Sedimentology of two cores from the Mid-shelf eastern Amundsen Sea Embayment@en

Inter-ice stream areas cover significant portions of Antarctica's formerly glaciated shelves, but have been largely neglected in past geological studies because of overprinting by iceberg scours. Here, we present results of the first detailed survey of an inter-ice stream ridge from the West Antarctic continental shelf. Well-preserved sub- and proglacial bedforms on the seafloor of the ridge in the eastern Amundsen Sea Embayment (ASE) provide new insights into the flow dynamics of this sector of the West Antarctic Ice Sheet (WAIS) during the Last Glacial cycle. Multibeam swath bathymetry and PARASOUND acoustic sub-bottom profiler data acquired across a mid-shelf bank, between the troughs of the Pine Island-Thwaites (PITPIS) and Cosgrove palaeo-ice streams (COPIS), reveal large-scale ribbed moraines, hill-hole pairs, terminal moraines, and crevasse-squeeze ridges. Together, these features form an assemblage of landforms that is entirely different from that in the adjacent ice-stream troughs, and appears to be unique in the context of previous studies of Antarctic seafloor geomorphology. From this assemblage, the history of ice flow and retreat from the inter-ice stream ridge is reconstructed. The bedforms indicate that ice flow was significantly slower on the inter-ice stream ridge than in the neighbouring troughs. While terminal moraines record at least two re-advances or stillstands of the ice sheet during deglaciation, an extensive field of crevasse-squeeze ridges indicates ice stagnation subsequent to re-advancing ice, which deposited the field of terminal moraines in the NE. The presented data suggest that the ice flow behaviour on the inter-ice stream ridge was substantially different from that in the adjacent troughs. However, newly obtained radiocarbon ages on two sediment cores recovered from the inter-ice stream ridge suggest a similar timing in the deglaciation of both areas. This information closes an important gap in the understanding of past WAIS behaviour in the eastern ASE. Our newly-documented bedforms will also serve as an important diagnostic tool in future studies for interpreting ice-sheet histories in similar inter-ice stream areas.冰间流区覆盖了南极洲此前被冰川覆盖的陆架大片区域，但由于冰山冲刷痕迹的叠加覆盖，过往地质研究对此类区域多有忽视。本文首次报道了西南极大陆架一处冰间流脊的详细勘测结果。在阿蒙森海盆东部（Amundsen Sea Embayment, ASE）的该脊段海底，保存完好的冰下与冰前床形地貌，为末次冰期旋回内西南极冰盖（West Antarctic Ice Sheet, WAIS）该区域的流动动力学特征提供了全新认知。研究团队通过在松岛-思韦茨古冰流（Pine Island-Thwaites, PITPIS）与科斯格罗夫古冰流（Cosgrove palaeo-ice streams, COPIS）槽谷之间的陆架中部浅滩采集的多波束条带测深与PARASOUND声学浅地层剖面仪数据，识别出大规模垄状冰碛、丘坑对、终碛以及裂隙挤压脊。上述地貌共同构成了一套与相邻冰流槽谷完全迥异的地貌组合，在既往南极海底地貌研究中堪称独树一帜。基于这套组合地貌，研究人员重建了该冰间流脊的冰流演化与退缩历史。床形地貌数据显示，冰间流脊区域的冰流速度显著低于相邻槽谷区域。尽管终碛记录了冰盖在冰消期至少两次前进停滞或重新推进的过程，但大范围的裂隙挤压脊场则指示：在东北部沉积终碛的冰流重新推进之后，该区域发生了冰体停滞。本次研究数据表明，冰间流脊区域的冰流行为与相邻槽谷区域存在显著差异。不过，从该冰间流脊获取的两根沉积物岩芯的全新放射性碳年代数据显示，两个区域的冰消期时间线大体一致。这一发现填补了学界对阿蒙森海盆东部区域西南极冰盖既往演化行为认知中的重要空白。本次新探明的床形地貌，也将为未来类似冰间流区域的冰盖历史解译提供重要的诊断工具。