Oceanography is the diverse branch of science dealing with the study of the oceans using chemistry, geology, physics, biology and technology to analyze this unique environment.
History of Oceanography
Formal study of the world's oceans began during the late 15th and early 16th centuries and the time period following. Christopher Columbus' discovery of the Americas in October of 1492 and Ferdinand Magellan's circumnavigation of the globe from 1519 to 1522 were two important voyages encouraged further systematic study of the oceans. In 1588, when Sir Frances Drake's British fleet defeated the Spanish Armada, Spain's long dominance of the seas ended. James Cook, a British navigator, went on three trips to map the seas and to explore them further. His primary goal was to find a huge continent to the south that had been sighted by the French during various expeditions.
The HMS Endeavour took to the seas in 1768 and during this voyage, Captain Cook succeeded in mapping most of New Zealand's coast on the eastern parts of Australia. He used John Harrison's chronometer, which enabled him to accurately measure time and therefore determine latitude and longitude to a greater degree of accuracy. On his second voyage, Cook took HMS Adventure and HMS Resolution around the Cape of Good Hope and on January 17, 1773 he sailed beyond the Antarctic Circle looking for the southern continent he had heard about. Instead, he found South Georgia and the South Sandwich Islands and was unable to travel further southward due to thick ice blocking his way.
Cook went on his last expedition from 1788 to 1789 and discovered the Hawaii. He travelled northwards to the Bering Sea but heavy pack ice barred his way further northward. On his return trip he went to Hawaii again and was killed in an argument over a stolen boat. His various explorations yielded important maps, detailed charts and notes describing coastal conditions as well as observations from naturalists and biologists he had on board with him.
After his discoveries were published, exploration of the southern oceans increased, and trade through those areas increased. Due to this, American Matthew Fontaine Maury realized the importance of gathering data on ocean winds and currents. He was the director of the US Naval Department of Charts and Instruments, and in 1855, he published The Physical Geography of the Seas which was an important milestone of oceanographic study. Its value was realized immediately and the work was valued by all sea captains.
The voyage of the HMS Beagle was another important voyage in the history of oceanography. Charles Darwin signed onto this voyage as a naturalist under Captain Robert Fitzroy. The expedition was to last from 1831 to 1836 and after it, Darwin published The Structure and Distribution of Coral Reefs in 1843 and The Origin of Species in 1859. His work relied heavily on the observations he made while sailing on the HMS Beagle.
Modern oceanographic study began in the early 1900s by Johannes Schmidt, and later in 1910 by Johan Hjort of Norway. Hjort studied primarily in the Mediterranean and the North Atlantic. In 1912, he published The Depths of the Ocean to illustrate his findings. Schmidt took Dana I and Dana II on voyages through to the 1920s exploring three oceans and creating enough data and observation to write the Dana Reports which are still in use in today's study.
From 1925 to 1927, the German ship Meteor used advanced equipment over a period of two years to collect data on temperature and salinity at 310 different points across the ocean. This analysis proved that the ocean is perhaps the most stable environment on the planet. Using acoustics, water circulation was also analyzed by George Wurst who formuated a theory of circulation which has proved to be accurate and is still recognized as such.
After World War II, many nations began to develop programs of oceanographic study, such as the Scripps Institution of Oceanography in the United States, and the Woods Hole Oceanographic Institution. Since the 1960's, a large portion of oceanographic research is devoted to mineral research and the search for oil and natural gas.
Study of Oceanography
The oceans take up 71% of the earth's surface area, equalling approximately 139 million square miles. The oceans' average depth is 12,200 feet and the deepest point lies in the Mariana Trench in the Pacific Ocean and is 36,200 feet below sea level. The oceans contain nearly 300 million cubic miles of water, which rose to the earth's surface as the planet cooled millions of years ago.
Water is formed by two hydrogen atoms and one oxygen atom. The two hydrogen atoms bond to the oxygen atom by sharing their single electron with the oxygen atom in an asymmetrical fashion. The two electrons supplied by the hydrogen are pulled closer to the oxygen's nucleus, creating a polarity within the molecule and making the hydrogen end of the molecule carry a slight positive charge and giving the oxygen end a slight negative charge. This property of molecular polarity creates weak hydrogen bonds between water molecules, with the negatively charged hydrogen ends of each water molecule attracting the positively charged oxygen ends of other water molecules.
These bonds are relatively weak but are responsible for many of the physical properties of water. These characteristics create water's ability to hold heat energy well; it would be in gaseous form at room temperature otherwise and would not exist as a liquid on the earth's surface, making life impossible. Another effect of this is that water acts as a stabilizing force in terms of climate change as it absorbs and releases heat as it evaporates and freezes.
It is water's properties as a solvent that allow seawater to exist; water can dilite many substances into their composite ions, such as the salts present in seawater.
Salts Present in Seawater
Ocean currents are another important aspect of oceanographic study. The sun and the rotation of the earth are the primary causes of ocean currents, but there are many other factors that affect this as well. Winds create fluxuations in temperature along the ocean's surface and coupled with changes in salinity from the addition or subtraction of freshwater are what create thermohaline circulation, which is based on shifts in water density.
Winds also are created as a result of unequal solar heating and as such there are ascending and descending columns of heated air across the globe that split across the earth's surface once cooled enough to reach it. The rotations of the planet causes this air to be deflected as it moves away from the equator, a phenomenon known as the Coriolis effect. This is what creates the Trade winds and Westerlies in the northern and southern hemispheres. These prevailing winds have a great effect on the ocean. They make the surface layer of the ocean move around the continents. Between the 60° lines of latitude there are large pairs of oval shaped patterns of circulation which are known as "gyres." They flow in a clockwise manner in the northern hemisphere. In the southern hemisphere, the prevailing winds create a "ring" of water that moves around the earth between latitude lines 45° and 60° south. This ring doesn't exist in the northern hemisphere because land masses prevent it from being created.
This is just the most basic overview of oceanography as a science; the occurances of tides, wave patterns, subsurface currents, and ocean chemistry are all vital to its study as well. Much of what I wrote about in my writeup in the ocean node applies here and vice versa. Oceanography is fascinating in how it draws from so many brances of science as it examines one of the most beautiful envorinments on earth.
H.V. Thurman. Introductory Oceanography. Macmillan, New York, 1994.
D. Wilson. The Circumnavigators. Constable, London, 1989.