1997-1998 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 involving the Earth's atmosphere, ocean, crust, and deep interior and the similar systems on other planets. The Department comprises 40 faculty, including two with primary appointments in Civil and Environmental Engineering, 209 graduate and undergraduate students, and approximately 150 staff members.

EDUCATIONAL ACTIVITIES

During the past academic year, 170 graduate students were registered in the Department (Course 12) and the MIT/Woods Hole Oceanographic Institution (WHOI) Joint Program (Course 12W). Each disciplinary area of EAPS continues to be ranked among the top graduate programs in the country, with most areas being rated either first or second nationally. 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 awards the Master of Science in Geosystems. The new Professional Masters program had a first year enrollment of five students this past year, with ten being projected for the 1999 academic year. 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 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 continues to maintain a strong presence within the undergraduate program at MIT. The Department continues to offer by far the most freshman advising seminars at the Institute, and EAPS faculty advised 10% of the freshman class for the fourth consecutive year. The EAPS Independent Activities Program (IAP) continues to be one of the most vibrant at MIT, and faculty have maintained a healthy Undergraduate Research Opportunities Program (UROP). 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 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.

FACULTY

Ronald G. Prinn, TEPCO Professor of Atmospheric Chemistry, became EAPS Department Head effective July 1, 1998, replacing Thomas H. Jordan who served as EAPS Department Head for a decade 1988 - 1998. The Department flourished under Professor Jordan's leadership. He continued to strengthen the Department by appointing exceptional young faculty addressing fundamental problems in the earth sciences. Professor Jordan recognized talent across the disciplines, and helped to create an environment where significant scientific advances were achieved. These advances allowed the Department to further enhance its national and international preeminence.

Robert D. van der Hilst was promoted to Associate Professor without tenure. Dara Entekhabi, Associate Professor with tenure in the Department of Civil and Environmental Engineering, was granted a joint appointment in EAPS.

Thomas H. Jordan was elected to the National Academy of Sciences, and was awarded the George P. Woolard Award by the Geological Society of America. Maria T. Zuber was appointed to the Earle A. Griswold Professorship. John P. Grotzinger was awarded the Waldemar Lindgren Distinguished Scholar Award in Geology. Rafael L. Bras was named the Horton Lecturer of the American Meteorological Society, and was awarded the Clarke Prize for excellence in water research by the National Water Research Institute. Clark B. Burchfiel was awarded the Friendship Medal of China, and elected a corresponding member of the Chinese National Academy of Sciences. Charles C. Counselman received the biennial Kershner Award of the Institute of Electrical and Electronics Engineers for his contributions to electronic positioning technology. R. Alan Plumb was elected a Fellow of the Royal Society (London) for his contributions to atmospheric science.

CURRENT RESEARCH

GEOLOGY AND GEOCHEMISTRY

Samuel Bowring's research group's most significant finding of the past year involves the largest extinction event (85% of all marine fauna) in Earth's history, the Permo-Triassic boundary. Using high precision U-Pb geochronology, this extinction has been constrained to have occurred over a very short interval of time -- between 160,000 and 10,000 years -- at 251.3 Ma. The extreme rapidity of this event suggests a catastrophic mechanism for the extinction (results published in Science magazine). Kip Hodges has focused his recent research on understanding the behavior of mountain ranges as complex systems, with an eye toward documenting positive and negative feedback relationships between thermal and deformational processes.

Timothy Grove and colleagues have used methods of experimental petrology to understand the nature of mantle/magma interactions in the formation of lavas from Kilauea volcano. They find that magmas have chemically eroded the shallow mantle beneath Kilauea as they ascend to the surface. The mass that reacts is on the order of two to three times the erupted magma mass. This process occurs at a relatively shallow depth of 42 km. Thus, any deep melting signature in the huge volcano is masked by shallow mantle/melt interaction. Frederick Frey's research continued to focus on understanding the evolution of large oceanic volcanoes that are attributed to partial melting of ascending regions of relatively hot mantle "plumes". In the Hawaiian Island region, a new result is that large areas of submarine volcanism occur 200-400 km distant from the main volcanoes. The temporal and spatial geochemical variations of these Hawaiian lavas show that several mantle sources contribute to Hawaiian volcanism, and that their proportions change systematically during the one million year growth of the volcano.

Leigh Royden and Clark Burchfiel spent time in the eastern and southeastern part of the Tibetan plateau studying the uplift and formation of the Tibetan plateau, and how the river drainage system off the plateau has been shaped and reshaped by tectonic and climatic effects. From field and modeling studies they hope to determine the age of uplift and river incision in this part of the plateau, which are thought to have greatly affected and been affected by global climate changes between about two and ten million years ago. 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. John Southard, in cooperation with Grotzinger, is building small scale models of submarine fans, and studying rapid deposition of sands from submarine turbidity currents to aid in exploration for petroleum in deep offshore areas. Kelin Whipple's research in this past year has yielded several papers focused on analysis of the dynamics of bedrock river incision, with implications for height limits of mountain ranges, timescales of landscape response to climatic and tectonic forcing, and hypothesized global scale interactions between climate, erosion, and tectonics using a combination of field, theoretical, and remote sensing approaches.

GEOPHYSICS

In the past year Robert van der Hilst has made further improvements to the high resolution tomographic models of aspherical mantle structure. After showing that the upper mantle transition zone does not produce layering of mantle convection, he is now working to obtain evidence for a complex change in seismic properties in the lower mantle (at approximately 2000 km), which may hint at chemical stratification at much larger depth than previously thought. The waveform imaging of the Australian continent is in its final stage, and scientists can now determine and evaluate the relationship between continental thickness and the age of its formation on the scale of an entire continent. In addition to his duties as Department Head, Professor Thomas Jordan participated in deployment of a large aperture seismic array in southern Africa as part of the multi-institutional, multi-disciplinary Kaapvaal Project. He and his group obtained preliminary results that indicate the presence of anisotropic deep structure beneath the ancient core of the Kaapvaal craton.

Chris Marone has focused on the frictional properties of granular materials, the rheology of brittle fault zones, and the mechanics of earthquakes. His recent work has shown that loading rate has an important effect on frictional healing and the evolution of fault strength during the seismic cycle. Experiments being carried out in his laboratory are leading to an important revision of the slip rate and friction constitutive laws that are heavily used in modeling of earthquake rupture. Supported by a von Humboldt prize, Brian Evans has been working during the last year at the Geoforschungs Zentrum in Potsdam, Germany, on the brittle ductile transition in rocks and on grain boundary structure and properties in carbonate and feldspar rocks. Peter Molnar, along with Philip England of Oxford University, has demonstrated that the Navier-Stokes equation, for which horizontal gradients in stress are balanced by the gravitational body force (via crustal thickness differences), governs the large scale deformation of Asia, which behaves as a non-linear viscous fluid.

Bradford Hager and colleagues published the best estimate to date of the signature of delayed postglacial rebound in Earth's gravity field, a result that requires a substantially more viscous mantle beneath Hudson Bay than had previously been recognized. Thomas Herring, with research scientists Robert King and Simon McClusky, has been applying the Global Positioning System to global and regional scale deformation problems, and to remote sensing atmospheric water vapor. Professor Herring has also been working on aircraft and spacecraft laser altimetry for topographic profiling. In fundamental studies of erosion, Professor Daniel Rothman has found novel theoretical and empirical evidence of coupled physical processes acting across widely disparate length scales in the evolution of natural landscapes.

Dale Morgan is developing extensive technologies for imaging underground caves and structures. He continues a variety of geophysical investigations of groundwater contaminant sites, and is also measuring and modeling electrical signals generated when rocks are fractured in an attempt to understand electrical phenomena in earthquake source regions. Robert Reilinger and Robert King 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. Nafi Toksöz, along with Robert Reilinger, Robert King and Simon McClusky, is coordinating an international project to use GPS to map crustal deformation in the Eastern Mediterranean, providing new constraints on lithospheric rheology and dynamics in this plate collision zone. They are also using new GPS measurements in Southern California and Northern Baja, Mexico to map deformation along the San Andreas fault system to quantify fault slip rates for earthquake hazard studies. Toksöz has also developed techniques for using seismic reflection measurements to characterize the orientation and density of fractures in petroleum reservoirs.

PLANETARY SCIENCE

Jack Wisdom 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's laser altimeter entered into orbit around Mars in September of 1997, and has been mapping elevations in the northern hemisphere with 30-cm range resolution. Preliminary findings have shown the Amazonis Planitia region to be the smoothest large scale surface yet identified in the solar system, and suggests possible origins due to a thick dust cover deposited by wind or deposition in a water rich environment. Among the many features that the altimeter has sampled are canyon systems and outflow channels where results are being used to quantify the energetics of erosion and water transport early in Mars' history. The instrument also made the first direct measurements of atmospheric cloud heights on Mars which will provide much needed constraints on the vertical structure of the atmosphere.

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. 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. James Elliot and colleagues recorded a stellar occultation by Neptune's largest moon, Triton, with the Hubble Space Telescope. From these data they have deduced that Triton's surface frost has been undergoing a period of global warming since the time of the Voyager encounter in 1989. Heidi Hammel obtained visible wavelength images of the atmosphere of Uranus using the Hubble Space Telescope. The data reveal cloud features in the planet's northern hemisphere, which permit the first determination of winds at those latitudes. She also has continued her ongoing studies of Neptune and Jupiter using Hubble imaging.

OCEANOGRAPHY

Jochem Marotzke has formulated a theory of the ocean's thermohaline circulation, which for the first time predicts the amount of cross equatorial mass transport purely from the external parameters of the idealized problem. Carl Wunsch and collaborators have shown that the heat transport of the ocean -- a primary deteriminant of the Earth's climate -- may well be controlled through mechanical mixing by the tides. If correct, it suggests that a knowledge of the tides through time may be critical to understanding climate change. Detlef Stammer has shown that there is a strong global scale correlation between sea surface temperature (SST) and the dynamical sea surface height, implying that accurate computation of SST requires understanding of the interior ocean dynamics. John Marshall has been studying possible mechanisms of decadal climate variability that involve the interaction of the atmosphere and ocean in middle and high latitudes. Paola Malanotte-Rizzoli and collaborators have been modeling the ocean's circulation in different regions of the world's oceans using data assimilation to constrain and improve the models. She is also investigating tropical/subtropical interactions through assimilation of TOPEX altimetry, and the physical biochemical dynamics of the Eastern Mediterranean and Black Sea ecosystems in the context of multinational collaborative programs. Glenn Flierl is conducting research on the instabilities of oceanic jets and the effects on their circulations, the generation of eddies in the mid-ocean, and the biological effects of time varying flows, including both changes in productivity and the influence of turbulence on the distribution of marine organisms. He is also studying vortex dynamics on Jupiter and in the solar nebula.

Edward Boyle's research group has shown that deep sea corals can be used to trace abrupt century scale changes in deep sea circulation. In a paper which garnered the cover of Science, they used precise Th-230/U dating, carbon-14 data, and trace cadmium measurements, and have shown that an abrupt decrease in the percentage of North Atlantic deep water occurred 15,400 years before present. John Edmond's recent summation of two decades work on the pristine rivers of the Tropics (Amazon, Orinoco) and the Arctic and sub-Arctic (Eastern Siberia] demonstrates that there is no correlation between weathering rates, CO2 consumption and climate. Global warming models must now be re-examined. Maureen Raymo has been studying a wide range of paleoclimate problems, including the mechanisms by which Earth's orbital variations control climate, the Cenozoic record of carbonate deposition and volcanism, and the climate conditions under which millennial scale variations in ocean thermohaline circulation occur.

Dara Entekhabi's research activities include topics in hydrology, land-atmosphere interaction and earth remote sensing. Last year Entekhabi assembled a group of research scientists from several universities and research institutes to develop a prospectus for the hydrologic sciences in the coming decades. The prospectus calls for a Second International Hydrologic Decade dedicated to coordinated international observations and data gathering on the global hydrological cycle and its role in the climatic system.

ATMOSPHERIC SCIENCE

Mario Molina and his research group have continued their laboratory studies of the mechanisms and rates of chemical reactions of atmospheric importance. Their results have led to significant improvements in the quantitative understanding of stratospheric ozone balance. Ronald Prinn and his colleagues have measured the recent rapid rise of hydrofluorocarbons and hydrochlorofluorocarbons (chlorofluorocarbon replacements) in the atmosphere, and used some of these gases to provide new estimates of atmospheric levels of the key oxidant OH, which agree well with their previous estimates based on trichloroethane. Reginald Newell's group has collected research and commercial aircraft measurements of atmospheric trace constituents that show layers about one kilometer thick that occupy a significant fraction of the atmosphere. They are now studying the sources and evolution of these layers and their associated radiative heating rates with the goal of assessing whether they should be included in atmospheric models. Peter Stone and his colleagues have completed several studies, which demonstrate that the stability of the ocean's thermohaline circulation is underestimated in global warming projections made with the most sophisticated coupled-atmosphere-ocean general circulation models.

Kerry Emanuel continued his work on adaptive sampling techniques, and analyzed the results of a field experiment conducted last year to test such methods. Edmund Chang analyzed observational data, and found that a majority of significant troughs are organized into wave packets that can be tracked for extended periods of time. He is now studying the forecasting implications of his findings. Alan Plumb and his students have continued their investigations of atmospheric transport, especially the theory of the "age of air", and of the dynamics of upper tropospheric and stratospheric vortices. Richard Lindzen and colleagues are examining the capacity of existing and planned satellite systems to directly ascertain climate sensitivity and feedback processes. During the past year Lindzen used atmospheric tides to demonstrate the need for anomalous solar absorption in the atmosphere, studied the observed climatic response to volcanoes to estimate climate sensitivity, and investigated the dynamic contribution to the seasonal cycle in carbon dioxide in order to show that previous estimates of the biospheric component have been too low.