Geochemical Ocean Sections Study

As part of the Geochemical Ocean Section Study (GEOSECS), the carbonate ion distribution in the Atlantic and Pacific Oceans was determined with high accuracy. This survey will be extended to the Indian Ocean in 1978. 

Bulk rock chemistry of hydrothermally altered midoceanic ridge basalt has been well studied and used to estimate the geochemical mass balances of oceans today (Wolery and Sleep, 1976 Humphris and Thompson, 1978 Mottl, 1983). In contrast, very few analytical data on hydrothermally altered volcanic rocks that recently erupted at back-arc basins are available. However, a large number of analytical data have been accumulated on the hydrothermally altered Miocene volcanic rocks from the Green tuff region in the Japanese Islands which are inferred to have erupted in a back-arc tectonic setting (section 1.5.3). 

The estimate for sea salt goes back to a detailed study of Eriksson (1959) of the geochemical cycles of chloride and sulfur. He calculated the rate of dry fallout of sea-salt particles from a vertical eddy diffusion model and then existing measurements of sea-salt concentrations over the ocean. This led to a global rate for dry deposition of 540 Tg/yr. Eriksson then argued that wet precipitation would remove a similar amount annually. It is now known, however, that wet precipitation is more effective than dry deposition in removing aerosol particles from the atmosphere, so that Eriksson s value must be an underestimate. The discussion in Section 10.3.5 suggests a flux rate for sea salt of about 5,000 Tg/yr. 

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