Abstract. Recent advances in geochemical techniques mean that several robust proxies now exist to determine the past carbonate chemistry of the oceans. Foraminiferal δ11B and alkenone carbon isotopes allow us to reconstruct sea-surface pH and pCO2 respectively, and the ability to apply both proxies to the same sediment sample would give strongly paired datasets and reduce sample waste. However, no studies to date have examined whether the solvents and extraction techniques used to prepare alkenones for analysis also impact the geochemistry of foraminifera within those sediments. Here we examine six species pairs of planktic foraminifera, with half being taken from non-treated sediments and half being taken from sediments where alkenones have been extracted. We look for visual signs of contrasting preservation and compare analyses of δ18O, δ13C, δ11B and trace elements (Li, B, Na, Mn, Mg, Sr, and U/Ca). We find no consistent geochemical offset between the treatments, and excellent agreement in δ11B measurements between them. Our results show that boron isotope reconstructions of pH in foraminifera from alkenone-extracted sediments can be applied with confidence.
Rising atmospheric CO 2 and falling ocean pH place an urgency on our efforts to understand the impact of CO 2 on Earth's ecosystems and climate Studies of past perturbations of Earth's carbon reservoirs and climate-ranging from glacialinterglacial cycles to mass extinction events-may provide valuable insights, but they require the ability to reconstruct changes in ocean-atmosphere CO 2 chemistry in Earth's past. Here, we provide an overview of the boron isotope pH proxy in marine carbonates and how it can be applied to reconstruct past ocean pH and atmospheric CO 2 .
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