Nutrients, oceanic distributions

Like barium and zinc, cadmium also shows a nutrient-like distribution in the ocean (Figure 10 Bmland, 1980 Loscher et al, 1998), more closely mirroring those of the labile nutrients, NO and PO4, than those of Si(OH)4 and alkalinity. Cadmium is taken up by phytoplankton and incorporated into organic material, accounting for the similarity of its profile to that of NO and PO4. Cadmium may also be adsorbed onto the surfaces of phytoplankton (Collier and Edmond, 1984). 

The lower euphotic zone (depths of 70-100 m), which is isolated from direct atmospheric inputs, is subjected to intensified processes of Fe scavenging that determine the extremely low concentration of 0.02 nM. At depths below 100 m, dissolved Fe exhibits the characteristic nutrient-type distribution observed in other zones of the Pacific Ocean (10, 161). The same authors emphasized that in regions where new production is high and intensified scavenging occurs within the surface mixed layer, the dissolved Fe concentration assumes concentrations similar to those they observed in the central gyre at depths of 70-100 m (159). 

Elements showing nutrient-like distribution often have long oceanic residence times, although shorter than conservative elements. The residence times of NO( silicon and DIP have been estimated to be 57 000,20000 and 69000 years respectively (Table 6.9). The vast reservoirs of nutrients in the deep ocean mean that increases in the concentrations of NO( in riverwaters due to human activity (see... 

Cobalt, and sometimes cadmium, can substitute for zinc in many zinc enzymes such as CA, leading to complex interactions among the three metals in marine algae (Figure 5). The presence of cadmium in CA appears to explain its nutrient-like distribution in ocean waters (Figure 2(e)), and the identification of a unique Cd-CA enzyme in marine diatoms means that it functions as a micronutrient in these organisms. Cobalt also occurs in vitamin Bi2, an essential... 

Although the oceanic distributions of rare earth elements somewhat resemble those of nutrients, their behaviors are clearly different in that they are not actively taken up by photoplankton but passively scavenged by particles. Elemental reactivity with suspended particles, which controls, together with sinking of particle aggregates, the mean oceanic residence times of not only REEs but also a number... 

Over much of the ocean (exclusive of upwelling regions, high-latitude areas and specific high-nutrient, low-chlorophyll regions) the vertical distribution of dissolved POt is represented by the shape of the profile displayed in Fig. 14-6, which is similar to the shape observed for the... 

Fig. 14-6 Profiles of potential temperature and phosphate at 21 29 N, 122 15 W in the Pacific Ocean and a schematic representation of the oceanic processes controlling the P distribution. The dominant processes shown are (1) upwelling of nutrient-rich waters, (2) biological productivity and the sinking of biogenic particles, (3) regeneration of P by the decomposition of organic matter within the water column and surface sediments, (4) decomposition of particles below the main thermocline, (5) slow exchange between surface and deep waters, and (6) incorporation of P into the bottom sediments.

Distribution of AOU at a depth of 4000 m. Units are mL O2/L seawater. To convert to (xmol O2/L seawater, multiply by 44.6. Source After Conkright, M. E., et al. (2002). Wotld Ocean Atlas 2001, Volume 4 Nutrients. NOAA Atlas NESDIS 52, U.S. Government Printing Office. (See companion website for color version.)... 

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