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 or ice 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 km² of 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 experienced margin oscillations during mid-Greenland Stadial 2, with an ice-accumulation centre in West Lewis existing into the latter part of Heinrich Stadial 1. Final ice-sheet deglaciation of NW mainland Scotland was punctuated by at least one other coherent readvance at c. 15.5 kabp, before significant ice-mass losses thereafter. At the glacial termination, c. 14.5 kabp, glaciers fed outwash sediment to now-abandoned coastal deltas in NW mainland Scotland around the time of global Meltwater Pulse 1A. Overall, this work on the BIIS NW sector reconstructs a highly dynamic ice-sheet oscillating in extent and volume for much of the last 45 000 years. Periods of expansive ice-sheet glaciation dominated by ice-streaming were interspersed with periods of much more restricted ice-cap or tidewater/fjordic glaciation. Finally, this work indicates that the role of ice streams in ice-sheet evolution is complex but mechanistically important throughout the lifetime of an ice sheet – with ice streams contributing to the regulation of ice-sheet health but also to the acceleration of ice-sheet demise via marine ice-sheet instabilities.

中文翻译：

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过去 45 000 年英爱冰盖进退的模式、风格和时间：来自苏格兰西北部和邻近大陆架的证据

预测冰盖未来对气候变暖和全球海平面上升的反应很重要，但也很困难。当由冰架缓冲的快速流动的冰川或冰流搁浅在海平面以下的床上时尤其如此。当这些冰架被移除时会发生什么？冰流和周围的冰盖如何响应突然改变的边界条件？为了解决这些问题和其他问题，我们提供了来自最后一个英国 - 爱尔兰冰盖 (BIIS) 以冰流为主的西北部分的新的地质、地貌、地球物理和地质年代学数据。研究区面积约 45 000 km ²苏格兰西北部和周围的大陆架。除了海底地貌测绘和第四纪沉积物分析外，我们还使用从陆上和海上收集的 100 多个新绝对年龄（包括宇宙成因核素暴露年龄、光激发发光年龄和放射性碳日期）来构建一个全行业的冰盖将所有可用证据与贝叶斯时间序列建模相结合的重建。使用这些信息，我们详细评估了冰盖前进/后退的历史，以及在最后一个冰川周期的不同时间，NW BIIS 部门不同区域之间的冰川学联系。结果显示了一个高度动态的，部分海洋，部分陆地，在过去 45 000 年中，冰盖部门因响应亚千年尺度气候（Dansgaard-Oeschger）循环而发生巨大变化。叠加在这些趋势上，我们确定了内部驱动的不稳定性，以更高的频率运行，受当地地形因素、潮水动力学和冰川消融期间的冰川反馈的制约。具体而言，我们的新证据表明，在格陵兰体育场 12 至 9 期间，西北 BIIS 部门存在广泛的海洋终止冰盖冰川作用——在主要的“晚期魏克塞尔”冰盖冰川作用之前。经过一段时间的冰川作用受限，在格陵兰岛间 8 到 6 号，我们发现了很好的证据表明苏格兰西北部冰盖迅速更新，明奇冰流终点到达格陵兰岛 5 号的大陆架边缘，也许只有简要地。西北地区的冰川消融经历了多个阶段。中部和内部大陆架上的几个接地带楔形和冰碛证明了在格陵兰岛 3 和 2 的整体退缩期间冰盖接地线或冰边缘的显着稳定，以及冰架的发展。在格陵兰体育场 3 的前半部分，全球海平面下降 c 时，NW Lewis 是当今第一个大面积冰川消融的地区。26 卡 在格陵兰体育场 3 的上半年，全球海平面下降 c. 26 卡 在格陵兰体育场 3 的上半年，全球海平面下降 c. 26 卡bp，然后是 Cape Wrath 在 c。24 ka bp。明奇海峡的地形限制可能促进了格陵兰体育场 2 早期冰架的发展，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因素。然而，c。20~19 ka bp ,随着接地线迁移到岸边加深水体, 恰逢海洋地质和床层强度发生显着变化, 冰流变得不稳定。我们发现，一旦开始，接地线后退以不间断的方式进行，前沿冰架迅速消失——首先是西部，然后是东部的海槽——最终在苏格兰西北部峡湾口的冰川稳定约 17 ka bp . 大约在同一时间，~19–17 ka bp，冰盖裂片重新进入东明奇 - 可能是对海洋不稳定引发的明奇槽中相邻冰流（和/或冰架）支撑损失的冰川学反应。在格陵兰体育场 2 中期期间，刘易斯上的一个独立冰盖也经历了边缘振荡，西刘易斯的一个积冰中心存在于海因里希体育场 1 的后期。苏格兰西北部大陆的最终冰盖消融至少被打断了在 c 处的另一种连贯阅读。15.5 ka bp，此后冰量显着减少。在冰川末端，c。14.5 ka bp，在全球融水脉冲 1A 时期，冰川将外流沉积物输送到苏格兰西北大陆现已废弃的沿海三角洲。总的来说，这项关于 BIIS NW 部门的工作重建了一个高度动态的冰盖，在过去 45 000 年的大部分时间里，其范围和体积都在振荡。以冰流为主的广阔冰盖冰川时期穿插着更受限制的冰盖或潮水/峡湾冰川时期。最后，这项工作表明，冰流在冰盖演化中的作用很复杂，但在冰盖的整个生命周期中具有重要的机械意义——冰流有助于调节冰盖健康，也有助于冰盖加速通过海洋冰盖的不稳定性而消亡。