ALBERT

Description: Arctic regions and their water bodies are affected by a rapidly warming climate. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay, and Lake Golzovoye, Siberia, Russia) over a period of 2 years. Sampling was carried out under ice cover (April) and in open water (July–August). The methane oxidation (MOX) rate and the fractional turnover rate (k′) in water and melted ice samples from the late winter of 2017 was determined with the radiotracer method. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 nmol L−1 vs. 31 nmol L−1), and mean winter MOX rate was low (0.023 nmol L−1 d−1). In contrast, Tiksi Bay winter methane concentrations were 10 times higher than in summer (103 nmol L−1 vs. 13 nmol L−1). Winter MOX rates showed a median of 0.305 nmol L−1 d−1. In Lake Golzovoye, median methane concentrations in winter were 40 times higher than in summer (1957 nmol L−1 vs. 49 nmol L−1). However, MOX was much higher in the lake (2.95 nmol L−1 d−1) than in either the river or bay. The temperature had a strong influence on the MOX (Q10=2.72±0.69). In summer water temperatures ranged from 7–14 ∘C and in winter from −0.7 to 1.3 ∘C. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice–water interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed methane concentration in the water column 100–1000 times higher. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water, no methane accumulation under ice was observed. In a changing, warming Arctic, a shorter ice cover period is predicted. With respect to our study this would imply a shortened time for methane to accumulate below the ice and a shorter time for the less efficient winter MOX. Especially for lakes, an extended time of ice-free conditions could reduce the methane flux from the Arctic water bodies.

Description: The thermokarst lakes of permafrost regions play a major role in the global carbon cycle. These lakes are sources of methane to the atmosphere although the methane flux is restricted by an ice cover for most of the year. How methane concentrations and fluxes in these waters are affected by the presence of an ice cover is poorly understood. To relate water body morphology, ice formation and methane to each other, we studied the ice of three different water bodies in locations typical of the transition of permafrost from land to ocean in a continuous permafrost coastal region in Siberia. In total, 11 ice cores were analyzed as records of the freezing process and methane composition during the winter season. The three water bodies differed in terms of connectivity to the sea, which affected fall freezing. The first was a bay underlain by submarine permafrost (Tiksi Bay, BY), the second a shallow thermokarst lagoon cut off from the sea in winter (Polar Fox Lagoon, LG) and the third a land-locked freshwater thermokarst lake (Goltsovoye Lake, LK). Ice on all water bodies was mostly methane-supersaturated with respect to atmospheric equilibrium concentration, except for three cores from the isolated lake. In the isolated thermokarst lake, ebullition from actively thawing basin slopes resulted in the localized integration of methane into winter ice. Stable δ13CCH4 isotope signatures indicated that methane in the lagoon ice was oxidized to concentrations close to or below the calculated atmospheric equilibrium concentration. Increasing salinity during winter freezing led to a micro-environment on the lower ice surface where methane oxidation occurred and the lagoon ice functioned as a methane sink. In contrast, the ice of the coastal marine environment was slightly supersaturated with methane, consistent with the brackish water below. Our interdisciplinary process study shows how water body morphology affects ice formation which mitigates methane fluxes to the atmosphere.

Description: The land-ocean interface in the Arctic is a sensitive environment facing severe changes due to rising global air temperatures. In particular, Arctic river deltas are rapidly changing permafrost landscapes which will become more dynamic due to sea-level rise, longer thaw periods, changes in river discharge, increased storm-surge flooding and thawing permafrost. As a result, previously frozen river delta deposits are becoming available for microbial decomposition as permafrost thaws. However, very few studies have focused on Arctic deltas and estimates of deltaic carbon stocks are even more limited. Therefore, we compiled 140 soil cores (new and already published soil cores), consisting of more than 1400 samples from 17 different deltas around the Arctic Ocean. In addition, we mapped the spatial extent of more than 250 Arctic deltas in order to accurately assess the carbon and nitrogen stock estimations for Arctic deltas. Our study shows that Arctic river delta deposits contain a considerable amount of carbon and nitrogen. The ongoing thaw and degradation of these permafrost deposits resulting from global climate warming might release additional carbon and nitrogen with implications for Arctic waters and biogeochemical cycles. The additional export of terrestrial carbon and nitrogen will alter biogeochemical processes not only in the nearshore zone, but throughout the Arctic Ocean. With this study we will improve our understanding of changing terrestrial carbon and nitrogen deposits and their contribution to a changing Arctic Ocean.

Description: Arctic coastlines are increasingly vulnerable to erosion due to warmer temperatures destabilizing frozen cliffs, reduced protection of sea ice cover and bigger waves, especially as freeze-up becomes delayed further into the fall storm season. We have coupled a bathystrophic storm surge model to a simple numerical model of erosion of a partially frozen cliff and beach. This is a first step towards parameterization of Arctic shoreline erosion for larger-scale models that are not able to resolve the fine spatial scale (0 - 40m) needed to capture shoreline erosion rates from years to decades.

Description: The thermal regime in sediment below the ocean or lakes is mostly governed by the sea or lake bed temperature and by the geothermal heat flow. This thermal regime will determine whether permafrost beneath water bodies is preserved or how rapidly it thaws. Thermal modelling uses mean annual bottom water temperatures to calculate permafrost presence or absence, while predictions of shallow sediment thermal regimes must be forced with time series of changing bottom water temperatures that also account for freezeback of the water column to the bottom, forming bottom-fast ice. However, continuous, annual measurements of bottom water temperatures in Arctic lakes and coastal marine settings are hard to obtain and therefore scarce. Waves and sea ice movement make deployment and recovery of instruments difficult. We provide a parameterization of the bottom water temperature function that relies on easier to obtain variables, such as the mean, minimum and maximum air temperature and the water depth, by comparing measured and modelled shallow sediment thermal regimes from the Arctic. We use a parameterization based on a simple cosine for the water temperature with mean temperature, amplitude and time shift and add the minimum water temperature to obtain a 4 parameter function. For shallow regions with bottom-fast ice, additionally the duration of the ice-growth and -melting period as well as the minimum air temperature are needed. We test our parameterizations with a globally unique data set of 4 years of ground temperature data collected from the seabed to a depth of 10 m from the near shore zone of the Mackenzie Delta. At the instrumented sites, permafrost is present beneath mostly freshwater bottom-fast and floating ice. Forward modeling of sediment temperatures is performed using the 1D heat transfer model CryoGrid with depth dependent thermal properties. We neglect advective processes and long-term temperature trends in the bottom water temperatures. Rough parameterization of the annual variation of water bottom temperatures reproduce measured water temperatures with a RMSE of 20-40 %. The resulting modeled sediment temperature field based on 10 years of repeated parameterized bottom water temperatures matches the modeled sediment temperature field based on measured water temperatures in terms of permafrost characteristics, including the depth of the active layer defined by the 0°C isotherm over the year. However, both modelled temperature fields yield significantly higher sediment temperatures than the measured sediment temperature field. This may be the result of choice of sediment thermal properties in the thermal model or shifts in the duration of bottom-fast ice contact or on-ice snow Since modelled temperature fields from both repeated measured and parameterized bottom water temperatures show the same deviation, it suggests that the bottom water temperatures were warmer during the measurement period than the average over the previous 10 years.

Description: Massive Arctic rivers are feeding ≈11% of the global river discharge into the Arctic Ocean, while the ocean stores only ≈1% of the global ocean volume. The ongoing rapid climate warming has led to pronounced changes in precipitation, active layer thickening, increased air and soil temperatures, increased riverbank and coastal erosion rates, extensive permafrost thaw and increasing freshwater discharge to the Arctic Ocean. Since most studies have focused on rivers or oceans itself and mainly during the late summer, near-shore coastal regions are understudied and crucial in determining the amount of carbon transported and/or released into the Arctic Ocean. Here, we investigated river-derived carbon dioxide (CO2) and methane (CH4) emissions from seven repeated transects of the Kolyma River and nearshore (120 km between Cherskiy and Ambarchik) over the entire open water season between June and September 2019. We estimated the cumulative gross delivery of river-derived CH4 and CO2 to the coastal ocean to be around 0.0008 Tg CH4 (800 000 kg) and 0.2 Tg CO2 (200 000 000 kg). Measurements reveal that more than 50% of the cumulative gross delivery is happening during the fresh period, making the season dynamics extremely important.

Description: Wind and wave conditions are a primary concern for many people living along the coastline, but when considering the partially frozen coastline in the Arctic, this concern is highlighted by the cascading detrimental thawing effects on indigenous cultural sites and subsistence practices. Media coverage has extensively shown cemeteries being washed away into the sea, ice cellars being inundated with floodwaters, and entire villages planning to relocate without having the funds to do so. If we take a look further offshore, sea state directly impacts the safety of subsistence hunters travelling by boat, leading to the fact that a lengthening open water season does not necessarily mean the same increase in the number of safely boat-able days. Beyond the scope of native communities, but still well within the lens of the media, professional sailors are constantly looking for products that improve their knowledge and forecasts of sea state to better inform which routes and actions they will take during months-long competitions. This talk will contain a broad overview of the specific uses of wave and wind information, citing specific examples from the authors’ own experience on coastal erosion model development and interaction with Arctic native coastal communities. A main goal of this talk is also to illuminate the incentives for the scientific community to be actively engaged in improving operational sea state products, from Arctic indigenous coastal communities to professional sailors, particularly in light of the increasing media attention to the general public.

Description: Permafrost coasts make up roughly one third of all coasts worldwide. Their erosion leads to the release of previously locked organic carbon, changes in ecosystems and the destruction of cultural heritage, infrastructure and whole communities. Since rapid environmental changes lead to an intensification of Arctic coastal dynamics, it is of great importance to adequately quantify current and future coastal changes. However, the remoteness of the Arctic and scarcity of data limit our understanding of coastal dynamics at a pan-Arctic scale and prohibit us from getting a complete picture of the diversity of impacts on the human and natural environment. In a joint effort of the EU project NUNATARYUK and the NSF project PerCS-Net, we seek to close this knowledge gap by collecting and analyzing all accessible high-resolution shoreline position data for the Arctic coastline. These datasets include geographical coordinates combined with coastal positions derived from archived data, surveying data, air and space born remote sensing products, or LiDAR products. The compilation of this unique dataset will enable us to reach unprecedented data coverage and will allow us a first insight into the magnitude and trends of shoreline changes on a pan-Arctic scale with locally highly resolved temporal and spatial changes in shoreline dynamics. By comparing consistently derived shoreline change data from all over the Arctic we expect that the trajectory of coastal change in the Arctic becomes evident. A synthesis of some initial results will be presented in the 2020 Arctic Report Card on Arctic Coastal Dynamics. This initiative is an ongoing effort – new data contributions are welcome!