Sunken battleships, leviathans, dark depths - such is the stuff of the deep and endless sea, at least in popular imagination. And few of us can fathom how much water is contained in all the oceans, which cover 71 percent of planet and account for 97 percent of its water.
At least, until now.
There are 1,332 billion cubic kilometers of ocean water on Earth. Yes, that’s kilometers.
So says Matthew Charette, a marine geochemist at Woods Hole Oceanographic Institution who has completed an “audit” of the seven seas using satellite measurements so sensitive they can detect the bulge of the ocean when an underwater mountain lurks below.
Mr. Charette conducted the project - described as a “new world map of the oceans ” - with co-investigator Walter H.F. Smith, a geophysicist with the National Oceanic and Atmospheric Administration. The pair released the findings from the gargantuan task on Thursday: Their scan of all the world’s oceans was complete, save for a few stray areas of the Arctic covered with ice.
It’s a lot more rugged down there than previously thought.
The new measurements reveal that ocean bottoms “are bumpier and more mountainous than had been imagined,” Mr. Smith said.
The researchers report that the world’s total ocean volume is 0.3 percent less than estimates made more than three decades ago. Alarmed environmentalists can relax, though. It’s not because the oceans are losing water. The new findings simply reflect more accurate measurements.
Curious scientists have been plumbing the depths of the proverbial bounding main for clues about ocean volume for centuries, with mixed results. One calculated with surprising accuracy.
Sir John Murray, a marine biologist and early oceanographer, dropped ropes weighted with lead from a seagoing steamship in 1887 to calculate that elusive final figure. The determined Scotsman came up with numbers that were only 1.2 percent greater than those reported by Mr. Charette and Mr. Smith more than a century later.
It was a tricky business from the get-go, apparently.
“Among the ancients, Aristotle, Posidonius, Pliny and other philosophers speculated as to the height of the land and the depth of the sea, but their ideas on the subject were necessarily vague, and they had usually to confess themselves in a special manner ignorant of the depth of the sea,” Mr. Murray wrote in his inaugural paper, published by the Scottish Geographical Magazine and read before the Royal Society of Edinburgh.
Meanwhile, the contemporary pair of researchers are not entirely satisfied with their conclusions.
Mr. Smith said satellite-based radar can’t “see” the ocean bottom, and spatial resolution is a problem, like an out-of-focus camera. The researchers are calling for more ship-based measurements to enhance their data - a formidable task, given that ship sonar has mapped only 10 percent of the Earth’s seafloor.
Time and cost are a factor. It would take a single ship 200 years to measure the entire ocean-floor depths, at a cost of $2 billion, the researchers said.
“NASA is spending more than that on a probe to the Jupiter moon Europa,” Mr. Smith observed.
Nevertheless, the findings also could play into several other topics of interest that indeed play into popular imagination, not to mention public argument.
“Accurate estimates of ocean depth and volume could tie in with the growing field of ocean observation and exploration, as well as climate-change models and estimates of salt in the oceans,” Mr. Charette noted.
“Ocean volume is a key constant in Earth science that should be reported accurately with the most current, state-of-the-art ocean area and mean depth estimates.”
The work was funded in part by the EarthWater Institute and has been published in the current issue of Oceanography, a science journal.