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31.
A.L. Carrera M.J. Mazzarino M.B. Bertiller H.F. del Valle E.M. Carretero 《Journal of Arid Environments》2009,73(2):192-201
In arid and semiarid ecosystems, primary productivity and nutrient cycling are directly related to the amount and seasonal distribution of precipitation. However, depending on morphological, phenological, physiological, and biochemical traits, plants may influence the quality and quantity of organic matter inputs to the soil and thus the biomass and activity of the soil biota responsible for carbon and nitrogen dynamics. In this paper, we review the available knowledge on plant functional traits and their impacts on ecosystem processes such as N and C cycling throughout the Monte Phytogeographical Province. We address the mechanisms of N conservation, the quantity and quality of leaf litterfall and root traits of the dominant plant life forms and their effects on decomposition processes, soil organic matter accretion, and soil-N immobilization and mineralization. We conclude that plant functional traits affect ecosystem processes in the Monte Phytogeographical Province since the chemistry of senesced leaves and root biomass exerts an important control on organic matter decomposition and N availability in soil. 相似文献
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Johanna K. Spiegel Nina Buchmann Olga L. Mayol-Bracero Luis A. Cuadra-Rodriguez Carlos J. Valle Díaz Kimberly A. Prather Stephan Mertes Werner Eugster 《Pure and Applied Geophysics》2014,171(9):2443-2459
We investigated cloud properties of warm clouds in a tropical montane cloud forest at Pico del Este (1,051 m a.s.l.) in the northeastern part of Puerto Rico to address the question of whether cloud properties in the Caribbean could potentially be affected by African dust transported across the Atlantic Ocean. We analyzed data collected during 12 days in July 2011. Cloud droplet size spectra were measured using the FM-100 fog droplet spectrometer that measured droplet size distributions in the range from 2 to 49 µm, primarily during fog events. The droplet size spectra revealed a bimodal structure, with the first peak (D < 6 µm) being more pronounced in terms of droplet number concentrations, whereas the second peak (10 µm < D < 20 µm) was found to be the one relevant for total liquid water content (LWC) of the cloud. We identified three major clusters of characteristic droplet size spectra by means of hierarchical clustering. All clusters differed significantly from each other in droplet number concentration ( \(N_{\rm tot}\) ), effective diameter (ED), and median volume diameter (MVD). For the cluster comprising the largest droplets and the lowest droplet number concentrations, we found evidence of inhomogeneous mixing in the cloud. Contrastingly, the other two clusters revealed microphysical behavior, which could be expected under homogeneous mixing conditions. For those conditions, an increase in cloud condensation nuclei—e.g., from processed African dust transported to the site—is supposed to lead to an increased droplet concentration. In fact, one of these two clusters showed a clear shift of cloud droplet size spectra towards smaller droplet diameters. Since this cluster occurred during periods with strong evidence for the presence of long-range transported African dust, we hypothesize a link between the observed dust episodes and cloud characteristics in the Caribbean at our site, which is similar to the anthropogenic aerosol indirect effect. 相似文献
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Time series of velocity profiles at two Chesapeake Bay entrance sites were used to characterize the subtidal variability of transverse flows off a cape. A shallow sampling site was located near Cape Henry over 6 m of water and separated from a deep site, 20 m deep, by a distance of 4 km. The velocity profiles showed that wind-induced subtidal variations in general masked curvature effects (centrifugal accelerations) that may produce secondary circulation associated with tidal flow around a cape. Such secondary circulation, consisting of flow away from the cape at surface and toward the cape at depth, was observed only during periods of weak winds. Most of the time, transverse flows were unidirectional throughout the water column and moved in opposite directions at the two sites examined. This caused convergence of transverse flow between the two sites under the influence of northerly winds and divergence of transverse flow with southwesterly winds. In addition to unidirectional and curvature-induced secondary flows, other modes of subtidal variability consisted of (1) two-layered responses with surface flow toward the cape, and (2) three-layered responses. These two- and three-layered structures were observed more frequently at the deep site, where greater stratification is expected, than at the shallow site.Responsible Editor: Iris Grabemann 相似文献
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M. Della Valle M. Kissler-Patig J. Danziger & J. Storm 《Monthly notices of the Royal Astronomical Society》1998,299(1):267-276
We have determined the absolute magnitude at maximum light of SN 1992A by using the turnover magnitude of the globular cluster luminosity function of its parent galaxy, NGC 1380. A recalibration of the peak of the turnover magnitude of the Milky Way clusters using the latest Hipparcos results has been made with an assessment of the complete random and systematic error budget. The following results emerge: a distance to NGC 1380 of 18.6 ± 1.4 Mpc, corresponding to ( m − M ) 31.35 ± 0.16, and an absolute magnitude of SN 1992A at maximum of M B (max) −18.79 ± 0.16. Taken at face value, SN 1992A seems to be more than half a magnitude fainter than the other SNe Ia for which accurate distances exist. We discuss the implications of this result and present possible explanations. We also discuss the Phillips relationship between rate of decline and the absolute magnitude at maximum, on the basis of nine SNe Ia, the individual distances of which have been obtained with Cepheids and the globular cluster luminosity function. The new calibration of this relationship, applied to the most distant SNe of the Calan–Tololo survey, yields H 0 = 62 ± 6 km s−1 Mpc−1 . 相似文献
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Daniela A. del Valle David J. Kieber Dierdre A. Toole John Bisgrove Ronald P. Kiene 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(2):166-177
Dimethylsulfoxide (DMSO) is an important degradation product of the climate-influencing gas dimethylsulfide (DMS). In the Ross Sea, Antarctica, dissolved DMSO (DMSOd) concentrations exhibited substantial seasonal and vertical variations. Surface water DMSOd concentrations in pre-bloom waters were very low (<1 nM) but increased rapidly up to 41 nM during the spring Phaeocystis antarctica bloom (late November). Increases in DMSOd concentrations lagged by several days increases in DMS concentrations. Although DMSOd concentrations reached relatively high levels during the spring bloom, concentrations were generally higher (36.3–60.6 nM) during summer (January), even though phytoplankton biomass and DMS concentrations had decreased by that time. During both seasons, DMSOd concentrations were substantially higher within the surface mixed layer than below it. DMSOd production from biological DMS consumption (BDMSC) was higher during late November (3.4–5.2 nM d?1) than during the summer (0.7–2.4 nM d?1); therefore, production via BDMSC alone could not explain the higher DMSOd concentrations encountered during the summer. Mixed layer-integrated DMSOd production from BDMSC was 2.5–13.7 times greater than production from dissolved DMS photolysis during the P. antarctica bloom, while photolysis contributed 1.3 times more DMSO than BDMSC before the bloom. The DMSO yield from BDMSC was consistently higher within the upper mixed layer than at depths below. Experimental incubations with water from the mixed layer showed that exposure to full spectrum sunlight for 72 h caused an increase in the DMSO yield whereas exposure to only photosynthetically active radiation did not. This suggests that ultraviolet radiation is a potential factor shifting the fate of biologically consumed DMS toward DMSO. In general, the highest DMSO yields from BDMSC were in samples with slow biological DMS turnover, whereas fast turnover favored sulfate rather than DMSO as a major end-product. This study provides the first detailed information about DMSOd distribution and production in the Ross Sea and points to DMSOd as an important biological and photochemical degradation product of DMS and a major reservoir of methylated sulfur in these polar surface waters. 相似文献
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Recent investigations into convection in Europa’s ice shell have been based on non-Newtonian (stress-dependent) or Newtonian
(stress-independent) viscosity for water ice. However, despite the wide use of Newtonian convection, experimentally observed
water ice flow is non-Newtonian, and analysis of stability against convection of the ice shell using updated flow laws has
been only performed for non-Newtonian rheologies. Here we use the flow law proposed for diffusion creep to analyze the possibility
of the onset of convection for Newtonian viscosity in relation to the thermal state of Europa. Our findings indicate that
for diffusion creep convection might have started, but that significantly lower heat flows (and equivalently higher shell
thicknesses) and/or grain sizes are required than for superplastic flow, which is the most probable flow mechanism if the
ice shell is convective. 相似文献