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Knowledge of the distribution of seabed sediments, benthic communities and their associated environment (biotopes) provides important baseline information for sustainable management of the oceans. The Barents Sea comprises a vast area of continental shelf spanning international boundaries, where this type of information is in increasing demand for management related issues in these high-latitude waters. Synthesis of existing data originally obtained for other purposes can provide an important first step in making the required information available, as well as helping to identify areas where further mapping should be prioritised. We present two related regional-scale maps recently generated for a large part of the Barents Sea continental shelf where varying amounts of existing data were available from Norwegian and Russian institutions: (1) a map showing the distribution of seabed surface sediments (1:3,000,000), and (2) a map showing the predicted distribution of benthic biotopes (4 km raster resolution) based on Random Forest modelling. The biotope map makes use of the sediment map as a key predictor variable, together with bathymetric, oceanographic and other environmental variables. Biotope classes are based on species composition as identified from benthic trawl samples. Compilation and synthesis of geo-referenced data from various sources can produce valuable results but can also lead to uncertainties in the resultant map products which are important to convey to data users. To support our thematic maps we present a confidence assessment of the foundation datasets contributing to the sediment map. We also discuss further issues related to map confidence and scope for updating the maps as new data become available.

Neva Bay is the shallowest and easternmost part of the Gulf of Finland (Baltic Sea). St. Petersburg, Russia's second largest city, occupies the coastal area where the Neva River debouches into Neva Bay. St. Petersburg has a protracted history of industrial, transportation and urban related activity that have affected Neva Bay. By the sealing off the bay from the eastern Gulf of Finland, the St. Petersburg Flood Protective Facility, which was constructed from the 1970's to 2011, transformed Neva Bay into a "technogenic" lagoon. Neva Bay sediments record a unique history of pollution near the metropolis. Heavy metal concentrations of most elements studied varied consistently throughout sediment cores. Temporal trends indicate that metals started to accumulate abruptly in the first half of the 20th century. Zinc, lead and copper were the first metals to reach contaminant thresholds implicating the regional base metal industry as a source. Significant increase in cadmium levels a decade or two later suggests pollution from the regional chemical industry. th and 21 st century scientific surveys reveal dramatic shifts in Neva Bay sedimentation processes over the last three centuries. The western part of Neva Bay has transitioned from a sanddominated system to one of mud accumulation with the aerial extent of mud deposition expanding significantly during the 20 th century. This inventory coupled with an understanding of primary natural and anthropogenic processes can help inform decision makers to support the overall ecological health of the bay.

A total of 26 samples of surface sediments collected in the Neva River (including the St. Petersburg city area) and in the Russian part of the Gulf of Finland were analyzed for 17 polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs), 12 dioxin-like polychlorinated biphenyls (dl-PCBs), and 10 polybrominated diphenyl ethers (PBDEs). The concentrations of total PCDD/Fs and dl-PCBs in sediments ranged from < 0.05 to 219 pg g d.w. and from 44 to 246,600 pg g d.w. respectively. The total World Health Organization toxic equivalent (WHO-TEQ) values varied between 0.01 and 59.0 pg g. In the majority of cases, the PCDD/F and dl-PCB concentrations do not exceed the threshold effect level (TEL) recommended by Helsinki Commission (HELCOM) as quantitative target for the sum of PCDD/Fs and dl-PCBs. The congener profile indicates that combustion is the primary source of PCDD/Fs in most of the studied samples. For the PCBs, the historical use of technical PCB products was identified as the major source. ΣPBDE concentrations ranged from 0.004 to 1.8 ng g d.w. The congener profile results show that BDE-47 (tetra-BDE) is the dominant congener in sediment samples. According to the sediment and water quality guidelines established in the EU (PNEC) and in Canada (FEQG), all the samples studied can be classified as lowly contaminated by PBDEs. The sediment concentrations of PCDD/Fs, dl-PCBs, and PBDEs measured in this study were comparable to or lower than those reported for other areas of the Baltic Sea.

Here, we present new results from seismic, geological, and geochemical studies conducted in 2015–2019 in the Petrozavodsk Bay of Lake Onego, NW Russia. The aims of these investigations were to (i) to characterize the structure of Quaternary deposits and (ii) provide new evidence of modern geodynamic movements and gas-seepage in Holocene sediments. The structure of the recovered deposits was composed of lacustrine mud, silt and sands from the Holocene, limno-glacial clays (varved clays) from the Late Glacial–Interglacial Transition, and glacial deposits (till) from the Late Pleistocene. The thickness of these deposits varied in different parts of the bay. Many pockmarks created by gases escaping and reaching sediment-water interface were observed in these deposits. Such pockmarks can play a significant role in the geochemical and biological processes in the bottom sediment surface, and gases that escape might modify the physicochemical characteristics of the environment.

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