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Images: A Drop in the Ocean

WHOI physical oceanographer Jim Ledwell pioneered techniques using a harmless chemical tracer to reveal how water flows deep within the ocean. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)
Senior engineering assistant Brian Guest (bottom right) directs the launch of the injection sled that Jim Ledwell and colleagues use to release a chemical tracer at specific depths in the ocean. Following the tracer's movements over several months allows the researchers to study rates of mixing and turnover far below the surface. (Photo by Uriel Zajaczkovski, Scripps Institution of Oceanography)
Scientist Jim Ledwell draws a sample from an instrument that collected water from various depths in the ocean. By determining tiny concentrations of a tracer chemical in thousands of such samples, he and his colleagues have been able to demonstrate how fast and how far waters mix in the ocean depths. (Photo by Cindy Sellers, Woods Hole Oceanographic Institution)
In the North Atlantic Tracer Release Experiment, or NATRE, WHOI scientist Jim Ledwell and colleagues released sulfur hexafluoride, a harmless chemical tracer, in the northeast Atlantic in 1992 and followed its winding, widening course over time. Thirty months after release, almost all of the tracer was still within 150 meters above or below the release point. The experiment showed that mixing in the deep ocean occurs at a far slower rate than in the upper ocean. (Based on data from the North Atlantic Tracer Release Experiment)
Scientist Jim Ledwell says the success of his tracer experiments is largely due to the skill and effort of senior engineering assistant Brian Guest, seen here (center) preparing to deploy hardhat floats as part of the DIMES experiment in the Southern Ocean. (Photo by Rick Krishfield, Woods Hole Oceanographic Institution)
Senior engineering assistant Brian Guest deploys a sound source into the Antarctic Circumpolar Current as part of a major experiment in the Southern Ocean in 2009. The sound source enabled researchers to track numerous floats that they had released into the current, to chart the position and movement of a mass of water within the current. (Photo by Jim Ledwell, Woods Hole Oceanographic Institution)
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