Estimating the Freshwater Flux from the Greenland Ice Sheet Workshop Report, American Geophysical Union, 2018

The Greenland Ice Sheet (GrIS) is a large store of freshwater in the global climate system. Freshwater is discharged from the GrIS into the ocean in three forms: 1) solid ice, through the calving of icebergs; 2) surface melt and runoff, as liquid water through above-sea-level melt and supraglacial streams or subglacial discharge of glaciated areas, and rivers draining watersheds of non-glaciated areas; and 3) submarine melt on the fronts and undersides of marine-terminating glaciers and ice shelves. Beyond sea level rise, the increasing GrIS freshwater flux is raising concerns due to its impacts on global ocean circulation given its proximity to dense water formation sites in the North Atlantic, on marine ecosystems in local and regional waters surrounding Greenland, and on local communities and industries that must navigate rapidly changing ice-related hazards. Notwithstanding its importance, estimates of the timing, magnitude, and distribution of freshwater discharge around Greenland are imperfect due to scarce observations and a limited understanding of how the freshwater is transformed by ice/ocean processes at the ice margins. To tackle this problem, we organized an international workshop to understand the current state of knowledge and identify the critical gaps and next steps in quantifying the future GrIS freshwater flux. The workshop was held prior to the 2018 American Geophysical Union Fall Meeting, included ~40 participants from nine countries, and focused on four goals: 1) connect the communities needed to quantify freshwater input from the GrIS to the ocean; 2) identify the needs of ocean/climate models for oceanic boundary conditions at GrIS margins; 3) define community needs and science gaps; and 4) prioritize how to improve estimates of the freshwater input from the GrIS to the ocean.格陵兰冰盖（Greenland Ice Sheet, GrIS）是全球气候系统中重要的淡水储存库。其向海洋排放淡水的形式主要有三种：1）固态冰：通过冰山崩解过程释放；2）表面融水与径流：以液态水形式排出，涵盖冰面以上海拔区域的融水、冰面溪流或冰川区域的冰下排水，以及非冰川覆盖流域的径流河道；3）海洋终止型冰川（marine-terminating glaciers）与冰架（ice shelves）的前缘及底部的海底消融。 除引发海平面上升外，格陵兰冰盖淡水通量的持续增加引发了广泛担忧：因其紧邻北大西洋高密度水形成区域，该通量变化会对全球大洋环流产生影响；同时会干扰格陵兰周边局地及区域海域的海洋生态系统，还会给需要应对快速演变的冰相关灾害的当地社区与产业带来挑战。 尽管其重要性不言而喻，但由于观测资料匮乏，且对冰缘处冰-海洋过程如何改造淡水的认知有限，当前对格陵兰周边淡水排放的时间、规模与分布的估算仍不够精准。 为解决这一难题，我们组织了一场国际研讨会，以期梳理当前的知识储备现状，明确量化未来格陵兰冰盖淡水通量的关键研究缺口与后续推进方向。本次研讨会于2018年美国地球物理联合会（American Geophysical Union, AGU）秋季年会前举办，共有来自9个国家的约40名参会者，设定了四项核心目标： 1）整合量化格陵兰冰盖向海洋输入淡水所需的跨领域科研力量； 2）明确海洋/气候模型对格陵兰冰缘海洋边界条件的需求； 3）界定科研社群的共性需求与现有科学研究空白； 4）优先规划优化格陵兰冰盖向海洋输入淡水估算方法的具体路径。