The World Ocean Mechanism or Machination?

Abstract

The evolution of life in the oceans proceeded in an almost leisurely fashion against a background of frenetic geological activity. Despite the intensity of the geological cycling, the available evidence suggests that the sedimentary material produced has remained tolerably uniform in composition over the last two thousand million years or so. This implies a corresponding uniformity in the composition of sea water over this period and it seems likely that the oceans are now at a steady state with respect to the fluxes of weathered material eroded from the continents and acid volatiles emanating from volcanic fissures. The overall composition of sea water was probably fixed in the first few hundred million years of the ocean's history by water-rock interactions that were controlled by simple chemical rules. As life evolved the most abundant elements in the oceans would be used in the metabolic processes provided they were able to perform the necessary biochemical functions. Consequently, there is a strong correlation between the composition of sea water and the degree to which particular elements contribute to the life process. The contemporary marine biota intervene in the overall geochemical cycle by recycling the elements and thereby gaining some control over the vertical and lateral distributions of the elements within the oceans. From the perspective of the Gaia hypothesis it is tempting to interpret the selective recycling of the elements in terms of a self-regulating biological community striving to maintain optimum conditions for photosynthesis in the warm, wind-mixed layer. The composition of sea water is therefore seen as the end product of an intricate interweaving of the physically and chemically possible and the biologically useful.