Global and regional ocean carbon uptake and climate change: sensitivity to a substantial mitigation scenario (original) (raw)
Under future scenarios of business-as-usual emissions, the ocean storage of anthropogenic carbon is 13 anticipated to decrease because of ocean chemistry constraints and positive feedbacks in the carbon-14 climate dynamics, whereas it is still unknown how the oceanic carbon cycle will respond to more 15 substantial mitigation scenarios. To evaluate the natural system response to prescribed atmospheric 16 "target" concentrations and assess the response of the ocean carbon pool to these values, 2 centennial 17 projection simulations have been performed with an Earth System Model that includes a fully coupled 18 carbon cycle, forced in one case with a mitigation scenario and the other with the SRES A1B 19 scenario. End of century ocean uptake with the mitigation scenario is projected to return to the same 20 magnitude of carbon fluxes as simulated in 1960 in the Pacific Ocean and to lower values in the 21 Atlantic. With A1B, the major ocean basins are instead projected to decrease the capacity for carbon Community Production (NCP) following changes in the subsurface equatorial circulation and 26 enhanced iron availability from extratropical regions. NCP is a proxy of the bulk organic carbon made 27 available to the higher trophic levels and potentially exportable from the surface layers. The model 28 results indicate that, besides the localized increase in the equatorial Pacific, the NCP of lower trophic 29 levels in the northern Pacific and Atlantic oceans is projected to be halved with respect to the current 30 climate under a substantial mitigation scenario at the end of the 21 st century. It is thus suggested that 31 changes due to cumulative carbon emissions up to present and the projected concentration pathways 32 of aerosol in the next decades control the evolution of surface ocean biogeochemistry in the second 33 half of this century more than the specific pathways of atmospheric CO 2 concentrations. 34 35 Keywords : Climate -Projections -Stabilisation -Ocean carbon cycle -Marine biogeochemical 36 model -PELAGOS -ENSEMBLES 37 38 39 45 and the ocean carbon pumps. These pumps (Volk and Hoffert 1985) work to maintain a higher 46 concentration of dissolved inorganic carbon (DIC) at depth than at the surface by means of biological 47 (the soft-tissue and carbonate pumps) and chemical processes (the solubility pump). The growth of 48
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