A first constraint on basal melt-water production of the Greenland ice sheet

Nanna B Karlsson,Jason E Box,Ian J Hewitt,Joseph A Macgregor,Kenneth D Mankoff,Niels J Korsgaard,William T Colgan,Fabien Gillet-Chaulet,Kristian K Kjeldsen,Robert S Fausto,Signe H Larsen,Anne M Solgaard,Michele Citterio,Douglas I Benn

doi:10.1038/s41467-021-23739-z

Abstract

The Greenland ice sheet has been one of the largest sources of sea-level rise since the early 2000s. However, basal melt has not been included explicitly in assessments of ice-sheet mass loss so far. Here, we present the first estimate of the total and regional basal melt produced by the ice sheet and the recent change in basal melt through time. We find that the ice sheet’s present basal melt production is 21.4 +4.4/−4.0 Gt per year, and that melt generated by basal friction is responsible for about half of this volume. We estimate that basal melting has increased by 2.9 ± 5.2 Gt during the first decade of the 2000s. As the Arctic warms, we anticipate that basal melt will continue to increase due to faster ice flow and more surface melting thus compounding current mass loss trends, enhancing solid ice discharge, and modifying fjord circulation.

Highlights

The Greenland ice sheet has been one of the largest sources of sea-level rise since the early 2000s
Mass loss from the Greenland ice sheet is determined via one of three methods: through estimates of ice volume change from satellite altimetry[1,2], by directly measuring mass changes using gravimetry[3] or by differencing between solid ice discharge and surface mass balance[4,5]
We have shown that the volume of basal melt water from the Greenland ice sheet is a non-negligible part of the total mass budget

Summary

Introduction

The Greenland ice sheet has been one of the largest sources of sea-level rise since the early 2000s. Uncertainty in the partition of ice-sheet mass loss between surface mass balance and ice discharge, including the failure to acknowledge the basal mass balance term, limits our understanding of changes in ice-sheet mass budget in response to recent climate change. This impedes our ability to capture complex interactions and feedbacks between ice sheets and the climate system. We use a multi-year surface velocity composite spanning 1995–201515, winter velocity maps from 2000/2001 to 2018/201916,17, and average decadal/multi-decadal surface melt-water volumes from 1991–201218 This allows us to construct a baseline basal-melt value against which we can compare likely changes in basal melt rates in the recent past. Our results demonstrate that basal melt is a nonnegligible component of the mass balance of the Greenland ice sheet, and that basal melt-water production is likely increasing and will continue to do so in the foreseeable future

Methods

Results

Conclusion