Extending the calibration of marine barite Pb isotope records

Lead isotopes in marine barite have been emerging as a new proxy for intermediate water conditions. Marine barite forms at intermediate water depths and incorporates Pb into its matrix at ~2ppm. The isotopic composition of this Pb is retained as the barite settles in the water column, allowing us to reconstruct the Pb isotopic ratios of intermediate water. Lead and its isotopes are introduced into the ocean primarily through the weathering of continental rock. These rocks may have distinct isotopic signatures, depending on the age of the eroded material and weathering style. Lead has a short residence time in the ocean. As a result of these characteristics, different water masses have distinct lead isotope signatures that depend on the Pb sources (riverine and atmospheric) to the water mass at the point of origin. Since anthropogenic pollution has irrevocably altered Pb concentrations and isotope ratios, calibration of Pb proxies relies on data collected from other sources. Currently, ferromanganese nodules have been utilized for seawater Pb reconstructions. As nodules form at the seafloor, for intermediate water depth these records are limited to isolated seamounts in the open ocean. As a result, the calibration of intermediate water column Pb isotopes requires the characterization of signatures using barite form a whole spectrum of regions. This study reports Pb isotopes in barite from a broad range of locations and extends the current core top data from the equatorial Pacific.