Alkenone isotopes show evidence of active carbon concentrating mechanisms in coccolithophores as aqueous carbon dioxide concentrations fall below 7 μmol L−1
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....
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| Format: | Text |
| Language: | English |
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2020
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| Online Access: | https://doi.org/10.5194/bg-2020-356 https://bg.copernicus.org/preprints/bg-2020-356/ |
| Summary: | 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 over-print one proxy method by which ancient atmospheric CO 2 is reconstructed using alkenone isotopes. Here I show that carbon concentrating mechanisms are likely used when aqueous carbon dioxide concentrations are below 7 μmol L −1 . I use published alkenone based CO 2 reconstructions from multiple sites over the Pleistocene, which allows comparison to be made with ice core CO 2 records. Interrogating these records reveal that the relationship between proxy- and ice core-CO 2 breaks down when local aqueous CO 2 concentration falls below 7 μmol L −1 . The recognition of this threshold explains why many alkenone based CO 2 records fail to accurately replicate ice core CO 2 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. |
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