The morphology of craters on Mercury: Results from MESSENGER flybys     

Olivier S. Barnouin  Maria T. Zuber  David E. Smith  Gregory A. Neumann  Robert R. Herrick  John E. Chappelow  Scott L. Murchie  Louise M. Prockter 《Icarus》2012,219(1):414-427

Topographic data measured from the Mercury Laser Altimeter (MLA) and the Mercury Dual Imaging System (MDIS) aboard the MESSENGER spacecraft were used for investigations of the relationship between depth and diameter for impact craters on Mercury. Results using data from the MESSENGER flybys of the innermost planet indicate that most of the craters measured with MLA are shallower than those previously measured by using Mariner 10 images. MDIS images of these same MLA-measured craters show that they have been modified. The use of shadow measurement techniques, which were found to be accurate relative to the MLA results, indicate that both small bowl-shaped and large complex craters that are fresh possess depth-to-diameter ratios that are in good agreement with those measured from Mariner 10 images. The preliminary data also show that the depths of modified craters are shallower relative to fresh ones, and might provide quantitative estimates of crater in-filling by subsequent volcanic or impact processes. The diameter that defines the transition from simple to complex craters on Mercury based on MESSENGER data is consistent with that reported from Mariner 10 data.  相似文献   

Biogeochemical and ecological functioning of the low-salinity water lenses in the region of the Rhone River freshwater influence,NW Mediterranean Sea     

Frédéric Diaz  Jean-Jacques Naudin  Claude Courties  Peggy Rimmelin  Louise Oriol 《Continental Shelf Research》2008

A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.  相似文献   

The role of innovation in advancing understanding of hydrological processes     

Louise J. Bracken  Ladan Cockshut  Jenny Taylor  Sarah Cotterill 《水文研究》2020,34(23):4404-4416

Innovation and understanding hydrological processes are intimately linked. Existing research has demonstrated the role of technological, societal, and political drivers in shaping and delivering new understandings in hydrological processes. In this paper we pose three research questions to explore how innovation can further our understanding of hydrological processes, if working towards the sustainable development goals (SDGs) provides a helpful focus, and whether specific mechanisms can be used to facilitate innovation and research into hydrological processes. First, we examine key aspects of innovation and explore innovation in the context of water security. We then present a series of innovation projects to determine their effectiveness in delivering innovation in managing hydrological processes, but also their contribution to scientific understanding. Our research suggests that product and process innovation were more closely related to increasing scientific understanding of hydrological processes than other forms of innovation. The NE Water Hub demonstrated that the design of the innovation ecosystem was crucial to its success and provides a model to integrate innovation and research more widely to further scientific understanding and deliver behaviour change to address the SDGs.  相似文献   

EUREC<Superscript>4</Superscript>A: A Field Campaign to Elucidate the Couplings Between Clouds,Convection and Circulation     

Sandrine Bony  Bjorn Stevens  Felix Ament  Sebastien Bigorre  Patrick Chazette  Susanne Crewell  Julien Delanoë  Kerry Emanuel  David Farrell  Cyrille Flamant  Silke Gross  Lutz Hirsch  Johannes Karstensen  Bernhard Mayer  Louise Nuijens  James H. RuppertJr.  Irina Sandu  Pier Siebesma  Sabrina Speich  Frédéric Szczap  Julien Totems  Raphaela Vogel  Manfred Wendisch  Martin Wirth 《Surveys in Geophysics》2017,38(6):1529-1568

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.  相似文献   

Greenland and Antarctica Ice Sheet Mass Changes and Effects on Global Sea Level   总被引：1，自引：0，他引：1  

Rene Forsberg  Louise Sørensen  Sebastian Simonsen 《Surveys in Geophysics》2017,38(1):89-104

Thirteen years of GRACE data provide an excellent picture of the current mass changes of Greenland and Antarctica, with mass loss in the GRACE period 2002–2015 amounting to 265 ± 25 GT/year for Greenland (including peripheral ice caps), and 95 ± 50 GT/year for Antarctica, corresponding to 0.72 and 0.26 mm/year average global sea level change. A significant acceleration in mass loss rate is found, especially for Antarctica, while Greenland mass loss, after a corresponding acceleration period, and a record mass loss in the summer of 2012, has seen a slight decrease in short-term mass loss trend. The yearly mass balance estimates, based on point mass inversion methods, have relatively large errors, both due to uncertainties in the glacial isostatic adjustment processes, especially for Antarctica, leakage from unmodelled ocean mass changes, and (for Greenland) difficulties in separating mass signals from the Greenland ice sheet and the adjacent Canadian ice caps. The limited resolution of GRACE affects the uncertainty of total mass loss to a smaller degree; we illustrate the “real” sources of mass changes by including satellite altimetry elevation change results in a joint inversion with GRACE, showing that mass change occurs primarily associated with major outlet glaciers, as well as a narrow coastal band. For Antarctica, the primary changes are associated with the major outlet glaciers in West Antarctica (Pine Island and Thwaites Glacier systems), as well as on the Antarctic Peninsula, where major glacier accelerations have been observed after the 2002 collapse of the Larsen B Ice Shelf.  相似文献   

Lipid biomarkers and bacterial lipase activities as indicators of organic matter and bacterial dynamics in contrasted regimes at the DYFAMED site, NW Mediterranean     

Nicolas Bourguet  Madeleine Goutx  Jean-Franois Ghiglione  Mireille Pujo-Pay  Genevive Mvel  Andr Momzikoff  Laure Mousseau  Catherine Guigue  Nicole Garcia  Patrick Raimbault  Romain Pete  Louise Oriol  Dominique Lefvre 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1454-1469

This study investigated the relationships between dissolved organic matter (DOM) composition and bacterial dynamics on short time scale during spring mesotrophic (March 2003) and summer oligotrophic (June 2003) regimes, in a 0–500 m depth water column with almost no advection, at the DYFAMED site, NW Mediterranean. DOM was characterized by analyzing dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and lipid class biotracers. Bacterial dynamic was assessed through the measurement of in situ bacterial lipase activity, abundance, production and bacterial community structure. We made the assumption that by coupling the ambient concentration of hydrolysable acyl-lipids with the measurement of their in situ bacterial hydrolysis rates (i.e. the free fatty acids release rate) would provide new insights about bacterial response to change in environmental conditions. The seasonal transition from spring to summer was accompanied by a significant accumulation of excess DOC (+5 μM) (ANOVA, p<0.05, n=8) in the upper layer (0–50 m). In this layer, the free fatty acids release rate to the bacterial carbon demand (BCD) ratio increased from 0.6±0.3 in March to 1.3±1.0 in June (ANOVA, p<0.05, n=8) showing that more uncoupling between the hydrolysis of the acyl-lipids and the BCD occurred during the evolution of the season, and that free fatty acids contributed to the excess DOC. The increase of lipolysis index and CDOM absorbance (from 0.24±0.17 to 0.39±0.13 and from 0.076±0.039 to 0.144±0.068; ANOVA, p<0.05, n=8, respectively), and the higher contribution of triglycerides, wax esters and phospholipids (from <5% to 12–31%) to the lipid pool reflected the change in the DOM quality. In addition to a strong increase of bacterial lipase activity per cell (51.4±29.4–418.3±290.6 Ag C cell⁻¹ h⁻¹), a significant percentage of ribotypes (39%) was different between spring and summer in the deep chlorophyll maximum (DCM) layer in particular, suggesting a shift in the bacterial community structure due to the different trophic conditions. At both seasons, in the chlorophyll layers, diel variations of DOM and bacterial parameters reflected a better bioavailability and/or DOM utilization by bacteria at night (the ratio of free fatty acids release rate to bacterial carbon demand decreased), most likely related to the zooplankton trophic behaviour. In mesotrophic conditions, such day/night pattern was driving changes in the bacterial community structure. In more oligotrophic period, diel variations in bacterial community structure were depth dependent in relation to the strong summer stratification.  相似文献   

Lateglacial/early Holocene palaeoenvironments in the southern North Sea Basin: new data from the Dudgeon offshore wind farm          下载免费PDF全文

Alex Brown  John Russell  Rob Scaife  Louise Tizzard  John Whittaker  Sarah F. Wyles 《第四纪科学杂志》2018,33(6):597-610

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Preparing California for a changing climate     

Louise Bedsworth  Ellen Hanak 《Climatic change》2012,111(1):1-4

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Air quality planning in California’s changing climate     

Louise Bedsworth 《Climatic change》2012,111(1):101-118

California is home to some of the worst air quality in the nation and ninety percent of the state’s population lives in areas that are out of attainment with at least one of the National Ambient Air Quality Standards. Increasing temperatures associated with climate change will make meeting air quality standards more difficult. Under a changing climate, additional emission reductions will be needed to achieve clean air standards. These additional emission reductions and associated costs are called the “climate penalty.” Air quality planning is the process of assessing the emission reductions needed to meet air quality standards and outlining the programs and policies that will be implemented to achieve these emission reductions. This paper reviews the challenges that a changing climate will pose for air quality planning in California and identifies opportunities for adaptation. While state air quality regulators in California are taking enormous strides to address global warming, less work is happening at the regional, air district level. Air districts are the agencies responsible for developing air quality improvement plans. An important first step for regional air quality regulators will be to quantify the climate penalty and understand their region’s vulnerability to climate change. Limitations in regulatory authority could impede measures to improve preparedness. Regional agencies will likely need to look to state and federal agencies for additional emission reductions.  相似文献   

The effects of deformation and permeability variation in controlling the formation of uranium deposits in the Alligator Rivers region,Northern Territory,Australia     

Peter Schaubs  Louise Fisher 《Journal of Geochemical Exploration》2009

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