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1.
Glycoproteins as biological antifreeze agents in antarctic fishes 总被引：17，自引：0，他引：17
A L DeVries 《Science (New York, N.Y.)》1971,172(988):1152-1155
The blood serums of Antarctic fishes freeze at -2 degrees C, which is approximately 1 degrees C below the melting points of their serums. This thermal hysteresis is due to the influence of serum glycoproteins. The temperatures of freezing and melting of aqueous solutions of the purified glycoproteins suggest that this thermal hysteresis results from the adsorption of the glycoprotein molecule onto the surface of ice crystals. 相似文献
2.
Temperature tolerance of some Antarctic fishes 总被引：22，自引：0，他引：22
Three species of Antarctic fishes which live in constantly near-freezing waters have a markedly low upper-lethal temperature of 6 degrees C ; this is the lowest upper-lethal temperature reported for any organism. The fishes survive supercooling to -2.5 degrees C. Data on brain metabolism in vitro support the hypothesis that the central nervous system is a primary site of thermal injury. 相似文献
3.
The arctic copepod Pseudocalanus can be highly aggregated in the first few centimeters under landfast ice during spring in concentrations up to 10/(6) per cubic meter. Chlorophyll-derived pigments in the water, the abundance of animals, and their gut pigment index show fluctuations that may be tidally related. Short-term grazing experiments performed at -1.7 degrees C, in which ice algae was used as food, yielded feeding rates comparable to the highest known for the genus. Arctic Pseudocalanus seem to feed opportunistically near the ice-water interface, either directly on the attached epontic (under ice) algae or as it erodes from the ice. 相似文献
4.
太湖银鱼和主要鱼类渔获量间的相关分析 总被引：1，自引：0，他引：1
根据太湖1973-2002年连续30年的鱼类渔获量统计资料,研究了太湖银鱼和主要鱼类渔获量间的相关关系.并根据2004-2005年的食性调查初步结果对相互关系的机制进行了分析.简单相关分析表明,太湖银鱼和鲌鱼、鲢鳙鱼渔获量间的正相关关系均达到极显著水平;偏相关分析表明,太湖银鱼和鲌鱼渔获量间的正相关关系达到极显著水平,和其它鱼类渔获量间的正相关关系达到显著水平,和鲢鳙鱼渔获量间的正相关关系虽然没有达到显著水平,但有一致趋势;简单相关和偏相关分析均表明,太湖银鱼和和鲚鱼渔获量间的相关关系均没有达到显著水平.分析认为:太湖银鱼渔获量的变化除受捕捞强度及环境理化等因素影响外,鲌鱼通过捕食调节,可能降低了鲚鱼和银鱼的食物竞争强度,从而有利银鱼增加;鲢、鳙鱼通过和鲚鱼的食物竞争,从而间接促进了银鱼种群数量发展. 相似文献
5.
The survival of Escherichia coli B/r WP2 (tryptophan-requiring) from ultraviolet irradiation when suspended in 0.067M phosphate buffer (pH 7) has been studied over the temperature range 22 degrees to -269 degrees C. In unfrozen suspensions there was no appreciable change in sensitivity between 22 degrees and -10 degrees C. The sensitivity in the presence of ice progressively increased by a factor of 7 when the temperature was lowered to -79 degrees C. Between -79 degrees and -196 degrees C the sensitivity decreased to less than four times the sensitivity at 22 degrees C and was not appreciably different at -269 degrees C. Evidence from experiments with bacteriophage T1 and E. coli WP2 HCR(-) (a strain unable to excise thymine dimers) indicates that a new, qualitatively different lesion, less amenable to repair, may replace the thymine dimer in E. coli irradiated at -79 degrees C. 相似文献
6.
Gilmour AE 《Science (New York, N.Y.)》1979,203(4379):438-439
Two temperature profiles recorded by a sensitive bathythermograph at the Ross Ice Shelf Project site (82 degrees 22.5'S, 168 degrees 37.5'W) are presented. From the shape of the profiles it is concluded that an inflow of water at intermediate depths provides a source of heat to drive a regime in which ice is melted from the interface at a depth of 360 meters. Melting maintains the temperature of a thick layer under the ice at about -2.14 degrees C, close to the ambient freezing temperature. A very well mixed layer about 35 meters thick was found at the seabed. 相似文献
7.
Karl DM Bird DF Björkman K Houlihan T Shackelford R Tupas L 《Science (New York, N.Y.)》1999,286(5447):2144-2147
Analysis of a portion of Vostok ice core number 5G, which is thought to contain frozen water derived from Lake Vostok, Antarctica (a body of liquid water located beneath about 4 kilometers of glacial ice), revealed between 2 x 10(2) and 3 x 10(2) bacterial cells per milliliter and low concentrations of potential growth nutrients. Lipopolysaccharide (a Gram-negative bacterial cell biomarker) was also detected at concentrations consistent with the cell enumeration data, which suggests a predominance of Gram-negative bacteria. At least a portion of the microbial assemblage was viable, as determined by the respiration of carbon-14-labeled acetate and glucose substrates during incubations at 3 degrees C and 1 atmosphere. These accreted ice data suggest that Lake Vostok may contain viable microorganisms. 相似文献
8.
Secondary ice crystals are thrown off when supercooled cloud drops are captured and freeze on a moving target in a cloud at -5 degrees C. The rate of production of these ice crystals is proportional to the rate of accretion of drops of the diameter >/=24 micrometers. 相似文献
9.
Freezing resistance in some Antarctic fishes 总被引：19，自引：0，他引：19
Measurements of serum freezing points in three Antarctic marine fishes indicated that they do not freeze in the -1.87 degrees C seawater because their blood is isosmotic to seawater. Concentrations of sodium chloride, urea, and free amino acids in the serum accounted for only half of the freezing-point depression of the serum. A protein containing carbohydrate was isolated which accounted for 30 percent of the freezing-point depression of the serum. 相似文献
10.
Monolayers of aliphatic long-chain alcohols induced nucleation of ice at temperatures approaching 0 degrees C, in contrast with water-soluble alcohols, which are effective antifreeze agents. The corresponding fatty acids, or alcohols with bulky hydrophobic groups, induce freezing at temperatures as much as 12 degrees C lower. The freezing point induced by the amphiphilic alcohols was sensitive not only to surface area per molecule but, for the aliphatic series (C(n)H(2n + 1)OH), to chain length and parity. The freezing point for chains with n odd reached an asymptotic temperature of 0 degrees C for an upper value of n = 31; for n even the freezing point reached a plateau of -8 degrees C for n in the upper range of 22 to 30. The higher freezing point induced by the aliphatic alcohols is due to formation of ordered clusters in the uncompressed state as detected by grazing incidence synchrotron x-ray diffraction measurements. The diffraction data indicate a close lattice match with the ab layer of hexagonal ice. 相似文献
11.
Braham RR 《Science (New York, N.Y.)》1959,129(3342):123-129
On the basis of presently available data, combined with present-day knowledge of the physics and chemistry of cloud particle development, it is possible to make the following generalizations about the mode of precipitation in natural clouds. 1) The all-water mechanism begins to operate as soon as a parcel of cloud air is formed and continues to operate throughout the life of the cloud. The ice-crystal mechanism, on the other hand, can begin to operate only after the top of the cloud has reached levels where ice nuclei can be effective (about -15 degrees C). Some clouds never reach this height; any precipitation from them must be through the all-water mechanism. In cold climates and at high levels in the atmosphere, the cloud bases may be very close to this critical temperature. In the tropics, approximately 25,000 feet separate the bases of low clouds from the natural ice level. 2) The number of large hygroscopic nuclei in maritime air over tropical oceans is entirely adequate to rain-out any cloud with a base below about 10,000 feet, provided the cloud duration and cloud depth is sufficient for the precipitation process to operate. Extensive trajectories over land will decrease the number of sea-salt particles, both because of sedimentation and removal in rain. Measurements show an order-of-magnitude decrease in the number of large particles as maritime air moves from the Gulf of Mexico to the vicinity of St. Louis, during the summer months. Measurements in Arizona and New Mexico show even smaller chloride concentrations, presumably because of the long overland trajectories required in reaching these areas. The maritime particles lost in overland trajectories apparently are more than replaced by particles of land origin. The latter are usually of mixed composition and are less favorable for the formation of outsized solution droplets. 3) Ice nuclei, required for the formation of ice crystals and for droplet freezing, are rather rare at temperatures higher than about -10 degrees C. This, of course, accounts for the fact that natural clouds undergo extensive undercooling. Because of the scarcity of suitable nuclei, precipitation through the ice phase usually is not found in clouds warmer than about -15 degrees to -20 degrees C. Natural cirrus clouds might provide ice nuclei for precipitation at somewhat higher temperatures, but this possibility has not been extensively studied. 4) Precipitation in tropical clouds invariably first develops through the all-water mechanism; points discussed in paragraphs 1, 2, and 3 above all work toward this end. Tropical clouds which reach to heights above about 25,000 feet also develop precipitation through snow pellets. The data for mid-latitude clouds are conflicting. Some measurements suggest that summer clouds in the central United States and in the semiarid Southwest develop rain largely through the all-water process; existing theories support such a suggestion. However, flight measurements indicate that there is considerably more ice and snow in the clouds than can be accounted for by present theory; as a consequence, one must be careful in ruling out the ice mechanism in these areas. It appears to me, however, that the ice particles in these clouds are best accounted for through the hypothesis of freezing of drops which have grown to fairly large size through diffusion of vapor. Thus, the ice would be only incidental to the precipitation development. Winter clouds in the central United States and almost all of the clouds of northern United States and Canada appear to precipitate largely through the ice-crystal mechanism. The relatively cold cloud bases and the continental sources of air masses in these regions appear to retard the warm-rain mechanism to the point where the ice mechanism dominates. But here again, a great deal of research must be completed before a firm conclusion can be drawn (18). 相似文献
12.
Vacuum sublimation of oriented single crystals of ice at temperatures from -110 to -60 degrees Celsius was studied by electron microscopy with the freeze-etch technique. Sublimation etches the ice surface to produce pits and asperities and above -85 degrees Celsius causes extreme surface roughening. The etch pits are ascribed to surface dislocations, and the extreme roughening is ascribed to the departure from unity of the vaporization coefficient. The asperities could not be attributed to impurities; they may be related to the whiskers that others have observed at higher temperatures. 相似文献
13.
The Antarctic ice sheet at Byrd Station has been core-drilled to bedrock; the vertical thickness of the ice is 2164 meters. Liquid water-indicative of pressure melting-was encountered at the bed. Heat flow through the base of the ice sheet is estimated at 1.8 microcalories per square centimeter per second. The minimum temperature was -28.8 degrees C at 800 meters; maximum ice density, 0.9206 at 1000 meters. Core studies reveal the existence of a chemically pure, structurally stratified sheet comprising bubbly ice to 900 meters that transforms to bubble-free deformed ice, with substantially vertically orientated c-axis structure, below 1200 meters. Below 1800 meters the deformed ice structure gives way to large annealed crystals. Several thin layers of dirt between 1300 and 1700 meters are tentatively identified as volcanic ash, and horizontally banded debris, including fragments of granite, is present in the basal ice. 相似文献
14.
A uniform oxygen isotope value of -25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial Lake Agassiz basin. The lake occupied parts of North Dakota and southern Manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of Canada. Ground water from thick late Pleistocene-age clay deposits elsewhere, a till in southern Saskatchewan, and a glaciolacustrine deposit in northern Ontario show the same value at similar depths. These sites are at about 50 degrees N latitude, span a distance of 2000 kilometers, and like the Lake Agassiz sites, have a ground-water velocity of less than a few millimeters per year. The value of -25 per mil is characteristic of meltwater impounded in the southern basin of Lake Agassiz. This value corresponds to an estimated air temperature of -16 degrees C, compared with the modern temperature of 0 degrees C for this area. 相似文献
15.
太湖银鱼产量变化和主要鱼类间关系的最优回归模型分析 总被引：1，自引：1，他引：0
根据太湖1973～2002年的鱼类分类产量统计资料,应用逐步回归分析方法,研究了太湖主要鱼类产量变化对银鱼的影响。结果表明:太湖银鱼和主要鱼类产量间的最优化回归模型为W=225.084 3+1.486 0 W3+0.087 7 W7(W为银鱼产量,W3为鲌鱼产量,W7为其他鱼类产量,n=30,R=0.868 0,P<0.000 1)。通径分析结果表明:鲌鱼对银鱼产量变化影响最大,其次是“其他鱼类,”其通径系数分别为:Py.3=0.890 8,P<0.000 1,Py.7=0.388 7,P=0.000 6。而鲚鱼、鲤鲫鱼、鲢鳙鱼、青草鱼产量变化对银鱼的影响不显著。 相似文献
16.
Spahni R Chappellaz J Stocker TF Loulergue L Hausammann G Kawamura K Flückiger J Schwander J Raynaud D Masson-Delmotte V Jouzel J 《Science (New York, N.Y.)》2005,310(5752):1317-1321
The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH4) and nitrous oxide (N2O) back to 650,000 years before the present. A combined record of CH4 measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 +/- 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH4 concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N2O record shows maximum concentrations of 278 +/- 7 ppbv, slightly higher than early Holocene values. 相似文献
17.
Distribution of hydrogen in the near surface of Mars: evidence for subsurface ice deposits 总被引：1，自引：0，他引：1
Boynton WV Feldman WC Squyres SW Prettyman TH Bruckner J Evans LG Reedy RC Starr R Arnold JR Drake DM Englert PA Metzger AE Mitrofanov I Trombka JI D'Uston C Wanke H Gasnault O Hamara DK Janes DM Marcialis RL Maurice S Mikheeva I Taylor GJ Tokar R Shinohara C 《Science (New York, N.Y.)》2002,297(5578):81-85
Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight. 相似文献
18.
Suppression of rain and snow by urban and industrial air pollution 总被引：14，自引：0，他引：14
Rosenfeld D 《Science (New York, N.Y.)》2000,287(5459):1793-1796
Direct evidence demonstrates that urban and industrial air pollution can completely shut off precipitation from clouds that have temperatures at their tops of about -10 degrees C over large areas. Satellite data reveal plumes of reduced cloud particle size and suppressed precipitation originating from major urban areas and from industrial facilities such as power plants. Measurements obtained by the Tropical Rainfall Measuring Mission satellite reveal that both cloud droplet coalescence and ice precipitation formation are inhibited in polluted clouds. 相似文献
19.
Thompson LG Mosley-Thompson E Davis ME Lin PN Henderson KA Cole-Dai J Bolzan JF Liu KB 《Science (New York, N.Y.)》1995,269(5220):46-50
Two ice cores from the col of Huascarán in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Würm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8 degrees to 12 degrees C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio zeta(18)O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5 degrees to 6 degrees C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries. 相似文献
20.
Emiliani C 《Science (New York, N.Y.)》1970,168(3933):822-825
The generalized isotopic paleotemperature curve reproduces absolute temperatures to within 1 degrees C; it closely reflects faunal changes; and its time scale is correct to within a very few percent back to at least 175,000 years. The average oxygen isotopic composition of the North American and European ice caps was about -9 per mil. 相似文献