OCEANOGRAPHY
The World’s Oceans
71% of the surface of the Earth is ocean
97% of all the Earth’s water is found in the oceans
The Pacific, Atlantic and the Indian oceans are the major oceans. These are listed in order of size and depth
A sea differs because it is part of an ocean that is surrounded by land on 3 sides
Properties of Ocean Water
Ocean water is a mixture of gases and solids dissolved in pure water
Oceanographers believe that ocean water contains all of the natural elements found on Earth, all but 5 of these
elements have been found
Salts in Ocean Water
Salinity is the amount of dissolved salts in ocean water. Sodium Chloride is the most common salt
Average salinity of the ocean is 35 parts per thousand (0/00)
Salt comes from volcanic activity, erosion of the land, and wave erosion of beaches
Lower salinity occurs where freshwater rivers enter the ocean
Salinity is higher where there is greater evaporation (equator) and in Polar Regions where only fresh water freezes
Animals using certain salts to build their shells can lower salinity
Gases in Ocean Water
Nitrogen, carbon dioxide, and oxygen are the most abundant gasses found in ocean water
Oxygen and carbon dioxide are essential for plant growth
There is more gas found at the surface of the water where plant growth occurs
Cold water holds more gas than warm water
When the colder denser water sinks to the bottom it carries oxygen rich water that aids in the survival of deep water
species
Temperature of Ocean Water
The sun is the major source of heat for the ocean
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Surface zone –Light Zone: 100-300 meters deep, temperature fairly constant, waves and surface winds mix the
water and transfer the heat downward
Thermocline: Found directly under the surface zone Temperature drops rapidly, Exists only because less dense
warm water floats on top of the more dense cold water and they do not mix, Depth varies due to ocean currents
Deep Zone or Dark Zone: Extremely cold water that extends from bottom of thermocline to the ocean floor,
Temperature decreases only slightly and averages 4 degrees Celsius, The zones do not occur in polar regions
Ocean Features
Continental Shelf: Surrounding nearly all continents is a shallow extension of that landmass, it is relatively shallow, tens
of meters deep, extends outward to the continental slope where the deep ocean truly begins, the best fishing, large
mineral deposits, and petroleum are found there
Continental Slope: The continental slope connects the continental shelf and the oceanic crust. It begins at the
continental shelf break, or where the bottom sharply drops off into a steep slope (the drop off). The continental slope,
continental shelf and continental rise make up the continental margin. Submarine canyons (deep V-shaped) cut through
many of the continental margins. Some of these have been carved by turbidity currents, which are bottom currents that
carry lots of sediment.
Turbidity current carry large amounts of these sediments in masses of moving water, it is like an underwater avalanche
Continental Rise:
Past the continental slope is the continental rise. As currents flow along the continental shelf and down the continental
slope, they pick up and carry sediments along and deposit them just below the continental slope.
These sediments accumulate (gather) to form the large, gentle slope of the continental rise.
Abyssal Plain: The sea floor is a huge flat area. It lies at depths of ~ 4000 to 6000 meters below the surface of the
ocean. Sea floor spreading occurs here, which means that there is volcanic action and a mid-ocean ridge where some of
the lava has cooled. There are also isolated volcanic mountains called sea mounts, and some black smokers, but most of
this area is flat and featureless. Atlantic and Indian oceans have largest abyssal plains because almost all the world’s
major rivers flow into them producing a large amount of sediment deposits in the plains
Seamounts: isolated volcanic mountains scattered across the ocean floor. Most common in the Pacific Ocean,
seamounts generally rise more than 1,000 meters above the sea floor, often forming islands.
When the action of plate tectonics moves a seamount-formed island away from the mid-ocean ridge, the ocean crust
sinks (isostasy), pulling the island beneath the surface. These submerged, often flat-topped, seamounts are called
guyots.
Mid Ocean Ridges: Mountain ranges under the ocean form an almost continuous mountain belt that extends from the
Arctic Ocean to North America. Rift Valleys form between the ridges.
Hydrothermal Vents are located along ridges. These are holes in the seafloor where fluid heated by magma erupts.
TRENCHES: Oceanic trenches are several hundred kilometers long but are narrow. They are the deepest parts of the
ocean floor. A trench marks the position at which one plate begins to go under another plate. They usually form a
volcanic arc (Ring of Fire). Oceanic trenches typically extend 3 to 4km (1.9-2.5 mi) below the level of the surrounding
oceanic floor. The deepest ocean depth to be sounded is in the Challenger Deep of the Marianna Trench at a depth of
10,991m (35,798 ft) below sea level
REEFS:
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Fringing reef: area along the shore where coral colonies have been able to grow. Fringing reefs occur close to
land and often extend out to sea for long distances.
2. Barrier reef: a well-defined coral zone separated from land by a lagoon. The lagoon is a shallow area with a
sandy floor, patch reefs, and patches of sea grass.
3. Atoll: ring-like formation of reefs with a lagoon inside the ring.
How do waves form?
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Wind blows over smooth water and creates surface ripples
The ripples form “chop” (short, steep waves) over time
Chop forms into regularly spaced swells
The swells become breakers on a distant shoreline.. Shape of shoreline affects size of breakers.
Waves and Tides
Factors that determine wave size are Wind velocity (speed and direction), Length of time the wind blows over the water
“Fetch”, and the distance along open water over which the wind blows
Wave dimensions increase until they reach the maximum size for the existing storm conditions. This is known as a fully
developed sea
Water Motion
Waves of Oscillation: The actual motion of a wave is a circular path. The energy of the wave moves forward. There is
no mass forward movement of water. This explains how a surfer or a buoy can bob along in the water and not be
pushed toward the shoreline.
Types of breakers
Plunging: offshore area is steep, waves peak rapidly on the steep sea floor, classic tube shape typical of Sunset Beach or
Waimea Bay
Spilling: flat near shore slope where waves lose energy by friction, waves build up slowly and the crest spills down the
face of the wave.
All waves contain swash (water that rushes onto beach) and backwash (water returning seaward to become part of next
wave)
Wave Refraction
When waves bend as they approach the shore line at an angle
Some water is discharged as a weak current within the surf zone called a longshore current.
The greater the angle of the wave, the greater the volume of water that is discharged into this current.
Consequences of longshore currents
The current can move sand grains as well as swimmers down the beach
Longshore currents can overflow through the surf zone during periods of big surf causing a rip current
Ocean Currents
Surface Currents: caused by wind patterns, several hundred meters deep, temp. depends on origin, have a circular
pattern of circulation and rotate just like wind patterns (CW in N. Hemisphere) Example: Gulf Stream, Can converge
making lines in the sea
Deep Ocean Currents: Caused by difference in density of the water, cold and salty water are very dense, Densest water
lies off Antarctica and flows north, Flow in opposite direction of surface currents, If the deep current comes close to
surface upwelling occurs. It brings nutrient rich foodstuffs to the surface. These areas are feeding grounds and fishing
industries are found there
Mapping the Ocean Floor
1872 first expedition, Challenger measured depth with a wire, Now we use echo sounding, radar sonar, and
seismographic surveys, Seasat: satellite that has made the most complete picture of ocean floor
Forms of Life
1. Plankton: Largest group of animals and plants. Float at the surface and can be found where the sun penetrates.
Main food for larger organisms.
2. Nekton: Ocean life that can swim, can search for food and avoid predators, found at all levels of the ocean,
seals, dolphin, sharks, barracudas
3. Benthos: live on ocean floor, plants, crabs, barnacles
Life Zones
1. Intertidal zone: lies between low and high tide lines (wet & dry), most changeable zone, difficult to survive
here, waves and tides cause a lot of movement, Anemones, crabs, mussels, seaweeds, flounder
2. Neritic Zone: Low tide line to edge of continental shelf, Sunlight penetrates, temperature constant, most rich in
life with many fishing grounds in zone, Fish, clams, snails, plants, plankton
Open – Ocean Zones:
3. Photosynthetic Zone: (Light zone) Sunlight penetrates the entire ocean to 200 m
4. Bathyal Zone: 200 m to 2000m, no sun, no plants, squid, octopus, whales
5. Abyssal Zone (dark zone): from 2000 m to 6000 m, no sun, little food, small animals that are strange looking,
very high pressure
Bioluminescence: chemical energy changes to light energy usually one color.