Trophic cascades and future harmful algal blooms within ice-free Arctic Seas north of Bering Strait: A simulation analysis     

John J. Walsh  Dwight A. Dieterle  F. Robert Chen  Jason M. Lenes  Wieslaw Maslowski  John J. Cassano  Terry E. Whitledge  Dean Stockwell  Mikhail Flint  Irina N. Sukhanova  John Christensen 《Progress in Oceanography》2011,91(3):312-343

Within larger ice-free regions of the western Arctic Seas, subject to ongoing trophic cascades induced by past overfishing, as well as to possible future eutrophication of the drainage basins of the Yukon and Mackenzie Rivers, prior very toxic harmful algal blooms (HABs) – first associated with ∼100 human deaths near Sitka, Alaska in 1799 – may soon expand. Blooms of calcareous coccolithophores in the Bering Sea during 1997–1998 were non-toxic harbingers of the subsequent increments of other non-siliceous phytoplankton. But, now saxitoxic dinoflagellates, e.g. Alexandrium tamarense, were instead found by us within the adjacent downstream Chukchi Sea during SBI cruises of 2002 and 2003. A previous complex, coupled biophysical model had been validated earlier by ship-board observations from the Chukchi/Beaufort Seas during the summer of 2002. With inclusion of phosphorus as another chemical state variable to modulate additional competition by recently observed nitrogen-fixers, we now explore here the possible consequences of altered composition of dominant phytoplankton functional groups [diatoms, microflagellates, prymnesiophyte Phaeocystis colonies, coccolithophores, diazotrophs, and dinoflagellates] in relation to increases of the toxic A. tamarense, responding to relaxation of grazing pressure by herbivores north of Bering Strait as part of a continuing trophic cascade. Model formulation was guided by validation observations obtained during 2002–2004 from: cruises of the SBI, CHINARE, and CASES programs; moored arrays in Bering Strait; other RUSALCA cruises around Wrangel Island; and SBI helicopter surveys of the shelf-break regions of the Arctic basin. Our year-long model scenarios during 2002–2003 indicate that post bloom silica-limitation of diatoms, after smaller simulated spring grazing losses, led to subsequent competitive advantages in summer for the coccolithophores, dinoflagellates, and diazotrophs. Immediate top-down control is exerted by imposed grazing pressures of the model’s herbivores and bottom-up control is also effected by light-, nitrate-, ammonium-, silicate-, and phosphate-modulated competition among the six functional groups of the simulated phytoplankton community. Similar to the history of the southern North Sea adjacent to the Rhine River, possible farming of northwestern Alaska and Canada, in conjunction with other human activities of ice retreat and overfishing, may lead to future exacerbations of poisonous phytoplankton. These potential killers include both toxic dinoflagellate and diazotroph HABs, deadly to terrestrial and marine mammals, as well as those of prymnesiophytes, some of which have already foamed beaches, while others have killed fishes of European waters.  相似文献   

Evaluation and error analysis: Kalman gain regularization versus covariance regularization     

Yanfen Zhang  Dean S. Oliver 《Computational Geosciences》2011,15(3):489-508

Ensemble size is critical to the efficiency and performance of the ensemble Kalman filter, but when the ensemble size is small, the Kalman gain generally cannot be well estimated. To reduce the negative effect of spurious correlations, a regularization process applied on either the covariance or the Kalman gain seems to be necessary. In this paper, we evaluate and compare the estimation errors when two regularization methods including the distance-dependent localization and the bootstrap-based screening are applied on the covariance and on the Kalman gain. The investigations were carried out through two examples: 1D linear problem without dynamics but for which the true Kalman gain can be computed and a 2D highly nonlinear reservoir fluid flow problem. The investigation resulted in three primary conclusions. First, if localizations of two covariance matrices are not consistent, the estimate of the Kalman gain will generally be poor at the observation location. The consistency condition can be difficult to apply for nonlocal observations. Second, the estimate of the Kalman gain that results from covariance regularization is generally subject to greater errors than the estimate of the Kalman gain that results from Kalman gain regularization. Third, in terms of removing spurious correlations in the estimation of spatially correlated variables, the performance of screening Kalman gain is comparable as the performance of localization methods (applied on either covariance or Kalman gain), but screening Kalman gain outperforms the localization methods in terms of generality for application, as the screening method can be used for estimating both spatially correlated and uncorrelated variables, and moreover, no assumption about the prior covariance is required for the screening method.  相似文献   

Ensemble Kalman filter for model updating – A special issue     

Geir Nævdal  Remus G. Hanea  Dean S. Oliver  Brice Vallès 《Computational Geosciences》2011,15(2):223-224

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The Solar Dynamics Observatory (SDO)     

W. Dean Pesnell  B. J. Thompson  P. C. Chamberlin 《Solar physics》2012,275(1-2):3-15

The Solar Dynamics Observatory (SDO) was launched on 11 February 2010 at 15:23 UT from Kennedy Space Center aboard an Atlas V 401 (AV-021) launch vehicle. A?series of apogee-motor firings lifted SDO from an initial geosynchronous transfer orbit into a circular geosynchronous orbit inclined by 28° about the longitude of the SDO-dedicated ground station in New Mexico. SDO began returning science data on 1 May 2010. SDO is the first space-weather mission in NASA’s Living With a Star (LWS) Program. SDO’s main goal is to understand, driving toward a predictive capability, those solar variations that influence life on Earth and humanity’s technological systems. The SDO science investigations will determine how the Sun’s magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere and geospace as the solar wind, energetic particles, and variations in the solar irradiance. Insights gained from SDO investigations will also lead to an increased understanding of the role that solar variability plays in changes in Earth’s atmospheric chemistry and climate. The SDO mission includes three scientific investigations (the Atmospheric Imaging Assembly (AIA), Extreme Ultraviolet Variability Experiment (EVE), and Helioseismic and Magnetic Imager (HMI)), a spacecraft bus, and a dedicated ground station to handle the telemetry. The Goddard Space Flight Center built and will operate the spacecraft during its planned five-year mission life; this includes: commanding the spacecraft, receiving the science data, and forwarding that data to the science teams. The science investigations teams at Stanford University, Lockheed Martin Solar Astrophysics Laboratory (LMSAL), and University of Colorado Laboratory for Atmospheric and Space Physics (LASP) will process, analyze, distribute, and archive the science data. We will describe the building of SDO and the science that it will provide to NASA.  相似文献   

Experimental Effects of the Grass Shrimp, Palaemonetes pugio, on Hard-Substrate Communities in Chesapeake Bay and an Adjacent Coastal Bay, USA     

Dean S. Janiak  Richard W. Osman 《Estuaries and Coasts》2012,35(4):1128-1136

With increased shoreline hardening and development, it is important to understand the ecological processes occurring in these and adjacent coastal habitats. A common species found associated with these hard-substrate habitats in Chesapeake Bay is the grass shrimp, Palaemonetes pugio. Caging experiments were conducted from June to August 2010 to examine the effects of shrimp on the recruitment and development of hard-substrate communities. Experiments were conducted at two low-salinity sites within Chesapeake Bay and one high-salinity site in an adjacent coastal bay in Virginia. The addition of grass shrimp reduced recruitment of polychaetes and scyphistomae of the sea nettle, Chrysaora quinquecirrha, and increased recruitment of encrusting bryozoans and the oyster, Crassostrea virginica. After 12?weeks, sea nettles at one low-salinity site, dominated predator-exclusion treatments. At the high-salinity site, oysters dominated when shrimp were present. Although it is unclear whether the results of short-term caging studies can be applied across larger temporal and spatial scales, the significant effects of grass shrimp on two important Chesapeake Bay species suggests that increases in hard-substrate habitat could have broader impacts within this and other systems.  相似文献   

20–100 keV properties of cataclysmic variables detected in the INTEGRAL/IBIS survey     

E. J. Barlow  C. Knigge  A. J. Bird  A. J Dean  D. J. Clark  A. B. Hill  M. Molina  V. Sguera 《Monthly notices of the Royal Astronomical Society》2006,372(1):224-232

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Characterization of lake water and ground water movement in the littoral zone of Williams Lake,a closed‐basin lake in north central Minnesota     

Paul F. Schuster  Michael M. Reddy  James W. LaBaugh  Renee S. Parkhurst  Donald O. Rosenberry  Thomas C. Winter  Ronald C. Antweiler  Walter E. Dean 《水文研究》2003,17(4):823-838

Williams Lake, Minnesota is a closed‐basin lake that is a flow‐through system with respect to ground water. Ground‐water input represents half of the annual water input and most of the chemical input to the lake. Chemical budgets indicate that the lake is a sink for calcium, yet surficial sediments contain little calcium carbonate. Sediment pore‐water samplers (peepers) were used to characterize solute fluxes at the lake‐water–ground‐water interface in the littoral zone and resolve the apparent disparity between the chemical budget and sediment data. Pore‐water depth profiles of the stable isotopes δ¹⁸O and δ²H were non‐linear where ground water seeped into the lake, with a sharp transition from lake‐water values to ground‐water values in the top 10 cm of sediment. These data indicate that advective inflow to the lake is the primary mechanism for solute flux from ground water. Linear interstitial velocities determined from δ²H profiles (316 to 528 cm/yr) were consistent with velocities determined independently from water budget data and sediment porosity (366 cm/yr). Stable isotope profiles were generally linear where water flowed out of the lake into ground water. However, calcium profiles were not linear in the same area and varied in response to input of calcium carbonate from the littoral zone and subsequent dissolution. The comparison of pore‐water calcium profiles to pore‐water stable isotope profiles indicate calcium is not conservative. Based on the previous understanding that 40–50 % of the calcium in Williams Lake is retained, the pore‐water profiles indicate aquatic plants in the littoral zone are recycling the retained portion of calcium. The difference between the pore‐water depth profiles of calcium and δ¹⁸O and δ²H demonstrate the importance of using stable isotopes to evaluate flow direction and source through the lake‐water–ground‐water interface and evaluate mechanisms controlling the chemical balance of lakes. Published in 2003 by John Wiley & Sons, Ltd.  相似文献   

INTEGRAL observations of the Small Magellanic Cloud     

V. A. McBride  M. J. Coe  A. J. Bird  A. J. Dean  A. B. Hill  K. E. McGowan  M. P. E. Schurch  A. Udalski  I. Soszynski  M. Finger  C. A. Wilson  R. H. D. Corbet  I. Negueruela 《Monthly notices of the Royal Astronomical Society》2007,382(2):743-749

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“卫星导航定位”课程实践教学创新体系改革     

周命端  丁克良  罗德安  黄鹤  刘旭春 《测绘工程》2017,26(7)

"卫星导航定位"课程是我校测绘类专业本科生的一门具有较强理论性和实践性的专业基础课,为强化学生知识运用能力、测绘实践操作能力、程序设计能力及科技创新能力,从实践教学内容更新及实践教学方法和手段优化等方面对该课程的实践教学创新体系(课间实验和集中实习)探索性改革,经两年的教学实践与持续改进,实际效果显著。  相似文献   

A cartographic modeling approach to isopleth mapping     

Jie Lin  Dean M. Hanink  Robert G. Cromley 《International journal of geographical information science》2017,31(5):849-866

Isopleth maps depict different types of standardized data densities, general ratios/rates, and proportions/percentages. In this study, we describe different paths each type of standardized data takes to construct isoplethic surfaces in a cartographic modeling framework. As suggested in previous research, an area-based pycnophylactic interpolator is preferred to point interpolators in isopleth mapping not only because it preserves the total volume in each aggregation unit but also because it is non-parametric and is able to incorporate ancillary data to increase the accuracy of a surface representation. Here, a general pycnophylactic method is used to generate isopleth maps of density surfaces, but a hybrid approach is proposed to address the small denominator problem that arises when mapping ratio/rate and proportion/percentage surfaces. Finally, we propose a value-by-perspective height mapping procedure to resolve the visual equalization problem associated with ratio/rate and proportion/percentage surfaces that enable one to distinguish among high rate/large denominator, high rate/small denominator, low rate/large denominator, and low rate/small denominator regions of the surface.  相似文献