Nansen bottles

During the cruises in the 1950s and 1960s, oceanographic measurements were performed by means of reversing thermometers (Wolf, 1959) and Nansen bottles. Since 1974, the seawater was collected in a rosette of tube samplers combined with the CTD (Voigt et al., 1976 Seehase, 1980). Between 1951 and 1960/1961, currents were measured by means of Ekman-Merz current meters (Helm, 1968). 

The answers are somewhat different when we ask whether we are sampHng the same universe. There are differences in water bottles - the choice would not be a stainless steel Nansen bottle with a brass valve if trace metals were being measured - but these are obvious sampling mistakes, not Hkely to occur, at least not more than once in a career. We would expect that filters with different physical structures, different pore sizes, and different composition would catch somewhat different distributions of particles, although the differences are not great [115]. Fess obvious are the differences in sediment traps, for example, which show up in comparative experiments [148,151]. The degree of difference... 

For recording vertical profiles of basic hydrochemical pararmeters in the sea (such as salinity, pH, oxygen and nutrient concentrations), water samples from different depths should be taken quasi-synchronously. On a number of ships, the famous Nansen bottle (Fig. 1-4) introduced more than 70 years ago (Knudsen, 1923,1929) is still part of standard oceanographic equipment. Even on modem research vessels it is often carried for comparison purposes and as a back-up. 

The use of Nansen bottles has some disadvantages, one being based on their construction. The closing mechanism impairs flushing of the sampler due to dead volumes and turbulent mixing. Modern samplers of the Nansen type are usually made of plastic materials such as polycarbonate (PC) and poly (vinyl chloride) (PVC) instead of brass (Table 1-2). Such samplers are less robust, but lighter, they are non-corrosive, greasing of the valves becomes unnecessary and interference with sample composition is minimized. 

Water for the analysis of suspended particles may be collected with any clean water sampler used for oceanographic work, e.g., Niskin bottles, Go-Flo bottles, Nansen bottles. Hydrobios water samplers (see also Chapter 1). The sample volume will depend on the expected concentration of POM. In nearshore and/or biologically productive water, 0.5-2 L usually is an adequate sample volume. Ten litres may be required in particle-poor open ocean waters such as the Sargasso Sea. For sampling large volumes of water, 30 L Niskin bottles are recommended. Even larger volumes may be sampled with in situ pumps. (See Chapters 1,2 and 13). 

At the sampling step, contamination from sampling bottles and hydrowire should be minimized [10], Old types of sampling devices such as Nansen and Knudsen are constructed mostly from brass, which may cause contamination of Cu and Zn into seawater. The recently developed Niskin plastic sampling bottle provides less contamination from the sampler walls. However, the materials used for the end-caps or springs, rubber or Teflon-coated stainless steel, sometimes release significant amounts of Ba, Cu, Sb and Zn [14]. 

Bottle samplers (e.g., Niskin, Nansen, Go-Flo, etc.) allow the collection of discrete water samples (0.5-30 L), whereas the acquisition of large volumes (100-1000 L) or a continuous... 

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