SEASONAL-VARIATIONS IN BE-7 ACTIVITY IN THE SEDIMENTS OF CAPE LOOKOUT-BIGHT, NORTH-CAROLINA

Short-term sediment accumulation rates were determined using activity distributions of 7Be in the surficial sediments of a station (A-1) in Cape Lookout Bight, North Carolina (USA). This semienclosed coastal marine basin is characterized by high annual accumulation rates. Protected from high energy conditions by its geomorphology, the relatively quiescent waters of the bight's interior cause it to act as an efficient settling trap for fine-grained sediment. Lack of bioturbation in the surface sediments allowed for variations in depth-integrated activity profiles of 7Be to be interpreted as short-term accumulation events. Beryllium-7 inventories exhibited seasonal cyclicity with inaxima occurring during spring (February through June). The inventory of 7Be ranged from 5.8 to 32.6 dpm cin-2 and was always well in excess of the atmospherically supported value ( x ̄ = 3.8 dpm cm-2; n = 15). Accumulation rates calculated froin 7Be activity profiles indicate that the delivery of particulate matter to the sediments of Cape Lookout Bight is not constant throughout an annual cycle. The highest monthly accumulation rates appeared to be associated with north/northeast storm activity. Inputs were generally highest during late winter/early spring when storm frequency is greatest. Short-term accumulation rates derived from this study agree with 210Pb rates calculated for a ten-year period of accumulation. The annual sediment accumulation rates for each of the two years over which the study was conducted was found to be 4.8 ±0.8 g cm-2 y-1 and 3.7 ± 1.2g cm-2y-1. © 1990.