Arctic Ocean acidification dynamics during 1993–2021 and its projections for the rest of this century

Dynamics of acidification of the Arctic Ocean through 1993–2021 and predictions of further tendencies of this process until the end of 2100 were assessed making use of both the GLODAPv.2021 and the Global Ocean Biogeochremistry Hindcast (GOBH) reanalysis data on pH. The projections of pH were performed by CMIP6 models for four scenarios of rates of socio-economic and agricultural development and emissions of greenhouse gases: SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5.The tendencies of pH decline over the last 27 years (1993–2019) as determined from the GLODAP in situ and the reanalysis data over 1993–2021 proved to be, respectively –0.9% (from 8.18–8.11) and –0.7% (from 8.10–8.05). Thus, the annual acidification rate as assessed from both data sources proved to be –0.03%.Through the percentile method-based comparison of consistency of historical observation data on pH with GBH model hindcast four best models were identified: MPI-ESM1–2-LR, NorESM2-MM, NorESM2-LM, and CMCC-ESM2. The projection results strongly indicate that the Arctic Ocean acidification will continue till the end of this century. The highest rates of pH decrease (–4.9% and –6.2%) were forecasted, respectively, for scenarios SSP3–7.0 and SSP5–8.5 that implied the global mean temperature increases by 3.6 °C and 4.4 °C, respectively. A comparison of the results obtained with the previously made assessments is indicative that by the end of the current century the rate of acidification (i. e. pH decrease) in the Arctic should be expected to be higher than that averaged over the World Oceans: the difference for each of the SSP scenarios proved to be –0.1.