Deep zone

Oxide minerals, e.g. Fe3+ ions and carbonate and seawater contents Deep zones of metals and very reduced minerals in the mantle Some parts of the atmosphere 03, N2/02 All such chemicals are thermodynamically unstable in the absence of air relative to C02, CH4 and H20 and in air all are unstable relative to C02 and H20 but all have considerable kinetic stability... 

The higher the AOU, the greater the amount of O2 removed since the water mass was last at the sea smfece. Thus, AOU increases with increasing distance from the site at which the subsurfece water mass was formed. Since the AOU increases with the age of the water mass, the pathway of deep-water circulation can be traced from the distribution of AOU in the deep zone. As shown in Figure 8.2, the AOU at 4000 m is lowest in polar regions, indicating these areas are the sites of deep-water formation. 

The vertical distribution of biolimiting elements is characterized by deep-water enrichments and surface-water depletions. As described above, this vertical segregation is caused by the remineralization of biogenic particles in the deep sea. Not all particulate matter that sinks into the deep zone is remineralized. Some survives to become buried in the sediments. How much of the biogenic particle flux escapes from surfece waters How much of this particle flux is remineralized in the deep zone How much is lost from the ocean by burial in the sediments What effect does this have on the concentrations of the biolimiting elements ... 

In the Pacific Ocean, most of the waters at 2500 m have a prefiormed phosphate concentration intermediate between NADW and AABW. Because preformed phosphate is a conservative tracer, it can be used to estimate the proportions of NADW and AABW present in the deep zones of the ocean basins. The average deep-water preformed phosphate concentration is 1.4 (jlM. This concentration would result from an equal-volume admixture of NADW and AABW. This conservative mixing estimate is based on the assumption that the preformed phosphate concentrations of the end-member water masses have remained constant over time scales at least as long as the mixing time of the ocean. 

Sinking particles transport trace elements to the sediments. Once in the sediments, chemical reactions can resolubilize a significant fraction of the particulate metals. This process is termed diagenetic remobilization and is the subject of the next chapter. The resolubilized elements can diffuse across the sediment-water interface into the deep zone. 

Evidence for seasonal fluctuations in the export of sinking POM from the euphotic zone has been obtained from sediment trap studies. As shown in Figure 23.3, seasonal variations in the flux of sinking biogenic hard and soft parts are detectable even in the deep zone. Furthermore, interannual variations in POC and PIC production lead to similar shifts in the deepwater fluxes of these particles. 

Hydrothermal vents and cold seeps, in deep zones of the oceans, are rich in microorganisms, mollusks, and worms, but without other forms of life that characterize the coasts (in particular photosynthetic organisms and their symbionts) and seamounts. 

Santosa, S.J., Mokudai, H., Takahashi, M. and Tanaka, S. (1996) The distribution of arsenic compounds in the ocean biological activity in the surface zone and removal processes in the deep zone. Applied Organometallic Chemistry, 10(9), 697-705. 

Figure 11.9 Schematic of articular cartilage structure showing the superficial, middle and deep zones, the tidemark boundary between the noncalcified and calcified cartilage layer, and the subchondral bone that underlies the articular cartilage.

Articular cartilage Superficial, intermediate, deep zones Absorbs shock... 

Figure 3.23. Diagram illustrating the zonal structure of articular cartilage. The superficial zone contains aligned collagen fibrils the intermediate zone contains unoriented collagen fibrils the deep zone contains collagen fibrils perperdicular to the subchondral bone.

The chondrocytes of the intermediate zone are more spherical than, and differ from, the cells of the superficial layer, which show surface polaritity. Chondrons are found in the intermediate layer. They consist of chondrocytes, pericellular matrix, and pericellular capsule. In this zone, the chondrocytes do not form vertical columns as extensively as is observed in the deep zone. At high magnification the collagen fibrils have a beaded appearance, which may reflect the high level of PGs seen in this region. 

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