EVALUATING THE ROLE OF CLIMATE COOLING IN ICEBERG PRODUCTION AND THE HEINRICH EVENTS

BOND et al.1 recently presented evidence for the frequent occurrence, in the Pleistocene epoch, of periods of massive iceberg discharge into the North Atlantic ocean ('Heinrich events'), each lasting a few thousand years. The cause of these events is uncertain, but one possibility1 is repeated advances of the Laurentide ice sheet during episodes of cooler climate. Here I examine this idea, using a model of the Laurentide ice sheet driven by orbitally forced variations in insolation, with and without three additional 3,000-yr-long cooling episodes, imposed just before the occurrence of the three most recent Heinrich events (H1, H2 and H3). In the model, the cooling event preceding H1 (when the climate was relatively warm and deglaciation was about to begin) led to increased calving, but those preceding H2 and H3 (which occurred during the last ice age, when the climate was very cold) led to reduced iceberg calving. It thus seems unlikely that the Heinrich events generally reflect a direct response of the Laurentide ice sheet to climate cooling.