The Ocean Floor Oceanography

The Vast World Ocean Suppose that all of the water were drained from the oceans. What would we see? Plains? Mountains? Canyons? Plateaus?

The Blue Planet Nearly 71 percent of the Earth’s surface is covered by global ocean.

The Blue Planet It has only been since the late 1800s that the ocean became an important focus of study.

The Blue Planet Oceanography is a science that draws on the methods and knowledge of geology, chemistry, physics, and biology to study the world ocean.

Geography of the Oceans Four main ocean basins: Pacific Ocean Atlantic Ocean Indian Ocean Arctic Ocean

Pacific Ocean Largest ocean Largest single geographic feature on Earth Deepest ocean avg. depth: 3940 meters.

Atlantic Ocean Half the size of the Pacific Relatively narrow compared to the Pacific

Indian Ocean Slightly smaller than the Atlantic Ocean, but about the same average depth. Located almost entirely in the southern hemisphere.

Arctic Ocean About 7% the size of the Pacific. Only a little more than one-quarter as deep as the rest of the oceans.

Mapping the Ocean Floor If all the water were drained from the ocean basins, a variety of features would be seen.

Mapping the Ocean Floor The topography of the ocean floor is as diverse as that of the continents.

Mapping the Ocean Floor Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor. Bathos=depth Metry=measurement

Mapping the Ocean Floor The first understanding of the ocean floor’s varied topography did not unfold until the 3.5 year voyage of the HMS Challenger.

HMS Challenger—1872-1876 127,500 km trip Went to every ocean except the Arctic. Sampled various ocean properties. Measured depth by lowering a long, weighted line overboard.

Mapping the Ocean Floor Today’s technology—particularly sonar, satellites, and submersibles—allow scientists to study the ocean floor in a more efficient and precise manner than ever before.

SONAR SOund Navigation And Ranging

SONAR Invented in the 1920s A type of electronic depth-sounding equipment. Also referred to as echo sounding.

SONAR Transmits sound waves toward the ocean bottom. A sensitive receiver intercepts the echo reflected from the bottom.

SONAR A clock precisely measures the time interval from sent to received. Depth can be calculated from the speed of sound in water—about 1500 m/s—and the time required for the sound wave to reach the bottom and return.

SONAR The depths determined from continuous monitoring of these echoes are plotted, and a map of the ocean floor is obtained.

SONAR Technology today allows to plot a narrow strip of ocean floor instead of a single point at a time.

SONAR When a ship uses multibeam sonar to make a map, the ship travels through the area in a regularly spaced back-and -forth pattern. AKA “mowing the lawn”

Satellites After compensating for waves, tides, currents, and atmospheric effects, scientists discovered that the ocean surface is not perfectly flat. Gravity attracts water toward more massive ocean floor features occur.

Satellites The differences in ocean-surface height cannot be seen with the naked eye, satellites, however, can detect the small differences.

Satellites Using a system similar to SONAR, instead using RADAR, radio waves, they can map the surface height differences as small as 3 to 6 cm difference.

Submersibles A submersible is a small underwater craft used for deep-sea research. First in 1934, William Beebe 923 meters off Bermuda, tethered to a ship

Submersible Used to collect data about areas that were previously unreachable by humans. 1960-Jacques Piccard, Trieste 10,912 meters untethered

Submersible They collect data, record video, use SONAR, and collect sample organisms with remotely operated arms. Alvin reach depths of 4000 meters, more than 4400 dives including at the Titanic

Submersible Today many submersibles are unmanned and operated remotely by computers.

Submersible Another unmanned submersible is being built with a goal to collect long-term data without interruption.

Ocean Floor Features Oceanographers studying the ocean floor have divided it into 3 main regions.

Ocean Floor Features The ocean floor features are the continental margins, the ocean basin floor, and the mid-ocean ridge.

Continental Margins The zone of transition between a continent and the adjacent ocean basin floor.

Continental Margin In the Atlantic Ocean, thick layers of undisturbed sediment cover the continental margin, which experiences little earthquake/volcanic activity

Continental Margin In the Pacific, oceanic crust is plunging beneath continental crust, which results in a narrow continental margin which results in earthquake/volcanic activity.

Continental Margin Some features common to the continental margin include: the continental shelf, the continental slope, and the continental rise.

Continental Shelf The gently sloping submerged surface extending from the shoreline.

Continental Shelf The shelf is almost nonexsitant along some coastlines, and may extend 1500 km along others.

Continental Shelf Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits.

Continental Shelf The waters here also contain important fishing grounds, which are significant sources of food.

Continental Slope Steeper than the shelf, it marks the boundary between continental crust and oceanic crust.

Continental Slope Deep, steep-sided valleys known as submarine canyons are cut into the continental slope.

Continental Slope Most information suggests that the submarine canyons have been eroded by turbidity currents.

Continental Slope Turbidity currents are occasional movements of dense, sediment-rich water down the continental slope.

Continental Rise A more gradual incline where the trenches do not exist.

Continental Rise May be hundreds of km wide compared to the relatively narrow continental slope.

Ocean Basin Floor Between the continental margin and mid-ocean ridge lies the ocean basin floor.

Ocean Basin Floor This region includes deep-ocean trenches, very flat areas known as abyssal plains, and tall volcanic peaks called seamounts and guyots.

Deep-Ocean Trenches Long, narrow creases in the ocean floor that form the deepest parts of the ocean.

Deep-Ocean Trenches Trenches form at sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle.

Deep-Ocean Trenches Most trenches are located along the margins of the Pacific Ocean

Deep-Ocean Trenches A portion of one trench—the Challenger Deep in the Mariana Trench—has been measured at a record 11,022 meters below sea level.

Abyssal Plains Deep, extremely flat features where thick accumulations of fine sediment have covered an otherwise rugged ocean floor.

Abyssal Plains The sediments that make up the abyssal plains are carried there by turbidity currents or deposited as a result of suspended sediments settling.

Seamounts and Guyots Submerged volcanic peaks that dot the ocean floor, which have not reached the ocean surface.

Seamounts and Guyots Steep-sided cone-shaped peaks found on the floors of all the oceans.

Seamounts and Guyots When a volcano reaches the surface it starts being eroded and may sink back into the ocean.

Seamounts and Guyots The once-active, now-submerged, flat-topped structures are called guyots.

Mid-Ocean Ridges Found near the center of most oceans, interconnected system of underwater mountains that have developed on new ocean crust.

Mid-Ocean Ridges Seafloor spreading occurs at divergent plate boundaries where two lithospheric plates are moving apart.

Mid-Ocean Ridges New ocean floor is formed at mid-ocean ridges as magma rises between the diverging plates and cool.

Mid-Ocean Ridges Hydrothermal vents form along mid-ocean ridges.

Mid-Ocean Ridges Hydrothermal vents are zones of mineral-rich water, heated by the hot, newly-formed oceanic crust.

Mid-Ocean Ridges As the super-heated, mineral-rich water comes in contact with the surrounding cold water, minerals and metals precipitate out and are deposited.

Seafloor Sediments Except for steep areas of the continental slope and the crest of the mid-ocean ridge, most of the seafloor is covered with sediments

Seafloor Sediments The thickness of the sediments varies from sparse coverage up to 10 km in some areas.

Seafloor Sediments Ocean-floor sediments can be classified according to their origin into three broad categories.

Seafloor Sediments The three categories are: Terrigenous Biogenous Hydrogenous

Terrigenous Sediments Consists primarily of mineral grains that were eroded from continental rocks and transported to the ocean.

Biogenous Sediments Consist of shells and skeletons of marine animals and algae.

Biogenous Sediments Calcareous ooze, produced from the calcium carbonate shells of organisms, is the most common biogenous sediment.

Biogenous Sediment Siliceous ooze, composed primarily of the shells of single-cell organisms with shells of silicon, along with phosphate- rich material, make up the other biogenous sediments.

Hydrogenous Sediment Hydrogenous sediment consists of minerals that crystallize from ocean water through various chemical reactions.

Hydrogenous Sediments Make up only a small portion of the over all seafloor sediments.

Hydrogenous Sediments Many different compositions Distributed in many different environments.

Hydrogenous Sediments Manganese Nodules, rounded, hard lumps of manganese, iron, and other metals, are often scattered across large areas of the deep ocean.

Hydrogenous Sediments Calcium Carbonates form by precipitation directly by ocean water in warm climates.

Hydrogenous Sediments Evaporites, formed in high evaporation rates and areas of restricted open-ocean circulation.

Seafloor Resources The ocean floor is rich in mineral and organic resources.

Seafloor Resources Recovering the resources involves technological challenges and high cost.

Energy Resources Oil and natural gas are the main energy products currently being obtained from the ocean floor.

Energy Resources Oil and natural gas are ancient remains of microscopic organisms.

Energy Resources Percentage of world oil production from off-shore rigs has increased from sparse amounts in the 1930s to more than 30% today.

Energy Resources There are rigs in Persian Gulf, Gulf of Mexico, off southern California, in the North Sea, and East Indies.

Energy Resources One environmental concern about offshore petroleum exploration is the possibility of oil spills.

Energy Resources Gas Hydrates are compact chemical structures made of water and natural gas.

Energy Resources Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean-floor sediments.

Energy Resources The bacteria produce methane gas along with small amounts of ethane.

Energy Resources An estimated 20 quadrillion cubic meters of methane are locked up in sediments containing gas hydrates.

Energy Resources The amount of methane is double the amount of Earth’s known coal, oil, and natural gas reserves combined.

Other Resources Other major resources from the ocean floor include sand and gravel, evaporative salts, and manganese nodules.

Sand and Gravel The offshore sand-and-gravel industry is second in economic value only to the petroleum industry.

Sand and Gravel Mined by offshore barges using suction devices.

Sand and Gravel Used for landfill, to fill in recreational beaches, and to make concrete.

Sand and Gravel In some cases, materials of high value, such as diamonds, can be found in the gravel.

Sand and Gravel Other materials found include: tin, platinum, gold, and titanium.

Manganese Nodules Hard lumps of manganese and other metals that precipitate around a smaller object, such as sand.

Manganese Nodules Contain high concentration of manganese, iron, and smaller concentrations of copper, nickel, and cobalt.

Manganese Nodules With current technology, mining the deep-ocean floor for manganese nodules is possible but not economically profitable.

Evaporative Salts When seawater evaporates, the salts increase in concentration until they can no longer be dissolved.

Evaporative Salts When the concentration becomes high enough, the salts precipitate out and form salt deposits.

Evaporative Salts These deposits can then be harvested for the halide—table salt.