Description: We measured dissolved and particular inorganic nitrogen concentrations in the Ems estuary (Germany). The sampling campaign was conducted on three days in August 2014 (05.08.2014– 07.08.2014) on board of the German research vessel Ludwig Prandtl. Water samples were taken regularly along the salinity gradient of the estuary irrespective of the state of the tide 2 m below the surface. For stations S276 to S280, only the Ferrybox measurements were taken 2 m below the surface. The water samples were taken by a Niskin-Bottle 2 m above the bottom. The water samples were filtered immediately and stored frozen for analysis of dissolved inorganic nutrient and nitrate stable isotope composition. Filtered samples for suspended particular matter (SPM) concentration, particular carbon and nitrogen content of SPM and nitrogen stable isotope composition of SPM were dried at 50°C and also stored frozen. An onboard membrane pump provided the on-line in situ FerryBox system with water from 2 m below the surface. It continuously measured oxygen, salinity, and temperature during our cruise. More information can be found in Sanders and Laanbroek (2018). The aims of the cruise were 1) to study spatial segregation of nitrogen turnover, 2) to identify the dominant nitrogen turnover processes in the water column and 3) to investigate controlling factors of the nitrogen cycle along the Ems estuary.

Description: We investigated nutrient input and retention in the Elbe River (Germany) at the river/estuarine transition with high agricultural loads of nitrogen. Surface water samples were taken at the weir Geesthacht (stream kilometre 585, 53°25'31''N, 10°20'10''E) from 2011 to 2021. In these samples, we analyzed nutrient concentrations, nitrate dual stable isotopes and suspended particulate matter composition. Usually, samples were taken once or twice per month. Aims of the study were to investigate 1) nitrate retention in the Elbe River and catchment, 2) seasonal dynamic of nitrate stable isotopes and 3) key nitrogen turnover processes and their respective controls over a ten year period.

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 samples were taken in June 2021 on the cruise AL557 in the Skagerrak and the central and southern North Sea. The samples were taken to analyze pore water concentrations of nutrients in order to monitor the nitrogen turnover processes taking place in the sediment. Pore water samples were taken with rhizon samplers (0.15 µm pore size, CSS; Rhizosphere, Netherlands) from intact sediment cores that were taken with a Multiple Corer. The samples were directly frozen until analysis on 7th and 8th March 2022. The nutrient concentrations (ammonia, silicate, phosphate, nitrite) were measured using a TECAN infinite 200 plate reader. Colorimetric methods according to Ringuet et al. (2011) for phosphate and silicate, Yu et al. (1994) for ammonia and Garcia-Robledo et al. (2014) were applied.

Description: Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits are still poorly quantified. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ~52 ka. We show that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt%).We found that the OM quality, which we define as the intrinsic potential to further transformation, decomposition, and mineralization, is also high as inferred by the lipid biomarker inventory. The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal kyr BP) and is overlaid by Last Glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso and anteiso-branched FAs relative to long chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits, suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C / N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease of HPFA values downwards along the profile probably indicates a relatively stronger OM decomposition in the oldest (MIS 3) deposits of the cliff.

Description: Total Suspended Matter (TSM), Particulate Organic Carbon (POC) and its isotopic composition were measured in water samples from the Lena River and its Delta (Sardakhskaya branch). Samples were taken in summer 2019 during the CACOON expedition (Fuchs et al., 2021a, b and 2022) along ~ 1600 km transect from Yakutsk downstream to the Lena Delta disembogue into the Laptev Sea. Water was filtered through pre-combusted (4.5 hours, 450 °C) and pre-weighed glass fiber filters (GF/F Whatman, 0.75 µm membrane, Ø 2.5 cm) for TSM content (difference in weights between dried filters with TSM and pre-weighed empty filters), POC concentration and δ13C-POC (Sercon 20-20 isotope ratio mass spectrometer coupled to an Automated Nitrogen Carbon Analyzer), ∆14C-POC analysis (accelerator mass spectrometer achieved on a Mini Carbon Dating System) and relative OC content in TSM (calculated by dividing the sample POC content by the TSM content). Our aim was to characterize POC along the Lena River over a transect from upper reaches of the Lena River north to the Lena delta in order to decipher the distribution, main sources, and transformation of POC on its way from the permafrost catchment to the Arctic Ocean.

Description: This dataset merges nitrogen data from the Yedoma domain. It includes numerous fieldwork campaigns, which take place since 1998. In total 467 samples from the active layer (seasonally thawed layer), 175 samples from perennially frozen Holocene cover deposits, 479 samples from thermokarst deposits in drained thermokarst, 175 in-situ thawed, diagenetically (anaerobic microbial decomposition possible during unfrozen phase) altered Yedoma deposits (called Taberite), and 917 samples from frozen Yedoma deposits are included. Moreover it includes a NH4+ and NO3- quantification basing on of 658 samples, including 378 data points for NH4+ (active layer, 93; Holocene cover, 108; thermokarst sediment, 138; Taberite, 0; Yedoma deposit, 39) and 542 data points for NO3- (active layer, 94; Holocene cover, 137; thermokarst sediment, 119; Taberite, 6; Yedoma deposit, 186). The bootstrapping code we adjusted for this study is available from Zenodo (Jongejans & Strauss, 2020, doi:10.5281/zenodo.3734247). The code is published under a GNU General Public License v3.0. The included areal estimation of the Yedoma domain was used from the IRYP database (Strauss et al., 2022, doi:10.1594/PANGAEA.940078).

Description: Dissolved and particulate Organic Carbon (DOC and POC) and their isotopic composition were measured in water samples from the Lena Delta (Sardakhskaya branch). Samples were taken in winter (April) and summer (August) 2019 during the CACOON expedition (Fuchs et al., 2021a, b and 2022) and in the summer 2017 and 2016 during previous Lena Delta sampling campaigns. Water was filtered through pre-combusted (4.5 hours, 450 °C) and pre-weighed glass fiber filters (GF/F Whatman, 0.75 µm membrane, Ø 2.5 cm) for DOC analyses, filters with rest suspended matter on it were used to analyse POC. δ13C of DOC and POC was measured by Sercon 20-20 isotope ratio mass spectrometer coupled to an Automated Nitrogen Carbon Analyzer, ∆14C of DOC and POC by accelerator mass spectrometer achieved on a Mini Carbon Dating System. Our aim was to highlight the variability in quantity and composition between seasons and suggest that permafrost deposits are degrading year around, impacting the release of organic matter through the Lena Delta.

Description: This data set includes the CTD cast locations, which were measured during the CACOON 2019 expeditions (Fuchs et al., 2021; Strauss et al., 2021) in the Lena Delta region in Siberia. The data collection took place during two field campaigns; the first one was in March-April 2019, the second one in August 2019. Measurements were taken with a handheld SontekTM CastAway sensor with an integrated GPS. The measured data include pressure, depth, temperature, conductivity, specific conductance, salinity, sound velocity, and density. In total, 31 depth profiles were measured from the Sardakhskaya main river channel in the Lena Delta to 80 km offshore in the Laptev Sea to specifically target the mouth area of the Sardakhskaya channel. The CTD was lowered from water surface with an additional ballast to make sure the small CTD device reached the sea (or river) bed. This data sets includes detailed data about the locations, time and duration of CTD measurements in the Lena Delta region.

Description: This data set includes measurement during the CACOON 2019 expeditions (Fuchs et al., 2021; Strauss et al., 2021) in the Lena Delta region in Siberia. The data collection took place during two field campaigns; the first one was in March-April 2019, the second one in August 2019. Measurements were taken with a handheld SontekTM CastAway sensor with an integrated GPS. The measured data include pressure (dbar; accuracy: 0.25%), depth (m; ±0.25%), temperature (°C; ±0.05°C), conductivity (mS/cm; 0.25%±0.005 mS/cm), specific conductance (mS/cm; 0.25%±0.005 mS/cm), salinity (practical salinity scale; ±0.1), sound velocity (m/s; ±0.15 m/s), and density (kg/m3; ±0.02 kg/m3). In total, 31 depth profiles were measured from the Sardakhskaya main river channel in the Lena Delta to 80 km offshore in the Laptev Sea to specifically target the mouth area of the Sardakhskaya channel. The CTD was lowered from water surface with an additional ballast to make sure the small CTD device reached the sea (or river) bed.