Multi-decadal retreat of marine-terminating outlet glaciers in northwest and central-west Greenland

Taryn E Black,Ian Joughin

doi:10.5194/tc-16-807-2022

Abstract

Abstract. The retreat and acceleration of marine-terminating outlet glaciers in Greenland over the past 2 decades have been widely attributed to climate change. Here we present a comprehensive annual record of glacier terminus positions in northwest and central-west Greenland and compare it against local and regional climatology to assess the regional sensitivity of glacier termini to different climatic factors. This record is derived from optical and radar satellite imagery and spans 87 marine-terminating outlet glaciers from 1972 through 2021. We find that in this region, most glaciers have retreated over the observation period and widespread regional retreat accelerated from around 1996. The acceleration of glacier retreat coincides with the timing of sharp shifts in ocean surface temperatures, the duration of the sea-ice season, ice-sheet surface mass balance, and meltwater and runoff production. Regression analysis indicates that terminus retreat is most sensitive to increases in runoff and ocean temperatures, while the effect of offshore sea ice is weak. Because runoff and ocean temperatures can influence terminus positions through several mechanisms, our findings suggest that a variety of processes – such as ocean-interface melting, mélange presence and rigidity, and hydrofracture-induced calving – may contribute to, but do not conclusively dominate, the observed regional retreat.

Highlights

The Greenland Ice Sheet has lost significant mass over the last few decades (Enderlin et al, 2014; Shepherd et al, 2020) as many of its glaciers have retreated (Hill et al, 2017; Howat and Eddy, 2011; King et al, 2020; Moon and Joughin, 2008; Murray et al, 2015), and ice flow has accelerated (Joughin et al, 2010; Moon et al, 2012; Rignot and Kanagaratnam, 2006)
Changes in ice discharge are often related to changes to glacier terminus positions, with terminus retreat into deeper water driving acceleration and upstream thinning (Howat et al, 2008; Joughin et al, 2008b)
We identify these dominant glaciers as those with a net change falling more than 2 standard deviations beyond the population mean, which yields four glaciers that dominate the area change: Jakobshavn Isbræ, Alison Glacier, Kjer Gletsjer, and Tracy Gletsjer

Summary

Introduction

The Greenland Ice Sheet has lost significant mass over the last few decades (Enderlin et al, 2014; Shepherd et al, 2020) as many of its glaciers have retreated (Hill et al, 2017; Howat and Eddy, 2011; King et al, 2020; Moon and Joughin, 2008; Murray et al, 2015), and ice flow has accelerated (Joughin et al, 2010; Moon et al, 2012; Rignot and Kanagaratnam, 2006). Surface mass balance has dominated Greenland’s mass loss in the past 2 decades, over half of the mass loss in northwest and centralwest Greenland is currently due to ice discharge (Mouginot et al, 2019), which has accelerated since 2000 in this region (King et al, 2020). Changes in ice discharge are often related to changes to glacier terminus positions, with terminus retreat into deeper water driving acceleration and upstream thinning (Howat et al, 2008; Joughin et al, 2008b). While glacier retreat and acceleration are generally linked to changes at the terminus, it remains unclear which processes are most responsible for controlling perturbations to calving rates and subsequent terminus retreat (Straneo et al, 2013)

Results

Discussion

Conclusion