1994-1995 Report to President

Research and education within the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) engage a broad array of scientific disciplines: geology, geophysics, geochemistry, physical and chemical oceanography, meteorology, atmospheric chemistry, and planetary sciences. Particular emphasis is placed on the study of the complex global geosystems of the atmosphere, ocean, crust, and deep interior of the Earth and planets. The Department comprises 40 faculty including one with a primary appointment in Civil and Environmental Engineering, 211 graduate and undergraduate students, and 118 permanent research staff, postdoctoral appointments and visiting scholars.

EDUCATIONAL ACTIVITIES

GRADUATE

At present the EAPS graduate program focuses on the Ph.D. degree. During the past academic year 186 graduate students were registered in the Department (Course 12), and the MIT-Woods Hole Oceanographic Institution (WHOI) Joint Program (Course 12W). The number of graduate students in the Department has remained constant for the past 15 years, and applicants continue to be among the best in the national and international pools. Although graduates with specialized training in geoscience still obtain good jobs, there is a growing need for scientists capable of approaching problems in a broad, systems-oriented context who can address environmental issues and problems associated with ecosystem change. EAPS has responded to these needs by teaching disciplinary topics within the context of integrated approaches to geosystems, and this has become a major force toward unifying the earth sciences. A master's degree Program in Applied Geosystems is now under development. This innovative program will provide education and training to prepare students for positions in industry requiring expertise in scientific computing, visualization and data inference. Students will also be exposed to economic and policy issues related to utilization of natural resources and mitigation of environmental problems. The goal of the program is to encourage a broad understanding of the interdisciplinary approach needed to solve complex problems encountered in geoscience industries today, as opposed to providing a narrowly defined curriculum centered on one primary discipline.

UNDERGRADUATE

EAPS faculty are involved in continuing efforts to improve the quality and scope of our undergraduate program. The bachelor of science curriculum has been reorganized to include three areas of concentration: geoscience, physics of atmospheres and oceans, and planetary science and astronomy. Each area of study encompasses a set of required courses, a sequence of field or laboratory subjects, and independent study or thesis preparation. An undergraduate minor degree program has also been developed to complement degrees in other disciplines, providing a foundation for careers that incorporate areas of earth science. The Department has expanded its Independent Activities Program (IAP), and EAPS now offers more IAP courses for credit than any other MIT department. The faculty have increased participation in freshman advising seminars, and this past year EAPS faculty advised 10% of the freshman class. EAPS continues its substantial participation in the Undergraduate Research Opportunities Program (UROP).

FACULTY

Two Assistant Professors were appointed to the faculty this year. Kelin Whipple, who recently received his Ph.D. from the University of Washington, is an outstanding young geologist specializing in the study of surface processes. His experience encompasses field work, laboratory experimentation, and numerical modeling, and his broad research interests offer the possibility for substantial interaction with other faculty. Robert van der Hilst, a seismologist from the Australian National University, will join the Department in January of 1996. His primary research accomplishments involve the application of seismic tomography to imaging subduction zones, where descending lithosphere plunges back into the mantle. Professor Marcia K. McNutt, a geophysicist with extensive experience in oceanographic research, has been named MIT Director of the MIT-Woods Hole Oceanographic Institution Joint Program in Oceanography and Oceanographic Engineering. Gordon H. Pettengill, Professor of Planetary Physics who worked in the area of planetary radar astronomy retired in February of this year.

HONORS

Professor Edward Boyle was awarded the A.G. Huntsman award from the Bedford Institution of Oceanography in recognition of research contributions to the marine sciences. Professor John Grotzinger was elected Fellow of the American Association for the Advancement of Science. Dr. Heidi Hammel was awarded both the Klumpke-Roberts Award of the Astronomical Society of the Pacific and the Vladimir Karapetoff Award from the MIT Office of the Provost. Professor Emeritus Edward Lorenz is the recipient of the 1995 Louis J. Batten Author's Award from the American Meteorological Society for his book, "The Essence of Chaos". Professor Gordon H. Pettengill was the 1995 recipient of the American Philosophical Society Magellanic Premium Award and the Fred Whipple Award from the Planetology Section of the American Geophysical Union (AGU). He was also elected a Fellow in the AGU. The Measurement of Air Pollution by Satellite (MAPS) Science Team, of which Professor Reginald E. Newell has been a member since its inception, received the National Aeronautics and Space Administration's (NASA) Group Achievement Award. Maureen Raymo was chosen the 1994-95 Joint Oceanographic Institutes Deep Earth Sampling (JOIDES) Distinguished Lecturer.

CURRENT RESEARCH

GEOLOGY AND GEOCHEMISTRY

In collaboration with Professor John Grotzinger, Professor Samuel Bowring's research group is using high-precision U-Pb zircon ages from volcanic rocks inter layered with late Precambrian to Cambrian fossil bearing rocks in Namibia, Canada, and Morocco to calibrate the rates of evolution of the biggest biological radiation in Earth history. Using this technique, it is possible to determine ages of rocks approximately 530 million years old with a level of precision that is less than 1 million years. Professor Grotzinger's research shows that the radiation of Ediacaran soft-bodied metazoans overlaps in time with the early Cambrian radiation of hard-bodied metazoans. Previously, these were regarded as two unrelated events, separated in time by almost 50 million years. This discovery has major implications for theories of the evolution of life. Professor Timothy Grove has been investigating the processes that lead to core formation in the terrestrial planets. By combining experimental studies and investigation of relative abundances of siderophile elements left in meteorite samples thought to have formed on Mars, it has been possible to set limits on the conditions for the formation of the Martian core. Professor Kip Hodges' work in the field of continental tectonics seeks to understand the interactions of gravity and plate-convergence forces in determining the structural architecture of mountain ranges. Results from the Annapurna region of the central Nepalese Himalayas indicate rapid (< 5 million year) alternations between contractional and extensional deformation on the scale of kilometers as the orogenic system attempts to maintain dynamic equilibrium. Professors Leigh Royden and Clark Burchfiel are continuing their work in China along the eastern margin of the Tibetan plateau, where they are studying the history of deformation and uplift of the plateau. Together with Principal Research Scientist Robert King, they have established a satellite geodetic network that covers most of the eastern margin of the plateau, a region approximately 1000 km in length. Results to date show that rocks of the Tibetan plateau are moving to the north and east relative to stable China, a result consistent with the geologic history of the region. Professor Fred Frey and colleagues have completed studies of the first 1 km of drill core from the Hawaiian Science Drilling Project, and found systematic temporal changes in the extent of melting, pressure of melt segregation and proportions of geochemically distinct source components. Dr. Peter Molnar, together with colleagues at the University of Washington, has synthesized evidence of alpine glaciation to show that in general alpine glaciers reached their maximum extents significantly earlier than continental ice sheets during the last glaciation. Professor John Southard is continuing his work on the intricacies of movement of sediment by currents and waves.

GEOPHYSICS

Professor Chris Marone continues work on the mechanics of earthquakes and faulting, and the frictional properties of rocks. Marone recently completed a study of repeating earthquakes on the Calaveras fault in California, in collaboration with scientists from the U.S. Geological Survey, which shows that laboratory measurements of fault healing are only consistent with field estimates if fault strength is high, on the order of 60MPa, and earthquake stress drop is a fraction of this value. Professor Brian Evans is investigating the interrelationship between permeability and plastic flow in rocks. Using a new device, he and his colleagues can now measure the evolution of permeability as rocks are deforming at high temperature and pressure, allowing measurements of changes in volume that result in dilation and compaction during deformation. Results will be important in understanding localization and faulting in the Earth. Professor Daniel Rothman has combined theoretical analyses, numerical simulations, and results from experiments to better understand how sedimentary rocks form and how fluids flow through them. Numerical simulation of multiphase flow through high-resolution 3D images of real sedimentary rocks has been compared to experiments, and has elucidated aspects of the size-dependence of macroscopic transport properties. Professor Thomas Herring has been developing models for the changes in the rotation of the Earth due to the torques applied by the Sun, Moon and planets from the analysis of very long baseline interferometry (VLBI) data. These models will be used to explain short and long period Earth rotation changes related to the coupling of the fluid core and solid inner core of the Earth. Herring and his students are also developing models for asymmetries in atmospheric refraction and for laser altimeter systems. Professors Herring and Bradford Hager and Dr. Robert King have shown that the observed surface displacements derived from the Global Positioning System (GPS) measurements after the Northridge earthquake are not predicted by the source mechanism inferred from seismology. The unusual displacements more likely resulted from growth of the folds overlying the fault plane. In a separate development, Hager has also determined the first reliable estimate of the average density anomaly associated with the deep keels of the continents. Professor Marcia McNutt has nearly completed analysis of 44,000 gravity measurements obtained from the People's Republic of China. The principal finding is that the Tibet Plateau has deformed in the manner of a "jelly sandwich" to the collision of India with Asia, such that geological deformation at the surface is de-coupled from plate tectonic motions in the mantle by a weak lower crust. During the past year Professor Thomas Jordan's research has been focused in two areas. The first is the study of an anomalous class of seismic events called "slow earthquakes". This work has shown that these earthquakes, which occur most frequently in the vicinity of mid-ocean ridges, are compound events, comprising an ordinary (fast) rupture, which is often preceded by a "quiet", or very slow, earthquake. These results have significant implications for theories of earthquake nucleation and, possibly, for short-term earthquake prediction. The second area of research is on the structure of the earth's upper mantle beneath continents. Studies have shown that the so-called Lehmann discontinuity is a feature that separates a region of seismic wave anisotropy in the shallow mantle from a more isotropic region at greater depths. This result has implications for the theories of the structure and evolution of continental deep structure. Professor Nafi Toksoz and Principal Research Scientist Robert Reilinger of the Earth Resources Laboratory headed an international GPS campaign in the Eastern Mediterranean/Middle East. This work has provided the first quantitative estimates of deformation rates in this zone of complex plate interaction, including slip rates on the N. Anatolian fault, shortening across the Caucasus Mountains, and large-scale crustal "extrusion". Principal Research Scientist Arthur Cheng and Research Associate William Rodi developed an improved algorithm to locate and characterize hydraulic fractures using the relative positions of each successive micro-earthquake generated in the fracturing process. It has potential applications in hydraulic fracturing in the geothermal, waste disposal, and petroleum industries. Professor Dale Morgan has continued to broaden the scope of the Earth Resources Laboratory in the directions of rock physics and environmental and engineering geophysics.

PLANETARY SCIENCE

Dr. Heidi Hammel, Principal Research Scientist was the Team Leader for Hubble Space Telescope (HST) imaging of the spectacular collision of comet Shoemaker-Levy 9 with Jupiter in July 1994, and was a team member of the NASA Infrared Telescope Facility comet crash observations. The event provided new data for probing Jupiter's upper stratospheric winds and atmospheric chemistry, along numerous other results. In collaboration with staff from the Lowell Observatory and Goddard Space Flight Center, she recently published HST images showing that Neptune's Great Dark Spot has disappeared, and that a new dark spot has developed in the northern hemisphere. Professor Timothy Dowling mapped and measured the speed of atmospheric waves emanating from the comet Shoemaker-Levy 9 impact sites on Jupiter from Hubble Space Telescope images, and determined a speed of 454 +/- 20 m/s, which implies a radius of deformation for the atmosphere of 1800 km. Professor James Elliot and colleagues have continued analyses of a stellar occultation by the comet Chiron, which is unusual in two respects. It exhibits outbursts at great distances from the sun, and its nucleus is much larger than any other known comet. They conclude that they have possibly detected a bound coma and that the jet-like features observed provide evidence that the coma material originates from just a few, small active areas, rather than from uniform sublimation over the entire nucleus. Professor Jack Wisdom is continuing his studies of the long term evolution of the solar system, including the evolution of the spin axis of Mars over the last 100 million years subject to torques from the chaotically evolving planetary system. It has been found that the obliquity, the tilt of the spin axis to the orbit normal, is wildly chaotic on this time scale. His group has studied the dynamical evolution of comets in the proposed Kuiper belt, a belt of comets outside the orbit of Neptune analogous to the asteroid belt. It was found that comets in this region evolve chaotically and slowly leak into Neptune-crossing orbits by a dynamical path quite analogous to the path that transports meteorites from the asteroid belt. Professor Charles Counselman, III having developed radio interferometry techniques for measuring the Earth's crustal motions, has begun applying these techniques to locate cellular-telephone "911" callers and cosmic sources of high-energy gamma rays.

OCEANOGRAPHY

Professor Edward Boyle completed the first field deployment of a moored in-situ trace element sampler for examining surface ocean chemical variability. Boyle also has recovered a proxy variability record for the chemical changes in the deep Pacific during the past 150,000 years, and has shown that the upper waters of the northwestern Indian Ocean were nutrient-depleted during the last glacial maximum. Professor John Edmond's group made a 1,700 km water sampling transit down the Upper Lena River in Siberia as part of a comparative study of chemical weathering processes in cold climates with those in the Tropics. Edmond's group recently participated in a successful ALVIN cruise to the Mid Atlantic Ridge (MAR) to investigate the effects of recent drilling on a major, active hydrothermal ore body. Professor Maureen Raymo is using carbon isotopes in marine organic matter as a proxy for past levels of CO2 in the ocean and atmosphere for studying climate variations over geological time scales. Professor Jochem Marotzke has combined historical hydrographic data from the Indian Ocean with a general circulation model he has devised to determine heat gain or loss across open boundaries in regional ocean models. Use of this method reverses the estimated flow direction of the deep currents. The results challenge the conventional interpretation that there is strong deep inflow from the south leading to anomalously strong upwelling. Professor John Marshall and his collaborators have developed a state-of-the-art ocean circulation model designed to exploit the new generation of massively parallel computers. A large multi-national sea-going experiment to observe convection in the Labrador Sea is planned for next year. Professor Paola Malanotte-Rizzoli and collaborators have been modeling the ocean's circulation in different regions using data assimilation to improve the models. Professor Glenn Flierl and his students are conducting research on packets of planetary waves in the Gulf Stream. In cooperation with the Globec program, Professor Flierl is also investigating the physical and biological dynamics of the Georges Bank region. The TOPICS/POSEIDON altimeter satellite continues to provide Professor Carl Wunsch and his group with unprecedented global coverage of the world ocean circulation. The observations render the sea surface topography with an absolute accuracy now approaching two centimeters, and are leading to descriptions of the time-evolving ocean which would otherwise be impossible.

METEOROLOGY

Professor Mario Molina and his students have investigated the mechanism of formation of polar stratospheric clouds. They have shown that at low temperatures significant amounts of nitric acid may be incorporated into liquid cloud particles; these particles freeze over Antarctica, but do not always freeze in the Arctic stratosphere. Laboratory results show that the cold, liquid particles are as efficient as ice in the catalytic activation of chlorine, which leads to high-latitude ozone depletion. Professor Ronald Prinn and his colleagues have recently reported results of 16 years of global measurements of the trace gas trichloroethane. This gas is important because it is involved in ozone depletion, and the hydroxyl (OH) concentrations determined from its atmospheric lifetime provide estimates of the lifetimes of most hydrogen containing gases involved in the ozone layer and climate. The deduced lifetimes are about 20% shorter than previously estimated, and OH concentrations are therefore about 20% higher. Professor Peter Stone and his colleagues have been coupling the climate model they developed to the Terrestrial Ecosystems Model developed at the Marine Biological Laboratory in Woods Hole. They have found that the ecosystems are sensitive to changes in temperature and CO2 concentrations, but not to changes in precipitation and cloud cover. Professor Kerry Emanuel developed a theory for the formation of the hurricane eye, and continued research on the statistical equilibrium characteristics of moist convection. He devised and implemented a method of optimizing schemes for representing cumulus convection in climate models. He also proposed a theory linking bolide impacts with global species extinction. Professor Richard Lindzen has shown that mixing by transient eddies conditions the extra tropical atmospheric response to stationary forcing by orography and heating. The intensity of these eddies is related to the geographical distribution of tropical heating. One consequence of this, confirmed by observational analysis, has been that the extra tropical consequences of El Niño and La Niña events is changed eddy variance rather than a particular pattern. Professor Reginald Newell's group, while studying the transport of carbon monoxide in the atmosphere based on MAPS results, discovered that some atmospheric trace constituents move about in the lower atmosphere in the form of filamentary structures, typically about 500 km wide and up to 12,000 km long. Water vapor is one such constituent, and its filaments are called atmospheric rivers. Last year the group discovered that when one of these rivers was entrained into a cyclone, it deepened rapidly and moved toward the head of the river, indicating possible consequences for weather forecasting. Professor Alan Plumb's group has advanced the concept of a "tropical pipe" within which most tropical air ascends with little injection of air from middle latitudes. They argue that knowing how much injection takes place is crucial to assessing the impact of supersonic aircraft on stratospheric ozone. Professor Edmund Chang continues to study factors affecting mid-latitude cyclogenesis using modeling and observational studies.