Chronologies of sedimentary processes in sediments of the FOAM site, Long Island Sound, Connecticut

Abstract

Distribution with depth of: ²³⁴Th_xs, ⁷Be, ²¹⁰Pb_xs, (super 239,240) Pu, selected trace elements, ¹⁴C (in both shells and organic fraction), pore water sulfate, and the diagenetic reaction products, solid phase organic carbon and sulfur. The ²³⁴Th_xs and ⁷Be data indicate that the upper 4 cm are well mixed on the time scale of about a year. The distributions of ²¹⁰Pb_xs, (super 239,240) Pu, and anthropogenic trace metal excesses in the (4-15) cm section are controlled by the mixing of the surface (0-4) cm sediment into this layer. The net sediment accumulation rate in the (0-15) cm layer is about 0.03 cm/yr. The average sediment accumulation rate in the ( approximately 18-100) cm layer, as determined from ¹⁴C ages of shell layers, is 0.094 + or - 0.021 cm/yr, perhaps a factor of approximately 2 lower than that estimated from diagenetic modeling of solid phase sulfur and organic carbon depth profiles.