We monitored Lena River outflow into the Laptev Sea at our station near the river mouth for over four years, collecting weekly or more frequent samples and analyzing concentrations of major dissolved components. Paired with discharge measurements, these data permitted calculations of fluxes, separation of source waters and detection of seasonal variability in catchment processes. A second monitoring site was established on the Mackenzie River’s East Channel, with help of Canadian partners and the INTERACT Transnational Access program. At this site, discharge measurements from Tsiigehtchic, Northwest Territories are complemented by discharge measurements via acoustic doppler profiler at the sampling site.

Data from both monitoring sites are freely and publically available. As a means of shortening the time between analysis, quality control and data publication, and improving access and usage, data from both sites are available via internet dashboards. For both locations, this has created opportunities for additional research groups to introduce measurement parameters to widen the range of catchment processes studied, for example tied to frazil ice formation or how river ice captures and records winter changes in water chemistry. Our next steps include tying these analyses of these data to wider catchment-scale studies, of permafrost thaw upstream of the monitoring site, and downstream in coastal waters out to 20 m water depth. At the Mackenzie River in particular, we coordinate with EU-Canadian cooperations such as the land-to-ocean project (FLOCHAR) and upcoming Beaufort Sea marine work (Arctic Pulse). This contribution describes the monitoring activities, lessons learned so far and the research needs and opportunities that are resulting.

Permafrost warms significantly due to climate change, exposing large amounts of soil organic matter to decomposition and releasing substantial amounts of greenhouse gases. Understanding the mechanisms of stabilization and mobilization of carbon (C) is key for the development of earth system models and for climate change mitigation strategies. Iron (Fe) is an important agent in the carbon-climate feedback-loop depending on its oxidation state. Our aim was to quantify the amount of C that is bound to different Fe-species, which differ in their physicochemical stability, and to understand the potential role thereof in a system of degrading permafrost.

We sampled permafrost soils along two environmental gradients from dry to wet conditions on Disko Island, Greenland. Selective iron extractions were applied using four extractants to analyse Fe-phases of different stability, along with C. Furthermore, one gradient has been equipped with soil monitoring stations for year-round measurements of moisture, temperature and redox potential in topsoil and subsoil.

Crystalline Fe was the largest Fe pool. We found more amorphous and less crystalline Fe in the wettest sites, compared to the dry sites. The most C was related to the chelated pools. At the dry sites, around half of the C was bound to Fe. At the wet sites, the relevance of Fe-bound C decreased compared to the dry sites. There, around 20% of the total C was bound to Fe. Records of the redox-regime revealed distinct patterns between oxic and anoxic conditions within the soil, due to alternating soil moisture. The water content of the soils led to an almost winter-long zero curtain, hindering soil temperature to drop below 0°C for 70 days at the driest and for 133 days at the wettest point. The patterns observed underline the importance of long-term measurements and of the timing of sampling

Permafrost regions, critical to global climate dynamics, are often overlooked as potential methane sinks, with research predominantly focusing on methane-emitting wetlands. This study, conducted as part of my PhD in the so-called MOMENT project, aims to address this gap by evaluating methane (CH₄) and carbon dioxide (CO₂) fluxes in a heterogeneous Arctic upland tundra landscape. Using a portable greenhouse gas analyzer, over 1000 in-situ measurements were collected during the thaw seasons of 2023 and 2024. The research was carried out in the glacial valley Blæsedalen on Disko Island in West Greenland, encompassing three transects along different slope forms with diverse soil-hydrological conditions. In addition, some first flux measurements near a mountain ice cap on a mountain plateau were carried out and parallel, environmental factors such as soil moisture, air and soil temperature, and meteorological conditions were monitored, alongside an extensive soil and vegetation analysis. In my presentation, I will summarize preliminary findings, offering insights into methane flux dynamics and their relationship with environmental variables.

More than 30% of the world’s coastlines are affected by permafrost, which is often rich in organic matter and ground ice and highly sensitive to climate change. Along these ice-rich coasts, rapid sea ice loss, rising temperatures, and stronger storms accelerate erosion. In expansive coastal lowlands, retreating coastlines transform thaw lakes and drained lake basins into thermokarst lagoons, forming through two main pathways: either as freshwater lakes that transition directly to brackish or saltwater lagoons, or through freshwater lakes that first drain, allowing permafrost to redevelop before subsequent seawater inundation.

As thawing progresses, organic carbon is exposed to microbial decomposition, releasing greenhouse gases (GHGs) like carbon dioxide (CO₂) and methane (CH₄), further contributing to climate warming. However, the role of thermokarst lagoons in the permafrost carbon cycle remains unclear. To investigate, we conducted long-term anoxic incubation experiments on surface samples from thermokarst lagoons, terrestrial permafrost, the active layer, and lake sediments. We focused on lagoon systems across the coastal lowlands of NE Siberia, N Alaska, and NW Canada, analyzing CO₂ and CH₄ production along land-sea transitions. Additionally, we mapped thermokarst lagoons along Arctic coastlines using remote sensing.

Our findings indicate that GHG production is significantly higher in lagoon sediments than in terrestrial permafrost, active layers, or lake sediments. While there are regional differences, the variation in GHG production across landscape types is more substantial. By combining incubation results with spatial mapping, we estimated that thermokarst lagoons could release an average of 3 Tg CO₂-equivalent annually by 2100. Although small in area (3,457 km²), thermokarst lagoons release over four times the CO₂-equivalent per unit area compared to thermokarst lakes, marking them as significant carbon release hotspots. As climate scenarios project accelerated coastal erosion and rising sea levels, thermokarst lagoons may play an increasingly important role in Arctic carbon budgets.

Subsea permafrost (SSPF) is expected to thaw at accelerating rates in the coming centuries as bottom water temperatures increase in the Arctic Ocean. Organic matter (OM) preserved in SSPF will become increasingly available to previously dormant microbes, leading to increased decomposition rates and, thus, production of methane (CH4), carbon dioxide (CO2), and the recycling of nutrients (nitrite NO2-, nitrate NO3- and phosphate PO43-). The consequences of the resulting benthic fluxes on Arctic Ocean primary production, acidification, and ultimately, atmospheric greenhouse gas emissions are still unquantified. The magnitude and evolution of these SSPF-derived fluxes are highly dependent (i) on the apparent reactivity of the organic matter and (ii) on the response of the resident, reactivating microbial communities in their changing habitat (frozen to thawed sediment).

Here, we present a novel model framework to quantify CO2, CH4, and nutrient benthic fluxes from 1900 to 2300 under different SSPF thawing scenarios. The model integrates observational and experimental data from three SSPF cores collected in the Laptev Sea. Eight core sections were selected to study the evolution of OM decomposition, microbial dynamics and CH4-CO2 production after thaw. We incubated sediment replicas at 4°C and 10°C for a period of one year. Methanogenesis rates were determined from CH4 and CO2 accumulation in the headspace. Additionally, nutrient and carbon cycling dynamics related to OM decomposition were explored through enzyme assays for extracellular leucine aminopeptidase, phosphatase, and β-glucosidase at different timepoints during the incubation period. The incubation data reveals the resident microbial community is immediately responsive to the transition from a frozen to a thawed environment, consuming OM as soon as the sediment is thawed. Through an integrated model-data approach, we will provide microbially informed predictions of SSPF-derived carbon and nutrient benthic fluxes on a local and regional scale.

Saline permafrost is primarily found in marine deposits beneath shallow shelf seas and can extend several kilometers inland from the present Arctic coastlines. On land, it forms when previously submerged marine sediments are exposed to the atmosphere, either due to sea level regression or post-glacial rebound. In Svalbard, northwest of Ny-Ålesund, the Kvadehuksletta region features a complex landscape of raised beach terraces, lagoons, paleo-lagoons (now lakes in partially drained basins), and surface seeps. To investigate how salts in uplifted marine deposits redistribute as permafrost forms under sub-aerial conditions, we conducted two main electrical resistivity tomography (ERT) surveys, one 2.3 km long and the other 1.0 km long. Both profiles began at the 2024 coastline and extended inland to higher elevations. The 2.3 km profile reached approximately 700 m beyond the Late Weichselian Marine Limit. Shallow sediment samples (0–200 cm deep) were collected to characterize near-surface porewater and sediment properties, and terrestrial laser scanning was performed along the 2.3 km transect. The ERT data suggest that salinity in permafrost is influenced by the duration and rate of uplift, as well as groundwater flow, which freshens porewater and may be partly controlled by the morphology of the intact bedrock surface. Consequently, the behavior of saline permafrost and cryopeg formation in the coarse-grained deposits of Svalbard may differ from that of finer-grained sediments in other Arctic regions, such as the Alaskan North Slope, where diffusive salt transport dominates in newly exposed marine sediments.