Alkenone isotopes show evidence of active carbon concentrating mechanisms in coccolithophores as aqueous carbon dioxide concentrations fall below 7 µmol L −1

Badger, Marcus P. S.

Coccolithophores and other haptophyte algae acquire the carbon required for metabolic processes from the water in which they live. Whether carbon is actively moved across the cell membrane via a carbon concentrating mechanism, or passively through diffusion, is important for haptophyte biochemistry. The possible utilization of carbon concentrating mechanisms also has the potential to over-print one proxy method by which ancient atmospheric inline-formulaCO2 concentration is reconstructed using alkenone isotopes. Here I show that carbon concentrating mechanisms are likely used when aqueous carbon dioxide concentrations are below 7 inline-formulaµmol Linline-formula−1. I compile published alkenone-based inline-formulaCO2 reconstructions from multiple sites over the Pleistocene and recalculate them using a common methodology, which allows comparison to be made with ice core inline-formulaCO2 records. Interrogating these records reveals that the relationship between proxy inline-formulaCO2 and ice core inline-formulaCO2 breaks down when local aqueous inline-formulaCO2 concentration falls below 7 inline-formulaµmol Linline-formula−1. The recognition of this threshold explains why many alkenone-based inline-formulaCO2 records fail to accurately replicate ice core inline-formulaCO2 records, and it suggests the alkenone proxy is likely robust for much of the Cenozoic when this threshold was unlikely to be reached in much of the global ocean.

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Badger, Marcus P. S.: Alkenone isotopes show evidence of active carbon concentrating mechanisms in coccolithophores as aqueous carbon dioxide concentrations fall below 7 µmol L−1. 2021. Copernicus Publications.

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Rechteinhaber: Marcus P. S. Badger

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