Identifying the biological control of the annual and multi-year variations in South Atlantic air–sea CO 2 flux

• Published in: Biogeosciences
• Main Authors: D. J. Ford, G. H. Tilstone, J. D. Shutler, V. Kitidis
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; South Atlantic Ocean
• Online Access: https://doi.org/10.5194/bg-19-4287-2022; https://doaj.org/article/31fe405059fc484ab1264926b43069da

The accumulation of anthropogenic CO 2 emissions in the atmosphere has been buffered by the absorption of CO 2 by the global ocean, which acts as a net CO 2 sink. The CO 2 flux between the atmosphere and the ocean, which collectively results in the oceanic carbon sink, is spatially and temporally variable, and fully understanding the driving mechanisms behind this flux is key to assessing how the sink may change in the future. In this study a time series decomposition analysis was applied to satellite observations to determine the drivers that control the sea–air difference of CO 2 partial pressure ( Δ p CO 2 ) and the CO 2 flux on seasonal and inter-annual timescales in the South Atlantic Ocean. Linear trends in Δ p CO 2 and the CO 2 flux were calculated to identify key areas of change. Seasonally, changes in both the Δ p CO 2 and CO 2 flux were dominated by sea surface temperature (SST) in the subtropics (north of 40 ∘ S) and were correlated with biological processes in the subpolar regions (south of 40 ∘ S). In the equatorial Atlantic, analysis of the data indicated that biological processes are likely a key driver as a response to upwelling and riverine inputs. These results highlighted that seasonally Δ p CO 2 can act as an indicator to identify drivers of the CO 2 flux. Inter-annually, the SST and biological contributions to the CO 2 flux in the subtropics were correlated with the multivariate El Niño–Southern Oscillation (ENSO) index (MEI), which leads to a weaker (stronger) CO 2 sink in El Niño (La Niña) years. The 16-year time series identified significant trends in Δ p CO 2 and CO 2 flux; however, these trends were not always consistent in spatial extent. Therefore, predicting the oceanic response to climate change requires the examination of CO 2 flux rather than Δ p CO 2 . Positive CO 2 flux trends (weakening sink for atmospheric CO 2 ) were identified within the Benguela upwelling system, consistent with increased upwelling and wind speeds. Negative trends in the CO 2 flux (intensifying sink for ...