Dense shelf-water and associated sediment transport in the Cap de Creus Canyon and adjacent shelf under mild winter regimes: insights from the 2021–2022 winter

Abstract. This study examines dense shelf water cascading (DSWC) and estimates the dense shelf-water and associated sediment transport in the Cap de Creus Canyon (northwestern Mediterranean) during the mild winter of 2021–2022. The FARDWO-CCC1 multiplatform survey in March 2022 revealed dense shelf waters on the continental shelf, which were transported to the canyon head. These cold, dense, and turbid waters, rich in dissolved oxygen and chlorophyll-a, downwelled along the canyon’s southern flank to depths around 350 m. During the observed downwelling event, estimated water and suspended sediment transport within the dense water vein were 0.3 Sv and 10⁵ metric tons, respectively, mainly confined to upper canyon reaches. These transports were low compared to extreme winters, likely due to the influence of freshwater inputs and moderate meteorological winter conditions. Transport magnitudes were higher in the upper canyon section than in the mid-canyon section, where transport was estimated at 0.05 Sv, including around 10⁴ metric tons of sediment. This observation suggests that during mild winters, while most of the dense water either remains on the shelf or the shelf-edge area, or flows southward along the coast, the Cap de Creus Canyon acts only as a partial sink for cascading waters. Mediterranean Sea Physics reanalysis data showed that the cascading season lasted approximately three months, from January to early April 2022, with several cascading pulses within the canyon. The highest dense shelf water transport occurred in mid-March, associated with easterly/south-easterly windstorms. This study confirms that remarkable dense shelf water and sediment transport occurs in the Cap de Creus Canyon, particularly along its southern flank, even during mild winters in absence of deep cascading and limited external forcing. Nevertheless, this phenomenon appears to make a significant contribution to the formation of Western Intermediate Water (WIW) in the region.