Acidification in Nordic waters: status, trends and implications for marine species

Recent studies on marine life show that the anthropogenic increase in atmospheric CO2 concentration can have negative impacts on growth and survival of groups of marine life such as corals and other calcifying organisms.

Increased CO2 concentration in the atmosphere, and hence in the oceans, lead to decreasing pH or increasing acidification, a process known as ocean acidification (OA). During the last century, the CO2 concentration in the atmosphere has risen from around 280 ppm to 400 ppm; this has led to a pH decrease in the oceans of 0.1. OA currently takes place at a rate corresponding to approximately -0.02 pH unit per decade and an increase in CO2 at around 2 ppm per year. The projections for atmospheric CO2 concentration is an increase to around 1000 ppm at the end of the century, which will lower pH in the oceans by 0.3-0.4. Although this may appear relatively small, a decrease in pH of 0.1 corresponds to an increase in acidity (“free” protons) of 25%, and 0.3-0.4 corresponds to an increase of 200-250%.

Coastal systems experience changes in pH over time exceeding those of the ocean by several orders of magnitude,
but the field is poorly studied, and the spatial variation is large. The Baltic Sea is no exception to this. pH changes in the Baltic Sea are tightly coupled to nutrient input, alkalinity (AT) of freshwater sources in addition to increased CO2 levels and warming. Acidification trends vary substantially among coastal systems and time of year, but have been reported up to 10 times faster than OA.

The TRIACID project has mapped acidification trends in the Baltic Sea during the past 40 years, in different regions, and identified areas with a general lack of data. The project has described spatial variation and trends in pH status, and the main drivers of changing pH have been identified. Given the spatial variation, the data gaps, and all the different drivers a detailed projection of the development is complicated but since we expect increasing CO2 concentration in the atmosphere, rising temperatures and decreasing nutrient input, the acidification trend will continue or accelerate in most of the region.

Carstensen J., Christense J., Gustafsson B., Gustafsson E. & Chierici M., 2018. Acidification in Nordic waters status, trends and implications for marine species. Nordic Council of Ministers Policy Brief TRIACID. Report.

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