Major currents gyres rings and eddies basin scale

Major currents, gyres, rings, and eddies (basin scale) • Winds and wind-driven basin circulation • Meanders, rings, eddies and gyres • The thermohaline circulation

Winds and wind-driven basin circulation Winds Unevenly heating by the sun Spinning sphere

Subpolar gyre Strong and narrow western boundary current Subtropical gyre

1. The Coriolis force causes the moving water to be deflected to the right of the wind (in NH). The net effect of winds in the upper ocean is a flow perpendicular to the wind (i. e. Ekman transport). 2. The strong western boundary currents are formed due to the variation of the Coriolis parameter with latitude.

Meanders, rings, eddies and gyres gyre

• Meanders: Jet stream develop large oscillations caused by its unstable. • Rings: Eddy pinched off from meander as it become too large. Anticlockwise and clockwise rotating rings are cold and warm rings, respectively. They contain water from the opposite side of the stream having the other side’s physical, chemical and biological properties. The interaction of meander and rings create significant vertical transports of nutrient and plankton which enhance biological activity

• Eddies: The closed circulation with horizontal scale of 10 -100 km and time scale of 10 -30 days. The upward and downward vertical velocities in cyclonic and anticyclonic will enhance biological productivity, respectively.

High surface Chl-a

• Gyres: A circular current that is confined by or associated with bathymetric features and covers a wide range of spatial scales.

The Thermohaline Circulation (north-south vertical circulation Sinking of dense water due to cooling in mid to high latitude.

• The global conveyor belt thermohaline circulation is driven primarily by the formation and sinking of deep water (from around 1500 m to the Antarctic bottom water overlying the bottom of the ocean) in the Norwegian Sea.

• This circulation is thought to be responsible for the large flow of upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelogo.

• The two counteracting forcings operating in the North Atlantic control the conveyor belt circulation: (1) thermal forcing (high-latitude cooling and the low-latitude heating) which drives a polar southward flow; and (2) haline forcing (net high-latitude freshwater gain and low-latitude evaporation) which moves in the opposite direction. In today's Atlantic thermal forcing dominates, hence, the flow of upper current from south to north.