Investigation of surface ocean carbon distribution using large global dataset

Abstract

Despite considerable progress in our understanding of marine biogeochemistry there are many unknowns. We have probably identified all the major processes (physical and geological as well as biological and chemical) influencing the carbon cycle, but the exact nature and magnitude of the different impacts remain to be fully determined. This study aims at taking advantage of a new wealth of carbonate system observational data coming out of the expansion of research into ocean carbon uptake and ocean acidification. The release of new large datasets (e.g., GLODAPv2: Global Ocean Data Analysis Project version 2) provides an opportunity to make advances in our fundamental understanding (Chapter 2). I compare the distributions of carbon, and some other related parameters (e.g., sea surface temperature, total alkalinity, and nutrients in Chapter 3; dissolved oxygen in Chapter 4) in the surface open ocean to expectations based on current understanding, and derive new understanding (including improved quantification and geographical localization of key processes) from investigation of discrepancies. To contribute to these goals, I have firstly improved the understanding of the drivers of the global open ocean surface DIC latitudinal gradient (Chapter 3), demonstrating that sea surface temperature effects on CO2 solubility and high-latitude upwelling (particularly in the Southern Ocean) are the two major factors. I have also clarified the different effects of upwelling depending on the timescale: the short-term effect of upwelling acts immediately, accounting for 98% of the observed nDIC latitudinal gradient; the long-term effect of upwelling acts on timescales of months to a year, accounting for 33% of the observed nDIC latitudinal gradient. Secondly, I have combined and compared the coupled changes in the surface ocean dissolved O2 and CO2 (Chapter 4) by developing a new technique, namely Carbon and Oxygen Relative to Saturation (CORS). By using this technique, I have identified regions and periods where processes are driving O2 and CO2 away from their equilibrium with the atmosphere. Thirdly, I have used a surface carbon balance calculation (by taking the Drake Passage as an example) to test the claim, based on SOCCOM float data, of significant rates of CO2 outgassing from the high-latitude Southern Ocean (Chapter 5). I have shown the implausibility of this finding in the Drake Passage, but with limitation in extrapolating my result to the broader Southern Ocean. I have also applied the CORS technique to float-measured/estimated O2 and CO2 data, showing that CORS is capable of distinguishing suspect data from credible data.

More information

Identifiers

ORCID for Yingxu Wu: orcid.org/0000-0002-7847-6215

ORCID for Toby Tyrrell: orcid.org/0000-0002-1002-1716

Catalogue record

Export record