Spatial variability of summertime aragonite saturation states and its influencing factor in the Bering Sea

The Bering sea is susceptible to ocean acidification driven by both human activities(anthropogenic CO_(2))and distinctive natural processes.To assess the situation of ocean acidification,we investigated the spatial variability of aragonite saturation states(ΩAr)in July 2010 during the 4th Chinese National Arctic Research Expedition(CHINARE).The surface waters were all oversaturated with respect to aragonite(ΩAr>1)due to high biological removal,andΩAr ranged from 1.43 to 3.17.The relatively lowΩAr values were found in the western Bering Strait and eastern nearshore region of the Bering Sea Shelf,which were associated with the upwelling and riverine input,respectively.In the subsurface,theΩAr decreased to generally low saturation states and were observed to be strongly undersaturated(ΩAr<1)in the bottom waters with a lowest value of 0.45,which might be caused by remineralization.However,unlike prior studies,the lowΩAr values in the shallow nearshore region were still above the saturation horizon throughout the water column,which were probably counteracted by high local primary production.In the context of climate change and increasing anthropogenic CO_(2)absorption,the suppression and undersaturation ofΩAr in the Bering Sea are not only attributed to the natural processes but also the accumulation of anthropogenic CO_(2).

Simulation of global ocean acidification and chemical habitats of shallow-and cold-water coral reefs

Using the UVic Earth System Model, this study simulated the change of seawater chemistry and analyzed the chemical habitat surrounding shallow- and cold-water coral reefs from the year 1800 to 2300 employing RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The model results showed that the global ocean will continue to absorb atmospheric CO2. Global mean surface ocean temperature will rise 1.1-2.8 K at the end of the 21st century across RCP scenarios. Meanwhile, the global mean surface ocean pH will drop 0.14--0.42 and the ocean surface mean con- centration of carbonate will decrease 20%--51% across the RCP scenarios. The saturated state of sea water with respect to calcite carbonate minerals （t2） will decrease rapidly. During the pre-industrial period, 99% of the shallow-water coral reefs were surrounded by seawater with t2 〉 3.5 and 87% of the deep-sea coral reefs were surrounded by seawater with aragonite supersaturation. Within the 21st century, except for the high mitigation scenario of RCP2.6, almost none shallow-water coral reefs will be surrounded by seawater with g2 〉 3.5. Under the intensive emission scenario of RCP8.5, by the year 2100, the aragonite saturation horizon will rise to 308 m under the sea surface from 1138 m at the pre- industrial period, thus 73% of the cold-water coral reefs will be surrounded by seawater with aragonite undersaturation. By the year 2300, only 5% of the cold-water coral reefs will be surrounded by seawater with aragonite supersaturation.

Processes Controlling the Carbonate Chemistry of Surface Seawater Along the 150°E Transect in the Northwest Pacific Ocean

The problem of ocean acidification caused by the increase of atmospheric carbon dioxide concentration is becoming increasingly prominent.Field observation in the northwest Pacific Ocean was carried out along the 150°E transect in November 2019.The distribution characteristics and influencing factors of the surface seawater carbonate chemistry,including dissolved inorganic carbon(DIC),total alkalinity(TA),pH,partial pressure of carbon dioxide(pCO_(2))and aragonite saturation state(Ω_(arag))were investigated.DIC and TA ranged from 1915 to 2014μmol kg^(−1)and 2243 to 2291μmol kg^(−1),respectively;DIC in general decreased with decreasing latitude,but TA had no clear latitudinal gradient.pCO_(2)values increased with the decrease of latitude and were all below the atmospheric pCO_(2)level,ranging from 332 to 387μatm.pH on the total hydrogen ion concentration scale(pH_(T))decreased with the decrease of latitude in the range of 8.044–8.110,whileΩ_(arag) increased with the decrease of latitude in the range of 2.61–3.88,suggesting that the spatial distributions of pH_(T) andΩ_(arag) were out of phase.Compared with the present,the predicted values of pH_(T) and Ω_(arag) by the end of this century would decrease remarkedly;larger declines were found in the higher pH_(T) and Ω_(arag) regions,resulting in the differences along the meridional gradient becoming smaller for bothpH_(T) and Ω_(arag).