| Summary: | Surface waters in the world oceans have already experienced a pH reduction of about 0.1 units (OSPAR, 2006.) The trend indicates further decrease of pH and is most probably due to increased uptake of atmospheric CO2 and less buffering capacity of ocean waters. The trend is similar in the waters surrounding Sweden. RESEARCH NEEDS Since there is an alarming absence of information regarding the effects of near-future levels of ocean acidification on Swedish marine taxa, there is a clear research need on: • investigations of the effects of ocean acidification on the early life-history stages of key ecosystem-structuring species, and commercially important species of fish and shellfish • ecosystem-level mesocosm studies of the impacts of ocean acidification on Swedish marine systems • improved regional-scale modelling of acidification mechanisms in Swedish coastal waters • testable ecosystem-scale food-web models to articulate with regional acidification models • improved definition of chemical equilibrium constants between pH, AT and CO2 in low saline waters. ACTIONS TO IMPROVE MONITORING At present, pH and AT are monitored monthly at standard depths at 7 stations in Skagerrak, Kattegat and Baltic Proper within the national monitoring programme. Of these are 2 located in coastal waters (Halland and Småland; Type 5 and 9). We recommend that Sweden work to improve the status of pH and AT to be Core variables instead of Main variables in HELCOM COMBINE “High frequency Sampling” program taking into account the last 15 years negative trends in pH in waters surrounding Sweden as well as in the global oceans. We recommend that besides the standard para-meters monitored in the national monitoring program, pH, AT and DIC should be monitored. For completeness, primary production should also be monitored. Below are three monitoring recommendations, where the first is divided into a lowest level and a recommended level. 1. Lowest level: Within the national monitoring program, at least one station per open sea area and all ...
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