Riverine-driven interhemispheric transport of carbon

• Published in: Global Biogeochemical Cycles
• Main Authors: Aumont, Olivier, Orr, J.C., Monfray, P., Ludwig, Wolfgang, Amiotte-Suchet, P., Probst, J.L.
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie dynamique et de climatologie (LODYC), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Centre de formation et de recherche sur l'environnement marin (CEFREM), Université de Perpignan Via Domitia (UPVD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Microbiologie des sols-GéoSol (GéoSol), Institut National de la Recherche Agronomique (INRA)-Université de Bourgogne (UB), Laboratoire des Mécanismes et Transfert en Géologie (LMTG), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), This work was funded by the Environment and Climate Programme of the European Community (ESCOBA-Ocean contract ENV4-CT95-0132 and ESCOBA-Biosphere contract ENVCT95-0111).
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2001
• Subjects: Meteorologie; Hydrologie; Transfert; [SDV.BBM.BC]Life Sciences [q-bio]/Biochemistry; Molecular Biology/Biochemistry [q-bio.BM]; North Pole; South Pole; South pole
• Online Access: https://hal.inrae.fr/hal-02677020; https://hal.inrae.fr/hal-02677020/document; https://hal.inrae.fr/hal-02677020/file/aum1.pdf; https://doi.org/10.1029/1999GB001238

International audience Controversy surrounds the role of the ocean in interhemispheric transport of carbon. On one hand, observations in the atmosphere and in the ocean both seem to imply that the preindustrial ocean transported up to 1 Pg C yr($^{-1}$) from the Northern to the Southern Hemisphere. On the other hand, three dimensional (3-D) ocean models suggest that global interhemispheric transport of carbon is near zero. However, in this debate, there has been a general neglect of the river carbon loop. The river carbon loop includes (1) uptake of atmospheric carbon due to inorganic and organic erosion on land, (2) transport of carbon by rivers, (3) subsequent transport of riverine carbon by the ocean, and (4) loss of riverine carbon back to the atmosphere by air-sea gas exchange. Although carbon fluxes from rivers are small compared to natural fluxes, they have the potential to contribute substantially to the net air-sea fluxes of CO$_2$. For insight into this dilemma, we coupled carbon fluxes from a global model of continental erosion to a 3-D global carbon-cycle model of the ocean. With rivers, total southward interhemispheric transport by the ocean increases from 0.1 to 0.35 $\pm$0.08 Pg Cyr($^{-1}$), in agreement with oceanographic observations. Resulting air-sea fluxes of riverine carbon and uptake of CO$_2$ by land erosion were installed as boundary conditions in a 3-D atmospheric model. The assymetry in these fluxes drives a preindustrial atmospheric gradient of CO$_2$ at the surface of -0.6 $\pm$ 0.1 $\mu$atm for the North Pole minus the South Pole and longitudinal variations that exceed 0.5 $\mu$atm. Conversely, the gradient for Mauna Loa minus South Pole is only -0.2 $\pm$ 0.1 $\mu$atm, much less than the -0.8 $\mu$atm gradient extrapolated linearly from historical atmospheric CO$_2$ measurements from the same two sites. The difference may be explained by the role of the terrestrial biosphere. Regardless, the river loop produces large gradients both meridionally and zonally. Accounting for the ...