Plenaries

Each morning, the science program starts with plenary lectures by eminent scientists. Confirmed speakers are listed below.

Sam Mukasa Sam Mukasa, University of New Hampshire, GS President
Volatiles in the Mantle: Impact on Intraplate Magmatism

Monday 15th August

Concentrations of the volatiles H2O, CO2, S, Cl, and F and elemental compositions of primary magmas and their sources can be estimated through the study of olivine-hosted melt inclusions in volcanic rocks, thereby providing insights about melting processes in the mantle. These volatiles play a major role in both the formation and evolution of mantle melts, and yet their impact on intraplate volcanism on the continents and in the ocean basins may be grossly underestimated. We have determined the major-oxide, trace-element and volatile (H2O, CO2, S, Cl, and F) concentrations of olivine-hosted melt inclusions from the Columbia River Plateau (CRP)-Snake River Plain (SRP) large igneous province, West Antarctic Rift System, and Iceland, all three areas with intraplate volcanism hypothesized to be related to plume activity.

Most of the samples we have analyzed record minimum H2O concentrations of 1 wt% or higher, exceeding the largest values obtained for subaerial eruptions in Hawaii of 0.8 wt%. The most H2O-rich lava in the SRP has 3.3 wt%, and in the Columbia River Basalts (CRB) values reach 4.2 wt% H2O. Concentrations in Icelandic and West Antarctic Rift melt inclusions reach values of 3.0 and 2.2 wt% H2O, respectively. Water and CO2 are correlated and follow magmatic degassing curves. Furthermore, the highest volatile concentrations are always found in the more primitive melt inclusions, based on major oxide and trace element abundances, indicating that the volatiles are of mantle origin, not artefacts of differentiation in the crust. The trace element and volatile variability, high concentrations of water, and recent studies of Os isotopes in these tectonic settings provide compelling evidence that the volatiles and chemical heterogeneity of the magma sources may be caused by the recycling of ancient oceanic crust.


Marc Hirschmann Marc Hirschmann, Univ. Minnesota
Deep Earth Volatile Cycles: From Ancient to Modern

Tuesday 16th August

Earths’ mantle is significant reservoir for key volatile species and exchange between the mantle and near-surface reservoirs (=”exosphere”) influences planetary climate and habitability as well as dynamical evolution of the interior. Volatile cycling is governed in large part through plate tectonic processes but also has significant influence on regulating the vigour of plate tectonics. Yet, it is not clear how this coupling between geodynamical and geochemical evolution arose or whether one was a prerequisite for the establishment of the other. Originally, much of Earth’s volatile inventory was presumably present as a thick atmosphere, in part because volatiles were probably delivered late in the accretion history and because of the efficiency of impact degassing. The early inventory of mantle H2O may descend from the magma ocean, in which portions of a steam atmosphere are dissolved in the magma and then precipitated with nominally anhydrous minerals. In contrast, low magmatic solubility of C-bearing species may suggest that the earliest mantle was depleted in C. Thus, the earliest Earth could have been characterized by an exosphere with low H/C and a mantle with high H/C – the reverse of the modern case in which the mantle has low H/C (as demonstrated by H/C ratios of minimally degassed oceanic basalts) and the exosphere high H/C. Thus, either some process retained carbon in the early mantle or subsequent evolution has preferentially sequestered carbon in the interior.

In this plenary review, I will consider the current state of the principal reservoirs of H and C and explore the possible key influence of magma ocean processes on the subsequent evolution of Earth’s volatile cycling.


Edouard Bard Edouard Bard, Collège de France
Geochemical Profiles to Study the Last Deglaciation and its Impact on Rivers

Wednesday 17th August

The last deglaciation is fascinating for climatologists as it allows to study first-order climate changes that accompanied the retreat of the large Laurentide and Fennoscandian ice-sheets. Between 21000 and 6000 years before present, the climate system experienced a complete reorganization of all its compartments, e.g. atmosphere, oceans, lakes and rivers together with their associated ecosystems and biogeochemical cycles.

Linking records of the last deglaciation on land and in oceans requires accurate dating and comparison of different geological archives. A complementary way is to measure geochemical tracers of terrestrial and marine origins in the very same sediments raised in coastal environments.

Paleoclimate records at a particular location witness the successive phases of the last deglaciation. These various events, pauses and accelerations, have been known for many years (famous events such as Heinrich #1, Bolling, MWP1A, Allerod, Younger Dryas…), but it is only recently that geochemistry has provided analytical techniques allowing to produce high-resolution time series of various proxies based on elemental ratios, organic compounds or stable and radiogenic isotopes measured in different sediment fractions: detrital, biogenic, authigenic phases or even interstitial waters.

To illustrate this growing research field, I will review what we know about deglacial sea level based on tropical corals and then go on to consider the associated changes in a few selected records from coastal zones, past river mouths or marginal seas. The aim is to illustrate the complex linkage between sea level rise, paleoclimatic changes and the reactivation of rivers during the last deglaciation.


Franck Selsis Franck Selsis, Laboratoire d'Astrophysique de Bordeaux
Exoplanet Atmospheres: From Hot to Habitable Worlds

Thursday 18th August

Current observational techniques allow us to detect a broad variety of extrasolar planets. In some cases we can measure properties such as the planetary radius, mass and temperature and constrain the structure, molecular composition and dynamics of their atmospheres. The diversity of observed exoplanets is extraordinary in terms of planetary system architectures, physical conditions and chemical compositions. I will present several striking cases that illustrate this diversity.

At two extremes of the known sample of exoplanets are hot gas giants, whose atmospheres constitute a puzzle for both physicists and chemists, and potentially "habitable" worlds which, despite very exotic properties, could host liquid water. I will focus on these two types of atmospheres and show that their modeling is a challenging but extremely rich subject. I will then discuss the prospects for the next step of exoplanet characterization.

(photo courtesy of CNRS/C. Lebedinsky)


Victoria Orphan Victoria Orphan, California Institute of Technology, Gast Lecturer
Microbial Partnerships and Methane-Oxidation in the Deep Sea

Friday 19th August

The ability to decipher the metabolic roles of microorganisms within living microbial ecosystems and to connect microbial metabolism with biosignatures preserved in the rock record represents some of the grand challenges in the field of Microbial Geobiology. The combination of molecular methods with stable isotope analysis (both natural abundance and as tracers) in modern environments represents a multidisciplinary approach that has been used successfully to characterize links between specific microorganisms and their ecophysiology in situ. In particular, the introduction of micron-scale isotopic analyses by secondary ion mass spectrometry (SIMS and nanoSIMS) to the study of microorganisms has enabled an unprecedented level of inquiry into the inner workings of microbial ecosystems. Integrating SIMS-based stable isotope analysis with microscopy and culture-independent metagenomics techniques, we have been investigating carbon and nutrient utilization by deep-sea microorganisms and symbiotic microbial consortia fuelled by methane in sediments and associated authigenic carbonates. Single cell characterization of methane-cycling archaea and sulphate-reducing bacteria have revealed significant inter and intra-group heterogeneity in both stable carbon isotopic signatures and nitrogen utilization, including differences in nitrogen fixation and assimilatory nitrate reduction. These cell-specific analyses have yielded new information regarding the isotopic variability, metabolic potential and interactions between individual microorganisms and the greater biological community in methane-based ecosystems.