Ten years of continuous monitoring of the EMSO shelf-slope observatory on the western margin of the Southern Adriatic

Since 2012, the shelf-slope observing site of the EMSO regional facility (European Multidisciplinary Seafloor and water column Observatory) along the western margin of the Southern Adriatic has been monitoring the dynamics of the near-bottom water, focusing on two distinct regions – the open slope and the Bari canyon.  Two moorings have been placed at these sites with the aim to investigate the dynamics associated with episodic dense shelf water (DSW) cascading down the slope. The consequential impact on deep-sea morphodynamics, biogeochemical cycles and food webs underscores the critical importance of this investigation. This process is linked to preconditioning processes that occur in the northern Adriatic Sea. The recurrence of cascading events has not been constant over the last decade and their impact has been determined by a detailed analysis of sedimentary processes triggered by the passage of the dense water flow. In the context of the PRIN-PASS project that integrates for the first-time high-resolution sequence stratigraphy with a quantitative assessment of modern sedimentary processes the sediment flux toward the deep Adriatic Pit was quantified by analysing the turbidity signal and the analysis of ADCP backscatter near the sea bottom during the flow pulses providing direct evidence for the active role of density current in bottom reshaping. The different response of the ADCP backscatter gives a qualitative indication of the transported particles. On the open slope, well-defined backscatter signals during flow peaks indicate prevalent resuspension processes that also impact fine sandy sediments. Conversely, in the canyon, lower agreement is attributed to the greater textural heterogeneity of particles. The data analysis has shown that the canyon is the dominant pathway of sediment transfer to the deep basin. Furthermore, it highlights that the hydrodynamic event predominantly responsible for the particle transfer to the deep basin is the DSW cascading, which, although only constituting a mere 1% of the total dataset, is responsible for more than 80% of the total down-slope sediment transfer. X-ray fluorescence (XRF) data from discrete seafloor samples further corroborated these findings highlighting a sediment transport along the Adriatic shelf with a sediment provenance from the Apennines. Moreover, the canyon appears the only sector showing seafloor sediment provenance from the Western Alps suggesting sediment transport up to 1000 km. DSW cascading, which is represented by short-lived current pulses, also contributes to the injection of oxygenated water into the 500-1000 m layer fostering the ventilation of the deep southern Adriatic basin. The activities carried out at the regional EMSO facility provide high-resolution observations of dynamic processes along the continental margin and the moorings represent a unique long-term observatory for assessing the impact of climate change.