Jun Korenaga received the James B. Macelwane Medal at the AGU Fall Meeting honors ceremony, which was held on 13 December 2006 in San Francisco, Calif. The medal is given for significant contributions to the geophysical sciences by an outstanding young scientist.
In a 1964 Science essay, “Strong inference,” the biophysicist John Platt elucidated how “certain systematic methods of scientific thinking may produce much more rapid progress than others.” Strong scientists entertain multiple hypotheses, as Thomas Chamberlin advised; they produce predictive models that can be tested and rejected, as Karl Popper required; and they filter out false hypotheses using diagnostic data, as Louis Pasteur so brilliantly demonstrated.
Jun Korenaga has shown how a young scientist can deliberately equip himself to make strong inferences about the solid Earth. As a Ph.D. student in the Woods Hole Oceanographic Institution-Massachusetts Institute of Technology (MIT) Joint Program, he was marvelously ambitious. Not content with a standard thesis project, he conceived an entire research program, for which he recruited not just one or two, but three, advisors—Steve Holbrook, Peter Kelemen, and myself. The problem he chose was the creation of the North Atlantic igneous province during the early Tertiary rifting of Greenland from Europe.
In 1996, he went to sea with Steve on the SIGMA expedition, collecting reflection and refraction data across the southeast Greenland continental margin. He interpreted this rich data set using novel inversion schemes of his own formulation. His results indicated that the thickened basaltic crust was produced by melting at relatively low temperature, at odds with the popular plume-head hypothesis.
With Peter, he considered basalt petrogenesis in more detail. They demonstrated that the trace-element signatures of high-magnesium basalts erupted since the opening of the North Atlantic, when corrected for olivine fractionation and combined with isotopic data, require long-lived major-element heterogeneity in the mantle source. Jun has since shown that this heterogeneity can be explained by subducted oceanic crust buoyantly trapped in the midmantle transition zone and subsequently entrained in the active convection caused by continental breakup.
Numerical modeling of this breakup process constituted the third component of Jun’s thesis. He was able to show how thick cratonic lithosphere can modulate small-scale convection in the upper mantle without reducing convective strength, and he used this mechanism to explain the excess magmatism during North Atlantic rifting.
Jun made rapid progress in numerical studies of convection during his postdocs at MIT and the University of California, Berkeley, deriving new scaling relations for the onset and breakdown of small-scale convection that properly account for the strong temperature and depth dependence of upper-mantle viscosity. These investigations elucidated upper-mantle convection beneath large ocean basins and set the stage for important papers on the structure of mantle plumes, the origin of the Ontong Java Plateau, and a radical reexamination of Earth’s thermal history.
In two influential papers, he explored how the compositional differentiation of oceanic mantle affected convection in the geologic past. Working backward from the present-day system, he argued that hotter mantle results in more sluggish plate tectonics. This unexpected inverse relationship between mantle temperature and heat flux has allowed him to erect a simple model that simultaneously satisfies geochemical constraints on the (low) abundance of heat-producing elements, petrological constraints on the (low) degree of secular cooling, and seismological constraints on the (low) degree of mantle stratification. John Platt, as well as William of Occam, would be pleased with this compelling synthesis.
The conclusions Jun has drawn about Earth’s thermal history are as controversial as they are profound, and it may take a while to know whether he has cut the Gordian knot. But the span of his research and the keenness of his insights illustrate what strong inference is all about. It is very fitting, therefore, that the AGU has awarded Jun Korenaga its 2006 James B. Macelwane Medal for his contributions to the fundamental understanding of mantle dynamics.
—THOMAS H. JORDON, University of Southern California, Los Angeles
Thank you, Tom, for those very kind words. I feel very honored to have been selected for the James B. Macelwane Medal, and I appreciate this opportunity to express my gratitude to my mentors. I first became interested in studying Earth history when I took a course taught by Professor Minoru Ozima, at the University of Tokyo. In retrospect, this starting point is appropriate for my somewhat multidisciplinary style, because his course was called Introduction to Geophysics, but what he actually taught was almost entirely geochemistry.
I have been very fortunate to meet the right people at the right times, and it all seems to happen by accident. When I was a masters student in Japan, I happened to be stuck on a U.S. vessel for about half a year and sailed with Ken Macdonald, Tanya Atwater, Don Forsyth, Dick Hey, and Dave Naar. There I met a few brilliant graduate students like Dan Scheirer, Chaz Weiland, and Yang Shen, and I thought it worth the pain of studying abroad if I could become like them. My advisor, Professor Kensaku Tamaki, generously encouraged me to pursue my enthusiasm.
My life at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology (MIT; Cambridge, Mass.) was much more than I expected. As Tom mentioned, I had three supervisors, but my original plan was to work just with Steve. Studying marine seismology was my primary objective, and Woods Hole was a paradise with Bob Detrick, Graham Kent, Ralph Stephen, John Colins, and Dan Lizarralde. But I had to do a second project for my qualifying, and Steve told me his fellow geologist had a nice small project even a geophysics student could easily do. Although it was anything but easy, this project with Peter on the Oman ophiolite turned out to be the most rewarding experience, which forever changed the way I think about science. Working with Peter opened my eyes not only to petrology but also to geodynamics, and Ken Koga, Nobu Shimizu, Henry Dick, Jack Whitehead, and Greg Hirth were always there to help me out.
In the middle of my Ph.D., Steve decided to leave for the University of Wyoming, and I had to find a new supervisor. Rafi Katzman suggested I ask Tom, and I could not thank him more for this wild idea. Tom was a very busy man, and I could see him only twice a year or so, but every meeting was inspirational, with a lifetime supply of fundamental issues yet to be addressed. From him, I learned how to see through superficial complexities and formulate a problem in the purest form. I was also lucky to get to know Shijie Zhong, who happened to be at MIT when I started to work on computational fluid mechanics.
I went to California for a postdoc and had a great time at the University of California, Berkeley interacting with Mark Bukowinski, Michael Manga, Mark Jellinek, and Raymond Jeanloz. Weekly gatherings at the Miller Institute had a unique atmosphere, in which I was compelled to revive my old interest and ponder some nagging issues in the thermal and chemical evolution of Earth.
I am grateful for my mentors, who let me try whatever I wanted to, so I encourage younger generations to be ambitious and expand your horizons, as Earth sciences have so much to offer. Studying such an integrated object like Earth requires more than a collection of specialists.
Now I am at Yale University (New Haven, Conn.), surrounded by interesting characters such as Shun Karato, Dave Bercovici, Jeff Park, Dave Evans, Mark Brandon, John Wettlaufer, Jay Ague, George Veronis, and Karl Turekian. My special thanks go to Shun, who nominated me for this medal. As a geodynamicist, it has been a tremendous privilege to work with the world’s best expert on mantle rheology. I would also like to thank Dave Stevenson, Claude Jaupart, and Slava Solomatov for supporting letters. It is an honor to be recognized by those I truly respect.
Last and most important, I thank my wife, Tomoko, who understands all of my dreams and ambitions and knows how to cheer me up in the most difficult times. Thank you.
—JUN KORENAGA, Yale University, New Haven, Conn.