Plankton organic matter

Turbidity Effect. Pesticide monitoring procedures try to extract the whole water sample as collected whether it is clear or turbid or contains large particulates (3, 4). The effects of turbid matter—i.e., suspended matter, such as clay, silt, finely divided organic matter, plankton and other microscopic organisms, and settleable matter—have not been delineated. 

Consequences of Ozone Depletion. Ozone depletion over Antarctica is causing renewed concern about the consequences of increased levels of UV reaching the earth s biosphere. One area of concern involves the free-floating microscopic plants, known collectively as phytoplankton (the grass of the sea), which through the process of photosynthesis, fix carbon dioxide into living organic matter. Phytoplankton forms the basis of the marine food chain on which zooplankton (animal plankton) and all other components of the ecosystem depend for their sustenance. 

Essentially all organic matter in the ocean is ultimately derived from inorganic starting materials (nutrients) converted by photosynthetic algae into biomass. A generalized model for the production of plankton biomass from nutrients in seawater was presented by Redfield, Ketchum and Richards (1963). The schematic "RKR" equation is given below ... 

To this point, organic matter in the ocean has been treated primarily as RKR average plankton. We now need to focus on the fate of this biologically produced organic carbon. 

Eppley, R. W. and Peterson, B. J. (1979). Particulate organic matter flux and planktonic new production in the deep ocean. Nature 282, 677-680. 

This equation describes the ratios with which inorganic nutrients dissolved in seawater are converted by photosynthesis into the biomass of "average marine plankton" and oxygen gas 02. The opposite of this reaction is respiration, or the remineralization process by which organic matter is enzymatically oxidized back to inorganic nutrients and water. The atomic ratios (stoichiometry) of this reaction were established by... 

Heterotrophic microbes consume organic matter to fuel respiration metabolisms that provide energy. Aerobic respiration of the Redfield-Richards planktonic organic matter can be represented stoichiometrically as... 

An estimate of the amoimt of organic matter respired since a water mass was last at the sea surfece can be inferred from its AOU and the stoichiometry given in Eq. 8.4. The respiration of 1 mol of POM comprised of average detrital plankton biomass requires the oxidation of 106 mol organic carbon. As per Eq. 8.6, this requires 106 mol O2 ... 

Since phosphorus is not oxidized diuang the respiration of organic matter, it does not contribute to the O2 uptake. Thus, 138 mol O2 is consumed diuang the respiration of 1 mol of average plankton detritus, making the molar ratio of organic carbon respired to O2 consumed equal to 106 138. 

In some sediments, downcore variations in the bulk chemical composition are interpretable as records of temporal shifts in the elemental composition of the sinking POM. Such shifts are caused by changes in the production of sinking POM, which are in turn the result of fluctuations in the abundance and diversity of the overlying plankton community. In nearshore sediments, fluctuations in river runoff and lateral transport can lead to shifts in the supply rate of terrigenous organic matter. An example of a nearshore sediment core in which such fluctuations have been recorded is shown in Figure 23.18. 

---