Wet deposition of trace metals to a remote site in Fiordland, New Zealand

Abstract

Cd, Cu, Fe, Mn, Pb, Zn, Ca, Mg, Na, pH, and 210 Pb were determined in rainwater collected at Paradise, a remote site in Fiordland, New Zealand, to evaluate sources and fluxes of atmospheric trace metals in the NZ region of the South Pacific westerlies. Individual rain events were sampled using rigorous trace metal clean protocols during 1993–1995. Air-mass trajectories showed an Australian and Southern Ocean influence on most samples. Ca, Mg, and Na were highly correlated with each other, over 2–3 orders of magnitude, and had a sea-salt aerosol source. Most of the Fe was not soluble in 0.03 M nitric acid after 48 h, suggesting low bioavailability after deposition to the ocean, whereas most of the Zn was soluble. Mean trace metal concentrations were similar to those at other Southern Hemisphere sites; with the lower concentrations comparable with those in present-day Antarctic snow. Trace metal concentrations spanned two orders of magnitude, and were not obviously related to air-mass trajectories. The seawater contribution to rainwater trace metals was negligible. Cd, Cu, Pb, and Zn were enriched in rainwater relative to crustal material, and a significant anthropogenic contribution to these elements is tentatively suggested. Limited Pb isotope data link anthropogenic Pb with high Pb enrichment. Cd, Pb, Zn, and H + were correlated with each other, suggesting a common source. Fe and Mn were correlated, and had a predominantly crustal dust source. Cd and Pb were correlated with 210 Pb , implying that these metals were associated with submicrometre-sized aerosols.