The Antarctic ice sheet and its probable bi-modal response to climate

Transcription

1 MASS BUDGETS : ICE AGES 347 ROBIN, G. DE Q. and ADIE, R. J The ice cover. Antarctic Research. ROBINSON, E. S On the relationship of ice surface topography to bed topography on the South Polar Plateau. J. Glaciology, Vol. 6, No. 43, SHUMSKY, P. A The fields of pressure and density in glaciers. Clac. Issled., No. 9. VORONOV, P. S On the dimensions of the Antarctic continent and the character of its denudation (in Russian). Problems of Arctic and Antarctic 17. WERTH, E Aufbau und Gestaltung von Kerguelen. Deutsche Südpolarexpedition Bd. II, H.2. WRIGHT, C. S. and PRIESTLEY, R. E Claciology. British Antarctic Expedition, The Antarctic ice sheet and its probable bi-modal response to climate BY MARIO B. GIOVINETTO Department of Geography, University of California-Berkeley, Ca., U.S.A. Contribution No. 225, Geophysical and Polar Research Center, Department of Geology, University of Wisconsin, Madison, Wise, U.S.A. ABSTRACT The net mass budget estimates reported elsewhere for the Amery Ice Shelf drainage system and the eastern and western parts of the Ross Ice Shelf system are combined with (i) an alternate estimate for the Amery Ice Shelf system, and (ii) alternate estimates for the eastern part of the Filchner Ice Shelf system. These systems make up the interior province of Antarctica and their combined net budget is estimated to be positive and in the order of (3 ± 1) g yr" 1. The Ross Ice Shelf system as a whole is the only system of the interior province for which the estimate of a positive net budget is significant ((18 ±5) g yr- 1 ); direct and indirect evidence confirms that the western part of the system is a region within the interior province where the net budget is positive. The interior province accounts for approximately one half of both the area and the mass of the ice sheet, and one third of the total mass input; engulfed ice shelves are the agents of drainage, and the net mass gain is equivalent to approximately one half the annual input in the province. The remaining drainage systems are split into three groups and make up the peripheral province. This province accounts for the remaining one half of both the area and the mass of the ice sheet, and two thirds of the total mass input; the agents of drainage are marginal ice shelves, glacier tongues and grounded ice termini. A comparison of the net budget for the interior province with data on sea level change during the last 100 years, indicates that the net budget in the peripheral province should be negative. Empirical and heuristic two-province models of the ice sheet suggest that

2 348 ISAGE its response is bi-modal to the present and as yet undetermined climatic regime. Introduction Recent mass budget studies for the Ross and Amery ice shelves drainage systems (Fig. 1) suggest net positive budgets greater than the error estimates by factors >\ and g3 (Budd et al., 1967; Giovinetto et al. 1966; Giovinetto and Zumberge, in press). These systems, and the eastern part of the Filchner Ice Shelf system, make up the interior province of Antarctica. The interior province accounts for approximately one half the area («^7 x 10 6 km 2 ) and more than one half of the ice mass (^1 X g) of the ice sheet (Giovinetto, 1964). In the following sections the budget estimates for each of the systems in the interior province are discussed in terms of a probable bi-modal 90 W-I ti=? I -H-90-E 600 KM FIG. 1. The drainage divides in Antarctica are depicted by lines of dashes and dots (after Giovinetto, 1964). The areas of the eastern and western parts of the Ross Ice Shelf drainage system (EF) are shaded with slanted and vertical lines, respectively. The areas of the Amery Ice Shelf (BC) and eastern Filchner Ice Shelf (J'K) drainage systems are also shaded. Ice discharge from the southern ice stream basin (SISB) may drain south and west of Berkner Island (Fig. 2).

3 MASS BUDGETS : ICE AGES 349 response of the ice sheet to the present and as yet undetermined climatic regime. The models proposed are dependent on assumptions related to the mass budget of the peripheral province of Antarctica and eustatic sea-level changes. The regimen of the interior province The Amery Ice ShelJ drainage system. Budd and others (1967) have estimated ice discharge across the northern boundary of the Amery Ice Shelf at (27 ± 9) g yr- 1 (Table 1). They estimate net accumulation TABLE 1 THE REGIMEN OF THE INTERIOR PROVINCE Drainage system Amery I.S. A.I.S. (alt.) R.I.S. (cast.) R.I.S. (west.) R.I.S. (whole) F.I.S. (east.) F.I.S. (east.; alt.) a All systems All systems (alt.) Area 10 5 km 2 16± 5 16±5 12 ±2 18 ±3 30 ±4 25 ±5 19 ± 5 71 ± 8 65 ±8 Input 10'Sgyr 1 85 ± ± ± ± J_ r ± 88 Output 1Q15 gyr-l 27 ±9 27 ±9 168 ± ± ± ± ± ± ± 45 Net budget 101«g yr-i 6±4t 10 ±4* 13±5 5±3 18±5*f 114-7* (5 ± 7)t 10"gyr-' (4± 1)* (3 ± m 1 Excluding the southern ice stream basin ("S.I.S.B.", Fig. 1). at the surface for the area of the Amery Ice Shelf drainage system at (85 i 43) 10 ]5 g yr" 1, and suggest that subglacial net mass flux on the ice shelf is relatively small; from these data the net budget is here estimated at (6 ± 4) g yr- 1. Budd and his colleagues estimated net accumulation at the surface for the whole area of the system assuming that the bulk of the net ablation at the surface in the Lambert Glacier (Fig. 1, between and south of B'B") and on the grounded ice sheet slopes to the east, south, and west of the glacier is lost as evaporation, deflation, and surface melt run-off which reach the sea somewhere in the southern part of the Amery Ice Shelf. However, evaporation is relatively small and it is improbable that surface melt run-off could reach the sea somewhere near the grounded ice boundary, where ice thickness is greater than 450 m (Budd, 1966). Moreover, the whole width of the Lambert Glacier is heavily crevassed, and a large proportion of the drifting snow and melt run-off would be trapped

4 350 ISAGE (cnglacial accumulation*); drifting snow and melt run-off also would accumulate on the flat surface of the ice shelf. Assuming that net abation at the surface of the Lambert Glacier is accounted for by englacial accumulation and by an increase of the rate of net accumulation at the surface of the ice shelf near the grounded ice boundary, the preceding estimate of mass input based on the data of Budd et al. (1967) could be replaced by an earlier estimate which is approximately 65 per cent greater ((131 ± 36) g yr" 1 ; Giovinetto, 1964). The resulting alternate estimate of the net budget ((10 ± 4) 10 1G g yr -1 ; Table 1) is greater than the error estimate by a factor of 2-5, indicating a probable positive budget. The Ross Ice Shelf drainage system. In Table 1 the area and mass input and output terms for the eastern and western parts of the Ross Ice Shelf system are compared with the same data for the whole system. The summation of input terms amounts to (349 ± 51) g yr" 1. The itemized terms follow: (i) Net accumulation at the surface in the eastern part, which includes the ice shelf, and the minimum estimate of net subglacial freezing are (208 ± 44) 1O 1S g yr" 1 and 45 x g yr- 1, respectively (Giovinetto and Zumberge, in press), (ii) Net accumulation at the surface in the western part is (96 ± 25) g yr -1 (Giovinetto et al., 1966). The rate of mass output across a drainage section not coincident with the ice terminus, and extending between Cape Spencer-Smith in 78 S, 167 3O'E and Edward VII Peninsula in 77 45'S, 158 W, is (168 ± 18) g yr~ a (Giovinetto and Zumberge, in press). Therefore, the net budget for the whole Ross Ice Shelf system is estimated here at (18 ± 5) g yr -1. The composite error (± 28 per cent) in this estimate confirms the positive estimates indicated for each of the two parts of the system; in the estimates for the eastern and western parts the standard errors are ± 38 per cent and ± 60 per cent, respectively. The eastern part of the Filchner Ice Shelf drainage system. The estimates of area and net accumulation at the surface of the eastern part of the Filchner Ice Shelf system are (25 ± 5) 10 5 km 2 and (200 ± 58) g yr- 1, respectively (Giovinetto, 1964). Using the same model adopted for the Ross Ice Shelf to estimate subglacial net mass flux (Giovinetto and Zumberge, in press), the minimum net freezing in the eastern part of the ice shelf is estimated to be approximately 15 X g yr- 1. The summation of net accumulation at the surface and net subglacial freezing is (215 ±58) g yr- 1 (Table 1). * As implied by Budd et al. (1967): "The crevasses may accumulate snow and melt water, but this does not imply a gain, but rather a redistribution of mass." Accounting for this redistribution, their estimate of net accumulation can be increased by g yr~ l to 95 x g yr" 1, i.e. the minimum estimate made by Giovinetto (1964). To be sure, this alternate estimate is not valid if a large proportion of the gross ablation in the area is due to evaporation.

5 MASS BUDGETS : ICE AGES 351 Ice discharge east of Berkner Island (Fig. 2), has been estimated by Behrendt (1962) and Lisignoli (1964). Their estimates are here revised combining the results of both studies: the mean ice velocity is approximately 1500 m yr -1, and the mean ice thickness for the 240 km segment is approximately 300 m. From these data, ice discharge is estimated at (108 ± 40) g yr' 1 (Table 1). This estimate is in agreement with those made by Behrendt and Lisignoli, although it is based on the mean ice thickness estimated by Behrendt (300 m), which is greater than that used by Lisignoli (250 m). The composite error (±37 per cent) is the summation of: (i) An error of approximately ± 20 per cent in the estimate of mean ice thickness, which Behrendt (1962 and personal communication) estimated from data on ice surface elevation, (ii) An error of approximately ± 30 per cent in the estimate of mean ice velocity, which Lisignoli (1964) estimated from changes in the grid-position of stations for periods from three to six years (the error in the standard astronomical determination of latitude in Antarctica is at least ± 1000 m; Chapman, personal communication). To be sure the relative error is very small in the estimate of velocities for the eastern segment of the drainage section, between General Belgrano Base (Fig. 2) and the Moltke Nunataks (approximately 78 10'S, 35 1O'W), but it is greater than ± 30 per cent in the western segment of the section, between General Belgrano Base and Berkner Island, (iii) An assumed error of approximately ± 10 per cent in the estimate of the smoothed length of the barrier. The net budget estimate ((11 ± 7) g yr -1 ) is greater than the error estimate by a factor of 1-6, and the result is inconclusive. This estimate is invalidated even further if there is ice shelf discharge toward the west along the southern edge of Berkner Island, a possibility not taken into account in the error estimate. Ice surface data collected along the route of aircraft flights and on landing sites during the and field seasons (Behrendt, 1965) suggest that a large ice stream may flow south and west of the Pensacola Mountains (Fig. 2, centered approximately at 83 3O'S, 52 00'W). If the ice contributed by this stream into the ice shelf ultimately discharges parallel and along the southern and western flanks of Berkner Island instead of the eastern flank, then the budget estimate would be smaller in relation to the error magnitude. An ice stream draining south and west of the Pensacola Mountains could account for a mass output of at least 5 X g yr~ a, i.e. for the whole net accumulation at the surface in the southern area of the system (Fig. 1). Ice shelf thickness data south of Berkner Island (Behrendt, 1962) and the recent discovery of a large zone of shear in the ice shelf (near the barrier and approximately 100 km west of Berkner Island as shown in the American Geographical Society's chart of Antarctica, 1:5,000,000, 1965) suggest that the ice stream may indeed exist, and that it may discharge westward and south of Berkner Island. If this is shown to be true by future field work, the

6 352 ISAGE KILOMETERS!! I! I I Co^'ot' initivol 200 mtitn cicept on Ice Shelf wt-.«re too meters is shown FIG. 2. Surface relief in the Filchner Ice Shelf area of Antarctica (after Behrendt, 1965), where a trough approximately from 87 S, 90" W, to 83 S, 60 W suggests that a large ice stream flows west of the Pensacola Mountains (approximately at 83 3O'S, 52 0O'W) and south and west of Bcrkner Island. area and the rate of mass input in a redefined "eastern part" of the Filchner Ice Shelf system would have to be reduced by excluding the southern ice stream basin (Fig. 1, "S.I.S.B."). An estimate of the net budget for a

7 MASS BUDGETS : ICE AGES 353 drainage system such as that would be within the error magnitude because: (i) The rate of mass output would remain the same; (ii) The rate of mass input would be reduced approximately by 5 x g yr~ x in terms of net accumulation at the surface, and by 1 X g yr~ l in terms of net subglacial freezing. Assuming, for purposes of discussion only, that the error estimates remain the same, the net budget for the eastern part of the Filchner Ice Shelf system excluding the southern ice stream basin is smaller than the error estimate. The net mass budget of the interior province. From the preceding sections, it is evident that except for the whole Ross Ice Shelf system, one cannot draw any conclusions on the regimen of each of the other two systems. However, if all systems in the interior province are combined to form a single drainage system, it is possible substantially to reduce the error in the estimates of area and net accumulation at the surface. The uncertainties on the placement of the drainage divides and the determination of net accumulation at particular locations are largest in the region where the three systems join (Giovinetto, 1964). For example, segments of drainage divides in the interior of East Antarctica were assigned maximum placement errors of ± 300 km, and the mean net accumulation in the area within the 5 g cm" 2 yr -1 isopleth was estimated at 3-0 ± 1-5 g cm" 2 yr -1 (Giovinetto, 1964). Recent data on ice surface topography (Zotikov et al., 1965; Beitzel, personal communication) and net accumulation (Picciotto et al., 1968) indicate that the magnitude of the errors assigned to factors used to estimate mass input were excessive, as intended, by at least a factor of 2. Nevertheless, without reducing the error estimates, but joining the three systems, and as a first approximation, the area and the rate of mass input for the three systems as a whole are estimated to be (71 ± 8) 10 5 km 2 and (695 ± 85) IO 15 g yi- 1, respectively (Table 1). This estimate of mass input incorporates the alternate net budget estimated for the Amery Ice Shelf system and includes the southern ice stream basin lying south-east of the Filchner Ice Shelf. The summation of the rates of mass output is (303 ~ 45) g yr" 1, and the net budget of the interior province is (4 -± 1) g yr" 1, indicating that the net budget is positive. This result is not changed by the consideration of the budget estimates of the Amery Ice Shelf system by Budd et al. (1967), and of the budget estimate of the eastern part of the Filchner Ice Shelf system excluding the southern ice stream basin (total area for all systems: (65 A z 8) 10 5 km 2 ), because the net budget would still be greater than the error estimate by a factor 2;3, i.e. (3 ^ 1) IO 17 g yr~'. The regimen of the interior province and eustatic sea level changes of the last hundred years Considering the magnitude of the error in the net budget estimate of the interior province, and the fact that subglacial net freezing in the ice shelves contributes at least 6 X 10 lf> g yr -1 to the net mass increase, the net

8 354 ISAGE budget of the inland ice is equivalent to a lowering of sea level of approximately 1 mm. yr" 1 (ocean area: 36 x 10 7 km 2 ). From the mid 1800's to the 1950's, sea level has been rising at a mean rate of approximately 1 mm yr" 1 (Fairbridge, 1961), although there are indications that the rate increased during the 193O's (Gutenberg, 1954), and decreased during the 1950's (Kaye, 1964). The summation of the observed eustatic rise and the estimated net mass increase of the Antarctic interior province amounts to a potential rise in sea level of approximately 2 mm yr- 1. The regimen of the grounded Antarctic ice notwithstanding, the phenomena related to the world's hydrological cycle which would contribute to a rising of sea level are: (i) An increase of the amount of free water on Earth, including groundwater, due to an addition of juvenile water, (ii) A decrease of absolute humidity in the atmosphere, (iii) A decrease of landlocked free water postceding the Industrial Revolution due to man's modification of natural drainage and overdraft of groundwater for irrigation in arid and semi-arid lands, (iv) An increase in the mean temperature of the world's ocean, (v) A negative net budget of the Greenland ice sheet. The water mass related to the first three phenomena is considered to be relatively very small, and the effect of the probable increase in the mean temperature of the ocean is also relatively small. Assuming that the increase of approximately 6 C determined for the surface-water temperature at tropical and subtropical latitudes since 11,000 BP (Emiliani, 1955 and 1957) represents approximately one half of the mean temperature change of surface-waters at all latitudes, and reducing this figure again by one half to account for the whole water mass (mean depth: ~38OO m) the sea level rise due to thermal expansion would be approximately 1 m, or a mean of 0-1 mm yr -1 ; this is only a fraction of the rise of 1 mm yr -1 observed, and of the equivalent rise of 2 mm yr -1 which seems likely for the last 100 years if we assume that the ice sheet's regimen does not change from decade to decade. On the basis of relative volume alone, the net budget of the Greenland ice can be assumed to be at a maximum in the order of g yr -1, thus accounting for approximately 15 per cent of the 2 mm yr" 1 potential rise. It follows that the major single source of water to maintain at least 80 per cent of the potential rate of increase is a negative budget in some or all of the Antarctic drainage systems which together make up the peripheral province of the ice sheet. An empirical model A net negative budget equivalent to 2 mm yr- 1 of the world's ocean represents a loss of approximately 7 x g yr -1. The model of Antarctica here postulated (Table 2) is characterized by: (i) An interior province which accounts for one half the area (and ^50 per cent of the mass) of the ice sheet and one third of the total mass input, where the outlets are relatively narrow and consist of engulfed ice shelves, and the net gain is equivalent to one half of the annual mass input in the province.

9 MASS BUDGETS : ICE AGES 355 TABLE 2 ICE SHEET MODELS Model type and province Empirical: Interior Peripheral Antarctica Heuristic: Int. (emp.; alt.) Per. (heur.) Antarctica Area 10 5 km Mass 10" g >\,vli IIA 2 2 Input 10 l 'gyr" Output 10"gyr Net budget 10» g yr (ii) A peripheral province which accounts for the remaining one half the area (and ^50 per cent of the mass) of the ice sheet, and two thirds of the total mass input, where the broad outlets consist of marginal ice shelves, glacier tongues, and grounded ice termini, and the net loss is equivalent to one half of the annual mass input in the province. This model cannot be substantiated at present. It requires a negative net budget for the whole ice sheet in the order of 3 x g yr- 1 at least until the late 1950's, when the eustatic rise of 1 mm yr -1 may have started to show a decline (Kaye, 1964). This requirement would render the model untenable considering that the net budget's error estimate for the whole ice sheet is ± 1 X g yr- 1 (Giovinetto, 1964). Nevertheless, the scant and indirect evidence there is agrees with the two-province model. In the peripheral province, near Mount Gaussberg (approximately 66 45'S, 89 10'E) the thickness of the ice sheet has decreased by an average of 8-1 m from 1902 to 1957; the minimum decrease is 5-8 m among the 15 points surveyed, and the maximum is 21-7 m (Feodosyev, in Dolgushin et ai, 1962). In addition, there is evidence of a recent thickness decrease in snow fields near the ice terminus at approximately 40 E and 110 c E in the peripheral province (Hollin, personal communication). In the interior province the first direct evidence of an increase in the thickness of the ice sheet was reported by Koerner (1964) at approximately 82 30'S, 'W. There, corrasion features caused by drifting snow on a granitic nunatak are being buried by the ice. Koerner indicates, however, that the area for which this ice thickness increase may be representative is unknown. Recent electromagnetic soundings across the ice shelf-grounded ice boundary in the eastern part of the Ross Ice Shelf drainage system show that the grounded ice is, or recently has been advancing (Robin et al., 1968). In addition, there is evidence of a significant increase in the rate of net accumulation at the surface at the South Pole from ca to 1957, but the area of the region for which there is a

10 356 ISAGE positive secular change of accumulation is unknown (Giovinetto and Schwerdtfeger, 1966). Part of the long-interval increase in the rate of accumulation could be explained by the position of the stratigraphie column relative to the snow surface's migrating ridge and trough topography, as implied by the findings of Gow and Rowland (1965). However, the cumulative sequence of short-interval increases in the rate of accumulation cannot be explained by the migration of topographic features alone. Unless relatively complex assumptions are brought into the discussion of sea level changes*, the relatively simple assumption that Antarctica can be ascribed the major role on present eustatic sea level changes, and a positive budget for the interior province, are the only effective constraints on the empirical model presented in Table 2. The facts that more than nine tenths of the ablation occurs at the periphery, and that the distribution of atmospheric and oceanic phenomena is approximately concentrical relative to either the pole of rotation or to the pole of maximum inaccesibility (approximately at 87 S, 65 E) suggest that, at present, the response of the ice sheet is bi-modal to the as yet undetermined climatic regime. This is not to say that the net budget is positive in all systems of the interior province; this is to say that the net budget is positive in at least one of the systems (or parts of it). The findings of Koerner (1964) and Robin et al. (1968), together with the estimates of Giovinetto and Zumberge (in press), indicate that the eastern part of the Ross Ice Shelf system may include basin(s) which contribute a large share of the net mass gain in the two-part system. An alternate (heuristic) model The viability of the hypothesis that at present the response of the ice sheet is bi-modal to the climatic regime is not affected by a consideration of a possible decrease in the rate of sea level change since the 1950's. Assuming that the rate of sea level change is close to zero or that a sea-level rise, if any, is due for example, to an increase in the mean temperature of the ocean, an alternate model of the peripheral province can be stated by ascribing to it a negative budget between 3 x g yr -1 and 4 x g yr -1 (Table 2). This reduces the rate of mass output from 22 x g y 1 to approximately 19 X g yr -1. It may be of significance that this total output figure for the peripheral province amounts to a mean outputf of approximately 9 X g km" 1 yr" 1. A comparable rate of output has been estimated (8 X g km- 1 yr" 1 ) by cross examining * Such as: (i) The relationship between continental isostasy and the depth of ocean basins; (ii) The variability of the rate of heat exchange at the air-sea interface and of geothermal heat flux; (iii) The effects of crustal differentiation on the shape of the geoid or of erosion and deposition on the mean porosity of the upper crust, etc. The probable secular variability of these phenomena cannot be easily fitted with the short-interval variability apparent in sea level records, except for a possible variability of the rate of heat exchange at the air-ocean interface. f The length of the ice terminus, excluding segments BC, EF, IJ and J'K, is approximately 20,500 km.

11 MASS BUDGETS : ICE AGES 357 twelve independent mass budget estimates for the whole ice sheet (Giovinetto, in press). This mean output rate was obtained by assigning specific ablation rates to particular glacier forms; the estimate, however, includes the drainage sections of the interior province, i.e. a total length of approximately 22,500 km. The alternate and heuristic model of the ice sheet shown in Table 2 still requires a bi-modal response to climate. Modifying the regimen of the interior province by adopting the smaller of the two budget estimates (Table 1), and to maintain balance (Table 2), the peripheral province is required to account for an input of 16 X g yr- 1, and an output of 19 X g yr -1. The net budget for the peripheral province is 3 X g yr -1, and for Antarctica is zero. As stated, the model closely fits the conclusion reached by Dolgushin et al. (1962) following the classical procedure of estimating the net budget for Antarctica as a whole: "The available evidence indicates that the ice sheet is in a state of equilibrium, but it is possible that the mass is somewhat increasing in the inland regions." To fit the alternate model, the only required modification of their statement is the assertion of a positive budget in the inland regions. Acknowledgements It is a pleasure to acknowledge the critical comments offered by C. R. Bentley and W. Schwerdtfeger. The research was supported by National Science Foundation Grant GA-245 to the University of Wisconsin. REFERENCES BEHRENDT, J. C Geophysical and glaciological studies in the Filchner Ice Shelf of Antarctica. J. Geophys. Res., Vol. 67, No. 1, p BEHRENDT, J. C Snow surface elevation in the Filchner Ice Shelf area, Antarctica. J. Glaciol., Vol. 5, No. 41, p BUDD, W The dynamics of the Amery Ice Shelf. J. Glaciol., Vol. 6, No. 45, p BUDD, W., LANDON SMITH, I. and WISH ART, E The Amery Ice Shelf. Proceedings of the International Conference on Low Temperature Science, I, Pt. 1, p , Sapporo, August, 1966, H. Oura, ed.; published by the Institute of Low Temperature Science, Hokkaido University, DOLGUSHIN, L. D., EVTEEV, S. A. and KOTUAKOV, V. M Current changes in the Antarctic ice sheet. International Union of Geodesy and Geophysics (I.A.S.H., Obergurgl Meeting). Publ. No. 58, p EMILIANI, C Pleistocene temperatures. J. Geol., Vol. 63, No. 6, p EMILIANI, C Temperature and age analysis of deep-sea cores. Science, Vol. 125, p FAIRBRIDGF, R. W Eustatic changes in sea level. In: Physics and Chemistry of the Earth, Ahrens, L. H. et al. eds., Pergamon Press, Vol. 4, p GIOVINETTO, M. B The drainage systems of Antarctica: accumulation (in American Geophysical Union, Mellor, M. ed., Antarctic Snow and Ice Studies, Antarctic Research Series). Vol. 2, p GIOVINETTO, M. B. (In press). The drainage systems of Antarctica: ablation. To be published by the American Geophysical Union in the Antarctic Research Series. GIOVINETTO, M. B., ROBINSON, E. S. and SWITHINBANK, C. W. M The regime of the western part of the Ross Ice Shelf drainage system. J. Glaciol., Vol. 6, No. 43, p

12 358 ISAGE GioviNETTO, M. B. and SCHWERDTFEGER, W Analysis of a 200 year snow accumulation series from the South Pole. Arch. MeteoroL, Geophys. Bioklimatoi, A, Vol. 15, No. 2, p GIOVINETTO, M. B. and ZUMBERGE, J. H The ice regime of the eastern part of the Ross Ice Shelf drainage system. Paper presented at the XIV Assembly IUGG, Commission of Snow and Ice, Berne, Sept. to Oct. 1967; to be published by the International Association of Scientific Hydrology, Gentbrugge. Gow, A. J. and ROWLAND, R On the relationship of snow accumulation to surface topography at "Byrd Station", Antarctica. X Glaciol., Vol. 5, No. 42, p GUTENBERG, B Postglacial uplift in the Great Lakes region. Archiv, f. Meteorlogie, Geophys. U. Bioklimatologie, A, Vol. 7, p KAYE, C. A The upper limit of barnacles as an index of sea level change on the New England Coast during the past 100 years. J. GeoL, Vol. 72, p KOERNER, R. M Firn stratigraphy studies on the Byrd-Whitmore Mountains traverse, In: Mellor, M., ed., Antarctic Snow and Ice Studies, Antarctic Research Series), American Geophysical Union, Vol. 2, p LISIGNOLI, C. A Movement of the Filchner Ice Shelf, Antarctica. Trans. Am. Geophys. Un., Vol. 45, No. 2, p PICCIOTTO, E., DEBREUCK, W. and CROZAZ, G Snow accumulation along the South Pole Dronning Maud Land traverse. In : Gow, A. J. et al., Eds., International Symposium on Antarctic Glaciological Exploration (ISAGE), Hanover, New Hampshire, U.S.A., 3-7 September Cambridge (Pub. No. 86ofIASH), p ROBIN, G. DE Q., SWITHINBANK, C. W. and SMITH, B. M. E Radio echo exploration of the Antarctic ice sheet. Paper presented at the International Symposium on Antarctic Glaciological Exploration, Hanover, Sept., ZOTIKOV, I. A., KAPITSA, A. P. and SOROKHTIN, O. G Thermal regime of the ice cover of central Antarctica. Info. Bull. Sov. Ant. Exped., Vol. 51, p Climatic causes of alpine glacier fluctuation, southern Victoria Land BY WAKEFIELD DORT, JUN. Department of Geology, The University of Kansas, Lawrence, Kansas, U.S.A. Introduction Although southern Victoria Land is well known for the present development of "oases" or dry (i.e. ice-free) valley areas, there is ample evidence that this region has been much more extensively glacierized in the past. Till and erratics are widespread; recessional moraines are numerous. The retreat has affected all types of glaciers outlet glaciers from the interior ice cap, piedmont glaciers along the coast, and local alpine glaciers emanating from cirques and high basins. Field evidence suggests that fluctuations of the alpine glaciers have been caused by local climatic variations in the mountainous area which, in turn, reflect regional changes.