Using Noble Gases to Distinguish Glacial Freshwater Sources from Greenland


2014 OCCI Project


The Greenland Ice Sheet is losing mass at unprecedented rates.  This excess fresh water is causing sea level to rise while also freshening the North Atlantic, which can impact the global ocean circulation and climate.  Understanding ongoing, and predicting future, changes in Greenland is therefore important to societies worldwide.  One key question in understanding glacier behavior, and hence ice sheet mass loss, is differentiating mass loss from surface melting (e.g.  by a warming atmosphere) and submarine melting (e.g.  by a warming ocean).  This issue is also critical to determining the rate and distribution of meltwater input into the ocean.  Yet distinguishing these two kinds of meltwater from glacier measurements is virtually impossible: submarine melting occurs under ice shelves or at margins of calving glaciers.  Instead, we propose to develop a new method to distinguish these two kinds of meltwater from ocean measurements downstream.  The idea is that if we can estimate the relative fraction of the two meltwater sources in the ocean waters around Greenland - we can eventually reconstruct their different discharge rates.

The proposed method builds on the work of Jenkins - who has used noble gases to identify submarine meltwater in ocean waters around Antarctica.  Here we propose to modify it to include differentiation of surface and submarine melt in Greenland (there is little or no surface melt in Antarctica).  The method relies on the fact that the two kinds of meltwater will have different noble gas signatures which, even when mixed with ocean water, will retain an indication of their origin.  The long-term implication is that by making relatively simple measurements at the margins of the Greenland Ice Sheet, and individual glaciers, one will be able to reconstruct the different volumes of surface versus submarine melt.

We propose to make the first noble gas measurements in the waters surrounding Greenland by taking advantage of an existing cruise of opportunity in which two of the PIs will be participating.  The proposed work builds on the large cumulative expertise of making and interpreting ocean measurements around Greenland.  It brings together an interdisciplinary WHOI team and has the potential to jump start a technique which will provide extremely valuable and currently unavailable information.  We expect that if this method works, these measurements will be widely used around Greenland and other retreating marine glaciers.