The influence of lithogenic material on particulate inorganic carbon measurements of coccolithophores in the Bay of Biscay

Following earlier data suggesting a decoupling between coccolithophore abundance and its suggested proxy, particulate inorganic carbon (PIC), we investigated this relationship in the Bay of Biscay (northwest European shelf), between December 2009 and July 2010. Coccolithophore abundance, coccolith calcite, and PIC were determined in surface waters (5-m depth) along a transect crossing the Bay. Emiliania huxleyi was the most abundant species of coccolithophore and the main contributor of coccolith calcite (55–64%). PIC ranged from 0.07 to 11.7 mmol C m−3, and coccolith calcite from 0.002 to 0.27 mmol C m−3. Total PIC exceeded coccolith calcite in all samples, with only ∼ 11% of the PIC attributed to coccoliths. Coccolithophores alone could not account for the PIC concentrations measured. Lithogenic particulate matter, with calcite and dolomite components, was observed in samples across the route and decoupled the relationship between PIC and coccolithophore abundance. Presence of lithogenic material and Mesozoic fossil coccoliths in the samples implies sediment resuspension. These findings question the suitability of PIC as a proxy for coccolithophore abundance and dynamics, particularly on or near continental shelves, where the resuspension and lateral transport of lithogenic calcite may decouple the potential relationship between PIC and coccolithophores.