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<p>The oceanic mixed layer (OML) plays a crucial role in linking the deep ocean with the atmosphere, influencing ocean–atmosphere interactions. The South Atlantic Convergence Zone (SACZ) is one of the dominant atmospheric systems over South America during summer, yet its impact on the upper ocean beyond sea surface temperature (SST) and Ekman pumping has not been fully explored. This study represents a first step in understanding OML dynamics, including wind-generated waves below the SACZ and the effect of the freshwater input in the surface buoyancy flux. In context, it is investigated how oceanic SACZ (OCNSACZ) episodes influence OML properties through vertical fluxes of heat, freshwater, and momentum. The results reveal distinct responses in different regions under the SACZ: (i) in the northern sector, OML deepening is associated with intensified wind stress, convective instability due to reduced solar radiation, and the generation of surface waves, which may enhance turbulence; (ii) in the southern sector, OML shallowing is linked to decreased wind stress, reduced convective stability due to intense precipitation, and the absence of locally generated waves. The study also suggests that the previously proposed negative feedback mechanism, wherein the ocean suppresses atmospheric convection via surface cooling, may be less effective than anticipated, as the expected cold-water entrainment is limited by OML shoaling. These findings emphasize the importance of considering wave effects and freshwater input in ocean–atmosphere interactions, providing new insights into OML variability under synoptic-scale atmospheric forcing.</p>

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Oceanic mixed layer depth variability forced by South Atlantic convergence zone episodes

  • 期刊论文

  • 发表日期：

    2025年8月6日

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  • Eliana B. Rosa,
  • Luciano P. Pezzi,
  • Mario F. L. de Quadro,
  • Jonas T. Carvalho,
  • Marcelo F. Santini,
  • Nelson Gouveia,
  • Pedro Dias,
  • João A. Lorenzzetti

摘要

The oceanic mixed layer (OML) plays a crucial role in linking the deep ocean with the atmosphere, influencing ocean–atmosphere interactions. The South Atlantic Convergence Zone (SACZ) is one of the dominant atmospheric systems over South America during summer, yet its impact on the upper ocean beyond sea surface temperature (SST) and Ekman pumping has not been fully explored. This study represents a first step in understanding OML dynamics, including wind-generated waves below the SACZ and the effect of the freshwater input in the surface buoyancy flux. In context, it is investigated how oceanic SACZ (OCNSACZ) episodes influence OML properties through vertical fluxes of heat, freshwater, and momentum. The results reveal distinct responses in different regions under the SACZ: (i) in the northern sector, OML deepening is associated with intensified wind stress, convective instability due to reduced solar radiation, and the generation of surface waves, which may enhance turbulence; (ii) in the southern sector, OML shallowing is linked to decreased wind stress, reduced convective stability due to intense precipitation, and the absence of locally generated waves. The study also suggests that the previously proposed negative feedback mechanism, wherein the ocean suppresses atmospheric convection via surface cooling, may be less effective than anticipated, as the expected cold-water entrainment is limited by OML shoaling. These findings emphasize the importance of considering wave effects and freshwater input in ocean–atmosphere interactions, providing new insights into OML variability under synoptic-scale atmospheric forcing.