Vanishing coccolith vital effects with alleviated carbon limitation

[摘要] By recreating a range of geologically relevant concentrations of dissolvedinorganic carbon (DIC) in the laboratory, we demonstrate that the magnitudeof the vital effects in both carbon and oxygen isotopes of coccolith calciteof multiple species relates to ambient DIC concentration. Under high DIClevels, all the examined coccoliths exhibit significantly reduced isotopicoffsets from inorganic calcite compared to the substantial vital effectsexpressed at low (preindustrial and present-day) DIC concentrations. Thesupply of carbon to the cell exerts a primary control on biologicalfractionation in coccolith calcite via the modulation of coccolithophoregrowth rate, cell size and carbon utilisation by photosynthesis andcalcification, altogether accounting for the observed interspecificdifferences between coccolith species. These laboratory observations supportthe recent hypothesis from field observations that the appearance ofinterspecific vital effect in coccolithophores coincides with the long-termNeogene decline of atmospheric CO₂ concentrations and bring furthervaluable constraints by demonstrating a convergence of all examined speciestowards inorganic values at high pCO₂ regimes. This study providespalaeoceanographers with a biogeochemical framework that can be utilised tofurther develop the use of calcareous nannofossils in palaeoceanography toderive sea surface temperature and pCO₂ levels, especially duringperiods of relatively elevated pCO₂ concentrations, as they prevailedduring most of the Meso-Cenozoic.

[学科分类] 地球化学与岩石