2. Ocean Currents
Ocean waters are constantly on the move. How they
move influences climate and living conditions for
plants and animals, even on land.
Currents flow in complex patterns affected by wind,
the water's salinity and heat content, bottom
topography, and the earth's rotation.
Types of Ocean
Currents
• Surface currents
– Anti-cyclonic current gyres are driven
by the westward flow of equatorial
surface wind.
– Gravity driven roll-back from the
resulting rise of western sea surface
runs equatorial counter current.
– Circum-Antarctic circulation, or “West
Wind Drift” is driven by Earth’s
rotation.
• Deep-water current
– This is thermohaline circulation or the
“Global Conveyor Belt”.
The North Atlantic Gyre System
The factors that govern the oceanic gyres
N. Equatorial
Current
Atlantic Ocean meridional section at 25°W
(a)
Potential Temperatures (°C)
http://sam.ucsd.edu/sio210/lect_6/
Atlantic Ocean meridional section at 25°W
(b)
Salinity (‰)
Atlantic Ocean meridional section at 25°W
(c)
Density at 0 dbar (s0F)
Atlantic Ocean meridional section at 25°W
(d)
Density at 4 dbar (s4F)
Atlantic Ocean meridional section at 25°W
(e)
Dissolved Oxygen (DO2 in ml/l)
South Atlantic meridional section at 25°W
(e)
Silicate content (umol/Kg)
Surface currents in the Paficific
Nike shoes and the Pacific gyre
The North Pacific gyre has been dropping off shoes around the Pacific
since 1990. The shoes washed ashore one at a time but were wearable
after a scrub-down to remove barnacles, algae, and tar. Beachcombers
held swap meets to find matched pairs
1.
2.
3.
4.
5.
6.
7.
8.
9.
shoe spill, May 27, 1990
250 recovered, March 26, 1991
200 recovered, May 18, 1991
100 recovered, January-February 1991
200 recovered, November-December 1990
200 recovered, February-March 1991
150 recovered, April 4, 1991
200 recovered, May 9-10, 1991
several recovered, January-March 1993
Pacific ocean meridional section at 150°W
(a)
Potential Temperatures (°C)
Pacific Ocean meridional section at 150°W
(b)
Salinity (‰)
Pacific Ocean meridional section at 150°W
(c)
Density at 0 dbar (s0F)
Pacific Ocean meridional section at 150°W
(c)
Density at 4 dbar (s4F)
Surface
currents in
the Indian
Ocean
Circum-Antarctic Circulation
Pacific at
normal
times
During the El Niño Times
The normal or La Niña conditions
Low air
pressure
High air
pressure
Warm surface
waters
Cold
deep waters
East
West
Equatorial
surface wind
Animation of Monthly-averaged Sea Surface Temperatures
http://www.nodc.noaa.gov/dsdt/sst_ani.htm
El Niño Continues to Grow:
Pacific Ocean Shows Higher
Than Normal Sea Surface
Heights
December 02, 2002
The latest image from NASA's
Jason oceanography satellite,
taken during a 10-day collection
cycle ending December 2, 2002,
shows the Pacific dominated by
two significant areas of higherthan-normal sea level (warmer
ocean temperatures). In the
central equatorial Pacific, the
large area of higher than normal
sea surface heights (warmer than
normal sea surface
temperatures) associated with
growing El Niño conditions has
recently migrated eastward
toward the coast of South
America. Meanwhile, the
influence of the 20- to 30-year larger than El Niño/La Niña pattern called the Pacific
Decadal Oscillation continues to create warm, higher-than-normal sea-surface heights
in the north Pacific that are connected in a warm horseshoe pattern with the western
and southern Pacific.
http://topex-www.jpl.nasa.gov/elnino/20021202.html
Geostrophic
Currents
Upwelling and
downwelling
The Ekman Spiral
The Ekman Spiral
Mapping the Gulf Stream
The Gulf Stream wobbles, much like the
streams on land, so creating rings and
eddies.
The Oceanic Conveyor Belt