Antarctic Science 9 (3): 336346 (1997)

Blanketing snow and ice; constraints on radiocarbon dating deglaciation in East Antarctic oases

DAMIAN 8. GORE School of Earth Sciences, Macquarie University, North Ryde, NSW 2109, Australia

Abstract: Radiocarbon dating of marine, lacustrine or terrestrial biogenic deposits is the main technique used to determine when deglaciation of the oases of East Antarctica occurred. However, at many of the oases of East Antarctica, including the Schirmacher Oasis, Stillwell Hills, Amery Oasis, Larsemann Hills, Taylor Islands and Grearson Oasis, snow and ice presently forms extensive blankets that fills valleys and some lake basins, covers perennial lake ice and in places overwhelms local topography to form ice domes up to hundreds of square kilometres in area. Field observations from Larsemann Hills and Taylor Islands suggest that under these conditions, terrestrial and lacustrine biogenic sedimentation is neither widespread nor abundant. If similar conditions prevailed in and around the oases immediately following retreat of the ice sheet, then a lengthy hiatus might exist between deglaciation and the onset of widespread or abundant biogenic sedimentation. As a result, radiocarbon dating might be a clumsy tool with which to reconstruct deglaciation history, and independent dating methods that record emergence of the hilltops from the continental ice must be employed as well.

Received 16 January 1997, accepted 4 June 1997

Key words: biogenic sediment, deglaciation, Quaternary, radiocarbon dating, superimposed ice

Introduction

Along the coast of East Antarctica lie a number of areas, or ‘oases’ (sensu Shumskiy 1957) that are presently free of the ice sheet, including Schirmacher Oasis, Stillwell Hills, Amery Oasis, Larsemann Hills, Vestfold Hills, Bunger Hills, Taylor Islands and Grearson Oasis (Fig. 1). The deglaciation chronologies of Larsemann, Vestfold and Bunger hills, and Grearson Oasis have been inferred by radiocarbon dating of marine, lacustrine or terrestrial biogenic deposits (e.g. Adamson & Pickard 1986a, Burgess et al. 1994, Colhoun & Adamson 1992, Fitzsimons & Domack 1993, Gillieson 1991, Goodwin 1993, Melles et al. 1994, Verkulich & Hiller 1994). While the radiocarbon technique provides minimum ages for deglaciation, to date no-one has discussed a possible lengthy hiatus in the onset of biogenic sedimentation following recession of the East Antarctic ice sheet. Factors that control the onset of biogenic sedimentation at any particular site, or the number of sites where biogenic sedimentation occurs, will therefore, be very important for accurate inference of the timing of retreat of the East Antarctic ice sheet using the radiocarbon technique.

This paper was prompted by two unusual and controversial scenarios. First, Gillieson et al. (1990) radiocarbon-dated six lake cores from Larsemann Hills (Fig. l), and determined a maximum age of 9410i180 yr BP (ANU 2749). Gillieson (1991) then proposed a Holocene deglaciation from an expanded East Antarctic ice sheet, consistent with the reconstruction of Stuiver et al. (1981). Later, Burgess et al. (1994) recovered in situ terrestrial moss from 1.5 m depth

within permafrosted post-glacial sediment at Larsemann Hills, and determined a radiocarbon date of24 9502710 yrw (ANU 8826). Possible reasons for this age disparity have not yet been addressed.

Second, the oldest, reliable lacustrine radiocarbon ages from Vestfold Hills (Fig. 1) are 83802110 y r m (ANU 8166; Fulford-Smith & Sikes 1996) and 8355k250 yr BP (Beta 4760; Adamson & Pickard 1983). However, more recently, Fabel et al. (in press) reported a cosmogenic isotope age of 1 2 3 1 . 6 kaBP, from a site within 2 km of the ice sheet. The dilemma here is that the exposure age of a site that is presently in the proglacial zone, is older than lake basins that lie between 10 and 20 km farther down ice. Either there was a hiatus in the onset of biogenic sedimentation in the lakes, or the terrestrial margin of the East Antarctic ice sheet retreated in a manner hitherto undescribed.

In this paper I present a testable hypothetical model concerning the effect of blanketing snow and ice on biogenic sedimentation in the oases of East Antarctica, that may be used to explain these scenarios. The model describes how perennial blankets of snow and ice might limit biogenic sedimentation in terrestrial, lacustrine and nearshore marine environments. Detailed observations on the extent of snow and ice, and organic deposits in Larsemann Hills and Taylor Islands are presented, and the extent of blanketing snow and ice in six other east Antarctic oases are discussed. Finally, the significance of blanketing snow and ice for resolution of the deglaciation history of the East Antarctic ice sheet is discussed.

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BLANKETING SNOW AND ICE 337

Influence of blanketing snow and ice on biogenic sedimentation

Blankets of snow and ice that cover large areas of formerly glaciated regions, may act to limit terrestrial, lacustrine and marine biogenic sedimentation, and other terrestrial biogenic deposits.

Terrestrial sedimentation

Snow and ice can occupy sites where terrestrial biogenic sediments and deposits would otherwise accumulate. Such sites include moist, lee-side hillslopes below snowpatches, and sediment-filled valley bottoms where moss-beds flourish from meltwater rivulets. Potential seabird habitats, such as crevices in bedrock cliffs and cavities beneath boulders, would also be filled with ice. Rare sections through the blankets of snow and ice in several of the East Antarctic oases (see descriptions of Schirmacher Oasis and Larsemann Hills below), have shown the ice to be several metres to tens of metres thick. Where the summits and upper slopes of ridges that emerge from these blankets of snow and ice are largely free of moss-beds, lichen and birds, sites of terrestrial biogenic sedimentation are extremely limited in number and extent.

Lacustrine sedimentation

Snow and ice can reduce lacustrine biogenic sedimentation in three ways. First, given conditions cold enough, lakes can freeze to their beds annually, or remain perennially frozen (dry-based lakes of Chinn 1993), preventing colonization by organisms. At the present day in the East Antarctic oases, lakes shallower than 3 m may freeze to their beds during cold winters, but during colder glacial times, lakes greater than 3 m depth would also have frozen to their beds, thawing only during climatic optima. Blake (1989) described a 5.5 m deep lake in the Canadian Arctic that is frozen to its bed at the present day. Fragments of algal material in the lower lake ice were dated, revealing that liquid water existed at the bed during the warmest part of the mid-Holocene Hypsithermal Interval. Blake inferred that, as the climate cooled slightly around 4500-3500 radiocarbon years ago, the lake ice thickened, incorporating the algae, until finally the lake froze to its bed and biogenic sedimentation became impossible. There are many other shallow polar lakes whose ice cover occupies a significant proportion of their photic zone. This occupation of the photic zone by ice can prevent or strongly reduce biogenic sedimentation in a lake.

Second, light attenuation by perennial lake ice can reduce the depth of the photic zone. Psrennial ice in wet-based lakes (sensu Chinn 1993) in the Dry Valleys can attain a maximum thickness between 3.5 and 6.0 m (McKay et al. 1985). Beneath such a thickness of perennial ice, photosynthetic activity and thus biogenic sedimentation is still possible (e.g. Hoare et al. 1964, Doran et al. 1994) as light can penetrate

I 00

-00 km Schirmacher ’ * Sample site of Burg& e t a ) . (1994

Grearson

0 2 k m U

I I

n 76d07’E

Fig. 1. Stornes Peninsula in Larsemann Hills, showing the ice dome and fields of perennial snow and ice that cover 34% of the area. The inset map of Antarctica shows the location of places discussed in the text, while the inset map of Larsemann Hills shows the location of the pre-Last Glacial Maximum radiocarbon date of Burgess et al. (1994).

through the ice to the water column along large, strongly oriented, vertical prismatic ice crystals (e.g. Chambers et al. 1986, Hoare et al. 1964, Loopmann 1988). Kaup (1995a, p. 287) measured the albedo of lake ice in the Schirmacher Oasis over a summer season, and found that it increased with age as air penetrated along the crystal boundaries. Wharton et al. (1993) offered an alternative explanation that scattering of light in the upper metre of the ice is controlled by small, refrozen crystals that cause the ice to appear white. Wharton et al. also record that from December to January, the opacity of the ice in Lake Hoare, Dry Valleys, increased because of thawing on the surface. Whatever the mechanism, averaged values from Kaup’s table 8.5, show that one-year lake ice has an albedo of 32, whereas multi-year lake ice has an albedo of 44. These data imply that the longer lake ice lasts, the less energy will reach the water column. This increase in albedo may not be as dramatic in the Dry Valleys lakes, due to constant renewal of the surface ice by strong ablation. Perennial lake ice at Lake Vanda during 1982, ablated by 0.55 m (Chinn 1993). As a result, the surface of the perennial lake ice at the Dry Valleys is rarely exposed to the air for more

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338 DAMIAN 6. GORE

than a year. The annual precipitation at the Dry Valleys is 10 mm water equivalent (Bromley 1986), in striking contrast to Vestfold Hills, where precipitation has been estimated to be 250 mm (Fitzsimons 1990) to 300 mm (Liljequist 1970, in Bronge 1996) water equivalent. Similarly, the annual average precipitation in the Schirmacher Oasis during 1961 and 1983 was measured at 265 mm water equivalent, with a maxima of 580 mm (Richter & Bormann 1995a, p, 216). Although not measured, perennial lake ice at the coastal East Antarctic oases may be much protected from ablation by a late summer to mid-spring cover of fallen or wind-drifted snow. If true, then perennial lake ice at the coastal East Antarctic oases may be more 'mature', with a resultant higher albedo, than that from the Dry Valleys. Importantly too, during colder glacial times, the lake ice would have been thicker. If all other parameters are constant, the fraction of incident solar energy reaching the water column is inversely proportional to lake ice thickness, and thus the potential for biotic activity is least where the ice is thickest.

Third, blankets of snow and ice over perennial lake ice may largely exclude the photic zone. The albedo of some ice versus snow covered lakes has been measured by Kaup (1995a). Again using averaged values from Kaup's table 8.5, whereas multi-year lake ice has an albedo of 44, snow- covered lake ice has an albedo of 83. The greater the snow cover, the less solar energy will reach the water column. As a working model, it is quite feasible for a photic zone to be absent, or largely so, from the water column below snow- covered perennial lake ice, causing primary productivity and biogenic sedimentation to be minimal.

Marine sedimentation

Ice shelf or perennial sea ice cover may result in decreased organic sedimentation in the nearshore marine environment. Domack et al. (1995) inferred that decreased total organic carbon in a section of sediment core taken near the Miiller Ice Shelf, reflected a cold period, characterized by persistent sea ice and limited primary productivity. Presumably the primary productivity might have been limited by attenuation of light by sea ice and overlying snow. Bartsch (1989) showed that light intensity in the sea ice in the Weddell Sea decreased by 90% within the upper 25 cm, while at the bottom of one-year sea ice, covered by 5 cm of snow, the light intensity was only 0.5% of the radiation at the surface. There is other, circumstantial evidence to support the notion of reduced marine biogenic sedimentation in low-light conditions. Pickard (1986) reported the observations of SCUBA divers who noted a depauperate benthic flora and fauna, and fossil- free sand on the sea floor beneath persistent snow drifts on the sea ice off Vestfold Hills. It is feasible that an extensive snow blanket over thick, multi-year sea ice might dramatically reduce the photic zone, and hence primary productivity and resultant biogenic sedimentation in the nearshore marine environment.

R.D. Powell (personal communication 1997) argues that nutrient supply, and not light, is a far greater control on marine biogenic sedimentation. In support of his argument, Powell & Dawber (in press) observed a diverse fauna beneath the floating tongue of Mackay Glacier, McMurdo Sound, including a living Antarctic scallopAdamussium colbecki at the grounding line. Similarly, Hain & Melles (1994) inferred a population of molluscs (A. colbecki and Nacella cf concinna) in dark conditions beneath the Fimbul Ice Shelf in the Lazarev Sea. The deaths of these free-living organisms would allow macro-fossils to form occasionally despite perennial ice cover and the absence of a photic zone. The extent to which biogenic sedimentation in the marine nearshore is reduced by perennial ice cover is unknown, but it is probably rather variable (see Powell & Dawber in press) and awaits further investigation.

Blanketing snow and ice in eight East Antarctic oases

The previous section examined some ways in which perennial snow and ice might act to reduce terrestrial, lacustrine and marine biogenic sedimentation in the East Antarctic oases. This section presents observations on the extent of perennial blankets of snow and ice in eight coastal oases from 11"E (Schirmacher Oasis) to 1lO"E (Grearson Oasis, Fig. l ) , to demonstrate that the model is broadly applicable along the East Antarctic coastline. I argue later that the extent of snow and ice in an oasis, as well as the presence or absence of perenniallake ice, is able to be correlated with either perennial sea ice cover, or the presence of ice shelf or glacier. Observations on these parameters will also be presented.

Larsemann Hills

Larsemann Hills is a -50 km2 area consisting of two main peninsulas, Stornes and Broknes (Fig. 1). Stornes is -25 km2 in area, and is surrounded by perennial sea ice that is held in behind small islets and grounded icebergs. Stornes hosts a -4.9 km2 dome of ice at its southern margin. The dome reaches 170 m above sea level, is higher than the continental ice sheet to the south and is joined to it by a narrow col (Fig. 1). I infer that the two ice masses are dynamically independent. During February 1992, an ice cliff section on the north-west periphery of the dome appeared free of continental debris, and I presume that the ice accumulated locally, rather than being remnant ice sheet. The ice is flowing slowly across its bed, and striae recording N-NNE flow crosscut older, regional NW striae. The younger striae indicate that the Stornes ice dome was formerly of greater extent and, presumably, thickness, following retreat of the continental ice sheet. The implication of this is that the ice dome would have prevented biogenic sedimentation on much of Stornes long after the ice sheet had retreated from it,

Extensive fields of snow-covered ice have formed from the in sifu firnification of snow, filling valleys and lake basins,

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BLANKETING SNOW AND ICE 339

and covering a total of 34% of the peninsula, especially in the central and southern parts (Figs 1 & 2). The hilltops and upper slopes of the ridges that protrude through the snow and ice fields are largely free of birds, vegetation or organic deposits. Near the north side of the dome, perennial snow and ice fields ramp onto perennial lake ice, and in some locations, thick superimposed ice creeps slowly into the lakes.

The internal stratigraphy of a thick, perennial snow and ice field (Fig. 1) that was not of continental interior origin, was investigated using a crevasse to gain access to a 15 m vertical cross-section. The upper metre was snow, the second and third metres were firn, and, judging by the resistance to crampon and ice axe blows, below three metres the substrate was ice. The crevasse tapered so that the stratigraphy could not be examined below 15 m depth, and the total depth could not be measured. The crevasse was bridged by snow and was discovered by accident, and was quite unexpected being a 0.5 km north of the ice dome and nearly 4 km north of the ice sheet. The setting is typical of many of the broad icy valley fills on Stornes. Lower parts of some of these icy valley fills exhibit flat, snow-covered perennial lake ice (Fig. 2). During my visits to Larsemann Hills in 1988-89, 1989-90 and 1992-93, most of the lakes on Stornes remained frozen.

Bruknes is -15 km2 in area, is 33% covered by perennial snow and ice, and in many other respects is similar to Stornes. The main difference between the two peninsulas is that whereas the sea ice around Stornes is perennial, only parts of the sea ice around Broknes are multi-year to perennial. Off the eastern coast of Broknes, the sea ice breaks out annually because there are few islands or grounded icebergs to pin it against the coast. Near areas where sea ice breaks out along the eastern and north-eastern margins of the peninsula, perennial snow and land ice is sparse. Much of the perennial

Fig. 2. View south-east over central Stomes Peninsula (February 1993). Extensive fields of snow and ice are widespread; only the upper hillslopes and tops of ridges and hills protrude free from the ice. The flat-lying area in the middle right is snow-covered perennial lake ice.

snow and ice lies south and north-west adjacent to the ice sheet or perennial sea ice. Most of the lakes thaw annually, and exhibit floating algal mats, reflecting the relatively rich biotic activity in the water column.

Gilliesonet al. (1990) reported 12 radiocarbon assays from six lake cores from Larsemann Hills. The youngest lake sediments, dated at 440280 yr BP (Beta 22249; Gilliesonet al. 1990, p. 31) were taken from areas where perennial snow and ice fields form extensive valley fills. Conversely, some of the oldest organic lake deposits, dated at 9410+180 yr BP (SUA 2749; Gillieson et al. 1990, p. Sl), were found in parts of Larsemann Hills where perennial snow and ice fields are not extensive. Similarly, while Gillieson et al. (1990) were not able to recover organic deposits from the floors of some perennially frozen lakes, they were able to core or grab sample successfully algal gyttjas from lakes that thaw seasonally.

Taylor Islands

Taylor Islands is a -27 km2 area surrounded by Edisto and Scott glaciers and the Shackleton Ice Shelf (Figs 1 & 3). Set within this area lies a southern and northern group of nunataks with a total area of <4 km2. The nunataks rise to a maximum of 120 m a.s.l., some 90 m above the surrounding

I

Perennial snow and ice 100°20E h

Fig. 3. Taylor Islands, showing the north and south group of nunataks. 86% of Taylor Islands is covered by perennial fields of snow and ice.

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340 DAMIAN B. GORE

glaciers and ice shelf. The area between the northern and southern nunataks is a broad, icy-filled valley some 2-3 km in width that lies 20-40 m above the surrounding glaciers and ice shelf (Fig. 3). Only some 14% of Taylor Islands stands above the surrounding perennial blanket of snow and ice. Although the highest summits are covered with till, the age of deglaciation of Taylor Islands has not yet been determined. Nunatak summits are as strongly weathered as parts of Bunger Hills that have been deglaciated since at least the start of the Holocene (Verkulich &Hiller 1994), andconsequently, Taylor Islands are likely to have been deglaciated for at least that time as well. Southern Taylor Islands are so strongly weathered that glacial striae and glaciated pavements could not be found, and some upper slopes have a felsenmeer derived from extensively frost-shattered bedrock. The largest moss-bed found on Taylor Islands is visible in the foreground of Fig. 4, but it was less than 10 cm thick and sub-fossil. Like the moss-beds, the mumiyo deposits at Taylor Islands were also thin (c2 cm). Mumiyo is the layered deposits of proventricular oil of the snow petrel (Pagodroma nivea) that is regurgitated as a defence mechanism when the birds are harassed at the nest by predators or other visitors. The age of the basal mumiyo should reflect the first occupation of the nest site by snow petrels. Since both moss-beds and mumiyo were thin and presumably young, they are of little use for radiocarbon dating of deglaciation. The lack of terrestrial biogenic deposits on Taylor Islands simply reflects that those areas that are emergent from the surrounding perennial blanket of snow and ice, contain few sites suitable for biogenic sedimentation.

Fig. 4. View north from southern Taylor Islands (February 1996). The perennial snow and ice shown is 2-3 km across, and the nunatak summits in the distance are the northern Taylor Islands. The dark-coloured patch in the foreground that slopes downhill to the left is a moss-bed, the largest accumulation of organic matter found in southern Taylor Islands. The nunatak summits are largely bare of moss-beds, mumiyo or any other organic matter.

Schirmacher Oasis

The Schirmacher Oasis (Fig. 1) is a 34 km2 area that lies between the ice sheet to the south, and an ice shelf to the north. The oasis is elongate, with the long axis lying normal to the direction of prevailing wind and drift-snow migration. Extensive fields of snow and firn, mapped onto the ‘Hydrographic map of the Schirmacher Oasis’ (annex 3 in Bormann & Fritzsche 1995), occupy -16% of the oasis. The most extensive fields of snow and firn lie adjacent to the ice sheet, reflecting the source of most of the drift snow. Numerous ponds and lakes are dammed behind the snow and firn fields (Richter & Bormann 1995b, annex 3 in Bormann & Fritzsche 1995). The damming of these lakes confirms the presence of ice within the snow and firn fields, because snow and firn are, by definition, permeable and would not form long-lasting reservoirs of any appreciable size. The meltwater channel in fig. 8.-7 of Richter & Bormann (1995b, p. 265) also shows clearly the presence of ice, more than 4 m thick, deep within a ‘firn ice’ (terminology of Richter & Bormann) field at the eastern end of the oasis. Many lakes in the oasis thaw annually.

Stillwell Hills and nearby areas

Stillwell Hills (Fig. 1) is a c . 96 km2 coastal area of rugged, low hills forming a peninsula and a number of smaller islands. The hills are bounded to the south by the ice sheet, to the west by a small outlet glacier and to the north and east by sea. The outlet glacier calves into sea ice that is pinned in behind small islands. Fold Island (-40 km’) lies immediately to the north of the main peninsula of Stillwell Hills and is separated from it by a narrow channel only a few hundreds of metres wide. An emperor penguin (Aptenodytes forsteri) rookery beside Fold Island indicates the presence of perennial sea ice there. 75% of Fold Island is covered by a dome of ice that calves into sea on its southern and western sides. This dome is not fed by the ice sheet and must be maintained by local drift snow and precipitation.

The main peninsula is 18% covered by perennial fields of superimposed ice. These ice fields fill the valleys, and abut lakes that appear to be perennially frozen. The extent of blanketing snow and ice over all of Stillwell Hills, including the islands, is 42%.

Thirty km NW of Stillwell Hills lies Law Promontory, and Broka and Havstein islands. A 227 km’ice dome covers 99% of Law Promontory. The ice dome is physically connected to the ice sheet to the south, and rises 200 m above the saddle where the two merge. The flow dynamics of the ice dome are probably largely independent of the ice sheet, rather like the Stornes dome in Larsemann Hills, or like Law Dome at the edge of Grearson Oasis (Adamsonet al. 1991). Like the Fold Island and Larsemann Hills domes, the Law Promontory ice dome must be nourished by local wind drift and precipitation rather than by ice from the continental interior. Broka Island,

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to the north of Law Promontory, is 22 km2in area and is 67% covered by perennial snowfields. Similarly, adjacent Havstein Island is 12 la2 in area and is 51% covered by perennial snowfields. Taken together, Stillwell Hills and nearby areas are dominated by perennial blankets of snow and ice.

Amery Oasis

Amery Oasis (Fig. 1) is a large area (>1800 km2, Adamson et al. 1997) that lies between the ice sheet, several large glaciers and the epishelf lake, Beaver Lake. While Beaver Lake is tidal, some 250 km of glacier and ice shelf separate it from the open sea of Prydz Bay. The four largest ice-free areas in Amery Oasis are Loewe, Manning and McLeod massifs, and Amery Peaks, which together occupy some 980 km2.

Loewe Massif is 30% covered by blanketing snow and ice, including a 92 krn2 dome of ice. The dome lies almost wholly on bedrock perched high above the surrounding glaciers, and is fed solely from snow drift and precipitation direct onto the ice. Alpine glaciers flow outwards from the dome onto adjacent rock and glacier surfaces. Plumes of snow, driven by south-westerly winds from the continental interior, are clearly visible on aerial photographs (e.g. photo 9194R, Run 24, ANT 441 1,12 Oct 1956) bypassing other parts of the oasis but climbing up and over, and depositing snow onto the Loewe Massif ice dome. It is not clear why some parts of the oasis, such as Loewe Massif, receive more drift snow than others. However, the aerial photographs may be used to infer that topographic diversion of katabatic winds carries wind- drifted snow away from some areas, whereas large ridges and massif edges that lie transverse to the wind act as ‘snow fences’, allowing the deposition of snow on their high plateaux or lee sides.

The Manning and McLeod massifs are 30% covered by blanketing snow and ice. A 14.7 km2 ice dome lies on the north-western edge of Manning Massif, and medial moraines visible on SPOT satellite imagery (Beaver Lake 1:lOO 000) and aerial photographs (e.g. photo 7183L, Run 4C, ANT 94, 18 Oct 1960) verify ice flows from the dome into Walker Valley glacier. Plumes of wind-drifted snow also pass over the north and western parts of Manning and McLeod massifs, and fieldsof blanketing snow andice are common. Conversely, the eastern Manning and McLeod massifs host fewer and smaller areas of blanketing snow and ice than the west. Again, the reasons for this are not fully resolved, but a combination of topographic channelling and sublimation of wind-drifted snow during transport, as well as enhanced melting of fallen snow at lower altitudes is likely. Aerial photographs (e.g. photo 9178R, Run 24, ANT 4411, 12 Oct 1956) show a plume of wind-drifted snow visible to the south- east of McLeod Massif declining in strength and finally disappearing from view in the north-east of the Massif. In viewof the declinein altitudeof thesurfacefrom>lOOOma.s.l. in the south-west to sea level in the north-east, it is possible

that much of snow sublimates as the air descends during northward transport.

Amery Peaks is 15% covered by blankets of snow and ice. The topography there is steep, and much of the land surface sheds snow directly onto small cirque glaciers or the larger glaciers that flow northward through the Peaks. In total, Amery Oasis is 28% covered by blanketing snow and ice. Lakes in Amery Oasis are characterized by perennial ice cover, with the exception of Radok Lake which thaws almost completely from time to time (D.A. Adamson, personal communication 1997).

Vestfold Hills

Vestfold Hills (Fig. 1) is a 413 km2 area bounded by the ice sheet to the east, an outlet glacier to the south and open sea to the north and west. Only 5% of the Hills are covered by blanketing snow and ice, though in those places damming by snowbanks and ice fields is common (e.g. Adamson & Pickard 1986b, Gore 1992). The most extensive fields of ice lie in the east, adjacent to the ice sheet and the source of the wind-drifted snow. The western parts of the hills have few perennial ice fields, with the exception of dunes and linear deposits of snow and ice that lie on the lee-side of hills. Layers of superimposed ice up to 6.5 m in thickness, formed from wind-drifted snow are also widespread along the ice sheet margin (Gore 1992, 1993). The sea ice off Vestfold Hills breaks out annually, and most lakes thaw annually, although some hypersaline lakes rarely freeze, even in the middle of winter (Barker 1981).

Bunger Hills

Bunger Hills (Fig. 1) is a c. 950 km2 area that is bounded by the ice sheet to the east, glacier to the south and west, and ice shelf to the north and north-west. Within these boundaries, lie c. 480 km2 of land and a number of marine inlets. Like Vestfold Hills, less than 5% of Bunger Hills is covered by blankets of snow and ice. Whereas most of those areas lie adjacent to the ice sheet, a substantial number of perennial ice fields lie on the lee-sides of hills in the south-western corner of the hills. There are no published data on the breakout of sea ice in the large marine inlets in the centre of the hills. However, reports from 1987 (E.A. Colhoun personal communication 1996), 1992 (extracted from Oasis Station logbook), 1994 (Melles 1994) and observationsfrom 1995 all indicate the presence of navigable marine waters during summer, allowing the inference that the sea ice in Bunger Hills breaks out annually. The presence of a sizeable population of Weddell seals also implies that sea ice breaks out annually. Most freshwater lakes in Bunger Hills thaw annually. Hypersaline lakes are rare in Bunger Hills, and the few that exist are frozen during winter. However, the ice cover on those hypersaline lakes typically melts prior to breakout of the sea ice on the inlets.

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342 DAMIAN B. GORE

Grearson Oasis

The Grearson Oasis (or Windmill Islands; Fig. 1) is a series of peninsulas and islands 75 kmz in area (Goodwin 1993), with the four largest peninsulas comprising 40 km2. The range in cover by perennial ice on the four peninsulas ranges from 48% to 84%, with an average cover of 68%. The cover of snow and ice on the islands appears proportionally less than on the peninsulas, but was not calculated due to the lack of distinction between terrestrial ice, sea ice and the fast ice foot on the imagery available. The few lakes on the islands tend to thaw annually, while the lakes on the peninsulas tend to remain frozen throughout the year.

Reliability of radiocarbon dating deglaciation

At the beginning of the paper I suggested ways by which blanketing snow and ice may limit biogenic sedimentation, and the above section shows that blanketing snow and ice covers 5 4 6 % of the coastal oases. However, additional problems with radiocarbon dating must be addressed before it is used as a tool with which to date deglaciation. Below, additional comments on the application of radiocarbon dating in marine, lacustrine and terrestrial environments are presented.

Marine organic deposits

Marine fossils useful for radiocarbon dating may be recovered from emergent shorelines and sea floor sediments. Vestfold and Bunger Hills exhibit well-formed and preserved marine terraces at less than 10 m a.s.1. that contain mid-Holocene shells and other macro-fossils (e.g. Pickard 1985, Colhoun & Adamson 1992), whereas rare, poorly-formed emergent shorelines to less than 3 m a.s.l., that do not appear to contain macro-fossils, occur at Larsemann Hills. Mid-Holocene fossils have been recovered from emergent shorelines to 32 m a.s.1. at Grearson Oasis (Hollin 1962). Emergent marine terraces are absent from the Schirmacher and Amery oases (Richter & Bormann 1995c, p.180, and Adamsonet al. 1997 respectively), were not found in Taylor Islands, and have not yet been reported from the other oases. Shoreline sediments are not only rare in distribution, they may also be unsatisfactory for determining deglaciation chronology. Dating of fossils (summary in Colhoun et al. 1992) and geophysical modelling (Zwartz et al. in press) indicate a mid-Holocene sea level highstand that was widespread along the coast of East Antarctica. Fossils taken from the highest emergent shorelines will, therefore, tend to return mid- Holocene age estimates. While such data may be useful for a number of reasons, Vestfold and Bunger hills are known to have been free of the ice sheet since at least the latest Pleistocene (Fabel et al. in press, Melles et a l in press respectively), some 5000-6000 years before the mid-Holocene sea level highstand. Accordingly, organic deposits from sites

other than emergent shorelines should also be sampled in order to date ice sheet retreat.

Organic deposits from the nearshore marine environment may also be used to construct a deglaciation chronology (e.g. Melles et al. 1994). However, dating sediments from the nearshore marine environment may also be unsatisfactory for four reasons. First, the marine reservoir effect is variable around Antarctica (e.g. Domack et al. 1989), depending on the ratio of 14C-depleted CO, derived from melting ice sheets vs. CO, derived from the atmosphere. This ratio must have been rather variable in the past as well, being controlled by melting episodes of the East Antarctic ice sheet.

Second, primary production in the nearshore marine during the early period of deglaciation might have been substantially limited, either by greatly reduced light associated with blankets of snow overlying perennial sea ice that is thought to have extended as much as 1500 km farther north (Hays 1978), or by nutrient-poor meltwater (cf. Powell & Dawber in press) that must have been released in massive amounts.

Third, the dispersed nature of the organic carbon, and the addition of lithogenic carbon, above the till/marine sediment transition (see Melles et aL in press) makes reliable radiocarbon dating of deglaciation difficult. Domack & Ishman (1993) and Domack et al. (1993) reported that the total organic carbon content of fjord bottom sediments decreased with proximity to a glacier margin at Andvord Bay, due to dilution by meltwater-transported terrigenous debris. Dilution by aeolian sediments may also be important locally.

Finally, turbation of bottom sediments by icebergs, bergy bits or sea ice occurs at depths as great as several hundred metres, mixing sediments of different ages and making accurate determination of the timing of onset of biogenic sedimentation in the nearshore marine environment difficult. Only in deep basins protected by shallow sills would ice turbation be absent.

Lacustrine sediments

Lacustrine sediments have also been used to construct deglaciation chronologies for the East Antarctic oases. The oldest lake cores recovered from Larsemann Hills (Gillieson etal. 1990), Vestfold Hills (Fulford-Smith & Sikes 1996) and Bunger Hills (Melles et al. 1994) have all returned radiocarbon age estimates of the latest Pleistocene to earliest Holocene, consistent with the glacial history presented in Stuiver et al. (1981). Goodwin (1993) presented early to mid-Holocene ages from lakes in Grearson Oasis, but no dates from lake cores have yet been reported from the other oases.

Early during deglaciation, lakes occupy ice-proximal positions. Cores from contemporary ice-proximal lakes in Bunger Hills (Melles 1994, p. 49) and Vestfold Hills (D. Zwartz personal communication 1997) show that sedimentation there is dominated by inorganic debris, making

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343 BLANKETING SNOW AND ICE

radiocarbon dating difficult or impossible (M. Melles personal communication 1997). Inorganic sedimentation may still dominate in lakes that are distant from the ice sheet. A number of studies of Dry Valleys lakes have indicated that inorganic sedimentation may occur through perennial lake ice (e.g. Simmons et al. 1986, Squyreset al. 1991, Andersen et aZ. 1993). Under very low levels of biogenic sedimentation, the deposition of lithogenic carbon through the perennial ice may render lake bed sediments unsuitable for radiocarbon dating.

Organic deposits in freshwater lakes typically acquire 14c in equilibrium with the atmosphere. However, ice-proximal lakes may derive carbon from old CO, that was formerly trapped as bubbles in the ice sheet. When those lakes are perennially frozen or strongly stratified, and gas exchange with the atmosphere is limited, then a correction may be required. The magnitude of that correction will be variable, but may be as much as 10 000 years (Doran 1997) and will be difficult to hindcast. Doran (1997) states that palaeolake deposits from Antarctica cannot be dated reliably using radiocarbon dating alone.

Terrestrial sediments

Terrestrial deposits that may be radiocarbon dated consist of either plant remains (e.g. Burgess et al. 1994) or mumiyo (e.g. Verkulich & Hiller 1994). Both of these types of deposits may form near to the ice sheet margin if conditions are favourable, and likewise both types of deposits may be found near to the tops of hills that emerge first from the ice sheet. Few very old plant remains have been reported, probably because of the difficulty of locating remains within perma-frosted sediment. However, given the importance of the site reported by Burgess et al. (1994), perhaps more efforts should be put toward permafrost drilling programs.

Dating of mumiyo from Bunger Hills has reinforced the notion of Holocene deglaciation there (Verkulich & Hiller 1994), whereas elsewhere in Antarctica mumiyo has been dated to beyond the range of conventional radiocarbon (Hiller et aZ. 1988). Because these terrestrial deposits may form close to the ice edge and near to hilltops, and are thus least affected by blankets of snow and ice that fill the valleys following retreat of the ice sheet, they are probably the best available archives for radiocarbon dating of deglaciation.

Discussion

The extent, thickness and longevity of blankets of snow and ice over land, and perennial lake and sea ice, is fundamental for the development of organic deposits in and around the East Antarctic oases. Observations from eight Antarctic oases suggest a link between the present-day extent of blanketing snow and ice and the occurrence of sea ice break- out. At Vestfold Hills, where blanketing snow and ice covers only 5% of the area, sea ice breaks out annually and some

large hypersaline lakes rarely freeze, even in winter. The ice fields all lie near to the ice sheet, far from the open ocean or the hypersaline lakes. At Bunger Hills, where blanketing snow and ice also covers around 5% of the land, the central marine inlets always appear to thaw through summer. Perennial snow and ice in Bunger Hills lies in areas distant from the marine inlets. In strong contrast, the oases where blanketing snow and ice reaches proportions of 1646% are surrounded either by perennial sea ice or by ice shelf and glacier. The presence of permanent ice around an oasis has two main effects. First, open water is dark and dramatically lowers the regional albedo of an oasis area. When the energy balance in an oasis changes in this way, perennial snow and ice fields are more likely to melt, exposing more dark rock and so on in a positive feedback. The second effect of open water is to act as a trap for wind-drifted snow. Several of the oases lie downwind of stretches of sea, in particular Stillwell Hills and nearby islands, Broknes at Larsemann Hills, and parts of Vestfold and Bunger Hills. Should the sea ice break out, then the areas downwind of the water will be largely deprived of the wind-drifted snow that constitutes much of the annual snow budget.

During colder glacial times, fringing sea ice off the East Antarctic oases must have been permanent, multi-season or at least much longer lasting than today. During those times, the area of blanketing snow and ice in all East Antarctic oases probably would have been greater than the areas documented in this paper. A significant proportion of the East Antarctic oases may have been barren of biogenic sedimentation, while remaining deglaciated. Climatic amelioration, leading to a resumption of annual breakout of sea ice, would have been marked by a rapid change in regional summer albedo, combined with the reduction in drift snow supply to parts of some oases. As a result, the snow and ice fields in the valley bottoms would have melted and more abundant terrestrial, lacustrine and marine biogenic sedimentation would have commenced. If radiocarbon dating of some biogenic sediments does simply reflect the transition to annual breakout of the sea ice, then a systematic error may have been introduced into determining the time of ice sheet retreat.

This hypothetical model is able to be tested by two distinct programs. First, a series of freshwater lakes should be chosen, that thaw annually, remain perennially frozen but relatively free of blanketing snow, and perennially frozen with a thick snow blanket. At each of these lakes, the depth of the photic zone, primary productivity and albedo of lake ice and snow should be measured. Also, cores should be taken to compare basal radiocarbon ages and more recent rates of biogenic sedimentation between the lakes. Inter-oasis comparison of lacustrine sedimentation rates is fraught with difficulty due to differences in water temperature (Kaup 1995b, p. 316) and nutrients derived from weathering of bedrock (Haendel & Kaup 1995, p. 313). However, comparison within an oasis would be an excellent way to test the hypothesis presented. A second, complementary way to

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DAMIAN B. GORE 344

proceed would be to use independent dating methods, discussed below, as close as possible to the lakes sampled and dated using radiocarbon.

If it can be demonstrated that radiocarbon dating of lake and nearshore marine sediments is an inadequate tool, how then should the deglaciation age of an oasis be determined? The first terrestrial places to emerge from a retreating ice sheet, and remain free of blanketing snow and ice are the summits and upper slopes of ridges and hills. Observations from Larsemann Hills and Taylor Islands show that these locations are largely free of moss, lichen and lacustrine sediments that might be dated using the radiocarbon technique. However, it is these places where dating efforts should be focussed. Four main techniques should be employed. First, radiocarbon dating of mumiyo has been used rather successfully to record the occupation of nest sites by snow petrels throughout the Last Glacial Maximum at several sites in Antarctica (Hiller et al. 1988), although the presence of suitable nesting crevices is a primary controlling factor. Fortuitous discoveries of terrestrial organic deposits may still occur (e.g. Burgess et al. 1994), and permafrost drill cores should be taken at sites that lie downslope of long-lived lee- side snowbanks, or near to lake shores, where moist sediments may have allowed the long-term growth and accumulation of plant material. Second, cosmogenic isotope exposure age dating has been used successfully in parts of Antarctica (e.g. Brook e t al. 1993, Klein et al. 1993) and some methodological problems experienced with the technique in Vestfold Hills appear to be largely resolved (see FabeI et al. in press). Third, optically stimulated luminescence dating (e.g. Rhodes & Pownalll994) has now been used successfully on glaciofluvial and glaciomarine sediments from Bunger Hills (Rhodes & Gore unpublished data). Finally, counting annual sedimentary lamina in marine basins, below the onset of abundant biogenic sedimentation, is largely untried and may be useful. Radiocarbon dating, as well as a range of independent dating techniques, must be applied to deposits on the hilltops, that emerge first from the continental ice, if the effects of blanketing snow and ice are to be minimized.

Conclusions

Blankets of perennial snow and ice are abundant in the East Antarctic oases, filling valleys and lake basins and covering perennial lake and sea ice. In some of these places biogenic sedimentation is precluded, whereas in others biogenic sedimentation may have been reduced by an unknown degree. The presence of open water appears to be the controlling factor for the abundance of blanketing snow and ice, as open water lowers the regional summer albedo, warming an oasis, as well as acting as a trap for wind-drifted snow. During colder, post-glacial times when sea ice must have been perennial along most of the East Antarctic coast, the oases there must have hosted fields of perennial snow and ice more extensive than those of the present day. Organic sedimentation

in those oases during colder, glacial times would have been greatly restricted by this superimposed ice, and the subsequent, fortuitous discovery of those sparse, old organic deposits at the present day is difficult as a result. Climatic amelioration would lead to the resumption of sea ice breakout, and allow the onset of more widespread and abundant biogenic sedimentation in an oasis. As a result, fluctuations of the East Antarctic ice sheet determined by radiocarbon assay of organic deposits in and around the oases may be greatly in error, and need verification using independent dating methods that date first emergence of the hill tops from the continental ice.

Acknowledgements

I thank the Australian Antarctic Division for logistic support, the Antarctic Science Advisory Committee and Joyce Vickery Scientific Research Fund for financial support, Andy Baird and Michelle Leishman for help in the field, Bruce Gore for helping to calculate the extent of snow and ice, Don Adamson, Eric Colhoun, Wes Blake Jr, John Smol and Rob Wharton Jr for helpful written communication or discussion, and Martin Melles and Ross Powell for constructive reviews.

References ADAMSON, D.A., COLHOUN, E.A. & LEDINGHAM, R. 1991. Geographic

observations and glacial history in East Antarctica. In Proceedings of the Second Edgeworth David Day Symposium, June 1989. Sydney: The University of Sydney, 124-130.

ADAMSON, D.A., MABIN, M.C.G. & LULY, J.G. 1997. Late Cenozoic development of landforms including Beaver and RadokLake basins in the Amery Oasis, Prince Charles Mountains, Antarctica. Antarctic Science, 9, 299-306.

ADAMSON, D.A. & PICKARD, J. 1983. Late Quaternary ice movement across theVestfoldHills, East Antarctica. InOuvm, R.L., Jmes,P.R. & JAGO, J.B., eds. Antarctic earth science. Canberra: Australian Academy of Science, 465-469.

ADAMSON, D.A. & PICKARD, J. 1986a. Cainozoic history of the Vestfold Hills. In PICURD, J., ed. Antarctic oasis. Sydney: Academic Press,

ADAMSON, D.A. & PICKARD, J. 1986b. Physiography and geomorphology of the Vestfold Hills. In PICKARD, J., ed. Antarctic oasis. Sydney: Academic Press, 99-139.

clastic sedimentation in Antarctic Dry Valley lakes. I n GneeN, W. & FRIEDMANN, I , eds. Physical and biogeochemical processes in Antarctic lakes. Antarctic Research Series, 59,71-81.

BARKER, R.J. 1981. Physical and chemical parameters of Deep Lake, Vestfold Hills, Antarctica. ANARE ScientificReport, No. 130,73 pp.

BARTSCH, A. 1989. Die Eisalgenflora des Weddellmeeres (Antarktis): Artentusemmensetzung und Biomass sowie dkophysiologie ausgewahlter Arten. [Sea ice algae of the Weddell Sea (Antarctica): species composition, biomass, and ecophysiology of selected species]. Reports on Polar Research, No. 63, 110 pp.

BLAKE JR, W. 1989. Inferences concerning climatic change from a deeply frozen lake on Rundfjeld, Ellesmere Island, Arctic Canada. Journal of Paleolimnology, 2,41-54.

BORMANN,~ . & FRITZSCHE, D. 1995. eds. TheSchirmacher Oasis, Queen Maud Land, East Antarctica, and its surroundings. Darmstadt: Justus Perthes Gotha, 448 pp.

63-97.

ANDBRSEN, D.W., WHARTON JR, R.A. & SOUYRES, S.W. 1993. Terrigenous

https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102097000412Downloaded from https://www.cambridge.org/core. IP address: 54.39.17.49, on 08 Apr 2018 at 08:04:00, subject to the Cambridge Core terms of use, available at

BLANKETING SNOW AND ICE 345

BRoMLBY, A.M. 1986. Precipitation in the Wright Valley. Newzealand Antarctic Record, Special Supplement, 6, 60-68.

BRONGE, C. 1996. Hydrographic and climatic changes influencing the proglacial Druzhby drainage system, Vestfold Hills, Antarctica. Antarctic Science, 8,379-388.

Chronology of Taylor Glacier advances in Arena Valley, Antarctica using in situ cosmogenic ’He and %e. Quaternary Research, 39,

BvRoess, J.S., SPATR, A.P. & SHEVLIN, J. 1994. The onset of deglaciation in the Larsemann Hills, Eastern Antarctica. Antarctic Science, 6,

BROOK, E.J., KURZ, M.D.. DBNTON, G.H. & ACKBRT, R.P.J. 1993.

11-23.

491-495. CHAMBBRS, J.L.C., WILSON, C.J.L. & ADAMSON, D.A. 1986. A

crystallographic study of the perennially frozen ice surface of patterned lake, Framnes Mountains, East Antarctica. Journal ofGlaciology, 32,

CHINN, T.J.H. 1993. Physical hydrology of the Dry Valley lakes. Antarctic Research Series, 59, 1-52.

COLHOUN, E.A. & ADAMSON, D.A. 1992. Raised beaches of the Bunger Hills, Antarctica. ANARE Report, No. 136,47 pp.

COLHOUN, E.A., MABIN, M.C.G., ADAMSON, D.A. & KIRK, R.M. 1992. Antarctic ice volume and contribution to sea-level fall at 20 000 yrsp from raised beaches. Nature, 358,316-319.

DoMAcK,E.W. & ISHMAN, S.E. 1993. Oceanographicandphysiographic controls on modern sedimentation within Antarctic fjords. Geological Society ofAmerica Bulletin, 105, 1175-1189.

1995. Late Holocene advance of the Miiller Ice Shelf, Antarctic Peninsula: sedimentological, geochemical and palaeontological evidence. Antarctic Science, 7,159-170.

DOMACK, E.W., JULL, A.J.T.,ANDERsoN, J.B., LINICK,T.W. & WILLIAMS, C.R. 1989. Application of Tandem Accelerator Mass-Spectrometer dating to Late Pleistocene-Holocene sediments of the East Antarctic continental shelf. Quaternary Research, 31,277-287.

cyclicity in organic matter preservation in Antarctic fjord sediments. Antarctic Research Series, 60, 265-272.

DORAN, P.T. 1997. Antarctic lake sediments: no easy date. In Program and Abs trac ts , American Socie ty of Limnologis ts and Oceanographers, ASLO 97, Aquatic Sciences Meeting, Santa Fe, USA, February 10-14, 1997, 148-149.

DoRAN,P.T., WHARTONJR, R.A. & BERRY LYONS, W. 1994. Paleolimnology of the McMurdo Dry Valleys, Antarctica. JournalofPaleolimnology,

FABEL, D., STONE, J., FmeLD, L.K. & Cxesswe~~, R.G. in press. Deglaciation of the Vestfold Hills, East Antarctica: cosmogenic isotope evidence from subglacial erratics. I n RICCI, C., ed. The Antarctic region.’ geological evolution and processes. Siena: Museo Nazionale dell’ Antartide.

FITZSIMONS, S.J. 1990. Ice-marginal depositional processes in a polar maritime environment, Vestfold Hills, Antarctica. Journal of Glaciology, 36, 279-286.

FITZSIMONS, S.J. & DOMACK, E.W. 1993. Evidence for Early Holocene deglaciation of the Vestfold Hills, East Antarctica. PolarRecord, 29,

FULFORD-SMITH, S.P. & SIKES, E.L. 1996. The evolution of Ace Lake, Antarctica, determined from sedimentary diatom assemblages. Palaeogeography, Palaeoclimatology, Palaeoecology, 124, 73-86.

GiLLIBSoN,D.S. 1991. Anenvironmental history oftwo freshwater lakes in the Larsemann Hilts, Antarctica. Hydrobiologia, 214,327-331.

GILLIeSoN, D., BvRGess, J.S., SPATE,A. & COCHRANE,A. 1990. An atlas of thelakesof theLarsemannHills, PrincessElizabethLand, Antarctica. ANARE Research Notes, No. 74,173 pp.

GOODWIN, I.D. 1993. Holocene deglaciation, sea-level change and the emergenceof the Windmill Islands, Budd Coast, Antarctica. Quaternary Research, 40, 70-80.

520-526.

DOMACK,E.W.,ISHMAN, S.E.,STEIN,A.B.,MCCL@NNBN,C.E. & JuLL,A.J.T.

DOMACK, E.W., MASHIOTTA, T.A. & BURKLBY, L.A. 1993. 300-Year

10,85-114.

237-240.

GoRe, D.B. 1992. Ice-dammingand fluvial erosion in the Vestfold Hills, East Antarctica. Antarctic Science, 4, 227-234,

GORE, D.B. 1993. Changes in the ice boundary of theVestfoldHills,East Antarctica, from 1947 to 1990. Australian GeographicalStudies, 31,

HAENDeL, D. & KAUP, E. 1995. Nutrients. I n BORMA”, P. & FRITZSCHE, D.,eds. The Schirmacher Oasis, Queen MaudLand, EastAntarctica, and its surroundings. Darmstadt: Justus Perthes Gotha, 312-316.

HAYS, J.D. 1978. A review of the Late Quaternary climatic history of Antarctic seas. I n VAN ZINDeReN BAKKER, E.M.,ed. Antarcticglacial history and world paleoenvironmenrs. Rotterdam: A.A.Balkema,

HILLER, A., WAND,^., KAMPF, H. & STACKEBRANDT, W. 1988. Occupation of the Antarctic continent by petrels during the past 35 000 years; inferences from a”C study of stomach oil deposits. Polar Biology, 9,

49-61.

57-70.

69-77. HOARE, R.A., POPPLEWBLL, K.B., &NSB, D.A., HBRDBRSON, R.A., PUBBLE,

W.M. & WILSON,A.T. 1964. Lake Bonney, Taylor Valley, Antarctica; a natural solar energy trap. Nature, 202,886-888.

HOLLIN, J.T. 1962. On the glacial history of Antarctica. Journal of Glaciology, 4(32), 173-195.

KALP, E. 1995a. Solar radiation in water bodies. In BORMANN, P. & FRITZSCHB, D., eds. TheSchirmacher Oasis, Queen MaudLand, East Antarctica, and its surroundings. Darmstadt: Justus Perthes Gotha,

KAUP, E. 1995b. Chlorophyll a and primary production. In BORMA”, P. & FRITZSCHB, D., eds. The Schirmacher Oasis, Queen Maud Land, East Antarctica, and its surroundings. Darmstadt: Justus Perthes Gotha, 316-319.

DEZFOULY-ARIOMANDY, B. 1993. Late Cenozoic history of East Antarctica, inferred from measurement of cosmogenic W e andMAl, produced in situ on bedrock surfaces. EOS Transactions of the American Geophysical Union, 74 (16), 154.

LILJBQUIST, G.H. 1970. Klimatologi Stockholm: Generalstabens Litografiska Anstalt, 527 pp.

LOOPMANN,A. 1988. The effect of climatic factors on the ice, temperature and oxygen regimes in the lakes of the Schirmacher Oasis during the summer season 1983-1984. In MARTIN, J., ed. Limnological studies in Queen Maud Land, East Antarctica. Tallinn: Valgus, 43-56.

Thickness of ice on perennially frozen lakes. Nature, 313,561-562. MELLES, M. 1994. ed. TheExpeditions NORILSWTAYMYR 1993 and

BUNGER OASIS 1993-94 of the AWI Research Unit Potsdam. Berichte zur Polarforschung, No. 148, 80 pp.

dating of lacustrine and marine sediments from the Bunger Hills, East Antarctica. Antarctic Science, 6,375-378.

W. in press. Late Pleistocene and Holocene environmental history of Bunger Hills, East Antarctica, as revealed by fresh-water and epishelf lake sediments. I n RICCI, C., ed. The Antarctic region: geological evolution andprocesses. Siena: Museo Nazionale dell’ Antartide.

PICKARD, J. 1985. TheHolocene fossilmarine macrofaunaof the Vestfold Hills, East Antarctica. Boreas, 14, 189-202.

PICKARD, J. 1986. The Vestfold Hills: A window on Antarctica. In PICKARD, J., ed. Antarctic oasis. Sydney: Academic Press 333-351.

POWELL, R.D. & DAWBER, M. in press. Polar glacier grounding line environments and their epifaunal communities with implications for the stratigraphic record. In RICCI, C. ,ed. TheAntarctic region:geological evolution andprocesses. Siena: Museo Nazionale dell’ Antartide.

RHODES, E.J. & POWNALL, L. 1994. Zeroing of the OSL signal in quartz from young glaciofluvial sediments. Radiation Measurements, 23,

RICHTER, W. & BORMANN, P. 1995a. Weather and climate. In BORMANN, P. & FRITZSCHE, D.,eds. The Schirmacher Oasis, Queen Maud Land,

286-290.

KLEIN, J., MACCHIAROLI, P., GIEGBNGACK, R., MIDDLETON, R., LAWN, B. &

McKAY, C.P., CLOW, G.D., WHARTON JR., R.A. & SQUYRBS, S.W. 1985.

MELLES, M., VERKULICH, S.R. & HBRMICHEN, W.-D. 1994. Radiocarbon

MELLES, M., KKJLBE, T., VERKULICH, S.R., PUSHINA, Z.V. & HUBBBRTEN, H.-

581 -585.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102097000412Downloaded from https://www.cambridge.org/core. IP address: 54.39.17.49, on 08 Apr 2018 at 08:04:00, subject to the Cambridge Core terms of use, available at

346 DAMIAN B. GORE

East Antarctica, and its surroundings. Darmstadt: Justus Perthes Gotha, 207-220.

RICHTER, W. & BORMANN, P. 1995b. Hydrology. I n BORMANN, P. & FRITZSCHE, D.,eds. The Schirmacher Oasis, Queen MaudLand, East Antarctica, and its surroundings. Darmstadt: Justus Perthes Gotha,

RICHTER,~. & BORMA”, P. 1 9 9 5 ~ . Geomorphology. In BORMA”, P. & FRITZSCHE, D.,eds. The Schirrnacher Oasis, Queen MaudLand, East Antarctica, and i f s surroundings. Darmstadt: Justus Perthes Gotha,

SIMMONS JR, G.M., WHARTONJR, R.A., MCKAY, C.P.,NEDELL,S. & =ow, G. 1986. Sand/& interactions and sediment deposition in perennially icesovered antarctic lakes. Antarctic Journal of the US, 21(5),

259-319.

171-206.

21 7-220. SomEs, S.W.,ANDERSEN,D.W.,NEDELL, S.S.& WHARTQN JR, R.A. 1991.

Lake Hoare, Antarctica: Sedimentation through a thick perennial ice cover. Sedirnentology, 38, 363-379.

SHUMSKIY, P.A. 1957. Glaciological and geomorphological reconnaissance in the Antarctic in 1956. Journal of Glaciology, 3,56-61.

STUIVER, M., DENTON, G.H., HuGREs,T.J. & FASTOOK, J.L. 1981. History of the Marine Ice Sheet in West Antarctica during the Last Glaciation: a working hypothesis, In DBNTON, G.H. & HuoHes, T.J., eds. The last great ice sheets. New York: John Wiley & Sons, 319-436.

VERKULICH, S.R. &HILLER, A. 1994. Holocene deglaciationof the Bunger Hills revealed by 14C measurements on stomach oil deposits in snow petrel colonies. Antarctic Science, 6,395-399.

Perennial ice covers and their influence on Antarctic lake ecosystems. I n GREEN, w. & FRIEDMANN, I., eds. Physical and biogeochemical processes in Antarctic lakes. Antarctic Research Series, 59,53-70.

ZWARTZ, D., LAMBECK, K., BIRD, M. & STONE, J. in press. Constraints on the former Antarctic Ice Sheet from sea-level observations and geodynamic modelling. In RICCI, C., ed. The Antarcfic region: geological evolution andprocesses. Siena: Museo Nazionale dell’ Antartide.

WHARTON JR, R.A., MCKAY, C.P., CLOW, G.D. & ANDERSEN, D.T. 1993.

https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0954102097000412Downloaded from https://www.cambridge.org/core. IP address: 54.39.17.49, on 08 Apr 2018 at 08:04:00, subject to the Cambridge Core terms of use, available at