Precise overgrowth composition during biomineral culture and inorganic precipitation

We introduce a method to analyze element ratios and isotope ratios in mineral overgrowths. This general technique can quantify environmental controls on proxy behavior for a range of cultured biominerals and can also measure compositional effects during seeded mineral growth. Using a media enriched in multiple stable isotopes, the method requires neither the mass nor the composition of the initial seed or skeleton to be known and involves only bulk isotope measurements. By harnessing the stability and sensitivity of bulk analysis the new approach promises high precision measurements for a range of elements and isotopes. This list includes trace species and select non-traditional stable isotopes, systems where sensitivity and external reproducibility currently limit alternative approaches like secondary ion mass spectrometry (SIMS) and laser ablation mass spectrometry. Since the method separates isotopically labeled growth from unlabeled material, well-choreographed spikes can resolve the compositional effects of different events through time. Among other applications, this feature could be used to separate the impact of day and night on biomineral composition in organisms with photosymbionts

Isotopic Constraints on the Chemical Evolution of Geothermal Fluids, Long Valley, CA

Abstract A spatial survey of the chemical and isotopic composition of fluids from the Long Valley hydrothermal system was conducted. Starting at the presumed hydrothermal upwelling zone in the west moat of the caldera, samples were collected from the Casa Diablo geothermal field and a series of monitoring wells defining a nearly linear, ~14 km long, west-to-east trend along the proposed fluid flow path Introduction The efficiency of heat extraction from geothermal reservoir rocks is limited by chemical processes and the physical characteristics of the reservoir. Specifically, mineral dissolution and precipitation and the geometry of heat and mass exchange between fluids and the reservoir lithologies of fractured dominated systems define the long term efficiency of heat extraction but are difficult to quantify and therefore predict. Increased knowledge about the water-rock exchange in geothermal systems and the size and spacing of the major fluid transporting fractures would be valuable information that impact decisions guiding the management of natural and enhanced geothermal systems

Groundwater “fast paths” in the Snake River Plain aquifer: Radiogenic isotope ratios as natural groundwater tracers

Preferential flow paths are expected in many groundwater systems and must be located because they can greatly affect contaminant transport. The fundamental characteristics of radiogenic isotope ratios in chemically evolving waters make them highly effective as preferential flow path indicators. These ratios tend to be more easily interpreted than solute-concentration data because their response to water-rock interaction is less complex. We demonstrate this approach with groundwater {sup 87}Sr/{sup 86}Sr ratios in the Snake River Plain aquifer within and near the Idaho National Engineering and Environmental Laboratory. These data reveal slow-flow zones as lower {sup 87}Sr/{sup 86}Sr areas created by prolonged interaction with the host basalts and a relatively fast flowing zone as a high {sup 87}Sr/{sup 86}Sr area

Sr-Nd isotope geochemistry of the early Precambrian sub-alkaline mafic igneous rocks from the southern Bastar craton, Central India

Sr–Nd isotope data are reported for the early Precambrian sub-alkaline mafic igneous rocks of the southern Bastar craton, central India. These mafic rocks are mostly dykes but there are a few volcanic exposures. Field relationships together with the petrological and geochemical characteristics of these mafic dykes divide them into two groups; Meso-Neoarchaean sub-alkaline mafic dykes (BD1) and Paleoproterozoic (1.88 Ga) sub-alkaline mafic dykes (BD2). The mafic volcanics are Neoarchaean in age and have very close geochemical relationships with the BD1 type. The two groups have distinctly different concentrations of high-field strength (HFSE) and rare earth elements (REE). The BD2 dykes have higher concentrations of HFSE and REE than the BD1 dykes and associated volcanics and both groups have very distinctive petrogenetic histories. These rocks display a limited range of initial 143Nd/144Nd but a wide range of apparent initial 87Sr/86Sr. Initial 143Nd/144Nd values in the BD1 dykes and associated volcanics vary between 0.509149 and 0.509466 and in the BD2 dykes the variation is between 0.510303 and 0.510511. All samples have positive εNd values the BD1 dykes and associated volcanics have εNd values between +0.3 and +6.5 and the BD2 dykes between +1.9 to +6.0. Trace element and Nd isotope data do not suggest severe crustal contamination during the emplacement of the studied rocks. The positive εNd values suggest their derivation from a depleted mantle source. Overlapping positive εNd values suggest that a similar mantle source tapped by variable melt fractions at different times was responsible for the genesis of BD1 (and associated volcanics) and BD2 mafic dykes. The Rb–Sr system is susceptible to alteration and resetting during post-magmatic alteration and metamorphism. Many of the samples studied have anomalous apparent initial 87Sr/86Sr suggesting post-magmatic changes of the Rb–Sr system which severely restricts the use of Rb–Sr for petrogenetic interpretation

High-temperature kinetic isotope fractionation of calcium in epidosites from modern and ancient seafloor hydrothermal systems

Calcium isotope ratios in epidote from epidosites in ophiolites of varying Phanerozoic ages have 44Ca/40Ca ratios that are lower by 0.1 to 0.6‰ relative to typical mid-ocean ridge hydrothermal fluids. Epidosites are inferred to form in high-temperature parts of seafloor hydrothermal systems at temperatures above 300 °C and where fluid fluxes are high, so the Ca isotopic composition of the epidote is likely to reflect fractionation during growth of crystals from aqueous solution. Available Ca isotope data from MOR hydrothermal vent fluids and mantle peridotites constrain the Ca of likely modern hydrothermal fluids to a narrow range at . A reactive-transport model is used to evaluate whether the Ca of hydrothermal fluids might have been higher during the Cretaceous and Late Cambrian, the ages of the Troodos, Oman, and Betts Cove ophiolites from which we have data. For these calculations we use the epidosite 87Sr/86Sr as a guide to the extent of Ca isotopic exchange that affected the ancient hydrothermal fluids, which were derived from seawater with higher Ca and Sr, and lower sulfate concentration, than modern seawater. The calculations suggest that the ancient hydrothermal fluid Ca values were not much different from modern values, with the possible exception of the Late Cambrian example. We infer that the epidote-fluid Ca isotope fractionation averaging to −0.6, is most likely due to kinetic isotope fractionation during mineral precipitation. There is evidence from the literature that hydrothermal epidote may commonly form from oversaturated solutions, which makes the kinetic isotope interpretation plausible. The equilibrium epidote-fluid Ca isotope fractionation is estimated to be based on recently reported DFT calculations. Our results suggest that kinetic calcium isotope fractionation can affect hydrothermal silicate minerals, and may be only slightly smaller in magnitude than the effects observed in Ca-bearing minerals at low temperature. Kinetic isotope effects during mineral growth could provide new insights into the formation mechanisms of hydrothermal silicate minerals

To respond or not to respond - a personal perspective of intestinal tolerance

For many years, the intestine was one of the poor relations of the immunology world, being a realm inhabited mostly by specialists and those interested in unusual phenomena. However, this has changed dramatically in recent years with the realization of how important the microbiota is in shaping immune function throughout the body, and almost every major immunology institution now includes the intestine as an area of interest. One of the most important aspects of the intestinal immune system is how it discriminates carefully between harmless and harmful antigens, in particular, its ability to generate active tolerance to materials such as commensal bacteria and food proteins. This phenomenon has been recognized for more than 100 years, and it is essential for preventing inflammatory disease in the intestine, but its basis remains enigmatic. Here, I discuss the progress that has been made in understanding oral tolerance during my 40 years in the field and highlight the topics that will be the focus of future research

Paleogene deepwater mass composition of the tropical Pacific and implications for thermohaline circulation in a greenhouse world

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94621/1/ggge1162.pd