Evidence for abrupt climate changes on millennial and shorter timescales is widespread in marine and terrestrial climate records. Rapid reorganization of ocean circulation is considered to exert some control over these changes, as are shifts in the concentrations of atmospheric greenhouse gases. The response of the climate system to these two influences is fundamentally different: slowing of thermohaline overturn in the North Atlantic Ocean is expected to decrease northward heat transport by the ocean and to induce warming of the tropical Atlantic, whereas atmospheric greenhouse forcing should cause roughly synchronous global temperature changes. So these two mechanisms of climate change should be distinguishable by the timing of surfacewater temperature variations relative to changes in deep-water circulation. […]
We find significant warming is documented for Heinrich event H1 (16,900-15,400 calendar years BP) and the Younger Dryas event (12,900-11,600 cal. Yr BP), which were periods of intense cooling in the northern North Atlantic. Temperature changes in the tropical and high-latitude North Atlantic are out of phase, suggesting that the thermohaline circulation was the important trigger for these rapid climate changes. In the high northern latitudes, the last deglaciation was punctuated by several brief returns to near-glacial climate. The most prominent of these events was the Younger Dryas cold period.
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