1. Bob Enick, Ph.D. (University of Pittsburgh).

    Microorganisms have existed on this planet for more than 3.6 billion years and represent the major drivers for the global biogeochemical cycles. There are about 1030 bacteria in the world, but just 1021 stars in the universe. It is clear that the microbial diversity of the world is a scientific frontier that is not only unexplored, but also of far greater than astronomical dimensions. The microbial ecology of The Arctic is intrinsically fascinating: the low temperatures, extreme seasonality are striking and yet this is a biologically active environment in which nutrients are turned over and pollutants are degraded. The study of the Arctic has gained new urgency as the most rapidly warming region on the planet. The microbial world will mediate much of the anticipated change. There is a ticking “bomb” buried in the Arctic tundra. Enormous quantities of naturally occurring greenhouse gasses are trapped in ice-like structures (clathrates) in the tundra and at the bottom of the seas. The microbial community is central to one of the most disturbing aspects of this warming: the fate of the 400 gigatons of methane locked in the frozen arctic tundra. The microbial community constitutes a lock, currently in a closed position, on these reserves of carbon and the fate of this reservoir. It is correspondingly desirable to understand the nature of this lock, which in turn implies a predictive understanding of the microbial ecology of Arctic soils in our present environment and in a putative and uncertain warmer future.

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  2. ESD welcomes Eric A. Davidson, Ph.D. (Woods Hole Research Center, MA).

    Soils carbon stocks are 2-4 times greater than atmospheric CO2-C and 3-6 times larger than aboveground plant biomass-C. Potential exists for C sequestration in soils, but there is also a large potential positive feedback to climate change as permafrost thaws and enzymatic decomposition of soil organic matter increases with warming. Enzymatic reaction rates are temperature sensitive when substrate is not limiting. However, substrate supply often, perhaps usually, limits enzymatic reaction rates in soils. Soil microbial community composition varies temporally and spatially, and the reactive properties of extracellular enzymes also can probably be changed by microorganisms in response to environmental cues. The C, N, and P assimilation enabled by extracellular enzyme activity affects the growth of microbial populations, their metabolism, and their enzyme synthesis. Do models need to represent all of these processes in 3-D space and in time? Ideally, the answer would be “yes,” but only if there is a viable approach to testing and validating model structures and parameterizations representing each process. When that is not possible, some aggregation is needed. A modular design enables progress on model components without losing sight of the way that components fit together. Admittedly, the Dual Arrhenius and Michaelis–Menten (DAMM) model does not yet attain all of these lofty goals, but it offers promise to build upon an integrated, modular approach to represent as parsimoniously as possible numerous key interacting processes in a heterogeneous matrix, and to keep making improvements until we get the DAMM thing right.

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  3. There is a growing body of evidence suggesting that vegetation mortality during drought or periods of high temperatures is rising across the globe. Research regarding the mechanisms of vegetation mortality has grown dramatically in the last five years, as has research on the consequences of mortality on climate forcing. This new research has also stimulated valuable debate regarding how universal or variable mortality mechanisms may be globally, and how much feedback there is upon climate. Resolving these questions is essential for improving global climate models due to the inherent land-climate feedbacks. I will review the evidence for the variety of hypothesized mechanisms of death and the subsequent potential climate forcing. I will conclude by outlining a vision towards resolving these scientific questions, with the ultimate goals of improving our understanding and modeling of climate-terrestrial impacts and feedbacks.

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  4. Greg Asner is an ecologist with the Carnegie Institution for Science and Stanford University. Here he presents new insights from the CAO program, shedding light on ways in which 3-D studies of ecosystems can improve scientific knowledge and accelerate natural resource and climate-change policy actions.

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  5. For many years, we have been making use of the Hawaiian Islands as models for understanding how soils and ecosystems develop and function. Results of this research show that the properties of soils exhibit sharp thresholds in both space and time, places where soil properties change abruptly with a small additional change in forcing. We have identified three major thresholds in Hawaiian soils – one associated with the accumulation of carbonate in dry soils, a second associated with the depletion of primary minerals in the rooting zone, and a third associated with iron reduction and phosphorus mobility.

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Distinguished Scientist Seminar Series

LBNL Earth Sciences Division

The ESD Distinguished Scientist Series is a monthly seminar featuring eminent individuals from various disciplines in the scientific community whose research is outstanding, interdisciplinary, and of broad interest to strategic interest initiatives in

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The ESD Distinguished Scientist Series is a monthly seminar featuring eminent individuals from various disciplines in the scientific community whose research is outstanding, interdisciplinary, and of broad interest to strategic interest initiatives in the earth sciences. Speakers normally spend a full day with researchers at Earth Sciences Division, LBNL, and the University of California, Berkeley.

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