Nutrient-type

The criteria for an element, such as Pb, to exhibit a maximum concentration in surface waters are that the only significant input must be at the surface (aeolian supply) and it must be effectively removed from the water column. Constituents such as As, Ba, Cd, Ni and Zn exhibit nutrient type behaviour. Those elements (Cd) associated with the soft parts of the organism are strongly correlated with phosphate and are... 

Some trace metals, such as iron and copper, have distributions that are strongly influenced by both recycling and relatively intense scavenging processes. Like nutrient-type elements, dissolved iron is observed to be depleted in remote oceanic surface waters such as high-nutrient, low-chlorophyll... 

Since sponges and radiolarians are not great players in particle flux, the rise of the diatoms must have profoundly altered the partitioning of silicic acid between surface and deep. The familiar nutrient-type distribution may have only existed for the last 50-100 million years. The approximate 14-fold drop in silicic acid concentration also suggests that the residence time of silicon in... 

In general, nutrient-type tracers have been used to infer the sources and mixing of deep-water... 

Reactive trace metals exhibit a range of biogeochemical behavior that can be characterized by two endmembers—nutrient type and scavenged type (Figure 10.22c,d). Nutrient-type metals, best exemplified by Zn and Cd, are primarily removed from surface waters by biogenic particles and then remineralized at... 

On the other hand, a nutrient-type trace metal like Zn attains a concentration of dissolved Zn that is approximately five times greater in the old, nutrient-rich deep waters of the North Pacific than they are in the young, nutrient-poor North Atlantic deep waters. Its distribution in both ocean basins is similar to that of silicic acid. The efficiency with which Zn is recycled in the ocean leads to its relatively long oceanic residence time. 

Studies carried out in oligotrophic areas of major oceanic gyres showed a marked surface depletion of major nutrients and nutrient type trace metals, but this is not the case in Antarctic waters and some other areas presenting nutrient-rich waters. The high levels of nutrients and the simultaneous low primary production in surface Antarctic waters constitute the so-called Antarctic Paradox . 

The distribution of Cu in sea water is intermediate between that of nutrient-type elements and that of scavenged elements in surface waters of oligotrophic regions... 

Dissolved and particulate concentrations of Fe have been shown to be quite low in the euphotic zone of the North Pacific oligotrophic and eastern equatorial Pacific waters. The dissolved concentration is normally lower than 0.1 nM and the particulate is about 0.2 nM. The concentration along the water column shows a nutrient-type vertical profile characterized by surface depletion and increase with depth. Iron concentration reaches typically values >0.5 nMat depths below 1000 m (158). 

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). 

Correlations between nutrients and nutrient-type elements such as As, Cd, Ni, or Zn as observed in oceanic regions (Boyle et al., 1976 Whitefield and Watson, 1983) were not found in the Baltic Sea. It was suggested that this is probably a result of the slightly higher... 

Fe behaves in seawater in part as a scavenged-type element and in part as a nutrient-type element as shown by the strong correlation of dissolved Fe with nitrate and phosphate at depths below 100 m. 

Scavenged type Trace metals such as Al, Co, Ce, and Bi, show surface enrichment and depletion in deep waters, in contrast to the opposite trend in nutrient types. These elements are highly particle-reactive and are rapidly removed from the water column by sinking particulate matter and/or by scavenging at the sediment-water interface. Their mean oceanic residence times are short (<10 -10 years). Interoceanic variations in their concentration can be large (e.g., Atlantic/Pacific concentration ratio 40 for Al) depending on kinetic balance between supply and removal for the specific basins. 

One of the important features of Figure 1 is that the concentration, even for trace elements, varies fairly smoothly and continuously with depth. This casts doubt on some erratic and highly discontinuous values unless there are obvious reasons for them, such as hydrothermal influence or difference in the water masses. The data shown in Figure 1 are largely based on filtered samples and therefore, can be referred as dissolved concentration. For conservative elements, it does not matter whether the water sample is filtered or not, since there is virtually no difference in the analytical results. For most nutrient-type elements, particle association in the open ocean is generally small (< 5%) and therefore, the gross features of unfiltered samples remains the same as... 

Scandium (Sc) exists in the - -3 oxidation state as Sc(OH)3 in sea water. Dissolved scandium has a nutrient-type vertical profile (Figure 5A), with low concentrations at the surface and enrichment at depth, yet no significant interocean fractionation is observed. Scandium was detected by neutron... 

Metals having nutrient type distributions (Fe, Ni, Zn, Ge, Se, Y, Ag, Cd, Ba, La) are characterized by surface water depletion and enrichment at depth. Surface depletion is caused by biological uptake, and... 

---