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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/bg-2019-158
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-158
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 May 2019

Submitted as: research article | 03 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Validation of carbon isotope fractionation in algal lipids as a PCO2 proxy using a natural CO2 seep (Shikine Island, Japan)

Caitlyn R. Witkowski1, Sylvain Agostini2, Ben P. Harvey2, Marcel T. J. van der Meer1, Jaap S. Sinninghe Damste1,3, and Stefan Schouten1,3 Caitlyn R. Witkowski et al.
  • 1Department of Marine Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research, Den Burg (Texel), 1790AB, The Netherlands
  • 2Shimoda Marine Research Center, University of Tsukuba, Shimoda, 415-0025, Japan
  • 3Department of Geosciences, Utrecht University, Utrecht, 3508 TA, The Netherlands

Abstract. Carbon dioxide concentrations in the atmosphere play an integral role in many earth system dynamics, including its influence on global temperature. Long-term trends can provide insights into these dynamics though reconstructing long-term trends of atmospheric carbon dioxide (expressed in partial pressure; PCO2) remains a challenge in paleoclimatology. One promising approach for reconstructing past PCO2 utilizes isotopic fractionation associated with CO2-fixation during photosynthesis into organic matter (Ɛp). Previous studies have focused primarily on testing estimates of Ɛp derived from species-specific alkenone compounds in laboratory cultures and mesocosm experiments. Here, we analyze Ɛp derived from general algal compounds from sites at a CO2 seep near Shikine Island (Japan), a natural environment with CO2 concentrations ranging from ambient (ca. 310 µatm) to elevated (ca. 770 µatm). We observed strong, consistent δ13C shifts in several algal biomarkers from a variety of sample matrices over the steep CO2 gradient. Of the three general algal biomarkers explored here, namely loliolide, phytol, and cholesterol, Ɛp positively correlates with PCO2 in agreement with Ɛp theory and previous culture studies. PCO2 reconstructed from the Ɛp of general algal biomarkers show the same trends throughout, as well as the correct control values, but with lower absolute reconstructed values than the measured values at the elevated PCO2 sites. Our results show that naturally-occurring CO2 seeps may provide useful testing grounds for PCO2 proxies and that general algal biomarkers show promise for reconstructing past PCO2.

Caitlyn R. Witkowski et al.
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Status: final response (author comments only)
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Caitlyn R. Witkowski et al.
Caitlyn R. Witkowski et al.
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Latest update: 22 Sep 2019
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Short summary
In this manuscript, we test a new approach for testing reconstructing PCO2 from the stable carbon isotopic fractionation that occurs during photosynthesis using general algal biomarkers across a modern, naturally-occurring high PCO2 gradient from a CO2 seep. We show that general algal biomarker-derived reconstructions of PCO2 does indeed increase with increasing proximity to the CO2 seep.
In this manuscript, we test a new approach for testing reconstructing PCO2 from the stable...
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