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

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.

Ice Thickness and Bed Elevation of the Northern and Southern Patagonian Icefields

“…Instead, we process the 2012 and 2016 gravity data at their own elevation, with minimal impact on data resolution, at the expense of longer calculations (Millan et al, ). To account for changes in gravity caused by geology below the modeled domain, we constrain the gravity inversion with observations from radar sounder, bathymetry, and elevation of exposed rock outcrops as in An et al (). Using a preliminary solution of the bed topography that combines (1) radar (WISE Q1,Q2, and CECs), (2) bathymetry, and (3) rock outcrops.…”

“…We compare the modeled and observed gravity (the difference is named the DC‐shift) over areas where we have reliable data and interpolate the DC‐shift over areas with no data using a minimum curvature algorithm (Figure S4). The DC‐shift varies with the underlying the geology of the region (An et al, ; Hodgson et al, ), for example, changes in crustal thickness and layer density associated with tectonic faults and active volcanoes. The results are low‐pass filtered to remove short‐wavelength variations and added to the observed gravity before the inversion (Millan et al, ).…”

“…During the inversion process, we calculate the gravity from the initial model and compared it to the observed gravity. The initial model is modified iteratively until we obtain the best match with the observed data (An et al, ; Millan et al, ; Muto et al, ; Tinto & Bell, ). We calculate the gravity misfit as the difference between modeled and observed gravity anomalies.…”

Revisiting Austfonna, Svalbard, with potential field methods – a new characterization of the bed topography and its physical properties

“…Glacial sliding and melting rates are often determined from Global Positioning System (GPS) measurements, satellite imagery and satellite altimetry (e.g. Przylibski et al, 2018;Bahr et al, 2015;Grinsted, 2013;Radić et al, 2013;Dunse et al, 2012;Gray et al, 2015;Moholdt et al, 2010b). The ice thickness and the ground topography at the glacier base, key factors in understanding the glacial-sliding and ice-melting mechanisms (Clarke, 2005), have proven challenging to derive.…”

Supplementary material to "New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations"

“…b) Millan et al, 2017 forward modelling result, tied to single coastal offset. c) Bathymetry derived using the "gravity shift method" (An et al, 2019…”