ALBERT

Description: Large amounts of the greenhouse gas methane are released from the seabed to the water column where it may be consumed by aerobic methanotrophic bacteria. This microbial filter is consequently the last marine sink for methane before its liberation to the atmosphere. The size and activity of methanotrophic communities, which determine the capacity of the water column methane filter, are thought to be mainly controlled by nutrient and redox dynamics, but little is known about the effects of ocean currents. Here, we report measurements of methanotrophic activity and biomass (CARD-FISH) at methane seeps west of Svalbard, and related them to physical water mass properties (CTD) and modelled current dynamics. We show that cold bottom water containing a large number of aerobic methanotrophs was rapidly displaced by warmer water with a considerably smaller methanotrophic community. This water mass exchange, caused by short-term variations of the West Spitsbergen Current, constitutes a rapid oceanographic switch severely reducing methanotrophic activity in the water column. Strong and fluctuating currents are widespread oceanographic features common at many methane seep systems and are thus likely to globally affect methane oxidation in the ocean water column.

Description: On three transects, in October, November and December 2018 with RV Uthörn dissolved methane was determined continuously . We used a degassing unit which was using surface water from the ship's water supply in an overflowing bucket. The gas mixture was subsequently analyzed with a Greenhouse Gas Analyzer from LosGatos. Conversion to methane concentration was performed with water samples, from which the methane content was determined with gas chromatography. Atmospheric methane was measured in certain intervals, by disconnecting the degasser, and connecting the Greenhouse Gas Analyzer with a tubing attached at about 6 m above the water surface at the ships upper deck. For basic hydrographic parameters were determined with a CTD (SSDA Sea and Sun Technology, Trappenkamp, Germany ) was placed in the same bucket as described above.

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 dataset is about temporal variability of dissolved methane along the freshwater-sea continuum in northern Germany. Sensors were installed at fixed stations at in total three sites at different water depths. This dataset is from the station in Geesthacht (53.4112 N, 10.4032 E) at about 2 meter depth. The data was obtained between 14 April and 29 September 2021) in high frequency measurements (1 min) with a methane sensor from Kongsberg (4H Jena model CONTROS HydroC CH4,). Methane concentrations were calculated according to manufacturer's instructions. Data on temperature were provided by from Vattenfall, Kernkraftwerk Krümel, a salinity of 0.01 was assumed. Special thanks to the colleagues from Vattenfall for the logistic and technical support. For the quality control of the data a local range of 0.1 – 5000 nmol/L was set, a technical range for the pump power 2 – 8. Watt, a spike and gradient value of 1. For a more detailed description see the article cited in References.

Description: The dataset is about temporal variability of dissolved methane along the freshwater-sea continuum in northern Germany. Sensors were installed at fixed stations at in total three sites at different water depths. This dataset is from the station in Heligoland (54.1833 N, 7.8667 E) at about 9-12m depth (depending on the tide). The data was obtained between 27 April and 28 October in high frequency measurements (1 min) with a methane sensor from Kongsberg (4H Jena model CONTROS HydroC CH4,). Methane concentrations were calculated according to manufacturer's instructions, based on temperature and salinity values from UW-node Heligoland (Fischer, Philipp; Happel, Lea; Brand, Markus; Eickelmann, Laura; Lienkämper, Miriam; Bussmann, Ingeborg; Anselm, Norbert; Brix, Holger (2022): Hydrographical time series data of Helgoland, Southern North Sea, 2021. PANGAEA, https://doi.org/10.1594/PANGAEA.950173). A gap in the salinity data was replaced with the median value of the observed time span (31.66). For the quality control of the data a local range of 0.1 – 1000 nmol/L was set, a technical range for the pump power 2 – 8. Watt, a spike and gradient value of 1. For a more detailed description see the article cited in References.

Description: On 25 and 26 of June in 2019 transects between Cuxhaven and Bremerhaven towards Helgoland were performed with the RV Prandtl and Uthörn. Basic hydrographic parameters were measured with two ferry boxes using the ships water supply. Data were saved once per minute. Dissolved methane was determined continuously. We used a degassing unit which was using surface water from the ship's water supply in an overflowing bucket. The gas mixture was subsequently analyzed with a Greenhouse Gas Analyzer from LosGatos. Conversion to methane concentration was performed with water samples, from which the methane content was determined with gas chromatography.

Description: Surface water samples of the river Elbe were taken in May 2021 with the vessel Zwergseeschwalbe between Geesthacht and Neu Darchau. Connecting cruises were performed from colleagues from Geesthacht towards Hamburg and from Elster towards Dömitz.

Description: The vessel Ludwig Prandtl was anchored for 48 h off Cuxhaven at Medem Reede. Water samples were taken approx. every 2 hours during daytime, while sensors were recording continuously. Water samples were taken from ferrybox outlet from surface (1 m).