CHARACTERIZING THE SUBGLACIAL ENVIRONMENT OF LEMON CREEK GLACIER USING SR AND ND ISOTOPE SYSTEMS

The role that the chemistry of subglacial meltwater plays in glacial hydrology is largely unknown. Quantifying the release of elements is of fundamental importance for understanding the interaction between subglacial meltwater and bedrock lithology. Isotopic tracers have widely been utilized as proxies to track fluxes in chemical weathering rates and identify water sources. Our study analyzes variation in both radiogenic (⁸⁷Sr/⁸⁶Sr) and stable (δ^88/86Sr) strontium along with radiogenic (¹⁴³Nd/¹⁴⁴Nd) neodymium isotopes in the suspended sediment load of subglacial meltwater collected over a single melt season at Lemon Creek Glacier, USA (LCG). Isotopic ratios were measured on a Thermal Ionization Mass Spectrometer and a natural double spike procedure was utilized to determine both radiogenic and stable strontium values to a high precision. ⁸⁷Sr/⁸⁶Sr and δ^88/86Sr are good proxies for changes in bedrock mineralogy as silicates and carbonates have distinct Sr isotope ratios. Differences allow variability in hydrological source to be tracked. Our results show a mean ratio of ~0.33 for δ^88/86Sr which is indicative of the Granitic bedrock of LCG. Additionally, δ^88/86Sr exhibits mass dependent fractionation due to weathering which demonstrates how integral Sr is to our understanding of the physical processes occurring within the subglacial environment. In comparison to Sr ratios, research has shown that the crustal age of the bedrock material is the most important control on the ¹⁴³Nd/¹⁴⁴Nd ratio. Our data shows a lack of correlation between ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr along with a slight trend towards more radiogenic ⁸⁷Sr/⁸⁶Sr values with time suggesting that, even as the residence time decreases over the melt season, the subglacial channels are stable with a congruently aged source of sediment. Analysis of the variation in the isotopic composition of the suspended sediment load provides important constraints on our understanding of the dynamics between subglacial meltwater and the bedrock in relation to changes in weathering and water mass source. Further application will be useful in modeling and comparing glacial systems.