Temporal and Spatial Hydrodynamic Variability in the Mallorca Channel (Western Mediterranean Sea) From 8 Years of Underwater Glider Data

Abstract

AbstractEight years of glider data are used to characterize the temporal and spatial variability of a region in the western Mediterranean that will constitute one of the targets for the calibration phase of the Surface Water and Ocean Topography (SWOT) satellite mission. The characteristic horizontal dimension of mesoscale instabilities in the Mallorca channel is 6.0 km. The temporal evolution of intermediate water masses is dominated by an increase over time of the characteristic temperature values. Western Mediterranean and Levantine Intermediate waters display an increase of the temperature extrema of 0.064 ± 0.002 and 0.044 ± 0.002 °C/year between 2011 and 2018, respectively. At the layer of Levantine Intermediate water the salinity temporal regression reveals a mean trend of 0.010 year−1. Temperature annual cycle shows an averaged temperature gradient of ∼6 °C in 6 months at the upper layer, with a disconnection with the annual cycle at 100‐m depth. The circulation across the channel is dominated by high‐frequency variability. The signature of eddies with radius ranging from 5 to 18 km is apparent in 16% of the transects analyzed and mainly in spring and summer, with a dominance of subsurface cyclonic eddies. Two‐way flow controls the annual cycle of the water transport through the channel with prevalence of the inflow of Atlantic water. Variations of water transport over timescales of weeks to months can be similar to those identifiable as seasonal changes.