Current status of coral takeover by an encrusting excavating sponge in a Caribbean reef          下载免费PDF全文

Ángela Marulanda‐Gómez  Mateo López‐Victoria  Sven Zea 《Marine Ecology》2017,38(1)

On Caribbean reefs, the excavating sponge Cliona tenuis opportunistically colonized dead skeletons of the elkhorn coral Acropora palmata after its massive die‐off in the 1980s. Further C. tenuis population increase occurred by colonization of other coral species, causing coral tissue death through undermining of live tissue and lateral growth. To follow up on a previous (2001) characterization of the abundance and size structure of C. tenuis at Islas del Rosario (Colombia), these factors were again estimated in 2014, along with its substratum utilization. The fate of sponge individuals colonizing massive coral colonies marked in 2001–2004 was also followed. By 2014 C. tenuis was still disproportionally occupying dead A. palmata branches, but its abundance and density, and the cover of other benthic elements, had not significantly changed over the 13‐year period, suggesting that a stasis has been reached. Cliona tenuis was thus initially favored in the 1980s, but substratum monopolization did not occur. From 2001 to 2014, small individuals increased in number and very large ones decreased, suggesting not only that new recruitment is occurring, but also that larger sponges are shrinking or fragmenting. Marked sponges continued killing corals over the first few years, but over longer times they retreated or died, allowing corals to resume upward growth. However, it could not be ascertained whether the sponge retreat was age‐related or the result of some environmental effect. The apparent preference for recently dead clean coral by larvae of C. tenuis and its current dynamics of recruitment, growth, fragmentation and mortality have stabilized its space occupation at Islas del Rosario.  相似文献   

Representing glaciers in a regional climate model     

Sven Kotlarski  Daniela Jacob  Ralf Podzun  Frank Paul 《Climate Dynamics》2010,34(1):27-46

A glacier parameterization scheme has been developed and implemented into the regional climate model REMO. The new scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale. The temporal evolution and the general magnitude of the simulated glacier mass balance in the European Alps are in good accordance with observations for the period 1958–1980, but the strong mass loss towards the end of the twentieth century is systematically underestimated. The simulated decrease of glacier area in the Alps between 1958 and 2003 ranges from −17.1 to −23.6%. The results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based on simplified concepts of glacier-climate interaction. However, realistic results can only be achieved by explicitly accounting for the subgrid variability of atmospheric parameters within a climate model grid box.  相似文献   

PGE distribution in massive sulfides from the P<Emphasis Type="SmallCaps">ACMANUS</Emphasis> hydrothermal field,eastern Manus basin,Papua New Guinea: implications for PGE enrichment in some ancient volcanogenic massive sulfide deposits     

Jan?Pa?avaEmail author  Anna?Vymazalová  Sven?Petersen  Peter?Herzig 《Mineralium Deposita》2004,39(7):784-792

The distribution of platinum group elements (PGE) in Cu- and Zn-rich samples from the Roman Ruins and Satanic Mills vent sites in the PACMANUS hydrothermal field (Papua New Guinea) was studied and compared to that from selected ancient volcanogenic massive sulfide (VMS) deposits. Samples from the Satanic Mills site are enriched in Pd and Rh when compared to samples from Roman Ruins and reach highest values in active and inactive Cu-rich black smoker chimneys and chalcopyrite-cemented dacite breccias (up to 356 ppb Pd and up to 145 ppb Rh). A significant positive correlation was established between Cu and Pd and Rh in samples from both vent sites. Comparisons of chondrite normalized patterns and values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides and probable source rocks (felsic volcanic rocks/MORB) along with the evidence for a magmatic component in the PACMANUS hydrothermal system indicate that leaching of back-arc volcanic rocks together with addition of magmatic volatiles to the convecting hydrothermal system was the most important factor for PGE enrichment at PACMANUS and likely at some PGE-enriched ancient VMS deposits.An erratum to this article can be found at Editorial handling: B. Lehmann  相似文献   

Natural Conversational Interfaces to Geospatial Databases   总被引：1，自引：0，他引：1  

Guoray Cai  Hongmei Wang  Alan M. MacEachren  Sven Fuhrmann 《Transactions in GIS》2005,9(2):199-221

Natural (spoken) language, combined with gestures and other human modalities, provides a promising alternative for interacting with computers, but such benefit has not been explored for interactions with geographical information systems. This paper presents a conceptual framework for enabling conversational human‐GIS interactions. Conversations with a GIS are modeled as human‐computer collaborative activities within a task domain. We adopt a mental state view of collaboration and discourse and propose a plan‐based computational model for conversational grounding and dialogue generation. At the implementation level, our approach is to introduce a dialogue agent, GeoDialogue, between a user and a geographical information server. GeoDialogue actively recognizes user's information needs, reasons about detailed cartographic and database procedures, and acts cooperatively to assist user's problem solving. GeoDialogue serves as a semantic ‘bridge’ between the human language and the formal language that a GIS understands. The behavior of such dialogue‐assisted human‐GIS interfaces is illustrated through a scenario simulating a session of emergency response during a hurricane event.  相似文献   

Cyclicities in Triassic platform carbonates: synchronizing radio-isotopic and orbital clocks     

Roland Mundil  Rainer Zühlke  Thilo Bechstädt  Arndt Peterhänsel  Sven O. Egenhoff  Felix Oberli  Martin Meier  Peter Brack  Hans Rieber 《地学学报》2003,15(2):81-87

ABSTRACT Sedimentary cycles recorded in young sediments are often attributed to fluctuations of the Earth's climate on a 10⁴−10⁶-year scale which in turn is governed by periodic variations in solar insolation linked to orbital (Milankovitch) parameters. A spectacular example of cyclic stratal patterns in ancient deposits is the Middle Triassic Latemar carbonate platform (W Dolomites, N Italy). Based on spectral analyses from previous studies, a superimposition of precession (∼20 ka) and eccentricity (∼100 ka) controlled sea-level fluctuations has been suggested to account for the stacking hierarchy at Latemar, with ∼20 ka being assigned to each highest-order depositional cycle. Zircon U–Pb isotopic ages from volcanic-ash layers within the cyclic succession, corroborated by biostratigraphic constraints, suggest that the average time interval for every individual cycle is significantly smaller than the shortest Milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy. However, our new spectral data indicate that cyclicities resembling Milankovitch characteristics might exist, but on an entirely different scale. Our findings show that frequency spectra should only be interpreted in combination with robust age control. They also encourage the search for complementary mechanisms controlling carbonate deposition.  相似文献   

Implication for mantle flow from the Hawaiian-Emperor chain     

Sven Maale  Ole Tjugen 《Earth and Planetary Science Letters》1988,91(1-2)

Assuming that Rayleigh-Benard flow occurs within the upper mantle, ascending plumes must undergo horizontal displacement during ascent that can be traced at the surface. It is shown that the Hawaiian-Emperor bend cannot be formed if the convection rate is of the same order of magnitude as the ascent rate of the plumes. The plume patterns obtained by push-pull or lithospheric sliding are similar to that of the Hawaiian-Emperor chain. Hence the present results support the sliding model.  相似文献   

Population density and zoning of olivine phenocrysts in tholeiites from Kauai,Hawaii     

Sven Maaløe  Ole Tumyr  Dodie James 《Contributions to Mineralogy and Petrology》1989,101(2):176-186

The population density of olivine phenocrysts of the tholeiites display an exponential variation, which is typical of igneous as well as contact metamorphic rocks. The exponential variation is explained by a new growth probability model, which is consistent with experimental work. The forsterite content of the olivine phenocrysts decreases with decreasing size. Various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber, after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place.  相似文献   

Pine forest microclimate simulation using different diffusivities     

Sven Halldin  Anders Lindroth 《Boundary-Layer Meteorology》1986,35(1-2):103-123

Proper understanding of, e.g., evaporation from a forest requires an understanding of its microclimate. A well established, steady-state model was used to simulate microclimate and evaporation of a sparse pine forest in central Sweden. Model input included profiles of turbulent diffusivity, boundary-layer resistance, stomatal resistance, wind speed, net and global radiation and needle area density. Momentum balance, energy balance and exponentially decreasing diffusivities were used to study the sensitivity of the evaporation rates and of the temperature and humidity profiles. Model output proved to be unreliable when measured temperature and humidity at the bottom of the stand were used instead of a measured ground heat flux as the lower boundary condition. Energy balance diffusivity was usually larger than momentum balance diffusivity at the canopy top but decreased rapidly to a minimum at approximately the height where the momentum balance diffusivity had its maximum. Energy balance diffusivity commonly showed a secondary maximum below the height of the maximum needle area density. Profiles of Richardson number showed that thermal effects became important just below the canopy top. Bluff-body effects distinguished the energy balance from the momentum balance diffusivity and both were subject to shelter effects. Total evaporation was not very sensitive to the choice of diffusivity when soil heat flux was given as the lower boundary condition.  相似文献   

An improved Kajak-type gravity core sampler for soft bottom sediments     

Sven Blomqvist  Berndt Abrahamsson 《Aquatic Sciences - Research Across Boundaries》1985,47(1):81-84

A new, modified model of the Kajak tube core sampler is presented. The new sampler is intended for use on soft sediments, and hence of light weight (12 kg). The improved sampler offers the following advantages. (1) increased robustness, (2) simplified attachment of the coring tube to the holder and valve assembly, permitting quick exchange of sampling tubes, (3) unimpeded flow of water through the tube during slow descent, (4) a reliable, automatic mechanism closing the top of the core tube after impact, and (5) an easily dismantled supporting frame, which also protects the sampler from damage against the side of the boat in rought weather. The operation of the sampler has been observedin situ and during ordinary shipboard collection of core samples, with satisfactory results.  相似文献   

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic     

Jan Mangerud  Sven Erik Lie  Harald Furnes  Inger Lise Kristiansen  Leif Lømo 《Quaternary Research》1984,21(1):85-104

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.  相似文献