1996-1997 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 geosystems in the Earth's atmosphere, ocean, crust, and deep interior and the similar systems on other planets. The Department comprises 42 faculty, including one with a primary appointment in Civil and Environmental Engineering, 221 graduate and undergraduate students, and 115 permanent research staff, postdoctoral appointments and visiting scholars.
During the past academic year, 185 graduate students were registered in the Department (Course 12) and the MIT-Woods Hole Oceanographic Institution (WHOI) Joint Program (Course 12W). The EAPS graduate program currently focuses on the Ph.D. degree, which is the goal of over 90% of its graduate students. There is a growing need, however, for professionals trained at the master's level who can solve geoscience problems in a broad, systems-oriented context. In response to this need, EAPS has developed a new degree program, which will award the Master of Science in Geosystems beginning this next academic year. This S.M. degree is designed to appeal to students seeking careers in industry as professional geoscientists, as well as working professionals who wish to expand their knowledge and opportunities in geoscience. It will prepare students for scientific and management careers in the environmental, natural resources, and technical consulting industries by providing skills in computer simulation and modeling of complex natural systems, as well as in scientific inference based on field observations and numerical modeling. A second major educational initiative has been the establishment of the Program in Atmospheres, Oceans and Climate (PAOC), which coordinates graduate study in atmospheric science, oceanography, and climate physics and chemistry. The Program, which replaces the Center for Meteorology and Physical Oceanography (CMPO) as the administrative unit in atmospheric sciences and oceanography, offers a broadly based curriculum for students interested in studying climate at the system level, and in performing research in oceanography and atmospheric science.
EAPS is continuing efforts to improve the quality and scope of its 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 concentration encompasses a set of required courses, a sequence of field and/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 geoscience. The Department has expanded its Independent Activities Program (IAP), and EAPS now offers more IAP courses for credit than any other MIT department. The Department continues to increase its participation in freshman advising seminars, and this past year, EAPS faculty advised over 10% of the freshman class. EAPS has maintained a strong Undergraduate Research Opportunities Program (UROP), despite changes in federal regulations that have increased the cost of UROPs to grants and contracts.
Professor Thomas Herring was promoted to Full Professor. Professors Chris Marone, Jochem Marotzke and Maureen Raymo were promoted to Associate Professor without tenure. Professor Kip Hodges was appointed Dean for Undergraduate Curriculum.
The highlight of an exciting year was the announcement that Nobel Laureate and EAPS Professor Mario Molina was named Institute Professor. Professor Jack Wisdom was appointed the Breene M. Kerr Professor. Professor Robert van der Hilst was awarded the James B. Macelwane Medal, and Professors Van der Hilst and Frederick Frey were elected Fellows of the American Geophysical Union.
Geology and Geochemistry
Professor Samuel Bowring's work on the Acasta gneisses continues, and he has documented rocks as old as 4.03 Ga. A 4.0-Ga tonalite contains inherited zircons that are as old as 4.06 Ga. This pushes back the age of the oldest crustal rocks on the planet, and indicates that older crust plays a role in the generation of tonalitic magmas. In addition, the work of Professor Bowring and his group has dramatically altered the time scale for early animal evolution. The new time scale for the middle and upper Cambrian will allow paleontological correlation of trilobites at the level of Jurassic ammonites. Through his research in central Nepal, Professor Kip Hodges is establishing the complex relations between east-west extension in the Tibetan plateau and north-south shortening in the Himalaya. Recent results suggest that the link may be a system of extensional faults that have operated as dissipative structures for the Himalayan orogenic system for at least 20 million years. Professor Tim Grove and his colleagues have been studying disequilibrium processes in earth materials by measuring solid state diffusion rates in common mantle minerals. They find that diffusion rates for trace elements are much slower than previously believed, and that diffusion rates vary systematically among rare earth elements by a factor of 30. These measurements provide new constraints on melting mechanisms, and on the behavior of trace elements during basalt magma production. Professor Fred Frey has been studying the ~115 m.y. record of volcanism attributed to the Kerguelen hot mantle plume located in the southern Indian Ocean. Based on the efforts of Frey and colleagues, the Ocean Drilling Program has scheduled a two month drilling program in 1998 that will sample the igneous crust of the Kerguelen Plateau.
Professor Clark Burchfiel is continuing his studies on the nature of intercontinental deformation within active plate boundary settings. In collaboration with Professor Leigh Royden and Principal Research Scientist Bob King, combined geologic, geodetic and geodynamic modeling has lead to a new interpretation for the formation of the Tibetan plateau that focuses on thickening of the crust in the eastern part of the plateau by lateral flow of weak lower crust. Studies in African/Eurasian convergent zone with Royden, King and Principal Research Scientist Rob Reilinger have shown that extensional tectonism reaches north of the North Anatolian fault into central Bulgaria, Macedonia and Albania and must be considered the northern part of the Aegean extensional regime. Professor John Southard, in collaboration with Professor John Grotzinger, is extending his work on sediment gravity flow deposition, looking further into the poorly understood rapid deposition of structureless sediment by powerful turbidity currents by means of high-speed cinematography. Professor Kelin Whipple is currently engaged in field studies (Sierra Nevada, Himalayas, and E. Tibet) and numerical modeling of river profiles and their response to tectonic uplift. He is also constructing a new flume in the Sediment Laboratory for experimental study of debris-flow hazards.
Professor Chris Marone's recent work has focused on friction constitutive laws and earthquake faulting. He has demonstrated a connection between shear-band width within laboratory faults and the stability of sliding, explaining why faults do not begin to strengthen immediately during the postseismic period, with important implications for earthquake nucleation size and stress drop. Professor Brian Evans is working on specifying constitutive laws for multi-phase rocks using theories developed for ceramic matrix composites. The results of experiments and modeling using a modified Eshelby-Morii-Tanaka theory indicate that the surprisingly large strengthening achieved by adding quartz particles to a calcite matrix must be accompanied by a paradoxical increase in interphase boundary sliding next to the quartz particles. Senior Research Scientist Peter Molnar has been pursuing convective instability of a lithosphere layer undergoing mechanical thickening due to horizontal shortening. Results are allowing Molnar and his colleagues to estimate amounts of lower lithosphere removed by such a process and the elapsed times required for it to occur.
Professor Bradford Hager and colleagues have developed a technique for spatial spectral localization of data on a sphere and have used it to quantify the signature of Laurentide deglaciation in Earth's gravity field. The mantle viscosity structure that fits the gravity signature, as well as the observed relaxation times for uplift beneath Hudson Bay and Fennoscandia, is substantially more viscous in the upper mantle than Professor Hager's models for tectonically active regions, consistent with the existence of the continental tectosphere. Professor Thomas Herring has been working to characterize the refractive properties of the Earth's atmosphere as applied to precise geodetic positioning applications, and to laser altimeter from Earth orbiting satellites. Professors Herring and Hager, and Principal Research Scientist Robert King have been active in the geodetic efforts of the Southern California Earthquake Center. The MIT group has played a prominent role, both in estimating the velocity field in southern California from existing GPS data and in developing the scientific justification for the newly-funded initiative to install > 200 continuously operating GPS receivers in the Los Angeles area. Professor Daniel Rothman has initiated new studies of the physics of granular media. The most important result thus far is a new model for vibrated sand that explains recent experimental observations of localized excitations.
Professor Robert van der Hilst and colleagues have finalized the processing of seismic data related to global earthquake activity between 1964 and 1995 and have used the vastly improved data for tomographic imaging of Earth's interior structure. The new images strongly suggest the continuation of many slabs of subducted lithosphere into the lower mantle, possibly to the core mantle boundary, which swings a decades old convection debate in favor of a circulation model that involves mantle wide overturn. Professor Marcia McNutt spent the first few months of her sabbatical year as a guest of the Universite Francaise du Pacifique in Tahiti helping the government assess their marine resources using satellite altimetry data. Her research has concentrated on documenting major continent-ocean differences in the viscosity structure of Earth's upper mantle to depths as great as 700 km.
Professor Dale Morgan and his students have completed environmental geophysics field studies at the Oak Ridge National Laboratory, the Massachusetts Military Reservation, and the Aberjona Superfund. Professor Morgan also successfully predicted, with three days warning, the largest seismic event in a swarm of earthquakes in Tobago. Professor Nafi Toksöz and his research group have developed a method of detecting fractured intervals in oil and gas reservoirs using seismic reflection data. These methods may help unlock vast US natural gas reserves, which are difficult to identify and produce. Principal Research Scientists Robert Reilinger and Robert King, Research Scientist Simon McClusky, and Professor Toksöz are coordinating two projects that use GPS measurements to map crustal deformation, one in the Eastern Mediterranean and the second in Southern California. These studies will provide constraints on lithospheric rheology and dynamics in plate collision zones, and will quantify fault slip for earthquake hazard studies. Professor Thomas Jordan, graduate student Rafi Katzman, and postdoctoral fellow Li Zhao have used new tomographic techniques to image small-scale convection in the upper mantle of the central Pacific Ocean. The pattern they have discovered indicates that the three major Pacific hotspots of Hawaii, Tahiti, and Marquesas are controlled by this upper-mantle convection, and that their associated topographic swells are underlain by high seismic shear velocities, an unexpected result with important geodynamical implications.
Professor Jack Wisdom is continuing his studies of the dynamical evolution of the solar system. Recent work has focused on the evolution of the Earth-Moon system. He has found that the Earth-Moon system passed through strong orbital resonances early in its evolution, which may resolve a long standing inconsistency between lunar formation scenarios and previous dynamical histories of the Earth-Moon system. Professor Maria Zuber and colleagues have used a General Circulation Model to analyze the nature of atmosphere-cryosphere mass exchange over seasonal cycles on Mars. Results indicate that ice deposition in the polar regions should produce a detectable change in the planet's gravity field, and time varying gravity analysis represents a new method for measuring seasonal variations of the planet's CO2 inventory. Professor Zuber's laser experiment was successfully launched on the Mars Global Surveyor spacecraft in November, 1996, and will arrive at Mars in September, 1997, and will map the planet's global topography for two Earth years.
Professor Richard Binzel has utilized ground based telescopes to investigate the compositional properties of asteroids passing near the Earth and has discovered numerous source bodies for the most common class of meteorites, the ordinary chondrites. Professor Binzel's continuing Hubble Space Telescope observations of the second largest asteroid (530 km diameter) Vesta have revealed an enormous 400 km impact basin, containing a 13 km high central peak, in the vicinity of the south pole. Color measurements of the basin suggest the exposure of the olivine upper mantle on this small planetary world. From a recent stellar occultation by Neptune's moon Triton, Professor Elliot and colleagues find that Triton's atmosphere is unexpectedly distorted from spherical symmetry, most likely indicating the presence of strong winds that are comparable to the sonic velocity of 140 m s-1. Professor Counselman developed a new kind of antenna for satellite geodesy, which distinguishes between radio waves arriving directly from the sky and waves reflected from the ground. This antenna promises to improve substantially the accuracy and speed of crustal-motion measurements. Principal Research Scientist Heidi Hammel has published an analysis of Hubble Space Telescope imaging of Neptune focusing on the stability of large-scale structures in the planet's atmosphere. She has also initiated a study of the atmosphere of Uranus and has continued follow-up studies of Jupiter since the collision of Comet Shoemaker-Levy 9, again using Hubble imaging.
Professor Jochem Marotzke has investigated the consequences of the observed enhanced mixing near the ocean margins on the large-scale ocean circulation. Numerical experiments have guided the formulation of the first published theory linking convective activity and the climatically important thermohaline circulation and its associated heat transport. Together with Principal Research Scientist Detlef Stammer and collaborators at MIT, he has computer generated the adjoint to the recently developed MIT ocean general circulation model, which provides unprecedented flexibility in model-sensitivity and data-fitting studies. Professor Carl Wunsch, working with Stammer and in collaboration with other members of the physical oceanography group, have begun producing three dimensional estimates of the global ocean circulation every few days. The work involves combining meteorological surface conditions, satellite altimetry and a general circulation model into a consistent picture of the time evolving ocean. Professor Paola Malanotte-Rizzoli and collaborators have been modeling the ocean's circulation in different regions using data assimilation to improve the models. She has started a collaboration for the study of tropical/subtropical interactions through assimilation of TOPEX altimetry and is also investigating the physical/biochemical dynamics of the Eastern Mediterranean and the Black Sea ecosystems in the context of multinational collaborative programs. Professor Glenn Flierl is conducting research on the relationship between the meandering of the Gulf Stream and the mean recirculations on either side, and on the dynamics of jets as they detach from the coast. He is also studying vortices in the ocean, in the Jovian atmosphere, and in the solar nebula including the role such flows might have in encouraging dust accumulation and planet formation. Professor John Marshall and his group have continued to develop climate modeling capability by exploiting atmosphere-ocean fluid isomorphisms to create, by leveraging off their previous work in ocean modeling, a coupled atmosphere-ocean model with a common hydrodynamic kernel. Hierarchies of coupled models are now being used to study aspects of middle and high-latitude atmosphere-ocean coupling designed to reveal possible mechanisms of decadal climate variability of phenomena such as the North Atlantic Oscillation.
Professor Edward Boyle has completed a study of the climate of the last interglacial period (130,000-115,000 years ago) for the subtropical western North Atlantic. This study shows that although the climate during most of this period was relatively stable in contrast to some reports based on Greenland ice cores, there is an abrupt century-scale event near the end of the period (118,000 years ago). Deep water chemistry indicates reduced North Atlantic Deep Water formation and a tripling of clay fluxes, marking the onset of neoglaciation. Professor John Edmond continues his work on the geochemistry of the big rivers of Eastern Siberia, and is extending work to the rivers and lakes of Central Asia. He is also working to establish the sources of dietary iodine, whose deficiency afflicts ~25% of the world's population with clinical symptoms. Professor Maureen Raymo and her collaborators have been studying a wide range of paleoclimate problems, including the cause of the eccentricity cycle in global ice volume, the impact of climate change on deep sea benthic diversity, and the climate conditions under which rapid variations in ocean thermohaline circulation occur.
Professor Mario Molina and his research group have determined the reaction rate and the branching ratio for HCl formation in the radical recombination reaction ClO + OH using the high-pressure turbulent-flow technique developed in their laboratory. The measurements indicate a 5% HCl yield, with important implications for the understanding of the chemistry of the stratosphere, particularly at higher altitudes. The mechanism of the SO3 + H2O reaction to form sulfuric acid was further elucidated, confirming that the reaction rate is second order in H2O, and that the reaction has an unusually large negative activation energy (~13 kcal/mole). The thermodynamics and nucleation rates for the formation of acid hydrates from ternary H2SO4/HNO3/H2O solutions was further investigated using a variety of experimental techniques, including infrared spectroscopy and optical microscopy involving micron-sized droplets that simulate polar stratospheric cloud particles. The results are important for the elucidation of the role of stratospheric clouds in ozone depletion. Professor Ronald Prinn and his colleagues recently reported very good news regarding the ozone layer. Measurements over the past 18 years from the Advanced Global Atmospheric Gases Experiment showed that the total chlorine contained in long-lived man-made chlorofluorocarbons and chlorocarbons reached a maximum value in the lower atmosphere in 1992, and began to decrease through 1996. This implies that ozone depletion by these gases is maximizing around the present time and that phase out of these chemicals is proceeding somewhat faster than demanded by the Montreal Protocol. Professor Reginald Newell flew on the NASA P3-B aircraft in a mission to measure troposheric ozone and associated trace constituents in the southeast Pacific. One unusual finding was of high ozone, characteristic of the lower stratosphere, in a stalactite-like tropical upper tropospheric area, which had been predicted from satellite observations.
Professor Peter Stone and his colleagues have completed the development of a new flexible climate model, specifically designed for use in studies of uncertainty in projections of global climate change. The model's representations of cloud processes and of mixing of heat into the deep ocean can be varied, thus making it possible for the model to reproduce the wide range of projections that have been made with the most sophisticated climate models, but the new model is computationally two orders of magnitude more efficient. Professor Kerry Emanuel spent two months at the National Centers for Environmental Prediction, running a field experiment designed to test the concept of adaptive sampling of the atmosphere, under a grant with Professor Ed Lorenz. He is also working on optimizing convection schemes for climate research, using field experimental data. Professor Edmund Chang investigated the properties of baroclinic waves in the atmosphere and mapped out the wave guides in which these waves preferentially propagate with maximum coherence. He also found that these wave packets, unlike individual waves, can stay coherent for an extended period of time, sometimes in excess of two to three weeks. He is currently working on applying these results to improving medium-range forecasting. Professor Dick Lindzen and colleagues have begun an examination of satellite and terrestrial data of various types in order to ascertain the possibility of direct measurement of climate sensitivity to various perturbations including increased levels of atmospheric carbon dioxide. Preliminary results suggest the absence of unique results for short-term perturbations with possible convergence over the long term. He is also examining seasonal cycles in anthropogenic gases to ascertain the relative importance of tropospheric and stratospheric transport. Professor Alan Plumb and colleagues have developed a new stratospheric transport model, based on the concept of a "tropical pipe" within which upwelling takes place, using data from the Upper Atmosphere Research Satellite to specify the circulation. His research group has also continued investigations of a wide range of problems in atmospheric dynamics.