Phytoplankton Biomass, Primary Production and Chemoautotrophic Production of the Western Black Sea in April 2003
Abstract
The Black Sea contains aerobic, suboxic and anoxic layers that support both photoautotrophic (PP) and chemoautotrophic (ChP) biological production. During the R/V Knorr cruise from 15-26 April 2003, chlorophyll-a, photoautotrophic (PP) and chemoautotrophic production (ChP) rates were determined in the western central gyre and southwest regions. Integrated chlorophyll-a concentrations in the euphotic zone were as low as 2.9 mg m-2 in the central western gyre, but increased to 22 mg m-2 in the SW shelf region. Integrated photoautotrophic production rates ranged from 70 to 827 mg C m-2 d-1. The lowest values were determined in the central gyre and the highest values were found at the shelf-break near Sakarya Canyon. Post-bloom conditions existed during this sampling period. Integrated ChP rates ranged from 282 to 1013 mg C m-2 d-1, which were almost always larger than PP at the same stations. ChP was equivalent to 45% to 83% of the total water-column production. There are three important observations in the Black Sea, and elsewhere. The first is that the highest values tend to be in the SW region, east of the Bosporus outflow. The second is that the maximum rates are observed in the upper layer of the sulfide zone. The third is that high rates of chemoautotrophy have also been measured in the redox transition zone of the Cariaco Basin (Taylor et al., 2001) where ChP is much deeper in the water column (240m to 450m). We can consider three possible controls on chemoautotrophic production. 1. Penetration of light into the sulfide-containing deep water may result in a zone of anaerobic primary production by photosynthetic bacteria like Chlorobium. Phototrophic production occurs but does not appear to be the main driver of ChP. 2. Chemosynthesis driven by the upward flux of chemical energy provided by reduced compounds (H2S, CH4, NH4+, Mn2+, Fe2+), with the redox shuttle between Mn (II, III, IV) species playing a significant role. 3) Oxygen ventilation from the Bosporus coupled with oxidation of sulfide. We conclude that redox cycling, enhanced by intense recycling of manganese species is the main overall control. Intrusions of O2 due to ventilation events results in local enhancement.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS43F2160M
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 1879 Watershed;
- HYDROLOGYDE: 1879 Watershed;
- HYDROLOGYDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL