Subglacial Access Working Group (SAWG): Access Drilling Priorities in Greenland

Summary

The Greenland Ice Sheet (GIS) contains ~7 meters of sea-level equivalent, suggesting a potentially profound effect on near-future human civilization and infrastructure in the currently warming climate. New evidence suggests nearly complete deglaciation of Greenland within the past ~1 Myr (Schaefer et al., 2016), but the pattern of deglaciation in space and time, as well as how common near-complete deglaciation has been over the Pleistocene, remain underconstrained. Modern ice-sheet models, which are used to forecast the sea-level contribution from Greenland, are rapidly improving; the extent to which they converge on projections of ice-sheet evolution across common forcings and boundary conditions is being tested by the ISMIP6 effort (Nowicki et al., 2016). The geothermal flux boundary conditions and the presence and character of subglacial tills (sediments), in particular, are datasets where improvements would improve the accuracy of ice-sheet model projections (Brinkerhoff et al., 2011; Pollard et al., 2012; Rogozhina et al., 2012). A new wealth of geophysical measurements have informed new, Greenland-wide maps of geothermal flux, yet such maps are tied to direct, in situ geothermal flux measurements rather sparsely and without complete consistency (Greve et al., 2017). The recent emergence of a subglacial till - hydrology model alongside indirect measurements of seasonal evolution of tills have pointed to an important role of subglacial tills in Greenland hydrology and ice flow. Presence or absence, as well as mechanical character, of these tills are not presently well constrained at the regional or ice-sheet scale, limiting future inclusion in ice-sheet models.

It should be possible to both collect cosmogenic isotope samples from subglacial bedrock cores (to inform patterns of past deglaciation) and to make direct measurements of the geothermal flux at the same subglacial access points. Promising sites for this work lie in northern Greenland, where (i) paleo-ice-sheet models suggest that past deglaciations initiated, (ii) Cenozoic passage of the Iceland Hot Spot implies elevated geothermal fluxes, and (iii) the basal ice is likely currently frozen.

Observations of subglacial tills will require separate boreholes, as locations with tills are poor targets for cosmogenic exposure dating, and thawed locations (which we expect to correlate with the presence of sediments) are not suitable for inferring geothermal flux.