ALBERT

Description: The community structure of sulfate-reducing bacteria (SRB) of a marine Arctic sediment (Smeerenburgfjorden, Svalbard) was characterized by both fluorescence in situ hybridization (FISH) by using group- and genus-specific 16S rRNA-targeted oligonucleotide probes. Samples stored in PBS-ethanol were diluted and treated by mild sonication. A 10-ml aliquot of a 1:40 dilution was filtered onto a 0.2-mm-pore-size type GTTP polycarbonate filter (Millipore, Eschborn, Germany). Hybridization and microscopic counting of hybridized and 49,69-diamidino-2-phenylindole (DAPI)-stained cells were performed as described previously from Snaidr et al. (1997, http://aem.asm.org/content/63/7/2884.full.pdf). Details of probes and formamide concentrations which were used are listed in futher details.. Means were calculated by using 10 to 20 randomly chosen fields for each filter section, which corresponded to 800 to 1,000 DAPI-stained cells. Counting results were always corrected by subtracting signals observed with probe NON338. The SRB community was dominated by members of the Desulfosarcina-Desulfococcus group. This group accounted for up to 73% of the SRB detected. The predominance was shown to be a common feature for different stations along the coast of Svalbard. In a top-to-bottom approach we aimed to further resolve the composition of this large group of SRB by using probes for cultivated genera. While this approach failed, directed cloning of probe-targeted genes encoding 16S rRNA was successful and resulted in sequences which were all affiliated with the Desulfosarcina-Desulfococcus group. A group of clone sequences (group SVAL1) most closely related to Desulfosarcina variabilis (91.2% sequence similarity) was dominant and was shown to be most abundant in situ, accounting for up to 54.8% of the total SRB detected.

Description: This dataset contains the results of granulometric and bulk geochemical analyses of Van Veen surface samples obtained by the Alfred Wegener Institute (AWI) in the course of the 2012 and 2013 summer field seasons. The sampling was performed along transects in depths generally 〈13 m, to a distance of about 〈5 km off Herschel Island. In 2012, 75 samples in Pauline Cove and in the vicinity of Simpson Point were obtained. Sample collection was expanded in 2013, on transects established the previous year, with additional locations in Tetris Bay and Workboat Passage. Samples consisted of approximately 100 g of the top 3-6 cm of sediment, and were frozen in the field and freeze dried at the AWI before undergoing analytical procedures. Sample locations were recorded with the onboard global positioning system (GPS) unit. Grain size distributions in our study were obtained using laser diffractometry at the AWI (Beckman Coulter LS200) on the 〈1 mm fraction of samples oxidized with 30% H2O2 until effervescence ceased to remove organics. Some samples were also sieved using a sieve stack with 1 phi intervals. GRADISTAT (Blott and Pye, 2001) was used to calculate graphical grain size statistics (Folk and Ward, 1957). Grain diameters were logarithmically transformed to phi values, calculated as phi=-log2d, where d is the grain diameter in millimeters (Blott and Pye, 2001; Krumbein, 1934). Freeze dried samples were ground and ground using an Elemetar Vario EL III carbon-nitrogen-sulphur analyzer at the AWI to measure total carbon (TC) and total nitrogen (TN). Tungsten oxide was added to the samples as a catalyst to the pyrolysis. Following this analysis, total organic carbon (TOC) was determined using an Elementar VarioMax. Stable carbon isotope ratios of 13C/12C of 118 samples were determined on a DELTAplusXL mass spectrometer (ThermoFisher Scientific, Bremen) at the German Research Centre for Geosciences (GFZ) in Potsdam, Germany . An additional analysis on 69 samples was carried out at the University of Hamburg with an isotope ratio mass spectrometer (Delta V, Thermo Scientific, Germany) coupled to an elemental analyzer (Flash 2000, Thermo Scientific, Germany). Prior to analysis, soil samples were treated with phosphoric acid (43%) to release inorganic carbon. Values are expressed relative to Vienna Peedee belemnite (VPDB) using external standards (USGS40, -26.4 per mil VPDB and IVA soil 33802153, -27.5 per mil VPDB).

Description: Climate change has a strong impact on permafrost coasts in the Arctic. With increasing air and water temperatures, ice-rich permafrost coasts will thaw, which will lead to enhanced thermokarst and erosion. Upon erosion, large amounts of organic carbon previously stored for thousands of years are remobilized and either emitted as greenhouse gases to the atmosphere, redeposited within the landward nearshore zone, or released into the ocean. Yet, little is known about carbon degradation before the organic matter enters the nearshore zone of the ocean. The objective of this study was to investigate these processes at ice-rich thermokarst coasts, by focusing on retrogressive thaw slumps. The study aimed at determining the quantity of organic carbon and nitrogen in undisturbed and non-disturbed (thermokarst affected) coastal stretches, to detect its degradation and accumulation pattern after thawing, as well as its fate in the nearshore of the ocean. A retrogressive thaw slump located on Herschel Island (Yukon Territory, Canada) was sampled systematically along transects from the undisturbed parts (tundra, permafrost headwall) to disturbed parts (mudpool and slump floor) and the nearshore zone (marine sediments). These thermokarst landforms are ideal study sites as they spatially expose different transport and accumulation stages of thawed permafrost sediments before entering the ocean. Total and dissolved organic carbon (TOC and DOC) as well as total and dissolved nitrogen (TN and DN) were analyzed to quantify carbon and nitrogen loss. C/N-ratios, stable carbon isotope concentrations (δ13C-TOC and δ13C-DOC), nutrient concentrations (ammonium, nitrite, nitrate), and lipid biomarkers were analyzed to estimate degradation, carbon metabolization, as well as nitrification and plant assimilation processes. Furthermore, dating of lead isotopes (Pb-210) in nearshore sediments and conductivity-temperature-depth (CTD) profiles of the sea water in front of the slump were analyzed to assess the possible fate of the organic material in the nearshore zone. Our results show a general decrease of TOC and DOC as well as TN and DN contents from undisturbed to disturbed zones. TOC/TN-ratios are lower in disturbed zones, especially when comparing to permafrost sediments only. DOC/DN-ratios are highest in the tundra and slump floor but in general lower in disturbed zones. Stable carbon isotopes differ only slightly with lower values in disturbed zones, especially when comparing disturbed areas with permafrost only. Nitrate and nitrite concentrations are highest in disturbed areas, while ammonium concentrations are highest in permafrost and mudpool sediments. In the marine sediment core, Pb-210 values hinted towards a well-mixed environment and non-continuous accumulation. CTD surveys showed frequent brackish and mixed water column conditions. These results lead to the assumption that sediments released through thermokarst activity are subject to strong degradation, which is supported by lower quantities of TOC and DOC as well as lower C/N-ratios in the disturbed zone. However, slightly lower values of stable carbon isotopes indicate that carbon is less degraded in the disturbed zone. High ammonium values in permafrost and mudpool sediments reflect an increasing activity of bacteria metabolizing organic material. No nitrate and nitrite was found in undisturbed parts, whereas detectable concentrations were found in disturbed parts, leading to the assumption that organic material has been subject to metabolization by bacteria. Lower DN-values in the slump floor reflected the nitrogen fixation by plants that recolonize the disturbed zones. We suggest that before entering the nearshore zone permafrost organic carbon and nitrogen is subject to substantial degradation and metabolization. Within the nearshore zone, the accumulated sediments are remobilized frequently and transported either along the shore or further offshore.

Description: Introduction: Thawing arctic subsea permafrost is a source of organic carbon in deep sediment layers. The permafrost that is at its thermal equilibrium releases biologically produced methane and a deep sulfate-methane transition zone (SMTZ) is formed due to sulfate-rich overlaying marine sediment layers. The process of methane oxidation in this anaerobic environment has been suggested1 but AOM associated microbial communities remain to be identified. Objectives: We aimed at providing evidence for anaerobic methanotrophic (ANME) archaeal communities at the deep SMTZ of the north-east Siberian Laptev Sea shelf. Material and methods: Two sediment cores were retrieved (77 m and 47.4 m deep) from the coastal shelf north of Cape Mamontov Klyk ‘C2’ (11.5 km offshore) and west to the Buor Khaya Peninsula ‘BK2’ (800 m offshore), respectively. Methane and sulfate concentrations as well as 13C isotope values of CH4 were measured and correlated with molecular analysis of microbial communities along the thaw front. Results: At the thaw front of BK2, at 23.7 meters below sea floor (mbsf) biologically produced methane (13 C= -70‰ VPDB) gets oxidized (13C= -29.8 ‰ VPDB)1. At the same depth, we found an increase in functional genes of methanogenic archaea (mcrA) and sulfate reducing bacteria (dsrB) analysed by quantitative PCR. Massive parallel tag-sequencing of the 16S rRNA gene showed an increase of ANME-2a/2b and ANME-2d sequences towards the thaw front in both cores. At the thaw front of the BK2 core, typical ANME-2 partners of the Desulfobacterales2were found to dominate the sulfate reducing bacterial community, whereas Desulfobaccasequences dominate in all samples of the C2 core. Theoretical methane oxidation rates (0.4-6 nmol cm-3d-1)1based on estimated methane fluxes showed higher values than typically found in subsurface sediments and are more similar to rates of margin SMTZs3. Conclusion: Our data indicate that active anaerobic methane oxidizer communities at the thaw front of subsea permafrost prevent methane from being released into the water column and subsequently to the atmosphere. Further analyses on lipid biomarkers and 14C-CH4isotopic rate measurements will determine how active these communities are in situ. 1. Overduin, P. P. et al.Methane oxidation following submarine permafrost degradation: Measurements from a central Laptev Sea shelf borehole. J. Geophys. Res. Biogeosciences2014JG002862 (2015). 2. Schreiber, L., Holler, T., Knittel, K., Meyerdierks, A. & Amann, R. Identification of the dominant sulfate-reducing bacterial partner of anaerobic methanotrophs of the ANME-2 clade. Environ. Microbiol.12, 2327-2340 (2010). 3. Knittel, K. & Boetius, A. Anaerobic Oxidation of Methane: Progress with an Unknown Process. Annu. Rev. Microbiol. 63, 311-334 (2009).