Nearly a quarter century ago, Greg Johnson was a freshly minted PhD in oceanography puttering north in the South Pacific Ocean. About every 35 miles, the boat he was on stopped and scientists dropped an instrument overboard to measure temperature and salinity at regular intervals all the way to the seafloor.
This process was repeated in a crisscross pattern throughout the world’s oceans over the course of the 1990s. “At the end of it, we had kind of a blurred snapshot of the state of the ocean in that decade all the way from the surface to the bottom from coast to coast,” he explained to NBC News.
The following decade, scientists re-sampled some transects for the sake of comparison. Taken together, the measurements collected during the World Ocean Circulation Experiment are the best — and for most of the oceans only — data available on temperature and salinity 1.4 miles below the surface.
Today, Johnson is spearheading a project to deploy a global array of robotic floats that will probe to a depth of 3.75 miles, allowing scientists to continuously monitor changing temperature and salinity in the entire ocean except for the deepest trenches.