Atmosphere Ocean Science Colloquium

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Ocean Boundary Conditions for Greenland's Fastest Outlet Glacier

Speaker: Carl Gladish, MIT

Location: Warren Weaver Hall 1302

Date: Wednesday, February 18, 2015, 3:30 p.m.

Synopsis:

The Greenland and Antarctic ice sheets have been contributing 0.59 +/- 0.20 mm/yr to global mean sea level since 1992. In the late 1990s, Greenland's fastest outlet glacier, Jakobshavn Glacier, began to flow faster into the ocean at the same time the West Greenland Current appeared to suddenly warm, based on summer CTD surveys along the coast, suggesting that ice discharge was controlled by ocean-induced melting at the glacier terminus. To investigate this, we collected in situ observations of fjord water properties near the marine terminus of Jakobshavn Glacier from 2009 to 2013. We confirmed that most of the 800 m tall face of the glacier terminus is exposed to water masses known to have warmed in the 1990s. However, although the glacier has relentlessly accelerated and retreated since the late 1990s, the fjord water properties have not remained uniformly warm. Indeed, in summer of 2010,the fjord temporarily cooled to temperatures last present in the 1980s. Besides showing that the glacier is not controlled inter-annually by ocean temperatures, this isolated anomaly showed that this fjord is renewal at least annually, despite the shallow sill at its entrance. Numerical modelling suggests the glacier itself drives this renewal: in summer, subglacial meltwater enters the fjord at depth and drives an overturning circulation that transports all the fjord basin water over the sill in about one month. Fjord waters thus track the external waters inter-annually. Using in situ observations only, we next related inter-annual variability of these waters to changes in the cool low-salinity waters of the East/West Greenland Current, the warm Irminger Current, and, in exceptional years like 2010, the much colder Baffin Current.