Short Cruise Report, RV ATAIR, Cruise 067I041-1, Bremerhaven – Thybor?n – Aberdeen, 22 Jul – 14 Aug 2025 3 1. Purpose of the Cruise & Research Objectives Cruise 067I041-1 with RV ATAIR served to carry out the annual large-scale North Sea Summer Survey (NSSS) on behalf of the Federal Maritime and Hydrographic Agency of Germany (BSH). Surveys similar to cruise 067I041-1 have been conducted by the BSH every year since 1998. These surveys generally follow a predefined net of standard stations forming zonal sections across the North Sea at different latitudes between 54°N and 60°N. Additional stations located to the south of 54°N form a loop-like station pattern extending to about 52°N near the southern entrance to the North Sea. In addition, two survey lines located to the west and east of the Orkney and Shetland Islands cover the inflow of Atlantic Water into the North Sea. The cruise is typically interrupted at halftime in order to allow for a crew and team change. The North Sea Summer Survey of 2025, cruise 067I041-1, started in Bremerhaven, Germany, on 22 July 2025, led to Thybor?n, Denmark, with a port stay in the period 03 to 06 August, and ended in Aberdeen, UK, on 14 August 2025 (see Fig. 1). The annual North Sea Summer Survey is usually carried out at or near the time when maximum stratification and phytoplankton productivity are expected to have passed their peak. The primary objective of cruise 067I041-1 is to assess the physical and chemical state of the North Sea in the summer of 2025, using data collected during the cruise. Large-scale data will be used to investi- gate the hydrographic state of the water column in different regions of the North Sea. Furthermore, temporal hydrographic changes will be addressed, which will become apparent when the data are put into context with data from previous cruises. Sampling water for radionuclide analysis is part of the BSH’s standard monitoring of radioactive contamination in the North Sea. This is based on several legal and regulatory provisions, as well as the corresponding requirements for fulfilling them. The sampling will assess spatial changes in the concentrations of these radionuclides, as well as changes over time compared to previous cruises. For the purpose of the cruise the BSH team has been joined by members from the Helmholtz Centre Hereon in Geesthacht, Germany. The Hereon group addresses three topical foci during cruise 067I041-1: carbonate system dynamics, trace metal dynamics and microplastic distribu- tions in the North Sea basin. Another cruise participant affiliated with both, the Max-Planck-Institute for Chemistry (MPIC), Mainz, Germany, and the Research Centre for Toxic Compounds in the Environment (RECETOX), Brno, Czech Republic, joined the cruise after a crew change in Thybor?n in order to analyse pesticides in air and water in the central to northern North Sea en route from Thybor?n/DK to Aberdeen/UK. Specific objectives related to cruise 067I041-1 addressing the state of the North Sea in the sum- mer of 2025 are the following: ? How far south does the Atlantic Water (AW) that enters the North Sea at its northern boundary spread in the summer of 2025? ? Where is the main inflow of AW into the North Sea in summer 2025? ? How far north does the AW entering the southern North Sea via the English Channel penetrate northwards in summer 2025?