Mustafa Ergin

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.

Partitioning of heavy metals in surface Black Sea sediments

Abstract Bulk heavy metal (Fe, Mn, Co, Cr, Ni, Cu, Zn and Pb) distributions and their chemical partitioning, together with TOC and carbonate data, were studied in oxic to anoxic surface sediments (0–2 cm) obtained at 18 stations throughout the Black Sea. TOC and carbonate contents, and available hydrographic data, indicate biogenic organic matter produced in shallower waters is transported and buried in the deeper waters of the Black Sea. Bulk metal concentrations measured in the sediments can be related to their geochemical cycles and the geology of the surrounding Black Sea region. Somewhat high Cr and Ni contents in the sediments are interpreted to reflect, in part, the weathering of basic-ultrabasic rocks on the Turkish mainland. Maximum carbonate-free levels of Mn (4347 ppm), Ni (355 ppm) and Co (64 ppm) obtained for sediment from the shallow-water station (102 m) probably result from redox cycling at the socalled ‘Mn pump zone’ where scavenging-precipitation processes of Mn prevail. Chemical partitioning of the heavy metals revealed that Cu, Cr and Fe seem to be significantly bound to the detrital phases whereas carbonate phases tend to hold considerable amounts of Mn and Pb. The sequential extraction procedures used in this study also show that the metals Fe, Co, Ni, Cu, Zn and Pb associated with the ‘oxidizable phases’ are in far greater concentrations than the occurrences of these metals with detrital and carbonate phases. These results are in good agreement with the recent studies on suspended matter and thermodynamic calculations which have revealed that organic compounds and sulfides are the major metal carriers in the anoxic Black Sea basin, whereas Fe-Mn oxyhydroxides can also be important phases of other metals, especially at oxic sites. This study shows that, if used with a suitable combination of the various sequential extraction techniques, metal partitioning can provide important information on the varying geological sources and modes of occurrence and distribution of heavy metals in sediments, as well as, on the physical and chemical conditions prevailing in an anoxic marine environment.

Heavy-metal geochemistry of surface sediments from the southern Black Sea shelf and upper slope

Abstract A wide variety of sediment types (mud to sandy gravel) was obtained at fourty-seven stations on the southern Black Sea shelf and upper slope and analyzed for their heavy-metal geochemistry. Distribution of grain size, carbonates, organic carbon and heavy metals show marked changes in the topography, biological activity and land geology of the region studied. Sediments constitued up to 39% CaCO3, mainly of biogenic origin from the shell remains of benthic organisms. Organic carbon contents of the sediments (0.13-3.09%) usually reflect the prevailing primary productivities in the Black Sea although significant terrigenous influences are also inferred. The heavy-metal concentrations largely indicate the influences from the geochemical weathering of terrigenous sources on land. In comparison with the average sedimentary rocks and other modern sediments from the adjacent regions, the concentrations of Cr, Ni, Cu, Zn and Pb are somehow higher in the surface sediments from the southern Black Sea. In particular, Cr, Ni and Cu are found in high abundances in the eastern parts of the study area. This is thought to reflect not only the well-mixed fine-grained nature of the sediments but also the possible contribution from metal-rich rocks (mafic and ultramafic sources) and associated economic mineral deposits in the catchment areas of rivers which drain this part of the coast. The presence of significant positive correlations between the concentrations of Cr and Ni, and Zn and Pb strongly suggest common sources and/or similar enrichment mechanisms for these metals. The relationships among the geochemical variables revealed that Fe and Mn (oxides, hydrates and sulfides), and organic phases together with the clay-and silt-sized grain fractions are the important associations of the studied heavy metals.

Distribution of surficial shelf sediments in the northeastern and southwestern parts of the Sea of Marmara: Strait and canyon regimes of the Dardanelles and Bosporus

Surficial sediment samples collected from the northeastern and southwestern shelf regions of the Sea of Marmara, together with data available from other sources, indicate marked variations in sediment compositions resulting from differences in topographical, hydrological and biological conditions. In the strait channels of the Dardanelles and Bosporus, where strong undercurrents prevail, the floor was covered mostly by coarse-grained sediments (rich in sand and gravel). However, in areas of relatively low energy conditions, sediments contained appreciable amounts of mud, with a tendency towards an increase in the amount of clay towards the open sea. The effects of the strong undercurrents on the bedforms was also apparent in the southern Strait of Bosporus where sidescan sonar surveys revealed the presence of asymmetrical sand ripples. Although terrigenous mud is the principal sediment type in the two canyons (Dardanelles and South Bosporus), the sediments, in particular on the floor of South Bosporus Canyon, show a distinct contrast between the inner N-S and outer E-W trending parts: along its axis, where depths are greatest, the outer part of the canyon appears to contain much more coarse sediment (in part derived from the benthic communities) than the inner canyon. In general, both the topography-related current regimes and the biological activities in the study areas mostly determine the types and modes of sediment distribution. Among the biogenic components, the calcareous corraline algae Rhodophycae (chiefly Lithothamnium calcareum and L. fruticolusum) and the molusc families Galeommatacae and Cerithiospidae are associated with the prevailing Mediterranean undercurrents, especially in the shallower waters of the junction of the Sea of Marmara and Strait of Bosporus. The relatively abundant mollusc species Mytilus galloprovincialis and Modiolus barbatus and the Trochidae in the Strait of Bosporus are largely affected by Black Sea waters. The wide range of carbonate concentrations in the sediments generally reflects the relative abundances of biogenic admixtures in the samples. High carbonate percentages in the sediments are usually associated with low mud contents, and vice versa. Interestingly, the organic carbon contents of the sediments generally increase with proximity to the Black Sea, suggesting influxes of appreciable amounts of organic matter from the Black Sea.

Organic carbon distribution in the surface sediments of the Sea of Marmara and its control by the inflows from adjacent water masses

Abstract The organic carbon contents and textural composition of a total of 166 surficial sediment samples (from 10 to 1226 m water depths) together with data on primary productivity rates and dissolved oxygen concentrations have been studied to investigate the main controls on the distribution of organic carbon buried within the modern sediments across the Sea of Marmara. The distribution of average annual primary production rates in the Sea of Marmara exhibits great lateral variations; the highest values are calculated for the southern shelf (161 gCm −2 year −1 ), the areas with high terrigenous input supplied by the southerly major rivers, and on the northeastern shelf (104 gCm −2 year −1 ) where organic- and nutrient-rich surface inflow from the Black Sea is prominent. The low primary productivities estimated for the southwestern shelfof the Sea of Marmara (64 gCm −2 year −1 ) suggest influences from the relatively organic- and nutrient-poor subsurface inflow from the Aegean or Mediterranean. Organic carbon contents in sediments from the northeastern (0.37–2.16%), northern (0.57–1.64%), southern (0.44–1.90%) and southwestern shelf regions (0.37–1.51%) all appear to be within the same range and show no direct relationship with surface productivity and oxygen deficiency in the Sea of Marmara. Production and accumulation of organic matter in the Sea of Marmara are believed to have been mostly affected by the inflow of relatively organic-rich Black Sea waters, by the southerly major rivers, and by inflow of organic-poor Aegean or Mediterranean waters. Lateral offshore transport in surface waters must have resulted in the decrease of organic carbon fluxes to the sediments.

Sea-level changes and related depositional environments on the southern Marmara shelf

Abstract Petrographic data obtained from 182 surface sediment samples together with the available bathymetric data are used to investigate the effects of the last major sea-level changes on shelf evolution in the southern Sea of Marmara. Grain-size analysis reveals the presence of at least three belts or zones which are rich in coarse-grained (sand and gravel) sediments. These coarse-grained belts which are up to 45 km long, 15 km wide, show up to 20 m of relief and are presently found at 40–80 m (average 60 m) water depths. Based on microscopic examination and residual analysis, the sediments from these belts are interpreted as indicators of high-energy shallow waters where detrital siliciclastics, with some benthic contribution, accumulated. The presence of a 62–65 m deep sill in the Canakkale Strait and the consideration of sea-level curves would suggest that the Marmara shelves must have been subaerially exposed down to −65 m water depths for about 10,000 yrs (22,000–12,000 yrs B.P.), sufficient time to modify former shelf topographies and form such bottom relief. While difficult to date, we believe that coarse-grained belts found on the southern Marmara shelf must be relict (i.e., former shorelines, beaches) and their formation is largely related to low stands of sea-level during the Late Pleistocene regression and early Holocene transgression. However, the available high-resolution seismic profiling data suggest that the neotectonism in this seismically active Sea of Marmara plays an important role to explain the raise of these older shorelines to their present levels on the sea-floor.

Geochemical characteristics of the recent sediments from the Sea of Marmara

Abstract Six box-cores, one boomerang core and one hundred sixty-six surface sediment samples recovered in the Sea of Marmara were analyzed in an attempt to establish the main controls on distribution and origin of trace metals within the oxic to suboxic basin of this sea. Surface and downcore data indicate that the abundance and distribution of the total metal concentrations for Fe, Ni, Zn, Cr, Co, Cu and Pb can largely be explained by the variable admixtures of terrigenous components in response to textural variations and biogenic calcareous components poor in metal contents. The distribution of Cr and Ni seems to be controlled, in part, by a contribution from the weathering of basic/ultrabasic sources on the coastal hinterland. A small but significant amount of Cu, Zn and Pb in sediments from the northeastern Sea of Marmara probably suggests a pollution effect from the northerly located Golden Horn Estuary that is known as one of the most polluted coastal regions of Turkey. Looking at the data, it seems that the Mn concentrations are unusually high in the deep-water sediments (4498–9127 ppm, carbonate free), along the east-west-trending Marmara Trough but low in sediments from the adjacent shallow waters (307–2059 ppm, carbonate free). The Mn enrichment in deep-water relative to shallow-water Marmara sediments is further indicated by the Fe/Mn ratios being, on average, 11–23 in deep waters and 34–69 in shallow waters. The contents of other metals (Fe, Ni, Zn, Cr, Co, Cu, Pb) in both shallow- and deep-water sediments fall nearly within the same range as those found in average crustal and sedimentary rocks, suggesting no significant enrichment of these metals in the deep Marmara basins. the downcore changes in the color, from reddish-brown at the surface (top 2–5 cm) to greenish-gray in the subsurface (5 cm), together with the occurrence of high Mn concentrations in the surface sediment layers in cores can be attributed, at least in part, to the diagenetic Mn enrichment within the sediment column. The usually low organic carbon contents and biogenic components present in sediments reflect that the well-known biogenic mechanism for the enrichment of Mn seems to be of minor importance in the deep Marmara waters. The generally low Mn concentrations contained in the surface (grab) and core sediments from the Black Sea and Aegean Sea approaching those of the Sea of Marmara do not provide any conclusion to support significant Mn contribution from these two adjacent seas, particularly from the so-called “manganese pump” zones in the shallow Black Sea waters. Comparison with other deep-sea sediments which have been deposited under the influences of hydrothermal activities, worldwide, suggests Mn enrichment in deep-water relative to shallow-water sediments of the Sea of Marmara, mainly as a result of hydrothermal contributions from this seismically active marine region. Based on the average Fe/Mn ratios obtained in cores, which tend to increase gradually from ∼11 in the deep Central Basin to ∼67–69 in the northeastern and southwestern shelves, the Central Basin of Marmara Trough can be considered as a possible, potential source for hydrothermal solutions leading to the enrichment of Mn in the deep Marmara waters. However, this remains to be further investigated.

Early diagenesis of organic matter in recent Black Sea sediments: characterization and source assessment

Abstract The organic matter in 9 recent (not more than 250 years old) and ‘organic-rich’ sediments from the southern Black Sea shelf and upper slope have been characterized semi-quantitatively by Pyrolysis/Gas Chromatography/Mass Spectrometry (PY/GC/MS) and13C Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance (CPMAS-NMR) spectrometry. The organic matter of 7 of the studied sediments was found to be ligno-carbohydrate with a proteinaceous component, one sediment appeared to contain oxidized coal dust and one contained thiophenes in association with pyrite. The ligno component is derived from grasses and soft wood lignin. Material entrapped in an anoxic environment contained the highest proportions of carbohydrate and protein. All the samples had suffered diagenesis as is generally shown by the attachment of carboxyl groups and the removal of methoxyl groups. The evidence suggests that diagenesis occurred whilst the particles traversed the oxic water column.

Distribution and texture of the bottom sediments in a semi-enclosed coastal inlet, the Izmit Bay from the eastern sea of Marmara (Turkey)

Thirty-one surficial sediment samples were collected from the floor of Izmit Bay with a grab onboard the RV Bilim in summer 1987 and analysed for their grain size, total carbonate, and organic carbon distribution. Low calcareous-terrigenous mud (2–45% CaCO3) with a relatively high silt percentage was the principal sediment type found on the floor of Izmit Bay. Sediments rich in sand and gravel usually occur in the narrow and shoal areas of the bay, where biogenic and topography-related hydrodynamic conditions are dominant factors controlling the nature of bottom deposits. The carbonates are made up almost entirely of the remains of calcareous organisms. Organic carbon concentrations of the sediments (0·35-1·62%) are probably associated with the high primary production rates in this region. Thus, the rates of sedimentation in the Izmit Bay calculated from the organic carbon and primary productivity data are estimated to be up to 70 cm/1000 years.

Source and depositional controls on heavy metal distribution in marine sediments of the Gulf of İskenderun, Eastern Mediterranean

The concentrations of major (Al, Mg, Fe, and Mn) and trace (Zn, Cr, Ni, Co, Cu, and Pb) elements as well as carbonate, organic carbon, and grain size distributions have been determined in surface sediments collected at 73 stations from the Gulf of Iskenderun. The shelf sediments of the Gulf of Iskenderun are largely muds but sediments with higher contents of sand and gravel also occur due to the presence of high biogenic CaCO3 contents (up to 80%) in the samples. The abundance and regional distributions of elements in the surface sediments of the Gulf are largely controlled by differences in grain size and in the level of dilution by skeletal/shell remains, and by the variation in composition of source materials. Mg, Ni, Cr, Co, and to a lesser extent Zn and Pb, are significantly enriched relative to their average crustal abundances. These metal enrichments are found especially in the eastern part along the SW-NE-trending areas of the Gulf and are mostly consistent with the chemical and mineralogical compositions of the major basic and ultrabasic source rocks present on the adjacent coast and hinterland. There is strong evidence that suggest that aluminosilicates, Fe and Mn compounds (possibly oxyhydroxides), and organic matter act as the most effective carriers for transfer of available metals (Zn, Cr, Ni, Co, and Cu) to the sediments.