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Project A2

Long-term variability of ocean chemistry: Implications for deep-time palaeothermometry and the carbon cycle

Romi Nambiar (PhD)

Principal Investigators: David Evans, Wolfgang Müller, Jens Fiebig, Silke Voigt (Goethe University Frankfurt), Laura Cotton (Portsmouth University), James Rae (University of St Andrews)

Ocean chemistry has undergone substantial secular changes throughout the Phanerozoic as a result of changes in large-scale geological processes such as continental weathering, seafloor spreading, and dolomite formation. Given that these processes also play a critical role in controlling the global carbon cycle, seawater chemistry reconstructions are of key importance in understanding the drivers of long-term CO2 variation, and to understand the relationship and feedback mechanisms between geochemical processes and atmospheric CO2. In addition, precise and accurate measurement of seawater chemistry are a prerequisite of the accurate application of CaCO3-based palaeoclimatic proxies beyond the residence time of calcium.

Biologically precipitated marine carbonates are excellent archives that can preserve records of palaeoseawater composition. This project will establish novel geochemical proxies in order to better constrain past changes in seawater composition based on the shallow-dwelling larger benthic foraminifera (LBF), including detailed calibration based on Recent and cultured material. Proxies including trace element ratios (K/Ca, Mg/Ca, and Na/Ca) as well as several isotope systems (𝛿26Mg, 𝛿41K) will be investigated in LBF to produce new, precise reconstructions of seawater chemistry for the Meso/Cenozoic.