Computer Science – Sound
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmos32c..06t&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #OS32C-06
Computer Science
Sound
4808 Chemical Tracers, 4825 Geochemistry, 4860 Radioactivity And Radioisotopes
Scientific paper
The flux of metals to the oceans from land masses follows two pathways, streams and the air. Elements supplied from continents to the oceans must pass either the gauntlet of the reactive estuarine environment if delivered by streams or the convective storm effects of continental margins if by air. Therefore it is difficult to assess the fluxes of metals like mercury, lead and osmium, which can be transported either by streams or through the air to the open ocean. The flux from volcanoes complicates the supply picture further. We have calculated the atmospheric flux of Os at New Haven, Connecticut based on measurements of Os concentrations on aerosols and the Pb-210 flux. If that flux were operative throughout the world oceans it would dominate the supply of Os to the oceans relative to the stream flux as discussed below and the residence time of Os in the world ocean would be several hundred years. This value is considerably shorter than the approximately ten thousand years required by the small geographic variability in Os-187/Os-188 ratios observed in the oceans. Most atmospherically transported Os from the continents must therefore be removed from the atmosphere at the continental margin and subject to subsequent removal from sea water into sediments by coastal processes. The best assessment of atmospheric Os delivery to the open ocean from the continents is through the analysis of fluxes of Al and Pb-210 via aerosols at the Pacific oceanic islands used in the SEAREX campaign. This flux is considerably smaller than the stream flux discussed below and therefore not a serious source of Os to the open oceans. The flux from streams is dependent on the degree of retention in estuaries. The evidence for retention is from reactive estuaries such as Long Island Sound. Strong flushing of estuaries or direct debouching of the river into the open ocean will result in an unattenuated transfer of Os to the open ocean. We presume that, on the basis of published results, about half of the Os delivered through the world estuarine zones actually reaches the open ocean. The residence time of Os in the oceans relative to this dominant source is about ten thousand years. The situation in the past may be more complex. A strong correlation of He-3 concentration with Os-187/Os-188 has been observed in the well studied north Pacific core, GPC3, prior to the sharp increase of aeolian sediment accumulation in the north Pacific about 35 million years ago. This correlation requires either: (1) a strong influence of a volcanic source of sediments coupled with a supply of Os from ophiolite weathering, both resulting from plate collisions or (2) the simultaneous supply of volcanic ash and mantle signature Os from volcanoes to the oceans. Either process would modify the continental source of Os even more strongly than at present. Evidence for the first possibility is found in Quaternary sediment cores and for the second in atmospheric measurements of Os at oceanic islands.
Turekian Karl K.
Williams George G.
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