Organic matter of the North Atlantic

The areas that we studied in the North Atlantic (53 and 60°N) and in the Labrador Sea in the summer were characterized by a wide variability of the concentrations of dissolved and particulate organic matter and its elemental composition both in the surface and in the deep waters. The concentrations of dissolved and particulate C_org varied within 69–360 μM and 0.7–25.6 μM, respectively; the N_org and P_org contents varied within 1.4–22.2 μM and 0.02–0.86 μM, respectively. The maximal concentrations were registered in the photic layer and in the zones of mixing between the waters of different genesis. The particulate matter contribution to the total organic matter (OM) content varied from 0.5 to 15.4%. The waters of the photic layer contained more particulate C_org than those of the near-bottom layer. The values of the C/N molar ratios from the surface to the bottom over the entire aquatic area surveyed varied 5-to 6-fold; at that, the values of the C/P molar ratios varied more than tenfold. In the most productive waters, the values of the C/N ratios were close to the Redfield ratios (6–10). The values of the C/P molar ratios varied from 160 in the photic layer to 4831 in the deep waters. The pronounced non-uniformity in the spatial distribution of the OM and its elemental composition is caused not only by the penetration of the waters of different origins but also by the changes in the microplankton metabolism under mixing of these waters.