Local surface winds modulate the ocean forcing of Pine Island Glacier

Abstract:

Pine Island Glacier terminates in a rapidly melting ice shelf, where ocean forcing of the melt rate has been implicated in the acceleration and retreat of the glacier. A set of mooring records close to the Pine Island ice shelf were recovered in 2014, two of which are combined to provide an unprecedented five-year time series of temperature, salinity and current velocity. These data reveal considerable seasonal and interannual variability in intermediate to deep ocean temperatures, of sufficient magnitude to make a substantial impact on the melt rate of Pine Island ice shelf. The seasonal cycle in ocean temperature is correlated with surface wind speed over the continental shelf, suggesting a role for local surface heat fluxes and convection in influencing the observed temperatures down to 600 m depth.

The period August 2011 to August 2013 was anomalously cold; comparison with ship-based summertime observations suggest the heat content at the glacier front in December 2012 was the coldest in the observational record. Similar cold anomalies are observed concurrently at other moorings within Pine Island Bay. This cold spell coincided with a reduction in the concentration of melt water observed, consistent with reduced melting implied by lower temperatures at the mooring locations near the ice shelf. Current observations suggest this was accompanied by a reversal in the circulation pattern around the bay, and the concurrent increase in salinity implies increased sea ice formation. Mooring records in one of the two continental shelf-edge depressions leading to PIG do not indicate a change in temperature during this cold period.