LAUSR

Abstract 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 from 15 to 25 April 2003, phytoplankton biomass (represented as chlorophyll-a), photoautotrophic and chemoautotrophic production (ChP) rates were determined in the southwestern Black Sea. Surface Chl-a concentrations ranged from 0.06 and 0.62 μg/ l for the whole study area. These low values suggest post-bloom conditions. Integrated chlorophyll-a concentrations in the euphotic zone were as low as 2.4 mg m−2 in the central gyre, while they were as high as 22 mg m−2 in the Rim current. Integrated photoautotrophic production rates ranged from 70 to 664 mgC m−2 d−1. The lowest values were observed in the western central gyre and the highest values were found at the regions around Sakarya Canyon. Integrated ChP rates were 282 and 1013 mgC m−2 d−1, which were equivalent to 45% and 83% of the overall water-column production for the central gyre and Rim current regions, respectively. Maximum rates are observed in the upper layer of the sulfide zone. The highest values of integrated ChP were in the vicinity of the Sakarya shelf and Rim current region. Extremely high values of ChP can occur in the Black Sea and appear to be driven by oxygen ventilation and redox cycling.