Other
Scientific paper
Apr 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982gecoa..46..651b&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 46, Issue 4, pp.651-666
Other
13
Scientific paper
Measurements of 238 U, 234 U, 230 Th, 232 Th, 231 Pa, Mn, Fe, Co, Ni, Cu, and Zn were made on 23 samples from core GPC-5, a 29-m giant piston core from a water depth of 4583 m on the northeastern Bermuda Rise (33°41.2'N, 57°36.9'W). This area is characterized by rapid deposition of sediment transported by abyssal currents. Unsupported 230 Th and 231 Pa are present throughout the core but, because of large variations in the sedimentation rate, show marked departures from exponential decay with depth. The trend with depth of the 231 Pa ex / 230 Th ex ratio is consistent with the average accumulation rate of 36 cm/1000 y reported earlier on the basis of radiocarbon dating and CaCO 3 stratigraphy. When expressed on a carbonate-free basis, concentrations of Mn, Co, Ni, Cu, Zn, 230 Th ex , and 231 Pa ex all show cyclic variations positively correlated with those of CaCO 3 . The correlations can be explained by a model in which all of these constituents, including CaCO 3 , are supplied to the sediments from the water column at a constant rate. Concentration variations are controlled mainly by varying inputs of terrigenous detritus, with low inputs occurring during interglacials and high inputs during glacials. Relationships between the metal and 230 Th ex concentrations permit estimates of the rates at which the metals are removed to the sediment by scavenging from the water column. The results, in g/cm 2 -1000 y, are: 4300 ± 1100 for Mn, 46 ± 16 for Ni and 76 ± 26 for Cu. These rates are somewhat larger than ocean-wide averages estimated by other methods, and the absolute rate of 230 Th accumulation in GPC-5 averages about nine times higher than production in the overlying water column. This part of the Bermuda Rise and similar bottom-current deposits may act as important accumulators of elements scavenged from seawater.
Bacon Michael P.
Rosholt John N.
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