The determination and distribution of cobalt and nickel in tropical Pacific water

Abstract

In a study of the bio-geo-chemical circulation of cobalt and the related transition element, nickel, in Hawaiian waters, it was decided to employ the colorimetric methods described by Thompson and Laevastu for the determination of trace quantities of both elements. Both procedures, nitroso-R method for cobalt and the dimethylglyoxime procedure for nickel, were found to be extremely sensitive to slight modifications. The methods were studied in detail, modified and improved, which resulted in a five-fold increase in sensitivity and therefore a reduction in sample size from ten to two liters. An increase in precision in the measurement of the colored chelate resulted by careful control of the pH and time during complex formation, conditions for decomposition of excess reagent, and choice of wavelength. For optimum recovery it was necessary to allow a minimum period of seven days to elapse following precipitation with sodium carbonate prior to filtration and analysis. A previously unreported, but significant "salt effect" was detected which required construction of a calibration curve prepared from sea water, or a correction factor in use of standards in distilled water. Monthly samples of water were taken in 1964 from the Johnson Island area and Koko Head, Oahu, and analyzed for cobalt and nickel. The Johnson Island water also had important parameters determined i.e., chlorophylls, carbon14 productivity, nitrate, phosphate, as well as temperature and salinity. After analysis, the results were programmed and correlated with the IBM 7040. The resulting relationships were indicative of typical subtropical water in both the upper mixed layer as well as the subsurface water below the pycnocline. The cobalt and nickel data lend evidence to a "non-crustal" or volcanic contribution to the salinity of the oceans.