An ice-sheet modelling framework to determine vulnerable regions of the Greenland Ice Sheet in the past

Abstract. The contribution of the Greenland Ice Sheet (GrIS) to sea-level rise is accelerating and there is an urgent need to characterize which sectors of the ice sheet are the most vulnerable. Estimating the volume of Greenland ice that was lost during past warm periods can support efforts to constrain the ice sheet's response to future warming. Sub-ice sediment and bedrock, retrieved from deep ice core campaigns or targeted drilling efforts, yield critical and direct information about past ice-free conditions. However, it is challenging to scale the few available sub-ice point measurements to the geometry of the entire ice sheet. Here, we provide a framework for assessing sea-level potential, which we define within an ensemble of ice-sheet model simulations as the amount the GrIS has contributed to sea level when a particular location in Greenland is ice free. An assessment of dominant sources of uncertainty in our paleo ice-sheet modelling, including climate forcing, ice-sheet initialization, and solid-Earth properties, reveals spatial patterns in the sensitivity of the ice sheet to these processes and related feedbacks. We find that the sea-level potential of central Greenland is most sensitive to lithospheric feedbacks and ice-sheet initialization, whereas the ice-sheet margins are most sensitive to climate forcing parameters. We map the GrIS response to warming, in order to (1) estimate of the region(s) of GrIS that likely contributed to the first meter(s) of global sea-level change across a range of plausible deglaciation scenarios, (2) guide future sub-glacial access efforts that can provide targeted information about the response of the ice sheet to past warming, and (3) contextualize existing and future datasets within a glaciologically coherent, full-geometry framework to establish the minimum GrIS contribution to past sea level when a particular location is ice-free. Through our ensemble approach, we can assign a plausible range of GrIS contributions to global sea level for deglaciated conditions at any site. Our results identify primarily areas in southwest Greenland, and secondarily north Greenland, as best-suited for subglacial access drilling that seeks to constrain the response of the ice sheet to past and future warming.