Oceans cover 71 percent of the earth’s surface. The Pacific alone is larger than all the continents combined. If the earth’s crust was smoothed out so that the ocean floors and continents were all level, sea water would cover the earth at a depth of 8,800 feet. If the water was evaporated the entire earth would be covered by 40 feet of salt.
The oceans are so deep that Everest could be placed in the Mariana Trench—the deepest point in the ocean—and be covered by a kilometer of water. Measured from the ocean floor, Mauna Kea on the Big Island of Hawaii is over 10,000 meters high, making it the largest mountain on Earth.
The oceans are great reservoirs of energy, minerals and gases. Water holds heat much more efficiently than air and ocean water absorbs 90 percent of the energy it receives. The oceans also absorb about half the carbon dioxide produced by human activity and blamed for global warming.
The ocean like the sky looks blue because shorter wavelengths like blue scatter widely are visible. Longer wavelengths like red do not scatter and thus are not visible. Salt water is more dense than fresh water water and supports a fish’s body better. Sea water is about 3.5 percent salt. Though the amount of salt in the world's oceans remains mostly unchanged, the brine concentration in the topmost layer varies around the globe.
The oceans are more complex and less understood than the weather. One of the main reason we understand so little about the sea and what is in it is because it much harder to explore than land. Marine scientists often describe oceans as the earth's circulatory system, performing numerous vital functions which make the planet habitable, such as creating more than half our oxygen, driving weather systems while modulating the atmosphere, as well as providing us with vital resources.
Composition of ocean water Websites and Resources: National Oceanic and Atmospheric Administration noaa.gov/ocean ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Ocean World oceanworld.tamu.edu ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Montery Bay Aquarium montereybayaquarium.org ;
Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Wikipedia article Wikipedia ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Coral Reef Pictures squidoo.com/coral-reef-pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.
Websites and Resources on Fish and Marine Life: MarineBio marinebio.org/oceans/creatures ; Census of Marine Life coml.org/image-gallery ; Marine Life Images marinelifeimages.com/photostore/index ; Marine Species Gallery scuba-equipment-usa.com/marine
History of the Oceans and Oceanography
lava enters the sea in Hawaii The oceans were first formed when the earth began to cool and water condensed on the earth's surface. These early oceans were full of chemical like iodine, chlorine and nitrogen. Water came from volcanic vents. Over time the oceans have been getting saltier. The salt has come mostly from weathered rock on land
Life first appeared in the oceans 3.5 billion years ago in the form of simple bacteria and algae almost exactly types of bacteria and algae that still exist today.
The science of oceanography began in 1872 century when the British government and the Royal Society launched a major oceanic expedition based from the HMS Challenger, a 265-foot converted naval warship. For four years the ship circled the globe and took measurements, collected creatures in nets, examined them with microscopes and preserved them in alcohol. The expedition collected 4,700 species new to science but not before two men went insane, two drowned and one committed suicide.
In the late 17th century astronomer Edmond Halley built the first “diving bell.” In 1934, two amateur scientist descended to 3,028 feet off Bermuda in a homemade bathysphere made from a steel ball with quartz peepholes. In 1960, an untethered craft, the Trieste, took a crew to the bottom of the Mariana Trench whose deepest point is—36,201 feet (11,033 meters)—or seven times deeper than the Grand Canyon.
Scuba gear was invented in 1953 by Jacques Cousteau and Emile Gagan.
Water from Comets
Marc Kaufman wrote in the Washington Post: “Water is everywhere on Earth, but nobody has ever been able to determine conclusively how it got here. Scientists know that the early Earth was far too hot to hold water or water vapor, but then, in relatively short geological time, the oceans appeared. [Source: Marc Kaufman, Washington Post October 20, 2011]
In a discovery that researchers say sheds important new light on that age-old question, a European team reported Thursday that it has found a very cold reservoir of water vapor in space that could explain where the water came from. The region they discovered is at the outer reaches of a dusty disk surrounding a star 175 light-years away. The star and disk are in the early stages of forming planets, much as Earth was formed some 4.5 billion years ago.
The scientists’ conclusion from the new finding: Life-giving H2O was almost certainly delivered to Earth via comets and asteroids known to originate in these cold but water-filled zones, which were assumed to also be present when our solar system was forming. “Our observations of this cold vapor indicates enough water exists in the disk to fill thousands of Earth oceans,” said astronomer Michiel Hogerheijde of Leiden Observatory in the Netherlands. Hogerheijde is the lead author of a paper describing these findings in the Oct. 21 issue of the journal Science.
Hogerheijde said the 10 million-year-old star his team examined, TW Hydrae, is the closest planet-forming star yet identified. Signs of the cold water vapor were detected by the Herschel Space Observatory, a European Space Agency satellite that looks for infrared light in the galaxy using the Heterodyne Instrument for the Far-Infrared, or HIFI. Efforts to find the cold water vapor in the past all failed because the instruments were not powerful enough to pick up the faint spectroscopic signals.
“It is a testament to the instrument-builders that such weak signals can be detected,” said Paul Goldsmith, NASA project scientist for the Herschel Space Observatory at the agency’s Jet Propulsion Laboratory in Pasadena, Calif. “These are the most sensitive HIFI observations to date.”
According to Hogerheijde, the cold water vapor detected is a small portion of the “ice reservoir” existing in the region. The ice crystals, which cover the widespread dust particles, form in conditions reaching 400 degrees below zero. But ultraviolet light from the star warms the ice enough to briefly release the vapor that was detected, Hogerheijde said.
The announcement comes weeks after a related finding that the water in some comets has the same chemical composition of Earth’s oceans. Previous detections had found water with a different isotopic make-up, suggesting that no more than 10 percent of the Earth’s water was delivered by comet. But data from the comet Hartley 2 found the ratio of heavy hydrogen (deuterium) to ordinary hydrogen to be almost exactly what it is in Earth’s oceans. “Now, in principle, all the water [in Earth’s oceans] could have come from comets,” said principal investigator Paul Hartogh of Germany’s Max Planck Institute.
Creation of Water and Likelihood of Oceans on Other Planets
Ocean births Planetary scientists have determined that huge amounts of graphite and silicon dust surround stars as they form. That material over time binds together to form larger bodies such as comets and asteroids and — around many stars — ultimately planets.
Earth formed about 4.5 billion years ago, they have concluded, and was then too close to the sun to hold much water or water vapor. But around 4.1 billion years ago began a period of “heavy bombardment,” when Earth was pummeled by comets and cold meteorites — both of which carry water — from the outer reaches of its disk.
The bombardment ended about 3.8 billion years ago, and at that point much of the Earth’s water was in place. The earliest forms of microbial life detected lived some 3.6 billion years ago, a relatively short geological period after the oceans had filled.
While there is growing evidence for the explanation that comets and wet asteroids delivered our oceans, some researchers hold that the water came primarily from other sources. For instance, water is believed to have been released from early volcanos that belched up molten material from deep within the planet, including H2O. Water could also leak out of certain minerals in rocks as the planet cooled. Hogerheijde said that while this early “outgassing” most likely played a role in making early Earth wet, the evidence is now persuasive that much of the water for our oceans was later delivered from afar.
“Scientists have long suspected there were these reservoirs of cold water vapor hiding in the outer regions of planet-forming disks, but until now we’ve only found signs of water vapor in hot regions closer to the suns,” Hogerheijde told the Washington Post, “Since the comets and cold asteroids are formed in the outer reaches, this was a problem for the theory that comets delivered the water to Earth. But now we have the cold reservoir in the region where comets are formed, and so the theory gets considerably stronger.” The logical extension, he said, is that water has also been delivered to some of the billions of exoplanets known to exist beyond our solar system, meaning there are likely to be many “ocean worlds” throughout the galaxies.
ocean floor map The seas cover the world’s deepest valleys, longest mountain ranges and most of the active volcanoes. Deep-sea trenches are the deepest points on the ocean. They are located at subduction zones often where continental and oceanic plate meet. More than 70 percent of the world’s oceans are over 1,000 meters deep. Sometimes fathoms are used to measure depth. One fathom equals about 6 feet or 1.822 meters.
Abyssal plains are located between continental slopes and mid-ocean ridges. The cover almost half of the deep ocean floor and are the smoothest surfaces on the planet. Seamounts are underwater mountains that stop short of breaking the surface of the sea and becoming islands. Many are volcanoes. By one count there are over 100,000 of them in the world’s oceans.
Hydrothermal vents—that spew out water hotter than 500 F and emit minerals such as hydrogen sulfide—are located is places here there is volcanic activity. Water seeps down through cracks in the sea floor and is heated by magma and rushes back to the surface through vents. Different chemical reactions occur where the mineral-laden vent water meets the cold water of the sea. The build up of sulfide minerals produces chimneys. Minerals nourish bacteria, which in turn feeds tube worms and mollusks that feed forms of life further up the food chain. The first ones were discovered near the Galapagos islands at a depth of 9,200 feet in 1977.
There are a number of active volcanoes under the sea, with deepest yet discovered about five kilometers below the surface in the Caymen Trench in Caribbean. The Caymen Trench is the world’s deepest undersea volcanic rift. It is still largely unexplored and was the setting for the James Cameron film The Abyss . About 100 million years ago, oxygen disappeared from much of the world’s oceans, wiping out a third of all ocean life. Many scientists think that sulphur produced by volcanoes was the culprit. They think that the amount of sulfur in the water changed the amount of phosphorous, which is vital for phytoplankton growth and this triggered an anoxic event depriving the oceans of oxygen.
Oceanic basin features
Currents are movements of water. They are driven mainly by prevailing winds and differences in water density, which changes with temperature and salinity of the seawater. The overall pattern of ocean circulation appears to driven by thermohaline circulation (“thermo” for heat and “haline” for salinity”)—a conveyor belt driven by the sinking of dense cold water in North Atlantic. This draws warm surface water (the Gulf Stream) from the south and sets in motion currents that affect all the world’s oceans.
Saline water that flows from warm areas to cold areas loses heat and becomes more saline as water evaporates. The coldness and high salinity makes the water more dense. It sinks into the oceans. As it does surface water moves in to displace it.
Prevailing winds both push water and create circulation by displacing water at the surface that allows upwelling— the upward flow of cold water from deep in the ocean to the surface of the sea. The cold oxygen-poor water is often rich in nutrients such as nitrates, phosphate and silicate that are consumed by creatures on the bottom of the food chain beginning with phytoplankton that in turn feed marine life further up the food chain.
Currents in coastal areas can be caused the ebb and flow of tides. In bays and straits where the water narrows the tides and currents can be quite strong. In some places such as the Bay of Fundy water levels can range 50 feet between low and high tide. In places where there are narrow straight currents can reach 15 knots when the tide ebbs and then lie still for 15 minutes or so and then start flowing with equal velocity in the other direction.
Currents can also be influenced by an influx of fresh water. Salt water is heavier than fresh water, As fresh water enters the systems it rides over ocean water and pulls some of the salt water into it, creating a sort of vacuum that draws in more deep ocean water.
Currents are vital for cooling, heating and providing water to terrestrial areas, and transferring heat from the Equator to the Poles.
The Gulf Stream is an ocean current that carries warm from the Gulf of Mexico and the Caribbean northward along the east coast of the United States and then branches into northeast-heading North Atlantic Current and southeast-heading Azores current, both of which bring warmth to Europe. The Gulf Stream discovered by Spanish navigators and first charted by Benjamin Franklin.
Ocean current map made in 1943
The Gulf Stream begins in the Caribbean Sea, a relatively shallow basin. Forces from the spinning of the earth and the trade winds push Caribbean waters north and west between Cuba and the Yucatan into the Gulf of Mexico. From there is like a vast warm river, 80 kilometers wide and 500 meters deep.
The Gulf Stream process begins with the Trade Winds (blowing from east to west), which blows Atlantic waters westward to the Gulf of Mexico. Here the water is stopped by Gulf water. Because of the configuration of the geography of the Yucatan peninsula, the water is forced northward between Cuba and Florida and joins waters of the Antilles current. Around Cape Hatteras, North Carolina, where the water is around 88°F in the summer and 69°F in the winter, the current begins heading eastward towards Europe.
The Gulf Stream route back to Europe was discovered in 1519 by the Spanish explorer Antonio de Albinos who was returning from Mexico and bravely decided to follow the currents east of Florida and north of Cuba. Before that time navigators followed Columbus’ southern route which took advantage of the prevailing westerly winds by not the strong force of the Gulf Stream current.
Gulf Stream, Weather and Fish
Gulf Stream map from 1943 London is farther north than Winnipeg; Denmark has the same latitude as the Aleutians; and southern France is almost as far north as Montreal. Yet winters in much of the European continent are relatively mild. This is due the mile-deep layer of warm water carried north by the Gulf Stream.
The water from the Gulf Stream/ North Atlantic Current courses through two vast gyres (ocean-wide eddies)—the Sub-Polar Gyre and the Sub-Tropical Gyre. The Gulf Stream runs warmer or cooler for periods of about 20 years which, scientists believe, may affect the positions of the westerly winds which in turn plays a major part in determining whether it will be a warm or severely cold winter.
Each summer the Gulf Stream captures millions of larval newborn fish from tropical waters and deposits them along the Northeast coast of the United States. The Gulf Stream travels like a meandering river, pulling ocean water from the Gulf of Mexico along the East Coast of the United States as it moves toward Britain. As it snakes through the Atlantic, whirlpools of warm water the size of multiple city blocks spin off and grab fish and carry them north. In recent years more tropical fish than ever have been showing up in northern waters. So many of them make there way to New York that tropical fish dealers there have been begun capturing them for pet stores.
Waves and Large Waves
Ocean waves are caused by winds. Waves breaking against the shore are called surf. They can vary in height from less than an inch to over 20 feet.
Large waves and good surfing waves are caused by a number of factors. The largest and best surfing waves are caused by large storms far at sea. The waves have a chance to build up and combine into large waves. They break when the waters gets shallow and the wind blows off the land and pushes them up some.
The huge waves in Hawaii are created by intense wintertime low-pressure systems that produce of succession of storms that generate huge ground wells that roll 1,500 miles across the north Pacific. One reason waves are so big in Hawaii is that the Hawaiian islands lack a continental shelf which slows the momentum of waves.
On the north shore of Oahu, a bed of limestone 135 meters off shore suddenly drops into a two-mile deep abyss. One surfer told National Geographic, "When jumbo swells surge in from the deep water at 30 miles per hour and encounter the coral shelf, the sudden rise in the ocean floor lifts each wave into a steep peak, then knocks the legs out from under it, causing the wave crest to pitch forward in a thundering curl of white water.”
At the Jaws surf break off of Maui waves average about 20 to 25 feet and sometimes top 30 feet. Every few years a rouge wave rolls in that is 60 feet high. Mammoth waves are also found off the coast of northern Chile, a secret island off Australia and the Cortes Bank off of San Diego where one surfer rode a 66-foot wave. These waves generally occur where steep undersea mountains or islands rise up from great depths and waves approach in a direction that are carried up the slopes, getting bigger as they rise.
These days, surfers are increasingly seeking thrilling but dangerous “slab” waves. These are caused when a wave moves in from deep water with no continental shelf or other obstacles to slow it down, then suddenly strikes a reef, causing the lower potion of the wave to suddenly stop, creating a wave that suddenly stands up. The wave draws water in front of it up its curve, transferred most of the volume to the lip, creating a huge tube.
Even more massive waves, called freak waves or rogues, develop in the open sea and are a serious danger to even the largest ships. Between 1984 and 2004 more than 200 super carriers were lost at sea, reportedly due to massive waves. These waves can reach heights of over a 100 feet and generate a force equal to 100 tons a square meter. The largest rogue wave on record, reported by the tanker Ranapo , reached a height of 110 feet and was generated by a gale in Pacific.
Large waves off Bermuda from Hurricane Igor
In March 2001, two tourist liners—the Bremen and Caledonia Star —both had their bridge windows smashed in by 100 foot waves in the South Atlantic. In September 1995, the QE2 was smashed by a 95 foot wave generated by Hurricane Luis. In January 1985, the Draupner oil rig in the North Sea was smashed by a 85-foot-high wave. In December 1978, a modern German cargo ship, the Munchen , sunk suddenly in the mid-Atlantic with the loss its entire 27-member crews, presumably from a freak wave.
Freak waves have been reported in mid Pacific and mid Atlantic generated by large storms. Off South Africa they occur with some regularity where the fast flowing Agulhas Current runs head on into waves generated by winds blowing in the opposite direction. Off of Norway they have been reported where waves are focused on one spot in a shallow sea bottom. Many are believed to be caused when several waves combine, forming a super massive wave, or an already large wave steals energy from other waves.
For a long time rogue waves were thought to be a myth or an exaggeration but careful analysis of satellite images over a three week period scientists spotted ten waves that were over 82 feet in height, indicating that not only do they exist but occur with more frequency than people had thought.
Book on Monster Waves
In a review of Susan Casey’s The Wave , John Lancaster wrote in the Washington Post, " The Wave" is exactly what its cover advertises: a book about huge waves and the equally outsize personalities who spend and occasionally risk their lives trying to measure, understand, predict and sometimes even ride them on surfboards...Casey's descriptions of these monsters are as gripping in their own way as any mountaineering saga from the frozen peaks of Everest or K2. [Source: John Lancaster, Washington Post, October 10, 2010]
Lest anyone doubt the potentially devastating effects of really big waves, Casey devotes another section of the book to tsunamis, such as the one that sloshed around a remote fjord in Alaska following an earthquake in 1958. The high-water mark on the mountains flanking Lituya Bay was measured at 1,740 feet.
waves create sea spray over U.S. Navy ship
The RSS Discovery, a British research vessel that was nearly pounded to smithereens by a massive storm in the North Atlantic in 2000. Instruments on board measured the "significant wave height" -- an average of the largest 33 percent of the waves -- at 61 feet, "the largest ever scientifically recorded in the open ocean" (some spiked as high as 100 feet). The episode added to growing evidence about the prevalence of so-called rogue waves, which can rise up unexpectedly from much smaller seas.
"Tow surfers," don’t catch waves the old-fashioned way — by paddling — they are catapulted onto them by partners riding personal watercraft. The technique allows surfers to catch waves that were previously considered too big to ride. The sport was pioneered by Laird Hamilton, who remains the undisputed king of the pursuit.
Giant waves include Jaws, an aptly named offshore break near his home in Maui, and Teahupoo (pronounced tay-ah-HOO-poo), a freakish Tahitian killer "with the personality of a buzz saw." On the later, Susan casey wrote in her Book The Wave , "As Teahupoo reared up it drained the water from the reef, turning the impact zone -- a lagoon that was mercilessly shallow to begin with -- into a barely covered expanse of sharp coral, spiky sea urchins and volcanic rock," she writes. "This happened in seconds, in an area maybe three hundred feet long. I stared. I had never seen a wave behave like this one."
Many believe there is a link between big waves and climate change. Lancaster wrote in the Washington Post, “A warming atmosphere means warmer seas, which mean larger and more violent storms, which means bigger and more destructive waves -- with potentially dire consequences for shipping and coastal erosion. As one climate scientist cheerfully tells her: "We're gonna get smacked. No doubt."
Ocean tides are caused by gravitational pulls of the moon and the sun. The pull of the sun is about half that of the moon because even though it larger it is much further from the earth than the moon. Incoming tides are called flood tides and outgoing ones are called ebb tides.
"The attractive forces of the moon and the sun operate to pile up ocean waters in a wave directly beneath them, forming at the same time a similar wave on the opposite side of the world. These tidal waves have a wavelength of one half the circumference of the earth and as the earth rotates they try to follow."
Most places have two high tides and two low tides a day. The difference between these tides vary around the world. The largest tides are caused in funnel-like bays like the Bay of Fundy. If there were no geological features high tides would repeat about every 12 hours and 25 minutes but due to variation in ocean depth, coast lines topography and other features the tides vary a great deal.
Tidal_bulge Higher-than-normal tides occur during the new moon spring tide when the sun and moon are on the same side of the earth, pulling together, or are lined up at opposites of the earth so that their pushing waves line up with the pulling waves. Lower-than-normal tides occur when the moon and sun are at right angles to one another when the moon is in its first quarter and third quarter. These are called neap tides.
Scientist don't completely understand all the mechanics of tides. Tidal dates and times are made on the basis of observation over time rather than calculations based of the movement of the sun and the moon. Exceptionally large tidal surges can be caused by large storms or extreme changes in atmospheric pressure.
Image Source: National Oceanic and Atmospheric Administration (NOAA) noaa.gov/ocean ; Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
© 2009 Jeffrey Hays
Last updated March 2011