Geographically different oceanographic responses to global warming during the Cenomanian-Turonian interval and Oceanic Anoxic Event 2

Oceanic Anoxic Event (OAE) 2 coincided with the Cenomanian-Turonian boundary ~ 93.9 Ma, and was one of the two most prominent and globally significant of the major mid-Cretaceous OAEs. A confluence of global warming, major large igneous province volcanism, and intensified hydrologic cycling preconditioned the earth system for widespread preservation of organic matter during OAE2; however the ultimate necessary ingredient was enhanced nutrient availability in oceanic surface waters. Here we present new Cenomanian-Turonian interval seawater Neodymium isotope data from the proto-Indian Ocean that demonstrates increased water column stratification during the pre- and post-OAE2 interval, punctuated by a transient decrease in this stratification immediately prior to the onset of OAE2 recorded at Ocean Drilling Program Site 763. The direct oceanographic responses to climate change on both longer- and short-term time scales observed in this region are distinct from those recorded in the northern, tropical and southern Atlantic basins. The transient de-stratification of the water column in the eastern proto-Indian Ocean likely did not contribute to the accumulation of organic-rich sediments in the region, indicating that weathering and/or hydrothermal inputs promoted enhanced surface water nutrient levels and hence primary productivity.