[B-PT02_1AM1] Biocalcification and the Geochemistry of Proxies

[BPT02-01] TOWARDS THE NEXT GENERATION OF CARBONATE-BASED PROXIES

*de Nooijer Lennart Jan¹、豊福 高志²、Bijma Jelle³、ライヒャルト ゲルトヤン⁴ (1.NIOZ - Royal Netherlands Institute for Sea Research、2.海洋研究開発機構、3.Alfred Wegner Institute for Polar- and Marine Science、4.NIOZ/Utrecht university)

Reconstructions of past climate and environments are largely based on stable isotopes and trace element concentrations measured on fossil foraminiferal calcite. Element and isotope composition of foraminiferal calcite roughly reflects seawater composition and physical conditions, which in turn, is related to paleoceanographic parameters. Additional biological controls on test composition biases such correlations and needs to be corrected for when aiming at precise and accurate reconstructions. The various physiological processes involved in foraminiferal biomineralization have, however, different impacts on different elements and isotopes. For instance transmembrane transport of Ca-ions has a large impact on Mg fractionation (and hence the Mg-temperature proxy), whereas is has very little effect on Na/Ca ratios (a novel proxy for salinity). Many foraminifera-based proxies are thus impacted by more than one physiological process, which can only be corrected for by 1) quantification of the impacts of these processes (ion pumping, photosynthesis, pH regulation, etc) on calcitic element and isotope composition and 2) combine high-resolution multi-element and isotope analysis to simultaneously correct for these impacts. Since trace metals and isotopes are affected by multiple parameters, combining analyses not only makes reconstructions more robust, but also fundamentally more accurate.