Editorial: Novel Isotope Systems and Biogeochemical Cycling During Cryospheric Weathering in Polar Environments

Abstract

Cryospheric weathering processes in permafrost and glaciated environments play an essential role in carbon cycling within the Earth system. Chemical weathering of silicate, carbonate and sulfidebearing rocks releases cations and anions that can consume (or release) atmospheric carbon dioxide (CO2), as well as biologically important nutrients such as phosphorous, iron and silicon, which can impact downstream ecosystems (Figure 1). How these cryospheric weathering processes will respond to future climate-driven changes in permafrost thaw and glacial melt is difficult to predict due to the role of complex forcing mechanisms and feedbacks. Isotope geochemistry utilizes changes in the relative abundance of different isotopes due to physical, chemical and biological reactions, allowing some of the complexities of cryospheric weathering processes to be unpicked. In recent years, there has been an explosion in the range of stable and radiogenic isotope systems used for the study of high-latitude environments, including isotopes of major elements such as carbon, oxygen, and silicon (e.g., Opfergelt et al., 2013; Kutscher et al., 2017), and trace metal isotopes such as strontium (Hindshaw et al., 2014), lithium (Murphy et al., 2019), iron (Zhang et al., 2015), uranium-series (e.g., Arendt et al., 2018) and rare earth elements (e.g., Clinger et al., 2016). This research topic explores some of the developments in high-latitude field and experimental studies that utilize such geochemical tools to trace the degree and nature of weathering reactions that play a critical role in carbon cycling. The nine contributions to the research topic involve the analysis of traditional (C, N, S, O) and non-traditional (Mg, Li, Si, Ge) isotopes from different samples types such as river waters, lake waters, rocks, sediments, or mineral separates from locations both in the Northern (Greenland, Iceland, Canada, Svalbard) and Southern Hemisphere (Patagonia, Antarctica). Two papers use isotope geochemistry to explore organic and inorganic carbon cycling within permafrost and active layer soils. Jones et al. show that biogeochemical processes and decomposition pathways of organic carbon in ice-wedge polygons in Svalbard are dependent upon water and organic carbon content. Sulfur (δ34S) and oxygen (δ18O) isotopes show that iron and sulfate reduction processes dominate in water saturated, high organic carbon environments, whereas sulfide oxidation dominates in drier areas with less organic carbon. Zolkos and Tank use an experimental approach in combination with stable carbon isotopes (δ13CO2) to show that carbonate weathering coupled with sulfide oxidation in recently or previously unthawed Canadian permafrost sediments is a net source of inorganic CO2 to the atmosphere, albeit partly counterbalanced by carbonate buffering