Oceanic reservoirs marine organic matter

Figure 12 DOM cycling in the ocean. DOM is initially produced as a by-product of marine production in the mixed layer. Carbon stable isotope data suggests that some fraction of this organic matter becomes incorporated into the longer-term reservoir of rather refractory DOM to be subducted into the deep ocean. Newly produced DOM may also assemble into particles to enter the POM cycle. POM is oxidized, or transported into the deep ocean on large, rapidly sinking particles where biological activity may cause further oxidation, or drive re-dissolution to HMW DOM.

From Fig. 6.1 it can be seen that the annual net primary production for land plants and marine plants is similar (c.60 and 40Gt, respectively), although the biomass of terrestrial plants is much greater than that of marine plants. This is an important demonstration of the fact that biomass is not necessarily a guide to productivity. There is another difference between the marine and terrestrial parts of the biochemical subcycle the residence time of C in the main reservoirs. From Fig. 6.1 it can be seen that the residence time of carbon in the terrestrial biota is c.5.5 years (i.e.600/110yr), and c.26 years (1600/60.6 yr) in soil organic matter. In contrast, the residence time of C in marine phyto-planktonic biomass is only c.2 weeks (1.5/40 yr), but c.338 years (39 000/115.3 yr) in oceanic dissolved carbon. 

To understand the cycle of natural hydrocarbons in the ocean, we need to know the size and the nature of different reservoirs in the marine biota and the flux and direction of organic carbon to them. Virtually all the organic matter of internal origin in the oceans is originally derived from photosynthetic marine algae in the euphotic zone. 

The portion of Earth and its atmosphere that can support life. The part (reservoir) of the global carbon cycle that includes living organisms (plants and animals) and life-derived organic matter (litter, detritus). The terrestrial biosphere includes the living biota (plants and animals) and the litter and soil organic matter on land, and the marine biosphere includes the biota and detritus in the oceans. 

The mass of the geosphere and the diversity of its chemical and mineral composition are the most substantial of all reservoirs [5] and it is the ultimate source of all elements. The mass of the entire geosphere dovm to 2 km depth is about 10 kg. The hydrosphere holds 1.4 X 10 kg of water, with 97.5% of it in the oceans. The hydrosphere amounts to 15% of the mass of the geosphere and hosts only about 5 X 10 kg of dissolved solids. The mass of the atmosphere is only 5 x 10 kg, which is a small fraction of the geosphere. The mass of dry organic matter in the biosphere is about 1.5 x 10 kg, contained mostly in land plants, with animals accounting for only 1% of the total and marine life for an even smaller fraction [6]. 

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