Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Murphy, MJ, Porcelli, DR, Von Strandmann, PAE, Hirst, CA, Kutscher, L, Katchinoff, JA, Morth, C-M, Maximov, T, Andersson, PS
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2018
• Subjects: Aldan; Arctic; Verkhoyansk; Active layer thickness; lena river; permafrost; Siberia
• Online Access: https://doi.org/10.1016/j.gca.2018.10.024; https://ora.ox.ac.uk/objects/uuid:ff830f1f-26f4-478c-90c3-20187641efa0

Increasing global temperatures are causing widespread changes in the Arctic, including permafrost thawing and altered freshwater inputs and trace metal and carbon fluxes into the ocean and atmosphere. Changes in the permafrost active layer thickness can affect subsurface water flow-paths and water-rock interaction times, and hence weathering processes. Riverine lithium isotope ratios (reported as δ7Li) are tracers of silicate weathering that are unaffected by biological uptake, redox, carbonate weathering and primary lithology. Here we use Li isotopes to examine silicate weathering processes in one of the largest Russian Arctic rivers: the Lena River in eastern Siberia. The Lena River watershed is a large multi-lithological catchment, underlain by continuous permafrost. An extensive dataset of dissolved Li isotopic compositions of waters from the Lena River main channel, two main tributaries (the Aldan and Viliui Rivers) and a range of smaller sub-tributaries are presented from the post-spring flood/early-summer period at the onset of active layer development and enhanced water-rock interactions. The Lena River main channel (average δ7Lidiss ∼ 19‰) has a slightly lower isotopic composition than the mean global average of 23‰ (Huh et al., 1998a). The greatest range of [Li] and δ7Lidiss are observed in catchments draining the south-facing slopes of the Verkhoyansk Mountain Range. South-facing slopes in high-latitude, permafrost-dominated regions are typically characterised by increased summer insolation and higher daytime temperatures relative to other slope aspects. The increased solar radiation on south-facing catchments promotes repeated freeze-thaw cycles, and contributes to more rapid melting of snow cover, warmer soils, and increased active layer thaw depths. The greater variability in δ7Li and [Li] in the south-facing rivers likely reflect the greater infiltration of melt water and enhanced water-rock interactions within the active layer. A similar magnitude of isotopic fractionation is observed between the ...