Abstract
Abstract. Petermann Fjord is a deep (>1000 m) fjord that incises the coastline of north-west Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5 and 70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deglacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line kilometres of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to bedrock or till surfaces (Facies I), subglacial deposition (Facies II), deposition from meltwater plumes and icebergs in quiescent glacimarine conditions (Facies III, IV), deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V) and the redeposition of material downslope (Facies IV). These sediment units represent the total volume of glacial sediment delivered to the mapped marine environment during retreat. We calculate a glacial sediment flux for the former Petermann ice stream as 1080–1420 m3 a−1 per metre of ice stream width and an average deglacial erosion rate for the basin of 0.29–0.34 mm a−1. Our deglacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system, and we conclude that glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in rates over a glacial–deglacial transition. Our new glacial sediment fluxes and erosion rates show that the Petermann ice stream was approximately as efficient as the palaeo-Jakobshavn Isbræ at eroding, transporting and delivering sediment to its margin during early deglaciation.
Highlights
The volume and distribution of glacial sediment in fjords is largely a function of the retreat behaviour of the marineterminating glaciers that occupy them
The sub-bottom profiles (SBP) data alone do not allow us to differentiate between these two types, but by correlating with airgun seismic-reflection profiles (AG) lines where the seismic basement is reached we can identify this facies as bedrock in Hall Basin
The seismic stratigraphy of Petermann Fjord and the adjacent Nares Strait area confirm the episodic retreat of ice streams in the area marked by grounding-zone wedge (GZW) deposits, followed by the deposition of sediment from meltwater plumes and icebergs
Summary
The volume and distribution of glacial sediment in fjords is largely a function of the retreat behaviour of the marineterminating glaciers that occupy them This sediment infill is the final product of material eroded across the catchment area, transported to the ice margin by glacial processes and released into fjord basins as grounded ice decays. The present decay of the Greenland Ice Sheet (GrIS), and its accelerating contribution to sea level rise (Chen et al, 2017), is occurring predominantly through mass loss from its marineterminating outlet glaciers (Mouginot et al, 2019) This will likely enhance glacial erosion rates and, sediment influx to the global ocean. Investigations of the sediment infill of fjords provide an important tool for quantifying rates of glacial erosion and sediment transport to the global ocean, as well as for reconstructing glacier behaviour and its drivers beyond the observational record
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
