Alkenone isotopes show evidence of active carbon concentrating mechanisms in coccolithophores as aqueous carbon dioxide concentrations fall below 7 µmolL-1

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Marcus Peter Sebastian Badger 


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 utilisation of carbon concentrating mechanisms also has the potential to overprint one proxy method by which ancient atmospheric CO2 is reconstructed using alkenone isotopes. Here I show that carbon concentrating mechanisms are likely used when aqueous carbon dioxide concentrations are below 7 µmolL-1. I use published alkenone based CO2 reconstructions from multiple sites over the Pleistocene, which allows comparison to be made with ice core CO2 records. Interrogating these records reveal that the relationship between proxy- and ice core- CO2 breaks down when local aqueous CO2 concentration falls below 7 µmolL-1. The recognition of this threshold explains why many alkenone based CO2 records fail to accurately replicate ice core CO2 records, and 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.



Biogeochemistry, Climate, Earth Sciences, Geochemistry, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics


alkenone, carbon concentrating mechanism, CO2, Coccolithophore, organic geochemistry, Pleistocene


Published: 2020-07-15 07:49

Last Updated: 2021-01-25 10:44

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CC BY Attribution 4.0 International

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This paper relies on previously published data.

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