Which direction do ocean gyres rotate in the northern hemisphere?

Ocean gyres rotate clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere, due to the Coriolis effect — the deflection of moving water caused by Earth's rotation.

Why is the west coast of North America cold?

The northern hemisphere gyre rotates clockwise, which drives cold polar water southward along the west coast of continents. This is why California has cold water despite its relatively warm climate.

How do you work out current direction along any coastline for the PADI exam?

Use the doodle method: draw a vertical line representing the continent, then draw a circle on each side representing the ocean gyres. Add clockwise arrows in the northern hemisphere or counter-clockwise in the southern hemisphere. Read the direction of the arrow where it touches the coastline to find the current direction.

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Currents — PADI IDC and Divemaster Theory

Watch Will Welbourn explain the Coriolis effect and ocean gyre circulation, including a simple doodle method that lets you work out current direction anywhere in the world.

What Causes Ocean Currents

The major ocean currents (gyres) are caused by the wind and the Earth's rotation — without both, they would not exist. Wind alone would not create circular ocean-wide circulation; it is the Earth's rotation that gives the wind its curve, and that curve is what drives the gyres. To understand why currents run the direction they do, you first need to understand what makes the wind curve — and that's the Coriolis effect.

Exam trap — wind alone is not the correct answer If a question asks what causes major ocean currents and lists "wind" as one option and "wind and the Earth's rotation" as another, the second answer is always correct. Wind is part of the picture, but without the Earth's rotation there would be no Coriolis effect and no circular gyre pattern.

The Coriolis Effect

Wind moves from high pressure to low pressure. The equator is generally low pressure; the poles are generally high pressure. So wind wants to travel in a straight line from the poles toward the equator. But the Earth is rotating — and that rotation causes the wind to curve.

In the northern hemisphere, wind curves to the right
In the southern hemisphere, wind curves to the left

Definition for your notes The Coriolis effect is the apparent curving of the path of moving objects (wind, water) due to the Earth's rotation. If the Earth were not rotating, wind would move in a straight line from high to low pressure.

How the Coriolis Effect Drives Ocean Circulation

The curving wind sets up ocean-wide circular current patterns — called gyres. The direction of that circulation flips between hemispheres:

Hemisphere	Wind curves	Ocean currents circulate
Northern	To the right	Clockwise
Southern	To the left	Counter-clockwise

Answering Coastline Current Questions in the Exam

PADI exams often take this one step further — instead of asking which direction the ocean circulates, they'll name a specific coastline and ask which direction the current runs along it. Here's a reliable method that works every time.

The doodle method

Draw a vertical line to represent the continent. Then draw a circle on each side of the line — one for the ocean on the west coast, one for the ocean on the east coast. Add arrowheads around each circle to show the direction of rotation: clockwise for the northern hemisphere, counter-clockwise for the southern. Now look at the side of each circle that is closest to the line (the coastline) — the arrowhead there tells you which direction the current runs along that coast.

Will Welbourn — ocean current direction doodle method

I really like this video to help you better understand the way the rotating earth causes a deflection of the wind and therefore the ocean gyres. Just imagine that ball is wind flowing from the poles to the equator.