North Pacific sea surface temperature gradients since the late Miocene

Climate model sensitivity studies have indicated that basin-wide sea surface temperature (SST) gradients may have been instrumental in determining past global temperatures, the strength and dimensions of Hadley cell circulation, and regional precipitation patterns (Brierley and Fedorov, 2010). However, a lack of SST data has made it difficult to determine the role of temperature gradients in shaping the climates of the late Miocene and Pliocene. To better characterize the evolution of meridional and zonal SST gradients in the subtropical North Pacific, we have generated alkenone SST reconstructions from ODP sites 1208, 1209, 1207, 1021, 1010 and DSDP Site 173. In conjunction with previously published data, these SST reconstructions indicate that the meridional and zonal SST gradients in the subtropical North Pacific were substantially reduced relative to modern during the late Miocene. The SST gradients subsequently strengthened through the Pliocene and Pleistocene epochs. Water vapor, cloud, and albedo feedbacks associated with these reduced late Miocene SST gradients may help to explain how warm late Miocene temperatures existed amidst levels of atmospheric pCO₂ that were near pre-industrial values.