ALBERT

Description: The Lena River is one of the biggest Russian rivers draining into the Laptev Sea. Due to predicted increasing temperatures, the permafrost areas surrounding the Lena Delta will melt at increasing rates. With this melting, high amounts of methane will reach the waters of the Lena and the adjacent Laptev Sea. Methane oxidation by methanotrophic bacteria is the only biological way to reduce methane concentrations within the system. However, the polar estuary of the Lena River is a challenging environment for bacteria, with strong fluctuations in salinity and temperature. We determined the activity (tracer method) and the abundance (qPCR) of aerobic methanotrophic bacteria. We described the methanotrophic population with MISA; as well as the methane distribution (head space) and other abiotic parameters in the Lena Delta in September 2013. In riverine water (S 〈 5) we found a median methane concentration of 22 nM, in mixed water (5 〈 S 〈 20) the median methane concentration was 19 nM and in polar water (S 〉 20) a median 28 nM was observed. The Lena River was not the methane source for surface water, and bottom water methane concentrations were mainly influenced by the concentration in surface sediments. However, the methane oxidation rate in riverine and polar water was very similar (0.419 and 0.400 nM/d), but with a higher relative abundance of methanotrophs and a higher estimated diversity with respect to MISA OTUs in the rivine water as compared to polar water. The turnover times of methane ranged from 167 d in mixed water, 91 d in riverine water and only 36 d in polarwater. Also the environmental parameters influencing the methane oxidation rate and the methanotrophic population differed between the water masses. Thus we postulate a riverine methanotrophic population limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population being well adapted to the cold and methane poor environment, but limited by the nitrogen content. The diffusive methane flux into the atmosphere ranged from 4–163 µmol m2 d−1 (median 24). For the total methane inventory of the investigated area, the diffusive methane flux was responsible for 8 % loss, compared to only 1 % of the methane consumed by the methanotrophic bacteria within the system.

Description: The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013. The median methane concentrations were 22 nmol L−1 for riverine water (salinity (S)  

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: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and seaair exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.

Description: Understanding river-sea-systems requires a thorough understanding of processes that span different Earth system compartments. To overcome issues related to the interaction of different scientific disciplines and compartments, such as different measurement and calibration standards, quality control approaches and data formats for specific environmental parameters, joint measurement campaigns have been initiated within the Helmholtz Association’s MOSES (Modular Observation Solutions for Earth Systems) project. Following multiple senor comparison and intercalibration campaigns in 2019, MOSES’ Hydrological Extremes event chain working group initiated joint field campaigns in summer 2020 covering the Elbe river from the Czech-German border to the tidal Elbe and further on into the estuary and the German Bight. The fundamental objective was to establish scientifically sound and resilient multi-ship applicable sampling procedures and to create reference data for the main environmental parameters for future investigation of extreme events such as flooding and drought and their overall impact on the catchment region and the adjacent estuarine area of a large European fresh water / marine system. The campaign involved four research vessels, four research centers and spanned nearly two months. Measurements included standard hydrological and oceanographic parameters, as well as quantities relevant to the nutrient and carbonate system. Furthermore, selected water quality indicators and atmospheric measurements were performed. In the fresh water section of the Elbe river measurements were taken while drifting with the water mass. In the tidal section of the river sampling was done against the ebb current while in the North Sea a grid covering a large part of the German exclusive economic zone (EEZ) was sampled. We detected a longitudinal increase of phytoplankton biomass along the 585 km freshwater part of the river towards the tidal system. In contrast, concentrations of dissolved nitrate and phosphate decreased to low values due the uptake by planktonic algae. The concentration of dissolved CO2 decreased caused by increasing photosynthesis while the concentration of methane increased along the river stretch, particularly in the most downstream part when sedimentation of phytoplankton increased the organic load of sediments. The tidal part of the transect showed a strong influence of Hamburg harbor on almost all quantities, while downstream towards the estuary, the effects of the tidal cycle dominated variabilities. In the marine area, elevated chlorophyll concentrations were mainly found near the west coast of Schleswig-Holstein, probably mostly influenced by the Eider river outflow or the adjacent tidal flats. While most of the measured parameters showed an expected behavior relative to their individual compartments, the transfer of quantities between the compartments revealed rather complex and sometimes difficult to understand behaviors and patterns, especially when considering a functional quantitative analysis. The first results of this trans-compartment campaign showed that a quantitative understanding of the fate and dynamics of water constituents across compartments from the spring to the sea needs enhanced scientific collaboration and awareness to finally come to a better integrated understanding of physical, biogeochemical and biological processes from the local to the global scale.

Description: Surface waters are known to be significant sources of greenhouse gases (CH4 and CO2), but our understanding of large scale patterns is still incomplete. The greenhouse gases in rivers originate both from in-stream processes and interactions with the catchment. For coastal seas, rivers are suspected to be one of the main source of greenhouse gases, while the role of the interjacent tidal flats is still ambiguous. Especially the reaction of the entire system on terrestrial hydrological extremes such as low flow situations are still under consideration. The functional understanding of such events and their impacts on the water chemistry along its transition pathway in the terrestrial and limnic compartment as well as in the coastal marine environment is crucially needed for the evaluation of its relevance in the Earth system. As part of a MOSES campaign (Modular Observation Solutions for Earth Systems) spanning disciplines as well as earth system compartments we investigated the aquatic as well as the atmospheric compartemt in and above the Elbe River from inland waters through the tidal section of the river and the estuary to the North Sea with the goal to explore spatial heterogeneity of CO2 and CH4 concentrations in the water and in ambient air above the water during a low water period in summer 2020. Overall, dissolved CH4 concentrations ranged over three orders of magnitude. Along the freshwater part of the transect, dissolved CH4 increased and weirs and harbors appeared to be hot spots of elevated CH4 concentrations both for the dissolved and atmospheric phase. We observed a longitudinal gradient of CO2 in the river which was closely linked to primary production. In the estuary and the marine part, dissolved CH4 concentrations of the transect were determined by the variability of temperature and salinity. Correlations with other water parameters revealed the complex regulation of dissolved CH4 concentrations along the freshwater-seawater continuum. For atmospheric CH4 above the North Sea, wind direction and wind speed proved to be crucial. Besides the typical diurnal fluctuations of atmospheric CO2 and CH4, an observed link between dissolved and atmospheric concentrations has to be further clarified.

Description: Permafrost thaw affects global climate, the land surface and coastal structures. Under subaquatic conditions, permafrost thaw is often more rapid than on land. The thaw depth below water bodies (taliks) and changes in biogeochemical gradients are difficult to predict. The influence of taliks and biogeochemical gradients on the production and release of the greenhouse gases methane and carbon dioxide is not clear yet. Although our research in this region has produced multi-decadal data sets, most of our knowledge on the methane cycle pertains only to the summer. We focus on water bodies in the Lena Delta region, including thermokarst ponds, lakes, lagoons and the marine shoreface. For most of the year, however, ice covers these water bodies, creating a barrier between the water column and the atmosphere, and changing benthic conditions. It is therefore important to assess methane-related processes during the ice-covered season. In spring 2017 we investigated the Lena Delta and Tiksi Bay at the end of winter, while still ice-covered. Thirty ice cores of different water bodies were obtained by Kovacs ice corer. The in situ temperature of the ice cores was measured immediately afterwards. Methane oxidation rates were determined with radio tracer method in melted ice core samples. Analyses of methane concentration and further hydrochemical analyses are on their way. Initial results indicate rather low activities of methane oxidation in the ice cores, but active biological processes in the water below.

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 δ13C-CH4 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.