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https://doi.org/10.5194/bg-2018-509
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-509
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Dec 2018

Research article | 17 Dec 2018

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

Sensitivity of atmospheric CO2 to regional variability in particulate organic matter remineralization depths

Jamie D. Wilson1,2, Stephen Barker2, Neil R. Edwards3, Philip B. Holden3, and Andy Ridgwell1,4 Jamie D. Wilson et al.
  • 1BRIDGE, School of Geographical Sciences, University of Bristol, UK
  • 2School of Earth and Ocean Sciences, Cardiff University, UK
  • 3School of Environment, Earth and Ecosystems, Open University, UK
  • 4Department of Earth Sciences, University of California, Riverside, USA

Abstract. The concentration of CO2 in the atmosphere is sensitive to changes in the depth at which sinking particulate organic matter is remineralised: often described as a change in the exponent "b" of the Martin curve. Sediment trap observations from deep and intermediate depths suggest there is a spatially heterogeneous pattern of b, particularly varying with latitude, but disagree over the exact spatial patterns. Here we use a biogeochemical model of the phosphorus cycle coupled with a steady-state representation of ocean circulation to explore the sensitivity of preformed phosphate and atmospheric CO2 to spatial variability in remineralisation depths. A Latin hypercube sampling method is used to simultaneously vary the Martin curve indepedently within 15 different regions, as a basis for a regression-based analysis used to derive a quantitative measure of sensitivity. Approximately 30% of the sensitivity of atmospheric CO2 to changes in remineralisation depths is driven by changes in the Subantarctic region (36°S to 60°S), simliar in magnitude to the Pacific basin despite the much smaller area and lower productivity. Overall, the absolute magnitude of sensitivity is controlled by export production but the relative spatial patterns in sensitivity are predominantly constrained by ocean circulation pathways. The high sensitivity in the Subantarctic regions is driven by a combination of high export production and the high connectivity of these regions to regions important for the export of preformed nutrients such as the Southern Ocean and North Atlantic. Overall, regionally varying remineralisation depths contribute to variability in CO2 of between ±5–15 ppm relative to a global mean change in remineralisation depth. Future changes in the environmental and ecological drivers of remineralisation, such as temperature and ocean acidification, are expected to be most significant in the high latitudes where CO2 sensitivity to remineralisation is also highest. The importance of ocean circulation pathways to the high sensitivity in Subantarctic regions also has significance for past climates given the importance of circulation changes in the Southern Ocean.

Jamie D. Wilson et al.
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Jamie D. Wilson et al.
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Short summary
The remains of plankton rain down from the surface ocean to the deep ocean acting to store CO2 in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. We found that the amount of CO2 stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean may be most impacted by climate change, the amount of CO2 they store in the deep ocean could also be affected.
The remains of plankton rain down from the surface ocean to the deep ocean acting to store CO2...
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