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Projections of future sea-level rise benefit from understanding the response of past ice sheets to warming during past Quaternary interglacials. Constraints on the extent of inland Greenland Ice Sheet retreat during the Middle Holocene (~8–4 thousand years before present) are limited because geological records of a smaller-than-modern phase largely remain beneath the modern ice sheet. We drilled through 509 metres of firn and ice at Prudhoe Dome, northwestern Greenland, to obtain sub-ice material yielding direct evidence for the response of the northwest Greenland ice sheet to Holocene warmth. Here we present infrared stimulated luminescence measurements from sub-ice sediments that indicate that the ground below the summit was exposed to sunlight 7.1 ± 1.1 thousand years ago. This proposed complete deglaciation of Prudhoe Dome, coeval to reduced extent at other ice caps across northern Greenland, is consistent with interglacial-only δ18O values from the Prudhoe Dome ice column and ice depth–age modelling. Our results point to a substantial response of the northwest Greenland ice sheet to early Holocene warming, estimated to be +3–5 °C from palaeoclimate data. This range of summer temperatures is similar to projections of warming by 2100 CE. 

In 2022, we sampled pro-ice samples in Inglefield Land, north of Prudhoe Dome. In 2023, we sampled bedrock and sediment samples from underneath 509 meters (m) of ice ('ASIG core') and under 100 m of ice ('Winkie Core'). These samples, the first of their kind, form the core of the GreenDrill project and have been analysed for multi-cosmogenic-isotopes, InfraRed Stimulated Luminescence (IRSL), and biomarkers. Cosmogenic nuclide analysis were done at Lamont and the University at Buffalo, IRSL measurements at UT Arlington, and biomarker analysis at University at Buffalo. This dataset holds Beryllium and Aluminum isotope data of the rock samples from Inglefield Land and of the 'ASIG core', drilled in 2023 at Prudhoe Dome Summit. 

Abstract. The lack of geological constraints on past ice-sheet change in marine-based sectors of the Greenland Ice Sheet (GrIS) following the Last Glacial Maximum limits our ability to assess (1) the drivers of ice-sheet change, and (2) the performance of ice-sheet models that are benchmarked against the paleo-record of GrIS change. Here, we provide new in situ 10Be surface exposure chronologies of ice-sheet margin retreat from the outer Scoresby Sund and Storstrømmen Glacier regions in eastern and northeastern Greenland, respectively. Ice retreated from Rathbone Island, east of Scoresby Sund, by ∼ 14.1 ka, recording some of the earliest documentations of terrestrial deglaciation in Greenland. The mouth of Scoresby Sund deglaciated by ∼ 13.2 ka, and retreated at an average rate of ∼ 43 m yr−1 between 13.2 and 9.7 ka. Storstrømmen Glacier retreated from the outer coast to within ∼ 3 km of the modern ice margin between ∼ 12.7 and 8.6 ka at an average rate of ∼ 28 m yr−1. Retreat then slowed or reached a stillstand as ice retreated ∼ 3 km between ∼ 8.6 ka to the modern ice margin at ∼ 8.0 ka. These retreat rates are consistent with late glacial and Holocene estimates for marine-terminating outlet glaciers across East Greenland, and comparable to modern retreat rates observed at the largest ice streams in northeastern, and northwestern Greenland. 

Abstract. The contribution of the Greenland Ice Sheet (GIS) to sea level rise (SLR) is accelerating and there is an urgent need to improve predictions of when and from what parts of the ice sheet Greenland will contribute its first meter. Estimating the volume of Greenland ice that was lost during past warm periods offers a way 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 as the amount the GIS has contributed to sea level when a particular location in Greenland is ice-free, from an ensemble of ice-sheet model simulations representing a wide range of plausible deglaciation scenarios. 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. Our framework allows us to quantify the local and regional uncertainty in sea-level potential, which we use to evaluate the GIS bedrock according to the usefulness of information sub-ice sediments and bedrock provide about past ice-sheet geometry. Through our ensemble approach, we can assign a plausible range of GIS 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.