Spatial and temporal variation of diverse inter‐tidal algal assemblages in Southwest O‘ahu          下载免费PDF全文

Traci Erin Cox  Heather L. Spalding  Michael S. Foster 《Marine Ecology》2017,38(3)

Spatial and temporal variation in tropical inter‐tidal communities is poorly known, making predictions about the effects of climate change and other anthropogenic disturbances difficult. Along Southwest O‘ahu, Hawai'i, local residents are concerned about the environmental effects of coastal development and the perceived loss of targeted algal species, which are collected for human consumption. To describe the coastal benthic community and better understand the processes that form and maintain it, the abundance and composition of macroalgae were sampled in the region's inter‐tidal zone from 2006 to 2015. Sixty‐six macroalgal species and two broad algal assemblages were identified that corresponded to substrate topography and sand influence at a similar tidal elevation. Along flat carbonate benches with a sand beach, Phaeophyceae and Rhodophytes occurred in almost equal proportions, while shores with slightly more topographic relief and angular substrate were dominated by Rhodophytes. Foliose or turf algal forms were most common. Surveys captured the local invasion of an alga, Avrainvillea sp. and significant declines in abundant macroalgae in 2015 after a period of unseasonably warm, calm water. Temporal changes in algal assemblages were related to maximum water temperature and wave height but not precipitation. Thus, algal assemblages appear to be structured by local beach morphology as they interact with sand and wave activity and episodically by unusual weather events. However, manipulation and continuous monitoring of the algal assemblages coupled to sensing of the localized environment is necessary to confirm factors related to assembly maintenance and recent species shifts.  相似文献   

Possible impacts of climate change on extreme weather events at local scale in south–central Canada     

Chad Shouquan Cheng  Heather Auld  Qian Li  Guilong Li 《Climatic change》2012,112(3-4):963-979

Synoptic weather typing and regression-based downscaling approaches have become popular in evaluating the impacts of climate change on a variety of environmental problems, particularly those involving extreme impacts. One of the reasons for the popularity of these approaches is their ability to categorize a complex set of meteorological variables into a coherent index, facilitating the projection of changes in frequency and intensity of future daily extreme weather events and/or their impacts. This paper illustrated the capability of the synoptic weather typing and regression methods to analyze climatic change impacts on a number of extreme weather events and environmental problems for south–central Canada, such as freezing rain, heavy rainfall, high-/low-streamflow events, air pollution, and human health. These statistical approaches are helpful in analyzing extreme events and projecting their impacts into the future through three major steps or analysis procedures: (1) historical simulation modeling to identify extreme weather events or their impacts, (2) statistical downscaling to provide station-scale future hourly/daily climate data, and (3) projecting changes in the frequency and intensity of future extreme weather events and their impacts under a changing climate. To realize these steps, it is first necessary to conceptualize the modeling of the meteorology, hydrology and impacts model variables of significance and to apply a number of linear/nonlinear regression techniques. Because the climate/weather validation process is critical, a formal model result verification process has been built into each of these three steps. With carefully chosen physically consistent and relevant variables, the results of the verification, based on historical observations of the outcome variables simulated by the models, show a very good agreement in all applications and extremes tested to date. Overall, the modeled results from climate change studies indicate that the frequency and intensity of future extreme weather events and their impacts are generally projected to significantly increase late this century over south–central Canada under a changing climate. The implications of these increases need be taken into consideration and integrated into policies and planning for adaptation strategies, including measures to incorporate climate change into engineering infrastructure design standards and disaster risk reduction measures. This paper briefly summarized these climate change research projects, focusing on the modeling methodologies and results, and attempted to use plain language to make the results more accessible and interesting to the broader informed audience. These research projects have been used to support decision-makers in south–central Canada when dealing with future extreme weather events under climate change.  相似文献   

Devil in the detail; The 1150–1000 Ma magmatic and structural evolution of the Ngaanyatjarra Rift,west Musgrave Province,Central Australia     

Paul M. Evins  R. Hugh Smithies  Heather M. Howard  Christopher L. Kirkland  Michael T.D. Wingate  Simon Bodorkos 《Precambrian Research》2010

Mafic and felsic rocks units of the Musgrave Province originally attributed to the c. 1075 Ma Giles Event of the greater Warakurna Large Igneous Province (LIP) are shown to be part of a complex sequence of magmatic and tectonic events punctuated over a span of at least 50 m.y. New geochronology and mapping resolve a sequence of at least 10 magmatic pulses with hiati of up to 10 m.y. consistent with a long-lived intracontinental rift setting. This rift, here named the Ngaanyatjarra Rift, features giant layered mafic-ultramafic Giles intrusions cut by a 10 km wide mafic-felsic magmatic shear zone. The latter is temporally related to the Warakurna LIP, however it is not clear that the Giles intrusions actually form part of the Warakurna LIP. Macroscopic folding and the formation of the large synmagmatic transpressional shear zone attest to synmagmatic basin inversion in the early stages of the rift. The extensive mafic to felsic volcanic rocks of the Tollu Group (traditionally grouped with the Giles Event) were emplaced 25–50 m.y. later than the c. 1075 Ma Warakurna LIP.  相似文献   

Mineralogical and chemical characteristics of some natural jarosites     

George A. Desborough  Heather A. Lowers  Jane M. Hammarstrom  Reinhard W. Leinz 《Geochimica et cosmochimica acta》2010,74(3):1041-108

This paper presents a detailed study of the mineralogical, microscopic, thermal, and spectral characteristics of jarosite and natrojarosite minerals. Systematic mineralogic and chemical examination of a suite of 32 natural stoichiometric jarosite and natrojarosite samples from diverse supergene and hydrothermal environments indicates that there is only limited solid solution between Na and K at low temperatures, which suggests the presence of a solvus in the jarosite-natrojarosite system at temperatures below about 140 °C. The samples examined in this study consist of either end members or coexisting end-member pairs of jarosite and natrojarosite. Quantitative electron-probe microanalysis data for several natural hydrothermal samples show only end-member compositions for individual grains or zones, and no detectable alkali-site deficiencies, which indicates that there is no hydronium substitution within the analytical uncertainty of the method. In addition, there is no evidence of Fe deficiencies in the natural hydrothermal samples. Hydronium-bearing jarosite was detected in only one relatively young supergene sample suggesting that terrestrial hydronium-bearing jarosites generally are unstable over geologic timescales.Unit-cell parameters of the 20 natural stoichiometric jarosites and 12 natural stoichiometric natrojarosites examined in this study have distinct and narrow ranges in the a- and c-cell dimensions. There is no overlap of these parameters at the 1σ level for the two end-member compositions. Several hydrothermal samples consist of fine-scale (2-10 μm) intimate intergrowths of jarosite and natrojarosite, which could have resulted from solid-state diffusion segregation or growth zoning due to variations in the Na/K activity ratio of hydrothermal solutions.  相似文献   

The Reliability of Ancient Eclipse Records     

Michael A. Heather 《Geophysical Journal International》1968,15(5):549-550

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Homogenization of a Darcy–Stokes system modeling vuggy porous media     

Todd Arbogast  Heather L. Lehr 《Computational Geosciences》2006,10(3):291-302

We derive a macroscopic model for single-phase, incompressible, viscous fluid flow in a porous medium with small cavities called vugs. We model the vuggy medium on the microscopic scale using Stokes equations within the vugular inclusions, Darcy's law within the porous rock, and a Beavers–Joseph–Saffman boundary condition on the interface between the two regions. We assume periodicity of the medium and obtain uniform energy estimates independent of the period. Through a two-scale homogenization limit as the period tends to zero, we obtain a macroscopic Darcy's law governing the medium on larger scales. We also develop some needed generalizations of the two-scale convergence theory needed for our bimodal medium, including a two-scale convergence result on the Darcy–Stokes interface. The macroscopic Darcy permeability is computable from the solution of a cell problem. An analytic solution to this problem in a simple geometry suggests that: (1) flow along vug channels is primarily Poiseuille with a small perturbation related to the Beavers–Joseph slip, and (2) flow that alternates from vug to matrix behaves as if the vugs have infinite permeability.  相似文献   

Resolving the chronology of recent lake sediments: an example from Devils Lake,North Dakota     

Heather A. Jacobson  Daniel R. Engstrom 《Journal of Paleolimnology》1989,2(2):81-97

Devils Lake is a closed, saline lake in North Dakota; it is typical of lake basins in the Great Plains Region, where windy conditions and fluctuating water-levels disturb sediment and confound chronostratigraphy. Pollen analysis and ²¹⁰Pb dating of two cores collected from bathymetrically contrasting embayments demonstrate (1) how certain agriculture-related pollen types differ in their value as chronostratigraphic markers, (2) how pollen and ²¹⁰Pb stratigraphies can be reconciled to determine the approximate depth of sediment mixing, and (3) the importance of coring-site selection, especially in lakes with unstable sedimentary conditions.  相似文献   

Editorial     

Heather A> Viles 《Area》2001,33(3):227-227

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Diffusion of Au, Pd, Re, and P in FeNi alloys at High Pressure     

Heather C. Watson  E. Bruce Watson 《Geochimica et cosmochimica acta》2008,72(14):3550-3561

Multi-anvil and piston cylinder experiments were performed to determine the effect of both pressure and temperature on the diffusivities of several siderophile elements in a Fe₉₀Ni₁₀ core-analog alloy. Activation energies were calculated to be between 244 and 257 kJ/mol for Re, Pd, and Au at 10 GPa, and 264 kJ/mol for P at 1 GPa. It was found that pressure has a marked negative effect on the diffusivities of Au, Re, and Pd, and activation volumes for these elements were calculated to be between 3 and 6 cm³/mol at 10 GPa. The effect of both temperature and pressure on P diffusion is noticeably less, and the absolute diffusivity of phosphorus is consistently higher than that of the other elements. It is inferred that the reason for this difference is because P is diffusing via an interstitial mechanism as opposed to Re, Pd, and Au which occupy regular lattice sites in the crystal. The effect of pressure and temperature together with depth in the Earth suggests that these elements may continue to exhibit different behavior at more extreme conditions. The significance of these new results lies in the ability to place constraints on many time-dependent processes that pertain to the formation and evolution of planetary cores, as well as the formation and cooling histories of other metal-rich bodies in the solar system, such as meteorites.  相似文献   

Editors' report 2002     

Mike BradshawEditor  Heather VilesCo-Editor 《Area》2003,35(1):3-4

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