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Colored dissolved organic matter (CDOM) absorption coefficients in the sea-surface microlayer and the underlying water during a mesocosm phytoplankton bloom in 2023

The effects of a phytoplankton bloom and photobleaching on colored dissolved organic matter (CDOM) in the sea-surface microlayer (SML) and the underlying water (ULW) were studied in a month-long mesocosm study, in May and June of 2023, at the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany. The mesocosm study was conducted by the DFG research group BASS (Biogeochemical processes and Air–sea exchange in the Sea-Surface microlayer, Bibi et al., 2025) in the Sea Surface Facility (SURF) of the ICBM. The facility contains an 8 m × 1.5 m × 0.8 m large outdoor basin with a retractable roof, which was closed at night and during rain events. The basin was filled with North Sea water from the adjacent Jade Bay. Homogeneity of the ULW in the basin was achieved by constant mixing of the water column. The daily SML and ULW samples were collected alternating in the morning, about 1 h after sunrise, and in the afternoon, about 10 h after sunrise. The alternation of sampling times intended to capture a potential effect of sun-exposure duration on DOM transformations and elucidated the day and night variability of the layers. The SML was collected via glass plate sampling (Cunliffe and Wurl, 2014). The ULW was sampled via a submerged tube and a connected syringe suction system in 0.4 m depth. The removed sample volume was refilled with Jade Bay water every day. SML and ULW samples were filtered through pre-flushed 0.7 µm Whatman GF/F and 0.2 nucleopore filters into brown bottles and were stored dark and at 4 °C until measurement within weeks of the study. The brown bottles were previously combusted at 500 °C. CDOM was measured with three liquid waveguide capillary cells (LWCC, WPI, USA) of different pathlengths (10 cm, 50 cm, 250 cm) to increase the measurement sensitivity following the protocols of Röttgers et al. (2024) using a spectral detector (Avantes, Netherlands) for a total spectral range from 230 to 750 nm. A sodium chloride (NaCl) solution was used for the salinity correction. The blank-corrected absorbance spectra were then converted into Napierian absorption coefficients (Bricaud et al., 1981).

Carbonate chemistry parameters calculated from measured pH, total alkalinity, salinity and temperature in the exposure mesocosms of a chronic Ostrea edulis alkalinity-enhancement exposure experiment

This dataset contains calculated carbonate chemistry parameters, including the concentrations of dissolved CO2, HCO3-, CO32- and dissolved inorganic carbon, the fugacity and partial pressure of CO2 and the saturation states of aragonite (Ωarag) and calcite (Ωcalc), for the exposure mesocosms. Values were calculated from pH, total alkalinity, salinity and temperature measured between 8 May and 10 July 2024, using the seacarb package (Orr et al., 2018) in R (V. 4.3.2). Measured pH values, which refer to the NBS scale, were first converted to the total scale using the total proton activity coefficient fH of Takahashi et al. (1982), lowering pH by 0.12 to 0.13 units across the measured salinity and temperature range. Calculations used the carbonic acid dissociation constants of Lueker et al. (2000), the bisulfate dissociation constant of Dickson (1990), the hydrogen fluoride constant of Perez & Fraga (1987), total boron after Uppström (1974) and the aragonite and calcite solubility products of Mucci (1983), all evaluated at in situ temperature and salinity. The conversion from the NBS to the total scale carries a residual uncertainty of about 0.01 to 0.02 pH units, because the liquid junction potential between the dilute calibration buffers and seawater is not fully captured by fH. This propagates to an uncertainty of roughly 5 to 15 % in calculated pCO2 and a correspondingly smaller uncertainty in the saturation states.

High-resolution measurements of essential climate variables in the North Sea from the autonomous surface vehicle HALOBATES during RV Heincke cruise HE650

During the RV Heincke cruise HE650 in the German Bight, the autonomous surface vehicle HALOBATES was deployed to obtain high-resolution measurements of key climate variables, including sea surface temperature (SST) and salinity (SSS). The platform sampled the upper ocean across five depths, extending from the near-surface layer (NSL; approximately 30–100 cm depth) to the sea-surface microlayer (SML), which occupies the uppermost millimetres of the ocean. Temperature and conductivity, from which salinity was derived, were measured using conductivity–temperature–depth (CTD) sensors integrated into HALOBATES' flow-through system. Additional temperature sensors mounted beneath the catamaran provided in situ observations at six NSL depths. Discrete water samples were used to calibrate the salinity measurements and account for potential sensor offsets. Meteorological conditions were simultaneously monitored using two data loggers equipped with meteorological stations installed on the catamaran. HALOBATES operated continuously during the deployment on 6th November 2024.

Physical oceanography during ALKOR cruise AL639

Conductivity-temperature-depth profiles were measured using a Sea&Sun CTM2049 CTD during RV ALKOR cruise AL639. The CTD was equipped with duplicate sensors for temperature, conductivity and oxygen. The oxygen sensor (galvanic oxygen micro-sensor (AMT)) was exchanged in the beginning of the year. All other sensors were calibrated in March 2024. The sensors are used throughout the year and no post-cruise calibration is applied. Data were connected to the station book of the specific cruise as available in the DSHIP database. This dataset presents conductivity–temperature–depth (CTD) profiles collected during the research cruise. The data were processed using a custom Python workflow designed to summarize, standardize, and prepare CTD measurements for publication. Raw sensor output files (.TOB format) were parsed using a dedicated reader that extracts header metadata and harmonizes variable naming conventions across all profiles. Quality control procedures included the removal of non-physical values, treatment of missing or malformed entries, and consistency checks across key variables such as pressure, temperature, conductivity, and derived parameters (e.g., salinity and oxygen). Oxygen values were scaled, and salinity values were corrected according to the respective CTD calibration. Sensor channels were standardized and renamed to ensure compatibility with common data standards. Pressure was linearly interpolated to a uniform 1 dbar grid, and all depth-dependent parameters were interpolated accordingly. Maximum recorded pressure was cross-checked against local bathymetry (elevation); in cases of mismatch, profiles were truncated at the maximum depth of the corresponding location. The workflow further includes visual quality control of oxygen saturation, station locations, and vertical profiles of temperature, salinity, and oxygen.

Physical oceanography during ALKOR cruise AL592

Conductivity-temperature-depth profiles were measured using a ADM-CTD SN MOCNET during RV ALKOR cruise AL592. The CTD was equipped with duplicate sensors for temperature, conductivity and oxygen. The oxygen sensor (galvanic oxygen micro-sensor (AMT)) was exchanged in the beginning of the year. The sensors are used throughout the year and no post-cruise calibration is applied. All other sensors of the CTD are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. This dataset presents conductivity–temperature–depth (CTD) profiles collected during the research cruise. The data were processed using a custom Python workflow designed to summarize, standardize, and prepare CTD measurements for publication. Raw sensor output files (.TOB format) were parsed using a dedicated reader that extracts header metadata and harmonizes variable naming conventions across all profiles. Quality control procedures included the removal of non-physical values, treatment of missing or malformed entries, and consistency checks across key variables such as pressure, temperature, conductivity, and derived parameters (e.g., salinity and oxygen). Oxygen values were scaled, and salinity values were corrected according to the respective CTD calibration. Sensor channels were standardized and renamed to ensure compatibility with common data standards. Geographic coordinates were converted from degrees and minutes to decimal degrees to improve geospatial usability. Pressure was linearly interpolated to a uniform 1 dbar grid, and all depth-dependent parameters were interpolated accordingly. Maximum recorded pressure was cross-checked against local bathymetry (elevation); in cases of mismatch, profiles were truncated at the maximum depth of the corresponding location. The workflow further includes visual quality control of oxygen saturation, station locations, and vertical profiles of temperature

Carbonate chemistry parameters calculated from measured pH, total alkalinity, salinity and temperature in the alkalization mesocosms of a chronic Ostrea edulis alkalinity-enhancement exposure experiment

This dataset contains calculated carbonate chemistry parameters, including the concentrations of dissolved CO2, HCO3-, CO32- and dissolved inorganic carbon, the fugacity and partial pressure of CO2 and the saturation states of aragonite (Ωarag) and calcite (Ωcalc), for the alkalization mesocosms. Values were calculated from pH, total alkalinity, salinity and temperature measured between 17 April and 19 June 2024, using the seacarb package (Orr et al., 2018) in R (V. 4.3.2). Measured pH values, which refer to the NBS scale, were first converted to the total scale using the total proton activity coefficient fH of Takahashi et al. (1982), lowering pH by 0.12 to 0.13 units across the measured salinity and temperature range. Calculations used the carbonic acid dissociation constants of Lueker et al. (2000), the bisulfate dissociation constant of Dickson (1990), the hydrogen fluoride constant of Perez & Fraga (1987), total boron after Uppström (1974) and the aragonite and calcite solubility products of Mucci (1983), all evaluated at in situ temperature and salinity. The conversion from the NBS to the total scale carries a residual uncertainty of about 0.01 to 0.02 pH units, because the liquid junction potential between the dilute calibration buffers and seawater is not fully captured by fH. This propagates to an uncertainty of roughly 5 to 15 % in calculated pCO2 and a correspondingly smaller uncertainty in the saturation states.

Schwerpunktprogramm (SPP) 1889: Regional Sea Level Change and Society (SeaLevel), Teilprojekt: Bestimmung von Wärmeänderungen im Ozean durch Kombination von Satellitengravimetrie, Argo und Radaraltimetrie - ROCSTAR

Veränderungen der Ozeanwärme sind eng mit dem Wärmefluss an der Ozean-Atmosphärengrenze verbunden und spielen daher eine wic--htige Rolle bei der Regulierung des Erdklimas. Allerdings weisen in-situ-Messungen immer noch hohe Ungenauigkeiten auf und sind nur in wenigen Regionen in ausreichender Anzahl vorhanden. ROCSTAR wird neue Einsichten in das Energiebudget der Erde durch die verbesserten Schätzungen der ozeanischen Temperatur (T) und des Salzgehalts (S) liefern. Durch die Kombination der geodätischen Raumverfahren mit Argo-Profilen, werden gleichzeitig die Temperatur, der Salzgehalt und regional variierende Meeresspiegelbeiträge ermittelt. Die daraus resultierenden Schätzungen umfassen die gesamte Ozeansäule und die zugehörigen sterischen Änderungen werden sowohl mit dem beobachteten Meeresbodendruck als auch mit den Meeresspiegelanomalien konsistent sein. Vor diesem Hintergrund verfolgt das Projekt folgende Ziele:1. Erhöhung der Genauigkeit der in sich konsistenten T- und S-Felder und Bereitstellung von realistischen Fehlerschätzungen2. Ermittlung der T- und S-Schätzungen in Regionen mit wenigen Beobachtungen und in den Tiefen des Ozeans3. Quantifizierung der Rolle, welche die flachen und tiefen Schichten des Ozeans in der Energiebilanz der Erde und im Meeresspiegel-Budget spielen4. Identifizierung und Untersuchung von Ozeanwärmehotspots und deren Verbindung zum terrestrischen Wasserkreislauf im Südosten Asiens. ROCSTAR wird innerhalb des SPP1189-Schwerpunkts WPA (Ursprung der regionalen Meeresspiegeländerungen) angesiedelt sein. Das Projekt befasst sich mit globalen Beobachtungen, führt aber intensive Untersuchungen im indischen Ozean und Westpazifik durch, welche die Hauptquellen für Feuchtigkeit, Zyklon und Taifun Entwicklung in der südostasiatischen Region darstellen. Darüber hinaus wird ROCSTAR aktiv an den Öffentlichkeitsarbeiten des SPPs teilnehmen und ein konzeptionelles Brettspiel entwickeln, um Nicht-Wissenschaftlern das regionale Meeresspiegelbudget näher zu bringen.

Trachurus trachurus in the Sylt Rømø bight in 2022

Due to changing temperature regimes in the North- and the Wadden Sea, a fish survey in the Sylt Rømø bight (SRB) was established in 2007 for at least ten years. The aim is to investigate the Wadden Sea fish fauna with special interest in changes of migration behavior, species composition and feeding habits. Since 2021 an assessment of the epibenthic species in the net hauls was included. Seven stations are sampled monthly inside the SRB. Two additional stations, one outside the bight, one close to the Danish border are sampled as references four times a year. For sampling a mini bottom trawl, total length 17 m, trawl opening 7 m, height 3 m with a mesh size of 36 mm in the wings, 16 mm in the mid part and 6 mm in the cod end is used. At every station one haul in the water column and another at the bottom are sampled, for 15 minutes at a speed of approximately 2 knots. The data will help to give a more detailed picture of food chains and energy flows inside the Wadden Sea.

Physical oceanography during RV HEINCKE cruise HE689

Conductivity-temperature-depth profiles were measured using a Seabird SBE 911plus CTD during RV HEINCKE cruise HE689. The CTD was equipped with duplicate sensors for temperature (SBE3plus), conductivity (SBE4) and oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer and an altimeter (PSA-916 Teledyne (Benthos)) were mounted to the CTD. Temperature, conductivity and oxygen sensors are calibrated by the manufacturer once a year before being mounted in January. They are used throughout the year and no post-cruise or in-situ calibration is applied. All other sensors are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. Processing of the data including removal of obvious outliers followed the procedures described in CTD Processing Logbook of RV HEINCKE (hdl:10013/epic.47427). The processing report for this dataset is linked below.

Physical oceanography during RV HEINCKE cruise HE678

Conductivity-temperature-depth profiles were measured using a Seabird SBE 911plus CTD during RV HEINCKE cruise HE678. The CTD was equipped with duplicate sensors for temperature (SBE3plus), conductivity (SBE4) and oxygen (SBE43). Additional sensors such as a WET Labs C-Star transmissometer, a WET Labs ECO-AFL fluorometer and an altimeter (PSA-916 Teledyne (Benthos)) were mounted to the CTD. Temperature, conductivity and oxygen sensors are calibrated by the manufacturer once a year before being mounted in January. They are used throughout the year and no post-cruise or in-situ calibration is applied. All other sensors are calibrated irregularly. Data were connected to the station book of the specific cruise as available in the DSHIP database. Processing of the data including removal of obvious outliers followed the procedures described in CTD Processing Logbook of RV HEINCKE (hdl:10013/epic.47427). The processing report for this dataset is linked below.

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