Eolian inputs of lead to the North Pacific

We evaluate the importance of natural eolian Pb to the dissolved oceanic Pb budget by measuring the isotopic composition of Pb in 35 Holocene and late Quaternary sediment samples from the North Pacific and in 10 samples of Chinese loess. When the Pacific is divided into sediments provinces based on published ε Nd and sedimentological data, Pb from the central North Pacific tends to be the most radiogenic and homogeneous due to the dominance of eolian Chinese loess. Lead from the marginal North Pacific and the sparsely sampled regions south of 5°N are less radiogenic and more variable owing to hemipelagic inputs from various volcanic arcs and older continental crust located around the Pacific Rim. 208Pb/ 204Pb ratios provide the most distinctive provenance information due to the relatively high ratios in Chinese loess. The Chinese loess samples come from 3 localities and span up to 2 Myr of time. Acetic-acid leachate, bulk loess, and loess silicate fractions were analyzed separately. Leachate Pb is considerably less radiogenic than silicate Pb. The isotopic composition of the silicate component closely matches the sediment data from the central North Pacific, confirming the dominance of eolian loess in this region. We divided up a suite of published hydrogenous Pb-isotope data from the Pacific Ocean according to their locations within the three independently defined sediment provinces. These data define three distinct fields differentiated primarily by their 206Pb/ 204Pb ratios, which increase going from the Central to Southern to Marginal provinces. This relationship with sediment province strongly suggests that natural eolian and probably hemipelagic inputs significantly impact the seawater Pb budget. Direct support for the dominance of eolian Chinese loess in the central North Pacific dissolved Pb budget comes from the close match between loess leachate Pb and the Central Province hydrogenous Pb data. Eolian inputs are likely to dominate local seawater Pb budgets only where eolian Pb fluxes are high relative to hemipelagic Pb fluxes and where the flux of Pb carried by deep water advection is low.