René Friedland

The future of the western Baltic Sea: two possible scenarios

Globally coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature. However, the global models do not perform as well on regional scales. Here, we present results from four 100-year, high-resolution ocean model experiments (resolution less than 1 km) for the western Baltic Sea. The forcing is taken from a regional atmospheric model and a regional ocean model, imbedded into two global greenhouse gas emission scenarios, A1B and B1, for the period of 2000 to 2100 with each two realisations. Two control runs from 1960 to 2000 are used for validation. For both scenarios, the results show a warming with an increase of 0.5–2.5 K at the sea surface and 0.7–2.8 K below 40 m. The simulations further indicate a decrease in salinity by 1.5–2 practical salinity units. The increase in water temperature leads to a prolongation of heat waves based on present-day thresholds. This amounts to a doubling or even tripling of the heat wave duration. The simulations show a decrease in inflow events (barotropic/baroclinic), which will affect the deepwater generation and ventilation of the central Baltic Sea. The high spatial resolution allows us to diagnose the inflow events and the mechanism that will cause future changes. The reduction in barotropic inflow events correlates well with the increase in westerly winds. The changes in the baroclinic inflows can be consistently explained by the reduction of calm wind periods and thus a weakening of the necessary stratification in the western Baltic Sea and the Danish Straits.

Climate Change Impacts on the Baltic Sea

Climate impact research is of increasing importance because politicians, local decision makers, and the society require guidance regarding the environmental effects of global warming. This information is needed on a regional scale which cannot be provided by global climate models. Therefore, tools are needed to translate global climate trends into a regional scale. Regional climate models are used to scale global climate simulations with coarser resolution to a finer grid. Beside the knowledge about atmospheric variables further information of the marine environment, especially for coastal regions, is important. Regional ocean models driven by regional climate models can provide scenarios for the future development of the marine environment. A Baltic Sea ecosystem model is used for scenario simulations to assess the potential development of the Baltic Sea within the next 100 years. The simulations show an increasing water temperature in the range of 2–3.5 K and a decrease in salinity by 1.5–2 g kg–1. Events with large suboxic areas are likely to increase in the western Baltic Sea. However, the uncertainties in the climate projections are high and for robust results more scenario simulations are needed.

Biotope map of the German Baltic Sea

Full-coverage maps on the distribution of marine biotopes are a necessary basis for Nature Conservation and Marine Spatial Planning. Yet biotope maps do not exist in many regions. We are generating the first full-coverage biotope map for the German Baltic Sea according to the HELCOM Underwater biotope and habitat classification system (HUB). Species distribution modelling is applied to create full-coverage spatial information of biological features. The results of biomass modelling of twelve target taxa and presence/absence modelling of three target taxa enabled the identification of biological levels up to HUB level 6. Environmental data on bathymetry, light penetration depth and substrate are used to identify habitat levels. HUB biotope levels were combined with HUB habitat levels to create a biotope map. Altogether, 68 HUB biotopes are identified in the German Baltic Sea. The new biotope map combining substrate characteristics and biological communities will facilitate marine management in the area.

Variation in benthic long-term data of transitional waters: Is interpretation more than speculation?

Biological long-term data series in marine habitats are often used to identify anthropogenic impacts on the environment or climate induced regime shifts. However, particularly in transitional waters, environmental properties like water mass dynamics, salinity variability and the occurrence of oxygen minima not necessarily caused by either human activities or climate change can attenuate or mask apparent signals. At first glance it very often seems impossible to interpret the strong fluctuations of e.g. abundances or species richness, since abiotic variables like salinity and oxygen content vary simultaneously as well as in apparently erratic ways. The long-term development of major macrozoobenthic parameters (abundance, biomass, species numbers) and derivative macrozoobenthic indices (Shannon diversity, Margalef, Pilou’s evenness and Hurlbert) has been successfully interpreted and related to the long-term fluctuations of salinity and oxygen, incorporation of the North Atlantic Oscillation index (NAO index), relying on the statistical analysis of modelled and measured data during 35 years of observation at three stations in the south-western Baltic Sea. Our results suggest that even at a restricted spatial scale the benthic system does not appear to be tightly controlled by any single environmental driver and highlight the complexity of spatially varying temporal response.

Ecosystem services provision today and in the past: a comparative study in two Baltic lagoons

The European Biodiversity Strategy asks EU Member States for an assessment, mapping and valuing of Ecosystem Services (ES). While terrestrial ES concept is advanced and different tools are available, they are largely lacking for coastal and marine systems. We develop a stepwise methodological process to assess ES in coastal and marine systems which we name Marine Ecosystem Services Assessment Tool. We applied it to two large Baltic lagoons, the Szczecin and the Curonian Lagoons demonstrating a quantitative and qualitative assessment approach. Firstly, an initial status is defined reflecting, according to the European Water Framework Directive, a past situation when the ecosystems where in a so called good ecological state. In both Baltic lagoons, this refers to a situation around 1960. Secondly, a present state is defined, assessed and compared to the initial status. Increasing anthropogenic impacts in Szczecin Lagoon caused an overall decrease ecological status which may influence the system’s ability to provide services. Assessing ES changes semi-quantitatively via 39 indicators and 22 services, we show a decrease in provisioning and regulating and maintenance and an increase of cultural services’ provision. According to 15 expert valuations, the Curonian Lagoon displays no changes in provisioning but an increase in regulating and maintenance and cultural service provision. We discuss how these results can serve different marine management approaches and support different polices. Through our application we show how the tool can be used to assess ES changes over time and thus provide key information on sustainable use and ES for future generations.

Aquatische Ökosysteme: Nordsee, Wattenmeer, Elbeästuar und Ostsee

Langzeitbeobachtungen von aquatischen Okosystemen zeigen nicht nur eine hohe Variabilitat, sondern auch graduelle Anderungen und sog. Regimeshifts: sprunghafte Anderungen im Funktionieren des gesamten Okosystems. Sowohl die naturliche Variabilitat hydrodynamischer und atmospharischer Prozesse auf verschiedenen Zeitskalen als auch menschliche Einflussnahmen wie beispielsweise CO2-Ausstos, Fischerei, Deichbau, Vertiefungen oder Eutrophierung tragen zu dieser komplexen okologischen Dynamik bei (z. B. Emeis et al. 2015).