The Global OceanThe Vast World Ocean
Objectives
• What is oceanography?• What is the extent and distribution of the
world’s oceans?• What techniques are used to map the
ocean floor?
What is oceanography?
• Interdisciplinary science• Draws on methods/knowledge of geology,
chemistry, physics, biology
Ocean Geography
• Earth’s surface area: ~510 million km2
• Oceans + marginal seas (Mediterranean, Caribbean, etc.): ~360 million km2 (71%)– Northern hemisphere: 61% water, 39% land– Southern hemisphere: 81% water, 19% land
Distribution of Land & Water
Uneven Land & Water Distribution
Four Ocean Basins +• Pacific
– > half of total ocean surface area – all continents could “fit” in it
– Deepest (3940 meters)• Atlantic
– Half the size of the Pacific– Average depth is 3339 meters– Land that drains into the Atlantic covers four
times that of either the Pacific or Indian oceans
Four Ocean Basins +• Indian
– About the same average depth as Atlantic but slightly smaller
– Mostly in Southern Hemisphere• Arctic
– Surface area is ~ 7% of Pacific Ocean– 25% as deep
Four Ocean Basins +• Southern Ocean
– Meeting of currents near Antarctica– Portions of Pacific, Atlantic & Indian south of
50 latitude
Four Ocean Basins +
Four Ocean Basins +
Comparing the Oceans to the Continents
• Continents – 840 meters above S.L. (average)
• Oceans – 3729 meters deep
The Global OceanAn Emerging Picture of the Ocean Floor
Mapping the Seafloor
• HMS Challenger (1872-1876)– 1st comprehensive study of global ocean– Measured water depth using weighted lines
Mapping the Seafloor
Mapping the Seafloor
Modern Bathymetric Techniques
• Bathymetry – measurement of ocean depths and the charting of the topography of the ocean floor
• SONAR – sound navigation and ranging
Modern Bathymetric Techniques• Echo sounders
– Early 20th century– Transmit sound wave
(ping) that echoes when it hits an object
– Travel time is measured – Depth =
1 meters1500 echo travel time in seconds2 sec
Mapping the Seafloor
Scientists "See" Ocean Floor via Sonar
Side Scan SONAR
Viewing the Ocean Floor From Space
• Radar altimeter measures ocean surface height variations induced by ocean floor topography.
• Better resolution but much higher cost if an echo sounder is used.
• When interesting features are discovered in satellite gravity measurements, these can be surveyed in fine detail by ships.
Seismic Reflection Profiles• Strong low-frequency sounds are
produced by depth charges.• Used to estimate the properties of the
Earth's subsurface from reflected seismic waves.
Provinces of the Ocean Floor
• Continental margins• Deep-ocean basins• Oceanic (mid-ocean) ridge
Provinces of the Ocean Floor
