Ocean mixed layer

The oceanic mixed layer (OML) is the ocean region adjacent to the air-sea interface and is typically tens of meter deep and due to the fact that it is well mixed, the temperature and salinity are fairly uniform. The rapidly changing below these uniform regions of temperature , salinity and density are called thermocline, halocline and pycnocline respectively.

Weather & climate :-

The OML mediates the exchange of mass moment, energy and heat b/w the atmosphere and the ocean and hence plays a central role in long term climate and weather. Oceans are heat reservoirs, gaining heat during spring and summer and loosing it slowly during fall and winter, and therefore act like a flywheel in matters related to weather and climate.

Biological significance :-

OML also plays an important role in the oceanic food chain. Primary production by phytoplankton is the first link in this chain. The need of an energy source in producing biomass restricts primary production to the upper ‘euphotic zone’, in which the solar insolation is strong enough to assist carbon fixation.

The mixing at the base of OML is also crucial to biological productivity. The OML is normally nutrient-poor and it is the injection of nutrients from the nutrient rich waters below the seasonal thermocline that permits higher levels of primary production. In fact it is the upwelling regions, where nutrient- rich water are forced into the OML and brought into the photic zone that provides most of the fish catch around the world.

Pollution :-

The OML constitutes the first link in the chain of oceanic pollution most of the pollution inn the global oceans takes place in the costal oceans through the OML, and therefore the fate of any pollutants accidentally or intentionally in the OML depends on the mixing and dispersion in the OML.