The stabilizing properties of mineral-organic carbon (OC) interactions have been studied in many soil environments (temperate soils, podzol lateritic soils, and paddy soils). Recently, interest in their role in permafrost regions is increasing as permafrost was identified as a hotspot of change. In thawing ice-rich permafrost regions, such as the Yedoma domain, 327-466 Gt of frozen OC is buried in deep sediments. Interactions between minerals and OC are important because OC is located very near the mineral matrix. Mineral surfaces and elements could mitigate recent and future greenhouse gas emissions through physical and/or physicochemical protection of OC. The dynamic changes in redox and pH conditions associated with thermokarst lake formation and drainage trigger metal-oxide dissolution and precipitation, likely influencing OC stabilization and microbial mineralization. However, the influence of thermokarst processes on mineral-OC interactions remains poorly constrained. In this study, we aim to characterize Fe, Mn, Al, and Ca minerals and their potential protective role for OC. Total and selective extractions were used to assess the crystalline and amorphous oxides or complexed metal pools as well as the organic acids found within these pools. We analyzed four sediment cores from an ice-rich permafrost area in Central Yakutia, which were drilled (i) in undisturbed Yedoma uplands, (ii) beneath a recent lake formed within Yedoma deposits, (iii) in a drained thermokarst lake basin, and (iv) beneath a mature thermokarst lake from the early Holocene period. We find a decrease in the amount of reactive Fe, Mn, Al, and Ca in the deposits on lake formation (promoting reduction reactions), and this was largely balanced by an increase in the amount of reactive metals in the deposits on lake drainage (promoting oxidation reactions). We demonstrate an increase in the metal to C molar ratio on thermokarst process, which may indicate an increase in metal-C bindings and could provide a higher protective role against microbial mineralization of organic matter. Finally, we find that an increase in mineral-OC interactions corresponded to a decrease in CO 2 and CH 4 gas emissions on thermokarst process.

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The permafrost active layer is a key supplier of soil organic carbon and mineral nutrients to Arctic rivers. In the active layer, sites of soil-water exchange are locations for organic carbon and nutrient mobilization. Previously these sites were considered as connected during summer months and isolated during winter months. Whether soil pore waters in active layer soils are connected during shoulder seasons is poorly understood. In this study, exceptionally heavy silicon isotope compositions in soil pore waters show that during late winter, there is no connection between isolated pockets of soil pore water in soils with a shallow active layer. However, lighter silicon isotope compositions in soil pore waters reveal that soils are biogeochemically connected for longer than previously considered in soils with a deeper active layer. We show that an additional 21% of the 0–1 m soil organic carbon stock is exposed to soil - water exchange. This marks a hot moment during a dormant season, and an engine for organic carbon transport from active layer soils. Our findings mark the starting point to locate earlier pathways for biogeochemical connectivity, which need to be urgently monitored to quantify the seasonal flux of organic carbon released from permafrost soils.

With rising temperatures, glaciers are retreating globally. The Greenland icecap has experienced record melt in the past decade (The IMBIE Team, 2020), amplifying freshwater discharge and transport of sediment and dissolved constituents (Hawkings et al., 2015;Meire et al., 2016). Cascading effects on downstream ecosystems remain uncertain, as additional nutrient input could enhance primary productivity in marine environments (e.g., Arrigo et al., 2017;Meire et al., 2017). Conversely, increased turbidity caused by the generally high suspended sediment loads of glacial outflow limits light penetration and thereby suppresses phytoplankton growth (Holding et al., 2019;Hopwood et al., 2020). In addition, retreating icecaps and glaciers expose previously covered landscapes to erosion, generally causing elevated sediment release until stabilization by colonizing vegetation (e.g., Ballantyne, 2002). Erosion rates are projected to increase throughout the Arctic due to rapid thaw and destabilization of permafrost (e.g., Hugelius et al., 2020;Olefeldt et al., 2016;Turetsky et al., 2020), as well as intensifying rain events caused by a shift from snow-to rain-dominated precipitation (e.g., Bintanja & Andry, 2017). Erosion of soils or recent vegetation litter can act as a carbon sink on geological timescales if the released organic carbon (OC) is rapidly buried in marine sediments (e.g., Hilton et al., 2015;Hovius et al., 2011). On the other hand, erosion constitutes a carbon source to the atmosphere if ancient permafrost soil or rock-derived (petrogenic) carbon is mineralized during transport or in marine environments (e.g.,