Examining Carbon Acquisition and Allocation in Coccolithophores: Carbon Accounting to Understand Paleoproductivity.

Abstract:

It is increasingly clear that coccolithophores actively manage their growth and carbon allocation in response to changing environmental conditions. For example, recent work has identified carbon-concentrating mechanisms in coccolithophores—in which the organisms actively enhance the abundance of CO₂ in the chloroplast by pumping in bicarbonate—as the source of vital isotope effects in coccolith calcite. Understanding the record for and consequences of this management in the geologic record remains challenging. Here we examine the geometry and geochemistry of coccoliths in surface sediments from the deep ocean to relate these measurements to the modern growth environment in the surface ocean. In this core-top dataset that spans a wide range of environmental and oceanographic settings, we measure the size and thickness of coccolith plates, the trace metal and stable isotopic carbon in coccolith calcite, as well as determine alkenone biomarker fluxes and alkenone carbon isotopic composition (εp). This holistic approach aims to elucidate the carbon acquisition and allocation strategies employed by modern coccolithophores and ultimately provide a better framework for interpreting paleoproductivity. This method may provide insight into the growth rate and carbon allocation of coccoliths in the past, and may improve our understanding of the influence of atmospheric CO₂ on coccolithophore communities.