Using SPIRAL (Single Pollen Isotope Ratio AnaLysis) to estimate C₃- and C₄-grass abundance in the paleorecord     

David M. Nelson  Feng Sheng Hu  Daniel R. Scholes  Neeraj Joshi  Ann Pearson 《Earth and Planetary Science Letters》2008,269(1-2):11-16

C₃ and C₄ grasses differ greatly in their responses to environmental controls and influences on biogeochemical processes (e.g. water, carbon, and nutrient cycling). Difficulties in distinguishing between these two functional groups of grasses have hindered paleoecological studies of grass-dominated ecosystems. Stable carbon isotopic analysis of individual grains of grass pollen using a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer holds promise for improving C₃ and C₄ grass reconstructions. This technique, SPIRAL (Single Pollen Isotope Ratio AnaLysis), has only been evaluated using pollen of known C₃ and C₄ grasses. To test the ability of SPIRAL to reproduce the abundance of C₃ and C₄ grasses on the landscape, we measured δ¹³C values of > 1500 individual grains of grass pollen isolated from the surface sediments of ten lakes in areas that span a large gradient of C₃- and C₄-grass abundance, as determined from vegetation surveys. Results indicate a strong positive correlation between the δ¹³C-based estimates of % C₄-grass pollen and the abundance of C₄ grasses on the landscape. The % C₄-grass pollen slightly underestimates the actual abundance of C₄ grasses at sites with high proportions of C₄ grasses, which can be corrected using regression analysis. Comparison of the % C₄-grass pollen with C/N and δ¹³C measurements of bulk organic matter illustrates the distinct advantages of grass-pollen δ¹³C as a proxy for distinguishing C₃ and C₄ shifts within the grass family. Thus SPIRAL promises to advance our understanding of grassland ecology and evolution.  相似文献   

European Forests And Global Changes edited by Paul Jarvis. Cambridge University Press, 1998. ISBN 0-521-58478-7, 380 pp. £60.00     

A. Henderson-Sellers  Director 《Global and Planetary Change》1999,21(4):239

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Spatial scale and habitat-dependent diversity patterns in nematode communities in three seepage related sites along the Norwegian Sea margin     

Saskia Van Gaever  Maarten Raes  Francesca Pasotti  & Ann Vanreusel 《Marine Ecology》2010,31(1):66-77

Assessing the relative contribution of local diversity to regional biodiversity may be the key to understanding large-scale and even global patterns in species diversity. Here, the contribution of habitat heterogeneity of cold seeps at three spatial scales [micro-scale (ms), macro-scale (10 to 100s of ms), and mega-scale (10 to 100s of km)] to the total nematode biodiversity (genus level) along the Norwegian continental margin is evaluated. Due to the development of higher resolution bathymetry and increased bottom sampling in recent years, continental margins, once regarded as monotonous landscapes, are now acknowledged to have a high degree of habitat complexity and diversity. By calculating the additive partitioning of gamma diversity in alpha and beta fractions, we examined to what extent habitat diversity of seep sites significantly increases the nematode genus composition and diversity at different spatial scales. Siboglinidae patches and control sediments yielded comparably high levels of nematode genus richness. They exhibited low turnover rates within and across the different seep sites. In contrast, the bacterial mats at Håkon Mosby Mud Volcano (HMMV) and the reduced sediments at the Nyegga pockmarks harboured genus-poor nematode communities with an equally high dominance of one or two species, which were different for each seep. Different habitats, in particular at the HMMV, contributed significantly to the seep nematode richness. This study demonstrates that the presence of distinct habitat types within multiple seep sites contributes to the high diversity of nematode communities inhabiting the seeps in the Norwegian deep sea.  相似文献   

High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions     

Laura McFarlane Tranquilla  April Hedd  Chantelle Burke  William A. Montevecchi  Paul M. Regular  Gregory J. Robertson  Leslie Ann Stapleton  Sabina I. Wilhelm  David A. Fifield  Alejandro D. Buren 《Estuarine, Coastal and Shelf Science》2010

Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird “wrecks” (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres (Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2–3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.  相似文献   

Oceanography from Space,Volume 13 in the Marine Science Series,J. F. R. Gower (Ed.), Plenum Press. No. of pages: 978. Price: $95.00     

A. Henderson-Sellers 《Geological Journal》1983,18(2):183-184

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Rapid recharge of fresh water to the halite‐hosted brine aquifer of Salar de Atacama,Chile          下载免费PDF全文

David F. Boutt  Scott A. Hynek  Lee Ann Munk  Lilly G. Corenthal 《水文研究》2016,30(25):4720-4740

We document, analyse, and interpret direct and rapid infiltration of precipitation to the southern margin of the Salar de Atacama halite‐hosted brine aquifer during two intense precipitation events in 2012–2013. We present physical, geochemical, and stable and radioactive isotope data to detail this influx of water. The two events differ distinctly in the mechanisms of recharge. The 2012 event did not produce direct precipitation onto the salar surface, while the 2013 event did. Both events are recorded by abrupt changes in head in observation wells along the halite aquifer margin. Spatially distributed water levels rose by over 30 cm during the larger 2013 event consistent with remotely sensed observations of surface water extent. The lithium concentration and stable isotopic composition of water indicate dilution of brine and dissolution of salt with fresh water. Tritium measurements of precipitation, surface water, and groundwater all indicate modern influx of water to the halite aquifer along the southern margin. We extend these observations by examining the response of the halite aquifer as a whole to precipitation events during the period of 2000–2010. This study suggests that local recharge to the aquifer during sporadic precipitation onto the halite nucleus is an important component of the modern water budget in this hyper‐arid environment. The rapid dissolution and salinization along the southern margin of the salar halite nucleus are aided by such precipitation events contributing a modern fresh water component to the water budget of the economically valuable lithium‐rich brine. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

THE INTERNATIONAL MOBILITY OF LABOR: NORTH AFRICAN MIGRANT WORKERS IN FRANCE*     

Ann M. Oberhauser 《The Professional geographer》1991,43(4):431-445

Since World War II, migrant labor has contributed significantly to Western Europe's economic growth. Initially, industries recruited and hired migrant workers to overcome labor shortages and downward demographic trends within the domestic work force. Since the recession of the mid-1970s, however, migrant labor has faced increasing job loss and restricted entry to many Western European countries. Throughout the postwar period, state immigration policy has supported industry, initially by assisting in the recruitment, and more recently, facilitating the repatriation of migrant workers. Economic and social disparities between developed core and underdeveloped peripheral countries are linked to international labor mobility. Certain sectors in the core benefit from the reserve labor force while emigration from peripheral countries partially contributes to these countries' economic problems. These issues are explored through a case study of the employment of North Africans in the French automobile industry.  相似文献   

Atmospheric physiography and meteoronomical modelling: the future role of geographers in understanding climate     

Ann Henderson‐Sellers 《The Australian geographer》1989,20(1):1-25

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Sub-grid scale precipitation in ALCMs: re-assessing the land surface sensitivity using a single column model     

Andrew J Pitman  Zong-Liang Yang  Ann Henderson-Sellers 《Climate Dynamics》1993,9(1):33-41

The sensitivity of a land surface scheme to the distribution of precipitation within a general circulation model's grid element is investigated. Earlier experiments which showed considerable sensitivity of the runoff and evaporation simulation to the distribution of precipitation are repeated in the light of other results which show no sensitivity of evaporation to the distribution of precipitation. Results show that while the earlier results over-estimated the sensitivity of the surface hydrology to the precipitation distribution, the general conclusion that the system is sensitive is supported. It is found that changing the distribution of precipitation from falling over 100% of the grid square to falling over 10% leads to a reduction in evaporation from 1578 mm y^–1 to 1195 mm y ^–1 while runoff increases from 278 mm y^–1 to 602 mm y^–1. The sensitivity is explained in terms of evaporation being dominated by available energy when precipitation falls over nearly the entire grid square, but by moisture availability (mainly intercepted water) when it falls over little of the grid square. These results also indicate that earlier work using stand-alone forcing to drive land surface schemes off-line, and to investigate the sensitivity of land surface codes to various parameters, leads to results which are non-repeatable in single column simulations.  相似文献   

Sensitivity of ecosystem models to the spatial resolution of the NCAR Community Climate Model CCM2     

C. Ciret  A. Henderson-Sellers 《Climate Dynamics》1998,14(6):409-429

 This study evaluates the sensitivity of ecosystem models to changes in the horizontal resolution of version 2 of the National Centre for Atmospheric Research Community Climate Model (CCM2). A previous study has shown that the distributions of natural ecosystems predicted by vegetation models using coarse resolution present-day climate simulations are poorly simulated. It is usually assumed that increasing the spatial resolution of general circulation models (GCMs) will improve the simulation of climate, and hence will increase our level of confidence in the use of GCM output for impacts studies. The principal goals of this study is to investigate this hypothesis and to identify which biomes are more affected by the changes in spatial resolution of the forcing climate. The ecosystem models used are the BIOME-1 model and a version of the Holdridge scheme. The climate simulations come from a set of experiments in which CCM2 was run with increasing horizontal resolutions. The biome distributions predicted using CCM2 climates are compared against biome distributions predicted using observed climate datasets. Results show that increasing the resolution of CCM2 produces a significant improvement of the global-scale vegetation prediction, indicating that a higher level of confidence can be vested in the global-scale prediction of natural ecosystems using medium and high resolution GCMs. However, not all biomes are equally affected by the increased spatial resolution, and although certain biome distributions are improved (e.g. hot desert, tropical seasonal forest), others remain globally poorly predicted even at high resolution (e.g. grasses and xerophytic woods). In addition, these results show that some climatic biases are enhanced with increasing resolution (e.g. in mountain ranges), resulting in the inadequate prediction of biomes. Received: 4 March 1997 / Accepted: 10 December 1997  相似文献