Browsing by Subject "Gulf of Finland"
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(2019)The Baltic Sea is a vulnerable marine environment and susceptible to pollution. The situation is especially severe in the Gulf of Finland due to a large catchment area compared to the size of the Gulf. The north eastern Gulf of Finland has been described as one of the most contaminated areas of the entire Baltic Sea, with extensive pollution load via river Kymi in the past. Still today, the currents bring contaminants from the eastern part of the Gulf – the Neva estuary and the Bay of Viborg. The concentrations of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Hg, Pb, Bi and La were studied in the surface sediments and three GEMAX cores. The vertical distribution revealed the temporal change in the metal accumulation. The spike in the Cs concentration, indicating the Chernobyl disaster in 1986, enabled the estimation of the accumulation of studied elements over time. The horizontal distribution maps based on the concentrations in the surface sediments enabled the discovery of the sites with most intense metal accumulation. Correlation coefficients showed the effect of carbon and sediment grain size in the distribution of metals. The comparison of the metal concentrations to the natural background levels and the Canadian sediment quality guidelines (SQGs) enabled the estimation of the degree of contamination of the area. The metal concentrations have declined during the last decades in the north eastern Gulf of Finland, indicating lower contamination input towards present day. However, in the oxidized Ravijoki core, the decline was not that obvious, probably due to metal scavenging by Fe and Mn oxides and bioturbation. The regional metal distribution was strongly affected by the grain size and carbon – most metals showed high positive correlations with carbon and finer sediment fraction. Mn was an exception, showing negative correlations with both carbon and clay, probably due to the Mn reduction at sites with high organic matter accumulation. The regional distribution pattern suggested main Cd pollution arriving from the eastern part of the Gulf. The distribution of Hg, Mo, Cu and Zn also suggested a possible source in the east. High concentrations of Hg, Pb and Cu were discovered in the outlets of river Kymi. According to the Canadian SQGs, the sediments in the north-eastern Gulf of Finland were contaminated. The situation is especially severe in the case of Zn – the higher reference value PEL, above which adverse biological effects frequently occur, was exceeded even in the oxidized Ravijoki sediments. The highest concentrations of the elements with defined SQGs (Cd, Cr, Zn, Cu, Hg, Pb and As) exceeded the lower reference values in the surface sediments, indicating that all these metals could, at least locally, pose a severe threat to benthic species.
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(2022)Eutrophication and harmful substances of anthropogenic origin threaten the state of the Baltic Sea and especially its geochemistry and oxygen levels near the seafloor. Water exchange between the Baltic Sea and the Atlantic Ocean can affect oxygen circulation and sedimentation rates, but they are considered very sporadic and it is unclear how the water circulation and flow rates affect element concentrations and sediment deposition in the near seafloor environments. One of the less studied basins is the Western Gulf of Finland and its seafloor environment. During the 2019 voyage, the seafloor located to the south of the city of Hanko was investigated through bathymetric sounding tools and other measurements in which element concentration and sediment deposition rate data was acquired. The sounding revealed a large channel cutting the seafloor which was hypothesized to influence the nearbottom conditions. The obtained data consisted of samples from 13 short, 40 cm sediment cores which were analysed for 137Cs activity, organic content, and grain size distribution. The goal of the thesis was to determine the intensity of water exchange taking place in the seabed channels between the mid-Baltic Sea and the Western Gulf of Finland and investigate the effect of the seafloor channel and flow rates on sediment and element deposition, their relationships, and how they affect the overall conditions in the study area. These relationships were analyzed through spatial and statistical methods by utilizing GIS-tools to interpolate the data obtained from the study locations by using the Inverse Distance Weighting (IDW) method, and by multielement analyses in the R-environment, namely Principal Component Analysis (PCA) and Partial Least Regression (PLS) to analyze grain size and element concentration correlations and combine them with obtained flow rate data. The results showed strong correlation in flow rate intensities between the Western Gulf of Finland and the mid-Baltic Sea, and they are strongly linked with sedimentation and element deposition rates. However, no long-term trend was identified for the seafloor channel velocity frequencies. The Cs-activity shows stronger sedimentation activity on the western side of the seafloor channel. The overall element and sediment deposition in the study area was largely controlled by monthly and seasonal current velocity fluctuations among other processes. The element concentration comparison showed weakened oxygen conditions in the study area with increased eutrophication and carbon burial since the 1950s. The principal Component Analysis showed smaller grain sizes (0.15 - 2 mm) having a stronger influence on the datasets with Mo, N, and C providing largest variation in the data. Interpolation showed oxygen, pH, and H2S to have more fluctuation in the study area, which can indicate changes in the vertical gradients in each sample point. It could also be determined that other measured concentrations, such as temperature, turbidity, and salinity do not respond very sensitively to water inflow fluctuations or sedimentation rate changes. The results indicate that harmful substances and eutrophication are most likely going to increase in the near-bottom environment in the Western Gulf of Finland, contributed by anthropogenic activity. Water exchange is likely to become more and more uneven, thus affecting the flow rate effects to the sediment deposition in the Baltic Sea. Further studies are needed to link these processes to large-scale global changes and the general state of changes happening in the Baltic Sea and its surrounding areas. The seafloor of the Western Gulf of Finland could also be studied further to gain a better understanding of longer timescale changes on the seafloor channel currents, and element and sediment deposition rates.
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