Microzooplankton herbivory in the Ross Sea, Antarctica     

David A. Caron  Mark R. Dennett  Darcy J. Lonsdale  Dawn M. Moran  Ludmilla Shalapyonok 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)

Microplankton abundances and phytoplankton mortality rates were determined at six stations during four cruises spanning three seasons in the Ross Sea polynya, Antarctica (early spring, Oct.–Nov. 1996; mid-late summer, Jan.–Feb. 1997; fall, Apr. 1997; mid-late spring, Nov.–Dec. 1997). Rates of microzooplankton herbivory were measured using a modified dilution technique, as well as by examining the rate of disappearance of phytoplankton (chlorophyll) in samples incubated in the dark (i.e. grazing in the absence of phytoplankton growth). Strong seasonal cycles of phytoplankton and microzooplankton abundance were observed during the study. Microzooplankton abundance varied by more than three orders of magnitude during the four cruises, and was positively correlated with phytoplankton biomass over the entire data set. Nevertheless, microzooplankton grazing was insufficient to impact significantly phytoplankton standing stocks during most of the experiments performed in this perenially cold environment. Only thirteen out of a total of 51 experiments yielded phytoplankton mortality rates that were significantly different from zero. The highest mortality rate observed in this study (0.26 d⁻¹) was modest compared with maximal rates that have been observed in temperate and tropical ecosystems. Results from twenty experiments examining the rate of decrease of phytoplankton biomass during incubations in the dark agreed quite well with the results of the dilution experiments performed at the same time. The range of mortality rates for the dark incubations was −0.09–0.06 d⁻¹, and the average was essentially zero (−0.01 d⁻¹). That is, chlorophyll concentration was virtually unchanged in samples incubated in the dark for 3 d. A number of factors appeared to contribute to the very low rates of microbial herbivory observed, including low water temperature, and the size and taxonomic composition of the phytoplankton assemblage. Based on our results we conclude that the seasonal, massive phytoplankton blooms observed in the Ross Sea are due, in part, to low rates of removal by microbial herbivores.  相似文献   

OH megamasers, starburst and AGN activity in Markarian 231     

A. M. S. Richards  J. H. Knapen  J. A. Yates  R. J. Cohen  J. L. Collett  M. M. Wright  M. D. Gray  D. Field 《Monthly notices of the Royal Astronomical Society》2005,364(2):353-366

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Modelling OH in regions of star formation     

R. C. Doel  D. Field  M. D. Gray  R. N. F. Walker 《Astrophysics and Space Science》1990,171(1-2):167-172

There is a large, diverse and rapidly growing body of OH observations from regions associated with star formation, the physical conditions of which are of great interest. To interpret these observations we need to calculate the populations of the OH energy levels using as accurate a model as is feasible. We have developed a large velocity gradient (LVG) model using the lowest 48 hyperfine states of OH and including the phenomenon of far-infrared line overlap using a new theory which treats all thermal and velocity overlaps. If we use a theory of maser propagation (Field and Gray, 1988) we are then able to see how competing maser lines develop.The generic behaviour which we find is in good agreement with the extensive maser observations of Gaume and Mutel 1987 and our calculations allow us to associate general physical conditions with the four ground state maser frequencies. In addition we are able to present preliminary results of the interpretation of the OH absorption observations of Guilloteauet al. (1984) and Walmsleyet al. (1986) for the compactHII region DR21.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain  相似文献   

Flying-fox species and Hendra virus spillover risk: comment on ‘Factors explaining the dispersal of Hendra virus disease in South-East Queensland’ by Burnham and Chong (2016)     

Hume Field  Dan Edson  Craig Smith 《国际地球制图》2017,32(6):697-698

The approach taken by Burnham and Chong to explain the occurrence of Hendra virus incidents in Australia, while analytically valid, is compromised by erroneous and incomplete biological data underpinning the analyses. Firstly, they erroneously state the peak mating, pregnancy and birthing periods in black, grey-headed and little red flying-foxes, thus their related interpretations and conclusions are flawed. Secondly, the reported association between grey-headed flying-fox density and HeV incidents is at odds with recent findings suggesting grey-headed flying-foxes are an insubstantial host. While this broader epidemiological perspective was not within their stated aims, it is appropriate that it be canvassed in discussion of their geo-spatial analyses given the level of horse-industry, public and media interest in Hendra virus and the potential for confusion and mixed messages regarding HeV exposure risk management. We suggest that a broader collaborative cross-disciplinary approach offers synergies that produce robust, real-world ‘one health’ outputs.  相似文献   

Modeling global Hammond landform regions from 250‐m elevation data          下载免费PDF全文

Deniz Karagulle  Charlie Frye  Roger Sayre  Sean Breyer  Peter Aniello  Randy Vaughan  Dawn Wright 《Transactions in GIS》2017,21(5):1040-1060

In 1964, E.H. Hammond proposed criteria for classifying and mapping physiographic regions of the United States. Hammond produced a map entitled “Classes of Land Surface Form in the Forty‐Eight States, USA”, which is regarded as a pioneering and rigorous treatment of regional physiography. Several researchers automated Hammond?s model in GIS. However, these were local or regional in application, and resulted in inadequate characterization of tablelands. We used a global 250 m DEM to produce a new characterization of global Hammond landform regions. The improved algorithm we developed for the regional landform modeling: (1) incorporated a profile parameter for the delineation of tablelands; (2) accommodated negative elevation data values; (3) allowed neighborhood analysis window (NAW) size to vary between parameters; (4) more accurately bounded plains regions; and (5) mapped landform regions as opposed to discrete landform features. The new global Hammond landform regions product builds on an existing global Hammond landform features product developed by the U.S. Geological Survey, which, while globally comprehensive, did not include tablelands, used a fixed NAW size, and essentially classified pixels rather than regions. Our algorithm also permits the disaggregation of “mixed” Hammond types (e.g. plains with high mountains) into their component parts.  相似文献   

Communication with extraterrestrial intelligence (CETI): Edited by Carl Sagan. MIT Press,Cambridge, Mass., 1973. 428 + xxxvi pp. Price $10.00     

George Field 《Icarus》1975,24(1):140-141

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A Benthic Terrain Classification Scheme for American Samoa   总被引：2，自引：0，他引：2  

Emily R. Lundblad  Dawn J. Wright  Joyce Miller  Emily M. Larkin  Ronald Rinehart  David F. Naar  Brian T. Donahue  S. Miles Anderson  Tim Battista 《Marine Geodesy》2006,29(2):89-111

Coral reef ecosystems, the most varied on earth, continually face destruction from anthropogenic and natural threats. The U.S. Coral Reef Task Force seeks to characterize and map priority coral reef ecosystems in the U.S./Trust Territories by 2009. Building upon NOAA Biogeography shallow-water classifications based on Ikonos imagery, presented here are new methods, based on acoustic data, for classifying benthic terrain below 30 m, around Tutuila, American Samoa. The result is a new classification scheme for American Samoa that extends and improves the NOAA Biogeography scheme, which, although developed for Pacific island nations and territories, is only applicable to a maximum depth of 30 m, due to the limitations of satellite imagery. The scheme may be suitable for developing habitat maps pinpointing high biodiversity around coral reefs throughout the western Pacific.  相似文献   

Considering ecosystem-based fisheries management in the California Current     

John C. Field  Robert C. Francis 《Marine Policy》2006

Recognizing that all management decisions have impacts on the ecosystem being exploited, an ecosystem-based approach to management seeks to better inform these decisions with knowledge of ecosystem structure, processes and functions. For marine fisheries in the California Current, along the West Coast of North America, such an approach must take into greater consideration the constantly changing climate-driven physical and biological interactions in the ecosystem, the trophic relationships between fished and unfished elements of the food web, the adaptation potential of life history diversity, and the role of humans as both predators and competitors. This paper reviews fisheries-based ecosystem tools, insights, and management concepts, and presents a transitional means of implementing an ecosystem-based approach to managing US fisheries in the California Current based on current scientific knowledge and interpretation of existing law.  相似文献   

Effect of biogeochemical diagenesis on sediment fabric in shallow marine carbonate sediments near the Dry Tortugas, Florida     

Yoko Furukawa  Dawn Lavoie  Kevin Stephens 《Geo-Marine Letters》1997,17(4):283-290

 Shallow marine carbonate sediments near the Dry Tortugas undergo extensive biogeochemical diagenesis upon deposition, resulting in postdepositional fabric comprised of micritic aggregates of clay-sized particles, a matrix of peloidal mud, and intraparticular cementation. Freshly deposited primary skeletons, mostly Halimeda fragments, yield micritic aggregates of clay-sized particles, which then form peloidal mud fabric upon compaction. The cryptocrystalline particles produced by micritization are later replaced by high magnesian calcite. Cementation is observed in the intra-particular microenvironment. However, no inter-particular, grain-binding cement was detected throughout the gravity core samples investigated.  相似文献   

A Middle Devensian woolly rhinoceros (Coelodonta antiquitatis) from Whitemoor Haye Quarry,Staffordshire (UK): palaeoenvironmental context and significance     

Danielle Schreve  Andy Howard  Andrew Currant  Stephen Brooks  Simon Buteux  Russell Coope  Barnaby Crocker  Michael Field  Malcolm Greenwood  James Greig  Phillip Toms 《第四纪科学杂志》2013,28(2):118-130

This paper reports the discovery of a rare partial skeleton of a woolly rhinoceros (Coelodonta antiquitatis Blumenbach, 1799) and associated fauna from a low Pleistocene terrace of the River Tame at Whitemoor Haye, Staffordshire, UK. A study of the sedimentary deposits around the rhino skeleton and associated organic‐rich clasts containing pollen, plant and arthropod remains suggests that the animal was rapidly buried on a braided river floodplain surrounded by a predominantly treeless, herb‐rich grassland. Highlights of the study include the oldest British chironomid record published to date and novel analysis of the palaeoflow regime using caddisfly remains. For the first time, comparative calculations of coleopteran and chironomid palaeotemperatures have been made on the same samples, suggesting a mean July temperature of 8–11 °C and a mean December temperature of between ?22 and ?16 °C. Radiocarbon age estimates on skeletal material, supported by optically stimulated luminescence ages from surrounding sediments, indicate that the rhino lived around 41–43 k cal a BP. The combined geochronological, stratigraphic and palaeoenvironmental evidence places the assemblage firmly within the Middle Devensian (Marine Oxygen Isotope Stage 3). This would agree with other regional evidence for the timing of aggradation for the lowest terrace of the Trent and its tributary systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献