Climate change and coral reef bleaching: An ecological assessment of long-term impacts,recovery trends and future outlook   总被引：2，自引：0，他引：2  

Andrew C. Baker  Peter W. Glynn  Bernhard Riegl 《Estuarine, Coastal and Shelf Science》2008

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.  相似文献   

How can we model subsurface stormflow at the catchment scale if we cannot measure it?     

Peter Chifflard  Theresa Blume  Katja Maerker  Luisa Hopp  Ilja van Meerveld  Thomas Graef  Oliver Gronz  Andreas Hartmann  Bernhard Kohl  Edoardo Martini  Christian Reinhardt‐Imjela  Martin Reiss  Michael Rinderer  Stefan Achleitner 《水文研究》2019,33(9):1378-1385

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Differential uplift on the boundary between the Eastern and the Southern European Alps: Thermochronologic constraints from the Brenner Base Tunnel     

Thomas Klotz  Hannah Pomella  Martin Reiser  Bernhard Fügenschuh  Massimiliano Zattin 《地学学报》2019,31(3):281-294

The Brenner Base Tunnel will connect Innsbruck (Austria) and Franzensfeste (Italy) by piercing two of the most important fault structures of the Alps: the Periadriatic fault system (PFS) and the Southern limit of Alpine metamorphism (SAM). (U‐Th)/He dating (apatite) and fission‐track analysis (apatite and zircon) on samples taken during excavation reveal a complex pattern of exhumation through time. The results yield temporal constraints for relative vertical block movement and fault activity. Furthermore, they indicate differential uplift of the northern block along the ~E–W striking PFS and allow locating the position of the SAM in the overtilted nappe stack south of the Tauern Window. Our data strongly support, for the first time, an ongoing north‐side‐up movement along this section of the PFS until at least the end of Miocene.  相似文献   

Force-directed layout of origin-destination flow maps   总被引：1，自引：0，他引：1  

Bernhard Jenny  Daniel M. Stephen  Ian Muehlenhaus  Brooke E. Marston  Ritesh Sharma  Eugene Zhang 《International journal of geographical information science》2017,31(8):1521-1540

This paper introduces a force-directed layout method for creating origin-destination flow maps. Design principles derived from manual cartography and automated graph drawing to increase readability of flow maps and graph layouts are taken into account. The origin-destination flow maps produced with our algorithm show flows with quadratic Bézier curves that reduce flow-on-flow and flow-on-node overlaps, and avoid sharp or irregular bends in flow lines. A survey of expert cartographers found that flow maps created with our automated method are similar in quality to manually produced flow maps.  相似文献   

Phenomenon-based Specification of the Digital Representation of Terrain Surfaces     

Bernhard Schneider 《Transactions in GIS》2001,5(1):39-52

The phenomenon known as 'terrain' is a continuous surface. However, when a digital terrain representation is based on a regular raster (i.e. a DEM) the digital surface is commonly not continuous. This is the case for the derivation of variables such as slope, aspect, and curvature values as performed in today's Geographic Information Systems (GIS). Often, there is no surface specified at all, as, for instance, when flow lines or watersheds are constructed. The discrepancy between the phenomenon to be modelled and its digital representation causes the terrain analysis results to be less accurate than they could be. Furthermore, if more than one type of terrain information is derived the results are likely to be based on different specifications of the seemingly same terrain surface. The combined application of the derivation results will likely introduce inconsistencies. This paper suggests founding the specification of digital terrain representations on a careful analysis of the properties of the phenomenon. The paper details the reasons for, and advantages of, continuous surface representations and emphasises the importance of a comprehensive documentation of the conceptual models underlying digital terrain representations. A review of suitable interpolation approaches for the specification of terrain surfaces is given. The paper discusses how the resulting digital surfaces are analysed and how measurement uncertainty may be accounted for.  相似文献   

Age,origin and geodynamic significance of a polymetamorphic felsic intrusion in the Ötztal Crystalline Basement,Tirol, Austria     

F. Bernhard  U. S. Klötzli  M. Thöni  G. Hoinkes 《Mineralogy and Petrology》1996,58(3-4):171-196

Summary A multi-method approach was applied to derive the age and origin of an orthogneiss body located in the central Kaunertal, western Ötztal Crystalline Basement (ÖCB). The Tieftal orthogneiss body is an internally differentiated, polymetamorphosed epizonal intrusion, embedded in amphibolites. It comprises leucocratic hedenbergite-hornblende-, hornblende- and biotite-hornblende-gneisses, but also some melanocratic rock types. The leucocratic Tieftal gneisses are granitic, have a near eutectic melt composition and share some features of A-type granites, such as high Na₂O+K₂O(8.07 to 8.58wt%), Zr (379 to 554ppm) and Y (58 to 79ppm) contents. The REE-patterns are rather flat ((La/Yb)_N=2.4 to 3.7), with distinct negative Eu anomalies. Single zircon evaporation dating of two samples and Sm-Nd dating of relict magmatic titanite resulted in ages of 487±7, 484±3 and 487±5Ma, respectively. The weighted mean of 485±3Ma is interpreted as the primary crystallization age of the Tieftal orthogneiss body. Rb-Sr whole rock dating results in a well defined regression line, corresponding to an age of 411±9Ma. This age clearly documents at least a partial resetting of the whole rock Rb-Sr system, which is most probably due to subsequent metamorphic overprint. The leucocratic Tieftal gneisses are isotopically rather primitive with an Nd _CHUR ^{485 Ma} value of +1.7 and a calculated magmatic initial⁸⁷Sr/⁸⁶Sr ratio of 0.7047. These data suggest a major mantle contribution. Most probably, they originated through fractionation of the magmatic precursors of the accompanying tholeiitic metabasites. The more primitive isotopic composition of ÖCB metabasites and some late Archean/early Proterozoic and Cambrian inheritance in Tieftal gneiss zircons suggest some involvement of old crustal rocks, too. The amount of crustal contamination can be calculated to be in the range of 10 to 40%. The Tieftal gneisses and the accompanying metabasites are interpreted as remnants of igneous rocks related to an early Ordovician rifting and incipient formation of new oceanic crust, an event which can be traced throughout the central and western European Variscan and Alpine terranes.

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Alter, Genese und geologische Bedeutung einer polymetamorphen felsischen Intrusion im Ötztalkristallin, Tirol, Österreich

Zusammenfassung Ein Vielzahl von Methoden wurde angewandt, um das Alter und die Genese eines Orthogneiskörpers im mittleren Kaunertal, westliches Ötztalkristallin, abzuleiten. Der Tieftal-Orthogneiskörper ist eine in Amphiboliten eingeschaltete, intern differenzierte, polymetamorph überprägte, epizonale Intrusion. Er umfaßt sowohl leukokrate Hedenbergit-Hornblende-, Hornblende- und Biotit-Hornblende-Gneise als auch untergeordnet melanokrate Gesteine. Die leukokraten Tieftal-Gneise besitzen einen granitischen, beinahe einer eutektischen Schmelze entsprechenden Chemismus; einige Parameter wie hohe Na₂O+K₂O(8.07 bis 8.58Gew%), Zr(379 bis 554ppm) und Y(58 bis 79ppm) Gehalte weisen auf eine A-Typ Affinität hin. Die SEE-Spektren sind nur gering fraktioniert ((La/Yb)_N=2.3 bis 3.7) und weisen eine markante negative Eu-Anomalie auf. Einzelzirkon-Evaporationsdatierungen an 2 Proben und eine Sm-Nd Datierung von reliktischem magmatischem Titanit ergeben Alter von 487±7, 484±3 und 487±5Ma. Der gewichtete Mittelwert von 485±3Ma wird als das primäre magmatische Kristallisationsalter des Tieftal-Orthogneiskörpers interpretiert. Eine Rb-Sr Gesamtgesteinsdatierung ergibt eine gut definierte Regressionsgerade mit einem Alter von 411±9Ma. Dieses Alter beweist eine postmagmatische Störung des Rb-Sr Gesamtgesteinssystems, die durch die metamorphen überprägungen verursacht wurde. Die leukokraten Tieftal-Gneise besitzen eine relative primitive isotopische Zusammensetzung mit einem Nd _CHUR ^{485 Ma} a Wert von +1.7 und einem zurückgerechneten magmatischen⁸⁷Sr/⁸⁶Sr Initialverhältnis von 0.7047. Diese Daten machen eine große Beteiligung von Mantelmaterial wahrscheinlich. Am ehesten entstanden die leukokraten Tieftal-Gneise durch magmatische Fraktionierungsprozesse aus den Ausgangsgesteinen der begleitenden tholeiitischen Metabasite. Die noch primitivere isotopische Zusammensetzung der Metabasite im Ötztalkristallin und spätarchaische/frühproterozoische sowie kambrische Komponenten in den Zirkonen der leukokraten Tieftal-Gneise weisen aber auch auf die Beteiligung alten krustalen Materials hin. Der Anteil der krustalen Komponente liegt im Bereich von 10 bis 40%. Der Tieftal-Orthogneiskörper und die begleitenden Metabasite werden als Relikte magmatischer Gesteine, die während eines frühordovizischen Riftings und der beginnenden Bildung neuer ozeanischer Kruste entstanden sind, gedeutet. Zeugen dieses Vorganges sind in allen variszisch und alpidisch geprägten Gebieten Westund Mitteleuropas zu finden.

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With 13 Figures  相似文献   

Real-time raster projection for web maps     

Bernhard Jenny  Bojan Šavrič  Johannes Liem 《International Journal of Digital Earth》2016,9(3):215-229

The virtual globe is the default visualization for Digital Earth applications, but it can only show one half of the Earth. This article introduces user-adjustable, on-the-fly projection of georeferenced raster images for web mapping and web GIS applications. This technique allows users to center a map on arbitrary locations, while still seeing the entire Earth surface. Modern web mapping libraries can apply map projection transformations to vector data in the browser, but they do not currently support the projection of raster images at interactive frame rates. We use the cross-platform WebGL (Web Graphics Library) graphics pipeline for hardware-accelerated projection of raster data in web browsers. Two algorithmic techniques – inverse per-fragment projection, and combined forward per-triangle and inverse per-fragment projection – for georeferenced raster imagery are documented. The resulting raster maps combine the ease of use and flexibility of interactive virtual globes with the ability to show the entire Earth. The adjustable projection of raster imagery allows users to observe global phenomena that are difficult to visualize on virtual globes or traditional maps with static projections.  相似文献   

The Structure of Coral Communities at Hurghada in the Northern Red Sea   总被引：1，自引：0，他引：1  

Bernhard  Riegl Branko  Velimirov 《Marine Ecology》1994,15(3-4):213-231

Abstract. The community structure of hard and soft corals, with an emphasis on hard corals, was determined by means of line-transects on 9 on-and off-shore reefs of different type and different wave exposure in the Northern Red Sea near Hurghada in Egypt. Coral communities were found to differentiate along a horizontal wind- and wave-exposure gradient. Exposed communities were dominated by Acropora species, sheltered communities by Porites species, and semi-exposed communities by Millepora species. Also, vertical within-reef zonations following a depth gradient were observed; these were unique for each exposure-determined community type. Average transect diversity was highest on semi-exposed reefs, lowest on sheltered reefs. Reef slopes were more diverse than other reef zones. The observed community structure was compared with data from the literature, and widely distributed, roughly comparable hard and soft coral communities were identified.  相似文献   

Groundwater isoscapes in a montane headwater catchment show dominance of well‐mixed storage          下载免费PDF全文

Bernhard Scheliga  Doerthe Tetzlaff  Gunnar Nuetzmann  Chris Soulsby 《水文研究》2017,31(20):3504-3519

We conducted an integrated groundwater–surface water monitoring programme in a 3.2‐km² experimental catchment in the Scottish Highlands by sampling all springs, seepages, and wells in six, spatially extensive synoptic surveys over a 2‐year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70% glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples were analysed for stable isotopes, Gran alkalinity and electrical conductivity. Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well‐mixed shallow, groundwater stores. Moreover, line‐conditioned excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and electrical conductivity of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotope composition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterized by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasizes the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.  相似文献   

What do biphasic flow experiments reveal on the variability of exposure on alluvial fans and which implications for risk assessment result from this?     

Diaz  Hector  Mazzorana  Bruno  Gems  Bernhard  Rojas  Ivan  Santibañez  Nicole  Iribarren  Pablo  Pino  Mario  Iroumé  Andrés 《Natural Hazards》2022,111(3):3099-3120

Sudden avulsions, unexpected channel migrations and backfilling phenomena are autogenic phenomena that can considerably change the propagation patterns of sediment-laden flows on alluvial fans. Once the initial and boundary conditions of the hazard scenario with a given return period are determined, the assessment of the associated exposed areas is based on one numerical, essentially deterministic, process simulation which may not adequately capture the underlying process variability. We generated sediment-laden flows on an experimental alluvial fan by following a “similarity-of-process concept”. Specifically, we considered a convexly shaped alluvial fan model layout featuring a curved guiding channel. As loading conditions, we defined a reference, an increased and a reduced level for the released water volume and the predisposed solid fraction, respectively. Further, we imposed two different stream power regimes and accomplished, for each factor combination, eight experimental runs. The associated exposure areas were recorded by video and mapped in a GIS. We then analysed exposure data and determined exposure probability maps superposing the footprints of the eight repetitions associated with each experimental loading condition. The patterns of exposure referred to the specific loading conditions showed a noticeable variability related to the main effects of the total event volume, the solid fraction, the interactions between them, and the imposed stream power in the feeding channel. Our research suggests that adopting a probabilistic notion of exposure in risk assessment and mitigation is advisable. Further, a major challenge consists in adapting numerical codes to better reflect the stochastics of process propagation for more reliable flood hazard assessments.

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