Chapter 24: Currents

Gyre

A circular current of water in the oceans. Surface currents are cause by surface winds, which are affected by the Coriolis Effect, and so by extension, surface currents in oceans tend to go circularly. If you look at the picture, the westerlies and the easterlies blow in a way that forms circular currents. As the Coriolis Effect changes based on hemisphere, in the Northern Hemisphere gyres flow clockwise while in the Southern Hemisphere gyres flow counterclockwise.

Ocean Currents

A continuous flow of water along a path in the ocean that often involves large water masses.

Basin

A region in which an ocean lies. So the Pacific Ocean and the Atlantic Ocean has their own basins.

Surface Currents

An ocean current that flows in the upper ocean. Surface currents are caused by surface winds, which are the prevailing winds, the Coriolis Effect, and by continental deflection.

Cold Currents

Cold currents are surface currents that contain cold water, generally flowing from the poles towards the equator on the eastern side of ocean basins. One cold current, the Labrador (north of New England) flows towards the Gulf Stream. When warm air of the Gulf Stream blows over the Labrador, thick fog occurs due to condensation.

Continental Deflection

Continental deflection occurs when an ocean current hits land. As the current can no longer flow in the direction it previously was due to the land, it gets deflected in another direction.

Countercurrents

Countercurrents are surface currents that flow in the opposite direction of the prevailing winds. Some countercurrents flow at the surface of the ocean or slightly below it. Countercurrents are formed at the equator as the trade winds push ocean water against the continents. This piles water on the western basin while leaving a deficit on the eastern basin, and so the countercurrent forms to return the water. Countercurrents are a form of continental deflection. The Cromwell Current is a countercurrent that flows 30 meters below the surface and it flows below the South Equatorial Current and is a major ocean current due to its size.

Deep Ocean Currents

Currents that flow in the lower ocean basins and are cause by density differences. Deep ocean currents are often composed of polar water because of their high density.

Density Currents

Density currents are caused by a water mass being denser than the surround water mass and so the denser water mass sinks down. The water mass then circulate in the deep ocean before resurfacing after a long time. Density currents are important because they bring oxygen down to the deep water, supporting life down there. Density currents are help distribute heat throughout the Earth. In the Atlantic Basin, there are three major density currents. From highest to lowest density goes the Antartic Bottom Water, North Atlantic Deep Water, and the Antartic Intermediate Water.

Spring Tides

Extra strong tides that are caused when the sun and the moon are aligned together, which happens during full moon and new moon. The sun's gravity and the moon's gravity act together to create stronger than usual tides. High tides are higher than usual and low times are lower usual.

Neap Tides

Extra weak tides that caused when the sun and moon are 90 degrees of each other, which happens at quarter moons. The sun's gravity and the moon's gravity act aginst one another to create weaker than usual tides. High tides are lower than usual and low tides are usual higher.

High Tide

High tides exist due to the gravity of the moon pulling the oceans towards the moon.

Low Tide

Low tides exist as more water are at the two high tides. The two high tides reduce the amount of water that is present at the other two sides of the Earth, causing low tides.

Cold Core Rings

Occasionally, the parts of the Gulf Stream wanders and become eddies/whirlpools. When the ring forms, it takes a column of water from the opposite side of the Gulf Stream. A ring that forms on the east side of the Gulf Stream takes cold water from the continent side and becomes a cold core ring. In the picture the red is the Gulf Stream

Warm Core Rings

Occasionally, the parts of the Gulf Stream wanders and become eddies/whirlpools. When the ring forms, it takes a column of water from the opposite side of the Gulf Stream. A ring that forms on the west side of the Gulf Stream takes warm water from the Sargasso Sea and becomes a warm core ring. In the picture the red is the Gulf Stream.

Mediterranean Density Current

The Mediterranean Sea is has a high density due to its high salinity. This high salinity is due to the Mediterranean having high temperature because polar deep water is not present in the sea (chapeter 22). When Mediterranean water flow out of the Straits of Gibraltar, it sinks because it is denser than North Atlantic surface water.

Perigee

The closest point of the moon's orbit to Earth. When the moon is at perigee, its effect on the tides are increased as it is closer to the Earth, thus increasing its gravitational effects.

Tidal Range

The difference between high and low tide. Tidal range differs between different bodies of water and is more visible in oceans than in lakes.

East Side of an Ocean Basin

The east side of an ocean basin (or the west side of continents) generally has a cold current running past it. This is because of how the gyres spin. In the Northern Hemisphere, the gyres spin clockwise, going higher in latitude and taking with it cold polar water before finally reaching the west side of a continent. Take for example the north western region of Africa. The North Atlantic Gyre rotates clockwise, and the upper half of the gyre flows through cold polar regions before finally reaching Northern Africa, bring that cold polar water as well.

Apogee

The furthest point of the moon's orbit to Earth. When the moon is at apogee, its effect on the tides are decreased as it is further from the Earth, thus decreasing its gravitational effects.

Indirect High Tide

The high tide on the side of the Earth that faces away from the moon is called the indirect high tide because its cause is indirect. Gravity is stronger the closer the objects are; the core of the Earth is closer to the moon than the ocean opposite to the moon, thus pulling the Earth towards the moon more than the ocean, causing a bulge of water to form behind, creating high tides. In the picture, the high tide to the left is the indirect high tide.

Direct High Tide

The high tide on the side of the Earth that faces the moon is called the direct high tide because the gravity of the moon is directly causing the high tide. Gravity is stronger the closer the objects are; the ocean on the side of the moon is closer than the Earth's core, thus pulling the ocean towards the moon more than the core, causing high tides. In the picture, the high tide to the right is the direct high tide.

V-Shaped Bays

The shape of a bay can affect the tidal range. The Bay of Fundy for example has a wide entrance from the Atlantic Ocean, but overtime narrows down. As water reaches the end of the "V", the water piles up, making high tides more noticiable, and on the flipside low tides more visible as well because there will be significantly less water. Another example is the Gulf of Mexico. The Gulf of Mexico's entrance is smaller than its shoreline. The rises at the entrance before falling back down as it spreads throughout the gulf, making its tides less noticiable.

Tides

The twice-daily rise and fall of the ocean surface due to the gravity of the moon and sun. The tides can be influenced by ocean basins, ocean floors, and shorelines. (Read high tide & low tide first) As the moon rotates around the Earth, it brings high tides as low tides around the Earth. And because the moon rises 50 mins later everyday, tides also occur 50 mins later everyday.

West Side of an Ocean Basin

The west side of an ocean basin (or the east side of continents) generally has a warm current running past it. This is due to how the gyres spin. In the Northern Hemisphere, gyres spin clockwise, going lower in latitude and taking with it warm equatorial water before finally reaching the east side of a continent. Take for example Japan. The North Pacific Gyre rotates clockwise, the lower half going through warm equatorial water before finally reaching Japan, bring that warm water.

Correct Reading

This set should be used as a condensed version of the textbook. This set will not touch on every single detail mentioned in the textbook, but it will try to explain major details and important information. It is better used by reading the cards instead of trying out games or the learning tool.

Upwelling

Upwelling is a vertical current in oceans. It is the rising of deep cold water to the surface. Upwelling can occur anywhere, but commonly occurs near the western sides of continents because the westerlies push water against the coastline. The Coriolis Effect combined with continental deflection curves the surface currents away from the continents. To replace the water that has moved away, deep water rises. Upwelling also occurs at 60 degrees south in the Antarctic Ocean. The prevailing winds there (the trade and the westerlies) move in opposite directions. This cause a depression which is filled by rising deep water. Upwelling is beneficial to life as upwelled water contains large amounts of nutrients that phytoplankton use to grow. When phytoplankton thrive, it provides more food for consumers and so areas of upwelling often become areas of life.

Warm Currents

Warm currents are surface currents that contain equatorial water, generally flowing on the western side of ocean basins. The Gulf Stream is a very important warm current, and because of it Ireland and the British Isles are warmer than they otherwise would be.

Seasons Effect on Currents

While seasons do not generally change the direction of ocean currents, seasonal winds like the monsoons can. When the direction of the monsoon winds reverse, the direction of ocean currents also reverse.