Environmental Engineering Reference
In-Depth Information
Figure 7. Dissolved oxygen and hydrogen sulfate (left panel), and nitrate and ammonium
(right panel) versus density from the center of the western gyre (Leg 7; Stn 12) during R/V
Knorr April 2003.
versus heterotrophic denitrification and how this varies with depth relative to
the distribution of nitrogen species still needs to be determined.
4.3 Phosphate
Phosphate only has one oxidation state but its distributions in the Black Sea
are clearly influenced by changes in the redox environment. The vertical profile
of phosphate has the most complicated structure of all the profiles of basic
chemical properties. The profiles in the central Black Sea are characterized by
two maxima and two minima [5, 14]. A representative profile from the center of
the western gyre is shown plotted versus depth and density in Fig. 9 (R/V Knorr
172-05; March 2003; Stn 7, E.Yakushev, unpublished data). The typical profile
shows that PO 4 concentrations are low (
0.15 µM) in the euphotic zone. They
increase to a maximum that coincides approximately with the NO 3 maximum
at about σ θ 15.50 kg m 3 . Phosphate then decreases to low concentrations
ranging from zero to 2.5 µMat σ θ 15.80 to 15.95 kg m 3 . This minimum is
well above the first appearance of sulfide. Finally, it increases to a maximum
(5 to 7.7 µM) in the upper part of the sulfide zone at σ θ 16.20 kg m 3 . The
density values of these maximums appear to be are very stable but profiles do
display distinct spatial and temporal variations [24] which are probably caused
Search WWH ::




Custom Search