This seasonal shift is due to the more intense rise in CO2 in warmer water. In summer, atmospheric temperatures rise in the Arctic, more sea ice melts, and the surface water grows warmer. This warming process becomes so intense that the acidification of the seawater increases much more rapidly and can no longer be compensated for by the photosynthesis of marine algae. “These new findings spell trouble for some types of Arctic fish, like the polar cod, which are already threatened by climate change,” says co-author Hans-Otto Pörtner, a biologist and climate researcher at the AWI. “The projected high temperatures will push Arctic fauna to their thermal limits or even beyond, particularly with regard to life stages in which they’re more fragile.” First author James Orr from the LSCE and IPSL adds: “Who would have thought that climate change could shift the time of maximum acidification by six months, when studies on seasonal biological rhythms only projected shifts of up to roughly a month?” “The fascinating thing about this study is the fact that the chemical winters will actually become chemical summers,” says Lester Kwiatkowski, a co-author from LOCEAN and the IPSL.
In their study, the experts analysed simulations of 27 Earth system models and prepared future climate scenarios. While doing so, for the first time they assessed the potential for seasonal shifts in acidification, including all related variables. Why? Because the degree of acidification isn’t determined by just one factor; it’s a complex interplay of physical and biological processes, influenced by the more intense warming of surface water in summer. These changes were more pronounced in scenarios with moderate and high greenhouse-gas emissions and were far milder in those with lower emissions. In the researchers’ eyes, this represents a glimmer of hope that key elements of the Arctic Ocean’s ecosystem can be preserved if mean global warming can be kept below 2°C.