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Past ice stream and ice sheet changes on the continental shelf off the Sabrina Coast, East Antarctica

机译：南极东部萨布丽娜海岸外陆架上过去的冰流和冰盖变化

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Our understanding of the response of the Antarctic ice sheet to climate and ocean changes requires the improvement of current ice-atmosphere-ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals, so that satellite gravity observations and isostatic models can be adjusted. However, large portions of the Antarctic margin remain understudied or lack suitable data. One key area where data are lacking, is the Sabrina Coast portion of the East Antarctic Ice Sheet (EAIS) margin where the Totten Glacier, which has the largest ice discharge in East Antarctica, is accelerating, thinning and loosing mass at high rates. In this work, we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the Dalton Ice Tongue and Moscow University ice shelf, east of the Totten Glacier. The data presented include multibeam swath bathymetry and multichannel seismic, focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre- and post-Miocene glacial strata. Sea floor scouring and iceberg keel marks on the outer shelf, associated with gullies on the upper slope indicate that ice expanded in the past and grounded ~5 km from the shelf edge at ~450–500 mbsl, extending ~155 km north of the current Moscow University Ice Shelf. A nearly 1000 m deep area in the inner-middle shelf, oriented NW with paleo-ice flow direction indicated by mega scale glacial lineations (MSGL) and drumlins, is interpreted as a cross shelf glacial trough. A series of geomorphic associations on the north-eastern side of the glacial trough includes glacial lobes, grounding zone wedges (GZW), glacial lineations and transverse ridges, which indicates slower ice, grounding line stabilization and collapse. These geomorphic associations are organized in 4 four sets representing different past ice-flow configurations reflecting changes in ice flow direction, grounding line position, location of fast and slow ice areas, and retreat pattern. Some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage, and others are with rapid grounding line collapse. A well-preserved series of GZWs occurring at different water depths implies they were formed during different glacial stages or cycles. The inferred diminishing ice thickness for consecutives GZWs indicates that the margin of the Antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles.The identification of different ice flow configurations, evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes. We observe that some of the described morphological associations are similar to those found in the Amundsen sea sector of the West Antarctic Ice Sheet (WAIS) where they are associated with ice sheet and ice stream collapse. Although further studies are needed to assess the precise timing and rates of the glacial processes involved, we conclude that there is enough evidence to support the hypothesis that the EAIS margin can behave as dynamically as the WAIS margin, especially during glacial retreat and icesheet margin collapse.
机译：我们对南极冰盖对气候和海洋变化的响应的理解要求改进当前的冰-大气-海洋模型，并在关键的时间间隔内准确确定边界条件，例如冰的厚度和范围，以便进行卫星重力观测和均衡模型可以调整。但是，南极边缘的大部分仍未被充分研究或缺乏合适的数据。缺少数据的一个关键领域是东南极冰原（EAIS）边缘的萨布丽娜海岸部分，托特冰川（Etten Glacier）在南极东部的出冰量最大，正在以高速率加速，变薄和变松。在这项工作中，我们介绍了对托尔顿冰川以东的道尔顿冰舌和莫斯科大学冰架近海大陆架进行的第一次地质和地球物理海洋调查的结果。呈现的数据包括多波束测深和多通道地震，重点关注中新世前和后冰川地层之间区域角不整合面上方的海床形态和沉积剖面。海底冲刷和外层架上的冰山龙骨痕迹，与上坡上的沟壑有关，表明冰在过去膨胀并在约450–500 mbsl处从层架边缘约5 km着陆，向当前北延伸155〜km。莫斯科大学冰架。内中陆架近1000 m的深处，西北向，古冰流向由巨型冰川系（MSGL）和鼓林所指示，被解释为跨架冰川槽。冰川槽东北侧的一系列地貌联系包括冰川裂片，接地带楔形物（GZW），冰川线和横向山脊，这表明冰变慢，接地线稳定和塌陷。这些地貌协会分为4组，每组4组，分别代表过去的冰流形态，这些形态反映了冰流方向，地线位置，快速和缓慢冰区的位置以及后退模式的变化。确定的某些地貌特征与有组织的冰川下排水的存在兼容，而另一些则具有快速的接地线塌陷。一系列保存完好的GZW在不同的水深处发生，意味着它们是在不同的冰川阶段或冰期形成的。推断的连续GZWs的冰层厚度减小表明，南极冰盖的边缘通过连续的冰川阶段或循环演变为大陆架的覆盖范围较小。不同冰流形态的识别，冰下水和过去冰缘的证据塌陷表明冰盖边缘动态变化，冰川条件和后退模式各不相同。我们观察到一些描述的形态学关联类似于在南极西部冰原（WAIS）的Amundsen海域发现的那些，它们与冰原和冰流塌陷有关。尽管需要进一步的研究来评估冰川过程的确切时间和速率，但我们得出结论，有足够的证据支持以下假设：EAIS边缘可以像WAIS边缘一样动态，尤其是在冰川退缩和冰盖边缘塌陷期间。

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