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1.
A simple hydrologic model of seawater circulation at ocean ridge axes implies that the transient occurrence of large volumes of buoyant, heated water in the oceanic water column (megaplumes) can be attributed to the emplacement of dikes in oceanic crust. For dikes to generate megaplume flow, the permeability of both the recharge areas and the upflow zone must be greater than that required for ordinary black smokers. An increase in permeability in the upflow zone by several orders of magnitude results from dike emplacement, and megaplume discharge ceases as the dike cools. Vigorous black smoker venting may not persist very long at a megaplume site after the event occurs. 相似文献
2.
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
3.
Oceanic primary production: estimation by remote sensing at local and regional scales 总被引：2，自引：0，他引：2
Satellites provide the only avenue by which marine primary production can be studied at ocean-basin scales. With maps of chlorophyll distribution derived from remotely sensed data on ocean color as input, deduction of a suitable algorithm for primary production is a problem in applied plant physiology. An algorithm is proposed that combines a spectral and angular model of submarine light with a model of the spectral response of algal photosynthesis. To apply the algorithm at large horizontal scale, a dynamic biogeography is needed for the physiological rate parameters and the biological structure of the water column. Fieldwork to obtain this type of data should be undertaken so that the use of satellite data in modern biological oceanography may be optimized. 相似文献
4.
Azam F Beers JR Campbell L Carlucci AF Holm-Hansen O Reid FM Karl DM 《Science (New York, N.Y.)》1979,203(4379):451-453
Seawater samples below the Ross Ice Shelf were collected through an access hole at J9, approximately 400 kilometers from the Ross Sea, Antarctica. The 237-meter water column had sparse populations of bacteria (8.7 x 10(6) to 1.2 x 10(7) per liter), microplankters (10(2) to 10(3) per cubic meter), and zooplankters (10 to 20 per cubic meter) at the depths studied. Microbial biomass estimates from cellular adenosine 5'-triphosphate measurements were very low (10 to 150 nanograms of carbon per liter), comparable with values for the abyssal ocean. Microbial populations assimilated tritiated D-glucose, thymidine, uridine, and adenosine triphosphate at extremely low rates, comparable with deep-sea heterotrophic populations. Sediment samples had 10(7) to 10(8) bacteria per gram (dry weight), which were metabolically active as shown by respiration of uniformly labeled D-[(14)C]glucose. From this study it cannot be determined whether these organisms in the water column and sediments constitute a functioning food web. 相似文献
5.
Environmental correlates of food chain length 总被引：8，自引：0，他引：8
In 113 community food webs from natural communities, the average and maximal lengths of food chains are independent of primary productivity, contrary to the hypothesis that longer food chains should arise when more energy is available at their base. Environmental variability alone also does not appear to constrain average or maximal chain length. Environments that are three dimensional or solid, however, such as a forest canopy or the water column of the open ocean, have distinctly longer food chains than environments that are two dimensional or flat, such as a grassland or lake bottom. 相似文献
6.
An unresolved issue in ocean science is the discrepancy between the food requirements of the animals living on the deep sea floor and their food supply, as measured by sediment traps. A 10-year time-series study of the water column off Monterey Bay, California, revealed that the discarded mucus feeding structures of giant larvaceans carry a substantial portion of the upper ocean's productivity to the deep seabed. These abundant, rapidly sinking, carbon-rich vectors are not detected by conventional sampling methods and thus have not been included in calculations of vertical nutrient flux or in oceanic carbon budgets. 相似文献
7.
Surface waters of the subtropical Sargasso Sea contain dissolved inorganic phosphate (DIP) concentrations of 0.2 to 1.0 nanomolar, which are sufficiently low to result in phosphorus control of primary production. The DIP concentrations in this area (which receives high inputs of iron-rich dust from arid regions of North Africa) are one to two orders of magnitude lower than surface levels in the North Pacific (where eolian iron inputs are much lower and water column denitrification is much more substantial). These data indicate a severe relative phosphorus depletion in the Atlantic. We hypothesize that nitrogen versus phosphorus limitation of primary production in the present-day ocean may be closely linked to iron supply through control of dinitrogen (N2) fixation, an iron-intensive metabolic process. Although the oceanic phosphorus inventory may set the upper limit for the total amount of organic matter produced in the ocean over geological time scales, at any instant in geological time, oceanic primary production may fall below this limit because of a persistent insufficient iron supply. By controlling N2 fixation, iron may control not only nitrogen versus phosphorus limitation but also carbon fixation and export stoichiometry and hence biological sequestration of atmospheric carbon dioxide. 相似文献
8.
Robinson LF Adkins JF Keigwin LD Southon J Fernandez DP Wang SL Scheirer DS 《Science (New York, N.Y.)》2005,310(5753):1469-1473
We present a detailed history of glacial to Holocene radiocarbon in the deep western North Atlantic from deep-sea corals and paired benthic-planktonic foraminifera. The deglaciation is marked by switches between radiocarbon-enriched and -depleted waters, leading to large radiocarbon gradients in the water column. These changes played an important role in modulating atmospheric radiocarbon. The deep-ocean record supports the notion of a bipolar seesaw with increased Northern-source deep-water formation linked to Northern Hemisphere warming and the reverse. In contrast, the more frequent radiocarbon variations in the intermediate/deep ocean are associated with roughly synchronous changes at the poles. 相似文献
9.
Acoustic waves transmitted over a 100-kilometer path in the Fram Strait marginal ice zone undergo Doppler shifts and fluctuations around these shifts, the former due to quasi-steady motion of both acoustic source and receiver and the latter to unsteady motions of the water column and ice cover. Internal waves and differential Doppler shift usually account for such fluctuations in the deep temperate ocean but only partially explain the results obtained in the marginal ice zone. There the fluctuations are more energetic and may be caused alternatively or additionally by comparably energetic fluctuations in ice-edge eddies or other mesoscale motions. 相似文献
10.
南极普里兹湾关键物理海洋学问题研究进展及未来趋势 总被引：5，自引：2，他引：3
南极普里兹湾及其邻近海域关键物理海洋学问题包括水团特性、环流特征和冰架 海洋 海冰相互作用过程等。该海域水团可以分为南极表层水、绕极深层水、南极底层水、南极陆架水和南极冰架水等,受外部条件影响,这些水团时空变化显著。普里兹湾区域的环流以普里兹湾流涡,西向的沿岸流和东向的绕极流,以及两者之间的南极辐散带的环流为主要特征,地形是环流特征的关键影响因素。埃默里冰架 海洋的相互作用过程显著影响普里兹湾海域的水团特性和环流状况。冰泵机制,是埃默里冰架外海水进入冰穴,并引起冰架底部消融和冻结的重要原因。冰架 海洋 海冰相互作用形成的低温高盐水,是普里兹湾形成南极底层水的潜在因素之一。加强现场观测,并建立高分辨率的冰架 海洋 海冰耦合模型系统是研究普里兹湾海域物理海洋学关键过程和变化机制的重要手段,是南极研究的发展趋势。 相似文献
11.
Beal RC 《Science (New York, N.Y.)》1980,208(4450):1373-1375
A well-organized, very low energy ocean swell system off the East Coast of the United States was tracked with the Seasat synthetic aperture radar from deep water, across the continental shelf, and into shallow, water. The results indicate that spaceborne imaging radar may be used to accurately measure ocean wavelength and direction, even in coastal areas and in the presence of a mixed ocean. 相似文献
12.
A major ecosystem shift in the northern Bering Sea 总被引：5，自引：0，他引：5
Grebmeier JM Overland JE Moore SE Farley EV Carmack EC Cooper LW Frey KE Helle JH McLaughlin FA McNutt SL 《Science (New York, N.Y.)》2006,311(5766):1461-1464
Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean. 相似文献
13.
A new method measures the oxygen-isotopic composition of dissolved sulfate ions and barium sulfate. Sulfate ions in the oceans are enriched in oxygen-18 by 9.5 per mille relative to mean ocean water and show only minor variations, probably because the exchange rate with water is slow enough to prevent local equilibrium with surface waters. Sulfate ions in saline lakes and brines have oxygen-18 enrichment of from 7 to 23 per mille relative to mean ocean water;the value of the highest enrichment observed is about the same as that of atmospheric oxygen. 相似文献
14.
Highly turbid bottom water at the margin of the Sohm Abyssal Plain was identified by its temperature, salinity, and oxygen content as originating upslope on the continental rise. The fact that the particulate concentrations were one to two orders of magnitude higher than are normally found in deep ocean waters suggests a turbidity current as the agent bringing this water downslope. 相似文献
15.
The carbon isotopic composition ((13)C/(12)C, expressed as δ(13)C) of fossil foraminifera is the primary tracer used to infer changes in past ocean ventilation, and its variations are interpreted by using the modern oceanic δ(13)C distribution as a framework. However, the present ocean δ(13)C distribution is strongly overprinted by isotopically light anthropogenic carbon dioxide. A correction for this oceanic C-13 Suess effect in the North Atlantic (NA) shows that the pristine NA δ(13)C distribution has a richer and more detailed structure that is more clearly related to water mass distributions. Our results revise some fundamental perceptions regarding glacial-interglacial ocean δ(13)C differences and allow paleo-δ(13)C variations to be understood within the context of modern climate variability. 相似文献
16.
建立了海洋立管的挠曲线微分方程，对两端固定约束的情况用无穷级数法求得其临界屈曲载荷计算式，并同时用能量法给出了其近似计算式。讨论了内外液压对管道纵向稳定性的影响，对平躺管道，外部液压的作用增加了管道的稳定性，内部液压的作用减小了其稳定性。计算结果可供管道设计时参考。 相似文献
17.
As continental ice from Antarctica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed. The melting rate is positively correlated with thermal forcing, increasing by 1 meter per year for each 0.1 degrees C rise in ocean temperature. Where deep water has direct access to grounding lines, glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature. 相似文献
18.
The mean oxygen-18 content of continental ice sheets during the last glacial maximum is estimated to deltaO(18)=-30 per mille or less, and the consequent change in the isotopic composition of the oceans at that time to 1.2 per mille or more. This means that at least 70 percent of the oxygen-18 variations found in shells of planktonic foraminifera from deep-sea cores between times of glacial maximums and minimums are due to isotopic changes in ocean water, and at most 30 percent to changes in ocean surface temperature. Hence, Emiliani's "paleotemperature" curve rather depicts the amount of ice on the continents in excess of that present today. In this sense it may be renamed a "paleoglaciation" curve. 相似文献
19.
Stoffyn M 《Science (New York, N.Y.)》1979,203(4381):651-653
Experimental evidence supports the hypothesis that the concentration and distribution of dissolved aluminum in ocean water are controlled by biological activity in the surface waters. The growth of the diatom Skeletonema costatum in artificial seawater media spiked with aluminum reduced the aluminum concentration to that actually found in surface open ocean waters (about 0.5 micrograms per liter). Furthermore, aluminum had a catalytic and limiting effect on the growth of the diatoms. 相似文献
20.
采用NCEP/NCAR再分析资料,计算了夏季哈德莱环流(H.C.)强度,分析了夏季H.C.强度年际、年代际变化特征,以及亚洲季风区夏季水汽输送的气候特征,并研究了夏季哈德莱环流强度与亚洲季风区水汽输送的关系。结果表明,1979~2010年夏季南半球H.C.强度有明显增强趋势,同时也有明显的年际变化。索马里东部洋面和印尼东部洋面是南半球水汽北转输入亚洲的重要区域;夏季南半球哈德莱环流强度与索马里东部洋面和印尼东部洋面的经向水汽输送呈显著的正相关关系,与在我国中东部—南海南部、阿拉伯海东南部的经向水汽输送呈显著的负相关关系。 相似文献