The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems at z≲ 1.5     

Joseph D. Meiring  Varsha P. Kulkarni  James T. Lauroesch  Celine Péroux  Pushpa Khare  Donald G. York  Arlin P. S. Crotts 《Monthly notices of the Royal Astronomical Society》2008,384(3):1015-1033

We present chemical abundance measurements from medium-resolution observations of eight subdamped Lyα (sub-DLA) absorber and two strong Lyman-limit systems at   z ≲ 1.5  observed with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II Clay telescope. These observations were taken as part of an ongoing project to determine abundances in   z _abs≲ 1.5  quasar absorption line systems focusing on sub-DLA systems. These observations increase the sample of Zn measurements in   z _abs≲ 1.5  sub-DLAs by ∼50 per cent. Lines of Mg  i , Mg  ii , Al  ii , Al  iii , Ca  ii , Mn  ii , Fe  ii and Zn  ii were detected and column densities were determined. Zn  ii , a relatively undepleted element and tracer of the gas-phase metallicity is detected in two of these systems, with  [Zn/H]=−0.05 ± 0.12  and  [Zn/H] > +0.86  . The latter one is however a weak system with   N _{H  I} < 18.8  , and therefore may need significant ionization corrections to the abundances. Fe  ii lines were detected in all systems, with an average Fe abundance of  〈[Fe/H]〉=−0.68  , higher than typical Fe abundances for DLA systems at these redshifts. This high mean [Fe/H] could be due to less depletion of Fe on to dust grains, or to higher abundances in these systems. We also discuss the relative abundances in these absorbers. The systems with high metallicity show high ratios of [Mn/Fe] and [Zn/Fe], as seen previously in another sub-DLA. These higher values of [Mn/Fe] could be a result of heavy depletion of Fe on to grains, unmixed gas, or an intrinsically non-solar abundance pattern. Based on cloudy modelling, we do not expect ionization effects to cause this phenomenon.  相似文献   

Nitrogen loads to estuaries from waste water plumes: modeling and isotopic approaches     

Kroeger KD  Cole ML  York JK  Valiela I 《Ground water》2006,44(2):188-200

We developed, and applied in two sites, novel methods to measure ground water-borne nitrogen loads to receiving estuaries from plumes resulting from land disposal of waste water treatment plant (WWTP) effluent. In addition, we quantified nitrogen losses from WWTP effluent during transport through watersheds. WWTP load to receiving water was estimated as the difference between total measured ground water-transported nitrogen load and modeled load from major nitrogen sources other than the WWTP. To test estimated WWTP loads, we applied two additional methods. First, we quantified total annual waste water nitrogen load from watersheds based on nitrogen stable isotopic signatures of primary producers in receiving water. Second, we used published data on ground water nitrogen concentrations in an array of wells to estimate dimensions of the plume and quantify the annual mass of nitrogen transported within the plume. Loss of nitrogen during transport through the watershed was estimated as the difference between the annual mass of nitrogen applied to watersheds as treatment plant effluent and the estimated nitrogen load reaching receiving water. In one plume, we corroborated our estimated nitrogen loss in watersheds using data from multiple-level sampling wells to calculate the loss of nitrogen relative to a conservative tracer. The results suggest that nitrogen from the plumes is discharging to the estuaries but that substantial nitrogen loss occurs during transport through the watersheds. The measured vs. modeled and stable isotopic approaches, in comparison to the plume mapping approach, may more reliably quantify ground water-transported WWTP loads to estuaries.  相似文献   

Thermochronometry and palaeomagnetism of the Archaean Nelshoogte Pluton, South Africa     

Paul W. Layer  Margarita Lopez-Martinez  Alfred Kröner  Derek York  & Michael McWilliams 《Geophysical Journal International》1998,135(1):129-145

²⁰⁷Pb/²⁰⁶Pb single-grain zircon, ⁴⁰Ar/³⁹Ar single-grain hornblende and biotite, and ⁴⁰Ar/³⁹Ar bulk-sample muscovite and biotite ages from the Nelshoogte trondhjemite pluton located in eastern Transvaal, South Africa, show that this granitoid had a protracted thermal history spanning 3213±4  Ma to about 3000  Ma. Whole-rock ⁴⁰Ar/³⁹Ar ages from cross-cutting dolerite dykes indicate that these were intruded at about 1900  Ma. There is no evidence of this or other, later events significantly affecting the argon systematics of the minerals from the pluton dated by the ⁴⁰Ar/³⁹Ar method.
  The pluton has a well-defined palaeomagnetic pole which is dated at 3179±18 (2 σ ) Ma by ⁴⁰Ar/³⁹Ar dating of hornblende. This pole (18°N, 310°E, A ₉₅=9°) yields a palaeolatitude of 0°, significantly different from other Archaean poles from the Kaapvaal Craton. The palaeolatitude difference implies that there was significant apparent polar wander during the Archaean. A second, overprinting magnetization seen in the pluton is also seen in the lower-Proterozoic dolerite dykes, and is consistent with other lower-Proterozoic (2150–1950  Ma) poles for southern Africa.  相似文献   

Ecosystem service values of sediment generation and entrapment by marginal coral reefs at Sodwana Bay,South Africa     

SCS Laing  MH Schleyer  JK Turpie 《African Journal of Marine Science》2020,42(2):199-207

Coral reefs provide a multitude of goods and services, some of which are difficult to value due to their intangible nature and the absence of markets to ascribe their relative worth. The coral reefs of Sodwana Bay on the northeast coast of South Africa provide several ecological goods and services, of which only two are considered here: namely, sediment generation and sediment entrapment. Both are deemed essential to the functioning of the Sodwana Bay economy. The replacement-cost method was used to estimate the annual financial cost of sediment provided to the study area if it were replaced by dredging. Sediment generation by the coral reefs was valued at R2.6–R4.8 million, and sediment entrapment valued at R71.8–R84.6 million, totalling between R74.4 million and R89.4 million (≈$5.6–$6.7 million, at R13.38/US$1) per year.  相似文献   

CLASS B0631+519: last of the Cosmic Lens All-Sky Survey lenses     

T. York  N. Jackson  I. W. A. Browne  L. V. E. Koopmans  J. P. McKean  M. A. Norbury  A. D. Biggs  R. D. Blandford  A. G. de Bruyn  C. D. Fassnacht  S. T. Myers  T. J. Pearson  P. M. Phillips  A. C. S. Readhead  D. Rusin  P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2005,361(1):259-271

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The Cosmic Lens All-Sky Survey – II. Gravitational lens candidate selection and follow-up     

I. W. A. Browne  P. N. Wilkinson  N. J. F. Jackson  S. T. Myers  C. D. Fassnacht  L. V. E. Koopmans  D. R. Marlow  M. Norbury  D. Rusin  C. M. Sykes  A. D. Biggs  R. D. Blandford  A. G. de Bruyn  K.-H. Chae  P. Helbig  L. J. King  J. P. McKean  T. J. Pearson  P. M. Phillips  A. C. S. Readhead  E. Xanthopoulos  T. York 《Monthly notices of the Royal Astronomical Society》2003,341(1):13-32

We report the final results of the search for gravitationally lensed flat-spectrum radio sources found in the combination of CLASS (Cosmic Lens All-Sky Survey) and JVAS (Jodrell Bank VLA Astrometric Survey). VLA (Very Large Array) observations of 16 503 sources have been made, resulting in the largest sample of arcsec-scale lens systems available. Contained within the 16 503 sources is a complete sample of 11 685 sources which have two-point spectral indices between 1.4 and 5 GHz flatter than −0.5, and 5-GHz flux densities  ≥30 mJy  . A subset of 8958 sources form a well-defined statistical sample suitable for analysis of the lens statistics. We describe the systematic process by which 149 candidate lensed sources were picked from the statistical sample on the basis of possessing multiple compact components in the 0.2-arcsec resolution VLA maps. Candidates were followed up with 0.05-arcsec resolution MERLIN and 0.003-arcsec VLBA observations at 5 GHz and rejected as lens systems if they failed well-defined surface brightness and/or morphological tests. To illustrate the candidate elimination process, we show examples of sources representative of particular morphologies that have been ruled out by the follow-up observations. 194 additional candidates, not in the well-defined sample, were also followed up. Maps for all the candidates can be found on the World Wide Web at http://www.jb.man.ac.uk/research/gravlens/index.html . We summarize the properties of each of the 22 gravitational lens systems in JVAS/CLASS. 12 are double-image systems, nine are four-image systems and one is a six-image system. 13 constitute a statistically well-defined sample giving a point-source lensing rate of  1:690 ± 190  . The interpretation of the results in terms of the properties of the lensing galaxy population and cosmological parameters will be published elsewhere.  相似文献   

CLASS B0445+123: a new two-image gravitational lens system     

M. K. Argo  N. J. Jackson  I. W. A. Browne  T. York  J. P. McKean  A. D. Biggs  R. D. Blandford  A. G. de Bruyn  K. H. Chae  C. D. Fassnacht  L. V. E. Koopmans  S. T. Myers  M. Norbury  T. J. Pearson  P. M. Phillips  A. C. S. Readhead  D. Rusin  P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):957-961

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Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤z_abs < 2     

Donald G. York  Pushpa Khare  Daniel Vanden Berk  Varsha P. Kulkarni  Arlin P. S. Crotts  James T. Lauroesch  Gordon T. Richards  Donald P. Schneider  Daniel E. Welty  Yusra Alsayyad  Abhishek Kumar  Britt Lundgren  Natela Shanidze  Tristan Smith  Johnny Vanlandingham  Britt Baugher  Patrick B. Hall  Edward B. Jenkins  Brice Menard  Sandhya Rao  Jason Tumlinson  David Turnshek  Ching-Wa Yip  Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,367(3):945-978

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New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA     

Joseph D. Meiring  James T. Lauroesch  Varsha P. Kulkarni  Celine Péroux  Pushpa Khare  Donald G. York  Arlin P. S. Crotts 《Monthly notices of the Royal Astronomical Society》2007,376(2):557-572

We present chemical abundance measurements from high-resolution observations of seven subdamped Lyα (sub-DLA) absorbers and one DLA system at   z < 1.5  . Three of these objects have high metallicity, with near or supersolar Zn abundance. Grids of cloudy models for each system were constructed to look for possible ionization effects in these systems. For the systems in which we could constrain the ionization parameter, we find that the ionization corrections as predicted by the cloudy models are generally small and within the typical error bars (∼0.15 dex), in general agreement with previous studies. The Al  iii to Al  ii ratio for these and other absorbers from the literature are compared, and we find that while the sub-DLAs have a larger scatter in the Al  iii to Al  ii ratios than the DLAs, there appears to be little correlation between the ratio and   N _{H  i}   . The relationship between the metallicity and the velocity width of the profile for these systems is investigated. We show that the sub-DLAs that have been observed to date follow a similar trend as DLA absorbers, with the more metal rich systems exhibiting large velocity widths. We also find that the systems at the upper edge of this relationship with high metallicities and large velocity widths are more likely to be sub-DLAs than DLA absorbers, perhaps implying that the sub-DLA absorbers are more representative of massive galaxies.  相似文献   

Microzooplankton Grazing in Green Water—Results from Two Contrasting Estuaries     

Joanna K. York  Barbara A. Costas  George B. McManus 《Estuaries and Coasts》2011,34(2):373-385

We measured seasonal variations in microzooplankton grazing in Long Island Sound (LIS) and San Francisco Bay (SFB). There was consistent evidence of nutrient limitation in LIS, but not SFB. We found higher chlorophyll a concentrations in LIS compared with SFB. In spite of differences in phytoplankton, there were no differences in microzooplankton abundance (summer: LIS, 12.4 ± 1.8 × 10³ indiv. L⁻¹; SFB, 14.1 ± 3.0 × 10³ indiv. L⁻¹), biomass (summer: LIS, 30.4 ± 5.0 μg C L⁻¹; SFB, 26.3 ± 5.9 μg C L⁻¹), or grazing rates (summer: LIS, 0.66 ± 0.19 day⁻¹; SFB, 0.65 ± 0.18 day⁻¹) between the two estuaries. In common with many other investigators, we found many instances of saturated as well as insignificant grazing. We suggest that saturation in some cases may result from high particle loads in turbid estuarine systems and that insignificant grazing may result from extreme saturation of the grazing response due to the need to process non-food particles.  相似文献