New Study in journal Nature reveals ’85 years of glacier growth & stability in East Antarctica

From CLIMATE DEPOT
Early aerial expedition photos reveal 85 years of glacier growth and stability in East Antarctica

Published: 25 May 2024 – Mads Dømgaard,  Anders Schomacker,  Elisabeth Isaksson,  Romain Millan,  Flora Huiban,  Amaury Dehecq, Amanda Fleischer,  Geir Moholdt,  Jonas K. Andersen &  Anders A. Bjørk 

Nature Communications: Our results demonstrate that the stability and growth in ice elevations observed in terrestrial basins over the past few decades are part of a trend spanning at least a century, and highlight the importance of understanding long-term changes when interpreting current dynamics. … However, in Antarctica, the scarcity of historical climate data makes climate reanalysis estimates before the 1970s largely uncertain^10,23, and observed trends cannot clearly be distinguished from natural variability^24,25. 

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By Marc Morano

https://www.nature.com/articles/s41467-024-48886-x

Early aerial expedition photos reveal 85 years of glacier growth and stability in East Antarctica

Published: 25 May 2024 – Mads Dømgaard,  Anders Schomacker,  Elisabeth Isaksson,  Romain Millan,  Flora Huiban,  Amaury Dehecq, Amanda Fleischer,  Geir Moholdt,  Jonas K. Andersen &  Anders A. Bjørk 

Nature Communications 

Abstract (Emphasis added) 

During the last few decades, several sectors in Antarctica have transitioned from glacial mass balance equilibrium to mass loss. In order to determine if recent trends exceed the scale of natural variability, long-term observations are vital. Here we explore the earliest, large-scale, aerial image archive of Antarctica to provide a unique record of 21 outlet glaciers along the coastline of East Antarctica since the 1930s. In Lützow-Holm Bay, our results reveal constant ice surface elevations since the 1930s, and indications of a weakening of local land-fast sea-ice conditions. Along the coastline of Kemp and Mac Robertson, and Ingrid Christensen Coast, we observe a long-term moderate thickening of the glaciers since 1937 and 1960 with periodic thinning and decadal variability. In all regions, the long-term changes in ice thickness correspond with the trends in snowfall since 1940. Our results demonstrate that the stability and growth in ice elevations observed in terrestrial basins over the past few decades are part of a trend spanning at least a century, and highlight the importance of understanding long-term changes when interpreting current dynamics.

Introduction

The East Antarctic Ice Sheet (EAIS) contains more than 52 m of potential sea level equivalent (SLE)¹. Recent observations indicate that the EAIS is more vulnerable than previously anticipated², and has made a considerable contribution to the continent-wide mass loss during the past decades³. The losses have primarily occurred in some of the marine-based catchments in Wilkes Land⁴, and are largely attributed to the intrusion of modified Circumpolar Deep Water (CDW)². The terrestrial catchments, where the majority of the ice is grounded above sea level, have recently shown a mass gain caused by increased accumulation^5,6,7,8, which has balanced some of the overall mass loss^9,10. Observational time series of glaciers in East Antarctica pre-dating the satellite era are rare¹¹ and consequently not long enough to determine if recent trends are independent of natural fluctuations^2,12. Historical datasets from early expeditions serves as a crucial link connecting records from the pre-satellite era, such as those derived from ice cores¹³ or geological¹⁴ and geomorphological evidence¹⁵, to quantitative observations of mass change acquired from satellites^5,6,7. While geological and geomorphological records cover longer time scales with temporal uncertainties of up to thousands of years^14,15, SMB estimates from ice cores are generally very local and spatially confined¹⁶. In contrast, data from historical aerial expeditions often provide extensive coverage across large areas, with detailed temporal and spatial information^17,18,19. Additionally, historical data provide an important baseline for forward modeling of glacier dynamics, allowing for long-term reanalysis data and more accurate model calibration²⁰. In Greenland and Svalbard, long-term observations from historical aerial images have been vital for determining the historical response of glaciers to climate change^18,19,21,22. However, in Antarctica, the scarcity of historical climate data makes climate reanalysis estimates before the 1970s largely uncertain^10,23, and observed trends cannot clearly be distinguished from natural variability^24,25.

Here, we rediscover and utilize the images from the earliest large-scale aerial photography campaign conducted on the Antarctic continent, allowing us to extend the era of observational records of glacier evolution back to the 1930s. Since the beginning of the 20^th century, several expeditions were launched to Antarctica with the aim of exploring and capturing aerial images for the production of geographical maps^{26,27,28,29,30}. However, just a handful of studies have previously used these data for generating digital elevation models (DEMs) and only for glaciers located in West Antarctica and the Antarctic Peninsula^11,31,32, dating back to 1947³². On the Antarctic Peninsula, these observations show widespread near-frontal surface lowering and inland stability since 1960³¹. On the other hand, historical observations of the Byrd Glacier over the past 40 years indicate a constant surface elevation, stable grounding line, and surface flow velocity¹¹.

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Currently, the earliest ice-sheet wide mass balance estimates start in the late 1970s^3,6,7, and since then all the sub-regions examined in this study have exhibited either an overall mass gain or been relative unchanged.

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Regardless of potential climatic changes, our results indicate that the glacier in Kemp and Mac Robertson Land and along Ingrid Christensen Coast, have accumulated mass during the past 85 years which inevitably have mitigated parts of the more recent mass loss from the marine basins in East Antarctica and the West Antarctic Ice Sheet (WAIS). This positive accumulation trend and positive mass balance is anticipated to persist as snowfall is expected to increase over the entire EAIS in the next century^54,55, and ice sheet modeling studies project positive mass balance estimates in all three sub-regions across all future RCP scenarios⁵⁶.

Lastly, we determine frontal changes of 21 glaciers from 1937 to 2023 (Table S1 and Fig. S11). From the 85 years of observations, we find two distinct regional patterns; one of constant glacier surface elevations and one of ice thickening.

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