Mesoscale features and their related submesoscale structures can transport heat, freshwater, and biogeochemical tracers (e.g., phytoplankton, oxygen, and carbon) from the surface to the interior. These structures may grow, decay, and redistribute energy through several dynamical processes. The study examines the evolution of small (~20 km) mesoscale eddies and the associated energetic pathways using a four-dimensional, three-month-long autonomous glider survey in the Balearic Sea, Western Mediterranean. The combined glider fleet covered nearly 15,978 km, accumulated 704 glider days, and completed more than 4,837 dives to depths of 700 m, measuring physical and biogeochemical properties. We investigate how energy is redistributed during mesoscale eddy merging and eddy splitting and how these processes relate to changes in flow divergence, strain, and vertical velocities. Scale-dependent diagnostics, support the presence of enhanced upscale kinetic energy transfer during merging, whereas splitting events exhibit strain-dominated dynamics and diminished cross-scale energy transfer. During eddy merging, vertical velocities reach values of up to 20 m day⁻¹. However, the spatial extent of significant vertical motion decreases, consistent with weakened frontogenesis along the eddy periphery and a redistribution of kinetic energy within the merging eddy. Examination of the baroclinic conversion, quantified through the eddy vertical buoyancy flux ⟨w′b′⟩, suggests higher vertical energy conversion during eddy merging. This is localized within areas where strain and frontogenetic activity occur. Although peak values of vertical energy conversion remain elevated, the fraction of the domain contributing to significant conversion decreases, indicating increasing spatial localization of energetic processes during merging. During eddy splitting, vertical velocities are substantially reduced (less than 10 m day⁻¹) following a frontolytic event in the northern eddy. Eddy splitting reduces positive and negative divergence, as well as eddy kinetic energy. Vertical velocities decrease from 20 m day⁻¹ to 10 m day⁻¹. The related baroclinic conversion declines during splitting, suggesting a decrease in vertical exchange under frontolytic conditions. Analysis of baroclinic energy transfers indicates vertical and horizontal pathways, with vertical conversion having a key role during eddy merging and a decreasing role during eddy splitting. Eddy merging is characterized by enhanced upscale transfer of kinetic energy across mesoscale and submesoscale ranges, whereas eddy splitting shows strain-dominated dynamics and reduced cross-scale energy transfer. The observations indicate that mesoscale eddy merging serves as an efficient mechanism for energy redistribution, while eddy splitting promotes energetic decay and reorganizes the vertical exchange.

We illustrate the use of our Lagrangian flow map analyses to quantify submesoscale transports and non-advective dynamics. We utilize our flow map predictions to extract dynamical regions and coherent structures, classify submesoscale processes, and inform classical analyses. Our emphasis is on the use of spatiotemporal flow maps to help differentiate the advective transports from time-integrated non-advective transformations of water masses and submesoscale features. Results are presented for real-time sea experiments with autonomous sensing platforms and probabilistic modeling systems in diverse ocean regions and dynamical regimes. They include the Nova Scotia Shelf-Slope and New England Seamount Chain regions, the Gulf of Mexico, the Balearic and Alboran Seas, and the Southern California Bight. Our analyses highlight regions of higher shear and mixing, Lagrangian energy and buoyancy dissipation rates, frontogenesis and frontolysis zones, and strong vertical and helical-spiral motions, including filaments and internal waves.

In the winter 2022, a multidisciplinary experiment in the Balearic Sea (northwestern Mediterranean Sea) combined multiplatform in-situ observations with high-resolution numerical simulations to investigate the evolution of a mesoscale oceanic front. The study focuses on analyzing the energy transfer from the mesoscale front to submesoscale cyclonic eddies (SCEs) and understanding their impact on subduction processes from the ocean surface to the interior, using a numerical simulation with 650 m horizontal resolution. The frontal evolution exhibited two distinct phases: (i) an intensification phase driven by strain-induced frontogenesis, and (ii) a subsequent decay phase occurring under conditions favorable to overturning instabilities, triggered by a down-front wind event. These processes enhanced vertical velocities through an ageostrophic secondary circulation across the front, contributing to upper-ocean restratification. Following the wind event, the front decayed and fragmented into smaller-scale structures, leading to the formation of SCEs along its edges. The formation of SCEs was associated with the frontal decay, as well as with centrifugal and gravitational instabilities, which transferred energy from the mesoscale front to the SCEs. These eddies exhibited a three-dimensional helical-spiral recirculation pattern that facilitated the vertical transport of water parcels. Submesoscale eddy-induced frontogenesis drove subduction into the mixed layer, intensified by submesoscale instabilities and guided by downward-sloping isopycnal surfaces at the eddy periphery.

A four-dimensional, three-month-long survey by eight gliders at the Balearic Sea in the western Mediterranean Sea was used to examine the evolution and variability of mesoscale eddies and related physical processes, including frontogenesis, and subduction. The combined glider fleet covered nearly 15978 km over the ground, performing 704 glider days while doing over 4837 dives to as deep as 700 m, measuring temperature, salinity, velocity, chlorophyll fluorescence, oxygen, and acoustic backscatter. The data was objectively mapped on 10 m vertical levels in space and time. Vertical and ageostrophic horizontal velocities were estimated using the omega equation. Uplift of the isopycnal surface, 28.9 kg/m³, ~70 m in 10 km, was observed in an asymmetric cyclonic eddy (CE) on April 29, 2022, with ~25 km width and ~35 km length. Downward velocities of ~20 m/day developed, with the CE axis shifted westward. After the first CE decay, the 28.9 isopycnal shoaled again in the east as another CE formed, where relative vorticity reached ~0.5f. The eddy axis shifted westward during CE growth, and the downward velocities were ~25 m/day during the eddy intensification. Then, the new cyclonic feature spread over before splitting again into two 15 km CEs on May 2. The two smaller CEs proceeded north and west until they vanished. An anticyclonic structure (20 km) developed within their separation. The glider observations reveal horizontal density gradients up to 0.5 kg/m³ over ~10 km. Both upwelling and downwelling were observed near the frontal interface by biochemical tracers.