Collaborative Research: Modeling ice-ocean Interaction for the Rapidly Evolving Ice Shelf Cavities of Pine Island and Thwaites Glaciers, Antarctica

西南极冰盖包含的冰足以使全球海平面上升3-4米。当冰川流流失到海洋的冰比被降雪取代的冰更多时，冰盖体积会下降，海平面会上升。当冰架存在时，冰川的速度就会减慢。冰架是冰盖的浮动延伸。因此，影响冰架厚度和范围的过程会影响冰层融化和海平面上升的速度。南极洲西部目前正在加速消融，其中大部分消融发生在阿蒙森海地区，这是由于松岛和斯韦茨冰川的排放造成的。这种损失是由于冰川冰架下相对温暖的海水循环增加，导致冰川融化而变薄。然而，冰架的融化还取决于冰架形状的变化如何影响冰架下方的海洋循环以及上游搁浅冰川的速度。对这些过程的了解有限，导致对未来冰损失的估计存在不确定性。这个跨学科的项目汇集了来自美国三个机构的冰川学家和海洋学家，研究不断变化的冰川流动、冰架形状和范围以及海洋环流之间的相互作用。数据和数值模型将被用来确定决定该地区融冰速度的关键过程。该项目团队将对博士后和研究生进行尖端建模技术方面的培训，并通过讲座、学校科学博览会和西雅图科学中心一年一度的极地科学周末教育公众有关南极冰川融化的知识。项目组将结合使用冰盖和海洋模型进行模拟，以减少松岛和斯韦茨冰川预计冰融化的不确定性，方法是：(1)评估随着冰架空洞通过融化和接地线后退而演变时，冰架融化速度将如何变化，以及(2)更好地了解陆架下部融化速度对附近大陆架海洋状况变化的敏感性。这些研究将减少冰损失和海平面上升估计的不确定性，并为未来完全耦合的冰盖/海洋模型的开发奠定基础。该项目将首先开发由现代观测到的区域海洋状况驱动的高分辨率冰架-洞穴环流模型，并用来自卫星观测的融化估计进行验证。接下来，将使用冰流模型来估计未来的接地撤退。使用海洋环流和冰流模型的迭代过程将模拟每个退缩阶段的融化速度。这些结果将有助于评估基于简化的融化速度模型的假设的有效性，该假设基于简化的融化速度模型，即南极洲西部阿蒙森海部分正在进行不稳定的崩溃。这些模型还将更好地了解融化对区域强迫的敏感性，例如绕极深水温度的变化和温跃层高度的风致变化。最后，几个半耦合的冰-海模拟将有助于确定海洋环流驱动的融化在未来几十年的影响。这些模拟将大大改善对远场海洋强迫、空穴环流和融化以及冰盖响应之间的联系的理解。

The West Antarctic Ice Sheet contains enough ice to raise global sea levels by 3-4 meters. Ice-sheet volume falls, and sea level increases, when more ice is lost to the ocean by glacier flow than is replaced by snowfall. Glacier speed is reduced when ice shelves, which are the floating extensions of the ice sheets, are present. Processes that affect ice shelf thickness and extent therefore influence the rates of grounded ice loss and sea-level rise. West Antarctica is currently losing ice, at an accelerating rate, with most loss occurring in the Amundsen Sea region via discharge from Pine Island and Thwaites glaciers. This loss was initiated by increased circulation of relatively warm ocean water beneath these glacier's ice shelves, causing them to thin by melting. However, this melting also depends on how the changing shape of the ice shelves affects the ocean circulation beneath them and the speeds of the grounded glaciers upstream. Limited understanding of these processes leads to uncertainties in estimates of future ice loss. This interdisciplinary project brings together glaciologists and oceanographers from three US institutions to study the interactions between changing glacier flow, ice shelf shape and extent, and ocean circulation. Data and numerical models will be used to identify the key processes that determine how rapidly this region can shed ice. The project team will train postdocs and graduate students in cutting-edge modeling techniques, and educate the public about Antarctic ice loss through talks, school science fairs, and Seattle Science Center's annual Polar Science Weekend. The project team will conduct simulations, using a combination of ice-sheet and ocean models, to reduce uncertainties in projected ice loss from Pine Island and Thwaites glaciers by: (i) assessing how ice-shelf melt rates will change as the ice-shelf cavities evolve through melting and grounding-line retreat, and (ii) improving understanding of the sensitivity of sub-shelf melt rates to changes in ocean state on the nearby continental shelf. These studies will reduce uncertainty on ice loss and sea-level rise estimates, and lay the groundwork for development of future fully-coupled ice-sheet/ocean models. The project will first develop high-resolution ice-shelf-cavity circulation models driven by modern observed regional ocean state and validated with estimates of melt derived from satellite observations. Next, an ice-flow model will be used to estimate the future grounding retreat. An iterative process with the ocean-circulation and ice-flow models will then simulate melt rates at each stage of retreat. These results will help assess the validity of the hypothesis that unstable collapse of the Amundsen Sea sector of West Antarctica is underway, which was based on simplified models of melt rate. These models will also provide a better understanding of the sensitivity of melt to regional forcing such as changes in Circumpolar Deep Water temperature and wind-driven changes in thermocline height. Finally, several semi-coupled ice-ocean simulations will help determine the influence of the ocean-circulation driven melt over the next several decades. These simulations will provide a much-improved understanding of the linkages between far-field ocean forcing, cavity circulation and melting, and ice-sheet response.