Investigating the roles of relative sea-level change and glacio-isostatic adjustment on the retreat of a marine based ice stream in NW Scotland
Investigating the roles of relative sea-level change and glacio-isostatic adjustment on the retreat of a marine based ice stream in NW Scotland
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研究相对海平面变化和冰川均衡调整对苏格兰西北部海洋冰流退缩的作用
DOI：
10.1016/j.quascirev.2021.107366
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发表时间：
2022
影响因子：
4
通讯作者：
Simms A
中科院分区：
文献类型：
--
作者：
Simms A
自末次盛冰期（LGM）以来冰盖消亡的记录提供了一个机会来测试不稳定机制的相对重要性，包括相对海平面（RSL）变化，控制冰盖退缩。在这里，我们研究了LGM之后苏格兰西北部Minch冰流（MnIS）消退期间的RSL变化记录，并使用该记录为当地的晚冰期预进（称为西罗斯预进）提供了额外的年龄限制。我们利用从西罗斯沿原MnIS侧翼的隔离盆地获得的新的和现有的RSL变化记录来验证该地区冰川-均衡调整（GIA）对该地区去冰RSL历史的可用预测。利用这些GIA模型预测，我们通过早期消冰，研究了在MnIS后退前沿的RSL变化的性质。我们从这些盆地中获得的新的放射性碳年龄证实了前MnIS内部槽内的冰川消融时间，并改进了西罗斯里德万斯的年龄，这两者都是由早期基于宇宙学的研究建立的。我们发现西罗斯readadvance在15.8±0.1 ka左右达到顶峰，比最近的建议稍早。在韦斯特罗斯的Gairloch附近，RSL在约16.1-16.5 ka从海平面以上约20米下降。三个隔离盆地记录了在接下来的~ 0.8 ka的RSL下降，从而可以将GIA预测结果与RSL观测结果进行比较。我们的新分析表明，冰锋处的RSL上升速率增加，与此同时，mni遇到了向陆地倾斜的床层，可能有助于mni从17.6 ka BP迅速退缩到16.4 ka BP。这一观测结果表明，冰川消融期间的GIA并不一定会像某些模型所表明的那样，引起海洋冰流的稳定RSL变化。沿着缩进冰缘，单个冰流前缘的RSL场可能受整个冰盖驱动的区域GIA信号控制，而不是局部冰锋。此外，冰期后反弹的稳定影响依赖于地球流变学，地球流变学足够弱，可以对冰盖退缩做出快速反应。在mni的情况下，冰流前端的RSL可能是由较早的冰块范围、位于高度凹陷的冰锋东部和南部的较大冰块以及不列颠群岛下方相对强烈的地球流变学所控制的。因此，在考虑冰川后反弹对海洋冰盖退缩的稳定影响时，需要考虑冰盖边缘的几何形状，例如今天在格陵兰岛和南极洲的冰盖边缘，以及它们下面的地球流变学。
The record of ice-sheet demise since the last glacial maximum (LGM) provides an opportunity to test the relative importance of instability mechanisms, including relative sea-level (RSL) change, controlling ice-sheet retreat. Here we examine the record of RSL changes accompanying the retreat of the Minch Ice Stream (MnIS) of northwest Scotland during the deglaciation following the LGM as well as use the record to provide additional age constraints on a local late-glacial readvance known as the Wester Ross Readvance. We use new and existing records of RSL change obtained from isolation basins in Wester Ross along the flanks of the former MnIS to test available glacial-isostatic adjustment (GIA) predictions of the deglacial RSL history for the region. Using these GIA model predictions we examine the nature of RSL change across the retreating front of the MnIS through the early deglaciation. Our new radiocarbon ages from these basins confirm the timing of deglaciation within the inner trough of the former MnIS as well as refines the age of the Wester Ross Readvance, both established by earlier cosmogenic-based studies. We find that the Wester Ross Readvance culminated around 15.8 ± 0.1 ka, slightly earlier than recent suggestions. Near Gairloch, Wester Ross, RSL fell from a marine limit ∼20 m above present at ∼16.1–16.5 ka. Three isolation basins record RSL fall over the following ∼0.8 ka allowing a comparison between GIA predictions and RSL observations. Our new analyses suggest that the rate of RSL rise increased at the ice front, in concert with the MnIS encountering a landward sloping bed potentially aiding the rapid retreat of the MnIS from 17.6 to 16.4 ka BP. This observation suggests that GIA during deglaciation does not necessarily induce a stabilizing RSL change to marine-based ice streams as some models have suggested. Along indented ice margins, the RSL field at the front of individual ice streams may be governed by the regional GIA signal driven by the ice sheet as a whole, rather than the local ice front. In addition, the stabilizing impact of post-glacial rebound is dependent on an Earth rheology weak enough to respond quickly to the ice-sheet retreat. In the case of the MnIS, the RSL experienced at the front of the ice stream was likely governed by the earlier ice mass extent, the larger ice masses lying to the east and south of the highly indented ice front, and the relatively strong Earth rheology beneath the British Isles. Thus, the geometry of the ice sheet margins, such as those in Greenland and Antarctica today, and the Earth rheology beneath them need to be taken into account when considering the stabilizing impact of post-glacial rebound on marine ice sheet retreat.