Meteoric 10Be as a Tracer of Chemical Weathering in Glacial Sediments

Subglacial environments are hotspots for chemical weathering with dynamic hydrological and microbial systems interacting with freshly produced meltwater and sediments. These chemical weathering processes can either drawdown or release atmospheric CO₂ depending on the type and extent of weathering pathways. This study delves into chemical weathering processes in subglacial environments and their broader implications for global geochemical cycling.

We employ meteoric ¹⁰Be, a cosmogenic nuclide, to assess the neoformation of silicate weathering products as the isotope can be incorporated into the crystal structure of clays, oxides, and oxyhydroxides. This study aims to determine the extent to which chemical weathering products within glacial sediments originated during the glacial period, distinguishing them from detrital minerals derived from underlying bedrock and modern soil formed in interglacial settings. Additionally, we aim to address an observational gap in the meteoric ¹⁰Be fallout measurements in the 50° – 70° latitude and high altitude. i.e., northern Britain and Ladakh respectively, thereby enhancing our understanding of the general distribution and behaviour of the isotope.­­­­

We measured the contemporary fallout rates from the upper horizon of moraines in glacial sediments, while the inherited portion of meteoric ¹⁰Be within the lower horizons serve as archives of sub-glacial and proglacial weathering processes. Sequential extractions were performed to quantify extent of chemical weathering by isolating and measuring meteoric ¹⁰Be in three forms: adsorbed in aqueous solution, precipitated with oxides/oxyhydroxides, and/or inside the crystal structure of authigenic clay minerals. The distribution of the isotope was assessed across different grain sizes to examine its dependence on grain size and its association with various chemical and mineral species examined through ICP-MS and XRD.

This is a novel approach to identify minerals of subglacial origin in post-glacial settings. The quantification of the abundance of synglacial silicate weathering products in these glacial sediments will allow inference to a chemical weathering rate under the British Ice Sheet – a heretofore unsolved problem that offers crucial insights into the effect of glaciation on climate dynamics.