Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Ilkka S. O. Matero / firstname.lastname@example.org / University of Leeds
Co-author: Lauren J. Gregoire, University of Leeds;
Ruza F. Ivanovic, University of Leeds;
Julia C. Tindall, University of Leeds;
Alan M. Haywood, University of Leeds;
The 8.2 ka event is a period of abrupt cooling of 1-3 °C across large parts of the Northern Hemisphere, which lasted for about 160 years. The consensus on the cause for this event has been the outburst of the proglacial Lakes Agassiz and Ojibway. These drained into the Labrador Sea in ~0.5-5 years and slowed the Atlantic Meridional Overturning Circulation (AMOC), thus cooling the North Atlantic region. However, climate models haven’t been able to reproduce the duration and magnitude of the cooling with this forcing without including additional centennial-length freshwater forcings, such as rerouting of continental runoff and ice sheet melt in combination with the lake release.
Here, we show that instead of being caused by the lake outburst, the event could have been caused by accelerated melt from the collapsing ice saddle that linked domes over Hudson Bay in North America. We forced a General Circulation Model with time varying meltwater pulses (100-300 year) that match observed sea level change, designed to represent the Hudson Bay ice saddle collapse. A 100 year long pulse with a peak of 0.6 Sv produces a cooling in central Greenland that matches the 160 year duration and 3 °C amplitude of the event recorded in ice cores. The simulation also reproduces the cooling pattern, amplitude and duration recorded in European Lake and North Atlantic sediment records. Such abrupt acceleration in ice melt would have been caused by surface melt feedbacks and marine ice sheet instability.
These new realistic forcing scenarios provide a means to reconcile longstanding mismatches between palaeoclimate reconstructions and models. They also allow for a better understanding of both the sensitivity of the climate models and processes and feedbacks in motion during the disintegration of continental ice sheets. In addition, they provide insights into the stability of the Atlantic Multidecadal Oscillation and freshwater-driven perturbations of the AMOC resulting from the accelerating melting of the Greenland Ice Sheet.