Oceanography studies the structure of the oceans: how they are created and destroyed. It explores how ocean topography varies from the shoreline and continental shelf to the ocean basin, abyssal plain and trenches. This unit studies the ocean as a habitat and the chemistry and properties of seawater, including how light and sound are transmitted. Learn how waves are formed and how the major currents move around ocean basins.
The Earth’s crust consists of six major plates and several smaller ones that move relative to each other. The direction of motion of each plate is determined by the nature of the plate boundary.
Plates separated by mid ocean ridges are moving apart and those separated by mid-ocean trenches and active mountain chains are moving toward each other. Some plates simply slide past one another moving neither toward nor away from each other. These are known as constructive plate margins. Passive plate margins slide alongside one another and are called conservative plate boundaries. An example is the San Andreas Fault in California, which is responsible for most of the earthquakes in the San Francisco-Los Angeles area.
This course explores the fascinating subject of Oceanography and is suitable for those wanting a career change and anyone interested in learning more about Oceans.
Ocean Margins and Plates
Active plate margins include subduction zones and sea-floor spreading and involve volcanic activity. They include destructive plate boundaries and constructive plate boundaries. The configuration of the oceans has changed many times over the Earth’s geological history – this is due to a process known as continental drift. The shape of an ocean and its features, depend on the stage of the ocean’s formation.
Young oceans have passive margins and mid-ocean ridges while declining oceans have many destructive plate boundaries, both at the ocean’s margins and within the ocean lithosphere. They may have submarine volcanoes and islands formed from the welling up of hot magma from the asthenosphere. Continental margins types vary as well, with passive margins and continental shelves in young and mature oceans and deep trenches (subduction zones) and narrow continental margins in declining oceans.
Ocean waters and Currents
Seawater is an unusually pure substance being almost 96.5% pure water, the rest being made up of dissolved substances, mainly sodium (Na+) and chloride (Cl-) which make seawater so remarkable. Water makes up 80 to 90% of the volume of marine organisms, provides support and buoyancy (thereby reducing the need for a heavy skeleton) and facilitates the chemical reactions necessary for life.
Without water, life on Earth would probably not exist.
Tides are really just extremely long period waves which only really become noticeable on the shoreline as the rise and fall of the tide. On most coastlines there are two high tides and two low tides over a 24hr period. The tidal range is the difference between the high tide mark and the low tide mark and can vary between just a few centimeters in the Mediterranean Sea to more than 15m in the Bay of Fundy off the east coast of Canada.
Tides can be accurately predicted and tide tables are available for the time and height of the tides.
Where winds blow consistently in speed and direction over the ocean, surface currents occur and represent large scale horizontal movements of water with shallow bands of water moving water slowly across the ocean. Some currents move vast amounts of water, more than 100 times the volume of water found in all the rivers on Earth. Such currents affect the rate of heat transport as well as the distribution of marine organisms.