Abstract
Two diver-collected cores of mud-rich sediment from the New York Bight apex have been analyzed for 238 U and 232 Th decay series nuclides with emphasis on 234 Th/ 238 U disequilibrium. Excess 234 Th is present in both cores and shows exponential decrease in the top 4 cm. Biogenic reworking by a deposit-feeding community characterized by a Nucula proxima-Nephtys incisa assemblage apparently controls the form of the 234 Th profiles. Mixing coefficients of 0·3–0·6×10 −6 cm 2 s −1 are calculated. no decrease of 210 Pb with depth (0–11 cm) is found nor is there any vertical structure in profiles of 228 Th. Episodic deposition followed by periods of stability cause the observed homogeneity of the longer lived nuclides as well as laminated horizons in the sediment. 234 U/ 238 U isotope ratios reflect addition of either sea water or sewage source uranium to the collection area.
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