Particulate and dissolved 210Pb activities in the shelf and slope regions of the Gulf of Mexico waters

Concentration profiles of dissolved and particulate Pb-210 were measured on horizontal transects of the continental shelf and slope regions of the Gulf of Mexico. Vertical profiles in the slope station in the presence and absence of warm-core ring enable us to evaluate the differences in the scavenging intensity of Pb-210. A comparison of the rate of production of Pb-210 in the overlying water column to that of its mean annual flux calculated from the sediment inventory allows us to get a better insight in to the lateral transport and deposition of Pb-210 to the slope sediments over a < 100 year time scale. Our results indicate that there is no general increase of dissolved or particulate Pb-210 concentration with depth. The scavenging residence time of Pb-210 for the entire 1500-m water column varied between 0.06 and 4.7 years. There was a strong correlation between the inventory of total (dissolved + particulate) Pb-210 and depth of the water column. The ratio of measured sediment inventory (F) of Pb-210 to its production (P) in the overlying water column varied between 0.69 and 1.63, suggesting that, at time, lateral inputs from boundary scavenging in a few sites are dominant, while in other places, vertical scavenging is the primary mechanism of transport for Pb-210. (C) 2002 Elsevier Science Ltd. All rights reserved.