PROTEVS-MED field experiments: Very High-Resolution Hydrographic Surveys in the Western Mediterranean Sea

Abstract

Abstract. From 2015 to 2018 four field experiments (7 legs) have been performed in the Western Mediterranean Basin during winter or early spring. The main objectives were the assessment of high-resolution modelling, the observation of mesoscale structure and associated ageostrophic dynamics. Thanks to the intensive use of a towed vehicle undulating in the upper oceanic layer between 0 and 400 meter depth (a SeaSoar), a large amount of very high resolution hydrographic transects (about 10.000 km) have been performed, observing mesoscale dynamics (slope current and its instabilities, anticyclonic eddies, sub-mesoscale coherent vortices, frontal dynamics convection events, strait outflows) and sub-mesoscale processes like stirring, mixed layer or symmetric instabilities. When available, the data were completed with velocities recorded by Vessel Mounted Acoustic Doppler Current Profiler (VMADCP) and by surface salinity and temperature recorded by ThermosalinoGraph (TSG). CTD casts have also been performed giving the background hydrography of the deeper layers when focusing on peculiar objects. In 2017, a free fall profiler (an MVP-200) has been deployed to manage even higher horizontal resolution. The aim of the survey was the dynamics and attention were paid to temperature, salinity and currents. Nevertheless, biological sensors (Chlorophyll a, Turbidity, Dissolved Oxygen etc.) have been opportunely carried out as they are able to provide complementary observations about the circulation. This data set is an unprecedented opportunity to investigate the very fine scale processes as the Mediterranean Sea is known for its intense and contrasted dynamics. It should be useful for modellers (who reduce the grid size below a few hundred meters) and expect to properly catch finer scale dynamics. Likewise, theoretical work could also be illustrated by in situ evidence embedded in this data set. The data are available through SEANOE repository (https://doi.org/10.17882/62352; Dumas et al., 2018).

Thermohaline Structures and Heat/Freshwater Transports of Mesoscale Eddies in the Bay of Bengal Observed by Argo and Satellite Data

“…As the thermohaline structure of eddies largely depends on the sign of background horizontal gradients of thermohaline in the upper ocean (e.g., [23,42]), the annual mean characteristics and its variability of SSS and SST are first shown in Figure 2. The SMOS SSS indicated systematically lower values over the bay compared to the values from the Argo data (Figure 2a,b), primarily due to the well−known difference between the skin salinity from the satellite and the 10−m salinity from Argo [26]. However, both datasets showed very similar SSS patterns, with SSS gradually decreasing from 34.5 psu at the equator to below 32 psu in northern bay, highlighting a consistent negative SSS meridional gradient over the entire bay (Figure 2a,b).…”

“…Also, 40% to 60% of the total SSS variability was caused by the SSS mesoscale variability (Figure 2c,d). The large mesoscale variability of SSS in northern bay may have been possibly caused by the combined influences of the intense eddy activity [14] and the sharp meridional gradient in SSS created by the considerable amount of freshwater into the northern bay [26].…”

“…To overcome this challenge, composite analyses of satellite altimeters and Argo data were recently used to reconstruct the mean structures of eddies in various regions of the global oceans (e.g., [18][19][20][21][22][23][24]). Some recent studies [25,26] explored the eddies' properties through unmanned marine vehicles and high−resolution CTD. Although a similar analysis was carried out in the western bay [27], only the vertical profiles (one−dimension) of the mean anomalies in temperature, salinity, and dynamic height inside eddies were depicted in the study, which suggests that both anticyclonic and cyclonic eddies have a single core vertical structure, with the core located at a depth of approximately 100 dbar.…”

Impact of moderately energetic fine-scale dynamics on the phytoplankton community structure in the western Mediterranean Sea

“…Following a satellite-based adaptive and Lagrangian sampling strategy, high-resolution coupled physical-biological sampling was performed during the PROTEVSMED-SWOT cruise in the southwestern Mediterranean Sea, south of the Balearic Islands (Dumas, 2018;Garreau et al, 2020). This cruise was operated in the context of the preparation for the new satellite mission Surface Water and Ocean Topography (SWOT; https://swot.jpl.nasa.gov/, https://swot.cnes.fr, last access: 3 December 2021).…”