ORGANIC-RICH Organic-rich sediments

Explain the key reasons why Pedersen and Calvert (1990) considered that dissolved oxygen was not an important control on the formation of organic-rich sediments, and why Tyson (2005) believed most of their arguments to be misleading or inappropriate for many ancient types of sediment.

Pedersen and Calvert (1990) considered that dissolved oxygen was not a fundamental control on the formation of organic-rich sediments. As primary production of organic matter in the open ocean, are because of a wide range of unicellular planktonic organisms whose activities, governed by nutrient supply and solar radiation. In the tropical ocean, the amount of light reaching the sea surface is never limiting but is often insufficient for sustained production at higher latitudes.

Light attenuation restricts photosynthesis to a relatively thin surface (euphotic) zone, which ranges from about 100-120 m in thickness in clear, open ocean waters to a few meters in turbid, nearshore regions (Tyson 2005 13). Nutrients normally are present in very low concentrations, in the euphotic zone, because they consumed the phytoplankton; at the water depth nutrients are deposit by bacterial degradation of the settling organic debris exported from the surface layers. Sustained plankton production can take place, therefore, only if nutrients are supply to the euphotic zone from below by vertical mixing or horizontal supply.

In marine sediments, the rate of supply indicates the concentration of organic carbon, the extent of preservation after burial, and the degree of dilution by other sedimentary components. The final factor emphasizes that the accumulation rates of all components determine through composition of sediment and that the absolute concentration of any given component must not be considered in isolation (Pedersen Calvert 1990 112). Nevertheless, the first-order control on the concentration of organic carbon in sediments can be taken to be the magnitude of the settling flux. The latest compilation of data for the Pacific Ocean shows that sediments containing more than 0.5% by weight carbon confined to the marginal areas close to the continents. In the open ocean carbon values are less than 0.25% in the dominant, poorly productive gyres, and only slightly higher and more productive, equatorial, sub-Arctic and sub-Antarctic regions.

A good deal of study is discovering the consequences of redundant sedimentation on marine environments. A 2002 study undertook by investigators from the Bigelow Laboratory for Ocean Science (Maine) discovered that expanded sedimentation having deleterious consequences on coral reefs (Clague 1981 80). Coral comprise photosynthetic algae on which they count for survival. The cloudy, sediment-rich water, therefore, murders the symbiotic algae in the coral, and the reef may be harshly impaired or even die.

Many kinds of sediment damage reefs and marine ecosystems because of the hurtful chemicals or waste they carry. A report released in 2005 by researchers at Texas A&M University disclosed that the dead zone in the Gulf of Mexico is getting bigger every year, covering more than seven 1000 rectangle miles (18,129 kilometers square) of the gulf. The dead zone evolves from fertilizer-rich sediments that run off farmlands along the Mississippi ...