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排序方式： 共有126条查询结果，搜索用时 390 毫秒
91.
R.G. Barlow R.F.C. Mantoura M.A. Gough T.W. Fileman 《Deep Sea Research Part I: Oceanographic Research Papers》1993,40(11-12)
The temporal and depth distributions of phaeopigments were determined during a spring bloom in the northeastern Atlantic in 1990 using reverse phase high performance liquid chromatography. Phaeopigment concentrations were very low (<8% by mole relative to chlorophyll a) and two forms of phaeophorbide and two forms of phaeophytin were separated and quantified. Phaeophorbides were the dominant phaeopigments, accounting for 80% of the total phaeopigment molar concentration, and phaeopigments closely tracked the variations in chlorophyll a by increasing during the development phase of the bloom and decliningin the post bloom stage. Production of phaeopigments was found to occur predominantly at night, and these rates exceeded the rates of phaeopigment destruction during the day. Lower phaeopigment-chlorophyll a ratios were determined for the surface waters, suggesting that photodegradation was possibly the primary mechanism of phaeopigment disappearance in the euphotic zone. A comparison of phaeopigment data and phyto- and zooplankton structure indicates that greater phaeopigment production and grazing pressure occurred in the development phase when diatoms dominated, while grazing and phaeopigment production declined in the post bloom stage dominated by prymnesiophytes. 相似文献
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We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s−1 (FWHM), to observe K i and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K i , two of which are also present in C2 . We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions ( b -values) of 0.2–0.3 km s−1 for the K i components, and 0.54±0.03 km s−1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K i and 420 K for C2 , although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures ( T k ≈10 K) and high densities ( n ≈106 to 107 cm−3 ) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell. 相似文献
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Marine control over negative power law scaling of mass wasting events in chalk sea cliffs with implications for future recession under the UKCP09 medium emission scenario 
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下载免费PDF全文 Coastal cliff erosion represents a significant geohazard for people and infrastructure. Forecasting future erosion rates is therefore of critical importance to ensuring the resiliency of coastal communities. We use high precision monitoring of chalk cliffs at Telscombe, UK to generate monthly mass movement inventories between August 2016 and July 2017. Frequency–magnitude analysis of our inventories demonstrate negative power law scaling over 7 orders of magnitude and, for the first time, we report statistically significant correlations between significant wave height (Hs) and power law scaling coefficients (r2 values of 0.497 and 0.590 for β and s respectively). Applying these relationships allows for a quantitative method to predict erosion at the site based on Hs probabilities and sea level forecasts derived from the UKCP09 medium emission climate model (A1B). Monte‐Carlo simulations indicate a range of possible erosion scenarios over 70 years (2020–2090) and we assess the impact these may have on the A259 coastal road which runs proximal to the cliffs. Results indicate a small acceleration in erosion compared with those based on current conditions with the most likely scenario at the site being 21.7 m of cliff recession by 2090. However, low‐probability events can result in recession an order of magnitude higher in some scenarios. In the absence of negative feedbacks, we estimate an ~11% chance that the A259 will be breached by coastal erosion by 2090. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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Nadine G. Barlow Sierra N. Ferguson Ryan M. Horstman Aviva Maine 《Meteoritics & planetary science》2017,52(7):1371-1387
We report on the first results of a large‐scale comparison study of central pit craters throughout the solar system, focused on Mars, Mercury, Ganymede, Rhea, Dione, and Tethys. We have identified 10 more central pit craters on Rhea, Dione, and Tethys than have previously been reported. We see a general trend that the median ratio of the pit to crater diameter (Dp/Dc) decreases with increasing gravity and decreasing volatile content of the crust. Floor pits are more common on volatile‐rich bodies while summit pits become more common as crustal volatile content decreases. Uplifted bedrock from below the crater floor occurs in the central peak upon which summit pits are found and in rims around floor pits, which may or may not break the surface. Peaks on which summit pits are found on Mars and Mercury share similar characteristics to those of nonpitted central peaks, indicating that some normal central peaks undergo an additional process to create summit pits. Martian floor pits do not appear to be the result of a central peak collapse as the median ratio of the peak to crater diameter (Dpk/Dc) is about twice as high for central peaks/summit pits than Dp/Dc values for floor pits. Median Dpk/Dc is twice as high for Mars as for Mercury, reflecting differing crustal strength between the two bodies. Results indicate that a complicated interplay of crustal volatiles, target strength, surface gravity, and impactor energy along with both uplift and collapse are involved in central pit formation. Multiple formation models may be required to explain the range of central pits seen throughout the solar system. 相似文献
97.
R. Barlow M. Kyewalyanga H. Sessions M. van den Berg T. Morris 《Estuarine, Coastal and Shelf Science》2008
An investigation of pigments, phytoplankton types and absorption characteristics was conducted in the Delagoa and Natal Bights during late winter and spring in the southwest Indian Ocean. The study demonstrated that small flagellates dominated the phytoplankton communities in both bights and were ubiquitous across a temperature range of 18–24 °C. Diatoms were dominant in patches of cool water (<22 °C) related to upwelling processes and were associated with elevated levels of phytoplankton biomass, while prokaryotes were observed to increase in warm waters >22 °C. Absorption coefficients varied closely with variations in chlorophyll a and specific coefficients were lower for diatoms compared to flagellates. Chlorophyll-specific coefficients also provided useful information on the level of pigment packaging and were related to the proportion of chlorophylls and carotenoids in the pigment pool. 相似文献
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