Abstract
ABSTRACTRapid dynamic changes of ocean-terminating outlet glaciers of the Greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood. Observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations. Here we compile a long-term record of dynamic changes of Eqip Sermia Glacier, West Greenland. Starting in 1912, we combine historical measurements of terminus positions, ice-surface elevation and flow velocity together with more recent in-situ and remote-sensing observations. In the 20th century, the glacier underwent small variations in terminus position and flow speed. Between 2000 and 2003, the terminus retreated substantially, but stabilized thereafter. In 2009, the northern terminus lobe started to retreat very rapidly; the southern lobe collapsed in 2013. The present terminus position, which has retreated by 4 km since 1920, is unprecedented in the historical record. Flow velocities were relatively stable until 2010. The recent acceleration reached threefold velocities in 2014 and rapidly affected the whole terminus region up to 15 km inland. Comparison with forcings from the atmosphere and the ocean over the past century shows that no dominant cause can be identified, and that local effects of bed geometry modulate the glacier response.
Highlights
During the past two decades, many outlet glaciers of the Greenland ice sheet (GrIS) have shown rapid and nonlinear terminus retreat, thinning and flow acceleration (Rignot and Kanagaratnam, 2006; Howat and others, 2007; Kjær and others, 2012; Moon and others, 2012) and have become important contributors to the observed increasing mass loss rates of the GrIS (Shepherd and others, 2012; IPCC, 2013)
The sudden onset and high magnitude of dynamic changes of Greenland outlet glaciers has raised concerns regarding their contribution to future sea-level rise (IPCC, 2013) but major limitations remain in understanding and predicting the dynamic behavior of such ocean-terminating glaciers (Vieli and Nick, 2011; Straneo and others, 2013)
It seems problematic to discern whether the dominant forcing is altered mass balance on the ice sheet or varying ocean temperatures in the proglacial fjord providing energy for submarine melt
Summary
During the past two decades, many outlet glaciers of the Greenland ice sheet (GrIS) have shown rapid and nonlinear terminus retreat, thinning and flow acceleration (Rignot and Kanagaratnam, 2006; Howat and others, 2007; Kjær and others, 2012; Moon and others, 2012) and have become important contributors to the observed increasing mass loss rates of the GrIS (Shepherd and others, 2012; IPCC, 2013). Longer-term and dense observational records exist only for very few glaciers such as Jakobshavn Isbrae (Weidick and Bennike, 2007; Csatho and others, 2008), Kangiata Nunata Sermia (Lea and others, 2014) and several southeast Greenland glaciers (Bjørk and others, 2012). These long-term records often exclusively measure the terminus position, and have relatively sparse temporal resolution before the satellite era, or rely strongly on indirect reconstructions based on proxies such as from sediment cores near Helheim Glacier (Andresen and others, 2012). Regarding the required century timescale of icesheet and sea-level projections into the future, the lack of longer-term observations constitutes a major limitation
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