Particle reworking in sediments from the New York Bight Apex: evidence from Th²³⁴/ U²³⁸ disequilibrium.

Two diver-collected cores of mud-rich sediment have been analyzed. Excess ²³⁴Th 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 ²³⁴Th profiles. No decrease of ²¹⁰Pb with depth (0-11 cm) is found nor is there any vertical structure in profiles of ²²⁸Th. Episodic deposition followed by periods of stability cause the observed homogeneity of the longer lived nuclides as well as laminated horizons in the sediment. ²³⁴U/²³⁸U isotope ratios reflect addition of either sea water or sewage source U to the collection area. -Authors