Contrasting drivers and trends of ocean acidification in the subarctic Atlantic

Pérez, F. F., Olafsson, J., Ólafsdóttir, S. R., Fontela, M., & Takahashi, T. (2021). Contrasting drivers and trends of ocean acidification in the subarctic Atlantic. Scientific Reports, 11(1), 13991. https://doi.org/10.1038/s41598-021-93324-3

Summary

The processes of warming and acidification (anthropogenic CO2 (Canth) accumulation, decreasing pHT (increasing [H+]T; concentration in total scale) and calcium carbonate saturation) in the subarctic zone of the North Atlantic are unequivocal in the time-series measurements of the Iceland (IS-TS, 1985–2003) and Irminger Sea (IRM-TS, 1983–2013) stations. Both stations show high rates of Canth accumulation with different rates of warming, salinification (water becoming more saline) and stratification (separation of the water column into layers with different densities caused by differences in temperature or salinity or both) linked to regional circulation and dynamics. At the IS-TS, advected and stratified waters of Arctic origin drive a strong increase in [H+]T, in the surface layer, which is nearly halved in the deep layer (44.7 ± 3.6 and 25.5 ± 1.0 pmol kg−1 yr−1, respectively). In contrast, the weak stratification at the IRM-TS allows warming, salinification and Canth uptake to reach the deep layer. The acidification trends are even stronger in the deep layer than in the surface layer (44.2 ± 1.0 pmol kg−1 yr−1 and 32.6 ± 3.4 pmol kg−1 yr−1 of [H+]T, respectively). The driver analysis detects that warming contributes up to 50% to the increase in [H+]T at the IRM-TS but has a small positive effect on calcium carbonate saturation. The Canth increase is the main driver of the observed acidification, but it is partially dampened by the northward transport of water with a relatively low natural CO2 content.