共查询到20条相似文献，搜索用时 31 毫秒
1.
Williams TM Davis RW Fuiman LA Francis J Le Boeuf BJ Horning M Calambokidis J Croll DA 《Science (New York, N.Y.)》2000,288(5463):133-136
Locomotor activity by diving marine mammals is accomplished while breath-holding and often exceeds predicted aerobic capacities. Video sequences of freely diving seals and whales wearing submersible cameras reveal a behavioral strategy that improves energetic efficiency in these animals. Prolonged gliding (greater than 78% descent duration) occurred during dives exceeding 80 meters in depth. Gliding was attributed to buoyancy changes with lung compression at depth. By modifying locomotor patterns to take advantage of these physical changes, Weddell seals realized a 9.2 to 59.6% reduction in diving energetic costs. This energy-conserving strategy allows marine mammals to increase aerobic dive duration and achieve remarkable depths despite limited oxygen availability when submerged. 相似文献
2.
G L Kooyman 《Science (New York, N.Y.)》1966,151(717):1553-1554
The probable maximum diving capacities of the Weddell seal were ascertained from observation of 959 dives and measurement of the depths of 381 dives. The deepest dive was 600 meters; the longest submergence was 43 minutes 20 seconds. 相似文献
3.
Respiration and deep diving in the bottlenose porpoise 总被引：3，自引：0，他引：3
A bottlenose porpoise was trained to dive untethered in the open ocean and to exhale into an underwater collecting funnel before surfacing from prescribed depths down to 300 meters. The animal was also taught to hold its breath for periods up to 4 minutes at the surface and then blow in the funnel. Alveolar collapse is probably complete at around 100 meters, and little pulmonary respiratory exchange occurs below that depth. Thoracic collapse was observ visually at 10 to 50 meters and by underwater television to 300 meters. 相似文献
4.
Roemmich D 《Science (New York, N.Y.)》1992,257(5068):373-375
Hydrographic time-series data recorded during the past 42 years in the upper 500 meters off the coast of southern California indicate that temperatures have increased by 0.8 degrees C uniformly in the upper 100 meters and that temperatures have risen significantly to depths of about 300 meters. The effect of warming the surface layer of the ocean and there by expanding the water column has been to raise sea level by 0.9 +/- 0.2 millimeter per year. Tide gauge records along the coast are coherent with steric height and show upward trends in sea level that vary from about 1 to 3 millimeters per year. 相似文献
5.
RW Davis LA Fuiman TM Williams SO Collier WP Hagey SB Kanatous S Kohin M Horning 《Science (New York, N.Y.)》1999,283(5404):993-996
The hunting behavior of a marine mammal was studied beneath the Antarctic fast ice with an animal-borne video system and data recorder. Weddell seals stalked large Antarctic cod and the smaller subice fish Pagothenia borchgrevinki, often with the under-ice surface for backlighting, which implies that vision is important for hunting. They approached to within centimeters of cod without startling the fish. Seals flushed P. borchgrevinki by blowing air into subice crevices or pursued them into the platelet ice. These observations highlight the broad range of insights that are possible with simultaneous recordings of video, audio, three-dimensional dive paths, and locomotor effort. 相似文献
6.
During certain treatments of decompression sickness following dives made with compressed air, the U.S. Navy advocates breathing helium-oxygen mixtures. However, stable nitrogen bubbles created within gelatin by decompression have been found to enlarge when the atmosphere was switched from nitrogen to helium without changing ambient pressure. This suggests that decompression sickness would be worsened by switching from nitrogen to helium in the breathing gas mixture. 相似文献
7.
Despite a reduction in liver and body weights of neonatal rats born and reared at a simulated altitude of 5790 meters (oxygen pressure, 76.36 millimeters of mercury), the hepatic enzyme tryptophan oxygenase develops prematurely in these stressed animals as compared to controls reared at sea level. Also, the specific activities remain distinctly elevated through the first 9 days of age; thus, the competence for premature synthesis ot tryptophan oxygenase is confirmed in neonatal rats. 相似文献
8.
Measurements of reactive mercury in ocean water in the Gulf Stream at depths from 250 to 4460 meters revealed lower and more consistent concentrations than have been reported in the western Atlantic. The mean and standard deviation of 24 values in a vertical profile were 4.1 +/- 1.0 nanograms per liter. A correlation was found between variations in mercury and silicate, suggesting a common link in their marine geochemistry. 相似文献
9.
Extracellular hemoglobin in the whole blood of Riftia pachyptila has a high oxygen affinity (P50 = 1.8 millimeters of mercury at 3 degrees C), a moderate decrease in oxygen affinity at higher temperatures (P50 = 2.7 millimeters of mercury at 14 degrees C), a small effect of carbon dioxide on oxygen affinity (Delta log P50/Delta pH =-0.12), and a high oxygen carrying capacity (up to 11 milliliters of oxygen per 100 milliliters of blood). These characteristics are compatible with the high oxygen demand of chemoautotrophic metabolism in the variable vent environment. 相似文献
10.
Shoemaker EM Batson RM Holt HE Morris EC Rennilson JJ Whitaker EA 《Science (New York, N.Y.)》1967,158(3801):642-652
Surveyor V landed in a small crater, 8.5 meters wide and 12.5 meters long, which was probably formed by drainage of surficial fragmental debris into a subsurface fissure. The lunar surface debris layer is exposed in the walls of this crater. At depths below about 10 centimeters, the debris appears to be composed mainly of shock-compressed aggregates, ranging from a few millimeters up to 3 centimeters in diameter, set in a matrix of less-coherent finer particles. Rocky chips and fragments larger than a millimeter are dispersed as a subordinate constituent of the debris. 相似文献
11.
Smith KD von Seggern D Blewitt G Preston L Anderson JG Wernicke BP Davis JL 《Science (New York, N.Y.)》2004,305(5688):1277-1280
A deep earthquake swarm in late 2003 at Lake Tahoe, California (Richter magnitude < 2.2; depth of 29 to 33 kilometers), was coeval with a transient displacement of 6 millimeters horizontally outward from the swarm and 8 millimeters upward measured at global positioning system station Slide Mountain (SLID) 18 kilometers to the northeast. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters per second up-dip along a 40-square-kilometer structure striking north 30 degrees west and dipping 50 degrees to the northeast. SLID's transient velocity of 20 millimeters per year implies a lower bound of 200 nanostrains per year (parts per billion per year) on local strain rates, an order of magnitude greater than the 1996 to 2003 regional rate. The geodetic displacement is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe. 相似文献
12.
Chemotransduction in the carotid body: K+ current modulated by PO2 in type I chemoreceptor cells 总被引：20，自引：0，他引：20
The ionic currents of carotid body type I cells and their possible involvement in the detection of oxygen tension (Po2) in arterial blood are unknown. The electrical properties of these cells were studied with the whole-cell patch clamp technique, and the hypothesis that ionic conductances can be altered by changes in PO2 was tested. The results show that type I cells have voltage-dependent sodium, calcium, and potassium channels. Sodium and calcium currents were unaffected by a decrease in PO2 from 150 to 10 millimeters of mercury, whereas, with the same experimental protocol, potassium currents were reversibly reduced by 25 to 50 percent. The effect of hypoxia was independent of internal adenosine triphosphate and calcium. Thus, ionic conductances, and particularly the O2-sensitive potassium current, play a key role in the transduction mechanism of arterial chemoreceptors. 相似文献
13.
Honjo S 《Science (New York, N.Y.)》1982,218(4575):883-884
Time-series sediment traps were deployed for an entire year at three depths (890, 2590, and 3560 meters) at a deepwater station (3860 meters) in the Panama Basin. The amount of horizontal and lithogenic particulate material arriving at the three depths was seasonally pulsed and directly reflected changes in surface primary production. Two spikes of organic flux were simultaneously recorded at all three depths: (i) a period of high productivity during regional upwelling in February through March and (ii) an unusual bloom of a single species of coccolithophorid during June through July. This latter spike delivered approximately 25 grams of coccolith per square meter of area at a depth of 3860 meters during less than 60 days. The flux of lithogenic particles increased with increasing depth and was seasonally correlated to surface production and current direction, and not to the detritus discharged in river flow. The data suggest that suspended clays are efficiently scavenged from the water column by rapidly sinking organic aggregates. 相似文献
14.
Berger WH 《Science (New York, N.Y.)》1968,159(3820):1237-1239
Radiolarian skeletons were placed at several depths on the taut mooring wire of a buoy in the central Pacific for 4 months. Recent radiolarian sediment dissolved at appreciable rates at depths shallower than 2000 meters; solution was greatest near the surface and decreased with depth. This pattern correlates with bathymetric distributions of dissolved silicon and of temperature. Siliceous Radiolaria from planktonic samples appeared to dissolve about eight times faster than those from sediment. Tripyleans seemed to be less resistant than polycystins. Acantharia dissolved completely at all depths. 相似文献
15.
Bronchograms and tracheograms of seals under pressure 总被引：4，自引：0，他引：4
Radiograms of the upper portion of the respiratory system were obtained at pressures up to 31.6 atmospheres absolute in the Weddell seal, Leptonychotes weddelli, and the northern elephant seal, Mirounga angustirostris. The trachea was considerably compressed but not fully collapsed at the highest pressures. No measurable change in the size of the bronchioles and smaller bronchi was observed. Measurements of total lung volume obtained simultaneously showed that the seals consistently dived with a small volume. 相似文献
16.
Berger WH 《Science (New York, N.Y.)》1967,156(3773):383-385
Samples of foraminiferal ooze were exposed to ocean water at various depths for 4 months, attached to the taut wire of a buoy in the central Pacific. Appreciable solution took place below 1000 meters and increased rapidly below 3000 meters and below 5000 meters. The fact that samples from different locations appear to dissolve at different rates suggests that the previous history of a sample determines its solubility. Solution is selective; it changes species composition, size distribution, content of damaged shells, and average particle weight of an assemblage. 相似文献
17.
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
18.
High activity of alpha-glycerophosphate dehydrogenase and low activity of glucose-6-phosphate dehydrogenase in adipose tissue of Weddell seals suggest that neutral fat may be assembled there from exogenous sources of fatty acids. Low activity of glucose-6-phosphate dehydrogenase in other tissues tested precludes assignment of the function of fatty-acid synthesis to any specific tissue and emphasizes uniqueness of adipose mass in seals. 相似文献
19.
某体温计厂附近土壤汞含量及影响因素研究 总被引：1，自引：0，他引：1
采集体温计厂周围300m内17个点的土壤作为样品,分析其全汞含量,并研究汞含量的影响因素。结果表明：距汞车间300m范围内土壤汞含量均超过背景值,土壤均表现出不同程度的汞污染。在体温计厂Hg车间排气口和排水口外的土壤属于极严重污染（Hg含量为8．65～19．77m昏／kg）,在100m范围内为重污染区（Hg含量为1．48～2．75mg／kg）,在100～300m范围内为中等污染区（Hg含量为0．15～0．95mg／kg）。分别为背景值的169、24、8倍。随着采样点到汞车间排气口距离的增加,土壤中汞的含量随之减少。土壤汞含量主要受当地主风向的影响。另外,在排气口和排水口附近往往汞含量极高。有机质含量对土壤中汞的含量有一定影响。 相似文献
20.
Miller SL 《Science (New York, N.Y.)》1969,165(3892):489-490
Measurements of the dissociation pressure of nitrogen hydrate and oxygen hydrate show that the clathrate hydrate of air with the formula (N(2), O(2)) 6H(2)O should exist below about 800 meters in the Antarctic ice sheet. This accounts for the disappearance of gas bubbles at depths greater than 1200 meters. The hydrate should exist from this depth to prise 0.06 percent of the ice. 相似文献