Talk by Benoit Lecavalier, University of Ottawa – Niels Bohr Institute - University of Copenhagen

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Talk by Benoit Lecavalier, University of Ottawa


Persistent Greenland data-model discrepancies

Abstract
An ice sheet model was constrained to reconstruct the evolution of the Greenland Ice Sheet (GrIS) from the Last Glacial Maximum (LGM) to present to improve our understanding of its response to climate change. The study involved tuning a glaciological model in series with a glacial isostatic adjustment and relative sea-level model. The study builds upon the work of Simpson et al. (2009) through four main extensions: (1) a larger constraint database consisting of relative sea-level, ice height and extent data; model improvements to the (2) climate and (3) sea-level forcing components; (4) accounting for uncertainties in non-Greenland ice. The research was conducted primarily to address data-model misfits and to quantify inherent model uncertainties with the Earth structure and non-Greenland ice. Our new model (termed Huy3) fits the majority of observations and is characterised by a number of defining features. During the LGM, the ice sheet had an excess of 4.7 m ice-equivalent sea level, which reached a maximum volume of 5.1 m ice-equivalent sea-level at 16.5 ka BP. Modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors. Southwest and Southeast Greenland began to retreat from the continental shelf by ~16 to 14 ka BP, thus responding in part to the Bølling-Allerød warm event (14 ka BP); subsequently ice at the southern tip of Greenland readvanced during the Younger Dryas cold event. In northern Greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the Younger Dryas to present-day conditions. Upon entering the Holocene (11.7 ka BP), the ice sheet soon became land-based. During the Holocene Thermal Maximum (HTM; 9-5 ka BP), air temperatures across Greenland were marginally higher than those at present and the GrIS margin retreated inland of its present-day southwest position by 40 to 60 km at 4 ka BP which produced a deficit volume of 0.16 m ice-equivalent sea-level relative to present. In response to the HTM warmth, our optimal model reconstruction lost mass at a maximum centennial rate of 103.4 Gt/a. Our results suggest that remaining data-model discrepancies are associated with missing physics and sub-grid processes of the glaciological model, uncertainties in the climate forcing, lateral Earth structure, and non-Greenland ice (particularly the North American component).