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1.
Robert Arfi Daniel Guiral Jean-Pascal Torreton 《Aquatic Sciences - Research Across Boundaries》1991,53(1):39-54
Chlorophyll pigments (CHL), primary productivity (PP) and particulate nitrogen (Np) in relation to several environmental factors were monitored during planktonic colonization of an aquaculture pond (Layo, Côte d'Ivoire). How interactions between the organisms are established in an initially azoic environment were investigated. From March, 15 (D1) to March, 31 (D16), the system transformation went through three stages. First, a precolonization by heterotrophic microbial community from D1 to D2 (Np < 1 m maximum at D2: 243 mg m–2; CHL around 0). Then, a pioneer microalgal community developped from D3 to D7 (maximum CHL on D6: 19 mg m–2; PP: 1.0 g C m–2 d–1) with a significant contribution of picoplankton (CHL and PP < 3 m: 33 and 23% of the total, respectively). Finally, a second microalgal colonization was noticed from D9 to D12 (maximum CHL: 55 mg m–2, PP: 2.8 g C m–2 d–1), largely dominated by nanoplankton (CHL and PP > 3 m: 95 and 99% of the total, respectively). Overall, photosynthetic activity appeared to be closely linked to algal biomass. The study of autotrophic biomass and activity in different size classes in relation to the other parameters allowed us to precise the origin of the biomass fluctuations. The first bloom appeared to be controlled by selective grazing on small algae. The second algal development ended when N requirement represented at least 69% of N supply (in the N — NH4 form). This control was enhanced by the appearance of rotifers, leading to a more complex equilibrium. 相似文献
2.
Jean-Pascal Torrton Emma Rochelle-Newall Aymeric Jouon Vincent Faure Sverine Jacquet Pascal Douillet 《Estuarine, Coastal and Shelf Science》2007,74(4):766
Hydrodynamic modeling can be used to spatially characterize water renewal rates in coastal ecosystems. Using a hydrodynamic model implemented over the semi-enclosed Southwest coral lagoon of New Caledonia, a recent study computed the flushing lag as the minimum time required for a particle coming from outside the lagoon (open ocean) to reach a specific station [Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental Shelf Research 26, 1395–1415]. Local e-flushing time was calculated as the time requested to reach a local grid mesh concentration of 1/e from the precedent step. Here we present an attempt to connect physical forcing to biogeochemical functioning of this coastal ecosystem. An array of stations, located in the lagoonal channel as well as in several bays under anthropogenic influence, was sampled during three cruises. We then tested the statistical relationships between the distribution of flushing indices and those of biological and chemical variables. Among the variables tested, silicate, chlorophyll a and bacterial biomass production present the highest correlations with flushing indices. Correlations are higher with local e-flushing times than with flushing lags or the sum of these two indices. In the bays, these variables often deviate from the relationships determined in the main lagoon channel. In the three bays receiving significant riverine inputs, silicate is well above the regression line, whereas data from the bay receiving almost insignificant freshwater inputs generally fit the lagoon channel regressions. Moreover, in the three bays receiving important urban and industrial effluents, chlorophyll a and bacterial production of biomass generally display values exceeding the lagoon channel regression trends whereas in the bay under moderate anthropogenic influence values follow the regressions obtained in the lagoon channel. The South West lagoon of New Caledonia can hence be viewed as a coastal mesotrophic ecosystem that is flushed by oligotrophic oceanic waters which subsequently replace the lagoonal waters with water considerably impoverished in resources for microbial growth. This flushing was high enough during the periods of study to influence the distribution of phytoplankton biomass, bacterial production of biomass and silicate concentrations in the lagoon channel as well as in some of the bay areas. 相似文献
3.
A two-dimensional global climate model is used to assessthe climatic changes associated with the new IPCC SRES emissions scenarios and to determine which kind of changes in total solar irradiance and volcanic perturbations could mask the projected anthropogenic global warming associated to the SRES scenarios. Our results suggest that only extremely unlikely changes in total solar irradiance and/or volcanic eruptions would be able to overcome the simulated anthropogenic global warming over the century. Nevertheless, in the critical interval of the next two decades the externally-driven natural climate variability might possibly confuse the debate about temperature trends and impede detection of the anthropogenic climate change signal. 相似文献
4.
Filip Lefebre Xavier Fettweis Hubert Gallée Jean-Pascal Van Ypersele Philippe Marbaix Wouter Greuell Pierluigi Calanca 《Climate Dynamics》2005,25(1):99-116
A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model
(RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological
observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the
available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the
model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and
size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic
modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning
the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a
proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a
sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than
60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM
offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface
climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations. 相似文献
5.
Séverine Bernardie Jean-Pascal Gilbert François Lebert Hubert Fabriol 《Pure and Applied Geophysics》2007,164(1):177-197
The monitoring of the stability of old mines constitutes an important research objective for our institution, BRGM. The study
reported here shows the contribution of high-frequency (>30 kHz) acoustic emissions to the detection of the damage within
a rock mass, during an experiment within a pilot site of an old flooded iron mine. The experiment consisted of recording all
the hydroacoustic events in a broad frequency band (between 30 Hz and 180 kHz), during 18 months. The monitoring network has
been calibrated by a triggered block fall that made it possible to highlight a relationship between the occurrence of high-frequency/low-frequency
hydroacoustic emissions and rock falls. The events recorded have been associated with the micro-failure of the rock mass near
the roof, prior to the detachment of the blocks. This monitoring showed important high-frequency hydroacoustic activity, which
may be associated with mechanical instabilities generated by the evolution of water pressure during the experiment. In conclusion,
the high-frequency hydroacoustic activity appears to be a good indicator of instability and, therefore, this new technique
constitutes a promising tool for monitoring abandoned underground cavities. 相似文献
6.
Emilie Vanvyve Nicholas Hall Christophe Messager Stéphanie Leroux Jean-Pascal van Ypersele 《Climate Dynamics》2008,30(2-3):191-202
Sensitivity studies with regional climate models are often performed on the basis of a few simulations for which the difference
is analysed and the statistical significance is often taken for granted. In this study we present some simple measures of
the confidence limits for these types of experiments by analysing the internal variability of a regional climate model run
over West Africa. Two 1-year long simulations, differing only in their initial conditions, are compared. The difference between
the two runs gives a measure of the internal variability of the model and an indication of which timescales are reliable for
analysis. The results are analysed for a range of timescales and spatial scales, and quantitative measures of the confidence
limits for regional model simulations are diagnosed for a selection of study areas for rainfall, low level temperature and
wind. As the averaging period or spatial scale is increased, the signal due to internal variability gets smaller and confidence
in the simulations increases. This occurs more rapidly for variations in precipitation, which appear essentially random, than
for dynamical variables, which show some organisation on larger scales. 相似文献
7.
Jean-Pierre Lefebvre Sylvain Ouillon Vu Duy Vinh Robert Arfi Jean-Yves Panché Xavier Mari Chu Van Thuoc Jean-Pascal Torréton 《Geo-Marine Letters》2012,32(2):103-121
In the Bach Dang–Cam Estuary, northern Vietnam, mechanisms governing cohesive sediment aggregation were investigated in situ
in 2008–2009. As part of the Red River delta, this estuary exhibits a marked contrast in hydrological conditions between the
monsoon and dry seasons. The impact on flocculation processes was assessed by means of surveys of water discharge, suspended
particulate matter concentration and floc size distributions (FSDs) conducted during a tidal cycle at three selected sites
along the estuary. A method was developed for calculating the relative volume concentration for the modes of various size
classes from FSDs provided by the LISST 100X (Sequoia Scientific Inc.). It was found that all FSDs comprised four modes identified
as particles/flocculi, fine and coarse microflocs, and macroflocs. Under the influence of the instantaneous turbulent kinetic
energy, their proportions varied but without significant modification of their median diameters. In particular, when the turbulence
level corresponded to a Kolmogorov microscale of less than ∼235 μm, a major breakup of flocs resulted in the formation of
particles/flocculi and fine microflocs. Fluctuations in turbulence level were governed by seasonal variations in freshwater
discharge and by the tidal cycle. During the wet season, strong freshwater input induced a high turbulent energy level that
tended to generate sediment transfer from the coarser size classes (macroflocs, coarse microflocs) to finer ones (particles/flocculi
and fine microflocs), and to promote a transport of sediment seawards. During the dry season, the influence of tides predominated.
The turbulent energy level was then only episodically sufficiently high to generate transfer of sediment between floc size
classes. At low turbulent energy, modifications in the proportions of floc size classes were due to differential settling.
Tidal pumping produced a net upstream transport of sediment. Associated with the settling of sediment trapped in a near-bed
layer at low turbulent energy, this causes the silting up of the waterways leading to the harbour of Haiphong. 相似文献
8.
Global scale patterns of continental fragmentation: Wilson's cycles as a constraint for long-term sea-level changes 总被引:1,自引:0,他引:1
We propose to characterize land–ocean distributions over Late Proterozoic to Phanerozoic times from measurement of perimeters and areas of continental fragments, based on paleomagnetic reconstructions. These measurements serve to calculate geophysically constrained breakup and scatter indexes of continental land masses from 0 to 1100 Ma. We then provide quantitative investigation and modelling of relationships between scatter of continental landmasses and mean age of the oceanic lithosphere during Mesozoic times, which appears to range from 56 to 62 Ma over the last 170 My. We then inverse the scatter of continental landmasses in terms of global oceanic crust mean age over the last 600 My, i.e. back in times where no measurement of seafloor accretion history is possible because of subduction. We finally show that the inferred evolution of oceanic lithosphere mean age over the Phanerozoic remarkably correlates in time with long-term sea-level changes since the Cambrian. 相似文献
9.
Navarro P Amouroux D Thanh ND Rochelle-Newall E Ouillon S Arfi R Van TC Mari X Torréton JP 《Marine pollution bulletin》2012,64(9):1789-1798
In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (~3kgTBT/day) and dry (~3gMMHg/day) seasons. 相似文献
10.