Search for: All records

The nature of chemical exchange between Earth’s core and mantle is fundamental to understanding their evolution. Tungsten-182 and helium-3 anomalies in volcanic rocks from deeply sourced mantle plumes have been attributed to core-mantle exchange. Hydrogen (H) is potentially abundant in the core. Therefore, H may also be a sensitive tracer of core-mantle exchange. We measured²H/¹H ratios (reported as δD) in olivine-hosted basaltic melt inclusions from a Baffin Island lava to test whether mantle plumes contain H from the core. The average δD value (−144 ± 24 per mil) is lower than some estimates for the average depleted upper mantle (δD ≈ −60 ± 20 per mil). The low δD composition likely derives from isotopic diffusion or H leakage from the core, not isotopic fractionation during magmatism or crustal contamination. Over geologic time, core-mantle exchange of H may have overprinted the isotopic composition of mantle plume source regions and much of the upper mantle. 

Abstract Supra‐permafrost submarine groundwater discharge (SGD) in the Arctic is potentially important for coastal biogeochemistry and will likely increase over the coming decades owing to climate change. Despite this, land‐to‐ocean material fluxes via SGD in Arctic environments have seldom been quantified. This study used radium (Ra) isotopes to quantify SGD fluxes to an Arctic coastal lagoon (Simpson Lagoon, Alaska) during five sampling periods between 2021 and 2023. Using a Ra mass balance model, we found that the SGD water flux was substantial and dependent on environmental conditions. No measurable SGD was detected during the spring sampling period (June 2022), when the lagoon was partially ice‐covered. During ice‐free periods, the main driver of SGD in this location is wind‐driven lagoon water level changes, not tides, which control surface water recirculation through sediments along the lagoon boundary. A combination of wind strength and direction led to low SGD fluxes in July 2022, with an SGD flux of (6 ± 3) × 10⁶ m³ d⁻¹, moderate fluxes in August 2021 and July 2023, which had an average flux of (17 ± 9) × 10⁶ m³ d⁻¹, and high fluxes in October 2022, at (79 ± 16) × 10⁶ m³ d⁻¹. This work demonstrates how soil and environmental conditions in the Arctic impact Ra mobilization, laying a foundation for future SGD studies in the Arctic and shedding light on the major processes driving Ra fluxes in this important environment. 

Supra-permafrost submarine groundwater discharge (SGD) in the Arctic is poorly understood, yet has the potential to increase over the coming decades due to climate change. This study uses radium (Ra) isotopes to investigate this process by constraining seasonal SGD inputs to an Arctic coastal lagoon (Simpson Lagoon, AK). Within this dataset are 224Ra, 223Ra, 228Ra, and 226Ra activities for surface water samples (lagoon, rivers) and groundwater samples across three seasons: thaw (June 2022), open water (August 2021 and July 2022), and freeze up (September/October 2022). Experimentally determined valued for Ra desorption from riverine suspended sediments and diffusive fluxes from bottom sediments are also included.