Open ocean metals

National Research Coundl Canada (1992) Certified Reference Material NASS-4 Open Ocean Seawater Reference Material for Trace Metals. National Research Council of Canada. Ottawa. National Research Council Canada (1995) Certified Reference Material CARP-i Groimd Whole Carp Reference Material for Organochlorine Compounds. National Research Council of Canada, Ottawa. 

Chung Y, Finkel R, Bacon MP, Cochran JK, Krishnaswami S (1983) Intercomparison of °Pb measurements at GEOSECS station 500 in the northeast Pacific. Earth Planet Sci Lett 65 393-405 Chung Y, Finkel R (1988) Po-210 in the Western Indian-ocean - distributions, disequilibria and partitioning between the dissolved and particulate phases. Earth Planet Sci Lett 88 232-240 Clegg SL, Whitfield M (1991) A generalized model for the scavenging of trace metals in the open ocean -... 

Clegg SL, Whitfield M (1992) A generalized model for the scavenging of trace metals in the open ocean -... 

Manganese and many other trace metals are present in open ocean waters at concentrations in the order of nmol/1 or less, and it is only relatively recently, when adequate contamination control measures have been applied during sampling and measurements, that accurate data have been obtained. 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

One with concentrations of metals corresponding to open-ocean surface water with an information value for total iron concentration. 

In the late 1980s, improvements in the measurement methods for trace metals in seawater lead to the observation that dissolved iron concentrations in the open ocean are... 

This leads to desorption of the minor and trace metals because the major cation ion concentrations are so high as to swamp any differences in relative adsorption affinity. As shown in Figure 5.1, desorption must play a minor role in the estuarine chemistry of iron because the net effect is a chemical removal. In the open ocean, adsorption of... 

The data presented in Table 11.1 indicate that the fluvial gross river flux is the major source of trace metals to the oceans and that most of this flux is in particulate form (fluvial gross particulate flux). But the majority of this particulate flux is trapped within estuaries, primarily via settling, and, hence, is not released into the open ocean. As a result, the fluvial net particulate flux is only about 10% of the fluvial gross particulate flux. In seawater, most of this particulate metal remains in solid form due to low solubilities. The particulate metals eventually settle to the seafloor and are subsequently buried in the sediments. In the case of iron, a small fraction of the particulate pool does dissolve. In the surface waters, solubilization of particulate iron can provide a significant amount of this micronutrient to the phytoplankton. 

Much of the trace metal demand of plankton in the open ocean may be supplied by the aeolian transport of dust. If trace metals limit plankton growth, the factors that control the transport of dust will also ultimately control the ocean s biological pump and, hence, atmospheric CO2 levels. This suggests the existence of powerful feedbacks among the processes that control global climate. For example, shifts in climate that lead to regional... 

Trace metals are introduced to the ocean by atmospheric feUout, river runoff, and hydrothermal activity. The latter two are sources of soluble metals, which are primarily reduced species. Upon introduction into seawater, these metals react with O2 and are converted to insoluble oxides. Some of these precipitates settle to the seafloor to become part of the sediments others adsorb onto surfaces of sinking and sedimentary particles to form crusts, nodules, and thin coatings. Since reaction rates are slow, the metals can be transported considerable distances before becoming part of the sediments. In the case of the metals carried into the ocean by river runoff, a significant fraction is deposited on the outer continental shelf and slope. Hydrothermal emissions constitute most of the somce of the metals in the hydrogenous precipitates that form in the open ocean. 

Schematic representation of manganese nodule end-member morphologies. The size of the arrows Indicates the proportion and direction of metal supply, (a) Typical situation In the open ocean with the nodules lying on an oxidized sediment substrate dominant mode of formation Is hydrogenous, (b) Typical situation In nearshore and freshwater environments with nodules lying on a sediment substrate that Is partly reducing In character. Dominant supply of metals Is via Interstitial waters from below the substrate surface. Source From Chester, R. (2003). Marine Geochemistry, 2nd ed. Blackwell, p. 425.

The mixture of organic constituents in the marine environment is extremely complex. Their origin is partly terrigenuous many compounds are produced in the marine environment itself. The different sources and their relative importance for the complexation of trace metals in estuaries, coastal seas and open ocean are riverine input, runoff from the coastal zone, resuspension, import of water mases, atmospheric input and in situ biological production. 

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Maring, H.B. and Duce, R.A. (1987) The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater. 1. Aluminium. Earth Planet. Sci. Letts, 84, 281-392. 

---