WHOI oceanographer Jim Ledwell has been selected as the winner of the 2007 Alexander Agassiz Medal, awarded by the U.S. National Academy of Sciences. Ledwell, a senior scientist in the Department of Applied Ocean Physics and Engineering, specializes in the use of chemical tracers to observe currents in the ocean. Established in 1913, the Agassiz Medal is awarded to an individual scientist for original and fundamental contributions to oceanography. The medal will be officially presented at an April 29 ceremony in Washington, DC. Past WHOI recipients of the Agassiz Medal include Henry Bigelow, Columbus Iselin, Alfred Redfield, Fritz Fuglister, John Steele, and Henry Stommel. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)

Jim Ledwell was a WHOI physical oceanographer and Ocean Pioneer known for his contributions to understanding of ocean circulation and mixing through tracer release experiments. In addition to being a brilliant scientist and mentor, Ledwell was, by all accounts, an extraordinary human being: kind, humble, and always positive. He was also a deeply committed advocate for peace.

Throughout his career, Ledwell used chemical tracers to measure gas ocean-atmosphere exchange and ocean mixing rates, but was best known for perfecting a system of injection and measurement that could be surveyed months–and in some cases, years–after the initial release. By measuring how the tracer spread along and across density-stratified layers of the ocean, Ledwell found that vertical mixing in the upper ocean interior was very weak–much less than what scientists thought necessary to balance the heat budget. This discovery revolutionized the field of physical oceanography, and fueled many investigations into the question of, “where does the ocean mix?”

Since joining WHOI in 1990 until he retired in 2015, Ledwell used tracer methods to study interdisciplinary problems such as zooplankton population dynamics, eddy-driven nutrient supply, and larval transport in the deep ocean. He was a Fellow of the American Geophysical Union and The Oceanography Society, and received honors from the U.S. National Academy of Sciences.

Despite his many contributions to the field of oceanography and skill as an analytical chemist, in Ledwell’s classic humble style, he attributed his achievements to the scientists, engineers, and technicians with whom he collaborated.

Learn more about this #OceanPioneer: go.whoi.edu/jim-ledwell