Ar and K partitioning between clinopyroxene and silicate melt to 8 GPa     

E.M. Chamorro  R.A. Brooker  J.-A. Wartho  B.J. WoodS.P. Kelley  J.D. Blundy 《Geochimica et cosmochimica acta》2002,66(3):507-519

The relative incompatibility of Ar and K are fundamental parameters in understanding the degassing history of the mantle. Clinopyroxene is the main host for K in most of the upper mantle, playing an important role in controlling the K/Ar ratio of residual mantle and the subsequent time-integrated evolution of ⁴⁰Ar/³⁶Ar ratios. Clinopyroxene also contributes to the bulk Ar partition coefficient that controls the Ar degassing rate during mantle melting. The partitioning of Ar and K between clinopyroxene and quenched silicate melt has been experimentally determined from 1 to 8 GPa for the bulk compositions Ab₈₀Di₂₀ (80 mol% albite-20 mol% diopside) and Ab₂₀Di₈₀ with an ultraviolet laser ablation microprobe (UVLAMP) technique for Ar analysis and the ion microprobe for K. Data for Kr (UVLAMP) and Rb (ion probe) have also been determined to evaluate the role of crystal lattice sites in controlling partitioning. By excluding crystal analyses that show evidence of glass contamination, we find relatively constant Ar partition coefficients (D_Ar) of 2.6 × 10⁻⁴ to 3.9 × 10⁻⁴ for the Ab₈₀Di₂₀ system at pressures from 2 to 8 GPa. In the Ab₂₀Di₈₀ system, D_Ar shows similar low values of 7.0 × 10⁻⁵ and 3.0 × 10⁻⁴ at 1 to 3 GPa. All these values are several orders of magnitude lower than previous measurements on separated crystal-glass pairs.D_K is 10 to 50 times greater than D_Rb for all experiments, and both elements follow parallel trends with increasing pressure, although these trends are significantly different in each system studied. The D_K values for clinopyroxene are at least an order of magnitude greater than D_Ar under all conditions investigated here, but D_Ar appears to show more consistent behavior between the two systems than K or Rb. The partitioning behavior of K and Rb can be explained in terms of combined pressure, temperature, and crystal chemistry effects that result in changes for the size of the clinopyroxene M2 site. In the Ab₂₀Di₈₀ system, where clinopyroxene is diopside rich at all pressures, D_K and D_Rb increase with pressure (and temperature) in an analogous fashion to the well-documented behavior of Na. For the Ab₈₀Di₂₀ system, the jadeite content of the clinopyroxene increases from 22 to 75 mol% with pressure resulting in a contraction of the M2 site. This has the effect of discriminating against the large K⁺ and Rb⁺ ions, thereby countering the effect of increasing pressure. As a consequence D_K and D_Rb do not increase with pressure in this system.In contrast to the alkalis (Na, K, and Rb), D_Kr values are similar to D_Ar despite a large difference in atomic radius. This lack of discrimination (and the constant D_Ar over a range of crystal compositions) is also consistent with incorporation of these heavier noble gases at crystal lattice sites and a predicted consequence of their neutrality or “zero charge.” Combined with published D_Ar values for olivine, our results confirm that magma generation is an efficient mechanism for the removal of Ar from the uppermost 200 km of the mantle, and that K/Ar ratios in the residuum are controlled by the amount of clinopyroxene. Generally, Ar is more compatible than K during mantle melting because D_Ar for olivine is similar to D_K for clinopyroxene. As a result, residual mantle that has experienced variable amounts of melt extraction may show considerable variability in time-integrated ³⁶Ar/⁴⁰Ar.  相似文献   

Isotopic composition of carbon and oxygen in desert fauna: investigations into the effects of diet, physiology, and seasonality     

Katherine F. Smith  Zachary D. Sharp  James H. Brown 《Journal of Arid Environments》2002,52(4):419

Carbon and oxygen isotope ratios of bone apatite were measured in 14 endothermic and ectothermic vertebrates native to the Chihuahuan Desert and collected in June and July of 1999 and 2000. The δ⁸O values of most reptiles were very high, up to 44‰ (standard mean ocean water (SMOW), some of the highestδ¹⁸ O values ever measured for an animal. The δ¹⁸O values of rodents and birds were lower (32±5‰ vSMOW), and the earless lizard Holbrookia maculata were the lowest of all species analysed (25‰). Omnivorous grasshopper mice (Onychomys torridus) had lower δ¹⁸O values than granivorous rodents. Results from oxygen analysis likely reflect variation in diet and body water flux differences between endotherms and ectotherms. Carbon isotope analysis revealed a dramatic shift in diet from C₃ plants in 1999 to C₄ plants in 2000 in most rodents and birds. Kangaroo rats and reptiles did not change, having a constantδ¹³ C value indicative of a C₃-based diet in both years. This suggests reliance on winter annual plant seed caches for kangaroo rats, but not other rodents. The carbon isotope data can be explained in terms of seasonal differences within and between years in the timing and intensity of the seasonal rainfall events, and the productivity of summer and winter annual plants. This study illustrates that stable isotope analysis is a powerful method for tracking dietary change and feeding behavior in desert vertebrates.  相似文献   

Macrophyte‐driven transient storage and phosphorus uptake in a western Wisconsin stream          下载免费PDF全文

Katherine J. Bohrman  Eric A. Strauss 《水文研究》2018,32(2):253-263

Investigations of phosphorus cycling and transport in streams lend insight into potential mechanisms of nutrient sequestration and can help mitigate human impacts. In this study, we examined the relationship between transient storage and phosphorus uptake in a cold‐water stream in western Wisconsin. Hydrological characteristics, nutrient spiralling metrics, macrophyte biomass, and geomorphological properties were quantified in 7 reaches of Spring Coulee Creek using injections of a conservative tracer alone or with added PO₄^3?. Fraction of median travel time due to transient storage (F_med²⁰⁰) was correlated with macrophyte biomass (r = .794, p = .033), and PO₄^3? uptake velocity was correlated with F_med²⁰⁰ (r = .756, p = .049). Stepwise linear regression was used to build models for transient storage and uptake velocity. Macrophyte biomass, stream bed slope, and riffle to pool ratio accounted for 99.6% of the variation in transient storage (p < .001). Transient storage, canopy cover, and slope accounted for 98.0% of the variation in uptake velocity (p = .002). This study shows that transient storage, primarily resulting from macrophyte beds, can be a significant factor regulating phosphorus uptake in stream ecosystems.  相似文献   

Lateral terminations of salt walls and megaflaps: An example from Gypsum Valley Diapir,Paradox Basin,Colorado, USA     

Frederic O. Escosa  Mark G. Rowan  Katherine A. Giles  Kyle T. Deatrick  Allison M. Mast  Richard P. Langford  Thomas E. Hearon  Eduard Roca 《Basin Research》2019,31(1):191-212

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Transformation of social capital during and after a disaster event: the cases Chañaral and Diego de Almagro,Atacama Region,Chile     

Castro-Correa  Carmen-Paz  Aldunce Ide  Paulina  Wyndham Vásquez  Katherine  Mena Maldonado  Dania  Pérez Tello  Sonia 《Natural Hazards》2020,103(2):2427-2440

Natural Hazards - This article analyzes the impact of socio-natural disasters on social capital at a local level, studying the cases of the communities of Chañaral and Diego de Almagro after...  相似文献   

Regime shifts: Can ecological theory illuminate the mechanisms?   总被引：2，自引：0，他引：2  

Jeremy S. Collie  Katherine Richardson  John H. Steele 《Progress in Oceanography》2004,60(2-4):281

“Regime shifts” are considered here to be low-frequency, high-amplitude changes in oceanic conditions that may be especially pronounced in biological variables and propagate through several trophic levels. Three different types of regime shift (smooth, abrupt and discontinuous) are identified on the basis of different patterns in the relationship between the response of an ecosystem variable (usually biotic) and some external forcing or condition (control variable). The smooth regime shift is represented by a quasi-linear relationship between the response and control variables. The abrupt regime shift exhibits a nonlinear relationship between the response and control variables, and the discontinuous regime shift is characterized by the trajectory of the response variable differing when the forcing variable increases compared to when it decreases (i.e., the occurrence of alternative “stable” states). Most often, oceanic regime shifts are identified from time series of biotic variables (often commercial fish), but this approach does not allow the identification of discontinuous regime shifts. Recognizing discontinuous regime shifts is, however, particularly important as evidence from terrestrial and freshwater ecosystems suggests that such regime shifts may not be immediately reversible. Based on a review of various generic classes of mathematical models, we conclude that regime shifts arise from the interaction between population processes and external forcing variables. The shift between ecosystem states can be caused by gradual, cumulative changes in the forcing variable(s) or it can be triggered by acute disturbances, either anthropogenic or natural. A protocol for diagnosing the type of regime shift encountered is described and applied to a data set on Georges Bank haddock, from which it is concluded that a discontinuous regime shift in the abundance of haddock may have occurred. It is acknowledged that few, if any, marine data are available to confirm the occurrence of discontinuous regime shifts in the ocean. Nevertheless, we argue that there is good theoretical evidence for their occurrence as well as some anecdotal evidence from data collection campaigns and that the possibility of their occurrence should be recognized in the development of natural resource management strategies.  相似文献   

Spitzer observations of M83 and the hot star, H ii region connection     

Robert H. Rubin  Janet P. Simpson  Sean W. J. Colgan  Reginald J. Dufour  Katherine L. Ray  Edwin F. Erickson  Michael R. Haas  Adalbert W. A. Pauldrach  Robert I. Citron 《Monthly notices of the Royal Astronomical Society》2007,377(4):1407-1418

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Lipids of marine Archaea: Patterns and provenance in the water-column and sediments   总被引：1，自引：0，他引：1  

Courtney Turich  Katherine H. Freeman  Maureen Conte  Stuart G. Wakeham 《Geochimica et cosmochimica acta》2007,71(13):3272-3291

We measured archaeal lipid distributions from globally distributed samples of freshwater, marine, and hypersaline suspended particulate matter. Cluster analysis of relative lipid distributions identified four distinct groups, including: (1) marine epipelagic (<100 m) waters, (2) marine mesopelagic (200-1500 m) and upwelling waters, (3) freshwater/estuarine waters, and (4) hypersaline waters. A pronounced difference in lipid composition patterns is the near absence of ring-containing glycerol dialkyl glycerol tetraethers (GDGTs) at high salinity. Different archaeal communities populate marine (mesophilic Crenarchaeota and Euryarchaeota), and hypersaline environments (halophilic Euryarchaeota) and community shifts can regulate differences in lipid patterns between marine and hypersaline waters. We propose that community changes within meosphilic marine Archaea also regulate the lipid patterns distinguishing epipelagic and mesopelagic/upwelling zones. Changes in the relative amounts of crenarchaeol and caldarchaeol and low relative abundances of ringed structures in surface waters differentiate lipids from the epipelagic and mesopelagic/upwelling waters. Patterns of lipids in mesopelagic (and upwelling) waters are similar to those expected of the ammonia-oxidizing Group I Crenarchaeota, with predominance of crenarchaeol and abundant cyclic GDGTs; non-metric multidimensional analysis (NMDS) shows this pattern is associated with high nitrate concentrations. In contrast, limited culture evidence indicates marine Group II Euryarchaeota may be capable of producing mainly caldarchaeol and some, but not all, of the ringed GDGTs and we suggest that these organisms, along with the Crenarchaeota, contribute to lipids in epipelagic marine waters. Calculated TEX₈₆ temperatures in mesopelagic samples (reported here and in published data sets) are always much warmer than measured in situ temperatures. We propose lipids used in the temperature proxy derive from both Euryarchaeaota and Crenarchaeota, and observed values of TEX₈₆ are subject to changes in their ecology as influenced by nutrient fluctuations or other perturbations. Applications of published core-top TEX₈₆-SST correlations require that (1) the surface waters are always composed of similar communities with the same temperature response and (2) that deeper water GDGT production is not transported to the sediments. Our lipid distribution patterns demonstrate both surface-water archaeal community differences (which accompany greater nutrient influxes, shoaling of mesopelagic Crenarchaeota during upwelling periods, and possibly due to an influx of terrestrial Archaea), and changes in organic matter transport through the water column can affect the distribution of lipids recorded in sediments. We therefore suggest that reported temperature shifts in ancient applications indicate TEX₈₆ lipids recorded not only temperature changes, but also changes in archaeal ecology, nutrient concentrations, and possibly oceanographic conditions.  相似文献   

Extremely red galaxy counterparts to 7C radio sources     

Chris J. Willott  Steve Rawlings  Katherine M. Blundell 《Monthly notices of the Royal Astronomical Society》2001,324(1):1-17

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours ( R − K >5.5) and we find that almost all of them lie in the redshift range 1< z <2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H α at z =1.45 and z =1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations that are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z ∼1.5 at least 1/4 of powerful radio jets are triggered in massive (> L *) galaxies, which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z ≳5. If a similar fraction of all z ∼1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10 and 100 per cent of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1< z <2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [O  ii ] at z =1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z ≳5 and these objects probably undergo at least two periods of active galactic nucleus activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z ∼1.5.  相似文献   

Six-color observations of the Eclipsing binary AR Cas     

Katherine C. Gordon  Gerald E. Kron 《Astrophysics and Space Science》1973,23(2):403-416

Depths and phases of both minima of AR Cas in six colors in 1959 are presented. Analysis leads to a color distribution for the secondary component which corresponds to spectral type A5–A7.  相似文献