Deglaciation of a major palaeo-ice stream in Disko Trough, West Greenland
Deglaciation of a major palaeo-ice stream in Disko Trough, West Greenland
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DOI：
10.1016/j.quascirev.2016.01.018
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发表时间：
2016-09-01
影响因子：
4
通讯作者：
Hiemstra, John F.
中科院分区：
文献类型：
--
作者：
Hogan, Kelly A.;Cofaigh, Colm O.;Hiemstra, John F.
最近的研究证实，在末次盛冰期（Last Glacial Maximum， LGM）期间，格陵兰岛中部西部的冰架断裂处有接地冰。在这里，我们结合了海洋沉积岩心数据，包括冰川海相岩相和IRD代理记录，以及地貌和声学相证据，来研究格陵兰冰盖西部主要出口（GrIS）横跨大陆架的退缩的性质和控制因素。这个包含Jakobshavns Isbra冰流的出口从迪斯科海槽的外大陆架迅速后退，主要是通过冰山崩解进行的，然而，在一个海槽变窄的中间大陆架上出现了小的后退停顿（几十年），形成了微妙的陆基带楔。到距今12.1万年，冰已经退缩到内陆大陆架的玄武岩悬崖和浅滩上，在那里它被固定和稳定了至少100年。在此期间，冰缘似乎在海槽上形成了一个冰裂湾，融化成为冰质量损失的重要机制。细粒沉积物（泥）与富含ird的沉积物（碎屑）交替沉积，形成了一种可能与季节气候循环有关的典型脱冰岩相。在温暖的夏季，来自附近冰缘的大量冰下融水沉积了泥质沉积物，而冬季主要是冰山崩解，导致了沉积物的沉积。这是大陆架背景下的第一个冰海相岩相，我们认为冰缘的裂裂-海湾结构，加上裂裂和融化之间的转换作为消融机制，通过引导融水和冰山通过内部槽，促进了其沉积。Disko槽内陆架上主要的静止站的出现表明，对当地地形的冰动力响应是GrIS该部分主要出口在退缩期间的行为的关键控制。(C) 2016年作者。Elsevier Ltd.出版。
Recent work has confirmed that grounded ice reached the shelf break in central West Greenland during the Last Glacial Maximum (LGM). Here we use a combination of marine sediment-core data, including glacimarine lithofacies and IRD proxy records, and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the Greenland Ice Sheet (GrIS) across the shelf. Retreat of this outlet, which contained the ancestral Jakobshavns Isbra ice stream, from the outer shelf in Disko Trough was rapid and progressed predominantly through iceberg calving, however, minor pauses in retreat (tens of years) occurred on the middle shelf at a trough narrowing forming subtle grounding-zone wedges. By 12.1 cal kyr BP ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf, where it was pinned and stabilised for at least 100 years. During this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice-mass loss. Fine-grained sediments (muds) were deposited alternately with IRD-rich sediments (diamictons) forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles. High influxes of subglacial meltwater, emanating from the nearby ice margins, deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons. This is the first example of this glacimarine lithofacies from a continental-shelf setting and we suggest that the calving-bay configuration of the ice margin, plus the switching between calving and melting as ablation mechanisms, facilitated its deposition by channelling meltwater and icebergs through the inner trough. The occurrence of a major stillstand on the inner shelf in Disko Trough demonstrates that the ice-dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the GrIS during retreat. (C) 2016 The Authors. Published by Elsevier Ltd.