Supplementary materials for PhD thesis - "The controls on biogeochemical proxies and shell calcification in modern planktonic foraminifera"

This dataset comprises the files contained on a CD-ROM which was attached to the thesis when it was submitted in 2015. It was uploaded to ORDO in 2025 for preservation purposes. For more information, please refer to the thesis  “The controls on biogeochemical proxies and shell calcification in modern planktonic foraminifera” via ORO. Abstract: Planktonic foraminifera (PF) shell biogeochemistry can be used to reconstruct past oceanic and climatic changes, but the influence of other environmental and biological interactions can compromise their use as reliable proxies. This study aims to develop their use as biogeochemical proxies by determining the primary controls on shell flux, morphometric parameters and geochemical variability in modern PF, and apply this to understand how recent anthropogenic ocean acidification has affected their calcification since the ‘pre-industrial’.<br><br>By using PF from a biweekly sediment-trap time series (years 1998-2000 &amp; 2008-2010), with nearby monthly hydrographic data from the Sargasso Sea in the oligotrophic North Atlantic, this study shows that PF contribute up to -40% of the calcium carbonate flux in the Sargasso Sea during the winter months when the mixed layer is deepest. Therefore factors affecting the mixed layer dynamics such as the North Atlantic Oscillation could potentially regulate PF and carbonate flux on decadal timescales. Shell calcification, estimated from shell morphometries of two species (<i>Globigerinoides ruber</i> (pink) and <i>Orbulina universa</i>) is primarily controlled by temperature and [CO₃^2-], rather than dependent on optimum growth conditions. Biological and calcification processes appear to significantly affect the trace element concentrations in PF; this study shows for the first time that calcification rate controls boron incorporation whereas growth processes appear to control uranium incorporation in <i>G. ruber</i> (p), <i>O. universa</i> and <i>Globorotalia truncatulinoides</i> (non-encrusted), suggesting that B/Ca and U/Ca are not reliable palaeo-pH proxies. The separation of morphotypes could vastly improve the accuracy of all PF trace element calibrations. Finally, by comparing the calcification of PF in the modern sediment trap samples with ‘pre-industrial’ surface sediments collected nearby in 1875, this study reports a 17-23% reduction in shell calcification of <i>O. universa</i> and <i>Globorotalia inflata</i>, caused by anthropogenic ocean acidification in the subtropical gyre. This inhibition in calcification is equivalent to a -24 μmol/kg reduction in [CO₃^2-], consistent with the modelled [C032] reduction since the ‘pre-industrial’.