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

南极西部冰盖所含的冰足以使全球海平面上升3-4米。冰盖体积下降，海平面上升，因为冰川流失去的冰比降雪补充的冰多。当冰架（冰原的浮动延伸部分）存在时，冰川的速度会减慢。因此，影响冰架厚度和范围的过程会影响接地冰的损失率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，大部分的损失发生在阿蒙森海地区，主要是由于松树岛和斯韦茨冰川的排放。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，导致它们因融化而变薄。然而，这种融化还取决于冰架形状的变化如何影响其下方的海洋环流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，研究冰川流动变化、冰架形状和范围以及海洋环流之间的相互作用。数据和数值模型将用于确定决定该地区冰脱落速度的关键过程。项目团队将培训博士后和研究生尖端的建模技术，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向公众宣传南极冰的损失。项目组将结合使用冰盖和海洋模型进行模拟，通过以下方式减少松岛冰川和思韦茨冰川预估冰损的不确定性：(i)评估冰架融化速率如何随着冰架空洞的融化和接地线的退缩而变化，以及（ii）提高对亚冰架融化速率对附近大陆架海洋状态变化的敏感性的理解。这些研究将减少对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/海洋模式的发展奠定基础。该项目将首先开发由现代观测到的区域海洋状态驱动的高分辨率冰架空洞环流模型，并通过卫星观测得出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搁浅退缩。然后，利用海洋环流和冰流模型的迭代过程将模拟每一退缩阶段的融化速率。这些结果将有助于评估基于融化速率简化模型的假设的有效性，即西南极洲阿蒙森海部分正在发生不稳定的崩塌。这些模式还将更好地了解融化对区域强迫的敏感性，例如环极深水温度的变化和由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未来几十年海洋环流驱动的融化的影响。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.