Lake Shira Level Changes in Late Holocene

正1 Introduction Meromictic Shira Lake is a good represfor detail climate modeling due to its locainformation and annually laminated bottomsediment column of 155 cm in length wahammer corer in the deepest(24 m)central in 2009.2 Sample Preparations and Measuring     

Rotating micro-structures in Antarctic cold basal ice: implications for glacier flow and its interpretation

Structural analyses were conducted in the basal zone of an Antarctic glacier. The studied basal ice sequence was retrieved from a 20-m-long subglacial tunnel dug at the margin of the glacier and is at the temperature of −17°C. For the first time, rotating clast systems embedded within debris-rich ice were thin-sectioned using specially designed cutting techniques. The observed structures reflect the occurrence of pervasive shearing at the base of the glacier, and can be used as shear sense indicators. In addition, some of these structures provide evidence for the presence of thin liquid films at the time of formation despite the marked freezing temperature of the ice. It is showed here that cautious analysis of deformation structures present in debris-bearing ice may bring insights not only into the flow dynamics of the embedding matrix, but also into the behaviour of the interstitial fluid network at the base of cold glaciers and ice sheets.     

Geochemical study of clays used as barriers in landfills

This is a hydraulic and geochemical study on 2 materials: natural clay (AN) and a regenerated material made up of a sand-bentonite (SB) mixture. The hydraulic part allowed us to conclude that a 10% industrial bentonite content mixed with sand offers hydraulic properties that are similar to those of AN material and are lower than the required standards. The geochemical properties of both AN and SB matrixes are comparable with those of some of the synthetic leachates studied. Furthermore, the Langmuir model helped us to identify the adsorption capacities of both matrixes with the following selectivities: Pb > Cu > Cd > Zn.     

Data-Assimilative Hindcast and Climate Forecast of Storm Surges with an ASGF Regression Model

ABSTRACT

This study demonstrates that long-term climate model solutions can be efficiently converted to storm surge time series at points of interest (POIs) for the future. The all-source Green's function (ASGF) regression model is used for this conversion. In addition to being data assimilative, the ASGF regression model can also simulate storm surges at a POI faster than the traditional modelling approach by orders of magnitude. This is demonstrated using the tidal gauge at Sept-Îles (Quebec, Canada) in the Gulf of St. Lawrence as the POI. First the ASGF regression model is used to assimilate 32 years of tidal gauge data, producing a continuous hindcast of storm surges and a set of best-estimate regression parameters. Second, the ASGF regression model with the best-estimate parameters is used to convert a Canadian Regional Climate Model solution (CRCM/AHJ) to an hourly time series of storm surges from 1961 to 2100. Gumbel's extreme value analysis (EVA) is then applied to the time series as a whole and also to tri-decadal segments. The tri-decadal approach is used to investigate whether there is any progressive shortening or lengthening of storm surge return periods as a result of future climate change. A method for correcting for bias due to the forcing field at the EVA level is also demonstrated.     

Length of the day and evolution of the Earth's core in the geological past

In this paper, we study quantitatively the effect of the Earth's core formation on the secular rate of change of the length of day (LOD). We find that for the present epoch, a growth rate of the core comprised between 1 and 10 mm/cy seems to be a plausible guess, leading to a relative de crease of LOD comprised roughly between 10 and 100 μs/cy. Such values do not affect significantly the observed secular in crease of LOD caused by tidal braking, which amounts to about 1.79 ms/cy. However, in the remote geological past, before the Phanerozoic, the effects of core growth may have been much more important, because the total change of LOD associated with core formation has been estimated by Birch in 1965 to be 2.4 hours for an initially undifferentiated cold Earth, and 3.1 hours for an initially undifferentiated hot Earth. We consider a number of scenarios, some of them corresponding to very early and/or very fast core formation, others corresponding to slow and/or late core formation. We show that palaeo‐LOD measurements seem to favour slow core formation during the Proterozoic, contrarily to the now largely prevailing hypothesis based on geochemical arguments that the iron core formed very early in the Earth's history and during a geologically short time interval (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Trace-element heterogeneity in rutile linked to dislocation structures: Implications for Zr-in-rutile geothermometry

The trace-element composition of rutile is commonly used to constrain P–T–t conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations related to the formation and evolution of microstructures. Here, we investigate trace-element migration in low-angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra-high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal-plastic deformation of a large rutile grain results in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low-angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast-diffusion pathways must be evaluated when applying high-resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr.