Case Study:
How do we know what the seafloor looks like?

The vastness of the ocean and the secrets of the submerged landscape contribute to its mystery. Seawater is opaque to light beyond a few hundred meters' penetration. Hence, there are no mountaintops one can scale to directly gaze at vast expanses of the abyssal seafloor.
William B. F. Ryan (1992) "An Introduction - Down to the Sea in a Ship" Oceanus, Woods Hole Oceanographic Institution, MA

Consider yourself a new student of marine geology and that you want to understand the technology used on ships for deriving data about the sea floor. Use the following questions as a guide.

  1. Why might a historical perspective be valuable?
  2. How has the technology changed? How has it stayed the same?
  3. How have the images of the seafloor changed within the past 50 years?

Begin by examining historical documents. Except when noted, text and images courtesy of The National Oceanic and Atmospheric Administration, U.S. Department of Commerce

Early History: Non-European or Western Culture
  • Early navigation was done by keeping in constant view of land.
  • Alexander the Great founded the first marine science library in 3rd century BC at Alexandria, Egypt.
    Early Longitude and LatitudeCartographers produced charts and maps representing a spherical earth on a flat surface with latitude (parallel to the equator) and longitude lines (running from pole to pole) dividing the surface of the earth. (NOAA Photo Library)

  • Between 300 and 600 AD, Polynesians colonized nearly every inhabitable island in southern Pacific Ocean.
  • Chinese invented the rudder, watertight hulls, and sophisticated sails on multiple masts, all of which were critical to sailing with large vessels.


The 1700's
  • The British Longitude Act of 1714, in the reign of Queen Anne, promised a prize of 20,000 English pounds for a solution to the longitude problem to anyone that could provide longitude to an accuracy of 1/2 degree. It was an immense amount of money at the time, the equivalent of millions of dollars today. Read Dava Sobel's explanation:
  • The British Longitude Act challenged many men, both of wealth and education, such as Astronomers, and men who worked with their hands, such as mechanics, to create an accurate way to tell time at sea. John Harrison a carpenter turned clock maker, born in 1693, proved to be the right man for the job, but it took him over 25 years, and he had to contend with Royal Society.
  • A story from 1725 recalls how fishermen could not find the sea floor. "Myth and the Sea: The Bottomless Abyss."

  • In 1768 H.M.S. Endeavor sailed out of Plymouth Harbor under the command of James Cook of the British Royal Navy.

The 1800's
First Bathymetric MapFirst attempt at a bathymetric map by Matthew Fontaine Maury. Published in The Physical Geography of the Sea. 1855. (NOAA Photo Library)
  • 1807 President Thomas Jefferson signed a law authorizing the formation of an agency to survey the coast.
  • In 1831, on a voyage in the H.M.S. Beagle, Charles Darwin deduced how atolls and reefs were formed around and upon volcanic islands.
  • In 1832 Charles Lyell Comments on Future Possibilities for Marine Archaeology.
  • Track of the flagship Vincennes first telegraph cable is laid across the Straits of Dover in 1851 and stimulates new technologies to protect, raise and lower cables to the sea floor.
  • In 1840 The First Modern (successful) Deep Ocean Sounding was taken with a line of 2,425 fathoms (1 fathom = 6 ft = 2 meters).
  • In 1855 M.F. Maury visualizes the seafloor and writes an account of it in his book "The Physical Geography"
  • On May 29, 1867, a 270-fathom dredge haul from a few miles north of Cuba yielded a basketful of living creatures which disproved that the sea floor was void of living organisms.
  • Early bathymetry map of the GulfThe first modern bathymetric map was created from soundings made in the Gulf of Mexico. (NOAA Photo Library)
    The First Accurate Bathymetric Chart was rendered in 1888.

The 1900's
  • The role of echo sounding in exploring the sea was first considered a supplementary device.
  • Looking for Atlantis: A Suggestion to Survey the Mid-Atlantic Ridge in 1940.
  • While exploring the Marianas Trench in 1960 humankind reached it's deepest depth.
  • A major development of the 1950s was the invention of the Precision Depth Recorder (PDR) at the Lamont Geological Observatory of Columbia University.
  • The discovery of a rift valley in the center of mid-ocean ridges was one of the most significant bathymetric discoveries ever made, but the significance was not realized right away. The following is an account from: "The Mid-Atlantic Rift Valley as Girl Talk"
Three Great Tools of the 1960s: Deep Tow instrument systems, multibeam sounding instruments, and manned research submersible.
  • The first was the Deep Tow instrument system, built and operated by the Scripps Institution of Oceanography.
  • Multibeam sounding instruments were the second major development of this period.
  • The third major instrument developed during this period was the manned research submersible.

  • In 1990 the U.S. Geological Survey collects data from a research vessel for mapping the sea floor and its underlying geology.

  • We visualize the hidden seascape with digital data sets, picture element by picture element, as tiles of a growing quilt, each stitched in the course of month-long expeditions. William B. F. Ryan (1992) "An Introduction - Down to the Sea in a Ship" Oceanus, Woods Hole Oceanographic Institution, MA



    With an historical perspective students are now ready to do some ocean exploring on their own.