The prevalence of terrestrial environments low in the essential trace element selenium (Se) results in large-scale Se deficiency worldwide. However, the underlying processes leading to Se-depleted environments have remained elusive. Here we show that over the last 6.8 million years (Ma) climatic factors have played a key role in the Se distribution in loess-paleosol sequences in the Chinese Loess Plateau (CLP), which lies in a severely Se-depleted region with a history of Se deficiency-related diseases. We use a combination of geochemical and paleoclimate data to demonstrate that during interglacial periods between 2.30 and 0.16 Ma, variations in the Se concentration in the CLP are potentially related to variability in Se input via East Asian monsoon-derived precipitation. Our results identify precipitation as an important controlling factor of Se distribution in monsoonal China. We suggest that atmospheric Se inputs via precipitation could also play an important role in other regions worldwide.

Atmospheric processes play an important role in the supply of the trace element selenium (Se) as well as other essential trace elements to terrestrial environments, mainly via wet deposition. Here we investigate whether the marine biosphere can be identified as a source of Se and of other trace elements in precipitation samples. We used artificial neural network (ANN) modeling and other statistical methods to analyze relationships between a high-resolution atmospheric deposition chemistry time series (March 2007-January 2009) from Plynlimon (UK) and exposure of air masses to marine chlorophyll a and to other source proxies. Using ANN sensitivity analyses, we found that higher air mass exposure to marine productivity leads to higher concentrations of dissolved organic carbon (DOC) in rainfall. Furthermore, marine productivity was found to be an important but indirect factor in controlling Se as well as vanadium (V), cobalt (Co), nickel (Ni), zinc (Zn), and aluminum (Al) concentrations in atmospheric deposition, likely via scavenging by organic compounds derived from marine organisms. Marine organisms may thus play an indirect but important role in the delivery of trace elements to terrestrial environments and food chains.

The main objective of this article is to document and demonstrate Os contamination of natural waters stored in commonly used plastic bottles, which have been acid washed. This observation is a direct result of development of reliable chemical separation and mass spectrometric procedures that have improved detection limits. In the 1990s, a number of attempts were made to determine the osmium concentration and isotope composition of seawater. Its low abundance in seawater and possible multiple oxidation states frustrated these efforts to precisely measure its concentration and isotope composition. Koide et al. (1996) used isotope dilution resonance ionization mass spectrometry to obtain the osmium concentration and isotope composition of seawater. A 25 L sample seawater was spiked with 190 Os tracer, and Os was separated using anion-exchange chromatography and purified using distillation. Sharma et al. (1997) reduced seawater and tracer Os by bubbling SO 2 (g) and then coprecipitating Os wiiron oxyhydroxide in 4-10 L samples. Osmium was oxidized in a sealed glass tube (Carius tube) and extracted using CCl 4 , purified, and measured using negative thermal ionization mass spectrometry (N-TIMS). These techniques required handling of large volume samples (4 to 25 kg). Three new techniques attempted to use smaller volume samples (50 g to 1.5 kg) and to equilibrate tracer and water Os by oxidizing it to a common oxidation state (= OsO 4 ). These techniques indicated that seawater Os concentration was 4-to 5-fold higher than determined by the previous studies. Levasseur et al. (1998) AbstractA low blank-high yield procedure for the accurate determination of seawater osmium concentration and isotope composition has been developed. The improvement in the detection limit has revealed a subtle temporal increase in the concentration of samples obtained during the GEOTRACES expeditions that were stored in high density polyethylene bottles. This increase in Os concentration is accompanied by significant decrease in the 187 Os/ 188Os ratio of the water indicating substantial contamination of waters in two out of three bottles that were investigated; the third bottle, which is not contaminated, shows evidence of Os removal. In comparison, analyses of another aliquot of water stored in a Teflon bottle show no contamination. Samples collected in low density polyethylene bottles during SAFe expedition have also been contaminated. Bottle cleaning with HNO 3 has directly/indirectly contributed to the bottle blank. We also find that a snow-melt sample stored in a Teflon bottle has remained uncontaminated for more than a year, despite having an Os concentration that is ~14 times lower than seawater. We conclude that the low level samples, such as seawater, need to be stored in Teflon bottles for accurate and precise estimate of Os concentration and isotope composition, although polypropylene bottles may be an acceptable alternative. A re-evaluation of previously published data and data obtained in the present study still indicates ...

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[1] We present Os and Sr isotope ratios and Os, Sr and major/trace element concentrations for river waters, spring waters and rains on the North Island of New Zealand. The Os and Sr data are used to examine whether the NINZ is a significant contributor of unradiogenic Os and Sr to the oceans. Major element chemistry is used to quantify weathering and CO 2 consumption rates on the island to investigate relationships between these processes and Os and Sr behavior. Chemical erosion rates and CO 2 consumption rates across the island range from 44 to 555 km À2 yr À1 and 95 to 1900 Â 10 3 mol CO 2 km À2 yr À1 , respectively. Strontium flux for the island range from 177 to 16,100 mol km À2 yr À1 and the rivers have an average flux normalized 87 Sr/ 86 Sr ratio of 0.7075. In agreement with the previous studies these findings provide further evidence that weathering of arc terrains contributes a disproportionally large amount of Sr to the oceans and consumes very large amounts of CO 2 annually compared to their areal extent. However, the 87 Sr/ 86 Sr from the NINZ is not particularly unradiogenic and it is likely not contributing significant amounts of unradiogenic Sr to the oceans. Repeated Os analyses and bottle leaching experiments revealed extensive and variable sample contamination by Os leaching from rigorously precleaned LDPE bottles. An upper bound on the flux of Os from NINZ can nevertheless be assessed and indicates that island arcs cannot provide significant amounts of unradiogenic Os to the oceans.