Efraín Moreles

Barrier layers (BLs) reduce vertical mixing and limit the cold‐thermocline‐water entrainment into the mixed layer, influencing a wide range of air–sea interaction processes and ocean dynamics. They are conventionally characterized by their barrier layer thickness (BLT), but BLT cannot quantify either the density‐stratification intensity or the cold‐entrainment resistance. We introduce Barrier Layer Insulation (BLI), an energy‐based metric quantifying the BL's insulating capacity as the energy a water parcel at the BL's base must overcome to cross it against negative buoyancy. We also define the BLI density rate to quantify the degree of insulation concentration per unit depth. Using 2.8 million Argo profiles from 2005 to 2024, we constructed the first global seasonal climatologies of BLI and BLI density rate. Results reveal systematic decoupling between BLT and BLI across ocean basins and seasons: depending on the salinity‐stratification vertical structure, the thickest BLs are not necessarily the most insulating. The regions most dynamically consequential for cold entrainment reduction are not those where BLs are thickest or most spatially extensive, but those where their insulation is most vertically concentrated. The BLT–BLI decoupling is strongest in mid‐ to high‐latitude regions during boreal winter; tropical regions exhibit thin but highly insulating BLs. BLT is insufficient to characterize the dynamical importance of BLs, and BLI provides a physically grounded framework for assessing their insulation, with implications for processes in which cold entrainment is relevant, such as tropical cyclone intensification, El Niño–Southern Oscillation preconditioning, monsoon dynamics, Madden‐Julian Oscillation convection, and ocean heat content variability.

A la par de dar a conocer fenómenos raros o intrigantes que ocurren en el océano, este relato da cuenta de los principales problemas ambientales que aquejan los mares del mundo: el cambio climático y la contaminación por plásticos. La narrativa es de forma atrayente y emula charlas entre el viento y las olas. La conclusión resalta los beneficios que el océano proporciona a la humanidad y ofrece recomendaciones para aminorar esos problemas y mejorar la salud de los océanos.

The mixed layer depth (MLD) is critical for understanding ocean-atmosphere interactions and internal ocean dynamics. Traditional methods for determining the MLD, commonly relying on constant temperature and density thresholds, may not adequately address spatial and temporal variations in local oceanographic conditions, thereby limiting their global consistency and applicability. An energy-based definition of the mixed layer could be a more physically consistent alternative to address this issue. We propose a physically derived and energy-based methodology that defines the mixed layer as the energetically homogeneous upper ocean layer in which water parcels can move with little or no buoyancy work. The threshold in buoyancy work, which determines the mixed layer globally throughout the year, was carefully investigated. An energy-based global monthly MLD climatology demonstrated the reliability of the methodology across diverse ocean conditions and its usefulness for studies spanning seasonal to climate time scales, from regional to large spatial scales. Our easy-to-implement MLD methodology provides a robust criterion that is globally and temporally consistent, maintaining quasi-homogeneity in energy, density, and temperature year-round for most of the global ocean. This study promotes the development of MLD energy-based methodologies that could offer significant potential for advancing the study of dynamic and thermodynamic processes, including heat content and vertical exchanges. Our methodology could also serve as a robust tool for validating ocean circulation models and supporting intercomparison studies in initiatives such as the Ocean Model Intercomparison Project (OMIP) and the International Coupled Model Intercomparison Project (CMIP). Future research will explore its applicability to high-frequency processes and regional variability, further enhancing its utility for understanding and modeling oceanic phenomena.

Density stratification affects mixing by limiting the interchange of properties along the water column. This stratification establishes barriers to the vertical displacement of water parcels, which interchange their properties between different layers of the ocean. Quantifying the intensity of these barriers, considering the direction (upward and downward) of the vertical displacement of a water parcel, is the main aim of this study. By employing the buoyancy energy required to displace a water parcel vertically, we propose the buoyancy potential energy (BPE) to analyze energy barriers in detail, describe the stability of a water parcel, and provide an objective integrated measure of stratification intensity in any vertical section of the water column. By illustrating the application of BPE in dynamical and ecological contexts, we demonstrate that it provides a complementary understanding of oceanic stratification. BPE is directly calculated from survey data, eliminating the need to diagnose turbulent processes, and has a straightforward numerical implementation. The routine application of BPE to study diverse ocean-atmosphere interaction processes (e.g., dynamical, thermodynamical, ecological, and biochemical) in which stratification plays a role can extend and enrich our understanding of them.

Density stratification affects mixing by limiting the interchange of properties along the water column. This stratification establishes barriers to the vertical displacement of water parcels, which interchange their properties between different layers of the ocean. Quantifying the intensity of these barriers, considering the direction (upward and downward) of the vertical displacement of a water parcel, is the main aim of this study. By employing the buoyancy energy required to displace a water parcel vertically, we propose the buoyancy potential energy (BPE) to analyze energy barriers in detail, describe the stability of a water parcel, and provide an objective integrated measure of stratification intensity in any vertical section of the water column. By illustrating the application of BPE in dynamical and ecological contexts, we demonstrate that it provides a complementary understanding of oceanic stratification. BPE is directly calculated from survey data, eliminating the need to diagnose turbulent processes, and has a straightforward numerical implementation. The routine application of BPE to study diverse ocean-atmosphere interaction processes (e.g., dynamical, thermodynamical, ecological, and biochemical) in which stratification plays a role can extend and enrich our understanding of them.

The mixed layer depth (MLD) is critical for understanding ocean-atmosphere interactions and internal ocean dynamics. Traditional methods for determining the MLD commonly rely on hydrographic thresholds that vary spatially and temporally with local oceanographic conditions, limiting their global consistency and applicability. To address this, we propose an energy-based methodology that defines the MLD as the depth at which the work done by buoyancy (WB) reaches 20 J m^-3. Based on the structural change in WB, the MLD criterion identifies the upper ocean's well-mixed layer in energetic terms. This approach provides a robust criterion based on physical principles, which is globally and temporally consistent and easy to implement. Our methodology aligns with turbulent boundary layer dynamics while maintaining quasi-homogeneity in density and temperature for most of the global ocean throughout the year. A global monthly MLD climatology derived from this method demonstrates its reliability across diverse oceanic conditions and its accuracy in regions and seasons where conventional methods struggle. Our study advances the development of MLD energy-based methodologies by providing a single energy value to define the MLD globally during all months. This energy-based approach could offer significant potential for advancing the study of dynamic, and thermodynamic processes, including heat content and vertical exchanges. It could also serve as a robust tool for validating ocean circulation models and to support intercomparison studies in initiatives such as the Ocean Model Intercomparison Project (OMIP) and the International Coupled Model Intercomparison Project (CMIP). Future research will explore its applicability to high-frequency processes and regional variability, further enhancing its utility for understanding and modeling oceanic phenomena.

The mixed layer depth (MLD) is critical for understanding ocean-atmosphere interactions and internal ocean dynamics. Traditional methods for determining the MLD commonly rely on hydrographic thresholds that vary spatially and temporally with local oceanographic conditions, limiting their global consistency and applicability. To address this, we propose an energy-based methodology that defines the MLD as the depth at which the work done by buoyancy (WB) reaches 20 J m^-3. Based on the structural change in WB, the MLD criterion identifies the upper ocean's well-mixed layer in energetic terms. This approach provides a robust criterion based on physical principles, which is globally and temporally consistent and easy to implement. Our methodology aligns with turbulent boundary layer dynamics while maintaining quasi-homogeneity in density and temperature for most of the global ocean throughout the year. A global monthly MLD climatology derived from this method demonstrates its reliability across diverse oceanic conditions and its accuracy in regions and seasons where conventional methods struggle. Our study advances the development of MLD energy-based methodologies by providing a single energy value to define the MLD globally during all months. This energy-based approach could offer significant potential for advancing the study of dynamic, and thermodynamic processes, including heat content and vertical exchanges. It could also serve as a robust tool for validating ocean circulation models and to support intercomparison studies in initiatives such as the Ocean Model Intercomparison Project (OMIP) and the International Coupled Model Intercomparison Project (CMIP). Future research will explore its applicability to high-frequency processes and regional variability, further enhancing its utility for understanding and modeling oceanic phenomena.