ALBERT

Description: River estuaries are responsible for high rates of methane emissions to the atmosphere. The complexity and diversity of estuaries require detailed investigation of methane sources and sinks, as well as of their spatial and seasonal variations. The Elbe river estuary and the adjacent North Sea were chosen as the study site for this survey, which was conducted from October 2010 to June 2012. Using gas chromatography and radiotracer techniques, we measured methane concentrations and methane oxidation (MOX) rates along a 60 km long transect from Cuxhaven to Helgoland. Methane distribution was influenced by input from the methane-rich mouth of the Elbe and gradual dilution by methane-depleted sea water. Methane concentrations near the coast were on average 30 ± 13 nmol L−1, while in the open sea, they were 14 ± 6 nmol L−1. Interestingly, the highest methane concentrations were repeatedly detected near Cuxhaven, not in the Elbe River freshwater end-member as previously reported. Though, we did not find clear seasonality we observed temporal methane variations, which depended on temperature and presumably on water discharge from the Elbe River. The highest MOX rates generally coincided with the highest methane concentrations, and varied from 2.6 ± 2.7 near the coast to 0.417 ± 0.529 nmol L−1 d−1 in the open sea. Turnover times varied from 3 to 〉1000 days. MOX rates were strongly affected by methane concentration, temperature and salinity. We ruled out the supposition that MOX is not an important methane sink in most of the Elbe estuary and adjacent German Bight.

Description: Rivers are suspected to be a main suppliers of greenhouse gases (methane and carbon dioxide) to coastal seas, while the role of the interjacent tidal flats is still ambiguous. In this study we investigated the role of the Elbe and Weser estuaries as source of methane to the North Sea. We used high spatially resolved methane measurements from an underway degassing system and subsequent analysis with cavity ring down spectroscopy. Thus, a high-resolution representation of the methane distribution in surface waters as well as of hydrographic parameters was obtained for several cruises with two ships in 2019. For most areas, riverine methane was simply diluted by seawater, overlain by a strong tidal signal. However, on several occasions unexpectedly high methane concentrations were observed. Further detailed analysis will elucidate the role of riverine versus tidal impact on coastal North Sea methane fluxes.

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: Measuring environmental variables over longer times in coastal marine environments is a challenge in regard to sensor maintenance and data processing of continuously produced comprehensive datasets. In the project “MOSES” (Modular Observation Solutions for Earth Systems), this procedure became even more complicated because seven large Helmholtz centers from the research field Earth and Environment (E&E) within the framework of the German Ministery of Educatiopn and Research (BMBF) work together to design and construct a large scale monitoring network across earth compartments to study the effects of short-term events on long term environmental trends. This requires the development of robust and standardized automated data acquisition and processing routines, to ensure reliable, accure and precise data. Here, the results of two intercomparison workshops on senor accuracy and precicion for selected environmental variables are presented. Environmental sensors which were to be used in MOSES campaigns on hydrological extremes (floods and draughts) in the Elbe catchment and the adjacent coastal areas in the North Sea in 2019 to 2020 were compared for selected parameters (temperature, salinity, chlorophyll-A, turbidity and methane) in the same experimentally controlled water body, assuming that all sensors provide comparable data. Results were analyzed with respect to individual sensor accuracy and precision related to an “assumed” real value as well as with respect to a cost versus accuracy/precision index for measuring specific environmental data. The results show, that accuracy and precision of sensors do not necessarily correlate with the price of the sensors and that low cost sensors may provide the same or even higher accuracy and precision values as even the highest price sensor types.