Testing the extent and timing of past glaciations on the largest sub-Antarctic island, South Georgia

亚南极岛屿是研究过去冰川和气候变化的理想地点，它们的古代冰川记录对于了解地球系统的各个方面都很重要。由于这些岛屿位于温暖的海洋气候和寒冷的极地气候之间，南极以下冰盖的大小为校准冰盖模型的敏感性提供了一个潜在的有价值的手段，确保用来迫使它们的气候参数是现实的，并且输出对未来有利。冰川事件的规模和时间的变化也可以提供有关区域和半球之间气候变化的机制和阶段的重要信息。同样的数据限制了冰川避难所的下落和持久性，并向生物学家提供了有关南大洋生物进化和多样性的地质条件的信息。为了改进冰盖模型，解释气候变化的模式，并解释世界海洋的生物多样性，需要关于南极洲以下冰川历史的信息。然而，与过去冰川的年龄、规模和数量有关的根本问题仍然没有答案。对于最大的亚南极岛屿南乔治亚岛来说，至少有一次重大的冰川推进已经从今天在该岛周围浅陆架海底发现的冰雕槽和沉积物脊(冰川)中得知。然而，它的年龄是未知的。与南极洲其他地区一样，最近的冰川作用--最后一次冰川盛期--很可能留下了冰盖推进和融化的最好记录。然而，即使在这一点上，也没有达成共识，两种相互矛盾的假设盛行：一种认为冰层范围有限，仅限于近岸峡湾；另一种认为冰盖很大，覆盖到该岛大部分地区周围的大陆架外部。哪个假设是正确的，答案在于对海底地形和沉积物的研究，这些尚未进行任何详细的调查。该项目提出了一项开创性的研究，首次从海洋角度研究南乔治亚州过去冰川的范围和时间。我将对以下假设进行可靠的检验：(1)最后一次冰期最大冰盖的范围有限，因此，在最后一次冰期之前达到大陆架外部界限的一个或多个主要冰盖冰川；或(2)最后一次冰川最大冰盖是广泛的，并在大陆架的地貌和沉积物中记录了退缩的年表。现有的和新收集的声纳水深数据将被用来以前所未有的详细程度绘制出南乔治亚大陆架上的冰川地貌。将对6个沉积物岩芯进行分析和年代测定，其中包括第一批从大陆架中找到的沉积物岩芯。该项目的目标将是标出前冰盖界限的冰雹，从陆架边缘到沿海峡湾。我将确定最广泛冰川的年龄，以及中间退缩或终极极限的年龄。对沉积物的物理分析将重建自上一次冰盛期以来的环境条件，直到现在，也许还会重建较早的冷暖期。解决保存在南极以下记录中的前陆架冰川的数量和范围将是该项目的一个主要成果，有关最后一次冰盖的行为和覆盖范围的重要新信息也将是该项目的一个主要成果。将在地球气候和进化史的背景下创造新的记录，并形成对亚南极冰川的第一个海洋古限制，造模者、气候科学家和生物学家受益。该项目还将提供基线地质数据，供生境测绘项目和渔业使用。这项研究将为南大洋冰和气候历史提供新的线索，并为未来研究近极地区过去的冰川变化设定新的议程。

The sub-Antarctic islands are ideally placed to investigate past ice and climate changes, with records of their ancient glaciation important for understanding various aspects of the Earth system. Due to the islands' unique location between warm-maritime and cold-polar climates, the size of sub-Antarctic ice-cap advances provide a potentially valuable means of calibrating the sensitivity of ice-sheet models, ensuring the climate parameters used to force them are realistic and the outputs 'good' for the future. Variations in the scale and timing of glacial events can also provide critical information on the mechanisms and phasing of climate changes between regions and hemispheres. The same data constrain the whereabouts and persistence of glacial refugia, and inform biologists on the geological conditions governing the evolution and diversity of life in the Southern Ocean. To improve ice-sheet models, explain patterns of climate change, and interpret the biodiversity of the world's oceans, information on sub-Antarctica's glacial past is required. However, fundamental questions relating to the age, magnitude, and number of past glaciations remain unanswered. For the largest sub-Antarctic island, South Georgia, at least one major glacial advance is already known from ice-carved troughs and sediment ridges (moraines) found on the sea-floor of the shallow shelf surrounding the island today. Yet its age is unknown. As in other parts of Antarctica, the most recent episode of glaciation - The Last Glacial Maximum - is likely to have left behind the best record of ice-cap advance and melting. However, even here, there is no consensus, with two conflicting hypotheses prevailing: one suggesting a limited ice extent, restricted to the near-shore fjords; the other proposing that the ice cap was extensive, reaching the outer parts of the shelf around most of the island. Answers to which hypothesis is correct lie in the study of the submarine topography and sediments, which have yet to be investigated in any detail. This project proposes a pioneering study to examine the extent and timing of past glaciations on South Georgia, from a marine perspective, for the first time. I will provide a robust test of the hypotheses that, either: (i) the Last Glacial Maximum ice cap was of restricted extent and thus that one or more major ice cap glaciations that reached outer shelf limits pre-date the last glacial period; or that (ii) the Last Glacial Maximum ice cap was extensive, and a chronology of retreat is recorded in the shelf's landscape and sediments. Existing and newly-collected sonar bathymetry data will be utilised to map out the glacial features on the South Georgia shelf in unprecedented detail. Six sediment cores, among the first recovered from the shelf, will be analysed and dated. The project will target moraines marking the limits of former ice-caps, from the shelf edge to the coastal fjords. I will determine the age of the most extensive glaciation, and the age of intermediate retreat or terminal limits. Physical analyses of sediments will reconstruct environmental conditions during and since the Last Glacial Maximum, to the present day, and perhaps through older cold or warm periods. Resolving the number and extent of former shelf glaciations preserved in sub-Antarctic records will be a major outcome of the project, as will vital new information on the behaviour and reach of the Last Glacial ice cap. New records will be set in the context of Earth's climate and evolutionary histories, and form the first marine palaeo-constraints on sub-Antarctic glaciation, benefiting modellers, climate scientists and biologists. The project will also provide baseline geological data for use by habitat mapping projects and fisheries. This research will shed new light on Southern Ocean ice and climate history, and set a new agenda for future study of past glacial change in the near-polar regions.