Computer Science
Scientific paper
Oct 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.4285m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 20, pp.4285-4298
Computer Science
7
Scientific paper
Radium isotope distributions on the continental shelf adjacent to the Amazon River are a complex function of salinity. The river and seawater endmembers for each radium isotope are low. Data from intermediate salinities plot as a highly scattered region above the conservative mixing line connecting the river and ocean endmembers. Spatial and temporal variability in sediment mixing and water residence times cause the scatter in the radium isotope data. We have used the distributions of 226 Ra, 228 Ra, and 224 Ra collected during four cruises representing different conditions on the shelf to construct inventories of radium due to nonconservative additions from sediments. Using estimates of water residence times, we calculate fluxes of these radium isotopes from the Amazon system. The amount of fresh river sediment entering the system each year is adequate to support the nonconservative flux of 226 Ra from the shelf sediments; however, the ultimate release of 226 Ra from the sediments requires weeks to months. To support the nonconservative flux of 228 Ra from this system, sediments of the 1-2 m thick surface mixed layer must be resuspended every two years. The resulting flux supports 15% of the 228 Ra entering the surface Atlantic Ocean. Release of 224 Ra from suspended sediments, primarily fluid mud, is more than adequate to support the inventory of 224 Ra on the Amazon shelf. Comparing the AmasSeds low discharge cruise (November 1991) to a low discharge sampling in December 1982 revealed no significant changes in the 226 Ra and 228 Ra distributions.
Astwood Heather
Lindstrom Candice
Moore Willard S.
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