Collaborative Research: Glacier-Ocean Interactions at a Greenland Ice Shelf at Tidal to Interannual Time Scales

在对未来全球海平面变化的预测中，大冰川冰盖海洋边缘的冰消失率是最大的未知数字。在一定的时间和空间尺度上，许多物理过程决定了这种质量损失，但它们在净损失或净收益和趋势中的相对作用却鲜为人知。该项目将研究特定系统Petermann Gletscher(PG)的冰川-海洋相互作用的物理学，利用数据改善对PG海洋边缘过程的理解，该过程将格陵兰冰盖(GIS)的很大一部分排放到一个深峡湾，通过一个厚达1800英尺的浮动冰架与纳尔斯海峡相连。冰架在过去几年经历了显著的后退，从2010年的80公里长到今天的50公里长。对纳雷斯海峡和彼得曼峡湾深水变暖的观察，以及在撤退前十年冰架变薄的观察，导致了一种假设，即冰架底部融化的增加导致了冰架的丧失。该项目的动机是Petermann Gletscher和Fjord系统的三个方面：(1)它作为地理信息系统质量损失门户的重要性；(2)Petermann Fjord海洋动力学与以前研究的格陵兰南部系统的比较；(3)PG作为一个受良好约束的系统对研究其他格陵兰北部和南极冰架系统质量损失过程及其对全球海平面上升的贡献的价值。该项目利用了对这一系统的最新观察，包括从冰架下系泊的持续卫星转播数据。该项目将通过支持培训两名研究生和三名本科生，包括一名来自STEM领域代表性不足群体的学生，促进发展多样化的STEM工作人员队伍。PI将继续与瑞典、英国和加拿大的合作者进行国际合作，这些合作是2015年在I/B Oden上进行的初步Petermann Gletscher研究的一部分。将通过皮？S网站、博客、不定期的媒体采访以及让国家印刷记者参加实地工作来促进与普通公众的接触。时间序列分析将描述次冰川水如何随着潮汐和季节的变化而沿中央融化水道变化。对平均状况的描述和变化的解释将借助2003至2015年间通过船舶在邻近海洋收集的海洋调查数据特性。时间域和频域统计分析都将揭示相关的时间和空间尺度。更具体地说，傅立叶变换、小波变换和希尔伯特变换将用于提供离散尺度上的幅度和相位估计。频域线性系统分析将揭示代表强迫(例如，海冰移动或不活动时的大气温度和风应力、潮汐)的多个时间序列与响应(例如，地表混合层深度、融水羽流的热含量、冰速度和基本融化速率)之间的输入-输出关系。对每个系泊处的GPS和压力传感器的数据进行分析，将确定当冰川厚度从365米过渡到100米时，每个地点的漂浮程度。夏季海洋调查描述了流入的大西洋水域将被基底液融化和直接注入淡水稀释。海洋融化冰川冰固-液相变的热力学约束导致了海洋温度和盐度(Gade线)的特征关系，该关系由融化潜热决定。第二条混合线来自冰架表面融化和径流直接流入峡湾。在一些峡湾系统中，这一组成部分包括接地线上游产生的大量冰下水。拟议的温度-盐度分析将揭示沿着中央融化通道的这种次冰川淡水来源的重要性。

The rate of ice loss at the ocean margins of the great glacial ice sheets is the largest unknown in predictions of future global sea level change. Many physical processes at a range of time and space scales determine this mass loss, but their relative roles in net loss or gain and trends are poorly understood. This project will investigate the physics of glacier-ocean interaction for a specific system, Petermann Gletscher (PG), using data to improve understanding of processes at the marine margin of PG that drains a large fraction of the Greenland Ice Sheet (GIS) into a deep fjord connected to Nares Strait via a floating, up to 1800 feet thick, ice shelf. The ice shelf has undergone significant retreat in the last few years, from 80 km long in 2010 to 50 km today. Observations of warming of the deep water in Nares Strait and Petermann Fjord, and of ice-shelf thinning during the decade preceding retreat, lead to a hypothesis that increased basal melting contributes to loss of the ice shelf. The project is motivated by three aspects of the Petermann Gletscher and Fjord system: (1) its importance as a gateway for GIS mass loss; (2) comparison of ocean dynamics in Petermann Fjord with previously studied southern Greenland systems; and (3) the value of PG as a well-constrained system for studying processes that contribute to mass loss from other northern Greenland and Antarctic ice-shelf systems and their contribution to rising global sea level. The project takes advantage of recent observations of this system, including ongoing satellite-relayed data from sub-ice-shelf moorings.This project would contribute to the development of a diverse STEM workforce through support for the training of two graduate and three undergraduate students, including a student from an under-represented group in STEM fields. The PI would continue his international collaborations with Swedish, English, and Canadian collaborators that were developed as part of the initial Petermann Gletscher study aboard I/B Oden in 2015. Outreach to the general public would be facilitated through the PI?s website, blog, occasional media interviews, and embedding national print journalists in the field work. Time series analyses will characterize how sub-glacial waters change along the central melt channel with the tides and seasons. Description of the average state and interpretation of variations will be aided by ocean survey data properties collected in the adjacent ocean by ship between 2003 and 2015. Both time- and frequency-domain statistical analyses will reveal correlation time and space scales. More specifically, Fourier, wavelet, and Hilbert transforms will be used to provide estimates of amplitude and phase at discrete scales. Frequency-domain linear system analyses will reveal input-output relations between multiple time series that represent forcings (e.g., atmospheric temperature and wind stress when sea-ice is mobile or absent, tides) and responses (e.g., depth of surface mixed layer, heat content of the meltwater plume, ice velocity and basal melt rate). Analyses of data from GPS and pressure sensors at each mooring will determine the degree of floatation at each site as the glacier transitions from 365 m to 100 m in thickness. Summer ocean surveys describe the inflowing Atlantic waters that will become diluted by basal melt and by direct injection of freshwater. Thermodynamic constraints on the solid-to-fluid phase transition of glacier ice melted by the ocean result in a characteristic relation of ocean temperatures and salinity (the Gade-line), which is set by the latent heat of melting. A second mixing line arises from ice-shelf surface melting and direct runoff into the fjord. In some fjord systems, this component includes a substantial discharge of subglacial water generated upstream of the grounding line. The proposed temperature-salinity analyses will reveal the importance of this sub-glacial freshwater source along the central melt-channel.