Upwelling events, coastal offshore exchange, links to biogeochemical processes - Highlights from the Baltic Sea Sciences Congress at Rostock University, Germany, 19-22 March 2007

The Baltic Sea Science Congress was held at Rostock University, Germany, from 19 to 22 March 2007. In the session entitled"Upwelling events, coastal offshore exchange, links to biogeochemical processes" 20 presentations were given,including 7 talks and 13 posters related to the theme of the session.This paper summarises new findings of the upwelling-related studies reported in the session. It deals with investigationsbased on the use of in situ and remote sensing measurements as well as numerical modelling tools. The biogeochemicalimplications of upwelling are also discussed.Our knowledge of the fine structure and dynamic considerations of upwelling has increased in recent decades with the advent ofhigh-resolution modern measurement techniques and modelling studies. The forcing and the overall structure, duration and intensity ofupwelling events are understood quite well. However, the quantification of related transports and the contribution to the overall mixingof upwelling requires further research. Furthermore, our knowledge of the links between upwelling and biogeochemical processes is stillincomplete. Numerical modelling has advanced to the extent that horizontal resolutions of c. 0.5 nautical miles can now be applied,which allows the complete spectrum of meso-scale features to be described. Even the development of filaments can be describedrealistically in comparison with high-resolution satellite data.But the effect of upwelling at a basin scale and possible changes under changing climatic conditions remain open questions

The dependence between bacterial production and environmental conditions in the Gulf of Gdańsk

Bacterial production, primary production and a number of other environmental factors were measured during six cruises in the Gulf of Gdańsk conducted in various seasons from 1995 to 2001. Bacterial production (BP) in the epipelagic layer ranged from 1.5% (April) to 80% (July) of the gross primary production (PP). Significant differences were observed between the BP/PP ratios in estuarine and open-water areas. The highest values were recorded in the coastal area and near the mouth of the river Vistula. It suggests that allochthonous organic matter has a great influence on BP. The correlations between particular parameters and regression analyses indicated that BP in the Gulf of Gdańsk depended on temperature, organic nitrogen concentration, PP, chlorophyll a concentration, organic phosphorus concentration, salinity and biochemical oxygen demand. Of all the independent variables, the temperature had the greatest impact on BP (R2 = 0.62). There was an inverse parabolic relationship between bacterial production and temperature. It appears that above a temperature of 12◦C bacterial production depended on substrates to a higher degree than on temperature. The negative correlation between BP and concentrations of mineral nitrogen and phosphorus in the annual cycle were probably due to an indirect dependence. A multiple regression equation, which included temperature and organic phosphorus concentrations, explained 78% of the variation in BP. Increasing BP resulted in an increasing biomass of bacterivorous nanoflagellates and of bacterivorous ciliates, which is indicative of bottom-up control in this segment of the trophic chain

Seasonal dynamics and activity of typical freshwater bacteria in brackish waters of the Gulf of Gdańsk

While typical freshwater and marine bacteria have been found to co-occur in brackish habitats, it is unknown if they are active members of the local bacterial assemblages or if their presence is the result of passive transport only. We followed the seasonal dynamics of typical freshwater bacteria (R-BT lineage of Betaproteobacteria; Ac1 Actinobacteria; LD12 Alphaproteobacteria) and of marine SAR11 Alphaproteobacteria in the brackish water of the Gulf of Gdańsk (southern Baltic Sea), and we assessed their incorporation of thymidine and leucine at three distinct environmental conditions. The temporal development of bacteria was driven not only by local conditions but also by phenomena resulting from the dynamic hydrology of the site. Both temperature and salinity were important factors influencing bacterial community composition, as reflected by the clear distinction of three assemblages in spring and summer and during a period of enhanced freshwater influx. During spring, high proportions of R-BT Betaproteobacteria and Ac1 Actinobacteria incorporated the radiolabeled tracers, and all three freshwater lineages were most active during the subsequent phase of low salinity. The summer period was characterized by highest abundances of Ac1 Actinobacteria and of both alphaproteobacterial lineages. All studied freshwater lineages were active members of the brackish water communities at specific environmental conditions, including LD12 Alphaproteobacteria, which have so far been considered to thrive exclusively in freshwater habitats. By contrast, the presence of the typical marine SAR11 bacteria seemed to result from passive inflow with more saline waters from the Baltic proper

Comparison of bacterial production in the water column between two Arctic fjords, Hornsund and Kongsfjorden (West Spitsbergen)

Bacterial production and the accompanying environmental factors were measured in the water columns of two Arctic fjords during the cruise in July and August 2013. Water samples were collected at six stations located in the central part of Hornsund and Kongsfjorden. In Hornsund, where average water temperatures were 1.25-fold lower than in Kongsfjorden, the bacterial production was twice as high (0.116 ± 0.102 vs 0.05 ± 0.03 mg C m−3 h−1). Statistical analysis indicated that chlorophyll a concentration itself was not a significant factor that affected bacterial production, in contrast to its decomposition product, pheophytin, originating from senescent algal cells or herbivorous activity of zooplankton. Single and multiple regression analysis revealed that water temperature, dissolved organic carbon (DOC), and pheophytin concentration were the main factors affecting bacterial production in both fjords

The occurrence and activity of sulphate-reducing bacteria in the bottom sediments of the Gulf of Gdańsk

The paper presents the results of investigations concerning the number, distribution and physiological activity of sulphate-reducing bacteria (SRB) inhabiting the bottom sediments of the Gulf of Gdańsk. The numbers of this group of bacteria range between 0.76 × 103 and 1.27 × 104 cells per g wet sediment. The bacterial sulphate reduction rate in bottom sediments of this area of the Baltic Sea varies from 1.89 to 31.6 nM SO2− 4 g−1 24 h−1. The numbers of SRB and their physiological activity were subject to considerable seasonal fluctuations, maximum values being noted in summer (June) and minima in spring (April). A direct relationship has been found between the number of SRB and hydrogen sulphide concentrations; there is, however, no such relationship with reference to sulphate concentrations. The numbers and distributions of SRB demonstrated considerable variation in a depth profile of bottom sediments. SRB inhabiting the bottom sediments of the Gulf of Gdańsk were able to use three different organic substrates (lactate, acetate, propionate) as electron donors and as carbon and energy sources

The occurrence and activity of sulphate-reducing bacteria in the bottom sediments of the Gulf of Gdańsk Gulf of Gdańsk Sediment Sulphate-reducing bacteria Sulphate reduction rate

Abstract The paper presents the results of investigations concerning the number, distribution and physiological activity of sulphate-reducing bacteria (SRB) inhabiting the bottom sediments of the Gulf of Gdańsk. The numbers of this group of bacteria range between 0.76 × 10 3 and 1.27 × 10 4 cells per g wet sediment. The bacterial sulphate reduction rate in bottom sediments of this area of the Baltic Sea varies from 1.89 to 31.6 nM SO 2− 4 g −1 24 h −1 . The numbers of SRB and their physiological activity were subject to considerable seasonal fluctuations, maximum values being noted in summer (June) and minima in spring (April). A direct relationship has been found between the number of SRB and hydrogen sulphide concentrations; there is, however, no such relationship with reference to sulphate concentrations. The numbers and distributions of SRB demonstrated considerable variation in a depth profile of bottom sediments. SRB inhabiting the bottom sediments of the Gulf of Gdańsk were able to use three different organic substrates (lactate, acetate, propionate) as electron donors and as carbon and energy sources

Bacterial community structure influenced by Coscinodiscus sp in the Vistula river plume

The Gulf of Gdansk is influenced by freshwater inflow from the River Vistula and by a wind-driven current along the coast. Bacterial communities from five stations along a salinity gradient were sampled during one day and analysed by terminal restriction fragment length polymorphism (T-RFLP), catalysed reporter deposition-fluorescence in situ hybridisation (CARD-FISH) and 16S rRNA gene libraries. On the day of sampling, we observed a probable current-driven seawater influx into the inner part of the gulf that separated the gulf into distinct water bodies. Members of the diatom Coscinodisrus sp. dominated one of these water bodies and influenced the bacterial community. The coexistence of typically freshwater and marine bacterioplankton populations in the Vistula river plume suggested an integration of some freshwater populations into the Baltic Sea bacterioplankton