Time series of δ26Mg variability in precipitation of north-west Germany

Abstract

This study presents δ²⁶Mg values, Mg²⁺ concentrations, δ¹⁸O and δ²H values of monthly collected rain and snow samples between 2014 and 2017 from north-west Germany. The δ²⁶Mg values of snow are similar to those of rain. Unlike δ¹⁸O and δ²H, neither δ²⁶Mg_{precipitation} values nor Mg²⁺ concentrations display a relationship with air temperature. In contrast, δ²⁶Mg_{precipitation} values and Mg²⁺ concentrations are correlated with precipitation amount. As previously suggested by other studies but now based on a larger data set, it is proposed that the δ²⁶Mg values and Mg²⁺ concentrations are affected by the mineralogical composition and amount of airborne dust. Consequently, a small number of random precipitation samples cannot represent the complex processes influencing the δ²⁶Mg_{precipitation} values. δ²⁶Mg_{precipitation} can be used to differentiate between seawater aerosols, carbonate and silicate dust. Silicate dust is typified by higher Mg concentrations and δ²⁶Mg values compared to carbonate dust. Concerning carbonates, dolostone dust has higher Mg concentrations and δ²⁶Mg values, while limestone dust is Mg-lean with lower δ²⁶Mg values. Dust of anthropogenic origin in the region can come from active limestone and dolostone quarries, surface mining of siliciclastics, and agriculture on silicate-rich soils. Although dust of this mineralogy can also be of natural origin, most natural dust consists of airborne silicates transported by wind systems from the Sahara to Europe. Higher δ²⁶Mg_{precipitation} values would indicate silicate or dolostone dust influx. Lower δ²⁶Mg_{precipitation} values suggest lower dust concentrations and a predominantly calcitic dust mineralogy. It appears that δ²⁶Mg_{precipitation} is most probably influenced by changes in weather conditions and natural and anthropogenic dust origin. This study implies that δ²⁶Mg_{precipitation} is a potential proxy for dust mineralogy and fluxes. Nevertheless, further research should include the determination of atmospheric dust mineralogy and their fractions as well as air mass back trajectory analysis to identify the source(s) of dust.