Spatial distribution and recent changes in carbon, nitrogen and phosphorus accumulation in sediments of the Black Sea (original) (raw)
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2000
A positive correlation between the finer grain size fractions (clay and/or silt) and TOC was well established long ago (Buchanan and Longbottom, 1970; Mayer, 1994; Tyson, 1995 etc.). The close association of the two components is probably explained by both the capacity of the finer particles to hinder the diffusion of the oxygen into the sediments, thus favoring the preservation of organic matter and the adsorp-tion of organic particles onto the charged surfaces of the clay minerals. The last process largely depends upon the specific surface of the sediment, so much so that sometimes this parameter is preferred over the percentage of finer fractions as independent variable, determining the TOC concentration in sediments. Of course there is not a unique, generally valid relation. There are important local variations, determined mainly by the local primary production, sedimentary rates and oxygen regime in the water column and sediments. The mathematical relation between the percentag...
Global Biogeochemical Cycles, 1994
Sedimentologic and geochemical studies of box and gravity cores recovered from the Black Sea during the first leg of a multileg international Black Sea expedition in 1988 allow reconstruction of the basinwide Holocene environmental history of the Black Sea. In the deeper parts of the basin, box cores typically recovered a flocculent surface layer ("fluff"), laminated coccolith marls of Unit I (25-45 cm thick), and the upper 5-10 cm of finely laminated, darkcolored sapropels of Unit II. Fine-grained, homogeneous mud turbidites are interbedded with Units I and II over much of the basin, but the stratigraphic position of these turbidites differs from site to site. The deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae. Sediment trap deployments in the Black Sea suggest that light and dark laminae couplets represent annual increments of sedimentation (i.e., varves); we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events. Distinctive groups of laminae in Unit I can be correlated across the entire deeper basin (a distance of more than1000 km). This implies a remarkable homogeneity in production, accumulation, and preservation of biogenic material over much of the Black Sea during deposition of Unit I. The change from deposition of finely laminated, organic carbon-rich sapropels (Unit II) to laminated, more calcareous, coccolithrich marls (Unit I) is thought to represent the crossing of a salinity threshold for Emiliania huxleyi. The varve chronology sets this change at about 1.63 ka (1633+100 yr B.P.), but the record of magnetic secular variation measured in several cores produces an age estimate of about 2.0 ka for the base of Unit I, or about 1.2 times the varve age. The average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of Unit I is 2.7 ka, or about 1.7 times the varve age. Following the initial change to coccolith-dominated sedimentation, deposition of sapropel resumed for at least one significant period, 1.56-1.25 ka. Since 1.25 ka, cycles of carbonate deposition with quasi-decadal periodicities have produced characteristic darker and lighter assemblages of laminae. These cycles may have been climatically driven. Geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in Unit I (averaging 35-45 g m '2 yr -•) than in sapropelic Unit II, which contains primarily detrital carbonate. The accumulation of lithogenic components in parts of Unit I is only 1.5 times the rate in Unit II. Deepwater organic carbon accumulation rates are somewhat higher in Unit I (3.5-4.5 g m-2yr '•) than in the upper part of Unit II. Organic carbon accumulation rates in Unit I are somewhat antithetic to those of carbonate, and on the basis of this and additional constraints placed by pyro!ysis and carbon isotopic analyses of organic material, it appears that terrestrial organic matter is an important component (perhaps >25%) of total organic carbon burial in the basin. Unit I in the western part of the Black Sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than Unit I in the eastern part. This difference between eastern and western Black Sea is to be expected because of the major rivers that empty into the western Black Sea from eastern Europe, Ukraine, and Russia. Shallow slope sites, but still within euxinic bottom waters, have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites, suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center. A comparison of the Black Sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions. For a given bulk accumulation rate the organic carbon accumulation rates, normalized to primary productivity, are about the same in both settings.
Geochemistry and sedimentology of shelf and upper slope sediments of the south-central Black Sea
Marine Geology, 2006
Eighty-five surface samples from oxic, suboxic and anoxic sites of the south-central Black Sea shelf consist predominantly of clayey silts and silty clays, reflecting the moderate-to-high energy, wave-dominated hydrological regime. Grain size data and net sediment transport patterns suggest that the western part of this shelf is an area of east-directed active sediment transport. With the, exception of localized nearshore zones, the eastern shelf is by contrast an area of major sediment deposition. The sediment transport vectors are correlated with patterns of surface water circulation and storm-generated longshore currents.
Reprint of Dissolved organic carbon and nitrogen in the Western Black Sea
Marine Chemistry, 2008
Dissolved organic carbon and nitrogen (DOC and DON) concentrations were measured in the Black Sea during May-June 2001. Sampling was conducted along a Shelf-Gyre transect, and was focused at the suboxic-anoxic interface at the deep stations; hypotheses were tested regarding trends in these variables across the transect and between sub-surface water layers. DOC and DON concentrations were higher (272 μM and 15 μM, respectively) on the Shelf compared to the Gyre (200 μM and 11 μM, respectively), as a result of terrigenous inputs and in situ net production. The bulk DOC:DON ratio was constant with distance and depth (approximately 15-19). DOM concentrations decreased with depth (average anoxic layer concentrations of 123 μM and 6.1 μM for DOC and DON, respectively), in contrast to earlier observations of increasing DOC concentration with depth. The deep Basin (2000 m) DOC concentrations were high compared to deep open ocean values (120 vs 45 μM). We suggest that the high deep DOC is a product of mixing of terrigenous (300 μM) and Aegean Sea (60 μM) DOC, with some in situ decomposition over the 600 year residence time for the deep water mass. High surface concentrations of DOC and DON and high DOC:DON ratios throughout the sampling region indicate the pervasive influence of remnant terrigenous DOM with some net production. The timescales for DOM Shelf-Basin exchange and decomposition could not be estimated due to a lack of geochemical tracer data.
Black Sea Basin: Sediment Types and Distribution, Sedimentation Processes
2000
The paper presents a part of the scientific activity of GEOECOMAR team during the IAEA project RER 2/003 Marine Environmental Assessment of the Black Sea Region, on board of R/V "Prof. Vodyanitskyi" and in laboratories. The Black Sea presents different sedimentological and geochemical characteristics in the eastern and western sub-basins. Whole sections of the Upper and Middle Holocene sediments were
2003
A 6-compartment biogeochemical model of nitrogen cycling and plankton productivity has been coupled with a 3D general circulation model in the Black Sea so as to quantify and compare, on a seasonal and annual scale, the typical internal biogeochemical functioning of the shelf and of the deep sea as well as to estimate the nitrogen (inorganic and organic) and water exchanges at the shelf break and at the continental slope-deep sea cross section. The model estimated vertically integrated gross annual primary production is 130 gC m -2 year -1 for the whole basin, 220 gC m -2 year -1 for the shelf and 40 gC m -2 year -1 for the central basin. In agreement with sediment trap observations, model results indicate a rapid and efficient recycling of particulate organic matter in the sub-oxic portion of the water column (60-80 m) of the open sea. More than 95% of the PON produced in the euphotic layer is recycled in the upper 100 m of the water column, 87 % in the upper 80 m and 67 % in the euphotic layer. The model estimates the annual export of POC towards the anoxic layer to 4 10 10 mol year -1 . This POC is definitely lost for the system and represents 2 % of the annual primary production of the open sea. It was found that biological processes on the north-western shelf are in approximate balance. Primary production is fuelled by in-situ recycling and river discharge and does not require a net nitrate input from the open sea. 22.2 % of the shelf production is not remineralized in the euphotic layer and is exported to below (20 %) or offshore (2.2 %). We estimate that the export of carbon from the shelf to the interior of the basin represents 1.7 % of the new production of the open sea. On the upper slope adjoining the north-western shelf, downwelling events are responsible for the transfer to the intermediate layer the biogeochemical components exported from the shelf. The shelf, and in particular the Danube Delta and the northern part, have been found efficient traps for the refractory material discharged by the Danube. Less than 33 % of the refractory material escape the shelf and less than 15 % leave the continental slope.
The relation between the grain size composition TOC (total organic carbon) concentration was examined by linear and non-linear regression analysis of analytical data for more than 500 sediment samples from the NW Black Sea. A significant dependency of the TOC concentration on the percentages of clay and especially the <16 µm fraction (clay plus fine and very fine silt) was identified, the model best fitting the analytical data being exponential. Three groups of sediment samples were identified using the K-means clustering technique, the deep sea sediment samples being clearly singled out.
2003
On the basis of the analysis of the many-year data on the vertical distributions of particulate organic carbon and nitrogen, we compute their annual average amounts for three typical layers of water in the deep part of the Black Sea: for a layer located above the oxycline and characterized by the formation of new portions of particulate organic matter in the course of photosynthesis, inside the oxycline, where the major part of oxygen is consumed and the major part of the flux of particulate organic matter is oxidized, and for the upper part of the anoxic zone characterized by the most active microbiological processes of oxidation of the organic substances and production of sulfides. The available literature data on sedimentation traps are used to study the downward annual average fluxes of particulate organic matter from the euphotic zone into the oxycline and into the anaerobic zone. The seasonal variability of the amounts and fluxes of particulate carbon and nitrogen is revealed. Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.