PB-210 AND PO-210 DISTRIBUTIONS AND DISEQUILIBRIUM IN THE COASTAL ANDSHELF WATERS OF THE SOUTHERN NORTH-SEA

Concentration profiles of Pb-210 and Po-210 were measured at 10 statio ns in the coastal and shelf areas of the southern North Sea. Scavengin g processes in this study area are revealed by Po-210/Pb-210 disequili brium and their distributions in the water column. Results for Po-210 show strong excess, relative to Pb-210, in both dissolved and particul ate forms, indicating an additional flux of Po-210 from the coastal an d shelf sediment. A significant maximum of the dissolved Po-210 and Pb -210 over the fine grained depositional area (Oyster Ground) was obser ved to correspond with resuspension of the underlying muddy sediments. The relative greater uptake rate of dissolved Po-210, derived from a box model calculation of mass balance, suggest that the Po-210 is more preferentially scavenged from the water column than Pb-210, probably due to its higher activity and its high recycling efficiency. The low concentration of Pb-210 in the study area is related to the low atmosp heric input of Pb-210, the high concentration of suspended matter and the high sediment resuspension rates. A comparison of the data between the water and sediment columns shows that the excess of Po-210 found in the water body could be balanced by only a small amount of deficit of Po-210 in the sediment,due to the characteristics of this continent al shelf area.