ABSTRACT
In all ecosystems nitrogen and phosphorous are continuously cycled. These two elements are the major nutrients for plant growth on earth and similarly in the marine environment for algae. The inorganic forms become part of organic molecules during primary production and through growth of organisms, forming the particulate material together with nonliving matter. During decay and active release, dissolved organic material is formed, some of which becomes highly recalcitrant, but finally a major fraction is remineralized to inorganic carbon, nitrogen, and phosphorus. Mineralization rates differ between the elements. A detailed study has shown high spatial and seasonal variability of particulate and dissolved organic matter in the North Sea from near-shore to open oceanic waters (Brockmann and Kattner, 1997). An excellent overview of the worldwide distribution of marine dissolved organic matter (DOM) has been compiled by Hansell and Carlson (2002). Dissolved organic nitrogen and phosphorus are still often missing from budget and global model calculations and have considerable shortcomings in the formulation of organic matter cycling in models (e.g., Toggweiler, 1989; Najjar et al., 2007), since methods are less well developed and less reliable than those for dissolved organic carbon (DOC; see Chapter 2).
