Pattern, style and timing of British-Irish Ice Sheet advance and retreat over the last 45 000 years: evidence from NW Scotland and the adjacent continental shelf
Pattern, style and timing of British-Irish Ice Sheet advance and retreat over the last 45 000 years: evidence from NW Scotland and the adjacent continental shelf
复制标题
过去 45 000 年来英国-爱尔兰冰盖进退的模式、风格和时间：来自苏格兰西北部和邻近大陆架的证据
DOI：
10.1002/jqs.3296
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发表时间：
2021
影响因子：
2.3
通讯作者：
Bradwell T
中科院分区：
文献类型：
--
作者：
Bradwell T
预测冰盖对气候变暖和全球海平面上升的未来反应是重要但困难的。尤其是当快速流动的冰川溪流，由冰架缓冲，在海平面以下的床上接地时。当这些冰架被移除时会发生什么？冰流和周围的冰盖如何应对突然改变的边界条件？为了解决这些问题和其他问题，我们提出了新的地质，地貌，地球物理和地质年代学数据，来自最后一个英国-爱尔兰冰盖（BIIS）的冰流主导的西北部门。研究区域覆盖苏格兰西北部约45，000平方公里及周围大陆架。除了海底地貌测绘和第四纪沉积物分析外，我们还使用了一套从陆上和海上收集的100多个新的绝对年龄（包括宇宙成因核素暴露年龄，光释光年龄和放射性碳年龄），以建立一个全部门的冰盖重建，将所有可用的证据与贝叶斯时序模型相结合。利用这些信息，我们提出了一个详细的评估冰盖前进/退缩的历史，和冰川之间的连接不同地区的西北BIIS部门，在不同的时间在末次冰期循环。结果显示，在过去的45000年中，一个高度动态的，部分海洋，部分陆地的冰盖部门经历了大规模的变化，以响应亚千年尺度的气候（Dansgaard-Oeschger）周期。叠加在这些趋势，我们确定内部驱动的不稳定性，以更高的频率运行，当地地形因素的条件下，在冰消期的气候动力学和冰川学反馈。具体来说，我们的新证据表明，在格陵兰Stadials 12至9期间，西北BIIS部门的广泛海洋终止冰盖冰川作用-在主要的“晚Weichselian”冰盖冰川作用之前。经过一段时间的有限冰川作用，在格陵兰Interstadial 8至6中，我们发现了苏格兰西北部快速更新冰盖的良好证据，Minch冰流终点到达格陵兰Stadial 5的大陆架边缘，也许只是短暂的。西北部的冰川消退经历了许多阶段。在中、内大陆架上的几个接地面楔和冰碛证明了在格陵兰3号和2号体育场的整体后退期间，冰盖接地面线或冰缘的显著稳定，以及冰架的发展。西北刘易斯是第一个实质性的今天的土地面积冰川消退，在格陵兰体育场3的上半年，在全球海平面降低c。26 kabp，其次是角愤怒在c。24 kabp.明奇海峡的地形限制可能促进了早期格陵兰2号体育场冰架的发展，为冰流提供了额外的支持，并在一定程度上缓冲了外部驱动力。然而，c. 20-19 kabp，随着接地线迁移到岸边加深的水中，与海洋地质和床强度的显着变化相一致，冰流变得不稳定。我们发现，一旦开始，接地线撤退以不间断的方式进行，前方冰架的快速损失-首先是在西部，然后是东部槽-在苏格兰西北部峡湾口的最终冰川稳定之前，大约17 kabp。大约在同一时间，大约19-17 kabp，冰盖瓣体重新前进到东明奇-可能是对海洋不稳定性引发的邻近冰流损失的冰川学反应（和/或冰架）支持在明奇槽。刘易斯上的独立冰帽也.
Predicting the future response of ice sheets to climate warming and rising global sea level is important but difficult. This is especially so when fast‐flowing glaciers orice streams, buffered by ice shelves, are grounded on beds below sea level. What happens when these ice shelves are removed? And how do the ice stream and the surrounding ice sheet respond to the abruptly altered boundary conditions? To address these questions and others we present new geological, geomorphological, geophysical and geochronological data from the ice‐stream‐dominated NW sector of the last British–Irish Ice Sheet (BIIS). The study area covers around 45 000 km2of NW Scotland and the surrounding continental shelf. Alongside seabed geomorphological mapping and Quaternary sediment analysis, we use a suite of over 100 new absolute ages (including cosmogenic‐nuclide exposure ages, optically stimulated luminescence ages and radiocarbon dates) collected from onshore and offshore, to build a sector‐wide ice‐sheet reconstruction combining all available evidence with Bayesian chronosequence modelling. Using this information we present a detailed assessment of ice‐sheet advance/retreat history, and the glaciological connections between different areas of the NW BIIS sector, at different times during the last glacial cycle. The results show a highly dynamic, partly marine, partly terrestrial, ice‐sheet sector undergoing large size variations in response to sub‐millennial‐scale climatic (Dansgaard–Oeschger) cycles over the last 45 000 years. Superimposed on these trends we identify internally driven instabilities, operating at higher frequency, conditioned by local topographic factors, tidewater dynamics and glaciological feedbacks during deglaciation. Specifically, our new evidence indicates extensive marine‐terminating ice‐sheet glaciation of the NW BIIS sector during Greenland Stadials 12 to 9 – prior to the main ‘Late Weichselian’ ice‐sheet glaciation. After a period of restricted glaciation, in Greenland Interstadials 8 to 6, we find good evidence for rapid renewed ice‐sheet build‐up in NW Scotland, with the Minch ice‐stream terminus reaching the continental shelf edge in Greenland Stadial 5, perhaps only briefly. Deglaciation of the NW sector took place in numerous stages. Several grounding‐zone wedges and moraines on the mid‐ and inner continental shelf attest to significant stabilizations of the ice‐sheet grounding line, or ice margin, during overall retreat in Greenland Stadials 3 and 2, and to the development of ice shelves. NW Lewis was the first substantial present‐day land area to deglaciate, in the first half of Greenland Stadial 3 at a time of globally reduced sea‐level c. 26 kabp, followed by Cape Wrath at c. 24 kabp.The topographic confinement of the Minch straits probably promoted ice‐shelf development in early Greenland Stadial 2, providing the ice stream with additional support and buffering it somewhat from external drivers. However, c. 20–19 kabp, as the grounding‐line migrated into shoreward deepening water, coinciding with a marked change in marine geology and bed strength, the ice stream became unstable. We find that, once underway, grounding‐line retreat proceeded in an uninterrupted fashion with the rapid loss of fronting ice shelves – first in the west, then the east troughs – before eventual glacier stabilization at fjord mouths in NW Scotland by ~17 kabp.Around the same time, ~19–17 kabp, ice‐sheet lobes readvanced into the East Minch – possibly a glaciological response to the marine‐instability‐triggered loss of adjacent ice stream (and/or ice shelf) support in the Minch trough. An independent ice cap on Lewis also …