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