SGER: Improving the Utility of Paleoproxies from Coccolith Chemistry: Calibration and Analytical Advances

Williams College, Williamstown MA

Investigators

Abstract

This SGER request funding to develop a new indicator of paleo-productivity of coccolithophorid algae, based on elemental (Sr/Ca) chemistry of coccolith calcite. Culture studies of a single species, Emiliania huxleyi, and analysis of coccoliths from sediment core tops in two transects across upwelling areas, suggest that coccolith Sr/Ca ratios vary with nutrient-stimulated changes in coccolithophorid growth rates. However, it is unclear whether these responses are widespread in the ocean, whether Sr/Ca variations in coccoliths are triggered by nutrient concentrations or the effect of nutrients on growth rate, whether a particular nutrient is responsible for this effect or if the state of nutrient limitation in general drives the response, and whether these responses are the same for different species. Calibration studies will be conducted through nutrient-limited culture of three additional species (Calcidiscus leptoporus, Coccolithus pelagicus, and Gephyrocapsa oceanica) and by analysis of time series plankton and sediment trap samples before, during, and after nutrient-stimulated bloom events. The very small amount of material collected in plankton samples and some sediment traps can be analyzed only through the development of a new ion probe (SIMS) technique capable of precise Sr/Ca measurements of individual or small groups of 10-20 picked coccoliths. In addition to improving calibration of the indicator, the SIMS ion probe technique will also benefit Sr/Ca analysis of downcore sediments for paleoproductivity determinations because it would eliminate elemental contributions from noncarbonate phases and permit determinations of Sr/Ca on pure samples of a given species or genera.