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Abstract This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation‐based products. The mean sea‐air CO2flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr−1based on an ensemble of reconstructions of the history of sea surface pCO2(pCO2products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at −2.1 ± 0.3 PgC yr−1by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr−1of terrestrially derived CO2, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO2products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr−1 decade−1, while biogeochemical models and inverse models diagnose an anthropogenic CO2‐driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr−1 decade−1, respectively. This implies a climate‐forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate‐driven variability exceeding the CO2‐forced variability by 2–3 times. These results suggest that anthropogenic CO2dominates the ocean CO2sink, while climate‐driven variability is potentially large but highly uncertain and not consistently captured across different methods.
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Atmospheric CO 2 and Sea Surface Temperature Variability Cannot Explain Recent Decadal Variability of the Ocean CO 2 Sink
Abstract The ocean is one of the most important sinks for anthropogenic CO2emissions. Here, I use an ocean circulation inverse model (OCIM), ocean biogeochemical models, and pCO2interpolation products to examine trends and variability in the oceanic CO2sink. The OCIM quantifies the impacts of rising atmospheric CO2, changing sea surface temperatures, and gas transfer velocities on the oceanic CO2sink. Together, these effects account for an oceanic CO2uptake of 2.2 ± 0.1 PgC yr−1from 1994 to 2007, and a net increase in the oceanic carbon inventory of 185 PgC from 1780 to 2020. However, these effects cannot account for the majority of the decadal variability shown in data‐based reconstructions of the ocean CO2sink over the past 30 years. This implies that decadal variability of the ocean CO2sink is predominantly driven by changes in ocean circulation or biology that act to redistribute both natural and anthropogenic carbon in the ocean.
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- Award ID(s):
- 1948955
- PAR ID:
- 10381067
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 7
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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