PII S0016-7037(01)00779-7 Advection and removal of 210Pb and stable Pb isotopes in the oceans: A general circulation model study

Abstract—Natural Pb-isotope variability in the oceans encodes information about the sources of continental material to the oceans, about ocean circulation, and about Pb removal. In order to use this information, we must understand the natural cycle of Pb in the oceans, which is overprinted by large anthropogenic input. In this study we use 210Pb, which has not been significantly anthropogenically perturbed, to investigate oceanic Pb. GEOSECS 226Ra and model-derived atmospheric fluxes of 210Pb are used to input 210Pb into an ocean general circulation model. Irreversible scavenging of this 210Pb onto settling biogenic particles and at the seafloor are tuned so that the model replicates the observed pattern of 210Pb in the oceans. The best-fit model run provides a map of the variability of residence time for Pb. The global average residence time of Pb in this model is 48 yr, but there is over an order of magnitude variation between areas of high and low productivity. This is expected to enhance provinciality of Pb isotope ratios in the oceans. Because stable Pb isotopes are expected to behave in seawater in a similar fashion to 210Pb, the pattern of removal of 210Pb derived by the model can be used to investigate the behavior of stable Pb isotopes. We use a simplified input of Pb consisting of five point sources representing major rivers and a disseminated dust input. Although this simplified input scheme does not allow precise reconstruction of Pb concentration and isotopes in the oceans, it allows us to answer some first-order questions about the behavior of Pb as an ocean tracer. With a total Pb input of 6.