Many species of jellyfish inhabit the Gulf Stream. Despite their ability to swim, jellyfish are considered plankton because their movement is mostly directed by the prevailing currents. True jellyfish are members of the phylum Cnidaria, while comb jellies are members of the phylum Ctenophora.
- The ocean is a dynamic body of water, constantly affected by factors including tides, waves, and currents.
- An ocean current is the steady flow of ocean water in a prevailing direction. Ocean currents can be thought of as rivers in the ocean.
- Currents are responsible for the vast majority of water movement on the Earth’s surface.
- Currents often move only a portion of the entire water column (conceptual column of water from the surface to the bottom). For example, some currents move only surface water, whereas other currents move only deep ocean water.
- Currents can be caused by differences in temperature or salinity between two water masses, or by wind.
- Currents affect weather, transportation of marine organisms, and the cycling of nutrients in the ocean.
- Knowledge of ocean currents is important for the shipping and fishing industries. It is also crucial in search-and-rescue operations.
There are three main types of currents:
1. Deep Ocean Currents: Water movement patterns more than 300 feet below the surface of the ocean.
- Deep ocean currents are usually driven by density differences between masses of water. Cold, salty water is denser than warm, less salty water. Deep ocean currents move more slowly than surface currents.
- The Global Ocean Conveyor Belt is an example of a water circulation pattern that is driven, in part, by deep ocean currents. It takes one water molecule 1,000 years to complete a full global circuit.
The global conveyor belt moves water throughout the world's oceans. Sea water freezes in the Arctic Ocean, excluding salt. The remaining cold, dense sea water sinks and moves south and east, carried by the rotation of the Earth. Deep water upwells off the coast of India and North America, where it travels south and west, and then north and west toward Antarctica to start the process again. A single water molecule completes this cycle in approximately 1,000 years.
- The Global Ocean Conveyor belt is important to the global food chain. It enriches nutrient-depleted surface waters by carrying them through the ocean’s deeper layers where nutrients are abundant. This enables the growth of algae and seaweed that support life in the ocean.
2. Tidal Currents: Currents generated by tides – long, periodic waves generated by the gravitational force of the sun and moon.
- Tidal currents are the horizontal movement of water, which accompany the rise and fall of water during tidal changes.
- Tidal currents do not flow in a continuous stream. Instead, they switch directions as the tide ebbs and flows.
- Tidal currents do not affect the open ocean. However, they can create very fast water movement as water flows in to and out of bays and estuaries.
Tidal currents often flow quickly through narrow openings between islands. In barrier island systems, such as the system off the coast of Southwest Florida, tidal currents bring ocean water through inlets into bays and estuaries, creating a dynamic and ecologically important ecosystem.
- Rapid tidal currents can transport sediments and marine life, including young animals and eggs.
3. Surface Currents: Ocean currents that occur at depths less than or equal to 300 feet. Surface currents are driven primarily by wind.
- Near shore, surface currents are often observed in the form of longshore currents (currents created by the energy released when waves break on the beach) and rip currents (the result of waves funneling out of a narrow opening)
- Surface ocean currents are found in the open ocean. They are driven by global wind patterns.
- As the Earth rotates, air moving above the Earth’s surface appears to be deflected, or curved. This deflection is known as the Corriolis (kôr’ē-ō’lĭs) effect, and as a result air in the Northern Hemisphere appears to be deflected to the right (when viewed from Earth) and air in the Southern Hemisphere appears to be deflected to the left (when viewed from Earth). Since wind is the major driver of ocean surface currents, the Coriolis effect greatly influences the path of global surface currents.
Currents in the Gulf of Mexico
- The Gulf of Mexico is characterized by numerous surface ocean currents, most of which are interconnected.
The currents in the Gulf of Mexico are influenced by the Corriolis effect and the shape of the Gulf basin. The Corriolis effect causes the loop current to rotate clockwise, while the shape of the basin allows the loop current to flow into the Gulf Stream.
- Most saltwater enters the Gulf of Mexico from the Caribbean Sea through a narrow passage between the Yucatan Peninsula and Cuba. This passage is called the Yucatan Channel, or the Straits of Yucatan.
Much of the water in the Yucatan Current follows the Yucatan Peninsula north and west, continuing toward the western Gulf. - The eastern portion of the Yucatan Current flows along the northern edge of Cuba and becomes the Florida Current.
- A third, central portion of the Yucatan Current flows northward, and then to the east, eventually turning southward towards the Florida Keys. This is called the Gulf Loop Current.
- On the far eastern side of the Gulf of Mexico, the Florida Current and the Gulf Loop Current combine and flow between the southern tip of Florida and Cuba. This flow of water forms the Gulf Stream. It is joined and strengthened by an Atlantic current (the Antilles Current).
- The Gulf Stream continues to flow northward along the eastern seaboard of North America, and eastward to northern Europe.
The Gulf Stream
- The Gulf Stream is a particularly strong current that carries warm water north from the Gulf of Mexico up the eastern coast of the United States and across the Atlantic to Western Europe.
- The Gulf Stream moves 100 times more water than all the rivers on Earth combined and flows 300 times faster than the Amazon – the world’s largest river.
Podcast: Learn About Ocean Currents
Review Questions
1. What is a current?
2. What are the three main causes of currents in the ocean?
3. List the three main classifications of currents.
4. What type of current is the Gulf Stream?
Glossary
Corriolis (kôr’ē-ō’lĭs) effect: The apparent (when viewed from Earth) deflection of objects (including air) above he surface of the Earth as a result of the Earth’s rotation. Objects in the Northern Hemisphere appear to curve to the right whereas objects in the Southern Hemisphere appear to curve to the left.
Current: The steady flow of water in a prevailing direction.
Deep Ocean Current: Water movement patterns more than 300 feet below the surface of the ocean.
Density: The mass per unit of volume of a substance.
Global Conveyor Belt: A large-scale ocean circulation pattern driven by wind and density differences in the ocean. Cool, high salinity water sinks in the North Atlantic, travels in deep ocean currents south to Antartica, east across the globe, and north to the North Pacific, where it rises to the surface due to upwelling. Water then moves in surface ocean currents south and west toward the tip of Africa and north via the Gulf Stream, returning finally to the North Atlantic.
Gulf Stream: A warm ocean current that flows from the Gulf of Mexico northward through the Atlantic Ocean.
Longshore Current: A current created by the energy released when waves break on the beach; these currents travel parallel to the beach.
Rip Current: A current that is the result of water funneling out of a narrow opening; the water flows away from land.
Surface Current: Ocean currents that occur at less than 300 feet below the surface of the ocean; most ocean currents are usually wind-driven.
Surface Ocean Current: Surface currents found in the open ocean (pelagic regions), driven mostly by global wind patterns.
Tidal Current: Currents generated by tides.
Tide: The rise and fall in sea level caused by the gravitational forces of the moon and sun in combination with the rotation of the Earth.