OPP-PRF Calving, Icebergs, and Climate

冰山通过控制冰盖上的淡水如何分配到海洋中来影响气候，在当前气候下，大约一半的冰盖质量损失归因于冰山崩解。冰山漂移和融化过程中沉积的淡水会影响海洋环流、海冰形成和生物初级生产力。此外，冰山从冰架上崩解，即冰盖的浮动延伸，可以通过减少冰架对上游接地冰向海流动提供的阻力应力，影响冰盖演化和海平面上升。从冰架上崩解出来的大部分冰块都是以板状冰山的形式出现的，这些冰山通常有几百米厚，长度和宽度都在几十到几百公里之间。当被称为裂缝的全层冰架裂缝扩展到冰架边缘时，就会发生板状崩解。这种破冰现象并不常见，在单个冰架上，每隔几十年就会发生一次。板状冰崩解行为的变化，即崩解事件的大小和频率，可以强烈地影响气候和冰盖的演变。然而，表格式的产犊行为，以及它对气候变化的反应，在气候模型中既没有得到很好的理解，也没有得到准确的表示。在这个项目中，将为气候模式开发一个表格式产犊参数化。参数化将根据一系列现实的和理想的世纪尺度的表格崩解模拟产生的数据推导，这些数据将在一个新的冰流和损伤框架下进行，该框架可以应用于单个冰盖-冰架系统的尺度：CD-MPM-SSA （shelfi - stream Approximation的连续损伤物质点法）。在这些模拟过程中，冰架的几何形状、冰的力学/流变特性和气候强迫（如海洋温度）将发生变化，以确定裂谷和裂陷的响应。从这些实验中得到的产犊参数化将在地球物理流体动力学实验室（GFDL）气候模型中实施，该模型将与粘合颗粒冰山模型相结合。然后，将进行实验，研究冰山崩解行为变化与气候之间的反馈关系。该项目的成功将提高我们对冰质量收支、冰盖演变和海洋淡水通量的理解和代表性，并将改进对气候变化和海平面上升的预测。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Icebergs influence climate by controlling how freshwater from ice sheets is distributed into the ocean, where roughly half of ice sheet mass loss is attributed to iceberg calving in the current climate. The freshwater deposited by icebergs as they drift and melt can affect ocean circulation, sea-ice formation, and biological primary productivity. Furthermore, calving of icebergs from ice shelves, the floating extensions of ice sheets, can influence ice sheet evolution and sea-level rise by reducing the resistive stresses provided by ice shelves on the seaward flow of upstream grounded ice. The majority of mass calved from ice shelves occurs in the form of tabular icebergs, which are typically hundreds of meters thick and on the order of tens to hundreds of kilometers in length and width. Tabular calving occurs when full-thickness ice shelf fractures known as rifts propagate to the edges of the ice shelf. These calving events are infrequent, often with decades between events on an individual ice shelf. Changes in tabular calving behavior, i.e., the size and frequency of calving events, can strongly influence climate and ice sheet evolution. However, tabular calving behavior, and how it responds to changes in climate, is neither well understood nor accurately represented in climate models.In this project, a tabular calving parameterization for climate models will be developed. The parameterization will be derived according to data generated from a series of realistic and idealized century-scale tabular calving simulations, which will be performed with a novel ice flow and damage framework that can be applied at the scale of individual ice sheet-ice shelf systems: the CD-MPM-SSA (Continuum Damage Material Point Method for Shelfy-Stream Approximation). During these simulations, the geometry of the ice shelf, mechanical/rheological properties of the ice, and climate forcings such as ocean temperature will be varied to determine the rifting and calving response. The calving parameterization derived from these experiments will be implemented in a Geophysical Fluid Dynamics Laboratory (GFDL) climate model, where it will be coupled with a bonded-particle iceberg model. Then, experiments will be run to study the feedback between changes in iceberg calving behavior and climate. Success of this project will improve our understanding and representation of the ice mass budget, ice sheet evolution, and ocean freshwater fluxes, and will improve projections of climate change and sea-level rise.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.