Environmental Engineering Reference
In-Depth Information
Photosynthesis
The process by which radiant energy from the sun is
transformed into chemical energy that can later be used to
reduce carbon dioxide to organic sugars, which in turn are
coupled to biochemical pathways to produce all compounds
necessary for cell growth.
Phytoplankton
Microscopic, often unicellular, floating autotrophs that live in
the ocean's surface layer and form the base of nearly all marine
food webs.
Reduction
Chemical reaction in which reactant gains electrons; half-
reaction paired with oxidation.
Definition of the Subject and Its Importance
The biogeochemistry of the world oceans has been studied for many decades, and
major advances in understanding have been linked with development of new
techniques and tools that allow the accurate representation of various organic and
inorganic pools within the water. The classic study of Redfield [
1
] showed that
some critical bioactive compounds (carbon, nitrogen, phosphorus, oxygen) occur in
particular ratios to one another that are relatively invariant over space and time and
provided a description of the relationship between the ratio of nitrogen to phospho-
rus (N:P) for inorganic and plankton pools. The processes that control these
compounds were assessed, and it was concluded that phosphorus concentrations
are largely controlled by terrestrial inputs, whereas nitrogen is under biological
control.
Subsequent studies have provided more detailed investigations of the processes
controlling these ratios. These studies benefited from the development
and standardization of methods for accurately measuring dissolved organic carbon
(DOC) and dissolved organic nitrogen (DON). The improved methodology, mostly
developed during the 1980s, allowed the spatial (vertical and horizontal) and
temporal changes of both DOC and DON to be quantitatively described.
Recognition of the importance of the flux of organic carbon to depth in
mediating the marine response to increased atmospheric carbon dioxide
concentrations stimulated development of technical approaches and instruments
for assessing and quantifying the biological pump. This component of marine
biogeochemical cycles is still a poorly constrained component of numerical models
developed for simulation of ocean carbon cycling and climate, and technological
approaches that result in better assessment of the flux of organic matter to depth
continue to be developed and refined. Also, numerical models of biogeochemical
processes are providing insights into critical processes and provide frameworks that
allow measurements to be projected over larger space and timescales. Continued
