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

在预测未来全球海平面变化时，大冰川冰盖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增加和趋势中的相对作用却知之甚少。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的很大一部分（GIS）排入通过浮动连接到纳雷斯海峡的深峡湾，厚达1800英尺，冰架。在过去几年里，冰架经历了重大的退缩，从2010年的80公里长减少到今天的50公里。在纳雷斯海峡和彼得曼峡湾的深水变暖的观测，以及在退缩前十年冰架变薄，导致一个假设，增加基底融化有助于冰架的损失。该项目的动机是彼得曼格莱切尔和峡湾系统的三个方面：（1）它作为地理信息系统质量损失门户的重要性;（2）彼得曼峡湾海洋动力学与以前研究的格陵兰南部系统的比较;（3）PG作为一个约束良好的系统，在研究其他北方格陵兰和南极冰造成质量损失的过程中的价值-大陆架系统及其对全球海平面上升的作用。该项目利用了最近对该系统的观测，包括从冰架下系泊处持续提供的卫星中继数据，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，该项目将有助于发展一支多样化的STEM劳动力队伍。 PI将继续与瑞典、英国和加拿大合作者进行国际合作，这些合作是2015年在I/B Oden上进行的最初Petermann Gletscher研究的一部分。 将通过PI促进与公众的联系？的网站，博客，偶尔的媒体采访，并在实地工作中嵌入国家印刷记者。 时间序列分析将描述冰下沃茨如何随着潮汐和季节沿着中央融化通道变化。2003年至2015年期间船舶在邻近海洋收集的海洋调查数据特性将有助于说明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，傅立叶、小波和希尔伯特变换将用于提供离散尺度下的振幅和相位的估计。频域线性系统分析将揭示代表强迫的多个时间序列之间的输入-输出关系（例如，当海冰是移动的或不存在时的大气温度和风应力，潮汐）和响应（例如，表面混合层的深度，融水羽的热含量，冰速度和基底融化速率）。对每个系泊处的全球定位系统和压力传感器的数据进行分析，将确定冰川厚度从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沃茨将被基底融化和淡水的直接注入稀释。海洋融化的冰川冰的固体到流体相变的热力学约束导致海洋温度和盐度的特征关系（加德线），这是由融化的潜热。第二条混合线来自冰架表面融化和直接流入峡湾的径流。在某些峡湾系统中，这一部分包括接地线上游产生的大量冰下水的排放。建议的温度-盐度分析将揭示这一冰下淡水来源的重要性，沿着中央融化通道。

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.