Nitrogen and noble gases in a glass sample from the LEW88516 shergottite     

Richard H. Becker  Robert O. Pepin 《Meteoritics & planetary science》1993,28(5):637-640

Abstract— A glass separate from the LEW88516 shergottite was analyzed by step-wise combustion for N and noble gases to determine whether it contained trapped gas similar in composition to the martian atmosphere-like component previously observed in lithology C of EETA79001. Excesses of ⁴⁰Ar and ¹²⁹Xe were in fact observed in this glass, although the amounts of these excesses are ≤20% of those seen in the latter meteorite, and are comparable to the amounts seen in whole-rock analyses of LEW88516. The isotopic composition of N in LEW88516 does not show an enrichment in ¹⁵N commensurate with the amount of isotopically-heavy N expected from the noble gases excesses. One must posit some extreme assumptions about the nature of the N components present in LEW88516 in order to allow the presence of the trapped nitrogen component. Alternatively, the N has somehow been decoupled from the noble gases, and was either never present or has been lost.  相似文献   

Solar wind noble gases and nitrogen in metal from lunar soil 68501     

Richard H. Becker  Robert O. Pepin 《Meteoritics & planetary science》1994,29(5):724-738

Abstract Noble gases and N were analyzed in handpicked metal separates from lunar soil 68501 by a combination of step-wise combustions and pyrolyses. Helium and Ne were found to be unfractionated with respect to one another when normalized to solar abundances, for both the bulk sample and for all but the highest temperature steps. However, they are depleted relative to Ar, Kr and Xe by at least a factor of 5. The heavier gases exhibit mass-dependent fractionation relative to solar system abundance ratios but appear unfractionated, both in the bulk metal and in early temperature steps, when compared to relative abundances derived from lunar ilmenite 71501 by chemical etching, recently put forward as representing the abundance ratios in solar wind. Estimates of the contribution of solar energetic particles (SEP) to the originally implanted solar gases, derived from a basic interpretation of He and Ne isotopes, yield values of about 10%. Analysis of the Ar isotopes requires a minimum of 20% SEP, and Kr isotopes, using our preferred composition for solar wind Kr, yield a result that overlaps both of these values. It is possible to reconcile the data from these gases if significant loss of solar wind Ar, Kr and presumably Xe has occurred relative to the SEP component, most likely by erosive processes that are mass independent, although mass-dependent losses (Ar > Kr > Xe) cannot be excluded. If such losses did occur, the SEP contribution to the solar implanted gases must have been no more than a few percent. Nitrogen is a mixture of indigenous meteoritic N, whose isotopic composition is inferred to be relatively light, and implanted solar N, which has probably undergone diffusive redistribution and fractionation. If the heavy noble gases have not undergone diffusive loss, then N/Ar in the solar wind can be inferred to be at least several times the accepted solar ratio. The solar wind N appears, even after correction for fractionation effects, to have a minimum δ¹⁵N value ≥+150‰ and a more probable value ≥+200‰.  相似文献   

Biological correlates of recruitment variability in North Sea fish stocks     

Pepin  P. 《ICES Journal of Marine Science》1990,47(1):89-98

  相似文献   

Effects of eastern redcedar encroachment on soil hydraulic properties along Oklahoma's grassland‐forest ecotone     

Tyson E. Ochsner  Apurba Sutradhar  Rachael Pepin 《水文研究》2012,26(11):1720-1728

In north‐central Oklahoma eastern redcedar (Juniperus virginiana), encroachment into grassland is widespread and is suspected of reducing streamflow, but the effects of this encroachment on soil hydraulic properties are unknown. This knowledge gap creates uncertainty in understanding the hydrologic effects of eastern redcedar encroachment and obstructs fact‐based management of encroached systems. The objective of this study was to quantify the effects of eastern redcedar encroachment into tallgrass prairie on soil hydraulic properties. Leaf litter depth, soil organic matter, soil water repellency, soil water content, sorptivity, and unsaturated hydraulic conductivity were measured near Stillwater, OK, along 12 radial transects from eastern redcedar trunks to the center of the grassy intercanopy space. Eastern redcedar encroachment in the second half of the 20th century caused the accumulation of 3 cm of hydrophobic leaf litter near the trunks of eastern redcedar trees. This leaf litter was associated with increased soil organic matter in the upper 6 cm of soil under eastern redcedar trees (5.96% by mass) relative to the grass‐dominated intercanopy area (3.99% by mass). Water repellency was more prevalent under eastern redcedar than under grass, and sorptivity under eastern redcedar was 0.10 mm s^?1/2, one seventh the sorptivity under adjacent prairie grasses (0.68 mm s^?1/2). Median unsaturated hydraulic conductivity under grass was 2.52 cm h^?1, four times greater than under eastern redcedar canopies (0.57 cm h^?1). Lower sorptivity and unsaturated hydraulic conductivity would tend to decrease infiltration and increase runoff, but other factors such as rainfall interception by the eastern redcedar canopy and litter layer, and preferential flow induced by hydrophobicity must be examined before the effects of encroachment on streamflow can be predicted. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Surface mean temperature from the observational stations and multiple reanalyses over the Tibetan Plateau     

Yan  Yuping  You  Qinglong  Wu  Fangying  Pepin  Nick  Kang  Shichang 《Climate Dynamics》2020,55(9-10):2405-2419

The Tibetan Plateau (TP), also called the “Third pole”, is sensitive to climate change due to extensive areas at high elevation presently dominated by snow and ice. In this study, observed surface temperature trends at 150 stations over the TP during 1979–2018 are analyzed and compared with surface temperatures from multiple reanalyses (NCEP1, NCEP2, ERA-Interim, MERRA, JRA55). Observed warming at the stations has a mean annual rate of 0.46 °C/decade during 1979–2018. Although all reanalyses underestimate observed temperatures (cold bias), most reproduce much of the inter-decadal variations of surface temperature shown in the observations. Absolute errors of mean surface temperature (reanalysis minus observation) are closely correlated with elevation errors, suggesting that parts of the cold bias can be interpreted by elevation errors of reanalysis. After elevation-temperature correction, about half of the cold bias is typically eliminated, more for both ERA-Interim and JRA55. Compared with the observations, corrected NCEP2 surface temperatures still have larger cold biases, and fail to capture the overall warming over the TP. Since the elevation-temperature correction fails to improve trend magnitudes even when a significant proportion of the bias has been removed, this suggests that a more sophisticated modeling of the lapse rate in each reanalysis is required to realistically model warming trends across complex topography.

  相似文献   

Seasonal patterns in zooplankton community structure on the Newfoundland and Labrador Shelf     

Pierre Pepin  Eugene Colbourne  Gary Maillet 《Progress in Oceanography》2011,91(3):273-285

We report on the patterns in zooplankton community structure on the Newfoundland and Labrador Shelf from seasonal collections along oceanographic sections during 2000–2007. We use a combination of constrained and unconstrained multivariate methods to assess latitudinal and cross shelf patterns in community structure. Both physical and biological features of the region are dominated by the cross-shelf gradient in water mass characteristics although there is evidence of a latitudinal gradient that may be a reflection of the influence of freshwater outflow from the Arctic. All analyses reveal a strong and consistent pattern in species composition among water masses that extends across spring, summer and autumn, although there are some variations that occur among seasons that reflect differences in development state of certain taxa. The strong association between community structure and water mass characteristics in the region may be the result of the Newfoundland and Labrador Shelf being at the intersection of several major oceanographic domains, bounded by strong Labrador and Gulf Stream currents, that allows the formation and persistence of well defined zooplankton communities. Our findings have implications for the region’s potential as a monitoring location for long term changes in ocean state.  相似文献   

Evolutionary models for two hyper-iron-poor low-mass stars     

Gregory J. Harris  Rachael Porter  A. E. Lynas-Gray  Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2007,377(4):1520-1530

  相似文献   

Irradiation records in regolith materials, II: Solar wind and solar energetic particle components in helium, neon, and argon extracted from single lunar mineral grains and from the Kapoeta howardite by stepwise pulse heating     

R.L Palma  R.H BeckerR.O Pepin  D.J Schlutter 《Geochimica et cosmochimica acta》2002,66(16):2929-2958

High-resolution stepped heating has been used to extract light noble gases implanted in a suite of 13 individual lunar ilmenite and iron grains and in the Kapoeta howardite by solar wind (SW) and solar energetic particle (SEP) irradiation. Isotopic analyses of gases evolved at low temperatures from the lunar grains confirm the neon and argon compositions obtained by Pepin et al. (Pepin R. O., Becker R. H., and Schlutter D. J., “Irradiation records in regolith materials, I: Isotopic compositions of solar-wind neon and argon in single lunar regolith grains”, Geochim. Cosmochim. Acta63, 2145-2162, 1999) in an initial study of 11 regolith grains, primarily ilmenites. Combination of the data sets from both investigations yields ²⁰Ne/²²Ne = 13.85 ± 0.04, ²¹Ne/²²Ne = 0.0334 ± 0.0003, and ³⁶Ar/³⁸Ar = 5.80 ± 0.06 for the lunar samples; the corresponding ³⁶Ar/³⁸Ar ratio in Kapoeta is 5.74 ± 0.06. The neon ratios agree well with those measured by Benkert et al. (Benkert J.-P., Baur H., Signer P., and Wieler R., “He, Ne, and Ar from the solar wind and solar energetic particles in lunar ilmenites and pyroxenes”, J. Geophys. Res. (Planets)98, 13147-13162, 1993) in gases extracted from bulk lunar ilmenite samples by stepped acid etching and attributed by them to the SW. The ³⁶Ar/³⁸Ar ratios, however, are significantly above both Benkert et al.’s (1993) proposed SW value of 5.48 ± 0.05 and a later estimate of 5.58 ± 0.03 from an acid-etch analysis of Kapoeta (Becker R. H., Schlutter D. J., Rider P. E., and Pepin R. O., “An acid-etch study of the Kapoeta achondrite: Implications for the argon-36/argon-38 ratio in the solar wind”, Meteorit. Planet. Sci.33, 109-113, 1998). We believe, for reasons discussed here and in our earlier report, that 5.80 ± 0.06 ratio most nearly represents the wind composition. The ³He/⁴He ratio in low-temperature gas releases, not measured in the first particle suite, is found in several grains to be indistinguishable from Benkert et al.’s (1993) SW estimate. Elemental ratios of He, Ne, and Ar initially released from grain-surface SW implantation zones are solar-like, as found earlier by Pepin et al. (1999). Gases evolved from these reservoirs at higher temperatures show evidence for perturbations from solar elemental compositions by prior He loss, thermal mobilization of excess Ne from fractionated SW components, or both.Attention in this second investigation was focused on estimating the isotopic compositions of both the SW and the more deeply sited SEP components in regolith grains. Several high-temperature “isotopic plateaus”—approximately constant isotopic ratios in gas fractions released over a number of consecutive heating steps—were observed in the close vicinities of the SEP ratios for He, Ne, and Ar reported by Benkert et al. (1993). Arguments presented in the text suggest that these plateaus are relatively free of interferences from multicomponent mixing artifacts that can mimic pure component signatures. Average SEP compositions derived from the stepped-heating plateau measurements are in remarkable agreement with the Zürich acid-etch values for all three gases.  相似文献   

NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ11B and Trace Element Ratio Value Assignment     

Joseph A. Stewart  Steven J. Christopher  John R. Kucklick  Louise Bordier  Thomas B. Chalk  Arnaud Dapoigny  Eric Douville  Gavin L. Foster  William R. Gray  Rosanna Greenop  Marcus Gutjahr  Freya Hemsing  Michael J. Henehan  Philip Holdship  Yu‐Te Hsieh  Ana Kolevica  Yen‐Po Lin  Elaine M. Mawbey  James W. B. Rae  Laura F. Robinson  Rachael Shuttleworth  Chen‐Feng You  Shuang Zhang  Russell D. Day 《Geostandards and Geoanalytical Research》2021,45(1):77-96

The boron isotopic ratio of ¹¹B/¹⁰B (δ¹¹B_SRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ¹¹B_SRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ¹¹B_SRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.  相似文献   

High‐resolution study of Icelandic tephras in the Kangerlussuaq Trough,southeast Greenland,during the last deglaciation     

Anne E. Jennings  Karl Grnvold  Rachael Hilberman  Mikie Smith  Morten Hald 《第四纪科学杂志》2002,17(8):747-757

Tephra abundance data and geochemistry in Late‐glacial and Holocene sediments on the East Greenland shelf are presented. Two well‐known tephras were identified from electron microprobe analysis of tephra shards picked from ash peaks in the cores. These are the Vedde Ash and Saksunarvatn Ash, which probably were deposited on the shelf after transport on drifting ice. The radiocarbon dates (marine reservoir corrected by −550 yr) that constrain the timing of deposition of the tephra layers compare well with the terrestrial and ice‐core ages of the tephras without requiring additional reservoir correction to align them with the known tephra ages. Several prominent tephra layers with a composition of Ash Zone 2 tephra punctuate the deglacial sediments. These tephra peaks coincide with significant light stable isotope events (signifying glacial meltwater) and fine‐grained sediments poor in ice‐rafted detritus. We interpret the Ash Zone 2 tephra peaks as sediment released from the Greenland Ice Sheet during strong melting pulses of the deglaciation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献