Precipitation composition at Cape Grim, 1977-1985
Ayers, G. P.
Ivey, J. P.
- Publisher: Tellus B
(issn: 1600-0889, eissn: 0280-6509)
Rainwater composition data resulting from monthly, wet-only collections of maritime rain at Cape Grim, Australia, in the period April 1977 to March 1985 have been critically appraised. High local wind speeds prove to be a major determinant of data quality: extremely high seasalt loadings (average rainwater sodium and chloride concentrations in the low millimolar range) make estimation of excess sulfate impossible against a background sulfate concentration of about 150 μeq/l derived from sea-salt. The extreme wind speeds also cause considerable erosion of the Cape surface, leading to the ubiquitous presence of local soil components in collected rainwater. Both the rainwater data and data from the analysis of local soil samples show that these soil components significantly elevate rainwater pH (observed mean 6.01) and the concentrations of potassium and calcium. Effects upon other ions appear to be minimal, but cannot be ruled out. Calculation of pH for rainwater having the long-term mean composition, but with the effects of local contamination excluded, yielded a value of 5.10. Further calculations in which sea-salt content of the rainwater was varied over the range observed at Cape Grim indicated that at this site, sea-salt alkalinity may be a major determinant of rainwater pH, leading to pH variations from < 5 to > 6.DOI: 10.1111/j.1600-0889.1988.tb00299.x