Chapter 14

Introduction Turn to page 396 & 397….. What does the ocean floor look like, what features are there, What is the shape of the ocean floor basin, etc. What do you see and what do you think?

New ocean lithosphere forms at mid-ocean ridges . New rock that forms there are very hot, therefore less dense then the surrounding rock. This causes the mid-ocean ridges to rise above the existing ocean floor. As the ocean plate cools it becomes denser and begins to sink.

Question: What are seamounts and guyots? Seamounts are islands that did not yet reach the ocean surface or will never reach the surface or did reach the surface and sank. Guyots are flattened volcanic peaks. What caused them to flatten on top? Wave activity can cut them off.

So how did they sink? As the ocean floor cooled and sank so did the islands, seamounts, and guyots. The shape of the ocean floor is in the shape of a parabola . Cooling of the ocean floor is faster right after it forms and continues to cool slowly. Cooling of the ocean floor is faster right after it forms and continues to cool slowly.

The distance away from the ridge is proportional to the square of the temperature of the ocean plate. Any curve with the formula y=x 2 is a parabola.

During the Cretaceous period sea level was 300 meters higher causing major flooding of the continents. Compare this to the fact that if all the ice in the world melted sea level would rise 80 meters. When plate velocities increase ridge systems become active raising the sea floor thus causing continental flooding.

Ocean Seafloor Mineral Factory Minerals tend to form at subduction boundaries both new and ancient. Why? Back to the mid-ocean ridge where water circulates through the mid-ocean ridge like a chemical factory removing metals and ores from the ocean crust.

Cold water is pulled into the crust, and as it heats up, it begins to dissolve out incompatible elements like metals. This happens at ocean vents called black smokers where the water is turned black. As the warm water rises, metals precipitate out onto the seafloor. As ocean crust moves it drops the metals into the ocean trench/subduction zone. Many of the minerals rise to the Earth’s surface in magma.

The Vast World Ocean The great oceans of the world cover about 71% of the Earth's surface and are divided by continents. Each ocean includes smaller bodies of water called seas, bays, and gulfs. Oceanography is a science that draws from many other science fields to study all aspects of the world oceans.

Geography of the Oceans If 71% of the Earth’s surface is covered by oceans then the continents must make up about 29% How many oceans basins are there actually? Would you believe 5

Oceans by name We will use all 5 ocean basins this year

Ocean Trivia Almost surrounded completely by land largest ocean ocean with most storm activity saltiest ocean has most of world’s fresh water going into it Arctic Pacific Indian Atlantic Atlantic

Mapping the Ocean Floor The topography of the ocean floor is as diverse as the continents. Features include: Chains of volcanoes Mountain ranges Trenches Submarine plateaus

How to Measure the Depth of the Oceans………………… Bathymetry – ( bathos = depth, metry = measurement ) is the measurement of ocean depths and the charting of the shape (topography) of the ocean floor. HMS Challenger – first ship designed to investigation of the oceans scientifically. Follow the Challenger journey

Technology: Sonar Satellites Submersibles

Sonar s ound n avigation a nd r anging Sound travels in water at about 1,500 meters per second

Multibeam sonar Charts created form ocean floor profiles.

Magnified 40 times to clearly show the features

Satellites measures the ocean surface height. Gravity attracts water to seamounts and guyots create a small rise in the ocean surface and trenches create small depressions.

Submersibles underwater craft designed to investigate the deep oceans. They can record data and pictures at extreme ocean depth.

Short History of Underwater Ocean Exploration and Technology 1st submarine - Turtle Huneley - civil war sub Submarines 1934 – William Beebe – 923 meters in a tethered steel sphere attached to a ship. bathyscaphs -deep diving subs 1960, Trieste – Jacques Piccard – 10,912 meters in the Mariana trench SCUBA - self - contained - underwater breathing – apparatus Who developed scuba gear?

Ocean Floor Features Continental Margins – zone of transition between continent and adjacent ocean basin Atlantic - Covered with thick layers of undisturbed sediments. This region has very little volcanic or earthquake activity. Why? Not associated with plate boundaries.

Pacific – The Pacific Ocean crust is plunging beneath continental crust. This is caused by volcanic and earthquake activity. The result of this activity is a narrow continental margin .

Continental Shelf Not all coastlines have a continental shelf. It extends from the shoreline to approximately 80 kilometers. It is approximately 130 meters in depth on its seaward side. Importance: Large mineral deposits Oil and natural gas Sand and gravel deposits Important fishing grounds

Continental slope Marks the edge of the continental shelf. Is a steeper drop to the ocean floor, between 50 and 250. Submarine canyons: Formed by erosion at least in part by turbidity currents . They form when sediments are disturbed by volcanic or earthquake activity. The muddy sediment that is now mixed in the water flows down the continental shelf and slope. Or they could have formed????????

Another possibility is that when sea level was much lower some rivers crossed the continental shelf causing erosion to form submarine canyons. What could have caused this……. Glaciers forming……… REALLY!!!!!!!

Continental Rise Areas at the base of the continental slope when sediments have accumulated. They may be hundreds of miles wide.

Other Features Trenches: subduction zones, sites of plate convergence Deepest is Mariana Trench = 11,022 meters in depth Abyssal plain Seamounts Guyots Mid-ocean ridges Hydrothermal vents Atolls

Mid-ocean ridges are very wide and may occupy ½ of the ocean floor, site of divergent plate boundary or sea floor spreading sites. They are broken into segments by transform faults.

Hydrothermal vents form along mid-ocean ridges. The water here is mineral rich; the hot newly formed crust comes in contact with cold ocean water causing minerals like sulfur, iron, copper, and zinc precipitate out and are deposited.

Seafloor Sediments terrigenous – originates on land. They consist primarily of mineral grains that were eroded from continental rocks and transported to the oceans. Coarse grain materials like sand settle quickly near the shore. Fine grained sediments like clay may take years to settle. 1centimeter of clay may take 50,000 years to form. Terrigenous sediments accumulate much quicker in areas like the Gulf of Mexico where the Mississippi enters the ocean. Deposits there may be several kilometers thick.

biogenous – consists of shells and skeletons of marine animals and algae. The most common type is calcareous ooze which forms from calcium carbonate shells and corals. The shells dissolve as the sink to lower depths. This sediment has the consistency of thick mud. Other sediments include siliceous ooze which is composed mostly of diatom shells made of silica. Phosphate rich biogenous sediments come from teeth, bones and scales of fish.

hydrogenous – consists of minerals that crystallize directly from ocean water through various chemical reactions.

Common types: Manganese nodules – made also of iron and other metals, they form around grains of sand and are scatter across large areas of the deep ocean floor. Calcium carbonates – form by precipitation directly from ocean water in warm climates. If this sediment is buried it can form limestone. Evaporites – form where evaporation rates are high and ocean circulation is restricted. As water evaporates the remaining water becomes saturated with dissolved minerals which begin to precipitate. These sediments are generally called “salts.” Three common minerals that form this way are halite, gypsum, and calcium sulfate .

Resources from the Seafloor Oil and natural gas – ancient remains of microscopic organisms that were buried before they could decompose. Exposed to pressure of overlying rocks and the Earth’s internal heat the remains were transformed into oil and natural gas. Major offshore reserves: Persian Gulf, Gulf of Mexico, off southern California, North Sea, and the East Indies. Possible new reserves may be off the coast of Alaska and the Canadian Arctic, Asian seas, Africa, and Brazil Problems: pollution of the oceans

Gas hydrates – occurs as methane hydrate or methane. Gas Hydrate is an ice-like crystalline solid formed from a mixture of water and natural gas, usually methane. They occur in the pore spaces of sediments, and may form cements, nodes or layers. These occur beneath permafrost areas on land and under the ocean floor at depths below 525 meters. Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean floor sediments. Other gases include ethane and propane. Chunks of gas hydrates look like metals and evaporate quickly when exposed to warm temperatures and less pressure. An estimated 20 quadrillion cubic meters of methane are locked in sediments. This is double the Earth’s coal, oil, and natural gas reserves combined.

Sand and gravel – used in construction and some are gem quality. Diamonds, platinum, titanium, and gold are found in these deposits. Manganese nodules – they include iron, copper, nickel, and cobalt. Cobalt – used to make strong allows of other metals. Can make cutting tools, magnets, and jet engine parts.

Evaporative salts – Of economic use is halite which is used in table salt, seasoning of food, curing, preserving food, agriculture, dying fabrics and de-icing roads.

Problems include … developing the tools to get them from the ocean floor establishing mining rights.

Chapter 14

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Chapter 14