Defense community perspectives on uncertainty and confidence judgments     

Marcus King  Sherri Goodman 《Climatic change》2011,108(4):803-809

In 2007, the CNA Military Advisory Board (MAB), an expert panel composed of 11 retired admirals and generals from the United States, identified climate change as a “threat multiplier” for instability in some of the most volatile regions of the world. (CNA MAB National security and the threat of climate change 2007)The Department of Defense reached a similar conclusion in last year’s Quadrennial Defense Review–a legislatively mandated analysis of the Defense Department’s strategy and priorities. This document frames the long-term course for policy decision-making at the highest levels. The reports demonstrate that climate change and energy are now mainstream elements of national security planning, and can be assessed within the frameworks used to evaluate other threats, risks, and responses. However, the exact magnitude of the threat posed by climate change is difficult to calibrate in part because the language used by scientists to predict uncertainty and the confidence levels of judgments is not sufficiently clear. The defense community has a vast amount of experience exploring and dealing with uncertainty. Scientists trying to better describe the effects of climate change may be able to draw lessons from the defense community’s approach to uncertainty including how to better communicate findings to wide audiences including policy-makers.  相似文献   

Biogenic carbon flows through the planktonic food web of the Amundsen Gulf (Arctic Ocean): A synthesis of field measurements and inverse modeling analyses   总被引：1，自引：0，他引：1  

Alexandre Forest  Jean-Éric Tremblay  Yves Gratton  Johannie Martin  Jonathan Gagnon  Gérald Darnis  Makoto Sampei  Louis Fortier  Mathieu Ardyna  Michel Gosselin  Hiroshi Hattori  Dan Nguyen  Roxane Maranger  Dolors Vaqué  Cèlia Marrasé  Carlos Pedrós-Alió  Amélie Sallon  Christine Michel  Colleen Kellogg  Jody Deming  Elizabeth Shadwick  Helmuth Thomas  Heike Link  Philippe Archambault  Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436

Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m⁻² calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m⁻², which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m⁻², a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m⁻²), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m⁻²). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain.  相似文献   

Erratum: Seasonal Occurrence of Cownose Rays (<Emphasis Type="Italic">Rhinoptera bonasus</Emphasis>) in North Carolina’s Estuarine and Coastal Waters     

M. April Goodman  Paul B. Conn  Eric Fitzpatrick 《Estuaries and Coasts》2011,34(3):652-652

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In situ U/Pb dating of impact‐produced zircons from the Vargeão Dome (Southern Brazil)     

Anne Nédélec  Jean‐Louis Paquette  Elder Yokoyama  Ricardo I. F. Trindade  Thierry Aigouy  David Baratoux 《Meteoritics & planetary science》2013,48(3):420-431

The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures.  相似文献   

Dynamic Study on Fracture Problems in Viscoelastic Sedimentary Rocks Using the Numerical Manifold Method     

Zhijun Wu  Louis Ngai Yuen Wong  Lifeng Fan 《Rock Mechanics and Rock Engineering》2013,46(6):1415-1427

The viscoelastic deformation behavior of a sedimentary rock under different loading rates is numerically modeled and investigated by the numerical manifold method (NMM). By incorporating a modified 3-element viscoelastic constitutive mode in the NMM, crack initiation and propagation criteria, and crack identification and evolution techniques, the effects of the loading rates on the cracking behavior of a sedimentary rock, such as crack open displacement, crack sliding displacement, crack initiation, crack propagation and final failure mode, are successfully modeled. The numerical results reveal that under a high loading rate (>1,000 MPa/s), due to the viscoelastic property of the sedimentary rock, not only the structural behavior deviates from that of elastic model, but also different cracking processes and final failure modes are obtained.  相似文献   

Temporal relationship between Holocene human occupation and vegetation change along the northwestern margin of the Central African rainforest     

Anne-Marie Lézine  Augustin F.-C. Holl  Judicaël Lebamba  Annie Vincens  Chimène Assi-Khaudjis  Louis Février  Émmanuelle Sultan 《Comptes Rendus Geoscience》2013,345(7-8):327-335

This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area.  相似文献   

Seasonal changes in zooplanktonic alkaline phosphatase activity in Toulon Bay (France): the role of Cypris larvae     

Jean N  Bogé G  Jamet JL  Richard S  Jamet D 《Marine pollution bulletin》2003,46(3):346-352

We studied zooplankton contribution to the total particulate phosphatase activity, the kinetics of this activity, the relation to the different taxonomic groups and the role of particle-bound bacteria. The activity of total particulate material collected from a liter of seawater was more elevated in May, June and August than during the rest of the year. These high activities resulted from a high contribution of the >90 microm fraction which account then for more than 60% of the total particulate activity. Two Michaelian processes with high and low V(max) were disclosed on this fraction. The high V(max) component was responsible for the high summer activities. During these periods, high densities of cirriped Cypris were found which were statistically correlated with this high V(max) component as with its specific activity. Moreover, the contribution of attached bacteria to these high activities was low. In return, this contribution was predominant during the periods of low activity. A simple method was developed to characterise this bacterial activity.  相似文献   

Microstructural Inhomogeneity and Mechanical Anisotropy Associated with Bedding in Rothbach Sandstone     

Laurent Louis  Patrick Baud  Teng-fong Wong 《Pure and Applied Geophysics》2009,166(5-7):1063-1087

This study present the result of conventional triaxial tests conducted on samples of Rothbach sandstone cored parallel, oblique (at 45 degrees) and perpendicular to the bedding at effective pressures ranging from 5 to 250 MPa. Mechanical and microstructural data were used to determine the role of the bedding on mechanical strength and failure mode. We find that samples cored at 45 degrees to the bedding yield at intermediate level of differential stress between the ones for parallel and perpendicular samples at all effective pressures. Strain localization at high confining pressure (i.e., in the compactive domain) is observed in samples perpendicular and oblique to the bedding but not in samples cored parallel to the bedding. However, porosity reduction is comparable whether compactive shear bands, compaction bands or homogeneous cataclastic flow develop. Microstructural data suggest that (1) mechanical anisotropy is controlled by a preferred intergranular contact alignment parallel to the bedding and that (2) localization of compaction is controlled by bedding laminations and grain scale heterogeneity, which both prevent the development of well localized compaction features.  相似文献   

Buried paleo-channels on the New Jersey continental margin: channel porosity structures from electromagnetic surveying     

Rob L. Evans  L. K. Law  B. St. Louis  S. Cheesman 《Marine Geology》2000,170(3-4):381-394

We report on a marine electromagnetic (EM) survey across two portions of the New Jersey continental margin that have been previously shown to contain buried paleo-channels. The EM method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries. Our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity, R, thought to represent a subaerially eroded surface, exposed during the late Wisconsinan glaciation. Channels that cut R are seen through increases in apparent porosity. Another seismically imaged channel sequence, which lies within the outer-shelf sediment wedge sequence above R, does not have an electrical signature, indicating that the sediments above and below the channel boundaries have similar physical properties.  相似文献   

Linear and non-linear theory of a parametric instability of hydrodynamic warps in Keplerian discs     

Charles F. Gammie  Jeremy Goodman  Gordon I. Ogilvie 《Monthly notices of the Royal Astronomical Society》2000,318(4):1005-1016

We consider the stability of warping modes in Keplerian discs. We find them to be parametrically unstable using two lines of attack, one based on three-mode couplings and the other on Floquet theory. We confirm the existence of the instability and investigate its non-linear development in three dimensions, via numerical experiment. The most rapidly growing non-axisymmetric disturbances are the most nearly axisymmetric (low- m ) ones. Finally, we offer a simple, somewhat speculative model for the interaction of the parametric instability with the warp. We apply this model to the masing disc in NGC 4258 and show that, provided the warp is not forced too strongly, parametric instability can fix the amplitude of the warp.  相似文献