Surface seawater samples

The stability of the organic components of surface seawater samples is more questionable, but can be tested over time for a wide variety of molecule classes. 

One comprehensive study of surface DMS concentrations was that of Andreae and Raemdonck (42). Hie concentration of DMS was determined in 628 surface seawater samples, collected at 0.05 and 3 m. From this data base they estimated that a global weighted-mean DMS concentration in surface waters is 3.2 nmol I/1, higher than the values obtained in earlier studies (21.441. They noted that the DMS concentrations varied significantly from one location to the next and suggested that this patchiness might be related to primary production and also species variations from locale to locale. The correlation between chlorophyll a and DMS concentration for 225 samples was r = 0.53, = 0.001. 

Surface seawater samples were taken using ships continuous non-toxic pump supplies, the average depth of intake being 3m. A 500ml bottle was carefully filled with the fast-flowing, bubble-free water and allowed to overflow for about a minute and then stoppered (ground glass). Hence, exposure to air and... 

We devised the following scheme to test the suitability of a widely used PVC sampler (General Oceanics, Inc., Miami, Fla.) with a Teflon coated stainless steel closing spring. During R/V Trident cruise 152 (May 8-19, 1974), we obtained both surface seawater samples and collections at depth for vertical mercury profiles (to 750m) at four stations between Narragansett, R.I. and Bermuda. The locations are... 

Fig. 3. Examples of mass spectra of n-hexane/dichloromethane (FI) extractable surfactants isolated by foam tower stripping from a bulk surface seawater sample (upper), an unslicked microlayer (centre), and a heavily slicked microlayer (lower). The spectra show the dominance of polyoxy components in the bulk seawater surfactants and different degrees of enrichment of more hydrophobic lipid surfactants in the microlayer. Note that these particular spectra were chosen to illustrate the range of composition observed and the impact on surface elasticity (see Figure 4), not to represent bulk seawater, unslicked and slicked microlayers generally...

All of the surface seawater samples were collected in 1L glass bottles capped with glass caps, from different sites on the Black Sea Coast The collection of the seawater samples was made from the surface, approximately to 10 m from the coast. Samples were filtered to remove particulate material and kept refrigerated at 4°C away from light prior to extraction, which was done within 24h. The extracts were analyzed before two weeks of collection. 

Collection of undisturbed discrete surface seawater samples from research vessels is not possible. To leave the contaminated water plume of the main vessel and to approach closer to the sea surface, suitable small tenders have to be used. Sampling is performed from the lee-side of the tender, >200m up-wind from the ship in an area not previously passed by any vessel. During sampling, the tender may be moved slowly at right angles to the direction of the prevailing surface currents. 

Fig. 23-4. A chromatogram from a surface seawater sample analysed according to the Tracer mode utilising the pre-column to get a heart-cut chromatogram (see text for details). The time axis (not to scale) is illustrated in the upper part of the figure. An open tubular trap as in Fig. 23-2 B heated in boiling...

Early measurements of " Th were on seawater samples and Th was co-precipitated from 20-30 L of seawater with iron hydroxide (Bhat et al. 1969). This procedure may not recover all of the " Th in the sample, and an alpha emitting Th isotope (e g., °Th or Th) is added as a yield monitor. Following chemical purification of the Th fraction by ion exchange chromatography, the Th is electrodeposited onto platinum or stainless steel planchets. The planchets are then counted in a low background gas-flow beta detector to measure the beta activity and subsequently with a silicon surface barrier detector to determine the alpha activity of the yield monitor. The " Th activity is thus determined as ... 

Changes in the distribution of organic compounds in a seawater sample can be due to physical, chemical, or biological factors. As a physical factor, we might consider the absorption of surface-active materials on the walls of the sample container. While this effect cannot be eliminated it can be minimised by the use of the largest convenient sample bottle, and the avoidance of plastic (especially Teflon) containers. Another possible method of eliminating this source of error would be to draw the sample directly into the container in which the analytical reaction is to be run. 

Ahern et al. [50] have discussed the separation of chromium in seawater. The method involved co-precipitation of trivalent and hexavalent chromium, separately, from samples of surface seawater, and determination of the chromi-... 

Tsunogai and Nozaki [6] analysed Pacific Oceans surface water by consecutive coprecipitations of polonium with calcium carbonate and bismuth oxychloride after addition of lead and bismuth carriers to acidified seawater samples. After concentration, polonium was spontaneously deposited onto silver planchets. Quantitative recoveries of polonium were assumed at the extraction steps and plating step. Shannon et al. [7], who analysed surface water from the Atlantic Ocean near the tip of South Africa, extracted polonium from acidified samples as the ammonium pyrrolidine dithiocarbamate complex into methyl isobutyl ketone. They also autoplated polonium onto silver counting disks. An average efficiency of 92% was assigned to their procedure after calibration with 210Po-210Pb tracer experiments. 

Bacon and Anderson [42] determined 230thorium and 228thorium concentrations, in both dissolved and particulate forms, in seawater samples from the eastern equatorial Pacific. The results indicate that the thorium isotopes in the deep ocean are continuously exchanged between seawater and particle surfaces. The estimated rate of exchange is fast compared with the removal rate of the particulate matter, suggesting that the particle surfaces are nearly in equilibrium with respect to the exchange of metals with seawater. 

The method was used for routine monitoring of dinitrotoluene concentrations in seawater from Dokai Bay, Japan. Both 2,6- and 2,4-dinitrotoluene were detected. Concentrations of 2,4-dinitrotoluene in surface water samples were higher than those in bottom water samples in 8 out of 10 samples. 

Chlordane has been detected in both groundwater and surface water at low levels of 0.001 to 0.01 pg/L (USEPA 1988). A high frequency of chlordane detection was noted in seawater samples collected from a Hawaiian marina up to 90% of all samples contained cw-chlordane, and 68% contained trans-chlordane (IARC 1979). Because of chlordane s use as a soil-injected insecticide and its persistence, it has the potential to contaminate groundwater, particularly when it is applied near existing wells (USEPA 1988). 

Helium-3 is a decay product of radioactive tritium (3H, half-life = 12.44 years) that has been produced by nuclear bombs as well as naturally by cosmic rays in the upper atmosphere. Because virtually all 3He atoms escape from the surface ocean to the atmosphere, the 3He/tritium ratio in subsurface seawater samples indicates the time since the water s last exposure to the atmosphere. Both 3He and tritium are measured by gas mass spectrometry. Alternatively, tritium may be measured by gas counting with a detection limit of 0.05 to 0.08 tritium unit, where 1 tritium unit represents a 3H/H ratio of lxl0 18. A degassed water sample is sealed and stored for several months to allow the decay product 3He to accumulate in the container. The amount of 3He is then measured by mass spectrometry, yielding a detection limit of 0.001 to 0.003 tritium unit when 400-gram water samples are used. With this technique, the time since a water mass left the surface can be determined within a range from several months to 30 years. 

The concentrations of DOC in major rivers typically range from 250 to 750 pM, and concentrations in the surface ocean range from 60 to 90 J.M (Table I). Most of the river data compiled in Table I are from the Amazon River system (Hedges et al., 1994, 2000), the Parana River system (Depetris and Kempe, 1993), and the Mississippi River (Benner and Opsahl, 2001). The seawater data are from surface water samples collected in the Pacific and Atlantic Oceans (see Table I for references). Total hydrolyzable neutral sugars (glucose, galactose, mannose, xylose, fucose, rhamnose, and arabinose) account for about 1-2% of river DOC and 2-6% of ocean DOC, indicating... 

Wurl, O., Obbard, J.P., 2005a. Chlorinated pesticides and PCBs in the sea-surface microlayer and seawater samples of Singapore. Mar. Pollut. Bull. 50, 1233-1243. 

In this pilot plant the UF pretreatment system is arranged in 2 trains, each housing 3 modules (PAN HF membranes, nominal pore size of 0.02 (im, MWCO 50 000, total effective surface area of 30 m2). Raw seawater (samples from Qingdao Jiaozhou Bay, the Yellow Sea of China) was first passed into a cartridge sand filter and successively feed to UF system, the UF permeate was then pumped to the RO system (spiral-wound composite polyamide) (Figure 12.1). 

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