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High-resolution measurements of essential climate variables in the North Sea from the autonomous surface vehicle HALOBATES during RV Heincke cruise HE626

The autonomous surface vehicle HALOBATES collected key climate variables, including sea surface temperature (SST) and salinity (SSS), during the RV Heincke cruise HE626 in the German Bight. HALOBATES recorded SST and SSS at seven different depths with a high vertical resolution of approximately 10 cm, ranging from the near-surface layer (NSL) (between 30 and 100 cm) to the sea-surface microlayer (SML) (uppermost millimeter). Temperature and conductivity (used for salinity calculation) were measured using conductivity, temperature, and depth (CTD) sensors connected to a flow-through system on HALOBATES. Additional temperature sensors were placed beneath the catamaran to capture in-situ temperature at six depths within the NSL. Salinity measurements were adjusted using discrete water samples to correct for any sensor biases. During the operation, two data loggers equipped with meteorological stations on the catamaran monitored essential weather conditions. HALOBATES was in operation from July 21, 2023, to August 8, 2023.

Microscale profiles of oxygen, pH and temperature through the sea surface microlayer in a mesocosm experiment during an algal bloom

The sea surface microlayer (SML) is the boundary layer on top of all oceans and is crucial for all exchange processes between the ocean and atmosphere. This less than 1 mm thick layer is heavily influenced by biological processes and events like algal blooms. To quantify the influence of an algal bloom in a controlled environment, we conducted a mesocosm study at the Sea sURface Facility (SURF) of the Institute for Chemistry and Biology of the Marine Environment (ICBM) in Wilhelmshaven, Germany (53.5148 °N, 8.1463°E). SURF is an 8.5 m long, 2 m wide and 1 m deep water basin, which can directly be filled with seawater from the Jade Bay, North Sea. The facility is equipped with a retractable roof, pumps for water circulation and dedicated mounts for multiple sensor systems. The mesocosm experiment was conducted from 18 May to 16 June 2023 as part of the project BASS (Biogeochemical processes and Air-sea exchange in the Sea-Surface microlayer). SURF was filled with seawater a few days before the start of the experiment (water depth 0.7 m). The water was then filtered and the surface skimmed to remove initial pollution. To prevent particle and microbial sedimentation during the experiment, the pumps operated at low speed to maintain gentle mixing of the water column. The roof of SURF was closed during the night, while it was open during the day except when it rained. To induce an algal bloom, a mix of nutrients (nitrogen, phosphorus and silicate) was added on 26 May, 30 May and 01 June. Based on the chlorophyll measurements which show the development of the bloom, three phases of the experiment were determined: the pre-bloom phase (18 May to 26 May), the bloom phase (27 May to 04 June) and the post-bloom phase (05 June to 16 June). Several physical, chemical and biological parameters were measured, which will be published in other datasets. To evaluate the impact of the algal bloom within the SML, oxygen concentration, pH, and temperature were measured in situ using microsensors (UNISENSE, Denmark) mounted on a MicroProfiling System (UNISENSE, Denmark). With this setup, direct in situ measurements inside both the thermal boundary layer and diffusion boundary layer at the sea surface can be made. One oxygen microsensor, two pH microsensors and three temperature microsensors were mounted on the microprofiler with their tips pointing upward to avoid disturbance in the SML. They were positioned a few centimeters apart. The microprofiler was used to automatically move the sensors down, from the air through the SML and into the underlying water over a total distance of 10 000 µm in steps of 125 µm (250 µm at the start of the experiment). At each depth, the sensors stayed for about 10 s, giving a mean value and a standard deviation over that time. Three of these measurements were taken at every depth before the sensor moved down to the next step. After completing a profile, the microprofiler returned to its initial position with the tips in the air to start the next profile. The resulting profiles mostly took between 40 to 50 minutes. These profiles were conducted continuously during day and night, except for small breaks to clean and if needed replace or readjust the sensors and recalibrate the pH sensors. The sensors' height required manual adjustment to position the tip precisely at the water surface (0 µm). Through this manual adjustment, small inaccuracies may occur. As a result, the sensor depth readings form the microprofiler system may not reflect the true sensor position, which can also vary between the sensors. The true sensor positions can later be obtained by analysing the measured profiles.

Biogeochemical variables from a Multidisciplinary BASS Mesocosm Study at Wilhelmshaven, 2023

This dataset contains biogeochemical variables measured during the same mesocosm experiment at Sea Surface Facility (SURF) in Wilhelmshaven, Germany (53.5148° N, 8.1461° E) in 2023. Variables include surfactants and nutrient concentrations, chlorophyll a, pigments, particulate and dissolved organic carbon and nitrogen, and several other biogeochemical parameters. These data complement the daily averaged physical parameters (PANGAEA DOI: https://doi.pangaea.de/10.1594/PANGAEA.983975) and together support the assessment of ecosystem and biogeochemical dynamics associated with the experiment, as described in the related publication Bibi et al., 2025.

Daily averaged physical parameters from the Multidisciplinary BASS Mesocosm Study at Wilhelmshaven, 2023

This dataset contains daily averaged physical and chemical parameters measured during a mesocosm experiment conducted at Sea Surface Facility (SUR) in Wilhelmshaven, Germany (53.5148° N, 8.1461° E) in 2023. Parameters include daily average air temperature, Daily Average Incoming Solar Irradiance, Daily Average Reflected Solar Irradiance, and Daily Average Albedo derived from in situ measurements. The dataset provides an overview of environmental conditions throughout the experiment, supporting the interpretation of biogeochemical and ecological processes described in the related publication Bibi et al., 2025.

Physical, chemical, and biogeochemical parameters from a mesocosm experiment at the Sea Surface Facility (SURF), Wilhelmshaven, Germany, spring 2023

This collection (bundled publication) includes datasets from a mesocosm experiment conducted in spring 2023 at the Sea Surface Facility (SURF), Wilhelmshaven, Germany (53.5148° N, 8.1461° E). The experiment initiated a phytoplankton bloom under controlled conditions to examine surface ocean biogeochemistry and sea-surface microlayer (SML) processes. Daily samples were collected from the SML and underlying water (40 cm depth) and analyzed for physical, chemical, and biological parameters. Measurements include meteorological conditions (air temperature, solar irradiance, and albedo), surfactants, nutrients, pigments, particulate and dissolved organic carbon and nitrogen, and additional biogeochemical variables. These datasets provide environmental and biogeochemical context supporting studies on surface ocean processes and are described in detail in the related publication Bibi et al. (2025).

High concentrations of ciprofloxacin reduced bacterial abundance and enrichment in the sea surface microlayer (SML) and underlying water (ULW) and exerted selective pressure on marine bacteria

The sea surface microlayer (SML) of marine environments is hostile, exposing bacteria to extreme conditions such as temperatures and salinity fluctuations, solar radiation, and the presence of toxic substances such as heavy metals, microplastics, and pharmaceutical compounds. Our study focused on investigating the ecotoxicological effects of varying ciprofloxacin concentrations (0, 10, 50, and 100 ng/ml) on bacterial abundance and enrichment in natural SML and underlying water (ULW) samples obtained from the southern North Sea. In addition, we analyzed the samples for the presence of ciprofloxacin and 25 other antibiotics, including lincomycin, clindamycin, clarithromycin, erythromycin, azithromycin, ofloxacin and novobiocin. Furthermore, we carried out antibiotic susceptibility tests on marine bacterial isolates cultivated in the presence of 100 ng mL ⁻¹, utilizing antibiotics commonly found in their natural habitats. We observed a decrease in bacterial abundance and enrichment in the SML and ULW when exposed to 50 and 100 ng/ml of ciprofloxacin. However, over time, the abundance and enrichment of bacteria increased at these concentrations, indicating resistance. The presence of 100 ng/ml of ciprofloxacin also exerted selective pressure on bacterial members in the SML and ULW, and we cultivated 42 marine and 55 nonmarine bacteria in the presence of 100 ng/ml of ciprofloxacin. Although ciprofloxacin was not detected, we found 11 other antibiotics, particularly in the SML. When we exposed marine bacteria to antibiotics such as novobiocin, ofloxacin, clarithromycin, erythromycin, and clindamycin found in the environment, we observed that some marine bacteria are resistant to these antibiotics. Our findings suggest that resistance in marine bacteria can be acquired through exposure to antibiotics released into coastal water bodies.

High-resolution measurements of essential climate variables in the North Sea from the autonomous surface vehicle HALOBATES during RV Heincke cruise HE614

The autonomous surface vehicle HALOBATES measured Essential Climate Variables (ECV), such as sea surface temperature (SST) and salinity (SSS), during the RV Heincke cruise HE614 in the German Bight. HALOBATES captured the SST and SSS at seven depths with a high vertical resolution of about 10 cm, from the near-surface layer (NSL) (between 30 and 100 cm) and the sea surface microlayer (SML) (upper millimeter). Conductivity, temperature, and depth (CTD) sensors measured temperature and conductivity (for salinity calculation) via a flow-through system on HALOBATES. Additional temperature sensors were mounted underneath the catamaran to measure in-situ temperature in situ at six depths in the NSL. Salinity was corrected with discrete water samples to remove biases between the sensors. Two data loggers with several meteorological stations on the catamaran captured important weather variables during operation time. The surfactant concentration was measured from discrete samples of SML and 100 cm depth. HALOBATES was operated between 01 March 2023 and 22 March 2023.

Distribution of pharmaceutical compounds in coastal waters of the North Sea in March 2023

We investigated the occurrence, spatial, and vertical distributions of 63 pharmaceutical compounds and six artificial sweeteners from the sea surface microlayer (SML) to five different depths (0 cm, 20 cm, 50 cm, 100 cm, and 150 cm) of the corresponding underlying waters in four stations of the North Sea. One station is a coastal area (Jade Bay), one station is an estuary (Bremerhaven), and the other two stations (NS_7 and NS_8) are open coastal waters. We will refer to each environment with the name in brackets throughout this publication. We collected seawater samples vertically from these stations and analyzed them using ultra-performance liquid chromatography - triple quadrupole mass spectrometry in tandem with ionization spray (UPLC-QqQMS/MS) (Bruker EVOQ Elite system Bruker, USA) at the Department of Physical Chemistry, University of Cádiz.

High-Resolution Measurements of Essential Climate Variables in the Harbor of Bremerhaven from the Autonomous Surface Vehicle HALOBATES during RV Heincke Cruise HE614

The autonomous surface vehicle HALOBATES measured Essential Climate Variables (ECV), such as sea surface temperature (SST) and salinity (SSS), during the RV Heincke cruise HE614 in the harbor of Bremerhaven. HALOBATES captured the SST and SSS at six depths with a high vertical resolution of about 10 cm, from the near-surface layer (NSL) (between 30 and 100 cm) and the sea surface microlayer (SML) (upper millimeter). Conductivity, temperature, and depth (CTD) sensors measured temperature and conductivity (for salinity calculation) via a flow-through system on HALOBATES. Additional temperature sensors were mounted underneath the catamaran to measure in-situ temperature at six depths in the NSL. Salinity was corrected with discrete water samples to remove biases between the sensors. Two data loggers with several meteorological stations on the catamaran captured important weather variables during operation time. HALOBATES was operated on 14 and 15 March 2023.

Analysis of antibiotics in environmental samples

Due to its location at the air-sea interface, the sea surface microlayer is prone to accumulating anthropogenic pollutants. We analyzed the presence of antibiotic compounds, including ciprofloxacin, in this area using ultra-performance liquid chromatography—triple quadrupole mass spectrometry in tandem with ionization spray (UPLC-QqQMS/MS) (Bruker EVOQ Elite system, Billerica MA). We compared the numbers and concentrations of these compounds in the microlayer to those found in the underlying water column.

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