Constraints on the duration and freshwater release of Heinrich event 4 through isotope modelling

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Abstract
Heinrich events1—abrupt climate cooling events due to ice-sheet instability that occurred during the last glacial period—are recorded in sediment cores throughout the North Atlantic Ocean2,3. Modelling studies have described likely physical mechanisms4,5,6 for these events, but the quantitative characteristics of Heinrich events are less well known. Here we use a climate model of intermediate complexity7 that explicitly calculates the distribution of oxygen isotopes in the oceans to simulate Heinrich event 4 at about 40,000 yr ago. We compare an ensemble of scenarios for this Heinrich event with oxygen isotope data measured in foraminiferal calcite of a comprehensive set of sediment cores8,9. From this comparison, we obtain a duration of 250 ± 150 yr and an ice release of 2 ± 1 m sea-level equivalent for Heinrich event 4, significantly reducing the uncertainties in both values compared to earlier estimates5,10,11,12,13,14 of up to 2,000 yr and 15 m of sea-level equivalent ice release, respectively. Our results indicate that the consequences of Heinrich events may have been less severe than previously assumed, at least with respect to Greenland climate and sea level.