Comparing Glacial-Geological Evidence and Model Simulations of Ice Sheet Change since the Last Glacial Period in the Amundsen Sea Sector of Antarctica

Since the Last Glacial Maximum ~20,000 years ago, the Antarctic Ice Sheet has undergone extensive changes, resulting in a much smaller present-day configuration. Improving our understanding of basic physical processes that played important roles during that retreat is critical to providing more robust model projections of future retreat and sea-level rise. Here, a limited-area nested ice sheet model was applied to the last deglacial retreat of the West Antarctic Ice Sheet in the Amundsen Sea Embayment (ASE), at 5 km resolution. The ice sheet response to climate and sea-level forcing was examined at two sites along the flowlines of Pine Island Glacier and Pope Glacier, close to the Hudson Mountains and Mount Murphy respectively, and the simulated responses compared with ice sheet thinning histories derived from glacial-geological data. The sensitivity of results to selected model parameters was also assessed. The model simulations predict a broadly similar response to ocean forcing in both the central and eastern ASE, with an initial rapid phase of thinning followed by a slower phase to the modern configuration. Although there is a mismatch of up to 5,000 years between the timing of simulated and observed thinning, the modeling suggests that the upstream geological records of ice surface elevation change reflect a response to retreat near the grounding line. The model-data mismatch could be improved by undertaking more-sophisticated regional bedrock/glacial isostatic adjustment modeling including regional variations in mantle viscosity, and spatially varying basal sliding properties on the continental shelf.

自约2万年前的末次冰盛期（Last Glacial Maximum）以来，南极冰盖（Antarctic Ice Sheet）经历了大范围演化，现今的空间格局已大幅萎缩。厘清该冰盖退缩过程中起到关键作用的基础物理机制，对构建更可靠的未来冰盖退缩与海平面上升预测模型具有重要意义。本研究针对阿蒙森海盆（Amundsen Sea Embayment, ASE）内西南极冰盖（West Antarctic Ice Sheet）的末次冰消期退缩过程，采用分辨率为5千米的有限区域嵌套冰盖模型开展模拟。我们分别在派恩岛冰川（Pine Island Glacier）与教皇冰川（Pope Glacier）的冰川流线沿线设置两个观测点位——前者邻近哈德逊山脉（Hudson Mountains），后者毗邻墨菲山（Mount Murphy）——针对气候与海平面强迫下的冰盖响应展开分析，并将模拟结果与冰川地质数据反演得到的冰盖变薄历史进行对比。此外，本研究还评估了模型参数选取对模拟结果的敏感性。模型模拟结果显示，阿蒙森海盆中部与东部区域对海洋强迫的响应整体相似，均呈现初始阶段快速变薄、随后进入缓慢调整直至达到现代冰盖格局的演化特征。尽管模拟与观测到的冰盖变薄时间存在最高可达5000年的偏差，但模型结果表明，上游区域的冰面高程变化地质记录，实则反映了接地线（grounding line）附近冰盖退缩的响应信号。若要改善模型与观测数据间的偏差，可通过构建更精细的区域基岩/冰川均衡调整（bedrock/glacial isostatic adjustment）模型实现，该模型需纳入地幔粘度（mantle viscosity）的区域差异与大陆架上基底滑动（basal sliding）属性的空间变化特征。