s: direct extracellular release during growth; release during predation by grazing organisms; and release during viral lysis of cells. The major mechanism for the removal of marine DOM is consumption by heterotrophic bacteria. The transfer of carbonand associated elements from marine DOM to bacteria forms the base of the microbial food web in the ocean. It is estimated that about half of the carbon fixed during photosynthesis by marine phytoplankton passes through DOM and the microbial food web. This component of marine DOM is very reactive and cycles rapidly, and includes many common biochemicals, such as amino acids and carbohydrates. These biological processes and cycling of DOM are most rapid in the upper hundred meters of the water column where there is sufficient sunlight for photosynthesis. Photochemical oxidation of DOM to carbon dioxide and carbon monoxide also occurs in the surface ocean, and recent estimates indicate this process is a quantitatively significant component of the ocean carbon cycle.
Most marine DOM is produced and consumed in the upper ocean (above 1000 m depth). The concentration of dissolved organic carbon in the deep ocean is about half of the concentration found in the surface ocean. The average depth of the world ocean is about 4000 m, so most marine DOM resides in the deep ocean (below 1000 m depth). Relatively little is known about biological processes and marine DOM cycling in the deep ocean, but several different types of data indicate deep marine DOM is resistant to biological utilization and degradation. A relatively small fraction of deep marine DOM is recognizable biochemicals, and its chemical structure and nature are largely unknown. Mixing of the world ocean occurs on a millennial time scale, and there is evidence indicating photochemical and biological processes occurring in surface waters enhance the oxidation of DOM from the deep ocean.
s: direct extracellular release during growth; release during predation by grazing organisms; and release during viral lysis of cells. The major mechanism for the removal of marine DOM is consumption by heterotrophic bacteria. The transfer of carbonand associated elements from marine DOM to bacteria forms the base of the microbial food web in the ocean. It is estimated that about half of the carbon fixed during photosynthesis by marine phytoplankton passes through DOM and the microbial food web. This component of marine DOM is very reactive and cycles rapidly, and includes many common biochemicals, such as amino acids and carbohydrates. These biological processes and cycling of DOM are most rapid in the upper hundred meters of the water column where there is sufficient sunlight for photosynthesis. Photochemical oxidation of DOM to carbon dioxide and carbon monoxide also occurs in the surface ocean, and recent estimates indicate this process is a quantitatively significant component of the ocean carbon cycle.
Most marine DOM is produced and consumed in the upper ocean (above 1000 m depth). The concentration of dissolved organic carbon in the deep ocean is about half of the concentration found in the surface ocean. The average depth of the world ocean is about 4000 m, so most marine DOM resides in the deep ocean (below 1000 m depth). Relatively little is known about biological processes and marine DOM cycling in the deep ocean, but several different types of data indicate deep marine DOM is resistant to biological utilization and degradation. A relatively small fraction of deep marine DOM is recognizable biochemicals, and its chemical structure and nature are largely unknown. Mixing of the world ocean occurs on a millennial time scale, and there is evidence indicating photochemical and biological processes occurring in surface waters enhance the oxidation of DOM from the deep ocean.
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