לוח שנה משולב

ABSTRACTS
Harry Elderfield -
History, applications to temperature, ice volume and ocean carbonate chemistry and new work on nano-scale coordination and distribution of Mg and B in foraminiferal calcite

TILMAN SPOHN
It is widely accepted that plate tectonics plays an important role for the Earth’s biosphere. It is also accepted that microbial life acts as catalyst in the long-term carbon silicate cycle. But a possible feedback with the evolution of the mantle is not well established. Rosing et al (2006) have speculated about a possible role of life in the growth of continents and Sleep et al. (2012) have discussed possible biomarkers in the composition of mantle derived rock. In this talk we discuss a possible role of the biosphere in the evolution of the mantle and the continental surface area by introducing a model for the water cycle of the Earth and of continental growth. We take the biosphere to enhance the weathering rate of rock, eventually leading to an increased rate at which sediments enter subduction zones. The subducted sediments contain water in pores and structurally bound in stable phases. In addition, clay-rich sediments are of low permeability and will reduce the dewatering of the oceanic crust at shallow depth. As a result, the rate at which water enters the Earth’s mantle is increased, resulting in increased continental production and mantle water regassing rates.  We speculate that the origin and evolution of life on Earth could have contributed to retain plate tectonics, an optimized continental surface area and a vigorously convecting wet mantle. 

MARK THIEMENS
The anomalous oxygen isotopic composition of meteoritic materials reflects the origination processes of the solar system. Oxygen is the most abundant element in meteoritic material and understanding the pervasive anomalies is needed to resolve the mechanism for solar system formation and evolution.  While it has previously been assumed to be a nuclear phenomena that theory has fortunately been abandoned. Presently, there are two models that are in consideration: photochemical self shielding, and gas phase chemical reactions that as a consequence of quantum mechanical symmetry dependencies in the formation events. Testing theories are formidably difficult due to the need for very short UV light (shielding of CO), or, high temperature controlled reactions to simulate the early condensation. Very recent work have tested these theories, as well as extended to other nebular gases such as nitrogen, a precursor to organics. These recent results will be discussed and compared to models as well as the solar system record.

GREGORY FALKOVICH
Abstract: I start from elementary explanation why winds blow: Large-scale winds are driven by the gradients of solar heating. Vertical gradients cause thermal convection on the scale of the troposphere depth (less than 10 km). Horizontal gradients excite motions on a planetary (10000 km) and smaller scales. Weather is mostly determined by the flows at intermediate scale (hundreds of kilometers). Where these flows get their energy from? The puzzle is that three-dimensional small-scale motions cannot transfer energy to larger scales while large-scale planar motions cannot transfer energy to smaller scales. In the talk, I'll describe experimental data that suggest one possible resolution of this puzzle. Plus some implications for wind energy and meteorology.

ASSAF VARDI
Marine photosynthetic microorganisms (phytoplankton) are the basis of marine food webs and are responsible for nearly half the global carbon-based net primary production. Phytoplankton can grow rapidly and form massive blooms that are regulated by environmental factors such as nutrients and light availability and biotic interactions with grazers and viruses. Viruses that infect marine algae are recognized as major ecological and evolutionary driving forces, shaping community structure and nutrient and energy cycling in the marine environment. We investigate one of the most ecologically important host-pathogen interactions between the cosmopolitan bloom-forming alga Emiliania huxleyi and its specific giant dsDNA virus (EhV). This fundamental host-virus interaction spans more than 10 orders of magnitude, from the individual cell (~10-6 m) to large scale patches (~105 m). This interaction controls massive algal blooms in the ocean and, consequently, determines the turnover and fate of more than 20% of the organic carbon in the ocean. We therefore explore these multi-scale interactions by both zooming in to explore the molecular mechanism of the “chemical arms race” during viral infection, and by zooming out to quantify the large scale impact of marine viruses on the fate of algal blooms in the ocean.

SUSAN TRUMBORE
Carbon enters terrestrial ecosystems primarily through fixation of CO2 by photosynthesis, but it returns to the atmosphere by a number of different processes on timescales that can range from hours to millennia.  Understanding the processes that control these timescales is critical for evaluating the potential of land to act as a C sink, and includes basic information about how ecosystems function.  The excess atmospheric radiocarbon produced by weapons testing in the 1960s provides a unique global tracer to evaluate the timescales of respiration and decomposition; some examples of what has been learned applying this tracer to measure terrestrial ecosystem C time lags will be presented.