Global deepwater circulation between 2.4 and 1.7Ma and its connection to the onset of Northern Hemisphere Glaciation

We have generated an early Pleistocene benthic isotopic record for the Ocean Drilling Program Site 807 (2804m) from the western equatorial Pacific. Between 2.4 and 1.7Ma, the benthic C-13 of this site and a few other deep Pacific sites was consistently higher than the Southern Ocean Site MV0502-4JC (4286m), pointing to a reversal relative to the current gradient and hence implying a different circulation regime. We reconstructed the deepwater mass distribution of this interval by using a collection of benthic isotope records from 15 Pacific and 10 Atlantic sites and a C-13-O-18 mixing model. A two-end-member mixing regime between the North Atlantic Deep Water (NADW) and the Antarctic Bottom Water (AABW), with properties very different from today, was identified. The Southern Ocean showed strong signs of stratification and AABW with low benthic C-13, but high O-18 values reached out to other basins only below similar to 4000m. In contrast, NADW ventilated most of the ocean interior, contributing similar to 70% to the Pacific Deep Water volumetrically. Our model results also reveal a strong remineralization effect at the bottom sites of the Pacific and the Atlantic, suggesting significant accumulation of respired carbon in the bottom water between 2.4 and 1.7Ma. We propose that such a circulation pattern was initiated by the reversal of salinity gradient between AABW and NADW from 3.0 to 2.4Ma, possibly linked to Antarctic sea ice expansion and reduced southward heat transport during the onset of Northern Hemisphere Glaciation.National Natural Science Foundation of China [41376043]SCI(E)ARTICLEbqhuang@pku.edu.cn111480-14973