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.
