Abstract
Abstract. The globally integrated sea–air anthropogenic carbon dioxide (CO2) flux from 1990 to 2009 is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr−1. The interannual variability in the sea–air flux is largely driven by large-scale climate re-organizations and is estimated at 0.2 Pg C yr−1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr−1) decade−1 to −0.50 (Pg C yr−1) decade−1 for the two decades under investigation. The OBGCMs and the data-based sea–air CO2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.
Highlights
The CryosphereThe global analysis of sea–air carbon dioxide (CO2) fluxes is part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project that assesses the input of anthropogenic CO2 into the atmosphere (Andres et al, 2012) and the fluxes of carbon between the ocean, atmosphere and terrestrial biosphere from 1990 to 2009
The fluxes are extrapolated to include the coastal regions by scaling to the increased surface area assuming that the fluxes in the coastal regions are the same as for the adjacent region used in the ocean inversion project (OIP)
An update of the sea–air CO2 flux based on the pCO2 climatology of Takahashi et al (2009) (T-09), and the average 20 yr cross-calibrated multiplatform (CCMP) wind product, yields an anthropogenic CO2 flux of -2.0 Pg C yr−1 with an uncertainty of 0.6 Pg C yr−1
Summary
The global analysis of sea–air carbon dioxide (CO2) fluxes is part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project that assesses the input of anthropogenic CO2 into the atmosphere (Andres et al, 2012) and the fluxes of carbon between the ocean, atmosphere and terrestrial biosphere from 1990 to 2009. R. Wanninkhof et al.: Global ocean carbon uptake: magnitude, variability and trends comprehensive assessments of carbon flows between the major labile reservoirs, data contributions and model output are provided on volunteer basis and for a set time period (1990– 2009). Seasonal changes of approximately 10 ppm over the Northern Hemisphere oceans are driven by the photosynthesis and respiration cycle of the terrestrial biosphere. Half of the anthropogenic CO2 emissions accumulate in the atmosphere with the remainder taken up by the ocean and the terrestrial biosphere
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