Nordic SeasAcidification

With prevailing low temperatures, ::: Due :: to :::: low ::::::: calcium :::::::: carbonate :::::::: saturation :::::: states, ::: and : deep winter mixing , and cold-water coral reefs ::: that ::::: brings :::::::::::: anthropogenic :::::: carbon :: to :::: the :::: deep ::::: ocean, the Nordic Seas is ::: and :::: their ::::::::: cold-water :::::: corals ::: are vulnerable to ocean acidification. Here : , we present a detailed investigation of changes in pH and aragonite saturation , and its impact on cold-water corals, in the Nordic Seas , from pre-industrial times to 2100, : by using in situ observations, gridded climatological 5 data, and Earth System Model (ESM) projections . From pre-industrial to present, the Nordic Seas surface pH has dropped by 0.06 on average, and the aragonite saturation horizon has moved from a depth of 2500 meter to 2000m, which is well below the cold-water coral habitats. Between 1981 and 2019 pH decreased by, on average, 0.10 in the Nordic Seas surface waters. The pH drop, mainly driven by an uptake of anthropogenic CO2, is significant all over::: for:::: three:::::::: different ::::: future:::::::: scenarios. : :::::: During ::: the ::::: period :: of ::::::: regular ::::: ocean :::::::::::::: biogeochemistry :::::::::: observations ::::: from ::::::::: 1981-2019 ::: the ::: pH :::::::: decreased :::: with ::::: rates :: of ::: 2-3 ::::: 10−3 10 :::: yr−1 :: in ::: the :::::: upper :::: 200 :: m :: of : the Nordic Seas, except in the Barents Sea Opening. We also find that the acidification has penetrated relatively deep, in some regions. ::: In :::: some ::::::: regions, ::: the ::: pH ::::::: decrease ::: can ::: be ::::::: detected down to 2000 m . This has ::::: depth. :::: This resulted in a significant decrease in ::::::: decrease :: of : the aragonite saturation state, which are ::: now :: is close to undersaturation in the depth layer of 1000-2000 min the modern ocean. Model projections indicate an additional surface ocean pH decrease of 0.1-0.4 until the year of 2100. In the high-emission scenario, RCP8. :::: The ::::: model :::::::::: simulations ::::::: suggest :: the ::: pH ::: of ::: the :::::: Nordic :::: Seas 15 :: to ::::::: decrease :: at :: an :::::: overall ::::: faster :::: rate :::: than :: the :::::: global ::::: ocean ::::: from :::::::::: preindustrial :: to ::::: 2100, ::::::: bringing ::: the :::::: Nordic ::::: Seas :: pH :::::: closer :: to ::: the ::::: global ::::::: average. :: In ::: the ::::::::: esmRCP8.5 , the entire ::::::: scenario, ::: the :::::: whole water column is projected to be undersaturated in aragonite by ::: with :::::: respect :: to :::::::: aragonite :: at : the end of the century, threatening Nordic Seas’ cold-water corals and their ecosystems. Under the emission-driven RCP4 :::: 21st ::::::: century, :::::::::: endangering ::: all :::: cold ::::: water ::::: corals ::: of ::: the :::::: Nordic ::::: Seas. :: In ::: the :::::::: esmRCP4.5 scenariothe saturation horizon is : , ::: the ::::::: deepest :::: cold ::::: water :::: coral ::::: reefs ::: are : projected to be lifted to 400-800 m by the end of this century, 20 endangering the deepest living cold-water corals :::::: exposed ::: to ::::::::::::: undersaturation. Exposure of :: all cold-water corals to corrosive waters can only be avoided under the emission-driven RCP2 :::: with ::::::: marginal ::::: under ::: the ::::::::: esmRCP2.6 scenario.