Notes – Chapter 12

Ocean W

aters and the Ocean

Floor

The Vast World Ocean

– Area of Continents and Oceans• Seventy one percent (71%) of the globe is covered with

oceans or seas.• Continents and islands compose the remaining twenty

nine percent (29 %).

The Vast World Ocean

–Distribution of Continents and Oceans • Northern Hemisphere - 61% Water / 39% Land• Southern Hemisphere – 81% Water / 19% Land

The Vast World Ocean

– Volume of Continents vs Oceans• Volume of land above sea level (continents) is 1/18 the

volume of the ocean.

The Vast World Ocean

– Height vs Depth• Average elevation of continents is 840 meters above

sea level.• Average depth of oceans is 3800 meters below sea

level.• If the Earth were perfectly smooth and spherical the

oceans would cover it to a uniform depth of 2000 meters.

The Vast World Ocean– Comparison of Major Oceans • Pacific Ocean

– Largest ocean, equal to the Atlantic and Indian together– Contains > half the world’s ocean water– Greatest average depth, 3940 meters

The Vast World Ocean– Comparison of Major Oceans • Atlantic Ocean

– Greatest north-south extension– Shallowest, average depth 3310 meters

The Vast World Ocean– Comparison of Major Oceans • Indian Ocean

– Smallest of the three major oceans– Mostly located in the southern hemisphere

Composition of Seawater

– Seawater – complex solution of salts, consisting of about 3.5 % dissolved mineral substances (normally range between 3.3% and 3.7% in the open ocean).• If all water evaporated a layer of salt 60 meters thick

would cover the ocean floor.

Composition of Seawater

• Salinity – proportion of dissolves salts to pure water, expressed in either parts-per-thousand or percentages (%)

Composition of Seawater

• Component Elements – Mostly sodium chloride (NaCl) but seawater contains more than 70 of Earth’s 92 naturally occurring elements.

Composition of Seawater

– Variation in Salinity – based on differences in the percentage of water, not differences in types of salts. • High Salinities – found where evaporation is high (sub

tropics) Ex. Persian Gulf and the Red Sea – exceeds 4.2%• Low Salinities – found where heavy precipitation dilutes

ocean water (near the mid latitudes and equator) Ex. Baltic Sea – less than 1.0%

Composition of Seawater

– Source of Salts – • Chemical Weathering of Rocks• Volcanic Eruptions

Resources From Seawater

– Salt– Fresh Water• Desalinization

– Gold

The Ocean’s Layered Structure

• Determined by differences in temperature and salinity at different depths

The Ocean’s Layered Structure

– Shallow Surface Mixed Zone• Warmest • Higher Salinity

The Ocean’s Layered Structure

– Transition Zone (Thermocline/Halocline)• Greatest Drop in Temperature

The Ocean’s Layered Structure

– Deep Zone• Coldest – Temperatures below 4 C• Lowest Salinity

Earth Beneath the Sea

– H.M.S. Challenger (1872-1876)• Trip went through every ocean except the Arctic• Sampled depths using a weighted line

Earth Beneath the Sea

– Echo Sounder (1920s)• Transmitted sound toward the ocean bottom and a

receiver measured how long it took for the sound waves to return. • Had to know how fast sound travels in water

(1500meters or 5000 feet per second)

Earth Beneath the Sea

Continental Margins

• Includes continental shelf, continental slope and continental rise.

Continental Margin

Continental Margin

Continental Margins

• Continental Shelf –gently sloping submerged surface extending from the shoreline toward the deep-ocean basin at the shelf break. • Flooded extension of continents, it can vary in size.• Can be a source of important minerals, petroleum, etc.

Continental Margins

• Continental Slope and Rise– Continental Slope – edge of the continental shelf

leading into deep waters and is the true edge of the continent.

– Continental Rise – gradual incline further seaward from the continental slope, sometimes nonexistent where the slope descends into a submarine canyon.

Submarine Canyons and Turbidity Currents

• Submarine Canyons• Extend to depths as great as 3 kilometers• Created by processes operating below the Earth’s surface

as well as turbidity currents

Submarine Canyons

Submarine Canyons and Turbidity Currents

• Turbidity Currents • downslope movement of dense sediment laden waters • eroding and accumulating more sediment as it moves

toward the ocean basin.

The Ocean Basin Floor

• Comprises 30% of Earth’s surface.

The Ocean Basin Floor

• Deep Ocean Trenches – long narrow troughs that are the deepest part of the ocean• Challenger Deep in the Marianna Trench is more than • 11,000 meters deep• Sites where crustal plates are plunging back into the

mantle

The Ocean Basin Floor

• Abyssal Plains – flattest places on Earth• Turbidity currents deposit their sediments here

The Ocean Basin Floor

• Seamounts – isolated volcanic peaks, maybe be islands or submerged• Some form from hotspots, some near plate boundaries

Mid Ocean Ridges

• Form an almost continuous underwater mountain chain through all major oceans

• Comprise 20% of Earth’s surface

Mid Ocean Ridges

• Rift zone – region where magma from the asthenosphere moves upward to create new crust

Coral Reefs and Atolls

• Coral Reefs• Constructed from the skeletal remains and secretions of

corals and certain algae, built up over time• Thrive in warm waters and rarely occur elsewhere, they

require clear, sunlit waters with very little variation in temperature

Coral Reefs and Atolls

• Atolls• Remains of coral reefs surround volcanic islands that have

since sank back into the ocean

Seafloor Sediments

• Terrigenous Sediment – “derived from land”• Weathered continental rock transported to the ocean

• Biogenous Sediment –“derived from organisms”• Shells or skeletons of marine animals and plants

• Hydrogenous Sediment – “derived from water”• Minerals that crystallize directly from seawater

Marianas Trench

• http://www.youtube.com/watch?v=KuPfn5faawE