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Title: Stable carbon isotope ratios of pristine carbohydrates preserved within nannofossil calcite
The geochemical characterization of phytoplankton-derived organic compounds found in marine sediments has been widely used to reconstruct atmospheric pCO2 thoughout the Cenozoic. This is possible owing to a well-established relationship between the carbon isotope ratios of phytoplankton biomass and CO2 concentration in the ambient seawater. An ideal molecular target for such proxy reconstructions would be degradation resistant on geologic timescales and unambiguously associated with known, experimentally tractable, organisms, so that species-specific models can be developed, calibrated, and applied to appropriate material. However, existing organic matter targets do not quite meet these criteria, primarily owing to ambiguity in the source species of recalcitrant compounds in deep time. Here we explore the potential of a novel organic carbon target for isotopic analysis: acidic polysaccharides extracted from the calcite plates (coccoliths) that are produced by all calcifying haptophytes. Carbohydrates are usually rapidly remineralized in sediments, but coccolith-associated polysaccharides (CAPs) are mechanically protected from diagenesis within the coccolith calcite lattice. Coccoliths can be taxonomically separated by size and identified, often to species level, prior to CAP extraction, providing a species-specific record. Coccolith morphology and composition are important additional sources of information, which are then unambiguously associated with the extracted CAPs. We find that carbon isotope ratios of CAPs changed in response to the environmental changes associated with a glacial cycle, which we attribute to temperature-driven changes in average growth rate. Once the underlying biosynthetic processes and the associated isotope effects are better understood, this archive of pristine organic matter has the potential to provide insight into phytoplankton growth rates and atmospheric pCO2 far beyond the Cenozoic, to when the first coccolithophores inhabited the surface ocean over 200 million years ago.  more » « less
Award ID(s):
2100537
PAR ID:
10541227
Author(s) / Creator(s):
; ; ;
Editor(s):
Catalano, Jeffrey; Passey, Benjamin H
Publisher / Repository:
Elsevier
Date Published:
Journal Name:
Geochimica et Cosmochimica Acta
ISSN:
0016-7037
Subject(s) / Keyword(s):
Carbon isotopes CO2 proxies Acidic polysaccharides Coccolithophores Alkenones
Format(s):
Medium: X Size: n/a Other: .pdf
Size(s):
n/a
Sponsoring Org:
National Science Foundation
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