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Seasonal Scale (seasonal + scale)
Selected AbstractsThe influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulationsFISHERIES OCEANOGRAPHY, Issue 6 2007GWENHAEL ALLAIN Abstract A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space,time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales , retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small-scale and meso-scale mechanisms were related to the variations in wind direction and intensity during spring and summer. Survival was also variable according to the origin of the drift trajectories, that is spawning distribution in space and time. The observed spawning distribution (according to field surveys) was compared with the spawning distribution that would maximize survival (according to the biophysical model) on a seasonal scale, which revealed factors not considered in the biophysical model (e.g. spawning behaviour of the different age classes). The variation of simulated survival according to spawning distribution was examined on a multi-annual scale and showed a coherent pattern with past and present stock structures. The interaction processes between the population (influence on spawning) and its environment (influence on survival) and its implications on recruitment and stock dynamics are discussed. [source] Impact of freshwater input and wind on landings of anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) in shelf waters surrounding the Ebre (Ebro) River delta (north-western Mediterranean)FISHERIES OCEANOGRAPHY, Issue 2 2004J. Lloret Abstract Time series analyses (Box,Jenkins models) were used to study the influence of river runoff and wind mixing index on the productivity of the two most abundant species of small pelagic fish exploited in waters surrounding the Ebre (Ebro) River continental shelf (north-western Mediterranean): anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). River flow and wind were selected because they are known to enhance fertilization and local planktonic production, thus being crucial for the survival of fish larvae. Time series of the two environmental variables and landings of the two species were analysed to extract the trend and seasonality. All series displayed important seasonal and interannual fluctuations. In the long term, landings of anchovy declined while those of sardine increased. At the seasonal scale, landings of anchovy peaked during spring/summer while those of sardine peaked during spring and autumn. Seasonality in landings of anchovy was stronger than in sardine. Concerning the environmental series, monthly average Ebre runoff showed a progressive decline from 1960 until the late 1980s, and the wind mixing index was highest during 1994,96. Within the annual cycle, the minimum river flow occurs from July to October and the wind mixing peaks in winter (December,April, excluding January). The results of the analyses showed a significant correlation between monthly landings of anchovy and freshwater input of the Ebre River during the spawning season of this species (April,August), with a time lag of 12 months. In contrast, monthly landings of sardine were significantly positively correlated with the wind mixing index during the spawning season of this species (November,March), with a lag of 18 months. The results provide evidence of the influence of riverine inputs and wind mixing on the productivity of small pelagic fish in the north-western Mediterranean. The time lags obtained in the relationships stress the importance of river runoff and wind mixing for the early stages of anchovy and sardine, respectively, and their impact on recruitment. [source] Large annual net ecosystem CO2 uptake of a Mojave Desert ecosystemGLOBAL CHANGE BIOLOGY, Issue 7 2008GEORG WOHLFAHRT Abstract The net ecosystem CO2 exchange (NEE) between a Mojave Desert ecosystem and the atmosphere was measured over the course of 2 years at the Mojave Global Change Facility (MGCF, Nevada, USA) using the eddy covariance method. The investigated desert ecosystem was a sink for CO2, taking up 102±67 and 110±70 g C m,2 during 2005 and 2006, respectively. A comprehensive uncertainty analysis showed that most of the uncertainty of the inferred sink strength was due to the need to account for the effects of air density fluctuations on CO2 densities measured with an open-path infrared gas analyser. In order to keep this uncertainty within acceptable bounds, highest standards with regard to maintenance of instrumentation and flux measurement postprocessing have to be met. Most of the variability in half-hourly NEE was explained by the amount of incident photosynthetically active radiation (PAR). On a seasonal scale, PAR and soil water content were the most important determinants of NEE. Precipitation events resulted in an initial pulse of CO2 to the atmosphere, temporarily reducing NEE or even causing it to switch sign. During summer, when soil moisture was low, a lag of 3,4 days was observed before the correlation between NEE and precipitation switched from positive to negative, as opposed to conditions of high soil water availability in spring, when this transition occurred within the same day the rain took place. Our results indicate that desert ecosystem CO2 exchange may be playing a much larger role in global carbon cycling and in modulating atmospheric CO2 levels than previously assumed , especially since arid and semiarid biomes make up >30% of Earth's land surface. [source] Evaporation estimation on Lake Titicaca: a synthesis review and modellingHYDROLOGICAL PROCESSES, Issue 13 2007François Delclaux Abstract The aim of this study was to validate evaporation models that can be used for palaeo-reconstructions of large lake water levels. Lake Titicaca, located in a high-altitude semi-arid tropical area in the northern Andean Altiplano, was the object of this case study. As annual evaporation is about 90% of lake output, the lake water balance depends heavily on the yearly and monthly evaporation flux. At the interannual scale, evaporation estimation presents great variability, ranging from 1350 to 1900 mm year,1. It has been found that evaporation is closely related to lake rainfall by a decreasing relationship integrating the implicit effect of nebulosity and humidity. At the seasonal scale, two monthly evaporation data sets were used: pan observations and estimations derived from the lake energy budget. Comparison between these data sets shows that (i) there is one maximum per year for pan evaporation and two maxima per year for lake evaporation, and (ii) pan evaporation is greater than lake evaporation by about 100 mm year,1. These differences, mainly due to a water depth scale factor, have been simulated with a simple thermal model ,w(h, t) of a free-surface water column. This shows that pan evaporation (h = 0·20 m) is strongly correlated with direct solar radiation, whereas the additional maximum of lake evaporation (h = 40 m) is related to the heat restitution towards the atmosphere from the water body at the end of summer. Finally, five monthly evaporation models were tested in order to obtain the optimal efficiency/complexity ratio. When the forcing variables are limited to those that are most readily available in the past, i.e. air temperature and solar radiation, the best results are obtained with the radiative Abtew model (r = 0·70) and with the Makkink radiative/air temperature model (r = 0·67). Copyright © 2007 John Wiley & Sons, Ltd. [source] The structure of the lunar semi-diurnal pressure tide L2THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 606 2005Stephen W. Goulter Abstract The Hough structure of the lunar semi-diurnal tide L2(p) in surface pressure is estimated using joint weightings by area and probable-error structure, on annual and Lloyd seasonal scales, with new data. Global representations, on seasonal and annual scales of the L2 wave, in both spherical harmonic and Hough function forms, are presented for the Haurwitz,Cowley dataset enlarged by the more recent tidal determinations of Hutchings and Palumbo. These are mainly for southern hemiphere island locations. The asymmetric Hough eigenfunction terms H32 are considerably larger than previously estimated, both annually and seasonally, a possible artefact of the earlier data analysis technique. They are consistent and identified with the well-known difference in phasing and amplitude of L2 by hemisphere. The dependence of the Hough structure on the order of the fitting and on the more extreme residuals is examined. It is stable for the smallest models (spherical harmonic terms up to degree 6 and order 3), to removal of the largest residuals from a first fitting, and to the two largest datasets. Seasonal changes in the Hough structure are discussed. The asymmetric results appear consistent with early frictional/thermal interpretations on the seasonal variation of L2. But the sensitivity of L2 to upper-air temperature structure is not consistently shown in the analyses for the main mode H(2, 2). Copyright © 2005 Royal Meteorological Society. [source] | ||||||||||