Energy In The Oceanic System

The ocean is constantly in motion. The energy that arrives into the oceanic system on the planetary scales create large scale mean flows that are constantly breaking down into smaller scales features. The most important source of energy is the differential solar heat, warmer in the equator and colder in the poles. With the water transport, also heat, nutrients, salt, organisms and chemical particles in the ocean are moved, regulating the planet whether, climate and marine ecosystems.

Both large scale and smaller scale oceanic currents, gyres and eddies, transport water masses long distances. Water masses are homogeneous bodies of seawater on their properties. These bodies of water have formed through surface processes that have their origin

The values of temperature and salinity of the water masses are acquired on the surface and in the mixed layer by heating, cooling, rain, evaporation, wind, waves and currents. Once they sink below the mixed layer, temperature and salinity may be changed only by mixing processes with adjacent water bodies. In these depths the temperature and salinity are conservative properties as there are no significant sources or sinks in the deep ocean. Seen from this perspective the temperature and salinity are not independent variables, and their knowledge allows us to recognize water masses. Oxygen is on the other hand, a non-conservative property, is acquired in surface and and is slowly reduced over time due to oxidation of organic matter and respiration of organisms.

Currents are coherent streams of water moving through the ocean. Currents are primary forced by winds blowing across the ocean surface and by differences in temperature, density and pressure of water. Currents are also governed by Earth rotation and the location of the continents. To study the movements of a volume of water in the ocean, the Newton’s second law (the acceleration to which is subjected a water volume is proportional to the sum of

The ocean is indeed a turbulent system and the ocean circulation is not a large scale and temporally stable phenomenon; it varies over an almost continuous frequency/wavenumber spectrum with space and time scales ranging from tens to thousands of kilometers and from days to year (Le Traon Pierre-Yves, 1999).

An instantaneous view of the ocean circulation would thus reveal areas of intense and small scale ocean currents almost everywhere and would be dominated by mesoscale variability. In particular, western boundary currents and the ACC are areas of intense mesoscale variability.

Open ocean currents which are part of the large scale gyre circulation are also often intense and narrow currents embedded with mesoscale eddies. At the eastern boundaries, superimposed on the broad equator-ward flow are energetic currents and coastal upwelling currents, which can be highly variable in space and time.

The mesoscale variability is the dominant signal in the ocean circulation. There is not a precise definition of mesoscale variability but it usually refers to a subclass of energetic motions with typical space and time scales of 50 to 500 km and 10 to 100 days.