GEOLOGICAL OCEANOGRAPHY 



By Andries Van de Ree 



Maritime Safety Dimsi&n 



U. S. Naval Ocearwgraphic Office 



Geological Oceanography is the application of the science of 

 Geology to the ocean basins. As such, it is directed toward all 

 aspects of geology. It includes the investigation and analysis of the 

 topography and the composition of the ocean floor, the study of vol- 

 canism, magnetics, gravity, seismism, heat flow. 



In the last two decades great strides have been made in our 

 knowledge of the ocean floor and its sediment layers. Three factors 

 have contributed to the advancement in this field. Firstly, instru- 

 mentation has progressed rapidly, giving us better tools for explo- 

 ration — improved echo sounders, more accurate electronic position 

 finding systems, gravity meters operating on surface ships, new 

 acoustic devices, electronic computers, and submersibles of various 

 sizes. Secondly, the U.S. Navy, in cooperation with others, has be- 

 gun surveying accurately the unknown part of the ocean floor to 

 publish bathymetric (deep measuring) charts urgently needed by 

 nuclear submarines capable of diving to great depths. Thirdly, in the 

 last few years the government has made additional resources avail- 

 able for both theoretical and applied ocean research. 



The ocean floor, covering approximately 72 percent of the earth's 

 surface, is divided into areas with the following common features: 



1. The continental shelves, the relatively shallow areas border- 

 ing the continents and a few large islands. 



2. The continental slopes and rises which usually extend from 

 the outer margin of the shelves to the deep sea floor. 



3. The deep sea floor, the domain with great depths where 

 abyssal plains are interspersed with great mountains, exten- 

 sive ridges, deep basins, valleys, canyons, troughs and 

 trenches. 



Before discussing each of these areas and some of the other 

 fields comprising Geological Oceanography separately, a background 

 is provided for the lay reader. 



HISTORICAL DEVELOPMENT 



For centuries, geology, as a physical science, was explored by 

 scientists who occupied themselves almost entirely with charting the 

 land and investigating basic geological principles. Geological 

 Oceanography was neglected until the latter part of the eighteenth 

 century when James Cook led a scientific expedition which not only 

 measured the ocean depths, but took many temperature observations 

 from 1772 to 1775. Soundings of real oceanographic importance were 

 taken in 1840 when Sir James Clark Ross obtained soundings of more 

 than 2,600 fathoms in the Antarctic. 



In those days, soundings were made with a hemp line. Lowering 

 and raising the lead to take a deep-sea sounding took hours. An 

 improvement in sounding was introduced in the middle of the nine- 

 teenth century by Lt. Matthew Fontaine Maury, U.S.N., using a can- 

 non shot attached to a ball of twine, which ran out rapidly. When 

 the bottom was reached, the twine was cut and the depth determined 

 from the length of twine remaining in the ball on board. However, 

 this method did not produce a bottom sample, so that one of Maury's 

 co-workers. Midshipman Brooke, U.S.N., invented an automatic de- 

 vice for detaching the extra weight from the sounding lead when it 

 hit bottom, with the result that a lighter line could be used to raise 

 the lead. Lt. Maury issued a bathymetric chart of a part of the 

 North Atlantic containing fewer than 200 soundings. 



In 1882, the U.S. Commission of Fish and Fisheries launched the 

 Albatross, the first ship ever built in this country for oceanographic 

 research. Under the leadership of Agassiz, the ship took more deep- 

 sea soundings than any other vessel up to that time. 



An important innovation in sounding was introduced by Thomson 

 (Lord Kelvin) in 1874 by using piano wire for sounding line instead 

 of hemp or twine. 



In the early twentieth century, a real boon to the progress of 

 oceanographic research was the development of the echo sounder. 

 It was a major breakthrough in increasing our knowledge of the 

 relief of the ocean floor. In 1923, the U.S. Coast and Geodetic Survey 

 used the first echo sounder on the Guide, and from 1925 to 1927 the 

 Meteor of the German Atlantic expedition made an extensive inves- 

 tigation and obtained numerous echo soundings in the middle and 

 southern part of the Atlantic Ocean, providing the scientific com- 

 munity with detailed profiles of the ocean floor in the explored area. 

 Comparing these profiles with those available from the continents, 

 it was found that irregularities in the ocean bottom in some areas 

 are as great as those on land. Echo-sounding lines of the U.S. Navy, 

 the Coast and Geodetic Survey, and others proved that in other 

 oceans, irregularities are also common. 



Shallow areas of the ocean floor are being explored by geologists 

 by swimming with scuba gear, which consists of one or more cylin- 

 ders of compressed air strapped to the back and a tube leading to 

 the mouth for breathing. 



Another means of increasing our knowledge was the develop- 

 ment of the deep-sea camera. In 1893, Boutan took underwater pic- 

 tures off the Mediterranean coast of France, but it was not until 

 1938 that Ewing and his group started to experiment with cameras 

 which could be used on the deep-ocean floor. Since then, many pic- 

 tures have been taken aiding the scientist in the examination of the 

 sea floor and the study of the sediment types. A team of scientists 

 of the U.S. Naval Research Laboratory has taken pictures of the 

 ocean floor where the submarine Thresher disappeared about 260 

 miles east of Boston. The photographs proved, without doubt, the 

 fateful end of the submarine. 



To transmit data rapidly, the research vessel Geronimo, operat- 

 ing in the Equatorial Atlantic Ocean in September 1963, sent ocean- 

 ographic information directly to the National Oceanographic Data 

 Center, Washington, D. C. via the Syncom satellite. 



The Oceanographer and the Discoverer, oceanographic survey 

 ships of the U.S. Coast and Geodetic Survey, are equipped with auto- 

 matic data processing systems to provide readings of shipboard 

 instruments and perform calculations for ships' laboratories simul- 

 taneously. Similar systems reflecting the latest state of the art have 

 also been installed on the latest U.S. Navy oceanographic research 

 ships. 



Fortunately for the advancement of marine geology, other 

 avenues of exploration were brought into play. In 1930, Otis Barton 

 constructed a diving sphere, called the "bathysphere", which was 

 lowered into the ocean by a wire. A more recent vintage of the div- 

 ing sphere is the bathyscaph Trieste, which descended to a depth of 

 5,966 fathoms in the Challenger Deep in the Pacific Ocean. 



Submersibles to explore the oceans by close observations are 

 being developed in ever-increasing numbers. One of the latest exper- 

 iments was the descent of the manned submersible Sealab II, 57 

 feet long and 12 feet in diameter, to a depth of 210 feet off San 

 Diego, California. A group of men lived and worked under pressure 

 for several days, occasionally outside the submersible. Pioneering 

 to habitate the ocean floor has begun. 



Another attack on the secrets surrounding the deep-sea floor is 

 the Mohole Project, which has the objective of piercing the earth's 

 crust and reaching the earth's mantle. To accomplish this goal, tech- 

 nical know-how should provide the tools to drill through some 15,000 

 feet of rock in a location where the ocean is about three miles deep. 

 Preliminary investigations were conducted by the drilling barge 

 Cuss I, which drilled a number of holes, the deepest being 601 feet 

 into the ocean bottom in water about two miles deep. The tests 

 showed that for drilling purposes, the platform should be kept 



