Postglacial land uplift patterns of south Sweden and the Baltic Sea region

Comparison of the land uplift pattern for the last 10,300 years, shown by studies of raised shorelines of the Baltic Ice Lake, with the pattern of present-day land uplift of Fennoscandia, shows that significant regional changes of uplift pattern have taken place. Some of these changes seem to be related to a halt in ice retreat during the Younger Dryas cold stage. It is also probable that some observed anomalies in the present uplift are not of glacio-isostatic origin, but are possibly related to structures in the lower lithosphere and upper mantle or large scale tectonics.     

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.     

Probable causes for cyanobacterial expansion in the Baltic Sea: Role of anoxia and phosphorus retention

This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,500¹⁴C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to 7,100¹⁴C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen. This is also verified by a contemporaneous drop in the δ¹⁵N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around 3 μmol g⁻¹ at the freshwater-brackish water transition. All P pools except the CaCO₃ fraction showed a distinct increase around 9,300¹⁴C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source of the sediment. Slightly after 4,000¹⁴C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased from around 75 to 25–30 μmol g⁻¹. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of 3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent anoxic conditions.     

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.     

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.     

Predicted effects from abatement action against eutrophication in two small bays of the Baltic Sea

The Baltic Sea has abnormal algal blooms during spring and summer which are effects of high concentrations of total phosphorus (TP) and other nutrients in the surface water. Björnöfjärden (BF), a coastal area connected to the Baltic Sea, is selected for investigating whether aluminium treatment of sediments may reduce TP concentrations in the water mass. The aim of this paper is to evaluate effects from different abatement actions in two bays, BF and Nyköpingsfjärden (NF). The four investigated scenarios are (1) no action, (2) reducing TP from local sources, (3) fixing TP in sediments with aluminium, and (4) decreasing TP concentrations in the outside sea. Magnitudes of different TP fluxes during the different scenarios were estimated using a dynamic mass balance model, CoastMab, which has previously been tested against data from Swedish coastal waters. Alternative actions such as aluminium treatment and reduction of TP from local sources would result in no or scant effect on the TP concentrations in the two bays according to model simulations. The only action which would result in a significant expected decrease in TP concentrations would be to decrease TP concentrations in the outside sea. It is concluded that BF and NF are not suitable for studying effects from local abatement action because of large TP fluxes from the outside sea.     

Seismostratigraphy and structural framework of the SW Baltic Sea

The SW part of the Baltic Sea between Scania, Rügen, Bornholm and Mön constitutes a complex crustal transition between the Baltic Shield and the accreted Phanerozoic provinces of the West European Platform. An integrated interpretation of marine reflection seismic data sets from the BABEL AC line and two commercial surveys offshore NE Germany and S Sweden have resulted in a complete view of the structural framework in the area. The general seismic picture can best be detected by two characteristic sets of reflection phases. The lower set is dominated by slightly dipping and vertically displaced prominent reflectors corresponding to downfaulted Lower Palaeozoic strata on top of the Precambrian basement. The upper set represents Mesozoic and Cenozoic coherent reflection phases including a thick Upper Cretaceous unit. The Caledonian deformation front is identified in the southern part of the investigated area as the border against which basement rocks have been affected by Caledonian metamorphism and deformation. Major structural elements also include the N–S trending Agricola–Svedala Fault and North Rügen-Skurup Fault. Several NW–SE trending faults are also identified including the Nordadler–Kamien Fault, Jutland–Mön Fault, Carlsberg Fault, Romeleåsen Fault Zone and the Fyledalen Fault Zone. The sedimentary record from NE German offshore wells and Scanian boreholes is compared with the seismic data. The Cambro-Silurian strata are composed mainly of quartzitic sandstones, shales and biomicritic limestones. The Silurian is dominated by grey, micaceous shale and micaceous siltstone deposited in a marginal basin. Upper Palaeozoic strata are merely encountered in the southernmost part of the investigated area. These include Zechstein strata. The Mesozoic deposits are dominated by a thick Cretaceous sequence of mainly limestones with interbedded sandstones.     

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.     

Evidence of the final drainage of the Baltic Ice Lake and the brackish phase of the Yoldia Sea in glacial varves from the Baltic Sea

A clay-varve chronology based on 14 cross-correlated varve graphs from the Baltic Sea and a mean varve thickness curve has been constructed. This chronology is correlated with the Swedish Time Scale and covers the time span 11530 to 10250 varve years BP. Two cores have been analysed for grain size, chemistry, content of diatoms and changes in colour by digital colour analysis. The final drainage of the Baltic Ice Lake is dated to c . 10800 varve years BP and registered in the cores analysed as a decrease in the content of clay. This event can be correlated with atmospheric Δ14 C content and might have resulted in an increase in these values recorded between 11565 and 11545 years BP. The results of the correlation between the varve chronology from the Baltic Sea, the Greenland GRIP ice core and the atmospheric Δ14 C record indicate that c . 760 years are missing in the Swedish Time Scale in the part younger than c. 10250 varve years BP. A change in colour from a brownish to grey varved glacial clay recorded c . 10770 varve years BP is found to be the result of oxygen deficiency due to an increase in the rate of sedimentation in the early Preboreal. The first brackish influence is recorded c . 10540 varve years BP in the northwestern Baltic Sea and some 90 years later in the eastern Gotland Basin.     

Erosion and uplift uncertainties in the Barents Sea, Norway

Three different types of methods are used to assess the ability to determine erosion amounts and to provide estimates of uncertainty. In the situation of dynamical indicator methods, such as seismic velocity, sonic logs, density logs, or drilling exponent methods, intrinsic assumptions and parameter values used provide only a broad statement on the resolution of uplift/erosion events. None of the methods is more accurate, at best, to better than ± 1 km and likely much worse. For geological model procedures, exemplified by considerations of Airy isostasy and by bed upturning near a salt dome in the Nordkapp Basin of the Barents Sea, the uncertainties are again of the order of ± 500–1000 m. With thermal indicator procedures, the bulk of the constraint information from available data is needed to determine paleoheat flux with little left over to constrain the erosion, implying a minimum uncertainty of ± 500 m on erosion determinations. No method seems capable of resolving erosional events to better than a minimum uncertainty of ± 500 m, and likely no better than ± 1 km.     

The geology of the southeastern Baltic Sea: a review

The Baltic Sea, particularly its southeastern part, is discussed in the paper. Investigations of regional character as well as specialized studies in the area are reviewed. General historical works are mentioned briefly. Previous surveys since the 1950s are presented by the subject studied. The compilation of geological structure of the SE Baltic Sea bottom and adjacent land of Balticum (Baltic States: Estonia, Latvia, Lithuania) is based on considerable amounts of summarized materials. The crystalline basement, sedimentary cover and Quaternary deposits are characterized in the comprehensive survey of geological structure. From a stratigraphical point of view, geological sequence of the platformal cover is comparatively complete: deposits of all geological systems (from the Archean to Cenozoic) are present in the Baltic Syneclise. Considering geotectonical cycles, the sedimentary cover of the syneclise is subdivided into four structural complexes. The thickness and distribution of Quaternary deposits are closely related to the recent bottom relief of the Baltic Sea that in turn is inherited from the Pre-Quaternary surface. Buried palaeo-valleys are characteristic of the Pre-Quaternary surface in the Baltic region and the Baltic Sea bottom. The Quaternary is characterized by layers of various geneses and by sharp changes of their thicknesses.     

Time-dependent modeling of the Baltic entrance area. 2. Water and salt exchange of the Baltic Sea

A time-dependent model for stratification and circulation within the Baltic entrance area (Gustafsson 2000) is tested against observed salinities for the period 1961–1993. Although the Baltic Sea is one of the largest estuarine systems on earth, this model could be applicable to smaller estuarine systems and embayments with tidal exchange. The seasonal cycle of freshwater flux across the sill area does not follow the seasonal cycle of freshwater supply to the Baltic Sea. The seasonal variation of the flux is a combined effect of the seasonal variation in freshwater supply, in Baltic mean sea level, and in dispersion of salt across the sills. The seasonal variation in dispersion of salt is due to the seasonal cycle of sea level variability. The model is used to predict the inflow of high saline water to the Baltic Sea. The resulting inflow time-series is consistent with variations in the deep-water salinity and temperature in the deeper parts of the Baltic Sea. A comparison with previous estimates of the magnitude of major Baltic inflows shows that the model is able to reproduce the characteristics fairly well although the magnitude of the flows of water and salt appears lower than other estimates. It is shown that a climatic change that increases the wind mixing does not significantly change the major inflows. Both increased amplitudes of sea level variations in the Kattegat and decreased freshwater supply to the Baltic Sea substantially increase the magnitude of the inflows. It is shown that deep-water renewal in the Baltic Sea is obstructed during years with high freshwater supply even if the sea level forcing is favorable to a major inflow.     

Fine spatial structure of flows on satellite radar image of the Baltic Sea

Satellite images of the sea surface demonstrate different dynamic processes at the water–air boundary and in the water layer. The objective of this investigation is to identify the fine structure of flows in the mesoscale vortex with the help of a specially developed method for flow estimation by ship wakes in the sea. The method described in this work made it possible to identify the jet nature and surges of flows in the mesoscale cyclonic vortex in the southern part of the Baltic Sea after long western and southwestern winds.