Synoptic hydrographic monitoring across the Kongsfjorden–Krossfjorden system and the Fram Strait: five-year time series from the Italian Arctic Marine Observing System

Abstract. Arctic fjords represent highly dynamic interfaces between the open ocean, the cryosphere, and terrestrial freshwater sources, where climate driven changes in heat, freshwater, and circulation are rapidly emerging. Here we present a five-year (2020–2025) oceanographic dataset from the Italian Arctic Marine Observing System, providing continuous moored observations across the Kongsfjorden–Krossfjorden fjord system and offshore the South Cape in the eastern Fram Strait off Svalbard. The marine observing system integrates four mooring sites with different hydrographic properties, delivering high-resolution time series of temperature, salinity, and ocean current both in the fjord, on the continental shelf and along the continental slope. The dataset is fully quality controlled following standardized procedures, ensuring long-term comparability across deployments. Thermohaline properties are used to classify water masses and characterize seasonal to interannual variability. The observations reveal contrasting regimes, with relatively stable deepwater offshore conditions and highly variable fjord environments governed by atmospheric forcing, freshwater input from glaciers, and shelf–fjord exchange processes. Episodic intrusions of Atlantic origin waters are detected at both fjord entrance and inner fjord sites, providing direct observational evidence of Atlantification processes. Owing to its temporal resolution, vertical coverage, and spatial distribution, the dataset supports a broad range of scientific and operational applications. The dataset is openly available through the Italian Arctic Data Center and fully compliant with FAIR (Findable, Accessible, Interoperable and Reusable) principles, contributing to sustained Arctic observing efforts and long-term assessments of Arctic–Atlantic interactions relevant to Arctic Ocean circulation and the Atlantic Meridional Overturning Circulation.