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How Ocean Currents Work and Why They're Important

Author: TED-EdTime: 2024-01-27 10:00:00

Table of Contents

Introduction to Ocean Currents

Ocean currents are complex systems that redistribute heat and nutrients around the world. They are driven by winds, changes in water density, tides, and the rotation of the Earth. Currents fall into two main categories: surface currents and deep ocean currents, which make up the top 10% and bottom 90% of ocean waters respectively.

Surface currents and deep ocean currents influence each other, combining to create a global conveyor belt that circulates water throughout the oceans. This article will explore what drives both types of currents, how they interact, and why researchers continue working to understand these powerful systems.

Surface Currents vs. Deep Ocean Currents

Surface currents control the motion of the top 400 meters of ocean water. They are primarily wind-driven - as wind blows across the ocean, it drags surface waters along with it. Those moving waters in turn pull on deeper layers underneath them. In contrast, deep ocean currents are mainly driven by changes in water density and salinity. As surface water moves towards the poles, it gets colder and saltier. This denser water then sinks and drives circulation patterns in the deep ocean.

How Currents Redistribute Heat

The large loops formed by surface currents, called gyres, act to redistribute heat because water holds onto heat more effectively than air. Deep ocean currents also transport heat through the thermohaline circulation that drives them - as cold dense waters sink and slowly rise again, they carry heat between depth and surface.

What Drives Ocean Surface Currents?

There are three main drivers of ocean surface currents:

Firstly, wind is the primary force. As wind blows across the ocean surface, it pulls the top layers of water along with it through friction. In the open ocean, wind-driven currents extend down 400 meters or more.

Secondly, near coastlines surface currents are also influenced by tides, which rhythmically raise and lower sea levels, pushing water back and forth.

Finally, the rotation of the Earth modifies surface current patterns, causing them to form rotating gyres rather than simply moving straight back and forth between the equator and poles.

The Coriolis Effect and Ocean Gyres

The Coriolis Effect causes the clockwise rotation of gyres in the Northern Hemisphere and counter-clockwise rotation in the Southern Hemisphere. This phenomenon arises because of Earth's own rotation.

Without the planet's spin, winds would just blow straight from high pressure areas at the poles to low pressure areas at the equator. But the spin curves wind patterns, creating loops. These wind loops in turn drag surface ocean waters into rotating gyres.

Wind Patterns and Rotation of the Earth

Air moving north from the equator is deflected to the east by Earth's rotation. Air moving south toward the equator gets deflected west. This Coriolis Effect makes the major wind streams flow in great loops north and south of the equator. Surface currents follow these wind patterns, forming the eastern and western boundary currents of the ocean gyres.

What Causes Deep Ocean Currents?

In contrast to wind-driven surface currents, deep ocean currents are prompted mainly by changes in seawater density at high latitudes. Evaporation and freezing make water saltier and colder. It also becomes denser.

This cold, dense water sinks deep into the ocean, while warmer water circulates up to replace it. This vertical movement is called thermohaline circulation and it drives the deep ocean currents.

The Global Conveyor Belt Current

The global conveyor belt is created by the linkage of surface and deep ocean currents in a complex global loop. It moves slowly - a few centimeters per second - but spans all the world's oceans.

Speed and Scale of the Conveyor Belt

The global conveyor belt circulates surface waters throughout Earth’s oceans and around the globe. It may take over 1000 years for a drop of water to complete a full circuit along this ocean current. Although it moves slowly, the global conveyor belt current stretches tens of thousands of kilometers long, making it the planet’s longest ocean current.

How the Conveyor Belt Impacts Climate

The global conveyor belt plays a key role moderating climates across the planet. As it transports heat around the world, it helps balance temperatures between equatorial and polar regions. There is evidence that rising ocean temperatures are slowing down the global conveyor belt. Scientists theorize this could severely impact weather systems in the North Atlantic and have unknown ripple effects globally.


Ocean currents regulate global climate, support marine ecosystems, and even transport rubber duckies lost at sea around the world. Surface and deep ocean currents are driven by an intricate combination of winds, water density, tides, Earth’s rotation and the interconnectedness of ocean waters.

Studying currents gives insight into how our planet works as an integrated system. As climate change progresses, understanding shifts in currents will be crucial for anticipating future effects and proposing viable solutions.


Q: What are the two main types of ocean currents?
A: Surface currents and deep ocean currents are the two main types.

Q: How do winds drive surface currents?
A: Surface currents are driven by winds that drag the top layers of water, causing a domino effect through the layers below.

Q: What causes deep ocean currents?
A: Density changes related to temperature and salinity cause cold, salty water to sink, driving deep ocean currents through thermohaline circulation.

Q: How do currents redistribute heat?
A: Currents circulate warm water from the equator towards the poles and colder water from the poles back down, regulating global temperatures.

Q: What is the Coriolis effect?
A: The Coriolis effect causes winds and currents to be deflected by the Earth's rotation, creating clockwise gyres in the northern hemisphere.

Q: What is the global conveyor belt?
A: The global conveyor belt is the longest current, circulating deep cold water up to the surface and around the world.

Q: How fast do currents move?
A: Surface currents can move over 1 meter/second, while deep ocean currents are much slower at a few cm/second.

Q: Why are currents important to study?
A: Ocean currents impact climate, weather, marine ecosystems and more, so understanding them is key for forecasting and preparation.

Q: How do currents affect climate change?
A: Changes in currents like the global conveyor belt slowing down can greatly impact climate around the world.

Q: Can currents be predicted and tracked?
A: Studying currents helps scientists model and predict them, while events like rubber duck spills give insight into real-time tracking.