During the research cruises BE03/2016 (08.03.2016), BE10/2016 (19.10.2016), BE10/2018 (23.10.2018), BE03/2019 (15.03.2019), L23-13 (13.09.2023 - 15.09.2023), Sagitta24-1 (16.09.2024), Sagitta24-2 (23.09.2024), Hai24VE2 (24.09.2024), L25-2b (09.02.2025 - 17.02.2025) and EMB374 (04.09.2025 - 13.09.2025), CTDs were deployed and sediment corers were retrieved at 99 stations in Kiel Bight in the southwestern Baltic Sea. Water column oxygen concentrations were determined using oxygen sensors attached to the CTD framework. At selected water depths, water samples were collected with Niskin bottles for the analysis of nitrate concentrations using an autoanalyzer. Short sediment cores (<50cm) were recovered using a Multicorer (MUC), Minicorer (MIC) or Rumohrlot (RL). Bottom waters were sampled from the supernatant water in the sediment cores. Solid phase sediment samples were analyzed for total organic carbon using an element analyzer. Porewater was extracted from the sediment cores using rhizones and analyzed for total alkalinity (titration), ammonium (photometer), sulfate (ion chromatography), hydrogen sulfide (photometer), dissolved iron (ICP-OES) and dissolved manganese (ICP-OES). The collected data will be used to (i) determine the spatial and temporal variability of hydrogen sulfide in bottom waters of the Kiel Bight, (ii) identify the controlling factors governing the accumulation of hydrogen sulfide at the seafloor, and (iii) establish an early warning system of sulfidic seafloor conditions for regional stakeholders in the Baltic Sea.
This dataset presents total organic carbon (TOC, wt%) contents in sediments at 19 stations in the Kiel Bight taken during the research cruises BE03/2016 (08.03.2016), BE10/2016 (19.10.2016), BE10/2018 (23.10.2018), BE03/2019 (15.03.2019), L23-13 (13.09.2023 - 15.09.2023), Sagitta24-1 (16.09.2024), Sagitta24-2 (23.09.2024), L25-2b (09.02.2025 - 17.02.2025) and EMB374 (04.09.2025 - 13.09.2025). Sediment cores (<50cm) were recovered using a Multicorer (MUC), Minicorer (MIC) or Rumohrlot (RL). The TOC analysis was performed using an Element Analyzer (Euro EA 3000). The data are used in combination with porewater and water column data to describe the sulfur geochemistry and cycling across different sites in the Kiel Bight and to identify the controlling factors governing the accumulation of hydrogen sulfide at the seafloor.
This dataset presents hydrogen sulfide (H2S) and nitrate (NO3-) concentrations in the water column at 15 stations in the Kiel Bight taken during the research cruises BE10/2018 (23.10.2018), BE03/2019 (15.03.2019), L23-13 (13.09.2023 - 15.09.2023), Hai24VE2 (24.09.2024) and EMB374 (04.09.2025 - 13.09.2025). Water samples were collected using Niskin bottles attached to a stainless-steel framework with CTD sensors. Concentrations of H2S and NO3- were measured photometrically (Hitachi U-2900). The data are used to describe seasonal hypoxia in the Kiel Bight water column and are combined with sediment and porewater data to identify controlling factors governing the accumulation of H2S at the seafloor. Furthermore, we compare the H2S measurements from the deepest Niskin bottle with bottom water H2S concentrations obtained from the benthic tracer profiler and from the overlying water in sediment cores. This allows us to illustrate H2S trends from several meters above the seafloor down to the sediment-water interface, and to discuss advantages and limitations of the different sampling techniques in characterizing geochemical conditions in the benthic environment.
This dataset presents porewater and bottom water data from 63 stations in the Kiel Bight taken during the research cruises BE03/2016 (08.03.2016), BE10/2016 (19.10.2016), BE10/2018 (23.10.2018), BE03/2019 (15.03.2019), L23-13 (13.09.2023 - 15.09.2023), Sagitta24-1 (16.09.2024), Sagitta24-2 (23.09.2024), L25-2b (09.02.2025 - 17.02.2025) and EMB374 (04.09.2025 - 13.09.2025). Short sediment cores (<50cm) were recovered using a Multicorer (MUC), Minicorer (MIC) or Rumohrlot (RL). At 22 of those stations, bottom water and porewater samples were analysed for total alkalinity (TA), ammonium (NH4+), sulfate (SO42-), hydrogen sulfide (H2S), dissolved iron (Fe2+) and dissolved manganese (Mn2+). At 41 stations, exclusively a bottom water sample was taken for H2S measurements. Bottom waters were sampled from the supernatant water in the sediment cores. Porewater samples were extracted from the sediments using rhizones. TA was determined by titration (METROHM 876 Dosimat Plus), NH4+ and H2S using a photometer (Hitachi U-2900), SO42- by Ion Chromatography (METROHM 761 Compact) and Fe2+ and Mn2+ by Inductively Coupled Plasma Optical Emission Spectroscopy (Varian 720-ES). The collected data will be used to determine the spatial and temporal variability of hydrogen sulfide in bottom waters of the Kiel Bight, (ii) identify the controlling factors governing the accumulation of hydrogen sulfide at the seafloor, and (iii) establish an early warning system of sulfidic seafloor conditions for regional stakeholders in the Baltic Sea.
This dataset presents dissolved oxygen (O2) concentrations in the water column at 38 stations in the Kiel Bight, collected during the research cruises BE10/2018 (23.10.2018), BE03/2019 (15.03.2019), L23-13 (13.09.2023 - 15.09.2023), Hai24VE2 (24.09.2024), and EMB374 (04.09.2025 - 13.09.2025). The O2 data were measured using a dissolved oxygen sensor (Sea-Bird, SBE43) attached to a stainless-steel framework with CTD sensors. The O2 water column data is used to describe the effect of seasonal hypoxia in the Kiel Bight and is combined with sediment and porewater data to identify controlling factors governing the accumulation of H2S at the seafloor.
From January 2022 to May 2023, temperature and salinity (only until March 2023) data were logged with a SEABIRD SBE 37-SMP MicroCAT CT in 2-minutes intervals at GEOMAR (Kiel, Germany) pier at 54°19'48.8N, 10°08'59.6E. The sensor system is mounted to a floating platform to ensure a continuous depth of 1 m at any time. After cleaning and other re-boots of the sensor package, temperature and salinity data tend to deviate from true values. Hence, 60 minutes of data after any re-boot (after sensor servicing with re-deployment, data download or power failure) were deleted. Due to massive fouling the conductivity sensor caused false salinity data during the last two months of this measurement period which were, hence, also deleted from the data set.
From June 2022 to May 2023, seawater temperature and salinity data were measured repeatedly by a hand-held salinity probe (WTW Handheld ProfiLine Multi 3320 with conductivity measuring cell TetraCon 325) at GEOMAR (Kiel, Germany) pier at 54°19'48.8N 10°08'59.6E. The seawater was continuously pumped from 1m depth to a container on the 'Kiel Outdoor Benthocosm' (KOB) platform in which the measurement took place. The sensor was calibrated prior to each measurement.
The dataset contains temperature, salinity, oxygen, velocity, chlorophyll and turbidity data from the stationary underwater fish observatory (UFO). The stationary UFO was deployed at 54°20.4375'N, 10°10.4463'E from 2021/03/05 to 2022/05/18 about 50 m from the eastern shore of the Kiel Fjord, at a depth of 6 m. The abiotic sensor instrumentation consists of an upward looking acoustic Doppler current profiler (ADCP; Teledyne Workhorse Sentinel 1200 kHz), a pumped conductivity, temperature, and depth sonde (CTD; Sea Bird Scientific MicroCAT) and a combined fluorometer and turbidity sensor (Sea Bird Scientific ECO FLNTUS). All sensors were placed ~1.0 m above the seafloor. Time series data for ADCP, CTD and fluorometer were downloaded and preprocessed to obtain average estimates at a frequency of 1 h. To guarantee the high quality of the measurements and the data output, the sensors are regularly serviced. After each survey, back in the laboratories, the raw data collected at sea are first checked for consistency, and then processed and calibrated according to international standards. To verify and calibrate the T, S, O2, CHL, and Turb data, a vertical CTD profile was measured fortnightly close to the two UFO sites. Additional water samples were taken to determine oxygen levels using the Winkler method and to determine Chlorophyll levels to calibrate the fluorometer.
From January 2020 to January 2022, temperature, salinity, and oxygen (only July 2020 - April 2021) data were logged with an AANDERAA oxygen sensor 3835 and a SEABIRD SBE 37-SI MicroCAT CT(D) in 10-minutes intervals at GEOMAR (Kiel, Germany) pier at 54°19'48.8N 10°08'59.6E. The sensor system is mounted to a floating platform such that a continuous depth of 1 m is ensured at any time. Oxygen data were corrected for salinity, temperature and depth following the manual for Aanderaa Optodes using the salinity and temperature measurements from the SEABIRD SBE 37-SI MicroCAT CT(D) sensor. After cleaning and other re-boots of the sensor package, temperature, salinity and oxygen data tend to deviate from true values. Hence, 60 minutes of data after any re-boot (after sensor servicing with re-deployment, data download or power failure) were deleted. Two major data gaps (January 2020 – July 2020, April 2021 – June 2021) are due to longer periods when the sensors were serviced in the workshop.
From January 2020 to October 2021, seawater temperature and salinity data were measured repeatedly by a hand-held salinity probe (WTW Handheld ProfiLine Multi 3320 with conductivity measuring cell TetraCon 325) at GEOMAR (Kiel, Germany) pier at 54°19'48.8N 10°08'59.6E. The seawater was continuously pumped from 1m depth to a container on the 'Kiel Outdoor Benthocosm' (KOB) platform in which the measurement took place. The sensor was calibrated prior to each measurement.
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