Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann Fjord and Nares Strait, NW Greenland

Abstract

Abstract. Petermann Fjord is a deep (> 1000 m) fjord that incises the coastline of northwest Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5–70 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-km 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 glaciomarine conditions (Facies III, IV); deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V); and the redeposition of material down slopes (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 meter 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 these rates over a glacial-deglacial transition. Our new fluxes and erosion rates show that the Petermann Ice Stream was approximately as efficient as the palaeo-Jakobshavn Isbrae at eroding, transporting and delivering sediment to its margin during early deglaciation.

Deglaciation controls on sediment yield: Towards capturing spatio-temporal variability

“…Although there is a body of more recent work that recognises some of the likely impacts of modern deglaciation (e.g. Orwin et al, 2010;Porter et al, 2010;Bendixen et al, 2017;Delaney et al, 2017;Knight and Harrison, 2017;Lane et al, 2017;Comti et al, 2019;Hogan et al, 2019), there has been little quantitative assessment of the potential impacts on sediment yields at regional or global scales. Indeed, as Hodgkins et al (2003, p.16) so acutely observed nearly two decades ago: "Attempts to infer longterm change in sediment yields at remote glaciated catchments are typically confounded by an absence of historic time series".…”

Glacial microsedimentology—a new lens to investigate glacial sediments—a review

“…The technique provides far greater detail on depositional and deformation histories of these sediments than obtained from macroscale studies alone in unravelling deformation histories of glacigenic sequences (cf. Damsgaard et al, 2020;Hogan et al, 2020;Greenwood et al, 2021).…”