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101.
A model describing macroalgal early life stages and adult dynamics was used to quantify the effects of non-adult forms on the productivity of adult macroalgae in a eutrophic estuary. Predictions indicate that during years with mild winters and low rainfall, spring blooms will occur at the expense of the growth and reproduction of overwintering adults and without the contribution of the spore bank. In these circumstances, there is a positive correlation between the intensity of the blooms and the biomass of overwintering adults until a maximum threshold value. On the contrary, in years with high rainfall and low or inexistent biomass of overwintering adults, the onset of adult’s growth depends on the biomass of viable dormant spores, the growing season occurs later and adult productivity is very limited. Long-term predictions for climate change scenarios suggest that, in general, global warming will have adverse affects on Ulva intestinalis productivity, with the adults being more affected than the early life stages. 相似文献
102.
Earthquake swarms are often assumed to be caused by magmatic or fluid intrusions, where the stress changes in the vicinity
of the intrusion control the position, strength and rate of seismicity. Fracture mechanical models of natural intrusions or
man-made hydrofractures pose constraints on orientation, magnitude, shape and growing rate of fractures and can be used to
estimate stress changes in the vicinity of the intrusions. Although the idea of intrusion-induced seismicity is widely accepted,
specific comparisons of seismicity patterns with fracture models of stress changes are rarely done.
The goal of the study is to review patterns of intrusion-induced earthquake swarms in comparison to the observations of the
swarm in NW Bohemia in 2000. We analyse and discuss the theoretical 3D shape of intrusions under mixed mode loading and apparent
buoyancy. The aspect ratio and form of the intrusion is used to constrain parameters of the fluid, the surrounding rock and
stress. We conclude that the 2000 NW Bohemia swarm could have been driven by a magmatic intrusion. The intrusion was, however,
inclined to the maximal principal stress and caused shear displacement additional to opening. We estimate that the density
diference between magma and rock was small. The feeding reservoir was possibly much larger than the area affected from earthquakes
and may be a vertical dike beneath the swarm region. 相似文献
103.
Agnès Mazot Alain Bernard Tobias Fischer Salvatore Inguaggiato Igan S. Sutawidjaja 《Journal of Volcanology and Geothermal Research》2008
Papandayan is a stratovolcano situated in West Java, Indonesia. Since the last magmatic eruption in 1772, only few hydrothermal explosions have occurred. An explosive eruption occurred in November 2002 and ejected ash and altered rocks. The altered rocks show that an advanced argillic alteration took place in the hydrothermal system by interaction between acid fluids and rocks. Four zones of alteration have been defined and are limited in extension and shape along faults or across permeable structures at different levels beneath the active crater of the volcano. 相似文献
104.
Janet M. Fischer Tara Reed-Andersen Jennifer L. Klug Alice G. Chalmers 《Estuaries and Coasts》2000,23(4):565-571
Geomorphology may be an important predictor of vegetation pattern in systems where suceptibility to disturbance is unevenly
distributed across the landscape. Salt marsh communities exhibit spatial pattern in vegetation at a variety of spatial scales.
In coastal Georgia, the low marsh is a virtual monoculture ofSpartina alterniflora interspersed with patches of species that are more typical of the high marsh. These localized disturbances are most likely
created by wrack mats, mats of dead vegetation which can compact and smother underlying vegetation creating bare patches for
colonization by high marsh species. We investigated the spatial pattern of disturbed patches along a 2 km section of Dean
Creek, a tidal creek at the southwestern end of Sapelo Island, Georgia, U.S. We used a discriminant model to explore the relationship
between tidal creek morphology (e.g., the presence of drainage channels and creek bends) and the spatial distribution of disturbed
patches. The model predicted vegetation pattern along the creek with relatively high accuracy (>70%). Areas where water movement
is slowed or multidirectional (e.g., along creek bends and near drainage channels) were most susceptible to disturbance. Our
findings suggest an important functional linkage between geomorphology and vegetation pattern in salt marsh communities. 相似文献
105.
Understanding the influence of climatic and non-climatic factors on geochemical signals in corals is critical for assessing coral-derived records of tropical climate variability. Porites microatolls form large, disk-shaped colonies constrained in their upward growth by exposure at or close to mean spring low water level, and occur on Indo-Pacific reefs. Microatolls appear suitable for paleoclimate reconstruction, however the systematics of the microatoll chemistry-climate relationship are yet to be characterized. In this study, the δ18O signal in Porites microatolls from well-flushed reef flats on Kiritimati (Christmas) Island, central Pacific was investigated for intra-coral (growth aspect and extension rate effects) and between-coral effects, and to explore the climate signal contained within their skeletons. Samples for δ18O analysis were taken from six individual transects from different positions within Porites microatoll XM22. The results show that: (1) the average standard deviation for the mean δ18O values of transects that represent the same time periods is 0.03‰, and is within measurement error for a single analysis (0.04‰); (2) the average standard deviation for time-equivalent, near-monthly samples along the transects within the same microatoll is 0.07‰ and; (3) comparison of the average δ18O values of records for different microatolls from across Kiritimati Island show only a small between-coral differences of 0.04‰ and 0.11‰ for different time periods. These differences in mean δ18O are within the range for intra- and inter-colony differences in seasonal and interannual δ18O reported for dome-shaped Porites. Based on these results, a stacked microatoll δ18O record was constructed for the period 1978-2007 for comparison with published coral δ18O records for nearby dome-shaped Porites. There is a systematic offset between the two types of records, which is probably due to variations in δ18O seawater across Kiritimati Island. Despite the offset, all records show similar amplitudes for the seasonal-cycle of δ18O, and there is a strong correlation (r = −0.71) between microatoll δ18O and local sea surface temperature (SST). The δ18O-SST slope relationship for microatolls is −0.15‰/°C, very similar to that reported for fast-growing domed corals (−0.18‰ to −0.22‰/°C). Statistical analysis of the stacked microatoll δ18O record shows that it is correlated with both local and large-scale climate variables (primarily SST) at semiannual, annual and interannual timescales. Our results show that the signal reproducibility and fidelity of skeletal δ18O in coral microatolls is comparable to that observed for more conventional coral growth forms. Longer-lived, and fossil, Porites microatolls, where they have grown in suitably flushed environments, are likely to contain δ18O signals that can significantly extend instrumental records of tropical climate variability. 相似文献
106.
107.
T.E. Johnson C.L. Kirkland D.R. Viete S. Fischer S.M. Reddy N.J. Evans B.J. McDonald 《地学前缘(英文版)》2017,8(6):1469-1478
The type locality for high-temperature,low-pressure regional metamorphism,the Buchan Block in NE Scotland,exhibits profound differences to the rest of the Grampian Terrane.These differences have led some to regard the Buchan Block as an exotic crustal fragment comprising Precambrian basement gneisses and cover rocks thrust into their current position during Grampian orogenesis.Although rocks of the Buchan Block are now generally correlated with Dalradian strata elsewhere,the origin of the gneisses and the cause of the high heat flow and associated magmatism is debated.We report SIMS U-Pb and LA-ICPMS Hf isotopic data in zircon from high-grade rocks from the northeast(Inzie Head Gneiss)and northwest(Portsoy)corners of the Buchan Block.Around Inzie Head,upper amphibolite to granulite facies metasedimentary gneisses coexist with diorite sheets that were emplaced contemporaneously with partial melting of their host rocks,at least locally.U-Pb geochronology indicates a crystallisation age for the diorite of 486±9 Ma.Highly-deformed diorites within the Portsoy Gabbro have a crystallisation age of 493±8 Ma.Ages of ca.490 Ma for magmatism and high-grade metamorphism,which are broadly contemporaneous with ophiolite obduction and the onset of orogenesis,are significantly older than the established peak of Grampian metamorphism(ca.470 Ma).We propose a new model for the Grampian Orogeny involving punctuated tectonothermal activity due to tectonic switching during accretionary orogenesis.Rollback of a NW-dipping subduction zone at ca.490 Ma produced a back-arc environment(the Buchan Block)with associated arc magmatism and high dT/dP metamorphism.Arrival of an outboard arc resulted in shortening(the initial phase of the Grampian Orogeny)at ca.488 Ma.Rollback of a NW-dipping subduction zone to the SE of the ca.488 Ma suture began at 473 Ma and led to lithospheric-scale extension,decompression melting and advective heating of the middle crust,producing the widespread ca.470 Ma Grampian(classic Barrovian and Buchan)regional metamorphism.Resumed hinge advance and the final phase of shortening cut off the heat supply at ca.465 Ma,marking the end of the Grampian Orogeny. 相似文献
108.
J. Tyler Faith David R. Braun Benjamin Davies Larisa R. G. DeSantis Matthew J. Douglass Irene Esteban Vincent Hare Naomi E. Levin Julie Luyt Robyn Pickering Mitchell J. Power Judith Sealy Deano Stynder 《第四纪科学杂志》2020,35(8):1007-1020
The Pleistocene ungulate communities from the western coastal plains of South Africa's Cape Floristic Region (CFR) are diverse and dominated by grazers, in contrast to the region's Holocene and historical faunas, which are relatively species-poor and dominated by small-bodied browsers and mixed feeders. An expansion of grassy habitats is clearly implied by the Pleistocene faunas, but the presence of ruminant grazers that cannot survive the summer dry season typical of the region today suggests other important paleoecological changes. Here we use dental ecometrics to explore the paleoecological implications of the region's Pleistocene faunas. We show that the dental traits (hypsodonty and occlusal topography) of the ungulates that occurred historically in the CFR track annual and summer aridity, and we use these relationships to reconstruct past aridity. Our results indicate that the Pleistocene faunas signal paleoenvironments that were on average less arid than today, including during the summer, consistent with other lines of evidence that suggest a higher water table and expansion of well-watered habitats. Greater water availability can be explained by lower temperature and reduced evapotranspiration during cooler phases of the Pleistocene, probably coupled with enhanced groundwater recharge due to increased winter precipitation. 相似文献
109.
Julia L. Barringer Timothy P. Wilson Zoltan Szabo Jennifer L. Bonin Jeffrey M. Fischer Nicholas P. Smith 《Environmental Geology》2008,53(6):1183-1199
Diurnal variations in particulate and dissolved As and metal concentrations were observed in mildly alkaline water from a
wetlands site on the Wallkill River in northwestern New Jersey. The site, underlain by glacial sediments over dolomite bedrock,
is 10 km downstream from a mined area of the Franklin Marble, host to Zn ores, also As and Mn minerals. In mid-September 2005,
maxima and minima in dissolved-oxygen-concentration and pH, typically caused by photosynthesis and respiration, occurred at
2000 and 0800 hours. Concentrations of dissolved As (1.52–1.95 μg/L) peaked at dusk (2000 hours), whereas dissolved Mn and
Zn concentrations (76.5–96.9 and 8.55–12.8 μg/L, respectively) were lowest at dusk and peaked at 1000 hours. These opposing
cycles probably reflect sorption and desorption of As (an anion), and Mn and Zn (cations) as pH varied throughout the 24-h
period. Doubly-peaked cycles of B, Cl, SO4, and nutrients also were observed; these may result from upstream discharges of septic-system effluent. Both recoverable
amd particulate Al, Fe, Mn, and Zn concentrations peaked between 0200 and 0600 hours. The particulate metals cycle, with perturbations
at 0400 hours, may be influenced by biological activity. 相似文献
110.
Stefan Gödeke Helmut Geistlinger Anko Fischer Hans-Hermann Richnow Mario Schirmer 《Environmental Geology》2008,55(6):1255-1261
Reactive tracer tests are performed to derive flow, transport and in situ biodegradation parameters. This paper describes
the 3D simulation of a reactive tracer test using the transition probability geostatistical approach. Fifty different equally
probable aquifer realizations were generated based on the geological information of 107 boreholes in an area of 62,500 m2. One realization was chosen for the reactive transport simulation based on the results of groundwater flow modeling and on
particle tracking calculations for the site. Field velocities at the site vary between 0.4 and 3 m/d. The transport of the
reactive tracers deuterium ring labeled toluene-d5 and fully deuterated toluene-d8 was simulated and first-order biodegradation rates of 0.017 d−1 for toluene-d5 and 0.012 d−1 for toluene-d8 were determined. 相似文献