Acidification, deoxygenation, nutrient and biomasses decline in a warming Mediterranean Sea

Abstract. The projected warming, nutrient decline, changes in net primary production, deoxygenation and acidification of the global ocean will dramatically affect marine ecosystems during the 21st century. Here we assess the climate change-related impacts in the marine ecosystems of the Mediterranean Sea in the middle and at the end of the 21st century using high-resolution projections of the physical and biogeochemical state of the basin under the Representative Concentration Pathways (RCPs) 4.5 and 8.5. The analysis shows significant changes in the dissolved nutrient content of the euphotic and intermediate layers of the basin, net primary production, phytoplankton respiration and carbon stock (including phytoplankton, zooplankton, bacterial biomass and particulate organic matter). The projections also show a uniform surface and subsurface reduction in the oxygen concentration driven by the warming of the water column and by the increase in respiration. Moreover, we observe an acidification in the upper water column, linked to the increase in the dissolved inorganic carbon content of the water column due to CO2 absorption from the atmosphere and the increase in respiration. The projected changes are stronger in the eastern Mediterranean due to the limited influence, in that part of the basin, of the exchanges in the Strait of Gibraltar.