Warming of the tropical Atlantic Ocean and slowdown of thermohaline circulation during the last deglaciation

Evidence for abrupt climate changes on millennial and shorter timescales is widespread in marine and terrestrial climate records(1-4). Rapid reorganiz ation of ocean circulation is considered to exert some control over these c hanges(5), as are shifts in the concentrations of atmospheric greenhouse ga ses(6). The response of the climate system to these two influences is funda mentally 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(7,8), whereas atmospheric greenhous e forcing should cause roughly synchronous global temperature changes(9). S o these two mechanisms of climate change should be distinguishable by the t iming of surface-water temperature variations relative to changes in deep-w ater circulation. Here we present a high-temporal-resolution record of sea surface temperatures from the western tropical North Atlantic Ocean which s pans the past 29,000 years, derived from measurements of temperature-sensit ive alkenone unsaturation in sedimentary organic matter. We find significan t warming is documented for Heinrich event HI (16,900-15,400 calendar years BP) and the Younger Dryas event (12,900-11,600 cal. yr BP), which were per iods of intense cooling in the northern North Atlantic. Temperature changes in the tropical and high-latitude North Atlantic are out of phase, suggest ing that the thermohaline circulation was the important trigger for these r apid climate changes.