| Summary: | 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.
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