Potential vorticity (PV) is a key parameter to analyze the generation and dynamics of oceanic mesoscale eddies. Adiabatic and diabatic processes can be involved in the generation of localized PV anomalies and vortices. However, PV is difficult to evaluate at mesoscale. In this study we argue that eddies created by diapycnal mixing or isopycnal advection of water-masses are associated with PV anomalies and significant isopycnal temperature/salinity anomalies (Ɵ’/S’). In contrast, eddies created by friction are associated with PV anomalies but with non-significant isopycnal Ɵ’/S’. Based on 18 years of satellite altimetry data and vertical Ɵ/S profiles from Argo floats, we analyze the isopycnal Ɵ’/S’ within new-born eddies in the tropical Atlantic Ocean (TAO) and discuss the possible mechanisms involved in their generation. Our results show that on density-coordinates system, both anticyclonic (AEs) and cyclonic (CEs) eddies can exhibit positive, negative or non-significant isopycnal Ɵ’/S’. Almost half of the sampled eddies do not have significant Ɵ’/S’ at their generation site, suggesting that frictional effects play a significant role in the generation of their PV anomalies. The other half of eddies, likely generated by diapycnal mixing or isopycnal advection, exhibits significant positive or negative anomalies with typical Ɵ’ of ±0.5°C. More than 70% of these significant eddies are subsurface-intensified, having their cores below the seasonal pycnocline. Refined analyses of the vertical structure of new-born eddies in three selected subregions of the TAO, show the dominance of cold (warm) subsurface AEs (CEs) likely due to isopycnal advection of large scale PV and temperature.

Tonia A. Capuano

and 7 more

Internal tides (ITs) in the Indonesian seas were largely investigated and hotspots of intensified mixing identified in the straits in regional models and observations. Both of them indicate strong mixing up to 10⁻⁴cm/s even close to the surface and show that tides at spring-neap cycle cool by 0.2°C the surface water at ITs’ generation sites.These findings supported the idea of strong and surfaced mixing capable of providing cold and nutrient-rich water favorable for the whole ecosystem. However, it has never been assessed through an ad-hoc study. Our aim is to provide a quantification of ITs impact on chlorophyll-a through a coupled model, whose physical part was validated against the INDOMIX data in precedent studies and the biogeochemical part is compared to in-situ samples and satellite products. In particular, explicit tides’ inclusion within the model improves the representation of chlorophyll and of the analyzed nutrients. Results from harmonic analysis of chlorophyll-a demonstrate that tidal forcing modify spring/neap tides’ variability on the regions of maximum concentration in correspondence to ITs’ génération areas and to plateau sites where barotropic tides produce large friction reaching the surface. The adoption of measured vertical diffusivities explains the biogéochemical tracers’ transformation within the Halmahera Sea and used to estimate the nutrients’ turbulent flux, with an associated increase in new production of ~25% of the total and a growth in mean chlorophyll of ~30%. Hence, we confirm the key role of ITs in shaping vertical distribution and variability of chlorophyll as well as nutrients in the maritime continent.