Climate influence on zinc isotope variations in a loess-paleosol sequence of the Chinese Loess Plateau

Zinc (Zn) is an essential micronutrient, and its isotopes are increasingly applied to understand trace metal biogeochemical cycling. Atmospheric deposition from anthropogenic or natural origins can perturbate the nutrient supply globally. However, our understanding on Zn isotope variations in natural mineral dust and during dust-climate interaction is still rare. This study presents Zn isotope data and leaching experiments with ammonium acetate buffering solution (pH = 5) on a loess-paleosol profile (S0-L3) from the Yimaguan section in the central Chinese Loess Plateau. The loess-paleosol sequence records the contributions from Asian mineral dust accumulation and chemical weathering, and the response to glacial-interglacial climate changes. Bulk loess-paleosol samples display limited Zn/Al (3.5 x 10(-4) - 4.5 x 10(-4)) and delta Zn-66 variations (0.17-0.30 parts per thousand & nbsp;). The mean delta Zn-66 of paleosol (0.19 +/- 0.01 parts per thousand & nbsp;, 2SD/root n, n = 11) is slightly lower than that of loess (0.24 +/-& nbsp;0.01 parts per thousand & nbsp;, 2SD/root n, n = 13). Correlations with magnetic susceptibility and grain size distribution suggest that bulk delta Zn-66 variations between loess and paleosol are not sensitive to glacial-interglacial source fluctuations or wind sorting, but could result from loess pedogenesis. The leachable Zn fractions have high delta Zn-66 values (0.80-1.29 parts per thousand) and display good positive correlations with Ca, Sr, Mg, Fe and Mn (r > 0.7), suggesting that carbonates are enriched in heavy Zn isotopes. Although Zn contents in carbonates are low (< 3%) and dissolution of carbonates alone cannot explain the bulk Zn/Al variations (~& nbsp;7% of Zn loss), significant carbonate weathering and biotic activities during loess pedogenesis could modify soil conditions (pH) and provide dissolved bicarbonate ions and organic ligands, which may facilitate the transport of heavy Zn isotopes by soil liquids. Conversely, the bulk delta Zn-66 of loess developed during glacial times were not modified by the low degree of chemical weathering, and thus the mean value of 0.24 parts per thousand & nbsp;for loess can be regarded as the average composition of the upper continental crust.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Zinc isotopes play a crucial role in understanding the biogeochemical cycling of trace metals. This study investigates the variations in zinc isotopes in a loess-paleosol profile and reveals the potential impacts of weathering and biogeochemical processes on the isotopic composition of zinc. The findings provide insights into the role of zinc in natural mineral dust and dust-climate interactions.