Bathymetry in Petermann fjord from Operation IceBridge aerogravity

Kirsty J Tinto,Robin E Bell,James R Cochran,Andreas Münchow

doi:10.1016/j.epsl.2015.04.009

Abstract

Petermann Glacier is a major glacier in northern Greenland, maintaining one of the few remaining floating ice tongues in Greenland. Monitoring programs, such as NASA's Operation IceBridge have surveyed Petermann Glacier over several decades and have found it to be stable in terms of mass balance, velocity and grounding-line position. The future vulnerability of this large glacier to changing ocean temperatures and climate depends on the ocean–ice interactions beneath its floating tongue. These cannot currently be predicted due to a lack of knowledge of the bathymetry underneath the ice tongue. Here we use aerogravity data from Operation IceBridge, together with airborne radar and laser data and shipborne bathymetry-soundings to model the bathymetry beneath the Petermann ice tongue. We find a basement-cored inner sill at 540–610 m depth that results in a water cavity with minimum thickness of 400 m about 25 km from the grounding line. The sill is coincident with the location of the melt rate minimum. Seaward of the sill the fjord is strongly asymmetric. The deepest point occurs on the eastern side of the fjord at 1150 m, 600 m deeper than on the western side. This asymmetry is due to a sedimentary deposit on the western side of the fjord. A 350–410 m-deep outer sill, also mapped by marine surveys, marks the seaward end of the fjord. This outer sill is aligned with the proposed Last Glacial Maximum (LGM) grounding-line position for Petermann Glacier. The inner sill likely provided a stable pinning point for the grounding line in the past, punctuating the retreat of Petermann Glacier since the LGM.

Highlights

IntroductionPetermann Glacier in northern Greenland (80.5◦N, 60◦W) drains 4% of the Greenland Ice Sheet and discharges ∼12 ± 1 Gt/yr (Rignot and Steffen, 2008) of ice into a 90 km-long, 20 km-wide fjord (Fig. 1)
Petermann Glacier is generally stable, with little observed change in surface elevation (Pritchard et al, 2009), grounding-line position (Rignot, 1998) or velocity (Moon et al, 2012), and velocities ranging from 100 m/yr in the interior to ∼1000 m/yr at the grounding line
An analysis of repeat IceBridge gravity lines in Greenland, which is a better way to assess the repeatability of measurements due to the along-track directionality of filtering, gives an root mean squared (RMS) difference of 0.72 mGal for data processed with a 70 s temporal filter (Boghosian et al, submitted for publication), which is the filter applied to the data used in this study

Summary

Introduction

Petermann Glacier in northern Greenland (80.5◦N, 60◦W) drains 4% of the Greenland Ice Sheet and discharges ∼12 ± 1 Gt/yr (Rignot and Steffen, 2008) of ice into a 90 km-long, 20 km-wide fjord (Fig. 1). Ice is 600 m thick at the grounding line, and supports a long floating ice tongue. In 2011, this tongue was 53 km-long and 150 m-thick at its calving front. Petermann Glacier is generally stable, with little observed change in surface elevation (Pritchard et al, 2009), grounding-line position (Rignot, 1998) or velocity (Moon et al, 2012), and velocities ranging from 100 m/yr in the interior to ∼1000 m/yr at the grounding line. Large tabular icebergs, calve periodically from the front of the tongue, but over a decadal timescale the calving front is considered stable (Münchow et al, 2014)

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Discussion

Conclusion