Contents of water, sulphur, total organic and inorganic carbon, XRF counts of Ti, S and Ca and radiocarbon ages of sediment core Co1008 from Skua Lake, Rauer Group, East Antarctica

Limited information on the East Antarctic Ice Sheet (EAIS) geometry during Marine Isotope Stage 3 (MIS 3; 60-25 ka) restricts our understanding of its behaviour during periods of climate and sea level change. Ice sheet models forced by global parameters suggest an expanded EAIS compared to the Holocene during MIS 3, but field evidence from East Antarctic coastal areas contradicts such modelling, and suggests that the ice sheet margins were no more advanced than at present. Here we present a new lake sediment record, and cosmogenic exposure results from bedrock, which confirm that Rauer Group (eastern Prydz Bay) was ice-free for much of MIS 3. We also refine the likely duration of the Last Glacial Maximum (LGM) glaciation in the region. Lacustrine and marine sediments from Rauer Group indicate the penultimate period of ice retreat predates 50 ka. The lacustrine record indicates a change from warmer/wetter conditions to cooler/drier conditions after ca. 35 ka. Substantive ice sheet re-advance, however, may not have occurred until much closer to 20 ka. Contemporary coastal areas were still connected to the sea during MIS 3, restricting the possible extent of grounded ice in Prydz Bay on the continental shelf. In contrast, relative sea levels (RSL) deduced from field evidence indicate an extra ice load averaging several hundred metres thicker ice across the Bay between 45 and 32 ka. Thus, ice must either have been thicker immediately inland (with a steeper ice profile), or there were additional ice domes on the shallow banks of the outer continental shelf. Further work is required to reconcile the differences between empirical evidence of past ice sheet histories, and the history predicted by ice sheet models from far-field temperature and sea level records.目前针对海洋同位素阶段3（Marine Isotope Stage 3, MIS 3；60~25 ka）期间东南极冰盖（East Antarctic Ice Sheet, EAIS）几何形态的相关资料较为匮乏，这限制了我们对其在气候与海平面变化时期演化行为的认知。基于全球参数驱动的冰盖模型显示，MIS 3时期的东南极冰盖相较全新世有所扩张，但东南极沿海地区的野外观测证据与该模拟结果相悖，表明当时冰盖边缘并未比现今更靠前。本文报道了一套全新的湖相沉积记录，以及基岩的宇宙成因暴露测年结果，证实普里兹湾（Prydz Bay）东部的劳尔群（Rauer Group）在MIS 3的大部分时段均处于无冰状态。同时我们还细化了该区域末次冰盛期（Last Glacial Maximum, LGM）冰川作用的可能持续时间。 劳尔群的湖相与海相沉积物记录显示，末次冰期倒数第二次冰退事件发生于50 ka之前。湖相沉积记录表明，约35 ka之后，区域气候由暖湿转向冷干。但大规模的冰盖重新前进可能直至接近20 ka时才发生。 MIS 3时期，现今的沿海区域仍与海洋相连，这限制了普里兹湾大陆架上接地冰的可能分布范围。与之相对，基于野外证据推导的相对海平面（Relative Sea Levels, RSL）显示，在45~32 ka期间，普里兹湾全域存在平均厚度达数百米的额外冰负载，即冰盖厚度较现今厚数百米。据此，要么是内陆邻近区域的冰体厚度更大（冰体剖面更陡峭），要么是外大陆架的浅滩区域存在额外的冰穹。目前仍需开展进一步研究，以协调冰盖历史的野外实证与基于远场温度及海平面记录的冰盖模型预测结果之间的差异。