Future ocean hypercapnia driven by anthropogenic amplification of the natural CO2 cycle

Data-based projections suggest that the natural CO 2 cycle could be amplified by up to ten times by 2100 in some oceanic regions if atmospheric CO 2 concentrations continue to increase, which could detrimentally affect major fisheries. Marine CO 2 is a potential threat to fisheries Elevated carbon dioxide concentrations in seawater, a phenomenon known as hypercapnia, can have detrimental effects on marine animals. This study finds that some oceanic regions may undergo an up to tenfold amplification of the natural cycle of carbon dioxide by 2100, if atmospheric carbon dioxide concentrations continue to rise throughout this century. It forecasts the onset of ocean hypercapnia events for atmospheric CO 2 concentrations higher than 650 p.p.m., with hypercapnia spreading to up to half of the surface ocean by the year 2100 under a high carbon dioxide emission scenario, with potential implications for major fisheries. High carbon dioxide (CO 2 ) concentrations in sea-water (ocean hypercapnia) can induce neurological, physiological and behavioural deficiencies in marine animals 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Prediction of the onset and evolution of hypercapnia in the ocean requires a good understanding of annual variations in oceanic CO 2 concentration, but there is a lack of relevant global observational data. Here we identify global ocean patterns of monthly variability in carbon concentration using observations that allow us to examine the evolution of surface-ocean CO 2 levels over the entire annual cycle under increasing atmospheric CO 2 concentrations. We predict that the present-day amplitude of the natural oscillations in oceanic CO 2 concentration will be amplified by up to tenfold in some regions by 2100, if atmospheric CO 2 concentrations continue to rise throughout this century (according to the RCP8.5 scenario of the Intergovernmental Panel on Climate Change) 11 . The findings from our data are broadly consistent with projections from Earth system climate models 12 , 13 , 14 , 15 . Our predicted amplification of the annual CO 2 cycle displays distinct global patterns that may expose major fisheries in the Southern, Pacific and North Atlantic oceans to hypercapnia many decades earlier than is expected from average atmospheric CO 2 concentrations. We suggest that these ocean ‘CO 2 hotspots’ evolve as a combination of the strong seasonal dynamics of CO 2 concentration and the long-term effective storage of anthropogenic CO 2 in the oceans that