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

测试最大的亚南极岛屿南乔治亚岛过去冰川作用的范围和时间

• 批准号: NE/K000527/2
• 负责人: Alastair Graham
• 金额: $ 5.48万
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FK000527%2F2
• 关键词: Testing; extent; timing; past; glaciations

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.

亚南极群岛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的独特位置，亚南极冰盖推进的大小为校准冰盖模型的灵敏度提供了一个潜在的有价值的手段，确保用于强迫它们的气候参数是现实的，并且输出对未来是“有益的”。冰川事件规模和时间的变化也可以提供关于区域和半球之间气候变化的机制和分阶段的关键信息。同样的数据限制了冰川避难所的位置和持久性，并告知生物学家控制南大洋生物进化和多样性的地质条件。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，需要有关亚南极洲冰川历史的信息。然而，与过去冰期的年龄、规模和数量有关的基本问题仍然没有答案。对于亚南极最大的岛屿南乔治亚岛来说，从今天围绕岛屿的浅大陆架海底发现的冰雕槽和沉积物脊（冰碛）中，至少已经知道了一次主要的冰川推进。然而它的年龄是未知的。和南极洲的其他地区一样，最近的一次冰期——末次盛冰期——很可能留下了冰帽前进和融化的最佳记录。然而，即使在这里，也没有达成共识，有两种相互矛盾的假设占主导地位：一种认为冰的范围有限，仅限于近岸峡湾；另一种说法是，冰帽覆盖范围很广，覆盖了岛屿大部分地区周围的冰架外部。对哪种假设是正确的答案在于对海底地形和沉积物的研究，这还有待于任何细节的调查。该项目提出了一项开创性的研究，首次从海洋的角度研究南乔治亚岛过去冰川的范围和时间。我将为以下假设提供一个强有力的检验：(I)末次冰期最大冰冠的范围是有限的，因此在末次冰期之前到达外大陆架极限的一个或多个主要冰冠冰川；或者（ii）末次冰期极大期冰盖范围广泛，陆架的景观和沉积物中记录了退缩的年表。现有的和新收集的声纳测深数据将用于以前所未有的细节绘制南乔治亚大陆架的冰川特征。首批从冰架上找到的6个沉积物岩心将被分析并确定年代。该项目将以从冰架边缘到沿海峡湾的冰碛为目标，这些冰碛标志着以前冰盖的界限。我将确定最广泛的冰川作用的年龄，以及中间退缩或最终限制的年龄。对沉积物的物理分析将重建末次盛冰期期间和之后的环境条件，直至今天，也许还会经历更久远的寒冷或温暖时期。解决亚南极记录中保存的前冰架冰川的数量和范围将是该项目的主要成果，关于末次冰期冰帽的行为和范围的重要新信息也将是该项目的主要成果。将在地球气候和进化历史的背景下设定新的记录，并形成亚南极冰川的第一个海洋古约束，使建模者、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的冰和气候历史提供新的线索，并为未来近极地地区过去冰川变化的研究制定新的议程。

项目成果

First evidence of widespread active methane seepage in the Southern Ocean, off the sub-Antarctic island of South Georgia

南乔治亚岛亚南极岛附近南大洋广泛活跃甲烷渗漏的第一个证据

• DOI: 10.1016/j.epsl.2014.06.036
• 发表时间: 2014
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Römer M

Dynamic ancient ice caps in the sub-Antarctic suggested by new mapping of submarine ice-formed landscapes

海底冰形成景观的新测绘表明亚南极地区的动态古代冰盖

• 发表时间: 2014
• 期刊: EGU General Assembly Conference Abstracts
• 作者: Graham Alastair

TESTING THE EXTENT AND TIMING OF PAST GLACIATIONS OFFSHORE OF THE SUB-ANTARCTIC ISLAND OF SOUTH GEORGIA

测试南乔治亚州亚南极岛近海过去冰川的范围和时间

• 发表时间: 2015
• 作者: Graham, A.G.C.

Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords

• DOI: 10.1016/j.quascirev.2013.12.005
• 发表时间: 2014-04-01
• 期刊: QUATERNARY SCIENCE REVIEWS
• 影响因子: 4
• 作者: Hodgson, Dominic A.;Graham, Alastair G. C.;Evans, David J. A.
• 通讯作者: Evans, David J. A.

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

• DOI: 10.1016/j.quascirev.2014.06.025
• 发表时间: 2014-09-15
• 期刊: QUATERNARY SCIENCE REVIEWS
• 影响因子: 4
• 作者: Bentley, Michael J.;Cofaigh, Colm O.;Zwartz, Dan
• 通讯作者: Zwartz, Dan