Global trace metal cycles and predictions

Abstract

A methodology and mathematical formulation are presented for development of the global geochemical cycles of trace metals. Global cycling models of As, Se, and Hg are discussed in detail and used to assess the impact of the activities of society on these element cycles. These models show that anthropogenic activities may have increased the global concentrations of these elements in rain, seawater, and perhaps in river water. Model calculations suggest that increased concentrations of these elements in the world's surface ocean by the year 2000 will be small. A two-reservoir, cycling model of trace metals in atmospheric particulates is developed and used to assess the sources of element enrichments in these particulates. The model enables prediction of trace metal enrichment factors in atmospheric particulates, where enrichment factor is defined as the metal/Al ratio in atmospheric particulates divided by the metal/Al ratio in soils. Correspondence between predicted and observed enrichment factors suggests that for some trace metals, their enrichments in atmospheric particulates are caused, at least in part, by the industrial and fossil fuel burning activities of society. Model calculations further show that cessation of these activities would result in a return of present-day or future enrichment factors to preindustrial values in less than one year.

Manuscript received 1 June 1978. This paper was presented at the Symposium “Predictive Models in the Earth Sciences” held as part of the Geological Society of America Annual Meeting, Seattle, Washington, November 8, 1977.