Diverse young stellar populations in the intermediate-redshift radio galaxies 3C 213.1 and 3C 459: implications for the evolution of the host galaxies     

K. A. Wills  C. Tadhunter  J. Holt  R. González Delgado  K. J. Inskip  J. Rodríguez Zaurín  R. Morganti 《Monthly notices of the Royal Astronomical Society》2008,385(1):136-146

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Community-level response of coastal microbial biofilms to ocean acidification in a natural carbon dioxide vent ecosystem     

Lidbury I  Johnson V  Hall-Spencer JM  Munn CB  Cunliffe M 《Marine pollution bulletin》2012,64(5):1063-1066

The impacts of ocean acidification on coastal biofilms are poorly understood. Carbon dioxide vent areas provide an opportunity to make predictions about the impacts of ocean acidification. We compared biofilms that colonised glass slides in areas exposed to ambient and elevated levels of pCO(2) along a coastal pH gradient, with biofilms grown at ambient and reduced light levels. Biofilm production was highest under ambient light levels, but under both light regimes biofilm production was enhanced in seawater with high pCO(2). Uronic acids are a component of biofilms and increased significantly with high pCO(2). Bacteria and Eukarya denaturing gradient gel electrophoresis profile analysis showed clear differences in the structures of ambient and reduced light biofilm communities, and biofilms grown at high pCO(2) compared with ambient conditions. This study characterises biofilm response to natural seabed CO(2) seeps and provides a baseline understanding of how coastal ecosystems may respond to increased pCO(2) levels.  相似文献   

Modelling the tidal mixing fronts and seasonal stratification of the Northwest European Continental shelf     

Jason Holt  Lars Umlauf 《Continental Shelf Research》2008

We investigate mixing processes under stratified conditions on the Northwest European Continental shelf using a numerical model (POLCOMS). Our results indicate that convection induced by vertical shearing of horizontal density gradients (‘shear-induced convection’) is a regularly occurring feature in the bottom and surface boundary layers in this open shelf-sea situation. Two types of turbulence models are investigated to study their capability for reproducing the observed location of tidal mixing fronts, and the physical processes occurring in seasonally stratified waters. The first model is a one-equation variant of the Mellor–Yamada model, whereas the second model combines a more recent second-momentum closure with a two-equation model. It is found that generally mean frontal positions (as estimated from ICES data) are predicted more accurately by the two-equation model. The one-equation model reproduces the mean frontal locations to 18.1 km (<3 grid spacings) and the two-equation model to 17.1 km; although in the Celtic Sea the accuracy is ∼33 and ∼12 km, respectively. Comparison with historical tide gauges, current metres, CTD stations, and thermistor chain data from the North Sea Project all show an improvement in accuracy when the two-equation model is used. This is particularly apparent in the model's ability to reproduce the spring–neap variability during stratification. We find that in the presence of shear-induced convection the routinely applied clipping of the turbulent length-scale, previously thought to be a minor ingredient in a turbulence model, has a dramatic effect on the results: if the length-scale clipping is not applied, substantial over-mixing is observed to occur. The causes and possible remedies of this effect are investigated. Overall our results demonstrate a sensitivity to the details of the turbulence model that is significantly greater than previously thought.  相似文献   

The influence of precipitate formation on the chemical oxidation of TCE DNAPL with potassium permanganate     

Michael R. West  Gavin P. Grant  Jason I. Gerhard  Bernard H. Kueper 《Advances in water resources》2008

A three-dimensional two-phase flow model is coupled to a non-linear reactive transport model to study the efficacy of potassium permanganate treatment on dense, non-aqueous phase liquid (DNAPL) source removal in porous media. A linear relationship between the soil permeability (k) and concentration of manganese dioxide precipitate ([MnO_2(s)]), k = k_o + S_rind [MnO_2(s)], is utilized to simulate nodal permeability reductions due to precipitate formation. Using published experimental column studies, an S_rind = −5.5 × 10⁻¹⁶ m² L/mg was determined for trichloroethylene (TCE) DNAPL. This S_rind was then applied to treatment simulations on three-dimensional TCE DNAPL source zones comprising either DNAPL at residual saturations, or DNAPL at pooled saturations.  相似文献   

Geographies of health: Therapeutic landscapes - by A. Williams     

Jason Myers 《New Zealand geographer》2009,65(1):86-87

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Climate of the past millennium inferred from varved proglacial lake sediments on northeast Baffin Island,Arctic Canada   总被引：1，自引：0，他引：1  

Elizabeth K. Thomas  Jason P. Briner 《Journal of Paleolimnology》2009,41(1):209-224

This study uses ^239+240Pu-dated varved sediments from Big Round Lake, a proglacial lake on northeast Baffin Island, Arctic Canada to generate a 1000-year-long, annual-resolution record of past climate. Varve thickness is positively correlated with July–August–September temperature measured at Clyde River, 70 km to the north of the lake (r = 0.46, p < 0.001). We therefore interpret the variability and trends in varve thickness to partially represent summer temperature. The coolest Little Ice Age temperatures occurred in this record from 1575 to 1760 AD and were approximately 1.5°C cooler than today (average from 1995 to 2005 AD) and 0.2°C cooler than the last millennium (average from 1000 to 2000 AD). Pre-twentieth-century warmth occurred during two intervals, 970–1150 AD and 1375–1575 AD; temperatures were approximately 1.2°C cooler than today, but 0.1°C warmer than the last millennium. The Big Round Lake varve-thickness record contains features similar to that reconstructed elsewhere in the eastern Canadian Arctic. This high-resolution quantitative record expands our understanding of arctic climate during the past millennium.

Elizabeth K. ThomasEmail:

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Radiocarbon dating of small terrestrial gastropod shells in North America     

Jeffrey S. Pigati  Jason A. Rech  Jeffrey C. Nekola 《Quaternary Geochronology》2010,5(5):519-532

Fossil shells of small terrestrial gastropods are commonly preserved in wetland, alluvial, loess, and glacial deposits, as well as in sediments at many archeological sites. These shells are composed largely of aragonite (CaCO₃) and potentially could be used for radiocarbon dating, but they must meet two criteria before their ¹⁴C ages can be considered to be reliable: (1) when gastropods are alive, the ¹⁴C activity of their shells must be in equilibrium with the ¹⁴C activity of the atmosphere, and (2) after burial, their shells must behave as closed systems with respect to carbon. To evaluate the first criterion, we conducted a comprehensive examination of the ¹⁴C content of the most common small terrestrial gastropods in North America, including 247 AMS measurements of modern shell material (3749 individual shells) from 46 different species. The modern gastropods that we analyzed were all collected from habitats on carbonate terrain and, therefore, the data presented here represent worst-case scenarios. In sum, ～78% of the shell aliquots that we analyzed did not contain dead carbon from limestone or other carbonate rocks even though it was readily available at all sites, 12% of the aliquots contained between 5 and 10% dead carbon, and a few (3% of the total) contained more than 10%. These results are significantly lower than the 20–30% dead carbon that has been reported previously for larger taxa living in carbonate terrain. For the second criterion, we report a case study from the American Midwest in which we analyzed fossil shells of small terrestrial gastropods (7 taxa; 18 AMS measurements; 173 individual shells) recovered from late-Pleistocene sediments. The fossil shells yielded ¹⁴C ages that were statistically indistinguishable from ¹⁴C ages of well-preserved plant macrofossils from the same stratum. Although just one site, these results suggest that small terrestrial gastropod shells may behave as closed systems with respect to carbon over geologic timescales. More work on this subject is needed, but if our case study site is representative of other sites, then fossil shells of some small terrestrial gastropods, including at least five common genera, Catinella, Columella, Discus, Gastrocopta, and Succinea, should yield reliable ¹⁴C ages, regardless of the local geologic substrate.  相似文献   

Health, sexuality and place: the different geographies of HIV-positive gay men in Auckland, New Zealand     

Myers J 《New Zealand geographer》2010,66(3):218-227

This paper employs interview narratives alongside participant-led photography and caption writing to examine the different daily geographies of 15 HIV-positive gay men in Auckland, New Zealand. Difference for these men is rooted in both their HIV status and their sexuality, and this difference has implications for their engagement with the world at a range of spatial and temporal scales. Giving voice to such experiences begins to answer calls for geographers to consider more deeply the connections between health, sexuality and place.  相似文献   

Isotope measurements of single ostracod valves and gastropod shells for climate reconstruction: evaluation of within-sample variability and determination of optimum sample size     

Jaime Escobar  Jason H. Curtis  Mark Brenner  David A. Hodell  Jonathan A. Holmes 《Journal of Paleolimnology》2010,43(4):921-938

Sediment cores from Lakes Punta Laguna, Chichancanab, and Petén Itzá on the Yucatan Peninsula were used to (1) investigate “within-horizon” stable isotope variability (δ¹⁸O and δ¹³C) measured on multiple, single ostracod valves and gastropod shells, (2) determine the optimum number of individuals required to infer low-frequency climate changes, and (3) evaluate the potential for using intra-sample δ¹⁸O variability in ostracod and gastropod shells as a proxy measure for high-frequency climate variability. Calculated optimum sample numbers (“n”) for δ¹⁸O and δ¹³C in the ostracod Cytheridella ilosvayi and the gastropod Pyrgophorus coronatus vary appreciably throughout the cores in all three lakes. Variability and optimum “n” values were, in most cases, larger for C. ilosvayi than for P. coronatus for δ¹⁸O measurements, whereas there was no significant difference for δ¹³C measurements. This finding may be explained by differences in the ecology and life history of the two taxa as well as contrasting modes of calcification. Individual δ¹⁸O measurements on C. ilosvayi in sediments from Lake Punta Laguna show that samples from core depths that have high mean δ¹⁸O values, indicative of low effective moisture, display lower variability, whereas samples with low mean δ¹⁸O values, reflecting times of higher effective moisture, display higher variability. Relatively dry periods were thus consistently dry, whereas relatively wet periods had both wet and dry years. This interpretation of data from the cores applies to two important periods of the late Holocene, the Maya Terminal Classic period and the Little Ice Age. δ¹⁸O variability during the ancient Maya Terminal Classic Period (ca. 910–990 AD) indicates not only the driest mean conditions in the last 3,000 years, but consistently dry climate. Variability of δ¹³C measurements in single stratigraphic layers displayed no relationship with climate conditions inferred from δ¹⁸O measurements.  相似文献   

Deformation correlations,stress field switches and evolution of an orogenic intersection: The Pan-African Kaoko-Damara orogenic junction,Namibia     

Ben Goscombe  David A. Foster  David Gray  Ben Wade  Antonios Marsellos  Jason Titus 《地学前缘(英文版)》2017,8(6):1187-1232

Age calibrated deformation histories established by detailed mapping and dating of key magmatic time markers are correlated across all tectono-metamorphic provinces in the Damara Orogenic System.Correlations across structural belts result in an internally consistent deformation framework with evidence of stress field rotations with similar timing,and switches between different deformation events.Horizontal principle compressive stress rotated clockwise ~180°in total during Kaoko Belt evolution,and~135° during Damara Belt evolution.At most stages,stress field variation is progressive and can be attributed to events within the Damara Orogenic System,caused by changes in relative trajectories of the interacting Rio De La Plata,Congo,and Kalahari Cratons.Kaokoan orogenesis occurred earliest and evolved from collision and obduction at ~590 Ma,involving E-W directed shortening,progressing through different transpressional states with ~45° rotation of the stress field to strike-slip shear under NW-SE shortening at ~550-530 Ma.Damaran orogenesis evolved from collision at ~555-550 Ma with NW-SE directed shortening in common with the Kaoko Belt,and subsequently evolved through ~90°rotation of the stress field to NE-SW shortening at ~512-508 Ma.Both Kaoko and Damara orogenic fronts were operating at the same time,with all three cratons being coaxially convergent during the 550-530 Ma period;Rio De La Plata directed SE against the Congo Craton margin,and both together over-riding the Kalahari Craton margin also towards the SE.Progressive stress field rotation was punctuated by rapid and significant switches at ~530-525 Ma,~508 Ma and ~505 Ma.These three events included:(1)Culmination of main phase orogenesis in the Damara Belt,coinciding with maximum burial and peak metamorphism at 530-525 Ma.This occurred at the same time as termination of transpression and initiation of transtensional reactivation of shear zones in the Kaoko Belt.Principle compressive stress switched from NW-SE to NNW-SSE shortening in both Kaoko and Damara Belts at this time.This marks the start of Congo-Kalahari stress field overwhelming the waning Rio De La Plata-Congo stress field,and from this time forward contraction across the Damara Belt generated the stress field governing subsequent low-strain events in the Kaoko Belt.(2)A sudden switch to E-W directed shortening at ~508 Ma is interpreted as a far-field effect imposed on the Damara Orogenic System,most plausibly from arc obduction along the orogenic margin of Gondwana(Ross-Delamerian Orogen).(3)This imposed stress field established a N-S extension direction exploited by decompression melts,switch to vertical shortening,and triggered gravitational collapse and extension of the thermally weakened hot orogen core at ~505 Ma,producing an extensional metamorphic core complex across the Central Zone.  相似文献