The ocean covers 71% of Earth’s surface and is constantly in motion. Large masses of water that move together, called ocean currents, transport heat, marine organisms, nutrients, dissolved gasses such as carbon dioxide and oxygen, and pollutants all over the world. Climate and ecosystems everywhere on Earth, even those far from the ocean, are affected by the ocean circulation.
On this page:
For the classroom:
Global Change Infographic
Ocean circulation is an essential part of How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic. Locate the ocean circulation icon and identify other Earth system processes and phenomena that cause changes to, or are affected by, ocean circulation.
What is ocean circulation?
Ocean circulation patterns, the movement of large masses of water both at and below the surface, are determined by atmospheric circulation patterns, variation in the amount of sunlight absorbed with latitude, and the water cycle. Surface currents, also called horizontal currents, are primarily the result of wind pushing on the surface of the water, and the direction and extent of their movement is determined by the distribution of continents. Currents, like winds in the atmosphere, do not move in straight lines because of the spin of the Earth, which causes the Coriolis effect.
Currents that move up and down in the water column, also called vertical currents, are created by differences in the density of water masses, where heavier waters sink and lighter waters rise. This type of ocean circulation is called thermohaline circulation (therme=heat, halos=salt) because the vertical movement is caused by differences in temperature and salinity (the amount of salt in water). Adding heat decreases the density of water, while adding salt increases the density of water. Thermohaline circulation occurs because winds move warm surface waters from the equator towards the poles, where the water cools and increases in density. Some of this water gets so cold that it freezes, leaving its salt behind in the remaining water, further increasing the density of this water. This cold, salty water near the poles (primarily in the North Atlantic and near Antarctica) sinks and spreads along the bottom and eventually rises back towards the surface of the ocean. It takes about 1000 years for water to circulate around what is called the global conveyor belt that moves water three dimensionally throughout the world’s ocean basins.
Earth system models about ocean circulation
This model shows some of the cause and effect relationships among components of the Earth system related to ocean circulation. While this model does not depict the ocean circulation patterns that results from atmospheric wind and density differences in water masses, it summarizes the key concepts involved in explaining this process. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page.
The model below shows some of the additional phenomena that ocean circulation patterns affect. Ocean circulation is such an important process in the Earth system because currents transport heat, oxygen, nutrients, and living organisms. Most of the sunlight absorbed by water on Earth’s surface gets stored in our oceans as heat, and heat from the atmosphere is also absorbed by the ocean, which increases the ocean’s temperature. This heat is then transported by currents and re-radiated, influencing regional air temperatures and climates all over the globe. For example, the Gulf Stream in the Atlantic Ocean brings heat from near the equator to Europe, making it much warmer than other areas at similar latitudes. Hover over the icons for brief explanations; click on the icons to learn more about each topic.
How human activities influence ocean circulation
The Earth system model below includes some of the ways that human activities affect, or are affected by, ocean circulation. As the world warms due to increased levels of greenhouse gases in the atmosphere from human activities, changes in ocean and atmospheric circulation patterns will alter regional climate and ecosystems around the globe. Hover over or click on the icons to learn more about these human causes of change and how they influence, or are influenced by, ocean circulation.
Explore the Earth System
Click the icons and bolded terms (e.g. nutrient levels, atmospheric circulation, etc.) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.
To learn more about teaching ocean circulation, visit the Teaching Resources page.