Evolution of Supraglacial Lakes on the Larsen B Ice Shelf in the Decades Before it Collapsed

A A Leeson,N Gourmelen,J M Van Wessem,E Forster,A Rice

doi:10.1029/2019gl085591

A A Leeson, N Gourmelen + Show 3 more

Open Access

https://doi.org/10.1029/2019gl085591

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Abstract

AbstractThe Larsen B ice shelf collapsed in 2002 losing an area twice the size of Greater London to the sea (3,000 km2), in an event associated with widespread supraglacial lake drainage. Here we use optical and radar satellite imagery to investigate the evolution of the ice shelf's lakes in the decades preceding collapse. We find (1) that lakes spread southward in the preceding decades at a rate commensurate with meltwater saturation of the shelf surface; (2) no trend in lake size, suggesting an active supraglacial drainage network which evacuated excess water off the shelf; and (3) lakes mostly refreeze in winter but the few lakes that do drain are associated with ice breakup 2–4 years later. Given the relative scale of lake drainage and shelf breakup, however, it is not clear from our data whether lake drainage is more likely a cause, or an effect, of ice shelf collapse.

Highlights

The Antarctic Peninsula (AP) has experienced extreme warming in the mid to late 20th Century, with air temperatures increasing by almost 2.5°C (e.g. Vaughan and Doake 1996, Skvarca et al, 1999), up to ~1990 (Turner, Lu et al 2016)
We use synthetic aperture radar (SAR) and optical satellite imagery to investigate the evolution of Supraglacial lakes (SGLs) on the Larsen B ice shelf (LBIS) prior to its collapse and find that lakes spread southwards at a rate consistent with firn air depletion, covering almost the entire ice shelf by 2002
RACMO2 does not simulate a temperature or surface melt trend during this period (Leeson et al, 2017). This suggests that ice shelf vulnerability is cumulative, and that accurate measurements and models of meltwater retention in firn are needed in order to assess the risk of collapse of other ice shelves

Summary

Introduction

The Antarctic Peninsula (AP) has experienced extreme warming in the mid to late 20th Century, with air temperatures increasing by almost 2.5°C (e.g. Vaughan and Doake 1996, Skvarca et al, 1999), up to ~1990 (Turner, Lu et al 2016). Supraglacial lakes (SGLs) form in surface depressions from ponded melt water They are a component of the ice surface hydrological network which includes streams and rivers (Glasser and Scambos, 2008). This network is important because it can route surface meltwater into lakes (Stokes et al, 2019), moulins (Langley et al, 2016) or off of the ice into the ocean (Bell et al, 2017). SGLs can drain laterally through supraglacial streams (Kingslake et al, 2015) or vertically via hydrofracture; when water-filled crevasses propagate through the full ice thickness (MacAyeal et al, 2003, Krawczynski et al, 2009). We investigate the potential role of SGLs in the collapse of LBIS by analyzing their evolution from 1979 to 2002 (Figure 1) using a combination of optical and synthetic aperture radar (SAR) satellite imagery (supporting table 1)

Data and Methods

Meteorological data

Southward spreading of lakes

Changes in lake characteristics and relationship with climate

Evidence for lake drainage

Conclusions