Hypoxia is a well-described phenomenon in the offshore waters of the Baltic Sea with both the spatial extent and intensity of hypoxia known to have increased due to anthropogenic eutrophication, however, an unknown amount of hypoxia is present in the coastal zone. Here we report on the widespread unprecedented occurrence of hypoxia across the coastal zone of the Baltic Sea. We have identified 115 sites that have experienced hypoxia during the period 1955–2009 increasing the global total to ca. 500 sites, with the Baltic Sea coastal zone containing over 20% of all known sites worldwide. Most sites experienced episodic hypoxia, which is a precursor to development of seasonal hypoxia. The Baltic Sea coastal zone displays an alarming trend with hypoxia steadily increasing with time since the 1950s effecting nutrient biogeochemical processes, ecosystem services, and coastal habitat.

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ABSTRACT. This article investigates variations of Δ 14 C and δ 13C of total organic carbon (TOC) in sediments as well as in humic acids, lipid, and phospholipid fractions isolated from the surface (0-3 cm) sediment samples collected in the Curonian Lagoon and in the Baltic Sea. This study was performed to estimate relative contributions of the marine and terrestrial inputs to organic carbon in sediments, to assess a possible effect of petroleum hydrocarbon contamination on radiocarbon signatures, and to elucidate a possible leakage of chemical warfare agents (CWA) at the Gotland Deep dumpsite. Depleted Δ 14 C values of the TOC (down to -453‰) and of the total lipid extracts (down to -812.4‰) were detected at the CWA dumpsite. Application of the compound-specific method indicated a possible effect of CWA on depleted Δ 14 C and δ 13 C values in the investigated organic carbon fractions. The obtained results have indicated the different origin and behavior of lipids and TOC at the CWA dumpsite as compared to the area affected by the terrestrial-freshwater OC input. The Δ 14 C data of the TOC and total lipid extracts showed that recent sediments at the CWA dumpsite contain an excess of fossil carbon capable of influencing the 14 C dating at the site.

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This study presents the distribution of trace elements (Hg, Cd, Pb, Cr, As, Cu, Ni, Zn, Co, V, Al, Li), organic carbon, δ 13 C org and radionuclides ( 90 Sr, 137 Cs, 239,240 Pu, 241 Am) in the Lithuanian part of the Baltic Sea and the Curonian Lagoon. Particulate matter (PM) and bottom sediment samples were collected during the sampling campaigns in the frame of the State monitoring and during several other investigations over the period of 1997-2011. The study area is characterized by variable loading with particulate matter. Averaged concentrations of the particulate matter in the water of the Curonian Lagoon area tended to be approximately 3 times higher in comparison with those measured in the Baltic Sea. Results showed a strong relation between metals and organic carbon in particulate matter (r=0.69-0.98, p<0.05). The correlation between metals and organic carbon in sediments was not so strong and varied in the range of 0.45-0.84. It was found out that the highest concentrations of trace elements in the Baltic Sea accumulated in the deepest stations of R7, 12A, 46 with the fine-grained, organic-rich sediments. Pollution was strongly pronounced in the Curonian Lagoon (including Klaipeda Strait area), elevated concentrations of metals were also measured in sediments of the plume of the Lagoon water, dumping of dredged material areas and in the aleurite sediments in the Baltic Sea. Higher level of elements accumulated in the surface sediments (0-3 cm), the difference between core layers was more evident at the deepest stations. According to the results, higher concentrations of radionuclides accumulated in PM and sediments as compared to marine water. The correlation of 137 Cs, 239,240 Pu and 241 Am with total organic carbon in bottom sediments was found to be 0.75-0.98. δ 13 C org in particulate matter, surface bottom sediments and humic substances of the Curonian Lagoon and the Baltic Sea ranged from -22.3 ‰ to -31.8 ‰. δ 13 C org values in the bottom sediment samples well correlated with δ 13 C org values in PM and humic acid samples.