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During the last ice age several quasi-periodic abrupt warming events tookplace. Known as Dansgaard-Oeschger (DO) events their effects were feltglobally, although the North Atlantic experienced the largest temperatureanomalies. Paleoclimate data shows that the fluctuations often occurred rightafter massive glacial meltwater releases in the North Atlantic and in bursts ofthree or four with progressively decreasing strengths. In this study a simpledynamical model of an overturning circulation and sea ice is developed with thegoal of understanding the fundamental mechanisms that could have caused the DOevents. Interaction between sea ice and the overturning circulation in themodel produces self-sustained oscillations. Analysis and numerical experimentsreveal that the insulating effect of sea ice causes the ocean to periodicallyvent out accumulated heat in the deep ocean into the atmosphere. Subjecting themodel to idealized freshwater forcing mimicking Heinrich events causesmodulation of the natural periodicity and produces burst patterns very similarto what is observed in temperature proxy data. Numerical experiments with themodel also suggests that the characteristic period of 1,500 years is due to thegeometry, or the effective heat capacity, of the ocean that comes under sea icecover.

Periodic fluctuations in deep water formation due to sea ice