Chapter 11.2, Ocean Currents

Density Current

A density current is the sinking and movement of dense water beneath surface water. By constantly moving large amounts of water around, it creates things like great fishing to strange weather.

Tidal Range

A tidal range is the difference between high tide and low tide. The shape of the coastline has a large effect on tidal range. For example, narrower areas can funnel the high tide into a smaller area, making it higher.

Deep Water Currents

Deep water currents are ocean currents that occur deeper than around 200m down, counting from the surface level. It has a major effect on the ocean's ecosystem and human activities.

Coastlines Developed by Waves

Depending on how waves erode and deposit rock, coastlines can become sandy beaches with low slopes or steep cliffs that rise like rock walls from the water.

Effect of Earth's Spin on Currents

Earth's spin on its axis affects both winds and ocean currents. Because it spins from west to east (counter-clockwise), winds and currents moving over it get their paths redirected depending on which side of the equator they're on. This is known as the Coriolis Effect. To someone standing on the northern hemisphere, the wind and currents would seem to be deflected to the right (east). To someone standing on the southern hemisphere, the wind and currents would seem to be deflected to the left (west).

Headlands

Headlands are sections of coastlines that extend into the ocean. They are usually made of harder rock than the surrounding land, which is why they haven't eroded back as much. However, waves hit them before reaching the shoreline, so they receive the main force from waves. Headlands absorb the energy, so the remaining waves spread out and can't erode very well.

Low Tide

Low tides occur because water is pulled to the bulges where the high tides are. This leaves the areas of low tide with less water. They are the areas between the two high tides.

Neap Tides

Neap tides occur when the Sun and Moon are not in line. This causes their gravitational pull on Earth's water to be reduced. This causes high tides to be not as high and low tides to be not as low.

Seastacks

Sea stacks are the remains of headlands that have been heavily eroded by ocean waves for millions of years.

Spring Tides

Spring tides occur when the Sun and Moon are lined up. Their combined gravitational pull creates especially high high tides, which causes low tides to be even lower. These occur twice a month.

Surface Currents

Surface currents are the currents found near the surface of the ocean. Their range extends from the surface to an average depth of 200m down. It has a major effect on the ocean's ecosystem and human activities.

Swells

Swells are large, rolling waves that form in the open ocean. Most are a few meters high, but some are over thirty meters high, or the height of a ten story building.

Antarctic Circumpolar Current

The Antarctic Circumpolar Current is the world's largest ocean current. It is in the Southern Ocean, and is 24 000 km long. It circles Antarctica, and carries 100 times more water than all the rivers on Earth combined, which is equal to three million cubic km.

Bulge

The bulge caused by the moon is what we call the high tide. There are two high tides at opposite sides of Earth, and the bulges are created because water in between them is pulled towards the bulge.

Deep Water

The deep water layer is from around 1000 to 5000 meters deep. Its temperature stays around four degrees Celsius

Causes of Deep Water Currents' Movement

The movements of deep water currents can be caused by the temperature and salinity of water

Sea Floor

The sea floor is at the base of the ocean, around 5000 meters below surface level. It is around four degrees Celsius.

Thermocline

The thermocline is a layer where the sun cannot be as consistent in warming it. The temperature drops rapidly here, ranging and moving from around 28 degrees Celsius to four degrees Celsius. It reaches from around 300 to 100 meters below the ocean's surface.

Gravity and Tides

Tides are caused by gravity. One high tide is caused by the Moon pulling the water towards it, and the other is caused by the Moon pulling Earth towards it and away from the water.

Tsunami

Tsunamis are the largest waves in the ocean. They are created by earthquakes on the ocean floor, a landslide, or a volcanic eruption near the coast that sends lots of material into the ocean.

Ocean Current

An ocean current is a large amount of ocean water that moves in one, unchanging direction. There are over twenty major ocean currents in the world. The enormous amounts of water transport lots of dissolved minerals, solar energy, oxygen, and carbon dioxide around Earth. Also, fish and plankton are moved.

Upwelling

And upwelling is the rising of water from the deep. It brings up nutrient-rich waters to the surface, which feeds plankton, a main food source for fish and other organisms in the ocean. Surface winds can cause upwellings too. Strong winds blowing the surface water away from the shore causes deep ocean water to rise and take its place.

Bays

Bays are indented areas in the coastline where the ocean reaches into the land. Waves that reach bays have lost most of their energy, so the waves slow down. Because of the slowing, the waves deposit some of the sediments eroded from the headlands onto the bays.

Breakers

Breakers are swells that reach shallow water. They are what surfers at the coast of Vancouver Island use to surf on.

High Tide

High tides are caused when the moon pulls Earth's ocean water towards it. This creates a bulge, or a high tide. The water on the other side of Earth is further from the Moon than Earth is, though, so the Moon is pulling Earth away from it. This creates a second bulge, or the high tide on the other side of Earth.

Ocean Waves Shaping Land

Ocean waves shape the land. When the waves hit a coastline, it can erode even the hardest rock. The force of the wave and type of rock decides how quickly the rock is eroded. However, the waves also deposit sediments. As a result of erosion and deposition, some coastlines have sandy beaches and others have steep cliffs that rise like rock walls.

Plankton

Plankton are microscopic plants and animals that are an essential food source for all other organisms in the ocean. They are carried around Earth by ocean currents.

The Coriolis Effect

The Coriolis Effect is one of the factors that affect the movement of surface currents. It is named after Gaspard-Gustave Coriolis, because of his significant accomplishments in science and math. It is caused by Earth's rotation, and results in the path of air being redirected clockwise (right) in the northern hemisphere and counter-clockwise (left) in the southern hemisphere.

Mixed Layer

The mixed layer is the same as the ocean surface. It is generally about 25-30 degrees Celsius. It is at around zero to 300 meters of depth. It is the warmest, as the sun heats the water.

Causes of Surface Currents' Movement

The movement of surface currents can be caused by wind action, Earth's spin, and the shape of continents.

Ocean Surface

The ocean surface is the same as the mixed layer. It is generally about 25-30 degrees Celsius. It is at around zero to 300 meters of depth. It is the warmest, as the sun heats the water.

The Effect of Continent Shape

The shape of continents is something that affects the movement of surface currents. It affects the way surface currents move like how a large rock in the path of water in a stream would affect the water in the stream's flow. Even though Earth's ocean water is all connected, we treat it as five different ocean basins because it's sort of separated by the natural barriers of the continents.

Water Salinity

The water's salinity is another factor that affects the movement of deep water currents. Water with high salinity is denser than water with low salinity. The densest (coldest, saltiest) water around the North and South Poles sink and flow along the ocean floor until they are warmed by the water near the equator. It can take from 500-2000 years for it to make it back to the ocean's surface.

Tide

Tides are the daily cycle of rising and falling ocean water. They are caused by the gravitational attraction between Earth, the Moon, and the Sun. The Moon's pull on Earth causes the ocean to bulge upwards, causing a high tide. The water on the opposite side bulges too, and the sides in between have their water pulled towards the bulges, creating a low tide.

Water Temperature

Water temperature is one of the things that make deep water currents move. Because the ocean doesn't have the same temperature at every depth and cold water is denser, cold water will sink beneath warmer water. The cold water will then begin to move along the ocean floor. This sinking and movement of dense water beneath surface water is called a density current. Also, this creates layers of water in the ocean.

Wind's Effect on Currents

Wind is one of the things that affect, and make surface currents move. Because wind is the result of masses of air moving from one place to another because of temperature differences, its movement often crosses over the ocean's surface. When this happens, its energy is transferred to the water molecules, which causes the ocean water to move.The direction and speed of ocean currents is directly connected to the direction and speed of the wind blowing over the water.