Technical note: No impact of alkenone extraction on foraminiferal stable isotope, trace element and boron isotope geochemistry

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.
