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The top 2-3 m of the ocean has the same heat capacity as the entire atmosphere above. Of the penetrating solar radiation, 50% is absorbed within the first 0.5 m of the ocean. Of the breaking surface wave kinetic energy, 50% dissipates within 20% of the significant wave height from the surface. These facts highlight the special role of the near-surface layer of the ocean in the ocean-atmosphere system.

The microlayer is involved in the heat and momentum transfer between the ocean and atmosphere and plays a vital role in the uptake of greenhouse gases by the ocean. A striking variety of physical, biological, chemical, and photochemical interactions and feedbacks occur in the ocean surface microlayer. There is a widely held presumption that the microlayer is a highly efficient and selective micro-reactor, effectively concentrating and transforming materials brought to the interface from the atmosphere and oceans by physical processes (Liss and Duce, 1997). These processes are very intriguing and potentially of great importance for remote sensing of sea surface temperature and salinity, climate change, and many other practical applications still waiting their time to come.

The main sources of turbulence in the near-surface layer of the ocean are breaking surface waves, shear, and convection. Upper ocean turbulence resulting from shear and convective instabilities may be substantially influenced by the diurnal cycle of solar radiation and by precipitation events. The shear that develops at the bottom of a shallow diurnal or rain-formed mixed layer can greatly increase the turbulence generation (though on relatively small scales) and thus the dissipation rate of turbulence. Below the mixed layer (, in the pycnocline), turbulence decays due to the stabilizing effect of buoyancy forces. The dramatic effect of stratification is observed under low wind speed conditions, when the turbulence regime depends strongly on near-surface stratification, while the strong stratification is also the result of reduced turbulent mixing.

In the oceanographic literature, the term is traditionally reserved for inhomogeneities relating to stratification, while the term, has often been applied to inhomogeneities associated with small-scale turbulence (Gregg, 1975).

The upper ocean is turbulent, in other words chaotic, because the Reynolds number is large. This chaos may include organized, so-called .

Breaking waves intermittently disrupt the air-sea interface. With increasing wind speed, the sharp interface between the air and water disappears for longer intervals (). Under extreme conditions of very high wind speeds, the concept of the air-sea interface becomes problematic: A two-phase environment with gradual transition from bubblefilled water to spray-filled air is formed.

The near-surface layer of the ocean is a principal component in several important applications. Traditional applications such as remote sensing and air-sea coupling in numerical models have been augmented by recent developments in ocean color, acoustic sensing and near-surface biology. Remote sensing from space can be efficiently complemented with remote sensing of the sea surface from inside the ocean. Optical and acoustical methods provide exciting opportunities in this direction.