University of Bristol, United Kingdom

Constraining deep-ocean circulation during past greenhouse climatic periods, such as the Cretaceous, is important for understanding meridional heat transfer processes, controls on ocean anoxia, and the relative roles of climate and tectonics in determining paleocirculation patterns. Ocean circulation models for the Late Cretaceous and early Paleogene suggest that significant deep-water production occurred in the Southern Ocean, but cannot constrain when this process commenced or what the temporal relationship was between opening tectonic gateways and Late Cretaceous climatic cooling. Nd-isotope data obtained from biogenic apatite (fish teeth and bones) are presented from lower bathyal and abyssal sites in the South Atlantic and Indian Oceans. During the mid-Cretaceous, relatively radiogenic Nd-isotope values suggest that deep-water circulation in these basins was sluggish with inputs likely dominated by seawater-particle exchange processes and, possibly, easily weathered volcanic terranes. In the Campanian-Maastrichtian the Nd-isotopic composition of proto-Indian and South Atlantic deep waters became less radiogenic, suggesting the onset of deep-water formation in the Southern Ocean (Southern Component Water, SCW), consistent with Paleogene reconstructions and ocean circulation models. A combination of Southern Hemisphere cooling and the opening of tectonic gateways during the Campanian likely drove the onset of SCW.