Growing seasonal extremes in ocean acidity
A new study published in the journal Nature Climate Change finds that if atmospheric CO2 continues to increase, the differences in extremes in surface-ocean acidity between summer and winter will roughly double by the end of the century. The amplified seasonality in acidity is projected to occur in all ocean regions. In the tropics and subtropics, associated impacts on organisms are likely to worsen during summer when acidity is highest and improve during winter when acidity is lowest; in colder ocean regions, these summer-winter tendencies are reversed. Future projections of these seasonal extremes come from nine Earth System Models that participated in the last Intergovernmental Panel on Climate Change Assessment Report. Projections were made not only for acidity (hydrogen ion concentration) but also for a saturation index that indicates how suitable conditions are for calcification, a process by which corals and shell builders produce hard skeletal material. The seasonal amplitude of that index (the aragonite saturation state) was found to generally decline as atmospheric CO2 increases. With time this could affect the ability of shell forming organisms to grow, with summer seawater conditions becoming less suitable for growth over most of the ocean.
Article: Kwiatkowski, L., & Orr, J. C. (2018). Diverging seasonal extremes for ocean acidification during the twenty-first century. Nature Climate Change, 8(2), 141-145. https://doi.org/10.1038/s41558-017-0054-0