Oceanic Boundary Conditions for Jakobshavn Glacier: Variability and Renewal of Ilulissat Icefjord Waters, 2001-2014

Abstract:

Jakobshavn Glacier, West Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. We collected hydrographic observations inside this silled fjord and from adjacent Disko Bay between 2001 and 2014. In the fjord basin, the summer mean temperature was 2.8 ^◦C from 2009 to 2013, excluding 2010, when it was 1 ^◦C cooler. Despite this variability, summer potential densities in the basin were in the narrow range 27.20 ≤ σ_θ≤ 27.31 and basin water properties matched those of Disko Bay in this density layer each summer. This relation has likely held since at least 1980, implying that basin waters from 2009 and 2011-2013 were similar to those in 1998 and 1999, when Jakobshavn Glacier began to retreat, while basin waters as cool as in 2010 were likely last present in the 1980s.

The 2010 basin temperature anomaly reflected larger-scale advection into Disko Bay, not local weather variability. This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Mooring time series and data from instrumented seals and halibut did not capture the 2010 anomaly but show that the basin and Disko Bay bottom temperatures vary little sub-annually, outside of summer, while fjord velocity profiles from summer 2013 imply a basin renewal timescale of about one month. Model simulations indicate that subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord can not, due to the sill at the mouth. The silled nature of Ilulissat Icefjord therefore makes its renewal dynamics different from Sermilik Fjord, in east Greenland, which is rapidly renewed by external forcing.