Simultaneous measurement of boron isotopes and the boron/calcium ratio in biogenic marine carbonates as a tool to reconstruct the marine carbonate system

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About one third of anthropogenically emitted CO2 dissolves in the oceans. This leads to a decrease in pH and is commonly termed “ocean acidification”. In order to understand how the ocean, including its eco-system, will respond to acidification, much can be learned from reconstructions of the ocean carbonate chemistry in the past history of the Earth. The simultaneous measurement of the boron isotopic composition ((11B) and of the boron to calcium ratio (B/Ca) on carbonates , such as foraminifera or corals, would allow to determine ocean “acidity”. In this study, we propose to, investigate the B incorporation using both, inorganic precipitation experiments and foraminiferal culture experiments in order to develop a mechanistic understanding of the proxy relationships. Then we will apply the calibrations to the fossil record. The simultaneous measurement of two proxies on the same sample (diachronous) will allow us to reconstruct changes in seasonality, which is one of the most important targets for present day climate understanding. We will use a sediment core from tha Arabian Sea to reconstruct changes in seasonality of the carbonate system (related to the monsoon activity) during the last glacial-interglacial cycle.