Authigenic Uranium in Marine Sediments of the Benguela Current Upwelling Region During the Last Glacial Period

Abstract

Anomalously high uranium contents and 238U/232Th activity ratios deposited during the oxygen isotope stages 2 to 4 are observed in the MD962085 core from the Benguela Current upwelling area. In conjunction with the activity ratio of 234U/238U, the high uranium contents found in this core can not be considered as detrital; instead, they must be of authigenic origin. The high biological productivity in the overlying seawater may have induced a high flux of organic matter resulting, directly or indirectly, in a reducing environment, and may have led to the addition of authigenic uranium to the sediments during the last glacial period. The correspondence between the variations in authigenic U content, %TOC, and 230Thex-nor-malized TOC flux supports this suggestion. The observed high paleoproductivity during the last glacial period of the core may be due to the greater intensity of upwelling in the Benguela Current upwelling system.

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