RELATION OF CONTINENTAL VOLCANISM TO THE ORIGIN OF THE MODERN MARINE ECOSYSTEM

By releasing sulfuric acid aerosols into the atmosphere, massive flood basalts situated on continental land masses may have triggered episodes of climatic cooling in the geologic past and are therefore commonly invoked as potential causes of mass extinction. Such eruptions, however, can discharge vast amounts of volcanic ash that are rich in biologically important nutrients. Laboratory experiments, as well as direct observations of the Kasatochi eruption in the Aleutian Islands, demonstrate that volcanic fallout can effectively fertilize ocean surface waters and enhance primary productivity in present-day environments. A major diversification of marine phytoplankton, which commenced as shallow epeiric seas formed during the initial fragmentation of Pangaea into Laurasia and Gondwanaland some two hundred million years ago, might also have been driven in part by continental volcanism. The growth of Recent species of diatoms, dinoflagellates, and calcareous nannoplankton is limited by iron, silica, and/or phosphate, which are all constituents of volcanic ash. Several large igneous provinces arose in the Mesozoic and Cenozoic Eras, suggesting a possible link between volcanic nutrient output and the secular increase in primary productivity that allowed the radiation of advanced predators and the expansion of actively burrowing infaunal life habits in the marine realm. Moreover, the emplacement of continental flood basalts and oceanic plateaus, which have been previously proposed as stimulatory agents in biotic evolution, often coincides closely in time. Gaseous emissions of carbon dioxide from volcanoes further fuel primary productivity by raising global temperatures and influencing rainfall patterns, thereby promoting weathering, erosion, and runoff of terrestrial sediments (and the various organic and inorganic nutrients they carry) towards adjacent coastal marine settings. These lines of evidence indicate that continental volcanism helped shape the modern marine ecosystem together with other factors, including submarine volcanism, widespread orogeny, and the Cretaceous appearance of flowering plants.