Impact of climate change on ecological quality indicators and biogeochemical fluxes in the baltic sea: A multi-model ensemble study

Abstract

Multi-model ensemble simulations using three coupled physical- biogeochemical models were performed to calculate the combined impact of projected future climate change and plausible nutrient load changes on biogeochemical cycles in the Baltic Sea. Climate projections for 1961-2099 were combined with four nutrient load scenarios ranging froma pessimistic business-as-usual to a more optimistic case following the Helsinki Commission0s (HELCOM) Baltic Sea Action Plan (BSAP). The model results suggest that in a future climate, water quality, characterized by ecological quality indicators like winter nutrient, summer bottom oxygen, and annual mean phytoplankton concentrations as well as annual mean Secchi depth (water transparency), will be deteriorated compared to present conditions. In case of nutrient load reductions required by the BSAP, water quality is only slightly improved. Based on the analysis of biogeochemical fluxes, we find that in warmer andmore anoxicwaters, internal feedbacks could be reinforced. Increased phosphorus fluxes out of the sediments, reduced denitrification efficiency and increased nitrogen fixation may partly counteract nutrient load abatement strategies. © 2012 Royal Swedish Academy of Sciences.