210Pb and 210Po distributions and disequilibrium in the coastal and shelf waters of the southern North Sea

Abstract

Concentration profiles of 210Pb and 210Po were measured at 10 stations in the coastal and shelf areas of the southern North Sea. Scavenging processes in this study area are revealed by 210Po/ 210Pb disequilibrium and their distributions in the water column. Results for 210Po show strong excess, relative to 210Pb, in both dissolved and particulate forms, indicating an additional flux of 210Po from the coastal and shelf sediment. A significant maximum of the dissolved 210Po and 210Pb over the fine grained depositional area (Oyster Ground) was observed to correspond with resuspension of the underlying muddy sediments. The relative greater uptake rate of dissolved 210Po, derived from a ☐ model calculation of mass balance, suggest that the 210Po is more preferentially scavenged from the water column than 210Pb, probably due to its higher activity and its high recycling efficiency. The low concentration of 210Pb in the study area is related to the low atmospheric input of 210Pb, 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 210Po found in the water body could be balanced by only a small amount of deficit of 210Po in the sediment, due to the characteristics of this continental shelf area.