The seas had already been sailed for centuries, and a small amount of research had been conducted on the Gulf Stream, formation of atolls and the use of chronometers to map out latitude and longitude. Even so, the launching of the Challenger Expedition a little over 100 years ago is considered by many to be the beginning of modern oceanography.
This venture, led by John Murray and Charles Wyville Thompson, set out from Portsmouth, England, in December of 1872 on a mission to record temperatures and chemistry of the sea water; measure ocean currents; determine the geology of the sea floor; and to discover the various types of creatures that lived in the water. The vessel traveled south on the Atlantic, around the Cape of Good Hope at the southern tip of Africa; sailed across the Indian Ocean to Australia and New Zealand; then to the Hawaiian Islands; then south around Cape Horn, the southern tip of South America. The mission ended in May of 1876, when HMS Challenger returned to England, after sailing a total of 68,890 miles.
Challenger was equipped with a laboratory and sampler instruments to grab rocks and mud off the ocean floor. Trawls and nets were employed to catch living creatures from different levels of the sea. There were a total of 362 sampling stations during this expedition, and 133 dredges. Winches-mechanical engines were used to let down sounding lines, which measured the depth of the water. To accomplish this process, a 200 pound weight attached to several miles of rope was tossed overboard. Once the weight hit the bottom, the rope was measured and the weight pulled back into the ship. It took an hour to perform a depth sounding in this manner, but the Challenger performed a total of 492 during the journey. Prior to this research, it had been believed that the deepest part of the ocean was azoic, or that it contained no life. This expedition found life even at the deepest levels – a total of 4,700 new species of plants and animals were discovered during the voyage.
During a depth sounding in the western Pacific, the Challenger discovered one of the deepest parts of the ocean at the Marianas Trench. At that location, from the surface of the ocean to the floor was 26,850 feet, or over four miles. Since that time, a deeper spot has been discovered near that area. Named after the expedition’s discovery, the Challenger Deep is the deepest spot in all the oceans, at 37,800 feet.
In 1912, a book was published that displayed the results of the Challenger Expedition, called "Science of the Sea." This writing explained the rudimentary methods employed by early oceanographers in obtaining data. For example, the sediment accumulation rates in the ocean were determined by the number of sharks’ teeth in the sample of sediment. A large amount of teeth meant that the sediment accumulation rate was very slow. Few sharks’ teeth in the sample led to a recording of high sediment accumulation. Using this data, Challenger scientists mapped out the relative distribution of sediment accumulation in the ocean. Although modern oceanographers have more precise results, the early method was quite accurate.
The 20th century ushered in World War I, and the use of submarines in warfare led to development of sonar and magnetometry in oceanography. SONAR is an acronym standing for “sound,” “navigation” and “ranging.” It enabled scientists to measure ocean depth by using sound waves rather than the cumbersome method employed by the Challenger. This echo sounding technique was first used by oceanographers in the 1920s in the S.S. Meteor, which explored the South Atlantic. One hundred years later, sonar is still used in making bathymetric, or contour, maps of the ocean floor.
The magnetometer, also originally developed for war, became a tool for oceanographers to discover the magnetic properties of rocks found on the ocean’s bottom.
From the early 1900s through the 1960s, scientists formed several hypotheses, including the Continental Drift theory, seafloor spreading and the theory of Plate Tectonics. Each of these theories was related to activity on and under the ocean’s floor.
In the 1950s and 1960s, echo sounding was used to map ocean ridges in the North Atlantic and the Pacific. Researchers discovered a chain of underwater mountains that continued for a thousand miles or more, that resembled volcanic rift zones. Due to this finding, it appeared that these ocean ridges had been formed by volcanoes on the sea floor. The lava that was spewed out cooled and solidified to become a new sea floor.
Further research with magnetometers showed that the magnetic particles within the cooled lava aligned with the earth’s magnetic field. Scientists then made a claim that over the history of the earth, the magnetic field had changed many times, with the north and south poles exchanging places. Therefore, rocks found on the sea bed may have either positive or negative magnetic anomalies, depending on when they were formed.
In 1968, there was a new development in oceanography, when the Deep Sea Drilling Project was launched. The Glomar Challenger, a 400-foot ship equipped with a drilling platform and scientific laboratories, had the technology not only to explore the bottom of the ocean, but also to drill through up to 2,500 feet of ocean sediment at a depth of 20,000 feet. The drilling process amassed long, thin cylinders of sediment and rock from beneath the ocean’s floor, called cores. Not only did these cores provide evidence to support seafloor spreading and plate tectonics, but they also provided a record of climate changes during the Earth’s history.
In 1985, the Ocean Drilling Program was created, with a larger ship and more advanced equipment. This ship had the capability to drill in water up to 27,018 feet deep.
Computer and satellite technology joined oceanography in the 1970s. SEASAT, launched on June 28, 1978, was the first satellite designed for oceanographic use. Its sensors provided information such as wind speed and direction, sea surface temperature, polar ice conditions and surface waves, along with imagery. In the 105 days of its orbit, SEASAT provided as much oceanographic data as had been collected in 100 years of exploration by ships.
Also during that time period, the National Oceanic and Atmospheric Administration placed a series of buoys across the tropical Pacific Ocean. Using satellite technology, these 70 units were designed to send oceanographic and atmospheric data to shore in real time.
Oceanographers today also use a number of remotely operated devices (ROVs), autonomous underwater vehicles (AUVs) and specially designed digital cameras, such as TowCam, to explore underwater. TowCam is able to take very high quality photographs of the sea bed at a depth of up to 20,000 feet. The device can also collect samples of rock, lava or water. Certain devices can even send live footage to Internet sources.
One day, oceanographic researchers hope to set up long-term observatories on the bottom of the sea which would continuously monitor various ocean properties and events.