Topic 3The Water Planet

GEOL 2503

Introduction to Oceanography

Earth?

Wouldn’t “Ocean” be a better name?

Water on the Earth’s Surface

• 71% of the Earth is covered by the oceans (139 million square miles)

• More than one-half of the world's population lives within 60 miles (100 km) of the ocean.

• Volume of water in the oceans = 1.37 billion cubic kilometers = 329 million cubic miles

• Volume of Earth:– approx: 1,100,000,000,000 cubic kilometers

• Volume of oceans:– 1,370,000,000 cubic kilometers

• Oceans make up only 0.125% of Earth’s volume

Ocean Surface area in square miles

Surface area in square kilometers

Of all oceans

Pacific 64,000,000 166,000,000 45.0%

Atlantic 31,600,000 82,000,000 22.2%

Indian 28,400,000 73,600,000 20.0%

Southern 13,523,000 35,000,000 9.5%

Arctic 4,700,000 12,173,000 3.3%

Total 142,223,000 368,773,000 100.0%

USA 3,794,083 9,826,630

Georgia 59,441 153,952

How much water exists in the oceans?One estimate of global water distribution:

Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed.

by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.

Water source Volume, in cubic mi

Volume, in cubic km

Percent of total water

Oceans, seas and bays 321,000,000 1,338,000,000 96.5

Total global water 332,500,000 1,386,000,000 100

Sphere Depths

• Assume Earth is a perfectly smooth ball• The oceans would cover the globe to a

depth of 2646 meters (ocean sphere depth).

• Add all of the remaining water from the land and the atmosphere would increase the depth by 75 meters to 2721 meters (total water sphere depth).

Sphere depth

The Global Ocean

Continents can be considered as islands in a single, world ocean.

Pacific

Atlantic

Indian

Ocean

The illustration shows how water evaporates from the ocean, land, and rivers. The evaporated water condenses in the cooler altitudes and falls to the ground as rain or snow. See http://ga.water.usgs.gov/edu/watercycle.html.

The Hydrologic Cycle

• Reservoirs—the places in which water resides

-oceans -lakes

-rivers -groundwater

-glaciers -atmosphere

-snow packs -sea ice

See previous slide and USGS web page

The Hydrologic Cycle

• Hydrologic cycle – typically know as the water cycle

• Evaporation water changes from a liquid to a gas as water vapor.

• Precipitation water that falls to the ground in many forms – ice, snow, rain, hail.

• Excess water on land returns to the ocean by rivers

What is Residence Time?

• Rate of removal from reservoirs must equal rate of addition to reservoirs

• Residence Time—time that water spends in any one reservoir

• Oceans oven have a residence time of thousands of years because of their size.

• Small reservoirs, such as the atmosphere, have short residence times, days to weeks.

The Distribution of Land and Water

• 70% of Earth’s landmasses are in the Northern Hemisphere

• Most of this land lies in the middle latitudes• The Southern Hemisphere is the water

hemisphere• Land in the water hemisphere is located in

the tropical latitudes and the polar region

The Oceans

• Three main oceans

-Pacific Ocean

-Atlantic Ocean

-Indian Ocean• The Arctic Ocean, considered the fourth

ocean, is really an extension of the North Atlantic

Figure 02_22

The Pacific Ocean

• Most surface area• Largest volume• Deepest in terms of single deepest spot• Deepest in terms of average depth• Circular shaped• Covers one-third of the globe

The Challenger Deep in the Mariana Trench is the deepest spot in the world.

The Atlantic Ocean

• Shallowest, rectangular shape• Has the most shallow adjacent seas

-Arctic Ocean

-Gulf of Mexico

-Caribbean Sea

-Mediterranean Sea• Covers about one-fifth of the globe

The Indian Ocean

• Smallest area• Very deep• Triangular shaped• Located mostly in the South Hemisphere• Covers about one-seventh of the globge

The Arctic Ocean

• Really a sea—an extension of the Atlantic Ocean

A Fifth Ocean?

• In the spring of 2000, the International Hydrographic Organization decided to delimit a fifth world ocean—the Southern Ocean (recall Balboa and the South Sea)

• It is the southern portions of the Atlantic Ocean, Indian Ocean, and Pacific Ocean.

• The Southern Ocean extends from the coast of Antarctica north to 60 degrees south latitude

• Northern boundary defined by an ocean current, not by land, so many do not consider this a true ocean

Ocean Surface area (square miles)

Surface area (square kilometers)

Of all oceans

Pacific 64,000,000 166,000,000 45.0%

Atlantic 31,600,000 82,000,000 22.2%

Indian 28,400,000 73,600,000 20.0%

Southern 13,523,000 35,000,000 9.5%

Arctic 4,700,000 12,173,000 3.3%

The Hypsographic Curve

• The hypsographic curve—graph of the depth/elevation versus Earth’s area

• 29% of the Earth’s surface is above sea level• 71% of the Earth’s surface is below sea level• 80% of land is below 2,000 meters elevation• 80% of the seafloor is deeper than 2,000 meters• Hints at composition of crust

Figure 02_23

Hypsographic curve – 2 views

Cumulative curve