Coral reef ecosystems protect shore from high-energy waves under climate change scenarios     

Cesar Villanoy  Laura David  Olivia Cabrera  Michael Atrigenio  Fernando Siringan  Porfirio Aliño  Maya Villaluz 《Climatic change》2012,112(2):493-505

Coral reefs and other coastal ecosystems such as seagrasses and mangroves are widely recognized to provide protection against the devastating effects of strong waves associated with tsunamis and storms. The predicted warming climate brings to fore the role of these ecosystems in providing protection against stronger typhoons that can result in more devastating waves of greater amplitude. We performed a model simulation of storm generated waves on a Philippine reef, which is located along the path of tropical storms, i.e., at least 10 typhoons on the average pass through the study site yearly. A model to simulate wave propagation was developed using Simulating Waves Nearshore (SWAN) and DELFT3D-WAVE computer simulation software. Scenarios involving local monsoonal wind forcing and storm conditions were simulated. In addition, as climate change may also result to increased relative sea level, a 0.3 m and 1 m rise in sea level scenarios were also used in the wave model simulations. Results showed that the extensive reef system in the site helped dissipate wave energy that in turn reduced wave run-up on land. A significant reduction in wave energy was observed in both climate change, i.e., stronger wind and higher sea level, and non-climate change scenarios. This present study was conducted in a reef whose coral cover is in excellent condition (i.e., 50 to 80% coral cover). Estimates of coral reef growth are in the same order of magnitude as estimates of relative sea level rise based on tide gauge and satellite altimeter data, thus it is possible that the role of reefs in attenuating wave energy may be maintained if coral reef growth can keep up with the change in sea level. Nonetheless, to maintain reef growth, it is imperative to manage coral reef ecosystems sustainably and to eliminate the stressors that are within human control. Minimizing activities such as illegal and destructive blast and poison fishing methods, pollution and siltation, is crucial to minimize the impacts of high-energy waves that may increase with climate change.  相似文献   

The structure of clusters with bimodal distributions of galaxy radial velocities. II: A1775     

A. I. Kopylov  F. G. Kopylova 《Astrophysical Bulletin》2009,64(3):207-216

We analyze the structure of the cluster of galaxies Abell 1775 (α = 13 ^h 42 ^m , δ = +26°22′, cz ≈ 21000 km/s), which exhibits a bimodal distribution of radial velocities of the containing galaxies. The difference of the subcluster radial velocities is ΔV ≈ 2900 km/s. We use the results of our photometric observations made with the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the spectroscopic and photometric data from the SDSS DR6 catalog to determine independent distances to the subclusters via three different methods: the Kormendy relation, photometric plane, and fundamental plane. We find that the A1775 cluster consists of two independent clusters, A1775A (cz = 19664 km/s) and A1775B (cz = 22576 km/s), each located at its own Hubble distance and having small peculiar velocities. Given the velocity dispersions of 324 km/s and 581 km/s and the dynamic masses within the R ₂₀₀ radius equal to 0.6 × 10¹⁴ and 3.3 × 1014 M _⊙, the A1775A and A1775B clusters have the K-band luminosity-to-mass ratios of 29 and 61, respectively. A radio galaxy with an extended tail belongs to the A1775B cluster.  相似文献   

Coulomb Collisions and Electron Acceleration in Sub-Dreicer Electric Fields of the Corona and Chromosphere     

Yu. T. Tsap  Yu. G. Kopylova 《Geomagnetism and Aeronomy》2017,57(8):996-1000

Based on single-particle approximation, the peculiarities of electron acceleration by the sub-Dreicer electric field in solar atmosphere have been considered. The elastic and inelastic collisions of fast electrons with hydrogen atoms have been taken into account within the Born approximation. The rate of energy gain by accelerated electrons is inversely proportional to the mean free path of the thermal particles. Electron acceleration can be more effective in the transition region and chromosphere than in the corona. Chromospheric electrons can achieve several hundred keV energy at distances of a few tens of kilometers.  相似文献   

Characteristics of the Energy Transfer by Alfvén Waves in the Solar Atmosphere     

Tsap  Yu. T.  Stepanov  A. V.  Kopylova  Yu. G.  Khaneichuk  O. V. 《Geomagnetism and Aeronomy》2020,60(4):446-451

Geomagnetism and Aeronomy - The propagation of linear Alfvén waves with periods of 10–200 s from the photosphere to the solar chromosphere under the conditions of an isothermal...  相似文献   

Pulsations of optical radiation during the flare of YZ CMi occurred on February 9, 2008     

B. E. Zhilyaev  Yu. T. Tsap  M. V. Andreev  A. V. Stepanov  Yu. G. Kopylova  R. E. Gershberg  M. N. Lovkaya  A. V. Sergeev  I. A. Verlyuk  K. O. Stetsenko 《Kinematics and Physics of Celestial Bodies》2011,27(3):154-159

One of the most powerful and long-lived flares on the active red dwarf YZ CMi is considered. The flare was observed in the U band at the Terskol Peak Observatory on February 9, 2008. During the formation of the flare over the course of 30 seconds, the flare-induced stellar luminosity increased and became more than 180 times the preflare value. The total duration of the flare was approximately one hour. At the flare maximum, quasi-periodic pulsations having a specified period of approximately 11 s, an initial modulation depth of 5.5%, and an exponential damping time of 29 s were discovered using wavelet analysis. Assuming that the pulsations were caused by fast magnetohydrodynamic oscillations of a flare loop, the following parameters were determined in the region of energy release using coronal seismology methods: plasma concentration (2 × 10¹⁰ cm⁻³), temperature (3 × 10⁷ K), and magnetic field strength (0.015 T).  相似文献   

Cosmic factors influence on the inter-annual variations of the green 557.7 Nm line and red 630.0 Nm line nightglow intensities and their possible coupling with cloud covering at Abastumani (41.75°N, 42.82°E)     

Maya Todua  Goderdzi G. Didebulidze 《Acta Geophysica》2014,62(2):381-399

We studied the inter-annual distributions of the nightglow intensities of the thermosphere atomic oxygen red 630.0 nm and green 557.7 nm lines observed from Abastumani during cloudless nights, the planetary geomagnetic Ap index, solar F_10.7, and galactic cosmic rays (GCRs) flux. It is demonstrated that: on magnetically weakly disturbed/ quiet conditions (Ap < 12) in equinoctial months the red line intensities are minimal, while those of the green line are maximal; the red line intensity increases in May-July and is comparatively low in June, where, unlike most mid-latitude regions, the green line intensity is maximal. The red and green line intensities increase with growing solar activity but their behaviors stay the same, which is considered as a possible regional manifestation of lower and upper atmosphere vertical coupling. It was also detected that, for cloudless nights in June, the number of magnetically disturbed day-nights is maximal and the decrease of the GCRs flux is the biggest during a year.  相似文献   

Variation in DOC and trace metal concentration along the heavily urbanized basin in Kathmandu Valley,Nepal   总被引：1，自引：0，他引：1  

Maya P. Bhatt  Kevin H. Gardner 《Environmental Geology》2009,58(4):867-876

Water samples were analyzed for DOC and trace metals from Bagmati River within Kathmandu valley, Nepal, to understand the variation trends of DOC and trace metals and their relationship along the drainage network. The variability in organic matter and wastewater input within the Bagmati drainage basin appeared to control DOC and most of the trace metal concentration. The large input of organic matter and wastewater creates anoxic condition by consuming dissolved oxygen and releasing higher concentrations of DOC, trace elements such as nickel, arsenic, barium, cadmium, and copper with downstream distance. Concentrations of DOC and trace metals like barium and zinc showed strong relationships with human population density and suggest that human activities have strong control on these parameters along the drainage network. The DOC and most of the trace metal concentration increased with downstream distance and appeared to be directly associated with human activities. The variation trends of most of the trace metals appeared to be the same; however, concentration varied widely. Inputs of organic matter and wastewater due to human activities appeared directly to be associated for the variation of DOC and trace metals along the Bagmati drainage network within Kathmandu valley.  相似文献   

Devising ‘policy packages’ for seismic retrofitting of residences     

Segal  Ehud  Negev  Maya  Feitelson  Eran  Zaychik  Danielle 《Natural Hazards》2017,89(1):497-519

Natural Hazards - Collapse of residential buildings is the major cause of death during earthquakes. Seismic retrofitting of residential buildings is a cost-effective way to reduce injury and death....  相似文献   

Microbial mat development and dolomite formation under pre-evaporitic conditions during the Atlantic in a temperate area: The Sarliève Lake (French Massif Central)     

Jean-Robert Disnar  Maya Stefanova  Jean-Gabriel Bréhéret  Jean-Jacques Macaire 《Organic Geochemistry》2011,42(9):1089-1098

The Sarliève marsh in the Limagne plain, in the heart of the French Massif Central, functioned as an endorheic lake during the Late Glacial and the Early and Middle Holocene. During the Late Boreal and the Atlantic it experienced drastic lowering of the water level as a result of dry and warm climatic episodes. Then, pre-evaporitic conditions triggered the deposition of sediment rich in organic matter (OM) and in carbonates including dolomite. Fifty-one samples from a ca. 1.8 m sediment core section covering the period were analysed using Rock–Eval pyrolysis and gas chromatography–mass spectrometry (GC–MS). Throughout the interval, the OM content remained notable to high [up to 13.35% total organic carbon (TOC)] and of good quality as indicated by low oxygen index (OI) values (<200 mg CO₂ g⁻¹ TOC) and high hydrogen index (HI) values (160–660 mg HC g⁻¹) which, as a rule, increased with increasing TOC content.In contrast to the acid fractions, which sometimes contained notable proportions of n-C₁₆ or n-C₁₈ fatty acids (FAs; analysed as the methyl esters, FAMEs), the neutral fractions were almost devoid of low molecular weight compounds. The latter were probably biodegraded during early diagenesis. Conversely, high molecular weight compounds were abundant in both fractions and were dominated by n-alkanols, n-alkanes, steroids and hopanoids in the neutrals and even numbered FAs and hopanoids in the acid fractions. The hopanoids were dominated by regular bishomohopanoids, accompanied by 2-methylated bishomohopanoids, as well as by unidentified bishomohopanoids with methylation in either the D or E ring. These distributions, typical for bacteria, provide support for previous hypotheses on the contribution of microorganisms to the studied record and for providing conditions for the precipitation and growth of dolomite and other pristine carbonate minerals [Bréheret, J.G., Fourmont, A., Macaire, J.J., Négrel, Ph., 2008. Microbially mediated carbonates in the Holocene lacustrine deposits of the Marais de Sarliève (French Massif Central) testify to the evolution of a restricted environment. Sedimentology 55, 557–578]. The preservation of the compounds was probably ensured by persistent reducing conditions during diagenesis, despite variable climatic conditions and related changes in lake level and sedimentation rate. Comparable distributions of hopanoic acids and hopanols, as well as roughly parallel variation with depth in the corresponding components in both fractions, strongly suggest that all the hopanoids derive from the same microbial precursors, slight shifts in the acid/alcohol ratio being governed by limited changes in redox conditions during early diagenesis.  相似文献   

Biological controls on dissolution of diatom frustules during their descent to the deep ocean: Lessons learned from controlled laboratory experiments     

Uta Passow  Megan A. French  Maya Robert 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(12):1147-1157

The majority of opal produced by diatoms dissolves during their sedimentation to the seafloor, but spatial and temporal variability of dissolution rates are large. Controlled laboratory experiments using live phytoplankton or phyto-detritus may help identify the different processes, including those that are biologically mediated or physico-chemically driven, that impact the dissolution of frustules and the aforementioned variability. Results of eight bSiO₂ dissolution experiments, seven of which were conducted at low temperatures (<6 °C) are presented within the context of earlier similar studies, and different phases of dissolution dynamics characterized. TEP concentration, aggregation and the physiological status of the diatoms determined the period during which diatoms may maintain the protective membrane that surrounds their frustule and effectively reduces or completely inhibits (lag period) dissolution for some time. Once diatoms loose the capability to maintain their protective membrane, bacterial activity compromises it. Physico-chemical dissolution, which depends on frustule structure and abiotic environmental conditions, begins once the protective membrane is damaged. The ability of diatoms to maintain their membrane, the bacterial composition and activity governing its degradation, and the physico-chemical dissolution dynamics of exposed frustules are all impacted by temperature. In our experiments instantaneous dissolution rates were not dependant on bSiO₂ concentration at low temperatures, although such a relationship was observed under otherwise identical conditions at 15 °C, implying that biotic factors rather than physico-chemical processes initially dominated dissolution at polar temperatures. Since inhibition of bSiO₂ dissolution at low temperatures was inhibited to a greater extent than organic matter degradation, we postulate that it was not reduced bacterial activity but the enhanced ability of diatoms to maintain their membrane and thus withstand microbial attack that caused the low initial dissolution rates at <6 °C. In situ, interactions between the different biotic and abiotic processes impacting dissolution combined with differences in sinking velocity of diatom aggregates and grazing effects could easily explain high spatial and temporal variability in the accumulation of diatoms on the seafloor. Simple calculations based on our experimental results suggest that Fragilariopsis kerguelensis, for example, would be appreciably more likely to reach the seafloor than Chaetoceros debilis if both grow at low growth rates, e.g. under growth limiting conditions. However, dissolution behavior of Chaetoceros debilis during sedimentation may differ under conditions where this species forms large blooms.  相似文献