Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

The transfer of land-based ice into the sea, via both meltwater runoff and iceberg calving, is now the leading cause of sea level rise. While the Greenland Ice Sheet as a whole contributed 0.73 ± 0.08 mm/yr of sea level rise during the 2005 to 2010 period, both in-situ and remotely sensed observations identify a slight thickening, or subtle mass gain, in the high-elevation ice sheet interior.

Two competing hypotheses have emerged to explain this high elevation ice sheet thickening. The first hypothesizes that millennial-scale ice sheet thickening is an anticipated result of relatively hard (or stiff) Holocene ice flowing down into the ice sheet and replacing relatively soft Last Glacial Period ice. The second hypothesizes that recent increases in snowfall, due to a warming atmosphere and increasing moisture content, is causing high-elevation thickening.

The objective of this work is to collect in-situ data and perform numerical simulations to permit the first large-scale and data-driven critical assessment of the theoretically elegant, but practically complex, notion that the gradual replacement of Last Glacial Period ice with Holocene ice is responsible for appreciable high-elevation thickening. This would potentially challenge the now widely accepted hypothesis that Greenland's interior is thickening due to snowfall.

This research will exploit recent advances in both remotely-sensed data products and in-situ instrumentation accuracy to assess the present-day magnitude of Greenland Ice Sheet interior thickening driven by subtle millennial-scale changes in ice rheology. This thickening will be computer modelled using a data-driven Monte Carlo approach. Simulated contemporary thickness change will be compared to in-situ measurements of thickness change obtained by at least two glaciological field campaigns in South Greenland.

Overturning the now canonical assumption of no appreciable high-elevation mass trends will potentially offer a transformative shift in our understanding recent Greenland Ice Sheet mass loss. The potential underestimation of recent iceberg calving, a key diagnostic modelling target, can result in underestimating projected iceberg calving in prognostic models used to simulate cryospheric sea level rise contribution. This proposed research thus directly addresses a well-defined and topical question of international significance.

Two concurrent doctoral students will lead the numerical modelling and in-situ portions of the research, respectively, assisted by five sequential undergraduate student assistants. An anticipated seven peer-reviewed publications will be submitted during the course of this proposed research. Outreach materials will be prepared and distributed via social media to disseminate project goals and results, as well as field activities, beyond scientific community with the help of media partners.