You are at the beach, standing at the edge of the water. Suddenly, you notice red flags waving, indicating danger offshore. The lifeguard warns you not to swim because of the hazardous currents. You wonder about the origins of this effect that prevents you from swimming.
Currents are found throughout the ocean—from its surface to the greatest depths of the sea. What are ocean currents? Why do they happen? How do they affect our climate?
The movement of a current is the result of “continuous and directed movements” of ocean water.
Even more simply, a current is the movement of water within water.
Currents are affected by several factors:
- variations in wind
- water density (due to changes in salt content or temperature)
Similar to riding a merry-go-round while throwing a baseball, ocean currents must follow a curved path as they travel across our continuously rotating planet.
The rotation of Earth on its axis, known as the Coriolis effect, causes currents in the northern hemisphere to flow clockwise and counter clockwise in the southern hemisphere. Some currents are short and temporary. Other oceanic currents are enormous flows of water that circle the globe for hundreds of years.
Currents are classified into two main categories: surface currents and deep ocean currents. Surface currents and deep-water currents interact to create the global conveyor belt. Currents are an essential part of Earth’s climate and play a key role in many important biological cycles.
Surface currents are influenced by wind systems that are driven by the sun’s energy. They transfer heat from the warmth of the equator to cold regions of the globe.
Deep ocean currents result from differences in temperature and salinity, known as thermohaline circulation.
As water becomes heavier with saltiness and cold, it sinks to the bottom. This water is replaced by additional surface water, which cools and sinks to the ocean floor.
Credit: US Global Change Research Program, Wikimedia Commons Ocean circulation works like a conveyor belt. Cold and salty currents sink to the bottom and warm shallow currents rise in a continuous cycle. The interaction of surface water and deep water creates the conveyor belt system.
Like a conveyor belt at a factory transports products, oceanic currents carry nutrients. Some oceanic currents flow short distances, while others flow very far to deliver nutrients. When parts and products are added to the conveyor belt, they are pulled through the machine and presented for further processing. In a similar way, currents deliver oxygen, heat, nitrogen, and other life-sustaining elements throughout the ocean.
However, the effects of climate change threaten these essential processes. Global warming is likely to increase rainfall in the North Atlantic as well as accelerate glacial melting. Increasingly warm freshwater added to the sea surface could inhibit the formation of sea ice, which prevents the changes in salt content that cause water to sink to the ocean floor. Consequently, the temperature of water carried by the currents would be altered. For example, the essential Gulf Stream which brings northwest Europe its unique temperate climate, would be affected.
A representation of the main cold and warm currents that regulate global climates is shown above.
Warming would have devastating effects on oceanic circulation and drastically alter global climates. Take action now to mitigate emissions and have a positive impact on “current” events!