Neogastroplites meets Metengonoceras: morphological response of an endemic hoplitid ammonite to a new invader in the mid-Cretaceous Mowry Sea of North America     

Margaret M. Yacobucci 《Cretaceous Research》2004,25(6):122

High levels of morphological variability have been attributed to various ecological and developmental mechanisms, including selection for ecological generalists in an unstable environment, inherent developmental plasticity, and the absence of competitors in an empty ecosystem. The late Albian–early Cenomanian hoplitid ammonite Neogastroplites of the Mowry Sea of North America, notorious for its extreme levels of intraspecific variability, is used as a test case of the idea that a lack of competitors promotes variability. The group responded to the invasion of a second ammonite, the engonoceratid Metengonoceras, into the Mowry Sea by spreading into a previously unoccupied region of morphospace, suggesting possible ecological character displacement and a release from constructional constraints. However, morphological variability did not decrease, as would be predicted by the competition model. The variability of Neogastroplites might instead result from environmental instability or developmental flexibility.  相似文献   

Lags in vegetation response to greenhouse warming   总被引：12，自引：0，他引：12  

Margaret B. Davis 《Climatic change》1989,15(1-2):75-82

Fossil pollen in sediments documents vegetation responses to climatic changes in the past. Beech (Fagus grandifolia), with animal-dispersed seeds, moved across Lake Michigan or around its southern margin, becoming established in Wisconsin about 1000 years after populations were established in Michigan. Hemlock (Tsuga canadensis), with wind-dispersed seeds, colonized a 50,000 km² area in northern Michigan between 6000 and 5000 years ago. These tree species extended ranges northward at average rates of 20–25 km per century. To track climatic changes in the future, caused by the greenhouse effect, however, their range limit would need to move northward 100 km per °C warming, or about 300 km per century, an order of magnitude faster than range extension in the past. Yet range extension in the future would be less efficient than in the past, because advance disjunct colonies have been extirpated by human disturbance, and because the seed source is reduced due to reductions in tree populations following logging. Many species of trees may not be able to disperse rapidly enough to track climate, and woodland herbs, which have less efficient seed dispersal mechanisms, may be in danger of extinction.  相似文献   

“The Deterministic Side of Geostatistics” by A. G. Journel     

Margaret Armstrong 《Mathematical Geosciences》1985,17(8):855-859

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Gases and trace elements in soils at the North Silver Bell deposit, Pima County, Arizona     

Margaret E. Hinkle  Clifford A. Dilbert 《Journal of Geochemical Exploration》1984,20(3):323-336

Soil samples were collected over the North Silver Bell porphyry copper deposit near Tucson, Arizona. Volatile elements and compounds in gases derived from the soils and metallic elements in the soils were analyzed in order: (1) to see which volatile constituents of the soils might be indicative of the ore body or the alteration zones; and (2) to distinguish the ore and alteration zones by comparison of trace elements in the soil.Plots of analytical data on trace elements in soils indicated a typical distribution pattern for metals around a porphyry copper deposit, with copper, molybdenum, and arsenic concentrations higher over the ore body, and zinc, lead, and silver concentrations higher over the alteration zones.Higher than average concentrations of helium, carbon disulfide, and sulfur dioxide adsorbed on soils were found over the ore body, whereas higher concentrations of carbon dioxide and carbonyl sulfide were found over the alteration zones.  相似文献   

Three decades of water quality measurements from the Upper Severn experimental catchments at Plynlimon,Wales: an openly accessible data resource for research,modelling, environmental management and education   总被引：1，自引：0，他引：1  

Colin Neal  Brian Reynolds  Dave Norris  James W. Kirchner  Margaret Neal  Phil Rowland  Heather Wickham  Sarah Harman  Linda Armstrong  Darren Sleep  Alan Lawlor  Clive Woods  Bronwen Williams  Matt Fry  Gwen Newton  Dan Wright 《水文研究》2011,25(24):3818-3830

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Geogas transport in fractured hard rock – Correlations with mining seismicity at 3.54 km depth, TauTona gold mine, South Africa     

Johanna Lippmann-Pipke  Jörg Erzinger  Martin Zimmer  Christian Kujawa  Margaret Boettcher  Esta Van Heerden  Armand Bester  Hannes Moller  Nicole A. Stroncik  Zeev Reches 《Applied Geochemistry》2011,26(12):2134-2146

An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM–DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60 m long were drilled at 3.54 km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N₂, 21% O₂, 1% Ar. The geogas components CO₂, CH₄, He and H₂ show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the ²²²Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5 × 10^-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ?1 × 10⁹ Nm, located within 1000 m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project.  相似文献   

Evolution of Ataúro Island: Temporal constraints on subduction processes beneath the Wetar zone, Banda Arc     

Kim S. Ely  Mike Sandiford  Margaret L. Hawke  David Phillips  Mark Quigley  Joao Edmundo dos Reis 《Journal of Asian Earth Sciences》2011,41(6):477-493

Ataúro is a key to understanding the late stage volcanic and subduction history of the Banda Arc to the north of Timor. A volcanic history of bi-modal subaqueous volcanism has been established and new whole rock and trace element geochemical data show two compositional groups, basaltic andesite and dacite–rhyolite. ⁴⁰Ar/³⁹Ar geochronology of hornblende from rhyo-dacitic lavas confirms that volcanism continued until 3.3 Ma. Following the cessation of volcanism, coral reef marine terraces have been uplifted to elevations of 700 m above sea level. Continuity of the terraces at constant elevations around the island reflects regional-scale uplift most likely linked to sublithospheric processes such as slab detachment. Local scale landscape features of the eastern parts of Ataúro are strongly controlled by normal faults. The continuation of arc-related volcanism on Ataúro until at least 3.3 Ma suggests that subduction of Australian lithosphere continued until near this time. This data is consistent with findings from the earthquake record where the extent of the Wetar seismic gap to a depth of 350 km suggests slab breakoff, as a result of collision, commenced at ∼4 Ma, leading to subsequent regional uplift recorded in elevated terraces on Ataúro and neighbouring islands.  相似文献   

Incorporation of Leucine and Thymidine by Estuarine Phytoplankton: Implications for Bacterial Productivity Estimates     

Margaret R. Mulholland  Andrea M. Rocha  George E. Boneillo 《Estuaries and Coasts》2011,34(2):310-325

Leucine and thymidine incorporation were examined in size-fractionated estuarine communities and in cultures of phytoplankton known to use dissolved organic nitrogen (DON). Cultured phytoplankton species were used to establish that phytoplankton took up leucine and thymidine into protein and DNA, respectively. Subsequently, incorporation of leucine and thymidine was measured in size-fractionated populations collected from the Lafayette River, VA, a eutrophic estuary where resident populations contain bloom-forming phytoplankton known to take up DON, and the Gulf of Mexico during a bloom of the mixotrophic red tide dinoflagellate, Karenia brevis. We examined the efficacy of size fractionation for determining phytoplankton versus bacterial incorporation of leucine and thymidine under conditions employed during bacterial productivity bioassays, and antibiotics were used to distinguish between bacterial and phytoplankton incorporation in cultured and natural populations. Results suggest that cultures and natural assemblages of phytoplankton can take up both leucine and thymidine when supplied at low concentrations (10 and 12 nmol L⁻¹, respectively) and during short incubations (15 min to 1 h). In natural populations, up to 95% of the leucine and thymidine incorporation during short bioassays was recovered in the >5.0-μm size fraction that contained ≤4.2% of the bacterial biomass.  相似文献   

Developing a long-term outlook for the Great Barrier Reef,Australia: A framework for adaptive management reporting underpinning an ecosystem-based management approach     

Kirstin Dobbs  Jon Day  Hilary Skeat  John Baldwin  Fergus Molloy  Laurence McCook  Margaret Johnson  Bruce Elliot  Andrew Skeat  Karen Vohland  David Wachenfeld  Richard Kenchington 《Marine Policy》2011

The Great Barrier Reef Outlook Report 2009 was the first produced in response to a newly legislated requirement for five-yearly reports on the status of and outlook for the Great Barrier Reef. It adopted an ecosystem approach, assessing all habitats and species, ecosystem processes and major uses. By then considering the factors affecting the ecosystem, coupled with an assessment of management effectiveness, it provided a risk-based forward-looking projection for the ecosystem. Rarely has such a comprehensive, ecosystem-based report been produced to guide government action. With no pre-determined path to follow for interpreting the legislative requirements, the Great Barrier Reef Marine Park Authority (GBRMPA) developed a repeatable structure and method for Great Barrier Reef Outlook Reports that impartially and consistently considers the evidence and clearly presents the findings. The GBRMPA worked closely with relevant Australian and Queensland Government agencies as well as researchers, industry representatives and the community while developing the report. That such a report must be produced every five years allows an overview of the effectiveness of management responses to be regularly assessed. It also provides a transparent means of highlighting and tracking emerging risks facing the Great Barrier Reef.  相似文献   

Ecological limits to terrestrial biological carbon dioxide removal   总被引：1，自引：1，他引：0  

Lydia J. Smith  Margaret S. Torn 《Climatic change》2013,118(1):89-103

Terrestrial biological atmospheric carbon dioxide removal (BCDR) through bioenergy with carbon capture and storage (BECS), afforestation/reforestation, and forest and soil management is a family of proposed climate change mitigation strategies. Very high sequestration potentials for these strategies have been reported, but there has been no systematic analysis of the potential ecological limits to and environmental impacts of implementation at the scale relevant to climate change mitigation. In this analysis, we identified site-specific aspects of land, water, nutrients, and habitat that will affect local project-scale carbon sequestration and ecological impacts. Using this framework, we estimated global-scale land and resource requirements for BCDR, implemented at a rate of 1 Pg C y^?1. We estimate that removing 1 Pg C y^?1 via tropical afforestation would require at least 7?×?10⁶ ha y^?1 of land, 0.09 Tg y^?1 of nitrogen, and 0.2 Tg y^?1 of phosphorous, and would increase evapotranspiration from those lands by almost 50 %. Switchgrass BECS would require at least 2?×?10⁸ ha of land (20 times U.S. area currently under bioethanol production) and 20 Tg y^?1 of nitrogen (20 % of global fertilizer nitrogen production), consuming 4?×?10¹²?m³ y^?1 of water. While BCDR promises some direct (climate) and ancillary (restoration, habitat protection) benefits, Pg C-scale implementation may be constrained by ecological factors, and may compromise the ultimate goals of climate change mitigation.  相似文献