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

Abstract

Benthic foraminiferal oxygen isotopic (δ18O) and carbon isotopic (δ13C) 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 δ18O and δ13C compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to ∼80 Ma and tentatively to ∼110 Ma. First‐order variations in interbasinal isotopic gradients delineate transitions from interior ocean heterogeneity during the Late Cretaceous (>∼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 δ18O gradients in the early Oligocene and link the variations in interbasinal δ18O 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.