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1.
Reconstruction of nutrient concentrations in the deep Southern Ocean has produced conflicting results. The cadmium/calcium (Cd/Ca) data set suggests little change in nutrient concentrations during the last glacial period, whereas the carbon isotope data set suggests that nutrient concentrations were higher. We determined the silicon isotope composition of sponge spicules from the Atlantic and Pacific sectors of the Southern Ocean and found higher silicic acid concentrations in the Pacific sector during the last glacial period. We propose that this increase results from changes in the stoichiometric uptake of silicic acid relative to nitrate and phosphate by diatoms, thus facilitating a redistribution of nutrients across the Pacific and Southern Oceans. Our results are consistent with the global Cd/Ca data set and support the silicic acid leakage hypothesis. 相似文献
2.
Coale KH Johnson KS Chavez FP Buesseler KO Barber RT Brzezinski MA Cochlan WP Millero FJ Falkowski PG Bauer JE Wanninkhof RH Kudela RM Altabet MA Hales BE Takahashi T Landry MR Bidigare RR Wang X Chase Z Strutton PG Friederich GE Gorbunov MY Lance VP Hilting AK Hiscock MR Demarest M Hiscock WT Sullivan KF Tanner SJ Gordon RM Hunter CN Elrod VA Fitzwater SE Jones JL Tozzi S Koblizek M Roberts AE Herndon J Brewster J Ladizinsky N Smith G Cooper D Timothy D Brown SL Selph KE Sheridan CC Twining BS 《Science (New York, N.Y.)》2004,304(5669):408-414
The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide. 相似文献
3.
The silica balance in the world ocean: a reestimate 总被引：8，自引：0，他引：8
Tréguer P Nelson DM Van Bennekom AJ Demaster DJ Leynaert A Quéguiner B 《Science (New York, N.Y.)》1995,268(5209):375-379
The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teramole = 10(12) moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years. 相似文献
4.
Sullivan CW Arrigo KR McClain CR Comiso JC Firestone J 《Science (New York, N.Y.)》1993,262(5141):1832-1837
A regional pigment retrieval algorithm for the Nimbus-7 Coastal Zone Color Scanner (CZCS) has been tested for the Southern Ocean. The pigment concentrations estimated with this algorithm agree to within 5 percent with in situ values and are more than twice as high as those previously reported. The CZCS data also revealed an asymmetric distribution of enhanced pigments in the waters surrounding Antarctica; in contrast, most surface geophysical properties are symmetrically distributed. The asymmetry is coherent with circumpolar current patterns and the availability of silicic acid in surface waters. Intense blooms (>1 milligram of pigment per cubic meter) that occur downcurrent from continental masses result from dissolved trace elements such as iron derived from shelf sediments and glacial melt. 相似文献
5.
杂交早稻威优8120在三叶期喷施防寒药剂,冷害后,成秧率、秧苗素质比对照提高;叶绿素含量、可溶性糖含量较对照增加;根系的脱氢酶活性亦明显增加.威优48作晚稻种植,在孕穗期和始穗期喷药,冷害后,剑叶的叶绿素含量、含氮量和硅化细胞数较对照均有不同程度的增加,但可溶性糖含量减少.试验结果表明,喷施药剂能增强籼型杂交水稻的耐冷性. 相似文献
6.
7.
水稻纹枯病抗性机制的研究 总被引：27，自引：0，他引：27
本试验选择5个对纹枯病抗感性不同的水稻品种，就它们的细胞组织结构、生化反应与抗性的关系进行了研究。结果表明：抗病品种的叶片蜡质含量和叶鞘硅化细胞数目都明显多于感病品种；人工接菌后，抗病品种的过氧化酶活性增加的速度和峰值都大于感病品种；抗病品种的多酚氧化酶和苯丙氨酸转氨酶活性也强于感病品种。试验还表明：品种的游离氨基酸含量与抗性没有相关性。 相似文献
8.
The surface area of silicic acid, a form of silica gel, has been determined by adsorption of methanol from a benzene solvent. The method is straightforward, uses inexpensive apparatus, and should be applicable to other particulate adsorbents. 相似文献
9.
A thin claystone layer found in nonmarine rocks at the palynological Cretaceous-Tertiary boundary in eastern Montana contains an anomalously high value of iridium. The nonclay fraction is mostly quartz with minor feldspar, and some of these grains display planar features. These planar features are related to specific crystallographic directions in the quartz lattice. The shocked quartz grains also exhibit asterism and have lowered refractive indices. All these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth. The shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile. 相似文献
10.
Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy. 相似文献
11.
Armbrust EV Berges JA Bowler C Green BR Martinez D Putnam NH Zhou S Allen AE Apt KE Bechner M Brzezinski MA Chaal BK Chiovitti A Davis AK Demarest MS Detter JC Glavina T Goodstein D Hadi MZ Hellsten U Hildebrand M Jenkins BD Jurka J Kapitonov VV Kröger N Lau WW Lane TW Larimer FW Lippmeier JC Lucas S Medina M Montsant A Obornik M Parker MS Palenik B Pazour GJ Richardson PM Rynearson TA Saito MA Schwartz DC Thamatrakoln K Valentin K Vardi A Wilkerson FP Rokhsar DS 《Science (New York, N.Y.)》2004,306(5693):79-86
Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments. 相似文献
12.
For 40 million years, diatoms have dominated the reverse weathering of silica on Earth. These photosynthetic protists take up dissolved silicic acid from the water and precipitate opaline silica to form their cell wall. We show that the biosilica of diatoms is an effective pH buffer, enabling the enzymatic conversion of bicarbonate to CO2, an important step in inorganic carbon acquisition by these organisms. Because diatoms are responsible for one-quarter of global primary production and for a large fraction of the carbon exported to the deep sea, the global cycles of Si and C may be linked mechanistically. 相似文献
13.
C B Bailey 《Science (New York, N.Y.)》1967,155(763):696-697
Urinary calculi were found in all but one of 14 calves given a ration associated with the formation of siliceous calculi. No calculi were found in a similar group of 14 calves given the same ration with sodium chloride added (4 percent). It is suggested that sodium chloride prevented calculus formation by in creasing water intake and urine volume, with a consequent reduction in the con-centration of silicic acid in the urine 相似文献
14.
Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibolebearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not. 相似文献
15.
K Iizasa RS Fiske O Ishizuka M Yuasa J Hashimoto J Ishibashi J Naka Y Horii Y Fujiwara A Imai S Koyama 《Science (New York, N.Y.)》1999,283(5404):975-977
Manned submersible studies have delineated a large and actively growing Kuroko-type volcanogenic massive sulfide deposit 400 kilometers south of Tokyo in Myojin Knoll submarine caldera. The sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters, has an area of 400 by 400 by 30 meters, and is notably rich in gold and silver. The discovery of a large Kuroko-type polymetallic sulfide deposit in this arc-front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits. 相似文献
16.
Williams SN 《Science (New York, N.Y.)》1985,229(4713):551-553
The response of a large geothermal system to magmatic resurgence was analyzed by a survey of soil gas radon and elemental mercury at 600 sites in the silicic Long Valley Caldera, California. The broad geochemical anomaly over the caldera has superimposed on it a small zone of pronounced radon enrichment and mercury depletion coincident with the surface projection of a postulated dike of rising magma. Soil gas geochemistry studies can complement traditional geophysical and geodetical methods in the evaluation of potential volcanic eruption hazards. 相似文献
17.
Numerous grains of gibbsite surrounded by zones of chlorite were found in six samples of sediment taken from Waimea Bay off the coast of Kauai, Hawaii. The chlorite has formed from the gibbsite, and growth bands in the chlorite either are parallel to chlorite-gibbsite interfaces or are concentric around small remnants of gibbsite. Aggregates were found that appeared to be composed of two or more gibbsite grains surrounded by chlorite bands that have grown together. The index of refraction of the chlorite ranged from 1.58 to 1.60 and the chlorite displayed anomalous blue interference colors. The gibbsite was formed on land under conditions of strong weathering and strong leaching. When transported to the sea, the gibbsite was deposited in a solution containing silicic acid, magnesium, potassium, and hydrogen ions, in which it is unstable. Chlorite, a stable mineral in this solution, replaced the gibbsite. 相似文献
18.
Alkalinity and formation of zeolites in saline alkaline lakes 总被引：1，自引：0，他引：1
The solubility of rhyolitic glass increases with increasing alkalinity, whereas the ratio of silicon to aluminum decreases with increasing alkalinity. The strong correlation observed between alkalinity and zeolite mineralogy in saline, alkaline lakes is thought to be a function of this relationship between pH and the Si/Al ratio. It is suggested that this function is a result of the reaction between silicic glass and alkaline solution whereby (i) a gel forms, whose Si/Al ratio is controlled by the Si/Al ratio of the solution, and (ii) a zeolite forms from the gel, whose Si/Al ratio is, in turn, controlled by the composition of the gel. 相似文献
19.
鸡皮中功能性极性脂质成分的分析研究 总被引：2，自引：1，他引：1
[目的]以鸡皮为原料,分析研究对鸡皮极性脂质的功能性成分,为提取开发利用提供理论依据.[方法]硅胶柱层析法分离总脂质中的中性和极性脂质,利用双向薄层层析法进行极性脂质成分鉴定,气相色谱法分析脂质的脂肪酸组成.[结果]蛋鸡皮及肉鸡皮中脂质含量分别为31.8; 和40.5;,其中极性脂质分别占总脂质的1.8;和3.2;,主要是磷脂酰乙醇胺(脑磷脂PE),磷脂酰胆碱(卵磷脂PC),磷脂酰丝氨酸(PS), 鞘磷脂(SM)和磷脂酰肌醇(PI).总脂质的脂肪酸组成油酸(C18:1)含量最高,其次是棕榈酸(C16:0).蛋鸡皮的亚油酸(C18:2)含量高于肉鸡皮.极性脂质中主要的脂肪酸是C18:1,C18:2和C16:0,主要的甲基缩醛是十六二甲基缩醛和十八二甲基缩醛.[结论]肉鸡皮中极性脂质含量高于蛋鸡皮,主要由磷脂酰乙醇胺、磷脂酰胆碱、磷脂酰丝氨酸、鞘磷脂和磷脂酰肌醇组成. 相似文献
20.
供试土壤分别采自日本山形县农业试验场（土壤A）和鹤冈市吉田农户的水稻田（土壤B）。将两种水稻土分别与硅酸钙和硅酸混合，在密闭条件下恒温培养4周，测定施硅对土壤氮矿化的影响。在培养土壤中加入^15N标记硫酸铵以评价施硅对加入土壤中氮去向的影响，结果表明：在培养1周内，施用硅酸钙1g.kg^-1,2g.kg^-1与不施硅相比，土壤 fu lk 0。2-0。3，NH4^ -N总积累量分别增加20%，26%（土壤A）和9%，11%（土壤B），土壤氮净矿化速率分别增加26%，35%（土壤A）和13%，13%（土壤B）。处理间差异在培养开始后的第1周大于第4周，硅酸对土壤pH及氮矿化速率没有影响，两种硅肥对施入土壤中氮的去向均无明显影响，研究结果揭示，硅酸钙促进土壤氮矿化的原因不是硅元素本身，其可能机制是通过增加土壤pH而加速氮的矿化。 相似文献