On the experimental silicification of microorganisms. III. Implications of the preservation of the green prokaryotic alga prochloron and other coccoids for interpretation of the microbial fossil record     

Susan Francis  Elso S. Barghoorn  Lynn Margulis 《Precambrian Research》1978,7(4):377-383

Evidence for Precambrian fossil eukaryotic microorganisms has been based on: (1) the presence of internal ‘spots’ which have been variously interpreted to be remains of nuclei or pyrenoids of photosynthetic plastids or other organelles; (2) tetrahedral tetrad arrangement of cells; (3) trilete scars interpreted to be indicative of meiotic division: (4) large cell diameters; and (5) putative mitotic cell divisions. These features have been reported in fossils preserved in Precambrian cherts. We have studied modern microbial mats, thought to be analogues of Precambrian fossil communities, and found they may be silicified by laboratory procedures. In microbial mats from Baja California we have found many ‘spot cells’ that we could identify as remains of cyanophytes. We have silicified the newly discovered large prokaryotic coccoid green alga Prochloron and have found that it, like many cyanophytes previously silicified, preserves its structure and maintains its initial dimensions. In laboratory-silicified prokaryotic organisms we have found that all of the above criteria, supposedly characteristic of eukaryotes, can be observed. We conclude that there is no compelling morphological evidence for fossil eukaryotic microbes from Precambrian cherts.  相似文献   

    

W. A. Heiskanen  J. Lamar Worzel  G. Lynn Shurbert  Paul Herget  Clair E. Ewing  Carl I. Aslakson  Simo Laurila  John R. Williams  David T. Williams  Bertil Hallert  Robert C. Fitzpatrick  W. M. Markowitz  S. P. Worden  Henry Wild Jr  W. Kneissl 《Journal of Geodesy》1955,29(2):55-78

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Testing GISS-MM5 physics configurations for use in regional impacts studies     

Barry H. Lynn  Cynthia Rosenzweig  Richard Goldberg  David Rind  Christian Hogrefe  Len Druyan  Richard Healy  Jimy Dudhia  Joyce Rosenthal  Patrick Kinney 《Climatic change》2010,99(3-4):567-587

The Mesoscale Modeling System Version 5 (MM5) was one-way nested to the Goddard Institute for Space Studies global climate model (GISS GCM), which provided the boundary conditions for present (1990s) and future (IPCC SRES A2 scenario, 2050s) five-summer “time-slice” simulations over the continental and eastern United States. Five configurations for planetary boundary layer, cumulus parameterization, and radiation scheme were tested, and one set was selected for use in the New York City Climate and Health Project—a multi-disciplinary study investigating the effects of climate change and land-use change on human health in the New York metropolitan region. Although hourly and daily data were used in the health project, in this paper we focus on long-term current and projected mean climate change. The GISS-MM5 was very sensitive to the choice of cumulus parameterization and planetary boundary layer scheme, leading to significantly different temperature and precipitation outcomes for the 1990s. These differences can be linked to precipitation type (convective vs. non-convective), to their effect on solar radiation received at the ground, and ultimately to surface temperature. The projected changes in climate (2050s minus 1990s) were not as sensitive to choice of model physics combination. The range of the projected surface temperature changes at a given grid point among the model versions was much less than the mean change for all five model configurations, indicating relative consensus for simulating surface temperature changes among the different model projections. The MM5 versions, however, offer less consensus regarding 1990s to 2050s changes in precipitation amounts. All of the projected 2050s temperature changes were found to be significant at the 95th percent confidence interval, while the majority of the precipitation changes were not.  相似文献   

A Mariner 9 atlas of the moons of Mars     

Joseph veverka  Michael Noland  Carl Sagan  James Pollack  Lynn Quam  Robert Tucker  Botand Eross  Thomas Duxbury  William Green 《Icarus》1974,23(2):206-289

This paper contains a complete set of the best enhancements of Mariner 9 high resolution television pictures of Phobos and Deimos, consisting of 27 different views of Phobos, and 9 of Deimos. Pertinent data about the pictures are arranged in convenient tabular and graphical form.  相似文献   

Historical trends in salinity and substrate in central Florida Bay: A paleoecological reconstruction using modern analogue data     

G. Lynn Brewster-Wingard  Scott E. Ishman 《Estuaries and Coasts》1999,22(2):369-383

Understanding the natural spatial and temporal variability that exists within an ecosystem is a critical component of efforts to restore systems to their natural state. Analysis of benthic foraminifers and molluscs from modern monitoring sites within Florida Bay allows us to determine what environmental parameters control spatial and temporal variability of their assemblages. Faunal assemblages associated with specific environmental parameters, including salinity and substrate, serve as proxies for an interpretation of paleoecologic data. The faunal record preserved in two shallow (<2 m) cores in central Florida Bay (Russell Bank and Bob Allen Bank) provides a record of historical trends in environmental parameters for those sites. Analysis of these two cores has revealed two distinct patterns of salinity change at these sites: 1) a long-term trend of slightly increasing average salinity; and 2) a relatively rapid change to salinity fluctuations of greater frequency and amplitude, beginning around the turn of the century and becoming most pronounced after 1940. The degree of variability in substrate types at each locality limits interpretations of substrate trends to specific sites. A common sequence of change is present in the Russell Bank and Bob Allen Bank cores: from mixed grass and bare-sediment indicators at the bottom of the cores, to bare-sediment dwellers in the center, to a dominance of vegetative-cover indicators at the top of the cores. Changes in interpreted salinity patterns around the turn of the century are consistent with the timing of the construction of the Flagler Railroad from 1905 to 1912, and the Tamiami Trail and the canal and levee systems between 1915 and 1928. Beginning around 1940, the changes in the frequency and amplitude of salinity fluctuations may be related to changes in water management practices, meteorologic events (frequent hurricanes coupled with severe droughts in 1943 and 1944), or a combination of factors. The correspondence of these changes in Florida Bay with changes in the terrestrial Everglades suggests factors affecting the entire ecosystem are responsible for the salinity and substrate patterns seen in Florida Bay.  相似文献   

Constructing rainfall depth-frequency curves considering a linear trend in rainfall observations     

Lynn Seo  Tae-Woong Kim  Minha Choi  Hyun-Han Kwon 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(3):419-427

Comprehensive flood prevention plans are established in large basins to cope with recent abnormal floods in South Korea. In order to make economically effective plans, appropriate design rainfalls are critically determined from the rainfall depth-frequency curves which take the occurrence of abnormal floods into consideration. Conventional approaches to construct the rainfall depth-frequency curves are based on the stationarity assumption. However, this assumption has a critical weak aspect in that it cannot reflect non-stationarities in rainfall observations. As an alternative, this study suggests the non-stationary Gumbel model (NSGM) which incorporates a linear trend of rainfall observations into rainfall frequency analysis to construct the rainfall depth-frequency curves. A comparison of various schemes employed in the model found that the proposed NSGM permits the estimation of the distribution parameters even when shifted in the future by using linear relationships between rainfall statistics and distribution parameters, and produces more acceptable estimates of design rainfalls in the future than the conventional model. The NSGM was applied at several stations in South Korea and then expected the design rainfalls to increase by up to 15–30% in 2050.  相似文献   

Sustaining Rocky Mountain Landscapes: Science,Policy, and Management for the Crown of the Continent Ecosystem     

Lynn M. Resler 《The Professional geographer》2013,65(3):432-434

In this commentary, we wish to draw from Kathryn's experience in Askole to complicate the argument we developed in favor of an autoethnographic sensibility in the earlier article in this issue (Butz and Besio 2004 ButzDavid KathrynBesio 2004 The value of autoethnography for field research in transcultural settings. The Professional Geographer 56 3 350 60 [Google Scholar]). Just as we used David's first-person singular voice in much of that article, we use Kathryn's voice here to reflect the central influence of her research circumstances on the points that we make. We will return to the first-person plural voice in the commentary's conclusion where we attempt to synthesize the lessons of our two sets of research experiences.  相似文献   

Global ecology: Towards a science of the biosphere     

Mitchell B. Rambler  Lynn Margulis  René Fester 《国际地球制图》2013,28(4)

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The potential for convection and implications for geothermal energy in the Perth Basin, Western Australia     

Heather A. Sheldon  Brendan Florio  Michael G. Trefry  Lynn B. Reid  Ludovic P. Ricard  K. Ameed R. Ghori 《Hydrogeology Journal》2012,20(7):1251-1268

Convection of groundwater in aquifers can create areas of anomalously high temperature at shallow depths which could be exploited for geothermal energy. Temperature measurements in the Perth Basin (Western Australia) reveal thermal patterns that are consistent with convection in the Yarragadee Aquifer. This observation is supported by Rayleigh number calculations, which show that convection is possible within the range of aquifer thickness, geothermal gradient, salinity gradient and permeability encountered in the Yarragadee Aquifer, assuming that the aquifer can be treated as a homogeneous anisotropic layer. Numerical simulations of convection in a simplified model of the Yarragadee Aquifer show that: (1) the spacing of convective upwellings can be predicted from aquifer thickness and permeability anisotropy; (2) convective upwellings may be circular or elongate in plan view; (3) convective upwellings create significant temperature enhancements relative to the conductive profile; (4) convective flow rates are similar to regional groundwater flow rates; and (5) convection homogenises salinity within the aquifer. Further work is required to constrain the average horizontal and vertical permeability of the Yarragadee Aquifer, to assess the validity of treating the aquifer as a homogeneous anisotropic layer, and to determine the impact of realistic aquifer geometry and advection on convection.  相似文献   

Application of a Weighted-Averaging Method for Determining Paleosalinity: A Tool for Restoration of South Florida’s Estuaries   总被引：1，自引：0，他引：1  

G. Lynn Wingard  Joel W. Hudley 《Estuaries and Coasts》2012,35(1):262-280

A molluscan analogue dataset is presented in conjunction with a weighted-averaging technique as a tool for estimating past salinity patterns in south Florida’s estuaries and developing targets for restoration based on these reconstructions. The method, here referred to as cumulative weighted percent (CWP), was tested using modern surficial samples collected in Florida Bay from sites located near fixed water monitoring stations that record salinity. The results were calibrated using species weighting factors derived from examining species occurrence patterns. A comparison of the resulting calibrated species-weighted CWP (SW-CWP) to the observed salinity at the water monitoring stations averaged over a 3-year time period indicates, on average, the SW-CWP comes within less than two salinity units of estimating the observed salinity. The SW-CWP reconstructions were conducted on a core from near the mouth of Taylor Slough to illustrate the application of the method.  相似文献