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Water is the medium of the oceans, the medium which carries all the substances and elements involved in the marine biogeochemical cycles. Water as found in nature almost always includes dissolved substances, so water has been described as the "universal solvent" for its ability to dissolve so many substances.
Like inorganic carbon, there are two main forms of organic carbon found in the ocean (dissolved and particulate). Dissolved organic carbon (DOC) is defined operationally as any organic molecule that can pass through a 0.2 μm filter. DOC can be converted into particulate organic carbon through heterotrophy and it can also be converted back to ...
In the ocean by volume, the most abundant gases dissolved in seawater are carbon dioxide (including bicarbonate and carbonate ions, 14 mL/L on average), nitrogen (9 mL/L), and oxygen (5 mL/L) at equilibrium at 24 °C (75 °F) [122] [123] [124] All gases are more soluble – more easily dissolved – in colder water than in warmer water. For ...
Colored dissolved organic matter (CDOM) is estimated to range from 20-70% of the carbon content of the oceans, being higher near river outlets and lower in the open ocean. [5] DOM can be recycled and put back into the food web through a process called microbial loop which is essential for nutrient cycling and supporting primary productivity. [ 6 ]
Subterranean water can then seep into the ocean along with river discharges, rich with dissolved and particulate organic matter and other nutrients. There are biogeochemical cycles for many other elements, such as for oxygen, hydrogen, phosphorus, calcium, iron, sulfur, mercury and selenium.
The rivers carry high coloured dissolved organic matter (CDOM) concentrations, shown here interfacing with ocean shelf water. [83] Marine sediments represent the main sites of OM degradation and burial in the ocean, hosting microbes in densities up to 1000 times higher than found in the water column. [84]
A decline in dissolved oxygen, and hence in the oxygen supply to the ocean interior, is a likely effect of the increase in stratification in the upper ocean. [15] Since oxygen plays a direct and important role in the cycles of carbon, nitrogen and many other elements such as phosphorus, iron and magnesium, de-oxygenation will have large ...
The balance of these carbonate species (which ultimately affects the solubility of carbon dioxide), is dependent on factors such as pH, as shown in a Bjerrum plot.In seawater this is regulated by the charge balance of a number of positive (e.g. Na +, K +, Mg 2+, Ca 2+) and negative (e.g. CO 3 2− itself, Cl −, SO 4 2−, Br −) ions.