A multivariate assessment of the coral ecosystem health of two embayments on the lee of the island of Hawai'i     

Parsons ML  Walsh WJ  Settlemier CJ  White DJ  Ballauer JM  Ayotte PM  Osada KM  Carman B 《Marine pollution bulletin》2008,56(6):1138-1149

Four coral-dominated coastal sites within two embayments (Kealakekua Bay and Honokōhau Bay) on the lee of the island of Hawai'i were studied to assess evidence of anthropogenic impacts in these relatively pristine locales. Nutrient-loading parameters were analyzed in relation to benthic composition data. Statistically, there were significant positive relationships between nitrate+nitrite, silicate, and ammonium with the abundance of macroalgae, coralline algae, and dead coral, and between delta(15)N and dead coral abundance. The north outside site of Kealakekua Bay and the south outside site of Honokōhau Bay appear to be most impacted by nutrient-loading factors in each bay, respectively. Comparisons with past nutrient data indicate that nutrient inputs have increased to the two bays, and that early impacts of these increased loadings are evident. It is predicted that at current nutrient-loading rates, the north sites of Kealakekua Bay and the south sites of Honokōhau Bay will exhibit evidence of further degradation in future years.  相似文献   

Searching for similarity in topographic controls on carbon,nitrogen and phosphorus export from forested headwater catchments   总被引：1，自引：0，他引：1       下载免费PDF全文

Samson G. Mengistu  Irena F. Creed  Kara L. Webster  Eric Enanga  Frederick D. Beall 《水文研究》2014,28(8):3201-3216

Topography influences hydrological processes that in turn affect biogeochemical export to surface water on forested landscapes. The differences in long‐term average annual dissolved organic carbon (DOC), organic and inorganic nitrogen [NO₃^?‐N, dissolved organic nitrogen (DON)], and phosphorus (total dissolved phosphorus, TDP) export from catchments in the Algoma Highlands of Ontario, Canada, with similar climate, geology, forest and soil were established. Topographic indicators were designed to represent topographically regulated hydrological processes that influence nutrient export, including (1) hydrological storage potential (i.e. effects of topographic flats/depressions on water storage) and (2) hydrological flushing potential (i.e. effects of topographic slopes on potential for variable source area to expand and tap into previously untapped areas). Variations in NO₃^?‐N export among catchments could be explained by indicators representing both hydrological flushing potential (91%, p < 0.001) and hydrological storage potential (65%, p < 0.001), suggesting the importance of hydrological flushing in regulating NO₃^?‐N export as well as surface saturated areas in intercepting NO₃^?‐N‐loaded runoff. In contrast, hydrological storage potential explained the majority of variations among catchments in DON (69%, p < 0.001), DOC (94%, p < 0.001) and TDP (82%, p < 0.001) export. The lower explanatory power of DON (about 15% less) compared with that of DOC and TDP suggests another mechanism influencing N export, such as controls related to alternative fates of nitrogen (e.g. as gas). This study shows that simple topographic indicators can be used to track nutrient sources, sinks and their transport and export to surface water from catchments on forest landscapes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Turkey Lakes Watershed,Ontario, Canada: 40 years of interdisciplinary whole-ecosystem research     

Kara L. Webster  Jason A. Leach  Paul W. Hazlett  Robert L. Fleming  Erik J. S. Emilson  Daniel Houle  Kara H. Y. Chan  Fariborz Norouzian  Amanda S. Cole  Jason M. O'Brien  Karen E. Smokorowski  Stephanie A. Nelson  Shelagh D. Yanni 《水文研究》2021,35(4):e14109

The Turkey Lakes Watershed (TLW) study is a federal, interdepartmental study established in 1979 to investigate the effects of acid rain on terrestrial and aquatic ecosystems. The 10.5 km² watershed, located in the Eastern Temperate Mixed Forest on the Canadian Shield, has been the site of multidisciplinary studies on biogeochemical and ecological processes conducted across plot to catchment scales. The whole-ecosystem investigative approach was adopted from the outset and has allowed research to evolve from its original (and continuing) acidification focus to include investigations on the effects of climate change, forest harvesting and other forest ecosystem perturbations. The extensive scientific and support infrastructure allows for collection of a comprehensive data record essential for understanding long-term environmental trends. Data include atmospheric deposition, meteorology, stream hydrology and chemistry, soil, pore and ground water properties, understory and overstory vegetation, lake and outflow physical and chemical properties, and aquatic macroinvertebrate and fish community composition and abundance. These data have contributed to over 400 published research papers and graduate theses. The watershed has also figured prominently in many continent-wide comparisons advancing fundamental watershed theory. The knowledge gained at TLW has influenced pollutant emission and natural resource management policies provincially, nationally and internationally.  相似文献   

Late orogenic, large-scale rotations in the Tien Shan and adjacent mobile belts in Kyrgyzstan and Kazakhstan   总被引：6，自引：1，他引：5  

Rob Van der Voo  Natalia M. Levashova  Ludmila I. Skrinnik  Taras V. Kara  Mikhail L. Bazhenov   《Tectonophysics》2006,426(3-4):335-360

Most of Kazakhstan belongs to the central part of the Eurasian Paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate. Of particular interest is the origin of strongly curved Middle and Late Paleozoic volcanic belts of island-arc and Andean-arc affinities that dominate the structure of Kazakhstan. We undertook a paleomagnetic study of Carboniferous to Upper Permian volcanics and sediments from several localities in the Ili River basin between the Tien Shan and the Junggar–Alatau ranges in southeast Kazakhstan. Our main goal was to investigate the Permian kinematic evolution of these belts, particularly in terms of rotations about vertical axes, in the hope of deciphering the dynamics that played a role during the latest Paleozoic deformation in this area. This deformation, in turn, can then be related to the amalgamation of this area with Baltica, Siberia, and Tarim in the expanding Eurasian supercontinent. Thermal demagnetization revealed that most Permian rocks retained a pretilting and likely primary component, which is of reversed polarity at three localities and normal at the fourth. In contrast, most Carboniferous rocks are dominated by postfolding reversed overprints of probably “mid-Permian” age, whereas presumably primary components are isolated from a few sites at two localities. Mean inclinations of primary components generally agree with coeval reference values extrapolated from Baltica, whereas declinations from primary as well as secondary components are deflected counterclockwise (ccw) by up to  90°. Such ccw rotated directions have previously also been observed in other Tien Shan sampling areas and in the adjacent Tarim Block to the south. However, two other areas in Kazakhstan show clockwise (cw) rotations of Permian magnetization directions. One area is located in the Kendyktas block about 300 km to the west of the Ili River valley, and the other is found in the Chingiz Range, to the north of Lake Balkhash and about 400 km to the north of the Ili River valley. The timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern Tarim, the Tien Shan and eastern Kazakhstan, so that the rotations cannot be attributed to island-arc or Andean-margin plate settings — instead we attribute the rotations to large-scale, east–west (present-day coordinates), sinistral wrenching in an intracontinental setting, related to convergence between Siberia and Baltica, as recently proposed by Natal'in and Şengör [Natal'in, B.A., and Şengör, A.M.C., 2005. Late Palaeozoic to Triassic evolution of the Turan and Scythian platforms: the pre-history of the palaeo-Tethyan closure, Tectonophysics, 404, 175–202.]. Our previous work in the Chingiz and North Tien Shan areas on Ordovician and Silurian rocks suggested relative rotations of  180°, whereas the Permian declination differences are of the order of 90° between the two areas. Thus, we assume that about 50% of the total post-Ordovician rotations are of pre-Late Permian age, with the other half of Late Permian–earliest Mesozoic age. The pre-Late Permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra-subduction setting, given the calc-alkaline character of nearly all of the pre-Late Permian volcanics in the strongly curved belts.  相似文献   

Dynamic subsidence of Eastern Australia during the Cretaceous     

Kara J. Matthews  Alina J. Hale  Michael Gurnis  R. Dietmar Müller  Lydia DiCaprio 《Gondwana Research》2011,19(2):372-383

During the Early Cretaceous Australia's eastward passage over sinking subducted slabs induced widespread dynamic subsidence and formation of a large epeiric sea in the eastern interior. Despite evidence for convergence between Australia and the paleo-Pacific, the subduction zone location has been poorly constrained. Using coupled plate tectonic–mantle convection models, we test two end-member scenarios, one with subduction directly east of Australia's reconstructed continental margin, and a second with subduction translated ~ 1000 km east, implying the existence of a back-arc basin. Our models incorporate a rheological model for the mantle and lithosphere, plate motions since 140 Ma and evolving plate boundaries. While mantle rheology affects the magnitude of surface vertical motions, timing of uplift and subsidence depends on plate boundary geometries and kinematics. Computations with a proximal subduction zone result in accelerated basin subsidence occurring 20 Myr too early compared with tectonic subsidence calculated from well data. This timing offset is reconciled when subduction is shifted eastward. Comparisons between seismic tomography and model temperature cross-sections, and an absence of subduction zone volcanism in eastern Australia in the Early Cretaceous provide support for the back-arc basin scenario.  相似文献   

Active tectonic and palaeoseismological features of the western section of Mustafakemalpaşa Fault; Bursa,NW Anatolia     

Alican Kop  Selim Özalp  Hasan Elmacı  Meryem Kara  Tamer Y. Duman 《Geodinamica Acta》2016,28(4):363-378

The Mustafakemalpa?a Fault (MF), located among Manyas, Ulubat and Orhaneli faults, is a right lateral strike-slip and 47 km in length. The MF begins with a pressure ridge at the west and exhibits complex jog terminations at east ends in restraining left stepovers. The western section of the fault bounds Miocene and Quaternary units and continues towards ?lyasç?lar. The central segment of the fault, starts with approximately 750-m leftward stepover, exhibits a sinusoidal geometry between Kapakl?oluk and Kabulbaba. In this section, MF traverses mountainous terrain and cuts Ophiolite, Jurassic limestones and Miocene detritals, forming dextral faulting features and gaining reverse component. The eastern section exhibits left stepping en-echelon pattern and consists 2.5-km offset on the Orhaneli River. In this study, palaeoseismological findings related to the Holocene activity and active tectonic properties of the MF are presented. The trenches exposed mismatched stratigraphy, demonstrating evidence of events across the fault. We identified three events (before BC 2190, later AD 1425 and 1850) that have occurred during the past 4000 years. We suggest a long non-characteristic recurrence interval and ~0.7 mm/y slip-rate for MF, based on trench data and offset of the Late Pliocene drainage of Orhaneli River.  相似文献   

Early taphonomy of benthic foraminifera in Storfjorden ‘sea-ice factory’: the agglutinated/calcareous ratio as a proxy for brine persistence     

Maria Pia Nardelli  Eleonora Fossile  Olivier Péron  Hélène Howa  Meryem Mojtahid 《Boreas: An International Journal of Quaternary Research》2023,52(1):109-123

The recurrent latent-heat polynya characterizing Storfjorden (Svalbard, Norway) triggers seasonal formation of thin first-year sea ice. This leads to the production of dense, salty, and corrosive brines that cascade towards the sea floor and mix with shelf waters. The bottom topography of the fjord is responsible for the retention of these dense waters in two central deep basins throughout the year. Recent studies show that living benthic foraminifera in Storfjorden are particularly affected by the persistence of brines on the sea floor, with a strong dominance of agglutinated (A) species and high degrees of dissolution of calcareous(C) faunas. Therefore, the A/C ratio, calculated on living faunas, was proposed as a proxy for brine persistence. In the present study we analyse the fossil faunas, found below the taphonomically active zone, to investigate the residual signal of the A/C proxy after the intense early taphonomic processes and challenge its applicability in sedimentary archives. Our results show that despite the generally high taphonomic loss inside the fjord, a high proportion of agglutinated species is still visible in fossil faunas at the stations experiencing regular and/or persistent presence of brine-enriched shelf waters. These results support the application of the A/C ratio in historical records to reconstruct the persistence of brines and indirectly the first-year sea ice formation in Storfjorden. This can be further applied to other Arctic fjords with similar settings and characterized by the production of brines during the winter–early spring season.  相似文献   

X-ray reverberation around accreting black holes     

P.?UttleyEmail author  E.?M.?Cackett  A.?C.?Fabian  E.?Kara  D.?R.?Wilkins 《Astronomy and Astrophysics Review》2014,22(1):72

Luminous accreting stellar mass and supermassive black holes produce power–law continuum X-ray emission from a compact central corona. Reverberation time lags occur due to light travel time delays between changes in the direct coronal emission and corresponding variations in its reflection from the accretion flow. Reverberation is detectable using light curves made in different X-ray energy bands, since the direct and reflected components have different spectral shapes. Larger, lower frequency, lags are also seen and are identified with propagation of fluctuations through the accretion flow and associated corona. We review the evidence for X-ray reverberation in active galactic nuclei and black hole X-ray binaries, showing how it can be best measured and how it may be modelled. The timescales and energy dependence of the high-frequency reverberation lags show that much of the signal is originating from very close to the black hole in some objects, within a few gravitational radii of the event horizon. We consider how these signals can be studied in the future to carry out X-ray reverberation mapping of the regions closest to black holes.  相似文献   

Climate change impacts on extreme precipitation of water supply area in Istanbul: use of ensemble climate modelling and geo-statistical downscaling     

Fatih Kara  Zuhal Akyurek 《水文科学杂志》2013,58(14):2481-2495

ABSTRACT

Numerous statistical downscaling models have been applied to impact studies, but none clearly recommended the most appropriate one for a particular application. This study uses the geographically weighted regression (GWR) method, based on local implications from physical geographical variables, to downscale climate change impacts to a small-scale catchment. The ensembles of daily precipitation time series from 15 different regional climate models (RCMs) driven by five different general circulation models (GCMs), obtained through the European Union (EU)-ENSEMBLES project for reference (1960–1990) and future (2071–2100) scenarios are generated for the Omerli catchment, in the east of Istanbul city, Turkey, under scenario A1B climate change projections. Special focus is given to changes in extreme precipitation, since such information is needed to assess the changes in the frequency and intensity of flooding for future climate. The mean daily precipitation from all RCMs is under-represented in the summer, autumn and early winter, but it is overestimated in late winter and spring. The results point to an increase in extreme precipitation in winter, spring and summer, and a decrease in autumn in the future, compared to the current period. The GWR method provides significant modifications (up to 35%) to these changes and agrees on the direction of change from RCMs. The GWR method improves the representation of mean and extreme precipitation compared to RCM outputs and this is more significant, particularly for extreme cases of each season. The return period of extreme events decreases in the future, resulting in higher precipitation depths for a given return period from most of the RCMs. This feature is more significant with downscaling. According to the analysis presented, a new adaption for regulating excessive water under climate change in the Omerli basin may be recommended.  相似文献   

Terrace pediments in Makhtesh Ramon,central Negev,Israel     

Josef Plakht  Natalia Patyk‐Kara  Nina Gorelikova 《地球表面变化过程与地形》2000,25(1):29-39

Terrace pediments occupy approximately 30 per cent of the bottom of the Makhtesh Ramon erosional cirque in the central Negev Desert, Israel. River terraces and terrace pediments are genetically connected landforms, where each terrace pediment corresponds with a fluvial terrace of the same relative height. A pediment and river terrace constitute a geomorphic pair and should be regarded as chronometrically synchronous morphological elements. The formation of the terrace pediment staircases is controlled mainly by local base level changes. The present‐day configuration and overall morphology of Makhtesh Ramon formed in the early stages of its development by both stream erosion and subsequent pedimentation. Less significantly, modification by intermittent erosion alternating with periods of stability, resulted in deepening of the Makhtesh Ramon bottom. The present‐day stepped relief throughout the Makhtesh valley is, thus, a composite feature. The overall rate of terrace pediment formation in Makhtesh Ramon ranges from 0·05 to 0·10 mm a⁻¹. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献