In:
Biogeosciences, Copernicus GmbH, Vol. 19, No. 17 ( 2022-09-09), p. 4287-4304
Abstract:
Abstract. The accumulation of anthropogenic CO2 emissions in
the atmosphere has been buffered by the absorption of CO2 by the global
ocean, which acts as a net CO2 sink. The CO2 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 CO2 partial pressure (ΔpCO2) and the
CO2 flux on seasonal and inter-annual timescales in the South Atlantic
Ocean. Linear trends in ΔpCO2 and the CO2 flux were
calculated to identify key areas of change. Seasonally, changes in both the ΔpCO2 and CO2 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 ΔpCO2 can act as an indicator to identify drivers of
the CO2 flux. Inter-annually, the SST and biological contributions to
the CO2 flux in the subtropics were correlated with the multivariate
El Niño–Southern Oscillation (ENSO) index (MEI), which leads to a weaker (stronger) CO2 sink in El
Niño (La Niña) years. The 16-year time series identified significant trends in ΔpCO2 and CO2 flux; however, these trends were not always
consistent in spatial extent. Therefore, predicting the oceanic response to
climate change requires the examination of CO2 flux rather than ΔpCO2. Positive CO2 flux trends (weakening sink for atmospheric
CO2) were identified within the Benguela upwelling system, consistent
with increased upwelling and wind speeds. Negative trends in the CO2
flux (intensifying sink for atmospheric CO2) offshore into the South
Atlantic gyre were consistent with an increase in the export of nutrients
from mesoscale features, which drives the biological drawdown of CO2.
These multi-year trends in the CO2 flux indicate that the biological
contribution to changes in the air–sea CO2 flux cannot be overlooked
when scaling up to estimates of the global ocean carbon sink.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-19-4287-2022
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2158181-2
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