20.11.2012: Joint FB2 / SFB 754 Seminar

Dienstag   um 10.00 c.t. (!), Hörsaal, Düsternbrooker Weg 20

Abstract

About 93.5 million years ago, the world’s oceans became depleted in oxygen during an event called the Cenomanian-Turonian oceanic anoxic event (OAE2). The spread and the causes of this event are still unclear. I compare data recording oxygenation of both seafloor (black shales) and sunlight ocean (green sulphur bacteria biomarkers) across OAE2 to biogeochemical simulations from a global Earth system model (GENIE). GENIE accounts for a warm climate ocean biogeochemistry (P, N, O2 cycles) and ocean/atmosphere carbon interactions of the Late Cretaceous. The model successfully reproduces the global distribution of low oxygen, suggesting a change in global anoxia from 5% to 50% at the height of the event. While the climate did warm at the anoxic event, the numerical modeling shows that oceanic temperature changes alone were not sufficient to reproduce the observed spread of anoxia. Instead, high levels of marine productivity appear to have driven the bulk of the oxygen depletion – the decay of these organisms at depth consumes oxygen. The productivity was potentially fuelled by the delivery of nutrients by enhanced continental weathering under greenhouse climate conditions and the recycling of phosphorus in increasingly anoxic sediments. The model also shows that palaeogeography contributes to pre-condition anoxia in the North Atlantic basin of the Late Cretaceous.