Bathymetry of Northwest Greenland Using “Ocean Melting Greenland” (OMG) High-Resolution Airborne Gravity and Other Data

Lu An,Romain Millan,Josh Willis,Kirsty Tinto,Eric Rignot

doi:10.3390/rs11020131

Abstract

Marine-terminating glaciers dominate the evolution of the Greenland Ice Sheet (GrIS) and its contribution to sea-level rise. Widespread glacier acceleration has been linked to the warming of ocean waters around the periphery of Greenland but a lack of information on the bathymetry of the continental shelf and glacial fjords has limited our ability to understand how subsurface, warm, salty ocean waters of Atlantic origin (AW) reach the glaciers and melt them from below. Here, we employ high-resolution, airborne gravity data (AIRGrav) in combination with multibeam echo sounding (MBES) data, to infer the bathymetry of the coastal areas of Northwest Greenland for NASA’s Ocean Melting Greenland (OMG) mission. High-resolution, AIRGrav data acquired on a 2 km spacing, 150 m ground clearance, with 1.5 mGal crossover error, is inverted in three dimensions to map the bathymetry. To constrain the inversion away from MBES data, we compare two methods: one based on the Direct Current (DC) shift of the gravity field (absolute minus observed gravity) and another based on the density of the bedrock. We evaluate and compare the two methods in areas with complete MBES coverage. We find the lowest standard error in bed elevation (±60 m) using the DC shift method. When applied to the entire coast of Northwest Greenland, the three-dimensional inversion reveals a complex network of connected sea bed channels, not known previously, that provide natural and varied pathways for AW to reach the glaciers across the continental shelf. The study demonstrates that the gravity approach offers an efficient and practical alternative to extensive ship mapping in ice-filled waters to obtain information critical to understanding and modeling ice-ocean interaction along ice sheet margins.

Highlights

The Greenland Ice Sheet (GrIS) has been losing mass and contributing to sea-level rise more than 1 mm/yr in the last two decades [1,2,3,4]
The inferred bed elevation is positively correlated with the gravity anomaly, i.e., a low bed elevation corresponds to a negative gravity anomaly and vice versa (Figure 5b)
Our results show that the outer shelf of NW Greenland is incised by a series of troughs that extend from the fjords and feed into major cross-shelf troughs of the mid to outer shelf, which are prominent features up to 250 km long and 100 km wide, namely the: (1) North Melville Bay Trough (NMBT), (2) Melville Bay Trough (MBT) and (3) South Melville Bay Trough (SMBT) (Figure 9) [34,35]

Summary

Introduction

The Greenland Ice Sheet (GrIS) has been losing mass and contributing to sea-level rise more than 1 mm/yr in the last two decades [1,2,3,4]. The mass loss is a combination of increased ice discharge of its marine-terminating glaciers and decreased surface mass balance from enhanced surface melt. Wide spread acceleration of glaciers has taken place [6] as subsurface, warm, salty, Atlantic Water (AW) spread more vigorously around the periphery of Greenland [7,8,9]. Subsurface ocean waters at the front of these glaciers became warmer, the melt rates of their calving faces increased, causing them to retreat and experience less buttressing, which in turn allowed the glaciers to speed-up [10,11,12]. The bathymetry of most glacial fjords in NW Greenland had not been surveyed. The most recent compilation of ocean bathymetry, the International Bathymetric Chart of the Arctic Ocean (IBCAOv3), does not include glacier fjords [16]

Methods

Results

Discussion

Conclusion