What makes mapping the ocean different than, say the remote Tibetan Plateau or the imposing Alps, is one very simple, yet very important thing: water. Advanced as we are, humans still can’t see through water. And unlike land which, thanks to our aerospace technology, we can see in almost frightening detail, we can’t lob something into space and have it take pictures of the ocean floor. The moon is hundreds of thousands of miles away, and Mars and Venus register in the millions of miles away, but they are so much easier to map because they aren’t under water!
Early efforts to map at least some of the ocean floor—especially those parts of it near shore in busy shipping areas—began, well in the age of shipping. Throughout centuries of maritime exploration, mariners relied on sounding—using long ropes and lead weights to estimate distances—to get some sense of the ground beneath them. Though undeniably useful, this method produced only the most rudimentary picture of what was lying below the waves.
SOUND INSTEAD OF SIGHT
Medalist William Maurice Ewing was one of the first to argue for systematic mapping of the seafloor beginning in the 1930s. He labored in near obscurity using instruments built out of coffee cans and car parts until WWII. Suddenly there was a huge incentive to understand the seafloor and Ewing took advantage of it.
Maurice Ewing (left) and Frank Press (right), circa 1950. Courtesy Lamont-Doherty Earth Observatory.
Ewing quickly realized that one of the best methods for underwater mapping was using not sight, but sound. Sonar had been in use since WWI, but under Ewing it advanced by leaps and bounds. Under his direction, Marie Tharp and Bruce Heezen produced the first geophysical map of the Atlantic Ocean. Ewing also discovered that the mysterious mid-Atlantic ridge—now recognized as the largest geological feature on the planet—was actually part of a global system of volcanic mountains.
Hydrographic data collected from multibeam sonar systems are used to update nautical charts. © National Ocean Service
As sonar technology—which bounces sound waves off the seafloor and measures how long they take to return—improved, so did our ocean maps, but even today there are huge limitations. Modern sonar equipment can produce incredibly detailed maps with a resolution of about 100m—meaning features larger than 100m (or about the size of a football field) are visible. But, sonar can only map narrow sections of the seafloor beneath the ship the instrument is attached to, so getting a complete picture is still a laborious process. Highly detailed sonar maps are still only available for about 10-15% of the ocean floor, an area roughly the size of Africa. (For comparison, China released a map of the lunar surface in 2012 with a resolution of about 7m or 23 feet.)