A multi-decadal assessment of Adriatic dense water dynamics at kilometer-scale

The focus of this study is the North Adriatic dense Water (NAddW), which forms in the Adriatic Sea during extreme winter cooling under hurricane-strength bora winds. NAddW plays a critical role in driving the thermohaline circulation, ventilating the deep layers, and influencing the biogeochemical properties of the Adriatic. Modeling the properties of this water mass at the climate scale presents significant challenges due to the complex coastal geomorphology of the Adriatic basin, which is inadequately represented by existing climate models. To address these challenges, the Adriatic Sea and Coast (AdriSC) kilometre-scale atmosphere-ocean climate model was used. This model consists of the Weather Research and Forecasting (WRF) model, with resolution of up to 3 km, and the Regional Ocean Modelling System (ROMS), with resolution of up to 1 km.

The 1-km results of a 31-year AdriSC simulation (1987–2017) were used to analyze the main phases of NAddW dynamics: generation, spreading, and accumulation. Regarding generation, NAddW densities are higher on the shallow northern Adriatic shelf compared to the deeper Kvarner Bay, driven by a median bottom temperature difference of 2°C. Notably, about one-third of the dense water is generated within the Kvarner Bay. In terms of spreading, NAddW mass transport peaks between February and May across most of the Adriatic, except along the western side of the Otranto Strait. Analyses of accumulation sites revealed that the bottom layer of the Kvarner Bay renews annually, whereas renewal occurs every 1–3 years in the Jabuka Pit and every 5–10 years in the deep Southern Adriatic Pit. Lastly, NAddW cascading and accumulation is more pronounced during basin-wide high-salinity conditions driven by circulation changes in the northern Ionian Sea. This three-decade kilometre-scale assessment provides a long-term overview of the Adriatic bottom thermohaline properties, aligning well with existing literature, which predominantly relies on observational studies.