Multiplatform and multidisciplinary observational approach to coupled atmospheric-coastal ocean processes in the southeast Bay of Biscay

Euskoos, the coastal observatory of the southeast Bay of Biscay, has been operational for over 15 years, collecting data on various physical variables in the region. Recent initiatives aim to develop an enhanced multidisciplinary observatory that can address critical needs related to the sustainable management of this coastal area and the challenges related to global change. Available observation infrastructures include a high-frequency radar system, a network of buoys, coastal and videometry stations, two gliders, and two autonomous surface vehicles equipped with biogeochemical and biological sensors. These technologies, combined with metocean models and satellite data, enable detailed study of small-scale coastal ocean processes and their coupling with atmospheric variability. In this presentation, we will analyze different data from recent glider campaigns in the southeast Bay of Biscay. Observations include sub-mesoscale processes such as coastal downwelling due to an intense storm and the exceptional extension of the Adour River plume to the east under the influence of northern winds.

In October 2022, a glider mission covered a storm event, collecting data on temperature, salinity, current velocity, and acoustic information on pelagic fish and vertebrates. During the storm, western winds reached velocities up to 17 m/s, and surface currents ranged between 20 and 65 cm/s, partially oriented toward the coast. The glider's salinity and temperature profiles showed a downlift of isopycnals by approximately 20 m in the near-surface water masses at the shelf-break. After the storm, the temperature and salinity profiles gradually returned to their initial state after five days. In November 2023, a second glider mission revisited the area and measured temperature, salinity, turbidity, chlorophyll-a (Chl-a), dissolved oxygen (DO), colored dissolved organic matter (CDOM), and nitrates. The glider monitored the Adour River plume with high spatiotemporal resolution. During the mission and under norther winds, maximum surface currents measured by the HF radar reached 74 cm/s, promoting the westward extension of the river plume, visible in satellite SST and Chl-a maps.

Better understanding the mechanisms of rapid coupling between atmospheric and oceanic processes in the coastal zone is vital for improving the prediction of currents, hydrographic conditions, and their effect on surface transport, or water mass exchanges, or biogeochemical cycles.