Ocean overturning since the Late Cretaceous: Inferences from a new benthic foraminiferal isotope compilation

Benthic foraminiferal oxygen isotopic (delta O-18) and carbon isotopic (delta C-13) trends, constructed from compilations of data series from multiple ocean sites, provide one of the primary means of reconstructing changes in the ocean interior. These records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records. We present new benthic foraminiferal delta O-18 and delta C-13 compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to similar to 80 Ma and tentatively to similar to 110 Ma. First-order variations in interbasinal isotopic gradients delineate transitions from interior ocean heterogeneity during the Late Cretaceous (>similar to 65 Ma) to early Paleogene (35-65 Ma) homogeneity and a return to heterogeneity in the late Paleogene-early Neogene (35-0 Ma). We propose that these transitions reflect alterations in a first-order characteristic of ocean circulation: the ability of winds to make water in the deep ocean circulate. We document the initiation of large interbasinal delta O-18 gradients in the early Oligocene and link the variations in interbasinal delta O-18 gradients from the middle Eocene to Oligocene with the increasing influence of wind-driven mixing due to the gradual tectonic opening of Southern Ocean passages and initiation and strengthening of the Antarctic Circumpolar Current. The role of wind-driven upwelling, possibly associated with a Tethyan Circumequatorial Current, in controlling Late Cretaceous interior ocean heterogeneity should be the subject of further research.