The Yearly Circulation of Chloride and Sulfur in Nature; Meteorological, Geochemical and Pedological Implications. Part I

Abstract

The circulation of air borne oceanic constituents is discussed to the extent available data permit. From data on sea salt particles in the atmosphere and their fall rate it is estimated that they are produced at a rate of the order of magnitude 1000 million tons a year over the ocean areas. About 90 per cent of this is precipitated over the oceans, the rest is carried into continents and is brought back to the sea in rivers. The estimated residence time for sea salt particles in the atmosphere is only a few days, higher for smaller particles, which lose their identity through coalescence, and lower for larger particles, lost by rainout or fallout. From the rate of production of sea salt particles in breaking waves it is concluded that about 0.3 per cent of the ocean areas is covered by breaking waves. On land the residence time of sea salt may vary from a few years in peripherally, drained humid areas to thousands of years in arid areas or areas without peripheral run-off.

Geochemical balance computations indicate that a major part of the sulfur in the atmosphere is of oceanic origin but does not originate as chloride through spray emitted from breaking waves. Of chemical reactions taking place in the atmosphere between sea salt constituents the release of HCl from sea salt particles due to absorption of oxidized sulfur dioxide seems to be quantitatively important and mainly responsible for variations in the Cl/Na ratio in precipitation. The deposition of chloride in precipitation over continents shows nicely the main areas of inflow of maritime air. Dry deposition of sea salt components seems to be an important process. The rate of which these constituents are carried to the ground from the air is about 1–2 cm per second, a figure concordant with the turbulent nature of air close to the ground.

As for proportions of sea salt components in precipitation some fractionation processes seems to take place at the sea surface (probably involving organic matter derived from surface films). In typical maritime areas there is always an excess cations over inorganic anions suggesting association of some cations with organic acid material in precipitation. The presence of sea salt components in groundwater can be taken advantage of in the estimation of regional evaporation using chloride as an indicator. Reduction of sulfur in groundwaters can cause precipitation of calcium and magnesium, thus modifying the chemical properties of groundwaters considerably. The role of air borne sea salt components for the development and properties of soils is discussed in principle.