Wellington 5 : 66 p. Barber, N. F. 954: Finding the direction of travel of sea waves. Nature (London) 74: : Some relations to be expected between the directional spectra of swell observed at different times and places on the ocean. New Zealand journal of science (): : A proposed method of surveying the wave state of the open ocean. New Zealand journal of science (): Barber, N. F.; Doyle, D. 956: A method of recording the direction of travel of ocean swell. Deep-sea research 3(3): Bardsley, E. 977: The natural history of Kaipara Harbour : A bibliography. New Zealand Oceanographic Institute miscellaneous publication 79: 40 P- Barker, P. H.; Denham, R. N. 970: RNZFA Tui oceanographic cruise T60 North eastern New Zealand waters. Defence Scientific Establishment report 73: p. Barker, P. H.; Kibblewhite, A. 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J.; Chiswell, S. M.; Lapennas, P. L.; Murtagh, R. A. Foster, B. A.; Wilkinson, V. H.; Battaerd, W. R. 983c: Coastal upwelling; cyclogenesis and squid fishing near Cape Farewell, New Zealand. In: Gade, H. ed. Coastal oceanography. Plenum Press. Bowman, M. J.; Kibblewhite, A. C; Ashe, D. E. 980: M, tidal effects in greater Cook Strait, New Zealand. Journal of geophysical research 85 : Bowman, M. J.; Kibblewhite, A. C; Chiswell, S. M.; Murtagh, R. A. 983a: Shelf fronts and tidal stirring in greater Cook Strait, New Zealand. Oceanologica acta6(): 9-9. Bowman, M. J.; Kibblewhite, A. C; Murtagh, R. A.; Chiswell, S. M.; Sanderson, B. C. 983b: Circulation and mixing in greater Cook Strait, New Zealand. Oceanologica acta 6(4): Bradford, J. M.; Ridgway, N. M.; Robertson, D. A.; Stanton, B. R. 980: Hydrology, plankton and nutrients in Hawke Bay, September 976. NZOI oceanographic field report 5 : 38 p. Brodie, J. W. 958: A note on tidal circulation in Port Nicholson, New Zealand. 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42 Heath Review of the physical oceanography of the seas around NZ 9 Carter, L.; Heath, R. A. 975: Role of mean circulation, tides, and waves in transport of bottom sediment on the New Zealand continental shelf. New Zealand journal of marine and freshwater research 9(4): Carter, L.; Herzer, R. H. 979: Hydraulic regime and its ability to transport sediment on the Canterbury continental shelf. New Zealand Oceanographic Institute memoir 83: 33 p. Cassie, R. M. 956: Spawning of the snapper, Chrysophrys auratus Forster in the Hauraki Gulf. Transactions of the Royal Society of New Zealand 84(): : Hydrology of Hauraki Gulf. Proceedings of the New Zealand Ecological Society 7: Chiswell, S. M. 977: Ocean wave spectral analysis. Site A for February to March 977. University of Auckland, Physics report : Ocean wave generation and forecasting; a study based on observations made off the west coast of the North Island, New Zealand. Unpublished MSc thesis, University of Auckland, New Zealand. 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N. 976: Bibliography of scientific studies of New Zealand mainland estuaries, inlets, lagoons, harbours and fiords. New Zealand Oceanographic Institute miscellaneous publication 75 : 40 p. Evans, J. H.; Ballantine, W. J. 983: The climate in 98. Report VI in a series on climatological observations and measurements made at the University of Auckland Marine Laboratory, Leigh from 967 onwards. Leigh Laboratory bulletin 0: p. Furkert, F. W. 947: Tidal compartments, their influence on dimensions of harbour entrance channels. Proceedings of the New Zealand Institution of Engineers 33: 95-. Garner, D. M. 953: Physical characteristics of inshore surface waters between Cook Strait and Banks Peninsula, New Zealand. New Zealand journal of science and technology, section B 35(3) : : Sea surface temperature in the South-west Pacific Ocean, from 949 to 95. New Zealand journal of science and technology, section B 36(3): a: The Sub-tropical Convergence in New Zealand surface waters. 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New Zealand journal of marine and freshwater research 3() : : Hydrological studies in the New Zealand region 966 and 967. Oceanic hydrology northwest of New Zealand. Hydrology of the north-east Tasman Sea. New Zealand Oceanographic Institute memoir 58 : 49 p. Garner, D. M.; Ridgway, N. M. 955: A note on tidal circulation in Lyttelton Harbour. New Zealand journal of science and technology, section B 37() : : Hydrology of New Zealand off-shore waters. New Zealand Oceanographic Institute memoir : 6 p.

43 0 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Garrett, C. J. R. 975: Tides in gulfs. Deep-sea research (): Gilmour, A. E. 960: Currents in Cook Strait. New Zealand journal of geologv and geophysics 3(3) : Gilmour, A. E.; Cole, A. G. 979: The Subtropical Convergence east of New Zealand. New Zealand journal of marine and freshwater research 3(4) : Godfrey, J. S.; Cresswell, G. R.; Golding, T. J.; Pearce, A. F.; Boyd, R. 980: The separation of the East Australian Current. Journal of physical oceanography 0(3): Gordon, A. L. 967: Structure of Antarctic waters between 0 W and 70 W. Antarctic map folio series 6: 0 p, 4 pis. Gordon, D. P.; Ballantine, W. J. 977: Cape Rodney to Okakari Point Marine Reserve. Review of knowledge and bibliography to December 976. Tane (supplement): 46 p. Habib, G.; Clement, I. T.; Fisher, K. A. 980: The purse-seine skipjack fishery in New Zealand waters. Fisheries Research Division, occasional publication 6: 39 p. Habib, G.; Voss, G. J.; Carey, C. L.; Swanson, P. M. 98: Hydrology and plankton of skipjack fishing grounds, north-east North Island, New Zealand. Fisheries Research Division occasional publication, data series 7: 43 p. Harris, T. F. W.; Hughes, T. S. 98: Deep water waves off Hicks Bay and the north-east coast, North Island. National Water & Soil Conservation Organisation. 74 p. Harris, T. F. W.; Hughes, T. S.; Valentine, E. M. 983: Deep water waves off Hicks Bay and the northeast coast, North Island. Water and soil miscellaneous publication 57: 5 p. Healy, W. B. (comp) 980: Pauatahanui Inlet an environmental study. New Zealand Department of Scientific and Industrial Research, information series 4: 98 p. Heath, R. A. 968: Geostrophic currents derived from oceanic density measurements north and south of the Subtropical Convergence east of New Zealand. New Zealand journal of marine and freshwater research (4): : Drift card observations of currents in the central New Zealand region. New Zealand journal of marine and freshwater research 3(): : Hydrology and circulation in central and southern Cook Strait, New Zealand. New Zealand journal of marine and freshwater research 5() : a: Choice of reference surface for geostrophic currents around New Zealand. New Zealand journal of marine and freshwater research 6( & ): b: The Southland Current. New Zealand journal of marine and freshwater research 6(4): a: Present knowledge of the oceanic circulation and hydrology around New Zealand 97. Tuatara 0(3) : b: Direct measurements of coastal currents around southern New Zealand. New Zealand journal of marine and freshwater research 7(4) : c: Meteorological effects on the surface circulation and hydrology of Tasman Bay, New Zealand. New Zealand journal of marine and freshwater research 7( & ): a: The lunar semi-diurnal tide in Cook Strait, New Zealand. Deutsche hydrographische Zeitschrift 7(5 & 6): b: Physical oceanographic observations in Marlborough Sounds. New Zealand journal of marine and freshwater research 8(4): c: Frictional influence on sea level oscillations in Otago Harbour, New Zealand. New Zealand journal of marine and freshwater research 8(): d: Sea level oscillations in Wellington Harbour. New Zealand journal of marine and freshwater research 8(): a: Oceanic circulation and hydrology off the southern half of South Island, New Zealand. New Zealand Oceanographic Institute memoir 7: 36 p. 975b: Oceanic circulation off the east coast of New Zealand. New Zealand Oceanographic Institute memoir 55: 80 p. 975c: Some aspects of the ocean circulation around New Zealand. In: Stanton, B. R. ed. Proceedings of the Regional Workshop on Circulation Studies in the South West Pacific, Wellington, - 5, November 974. New Zealand Oceanographic Institute miscellaneous publication 65: d: Stability of some New Zealand coastal inlets. New Zealand journal of marine and freshwater research 9(4): a: Models of the diffusive-advective balance at the Subtropical Convergence. Deep-sea research 3: b: Oceanic circulation in the head of the Hikurangi Trench, east coast, New Zealand. New Zealand journal of marine and freshwater research 0(4): c: M, tidal currents in Cook Strait. New Zealand Oceanographic Institute Chart, miscellaneous series d: Broad classification of New Zealand inlets with emphasis on residence times. New Zealand journal of marine and freshwater research 0(3): e: Circulation in Tasman Bay. New Zealand journal of marine and freshwater research 0(3): f: Tidal variability of flow and water properties in Pelorus Sound, South Island, New Zealand. New Zealand journal of marine and freshwater research 0():

44 Heath Review of the physical oceanography of the seas around NZ 976g: Factors controlling the entrance crosssectional areas of four inlets (Note). New Zealand journal of marine and freshwater research 0(4): h: The response of several New Zealand harbours to the 960 Chilean tsunami. In : Heath, R. A.; Cresswell, M. ed. Tsunami Research Symposium 974. Bulletin of the Royal Society of New Zealand 5: a: Phase distribution of tidal constituents around New Zealand. New Zealand journal of marine and freshwater research (): b: Heat balance in a small coastal inlet, Pauatahanui Inlet, North Island, New Zealand. Estuarine and coastal marine science 5: a: Semi-diurnal tides in Cook Strait. New Zealand journal of marine and freshwater research (): b: Atmospherically induced water motions off the west coast of New Zealand. New Zealand journal of marine and freshwater research (4): a: Transmission of tidal energy over a plateau. Deutsche hydrographische Zeitschrift 3(6): b: Resonant over-tide across and along Tasman Bay, New Zealand. Estuarine and coastal marine science 8: c: Edge waves on the New Zealand east coast. Marine geodesy (4): a: Eastwards oceanic flow past northern New Zealand. New Zealand journal of marine and freshwater research 4(): b: Current measurements derived from trajectories of Cook Strait swimmers. New Zealand journal of marine and freshwater research 4(): a: Oceanic fronts around southern New Zealand. Deep-sea research 8A(6): b: Variations of the semi-diurnal tidal admittance near New Zealand. Deep-sea research 8A(8): c: Estimates of the resonant period and Q in the semi-diurnal tidal band in the North Atlantic and Pacific Oceans. Deep-sea research 8A(5): Id: Tidal asymmetry on the New Zealand coast and its implications for the net transport of sediment. New Zealand journal of geology and geophysics 4(3): le: Physical oceanography of the waters over the Chatham Rise. NZOI oceanographic summary 8: 5 p. 98a: Temporal variability of the waters of Pelorus Sound, South Island, New Zealand. New Zealand journal of marine and freshwater research 6(): b: What drives the mean circulation on the New Zealand west coast continental shelf? New Zealand journal of marine and freshwater research 6(): c: Generation of - to 3-hour oscillations on the east coast of New Zealand. New Zealand journal of marine and freshwater research 6(): a: Observations on Chatham Rise currents. New Zealand journal of marine and freshwater research 7(3): b: Tidal currents in the Southwestern Pacific Basin and Campbell Plateau, southwest of New Zealand. Deep-sea research 30 (4A): c: Generation of the M 4 tide in Cook Strait. Deutsche hydrographische Zeitschrift 35(6): : Tidal observations on the West Coast, South Island, New Zealand. New Zealand journal of marine and freshwater research 8(): 5-6. (in press): Large scale influence of the New Zealand seafloor topography on the South Pacific Ocean Western Boundary Currents. Australian journal of marine and freshwater research. Heath, R. A.; Shakespeare, B. S. 977: Summer temperatures and salinity distribution on three small inlets on the west coast, North Island, New Zealand. New Zealand Oceanographic Institute records 3(7): Heath, R. A.; Greig, M. J. N.; Shakespeare, B. S. 978: Circulation and hydrology of Manukau Harbour. New Zealand journal of marine and freshwater research (3): Heath, R. A.; Shakespeare, B. S.; Greig, M. J. N. 983: Physical oceanography of Rangaunu Harbour, Northland, New Zealand. New Zealand journal of marine and freshwater research 7(4): Hendershott, M. C. 97: The effects of solid earth deformities on global ocean tides. Geophysical journal of the Royal Astronomical Society (London) 9: Hickman, R. W. 979: Seasonal hydrology of Port Fitzroy, Great Barrier Island, New Zealand. New Zealand journal of marine and freshwater research 3(): Hume, T. M. 980: Index to published and unpublished hydrological data for selected areas of the Waitemata and Manukau Harbours. Internal report. Water & Soil Section, Ministry of Works & Development, Auckland. 3 p. Hume, T. M.; Harris, T. F. W. 98: Bibliography of oceanography and sedimentology for the Northland-Auckland coast. Water & soil miscellaneous publication 8: 63 p. Hurley, D. E. 959: The growth of Teredo (Bankia australis Caiman) in Otago Harbour. New Zealand journal of science and technology (3): Hurley, D. E.; Burling, R. W. 960: The ecological significance of some early sea temperature records from Otago Harbour. New Zealand journal of geology and geophysics 3(4): Huthnance, J. M. 98: A note on baroclinic Rossby Wave reflection at sea-floor scarps. Deep-sea research 8A: 83-9.

45 New Zealand Journal of Marine and Freshwater Research, 985, Vol. 9 Hydrographic Branch 960: Chart Wellington to Patea including Cook strait, :00,000. Chart NZ : Karamea River to Stephens Island, :00,000. Chart NZ 6. Hydrology Working Group 980: Auckland combinedcycle power station investigations. Hydrology of the Waitemata and Manukau Harbours. Report to the Electricity Division of the Ministry of Energy. 68 p. Ippen, A. T.; Harleman, D. R. F. 96: One-dimensional analysis of salinity intrusion in estuaries. US Army Corps of Engineers, Waterways Experimental Station, Vickesburg, Massachusetts technical bulletin 5. Irwin, J. 978: Porirua Harbour bathymetry, : NZOI chart, miscellaneous seris 49. JARMAC Report 98: Report of the albacore survey by the RV Kaio Maru No. 5 in New Zealand waters, 98. Japan Marine Fishery Resource Centre, Tokyo, no. 0. Jeffreys, H. 970: The earth its origin, history and physical constitution. Cambridge University Press. 40 p. Jillett, J. B. 969: Seasonal hydrology of waters off the Otago Peninsula, southeastern New Zealand. New Zealand journal of marine and freshwater research 3(): : Zooplankton and hydrology of Hauraki Gulf, New Zealand. New Zealand Oceanographic Institute memoir 53: 03 p. Jillett, J. B.; Mitchell, S. F. 973: Hydrological and biological observations in Dusky Sound, south-western New Zealand. In : Fraser, R. comp. Oceanography of the South Pacific 97. NZ National Commission for UNESCO, Wellington Kibblewhite, A. C; Bergquist, P. R.; Foster, B. A.; Gregory, M. R.; Miller, M. C. 98: Maui Development Environmental Study Report on Phase Two Report prepared by the University of Auckland for Shell BP and Todd Oil Services Ltd. 74 p. Kirk, R. M. 97: Statistical summary of sea state observations in New Zealand, 97. Unpublished report. (Available from Geography Department, University of Canterbury, Christchurch, New Zealand.) Knox, G. A.; Kilner, A. R. 973: The ecology of the Avon- Heathcote Estuary. Unpublished report to the Christchurch Drainage Board by the Estuarine Research Unit, Department of Zoology, University of Canterbury, Christchurch, New Zealand. 358 P- Laing, A. C. M. 954: Note on tsunamis reaching New Zealand. New Zealand journal of science and technology 35 : Lesser, J. H. R. 978: Phyllosoma larvae ofjasus edwardsii (Hutton) (Crustacea : Decapoda : Palinuridae) and their distribution off the east coast of the North Island, New Zealand. New Zealand journal of marine and freshwater research (4): McCartney, M. S. 977: Subantarctic mode water. In: Angel, M. ed. A voyage of discovery. Deep-sea research 4 (supplement): Marine Information Advisory Service 98: Catalogue of instrumentally-measured wave data. Institute of Oceanographic Sciences, Wormley, Surrey. Marine Information and Advisory Service publication no.. Marshall, B. 977: Northland, New Zealand, a geographical bibliography, Department of Geography, University of Auckland, New Zealand. 6 p. Mercer, S. F. M. 979: Hydrology of the north-east of the North Island Fisheries Research Division occasional publication 7: 8 p. Paul, L. J. 968: Some seasonal water temperature patterns in the Hauraki Gulf, New Zealand. New Zealand journal of marine and freshwater research (3): Pickrill, R. A. 979: Wind waves in New Zealand : an annotated bibliography. New Zealand Oceanographic Institute miscellaneous publication 88: 7 p. Pickrill, R. A.; Mitchell, J. S. 979: Ocean wave characteristics around New Zealand. New Zealand journal of marine and freshwater research 3(4): Quinn, J. 978: The hydrology and plankton of Otago Harbour. Unpublished BSc Hons dissertation, Department of Zoology, University of Otago, Dunedin, New Zealand. Ralph, P. E.; Hurley, D. E. 95: The settling and growth of wharf-pile fauna in Port Nicholson, Wellington, New Zealand. Zoology publications from Victoria University of Wellington 9: p. Reid, J. L. 965: Intermediate waters of the Pacific Ocean. Johns Hopkins oceanographic studies : 85 p. Ridgway, N. M. 960: Surface water movements in Hawke Bay, New Zealand. New Zealand journal of geology and geophysics 3(): : Nearshore surface currents in southern Hawke Bay, New Zealand. New Zealand journal of geology and geophysics 5(4): : Temperature and salinity of sea water at the ocean floor in the New Zealand region. New Zealand journal of marine and freshwater research 3(): : Hydrology of the southern Kermadec Trench region. New Zealand Oceanographic Institute memoir 56: 8 p. 977: Currents and hydrology in Tasman and Golden Bays, South Island, New Zealand. New Zealand journal of marine and freshwater research (): : Hydrological conditions and circulation off the west coast of the North Island, New Zealand. New Zealand journal of marine and freshwater research 4(): : Tsunami hazard in New Zealand. In : Natural hazards in New Zealand. Speden, I.; Crozier, M. J. comp. New Zealand National Commission for UNESCO, Wellington. Ridgway, N. M.; Heath, R. A. 975: Hydrology of the Kermadec Islands region. New Zealand Oceanographic Institute memoir 73: 8 p.