Assessment of a field incubation method estimating primary productivity in rockpool communities     

Laure M.-L.J. Noël  John N. Griffin  Richard C. Thompson  Stephen J. Hawkins  Michael T. Burrows  Tasman P. Crowe  Stuart R. Jenkins 《Estuarine, Coastal and Shelf Science》2010

An open incubation method has been used in many studies to directly estimate primary productivity and ecosystem functioning by measuring photosynthetic and respiratory rates in intertidal rockpool communities. The method measures changes in dissolved oxygen concentrations recorded in situ during an artificial dark period (respiration) and a natural light period (net primary productivity). Although this method has yielded interesting results, its advantages and limitations have yet to be thoroughly tested. The accuracy of the method was investigated in a controlled laboratory environment and compared with field incubations. Atmospheric oxygen diffusion across the air–water interface did not affect incubation measurements under low wind speed (<2 m s⁻¹). Temperature increases during incubations were not greater than in natural rockpools and did not affect primary productivity. The major problem was the oxygen supersaturation which inhibited photosynthesis, thus leading to an underestimation of primary production. To allow comparable measurements, net primary productivity needs to be recorded during the linear phase of the photosynthetic process (<30 min of light) before water reaches supersaturation (<160%). This method gives rapid and reliable estimates of primary productivity thereby allowing biodiversity and ecosystem functioning relationships to be tested using rockpools as natural mesocosms.  相似文献   

Slab melt as metasomatic agent in island arc magma mantle sources, Negros and Batan (Philippines)   总被引：2，自引：0，他引：2  

Fernando G. Sajona  Rene C. Maury  Gaëlle Prouteau  Joseph Cotten  Pieree Schiano  Hervé Bellon  Laure Fontaine 《Island Arc》2000,9(4):472-486

Abstract Two new cases of association of adakites with ‘normal’ island arc lavas and transitional adakites are recognized in the islands of Batan and Negros in northern and central Philippines, respectively. The Batan lavas are related to the subduction of the middle Miocene portion of the South China Sea basin along the Manila trench; those of Negros come from the almost aseismic subduction of the middle Miocene Sulu Sea crust along the Negros trench. The occurrence of the Batan adakites is consistent with previous findings showing adakitic glass inclusions within minerals of mantle xenoliths associated with Batan arc lavas. The similarity of adakite ages (1.09 Ma) and that of the metasomatized xenoliths (1 Ma) suggests that both are linked to the same slab‐melting and metasomatic event. Earlier Sr, Pb and Nd‐isotopic studies, however, also reveal the presence of an important sediment contribution to the Batan lava geochemistry. Thus, the role played by slab melts, assumed to have mid‐ocean ridge basalts‐like (MORB) isotopic characteristics, in enriching the Batan subarc mantle is largely masked by the sediment input. The Negros adakites are present only in Mount Cuernos, the volcanic center nearest to the Negros trench. Batch partial melting calculations show that the Negros adakites could be derived from a garnet amphibolitic source with normal‐MORB (N‐MORB) geochemistry. This is supported by the MORB‐like isotopic characteristics of the Mount Cuernos lavas. The volcanic rocks from the other volcanoes consist of normal arc and transitional adakitic lavas that have slightly higher Sr‐ and Pb‐isotopic ratios, probably due to slight sediment input. Mixing of adakites and normal arc lavas to produce transitional adakites is only partly supported by trace element geochemistry and not by field evidence. The transitional adakites can be modeled as partial melts of an adakite‐enriched mantle. Trace element enrichment of non‐adakitic lavas could reflect the interaction of their mantle source with uprising slab melts, as metasomatic mantle minerals scavenge certain trace elements from the adakitic fluids. Therefore, in arcs beneath which thick (up to 2 km) continent‐derived detrital sediments are involved in subduction, like in Batan, the sediment signature can overwhelm the slab melt input. In arcs like Negros where slow subduction could cause a more efficient scraping of thinner (approximately 1 km) detrital sediments, the contribution of slab melts is easier to detect.  相似文献   

Contingencies of environmental justice: the case of individual mobility and Grenoble’s Low-Emission Zone     

Laure Charleux 《Urban geography》2013,34(2):197-218

Low-emission zones (LEZs) are core urban areas where vehicles that are deemed especially polluting are prohibited, in the hope of reducing the population’s exposure to outdoor air pollution. LEZs have proliferated in Europe during the past decade. While an emerging body of literature considers LEZs’ impacts on pollution, studies thus far have not tackled LEZs’ impacts on mobility. This article uses household-travel survey data to assess how a projected LEZ in Grenoble, France could affect individuals’ mobility, specifically enquiring whether or not the impact would be socially differentiated and might constitute a social injustice. Four likely scenarios are considered and logistic regressions show that, indeed, the probability that people will be affected by the LEZ is related to their social group. However, interpretations in terms of social justice may vary, depending on the reference population considered and hypotheses regarding the reduction of pollution exposure.  相似文献   

A modification of the time-geographic framework to support temporal flexibility in ‘fixed’ activities     

Laure Charleux 《International journal of geographical information science》2013,27(7):1125-1143

The time-geographic distinction between fixed and flexible activities is widely acknowledged to be a somewhat arbitrary dichotomy but is still the current modus operandi for time-geographic calculations. This paper proposes a modification of the classic time-geographic framework to support temporal flexibility in ‘fixed’ activities. This modification is crucial for time-geographic calculations on public transit networks with a low frequency of service, which would otherwise return unstable results.  相似文献   

Turn calculations for the indoor application of the fewest turns path algorithm     

Ann Vanclooster  Nina Vanhaeren  Pepijn Viaene  Kristien Ooms  Laure De Cock  Veerle Fack 《International journal of geographical information science》2013,27(11):2284-2304

ABSTRACT

Present-day indoor navigation systems are often not well adapted to the specific needs and requirements of its users. This research aims at improving those indoor navigation systems by providing navigation support that cognitively closer to user preferences and behaviour. More specifically, the focus is on the implementation of an accurate turn calculation method in a turn minimization algorithm, aiming to lower the complexity of routes and route instructions. This new-introduced perception-based turn calculation procedure is based on a direct door-to-door walking pattern, and, in contrast to previous algorithms, independent of the underlying indoor network type. It takes into account the effects of geometry of indoor space on human movement. To evaluate its functioning, both the traditional algorithm and the proposed perception-based algorithm are applied in the fewest turns path algorithm. It is demonstrated that the proposed algorithm accurately calculates turns in alignment with people’s perception. The implementation of the calculation algorithm in the fewest turns path algorithm also allows future applications in indoor simplest path algorithms, and overall contributes to cognitively richer indoor navigation systems.  相似文献   

A strategy for producing refined currents in the Equatorial Atlantic in the context of the search of the AF447 wreckage     

Marie Drévillon  Eric Greiner  Denis Paradis  Christophe Payan  Jean-Michel Lellouche  Guillaume Reffray  Edmée Durand  Stéphane Law-Chune  Sylvain Cailleau 《Ocean Dynamics》2013,63(1):63-82

On the night of 1st June 2009, a Rio-Paris Air France flight (AF447) disappeared in a highly variable and poorly observed part of the western tropical Atlantic Ocean. The first debris was located 5 days after the accident. Several reverse drift computations were conducted in order to define the likely position of the wreckage. Unfortunately, the performance of the operational ocean analyses available in the region of interest ranges from 80 to 100 km of positioning error after 5 days of inverse drift computation. In preparation of the third phase of research of the wreckage at sea, a series of numerical experiments was performed at Météo-France and Mercator Océan in an attempt to better compute the surface currents in the region and for the period of the accident of the AF447 (May and June 2009). Tailored high-resolution atmosphere and ocean reanalyses were first produced respectively at Météo-France and Mercator Océan. Several nested experiments were then performed with a small and flexible ocean model limited to the region of interest. The date of the initial conditions and the type of atmospheric forcing fields were varied in order to produce a small ensemble from which information on the sensitivity to these changes could be derived. Probabilistic and statistical combinations between model and observations were tested and a solution was finally selected by means of a comparison of drift computations with independent surface drift observations.  相似文献   

The suitability of annual tree growth rings as environmental archives: Evidence from Sr,Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed     

Peter Stille  Anne-Désirée Schmitt  François Labolle  Marie-Claire Pierret  Sophie Gangloff  Florian Cobert  Eric Lucot  Florence Guéguen  Laure Brioschi  Marc Steinmann  François Chabaux 《Comptes Rendus Geoscience》2012,344(5):297-311

The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces’ root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.  相似文献   

New UPb zircon ages from Tonga (Cameroon): coexisting Eburnean–Transamazonian (2.1 Ga) and Pan-African (0.6 Ga) imprints     

Evine Laure Tanko Njiosseu  Jean-Paul Nzenti  Théophile Njanko  Badibanga Kapajika  Anne Nédélec 《Comptes Rendus Geoscience》2005,337(6):551-562

The central domain of the Pan-African Belt in Cameroon is characterized by abundant porphyritic granitoids, which were emplaced synkinematically and variably orthogneissified in relation with ENE-striking steeply dipping transcurrent shear zones. These plutonic rocks have intermediate to felsic compositions and constitute a high-K calk-alkaline series. Conventional UPb zircon dating yields an age of 618 Ma for this syntectonic Pan-African magmatism in the Tonga area. The country rocks are made of metabasites (garnet amphibolites) and tonalitic to trondhjemitic gneisses, which suffered two distinct orogenic cycles: the first one is the Palaeoproterozoic Eburnean–Transamazonian cycle at 2.1 Ga and the second one is the Pan-African orogenesis. These new ages confirm the existence of an extensive Palaeoproterozoic crust in Cameroon and question the areal extent of the Congo–São Francisco craton towards the north. To cite this article: E.L. Tanko Njiosseu et al., C. R. Geoscience 337 (2005).  相似文献   

Barium and strontium uptake into larval protoconchs and statoliths of the marine neogastropod Kelletia kelletii     

Danielle C. Zacherl  Georges Paradis 《Geochimica et cosmochimica acta》2003,67(21):4091-4099

The trace elemental composition of calcified larval hard parts may serve as useful tags of natal origin for invertebrate population studies. We examine whether the trace metal barium (Ba) deposits into the calcium carbonate matrix of molluscan larval statolith and protoconch in proportion to seawater Ba concentration at two temperatures (11.5 and 17°C). We also examine strontium (Sr) uptake as a function of temperature. Using encapsulated larvae of the marine gastropod, Kelletia kelletii, reared in the laboratory under controlled conditions, we demonstrate a significant inverse effect of temperature and a positive effect of seawater Ba/Ca ratio on Ba incorporation into larval carbonates. Ba/Ca partition coefficients (D_Ba) in protoconch were 1.13 at 11.4°C and 0.88 at 17.1°C, while D_Ba in larval statolith measured 1.58 at 11.4°C and 1.29 at 17.1°C. Strontium incorporation into statoliths is also inversely affected by temperature, but there was a significant positive effect of temperature on Sr incorporation into protoconch. These data suggest larval statoliths and protoconchs can meaningfully record variation in seawater physical and chemical properties, and, hence, have potential as natural tags of natal origin.  相似文献   

Post-depositional realignment of magnetic grains and asymmetrical saw-tooth patterns of magnetization intensity     

Laure Meynadier  Jean-Pierre Valet 《Earth and Planetary Science Letters》1996,140(1-4):123-132

Recent paleomagnetic records suggest that the geomagnetic field intensity has a saw-tooth shape matching the succession of polarity intervals. An alternative hypothesis, that mechanisms linked to the acquisition of magnetization would induce similar saw-toothed records, has been tested by several simulations of post depositional reorientations of magnetic grains. Exponential functions used to date to describe post-depositional magnetization (pDRM) processes do not account for the combination of saw-toothed fluctuations and reasonable delays in the recording of the position of the reversals. At least half of the magnetization must be locked in within a few centimetres below the surface. If not, large delays, which are not observed in the data, are introduced in the stratigraphic positions of the reversals. In addition, the rest of the magnetization must be acquired over depths involving several tens of meters to duplicate a saw-toothed shape. These conclusions are reached with or without incorporating intensity variations across reversals. If the original signal is, in fact, asymmetrical then the pDRM must be very limited to remain coherent with the measurements, since the distortions and the offsets induced by the pDRM smoothing are considerably amplified. We conclude that simulations of saw-tooth patterns of relative paleointensity by pDRM processes have consequences that are difficult to reconcile with our present knowledge of the physical properties of deep-sea sediments. Above all, the hypothesis that the saw-tooth is an artifact of the magnetization acquisition process would have major implications for any sedimentary record of geomagnetic features.  相似文献