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Abstract: Methane in the sediments of the Bay of Puck occurs in the form of free gas bubbles and is released from the sediments into near-bottom water in the form of a flux. The sediments of the Bay of Puck also contain methanogens whose biological activity results in the production of methane. Research carried out in the coastal areas of the bay along the Hel Peninsula proved the existence of a methane flux ranging from 0.81mmolm−2 d−1 to 33.41mmolm−2 d−1 in 2011, while in 2010 ranged from 0.91mmolm−2 d−1 to 49.15mmolm−2 d−1. Seasonal and annual fluctuations were also observed. Other factors contributing to the change in methane flux are water temperature and other environmental factors. An increase in temperature causes an increase in the flux. Fluctuations of the flux within individual sampling sites were also observed. A test performed with specific methanogenic inhibitor—sodium dodecyl sulfate (SDS) unexpectedly revealed higher methane concentrations (10–13%) in samples to which SDS was added. We speculate that these higher methane concentration result from the lysis of methane-forming bacteria cells when exposed to SDS. [Copyright &y& Elsevier]

The Baltic Sea is characterized by hyposaline surface waters, hypoxic and anoxic deep waters and sediments. These conditions, which in turn lead to a steep oxygen gradient, are particularly evident at Landsort Deep in the Baltic Proper. Given these substantial differences in environmental parameters at Landsort Deep, we performed a metagenomic census spanning surface to sediment to establish whether the microbial communities at this site are as stratified as the physical environment. We report strong stratification across a depth transect for both functional capacity and taxonomic affiliation, with functional capacity corresponding most closely to key environmental parameters of oxygen, salinity and temperature. We report similarities in functional capacity between the hypoxic community and hadal zone communities, underscoring the substantial degree of eutrophication in the Baltic Proper. Reconstruction of the nitrogen cycle at Landsort deep shows potential for syntrophy between archaeal ammonium oxidizers and bacterial denitrification at anoxic depths, while anaerobic ammonium oxidation genes are absent, despite substantial ammonium levels below the chemocline. Our census also reveals enrichment in genetic prerequisites for a copiotrophic lifestyle and resistance mechanisms reflecting adaptation to prevalent eutrophic conditions and the accumulation of environmental pollutants resulting from ongoing anthropogenic pressures in the Baltic Sea. [ABSTRACT FROM AUTHOR]

Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Resulting local anomalies in the morphology and physical properties of surface sediments are usually explored with seismo-acoustic imaging techniques. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for a first time with a high-resolution survey of freshwater seeps in Eckernförde Bay (SW Baltic Sea). We demonstrate that EM profiling, complemented and validated by acoustic as well as sample-based rock magnetic and geochemical methods, can create a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

To simulate transport of clastic material in the Baltic a sediment transport module is linked to a Baltic Sea Model that is based on the Modular Ocean Model-MOM3. In order to describe the properties of the seabed sediment parameters as mean grain size, critical shear velocity and bed roughness length must be provided as input data to the numerical model system. To obtain maps of these quantities for the Baltic Sea area the proxy-target concept is applied. As proxy-variable the mean grain size of the sediment types is used. For different sediment samples the critical shear velocity was measured and serves as the target variable. Using the relation between the sediment classifications based on the mean grain size (proxy) and the measured critical shear velocity (target) a map of the critical shear velocity in the Baltic is derived. In January 1993 several extreme strong storm events occurred in the Baltic. Using this period for a model calculation maximum values of current and wave induced bottom shear velocities were obtained. Comparing these model results with the critical shear velocity distribution provided by the proxy-target concept we identify potential erosion areas. Further we show the transport path of material initially deposited in the Mecklenburgian Bight. [ABSTRACT FROM AUTHOR]

Wake waves from fast ferries create significant changes in the optical parameters of sea water in the near-bottom layer with a thickness of about 1 m in coastal areas of Tallinn Bay with depths of about 2-5 m. The suspended matter remains in the water column for about 5 mm. Rough quantitative estimates, based on the wave-induced increase of the suspended matter in the water column per unit of bottom of the coastal area (about 1 g m-2) suggest that the bulk influence of fast ferry traffic in Tallinn Bay may result in an annual loss of the order of 100 L of fine sediments from each metre of the coastal line. [ABSTRACT FROM AUTHOR]