Orbital control on marine biological productivity at the Oligocene-Miocene transition? Influence on global cooling and pCO2atm.

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During the first proposal period, we investigated the Oligocene-Miocene transition, a period of rapid cooling and Antarctic ice extension, at three of 5 ODP Sites planned in this study. The geological period is marked by a change in global carbon reservoirs, as reflected in a 1‰ positive carbon isotope excursion and distinct 400 kyrs cyclicity in the δ13C signal. In the project, we analyse whether open ocean biological productivity increased during the time interval at the Oligocene-Miocene boundary and led to the sequestration of additional and isotopically depleted carbon in marine sediments, and whether marine productivity variations match the δ13C cycles. First results from 3 Atlantic ODP locations confirm our hypotheses that marine productivity variations are orbitally forced and we could show that there is a link between marine productivty, climate change and pCO2atm via CO2 sequestration in sediments in the Atlantic Ocean. Here we apply for funds to conclude our investigation. In the work to come, we will extend the regional coverage of our records by analyzing two ODP sites in the Indo-Pacific ocean, that will allow to see whether the observed productivity increase at the Oligocene-Miocene transition is an Atlantic or a global phenomenon. This question will be the basis for modeling experiments of L.Francois. We further aim to reconstruct atmospheric carbon dioxide concentrations during the cooling period by means of an analysis of terrestrial flora and stomatal density.