Recent results on the Greenland Aquifer from remote sensing and in situ measurements

Abstract:

The accelerating loss of mass from the Greenland ice sheet is a major contribution to current sea level rise (SLR) with increased meltwater runoff responsible for half of this mass loss increase, yet the mechanisms and timescales involved in allowing surface meltwater to reach the ocean are poorly understood. The recent discovery of an extensive liquid water reservoir within the Greenland ice sheet firn further complicates the relationship of melt to SLR, since the aquifer system may be either buffering or accelerating SLR. However, even the most fundamental questions about the firn aquifer remain unanswered.

A suite of remote sensing data sets coupled with in situ measurements and modeling are used to further constrain the spatial and temporal extent of the Greenland firn aquifer. NASA’s Operation IceBridge Accumulation Radar from 2011-2014 are used to map the extent over a majority of the suspected areas. Repeated flight lines are used for multi-temporal analysis which generally indicates stable water depths, however, some changes in extent are detected. We have also tested a variety of ground based radar frequencies for detection of the top and bottom interfaces of the aquifer. Mapping of the retention of liquid water in the firn from space is demonstrated using an active microwave satellite scatterometer (ASCAT). This data set provides near daily observations of the aquifer recharge and freeze process at and below the surface over an integrated penetration depth. One full year of bore hole temperature measurements reveal progression of the aquifer recharge and refreezing from the surface. This provides insight into the thermodynamics and for comparison with satellite data to constrain the ASCAT observable depth of liquid water.