Deep-water sampling

A spherical glass vessel has been suggested as a low contamination device to sample seawater and extract it with a water immiscible organic solvent Gaul and Ziebarth, 1983 Theobald et al., 1990). Its volume, however, is limited to 20-100 L, and no separation of suspended and dissolved phases is feasible. 

In situ sampling/filtration/extraction systems offer the most favourable conditions for accurate determinations of organic trace compounds in seawater. 

The Kiel in situ pump system (KISP) for filtration and extraction of trace organics at the depth of sampling Petrick et al, 1996) is suitable for volumes of up to 2000 L or more (depending on particle concentration) and depths in excess of 6000 m. Sufficient amounts of PAH and CB may thus be collected in open-ocean waters to allow their analytical determination at concentration levels around or below 0.01 pg/L. The sampler is depicted in Fig. 22-1 (technical details can be found in Chapter 2). 

The operation of the unit is software controlled, and essential data are recorded for later evaluation. The sample water only comes in contact with Teflon, stainless steel and polyethylene. Before the water passes through the adsorption column it is filtered to collect suspended particles for separate analysis. Another reason is that no particles should collect on 

After retrieval of the sampler, the filter and resin cartridges are removed. Filters are stored at -20°C, resin cartridges at +4°C. Data are read from the system s on-board computer, and the batteries are recharged. Several units can be attached to the hydrographic wire to obtain vertical profiles of concentrations. Full details of the procedure have been published by Petrick et al. (1996). As blank determinations are part of the standard procedures, contamination can be checked and eliminated, if necessary. Procedural blanks may be kept as low as 0.001 pg/L in a 1000 L sample. Solutes may thus be determined reliably at the 0.005 pg/L concentration level with a 5 1 signal to noise ratio. 

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Reliable deep-water sampling is a special and demanding art. It usually has to be done from the research vessel. Special devices and techniques have been developed to provide reliable samples. 

For example deep water samples from the North Atlantic, Pacific, and Antarctic Oceans show 8lsO 0.05, —0.15 and —0.40%o, respectively. 

Several examples in which DOM was adsorbed to a single type of XAD resin can be used to illustrate some basic trends. Stuermer and Harvey (1977) adsorbed DOM from surface and deep samples in the Sargasso Sea on a column of XAD-2 resin, which was back-eluted with NH4OH and CH3CH2OH to recover the hydro-phobic acid fraction (HbA) and hydrophobic neutral fraction (HbN) of marine DOM. HbA and HbN fractions accounted for 4.5% and 3.4%, respectively, of DOM in the surface water sample. In contrast, 22.5% of DOM in the deep water sample was isolated as the HbA fraction, and an additional 8.2% of DOM was isolated in the HbN fraction. Slauenwhite and Wangersky (1996) used XAD-2 resin to adsorb DOM from coastal surface samples in Halifax Harbour. Using both NaOH and CH3OH as eluents, they were able to recover less than 15% of DOM (HbA and HbN combined). Druffel et al. (1992) used XAD-2 resin for adsorption and NaOH for desorption of DOM to recover 22% + 2% of marine DOM from four samples... 

Deep water sampling procedures are similar to those for surface water sampling, the difference is in the sample delivery method. There are several types of discrete depth liquid samplers available today to perform this task, such as glass weighted bottles, Wheaton bottles, Kemmerer samplers, or electrical pumps. 

Deep water samples (more than 20 m from the surface) can be collected directly from the ship, using a sampling bottle immersed to the desired depth by a non-metallic hydrowire, normally a Kevlar cable because of its mechanical characteristic of low extendibility. 

Deep water samples were collected directly from the ship, using a 20-30 1 sampling bottle (Teflon -coated and with pressurization capability, Go-Flo, General Oceanics, USA) which was immersed by means of a non-metallic (Kevlar) hydrowire. To sink the bottle a plastic covered ballast was used, attached to the wire at least 20 m below the bottle. 

Few investigations on arsenite oxidation in the marine environment have been published (15,16). Andreae (15) found lower concentrations of arsenite in surface water samples than in deep water samples from the Pacific Ocean. He found arsenite concentrations in surface waters in the range of 0.15-0.01 parts per billion (ppb), whereas below 400 m he found the average concentration to be 7.9 parts per thousand (ppt). He attributed this difference in concentration between surface and deep water to biological uptake and transport. Andreae s measurement of an observed ratio of As(V)/As(III) in deep water of 2.5 x 10 indicated to him a thermodynamic disequilibrium, because at equilibrium the expected ratio was 10 based on a pE of 8.0 and standard activity coefficients of the two arsenic species in seawater. The observed ratio would be expected at a pE of 2.0. Andreae... 

Bq/g and 4.44 Bq/g, respectively, in surface sediments in the northwest part of the lagoon, respectively. Concentrations of soluble and particulate Pu and Am in surface and deep water samples show distributions similar to the sediment samples. Continuous circulation of water in the lagoon and exchange of water with the open ocean results in removal of 111 GBq/a for Am and 222 GBq/a for into the North Equatorial Current (Donaldson et al. 1997). 

LiquidsISolutions (mainly various types of water) have to be carefully sampled to avoid contamination e.g., early analyses of lead in ocean water showed too high results because of contamination of sea water from the boat itself. Water samples are usually filtered through membranes with 0.45 or 0.2 pm pore size to separate liquid and particulate matter. Waters from greater depths are sampled with special deep water sampling devices. 

There is slow but progressive oxidation of dissolved Ce(HI) to particulate Ce(IV) in the deep waters as they age in transport from the North Atlantic to the North Pacific and Indian Oceans (Elderfield 1988, German et al. 1995). This redox-driven oxidation is reflected in the development of more negative Ce anomalies along the path of deep water transport. This feature is apparent when one compares the deep water samples of the western North Pacific with those of the South Atlantic (figs. 14d, e). Between these two locations the Ce anomalies change by about 50% (from 0.12 to 0.06). 

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