John H. Martin

Sampling and analytical methods for the determination of copper, cadmium, zinc, and nickel at the nanogram per liter level in sea water

Abstract Sea-water samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative, uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and electrothermal atomization is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection limits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in sea water at their natural ng l -1 concentration levels is therefore possible. Samples analyzed by this procedure and by concentration on Chelex-100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from sea water by Chelex-100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement.

Zinc in north-east Pacific water

ALMOST all lead data for the marine environment are inaccurate, contends Patterson1, because of gross contamination from faulty sampling and analytical procedures. Most marine chemists assume that similar problems are associated with other trace elements as well. Hence, clean sampling and analytical techniques have been adopted. These procedures, in conjunction with the improvement of analytical instrumentation, have resulted in reports on Cu, Ni and Cd (refs 2–4; 3, 5; and 3, 6–8 respectively) levels in seawater that are at least an order of magnitude lower than those previously thought to exist. We report here that Zn concentrations (10–600 ng l−1) are also considerably lower than previously published estimates of 1–30 µg l−1 and that its vertical distribution (surface depletion, deep enrichment) is very similar to that of a major plant nutrient; that is, silicate.

We still say iron deficiency limits phytoplankton growth in the subarctic Pacific

The failure of Banse (1990) to use a reasonable initial particulate organic nitrogen (PON) value resulted in erroneously high, and physiologically impossible, estimates of phytoplankton growth rates. To correct this situation, we used an initial PON value of 1 μmol PON L−1 for both experimentals and controls; rates similar to those expected under prevailing light and temperature conditions were obtained. This reinterpretation of our data again demonstrates the dramatic effects that are observed when small quantities of iron are made available to the phytoplankton inhabiting offshore subarctic Pacific waters.