Temperature Gradients Across the Pacific Ocean During the Middle Miocene

Sea surface temperatures (SSTs) of the tropical Pacific Ocean exert powerful controls on regional and global climates. Previous studies have suggested that during warm climate phases, east-west temperature gradient collapsed. To date, there has been no high-resolution reconstruction sea conditions in both east west Miocene Climate Optimum (MCO) across middle transition (MMCT); therefore, our understanding mean oceanographic state this major climatic shift is limited. Here, we present new SST reconstructions for eastern (15.5–13.3 Ma) which show a clear ∼4°C warmest interval Neogene, implying processes produce modern were active. There MMCT indicating was not impacted by cooling ice growth. We find 2°C equatorial Pacific, lags benthic foraminiferal δ18O positive 150 kyr, did decrease synchronously with expansion Antarctic sheet. Reconstructed variations composition seawater, determined combining Mg/Ca records, reveal freshening after 13.8 Ma, suggesting changes hydrological cycle fronts response to icehouse regime.