Modeling Nutrient Transports and Exchanges of Nutrients Between Shallow Regions and the Open Baltic Sea in Present and Future Climate

Abstract

We quantified horizontal transport patterns and the net exchange of nutrients between shallow regions and the open sea in the Baltic proper. A coupled biogeochemical-physical circulation model was used for transient simulations 1961-2100. The model was driven by regional downscaling of the IPCC climate change scenario A1B from two global General Circulation Models in combination with two nutrient load scenarios. Modeled nutrient transports followed mainly the large-scale internal water circulation and showed only small circulation changes in the future projections. The internal nutrient cycling and exchanges between shallow and deeper waters became intensified, and the internal removal of phosphorus became weaker in the warmer future climate. These effects counteracted the impact from nutrient load reductions according to the Baltic Sea Action Plan. The net effect of climate change and nutrient reductions was an increased net import of dissolved inorganic phosphorus to shallow areas in the Baltic proper.

ECOSUPPORT: A Pilot Study on Decision Support for Baltic Sea Environmental Management

“…In future climate, water temperatures are projected to increase and salinities are projected to decrease (due to the increased total freshwater supply), which is in accordance with earlier studies (e.g., Arheimer et al 2012;Meier et al 2012;Neumann et al 2012). Despite the high uncertainties involved, which are due to model shortcomings and unknown future scenarios of external nutrient loads, a basic conclusion seems to be that climate change can be expected to reinforce oxygen depletion, to increase phytoplankton biomass, and to reduce water transparency and biodiversity (due to decreased salinity) (e.g., Eilola et al 2012;Meier et al 2011bMeier et al , 2012Neumann et al 2012). Further, we found that in future climate, cod biomass may decrease and sprat biomass may increase assuming present day estimates of sustainable fishing (e.g., MacKenzie et al 2012;Niiranen et al 2012).…”

“…For dynamical downscaling, a high-resolution coupled atmosphere-ice-ocean-land surface model (the Rossby Centre Atmosphere Ocean model, RCAO), with lateral boundary data from global General Circulation Models (GCMs), was used to project the future climate of the Baltic Sea region (Meier et al 2011a. The regional scenario simulations differ depending on the applied GCM at the lateral boundaries and depending on the utilized Furthermore, three state-of-the-art coupled physicalbiogeochemical models were used to calculate changing concentrations of nitrate, ammonium, phosphate, autotrophs, zooplankton, detritus and oxygen, i.e., BALTSEM, ERGOM and RCO-SCOBI (Meier et al 2011bEilola et al 2012;Neumann et al 2012). Higher trophic levels were assessed with a food web model for the Baltic proper and statistical fish population models (MacKenzie et al 2012).…”

“…The ECOSUPPORT work plan was built on the confidence of models' capacity to simulate the changing climate, and included the following aspects: (i) the assessment of predictive skills of the models by comparing observed and simulated past climate variability (i.e., quantification of model uncertainties) and analyzing causes of observed variations (e.g., Gustafsson et al 2012;Meier et al 2012;Niiranen et al 2012), (ii) the performance of multi-model ensemble simulations of the marine ecosystem for 1850-2100, forced by reconstructions of the past climate (e.g., Gustafsson et al 2012;Ruoho-Airola et al 2012) and various future greenhouse gas emission scenarios and airand river-borne nutrient load scenarios (ranging from a pessimistic business-as-usual to the most optimistic case) (e.g., Arheimer et al 2012;Eilola et al 2012;MacKenzie et al 2012;Meier et al 2012;Neumann et al 2012), (iii) the analysis of projections for the future Baltic Sea ecosystem, using a probabilistic approach accounting for uncertainties caused by biases of regional and global climate models, lack of process description in state-of-the-art ecosystem models, unknown greenhouse gas emissions and nutrient loadings as well as natural variability (e.g., Arheimer et al 2012;MacKenzie et al 2012;Meier et al 2012;Neumann et al 2012;Niiranen et al 2012), (iv) the assessment of climate change impacts on the marine biota, like effects of ocean acidification (e.g., Havenhand 2012), biodiversity and fish populations with focus on cod, sprat and herring (e.g., MacKenzie et al 2012;Niiranen et al 2012), (v) a socioeconomic impact assessment (e.g., Piwowarczyk et al 2012), (vi) the generation of a freeaccess data base of scenario model results and tools to access the database with the help of a decision support system (DSS) 2 and finally (vii) the dissemination of project results to stakeholders, decision makers and the public (see below).…”

Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

“…This model handles biological and ecological processes in the sea as well as sediment nutrient dynamics. SCOBI is coupled to RCO (e.g., Eilola et al, 2012Eilola et al, , 2013Eilola et al, , 2014. With the help of a simplified wave model, resuspension of organic matter is calculated from the wave and current-induced shear stresses (Almroth-Rosell et al, 2011).…”

Improving the multiannual, high-resolution modelling of biogeochemical cycles in the Baltic Sea by using data assimilation

“…1) nutrient cycling and nutrient reduction scenarios (e.g. Eilola et al, 2012;Meier et al, 2012;Neumann et al, 2012;Omstedt et al, 2012). Ecological and biogeochemical models with varying levels of complexity are under continuous evolution, and recently a coupled highresolution three-dimensional (3D) models including also the North Sea are developed at the Swedish Meteorological and Hydrological Institute (SMHI) (Kuznetsov et al, manuscript in preparation) and other institutes around the Baltic Sea (Maar et al, 2011;Daewel and Schrum, 2013).…”