Salt Provenance and Migration in Sediment Core Samples From Dry Valleys, Antarctica

The McMurdo Dry Valleys are characterized by hyperarid conditions and extensive salt accumulation. Soluble ions are present in high concentrations in soil and sediment from multiple potential sources, including weathering of minerals, inheritance from original deposits, and eolian transport of marine salts and atmospheric dust. We are exploring the usefulness of magnesium isotope variations as an additional constraint on ion provenance and migration. We extracted soluble salts from soil and sediment using three sequential water extractions. Magnesium is purified by removing all other soluble ions present in salt extracts using a series of two different ion exchange resins. Finally, magnesium isotope ratios are determined using a Nu Plasma multi-collector inductively coupled plasma mass spectrometer. We analyzed core samples collected in the 1970s during the Dry Valley Drilling Project (DVDP). Soil salt extracts from Taylor Valley, at low altitude near the Ross Sea, possess magnesium isotope values of -0.87‰ to -1.00‰ δ25MgDSM3 and -0.48‰ to -0.54‰ δ26MgDSM3. These values overlap with published values for modern marine water. Ca/(Na+K) and Mg/(Na+K) ratios in these near marine samples are nearly identical to modern marine water. Samples from Wright Valley, further from the Ross Sea, contain proportionally more Ca and Mg than (Na+K), suggesting an alternate provenance. We plan to analyze the salt extracts from the Wright Valley DVDP core for magnesium isotope ratios to assess variability of salt provenance. Additionally, potential magnesium isotope variation with depth in the core may indicate migration of water and salt below the soil surface.