Fluctuations of the oceanic Ca isotopic budget and environmental changes during highly dynamic transitions of the Cenozoic.

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IODP Expeditions 320 and 321 retrieved well preserved continuous core material from the equatorial eastern Pacific that provides an excellent archive for reconstructions of Cenozoic climate, a period which is known for its times of rapid and extreme climate variability. Besides reconstruction of temperature and salinity fluctuations, a main aim of this expedition was to enhance the understanding of carbon cycling, in particular the interplay of carbonate compensation depth (CCD), CaCO3-dissolution and productivity. Major and rapid changes in the Pacific CCD during the Cenozoic reveal strong dynamics in the oceanic C and Ca budget. The exact role of Ca is yet unclear; in particular the Ca sources for the massive pelagic CaCO3 deposition during CCD deepening need to be further constrained (continental input, shelf-weathering, uncompensated consumption of dissolved Ca). Based on microfossil records, we will reconstruct the fluctuations of δ44/40Ca of the paleo seawater, model the oceanic Ca budget during key periods of climate change, and better constrain the role of Ca in terms of input, redistribution and output during times of massive CCD changes and important stratigraphic transitions.