Cold water intrusion in the eastern gulf of Alaska in 2002

Transcription

1 Atmosphere-Ocean ISSN: (Print) (Online) Journal homepage: Cold water intrusion in the eastern gulf of Alaska in 2002 William Crawford, Peter Sutherland & Peter van Hardenberg To cite this article: William Crawford, Peter Sutherland & Peter van Hardenberg (2005) Cold water intrusion in the eastern gulf of Alaska in 2002, Atmosphere-Ocean, 43:2, , DOI: /ao To link to this article: Published online: 21 Nov Submit your article to this journal Article views: 94 View related articles Citing articles: 14 View citing articles Full Terms & Conditions of access and use can be found at

2 Cold Water Intrusion in the Eastern Gulf of Alaska in 2002 William Crawford 1*, Peter Sutherland 2 and Peter van Hardenberg 2 1 Institute of Ocean Sciences, Fisheries and Oceans Canada 9860 West Saanich Road, P.O. Box 6000, Sidney BC V8L 4B2 2 University of Victoria, Victoria BC [Original manuscript received 16 January 2004; in revised form 23 November 2004] ABSTRACT A patch of anomalously cold and fresh oceanic water appeared off the west coast of North America during the summer of The coldest anomaly resided 100 to 150 m below the surface, and was the coldest anomaly ever measured in summer. The motion of this water mass is tracked through the Gulf of Alaska in early 2002 and into the following year. It may have formed near the centre of the Alaskan Gyre during previous winters and advected eastward onto the continental margin. Examination of summer temperature anomalies at this range of depths in the south-east Gulf of Alaska over the previous 35 years shows that the anomalies responded to interannual wind anomalies attributed to the El Niño Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). Gulf of Alaska temperatures lag these signals, offering hope that future temperature changes will be predicted. RESUMÉ [Traduit par la rédaction] Une étendue d eau océanique anormalement froide et douce est apparue au large de la côte ouest de l Amérique du Nord durant l été L anomalie la plus froide se trouvait de 100 à 150 m sous la surface et c était la plus froide anomalie jamais mesurée en été. Le mouvement de cette masse d eau est suivi à travers le golfe d Alaska vers le début de 2002 et jusque dans l année suivante. Elle peut s être formée près du centre de la circulation de l Alaska durant les hivers précédents et s être déplacée vers l est jusqu à la marge continentale. L examen des anomalies de température en été dans cet intervalle de profondeurs dans le sud-est du golfe d Alaska au cours des 35 années précédentes montre que les anomalies correspondaient aux anomalies de vent interannuelles attribuées au El Niño oscillation australe (ENSO) et à l oscillation décennale du Pacifique (ODP). Les températures dans le golfe d Alaska affichent un retard par rapport à ces signes, ce qui permet de penser que les futurs changements de température seront prédits. 1 Introduction Cold and fresh sea water appeared off the west coast of Oregon (OR), Washington State (WA) and British Columbia during the summer of 2002 (e.g., Freeland et. al., 2003). The coldest anomalies appeared in the halocline (where the vertical density gradient is determined mainly by salinity) at depths between 100 and 150 m below the ocean surface. Minimum temperatures were close to 7.5 C off Oregon at N (e.g., Wheeler et al., 2003) and 6.5 C near southern Vancouver Island (e.g., Freeland et. al., 2003). The geographical region is displayed in Fig. 1. A series of papers describe the evolution and motion of this cold anomaly in surface waters of the Gulf of Alaska and its eastern continental margin. Winds in the Gulf of Alaska in the preceding six months first brought cooler surface, subarctic waters into the eastward-flowing North Pacific Current, then accelerated this current toward the coastal regions of Vancouver Island to Oregon (e.g., Murphree et al., 2003). This wind pattern established in the 1998/99 winter and persisted for the next three winters (e.g., Bond et al., 2003). A variety of ocean measurements observed the southward motion of this surface anomaly on the continental margin. Satellite altimeter measurements revealed stronger than normal southward flow at the surface along the continental margin in the 18 months prior to the summer of 2002 (e.g., Strub and James, 2003). Lagrangian surface drifters moved faster toward the south along the Oregon coast in 2002 than in each of the previous four years (e.g., Barth, 2003). Anomalous winds near the coast upwelled cold waters and advected them southward at the surface (e.g., Murphree et al., 2003). Interestingly, the surface cold water anomaly did not persist into the summer of 2002 in Canadian waters. Surface seawater temperatures from June to August of 2002 were somewhat warmer than in the preceding two years at the Amphitrite coastal observing station (Fig. 1) on the southwest coast of Vancouver Island. At Pine Island, to the north of Vancouver Island (Fig. 1), the surface waters in summer were as warm as, or warmer than, they were during the preceding two years. The cold surface waters noted in spring *Corresponding author: crawfordb@pac.dfo-mpo.gc.ca ATMOSPHERE-OCEAN 43 (2) 2005, Canadian Meteorological and Oceanographic Society

3 120 / William Crawford et al. Fig. 1 Geographical features of the eastern Gulf of Alaska. The asterisk (*) denotes the location of Argo profiler The continental shelf is indicated by the 200-m contour by previous studies seemed to have been replaced by warmer water, perhaps due to the changes in atmospheric forcing in mid-2002 noted by Murphree et al. (2003) and by Freeland and Cummins (2005). However, cold, subsurface water persisted into the summer of A few papers note the subsurface properties of this anomaly near Vancouver Island and Oregon. Subsurface waters arriving off Oregon were much richer in nutrients than normally found in summer, and more than 0.5 C colder than any previous summer observation (e.g., Wheeler et al., 2003). Enhanced nutrient levels doubled the local chlorophyll stocks, which in turn sank and drew down the already low oxygen levels in bottom waters, leading to eutrophication (e.g., Wheeler et al., 2003). Ocean current measurements on the Oregon shelf in 81 m of water revealed an enhanced southward flow during the first six months of 2002, with cumulative southward anomalous displacement of almost 1600 km at a depth of 10 m, decreasing to 700 km at a depth of 64 m (e.g., Kosro, 2003). However, these studies do not determine the motion or source of the subsurface cold anomaly in the halocline prior to its appearance near Vancouver Island, Washington and Oregon. We examined measurements of water properties in the gulf to track the cold anomaly in early 2002, using the Argo array of ocean profilers (e.g., Argo Science Team, 1998) launched into the Gulf of Alaska, supplemented by ship-based observations when available. Figure 2 displays a sequence of temperature profiles between July 2001 and July 2002 measured by Argo profiler about 140 km west of Vancouver Island in 2100 m of water. (Argo profilers sample temperature and salinity from a depth of 2000 m to the ocean surface every 10 days, then sink to a depth of 2000 m to drift for 10 days.) This instrument profiled near 48.8 N, W (Fig. 1) between May 2002 and July 2002, and stayed within 100 km of this point prior to May From July 2001 to March 2002 the surface mixed layer cooled and the upper thermocline warmed, leading to a nearly uniform-temperature upper water column in March. Interestingly, waters below 120 m were coldest in July 2001 and again in July The anomalous cooling began at depths between 40 and 110 m in May 2002, and deepened to depths between 80 and 190 m in July This final cooling was greatest between 90 and 140 m, and was caused by cold water advection into the region. It could not have cooled locally by vertical mixing alone. The full horizontal extent of this cold anomaly can be observed by comparing the four panels of Fig. 3. The top left panel (Fig. 3a) presents multi-year average summer temperatures at a depth of 100 m in the Gulf of Alaska. (Summer is

4 Cold Water Intrusion in the Eastern Gulf of Alaska in 2002 / 121 Fig. 2 Temperature profiles measured in the eastern Gulf of Alaska between July 2001 and July 2002 defined as 1 July to 30 September.) This average is based on observations in archives at the Institute of Ocean Sciences in British Columbia, the Marine Environmental Data Service in Ottawa and the National Ocean Data Center in Washington, DC. (Observations were excluded from summers influenced by large El Niño or La Niña events: 1958, 1983, 1992, 1998 and 1999.) The remaining panels (Figs 3b to 3d) show summer temperature anomalies at a depth of 100 m for the years 2001 to 2003, based on archived expendable bathythermograph (XBT), CTD and Argo observations. The cold subsurface anomaly grew in 2002 and extended over the gulf east of 145 W and south of 55 N, and possibly into other regions where data coverage was poor in The anomaly declined by the summer of Salinity and density of the cold anomaly Three times a year the Canadian Coast Guard Ship John P. Tully samples water properties from the surface to a depth of 1500 m along Line-P, a series of oceanic stations between the southern end of Vancouver Island (48.5 N, W) and Ocean Station Papa (OSP) at 50 N, 145 W. The measurements reveal that minimum temperatures of the cold layer along Line-P in 2001 and 2002 appeared at a salinity of 33.0±0.2 and a sigma-t of 26.0±0.2 kg m -3, with small spatial or temporal variation. This water mass resided in the halocline between a depth of 125 and 150 m. To examine the north south extent of this feature we examined data archives of Argo profilers released into the gulf as part of the global Argo deployment program (e.g., Argo Science Team, 1998). We found that the depths of the 33.0 salinity surface and the sigma-t 26.0 density surface in the eastern gulf in early 2002 rarely differed by more than 10 m in waters beyond the continental margin, implying little modification of this salinity surface by mixing with other waters. Waters in the halocline change temperature slowly, mainly due to mixing with warmer waters in the upper mixed layer, with maximum mixing expected when the surface mixed layer reaches its annual maximum depth in March of most years. We expect the source region of this cold anomaly in the halocline was where the 33.0 salinity waters last contacted the ocean surface mixed layer in winter. To search for this region, we examined all Argo profile records from 3 to 12 March 2002 to determine a mixed layer depth and the depth of the 33.0 isohaline. In the eastern gulf, at the latitude range of Vancouver Island, we observed the 33.0 surface to lie an average of 30 m below the base of the surface mixed layer (determined subjectively), which itself had an average depth of 100 m. Figure 4 plots the vertical distance of the

5 a b c d 122 / William Crawford et al. Fig. 3 Average summer temperature ( C) at a depth of 100 m (a), and summer anomalies at 100-m depth in 2001 (b), 2002 (c), and 2003 (d).

6 Cold Water Intrusion in the Eastern Gulf of Alaska in 2002 / 123 Fig. 4 Depth in metres of the 33.0 salinity surface below the base of the mixed layer, 1 to 10 March Black dots denote CTD and Argo float positions. Mixed layer salinity is >33.0 to the north-west of the zero contour. Contours west of 150 W and south of 45 N rely on data points outside the border of this image, and are not reliable. Fig. 5 Temperature ( C) on the 33.0 salinity surface, 1 to 10 March 2002, based on CTD and Argo profiles. Black dots denote profile locations salinity surface below the base of the mixed layer in early March 2002, based on automated contouring software and a criterion of 0.1 C cooling as the mixed layer depth. A zero distance in Fig. 4 reveals the 33.0 salinity surface to be in the mixed layer, or a saltier mixed layer. This condition was found throughout most of the north-west Gulf of Alaska from December 2001 to April (Note that contouring is unreliable in regions of sparse observations, such as the western and north-western gulf, and south of 45 N where the closest profilers are at 37 N.) The region near to, or west of, the zero contour could be a source (or ventilation) region of the cold anomaly. Over the eastern gulf the 33.0 salinity surface

7 124 / William Crawford et al. only, so the results do not apply to lower depths, but are relevant for our cold anomaly at 125-m depth. Temperatures on the 33.0 salinity surface in early March 2002 displayed a very distinct tongue of cold water extending 1700 km from the centre of the Alaska Gyre in a south-easterly direction toward the west coast of North America. Figure 5 displays a typical example for early March Although the Argo profiler density is sparse in the western gulf, leading to unreliable contouring, the coverage east of OSP and north of 46 N is sufficiently dense to support accurate contouring. Temperatures along this tongue ranged from 4.5 C to 7 C, with a gradual warming of water on the 33.0 surface toward the south-east in the gulf that might be attributed to storm-driven mixing in winter as noted by Large et al. (1986). The tongue was first observed in February 2002, when the Argo array was sufficiently extensive to resolve it, and was still present in the summer of 2003, weakening and broadening slightly near the end of We seem to have observed the subsurface advection of waters that ventilated in mid-gyre during a previous winter. A time series of three plots is shown in Fig. 6 for a subregion of Fig. 5. These three illustrate the approach of the cold water anomaly toward the continental margin between February and July (Contours in Figs 5 and 6 are most accurate near data points denoted by open circles. The warm feature near 52.5 N, 136 W in March 2002 is a Haida Eddy of radius 80 km.) The 6.5 C contour in February 2002 extended as far inshore along Line-P as 129 W, and the 7.5 C contour ranged from 127 W to W. By May 2002 the 6.5 C contour had reached the 200-m-deep shelf break off the northern end of Vancouver Island near 128 W, and the 7.5 C contour reached the shelf break at 126 W. (This advection caused the cooling observed in May 2002 in Fig. 2.) By the end of June and into early July 2002 both the 6.5 C contour and the 7.5 C contour had reached the shelf break west of the mouth of Juan de Fuca Strait at 48.5 N. Fig. 6 Temperature ( C) on the 33.0 salinity surface in the south-eastern Gulf of Alaska based on CTD and Argo profiles. Black dots denote profile locations, (a) February 2002; (b) May 2002; (c) June July lies between 10 and 40 m below the mixed layer base, with an average of 30 m as noted above. Properties of 33.0 salinity water should change little at this depth. However, we expect some warming of this anomaly during winter, due to the penetration of mixed layer water into the upper thermocline during severe storms. Large et al. (1986) found the mixed layer turbulence generated by each autumn storm near OSP led to maximum warming by 1.5 ±1.3 C at depths of 1.3L, where L is the mixed layer depth, and found more minor warming to depths of 1.7L. Their instruments sampled in the top 120 m 3 Geostrophic flow Progression of the cold anomaly in Figs 5 and 6 suggests eastward flow along the 33.0 salinity surface. Additional evidence of such flow is available from geostrophic motion determined from contours of the dynamic height anomaly in the halocline. We computed the dynamic height anomaly derived from Argo profiler measurements at depths of 100, 125, 150, and 225 m with respect to the 1900 m surface. The 100-, 125- and 150-m depths represent the cold water anomaly depth range discussed in the previous section, and the 225-m surface was adjacent to, but below that range. The 1900-m surface was chosen as a reference depth for dynamic height calculations because some Argo profilers started sampling slightly above the nominal 2000-m depth. The absolute current at 2000 m is known with some accuracy because the Argo floats behave like Lagrangian drifters at that depth, surfacing only briefly to transmit data. Drifter speeds at the 2000-m depth were small compared to

8 Cold Water Intrusion in the Eastern Gulf of Alaska in 2002 / 125 geostrophic speeds of the cold anomaly at 125 m during the spring of Useful images of the dynamic height anomaly began in early March 2002, following the launch of nine Argo profilers along 47 N, between the continental margin and 150 W. One example of this calculation at 125 m is presented in Fig. 7a. Similar images (not shown) were found in April and May Geostrophic flow occurs along lines of constant dynamic height with higher heights on the right side of the flow. This flow, in late June 2002, was eastward over a north south latitude range of 47 N to 50 N. The eastward geostrophic flow in early 2002 extended from the western limit of high-resolution data at 150 W and the shoreward limit of data at 128 W. Flow speeds generally ranged between 5 and 10 cm s 1 and varied little, generally <3 cm s 1, between 100 and 150 m. The flow direction was also uniform. The depth of this shoreward flow extended to at least 225 m; however its speed was greatly reduced. Geostrophic flow in June 2003 and 2004 (Figs 7b and 7c) was directed more to the north-east, so that the cool waters, were unlikely to reach the continental shelf at, or south of, Vancouver Island. This more northerly flow, at 120-m depth, in 2003 was also noted in surface flow patterns in this region presented by Freeland and Cummins (2005), based on dynamic height contours computed from Argo profilers. Both show anticyclonic flow in summer 2004 around Haida The contours of Fig. 7c suggest the flow would have deflected northward in the absence of this Haida Eddy. 4 Interannual variability along Line-P. The cold water anomaly appeared in the eastern Gulf of Alaska following several years of cooling associated with a winter wind pattern in the gulf described by Bond et al. (2003). To examine past temperatures in the gulf at the depth of this anomaly and past behaviours of larger scale climate processes in the ocean, we examined records of subsurface temperature, as well as time series of Multi-Variate El Niño Southern Oscillation (ENSO) Indices (MEI) and the Pacific Decadal Oscillation (PDO) indices for 37 years in the eastern gulf. a Observations of Subsurface Temperature Only along Line-P are there sufficient subsurface temperature observations to compile a 37-year record that resolves interannual changes in temperature. This time period covers the extent of reasonably regular sampling of water temperature along Line-P by Canadian research ships and weatherships. The Line- P temperature time series was augmented with CTD and hydro bottle measurements by other research cruises and by XBT profiles from ships-of-opportunity and naval vessels. We searched through three ocean data archives for these observations: (a) Institute of Ocean Sciences in Sidney, BC, Canada (b) Marine Environmental Data Service in Ottawa, ON, Canada (c) US National Oceanographic Data Center in Washington, DC, USA. Fig. 7 Dynamic height anomaly (dynamic metres) between 125- and metres depth. Black dots denote Argo profiler locations, (a) June 2002, (b) June 2003, (c) June Observations were applied to our Line-P data if the station was within 100 km of Line-P. Observations were separated into seasonal bins, with only the summer bin (July August September) at depths between 100 and 150 m considered here. Profiles of summer temperatures since 1968 are sufficiently frequent and regular to permit us to plot continuous contours of temperature in the time-longitude space of a Hovmüller diagram, presented in Fig. 8b. Figure 8b presents the summer-average, 100- to 150-m temperature anomaly along Line-P for the summers of 1968 to Our cold anomaly began at the western end of Line- P in summer 2000, and progressed eastwards in time, reaching the continental margin in summer This cold anomaly continued into 2004 in the west and central Line-P, but reverted to neutral conditions with a few warm patches in the summer of 2004 east of 130 W.

9 126 / William Crawford et al. Fig. 8 (a) Pacific Decadal Oscillation (PDO), computed by Mantua et al. (1997). Red denotes warm, positive phase; (b) Hovmüller diagram of summer temperature anomaly ( C) averaged between the depths of 100 and 150 m along Line-P, 1968 to 2004, based on observations within 100 km of Line-P. The x-axis denotes longitude. (c) Multi-variate ENSO index (MEI), computed by NOAA-CIRES Climate Diagnostic Center. Red denotes El Niño phase. b Multi-Variate ENSO Index (MEI) and Pacific Decadal Oscillation (PDO) Figure 8a presents the PDO monthly time series adapted from the time series prepared by Nathan Mantua (personal communication, 2004). The PDO is a pattern of Pacific climate variability computed as the principal component of North Pacific monthly sea surface temperature variability (e.g., Mantua et al., 1997). Figure 8c presents the MEI time series prepared by the National Oceanic and Atmospheric Administration-Cooperative Institute for Research in Environmental Sciences (NOAA- CIRES) Climate Diagnostic Center at the University of Colorado at Boulder. This indicator series is based on a composite of several tropical time series that vary with the Southern Oscillation and with El Niño-La Niña events. c Comparison of Indices with Subsurface Temperatures Clearly one can see a visual correlation between these time series. During a positive (warm) phase of PDO, winds in the eastern Gulf of Alaska tend to blow more strongly from the south or south-west. The same winds are strengthened during the positive (El Niño) phase of MEI in the northern hemisphere, because the Aleutian Low normally strengthens during El Niño winters. Therefore, positive phases of PDO and MEI tend to strengthen southerly winds along the North American west coast, especially in winter, carrying warmer waters northward. This warming persisted into summer. Similarly, a negative (cold) phase of PDO and negative (La Niña) phase of MEI will combine to reduce these winter winds, or to strengthen winds toward the south in summer, cooling the waters of the eastern Gulf of Alaska. The winter winds of 1999 to 2002 have been described well by Bond et al. (2003), who note that the normal PDO winter conditions were present but not dominant during these winters. Instead, the Aleutian Low was pushed farther north than normal, and the air-pressure pattern was better represented by the second mode of North American sea surface temperature variability now referred to as the Victoria Mode, which is associated with winds from the west-south-west along Line-P. Such winds are expected to upwell cold water to the north of Line-P. Associated with this upwelling, or actually driving it, was outflow of surface water from the mid-aleutian Low. The outflow was toward Line-P on the south side of the low. Therefore, this four-winterlong pattern of winds could have carried anomalously cold water toward Line-P, which then advected eastward in the eastern gulf, below the surface mixed layer. Our summer plot in Fig. 8b reveals it as a subsurface cool layer, advancing eastward in time.

10 Cold Water Intrusion in the Eastern Gulf of Alaska in 2002 / 127 Coastal trapped waves and mesoscale eddies also link MEI to the warm anomalies along Line-P. The warm waters near Peru and Ecuador can set up a northward-travelling coastal trapped wave along the west coasts of North America that reaches Line-P during very strong El Niño events. The stronger Aleutian Low during El Niño winters also pushes coastal warm waters northward. During extreme El Niño winters, such as and , the winds of severe storms that hit the California coast also set up continental shelf waves carrying warmer waters northward. If these waters reach the Queen Charlotte Islands of western Canada they are likely to form larger Haida Eddies, one of which was observed on Line- P in A weaker North Pacific High during El Niño events will reduce the strength of upwelling winds along the North American west coast, permitting warmer water to remain at the coast, and northward travelling coastal trapped waves to penetrate to higher latitudes. Many of these processes are present in the time series of Fig. 8, as noted below. The shift from generally cold waters on Line-P to generally warmer waters in the later 1970s followed shifts in both ENSO and PDO signals. The 1972 El Niño event was particularly strong off Peru, but its influence at Line-P can barely be observed. A cold phase of PDO dominated the entire period of the late 1960s to the late 1970s, and would be expected to have suppressed warming by the 1972 El Niño in the Gulf of Alaska, including Line-P. The very cold waters on Line-P in 1990 followed La Niña and cold PDO phases. The two strongest ENSO events of this period were the and events, which took place during warm PDO phases. Both events were followed by generally warmer waters along Line-P, with some Line-P regions experiencing the warmest anomalies in the entire series. The warm anomaly at 134 W in 1998 is Haida-1998, the largest Haida Eddy ever observed (e.g., Crawford, 2002). The warm water anomaly at 136 W in 1995 is Haida Haida Eddies form every winter west of the Queen Charlotte Islands and drift into the Gulf of Alaska (e.g., Crawford and Whitney, 1999). Haida-1998 and Haida-1995 drifted farther south than other eddies, and both crossed Line-P several months after their formation. As noted above, the lag of temperature anomalies along Line-P behind the climate indicator time series may provide us with an opportunity to predict subsurface temperature anomalies in the eastern Gulf of Alaska. 5 Discussion and conclusions Our analyses reveal a steady eastward flow of the cold anomaly in the halocline below the surface mixed layer in Several previous studies have found similar flows from the west and north-west at OSP. For example, careful analyses of air-sea heat flux and heat storage in the upper 120 m (e.g., Tabata, 1965; Large et al., 1986) revealed that there must be horizontal advection of cold water in the halocline toward OSP to achieve heat balance over an annual cycle. Horizontal temperature gradients in the halocline indicate this flux arrives from the north-west quadrant. Thomson et al. (1990) found an eastward current of 4 to 10 cm s 1 in the halocline in the gulf near 50 N and between 160 W and 140 W, based on surface drifters with deep drogues at 100 to 120 m below the surface. This speed is comparable to the geostrophic speed we found at a depth of 125 m. Source regions for the cold water anomaly can be found by locating areas where the density surface (σ t ) of 26.0 kg m 3 is within the surface mixed layer. Figure 3a suggests this region was to the north-west of OSP in March 2002, near the centre of the Alaskan Gyre, where surface temperatures are generally lowest in winter, and densities are highest (e.g., Freeland et al., 2003). The NOAA-CIRES Climate Diagnostics Center provides historical, monthly, sea surface temperatures (SSTs) on their Internet site. March SSTs plotted with these data reveal the mid-alaskan Gyre was colder after 1998 than in the two preceding winters, with minor differences among these four post-1998 years. Murphree et al. (2003) note that SSTs in most of the north-east Pacific Ocean were negative during the winter. These anomalies could have enhanced the cold anomaly in the gyre. The temperature anomaly was computed from depths between 100 m and 150 m along Line-P for the years 1966 to The coldest anomaly occured in 2002, but more importantly, the temperature anomaly correlates visually with larger-scale climate signals such as the Multivariate ENSO Index (MEI), and the Pacific Decadal Oscillation (PDO). Cold and warm anomalies lag these climate time series, offering the expectation that future cold and warm anomalies will be predicted. Acknowledgements Peter Sutherland and Peter van Hardenberg were supported by grant GR303 awarded to Michael Stacey of the Royal Military College by the Canadian Foundation for Climate and Atmospheric Sciences. Other funding was provided by Fisheries and Oceans Canada. Argo profilers in the Gulf of Alaska were provided by Fisheries and Oceans Canada, and by the Canadian Climate Action Fund, through programs run by Howard Freeland that also supported Peter van Hardenberg. Ship-based CTD measurements in the Gulf of Alaska in 2002 and 2003 were taken from the CCGS John P. Tully by the following senior scientists: David Mackas, Frank Whitney, Marie Robert and Richard Thomson. Most of the temperature measurements around Vancouver Island were provided by scientists of Fisheries and Oceans Canada: David Mackas, Hugh MacLean, Diane Masson, Angelica Pena, Dario Stucchi, Richard Thomson, David Welch, Frank Whitney. Nanoose measurements were provided by staff of the Department of Defence, Canada.

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