Interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry

The relative timings of the last deglacial warming in the Southern and Northern hemispheres are not well constrained, but are a crucial component in understanding the mechanisms of deglaciation(1). A clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high-resolution temperature records that can be tied to the absolute calendar timescale. Moreover, the quantification of tropical temperatures during the last glacial cycle is controversial(2-8). Here we apply the alkenone method of sea surface temperature reconstruction(9,10) to several high-resolution sediment cores recovered from the tropical Indian Ocean between 20 degrees N and 20 degrees S. The inferred initial sea surface temperature warming similar to 15,000 calendar years ago at 20 degrees S is in phase with Northern Hemisphere sea (this study) and air(11) temperature changes, but lags Antarctic warming(12-14) by several millennia. This finding, along with the results of recent modelling studies(15,16), provides strong support for the idea that changes in the ocean's global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation.