Topographic Controls on Post-Oligocene Changes in Ice-sheet Dynamics, Prydz Bay Region, East Antarctica

Within the general trend of post-Eocene cooling, the largest and oldest outlet of the East Antarctic Ice Sheet underwent a change from ice-cliff to ice-stream and/or ice-shelf dynamics, with an associated switch from line-source to fan sedimentation. Available geological data reveal little about the causes of these changes in ice dynamics during the Miocene Epoch, or the subsequent effects on Pliocene-Pleistocene ice-sheet history. Ice-sheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice-sheet extent and dynamics in the Lambert-Amery system at Prydz Bay. The modeling shows how the topography and bathymetry of the Lambert graben and Prydz Bay control ice-sheet extent and flow. The changes in bathymetric volume required for shelf-edge glaciation correlate well with the Prydz Channel fan sedimentation history. This suggests a negative feedback between erosion and glaciation, whereby the current graben is overdeepened to such an extent that shelf-edge glaciation is now not possible, even if a Last Glacial Maximum environment recurs. We conclude that the erosional history of the Lambert graben and Prydz Bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the East Antarctic Ice Sheet, once the necessary initial climatic conditions for glaciation were achieved at the start of the Oligocene Epoch.

在始新世（Eocene）后降温的整体趋势下，东南极冰盖（East Antarctic Ice Sheet）规模最大且历史最悠久的流出通道，经历了从冰崖动力模式向冰流/冰架动力模式的转变，同步伴随沉积模式从线源沉积向扇状沉积的转换。现有地质资料对中新世（Miocene Epoch）期间这些冰动力变化的成因，以及其对上新世-更新世冰盖演化历史的后续影响，仍鲜有揭示。冰盖数值模拟（Ice-sheet numerical modeling）结果显示，床形地貌（bed morphology）可能是驱动普里兹湾（Prydz Bay）兰伯特-埃默里系统（Lambert-Amery system）冰盖范围与动力模式发生变化的核心因素。该模拟阐明了兰伯特地堑（Lambert graben）与普里兹湾的地形及水深地形（bathymetry）如何调控冰盖范围与冰流运动。陆架边缘冰川作用（shelf-edge glaciation）所需的水深体积变化，与普里兹海峡扇状沉积记录（Prydz Channel fan sedimentation history）高度吻合。这表明侵蚀与冰川作用间存在负反馈机制：当前兰伯特地堑被过度深挖至如此程度，即便末次盛冰期（Last Glacial Maximum）的环境重现，陆架边缘冰川作用也已无法发生。我们得出结论：在渐新世（Oligocene Epoch）初期具备冰川作用所需的初始气候条件后，兰伯特地堑与普里兹湾的侵蚀历史，连同周边山脉的隆升历史，共同主导了东南极冰盖这一区域的演化历程。