Deglaciation-Induced Climate Variability

Abstract

A previously developed two-dimensional-basin model of the global thermohaline circulation has been asynchronously coupled to an atmospheric energy balance model in support of analyses of the low frequency variability of the climate system. The coupled model, which has previously delivered successful simulations of the Dansgaard-Oeschger oscillations revealed in deep ice-core isotopic data from Summit, Greenland, is herein applied to the last deglaciation event of the current ice age in order to investigate the response of the climate system to transient meltwater forcing. The model employs hydrological forcing functions that consist of two components, one that is related to sea level and constrained by coral-based records of LGM to present sea level history, and a second that is unrelated to sea level and is assumed to exist because of the existence of the continental ice sheets that bounded the region of the North Atlantic basin where deep water is today. Our results show that the model successfully explains the occurrence of a YoungerDryas-like cool period regardless of the detailed properties of the sea level-related meltwater event that is observed to have followed this millennium-long return to glacial conditions. In order to successfully explain the occurrence of the Bulling/Allerod warm period that occurred prior to the Y-D, however, the model requires the action of the additional "background" anomaly that is unrelated to sea level. We explore the impact on climate response of the properties of these two components of the anomalous forcing.