2 The Blue PlanetNearly 71% of Earth’s surface is covered by the global oceanIt has only been since the late 1800s that the ocean became an important focus of scientific studiesOceanography – a science that draws on the methods of geology, chemistry, physics and biology to study all aspects of the world ocean
4 Geography of the Oceans The world ocean can be divided into four main ocean basins – the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic OceanThe Pacific Ocean is the largest ocean and the largest geographic feature on Earth (deepest at an average depth ~ 3940 m)The Atlantic Ocean is about half the size of the Pacific, and much more narrowThe Indian Ocean is slightly smaller than the Atlantic, but has about the same average depthThe Arctic Ocean is only about 7% the size of the Pacific and about ¼ as deep as the rest of the oceans
6 Concept Check What are the four main ocean basins? Pacific Ocean, Atlantic Ocean, Indian Ocean, and Arctic Ocean
7 Mapping the Ocean Floor If all the water were drained from the oceans, we would see everything from chains of volcanoes, tall mountain ranges, trenches, and large submarine plateausThe topography of the ocean floor is as diverse as that of continentsBathymetry – the measurement of ocean depths and the charting of the shape or topography of the ocean floorToday’s technology – particularly sonar, satellites, and submersibles – allows scientists to study the ocean floor in a more efficient and precise manner than ever before
9 Sonar Sonar is an acronym for sound navigation and ranging It works by transmitting sound waves toward the ocean bottomA sensitive receiver intercepts the echo reflected from the bottomThen a clock precisely measures the time interval to fractions of a secondDepth can be calculated from the speed of sound in water and the time required for the energy pulse to reach the ocean floor and return
11 SatellitesWe can now measure the shape of the ocean floor from space with satellites orbiting EarthGravity attracts water towards regions where massive ocean floor features occurThis produces relative elevated areas on the ocean surface by mountains and ridges and depressions at canyons and trenchesDevices on satellites can measure variations in sea-surface height as small as 3-6 cmUsing this data and sonar data, scientists are creating detailed maps of the ocean floor
13 Concept CheckHow do satellites help us learn about the shape of the seafloor?Satellites bounce microwaves off the ocean surface. Outgoing radar pulses are reflected back to the satellite and can be used to detect differences in sea surface height that can be correlated to seafloor features.
14 SubmersiblesSubmersible – a small underwater craft used for deep-sea researchThey are used to collect data about areas of the ocean that were previously unreachable by humansMost submersibles are unmanned and operated by computers