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 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.
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.
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.
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.
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.
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.
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.