Lesson 5:

Oceanic Circulation

What you should know by the end of this lesson:

How ocean currents are created and affected
How ocean currents redistribute global energy

What are Ocean Currents?

Surface ocean currents are caused by the force and friction of winds moving the ocean surface. They generally go in the direction of the prevailing wind - the usual wind direction. As such, they have links to the atmospheric cells.

Warm currents move warm water (energy) away from the equator, towards the poles.
Cold currents move cool water away from the poles, towards the equator.

These cycles of warm and cold currents often form loops in large, unobstructed bodies of water (e.g. oceans). These are called gyres. Gyres move clockwise (towards the right) in the Northern Hemisphere and anti-clockwise (towards the left) in the Southern Hemisphere.

Factors Affecting Ocean Circulations

Digital Workbook (or with printer access)

Ensure you have a copy of the definition of a Gyre
Download a copy of the worksheet for this lesson
Add in some of the main ocean currents to the map
Annotate the 4 factors which affect the movement of the ocean currents. You may wish to highlight specific areas in the globe where this occurs.

Paper Jotter (No printer access)

Ensure you have a copy of the definition of a Gyre
Take a copy of each of the 4 factors which affect global ocean currents
Draw small diagrams to show them occurring and how they affect ocean currents

Coriolis Effect

Deflects currents to the right in the N. Hemisphere forcing currents to flow clockwise

Planetary Winds

Global Winds cause surface friction and help to drive Ocean Currents. The Trade winds drive Equatorial Currents to the West

Salinity

Water with a high salt content (around the poles) is heavy and sinks down drawing in surface currents to replace them

Shape of Land Masses

Landmasses obstruct and divert ocean currents often splitting a current into two

Thermohaline Circulation

Digital Workbook & Paper Jotter

Take your own annotated diagram of how the Thermohaline Circulation works
Add a quick explanation of the diagram alongside it.
Make sure you finish off the explanation by linking the Thermohaline to the Global Conveyor Belt.

Differences in water density, resulting from the variability of water temperature (Thermo) and salinity (haline), also cause ocean currents.

This process is known as thermohaline circulation. In cold regions, such as the North Atlantic Ocean, ocean water loses heat to the atmosphere and becomes cold and dense. When ocean water freezes, forming sea ice, salt is left behind causing surrounding seawater to become saltier and denser. Dense-cold-salty water sinks to the ocean bottom. Surface water flows in to replace the sinking water, which in turn becomes cold and salty enough to sink.

Global Conveyor Belt

Thermohaline Circulation "starts" the global conveyor belt, a connected system of deep and surface currents that circulate around the globe on a 1000 year time span. This global set of ocean currents is a critical part of Earth’s climate system as well as the ocean nutrient and carbon dioxide cycles.

North Atlantic

The North Atlantic has a number of very important ocean currents which all help

to redistribute energy.

The North Equatorial Current is warmed at the equator and, thanks to the direction of the

trade winds, travels west. It warms the waters of the Gulf of Mexico and travels East across the Atlantic, bringing warmer-than-average ocean temperatures to the west of Europe via the North Atlantic Drift. The Labrador and East Greenland currents take cold waters from the Arctic south. They interact with the North Atlantic Drift and some are taken further south to the equator via the Canaries Current.