Matter cycle

Figure 5. Schematic presentation of organic matter cycle in the ocean. DOM—dissolved organic matter POM—particulate organic matter (from Engel and Macko, 1993).

Ziegler, S., and R. Benner. 2000. Effects of solar radiation on dissolved organic matter cycling in a subtropical seagrass meadow. Limnology and Oceanography 45 257-266. 

Microbial Extracellular Enzymes and Their Role in Dissolved Organic Matter Cycling... 

Shallow zones of DOM and POM production are inherently linked with the cycling and exchange of the adjacent deep channel environments of estuaries (Malone et al., 1986 Kuo and Park, 1995). Recent models have now included shallow environments in the wider-scale predictive models of organic matter cycling of estuaries (Pinckney and Zingmark, 1993 Madden and Kemp, 1996 Buzzelli et al., 1998). 

The abundance and ratios of important elements in biological cycles (e.g., C, H, N, O, S, and P) provide the basic foundation of information on organic matter cycling. For example, concentrations of total organic carbon (TOC) provide the most important indicator of organic matter since approximately 50% of most organic matter consists of C. As discussed in chapter 8, TOC in estuaries is derived from a broad spectrum of sources with very different structural properties and decay rates. Consequently, while TOC provides essential information on spatial and temporal dynamics of organic matter it lacks any specificity to source or age of the material. 

Arnosti, C. (2003) Microbial extracellular enzymes and their role in dissolved organic matter cycling. In Aquatic Ecosystems Interactivity of Dissolved Organic Matter (Findlay, S.E.G, and Sinsabaugh, R.L., eds.), pp. 316-337, Academic Press, New York. 

In effect, stars return between about 50% and 90% of their initial mass by winds or by explosive mass ejection. Figure 2.3 gives an overview of the relative contributions of the different stellar types to the total mass replenishment. The mass returned by the stars becomes part of the ISM and serves as raw material for the formation of the next stellar generations. In this way part of the baryonic matter in a galaxy is continuously cycled between stars and the interstellar matter. Only the very-low-mass stars (initial masses < 0.8 M0) are not involved in this matter cycle because they have lifetimes exceeding the present age of the Universe and have not yet evolved very much. Some fraction of the matter therefore accumulates in very-low-mass stars and in stellar remnants, but at least part of this loss from the matter cycle... 

The average lifetimes of dust grains in the ISM of about 0.5 Gyr have to be compared with a turnaround time of about 2.5 Gyr for the matter cycle between stars and the ISM, which would result in a small depletion S 0.8 of the refractory elements in the ISM into dust, if depletion of the refractory elements in the returned mass from stars was strong and if no accretion of refractory elements onto dust occurred in the ISM. This clearly contradicts the high observed depletion in the ISM. Hence, most of the interstellar dust is formed in the ISM and is not stardust (Draine 1995 Zhukovska et al. 2008). The most likely place for dust growth in the ISM is in the dense molecular clouds (Draine 1990), but the processes responsible for growth are presently unknown. 

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