THE SOUTH EQUATORIAL CURRENT SYSTEM

1. THE SOUTH EQUATORIAL CURRENT SYSTEM Sushmita Patwardhan,PhDCandidate,Graduate Program in Oceanography

2. Southern Hemisphere. • In Indian, Pacific and Atlantic oceans. • THE SOUTH EQUATORIAL CURRENT • THE SOUTH EQUATORIAL UNDER CURRENT • THE SOUTH EQUATORIAL COUNTER CURRENT

3. THE SOUTH EQUATORIAL CURRENT • Westward flowing current with a depth of 100 m. • Northern boundary is at 4°N and southern boundary is between 15°S- 25°S depending on time of the year and longitude. • It’s a geostrophic flow. • It can be divided into three branches: 1.Southern South Equatorial Current (SSEC) 2.Central South Equatorial Current (CSEC) 3.Northern South Equatorial Current (NSEC)

5. CURRENTS OF THE WORLD

6. SOUTHERN SOUTH EQUATORIAL CURRENT • It flows westwards. • It is fed by the Benguela Current. • SSEC turns northwards at 30°W. • Bulk of the flow joins the North Brazil Current. • Northern branch also feeds SECC. • A small part flows south pole wards and joins the Brazil Current. • Sluggish flow. • Average transport is 20 Sv for upper 500m.

7. CENTRAL SOUTH EQUATORIAL CURRENT • Located between South Equatorial Undercurrent and South Equatorial Counter Current. • It bifurcates around 5-6°S. • Northern flow merges with North Brazil Current. • Part of the northern flow turns north-eastwards and supplies to the SEUC. • Southern part initially flows southwestwards and then makes a turn towards the north around 9°S and joins the southernmost part of the SSEC. • Average transport is 17 Sv in upper 200m and maximum is 29Sv.

9. THE NORTHERN SOUTH EQUATORIAL CURRENT • Located between 1°N and SEUC (3-5°S). • Speed is 30cm/s. • Volume transport is 12 Sv in upper layer.

10. TEMPERATURE AND SALINITY • The Southern South Equatorial Current is more saline than the Central and Northern branches. • Salinity of: SSEC: 37-37.2 CSEC and NSEC: 36-36.2 • Temperature: 26-28°C at the surface and 22-24°C at a depth of 100m. • The annual temperature is pretty stable with a season variability of 4°C.

11. THE SOUTH EQUATORIAL UNDERCURRENT • Eastward flowing subsurface current. • Depth is between 100-1000m. • Flow is maximum in boreal fall i.e. Sept-Oct and minimum in boreal spring i.e. April-June. • The SEUC has oxygen rich water. • Flow in the surface above the SEUC is towards the east during austral summer and towards the west during austral winter. • The transport is about 15 Sv. • Salinity is less then 36

13. THE SOUTH EQUATORIAL COUNTER CURRENT • It flows eastwards. • Flow is from surface to depth of 400m. • Is formed around 30°W. • Crosses the South Atlantic up to Prime Meridian. • Around 5°S it is entrained by the CSEC. • Surface water is warm and salty. • High oxygen concentration. • Salinity 36.2 at surface and 38 at depth of 400m.

14. IMPORTANCE OF THE SECS • It transfers net heat from the Southern Hemisphere to the Northern Hemisphere. • It links the two important subtropical gyres of the Atlantic Ocean. • The Brazil current is an important western boundary current in the South Atlantic gyre. • Plays a role in formation of Gulf stream. • Replenishes water in the North Indian Ocean.

15. REFERENCES • http://oceancurrents.rsmas.miami.edu/atlantic/south-equatorial.html • http://oceanmotion.org/html/introduction-general.htm • LotharStramma.1991.Geostrophic transport of the South Equatorial Current in the Atlantic. Journal of Marine Research,49,281-294. • http://www.gfdl.noaa.gov/bibliography/related_files/sgp0102.pdf