Short Cruise Report, RV ATAIR, Cruise 067I041-1, Bremerhaven – Thybor?n – Aberdeen, 22 Jul – 14 Aug 2025 5 2. Scientific Tools & Methods The scientific tools used during the cruise included profiling of the entire water column using a Conductivity-Temperature-Depth (CTD) unit of type SBE9/11 equipped with two sets of T/C sen- sors that was attached to a carousel water sampler system of type SBE32. Additional sensors on the CTD-unit included a SBE43 sensor to measure dissolved oxygen, a transmission sensor to measure turbidity and fluorescence, and an altimeter of type Valeport to determine the distance of the underwater unit from the sea bottom in order to avoid contact. The carousel water sampler was fitted with a varying number of 10 L Niskin bottles and occasionally a 10 L GoFlo bottle. The latter did not properly work during the cruise until arrival in Thybor?n/DK. Water samples were taken from the near-bottom and the near-surface (5 and 10 dbar) and sampling levels in-between depending on the water depth. Water sampling served to determine concentrations of salinity, density, chlorophyll-A, plankton, dissolved inorganic carbon (DIC), alkalinity, nutrients, and various trace metals (see station list in Table 5). Chlorophyll-A and plankton sampling was limited to stations visited during daylight as the sample processing required knowledge of the Secchi depth, which was estimated from low- ering a Secchi disc. Water sampling with respective to estimating the concentrations of the radi- onuclides cesium-137 (137Cs), strontium-90 (90Sr) and tritium (3H) was limited to the surface wa- ters of a predefined number of stations between Bremerhaven and Thybor?n (southern to central North Sea). Sampling for radionuclides based on water samples was not continued afterwards. On the second leg of the cruise, between Thybor?n/DK and Aberdeen/UK, pesticide sampling was carried out using an air sampler and a water sampler system. The latter system was used on typically two to three stations per section across the North Sea, the air sampler along a number of transects (see Table. 4). Salinity samples were analysed already during the cruise using a salinometer in order to check sensor performance. Also, samples for DIC and alkalinity were also analysed during the cruise using a VINDTA system. Water samples for other parameters were prepared for storage and conserved for laboratory analysis at home through e.g. freezing. In total, 114 stations were conducted using the CTD/water sampler system (Figure 1 and Table 5). Three of them were visited twice, before and after the port stay in Thybor?n/DK. A vessel-mounted Acoustic Doppler Current Profiler (vmADCP) system operating at 150 kHz in narrow-band mode provided upper water column velocity data during the cruise. Further on-board measurements focused on standard meteorological data, water depth on the station locations and along the cruise track, near-surface values for water temperature, salinity, fluorescence/chloro- phyll and turbidity, and finally automatic standard on-board sampling for air chemistry and radio- nuclides. Filtration of surface waters on transects between stations was carried out in order to estimate the polymer type, size and number concentration of microplastics in the surface layers (see Table 3). Four surface drifters were deployed on behalf of the University of Oldenburg, Institute for Chem- istry and Biology of the Marine Environment (ICBM), in order to reveal regional details of the surface circulation (Table 2). Oceanographic data analysis will be carried out together with national and international collabo- rators as part of BSH’s contribution to the international Working Group on Oceanic Hydrography