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1.
An empirical model of carbon flux and (14)C-derived ages of the water in the Canada Basin of the Arctic Ocean as a function of depth was used to estimate the long-term rate of primary production within this region. An estimate can be made because the deep waters of the Canadian Basin are isolated from the world oceans by the Lomonosov Ridge (sill depth about 1500 meters). Below the sill, the age of the water correlates with increased nutrients and oxygen utilization and thus provides a way to model the average flux of organic material into the deep basin over a long time period. The (14)C ages of the deep water in the Canada Basin were about 1000 years, the carbon flux across the 1500-meter isobath was 0.3 gram of carbon per square meter per year, and the total production was 9 to 14 grams of carbon per square meter per year. Such estimates provide a baseline for understanding the role of the Arctic Ocean in global carbon cycling. 相似文献
2.
Shallow, seaward portions of modern coral reefs produce about 4 kilograms of calcium carbonate per square meter per year, and protected areas produce about 0.8 kilogram per square meter per year. The difference is probably largely a function of water motion. The more rapid rate, equivalent to a maximum vertical accretion of 3 to 5 millimeters per year, places an upper limit on the potential of modern coral reef communities to create a significant vertical structure on a rising sea. 相似文献
3.
杂交棉种植密度与留叶枝对产量及其构成因素的互作效应研究 总被引：7，自引：3，他引：4
以杂交棉鲁棉研25号为试验材料,采用裂区设计,于2008年在山东临清、嘉祥和金乡三地大田条件下研究了种植密度与留叶枝对产量及其构成因素等的互作效应。结果表明：密度和整枝对杂交棉产量、产量构成以及熟相有显著的互作效应。去叶枝情况下,低密度（3.00株/m2）和高密度（7.50株/m2）处理的产量低,中高密度（4.50-6.00株/m2）的产量较高;留叶枝条件下,低密度（3.00株/m2）产量最高,中高密度（4.50-6.00株/m2）的产量居中,而高密度（7.50株/m2）处理的产量还是最低;整枝条件下4.50株/m2密度处理的籽棉和皮棉产量比3.00株/m2分别增产4.93%和5.51%,而留叶枝条件下3.00株/m2的籽棉产量比4.50株/m2高4.03%。低密度（3.00株/m2）下留叶枝的铃数多于去叶枝的铃数,但随密度增加（4.50株/m2及以上）,留叶枝的铃数显著少于去叶枝的铃数;留叶枝和增加密度都会降低铃重。密度与整枝对棉柴比没有显著的互作效应,但都可显著影响生物产量。密度与整枝对棉花早熟性也有互作效应,去叶枝的早熟性好于留叶枝的处理,随密度增加,早熟性降低。 相似文献
4.
Lowell TV Heusser CJ Andersen BG Moreno PI Hauser A Heusser LE Schlüchter C Marchant DR Denton GH 《Science (New York, N.Y.)》1995,269(5230):1541-1549
A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and >/=33,500 carbon-14 years before present ((14)C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000(14)C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720(14)C yr B.P., and at the beginning of the Younger Dryas at 11,050 (14)C yr B. P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges. 相似文献
5.
Measurements of radon-222 in seawater suggest the following. The radium-226 content of surface water in both the Atlantic and Pacific oceans is uniformly close to about 4 x 10(-14) gram per liter. The deep Pacific has a concentration of radium-226 that is four times higher and the deep Atlantic a concentration twice as high as that of the surface. These distribution profiles can be explained by the same particle-settling rate for radium-226 from surface to depth for the two oceans and by a threefold longer residence time of water in the deep Pacific than in the deep Atlantic. The vertical distribution of the deficiency of radon-222 in the surface water of the northwest Pacific Ocean suggests a coefficient of vertical eddy diffusion as high as 120 square centimeters per second and a gas-exchange rate for carbon dioxide in surface water between 14 and 60 moles per square meter per year. Vertical profiles of the excess of radon-222 in near-bottom water of the South Atlantic give coefficients of vertical eddy diffusion ranging from 1.5 to more than 50 square centimeters per second. 相似文献
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7.
三倍体毛白杨地上凋落物对林龄的响应 总被引：1，自引：0，他引：1
2008年3月至2009年3月,对不同林龄(3a、5a、6a、7a)的三倍体毛白杨纸浆林地上凋落物动态变化进行分析研究。结果表明,不同林龄林分的凋落物量随林龄的增加而增加,全年凋落物总量为(216.03±59.73)～(482.38±101.34)g·m-2·a-1;凋落物的月动态变化表现为单峰曲线,最大凋落量出现在10月份;通过凋落物归还林地的N、P量及能量均随林龄的增加而增加,表现出与凋落物量相同的月动态规律。由凋落物归还的N为1.84～2.89g·m-2·a-1,归还的P为0.58～1.17g·m-2·a-1,归还到林地的能量为3.96×106～8.89×106J·m-2·a-1。 相似文献
8.
棉田不同杂草群落对棉花生长和产量的影响 总被引：1，自引：0，他引：1
于2011～2012年在山东省茌平县棉田中人为设置无草区和禾本科杂草、莎草科杂草、阔叶类杂草、混合杂草自然发生区,研究了不同杂草群落对棉花生长和产量的影响。结果表明,禾本科杂草区以牛筋草[Eleusine indica(L.)Gaertn.]为主,总密度为338.75～505.13茎/m2,棉花产量损失为69.7%～69.8%;莎草科杂草区以异型莎草(Cyperus difformis L.)为主,杂草密度为260.75茎/m2,产量损失为57.7%～59.4%;阔叶类杂草区以藜(Chenopodium album L.)、醴肠[Eclipta prostrata(L.)L.]为主,杂草总密度为208.25～316.0茎/m2,产量损失为87.5%～88.9%;混合杂草区杂草群落2011年主要以藜、醴肠、牛筋草等为主,2012年以牛筋草、异型莎草为主,总密度为366.00～410.0茎/m2,产量损失达90.5%～90.7%。以杂草单茎危害率衡量不同类型杂草对棉花产量损失的影响依次为阔叶类杂草>莎草科杂草=禾本科杂草。杂草危害直接影响棉花生长,对棉花产量构成因素均有影响,其中对棉花成铃数影响最大,杂草生长区比无草区成铃数减少45.2%～87.3%,果枝数减少21%～64%,单铃重减少6.7%～24.5%。此外,杂草的生长也直接威胁到棉花植株的保苗效果。 相似文献
9.
Production in the western Bering Strait is estimated at 324 grams of carbon per square meter per year over 2.12x 10(4) square kilometers. An ice-reduced growing season makes this large amount of primary production unexpected, but it is consistent with the area's large upper trophic level stocks. The productivity is fueled by a cross-shelf flow of nutrient-rich water from the Bering Sea continental slope. This phytoplankton production system from June through September is analogous to a laboratory continuous culture. 相似文献
10.
T J Chow K W Bruland K Bertine A Soutar M Koide E D Goldberg 《Science (New York, N.Y.)》1973,181(99):551-552
The present anthropogenic lead fluxes into sediments from the Santa Monica, San Pedro, and Santa Barbara basins of Southern California are, respectively, 0.9, 1.7, and 2.1 micrograms of lead per square centimeter of sea bottom per year; the natural (prepollution) rates for these three basins were, respectively, 0.24, 0.26, and 1.0 microgram of lead per square centimeter per year. Studies of isotopic composition indicate that lead pollutants in coastal sediments are derived mainly from the combustion of lead additives in gasoline. 相似文献
11.
Atmospheric dimethyl sulfide (DMS) measurements were made on the Atlantic Coast of the United States at Wallops Island and Cape Henry, Virginia, during June 1975. The very low concentrations, typically less than 30 parts per trillion observed at the Cape Henry site, were thought to result from the smog chemistry associated with the Norfolk metropolitan area. Atmospheric DMS concentrations at the Wallops Island site were much higher, having a geometric mean of 58 parts per trillion and a geometric standard deviation of 2.1. At this site the DMS source strength was estimated to be 6 milligrams of sulfur per square meter per year. Because of wind conditions during this experiment, the DMS source strength is thought to be representative of the DMS source strength of the ocean in the Wallops Island area and is much less than the 130 milligrams of sulfur per square meter per year needed to balance the ocean-atmosphere portion of the global sulfur budget. 相似文献
12.
Measurements in the interstitial waters of pelagic red clay and carbonate ooze sediments in the central equatorial Pacific show that the dissolved oxygen content decreases with depth and levels off at nonzero values. The supply of reactive organic carbon introduced by bioturbation limits oxygen consumption at depth in the sediment. These gradients should produce diffusive fluxes across the sediment-water interface that average about 8.8 x 10(-14) mole per square centimeter per second or 0.08 milliliter per square meter per hour. 相似文献
13.
The impact of boreal forest fire on climate warming 总被引：1，自引：0，他引：1
Randerson JT Liu H Flanner MG Chambers SD Jin Y Hess PG Pfister G Mack MC Treseder KK Welp LR Chapin FS Harden JW Goulden ML Lyons E Neff JC Schuur EA Zender CS 《Science (New York, N.Y.)》2006,314(5802):1130-1132
We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 +/- 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 +/- 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming. 相似文献
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15.
Sturges WT Wallington TJ Hurley MD Shine KP Sihra K Engel A Oram DE Penkett SA Mulvaney R Brenninkmeijer CA 《Science (New York, N.Y.)》2000,289(5479):611-613
We detected a compound previously unreported in the atmosphere, trifluoromethyl sulfur pentafluoride (SF(5)CF(3)). Measurements of its infrared absorption cross section show SF(5)CF(3) to have a radiative forcing of 0.57 watt per square meter per parts per billion. This is the largest radiative forcing, on a per molecule basis, of any gas found in the atmosphere to date. Antarctic firn measurements show it to have grown from near zero in the late 1960s to about 0.12 part per trillion in 1999. It is presently growing by about 0.008 part per trillion per year, or 6% per year. Stratospheric profiles of SF(5)CF(3) suggest that it is long-lived in the atmosphere (on the order of 1000 years). 相似文献
16.
In 1979 two areas of upwelling were observed off Somalia, one near 10 degrees N and one near 5 degrees N. The areas of upwelling were characterized by sea surface temperatures between 17 degrees and 22 degrees C, high concentrations of surface nutrients (5 to 20 micromoles of nitrate per liter) and surface chlorophyll a (0.4 to 5.0 milligrams per cubic meter), primary productivity averaging 1.7 grams of carbon per square meter per day, and a phytoplankton assemblage dominated numerically by the diatom Nitzschia delicatissima. 相似文献
17.
稻田双穗雀稗生物学特性、发生危害及防控 总被引：1，自引：0，他引：1
2010年对鄱阳湖区东北部、中部、西南部三地的中晚稻田抽样调查表明,该区稻田双穗雀稗的发生频率为70.69%～86.21%,发生密度为0.12～0.29株/m2。对机插晚稻田间双穗雀稗的危害损失测定表明,水稻产量损失与双穗雀稗密度、植株鲜重有显著的正相关性,在产量损失构成因素中以有效穗数、穗实粒数影响占主导;每1.26 m2内有双穗雀稗1、2、3、5株,产量损失率分别达到17.24%、27.33%、49.13%、57.78%,每株双穗雀稗可使水稻减产11.0%～17.0%。提出了耕前灭生除草、农艺措施控草、苗期使用选择性除草剂的综合防控技术。 相似文献
18.
对新优６３等９个籼型杂交稻组合的产量性状分析和１９９１～１９９４年江西省及南方区试资料比较，结果表明：新优６３的单位面积有效穗与生产上一些应用组合无显著差异，单位面积实粒数显著少于部分应用组合，其增产的主要原因是千粒重极显著地高于其他供试组合。进而对新优６３的有效穗、每穗总粒数、每穗实粒数、结实率、千粒重等５个经济性状与产量间进行相关和通径分析，进一步表明：该组合千粒重大是其特殊的增产原因。本文指出：通过重粒型组合的选育可能是突破目前三系籼型杂交晚稻组合产量徘徊的一条有效途径 相似文献
19.
Solomon S Daniel JS Neely RR Vernier JP Dutton EG Thomason LW 《Science (New York, N.Y.)》2011,333(6044):866-870
Recent measurements demonstrate that the "background" stratospheric aerosol layer is persistently variable rather than constant, even in the absence of major volcanic eruptions. Several independent data sets show that stratospheric aerosols have increased in abundance since 2000. Near-global satellite aerosol data imply a negative radiative forcing due to stratospheric aerosol changes over this period of about -0.1 watt per square meter, reducing the recent global warming that would otherwise have occurred. Observations from earlier periods are limited but suggest an additional negative radiative forcing of about -0.1 watt per square meter from 1960 to 1990. Climate model projections neglecting these changes would continue to overestimate the radiative forcing and global warming in coming decades if these aerosols remain present at current values or increase. 相似文献
20.
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