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Oceanography 8th Grade What are Earth’s five main oceans? Almost three-fourths of Earth is covered by ocean water. On a map, the continents appear as huge islands surrounded by a vast global ocean. Earth’s global ocean is divided into five main oceans. In decreasing order of size, they are the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. What are some characteristics of ocean water? The chemical characteristics of ocean water include salinity, or the amount and type of dissolved salts. Chemical characteristics also include the amount and type of gases in the seawater. The physical characteristics of ocean water include temperature and density. The overall salinity of seawater is about 3.5 percent. The salinity of seawater has remained relatively steady, but it varies from place to place depending on the entry of freshwater streams, precipitation, and rate of evaporation. The ocean has three temperature layers by depth. The top layer, or surface zone, is the warmest layer. In the next layer, the thermocline, water temperature drops with increased depth faster than it does in other layers. The deep zone is the deepest layer and the coldest. By latitude, surface water is warmest near the equator and coldest near the poles. By season, surface water is warmest in summer and coldest in winter. Density is a measure of the mass of a substance divided by its volume. The density of ocean water depends on temperature and salinity. How is the ocean floor studied? To learn about the ocean floor, scientists use technology such as sonar, drills, underwater exploration vessels, and satellites. Sonar, which stands for sound navigation and ranging, uses sound waves to measure distances. Sonar data can be used to make maps of the ocean floor. Satellites can measure variations in the height of the ocean’s surface. The ocean floor’s features can affect the height of the water above them. To explore the oceans, scientists use underwater vessels, some of which have pilots and researchers. Other vessels are remotely operated. Using equipment on large ships, scientists can drill and collect cores, or long tubes of rock and sediment, from the sea floor. What are the two main regions of the ocean floor? The two main regions of the ocean floor are the continental margin and the deep-ocean basin. The continental margin is the edge of the continent that is covered by the ocean. The continental margin is divided into the continental shelf, the continental slope, and the continental rise. The deep-ocean basin begins at the end of the continental margin and extends under the deepest parts of the ocean. The deep-ocean basin includes narrow depressions and flat, smooth plains. What are the features of the ocean floor? A long, undersea mountain chain that forms along the floor of the ocean is called a mid-ocean ridge. Mid-ocean ridges occur at the boundaries of Earth’s tectonic plates, where plates move apart from each other. This motion creates a crack in the ocean floor called a rift, allowing hot magma to move upward through the rift and cool to form new rock. The large, flat, almost level area of the deep- ocean basin is called the abyssal plain. This area is covered with layers of fine sediment. A long, narrow depression in the deep-ocean basin is called an ocean trench. It forms where one tectonic plate subducts another plate. Volcanoes and earthquakes are common in and along subduction zones. Submerged volcanic mountains on the ocean floor are called seamounts. They may form at tectonic plate boundaries and also far from plate boundaries over places called hot spots. If a seamount grows above sea level, it becomes a volcanic island. What are some properties of a wave? A wave is any disturbance that transfers energy through matter or empty space. An ocean wave is a disturbance that transfer energy through ocean water. A wave is made up of two main parts: a crest, which is the highest point of the wave, and a trough, the lowest point of the wave. The distance between two adjacent wave crests or troughs is a wavelength. Wave amplitude is half the distance between the crest and the trough. Frequency is the number of waves produced in a given amount of time. Wave period is a measurement of how much time it takes for a wave to pass a fixed point. It is the inverse of frequency. Wave speed is how fast a wave travels. To calculate a wave’s speed, multiply its wavelength by its frequency. What causes ocean waves? Ocean waves are a type of wave known as a mechanical wave. Mechanical waves carry energy through matter, such as water. Most ocean waves form when energy in the atmosphere is transferred to the ocean’s surface. Wind blows across the water’s surface and transfers energy to the water, and this energy is carried by the wave. Ocean waves can also be produced by underwater earthquakes, underwater landslides, and underwater volcanoes. If a meteorite or an asteroid landed in the ocean, it could displace enough water to cause large waves. What happens when a wave moves through the water? Ocean waves are formed when wind transfers energy to the water. As the energy moves through the water, so do the waves. The water itself does not travel with the energy. But water at the surface undergoes circular movement. Wave energy affects surface water to a depth of about half a wavelength. What happens when a wave reaches the shore? Ocean waves transfer energy to the shore; water at the wave bottom slows, but water at the top travels at the original speed. Waves break as gravity pulls crests down. What is a tsunami? A tsunami is a series of waves that form when a large volume of ocean water is suddenly moved up or down. This movement can be caused by earthquakes, volcanic eruptions, landslides, or the impact of a meteorite or asteroid. When a tsunami approaches land, the waves slow down and get taller as they interact with the ocean floor. What are ocean currents? Ocean currents are stream-like paths of water in the ocean. A surface current is an ocean current near the surface caused by wind. What affects surface currents? The Coriolis effect causes surface currents to curve right or left. Continental deflection causes currents to change direction when flowing toward land. Energy from surface winds can transfer to water, causing surface currents. How do deep currents form? A deep current is a stream-like movement of ocean water far below the surface. It forms when surface water becomes denser than water below, causing it to sink and become a deep current. What are convection currents and how do they transfer energy? A convection current is any movement of matter resulting from density differences. Convection currents transfer energy when warm water is moved to colder regions. What is upwelling? Upwelling is the movement of deep, cold, nutrient-rich water to the surface. Upwelling brings nutrients from the deep ocean to the surface. What do ocean currents transport? Surface and deep currents and upwelling move ocean water through ocean basins. Matter transported by currents includes water and dissolved solids and gases. Energy is transported from areas near the equator toward Earth’s poles.