Stable tungsten isotope systematics on the Earth's surface

Stable tungsten isotopes (delta W-186/184) show great potential for tracing the cycling of materials among geological reservoirs. This work investigates the behavior of stable W isotopes on the Earth's surface by presenting new delta W-186/184 data of granitic rocks, loess, river water, fluvial sediments, regolith, estuarine seawater, and marine sediments. The investigated granites document significant W isotopic heterogeneity (-0.08 to 0.16%) of the upper continental crust (UCC). In contrast, the eolian loess sourced from the vast crustal surface shows a high degree of homogeneity with an average delta W-186/184 of 0.01 +/- 0.01 %(mean +/- 2 x standard error). The delta W-186/184 of river water (0.17 to 0.71%) is significantly higher than that of the corresponding bedrock, which is likely to be caused by preferential uptake of light W isotopes by the authigenic precipitates. The delta W-186/184 and W concentration of river water also show a correlation with the lithological sources of weathering solute, the extrapolation of which results in a global riverine W flux of 17 x 10(6) mol yr(-1) and a W flux-weighted average delta W-186/184 of 0.37%. Data from the Yangtze estuary likely suggest a contribution of benthic W reflux from estuarine sediments to the ocean. However, benthic reflux, as well as hydrothermal W inputs, is insignificant compared to riverine input. The recalculated oceanic residence time of W is similar to 4 kyrs, which is much shorter than previously thought. Sinks of W in the ocean are mainly associated with non-euxinic sediments, where the enrichment of W correlates with that of Mo. Constraints from the oceanic Mo budget give a W sink of 19 x 10(6) mol yr(-1) in non-euxinic sediments, which nearly balances the riverine input. A simple box model shows that the steady-state delta W-186/184 of seawater (which can be achieved on time scales more than several times the residence time of W in seawater) is mainly controlled by the 8186/184W of riverine input and the partition of W into different sinks with varying fractionation factors. (C) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Stable tungsten isotopes have the potential to trace material cycling among geological reservoirs. This study investigates the behavior of stable W isotopes on the Earth's surface and finds significant heterogeneity in granitic rocks and a high degree of homogeneity in eolian loess. River water shows higher W isotope values than bedrock, likely due to preferential uptake of lighter W isotopes. The study also provides insights into the sinks and residence time of W in the ocean, with significant contributions from non-euxinic sediments.