Ö. Baştürk

Heavy metal concentrations in surface sediments from the two coastal inlets (Golden Horn Estuary and İzmit Bay) of the northeastern Sea of Marmara

A total of 57 surficial sediment samples collected in the Golden Horn Estuary and Izmit Bay (northeastern Marmara Sea) was analyzed for the heavy metals Fe, Mn, Cr, Ni, Co, Zn, Pb, and Cu and the results were compared with various natural and anthropogenic sources. It was observed that the concentrations of Zn, Cu, Pb, and, to some extent Cr, in the Golden Horn sediments are comparable with those in most other seas in the vicinity of highly industrialized and densely populated regions. Based on calculations from the metal: Al and metal: Fe ratios, the bottom sediments of Golden Horn were found to be enriched in Zn, Cu, Pb, and to a lesser extent Cr, by factors of up to 192 compared with the regional background levels of these metals. Fe, Mn, Co, and to some extent Ni, are mostly at natural levels. In contrast, the metal levels of the bottom sediments in Izmit Bay are significantly lower and they appear to be controlled by lithogenic rather than the anthropogenic influences. Highly significant correlation coefficients between the metals Zn, Cu, and Pb are widely attributed to the common sources of these metals, the metal smelters and shipyards in the vicinity of the areas studied. Based on the numerical value of the geoaccumulation index of heavy metals, it was found that the bottom sediments of Izmit Bay can be regarded as basically uncontaminated. Exceptionally high Igeo values are found for the bottom sediments of the Golden Horn, indicating moderate to extreme contamination in this region by the metals Pb, Zn, Cu, and Cr. The presence of a large number of anthropogenic metal point sources, higher river run-off via the two major creeks, particularly coastal topography and hydrodynamic conditions, associated with the very high sedimentation rates, all strongly favour the accumulation of anomalously high metal concentrations in the Golden Horn Estuary, while the opposite is true for Izmit Bay.

Transport and distribution of nutrients and chlorophyll-a by mesoscale eddies in the northeastern Mediterranean

Abstract The distribution of nutrient elements and chlorophyll- a in the Northern Levantine Basin (NLB) were investigated in some detail and are discussed together with the physical aspects of the region in the present study. The surface circulation pattern of the NLB was studied and the structure of the relatively large-scale Rhodes cyclonic gyre, which is located between Rhodes and Cyprus, was investigated for the same time period. The most important characteristics of this cyclonic gyre are the upwelling of nutrient-rich deep waters within the gyre and the reverse phenomenon at the peripheries. Anticyclonic circulation systems generally surround the Rhodes cyclonic gyre; the permanent ones are located in the southern part of the Rhodes gyre, in the Cilician Basin, and off Iskenderun Bay. The vertical distribution of nutrients in the water column shows completely reversed trends and the nutrient gradient ranges between 300–400 m in the central parts of the anticyclonic systems. Thus downwelling processes also occur in the NLB and the formation of Levantine Intermediate Water (LIW) observed in the NLB matches the chemical data presented here. This special vertical and spatial distribution of nutrients affects the distribution of the phytoplankton population, as the patches of primary producers are aggregated in the central parts of the Rhodes gyre. This is confirmed by the chlorophyll- a data and the unexpected content of neuston net collection in the same region. The concentration of chlorophyll- a was relatively high at offshore stations, such as in the central parts of the cyclonic gyres, where zooplankton, small shrimp and fish larvae, etc., were observed in large quantities.

Identification of the oxic/anoxic interface by isopycnal surfaces in the black sea

The analysis of hydrochemical data collected in the Black Sea since 1987 shows that the upper boundary of the oxic/anoxic interface zone coincides with the nitrate maximum at the depths of σ t ⋍ 15.40 ± 0.10 isopycnal surface. Its lower boundary corresponds to the phosphate maximum depth at σt ⋍ 16.20 ± 0.05 isopycnal surface, independent of the geographical location and seasion. In the absence of the continuous pump cast measurement system, and when the oxygen and sulphide concentrations are too low to be measured with sufficient precision within the interface zone, such features of the oxygen-nitrate and H2S-phosphate correlations at specific density levels provide a direct and practical way to identify the oxic/anoxic interface zone. This, in turn, allows for a more precise and systematic water sampling for studying the complex biogeochemistry of the layer.

Vertical variations in the principle chemical properties of the Black Sea in the autumn of 1991

Abstract Basin-wide principal hydrochemical data for the upper 500 m of the Black Sea were obtained at a total of 197 stations during a multi-ship, multi-institutional, Hydroblack -91 cruise in September 1991. Only offshore stations, 38 from the 1991 joint cruise, 5 from R/V Knorr (1988), 16 from R/V Atlantis-II (1969), and 9 from R/V Bilim (1990) cruises, are considered in conjunction with the present and past data as a function of potential density rather than depth. The oxycline, coinciding with the upper boundary of the permanent pycnocline (σΘ = 14.2–14.3), extended down to the σΘ = 15.3–15.4 surfaces during warm periods (June–September) and to the σΘ = 15.75 surface during spring periods. The lower boundary of the oxycline (O2 ⩽ 20 μM) has remained constant within the last two decades when past and present spring data are considered, but has risen by 0.30 density units when late summer-autumn data are considered. Independent of the geographical location, the base of the transition layer was established at the σΘ = 16.15–16.20 surfaces where H2S ⩾ 5 μM. Nitrate and phosphate reached their maxima at σΘ = 15.3–15.4 surfaces and then decreased steadily with different slopes until the σΘ = 15.85 –15.95 surfaces. At the anoxic interface, phosphate concentration increases about 10 fold from ∼ 0.02 –0.5 μM at the σΘ = 15.85 –15.90 surface to 4 –6 μM at the σΘ = 16.15 –16.20 surface. Comparison with the data from the 1970s suggests that both the maximum values and the depth integrated mass of nitrate (g NO3—N/m2) between the σΘ = 14.2 and 16.0 surfaces have increased 2–3 fold, and the density surface where the NO3 maximum is established has shifted by 0.30 units in the late 1980s.

DDT, DDE, and PCB residues in fish, crustaceans and sediments from the eastern Mediterranean coast of Turkey☆

Abstract Residues of DDE, DDT and PCBs were determined in four different commercial bony fishes: grey mullet, red mullet, striped mullet and gold bandgoat fish, as well as in shrimps, limpets and sediments obtained from the eastern Mediterranean coast of Turkey. The PCB levels in living organisms and sediments were found to be very low, and in most cases below the detection limits. The DDE and DDT values were relatively high compared to PCBs and there was a linear correlation between the organochlorine residue concentrations and the extractable organic material of the analysed samples.

Reduction of volatile halocarbons in anoxic seawater, results from a study in the Black Sea

Abstract The Black Sea is characterised by an oxic surface water layer and anoxic deep water rich in both hydrogen sulphide and methane, and in between a suboxic zone with very low concentrations of both oxygen and hydrogen sulphide. This makes the Black Sea a useful site for the study of oxidation-reduction reactions in seawater. In this study, the distributions of tetrachloromethane, trichloromethane, 1,1,1,-trichloroethane, dibromomethane, dibromochloromethane and bromodichloromethane across the oxic-anoxic interface were related to the oxygen/hydrogen sulphide concentrations and thereby the redox potential gradient. All of the investigated halocarbons decrease rapidly in concentration as the oxygen decreases, most likely due to reduction. The results show that the higher the redox potential of a halocarbon, the higher up in the water column, i.e. at a higher oxygen level, reduction occurs. Most of the tetrachloromethane is transformed to trichloromethane as an intermediate product.

Elemental composition of seston and nutrient dynamics in the Sea of Marmara

The Sea of Marmara, an intercontinental basin with shallow and narrow straits, connects the Black and Mediterranean Seas. Data obtained during 1991–1996 have permitted the determination of the elemental composition of seston in the euphotic zone and the N: P ratio of the subhalocline waters of the Marmara Sea. Since primary production is always limited to the less saline upper layer (15–20 m), of the Marmara Sea, the subhalocline waters of Mediteranean origin are always rich in nutrients (NO3 + NO2 = 8–10 µm, PO4 = 0.8–1.2 µm) but depleted in dissolved oxygen (30–50 µm) throughout the basin, yielding an - 02: N: P ratio of 178: 9: 1. Pollution of the surface waters since the 60s has modified the subhalocline nutrient chemistry slightly. In the euphotic zone, the N: P ratio of the seston changes from 5.9 to 9.5 between the less and more productive periods. Though the biology of the Marmara has changed significantly during the previous two decades, the close relationship observed between the elemental composition of the surface seston and the NO3: PO4 ratio of the subhalocline waters strongly suggests that during the whole year primary production throughout the basin and POM export to the lower layer remain nitrogen-limited. This suggestion needs to be confirmed by bio-assays, biological studies and sediment trap data from the upper subhalocline depths. Nonetheless, the counterflows in the Marmara basin possess relatively low N: P ratios in both dissolved and particulate nutrients and extend as far as the adjacent seas.

Variations in the Vertical Structure of Water Chemistry within the Three Hydrodynamically Different Regions of the Black Sea

High-resolution, basin-wide chemical data reveal that the Black Sea upper layer possesses distinct chemical features at specific density surfaces, but with some noticeable regional differences in their positions and magnitudes. The nitracline, is consistently established at smaller density surface relative to the phosphocline over the basin; thus, N:P molar ratios appear to be unexpectedly high (40–80) within the upper nutricline, especially in the anticyclonic regions (ACR). The ratio drops to levels of 4–8 at the nitrate maxima formed within the base of the main oxycline. Phosphate profiles display a prominent minimum within the suboxic zone of the cyclonic regions (CR), which weakens markedly within the coastal regions and rim current. Vertical distributions of chemical ratios have led to valuable information on the relative fluxes in the oxic/anoxic transition zone as well as the quality of data sets from different years.

Comparison of five humic acids

Abstract The ultimate analyses, u.v-visible absorption spectra, fluorescence spectra and i.r. spectra of five humic acids have been studied. One was obtained commercially from peat, two from organic-rich soils, one from an estuary and one from a marine sediment. The u.v. spectra were used to compare average molecular weights which varied from 800 to 7000 and increased with the atomic H C ratio. Fluorescence appeared to be due to poly-nuclear aromatic structures. All the humic acids showed maximum excitation at 360 nm and developed maximum emission in the range 430–455 nm but the humic acids from sediments showed an additional emission maximum at ~410 nm. Fluorescence from the peat humic acid was broad and secondary emission was observed with a maximum at 520 nm which was attributed to the formation of excimers. Fluorescence has been used to monitor the interaction of cations with humic acids in solutions of different ionic strengths which shows promise for distinguishing between metat—humate complex formation and the coagulation of a colloid. The structures of the humic acids are discussed in terms of the structures possessed by lignites.

Spatial Isopycnal Analysis of the Main Pycnocline Chemistry of the Black Sea: seasonal and interannual variations

The results of 1991–1994 basin-wide investigations have been analysed using the method of spatial isopycnal analysis. Seasonal and interannual variations of phosphates, nitrates, dissolved oxygen and the suboxic zoneare revised. The range and possible reasons of spatial and temporal variations in the density-dependent vertical profiles of nutrients and oxygen in the layer of the main pycnocline, in the thickness and the position of suboxic zone of the Black Sea are discussed.