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1.
The tritium and carbon-14 activities of seawater samples collected from 22 to 200 meters below the ice at the Ross Ice Shelf Project ice hole are reported. The tritium results show that the waters below the ice have exchanged with Ross Sea water since the advent of nuclear testing. The carbon-14 results indicate that waters in the upper layer exchange in time periods of less than 6 years. Measurements of these isotopes in seawater under the Ross Ice Shelf in McMurdo Sound show that this water has a different history. 相似文献
2.
Recent determinations of high production rates (up to 30 percent of primary production in surface waters) implicate free-living marine bacterioplankton as a link in a "microbial loop" that supplements phytoplankton as food for herbivores. An enclosed water column of 300 cubic meters was used to test the microbial loop hypothesis by following the fate of carbon-14-labeled bacterioplankton for over 50 days. Only 2 percent of the label initially fixed from carbon-14-labeled glucose by bacteria was present in larger organisms after 13 days, at which time about 20 percent of the total label added remained in the particulate fraction. Most of the label appeared to pass directly from particles smaller than 1 micrometer (heterotrophic bacterioplankton and some bacteriovores) to respired labeled carbon dioxide or to regenerated dissolved organic carbon-14. Secondary (and, by implication, primary) production by organisms smaller than 1 micrometer may not be an important food source in marine food chains. Bacterioplankton can be a sink for carbon in planktonic food webs and may serve principally as agents of nutrient regeneration rather than as food. 相似文献
3.
Kennett JP 《Science (New York, N.Y.)》1966,153(3732):191-193
In the Ross Sea, Antarctica, distributions of calcareous Foraminifera and other calcareous microorganisms are dominantly controlled by a shallow calcium carbonate solution boundary that occurs at depths of about 500 meters. Possible causes of substantial undersaturation of Ross Sea bottom waters in calcium carbonate are very low temperatures and high salinities, which favor the solution of calcium carbonate and, possibly, high concentrations of carbon dioxide. 相似文献
4.
The carbon-14 distribution in the abyssal waters of the world oceans indicates replacement times for Pacific, Indian, and Atlantic ocean deep waters (more than 1500 meters deep) of approximately 510, 250, and 275 years, respectively. The deep waters of the entire world ocean are replaced on average every 500 years. 相似文献
5.
兴隆山自然保护区土壤的形成与分布 总被引：2，自引：0，他引：2
本文研究了由前震旦系和震旦系岩层构成的兴隆山土壤的形成和分布。结果表明:土壤形成及分布与气候、植被和海拔有显著的相互关系。随着海拔高度由2300米到3500米,温度由暖变寒,湿度由干燥到湿润,植被由落叶阔叶林(在2300米～2600米海拔范围)到以阔叶林为主的针阔混交林(2600米～3000米),再过渡到亚高山(3000米～3500米)和高山(>3500米)灌丛草甸,土体淋溶由弱变强,3000米以上土壤风化变成寒冻风化为主,相应的土壤类型依次由石灰性灰褐土和典型灰褐土到淋溶灰褐土,渐变到亚高山灌丛草甸土,到高山草甸土和高山灌丛草甸土,其中淋溶灰褐土面积最大。丰富的兴隆山土壤资源和它们相应的地理要素一起共同构成了黄土高原西部独特的生态环境。 相似文献
6.
Bernstein RE Betzer PR Feely RA Byrne RH Lamb MF Michaels AF 《Science (New York, N.Y.)》1987,237(4821):1490-1494
Data on particulate strontium sulfate fluxes and strontium to chlorinity ratios were compared to provide insights into the strontium cycle of the North Pacific. Freedrifting sediment traps were used to derive large particle fluxes between depths of 100 and 3500 meters in the eastern and western North Pacific Ocean. Flux data revealed substantial quantities of acantharian skeletons and cysts (both made of strontium sulfate) settling through the upper kilometer of the water column. The greatest fluxes of celestite were detected at 400 meters. Minimal to nondetectable fluxes noted at and below 900 meters provide evidence that by this horizon, the majority of acantharian specimens had dissolved, thereby contributing to the pool of dissolved strontium. Growth and subsequent dissolution of acantharians in the upper kilometer are qualitatively consistent with the well-developed minimum and maximum strontium to chlorinity ratios that are consistently noted in these waters. These fluxes of particulate strontium and model calculations for fluxes of dissolved strontium indicate that acantharians play an important role in the ocean's strontium budget. 相似文献
7.
Druffel EM 《Science (New York, N.Y.)》1982,218(4567):13-19
Radiocarbon analyses and stable isotope measurements are presented foro recent cores of banded corals from the Florida Straits. These values provide a record of variations in the ratio of carbon-14 to carbon-12 in the dissolved inorganic carbon in the surface waters of the Gulf Stream from A.D. 1642 to 1800. An increase in the carbon-14/carbon-12 ratio of 7 per mil for coral growth during the early 1700's was most likely induced by an increase in the carbon-14/carbon-12 ratio of 20 per mil in the atmospheric carbon dioxide that occurred at about 1700. The ratios of oxygen 18 to oxygen-16 in these coral bands show a small decrease of a water temperature ( approximately 1 degrees C) during the latter part of the Little Ice Age (1700 to 1725). These results support the hypothesis that the increase in atmospheric carbon-14 at about 1700, and possibly the temperature change as well, was caused by a decrease in solar activity (Maunder sunspot minimum). 相似文献
8.
Margolis SV Kroopnick PM Goodney DE Dudley WC Mahoney ME 《Science (New York, N.Y.)》1975,189(4202):555-557
Oxygen-18 and carbon-13 analyses of well-preserved calcareous nannofossils have been compared with those of foraminifera contained in Cenozoic cores collected in the Southern Ocean during the Deep Sea Drilling Project. The results indicate that calcareous nannofossils deposit calcium carbonate at or near equilibrium with oceanic surface waters and that they can be used as paleotemperature indicators. 相似文献
9.
Feely RA Sabine CL Hernandez-Ayon JM Ianson D Hales B 《Science (New York, N.Y.)》2008,320(5882):1490-1492
The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of approximately 40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area. 相似文献
10.
Taylor RE Payen LA Gerow B Donahue DJ Zabel TH Jull AJ Damon PE 《Science (New York, N.Y.)》1983,220(4603):1271-1273
A morphologically modern human skeleton from Sunnyvale, California, previously dated by aspartic acid racemization to be approximately 70,000 years old and by uranium series isotopic ratios to be 8300 and 9000 years old, appears to be younger when dated by the carbon-14 method. Four carbon-14 determinations made by both decay and direct counting on three organic fractions of postcranial bone support a middle Holocene age assignment for the skeleton, probably in the range of 3500 to 5000 carbon-14 years before the present. This dating evidence is consistent with the geologic, archeological, and anthropometric relationships of the burial as well as previously determined carbon-14 determinations on associated materials. 相似文献
11.
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
12.
The feasibility of measuring carbon-14 and tritium in vivo has been demonstrated in the rat; thin scintillation detectors were used for the measurement of bremsstrahlung produced by these soft beta emitters. Measurements of tritium in vivo are limited to the study of surface phenomena, whereas bremsstrahlung produced by carbon-14 may be detected from depths of several centimeters. 相似文献
13.
In seawater enriched with carbon-14-labeled sodium hydrogen carbonate the sacoglossan Placobranchus ocellatus when exposed to light incorporates carbon-14 at a rate 50-fold of that for animals kept in the dark. 9,10-Deoxytridachione, a secondary metabolite of the mollusk, undergoes a photorearrangement to photodeoxytridachione in vivo. 相似文献
14.
Lal D 《Science (New York, N.Y.)》1977,198(4321):997-1009
Analyses of suspended particulate matter larger than 1 micrometer, filtered from thousands of liters of surface and deep waters during GEOSECS expeditions to the Atlantic and Pacific oceans, have provided new information on the nature and time scales of chemical processes associated with the particles. Trace element and radionuclide data show that particles scavenge trace elements such as Th, Pu, Fe, Pb, and Cu from the ocean column, thereby controlling their concentrations. For other elements, however, particles are a source: carbon and silicon, for example, are introduced at depths as sinking particles dissolve. Studies of both particulate concentrations by filtration of seawater and particulate fluxes by using sediment traps seem necessary to delineate the intricate nature of chemical processes in the oceans. 相似文献
15.
Average species durations were estimated for 131 commonly occurring modern species. The duration of species occurring at depths of less than 200 meters is 16 million years, while for those at greater than 200 meters and at all depths it is 25 to 26 million years. Species (less than 200 meters) distributed from Florida to Newfoundland and from Florida to Cape Hatteras have about the same durations (18 to 20 million years). The duration for species restricted to north of Cape Hatteras is only 7 million years. The data suggest that evolutionary rates are greater in shallower than in deeper depths and greatest in the shallower northern area. 相似文献
16.
Radiocarbon ages for the marine late Pleistocene stratigraphic units of the Baldwin Hills are 36,200 +/- 2,750 years and 28,450 +/- 2,600 years, respectively, defining the termination of marine deposition in this area of the Los Angeles Basin at less than 28,000 years ago. Faunas of the older sample suggest that water depths were about 100 meters at the time of deposition. Shoaling of waters by deposition resulted in very shallow marine to nonmarine conditions about 28,000 years ago. The average rates of uplift for the past 36,000 years have been between 0.5 and 0.8 meter per 100 years. 相似文献
17.
Thyroxine labeled with carbon-14 and iodine-125 was perfused through surviving rat hearts. Only when unlabeled triiodothyronine was added as a carrier could the newly formed doubly labeled triiodothyronine be isolated. The fact that this triiodothyronine was labeled with the correct ratio of carbon-14 to iodine-125 indicated that it originated from thyroxine. Approximately 5 percent of the initial carbon-14 radioactivity was found in the recovered triiodothyronine. 相似文献
18.
Knox AS 《Science (New York, N.Y.)》1969,165(3895):795-797
Organic sediments beneath historic Lafayette Park mark the site of a freshwater marsh which bordered the Potomac River when it was 15 meters above its present level. Plant microfossils and ice-rafted boulders indicate a climate much colder than now. The carbon-14 age of more than 45,000 years and palynological studies suggest an early Wisconsin age. 相似文献
19.
A layer of water at a depth of 200 meters containing 3 to 12 milligrams per liter of oil was found during February and March 1978 over a distance of 800 nautical miles in the southwest North Atlantic and the eastern Caribbean. The geochemistry and carbon-14 activity of the oil shows it to be a weathered crude, probably from a submarine seep. Although the dimensions of the oily layer were not determined, conservative estimates indicate that more than I megaton could have been present. 相似文献
20.
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