Dilek Ediger

Characteristics of deep chlorphyll maximum in the Northeastern Mediterranean with respect to environmental conditions

Abstract The vertical distribution of chlorophyll-a was recorded throughout the northern part of the Levantine Basin of the eastern Mediterranean and was related to patterns of the physical dynamics for October 1991–March 1994 period. A well developed deep chlorophyll maximum (DCM) was observed in the northern Levantine Basin (NLB), with concentrations greater than 1 μg/L at depths ranging from 45 to 100 m on average. Chlorophyll-a concentrations ranged between 0.01 (in surface waters, Oct. 1991) and 3.07 μg/L (in subsurface waters, March 1992). In general high concentrations of chlorophyll-a were observed in late winter. In cyclonic regions the depths of the DCM and the nutricline coincided and relatively high concentrations were observed at shallowe depths at relatively high percentages of surface light. In anticyclonic regions the DCM (at low level of concentration) were located at the base of the euphotic zone and much above the nutricline. Well defined DCM feature was not prominent since at most of the stations, uniform distributions of chlorophyll-a were observed in the euphotic zone during the cooler winter conditions in 1992. The chlorophyll concentrations were significantly high in this winter when compared with those of ordinary mild winters. Because of the relatively low chlorophyll-a concentration resulting most probably low phytoplankton biomass in the basin and low input of material from the land, a thick euphotic zone forms with an average value ∼ 80 m. Euphotic zone is nutrient depleted and the concentrations are close to detection limits (e.g. 0.02 μM for phosphate and > 0.05 μM for nitrate) and in general they do not show significant variations. Nutricline takes place in the euphotic zone in cyclonic regions. In anticyclonic regions, the main nutricline is deep (as deep as 600 m). In cooler winter conditions in 1992, very high concentrations of both nitrate and phosphate (almost equal to deep values) were observed in the euphotic zone in the cyclonic Rhodes region. In deep waters phosphate and nitrate concentrations stay almost constant at the levels of nearly 0.2 and 5.5 μM, respectively.

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.

Abundance and Elemental Composition of Particulate Matter in the Upper Layer of Northeastern Mediterranean

Suspended particulate (POC PON, PP) profiles obtained in 1991-1994 indicate the existence of characteristic subsurface maxima near the base of the euphotic zone in the cyclonic Rhodes gyre and its peripheral waters in the Northeastern Mediterranean. Interestingly the N:P of the bulk seston was reasonable during stratification seasons when the surface water was relatively poor in phosphate; but the ratio was unexpectedly low (N:P=6-12) in the late winter of 1992 when the surface layer of Rhodes gyre was occupied with nutrient rich deep waters.