Trace elements in the oceans

Abstract

Trace elements are present in sea water at concentrations that range down to picomoles per litre (pmol 1-1) and even lower. Such small concentrations pose extreme analytical problems, and it is only recently that these have been fully overcome. It is now known, for example, that contamination and the lack of sufficiently precise analytical techniques have led to reported concentration data that for some trace elements were too high by factors as much as 103. Because of this, real trends in the trace element data were sometimes totally masked by noise in the system, creating what Chester (1985) described as a ‘frustration barrier’, which prevented marine chemists from being able to relate trace metal distribution patterns to a consistent oceanographic framework. However, in a keynote review, Bruland (1983) pointed out that the mid-1970s had seen a quantum leap in our knowledge of the oceanic distributions of trace elements. This leap had become possible as a result of major improvements in both analytical and collection techniques, especially with regard to the elimination of sample contamination, which allowed the noise to be filtered out of the data. A selection of the new trace element concentration data in sea water is given in Table 11.1. At the same time that trace element concentration data were being refined, there were also advances in our understanding of the speciation of the elements in sea water.