The petrochemical method for recognizing geodynamic formation settings of igneous rocks (Shmidt Terrane,Sakhalin)     

V. M. Grannik  B. V. Levin 《Doklady Earth Sciences》2011,441(2):1607-1610

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New insights on the trophic ecology of bathyal communities from the methane seep area off Concepción,Chile (~36° S)     

Germán Zapata‐Hernández  Javier Sellanes  Andrew R. Thurber  Lisa A. Levin  Frédéric Chazalon  Peter Linke 《Marine Ecology》2014,35(1):1-21

Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEA_B) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.  相似文献   

Alteration of benthic communities associated with copper contamination linked to boat moorings     

Carlos Neira  Lisa A. Levin  Guillermo Mendoza  Alberto Zirino 《Marine Ecology》2014,35(1):46-66

Although copper (Cu) is an essential element for life, leaching from boat paint can cause excess environmental loading in enclosed marinas. The effects of copper contamination on benthic macrofaunal communities were examined in three San Diego Bay marinas (America's Cup, Harbor Island West and East) in Southern California, USA. The distribution of Cu concentration in sediments exhibited a clear spatial gradient, with hotspots created by the presence of boats, which in two marinas exceeded the effect range medium (ERM). Elevated sediment Cu was associated with differences in benthic assemblages, reduced species richness and enhanced dominance in America's Cup and Harbor Island West, whereas Harbor Island East did not appear to be affected. At sites without boats there were greater abundances of some amphipods such as the species Desdimelita sp., Harpinia sp., Aoroides sp., Corophium sp., Podocerus sp., bivalves such as Lyonsia californica, Musculista senhousia, Macoma sp., and polychaetes such as Diplocirrus sp. In contrast, at sites with boats, densities of Pseudopolydora paucibranchiata, Polydora nuchalis, Euchone limnicola, Exogone lourei, Tubificoides spp. were enhanced. The limited impact on Harbor Island East suggests not only lower Cu input rates and increased water flushing and mixing, but also the presence of adequate defense mechanisms that regulate availability and mitigate toxic impacts. At all three marinas, Cu in tissues of several macrobenthic species exhibited Cu bioaccumulation above levels found in the surrounding environment. The annelids Lumbrineris sp. and Tubificoides spp., and the amphipod Desdimelita sp. contained high levels of Cu, suggesting they function as Cu bioaccumulators. The spionid polychaetes Polydora nuchalis and Pseudopolydora paucibranchiata had much lower Cu concentrations than surrounding sediments, suggesting they function as Cu bioregulators. The macrobenthic invertebrates in San Diego Bay marinas that tolerate Cu pollution (e.g. P. nuchalis, P. paucibranchiata, Euchone limnicola, Typosyllis sp., Tubificoides sp.) may function as indicators of high‐Cu conditions, whereas the presence of Cu‐sensitive species (e.g. Podocerus sp., Aoroides sp., Harpinia sp., Macoma sp., Lyonsia californica) may indicate healthier conditions (less Cu‐stressed). Parallel responses by faunas of Shelter Island Yacht Basin, also in San Diego Bay, suggest potential for development of regional Cu contamination assessment criteria, and call for functional comparisons with other marinas and coastal water bodies.  相似文献   

Rapid incision of a small,coarse and steep fan‐delta in response to base‐level fall: the case of Nahal Qedem,the Dead Sea,Israel     

Yael Storz‐Peretz  Dan Bowman  Jonathan B. Laronne  Tal Svoray 《地球表面变化过程与地形》2011,36(4):467-480

The Dead Sea has been continuously dropping 0·4–1·0 m yr^?1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non‐tectonic base‐level fall. The aim of this work is to study the short‐term ongoing erosive response to a rapid base‐level drop in a small, steep‐fronted, erodible fan‐delta setting. The work explores the controls of the steep Qedem fan‐delta, guided by its clinoform structure, on its incision. Longitudinal profiles of the fan‐delta and of its entrenched channel were measured in the field. Sedimentary facies changes – fluviatile, shallow lacustrine and beach – were followed along exposures. The existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision. The field study was combined with digital elevation models (DEMs) that were extracted from pairs of overlapping aerial photos. Maps of erosion and deposition were prepared using a change detection algorithm. The longitudinal profile of the entrenched channel was found to be steep and linear. The outlet temporarily ‘hangs’ elevated and ungraded above the retreating lake level, indicating years without incision flow events, which cause lags in response to the rapid lake level drop. In spite of the large boulders, the small drainage basin and precipitation volume over the basin of the Qedem, the recorded vertical incision rates in the unconsolidated sediments are as high as 0·8 m yr^?1, i.e. similar to those of the largest wadis draining to the Dead Sea. The steep front of the fan‐delta is suggested to be a main factor controlling the efficient incision. A unique transport mechanism of rolling boulders, following undercutting, contributed to the entrenchment efficiency. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

New data about tsunami evidence on Russia’s Pacific coast based on instrumental measurements for 2009–2010     

Shevchenko  G. V.  Ivel’skaya  T. N.  Kovalev  P. D.  Kovalev  D. P.  Kurkin  A. A.  Levin  B. V.  Likhacheva  O. N.  Chernov  A. G.  Shishkin  A. A. 《Doklady Earth Sciences》2011,438(2):893-898

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Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels     

F. Joel Fodrie  Bonnie J. Becker  Lisa A. Levin  Kristen Gruenthal  Pat A. McMillan 《Journal of Sea Research》2011,65(1):141-150

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels (Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78–87% of all cases. Settlement varied between 2 and 27 settlers gram-byssus^?1 week^?1 at SIO and HI, and both sites were characterized by 2–3 weeks with “high” settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between “high” and “low” settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations.  相似文献   

Non-linear r‐modes in a spherical shell: issues of principle     

Yuri Levin  Greg Ushomirsky 《Monthly notices of the Royal Astronomical Society》2001,322(3):515-522

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Atmospheric loss of energetic electrons in the Jovian synchrotron zone     

K. Wang  S.J. BoltonS.M. Gulkis  S.M. Levin 《Planetary and Space Science》2002,50(3):277-285

For decades, ground-based radio observations of Jovian synchrotron radiation have shown emission originating predominantly from the equatorial region and from high-latitude regions (lobes) near L∼2.5. The observations show a longitudinally asymmetric gap between the emission peaks of the lobes and the atmosphere of Jupiter. One possible explanation for these gaps is the loss of electrons through collisions with atmospheric neutrals as the electrons bounce along magnetic field lines and drift longitudinally in the presence of asymmetric magnetic fields. To assess this hypothesis, we applied the recently developed O6 and VIP4 magnetic field models to calculate the trajectories of electrons as they drift longitudinally in Jupiter's magnetic field, and derive the sizes of their equatorial drift loss cones. We then identified the shells on which electrons would be lost due to collisions with the atmosphere. The calculated drift loss cone sizes could be applied in future to the modeling of electron distribution functions in this region and could also be applied to the study of Jovian auroral zone. This method also allowed us to compute the shell-splitting effects for these drifting electrons and we find the shell-splitting to be small (?0.05R_J). This justifies a recent modeling assumption that particles drift on the same shells in a three-dimensional distribution model of electrons. We also compared the computed gaps with the observed gaps, and found that the atmospheric loss mechanism alone is not able to sufficiently explain the observed gap asymmetry.  相似文献   

Lightning generation in planetary atmospheres     

Zev Levin  William J. Borucki  Owen B. Toon 《Icarus》1983,56(1):80-115

The possibilities of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. Recent measurements of cloud structure and whistlers, as well as optical observation of lightning on Jupiter, suggest that charge separation and lightning discharges occur on other planets in ways similar to those in which they occur on Earth. Using these terrestrial ideas, it is concluded that lightning on Venus will probably be found in clouds that are located in regions of convection such as those observed downwind of the subsolar point. It is also possible that if volcanoes on Venus are erupting, they too can produce lightning discharges in their plumes although it seems unlikely that this process can account for the observed rate of discharge. Jovian lightning is most probably generated in the lower water-ice clouds. These clouds are of moderate temperatures and have strong convection and large mass loading, all important ingredients for electrical buildup. Lightning is all but ruled out for Mars, even though some electrification is possible owing to the large dust storms on that planet.  相似文献   

Unusual eruption of the Main Pugachevo Gas-Water-Lithoclastic volcano of Sakhalin in winter 2005     

O. A. Mel&#;nikov  B. V. Levin  V. V. Ershov 《Doklady Earth Sciences》2006,411(8):1209-1211

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