210 Pb- 226 Ra: radioactive disequilibrium in the deep sea

• Main Authors: Craig, H., Krishnaswami, S., Somayajulu, B. L. K.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier Science 1973
• Subjects: Pacific; North Atlantic Deep Water; North Atlantic
• Online Access: http://repository.ias.ac.in/16701/; http://linkinghub.elsevier.com/retrieve/pii/0012821X73901945

210 Pb and 226 Ra profiles have been measured in the North Atlantic and North Pacific Deep Water. The 210 Pb activity is 25% to 80% of that of 226 Ra, averages about 50% in each profile, and is lowest in the bottom water. This deficiency of 210Pb relative to 226 Ra shows that 210 Pb is rapidly and continually scavenged from deep water, probably by adsorption on particulate material sinking from the surface. A method is developed for simultaneous application of the vertical diffusion-advection model to 226 Ra and 210 Pb deep-water profiles, and the in-situ source terms for both isotopes are obtained as a function of the parametric upwelling velocity. For a positive source term for 226Ra in deep water, the parametric velocity is limited to a small range (3-12 m/y) and the deep-Pacific residence time of lead is 54 yr, a value two orders of magnitude smaller than residence times estimated from stable lead concentrations. The model calculations show that an in-situ scavenging process, acting throughout the water column, is required to remove the Pb. Box model calculations yield a similar short residence time for lead in North Atlantic Deep Water, indicating that radioactive disequilibrium for 210 Pb, due to fast scavenging, is a general phenomenon through the deep sea.