Drill-site selection for cosmogenic-nuclide exposure dating of the bed of the Greenland Ice Sheet

Abstract

Abstract. Direct observations of the size of the Greenland Ice Sheet during Quaternary interglaciations are sparse yet valuable for testing numerical models of ice-sheet history and sea level contribution. Recent measurements of cosmogenic nuclides in bedrock from beneath the Greenland Ice Sheet collected during past deep-drilling campaigns reveal that the ice sheet was significantly smaller, and perhaps largely absent, sometime during the past 1.1 million years. These discoveries from decades-old basal samples motivate new, targeted sampling for cosmogenic-nuclide analysis beneath the ice sheet. Current drills available for retrieving bed material from the US Ice Drilling Program require < 700 m ice thickness and a frozen bed, while quartz-bearing bedrock lithologies are required for measuring a large suite of cosmogenic nuclides. We find that these and other requirements yield only ∼ 3.4 % of the Greenland Ice Sheet bed as a suitable drilling target using presently available technology. Additional factors related to scientific questions of interest are the following: which areas of the present ice sheet are the most sensitive to warming, where would a retreating ice sheet expose bare ground rather than leave a remnant ice cap, and which areas are most likely to remain frozen bedded throughout glacial cycles and thus best preserve cosmogenic nuclides? Here we identify locations beneath the Greenland Ice Sheet that are best suited for potential future drilling and analysis. These include sites bordering Inglefield Land in northwestern Greenland, near Victoria Fjord and Mylius-Erichsen Land in northern Greenland, and inland from the alpine topography along the ice margin in eastern and northeastern Greenland. Results from cosmogenic-nuclide analysis in new sub-ice bedrock cores from these areas would help to constrain dimensions of the Greenland Ice Sheet in the past.

Geologic Provinces Beneath the Greenland Ice Sheet Constrained by Geophysical Data Synthesis

“…Foremost is the modern context it provides for new applications of existing methods (e.g., interpretation of new seismic, gravity or magnetic data sets), evaluation of aerogeophysical data sets beyond those we considered, or tracing the provenance of offshore sediments (e.g., White et al., 2016). Another application could be exploring relations between these apparent province boundaries and other subglacial properties of geophysical, glaciological, geomorphological or geochemical interest, such as geothermal heat flow (Jones et al., 2021), bedrock erodibility (Campforts et al., 2020), basal friction (Maier et al., 2022), drainage history (Jess et al., 2020; Keisling et al., 2020), or isotope geochemistry (Briner et al., 2022; Colville et al., 2011). While our results were based on conventional manual delineation of province boundaries and interpretation, machine learning techniques could also be applied to reveal such structures with reduced influence from expert biases (e.g., Colgan et al., 2022; Li et al., 2022; Rezvanbehbahani et al., 2017).…”

Drilling Ice and Subglacial Rock Cores for Scientific Discovery in a Changing Climate

“…Both the IDP ASIG and the ice-enabled Winkie drills have been successfully used to retrieve subglacial sediment and rock cores. Briner and others [ 22 ] conducted investigations to identify regions of the Greenland Ice Sheet where the ice sheet is less than 700 m thick and the bed of the ice sheet is likely to be frozen with underlying quartz-bearing rock lithologies that are amenable to cosmogenic nuclide analysis. They identified regions in northern, northwestern, and northeastern Greenland that Drilling Ice and Subglacial Rock Cores for Scientific Discovery in a Changing Climate DOI: http://dx.doi.org/10.5772/intechopen.1004695 meet the criteria and thus are likely to hold evidence of whether the ice sheet disappeared in past interglacial times 420,000 and 120,000 years ago, along with the rate of melt.…”