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1.
Thomas F. Wever Hannelore M. Fiedler Gunther Fechner Friedrich Abegg Ingo H. Stender 《Geo-Marine Letters》1997,17(4):246-252
Between 2 and 6 February, 1995, a 25 km2 area at the Dry Tortugas (Florida Keys) was surveyed with a 100 kHz side-scan sonar system and 3.5-kHz subbottom profiler.
The side-scan system revealed a pattern of alternating high and low backscatter. The subbottom profiler showed areas with
no acoustic penetration between sediment troughs. The combination of both methods allowed delineation of the boundaries in
high-backscatter regions, and sediment samples allowed correlations between high backscatter and coarser-grained sediments. 相似文献
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Differentiation in reproductive traits of geminate mangrove crabs of the genus Aratus (Decapoda: Brachyura) across the Central American Isthmus
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The mangrove crab Aratus pisonii was considered to have an amphi‐American distribution; however, a recent study revealed that the Eastern Tropical Pacific populations were genetically distinct, thus representing a new species: Aratus pacificus. These species separated by the Isthmus of Panama have diverged under different environmental conditions that may have influenced their reproductive biology. As the available information about this genus concerns almost exclusively the Caribbean species, the aim of the present study was to analyse and compare reproductive aspects of A. pacificus and A. pisonii obtained from both the Pacific and Caribbean coasts of Costa Rica. Females were collected from April 2011 to April 2012, and reproductive features such as breeding season, size distribution of ovigerous females, fecundity, reproductive output, embryo volume and embryo water content were assessed. Both species produced embryos during the entire sampled period. Most females of A. pacificus carrying embryos close to hatching were found during the rainy season. Ovigerous females of A. pisonii were substantially larger and reached sexual maturity at a larger size than females of A. pacificus. Embryo production started in A. pacificus at a smaller female size than in A. pisonii. As fecundity increased with female size, the average fecundity was lower in A. pacificus. Females of A. pisonii produced larger embryos, which might be related to lower food availability: higher energy content in the embryo enhances the chances of larval survival. These data regarding reproductive features of the Pacific and Caribbean species support the conclusion to separate A. pacificus from A. pisonii. 相似文献
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The frequent coincidence of volcanic forcing with El Niño events disables the clear assignment of climate anomalies to either volcanic or El Niño forcing. In order to select the signals, a set of four different perpetual January GCM experiments was performed (control, volcano case, El Niño case and combined volcano/El Niño case) and studied with advanced statistical methods for the Northern Hemisphere winter. The results were compared with observations. The signals for the different forcings are discussed for three variables (temperature, zonal wind and geopotential height) and five levels (surface, 850 hPa, 500 hPa, 200 hPa and 50 hPa). The global El Niño signal can be selected more clearly in the troposphere than in the stratosphere. In contrast, the global volcano signal is strongest in the stratospheric temperature field. The amplitude of the perturbation for the volcano case is largest in the Atlantic region. The observed effect of local cooling due to the volcanic reduction of shortwave radiation over large land areas (like Asia) in subtropical regions, the observed advective warming over Eurasia and the advective cooling over Greenland are well simulated in the model. The radiative cooling near the surface is important for the volcano signal in the subtropics, but it is weak in high latitudes during winter. A statistically significant tropospheric signal of El Niño forcing occurs in the subtropics and in the midlatitudes of the North Pacific. The local anomalies in the El Niño forcing region in the tropics, and the warming over North America in middle and high latitudes are simulated as observed. The combined signal is different from a simple linear combination of the separate signals. It leads to a climate perturbation stronger than for forcing with El Niño or stratospheric aerosol alone and to a somewhat modified pattern. 相似文献
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Ingo Findenegg 《Aquatic Sciences - Research Across Boundaries》1967,29(1):125-144
Ohne Zusammenfassung 相似文献
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Ingo Haag 《洁净——土壤、空气、水》2006,34(6):549-559
In this paper the Basic Water Quality Model (BWQM) for the central part of River Neckar is used to analyse the oxygen budget and to assess the potentials of various measures to prevent or mitigate critical dissolved oxygen (DO) declines. It is shown that the oxygen budget is mainly governed by phytoplankton dynamics. The excessive growth of algae and the sudden break down of the resulting algal blooms may cause episodic DO depressions. Therefore, to stabilise the oxygen budget in a sustainable way, eutrophication has to be controlled within the central part of River Neckar and the upstream regions. The only feasible way to reach this goal appears to be a further drastic reduction of phosphorus emissions. In addition, it is indispensable to hold the very high standards of biochemical oxygen demand and ammonium retention at the wastewater treatment plants. A worse performance of the treatment plants would dramatically aggravate critical DO declines which may be caused by algae dynamics. As long as the oxygen budget is not completely stabilised, weir and turbine aeration can be used to mitigate DO depressions. It could be shown that the potentials of these measures suffice to keep DO at a tolerable level. However, due to the long travel times in River Neckar, it is important to start aeration up to several days before the DO minimum is reached. 相似文献