Upper-ocean transport mechanisms from the Gulf of Maine to Georges Bank, with implications for Calanus supply     

C.G. Hannah  C.E. Naimie  J.W. Loder  F.E. Werner 《Continental Shelf Research》1997,17(15):1887-1911

Potential upper-ocean pathways for the supply of biota from the Gulf of Maine to Georges Bank are investigated by numerically tracking particles in realistic 3-d seasonal-mean and tidal flow fields. The flow fields, obtained from a prognostic model forced by observed M₂ tides and seasonal-mean wind stress and density fields, include the major known observational features of the circulation regime in winter, spring and summer — a wind-driven surface layer (in winter and early spring) overlying seasonally-evolving baroclinic and tidally-rectified topographic gyres. The surface layer in winter and early spring, with generally southward drift for typical northwesterly wind stress, can act as a conveyor belt for the transport of biota to Georges Bank, provided that the biota can spend a substantial fraction of time in the surface Ekman layer. The numerical experiments indicate that the upper-ocean drift pathways for biota in the southern Gulf of Maine are strongly sensitive to biological and/or physical processes affecting vertical position in relation to the surface Ekman layer and horizontal position in relation to topographic gyres. The seasonality and location of the identified pathways are generally consistent with observed distributional patterns of Calanus finmarchicus based on the 11-year MARMAP surveys.  相似文献   

Regional modeling of climate change impacts on smallholder agriculture and ecosystems in Central America     

Lee Hannah  Camila I. Donatti  Celia A. Harvey  Eric Alfaro  Daniel Andres Rodriguez  Claudia Bouroncle  Edwin Castellanos  Freddy Diaz  Emily Fung  Hugo G. Hidalgo  Pablo Imbach  Peter Läderach  Jason P. Landrum  Ana Lucía Solano 《Climatic change》2017,141(1):29-45

Climate change will have serious repercussions for agriculture, ecosystems, and farmer livelihoods in Central America. Smallholder farmers are particularly vulnerable due to their reliance on agriculture and ecosystem services for their livelihoods. There is an urgent need to develop national and local adaptation responses to reduce these impacts, yet evidence from historical climate change is fragmentary. Modeling efforts help bridge this gap. Here, we review the past decade of research on agricultural and ecological climate change impact models for Central America. The results of this review provide insights into the expected impacts of climate change and suggest policy actions that can help minimize these impacts. Modeling indicates future climate-driven changes, often declines, in suitability for Central American crops. Declines in suitability for coffee, a central crop in the regional economy, are noteworthy. Ecosystem models suggest that climate-driven changes are likely at low- and high-elevation montane forest transitions. Modeling of vulnerability suggests that smallholders in many parts of the region have one or more vulnerability factors that put them at risk. Initial adaptation policies can be guided by these existing modeling results. At the same time, improved modeling is being developed that will allow policy action specifically targeted to vulnerable groups, crops, and locations. We suggest that more robust modeling of ecological responses to climate change, improved representation of the region in climate models, and simulation of climate influences on crop yields and diseases (especially coffee leaf rust) are key priorities for future research.  相似文献   

Hydrogen bond effects on compressional behavior of isotypic minerals: high-pressure polymorphism of cristobalite-like Be(OH)<Subscript>2</Subscript>     

Hannah Shelton  Madison C. Barkley  Robert T. Downs  Ronald Miletich  Przemyslaw Dera 《Physics and Chemistry of Minerals》2016,43(8):571-586

Three isotypic crystals, SiO₂ (α-cristobalite), ε-Zn(OH)₂ (wülfingite), and Be(OH)₂ (β-behoite), with topologically identical frameworks of corner-connected tetrahedra, undergo displacive compression-driven phase transitions at similar pressures (1.5–2.0 GPa), but each transition is characterized by a different mechanism resulting in different structural modifications. In this study, we report the crystal structure of the high-pressure γ-phase of beryllium hydroxide and compare it with the high-pressure structures of the other two minerals. In Be(OH)₂, the transition from the ambient β-behoite phase with the orthorhombic space group P2₁2₁2₁ and ambient unit cell parameters a = 4.5403(4) Å, b = 4.6253(5) Å, c = 7.0599(7) Å, to the high-pressure orthorhombic γ-polymorph with space group Fdd2 and unit cell parameters (at 5.3(1) GPa) a = 5.738(2) Å, b = 6.260(3) Å, c = 7.200(4) Å takes place between 1.7 and 3.6 GPa. This transition is essentially second order, is accompanied by a negligible volume discontinuity, and exhibits both displacive and reversible character. The mechanism of the phase transition results in a change to the hydrogen bond connectivities and rotation of the BeO₄ tetrahedra.  相似文献   

Catalyzing mitigation ambition under the Paris Agreement: elements for an effective Global Stocktake     

Lukas Hermwille  Anne Siemons  Hannah Förster  Louise Jeffery 《Climate Policy》2019,19(8):988-1001

The Global Stocktake (GST) takes a central role within the architecture of the Paris Agreement, with many hoping that it will become a catalyst for increased mitigation ambition. This paper outlines four governance functions for an ideal GST: pacemaker, ensurer of accountability, driver of ambition and provider of guidance and signal. The GST can set the pace of progress by stimulating and synchronizing policy processes across governance levels. It can ensure accountability of Parties through transparency and public information sharing. Ambition can be enhanced through benchmarks for action and transformative learning. By reiterating and refining the long term visions, it can echo and amplify the guidance and signal provided by the Paris Agreement. The paper further outlines preconditions for the effective performance of these functions. Process-related conditions include: a public appraisal of inputs; a facilitative format that can develop specific recommendations; high-level endorsement to amplify the message and effectively inform national climate policy agendas; and an appropriate schedule, especially with respect to the transparency framework. Underlying information provided by Parties complemented with other (scientific) sources needs to enable benchmark setting for collective climate action, to allow for transparent assessments of the state of emissions and progress of a low-carbon transformation. The information also needs to be politically relevant and concrete enough to trigger enhancement of ambition. We conclude that meeting these conditions would enable an ideal GST and maximize its catalytic effect.

Key policy insights

• The functional argument developed in this article may inspire a purposeful design of the GST as its modalities and procedures are currently being negotiated.

• The analytical framework provided serves as a benchmark against which to assess the GST's modalities and procedures.

• Gaps and blind spots in the official GST can and should be addressed by processes external to the climate regime in academia and civil society.

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Erratum to: The Alpine nappe stack in western Austria: a crustal-scale cross section     

Hannah Pomella  Hugo Ortner  Michael Zerlauth  Bernhard Fügenschuh 《International Journal of Earth Sciences》2015,104(3):747-748

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Petrology and geochemistry of the 2014–2015 Holuhraun eruption,central Iceland: compositional and mineralogical characteristics,temporal variability and magma storage     

S?mundur?A.?HalldórssonEmail author  Enik??Bali  Margaret?E.?Hartley  David?A.?Neave  David?W.?Peate  Guemundur?H.?Guefinnsson  Ilya?Bindeman  Martin?J.?Whitehouse  Morten?S.?Riishuus  Gro?B.?M.?Pedersen  Sigureur?Jakobsson  Rob?Askew  Catherine?R.?Gallagher  Esther?R.?Guemundsdóttir  Jónas?Gudnason  William?M.?Moreland  Birgir?V.?óskarsson  Paavo?Nikkola  Hannah?I.?Reynolds  Johanne?Schmith  Thorvaldur?Thordarson 《Contributions to Mineralogy and Petrology》2018,173(8):64

The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n?=?62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014–2015 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Bárðarbunga volcanic system, consistent with seismic observations for magma ascent close to the Bárðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8?±?5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with the efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, requires a more complex earlier magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions.  相似文献   

Predicting river ecosystem response to glacial meltwater dynamics: a case study of quantitative water sourcing and glaciality index approaches     

Lee E. Brown  Alexander M. Milner  David M. Hannah 《Aquatic Sciences - Research Across Boundaries》2010,72(3):325-334

Glacier retreat and thinning are occurring in many regions of the world, leading to significant changes in river discharge, water quality and aquatic ecosystems. Therefore, it is increasingly necessary for environmental scientists and managers to develop and adopt methods that link changes in meltwater dynamics and biotic response to better understand and predict future ecosystem change in glacially influenced rivers. To this end, two approaches have been developed recently: (1) the ARISE quantitative meltwater contribution approach of Brown et al. (Freshw Biol 54:1357–1369, 2009b) and (2) the glaciality index (GI) of Ilg and Castella (Freshw Biol 51:840–853, 2006), which provides a measure of glacial runoff influence on stream ecosystems based on four environmental variables (water temperature, channel stability, electrical conductivity and suspended sediment concentration). However, the relative performance and potential complementarities of these two approaches have yet to be evaluated. We conducted a methodological comparison using detailed hydrological, water quality and biological datasets collected over two summers in the French Pyrénées. Analyses revealed strong and significant correlation between ARISE meltwater contributions and the GI. However, the ARISE approach performed better when differentiating glacial influence between streams and over time. Both approaches were significant predictors of macroinvertebrate taxonomic richness, beta diversity, the number of EPT genera and total abundance, although regression models were typically stronger for the ARISE meltwater contribution approach. At the species level, ARISE performed better for predicting the abundance of 13 of the 20 most common taxa. We propose both approaches are valuable for assessing the effects of decreasing meltwater contributions on river ecosystems at the community level but this case study suggests ARISE was better able to identify subtle differences in hydrological change, community response and the abundance of individual taxa. Comparative studies from other catchments are required to further evaluate the two methods.  相似文献   

Entanglements of marine mammals and seabirds in central California and the north-west coast of the United States 2001-2005     

Emma Moore  Shannon Lyday  Kate Litle  Hannah Nevins  Joe Mortenson  Melanie Piazza  Derek Lee  Sarah Allen 《Marine pollution bulletin》2009,58(7):1045-1051

Entanglement records for seabirds and marine mammals were investigated for the period 2001-2005. The entanglement records were extracted from databases maintained by seven organizations operating along the west coast of the United States of America. Their programmes included beach monitoring surveys, rescue and rehabilitation and regional pinniped censuses. Records of 454 entanglements were documented in live animals and in carcasses for 31 bird species and nine marine mammal species. The most frequently entangled species were Common Murres, Western Gulls and California sea lions. The entanglement materials identified were primarily fishing related. Entanglements were recorded every year suggesting that although the incidence level differs annually, entanglement is a persistent problem. It is recommended that each programme records details in standardized categories to determine entanglement material sources. Numbers of entanglements observed during these surveys are likely to be a conservative view of the actual entanglement rate taking place at sea.  相似文献   

River temperature regimes of England and Wales: spatial patterns,inter‐annual variability and climatic sensitivity          下载免费PDF全文

Grace Garner  David M. Hannah  Jonathan P. Sadler  Harriet G. Orr 《水文研究》2014,28(22):5583-5598

Identification of the most sensitive hydrological regions to a changing climate is essential to target adaptive management strategies. This study presents a quantitative assessment of spatial patterns, inter‐annual variability and climatic sensitivity of the shape (form) and magnitude (size) of annual river/stream water temperature regimes across England and Wales. Classification of long‐term average (1989–2006) annual river (air) temperature regime dynamics at 88 (38) stations within England and Wales identified spatially differentiable regions. Emergent river temperature regions were used to structure detailed hydroclimatological analyses of a subset of 38 paired river and air temperature stations. The shape and magnitude of air and water temperature regimes were classified for individual station‐years; and a sensitivity index (SI, based on conditional probability) was used to quantify the strength of associations between river and air temperature regimes. The nature and strength of air–river temperature regime links differed between regions. River basin properties considered to be static over the timescale of the study were used to infer modification of air–river temperature links by basin hydrological processes. The strongest links were observed in regions where groundwater contributions to runoff (estimated by basin permeability) were smallest and water exposure time to the atmosphere (estimated by basin area) was greatest. These findings provide a new large‐scale perspective on the hydroclimatological controls driving river thermal dynamics and, thus, yield a scientific basis for informed management and regulatory decisions concerning river temperature within England and Wales. © 2013 The Authors. Hydrological Processes published by John Wiley & Sons, Ltd.  相似文献   

The Monitoring Network of the Vancouver 2010 Olympics   总被引：1，自引：0，他引：1  

Paul Joe  Bill Scott  Chris Doyle  George Isaac  Ismail Gultepe  Douglas Forsyth  Stewart Cober  Edwin Campos  Ivan Heckman  Norman Donaldson  David Hudak  Roy Rasmussen  Paul Kucera  Ron Stewart  Julie M. Thériault  Teresa Fisico  Kristen L. Rasmussen  Hannah Carmichael  Alex Laplante  Monika Bailey  Faisal Boudala 《Pure and Applied Geophysics》2014,171(1-2):25-58

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