We study mesoscale eddy characteristics in the Tropical Atlantic Ocean (TAO), using 23 years of daily altimetry sea level anomalies (SLA). Eddies are mainly generated in the eastern boundary upwelling systems (EBUS) and in the Brazil Current (BC) region. Their westward propagation speed reaches 20 cm.s^‐1 in equatorial areas, decreasing with latitudes. They present typical amplitudes of 1‐5 cm. The largest and most energetic eddies are observed in the equatorial region, especially in the North Brazil Current (NBC) retroflection. The seasonal cycle of the eddy characteristics shows higher amplitudes along the NBC retroflection and the western part of the North Equatorial Countercurrent (NECC). A new criterion, based on altimetry data, determines the probability that barotropic instability of mean surface currents is responsible for eddy generation. We find a strong likelihood that the later plays a key role along the NECC, whereas other mechanisms must be invoked for the NBC region.

This study investigates the effect of mesoscale eddies on air–sea heat and fresh water exchange in the tropical Atlantic Ocean (TAO) using 8 years of satellite altimetry data, combined with sea surface temperature (SST), latent and sensible heat fluxes (LHF and SHF), infrared fluxes (IRF) and precipitation (PR) data. Results indicate that approximately ∼40% of cyclonic eddies contribute to warm SST anomalies, and ∼40% of anticyclonic eddies contribute to cold SST anomalies. Eddies were found to play a role in the variability in LHF, SHF and IRF, contributing 10–35% of their total variability, with the largest contributions observed beneath the intertropical convergence zone (ITCZ) and frontal SST areas. Composite analysis of SST and heat flux anomalies over eddies suggested that the anomalies created through horizontal advection processes may not significantly impact the overall LHF, SHF and IRF over eddies, contrary to vertical processes. Despite a lack of clear correlation between heat flux and PR anomalies over eddies in the TAO, significant correlations were found beneath the ITCZ, suggesting that eddies may impact both heat fluxes and PR in the ITCZ region. This study provides an original contribution to the understanding of the impact of ocean mesoscale eddies on the atmosphere in the TAO.

Based on 18 years of satellite altimetry data and temperature/salinity (θ/S) profiles from Argo floats, we analyze the isopycnal θ/S anomalies (θ'/S') within newborn eddies in the tropical Atlantic Ocean (TAO). Our results show that on density‐coordinates, both anticyclonic eddies (AEs) and cyclonic eddies (CEs) can exhibit positive, negative, or nonsignificant θ'/S'. Almost half of the sampled eddies do not have significant θ'/S' at their generation site. The other half exhibits significant positive or negative θ', up to ±0.5°C typically. More than 70% of them have a subsurface signature. Refined analyses of the vertical structure of new‐born eddies in three selected subregions show the dominance of cold (warm) subsurface AEs (CEs) likely due to isopycnal advection of large‐scale potential vorticity (PV) and θ. PV is a key parameter to analyze eddy generation and dynamics. Isopycnal advection, friction or diapycnal mixing can be involved in the generation of PV anomalies from which vortices can then emerge. However, it is difficult to evaluate PV at mesoscale. In this study, we propose to combine θ'/S' and PV anomalies to analyze which process could be involved in its transformation in the ocean. We argue that eddies created by diapycnal mixing or isopycnal advection of water‐masses are associated with PV anomalies and significant θ'/S'. In contrast, a frictional forcing also creates PV anomalies but without modifying θ/S. Even though our results remain qualitative, the proposed diagnostics can be of interest to validate realistic models and then use them to analyze the PV anomaly sources.

In this paper, we analyse the results from a numerical model at high resolution. We focus on the formation and maintenance of subsurface equatorial currents in the Gulf of Guinea and we base our analysis on the evolution of potential vorticity (PV). We highlight the link between submesoscale processes (involving mixing, friction and filamentation), mesoscale vortices and the mean currents in the area. In the simulation, eastward currents, the South and North Equatorial Undercurrents (SEUC and NEUC respectively) and the Guinea Undercurrent (GUC), are shown to be linked to the westward currents located equatorward. We show that east of 20° W, both westward and eastward currents are associated with the spreading of PV tongues by mesoscale vortices. The Equatorial Undercurrent (EUC) brings salty waters into the Gulf of Guinea. Mixing diffuses the salty anomaly downward. Meridional advection, mixing and friction are involved in the formation of fluid parcels with PV anomalies in the lower part and below the pycnocline, north and south of the EUC, in the Gulf of Guinea. These parcels gradually merge and vertically align, forming nonlinear anticyclonic vortices that propagate westward, spreading and horizontally mixing their PV content by stirring filamentation and diffusion, up to 20° W. When averaged over time, this creates regions of nearly homogeneous PV within zonal bands between 1.5° and 5° S or N. This mean PV field is associated with westward and eastward zonal jets flanking the EUC with the homogeneous PV tongues corresponding to the westward currents, and the strong PV gradient regions at their edges corresponding to the eastward currents. Mesoscale vortices strongly modulate the mean fields explaining the high spatial and temporal variability of the jets.

The ocean region off the Amazon shelf including the shelf break presents a hotspot for internal tide (IT) generation, yet its impact on phytoplankton distribution remains poorly understood. While previous studies have extensively examined the physical characteristics and dynamics of ITs, their biological implications – particularly in nutrient-limited environments – remain underexplored. To address this question, we analyzed a 26 d glider mission deployed over September–October 2021 sampling hydrographic and optical properties (chlorophyll a) at high resolution along an IT pathway as well as satellite chlorophyll a and altimetry data to assess mesoscale interactions. Chlorophyll a dynamics were analyzed under varying IT intensities, comparing strong (HT) and weak (LT) internal tide conditions. Results reveal that ITs drive vertical displacements of the deep chlorophyll maximum (DCM) from 15 to 45 m, accompanied by 50 % expansion in its thickness during HT events. This expansion is observed with a dilution of the chlorophyll a maximum concentration within the DCM depth. While direct turbulence measurements were not collected, the observed vertical redistribution of chlorophyll a is indicative of tidally driven cross-isopycnal exchanges, the only physical mechanism explaining the transfer of biomass above and below the DCM. At the surface, turbulent fluxes provide 38 % of the chlorophyll a input, while the remainder is supplied by in situ biological activity. Notably, total chlorophyll a in the water column increases by 14 %–29 % during high internal tide phases, indicating a net enhancement of primary productivity driven by the combined effects of vertical mixing and stimulated surface-layer biological activity. These findings indicate that internal tides can be an important driver of chlorophyll a distribution and short-term biological variability in our study region. By reshaping the vertical chlorophyll a profile through vertical mixing, active internal tides influence primary productivity and may contribute to carbon cycling, particularly in oligotrophic oceanic environments where both a deep chlorophyll maximum and strong internal tides are present.

The ocean region off the Amazon shelf including shelf-break presents a hotspot for Internal Tides (ITs) generation, yet its impact on phytoplankton distribution remains poorly understood. These baroclinic waves, generated by tidal interactions with topography, could modulate nutrient availability and primary production both by mixing and advection. While previous studies have extensively examined the physical characteristics and dynamics of ITs, their biological implications, particularly in nutrient-limited environments,remain underexplored. To address this question, we analysed a 26-day glider mission deployed in September–October 2021 sampling hydrographic and optical properties (chlorophyll-a) at high resolution along an IT pathway, satellite chlorophyll-a and altimetry data to assess mesoscale interactions. Chlorophyll-a dynamics were analysed under varying IT intensities, comparing strong (HT) and weak (LT) internal tide conditions. Results reveal that ITs drive vertical displacements of the Deep chlorophyll Maximum (DCM) from 15 to 45 meters, accompanied by a remarkable 50% expansion in its thickness during HT events. This expansion is observed with a dilution of the chlorophyll-a maximum concentration within the DCM depth. Turbulent cross-isopycnal exchanges driven by tides redistribute chlorophyll-a into adjacent layers above and below the DCM. At the surface, turbulent fluxes contribute to 38% of the chlorophyll-a supply, which directly influences primary production. Notably, the total chlorophyll-a content in the water column increases by 14-29% during high internal tide phases, reflecting a net enhancement of primary productivity. This increase results from the combined effect of vertical mixing and stimulated biological activity in the surface layer. These findings highlight the role of ITs as a key driver of chlorophyll-a distribution and short-term biological variability, reshaping the vertical chlorophyll-a profile and regulating primary productivity and potentially carbon cycling in oligotrophic oceanic systems.