GEOTRACES IC1 (BATS) contamination‐prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration

Abstract

The stable isotope composition of radiogenic and natural elements provides a powerful tool for unraveling element sources and biogeochemical processes in the marine environment. Depending on the element, trace element isotope ratios can (1) narrow possible sources of the element in a sample and/or (given a temporal history boundary condition) constrain the time the when the element departed the ocean surface (e.g., Pb, Nd), (2) provide information on redox processes that the element is directly or indirectly involved in (e.g., Fe, Mo, Tl), (3) indicate the extent of biological uptake and/or ocean mixing of the element (e.g., Cd, Zn).However, these trace metals occur at picomolar to nanomolar concentrations, and precise stable isotope measurements require 100-1000 times more sample than required for concentration determination. AbstractWe report data on the isotopic composition of cadmium, copper, iron, lead, zinc, and molybdenum at the GEOTRACES IC1 BATS Atlantic intercalibration station. In general, the between lab and within-lab precisions are adequate to resolve global gradients and vertical gradients at this station for Cd, Fe, Pb, and Zn. Cd and Zn isotopes show clear variations in the upper water column and more subtle variations in the deep water; these variations are attributable, in part, to progressive mass fractionation of isotopes by Rayleigh distillation from biogenic uptake and/or adsorption. Fe isotope variability is attributed to heavier crustal dust and hydrothermal sources and light Fe from reducing sediments. Pb isotope variability results from temporal changes in anthropogenic source isotopic compositions and the relative contributions of U.S. and European Pb sources. Cu and Mo isotope variability is more subtle and close to analytical precision. Although the present situation is adequate for proceeding with GEOTRACES, it should be possible to improve the within-lab and between-lab precisions for some of these properties.

Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean

“…The analytical protocol has been previously published (46), validated by the GEOTRACES intercalibration exercise (47) and an intercomparison study (48).…”

Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution

“…On each analytical date, we calibrated the instrument by running NBS981 and normalized measured sample isotope 30 ratios to our measured raw NBS981 isotope ratios to those established by Baker et al (2004) We have intercalibrated Pb isotope analyses with two labs as reported in Boyle et al (2012). The outcome of that intercalibration suggests that the accuracy of our measurements approaches the internal analytical reproducibility we note above.…”

“…GEOVIDE samples were analysed during 11 mass spectrometry sessions by the method of Reuer et al (2003) as modified by Boyle et al (2012). In brief, ~500mL of seawater was pre-concentrated using a low-blank double magnesium hydroxide co-precipitation, induced by minimal addition of high-purity ammonia solution and mixing 15 (typically 8µL ammonia per 1mL seawater sample).…”

“…They were then transferred into a clean container (class-100) for sampling. For Stations 1,11,15,17,19,21,25,26,29,32 samples were filtered with 0.2 µm capsule filters (SARTOBRAN® 300,Sartorius). For all other stations (13, 34, 36, 38, 40, 5 42, 44, 49, 60, 64, 68, 69, 71, 77) seawater was filtered directly through paired filters (Pall Gelman Supor 0.45µm polystersulfone, and Millipore mixed ester cellulose MF 5 µm) mounted in Swinnex polypropylene filter holders, following the Planquette and Sherrell (2012) method.…”

Urea and nickel utilization in marine cyanobacteria as evaluated by incubation, proteomic, and uptake techniques

“…Nickel, iron and other bioactive trace metals are key to understanding global biogeochemical cycles. Efforts to map the global distributions of dissolved and particulate trace metals is progressing especially with the recent international GEOTRACES field expedition results (Bishop et al 2012;Boyle et al 2012;Noble et al 2012;Rousseau et al 2013;Butler et al 2013;Twining and Baines 2013;Kondo and Moffett 2013). Expanding surveys of trace metals allow more detailed investigation on the relationship between primary, secondary, and colimiting nutrients (Arrigo 2005;Moore et al 2013).…”