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

南极洲西部冰盖所含的冰足以使全球海平面上升3-4米。当更多的冰通过冰川流流失到海洋中而不是被降雪所取代时，冰盖体积就会福尔斯，海平面就会上升。当冰架存在时，冰川的速度会降低，冰架是冰盖的浮动延伸。因此，影响冰架厚度和范围的过程也会影响地面冰损失和海平面上升的速度。南极洲西部目前正在以加速的速度失去冰，大部分损失发生在阿蒙森海地区，来自松岛和思韦茨冰川的排放。这种损失是由这些冰川冰架下相对温暖的海水循环增加引起的，导致冰川融化变薄。然而，这种融化也取决于冰架形状的变化如何影响它们下面的海洋环流以及上游地面冰川的速度。对这些过程的有限了解导致未来冰损失估计的不确定性。这个跨学科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如何迅速摆脱冰的关键过程。该项目团队将培训博士后和研究生的尖端建模技术，并通过讲座，学校科学博览会和西雅图科学中心的年度极地科学周末教育公众南极冰损失。项目小组将利用冰盖和海洋模型进行模拟，以减少预测松岛和思韦茨冰川冰损失的不确定性，方法是：㈠评估随着冰架空洞通过融化和地面线后退而演变，冰架融化速度将如何变化，和（ii）增进对大陆架下融化速率对附近大陆架海洋状况变化的敏感性的了解。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。该项目将首先根据现代观测到的区域海洋状况建立高分辨率冰架空洞环流模型，并用卫星观测得出的融化估计数加以验证。接下来，将使用冰流模型来估计未来的接地撤退。然后，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率。这些结果将有助于评估假设的有效性，即南极洲西部阿蒙森海部分的不稳定崩溃正在进行中，这是基于简化的融化速率模型。这些模型也将提供一个更好的了解融化的敏感性区域强迫，如环极深水温度的变化和风驱动的温跃层高度的变化。最后，几个半耦合的冰海洋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。这些模拟将大大提高对远场海洋强迫、空洞环流和融化以及冰盖响应之间联系的理解。

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.