Physics
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51.1743h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 6, pp.1743-1754
Physics
4
Scientific paper
Nine natural decay-series isotopes were measured in six box cores collected from a transect across the Santa Monica Basin. The 210 Pb-derived sedimentation rate decreases from ~80 mg/cm 2 -yr at the slope to ~20 mg/cm 2 -yr in the deep central basin. Sediment mixing prevails in sites underlying oxic waters, but is subdued in the anoxic deep basin below the sill depth. Uranium contents in sediments are controlled by levels of authigenic U, which are higher in the more reduced condition in the deep basin. Most of the authigenic U results from precipitation within the sediments. The 232 Th- 228 Th disequilibrium in sediments indicates that 228 Ra is lost from the sediments from a depth of ~ 10 cm upward. Modelling the distribution of excess 228 Th and 234 Th in the surficial layers of the deep basin sediments results in a mean sediment mixing coefficient of 0.2 cm 2 /yr and a sedimentation rate close to that based on 210 Pb. There is no evidence of changing sedimentation rate in the central basin during the past century. Fluxes of excess 210 Pb, 230 Th and 231 Pa to the central Santa Monica Basin sediments are much higher than what can be predicted from local supply. Advective input of open ocean waters coupled with enhanced scavenging of these reactive nuclides at the ocean margin is considered to be the primary cause.
Huh Chih-An
Noshkin Victor E.
Small Lawrence F.
Zahnle Debra L.
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