Evolution of the Oceanic 13C Suess Effect in the Southeastern Indian Ocean Between 1994 and 2018. (19th April 2021)

• Record Type: Journal Article
• Authors: Williams, Thomas J.; Wagner, Amy J.; Sikes, Elisabeth L.; Martin, Ellen E.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-19
• Subjects: carbon cycle -- chemical oceanography -- Indian Ocean -- Southern Ocean -- stable carbon isotopes -- Suess effect; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009402
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The decrease in δ 13 C of dissolved inorganic carbon (δ 13 CDIC ) owing to uptake of anthropogenic CO2 (the oceanic 13 C Suess effect) in the Southeastern Indian Ocean over the last decade was calculated using an extended multiparameter linear regression technique. Samples collected on the CROCCA‐2S (Coring to Reconstruct Ocean Circulation and Carbon Dioxide Across 2 Seas) cruise in November–December 2018 were compared to samples from the CLIVAR (Climate and Ocean: Variability, Predictability, and Change) and OISO (Océan Indien Service d'Observation) programs from 2007 to 2009. Surface ocean δ 13 CDIC decreased by an average of −0.53 ± 0.04‰ across this period, at an average rate of −0.053 ± 0.004‰ per year. This rate of δ 13 CDIC change is an increase from −0.021 ± 0.024‰ per year between 1994 and 2008. We find that the interior water mass most impacted by the oceanic 13 C Suess effect between 2008 and 2018 was Subantarctic Mode Water (SAMW), within which δ 13 CDIC decreased by −0.044 ± 0.002‰ per year. Using previously published relationships between the oceanic 13 C Suess effect and anthropogenic carbon, we estimate the annual storage of anthropogenic carbon within SAMW in the southeastern Indian Ocean has increased from ∼2.0 ± 0.2 μmol/kg per year between 1994 and 2008 to 5.5 ± 0.6 μmol/kg per year between 2008 and 2018. Plain Language Summary: We measured the ratio of carbon isotopes within seawater to identify the amount of atmospheric carbon sourced from the burning of biomass and fossil fuels which has been absorbed into the southeastern Indian Ocean over the last decade. We find that the rate at which this human‐sourced carbon is being absorbed by the ocean has increased up to 3‐fold over this time period, when compared with the period between 1994 and 2008. Key Points: The oceanic Suess effect disproportionately affects Subantarctic Mode Water (SAMW), within which δ 13 C has decreased by c. −0.44‰ from 2008 to 2018 The observed δ 13 C change of −0.044‰/year represents roughly a 3‐fold increase in the rate of δ 13 C change compared to 1994–2008 Between 2008 and 2018 SAMW in the SE Indian Ocean absorbed 5.5 ± 0.6 μmol/kg −1 of anthropogenic carbon per year