Sea‐level and ocean‐current control on carbonate‐platform growth,Maldives, Indian Ocean     

Christian Betzler  Jörn Fürstenau  Thomas Lüdmann  Christian Hübscher  Sebastian Lindhorst  Andreas Paul  John J. G. Reijmer  André W. Droxler 《Basin Research》2013,25(2):172-196

Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region.  相似文献   

Seasonal extreme rainfall variability over India and its association with surface air temperature     

Sardana  Divya  Kumar  Prashant  Weller  Evan  Rajni 《Theoretical and Applied Climatology》2022,147(1-2):185-204

Theoretical and Applied Climatology - Spatial variability in catchment processes is crucial for hydrologic and water resources planning and management. The spatial density of ground-based rain...  相似文献   

Exploring Granger causality between global average observed time series of carbon dioxide and temperature   总被引：2，自引：0，他引：2  

Evan Kodra  Snigdhansu Chatterjee  Auroop R. Ganguly 《Theoretical and Applied Climatology》2011,104(3-4):325-335

Detection and attribution methodologies have been developed over the years to delineate anthropogenic from natural drivers of climate change and impacts. A majority of prior attribution studies, which have used climate model simulations and observations or reanalysis datasets, have found evidence for human-induced climate change. This papers tests the hypothesis that Granger causality can be extracted from the bivariate series of globally averaged land surface temperature (GT) observations and observed CO₂ in the atmosphere using a reverse cumulative Granger causality test. This proposed extension of the classic Granger causality test is better suited to handle the multisource nature of the data and provides further statistical rigor. The results from this modified test show evidence for Granger causality from a proxy of total radiative forcing (RC), which in this case is a transformation of atmospheric CO₂, to GT. Prior literature failed to extract these results via the standard Granger causality test. A forecasting test shows that a holdout set of GT can be better predicted with the addition of lagged RC as a predictor, lending further credibility to the Granger test results. However, since second-order-differenced RC is neither normally distributed nor variance stationary, caution should be exercised in the interpretation of our results.  相似文献   

The age of orogenesis in the Nambucca Slate Belt: A K‐Ar study of low‐grade regional metamorphic rocks     

Evan C. Leitch  Ian McDougall 《Australian Journal of Earth Sciences》2013,60(3-4):111-119

K‐Ar ages of biotite and hornblende from undeformed granodiorite plutons and of slaty and phyllitic rocks, ranging from prehnite‐pumpellyite metagreywacke to greenschist fades, have been determined in an attempt to define the age of orogenesis in the eastern part of the Nambucca Slate Belt. The plutons have K‐Ar ages of 226–227 m.y. (biotite) and 228–231 m.y. (hornblende) that provide a younger age limit for deformation. The lower grade metamorphic rocks yield a range of ages including some comparable with the depositional age of the rocks as indicated by fossils. Rocks of pumpellyite‐actinolite and greenschist facies give a more coherent group of ages which suggest orogenesis at about 250–255 m.y. Specimens of these latter rocks that have been affected by a later structural episode than that during which slaty cleavage formed, yield slightly older ages, which may result from the inclusion of minor amounts of environmental excess ⁴⁰Ar.

Support for the 250–255 m.y. age comes from previously determined radiometric ages from the western part of the Slate Belt, although the presence of granitic bodies perhaps as old as 289 m.y., some closely associated with high‐grade regional metamorphic rocks, may indicate the presence of additional earlier orogenic movements in this region.  相似文献   

Clues from Current High CO2 Environments on the Effects of Ocean Acidification on CaCO3 Preservation     

Andreas J. Andersson  Nicholas R. Bates  Marlene A. Jeffries  Kyra Freeman  Charles Davidson  Shaun Stringer  Evan Betzler  Fred T. Mackenzie 《Aquatic Geochemistry》2013,19(5-6):353-369

Acidification of surface seawater owing to anthropogenic activities has raised serious concerns on its consequences for marine calcifying organisms and ecosystems. To acquire knowledge concerning the future consequences of ocean acidification (OA), researchers have relied on incubation experiments with organisms exposed to future seawater conditions, numerical models, evidence from the geological record, and recently, observations from aquatic environments exposed to naturally high CO₂ and low pH, e.g., owing to volcanic CO₂ vents, upwelling, and groundwater input. In the present study, we briefly evaluate the distribution of dissolved CO₂–carbonic acid parameters at (1) two locations in the Pacific and the Atlantic Ocean as a function of depth, (2) a mangrove environment in Bermuda, (3) a seasonally stratified body of water in a semi-enclosed sound in Bermuda, and (4) in temporarily isolated tide pools in Southern California. We demonstrate that current in situ conditions of seawater pCO₂, pH, and CaCO₃ saturation state (Ω) in these environments are similar or even exceed the anticipated changes to these parameters in the open ocean over the next century as a result of OA. The observed differences between the Pacific and Atlantic Oceans with respect to seawater CO₂–carbonic acid chemistry, preservation of CaCO₃ minerals, and the occurrence and distribution of deep-sea marine calcifiers, support the hypothesized negative effects of OA on the production and preservation of CaCO₃ in surface seawater. Clues provided from shallow near-shore environments in Bermuda and Southern California support these predictions, but also highlight that many marine calcifiers already experience relatively high seawater pCO₂ and low pH conditions.  相似文献   

Carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp (Miocene, Great Bahama Bank)     

C. Betzler  M. Pfeiffer  S. Saxena 《International Journal of Earth Sciences》2000,89(1):140-153

Received: 10 May 1999 / Accepted: 16 October 1999  相似文献   

The Application of Biological Treatment to a Landfill Leachate     

Evan K. Nyer 《Ground Water Monitoring & Remediation》1988,8(4):61-65

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Evaluation and comparison of spatial interpolators   总被引：16，自引：0，他引：16  

Dennis Weber  Evan Englund 《Mathematical Geology》1992,24(4):381-391

This study evaluates 15 different estimators to determine their relative merits in estimating block concentrations at contaminant waste sites. The evaluation was based on 54 subsets of data drawn from an exhaustive set of 19,800 data. For each subset, 198 block estimates were made with each estimator. The measurements of estimation quality were a linear loss function and a more standard statistic, the mean square error. The linear loss function showed that seven of the estimators produced scores close enough to be within the same statistical population. Results based on the mean square error were similar. The surprising results of this study were that inverse distance and inverse distance squared both produced better scores than kriging.  相似文献   

Using Laboratory Data to Design a Full-Scale Treatment System     

Evan K. Nyer 《Ground Water Monitoring & Remediation》1992,12(1):85-87

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Glutathione-mediated chlorothalonil detoxification in channel catfish gills     

Evan P. Gallagher  Richard T. Di Giulio 《Marine environmental research》1992,34(1-4)

Maintenance of the glutathione (GSH) pathway is critical in guarding against the toxic effects of a variety of pollutants. However, despite their importance as an initial line of defense against waterborne toxicants, little is known regarding the role of fish gills in GSH-mediated xenobiotic metabolism. In these studies, the role of channel catfish gills in the detoxification of 2,4,5,6-tetrachloroisophthalonitrile (chlorothalonil), an electrophilic fungicide, was examined. Chlorothalonil was metabolized in vitro by gill cytosolic and microsomal glutathione S-transferases (GSTs). Chlorothalonil metabolism by cytosolic fructions was reduced markedly when GSH was omitted from reaction mixtures. Microsomal metabolism of chlorothalonil did not occur in the absence of GSH and in the presence of an NADPH-regenerating system lacking GSH. Channel catfish exposed in vivo to chlorothalonil had increased gill GSH and cysteine concentrations after 72 h exposure, and increased gill gamma-glutamylcysteine synthetase (GCS) activity at 144 h of exposure. Our results show that the gills play an important role in the metabolism and detoxification of chlorothalonil in the channel catfish. Catfish can maintain elevated gill GSH concentrations in the presence of chlorothalonil by increasing gill cysteine concentrations.  相似文献