2. Ocean Currents

Currents flow in complex patterns affected by wind, the water's salinity and heat content, bottom topography, and the earth's rotation.

Ocean waters are constantly on the move. How they move influences climate and living conditions for plants and animals, even on land.

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

Gulf

stream

N. Equatorial Current

Canary

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 (0F)

Atlantic Ocean meridional section at 25°W(d) Density at 4 dbar (4F)

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)

Su

rface curren

ts in th

e Paficific

1. shoe spill, May 27, 19902. 250 recovered, March 26, 19913. 200 recovered, May 18, 19914. 100 recovered, January-February 19915. 200 recovered, November-December 19906. 200 recovered, February-March 19917. 150 recovered, April 4, 19918. 200 recovered, May 9-10, 19919. several recovered, January-March 1993

Nike shoes and the Pacific gyreThe 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

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 (0F)

Pacific Ocean meridional section at 150°W(c) Density at 4 dbar (4F)

Surface currents in the Indian

Ocean

Circu

m-A

ntarctic C

irculatio

n

Pacific at normal times

Du

ring

the E

l Niñ

o T

imes

Equatorial surface wind

High air pressure

Wes

tE

astCold deep waters

Equatorial counter current

The normal or La Niña conditions

Warm surface waters

Low air pressure

http://www.nodc.noaa.gov/dsdt/sst_ani.htm

Animation of Monthly-averaged Sea Surface Temperatures

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 higher-than-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