Carbon isotopic fractionation by the marine diatom Phaeodactylum tricornutum under nutrient- and light-limited growth conditions     

Nicolas Cassar  Brian N. Popp 《Geochimica et cosmochimica acta》2006,70(21):5323-5335

A theoretical model was developed to explain the characteristics of carbon isotopic fractionation (ε_P) by the marine diatom Phaeodactylum tricornutum under nutrient- and light-limited growth conditions. The model takes into consideration active transport and diffusion of inorganic carbon through the cell membrane and chloroplast membrane and the energetic tradeoff between production of Rubisco and operation of a carbon-concentrating mechanism to achieve a given growth rate. The model is able to explain 88% of the variance in experimental ε_p data reported in this study and in previous work and is able to account for the observed pattern of Rubisco activity in nitrate-limited chemostats. Two important implications of the model include the fact that ε_p is not a unique function of the ratio of growth rate to external CO₂ concentration (as opposed to the predictions of several previous models) and that changes in light-limited and nutrient-limited growth rates have opposite effects on the fraction of CO₂ taken up by the chloroplast that is lost to diffusion and hence on certain patterns of carbon isotopic fractionation.  相似文献   

A simulation study of the errors of omission and commission for GRACE RL01 gravity fields     

Brian Gunter  John Ries  Srinivas Bettadpur  Byron Tapley 《Journal of Geodesy》2006,80(7):341-351

This paper examines the influence that certain omission and commission errors can have on the gravity field models estimated from the initial release of data (RL01) from the Gravity Recovery And Recovery Experiment (GRACE) satellite mission. The effects of omission errors were analyzed by limiting the degree and order to which the GPS and K-band range-rate (KBR) measurement partials were extended in the solution process. The commission error studies focused on the impact of an imperfect mean reference gravity field model on the solution. Combinations of both of these error sources were also explored. The nature of these errors makes them difficult to distinguish from the true gravity signal, so the exploration of these error sources was performed using simulations; however, comparisons to real-data solutions are provided. The results show how each of the specific error sources investigated influences the gravity field solution. The simulations also show how all of the errors examined can be sufficiently mitigated through the appropriate choice of processing parameters.  相似文献   

Charcoal morphotypes in lake sediments from British Columbia (Canada): an assessment of their utility for the reconstruction of past fire and precipitation     

Mihaela D. Enache  Brian F. Cumming 《Journal of Paleolimnology》2007,38(3):347-363

Quantitative analysis of variations in morphological types of charcoal were undertaken in sediment cores from three lakes on the Interior Plateau (BC, Canada) over the period AD 1919–2000. Seven distinct morphological types of charcoal were identified based on particle shape and structural features and were compared with seasonal precipitation and recorded area burned within 20 km-radius of study lakes. Fragile-type charcoal fragments, termed type M, displayed significant relationships to recorded area burned in sediment cores from Prosser (r ² = 0.5; p = 0.0001) and Opatcho (r ² = 0.2; p = 0.02) lakes. However, nonsignificant correlations (p > 0.05) were found between total charcoal and area burned. Robust and highly elongated morphotypes C and F were correlated to recorded spring precipitation (r ² = 0.5; p = 0.002) in Opatcho Lake. Charcoal from a sediment core from Big Lake, the lake with the largest watershed, was significantly but inversely related to past fires (r ² = 0.44; p = 0.0003), suggesting important contributions from secondary transportation and deposition. Models were developed to infer relative area burned and precipitation for the study lakes. Our results suggest that charcoal morphotypes are related to the biogeoclimatic and lake watershed characteristics. This study also suggest that charcoal morphotypes can provide insights on past fire and climate, which was not possible based on traditional analysis of total charcoal.  相似文献   

Tsunami Warnings: Understanding in Hawai‘i     

Chris E. Gregg  Bruce F. Houghton  Douglas Paton  David M. Johnston  Donald A. Swanson  Brian S. Yanagi 《Natural Hazards》2007,40(1):71-87

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Cenozoic volcanism in Southwestern New Mexico.: W.E. Elston and S.A. Northrop (Editors). New Mexico Geological Society Special Publication No. 5, 1976, 151 pp., US $ 13.50. Available from the New Mexico Geological Society,New Mexico Bureau of Mines and Mineral Resources,Campus Station,Socorro, N.M. 87801, U.S.A.     

Brian H. Baker 《Journal of Volcanology and Geothermal Research》1976,1(4):387-388

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Waituhi: A Place in Maori New Zealand     

Brian J. Murton 《New Zealand geographer》1979,35(1):24-33

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Higher-degree moment tensors – the importance of source finiteness and rupture propagation on seismograms     

Brian W. Stump  Lane R. Johnson 《Geophysical Journal International》1982,69(3):721-743

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Winter-spring precipitation reconstructions from tree rings for northeast Mexico     

Jose Villanueva-Diaz  David W. Stahle  Brian H. Luckman  Julian Cerano-Paredes  Mathew D. Therrell  Malcom K. Cleaveland  Eladio Cornejo-Oviedo 《Climatic change》2007,83(1-2):117-131

The understanding of historic hydroclimatic variability is basic for planning proper management of limited water resources in northeastern Mexico. The objective of this study was to develop a network of tree-ring chronologies to reconstruct hydroclimate variability in northeastern Mexico and to analyze the influence of large-scale circulation patterns, such as ENSO. Precipitation sensitive tree-ring chronologies of Douglas-fir were developed in mountain ranges of the Sierra Madre Oriental and used to produce winter-spring precipitation reconstructions for central and southern Nuevo Leon, and southeastern Coahuila. The seasonal winter-spring precipitation reconstructions are 342 years long (1659–2001) for Saltillo, Coahuila and 602 years long (1400–2002) for central and southern Nuevo Leon. Both reconstructions show droughts in the 1810s, 1870s, 1890s, 1910s, and 1970s, and wet periods in the 1770s, 1930s, 1960s, and 1980s. Prior to 1800s the reconstructions are less similar. The impact of ENSO in northeastern Mexico (as measured by the Tropical Rainfall Index) indicated long-term instability of the Pacific equatorial teleconnection. Atmospheric circulation systems coming from higher latitudes (cold fronts or `nortes’) and others developed in the Gulf of Mexico (tropical storms, hurricanes) also influence the climatic conditions characterizing this region. The recent development of new and longer tree-ring chronologies for the region will contribute to a better understanding of the interannual and multidecadal climatic variability of northeastern Mexico.  相似文献   

Speckle filtering of Synthetic Aperture Radar images using filters with object-size-adapted windows     

Sahel Mahdavi  Bahram Salehi  Cecilia Moloney  Weimin Huang  Brian Brisco 《International Journal of Digital Earth》2018,11(7):703-729

Speckle degrades the radiometric quality of a Synthetic Aperture Radar (SAR) image. Previous methods for speckle reduction have used a fixed-size window for filtering the entire image. This, however, may not be effective for the entire image, as land covers of different sizes require different filtering windows. In this paper, a novel method is proposed by which each pixel in the image is filtered with a window appropriate for the size of object within it. The real in-phase and the imaginary quadrature components of the SAR images determine the best window size and the pixels in the intensity image are filtered using their own optimal windows. The proposed method is presented for both single- and multi-polarized SAR images, and the results of several common filters that were modified are presented. This approach is applied to two RADARSAT-2 images: one over San Francisco, California, USA and the other over St. John’s, Newfoundland and Labrador, Canada, producing results that were similar to, or outperformed, comparable filters while retaining details and suppressing speckle effectively. While the method was successful for single-look intensity data, it offers great potential for multi-look and amplitude data as well.  相似文献   

Abundance and Distribution of Reef-Associated Fishes Around Small Oil and Gas Platforms in the Northern Gulf of Mexico’s Hypoxic Zone     

David B. Reeves  Edward J. Chesney  Ryan T. Munnelly  Donald M. Baltz  Brian D. Marx 《Estuaries and Coasts》2018,41(7):1835-1847

Oil and gas platforms (platforms) provide high-relief habitat in the northern Gulf of Mexico’s hypoxic zone that are important to associated fishes. Hypoxia develops near the bottom and reef-associated fishes utilize vertical structure in the well-oxygenated waters overlaying hypoxia. A video array was used to profile the water column and to estimate abundances and depth distributions of fishes before, during, and after summer hypoxia at platforms experiencing intense (seaward) and mild hypoxia (shoal). Gray snapper abundance increased at shoal platforms (10× greater after vs. before the hypoxia season), while abundance remained stable at seaward platforms. However, there was no significant relationship between gray snapper abundance and oxygen concentrations. Sheepshead, Atlantic spadefish, blue runner, and Atlantic bumper abundances varied throughout the summer, but there was no significant effect of hypoxia. Occupation of bottom waters by fishes was consistent throughout the study period at shoal platforms, but fishes were rarely observed in the bottom 3 m and congregated in the water immediately above the hypoxic layer when hypoxia was present at seaward platforms. Nevertheless, patterns of fish abundances were not driven by the presence or absence of hypoxia. The vertical dimension of platforms is a unique and key aspect of their ecological value, especially in the hypoxic zone, and should be considered for artificial reef management.  相似文献