Identifying the biological control of the interannual and long-term variations in South Atlantic air-sea CO2 flux
The accumulation of anthropogenic CO 2 emissions in the atmosphere has been buffered by the global oceans absorbing CO 2 and acting as a net CO 2 sink. The CO 2 flux between the atmosphere and the ocean, that collectively results in the oceanic carbon sink, is spatially and temporally variable, and...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
| Published: |
2022
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/bg-2022-54 https://bg.copernicus.org/preprints/bg-2022-54/ |
| Summary: | The accumulation of anthropogenic CO 2 emissions in the atmosphere has been buffered by the global oceans absorbing CO 2 and acting as a net CO 2 sink. The CO 2 flux between the atmosphere and the ocean, that 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 interannual time scales 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 correlated with biological processes in the subpolar regions (south of 40° S). The Equatorial Atlantic indicated that biological processes were 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. Interannually, the SST and biological contributions to the CO 2 flux in the subtropics were correlated with the Multivariate ENSO Index (MEI) leading 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 magnitude or 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 atmospheric CO 2 ) offshore into the South Atlantic Gyre, were consistent with an increase in the export of nutrients in mesoscale features, which drive biological drawdown of CO 2 . These long-term trends in the CO 2 flux indicate that the biological contribution to changes in the air-sea CO 2 flux cannot be overlooked when scaling up to estimates of the global ocean carbon sink. |
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