Measurements on cores from the Ontong Java Plateau demonstrate that on-equator sediment accumulates more Th-230 than is produced in the overlying water column. In contrast, cores from 3.8 degrees N accumulate an amount of excess Th-230 more nearly equal to that produced in the overlying water column. Taken together with the observation that both the CaCO3 and non-CaCO3 components of the sediment accumulate at approximately twice the rate in on-equator than in off-equator cores [Broecker et al., 1999], this requires either that the rain of the larger amount of organic matter generated above the equatorial upwelling plume entrains excess clay and Th-230 during its fall to the sea floor or that physical transport processes, either in the upper ocean or near the sea bed, redistribute sediments in such a way that they preferentially accumulate-in a narrow (+/- 1 degrees latitude) equatorial-centered belt.
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