The central themes that run through my research are the processes that modify solid surfaces, and the spatial and temporal scales that control environmental processes on the Earth. Because surfaces lie at the interface between the solid interior of a planet (from the shallow subsurface to the deep interior) and the fluid exterior (atmosphere, hydrosphere, etc.), their composition and morphology record the interesting interplay between interior and exterior processes. The interplay between interior and exterior processes modifies the surface in many ways, depending on the specific processes involved and the time scale over which they operate. These modifications are reflected in the material properties of the surface (composition, texture, physical state) and thus surfaces integrate and record the nature and evolution of processes that have acted upon them.
The types of topics that I have investigated under this general heading range from climate change on Mars as recorded in the polar regions and mid-latitude deposits to the dynamics of arid regions on Earth in response to natural and anthropogenic forcing. These are outlined in more detail below.
The fundamental tool that I use to investigate these science topics is remote sensing. The strengths of remote sensing lies in the synoptic coverage that imaging systems afford, and that the measurements of reflected and emitted radiation carry fundamental information about the material properties. Through the use of models and analytical techniques, remotely sensed data can be reduced to provide useful information about the material properties of surfaces. However, the real challenge is to then use that information effectively and address important scientific questions. The specific questions that can be addressed vary, depending on the planet, local conditions, and the time-scales relevant to the particular processes involved.
Environmental Science Research Topics
The environment of the Earth holds many exceptional science challenges in the coming decades, and the scope of the problems requires interdisciplinary and multi-disciplinary approaches. Because of the spatial and temporal coverage, remote sensing is an important tool for gathering fundamental data on how the Earth's systems function and change with time. I have established several areas of research within this context which involve interdisciplinary research efforts.
Land Use and Land Cover Change (LULCC) in Semi-Arid Regions
One research theme is the response of arid/semi-arid systems (geologic and ecologic) to stochastic environmental stress The productivity of sparsely vegetated arid and semi-arid biomes is fundamentally limited by soil moisture, and hence their thresholds and rates of change in response to changing climate are lower than for humid and tropical systems. This sensitivity to change, coupled with a large area of the Earth's terrestrial surface covered by these systems (~30%) places a large importance on their role in global change. However, we still lack a fundamental understanding of what the modes of response are at regional scales, the physical determinants underlying the response, and ultimately what the climatological thresholds are. Such an understanding is central to developing predictive models of systems response to fundamental changes in climate. Current research is concentrated on the Great Basin-Mojave Desert region of the Southwest U.S. Here I am interested in range of responses of surfaces across a very large region to identify "normal" responses to variations in rainfall, climate, etc. and anomalous responses indicative of systems that are evolving rapidly. The overall strategy involves analysis of multi-temporal remote sensing data which is coupled to field studies of vegetation and soil characteristics. This is a multi-disciplinary research effort involving researchers from several institutions with expertise in soils, hydrology, and ecology.
Spatial and Temporal Dynamics of Estuaries
Coastal embayments and estuaries are important ecosystems containing a number of critical habitats and resources. They are currently threatened by changes to their surrounding watersheds. In addition, a fundamental environmental challenge is understanding exchanges of energy and nutrients across the land-sea boundary in coastal regions. Although there has been a wealth of new knowledge generated over the last decade about these estuarine ecosystems, the spatial and temporal patterns of biologic and physical processes, as well as anthropogenic influences are not fully understood. We are using remotely sensed data in coordination with field and long term observations to study these processes Narragansett Bay, Rhode Island . This effort involves interdisciplinary research with faculty and students from other departments at Brown (Ecology, Environmental Studies). A unique aspect of the research is the partnership with state and local agencies (Save the Bay, state Department of Environmental Management) and local business (Applied Science Associates). Thus the project involves exciting scientific challenges, but also a significant component of applied research where the fundamental results and findings are transferred to local business for use in product development and estuarine analyses, and to state and local agencies for use in there efforts to promote wise use of this common resource.
Planetary Research Topics
On the Moon, the compositional evolution of the surface is dominated by lateral mass transport due to the accumulated effects of impacts, and space weathering due to micrometeorites and solar wind. I have been investigating the former, with particular interest in boundaries between mare (volcanic plains) and highlands (largely feldspathic, heavily cratered uplands). These boundaries are important geologically, and because of the large compositional contrast across them, are excellent for examining the overall effects of lateral mass transport. Theoretical considerations suggest that lateral mass transport across such boundaries is minor and compositional gradations across them should be no greater than ~10 km. Yet, compositional analysis of these boundaries with remote sensing shows much wider compositional gradations across many boundaries. In addition, there are distinct systematics and associations with geologic feature which cannot be accommodated by simple lateral mass transport models. These findings are now opening up new avenues for research into the geologic processes that predate the boundaries. This will have implications for understanding the early volcanic history of the Moon, interrelationships between volcanic and impact processes, and the thermal evolution of the Moon which is to some extent obscured by the latest volcanic, impact, and basin deposits.
The surface of Mars records a long and interesting history that shares some aspects with the Moon (volcanism, impact processes), but is distinct in that Mars has an atmosphere that has apparently undergone both long term evolution as well as cyclic variations due to changes in orbital precession and obliquity. Though Mars has not been forthcoming with its secrets in terms of surface composition, recent advances in technology and analytical capabilities have permitted myself and coworkers to show that volcanic compositions on the surface of Mars are dominated by 2-pyroxene basalts, analogous in some ways to terrestrial komatiites and directly comparable to the basaltic SNC meteorites. Also there are difference in the composition across the planet in regions sampled thus far. However, we have data for only 10% of the planet, of that only ~10% is relatively unaltered. An important future avenue of research will evolve in mapping other weakly altered volcanic regions to piece together a more detailed understanding of the volcanic diversity and evolution of Mars.
The vast majority of Mars, however, is covered by a mantle of variable altered material that is at times mobile. A central question that I am interested in is what are the chemical and physical pathways by which pristine crust becomes altered. Because rates of weathering under current climatic conditions are much too slow to produce significant alteration, much of what we see today must have occurred in the past under very different conditions than the present. Thus the question of weathering and alteration includes considerations of climate change and/or evolution. I have recently become interested in this area of research as a consequence of results for the composition of the altered surface of Mars derived from remote sensing. These results indicate that duricrusted soils on Mars (dust deposits cemented by sulphate salts) may be critical intermediate staging grounds for the low-temperature formation of hematite. Duricrust formation is likely coupled to surface-atmosphere exchange of water and the efficiency of this process varies with the obliquity of the spin axis of Mars. The specific ferric mineralogy in these soils are indicators of the environmental conditions of formation and thus soil formation on Mars may be used as an indicator of paleoclimatic conditions. With the current plan for orbital and landed science missions to Mars in the next decade, there will be excellent opportunities to investigate these processes and questions with the data to be returned from these mission.
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