Geological constraints on Antarctic palaeo‐ice‐stream retreat
Geological constraints on Antarctic palaeo‐ice‐stream retreat
复制标题
南极古冰流退缩的地质限制
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
R. Larter
中科院分区：
文献类型：
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作者：
C. Ó. Cofaigh;J. Dowdeswell;J. Evans;R. Larter
保存在南极大陆架测深槽中的海底地貌表明，在末次盛冰期之后，冰流在大陆架上的退缩方式在不同的槽之间是不同的。从地质证据中推断出三种后退方式：快速后退、幕式后退和缓慢后退。冰流漂浮和崩解导致的快速后退通过保存未改变的流线型冰下底形的地貌组合记录下来，包括记录沿着这些槽流动的大尺度冰川线理（MSGL）。这些细长的底形没有被横向于冰流形成的退缩冰川地貌（如冰碛或接地带楔形）覆盖，并且覆盖的冰消沉积物很薄。第二种类型的地貌组合由MSGL叠加或被横向接地带楔中断组成。这种组合意味着连续接地带位置之间的幕式后退。第三类地貌组合是众多的、密集的、后退的冰碛和间歇性的接地带楔，它们覆盖并中断了MSGL。这个组合记录了大陆架上的冰缓慢后退的过程。不同水深槽之间的冰流退缩风格的变化表明，南极古冰流在末次冰期循环结束时对外部强迫的反应并不一致。相反，它们的历时后退反映了以水深和流域大小为形式的地方控制的主导地位。更广泛地说，这些数据表明，在反向河床坡度地区的海基冰盖退缩不一定是灾难性的，它们为试图预测大型极地冰盖动态的数值模型提供了重要的约束。版权所有© 2008约翰威利父子有限公司.
Submarine landforms preserved in bathymetric troughs on the Antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs. Three styles of retreat are inferred from the geological evidence: rapid, episodic and slow. Rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega‐scale glacial lineations (MSGLs) that record streaming flow along these troughs. These elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding‐zone wedges, and overlying deglacial sediments are thin. A second type of landform assemblage consists of MSGLs overprinted or interrupted by transverse grounding‐zone wedges. This assemblage implies episodic retreat between successive grounding‐zone positions. The third type of landform assemblage is that of numerous, closely spaced, recessional moraines and intermittent grounding‐zone wedges that overlie and interrupt MSGLs. This assemblage records the slow retreat of grounded ice across the shelf. Variation in the style of ice stream retreat between the different bathymetric troughs indicates that Antarctic palaeo‐ice‐streams did not respond uniformly to external forcing at the end of the last glacial cycle. Rather, their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size. More broadly, these data show that retreat of marine‐based ice sheets in areas of reverse bed slope is not necessarily catastrophic, and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets. Copyright © 2008 John Wiley & Sons, Ltd.