Oceanic sources, sinks, and transport of atmospheric CO₂

• Published in: Global Biogeochemical Cycles
• Other Authors: Gruber, Nicolas (author), Gloor, Manuel (author), Mikaloff Fletcher, Sara (author), Doney, Scott (author), Dutkiewicz, Stephanie (author), Follows, Michael (author), Gerber, Markus (author), Jacobson, Andrew (author), Joos, Fortunat (author), Lindsay, Keith (author), Menemenlis, Dimitris (author), Mouchet, Anne (author), Müller, Simon (author), Sarmiento, Jorge (author), Takahashi, Taro (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2009
• Subjects: Air-sea carbon flux; Carbon flux; Pacific; Southern Ocean
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-002-634; https://doi.org/10.1029/2008GB003349

We synthesize estimates of the contemporary net air-sea CO₂ flux on the basis of an inversion of interior ocean carbon observations using a suite of 10 ocean general circulation models (Mikaloff Fletcher et al., 2006, 2007) and compare them to estimates based on a new climatology of the air-sea difference of the partial pressure of CO₂ (pCO₂) (Takahashi et al., 2008). These two independent flux estimates reveal a consistent description of the regional distribution of annual mean sources and sinks of atmospheric CO₂ for the decade of the 1990s and the early 2000s with differences at the regional level of generally less than 0.1 Pg C a⁻¹. This distribution is characterized by outgassing in the tropics, uptake in midlatitudes, and comparatively small fluxes in thehigh latitudes. Both estimates point toward a small (∼ -0.3 Pg C a⁻¹) contemporary CO₂ sink in the Southern Ocean (south of 44°S), a result of the near cancellation between a substantial outgassing of natural CO₂ and a strong uptake of anthropogenic CO₂. A notable exception in the generally good agreement between the two estimates exists within the Southern Ocean: the ocean inversion suggests a relatively uniform uptake, while the pCO₂-based estimate suggests strong uptake in the region between 58°S and 44°S, and a source in the region south of 58°S. Globally and for a nominal period between 1995 and 2000, the contemporary net air-sea flux of CO₂ is estimated to be -1.7 ± 0.4 Pg C a⁻¹ (inversion) and -1.4 ± 0.7 Pg C a⁻¹ (pCO₂-climatology), respectively, consisting of an outgassing flux of river-derived carbon of ∼+0.5 Pg C a⁻¹, and an uptake flux of anthropogenic carbon of −2.2 ± 0.3 Pg C a⁻¹ (inversion) and -1.9 ± 0.7 Pg C a⁻¹ (pCO₂-climatology). The two flux estimates also imply a consistent description of the contemporary meridional transport of carbon with southward ocean transport throughout most of the Atlantic basin, and strong equatorward convergence in the Indo-Pacific basins. Both transport estimates suggest a small hemispheric asymmetry with a ...