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The almost linear relationship between cadmium (Cd) and phosphate (PO4) in the oceans has been used extensively as a paleoproxy to investigate historical nutrient cycling. However, our limited understanding of oceanic Cd cycling and the mechanism of the Cd/PO4 relationship limits the reliability of this paleoproxy particularly in the surface waters of the Southern Ocean.

Our general goal is to measure Cd:PO4 ratios, and the Cd isotopic signature in waters, phytoplankton and other organisms in the marine food chain in the STC in order to confirm, for the first time, that the unusual Cd:PO4 properties of these waters are indeed controlled by anomalously high uptake of Cd by phytoplankton.

In addition, we will compare the observed Cd:PO4 properties and associated isotopic fractionation with comparable measurements in the adjacent ST, SA and Polar Front waters, thus covering a wide and globally significant range in currently-observed Cd:PO4 properties.

Shipboard and laboratory culture experiments, using both native and model organisms, will be conducted to determine the factors controlling Cd uptake and Cd isotopic fractionation in phytoplankton; in particular the relationship between Cd uptake rates and Fe status, Zn2+ bioavailability, pCO2 and CA activity and to determine the biogeochemical factors controlling this biological uptake. (Claudine Stirling, Keith Hunter, Russell Frew, Melanie Gault-Ringold, Toyin Adu, Afroza Bulbul)

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