How much did the N. American ice sheet contribute to the Meltwater Pulse 1a sea level rise event ?

Abstract:

Meltwater Pulse 1a (MWP1a; 14,600 years ago), is the largest rapid sea level rise event observed in geological records (~15 m in < 350 years). Its relative synchronicity with the unexplained and abrupt Northern Hemisphere Bolling warming (Deschamps et al., 2012) makes it a particularly interesting event. In order to understand the link between ice sheets, sea level and climate changes during that time, we must first determine the sources and causes of the sea level change. A recent study by Gregoire et al. (2012) modelled the evolution of North American and Greenland ice cover over the last deglaciation and suggested that the collapse of an ice saddle between the Laurentide and Cordilleran Ice Sheets could have been a major contributor to the meltwater pulse. However, the relative contributions of the Antarctic, North American and Eurasian ice sheets to MWP1a remain unconstrained.

We combined analysis of ice sheet modelling uncertainty with sea level fingerprinting to constrain the contribution of the North American ice sheet to MWP1a.

To explore uncertainties in climate and ice sheet processes, we performed ensembles of ice sheet model simulations with Glimmer-CISM, forced by transient deglacial experiments from two General Circulation Models (FAMOUS and CCSM3). The results were then compared with geological reconstructions of ice extent and sea level change to evaluate a probability distribution for the Northern American ice sheet contribution to MWP1a.

We also predicted the gravitationally self-consistent sea-level changes associated with the ice model simulations to explore whether the Laurentide-Cordilleran saddle collapse could have been the dominant source of MWP1a on the basis of fits to far-field sea-level records at Barbados, Tahiti and Sunda Shelf.

Based on these interdisciplinary and multi-model results, we present a new scenario for the relative contributions of the different ice sheets to MWP1a.