Water level as the main driver of the alternation between a free-floating plant and a phytoplankton dominated state: a long-term study in a floodplain lake   总被引：3，自引：0，他引：3  

Inés O’Farrell  Irina Izaguirre  Griselda Chaparro  Fernando Unrein  Rodrigo Sinistro  Haydée Pizarro  Patricia Rodríguez  Paula de Tezanos Pinto  Ruben Lombardo  Guillermo Tell 《Aquatic Sciences - Research Across Boundaries》2011,73(2):275-287

This 10-year field data study explores the relevance of water level fluctuations in driving the shift from a free-floating plant (FFP) to a phytoplankton dominated state in a shallow floodplain lake from the Lower Paraná River. The multi-year natural flood pulse pattern in the Lower Paraná River drove the ecosystem regime from a FFP-dominant state during very high waters (1998–1999) to absolute phytoplankton prevalence with blooms of nitrogen fixing Cyanobacteria during extreme low waters (2008–2009). Satellite images support the observed changes over the decade and show the decrease of the surface lake area covered by FFP as well as the modification of the spectral firm in open waters, which documents the significant increases in phytoplankton chlorophyll a concentrations. We discuss the possibility that, despite a slow eutrophication in these highly vegetated systems, water level changes and not nutrients account for the shift from a floating macrophyte community to phytoplankton dominance. Cyclic shifts may occur in response to the seasonal floodpulse, but more strongly, as indicated by our results, in association to the extreme drought and flood events related to the El Niño Southern Oscillation, which is linked to discharge anomalies in the Paraná River.  相似文献   

Equatorial electrojet plasma irregularities observed during late afternoon by the 30 MHz coherent scatter radar in São Luís,Brazil     

E.B. Shume  E.R. de Paula  E.A. Kherani  M.A. Abdu  C.M. Denardini 《Journal of Atmospheric and Solar》2011,73(11-12):1560-1567

Coherent scatter radar observations conducted right before twilight by the 30 MHz radar in São Luís (Brazil) during both quiet (December 10, 2001) and disturbed (December 12, 2001) conditions detected type I echoes on the shoulders of broad type II spectra (near zero Doppler velocity). Zonal electric fields inferred from the São Luís ionosonde have a larger magnitude during the period where these spectral observations were made than on December 18, 2001 when type I echoes were not observed during late afternoon. The IMF B_z and AE index indicate that the extended geomagnetic disturbance in the afternoon of December 12, 2001 has allowed the interaction between disturbance dynamo and prompt penetration electric fields. The latter electric field component could have exceeded the former to give rise to the observed electric fields, and make possible observation of type I echoes.  相似文献   

Paired Measurements of Foraminiferal δ~ (18) O and Mg/Ca Ratios of Indian Monsoons Reconstructed from Holocene to Last Glacial Record     

Badanal MAHESH  Virupaxa BANAKAR  George BURR 《《地质学报》英文版》2011,(4)

The effect of seasonally reversing monsoons in the northern Indian Ocean is to impart significant changes in surface salinity(SS).Here,we report SS changes during the last 32 kyr in the Lakshadweep Sea(southeastern Arabian Sea)estimated from paired measurements of δ~(18)O and sea surface temperature(SST)using Globigerinoides sacculifer,an upper mixed layer dwelling foraminifera.The heaviest δ~(18)O_(G.sacculifer)(-0.07±0.08‰)is recorded between 23 and 15 ka,which could be defined as the last glacial maxi...  相似文献   

Can added value be expected in RCM-simulated large scales?     

Emilia Paula Diaconescu  René Laprise 《Climate Dynamics》2013,41(7-8):1769-1800

Nested Limited-Area Models require driving data to define their lateral boundary conditions (LBC). The optimal choice of domain size and the repercussions of LBC errors on Regional Climate Model (RCM) simulations are important issues in dynamical downscaling work. The main objective of this paper is to investigate the effect of domain size, particularly on the larger scales, and to question whether an RCM, when run over very large domains, can actually improve the large scales compared to those of the driving data. This study is performed with a detailed atmospheric model in its global and regional configurations, using the “Imperfect Big-Brother” (IBB) protocol. The ERA-Interim reanalyses and five global simulations are used to drive RCM simulations for five winter seasons, on four domain sizes centred over the North American continent. Three variables are investigated: precipitation, specific humidity and zonal wind component. The results following the IBB protocol show that, when an RCM is driven by perfect LBC, its skill at reproducing the large scales decreases with increasing the domain of integration, but the errors remain small even for very large domains. On the other hand, when driven by LBC that contain errors, RCMs can bring some reduction of errors in large scales when very large domains are used. The improvement is found especially in the amplitude of patterns of both the stationary and the intra-seasonal transient components. When large errors are present in the LBC, however, these are only partly corrected by the RCM. Although results showed that an RCM can have some skill at improving imperfect large scales supplied as driving LBC, the main added value of an RCM is provided by its small scales and its skill to simulate extreme events, particularly for precipitation. Under the IBB protocol all RCM simulations were fairly skilful at reproducing small scales statistics, although the skill decreased with increasing LBC errors. Coarse-resolution model simulations have difficulties in simulating heavy precipitation events, and as a result their precipitation distributions are systematically shifted toward smaller intensity. Under the IBB protocol, all RCM simulations have distributions very similar to the reference field, being little affected by LBC errors, and no significant differences were found between the small scales statistics and the precipitation distributions obtained over different RCM domains.  相似文献   

Stratospheric ozone depletion: a key driver of recent precipitation trends in South Eastern South America     

Paula L. M. Gonzalez  Lorenzo M. Polvani  Richard Seager  Gustavo J. P. Correa 《Climate Dynamics》2014,42(7-8):1775-1792

On a hemispheric scale, it is now well established that stratospheric ozone depletion has been the principal driver of externally forced atmospheric circulation changes south of the Equator in the last decades of the 20th Century. The impact of ozone depletion has been felt over the entire hemisphere, as reflected in the poleward drift of the midlatitude jet, the southward expansion of the summertime Hadley cell and accompanying precipitation trends deep into the subtropics. On a regional scale, however, surface impacts directly attributable to ozone depletion have yet to be identified. In this paper we focus on South Eastern South America (SESA), a region that has exhibited one of the largest wetting trends during the 20th Century. We study the impact of ozone depletion on SESA precipitation using output from 6 different climate models, spanning a wide range of complexity. In all cases we contrast pairs of model integrations with and without ozone depletion, but with all other forcings identically specified. This allows for unambiguous attribution of the computed precipitation trends. All 6 climate models consistently reveal that stratospheric ozone depletion results in a significant wetting of SESA over the period 1960–1999. Taken as a whole, these model results strongly suggest that the impact of ozone depletion on SESA precipitation has been as large as, and quite possibly larger than, the one caused by increasing greenhouse gases over the same period.  相似文献   

Verification of mid-ocean ballast water exchange using naturally occurring coastal tracers   总被引：2，自引：0，他引：2  

Murphy K  Boehme J  Coble P  Cullen J  Field P  Moore W  Perry E  Sherrell R  Ruiz G 《Marine pollution bulletin》2004,48(7-8):711-730

We examined methods for verifying whether or not ships have performed mid-ocean ballast water exchange (BWE) on four commercial vessels operating in the Pacific and Atlantic Oceans. During BWE, a ship replaces the coastal water in its ballast tanks with water drawn from the open ocean, which is considered to harbor fewer organisms capable of establishing in coastal environments. We measured concentrations of several naturally occurring chemical tracers (salinity, six trace elements, colored dissolved organic matter fluorescence and radium isotopes) along ocean transects and in ballast tanks subjected to varying degrees of BWE (0-99%). Many coastal tracers showed significant concentration changes due to BWE, and our ability to detect differences between exchanged and unexchanged ballast tanks was greatest under multivariate analysis. An expanded dataset, which includes additional geographic regions, is now needed to test the generality of our results.  相似文献   

The role of true polar wander on the Jurassic palaeoclimate     

María Paula Iglesia Llanos  Claudia Beatriz Prezzi 《International Journal of Earth Sciences》2013,102(3):745-759

From the Late Carboniferous until the Middle Jurassic, continents were assembled in a quasi-rigid supercontinent called Pangea. The first palaeomagnetic data of South America indicated that the continent remained stationary in similar present-day latitudes during most of the Mesozoic and even the Palaeozoic. However, new palaeomagnetic data suggest that such a scenario is not likely, at least for the Jurassic. In order to test the stationary versus the dynamic-continent model, we studied the Jurassic apparent polar wander paths of the major continents, that is, Eurasia, Africa and North America that all in all show the same shape and chronology of the tracks with respect to those from South America. We thus present a master path that could be useful for the Jurassic Pangea. One of the most remarkable features observed in the path is the change in pole positions at ~197 Ma (Early Jurassic), which denotes the cessation of the counter-clockwise rotation of Pangea and commencement of a clockwise rotation that brought about changes in palaeolatitude and orientation until the end of the Early Jurassic (185 Ma). Here, we analyse a number of phenomena that could have triggered the polar shift between 197 and 185 Ma and conclude that true polar wander is the most likely. In order to do this, we used Morgan’s (Tectonophysics 94:123–139, 1983) grid of hotspots and performed “absolute” palaeogeographical reconstructions of Pangea for the Late Triassic and Jurassic. The palaeolatitudes changes that we observe from our palaeomagnetic data are very well sustained by diverse palaeoclimatic proxies derived from geological and palaeoecological data at this time of both the southern and northern hemispheres.  相似文献   

Effects of non-carbonaceous meteoritic extracts on the germination, growth and chlorophyll content of edible plants     

Vicente Marcano  Paula Matheus  Nelson Falcon 《Planetary and Space Science》2005,53(12):1263-1279

We have conducted an investigation on the effects that the extracts of a non-carbonaceous meteorite could have on the germination and growth of plants and the ability of non-carbonaceous meteoritic resource to serve as nutrient source for young plants of edible types. Selected plants were two dicotyledons (Lycopersicon esculentum and Daucus carota) and one monocotyledon (Zea mays). Solution cultures were developed using seeds, seedlings and seed-embryos. Meteoritic powder was obtained from the Vigirima mesosiderite, which was analyzed by X-ray diffraction and atomic absorption spectrometry (AAS). Results showed that extracts having variable concentrations of meteoritic matter favored an earlier germination in some plant species but the increase of the concentrations produced a decreased germination. However, total germination rate was higher in the presence of meteoritic extracts than in the presence of controls in the all species. A high metabolic yield in the protein synthesis was seen in dicotyledons utilizing Type-A and B extracts having concentrations of 4.16-8.33×10³ mg l⁻¹. Phaeophytinization index and chlorophyll a/b ratio, suggesting a negative effect of the heavy metals or acidic ions over the photosynthetic activity when extracts having high meteoritic concentrations were utilized. However, a higher chlorophyll (a) production in comparison to that of chlorophyll (b) was seen in extracts (Type-A and -B) with low concentrations of meteoritic matter. On the other hand, Z. mays seed-embryos growing in extracts (Type-D) having 3.53×10⁴ mg l⁻¹ of meteoritic matter showed a protein production (9.81×10⁻² mg protein mg wet wt⁻¹) higher than that observed in seed-embryos coming from extracts having lower concentrations. However, in Murashige medium, the seed-embryos exhibited a enhanced growth and a relatively higher protein production (10.3×10⁻² mg protein mg wet wt.⁻¹). Further, chlorophyll (a+b) synthesis was higher in Murashige medium than in meteoritic extracts but chlorophyll a/b ratio was <1 in all extracts and controls. Our results suggest the usefulness of the non-carbonaceous meteoritic resource as a complementary soil component or fertilizers for culture of edible plants in space settlements and mainly for the production of young plants due to the positive metabolic effects on the chlorophyll synthesis, mitochondrial metabolism and cellular division caused by PO₄³⁻, Fe²⁺, Cu²⁺ and Ca²⁺ ions. Earlier germination responses obtained in the present experiments demonstrated the possibility to utilize germination chambers in space having wet substrates containing meteoritic-powder solutions to obtain a higher number of seedlings in a minimum degree of time. These results also reveal the biological potential of this non-carbonaceous meteoritic matter for the growth of organisms in the early Earth, Mars, and probably in other planetary bodies beyond our Solar system.  相似文献   

GEOALGAR项目:地震活动性和断层面解的初步结果     

F.Carrilho　P.Teves-Costa　I.Morais　J.Pagarete　R.Dias 《国际地震动态》2004,(10):27-36

2000年5月发起的GEOALGAR项目旨在致力于阿尔加维地区的地球动力学监测和地震区划. 本文简单介绍一下该项目的目标和有关1999-2000年地震记录分析的初步结果. 经过地震记录和速度模型参数的同步反演, 对两个选定区域的震源位置进行了重新定位. 区域1使用了25个1999-2000年间发生的ML≥2.0的地震, 区域2使用了125个. 结果表明, 主要有两个地区的地震较多 一个是蒙希克地区(在内陆), 另一个是瓜达尔基维尔浅滩(范围从36.4°N, 8°W～36.8°N, 7.2°W). 区域1, 震源校正的幅度相对较小, 震源比原先定位的深度稍微深一些; 而对于区域范围内其他更多的地震, 震源校正的幅度较大, 震源的位置变得更浅.对于近期发生的地震也做了断层面解的估计, 结果表明, 最优解受到走滑运动的控制, 这与NW-SE至NNW-SSE方向的水平挤压控制的应力一致, 有两个地震例外, 它们呈现的是逆冲机制, 最大水平挤压应力方向稍微转向N-S. 这与其他作者先前研究的结果也是一致的.重新定位后的震中位置在空间分布上显得更加有条理, 表明它与一些已知的构造特征可能相关. 然而, 断层面解的结果与新构造特征很难相关起来.  相似文献   

Evaluation of daily precipitation statistics and monsoon onset/retreat over western Sahel in multiple data sets     

Diaconescu  Emilia Paula  Gachon  Philippe  Scinocca  John  Laprise  René 《Climate Dynamics》2015,45(5-6):1325-1354

Climate Dynamics - The West Africa rainfall regime constitutes a considerable challenge for Regional Climate Models (RCMs) due to the complexity of dynamical and physical processes that...  相似文献