Mathematical expressions used in amino acid racemisation geochronology—A review

A variety of mathematical expressions that describe changes over time (t) in the extent of amino acid racemisation (AAR, expressed as the ratio of d- to l-amino acid isomers or epimers) have been used in Quaternary geochronology. The integrated rate equation was first used to estimate fossil age from D/L but its geochronological utility is disadvantaged by uncertainties regarding the conformity of AAR in fossil protein to apparent reversible first-order kinetics for the entire reaction history. ‘Non-linear’ models have subsequently been used to relate D/L to t. The logarithmic equation successfully applied to Atlantic Coastal Plain research has not achieved widespread application, perhaps due to the regional calibration required if sensitivity to temperature is to be modelled, or the difficulties encountered when extending the model to include fossils with D/L<0.1. Success producing a linear correlation between D/L transformed with a power function and t has seen this approach emerge as one of the most commonly applied in AAR geochronology in recent years. Like parabola curve fitting, which has been applied to trends in D/L versus t in a variety of fossils and geographic settings, power transformations may not be suitable for geochronological modelling during the latter stages of amino acid diagenesis. Several studies have demonstrated the utility of simple and contingent linear equations for relating D/L to t. Future research should aim to reduce reliance on independent calibration and explore the geochronological benefits of AAR in pools other than the total hydrolysable amino acids.     

Building comparable global change vulnerability assessments: The vulnerability scoping diagram

Advancing vulnerability science depends in part on identifying common themes from multiple, independent vulnerability assessments. Such insights are difficult to produce when the assessments use dissimilar, often qualitative, measures. The Vulnerability Scoping Diagram is presented to facilitate the comparison of assessments with dissimilar measures. The diagram is illustrated with recent research on drought vulnerabilities, showing that common insights into vulnerability may emerge if independent research teams use a common structure for organizing information about exposure, sensitivity and adaptive capacity—even if the underlying measures differ between assessments. Broadly adopting this technique, which is grounded in the “Eight Steps” methodological protocol [Schröter, D., Polsky, C., Patt, A., 2005. Assessing vulnerabilities to the effects of global change: an eight step approach. Mitigation and Adaptation Strategies for Global Change 10(4), 573–595], will enable a vulnerability meta-analysis, the lessons from which may permit places to identify helpful adaptation or mitigation options without first having to conduct their own vulnerability assessments.     

Microbial ecology of the stratified water column of the Black Sea as revealed by a comprehensive biomarker study

The stratified water column of the Black Sea is partitioned into oxic, suboxic, and euxinic zones, each characterized by different biogeochemical processes and by distinct microbial communities. In 2003, we collected particulate matter by large volume in situ filtration at the highest resolution to date for lipid biomarker analysis and bacterioplankton for enumeration of major prokaryotic groups. Abundances of several prokaryotic groups were estimated using CARD-FISH probes specific for Bacteria, Archaea (Crenarchaeota and Euryarchaeota), epsilonproteobacteria (mainly sulfide oxidizers) and sulfate reducing bacteria. We also measured a wide range of bacterial and archaeal lipid biomarkers. Depth distributions of diagnostic biomarkers are matched with zonation of microbial processes, including aerobic bacterial oxidation of methane, oxidation of ammonium by bacteria and archaea, metal reduction, and sulfide oxidation at the chemocline, and bacterial sulfate reduction and anaerobic oxidation of methane by archaea in the anoxic zone. Cell densities for archaea and sulfate reducing bacteria are estimated based on water column biomarker concentrations and compared with CARD-FISH results.     

STAMP: spatial–temporal analysis of moving polygons

Research questions regarding temporal change in spatial patterns are increasingly common in geographical analysis. In this research, we explore and extend an approach to the spatial–temporal analysis of polygons that are spatially distinct and experience discrete changes though time. We present five new movement events for describing spatial processes: displacement, convergence, divergence, fragmentation and concentration. Spatial–temporal measures of events for size and direction are presented for two time periods, and multiple time periods. Size change metrics are based on area overlaps and a modified cone-based model is used for calculating polygon directional relationships. Quantitative directional measures are used to develop application specific metrics, such as an estimation of the concentration parameter for a von Mises distribution, and the directional rate of spread. The utility of the STAMP methods are demonstrated by a case study on the spread of a wildfire in northwestern Montana.      

High-velocity stars from decay of small stellar systems

In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3 ≤  N  ≤ 10, and various mass spectra, initial velocities and initial configurations). The numerical treatment uses the CHAIN1 code (Mikkola &38; Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s⁻¹. These numerical experiments confirm that small N -body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s⁻¹ is ∼1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc.     

The breakdown of potassium feldspar at high water pressures

The equilibrium position of the reaction between sanidine and water to form “sanidine hydrate” has been determined by reversal experiments on well characterised synthetic starting materials in a piston cylinder apparatus. The reaction was found to lie between four reversed brackets of 2.35 and 2.50 GPa at 450 °C, 2.40 and 2.59 GPa at 550 °C, 2.67 and 2.74 GPa at 650 °C, and 2.70 and 2.72 GPa at 680 °C. Infrared spectroscopy showed that the dominant water species in sanidine hydrate was structural H₂O. The minimum quantity of this structural H₂O, measured by thermogravimetric analysis, varied between 4.42 and 5.85 wt% over the pressure range of 2.7 to 3.2 GPa and the temperature range of 450 to 680 °C. Systematic variation in water content with pressure and temperature was not clearly established. The maximum value was below 6.07 wt%, the equivalent of 1 molecule of H₂O per formula unit. The water could be removed entirely by heating at atmospheric pressure to produce a metastable, anhydrous, hexagonal KAlSi₃O₈ phase (“hexasanidine”) implying that the structural H₂O content of sanidine hydrate can vary. The unit cell parameters for sanidine hydrate, measured by powder X-ray diffraction, were a = 0.53366 (±0.00022) nm and c = 0.77141 (±0.00052) nm, and those for hexasanidine were a = 0.52893 (±0.00016) nm and c = 0.78185 (±0.00036) nm. The behaviour and properties of sanidine hydrate appear to be analogous to those of the hydrate phase cymrite in the equivalent barium system. The occurrence of sanidine hydrate in the Earth would be limited to high pressure but very low temperature conditions and hence it could be a potential reservoir for water in cold subduction zones. However, sanidine hydrate would probably be constrained to granitic rock compositions at these pressures and temperatures. Received: 6 May 1997 / Accepted: 2 October 1997     

A two-layer αω-dynamo model with dynamic feedback on the ω-effect

In an attempt to produce a simple representation of an interface dynamo, I examine a dynamo model composed of two one-dimensional (radially averaged) pseudo-spherical layers, one in the convection zone and possessing an α-effect, and the other in the tachocline and possessing an ω-effect. The two layers communicate by means of an analogue of Newton's law of cooling, and a dynamical back-reaction of the magnetic field on ω is provided. Extensive bifurcation diagrams are calculated for three separate values of η, the ratio of magnetic diffusivities of the two layers. I find recognizable similarities to, but also dramatic differences from, the comparable one-layer model examined by Roald &38; Thomas. In particular, the solar-like dynamo mode found previously is no longer stable in the two-layer version; in its place there is a sequence of periodic, quasi-periodic and chaotic modes probably created in a homoclinic bifurcation. These differences are important enough to provide support for the view that the solar dynamo cannot be meaningfully modelled in one dimension.     

Experimental hydrogen isotope studies III: Diffusion of hydrogen in hydrous minerals,and stable isotope exchange in metamorphic rocks

Diffusion parameters for hydrogen diffusion in epidote-group minerals and micas have been measured under hydrothermal conditions, or calculated from existing experimental data, for bulk hydrogen isotope exchange experiments between hydrous minerals and water. Activation energies in the range 14 to 31 kcals/g-atom H are comparable to those derived by application of kinetic theory to experimental hydrogen isotope exchange data, and to those for oxygen diffusion in minerals under hydrothermal conditions. Diffusion of hydrogen in epidote is about four orders of magnitude faster than in muscovite, and about two orders of magnitude faster than in zoisite. Hydrogen diffusion in micas is about five orders of magnitude faster than oxygen diffusion, and hydrogen transport occurs dominantly parallel to the layers rather than parallel to the c-axis as for oxygen.Rapid hydrogen transport in minerals may proceed by hydrolysis of Si-O and Al-O bonds, followed by exchange of hydrolyzed oxygens with slower-diffusing (OH) or H₂O. Water appears to be essential for stable isotope exchange between minerals in slowly cooling metamorphic rocks.Stable isotope data for regional metamorphic mineral assemblages suggests that water is usually present in small amounts during cooling of prograde regional metamorphic systems, and estimated closure temperatures for cessation of stable isotope exchange are often more comparable to those calculated from diffusion data than to likely temperatures of metamorphism.Alpine deformation of the Hercynian Monte Rose Granite (Frey et al. 1976) permitted access of water and initiated stable isotope exchange amongst coexisting minerals. The diffusional behaviour of species in relict Hercynian muscovites is consistent with available experimental diffusion data.     

Gas adsorption on crushed quartz and basalt

The new surfaces generated by crushing rocks and minerals adsorb gases. Different gases are adsorbed to different extents so that both the total amount and composition of the released gases are changed. This affects the interpretation of the composition of the gases obtained by vacuum crushing lunar basalts, meteorites and minerals with fluid inclusions.     

Salinity stress in harpacticoid copepods

Three species of intertidal harpacticoid copepods,Tigriopus japonicus, Tachidius brevicornis andTisbe sp., were tested for their response to salinities ranging from 0‰ to 210‰. At 90‰Tigriopus became dormant, but could be reanimated if placed in 30‰ seawater within 18 hours.Tachidius became dormant at 60‰ but could also be revived if placed in 30‰ seawater.Tisbe died shortly after an exposure to seawater of 45‰. Death was brought about inTigriopus andTachidius by salinities of 150‰. Naupliar, copepodite, and adult stages ofTigriopus withstood the salinities equally well, while egg sacs could tolerate five times the length of exposure of these stages. The respiratory rate ofTigriopus was 3.76 (±1.32) μl 0₂ hr^?1 for active adults and 0.03 (±0.01) nl 0₂ hr^?1 mg dry wt^?1 for adults in the dormant state. The duration of dormancy, with successful revival, appears to be limited to the time before the loss of the vital water content of the tissues due to the high osmotic pressure. The ability to enter dormancy in times of stress may have high survival value to some intertidal copepods.