Control of the repeatability of high frequency multibeam echosounder backscatter by using natural reference areas     

Marc Roche  Koen Degrendele  Christophe Vrignaud  Sophie Loyer  Tim Le Bas  Jean-Marie Augustin  Xavier Lurton 《Marine Geophysical Researches》2018,39(1-2):89-104

The increased use of backscatter measurements in time series for environmental monitoring necessitates the comparability of individual results. With the current lack of pre-calibrated multibeam echosounder systems for absolute backscatter measurement, a pragmatic solution is the use of natural reference areas for ensuring regular assessment of the backscatter measurement repeatability. This method mainly relies on the assumption of a sufficiently stable reference area regarding its backscatter signature. The aptitude of a natural area to provide a stable and uniform backscatter response must be carefully considered and demonstrated by a sufficiently long time-series of measurements. Furthermore, this approach requires a strict control of the acquisition and processing parameters. If all these conditions are met, stability check and relative calibration of a system are possible by comparison with the averaged backscatter values for the area. Based on a common multibeam echosounder and sampling campaign completed by available bathymetric and backscatter time series, the suitability as a backscatter reference area of three different candidates was evaluated. Two among them, Carré Renard and Kwinte, prove to be excellent choices, while the third one, Western Solent, lacks sufficient data over time, but remains a valuable candidate. The case studies and the available backscatter data on these areas prove the applicability of this method. The expansion of the number of commonly used reference areas and the growth of the number of multibeam echosounder controlled thereon could greatly contribute to the further development of quantitative applications based on multibeam echosounder backscatter measurements.  相似文献   

Zooplankton and forage fish species off Peru: Large-scale bottom-up forcing and local-scale depletion   总被引：6，自引：5，他引：1  

Patricia Ayn  Gordon Swartzman  Arnaud Bertrand  Mariano Gutirrez  Sophie Bertrand 《Progress in Oceanography》2008,79(2-4):208

The Humboldt Current System, like all upwelling systems, has dramatic quantities of plankton-feeding fish, which suggested that their population dynamics may ‘drive’ or ‘control’ ecosystem dynamics. With this in mind we analysed the relationship between forage fish populations and their main prey, zooplankton populations. Our study combined a zooplankton sampling program (1961–2005) with simultaneous acoustic observations on fish from 40 pelagic surveys (1983–2005) conducted by the Peruvian Marine Research Institute (IMARPE) and landing statistics for anchoveta (Engraulis ringens) and sardine (Sardinops sagax) along the Peruvian coast from 1961 to 2005. The multi-year trend of anchoveta population abundance varied consistently with zooplankton biovolume trend, suggesting bottom-up control on anchovy at the population scale (since oceanographic conditions and phytoplankton production support the changes in zooplankton abundance). For a finer-scale analysis (km) we statistically modelled zooplankton biovolume as a function of geographical (latitude and distance from the 200-m isobath), environmental (sea surface temperature), temporal (year, month and time-of-day) and biological (acoustic anchovy and sardine biomass within 5 km of each zooplankton sample) covariates over all survey using both classification and regression trees (CART) and generalized additive models (GAM). CART showed local anchoveta density to have the strongest effect on zooplankton biovolume, with significantly reduced levels of biovolume for higher neighbourhood anchoveta biomass. Additionally, zooplankton biovolume was higher offshore than on the shelf. GAM results corroborated the CART findings, also showing a clear diel effect on zooplankton biovolume, probably due to diel migration or daytime net avoidance. Apparently, the observed multi-year population scale bottom-up control is not inconsistent with local depletion of zooplankton when anchoveta are locally abundant, since the latter effect was observed over a wide range of overall anchoveta abundance.  相似文献   

Foraging ecology of an endemic shorebird, the African Black Oystercatcher (Haematopus moquini) on the south–east coast of South Africa     

Sophie Kohler  Bo Bonnevie  Christopher McQuaid  Sbastien Jaquemet 《Estuarine, Coastal and Shelf Science》2009,84(3):361-366

We investigated small–medium (1–300 km) scale variation in the foraging ecology of the African Black Oystercatcher during its breeding season, using traditional diet analysis coupled with carbon and nitrogen stable isotope analysis. Fieldwork was conducted between January and March 2006 and 2007, on rocky shores on the south–east coast of South Africa at East London, Kenton and Port Elizabeth. Middens of shelled prey left by adults feeding their chicks were collected from five territories and the abundances of the collected prey on the foraging areas were estimated using quadrats. Blood samples from 45 birds (16 females, 10 males and 19 chicks) and tissues from the predominant prey species on the territory of each breeding pair were collected for isotope analysis. The Manly–Chesson selectivity index revealed that adults feed their chicks preferentially with the limpet Scutellastra cochlear and the Mediterranean mussel Mytilus galloprovincialis, if available. A slight enrichment in the ¹⁵N stable-carbon isotope signature was observed towards the west in both prey and oystercatchers. Differences in isotope signatures between males and females from the same breeding pair indicate sex-related differences in the diet. Both had signatures indicating a mixed diet, but with males exhibiting a signature closer to that of limpets and females closer to that of mussels. In the single case where mussels were rare on the feeding territory, the two members of a pair showed carbon signatures which were identical and very similar to that of limpets. These results indicate dietary partitioning between genders in breeding pairs.  相似文献   

The relationship of anchovy and sardine to water masses in the Peruvian Humboldt Current System from 1983 to 2005   总被引：6，自引：1，他引：6  

Gordon Swartzman  Arnaud Bertrand  Mariano Gutirrez  Sophie Bertrand  Luis Vasquez 《Progress in Oceanography》2008,79(2-4):228

The Humboldt Current System (HCS) is dominated by two pelagic species; Peruvian anchovy or anchoveta (Engraulis ringens) and sardine (Sardinops sagax). Using data from 43 acoustic surveys conducted from 1983 through 2005 by the Peruvian Marine Institute (IMARPE), we examined the distribution of these two species relative to water masses. We tested the hypothesis that anchovy was found more frequently in upwelled cold coastal water (CCW) and mixed waters (MCW) than in other water types and that sardine was more associated with more offshore oceanic surface subtropical water (SSW). Surface temperature, salinity, latitude, season and distance to the coast data were used to define water masses. Results using generalized additive models (GAM), modelling sardine and anchovy presence–absence as a function of year, water body, bottom depth and latitude, showed that anchovy were primarily found in CCW and MCS, while sardine were more ubiquitous relative to water masses with some predilection for SSW. These results were supported by various indexes of anchovy and sardine distribution versus water mass as well as temporal and location variables.  相似文献   

Record of plate boundary metamorphism during Gondwana breakup from Lu–Hf garnet geochronology of the Alpine Schist,New Zealand          下载免费PDF全文

Sophie I. Briggs  John M. Cottle  Matthijs A. Smit 《Journal of Metamorphic Geology》2018,36(7):821-841

The Zealandia portion of the Pacific–Gondwana margin underwent widespread extension, fragmentation, separation and subsidence during the final stages in the breakup of Gondwana. Although these processes shaped the geology of New Zealand, their timing and the timing of subduction cessation in the region remain unclear. To investigate the timing of these processes, we used Lu–Hf garnet geochronology to date six samples of the Alpine Schist, which represents the metamorphic section of the former Zealandia margin. The garnet dates range from 97.3 ± 0.3 to 75.4 ± 1.3 Ma. Compositional zoning in garnet indicates that the spread in ages results from diachronous metamorphism in the upper plate at the Pacific–Gondwana margin, occurring concurrently with rifting of Zealandia from East Gondwana via opening of the Tasman Sea. Clear spatial trends in the timing of garnet growth throughout the Alpine Schist are absent, indicating that either regional age trends were offset by post‐metamorphic deformation, or that metamorphism did not result from a single regional heat source, and was instead driven by short‐duration, spatially dispersed processes such as episodic fluid‐fluxing or mechanical heating. Diachronous metamorphism of the Alpine Schist can be attributed to heat conduction from the rising upper mantle during widespread extension, progressive burial and heating of accretionary wedge sediments during ongoing horizontal shortening, or fluid‐fluxing sourced from a subducting and dehydrating Hikurangi Plateau. These results indicate that during separation of Zealandia from East Gondwana in the late Cretaceous, the crust at the Pacific–Gondwana margin remained hot, potentially facilitating the extensive thinning of the Zealandia lithosphere during this time.  相似文献   

Quantification of cloud water interception in the canopy vegetation from fog gauge measurements          下载免费PDF全文

Christian Gonzalo Domínguez  Miguel Francisco García Vera  Cédric Chaumont  Julien Tournebize  Marcos Villacís  Noemi d'Ozouville  Sophie Violette 《水文研究》2017,31(18):3191-3205

With changes in climate looming, quantifying often‐overlooked components of the canopy water budget, such as cloud water interception (CWI), is increasingly important. Commonly, CWI quantification requires detailed continuous measurements, which is extremely challenging, especially when throughfall is included. In this study, we propose a simplified approach to estimate CWI using the Rutter‐type interception model, where CWI inputs in the canopy vegetation are proportional to fog interception measured by an artificial fog gauge. The model requires the continuous acquisition of meteorological variables as input and calibration datasets. Throughfall measurements below the forest are used only for calibration and validation of the model; thus, CWI estimates can be provided even after the cessation of throughfall monitoring. This approach provides an indirect and undemanding way to quantify CWI by vegetation and allows the identification of its controlling factors, which could be useful to the comparison of CWI in contrasting land covers. The method is applied on a 2‐year dataset collected in an endemic highland forest of San Cristobal Island (Galapagos). Our results show that CWI reaches 21% ± 6% of the total water input during the first year, and 9% ± 2% during the second one. These values represent 32% ± 10% and 17% ± 5% of water inputs during the cool foggy season of the first and second year, respectively. The difference between seasons is attributed to a lower fog liquid water during the second season.  相似文献   

The dynamical structure of intense Mediterranean cyclones     

Emmanouil Flaounas  Shira Raveh-Rubin  Heini Wernli  Philippe Drobinski  Sophie Bastin 《Climate Dynamics》2015,44(9-10):2411-2427

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Interactions between groundwater and seasonally ice‐covered lakes: Using water stable isotopes and radon‐222 multilayer mass balance models          下载免费PDF全文

Marie Arnoux  Elisabeth Gibert‐Brunet  Florent Barbecot  Sophie Guillon  John Gibson  Aurélie Noret 《水文研究》2017,31(14):2566-2581

Interactions between lakes and groundwater are of increasing concern for freshwater environmental management but are often poorly characterized. Groundwater inflow to lakes, even at low rates, has proven to be a key in both lake nutrient balances and in determining lake vulnerability to pollution. Although difficult to measure using standard hydrometric methods, significant insight into groundwater–lake interactions has been acquired by studies applying geochemical tracers. However, the use of simple steady‐state, well‐mixed models, and the lack of characterization of lake spatiotemporal variability remain important sources of uncertainty, preventing the characterization of the entire lake hydrological cycle, particularly during ice‐covered periods. In this study, a small groundwater‐connected lake was monitored to determine the annual dynamics of the natural tracers, water stable isotopes and radon‐222, through the implementation of a comprehensive sampling strategy. A multilayer mass balance model was found outperform a well‐mixed, one‐layer model in terms of quantifying groundwater fluxes and their temporal evolution, as well as characterizing vertical differences. Water stable isotopes and radon‐222 were found to provide complementary information on the lake water budget. Radon‐222 has a short response time, and highlights rapid and transient increases in groundwater inflow, but requires a thorough characterization of groundwater radon‐222 activity. Water stable isotopes follow the hydrological cycle of the lake closely and highlight periods when the lake budget is dominated by evaporation versus groundwater inflow, but continuous monitoring of local meteorological parameters is required. Careful compilation of tracer evolution throughout the water column and over the entire year is also very informative. The developed models, which are suitable for detailed, site‐specific studies, allow the quantification of groundwater inflow and internal dynamics during both ice‐free and ice‐covered periods, providing an improved tool for understanding the annual water cycle of lakes.  相似文献   

On the use of imagery for climate change engagement     

Saffron J. O’Neill  Maxwell Boykoff  Simon Niemeyer  Sophie A. Day 《Global Environmental Change》2013,23(2):413-421

This article answers calls from scholars to attend to a research gap concerning the visual representation of climate change. We present results from three Q-methodology workshops held in Melbourne (Australia), Norwich (UK) and Boulder (USA) investigating engagement with climate change imagery drawn from mass media sources. Participants were provided with a concourse of climate change images drawn from a newspaper content analysis carried out across all three countries, and asked to carry out two Q-sorts: first, for salience (‘this image makes me feel climate change is important’) and second, for efficacy (‘this image makes me feel I can do something about climate change’). We found results remarkably consistent both across and within country cohorts. This may indicate the presence of a dominant, mainstream discourse around climate imagery. We found that imagery of climate impacts promotes feelings of salience, but undermines self-efficacy; that imagery of energy futures imagery promotes self-efficacy; and that images of politicians and celebrities strongly undermine saliency, and undermine self-efficacy for the Australian cohort. These results, if widely replicable, have implications for climate change communication and engagement. Our results suggest that imagery plays a role in either increasing the sense of importance of the issue of climate change (saliency), or in promoting feelings of being able to do something about climate change (efficacy) – but few, if any, images seem to do both. Communications strategies should assess the purpose of their messages, considering these findings regarding salience and efficacy in this study, and choose to employ images accordingly.  相似文献   

Comparing the atmosphere to a bathtub: effectiveness of analogy for reasoning about accumulation     

Sophie Guy  Yoshihisa Kashima  Iain Walker  Saffron O’Neill 《Climatic change》2013,121(4):579-594

Understanding the process of accumulation is fundamental to recognising the magnitude and speed of emissions reduction required to stabilise atmospheric CO₂ and, hence, global temperature. This research investigated the effectiveness of analogy for building understanding of accumulation among non-experts. Two studies tested the effects of analogy and graphical information on: (1) performance on a CO₂ stabilisation task; and (2) preferred level of action on climate change. Study 1 was conducted with a sample of undergraduate students and Study 2, with a sample of the Australian public. In the student sample, analogical processing significantly improved task performance when information about emission rates was presented in text but not when it was presented in graph format. It was also associated with greater preference for strong action on climate change. When tested with the public, analogy and information format independently influenced task performance. Furthermore, there was a marginal effect of education such that the analogy especially might have helped those with at least high school attainment. Our results show that analogy can improve non-experts’ understanding of CO₂ accumulation but that using graphs to convey emissions rate information is detrimental to such improvements. The results should be of interest to climate change communicators, advocates, and policy-makers.  相似文献