Daria Ryabchuk

On the genesis of some bottom and coastal features in the Eastern Gulf of Finland

An investigation undertaken recently by the Division of Regional Geoecology and Marine Geology of the Karpinsky All-Russian Research Geological Institute in the coastal zones of the Eastern Gulf of Finland allowed finding some specific relief forms of both near-shore bottom topography and shoreline shape. First of all, among the most interesting objects, the sand ridges on the surface of submarine terrace (between Repino locality and Cape Lautaranta) should be mentioned. These ridges are elongated at an angle to the shoreline and are located beyond the limits of wave action. The other interesting morphological type is represented by longshore sand waves up to some hundreds of meters long and some tens of meters wide near the Bol’shaya Izhora locality. Longshore sand waves move along the southern coast of the gulf, this causing alteration of erosion and accretion zones and leading to formation and degradation of the sand spits. Shore-face-connected ridges are believed to develop under the action of drift currents generated during the passage of deep west cyclones. It is shown that the ridge turned toward the current gives rise to a convergence of the cross-shore flows over the crest and provokes a shift of the maximum velocity toward the front side of the structure. Associated changes in sediment discharges result in accumulation and growth of the ridge. The origin of wavelike features in the shoreline contour (longshore sand waves) is due to a very oblique wave approach caused by predominance of the west winds blowing along the axis of the gulf. Under these conditions a small perturbation of the shoreline contour is shown to manifest a trend to increase with time.

Development of the coastal systems of the easternmost Gulf of Finland, and their links with Neolithic–Bronze and Iron Age settlements

Abstract We examine three questions concerning the post-glacial geological history of the eastern Gulf of Finland: (1) the amplitude of the Holocene sea-level regressions; (2) the time and mechanism of the development of large sand accretion forms (bars and spits), including dunes; and (3) the sea-level changes and coastal development over the last 4 kyr. Recent on-land geoarchaeological studies, as well as detailed marine geological research of the Gulf of Finland nearshore bottom, have provided new data for developing a hypothesis about the palaeogeographical development of the area. Geoarchaeological studies carried out around Sestroretsky Artificial Lake and within Okhta Cape, as well as analyses of previous studies of the Neolithic–Early Metal settlements, have shed new light on some aspects of coastal system development. Geographical information system (GIS)-based modelling of Holocene shorelines for the different time periods can be useful for future archaeological research. A series of submarine terraces was found at the bottom of the Gulf (sea depths from 10 to 2 m). The analysis of marine geological data (submarine terraces) and distribution of archaeological sites can be explained by a possible rise in relative sea level in the Gulf of Finland at 5 ka BP and a regression around 3 ka BP.

Modeling of storm-induced deformations of a sandy coast (based on the example of the eastern Gulf of Finland)

An improved version of the CROSS-P model for the simulation of storm-induced deformations in coastal profiles is suggested. It is shown that the model reproduces the formation of the erosion profile adequately both in the laboratory and field conditions. Though the main features of the accretion profile are also reflected in the model, further testing based on more relevant data is needed. The profile types predicted by the model agree with the well-known empirical criterion. An important new step is that the foredune overflow effect caused by storm surges is also included into the model. The model is applied to the coasts of the eastern Gulf of Finland exposed to high storm surges. This makes it possible to present the coast change as a result of a conveyor delivering sand material from the foredune to the beach under the impact of extreme storms. During the periods of low wave activity, this conveyor transports the beach material to the underwater slope. The sediment conveyer works only in one direction; thus, the losses of the dune material turn out to be irreversible. Modeling shows that, during the foredune overflow process (typical for the southern segment of the studied area), a certain amount of sediments is carried on to the rear dune slope, and the dune belt gradually moves inland simultaneously decreasing in height. It is expected that the destructive trends in the coastal evolution will continued within the nearest decades.

Benthic Habitats and Benthic Communities in Southeastern Baltic Sea, Russian Sector

Publisher Summary The southeastern Baltic Sea (SEB) is a part of an intracontinental shelf basin of the Atlantic Ocean, located within a large depression of the Baltic Shield and Russian plate of the East European Platform. The Baltic Sea underwent several stages of development, from a freshwater ice-lake to semi-enclosed brackish-water sea. Such development was a result of climatic change, gradual melting of the ice sheet, eustatic sea-level rise, and glacio-isostatic uplift of the Baltic Shield. Broadscale geomorphic features of the area are lagoon plain, shallow water area, gentle slope, and relatively deep water area of the Gdansk Deep (sea depth 80–110 m). The dissolved oxygen content of bottom water in the Gdansk Deep is close to zero. Salinity, nutrient concentration, and oxygen condition in water layers below the halocline are influenced by periodical North Sea inflows. Ecological condition is far from pristine. Moderate nutrient loading, intensive shipping, limited fisheries, the presence of exotic species, oil-drilling platform with underwater pipelines, and three underwater cables all affect the environmental condition of the study area. Two broad groups of benthic habitats are soft-sediment bottoms (89% of surface area) and hard substrate (11%). Benthic faunal assemblages on hard substrata vary in terms of species diversity and abundance, but are dominated by sessile suspension feeders, whereas soft-bottom assemblages are dominated by selective and nonselective deposit feeders. Biodiversity and biomass reach maximum values on hard substrates located between 10 and 25 m water depth; benthos have been absent from depths >83 m in recent years due to oxygen depletion.

Concept of state cadastre of the marine coastal zone of the Russian Federation

State Cadastre of the marine coastal zone of the Russian Federation (RF SCMCZ) is created to ordering of information about resources and capabilities of the coastal zone as a set of data, including qualitative and quantitative inventory of the objects or phenomena and their economic evaluation. The main legal acts necessary for the preparation of methodological and legal foundations of the RF SCMCZ and its filling are the Constitution of the Russian Federation, Land, Water and Forestry Codes and Cadastres, and other laws of the Russian Federation. RF SCMCZ is complex structure document that includes a multi-stage information on administrative, economic, legal, environmental and socio-economic characteristics of a single (coherent) area above and below the modern sea level. RF SCMCZ should be regarded as specially organized set of software and hardware tools to enter, store, save, visualize, analyze, synthesize and present in an easy to use spatially widespread (geographically referenced) information of the marine coastal zones of the Russian Federation. The model of RF SCMCZ as an Information System (IS) realized on the Russian sector of the Baltic Sea which consist the Eastern Gulf of Finland and the Kaliningrad area including their coastal zone.

The coastal profile in the eastern Gulf of Finland: The results of a survey and the reconstruction of the evolution in the Late Holocene

The studies carried out by the Karpinskii All-Russia Research Institute of Geology using side-scan profiling, echo sounding, and surface sediment sampling allowed revealing the detailed structure of the underwater coastal slope in the eastern Gulf of Finland. In particular, a submarine sand terrace was found at depths of 4–5 m. An attempt at the reconstruction of the coastal evolution over the period of the Late Holocene was made using mathematical modeling in order to explain the observed morphology of the submarine coastal slope. The key assumption of the concept suggested is that, at the earlier stage, the tectonic processes played the main role, while, at the later stage, the sea-level changes were of greater importance. The tectonic block comprising the investigated area of the Gulf of Finland at first rapidly increased and then it stabilized and was influenced by the sea level’s rise. These processes resulted in the formation of a series of terraces. The earlier of those are now located on dry land, while the later terraces are observed on the submarine slope. Within the concept proposed, the coastal evolution in the Late Holocene appears as a process of the gradual erosion of the above-water terraces and the formation of new underwater terraces. During the transgressive phases, the rate of the coast’s recession reached 0.5 m year−1, while decreasing by a factor of two during the intermediate stages. The submarine terrace developed over the period of 3.2–1.2 thousand years ago, and it extended in equal measure due to the coast’s recession and the material’s accumulation near its external edge. During that period, the coast retreated by approximately 500 m, while the average accumulation rate could have been as high as 0.7 m3 m−1 year−1.

Seafloor Desertification – A Future Scenario for the Gulf of Finland?

The Gulf of Finland is a shallow semi-enclosed sea area which due to strong anthropogenic pressure and poor water exchange is very sensitive to eutrophication. During its whole postglacial history, the seafloor of the gulf has been periodically anoxic, and anoxia below halocline can thus be seen as a natural phenomenon. During the last decades, however, this has been accompanied by a yearly repeated seasonal anoxia in the shallower basins above halocline. This yearly repeated shallower anoxia is triggered by substantial eutrophication of the sea and is a clear signal of anthropogenic pressure. The seasonal anoxia has during the last decades propagated to basins with water depths less than 20 m. The areal coverage of anoxia has thus expanded substantially. Phosphorus which is bound to oxic seafloor sediments is easily released during episodes of anoxia, which further intensifies eutrophication. It has been estimated that the concretion fields of the eastern Gulf of Finland, only, contain more than 330,000 tons of P2O5 which is equal to some 175,000 tons of elementary phosphorus. In case of shallowing of the area of permanent anoxia, these concretion fields would become anoxic, which would lead to rather rapid dissolution of the concretions and a release of a large amount of phosphorus together with the heavy metals which today are bound to the concretions.

Geological Hazard Potential at the Baltic Sea and Its Coastal Zone: Examples from the Eastern Gulf of Finland and the Kaliningrad Area

Geological hazards may threaten human life, may result in serious property damage, and may significantly influence normal development of biota. They are caused by natural endogenic and exogenic driving forces or generated by anthropogenic activities. An interaction of geological processes and intense anthropogenic activities, e.g., construction of buildings, harbors, oil and gas pipelines, hydroengineering facilities, and land reclamation, has resulted in hazard potential, especially for the densely populated areas of the Russian Baltic coastal zone. These hazards may in addition be harmful for the sensitive ecosystem of the Baltic Sea. Mapping and assessment of the geological hazard potential should be the main objectives of an integrated management program for the protection of coastal zones. This study documents the first step in that process for the Russian sector of the Baltic Sea and its coastal zone. A major part of endogenic hazard potential both in the Kaliningrad area and in the eastern Gulf of Finland remains at low- or medium-risk levels, but analysis of the recent environmental conditions at the seabed of the Russian sector of the Baltic Sea and, especially, within its coastal zone shows that during the last years the activity of exogenic geological processes has increased significantly. The highest risk within both studied areas has been caused by coastal and bottom erosion. In addition, in shallow area near the shore bottom of the eastern Gulf of Finland, “avalanche” sedimentation and sediment pollution can produce hazardous situations as well.