Cruise Report, RV ATAIR, Cruise 067I033-1, Bremerhaven – Thybor?n – Aberdeen, 23 Jul – 15 Aug 2024 11 5. Scientific Tools & Methods 5.1 Overview Scientific tools that were in use during the cruise comprised profiling of the entire water column using a Conductivity-Temperature-Depth (CTD) unit attached to a carousel water sampler sys- tem and equipped with a number of sensors that will be detailed in the following sections. Additional sensors attached to the CTD-unit involved a sensor measuring dissolved oxygen, a dual-wavelength sensor measuring simultaneously both turbidity and fluorescence, and an al- timeter for determining the distance of the underwater unit to the sea bottom in order to avoid contact. The carousel water sampler was equipped with a fixed number of 10 L sampling bottles to allow for taking water samples at discrete depths of the water column. Water sampling activi- ties consisted of taking oxygen and salinity samples for the sake of calibrating the conductivity and oxygen sensors of the CTD unit. Further water samples addressed analysing water den- sity, chlorophyll-a and phytoplankton, dissolved inorganic carbon (DIC), nutrients, trace metals including mercury and lead for shore-based laboratory analyses. In total, 92 stations involving the CTD/water sampler system were carried out. Secchi depth determination, water sampling for chlorophyll-a and phytoplankton were only performed on daylight stations. A vessel-mounted Acoustic Doppler Current Profiler (VMADCP) system operating at 150 kHz and in narrow-band mode delivered oceanic velocity data of the upper water column during the cruise. Further underway measurements focused on standard meteorological data, water depth, near-surface values for water temperatures, salinity, fluorescence/chlorophyll and tur- bidity. An inert filtration cascade connected to the vessel’s clean seawater system was active along several transects to obtain particulates in surface water for shore-based laboratory anal- ysis of microplastics. 5.2 CTD Sensor Unit & Water Sampler Setup During cruise 067I033-1 a profiling conductivity-temperature-depth (pressure) sensor unit (CTD) of type Sea-Bird Electronics (SBE) 9plus (“CTD Sonde S6”) was in use. It was operated and powered from out of the vessel’s hydrography lab via a deckunit of type SBE11plus. The CTD sensor package was mounted horizontally in the lower part of a water sampler frame (K7) of type SBE32 potentially carrying up to 12 Niskin bottles of 10 L volume. The corresponding bottle release module is suitable for 24 bottles. Starting with position 1, every second bottle release position was chosen when closing any water sampler bottles. In addition to a set of Niskin bottles, the water sampler was equipped with one 10 L PTFE-coated Go-Flo bottle that was used for sampling of dissolved trace metals. All devices and sensors that were in use are listed in Table 5.1; the water sampler bottle set-up is listed in Table 5.2. The recording of the