Climate-related changes in marine ecosystems simulated with a 3-dimensional coupled physical-biogeochemical model of the Baltic Sea

• Published in: Climate research Vol. 48; no. 1; pp. 31 - 55
• Main Authors: Meier, H. E. Markus, Eilola, Kari, Almroth, Elin
• Format: Journal Article
• Language: English
• Published: Inter-Research 19-07-2011
• Subjects: Baltic Sea Action Plan; Climate change; Climate models; Eutrophication; Freshwater; Marine ecosystems; Nitrogen; Numerical modeling; Oxygen; Phosphates; Phosphorus; Phytoplankton; Pollution load; Scenarios; Seas; Sediments; ANE, Denmark, Bornholm; ANE, Baltic Proper; ANE, Baltic Sea, Bothnia Gulf, Bothnian Bay; ANE, Baltic Sea, Gotland Basin
• ISSN: 0936-577X; 1616-1572; 1616-1572
• DOI: 10.3354/cr00968

The combined effect of changing climate and changing nutrient loads from land due to altered land use, sewage water treatment and emissions was studied using a 3-dimensional high-resolution coupled physical-biogeochemical model for the Baltic Sea. Results suggest that global warming causes increased water temperatures and reduced sea ice cover, combined (eventually) with increased winter mean wind speeds and increased river runoff. The projected hydrographic changes could therefore have significant effects on the marine ecosystem. These changes may compete with nutrient load reductions—presently under discussion—that aim to improve the ecological status of the Baltic Sea. Targets that may be sufficient in the present climate might fail under future climate conditions. Using the model, we investigated 4 climate change scenarios and 3 nutrient load scenarios, ranging from a pessimistic 'business as usual' to the 'most optimistic' case (including the Baltic Sea Action Plan, BSAP). In addition, using cause-and-effect studies, we analyzed changing simulated nutrient cycles, oxygen concentrations, and phytoplankton concentrations. As model results for the northern part of the Baltic (Bothnian Bay and Bothnian Sea) are not reliable, we focus the analysis on the Baltic proper, including the Arkona, Bornholm and Gotland basins. The degree of nutrient reduction in nutrient-load reduction scenarios is likely to differ under a future climate, but actions of the BSAP will reduce phytoplankton concentrations also in the future climate. However, the sensitivity of non-linear responses to climate change depends on processes that are not well understood, with current understanding limited by modelling uncertainties (e.g. in the long-term functioning of Baltic Sea sediments as sources and sinks of nutrients).