Methane fluxes in the southeastern Baltic Sea

New data from surveys of gas-bearing mud areas in the Gdansk Deep (southeastern Baltic Sea) were collected during four research cruises in 2009–2011. These revealed the presence of seven large pockmarks apart from the three already known, and enabled significant improvement of the existing digital map of gassy mud distribution. Based on geochemical sediment analyses, calculated diffusive methane fluxes from the upper (0–5?cm) seabed layer into near-bottom waters were highest—3.3?mmol/(m²?day)—in pockmark mud, contrasting strongly with the minimum value of 0.004?mmol/(m²?day) observed in typical, background mud. However, fluxes of less than 0.1?mmol/(m²?day) were observed in all sediment types, including pockmarks. In a newer attempt to roughly estimate budgets at a more regional scale, diffusive methane venting amounts to 280?×?10⁶?mmol/day for southeastern Baltic Sea muddy sediments. Elongated pockforms in the southern Gotland Deep, known since the end of the 1980s as pockmarks, had methane concentrations that were similar to those of gassy mud from the Gdansk Basin, and there was no geo-acoustic evidence of considerably increased gas levels.     

Metal sources to the Baltic clam Macoma balthica (Mollusca: Bivalvia) in the southern Baltic Sea (the Gulf of Gdansk)

Metal concentrations of Cu, Fe, Mn, Ni, Pb and Zn in an infaunal facultative deposit-feeding bivalve, the Baltic clam Macoma balthica, in the Gulf of Gdansk (southern Baltic Sea) were assessed and compared to selected concentrations of metals in the environment. Between October 1996 and September 1997, dissolved and easy extractable (by 1M HCl) metal fractions of total suspended particulate matter (TPM) in the overlying water and of surficial sediments (<63 microm) were measured monthly at five sublittoral sites in the Gulf of Gdansk, and accumulated tissue metal concentrations in M. balthica were determined simultaneously. The study highlights the importance of sediment geochemistry as a factor modifying ambient trace metal bioavailabilities. Surficial sediments appeared to contribute most to the accumulation of Cu and Pb in M. balthica, reflecting the high metal availability in the Gulf. Assimilation of Cu from sediments is controlled by Mn components possibly through an inhibitory effect of Mn oxyhydroxides, while Pb accumulation from sediments depends on the organic content of the sediment. A dual metal uptake pathway, with a suspended particulate-bound fraction and surficial sediments, was apparent for Mn and Zn. Partitioning of Mn in sediments was related to the concentration of labile Fe, with increased levels of Fe tending to inhibit the accumulation of Mn by the clam. Tissue accumulated Zn might have been altered by the clam's internal regulation, making Zn tissue concentrations, to some degree, independent of its environmental level. The principal source of Ni accumulated by the clams exists in the soluble phase.     

Development of barrier-lagoon systems in the southeastern Baltic Sea

A comparative study of the geological structure and evolution of the Curonian and Vistula spits representing large barrier-lagoon systems in the southeastern Baltic Sea reveals some geological and geomorphologic differences against the background of their general similarity. It is shown that morphological structures in the Vistula Spit are smaller. The grain-size analysis of the spit sediments demonstrates that eolian sands constitute all the structures of the spits down to the water level and below it (down to depths of 2 m), except for beaches and low lagoonal terraces. This means that the eolian relief on the maritime plain started forming when the sea level was approximately 4 m below its present-day position. Subsequently, they were growing beyond the wave influence. The sea-level rise resulted in the erosion of the coasts of the spits on both the sea and the lagoon sides and provided an intense landward transport of eolian material.     

Egg production of turbot,Scophthalmus maximus,in the Baltic Sea

In the brackish water Baltic Sea turbot spawn at ~ 6–9 psu along the coast and on offshore banks in ICES SD 24–29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378–3474 oocytes/g somatic weight) compared to those from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05 ± 0.03 mm diameter and 46.8 ± 6.5 μg dry weight; mean ± sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish.     

Peculiarities in the distribution of hydrocarbons in the southeastern part of the Baltic Sea

Data on the contents and compositions of the hydrocarbons (HCs)—aliphatic (AHCs) and polycyclic aromatic (PAHs)—are provided in comparison with the contents of the total organic carbon (C_org), the lipids in the particulates, and the C_org in bottom sediments. Particular attention has been paid to the distribution of the HCs in the water area of the Kravtsov oil field. It has been established that the concentrations of AHCs in the water are governed by the content of particulates, and the elevated AHC concentrations are confined to the coastal areas. In the water area of platform D-6, the sandy bottom sediments were notable for the great variability of the HC concentrations, both laterally and from year to year. In the summer of 2010, the content of AHCs averaged 40 μg/g (19% in the C_org), and that of PAHs, 23 ng/g. Natural seepage from the sediment mass is considered to be a source of HCs along with oil contamination.     

Large accumulative forms of relief on the southeastern coast of the Baltic Sea

The paper describes the conditions of formation of large accumulative forms on the southeastern coast of the Baltic Sea and presents the results of a comparative analysis of these structures. It has been established that Baltic barrier–lagoon systems have a complex geological and geomorphologic structure. Sandy barriers, which are, in general, marine accumulative formations, often comprise various fragments of different genesis (moraine remnants, glaciolacustrine and deltaic plains, etc.). The formation and development of large accumulative forms in the southeastern Baltic occurred against the background of sea level fluctuations in the Littorina time following a unified scenario for the entire coast.     

Wintertime temperature-salinity characteristics in the southeastern Hwanghae (Yellow Sea)

Wintertime temperature-salinity properties of the southeastern Hwanghae (Yellow Sea) were analysed, based on long-term hydrographic data gathered between 1961 and 1980. A strong thermohaline front is formed in the area west of Cheju-do (along 33?40′N in the region bounded by 124? E and 126?20′E) during winter and extends to the bottom. This surface-to-bottom front, running from west to east, divides water properties into two types: one type of low temperature and low salinity to the north of the front and another one of high temperature and high salinity to the south of the front. The existence of the front suggests that there is no northward flow in the study area, a finding which runs counter to the conventional belief that there is the Hwanghae Warm Current carrying waters of high temperature and salinity to the north. T-S diagrams show that in winter the Hwanghae Warm Current Water and the Hwanghae Cold Water are the representative water masses in the study area.     

Observation and modeling of upwelling in the southeastern Baltic

The specific features of the upwelling in the southeastern Baltic have been studied by comparing the field observations and numerical simulations. The upwelling registered in October 2005 (when a gale caused by a northeastern wind with a velocity of 15 m/s continued for about three days after a period of relatively calm weather during which the thermohaline structure was in the state close to the summer one) has been considered in detail. The gale caused a decrease in the temperature by approximately 4°C in the along-shore belt with a width of about 8 km in the region with depths of about 25 m located at a distance of approximately 8 km from the shore. The changes in the thermohaline structure that originated as a result of this gale were simulated using a 3D numerical model based on the Princeton Ocean Model (POM). This made it possible not only to consider the variability of the thermohaline fields at the observation region but also to study a rather wide region and to consider the field of velocity in addition to the fields of temperature and salinity. Subsequently, the numerical model made it possible to estimate the upwelling effect during cooling of the upper layer, which was more intense than the effect of turbulent mixing by an order of magnitude. It was confirmed that the specific features of the upwelling spatial structure depend on the geographic position of the upwelling observation region and on the velocity and duration of the wind that causes the upwelling.     

Morphological differences in Macoma balthica (Bivalvia,Tellinacea) from a Dutch and three southeastern United States estuaries

Field collections of the bivalve Macoma balthica in the Dutch Wadden Sea and three southeastern United States estuaries revealed morphological differences between populations of the two sides of the Atlantic Ocean. Individuals of the same age showed much larger shell lengths at the American stations. In addition, bivalves of the same body weight had higher siphon weights at the American stations than at the Dutch stations. This difference in siphon size was related to their burying depths. The American population, which invested more in heavier siphons, was able to burrow much deeper into the sediment (up to 30 cm). Deep burial may be an adaptation to avoid exposure to the high southern temperatures. Furthermore, it may serve as a refuge from blue crab predation. The results of our comparison between the southern American population and the European support the suggestion that populations of M. balthica living in these two regions should be considered separate and sibling species.     

Particulate organic carbon (POC) in surface sediments of the Baltic Sea

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm^–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm^–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm^–3) and moderate POC concentrations (4–7 mg cm^–3). Furthermore, sediment mass accumulation rates (MAR), based on ²¹⁰Pb and ¹³⁷Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m^–2 year^–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.     

Photochemical production of ammonium and transformation of dissolved organic matter in the Baltic Sea

The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH₄⁺ L^− 1 d^− 1. Estimated areal daily production rates ranged between 37 and 237 μmol NH₄⁺ m^− 2 d^− 1, which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.     

Population biology and secondary production of the harvested clam Tivela mactroides (Born, 1778) (Bivalvia,Veneridae) in Southeastern Brazil

The population structure, growth and production of the trigonal clam Tivela mactroides were investigated by monthly sampling between January 2003 and October 2004 in two areas (southern and northern) of the intertidal and subtidal zones of Caraguatatuba Bay, Southeastern Brazil. Intertidal sampling was carried out in each area along eight transects perpendicular to the shoreline. In the subtidal zone of both areas, one 50‐m dredging was performed along five sampling stations arranged on three transects perpendicular to the coast. The intertidal abundance of T. mactroides was higher in the southern (more dissipative conditions) than in the northern area. High abundances occurred in February–March 2004 in the south and in September 2004 in the north. The size structure showed that younger individuals dominated in the sublittoral, indicating that recruitment occurs in this zone, followed by the migration of these individuals to the intertidal, where they complete their life cycle. Tivela mactroides showed continuous reproduction, with 26 cohorts detected in the study period. The lower estimates for the growth index (?′ = 3.22), mortality rate (Z = 2.10 year^?1) and turnover rate (P/B = 1.21 year^?1), and conversely the longer life span (2.5 years) of T. mactroides in Caraguatatuba Bay (24°S) compared with Venezuelan populations (10°N) suggests a latitudinal pattern of these life‐history traits. The high production of T. mactroides in Caraguatatuba Bay was due to continuous recruitment and rapid and continuous growth, and demonstrates the importance of T. mactroides as a biological resource for many marine species and for the local residents.     

Composition of ferromanganese nodules from Riga Bay (Baltic Sea)

An average sample of ferromanganese nodules from Riga Bay was investigated by analytical electron microscopy coupled with atomic absorption, neutron activation, and ICP-MS methods. It is established that the nodules consist of colloform and poorly crystallized Fe and Mn hydroxides with an admixture of dispersed inclusions of better crystallized particles allowing revealing their mineralogical nature by the microdiffraction method. The major mineral phases are ferroxigite and Fe-vernadite with subordinate magnetite, asbolane, and todorokite. The chemical composition of the nodules is dominated by iron followed by cobalt and lead, while nickel, molybdenum, and tungsten associate with the manganese phase. The concentration of several minor elements in the Riga Bay nodules is slightly lower as compared with their average values for the entire Baltic Sea; some elements such as silver, bismuth, cadmium, niobium, tin, and thallium were never analyzed before.     

Benthic re-colonization in post-dredging pits in the Puck Bay (Southern Baltic Sea)

The stage of benthic re-colonization at a site formed by sand extraction was investigated some 10 years after the cessation of dredging. The examined post-dredging pit is one of five deep (up to 14 m) pits created with a static suction hopper on the sandy, flat and shallow (1–2 m) part of the inner Puck Bay (the southern Baltic Sea). The topography of the dredged area makes a specific trap for different kinds of organic matter. It is created by the small areas of post-dredging pits as compared to their depths. As a result, organic matter accumulation leads to anaerobic conditions and hydrogen sulfide formation. Macrofauna was not found to occur permanently in the deepest part (11 m) of the cup-shaped depression, which was characterized by its small area (0.2 km²) and steep walls. However, permanent occurrence of meiofauna (max. 180 ind. 10 cm⁻², mainly Nematoda) was noted. Undoubtedly, re-colonization of benthic fauna assemblages, typical of shallow and sandy seabed of the Puck Bay, will not follow in a natural way in the area of post-dredging pits. Also, it could not be expected that the re-colonization sequence would result in the formation of a structure similar to that of the natural depression (the Kuźnica Hollow).     

Geological structure of the Curonian Spit (of the Baltic Sea) and its evolution history (revised)

The origin and evolution history of the Curonian Spit in the Baltic Sea are discussed based on geological and geomorphologic data. Evidence of the correlation between the spit formation stages and the Holocene sea level oscillations is presented. The ledges of moraine basement and marine accumulative features formed a single barrier. Its subsequent transformation occurred under the influence of the wave-related lithodynamic and eolian processes.