Enrichments in Hg, Cd, As, and Sb in recent sediments of Azores-Iceland Ridge

Abstract

Mercury, cadmium, arsenic, and antimony were analyzed in cores sampled on the Azores-Iceland Ridge. High values of 780 Ixg • kg -t for Hg, 1.7 I~g.g ~ for Cd, 87 ~g "g ~ for As, and 8, 1 ~tg. g-~ for Sb occur in the rift Valley and transform faults. These enrichments, strictly linked to the ridge, COuld not have an allochtonous origin. A local hydrogenous flux may explain this phenomenon. These metallic enrichments may be connected to a hydrothermal activity extended between 43 ° N and 47 ° N.

Clay Sedimentology

“…The hydro thermal plumes are dispersed laterally as far as 2000 km from the spreading axis. Other chemical markers of the hydrothermal impact in ridge axes and of dilution gradients in deep-sea sediments may be used, as for instance mercury, cadmium, arsenic, antimony, and selenium (e.g., Grousset andDonard 1984, Fournier-Germain 1986). At about 30 o S, the plumes are advected eastwards because of change in the direction of currents ( Fig.13.12).…”

Current Methods of Estimating Atmospheric Mercury Fluxes in Remote Areas

“…These conclusions were in accord with earlier studies of Hg enrichment in sediments over the East Pacific Rise (125) and in authigenic sediments near submarine volcanoes (126) and have been substantiated by other studies of the East Pacific Rise (127,102). Elevated Hg levels are also associated with the Mid-Atlantic Ridge (Table 3), evidenced by Hg emissions from Icelandic geysers (128) and by elevated Hg concentrations in Iceland-Azores ridge sediments compared to abyssal plain sediments (129). On the basis of crustal heat flow data, it could be calculated that mid-ocean ridges in themselves contribute enough Hg to the oceans (1860-3720 Mg yr-1; Table 3) to account for the annual flux from the oceans to the atmosphere (Table 1).…”

A coupled natural immobilisation mechanism for mercury and selenium in deep-sea sediments

“…Most investigations have been made in coastal environments near major industrial or urban discharge points, where recent pollution can increase sediment mercury concentrations by 3-4 orders of magnitude (to 250,000 ppb; GESAMP, 1990) above natural background levels (e.g., Young et al 1973;Skei and Paus, 1979). Second, naturally enhanced Hg levels are also observed in sediments which are influenced by hydrothermal activity near mid-ocean ridges or other plate boundaries including the compressional type (Jonasson and Boyle, 1972;Bostrom and Fisher, 1969;Toth 1980;Kadko, 1980;Grousset and Donard, 1984). The third Hg-enriched environment is C org -rich (Jonasson and Boyle, 1972) or pyritic (Huerta-Diaz and Morse, 1992) reducing sediments.…”