The top layers of water bodies, a most important although relatively neglected piece of the biosphere plumbing

Abstract

Reducing power from light is used by plant life in ways that shift along ecological succession. When nutrients are non limiting, growth prevails; when essential nutrients (in the first place P) become scarce, reducing power is applied somehow and otherwise, often, as in red tides, in the synthesis of toxics. On land, the same reducing capacity results in the production of wood, terpenes, essences, cork or rubber. In water bodies, reduction of nitrate at least adds nitrite to the environment. Very likely this explains the common presence of nitrite-enriched layers around the levels of twilight. A large fraction of the generating capacity might be expected to come from the small prokaryota of phytoplankton, which almost global ubiquity and capacity to persist alive in a state of forced minimal activity are known. The result might be a kind of one-way plankton surface valve, that isolates partially and in some chemical aspects the deeper ocean from the top layers. One could perhaps speak of a surface valve with a planetary role.