Bimodal character of latitudinal earthquake distributions in the pacific region as a manifestation of global seismicity   总被引：1，自引：0，他引：1  

B. V. Levin  E. V. Sasorova 《Doklady Earth Sciences》2009,424(1):175-179

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Macrofaunal succession in sediments around kelp and wood falls in the deep NE Pacific and community overlap with other reducing habitats     

Angelo F. Bernardino  Craig R. Smith  Amy Baco  Iris Altamira  Paulo Y.G. Sumida 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(5):708-723

Sunken parcels of macroalgae and wood provide important oases of organic enrichment at the deep-sea floor, yet sediment community structure and succession around these habitat islands are poorly evaluated. We experimentally implanted 100-kg kelp falls and 200 kg wood falls at 1670 m depth in the Santa Cruz Basin to investigate (1) macrofaunal succession and (2) species overlap with nearby whale-fall and cold-seep communities over time scales of 0.25–5.5 yr. The abundance of infaunal macrobenthos was highly elevated after 0.25 and 0.5 yr near kelp parcels with decreased macrofaunal diversity and evenness within 0.5 m of the falls. Apparently opportunistic species (e.g., two new species of cumaceans) and sulfide tolerant microbial grazers (dorvilleid polychaetes) abounded after 0.25–0.5 yr. At wood falls, opportunistic cumaceans become abundant after 0.5 yr, but sulfide tolerant species only became abundant after 1.8–5.5 yr, in accordance with the much slower buildup of porewater sulfides at wood parcels compared with kelp falls. Species diversity decreased significantly over time in sediments adjacent to the wood parcels, most likely due to stress resulting from intense organic loading of nearby sediments (up to 20–30% organic carbon). Dorvilleid and ampharetid polychaetes were among the top-ranked fauna at wood parcels after 3.0–5.5 yr. Sediments around kelp and wood parcels provided low-intensity reducing conditions that sustain a limited chemoautrotrophically-based fauna. As a result, macrobenthic species overlap among kelp, wood, and other chemosynthetic habitats in the deep NE Pacific are primarily restricted to apparently sulfide tolerant species such as dorvilleid polychaetes, opportunistic cumaceans, and juvenile stages of chemosymbiont containing vesicomyid bivalves. We conclude that organically enriched sediments around wood falls may provide important habitat islands for the persistence and evolution of species dependent on organic- and sulfide-rich conditions at the deep-sea floor and contribute to β and γ diversity in deep-sea ecosystems.  相似文献   

Impacts of Climate-Related Drivers on the Benthic Nutrient Filter in a Shallow Photic Estuary     

Iris C. Anderson  Mark J. Brush  Michael F. Piehler  Carolyn A. Currin  Jennifer W. Stanhope  Ashley R. Smyth  Johnathan D. Maxey  Meaghan L. Whitehead 《Estuaries and Coasts》2014,37(1):46-62

In shallow photic systems, the benthic filter, including microphytobenthos and denitrifiers, is important in preventing or reducing release of remineralized NH₄ ⁺ to the water column. Its effectiveness can be impacted by climate-related drivers, including temperature and storminess, which by increasing wind and freshwater delivery can resuspend sediment, reduce salinity and deliver nutrients, total suspended solids, and chromophoric dissolved organic matter (CDOM) to coastal systems. Increases in temperature and freshwater delivery may initiate a cascade of responses affecting benthic metabolism with impacts on sediment properties, which in turn regulate nitrogen cycling processes that either sequester (via microphytobenthos), remove (via denitrification), or increase sediment nitrogen (via remineralization, nitrogen fixation, and dissimilatory nitrate reduction to ammonium). We conducted a seasonal study at shallow stations to assess the effects of freshwater inflow, temperature, wind, light, and CDOM on sediment properties, benthic metabolism, nitrogen cycling processes, and the effectiveness of the benthic filter. We also conducted a depth study to constrain seasonally varying parameters such as temperature to better assess the effects of light availability and water depth on benthic processes. Based on relationships observed between climatic drivers and response variables, we predict a reduction in the effectiveness of the benthic filter over the long term with feedbacks that will increase effluxes of N to the water column with the potential to contribute to system eutrophication. This may push shallow systems past a tipping point where trophic status moves from net autotrophy toward net heterotrophy, with new baselines characterized by degraded water quality.  相似文献   

Relationships between tissue concentrations of paralytic shellfish toxins and antioxidative responses of clams, Ruditapes philippinarum     

Choi NM  Yeung LW  Siu WH  So IM  Jack RW  Hsieh DP  Wu RS  Lam PK 《Marine pollution bulletin》2006,52(5):572-578

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Monitoring of the eruption of the Sarychev Peak Volcano in Matua Island in 2009 (central Kurile islands)     

Levin  B. W.  Rybin  A. V.  Vasilenko  N. F.  Prytkov  A. S.  Chibisova  M. V.  Kogan  M. G.  Steblov  G. M.  Frolov  D. I. 《Doklady Earth Sciences》2010,435(1):1507-1510

In June 2009, one of the greatest eruptions of the Sarychev Peak volcano in Matua Island (48°06′ N, 153°12′ E) for the recent historical period occurred. With the help of satellite sounding methods, the first signs of volcanic activity were recorded and all the stages of the explosive eruption were traced. During the expeditionary investigations in the active volcano, unique data on the character of the eruption were obtained. The volume of erupted material was 0.4 cubic km, which lead to an increased area of Matua Island by 1.4 square km. The GPS observation station set at the distance of 7 km from the volcano recorded the rapid displacement of the Earths’s surface during the first two days of the active phase of eruption. This eruption of the Sarychev Peak volcano occurred 2.5 years after the catastrophic Simushir earthquakes in the period of intensive relaxation of stresses in the middle of the central part of the Kurile island arc.  相似文献   

The Copernican principle in compact space–times     

John D. Barrow  Janna Levin 《Monthly notices of the Royal Astronomical Society》2003,346(2):615-618

Copernicus realized that we are not at the centre of the Universe. A universe made finite by topological identifications introduces a new Copernican consideration: while we may not be at the geometric centre of the Universe, some galaxy could be. A finite universe also picks out a preferred frame: the frame in which the universe is smallest. Although we are not likely to be at the centre of the Universe, we must live in the preferred frame (if we are at rest with respect to the cosmological expansion). We show that the preferred topological frame must also be the comoving frame in a homogeneous and isotropic cosmological space–time. Some implications of topologically identifying time are also discussed.  相似文献   

Simulation of gas dynamics and radiation in volcanic plumes on Io     

J. Zhang  D.B. Goldstein  N.E. Gimelshein  D.A. Levin 《Icarus》2003,163(1):182-197

Modeling results of volcanic plumes on Jupiter’s moon Io are presented. Two types of low density axisymmetric SO₂ plume flows are modeled using the direct simulation Monte Carlo (DSMC) method. Thermal radiation from all three vibrational bands and overall rotational lines of SO₂ molecules is modeled. A high resolution computation of the flow in the vicinity of the vent was obtained by multidomain sequential calculation to improve the modeling of the radiation signature. The radiation features are examined both by calculating infrared emission spectra along different lines-of-sight through the plume and with the DSMC modeled emission images of the whole flow field. It is found that most of the radiation originates in the vicinity of the vent, and non-LTE (non-local-thermodynamic equilibrium) cooling by SO₂ rotation lines exceeds cooling in the v₂ vibrational band at high altitude.In addition to the general shape of the plumes, the calculated average SO₂ column density (∼10¹⁶ cm⁻²) over a Pele-type plume and the related frost-deposition ring structure (at R ∼ 500 km from the vent) are in agreement with observations. These comparisons partially validate the modeling. It is suggested that an observation with spatial resolution of less than 30 km is needed to measure the large spatial variation of SO₂ near a Pele-type plume center. It is also found that an influx of 1.1 × 10²⁹ SO₂ s⁻¹ (or 1.1 × 10⁴ kg s⁻¹) is sufficient to reproduce the observed SO₂ column density at Pele. The simulation results also show some interesting features such as a multiple bounce shock structure around Prometheus-type plumes and the frost depletion by plume-induced erosion on the sunlit side of Io. The model predicts the existence of a canopy shock, a ballistic region inside the Pele-type plume, and the negligible effect of surface heating by plume emission.  相似文献   

Quantifying Annual Nitrogen Loads to Virginia’s Coastal Lagoons: Sources and Water Quality Response   总被引：3，自引：0，他引：3  

Juliette Christina Poleto Giordano  Mark J. Brush  Iris C. Anderson 《Estuaries and Coasts》2011,34(2):297-309

Coastal lagoons of the Delmarva Peninsula receive varying annual nitrogen loads because of differing land uses. Extensive development and agriculture contribute to elevated nutrient loads in Maryland and Delaware. Agriculture and forests dominate Virginia’s landscape, suggesting these systems receive lower loads. We used a watershed model to achieve three objectives: (1) quantify loads to Virginia lagoons; (2) determine the sources of the loads; and (3) project changes in annual loads under different development scenarios. Model simulations indicated that some Virginia lagoons receive relatively high annual nutrient loads (kg N year⁻¹) due to intensive agriculture and a high watershed/lagoon areal ratio. Model projections also suggested that increased agricultural and residential development in Virginia could lead to annual loads (kg N year⁻¹) typical of impacted Maryland systems. A comparison of Maryland and Virginia water quality responses to nutrient loading suggested that Virginia’s lagoons exhibit a different response to nutrient loading, though the exact mechanism for this difference is unclear.  相似文献   

Seagrass Meadows Modify Drag Forces on the Shell of the Fan Mussel <Emphasis Type="Italic">Pinna nobilis</Emphasis>     

Iris E. Hendriks  Miguel Cabanellas-Reboredo  Tjeerd J. Bouma  Salud Deudero  Carlos M. Duarte 《Estuaries and Coasts》2011,34(1):60-67

We assess the sheltering effect of Posidonia oceanica meadows on drag forces exerted on shells of the fan mussel Pinna nobilis. We examine a range of shell sizes under four unidirectional flow speeds (0.05–0.34 m s⁻¹) and two oscillating regimes. Three meadow densities are evaluated and a control without vegetation. We found that the attenuating effect of the meadow on drag forces experienced by bivalves is determined by the form of the hydrodynamic energy, e.g., as unidirectional flow or wave action. In tidal currents, the meadow protects most sizes of bivalves, with a higher efficiency for dense meadows, while in wave dominant zones the meadow reduces drag forces for bivalves with shell areas below a threshold of 0.019 m², whereas larger animals experience increased drag forces within the meadow independent of meadow density. Reduction of shoot density in seagrass meadows might therefore not affect the effectiveness of the canopy to reduce drag forces on associated species like the fan mussel in wave-dominated areas while increased storm frequency could result into losses of larger individuals during periods of high wave action.  相似文献   

Arctic versus temperate comparison of risk assessment metrics for 2-methyl-naphthalene     

Olsen GH  Smit MG  Carroll J  Jæger I  Smith T  Camus L 《Marine environmental research》2011,72(4):179-187

Reliable risk assessment approaches for Arctic environments are requested to manage potential impacts associated with increased activities in Arctic regions. We performed toxicity tests on Arctic and temperate species exposed to the narcotic acting oil component, 2-methyl naphthalene. The experimental results were used to quantify concentration causing lethality to 50% of exposed individuals and no-effect concentration (individual level). For estimates at community level, the hazardous concentrations affecting 5% and 50% of the species were calculated from sensitivity distribution curves. These survival metrics were then used to elucidate whether temperate toxicity data used in risk assessment are sufficiently representative for the Arctic. Taking data uncertainty into consideration, we found no regional difference in tolerances to 2-methyl naphthalene either at the species level or at the community level. Hence these data support a conclusion that values of survival metrics for temperate regions are transferrable to the Arctic for the chemical 2-methyl naphthalene, as long as extrapolation techniques are properly applied and uncertainties are taken into consideration.  相似文献