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Surface and mid-water sources of organic carbon by photoautotrophic and chemoautotrophic production in the Black Sea

Yılmaz, Aysun
Coban-Yildiz, Yesim
Telli-Karakoc, Fatma
Bologa, Alexandru
The multilayered surface waters of the Black Sea contain aerobic, suboxic and anoxic layers that support both photoautotrophic (PP) and chemoautotrophic (ChP) biological production. During the R/V Knorr cruise in May-June 2001, phytoplankton biomass (represented as chlorophyll-a), photo autotrophic and chemoautotrophic production (ChP) rates were determined in the western Black Sea. Integrated chlorophyll-a concentrations in the euphotic zone were as low as 2.2 mg m(-2) in the central gyre, while they were as high as 19.9mg m(-2) in the NW shelf region. Integrated photoautotrophic production rates ranged from 112 to 355mg C m(-2) d(-1). The lowest values were determined in the central gyre and the highest values were found at the shelf-break station near the Bosphorus, the NW shelf/shelf-break area and in the Sevastopol eddy. Primary production and chlorophyll-a data revealed that post-bloom conditions existed during this sampling period. Bioassay experiments showed that under optimum light conditions, photo autotrophic production was nitrogen-limited. ChP increased in the redox transition zone and coincided with the lower boundary of the fine particle layer. The maximum values were shallower (at sigma(theta) = 16.25) in the central gyre and deeper (at sigma(theta) = 16.5) in the shelf-break region near Sakarya Canyon. Integrated ChP rates were 63 and 1930 mg C m(-2) d(-1), which were equivalent to 30% and 89% of the overall water-column production for the central gyre and Sakarya Canyon regions, respectively. (c) 2006 Elsevier Ltd. All rights reserved.