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Many northern hemisphere climate records show a series of rapid climate changes - Dansgaard-Oesgher (D-O) cycles - that recurred on centennial to millennial timescales throughout most of the last glacial period. They consist of sudden warming jumps of order 10°C, followed generally by a slow cooling lasting a few centuries, and then a rapid temperature drop into a cold period of similar length. Most explanations for D-O events call on changes in the strength of the Atlantic meridional overturning circulation (AMOC), but the mechanism for triggering and pacing such changes is uncertain. Changes in freshwater delivery to the ocean are assumed to be important.
Here, we investigate whether the proposed AMOC changes could have occurred as part of a natural relaxation oscillation, in which runoff from the northern hemisphere ice sheets varies in response to each warming and cooling event, and in turn provides the freshwater delivery that controls the ocean circulation. In this mechanism the changes are buffered and paced by slow changes in salnity of the Arctic ocean. We construct a simple model to investigate whether the timescales and magnitudes make this a viable mechanism.