Geochemistry of ferromanganese nodules in the Gulf of Finland, Baltic Sea

Distribution of the major and trace elements in ferromanganese nodules, which are buried or exposed on the seafloor, and in host sediments was studied in ten concretion/sediment pairs by various physical and chemical methods. It has been established that, in addition to Fe and Mn, a limited number of the major and trace elements (P, Ca, Sr, Ba, Mo, Co, Zn, Ni, As, Pb, Sb, Tl, U, W, Y, and Ga included) is accumulated with a variable degree of intensity (relative to sediments) in the concretions. As compared to host sediments, the maximal content of Mn in concretions is 100 times higher, whereas maximal contents of all other elements listed above vary from more than one to 10–20 times. Manganese and, to a lesser extent, Ba and Sr are concentrated in the buried concretions. Other elements are primarily concentrated in concretions exposed on the sea-floor. The occurrence mode of concretions and compositional data on interstitial water suggest that metals in the concretions were derived from seawater and suspended particulates, in addition to sediments. Burial of concretions in the sediment pile is accompanied by the alteration of their composition, accumulation of Mn (relative to Fe), and loss of several associated metals.     

Holocene sea-level changes and glacio-isostasy in the Gulf of Finland, Baltic Sea

Shoreline displacement in the eastern part of the Gulf of Finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in Virolahti in southeastern Finland and on the Karelian Isthmus, and in Ingermanland in Russia. Study methods were diatom analyses, sediment lithostratigraphical interpretation and radiocarbon dating. In southeastern Finland, the marine (Litorina) transgression maximum occurred ca. 6500–6200 ¹⁴C yr BP (7400–7100 cal. yr BP). In areas of the slower land uplift rate on the Karelian Isthmus and in Ingermanland, the transgression maximum occurred ca. 6400–6000 ¹⁴C yr BP (7300–6800 cal. yr BP). The highest Litorina shoreline is located at ca. 23 m above present sea-level in southeastern Finland, whereas in the eastern part of the Karelian Isthmus, near St. Petersburg, it is located at ca. 8 m above present sea-level. The amplitude of the Litorina transgression in Virolahti area is ca. 4 m, whereas on the Karelian Isthmus and in Ingermanland the amplitude has varied between 5 and 7 m. The regional differences between areas are solely due to different glacio-isostatic land uplift rates. The seven basins studied in this research were connected to the Baltic Sea basin during the Litorina Sea stage and their diatom and lithostratigraphical records indicate a single, smooth Litorina transgression.     

Groundwater discharge to the Gulf of Finland (Baltic Sea): ecological aspects

The Gulf of Finland lies in the eastern part of the Baltic Sea. The surface area is 29,700 km² and the average depth of the basin is 38 m. Groundwater discharge to the Gulf of Finland equals 0.6 km³/year and this discharge is composed of many different chemical compounds. Groundwater discharge into the Gulf of Finland is dispersal. The coastal area of the Gulf of Finland can be divided into four zones with different geological, hydrogeological and discharge properties. The amount of direct groundwater discharge to the sea may be estimated using several geological and hydrogeological methods.     

Contamination of harbor sediments in the eastern Gulf of Finland (Neva Bay), Baltic Sea

 The areal distribution of oil products and various trace metals have been studied in bottom surface deposits from the harbors of Neva Bay. The data of contents were normalized to natural background concentrations. Also the size and biomass of benthos groups were analyzed. The results show clearly that industrial discharges have elevated levels of contamination in the sediments. Few efficient measures against environmental contamination have been taken. The sediments contain very high concentrations of oil products and such heavy metals as Hg, Pb, Cu, and Zn. The benthic organisms most sensitive to heavy metal contamination are Chironomidae. The dredging and dumping of the contaminated deposits can lead to secondary contamination of the Gulf of Finland and the Baltic proper. Received: 18 November 1996 · Accepted: 17 March 1997     

Palaeoenvironment of the Karelian Isthmus, the easternmost part of the Gulf of Finland, during the Litorina Sea stage of the Baltic Sea history

The palaeoenvironment of the Karelian Isthmus area during the Litorina Sea stage of the Baltic Sea history, between 8.0 and 4.5 kyr BP (8.8-5.2 cal. kyr BP), was reconstructed by studying four sites located on the Karelian Isthmus in Russia. Methods included diatom and pollen analyses, sediment lithostratigraphical interpretation and ¹⁴C dating. The brackish-water (Litorina) transgression began c. 7.7 kyr BP (8.45 cal. kyr BP) in the Karelian Isthmus area. The transgression maximum occurred between 6.7 and 5.7 kyr BP (7.6-6.5 cal. kyr BP), depending on the glacio-isostatic land uplift rate. Regarding the vegetation, the maximum occurrence of temperate deciduous trees took place at the same time. The transgression was interrupted by a short-lived sea-level standstill during the middle phase of the main transgression, c. 6.3 kyr BP (7.2 cal. kyr BP), on the eastern part of the isthmus. The highest Litorina shoreline is located between 8 and 13 m above present sea-level and the amplitude of the Litorina transgression has varied between 5 and 7 m. The 8.2-kyr cold event is not evident, but the sea-level standstill around 6.3 kyr BP (7.2 cal. kyr BP) could reflect a cool episode at that time in the Karelian Isthmus area.     

Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea

Hutri, K.-L., Heinsalu, A., Kotilainen, A. T. & Ojala, A. E. K. 2007 (January): Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea. Boreas , Vol. 36, pp. 56–64. Oslo. ISSN 0030–9483.
Deformation structures in submarine Holocene sediments caused by palaeoseismicity have recently been found in the Olkiluoto area, Gulf of Bothnia, Baltic Sea, within old fracture zones of bedrock. In this study, the palaeoseismic event(s) was dated and the palaeoenvironment was characterized using palaeomagnetic, biostratigraphical and lithostratigraphical methods, thereby enhancing the reliability of the chronology. The variations in the inclination and declination of the Olkiluoto sediment core showed very good correlation with the palaeosecular variations recorded in the annually laminated long lake sediment record from Lake Nautajarvi in central Finland. Combined litho-, bio- and palaeomagnetic stratigraphy revealed an age estimation of 10 650 to 10 200 cal. yr BP for the palaeoseismic event(s), which coincides with postglacial bedrock faulting in northern Fennoscandia.     

Late Weichselian and Holocene seismostratigraphy and depositional history of the Gulf of Riga,NE Baltic Sea

The Lateglacial and postglacial sequence in the northern Gulf of Riga is sedimentologically subdivided into nine distinctive layers. In the seismo‐acoustic sequence these layers are correlated with seven seismic/acoustic units, which largely reflect different stages in the development of the Baltic Sea. A uniform layer of the Late Weichselian till, a layer of waterlain glacial diamicton (WGD), a varved succession of the Baltic Ice Lake, a brackish‐water/freshwater sandy/silty clay of Yoldia Sea, a FeS‐rich layer of Ancylus Lake and discordantly bedded sand of the Litorina Sea and present‐day gyttja are revealed both in sediment cores and in acoustic recordings. In general, the lateral extent of the distinguished sediment layers is gradually shrinking upwards in the Quaternary sequence towards the deepest, central depression of the gulf. Two distinguished regional discontinuities divide the Lateglacial and postglacial sediment sequence into three allounits: glacial diamicton deposits in the lower part; ice‐proximal WGD, glaciolacustrine and postglacial lake/marine deposits in the middle; and brackish‐water marine deposits in the uppermost part of the sequence. The presented detailed seismostratigraphic subdivision of the Quaternary sediment sequence of the Gulf of Riga permits a correlation/comparison with similar sequences across the Baltic Sea and in other former glaciated basins.     

The subfossil seals of Finland and their relation to the history of the Baltic Sea

The occurrence of seals in the Finnish prehistoric fauna and in the Baltic since the end of the last glaciation is discussed on the basis of subfossil remains in refuses at cultural sites, and stray finds. The species represented are the harp ( Phoca groenlandica Müller), the ringed seal ( Phoca hispida Schreb.), and the grey seal ( Halicoerus grypus (Fabr.)), of which the latter two are native in the recent fauna, whereas the former has since become extinct in the Baltic. The earliest seals, which probably immigrated to the Yoldia Sea, were ringed seals, whereas the subfossil harp seals are solely found in sediments of the Litorina Sea stage.     

Phosphorus recycling and burial in Baltic Sea sediments with contrasting redox conditions

In this study, redox-dependent phosphorus (P) recycling and burial at 6 sites in the Baltic Sea is investigated using a combination of porewater and sediment analyses and sediment age dating (²¹⁰Pb and ¹³⁷Cs). We focus on sites in the Kattegat, Danish Straits and Baltic Proper where present-day bottom water redox conditions range from fully oxygenated and seasonally hypoxic to almost permanently anoxic and sulfidic. Strong surface enrichments of Fe-oxide bound P are observed at oxic and seasonally hypoxic sites but not in the anoxic basins. Reductive dissolution of Fe-oxides and release of the associated P supports higher sediment-water exchange of PO₄ at hypoxic sites (up to ∼800 μmol P m⁻² d⁻¹) than in the anoxic basins. This confirms that Fe-bound P in surface sediments in the Baltic acts as a major internal source of P during seasonal hypoxia, as suggested previously from water column studies. Most burial of P takes place as organic P. We find no evidence for significant authigenic Ca-P formation or biogenic Ca-P burial. The lack of major inorganic P burial sinks makes the Baltic Sea very sensitive to the feedback loop between increased hypoxia, enhanced regeneration of P and increased primary productivity. Historical records of bottom water oxygen at two sites (Bornholm, Northern Gotland) show a decline over the past century and are accompanied by a rise in values for typical sediment proxies for anoxia (total sulfur, molybdenum and organic C/P ratios). While sediment reactive P concentrations in anoxic basins are equal to or higher than at oxic sites, burial rates of P at hypoxic and anoxic sites are up to 20 times lower because of lower sedimentation rates. Nevertheless, burial of reactive P in both hypoxic and anoxic areas is significant because of their large surface area and should be accounted for in budgets and models for the Baltic Sea.     

Recolonisation by Macrobenthos Mobilises Organic Phosphorus from Reoxidised Baltic Sea Sediments

In recent decades, eutrophication has increased the extent of hypoxic and anoxic conditions in many coastal marine environments. In such conditions, the nutrient flux across the sediment?Cwater interface is a key process controlling the biogeochemical dynamics, and thereby the level and character of biological production. In some areas, management attempts to drive the ecosystem towards phosphorus (P) limitation, which calls for reliable knowledge on the mechanisms controlling P-cycling. We report a well-controlled laboratory experiment on benthic fluxes of P, when shifting from a state of hypoxic and azoic sediments to oxic and zoic bottom conditions. Adding any of three types of macrobenthic fauna (mysid shrimp, pontoporeid amphipod and tellinid clam) to oxygenated aquarium sections resulted in benthic P fluxes that differed consistently from the azoic control sections. All species caused liberation of dissolved organically bound P (DOP) from the sediment, in contrast to the azoic systems. The shrimp and the amphipod also resuspended the sediment, which resulted in a release of P bound to particles (>0.45???m). Dissolved inorganic phosphate (DIP) was released during hypoxic conditions, but was taken up after oxygenation, irrespective of the presence or absence of bottom fauna. In the presence of fauna, the uptake of DIP roughly equalled the release of DOP, suggesting that the benthic efflux of DOP following oxygenation and bottom fauna (re)colonisation might be considerable. This is an hitherto overlooked animal-controlled nutrient flux, which is missing from coastal marine P budgets.     

Variability in inorganic and organic nitrogen uptake associated with riverine nutrient input in the Gulf of Riga, Baltic Sea

Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1⁻¹ in the northern region (mouth) and 41±5 μg-at N 1⁻¹ in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with¹⁵N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1⁻¹ h⁻¹ in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 μg-at N 1⁻¹ h⁻¹ in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells <5 μm, while up to 67% of the community in the northern part was composed of cells >5 μm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf.     

Long-term Changes and Controlling Factors of Phytoplankton Community in the Gulf of Riga (Baltic Sea)

Trends in phytoplankton monitoring data (1976–2008) from the Gulf of Riga were investigated and linked to environmental factors. Annual means of spring phytoplankton biomass correlated to phosphorus input from land and shifts between diatoms and dinoflagellates were attributed to potential Si limitation and time of sampling relative to the spring phytoplankton succession. The summer phytoplankton biomass, which more than doubled over the study period, was related to the abundance of summer copepods that similarly declined. Cyanobacterial blooms proliferated in summer and the proportion of diatoms similarly declined when the winter–spring inorganic N/P ratio was low. The chlorophyte proportion in summer increased over the study period, and this was linked to increasing temperatures favoring their higher growth rates. The dinoflagellate proportion appeared to decrease with temperatures above a threshold of 15.5°C. Although nutrient inputs and their ratios are important factors for the phytoplankton community, this study suggests that climate change and overfishing could be equally important.     

Scaling the Baltic Sea environment

The Baltic Sea environment has since the early 1970s passed through several phases of spatial objectification in which the ostensibly well-defined semi-enclosed sea has been framed and reframed as a geographical object for intergovernmental environmental politics. Based on a historical analysis of this development, this article suggests that environmental politics critically depend on the delineation of relatively bounded spaces that identify and situate particular environmental concerns as spatial objects for politics. These spaces are not simply determined by ‘nature’ or some environmental-scientific logic, but should rather be seen as temporal outcomes of scale framing processes, processes that are accentuated by contemporary conceptions of the environment (or nature) in terms of multi-scalar ecosystems. This has implications for how an environmental concern is perceived and politically addressed.     

Endmember analysis of heavy-metal pollution in surficial sediments from the Gulf of Gdansk and the southern Baltic Sea off Poland

Thirty one bulk (<2 mm) samples of surficial sediments from the Gulf of Gdansk and the Southern Baltic Sea off Poland were analyzed for 20 elements and the resulting compositional dataset was subjected to endmember analysis. The compositions of 4 endmember estimates were constructed and the abundances of these endmembers were calculated for each sample. Copper, Zn and Ag appear on one endmember and Cd and Pb on another. This suggests that Cu, Zn and Ag are introduced into the Gulf of Gdansk principally from the Vistula River whereas Cd and Pb are introduced as a result of atmospheric and riverine transport of these elements. The dual source of Cd and Pb into the Gulf of Gdansk may explain the complex interelement relationships displayoed by these elements in the sediments from this region.     

Ferromanganese ore process in the Baltic Sea

In depressions of the Baltic Sea, where the bottom is periodically marked by stagnation, silt contains as much as 5% Mn (up to 17% in some layers) and 9–10% C_org. Silt in such depressions is laminated. The marine sediment sequence is stratified due to the influx of oceanic water into sea: the upper layers are oxic, while the lower (near-bottom) layers are hydrosulfuric. Boundary between them is represented by the transitional O₂-H₂S layer. This zone (redox barrier) is marked by drastic variation in Eh. Zone below this barrier is characterized by the accumulation of huge amounts of the dissolved manganese (Mn²⁺) and iron (Fe²⁺), which diffuse from the hydrosulfuric layer into the oxic layer under the influence of gradient and precipitated as suspeusion with as much as 15% Fe and 45% Mn. When fresh oxygenated saline water is transported to depressions, the hydrosulfuric setting gives way to oxic one and the dissolved elements are transformed into the particulate phases as hydroxides and geologically instantly precipitated at the bottom. After 5–10 yr, the setting changes; hydrogen sulfide is again delivered to water column from the bottom. This is accompanied by supply of the dissolved Mn²⁺ and Fe²⁺ previously accumulated as gel-type sediment at the bottom. Thus, the cycle of elements is repeated. The latter, however, is not completely dissolved. Some portion remains at the bottom as black rhodochrosite microlayers (laminas) that contain as much as 29% Mn. The black laminas accumulated during aeration include remains of bottom foraminifers. In addition, the bottom comprises pale diatom laminas and brownish gray varieties composed of clayey and organic substances. Bulk samples of the laminated silt contain as much as 12.9% Mn or 26.9% MnCO₃. Depressions in the Baltic Sea represent a unique site of the Earth marked by accumulation of the carbonate-manganiferous sediments at present. We believe that Oligocene manganese carbonate-oxide ores described by N.M. Strakhov and coauthors were accumulated in the same manner. Compositions of manganiferous sediments in the Baltic region and some ancient ores in Europe are compared. The author studied five stages of Mn accumulation and sediment transformation into ores.     

Distribution,production and consumption of nitrous oxide in the Baltic Sea

Nitrous oxide supersaturation was measured in the Bothnian Bay, Bothnian Sea and four depth zones of the Baltic proper along with O₂, NO^?₃, NO^?₂ and other parameters useful in interpreting the sources of the N₂O. In the Baltic Sea supersaturation of N₂O (123%) was found in the surface water of 0 to 0.5 m. The supersaturation resulted in a flux of N₂O to the atmosphere of 2.8 × 10^?2Tg N · yr^?1 which was 5% of the estimated total nitrogen loss for the Baltic. For the entire photic zone (0 to 20 m) the N₂O saturation was 135%. The source of the N₂O is not clear, as the nitrification and denitrification were ruled out as sources. The N₂O saturation was the lowest (118%) in the intermediate zone. Nitrification appears to be the likely N₂O sorce in this region. At the halocline zone, an increasing oversaturation of N₂O (200 to 300%) correlated with decreasing O₂ concentrations and increasing NO^?₃ concentrations, indications of nitrification. Of the NH⁺₄ that was oxidized to NO^?₃, 0.56% was produced as N₂O. In the deep water zone, the supersaturation of N₂O remained very high (150 to 200%). Sufficient O₂, high NO^?₃ and the presence of nitrifying activity suggested nitrification as most likely source, however in deeper waters of this zone where oxygen was less than 2% saturation the N₂O production could be due to denitrification. In anoxic waters the N₂O concentrations rapidly decreased to zero suggesting N₂O consumption by denitrification, further evidenced by a developing nitrate anomaly.     

Spatial Distribution of Holocene Benthic Foraminifera,Northeastern Aegean Sea

The distribution of Holocene benthic foraminifera in the Gokceada-Bozcaada-Canakkale triangle was investigated in 31 surface-sediment samples. The sediments can be classified as muddy to gravelly-muddy sand with rare occurrences of muddy gravel and gravelly sand. The fauna exhibits high diversity and richness, and the populations increase in diversity and richness depending on the number of specimens. One hundred sixty (160) species were found. Eight benthic fossil assemblages, comprising only calcareous species, were identified in the region: Porosononion subgranosum (Egger), Ammonia compacta Hofker, Asterigerinata mamilla (Williamson), Rosalina bradyi Cushman, Elphidium crispum. (Linne), Cassidulina carinata Silvestri, Brizalina spathulata (Williamson) and Valvulineria bradyana (Fornasini). In order to analyze the samples statistically, the main foraminiferal parameters were calculated, namely, species richness (d'), Shannon-Wiener diversity (H) and evenness (J'). Finally, Q-mode cluster analysis was applied to the Bray-Curtis measure of similarity using the weighted pair-group method, and the ordination of the samples was plotted using an MDS plot. Eight benthic fossil assemblages, dominated by calcareous, hyaline-wall-bearing species, characterize the northeastern Aegean Sea.     

Biogenic components of the Baltic Sea sediments

The contents of biogenic components in 1511 samples of the Baltic Sea sediments (depth range 0–5 cm) are studied, and maps of their distribution are compiled. The sediments contain < 13.03% C_org, < 1.33% N, < 9.0% SiO_2am, < 5.0% CaCO₃, and < 1.45% P. The maximum and elevated contents of components are found in the mud of the sea deeps. The more fraction < 0.01 mm the sediments contain, the higher are the contents of components. Four facies types of carbonaceous mud, precursors of shales, have been recognized: (1) shallow-water (lagoon) lime sapropel, (2) carbonaceous mud of the shallow-water Gulf of Finland, (3) carbonaceous mud of the middle-depth Baltic Sea, and (4) laminated carbonaceous metal-bearing mud. The latter type of mud is strongly enriched in manganese and ore-forming trace elements, which points to its formation in the stagnant environment. In composition the Baltic Sea mud is similar to petroliferous mudstones of the Bazhenov Formation in West Siberia and to ancient black shales.     

Iodine-129 enrichment in sediment of the Baltic Sea

Sediments are an excellent archive for evaluation of time-series environmental contamination of water systems. Measurements of ultra-trace radioactive species, such as ¹²⁹I, provide information for both chronologic calibration and anthropogenic emissions during the nuclear era. Here data are presented on ¹²⁹I and other chemical parameters from two sediment cores collected in the Baltic Sea during 1997. The sediment sections have a relatively uniform grain size (clay–mud) and cover a period of about 50 a. Distribution of ¹²⁹I in the sediment strongly relates to the liquid release records from the nuclear reprocessing facilities at Sellafield and La Hague. However, syn- and post-depositional alteration of organic matter at the sediment–water interface and within the sediment column may have contributed to slightly obliterating the anthropogenic ¹²⁹I signals. Indication of Chernobyl-derived ¹²⁹I occurs in the sediment profile, but is apparently overridden by the overwhelming flux from the nuclear reprocessing facilities. Although the record did not cover the pre-nuclear era (before 1945) sections, the ultra sensitive ¹²⁹I profile provides a potential tool for relative dating and monitoring sources of water and sediment to the region.