Euphotic zone depth limit

Produce the densest ballasts observed In sinking particles destroyed in regions where the mixing depth of the ocean is below the euphotic zone. Their calcification rate is reduced at low pH. Zn limited... 

In the upper water layer silicate is depleted by phytoplankton down to 0.4-2 xM, e.g., down to a limiting level [23]. Below the euphotic zone it continuously increases up to 40-60 xM at 100 m depth. 

Nitrogen Transformations. Nitrogen transformations are always complicated at oxic-anoxic interfaces because of the large number of oxidation states available for N. The most interesting aspect about N distributions in the Black Sea is that the concentration of NH4+ decreases to below the detection limit at a, = 15.95 (Figure 6), which is about 0.35 density units deeper than the isopycnal where 02 decreases to less than 10 p,M (Table II). Nitrate is below detection in the euphotic zone and increases below this depth region because of nitrification. The N03" maximum is at cr, = 15.40 (Figure 6), which is about the density at which 02 decreases to less than 10 xM. Nitrate then decreases with depth, most likely because of denitrification. 

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