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，大冰原海洋边缘的冰损失率是最大的未知数。在一系列时间和空间尺度上的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中的相对作用和趋势却知之甚少。该项目将调查一个特定系统的冰川-海洋相互作用的物理学，Petermann Gletscher (PG)，使用数据来提高对PG海洋边缘过程的理解，该过程将格陵兰冰盖（GIS）的很大一部分排入一个深峡湾，通过一个漂浮的，高达1800英尺厚的冰架与纳尔斯海峡相连。在过去的几年里，冰架经历了重大的退缩，从2010年的80公里长到今天的50公里长。对纳尔斯海峡和彼得曼峡湾深水变暖的观测，以及对退缩前十年冰架变薄的观测，导致了一种假设，即基底融化的增加导致了冰架的损失。该项目的动机来自Petermann Gletscher和Fjord系统的三个方面：(1)它作为GIS质量损失门户的重要性；(2)彼得曼峡湾的海洋动力学与先前研究的南格陵兰系统的比较；(3) PG作为一个良好约束系统的价值，可用于研究导致其他格陵兰北部和南极冰架系统质量损失的过程及其对全球海平面上升的贡献。该项目利用了该系统最近的观测数据，包括从冰架下系泊处持续传回的卫星数据。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，从而促进多元化STEM劳动力的发展。PI将继续他与瑞典、英国和加拿大合作者的国际合作，这些合作是2015年在I/B奥登进行的最初彼得曼·格莱彻研究的一部分。透过宣传纲领，促进与公众的接触。S网站、博客，不定期的媒体采访，以及嵌入全国纸媒记者的实地工作。时间序列分析将描述沿中央融化通道的冰下水如何随潮汐和季节变化。2003年至2015年期间，船舶在邻近海域收集的海洋调查数据属性将有助于描述平均状态和解释变化。时域和频域的统计分析将揭示相关的时间和空间尺度。更具体地说，傅里叶变换、小波变换和希尔伯特变换将用于在离散尺度上提供幅度和相位的估计。频域线性系统分析将揭示多个时间序列之间的输入输出关系，这些时间序列表示强迫（例如，海冰移动或不存在时的大气温度和风应力，潮汐）和响应（例如，表面混合层深度，融水羽流的热含量，冰速度和基本融化速率）。对每个系泊处的GPS和压力传感器的数据进行分析，将确定冰川厚度从365米转变为100米时，每个地点的漂浮程度。夏季海洋调查显示，流入大西洋的海水将因基底融化和淡水的直接注入而被稀释。受海洋融化的冰川冰固-流相变的热力学约束，形成了由融化潜热设定的海洋温度-盐度特征关系（gade线）。另一条混合线来自冰架表面的融化和直接流入峡湾的径流。在一些峡湾系统中，这个组成部分包括在接地线上游产生的大量冰下水的排放。提出的温度-盐度分析将揭示沿中央融化通道的冰下淡水来源的重要性。

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.