About 71% of the surface of the planet is covered in salt water. Beneath the depth averages 3,8 km giving it a volume of 1370 x 106 km3. Since life exists throughout this immense volume, the oceans constitute the single largest repository of organisms on the planet.
These organisms include representatives of all phylums and are tremendously varied but all are subject to the properties of the sea water that surrounds them and many features common to these plants and animals are the results of adaptations to the watery medium and its movements. Its necessary therefore, to examine the physical and chemical conditions of seawater and aspects of its motion (oceanography) and look at the environment where the organisms live.
The mean depth is 4km and its interconnected from the Arctic to Antarctic. Seawater flows freely among the basins transporting dissolved materials, heat and marine organisms. Seawater mixes from basin to basin/per 1000years but regional characteristics of the seawater do exist. The major basins are the Pacific, Atlantic, Indian, Arctic, Southern ocean and the boundaries are artificially defined.
Seawater mix
Movement of water moderates world climate by distributing heat from equatorial water to the poles. Warm currents flow toward the poles from the equator (Gulf Stream) heating northern latitudes. Cold water from the Arctic and Antarctic basins flow beneath the oceans surface toward the tropics...cooler water near the equator.
PLATE TECTONICS
There are 8 major plates, up to 100 miles thick and move slowly. They know the direction and speed so can figure out what the continent was like before it moved. The Atlantic has been growing for 150 mil years.The theory of continental drift or plate tectonics was only established in the 1960's. 200 million years ago, Pangaea fractured and started moving apart 180 mil. yrs ago.
The force that moves the plates over the semi-solid layer of the upper mantle /asthenosphere is the convection currents (large temp. difference between the mantle and crust) and moves plates either 1. apart, 2. together or 3. laterally.
1. apart new material rise as magna /molten rock filling spaces (rifts form mid ocean ridge.
evidence 1965 research vessel Eltanin did magnetic studies
1969 Glomar Challenger did cores from Pacific ant ridge
1977 Project Famous used submersibles
2. Converge one plate dives under another, crumples and forms trenches...usually but not always (mountains) the area is called a seduction zone
Island arcs formed/volcanoes/ from turbulence from the melting of the descending plate.
3. Lateral-sideswipe and cause earthquakes volcanoes and deformations
Mineral deposits in trenches and ridge areas related to tectonic movements.
Geo-sil theory concentration of copper and other metals form as plates melt and separates from crust material, rise in subduction zone near trenches and continues rising until it cools and gets exposed by weathering rocks.
Hydrothermal vents...water percolates into fissures around the rift valley, sinks and heats to 320'C in fissures (pressure) and the heated water dissolves metals and it rises to the seafloor surface, openings flow through the hydrothermal vents, mix with cold water, minerals settle to bottom forming deposits. Robert Ballard witnessed milky bluish clouds spewing in a Pacific rift zone.
The ocean floor.
Prior to the 1920's, they used weighted rope to probe depths. 1920's the echo sounder (SONAR-(sound navigation and ranging) which analyzed sound waves which bounced off the oceans bottom and returned to the ship. The Meteror (1925-7) did the 1st ocean survey with sonar.
Common topographical features of the oceans include: Continental margin and deep sea as the major divisions.
Continental Margin
Continental shelf-underwater extension of the continental land mass. 8% of the total surface area of the world ocean, yet its one of the most productive parts of the ocean. It gradually drops down to the 100-200m depth. Continental slope begins where continental shelf plunges down. As the steepness decreases, this zone is called the continental rise.
Underwater canyons occur in the margins which resulted from 1> ocean level was lower with rivers flowing over them eroding the soft sediments making deep gouges. 2. Underwater landslides along the sides of the canyons make the canyon bigger.
profiles of the ocean floors developed from wartime advances and these described patterns of underwater trenches, Mt. ranges and volcanoes along the flat abyssal plane. The idea that the earths crust is composed of movable rigid plates floating on a denser mantle formed.
SEA LEVEL
The sea level has undergone dramatic changes. 15000 years ago 120m below present level. As it fell portions of the continental shelf were exposed changing position of coastline. Ice age/Wisconsin glacial period, the ocean water froze into glaciers.
Soft sediment of the shelf exposed to erosion from rivers and hen the glaciers started to melt, excess water cut canyons into the shelf. Ocean refilled, flooding shelf and forming underwater canyons. The rise slowed 3000 years ago and has only risen 10m since. It is still rising. CO2 warming and will flood in next 1000 years.. Green House effect.
