OceanOcean CurrentsCurrents

Ocean Currents

There are two types of ocean currents:1. Surface Currents: are wind driven and

affect about 10% of the ocean water, but cover the entire ocean surface.

2. Thermohaline Currents: (heat/salt) = density driven currents. They occur deeper in the ocean and affect ~ 90% of the ocean water.

Hot/Cold Currents

Warm Currents: Gulf Stream, Alaskan, Kuroshio, Brazil, South Equatorial, North Equatorial, East Australian, North Atlantic, North Equatorial, East Australian

Cold Currents: West Wind Drift, Humboldt, California, Canary, Bengula, West Australian, Labrador, Gulf Stream,

Surface Currents

Surface currents are mostly horizontal currents.

These currents follow the pattern of the wind e.g. the Westerlies/ Trade winds

They occur from the surface down to a few hundred meters.

Generally travel clockwise in the northern hemisphere and counter clockwise in the southern hemisphere.

Significance of surface currents

Surface currents cause the general “mixing” of the worlds oceans and waters

move nutrients from more productive areas to less productive areas of the oceans.

Important role in migration and the movement of many less active (or passive) organisms.

Deep currents

Thermohaline currents are driven by density and temperature changes in water.

These currents are also known as the “ocean’s conveyor belt”

They flow under the surface of the ocean and move significant amounts of ocean water vertically.

Significance of deep currents Form upwelling: the drawing up of cold

water from deeper regions to shallow waters throughout the Ocean

Result: all ocean nutrients don’t end up settling on the bottom: surface organisms can benefit from decomposers, cycle nutrients and sustain life.

So what is downwelling?

What affects currents?What affects currents?

Currents flow in complex patterns affected Currents flow in complex patterns affected by the placement of the continents and by the placement of the continents and land masses, wind, the water's salinity and land masses, wind, the water's salinity and heat content (temperature), bottom heat content (temperature), bottom topography, and the earth's rotation (aka topography, and the earth's rotation (aka Coriolis Effect: water moves clockwise in Coriolis Effect: water moves clockwise in the Northern Hemisphere and counter-the Northern Hemisphere and counter-clockwise in the Southern Hemisphere). clockwise in the Southern Hemisphere).

Ocean CurrentModel

© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

GyresGyres

These currents are deflected by the These currents are deflected by the continents and driven by surface winds, continents and driven by surface winds, causing them to bend and create large causing them to bend and create large current loops called circulation gyres. current loops called circulation gyres.

The centers often collect floating mats of The centers often collect floating mats of seaweed and garbage. (Sargasso Sea seaweed and garbage. (Sargasso Sea and the N. Pacific gyre garbage patch.)and the N. Pacific gyre garbage patch.)

The key variables that affect water density:The key variables that affect water density:

1.1. Temperature: Denser water sinks (cold), Temperature: Denser water sinks (cold), less dense water rises (warm)less dense water rises (warm)

Cold-water currents occur as the cold water Cold-water currents occur as the cold water at the poles sinks and slowly moves toward at the poles sinks and slowly moves toward the equator, and opposite for warm water.the equator, and opposite for warm water.

2.2. Salinity – Saltier water = more dense, Salinity – Saltier water = more dense, therefore sinkstherefore sinks

““The Great Conveyor Belt”The Great Conveyor Belt”

A global "conveyor belt"A global "conveyor belt" is set in motion is set in motion when cold water forms in the Northern when cold water forms in the Northern Atlantic, sinks, moves south, and Atlantic, sinks, moves south, and circulates around Antarctica, and then circulates around Antarctica, and then moves northward to the Indian, Pacific, moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand and Atlantic basins. It can take a thousand years for water from the North Atlantic to years for water from the North Atlantic to find its way into the North Pacific. find its way into the North Pacific.

Conveyor Belt