Multi-scale ocean variability in the Ibiza Channel over 14-year repeated glider missions

Melanie Juza^1*Emma Heslop²Nikolaos D. Zarokanellos¹Joaquín Tintoré^1,3

• ¹Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB), Palma de Mallorca, Spain
• ²Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO), Paris, France
• ³Mediterranean Institute for Advanced Studies, Spanish National Research Council (CSIC), Esporles, Spain

The increasing capability of multi-platform observing systems has enabled the better understanding of the wide-ranged spatio-temporal ocean variability and its implications for ocean biogeochemistry and marine life. The Ibiza Channel, located in the western Mediterranean Sea, is a well-established hotspot of ocean warming and biodiversity, and where high (sub-)mesoscale variability with impacts on marine ecosystems takes place. In this context, the Balearic Islands Coastal Observing and Forecasting System (SOCIB) has been operating glider missions in the Balearic Channels through a quasi-continuous endurance line called "Canales" since 2011. In this study, the importance of high-resolution monitoring along a sustained observation line at a key choke point has been demonstrated. A glider-adapted methodology has been implemented to compute geostrophic velocities from hydrographic profiles in the Ibiza Channel. Northward and southward transports of the total and water mass flows are then derived across each transect. Their seasonal variability is well captured across the Ibiza Channel with major southward flow in winter-spring and northward flow in late-summer. During the period 2011-2024, high temporal variability is also observed and explained through the analyses of regional circulation and water mass dynamics such as the inflow of recent Atlantic Water or the southward propagation of recently formed Western Intermediate Water and Western Mediterranean Deep Water. Also, 14-year glider data have well captured the regional interannual variability and long-term trends in response to climate change. Warming and salinification have been observed for all water masses from surface to deep layers except for the Atlantic Water of recent origin showing a decreasing salinity trend. Sustainable and highresolution monitoring of the ocean is crucial to better understand the processes involved in the ocean variability at different spatio-temporal scales, as well as the impact of climate change and human activities particularly in coastal areas and thus to respond to worldwide societal challenges.