1] Bolin Centre for Climate Research, Department of Physical Geography & Quaternary Geology, Stockholm University, S-10691 Stockholm, Sweden [2] School of Earth & Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.
1] School of Earth & Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia [2] Institute of Earth & Environmental Sciences, University of Potsdam, D-14776 Potsdam, Germany.
Nat Commun. 2014 May 9;5:3815. doi: 10.1038/ncomms4815.
The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.
长达一个世纪的关于被第四纪冰川反复覆盖的内峡谷起源的争论，取决于这些峡谷是由陆上河流侵蚀形成的河流地貌，还是在冰下切割形成的冰川地貌。在这里，我们应用宇宙成因核素暴露定年法对 500 公里长的前芬诺斯堪的亚冰盖边缘的七个内峡谷进行了研究，同时还绘制了一张新的冰川消退图。我们发现，暴露的时间与无冰条件的出现相吻合，这强烈表明峡谷是由有组织的冰川下融水切割而成的，同时被上方的冰屏蔽了宇宙射线。鉴于融水通道侵蚀基岩和排出碎屑所需的极高水力效率，我们推断内峡谷是冰盖经历强烈表面融化的产物。在我们的七个峡谷中，没有发现冰川后河流侵蚀的痕迹，这意味着在多个冰川周期中，冰川下融水是波罗的海盾地山谷加深的关键驱动因素。
