The Water-mass Signature and Pathways of Greenland Ice Sheet Meltwater in the Arctic and North Atlantic as Inferred by an Inverse Method

Jake Gebbie, Physical Oceanography


Arctic Research Initiative
2011 Funded Project


Nearly all Greenland outlet glaciers show thinning, retreat, and acceleration of ice flow over the past few decades.  These processes are responsible for about 50% of the net loss of Greenland’s ice, with direct consequences for global sea-level rise.  The outlet glaciers terminate in the multitude of fjords that ring Greenland, where contact with warming ocean waters may contribute to the observed recent changes.  Besides the effects of the ocean on the Greenland ice, large quantities of meltwater are supplied to the ocean in the fjords, leading to the transformation of the properties of seawater with consequences for the ocean circulation.  The properties of the meltwater are quite distinct: very cold, fresh, super-saturated in dissolved oxygen, and with an abundance of light oxygen-isotopes.  Such waters are present in relatively small volumes in the open ocean, but the distinctness of the signal gives hope that their influence on seawater properties can be tracked far from the source region.  Here we build upon a new statistical technique (Total Matrix Intercomparison, TMI) that combines hydrographic information collected from research cruises during the World Ocean Circulation Experiment (WOCE) and a numerical model of ocean pathways.  Previously, this method quantified the volume of ocean water that originates from the global sea surface with over 10,000 unique water sources, and here we propose to extend the method to include sources of water from the Greenland outlet glaciers.  The goal is to reconstruct the location of the sources of meltwater, including the particular fjord and the depth of the injection, which has important implications for understanding submarine melting at the ice-ocean interface.  Furthermore, the total volume of meltwater from each location can be ascertained, and with the addition of circulation rate constraints, the meltwater rate is recovered.  Finally, the proposed method allows the tracking of the path of meltwater in the open ocean, a quantitative estimate of its dilution in ambient waters, and a large-scale view of how coastal meltwater is mixed into the ocean interior.  The pathways are critical because they have been fingered in circulation models as a link between ice sheet melt and the basin-wide Atlantic circulation, a process implicated in both the Ice Ages and future climate scenarios, but we have relatively-little observational information to determine the validity of that view.  This project will develop the mathematical framework that allows the fusion of models and observations in the Arctic, with an eye toward including in-situ information from other ARI projects in one synthesis, a means of adding value to new and existing data sets.