Uncertainties in projections of the baltic sea ecosystem driven by an ensemble of global climate models

Many coastal seas worldwide are affected by human impacts such as eutrophication causing, inter alia, oxygen depletion, and extensive areas of hypoxia. Depending on the region, global warming may reinforce these environmental changes by reducing air-sea oxygen fluxes, intensifying internal nutrient cycling, and increasing river-borne nutrient loads. The development of appropriate management plans to effectively protect the marine environment requires projections of future marine ecosystem states. However, projections with regional climate models commonly suffer from shortcomings in the driving global General Circulation Models (GCMs). The differing sensitivities of GCMs to increased greenhouse gas concentrations affect regional projections considerably. In this study, we focused on one of the most threatened coastal seas, the Baltic Sea, and estimated uncertainties in projections due to climate model deficiencies and due to unknown future greenhouse gas concentration, nutrient load and sea level rise scenarios. To address the latter, simulations of the period 1975–2098 were performed using the initial conditions from an earlier reconstruction with the same Baltic Sea model (starting in 1850). To estimate the impacts of climate model uncertainties, dynamical downscaling experiments with four driving global models were carried out for two greenhouse gas concentration scenarios and for three nutrient load scenarios, covering the plausible range between low and high loads. The results suggest that changes in nutrient supply, in particular phosphorus, control the long-term (centennial) response of eutrophication, biogeochemical fluxes and oxygen conditions in the deep water. The analysis of simulated primary production, nitrogen fixation, and hypoxic areas shows that uncertainties caused by the various nutrient load scenarios are greater than the uncertainties due to climate model uncertainties and future greenhouse gas concentrations. In all scenario simulations, a proposed nutrient load abatement strategy, i.e., the Baltic Sea Action Plan, will lead to a significant improvement in the overall environmental state. However, the projections cannot provide detailed information on the timing and the reductions of future hypoxic areas, due to uncertainties in salinity projections caused by uncertainties in projections of the regional water cycle and of the mean sea level outside the model domain.publishedVersio

Impacts of changing society and climate on nutrient loading to the Baltic Sea

This paper studies the relative importance of societal drivers and changing climate on anthropogenic nutrient inputs to the Baltic Sea. Shared Socioeconomic Pathways and Representative Concentration Pathways are extended at temporal and spatial scales relevant for the most contributing sectors. Extended socioeconomic and climate scenarios are then used as inputs for spatially and temporally detailed models for population and land use change, and their subsequent impact on nutrient loading is computed. According to the model simulations, several factors of varying influence may either increase or decrease total nutrient loads. In general, societal drivers outweigh the impacts of changing climate. Food demand is the most impactful driver, strongly affecting land use and nutrient loads from agricultural lands in the long run. In order to reach the good environmental status of the Baltic Sea, additional nutrient abatement efforts should focus on phosphorus rather than nitrogen. Agriculture is the most important sector to be addressed under the conditions of gradually increasing precipitation in the region and increasing global demand for food. (C) 2020 The Authors. Published by Elsevier B.V.Peer reviewe

The influence of increasing water turbidity on the sea surface temperature in the Baltic Sea: A model sensitivity study

The aim of the present study is to investigate the influence of enhanced absorption of sunlight at the sea surface due to increasing water turbidity and its effect on the sea surface temperatures (SST) in the Baltic Sea. The major question behind our investigations is, whether this effect needs to be included in Baltic Sea circulation models or can be neglected. Our investigations cover both, mean state and SST trends during the recent decades. To quantify the impact of water turbidity on the mean state different sensitivity ocean hind-cast experiments are performed. The state-of-the art ocean model RCO (Rossby Centre Ocean model) is used to simulate the period from 1962 to 2007. In the first simulation, a spatially and temporally constant value for the attenuation depth is used, while in the second experiment a climatological monthly mean, spatially varying attenuation coefficient is derived from satellite observations of the diffuse attenuation coefficient at 490 nm. The inclusion of a spatially varying light attenuation leads to significant SST changes during summer. Maximum values of + 0.5 K are reached in the Gulf of Finland and close to the eastern coasts, when compared to a fixed attenuation of visible light of 0.2 m− 1. The temperature anomalies basically match the pattern of increased light attenuation with strongest effects in shallow waters. Secondary effects due to changes in the current system are of minor importance. Similar results are obtained when considering trends. In the absence of long-term basin wide observations of attenuation coefficients, some idealizations have to be applied when investigating the possible influence of long-term changes in water turbidity on the SST. Two additional sensitivity experiments are based on a combination of long-term Secchi depth station observations and the present day pattern of water turbidity, as observed by satellite. We show the potential of increased water turbidity to affect the summer SST trends in the Baltic Sea significantly, while the estimated effect is apparently too small to explain the overall extreme summer trends observed in the Baltic Sea. Highlights ► Investigation of the modeled influence of water turbidity on the sea surface temperature (SST) of the Baltic Sea. ► Hind-cast simulations (1962–2007) with different attenuation depths, using the regional ocean model RCO. ► The inclusion of an observed spatially varying light leads regionally to significant SST changes during summer. ► Secondary effects due to changes in the current system are of minor importance. ► The influence of increasing water turbidity on SST trends is regionally statistically significant while the effect is rather small

On the dynamics of oxygen, phosphorus and cyanobacteria in the Baltic Sea; A model study

Oxygen and phosphorus dynamics and cyanobacterial blooms in the Baltic Sea are discussed using results from the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). The high-resolution circulation model is used to simulate the time period from 1902 to 1998 using reconstructed physical forcing and climatological nutrient loads of the late 20th century. The analysis of the results covers the last 30 years of the simulation period. The results emphasize the importance of internal phosphorus and oxygen dynamics, the variability of physical conditions and the natural long-term variability of phosphorus supplies from land on the phosphorus content in the Baltic Sea. These mechanisms play an important role on the variability of available surface layer phosphorus in late winter in the Baltic Sea. The content of cyanobacteria increases with the availability of phosphorus in the surface layers of the Baltic proper and the probability for large cyanobacteria blooms in the model is rapidly increased at higher concentrations of excess dissolved inorganic phosphorus in late winter. The natural increase of phosphorus supplies from land due to increased river runoff since the early 1970s may to a large degree explain the increased phosphorus content in the Baltic proper. Another significant fraction of the increase is explained by the release of phosphorus from increased anoxic areas during the period. These results refer to the long-term variability of the phosphorus cycle. In accordance to earlier publications is the short-term (i.e. interannual) variability of the phosphorus content in the Baltic proper mainly explained by oxygen dependent sediment fluxes

Data from: Spatio-temporal dynamics of a fish predator: density-dependent and hydrographic effects on Baltic Sea cod population

Understanding the mechanisms of spatial population dynamics is crucial for the successful management of exploited species and ecosystems. However, the underlying mechanisms of spatial distribution are generally complex due to the concurrent forcing of both density-dependent species interactions and density-independent environmental factors. Despite the high economic value and central ecological importance of cod in the Baltic Sea, the drivers of its spatio-temporal population dynamics have not been analytically investigated so far. In this paper, we used an extensive trawl survey dataset in combination with environmental data to investigate the spatial dynamics of the distribution of the Eastern Baltic cod during the past three decades using Generalized Additive Models. The results showed that adult cod distribution was mainly affected by cod population size, and to a minor degree by small-scale hydrological factors and the extent of suitable reproductive areas. As population size decreases, the cod population concentrates to the southern part of the Baltic Sea, where the preferred more marine environment conditions are encountered. Using the fitted models, we predicted the Baltic cod distribution back to the 1970s and a temporal index of cod spatial occupation was developed. Our study will contribute to the management and conservation of this important resource and of the ecosystem where it occurs, by showing the forces shaping its spatial distribution and therefore the potential response of the population to future exploitation and environmental changes

Standardised CPUE of cod and hydrographic data

The dataset contains information on all the variables at the aggregation level of individual bottom trawl hauls as used in the analyses presented in "Spatio-temporal dynamics of a fish predator: density-dependent and hydrographic effects on Baltic Sea cod population". Year: year when the cod sample was collected; Lon: longitude (decimal-degree) of the position where the cod sample was collected; Lat: latitude (decimal-degree) of the position where the cod sample was collected; Depth: bottom depth (m) where the cod sample was collected; AG3: catch-per-unit-effort (kg/h) of cod of age 3+ of the trawl station; Oxy: modelled bottom oxygen (ml/L) associated to the trawl station; Sal: modelled bottom salinity (psu) associated to the trawl station; Crv: cod reproductive volume (km3) estimated for the year and ICES subdivision of the trawl station; Stk: stock size (thousands) of the eastern Baltic cod in the year of the sample from stock assessment (ICES 2013)