Ensemble, water isotope–enabled, coupled general circulation modeling insights into the 8.2 ka event

Freshwater forcing has long been postulated as a catalyst for abrupt climate change because of its potential to interfere with thermohaline circulation (THC). The most recent example may have occurred about 8.2 ka ago with the sudden drainage of glacial lakes Agassiz and Ojibway into the Hudson Bay. We perform an ensemble of simulations for this freshwater release using the fully coupled atmosphere ocean general circulation model, Goddard Institute for Space Studies ModelE‐R. In all cases, simulated effects include reduced ocean heat transport and enhanced atmospheric heat transport in the Atlantic, increased surface albedo (through greater low cloud and sea ice cover), and local cooling of up to 3°C. Our suite of ensemble experiments allows us to examine the importance of the initial ocean state, in particular the presence or absence of Labrador Sea Water, in controlling the magnitude and length of the climate response. Water isotope tracers included in this model provide an improved means for direct comparisons of the modeled tracer response to water isotope–based, climate proxy data. Comparison of model simulations to data implies that there was an abrupt approximate halving of Atlantic THC, hence providing strong support for the hypothesis that the 8.2 ka event was caused by an abrupt release of fresh water into the North Atlantic.