Abstract
Abstract. We have extended the record of flow speed on Jakobshavn Isbræ through the summer of 2013. These new data reveal large seasonal speedups, 30 to 50% greater than previous summers. At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as great as that in the mid-1990s, while the peak summer speeds are more than a factor of four greater. These speeds were achieved as the glacier terminus appears to have retreated to the bottom of an over-deepened basin with a depth of ~ 1300 m below sea level. The terminus is likely to reach the deepest section of the trough within a few decades, after which it could rapidly retreat to the shallower regions ~ 50 km farther upstream, potentially by the end of this century.
Highlights
The speeds of many of Greenland glaciers have varied dramatically over the last two decades (Howat et al, 2008; Moon et al, 2012), which has contributed to the ice sheet’s increasingly negative mass imbalance (Rignot and Kanagaratnam, 2006; Shepherd et al, 2012; van den Broeke et al, 2009)
Such results are consistent with the large summer speedups in 2012 and 2013 when the terminus appears to have reached the bottom of an overdeepened basin (Fig. 3), which occurred after the terminus retreated more than a kilometre farther inland than previous summers
Our results show that Jakobshavn Isbræ has accelerated to speeds unprecedented in its observational record as its terminus has retreated to a region where the bed is ∼ 1300 m below sea level
Summary
The speeds of many of Greenland glaciers have varied dramatically over the last two decades (Howat et al, 2008; Moon et al, 2012), which has contributed to the ice sheet’s increasingly negative mass imbalance (Rignot and Kanagaratnam, 2006; Shepherd et al, 2012; van den Broeke et al, 2009). Nowhere are such changes more evident than on Greenland’s fastest glacier, Jakobshavn Isbræ (Fig. 1), which sped up more than twofold over the last decade and a half (Joughin et al, 2012a). As a consequence of this speedup, Jakobshavn Isbræ alone has contributed nearly 1 mm to global sea level over the period from 2000 to 2011 (Howat et al, 2011)
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