共查询到20条相似文献，搜索用时 31 毫秒
1.
Two ice cores, covering 1500 years of climatic information, from the summit (5670 meters) of the tropical Quelccaya ice cap, in the Andes of southern Peru, provide information on general environmental conditions including droughts, volcanic activity, moisture sources, temperature, and glacier net balance. The net balance record reconstructed from these cores reflects major precipitation trends for the southern Andes of Peru. These records indicate extended dry periods between 1720 and 1860, 1250 and 1310, and 570 and 610; wet conditions prevailed between 1500 and 1720. Establishing a tropical precipitation record may help explain climatic fluctuations since the tropical evaporation-precipitation cycle is a principal mechanism driving the atmospheric circulation. 相似文献
2.
The little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap 总被引：2，自引：0，他引：2
Thompson LG Mosley-Thompson E Dansgaard W Grootes PM 《Science (New York, N.Y.)》1986,234(4774):361-364
The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event. 相似文献
3.
Campbell IH Czamanske GK Fedorenko VA Hill RI Stepanov V 《Science (New York, N.Y.)》1992,258(5089):1760-1763
Uranium-lead ages from an ion probe were taken for zircons from the ore-bearing Noril'sk I intrusion that is comagmatic with, and intrusive to, the Siberian Traps. These values match, within an experimental error of +/-4 million years, the dates for zircons extracted from a tuff at the Permian-Triassic (P-Tr) boundary. The results are consistent with the hypothesis that the P-Tr extinction was caused by the Siberian basaltic flood volcanism. It is likely that the eruption of these magmas was accompanied by the injection of large amounts of sulfur dioxide into the upper atmosphere, which may have led to global cooling and to expansion of the polar ice cap. The P-Tr extinction event may have been caused by a combination of acid rain and global cooling as well as rapid and extreme changes in sea level resulting from expansion of the polar ice cap. 相似文献
4.
Koerner RM 《Science (New York, N.Y.)》1977,196(4285):15-18
Valuable paleoclimatic information can be gained by studying the distribution of melt layers in deep ice cores. A profile representing the percentage of ice in melt layers in a core drilled from the Devon Island ice cap plotted against both time and depth shows that the ice cap has experienced a period of very warm summers since 1925, following a period of colder summers between about 1600 and 1925. The earlier period was coldest between 1680 and 1730. There is a high correlation between the melt-layer ice percentage and the mass balance of the ice cap. The relation between them suggests that the ice cap mass balance was zero (accumulation equaled ablation) during the colder period but is negative in the present warmer one. There is no firm evidence of a present cooling trend in the summer conditions on the ice cap. A comparison with the melt-layer ice percentage in cores from the other major Canadian Arctic ice caps shows that the variation of summer conditions found for the Devon Island ice cap is representative for all the large ice caps for about 90 percent of the time. There is also a good correlation between melt-layer percentage and summer sea-ice conditions in the archipelago. This suggests that the search for the northwest passage was influenced by changing climate, with the 19th-century peak of the often tragic exploration coinciding with a period of very cold summers. 相似文献
5.
Thompson LG Mosley-Thompson E Davis ME Bolzan JF Dai J Klein L Yao T Wu X Xie Z Gundestrup N 《Science (New York, N.Y.)》1989,246(4929):474-477
Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Würm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative delta(18)O ratios, increased dust content, decreased soluble aerosol concentrations, and reduced ice crystal sizes than the Holocene part. These changes occurred rapidly approximately 10,000 years ago. In addition, the last 60 years were apparently one of the warmest periods in the entire record, equalling levels of the Holocene maximum between 6000 and 8000 years ago. 相似文献
6.
A glacial varve chronology from New England spanning the 4000-year period from 17,500 to 13,500 calendar years before the present was analyzed for evidence of climate variability during the late Pleistocene. The chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Nino-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today. This interannual variability largely disappears by the young end of the 4000-year chronology, with only the highest frequency components (roughly 3-year period) persisting. This record provides evidence of ENSO-like climate variability during near-peak glacial conditions. 相似文献
7.
Bornemann A Norris RD Friedrich O Beckmann B Schouten S Damsté JS Vogel J Hofmann P Wagner T 《Science (New York, N.Y.)》2008,319(5860):189-192
The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35 degrees C. High-amplitude sea-level changes and positive delta18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New delta18O data from the tropical Atlantic show synchronous shifts approximately 91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming. 相似文献
8.
Broecker WS 《Science (New York, N.Y.)》1975,188(4193):1116-1118
Two arguments are presented, one in favor of the existence of thicker ice in the Arctic Ocean during glacial time, and the other in favor of a full-fledged Arctic ice cap. The first is based on the Greenland air temperature record obtained from isotopic studies of the Camp Century ice core. The second is based on the oxygen isotope record of benthic foraminifera from a deep Pacific Ocean core. 相似文献
9.
In the western tropical Pacific, the interannual migration of the Indonesian Low convective system causes changes in rainfall that dominate the regional signature of the El Ni?o-Southern Oscillation (ENSO) system. A 96-year oxygen isotope record from a Tarawa Atoll coral (1 degrees N, 172 degrees E) reflects regional convective activity through rainfall-induced salinity changes. This monthly resolution record spans twice the length of the local climatological record and provides a history of ENSO variability comparable in quality with those derived from instrumental climate data. Comparison of this coral record with a historical chronology of EI Ni?o events indicates that climate anomalies in coastal South America are occasionally decoupled from Pacific-wide ENSO extremes. Spectral analysis suggests that the distribution of variance in this record has shifted among annual to interannual periods during the present century, concurrent with observed changes in the strength of the Southern Oscillation. 相似文献
10.
Cenozoic deep-Sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite 总被引：2，自引：0，他引：2
A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (delta(18)O) record and defines an overall cooling of about 12 degrees C in the deep oceans with four main cooling periods. Used in conjunction with the benthic delta(18)O record, the magnesium temperature record indicates that the first major accumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures. 相似文献
11.
Caillon N Severinghaus JP Jouzel J Barnola JM Kang J Lipenkov VY 《Science (New York, N.Y.)》2003,299(5613):1728-1731
The analysis of air bubbles from ice cores has yielded a precise record of atmospheric greenhouse gas concentrations, but the timing of changes in these gases with respect to temperature is not accurately known because of uncertainty in the gas age-ice age difference. We have measured the isotopic composition of argon in air bubbles in the Vostok core during Termination III (approximately 240,000 years before the present). This record most likely reflects the temperature and accumulation change, although the mechanism remains unclear. The sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800 +/- 200 years and preceded the Northern Hemisphere deglaciation. 相似文献
12.
Ocean Drilling Program Site 1119 is ideally located to intercept discharges of sediment from the mid-latitude glaciers of the New Zealand Southern Alps. The natural gamma ray signal from the site's sediment core contains a history of the South Island mountain ice cap since 3.9 million years ago (Ma). The younger record, to 0.37 Ma, resembles the climatic history of Antarctica as manifested by the Vostok ice core. Beyond, and back to the late Pliocene, the record may serve as a proxy for both mid-latitude and Antarctic polar plateau air temperature. The gamma ray signal, which is atmospheric, also resembles the ocean climate history represented by oxygen isotope time series. 相似文献
13.
陈宗瑜 《云南农业大学学报(自然科学版)》1999,14(3):323-327
通过对树木年轮、冰核、珊瑚等的测定和分析获得的古气候记录研究成果,评述了ENSO的演变规律及强度变化特征,指明了ENSO是可查证记录以来就己存在的现象。 相似文献
14.
Application of a simple linear model to the earth's ice volume record of the past 730,000 years indicates that although forcing by variations in the earth's orbital parameters of tilt and precession is real, it is small (less than 25 percent of the variance in the record). No relationship with the eccentricity is observed. This indicates that the Pleistocene glacial variations are largely stochastic in nature. 相似文献
15.
Kieffer HH Chase SC Martin TZ Miner ED Palluconi FD 《Science (New York, N.Y.)》1976,194(4271):1341-1344
Broadband thermal and reflectance observations of the martian north polar region in late summer yield temperatures for the residual polar cap near 205 K with albedos near 43 percent. The residual cap and several outlying smaller deposits are water ice with included dirt; there is no evidence for any permanent carbon dioxide polar cap. 相似文献
16.
Mayewski PA Meeker LD Whitlow S Twickler MS Morrison MC Alley RB Bloomfield P Taylor K 《Science (New York, N.Y.)》1993,261(5118):195-197
One of the most dramatic climate change events observed in marine and ice core records is the Younger Dryas, a return to near-glacial conditions that punctuated the last deglaciation. High-resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the arctic atmosphere at this time. This record shows that both the onset and the termination of the Younger Dryas occurred within 10 to 20 years and that massive, frequent, and short-term (decadal or less) changes in atmospheric composition occurred throughout this event. Changes in atmospheric composition are attributable to changes in the size of the polar atmospheric cell and resultant changes in source regions and to the growth and decay of continental biogenic source regions. 相似文献
17.
The Neoproterozoic glaciations supposedly ended in a supergreenhouse environment, which led to rapid melting of the ice cover and precipitation of the so-called cap carbonates. If Earth was covered with ice, then extraterrestrial material would have accumulated on and within the ice and precipitated during rapid melting at the end of the glaciation. We found iridium (Ir) anomalies at the base of cap carbonates in three drill cores from the Eastern Congo craton. Our data confirm the presence of extended global Neoproterozoic glaciations and indicate that the duration of the Marinoan glacial episode was at least 3 million, and most likely 12 million, years. 相似文献
18.
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
19.
A continuous record of oxygen-18 (delta(18)O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole-an open fault zone at Ash Meadows, Nevada-between 50 and 310 ka (thousand years ago). The configuration of the delta(18)O versus time curve closely resembles the marine and Antarctic ice core (Vostok) delta(18)O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 +/- 3 ka, at least 17,000 years earlier than indicated by the marine delta(18)O record and 7,000 years earlier than indicated by the less well dated Antarctic delta(18)O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine delta(18)O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages. 相似文献
20.
Measurements of the dissociation pressure of carbon dioxide hydrate show that this hydrate (CO(2) . 6H(2)O) is stable relative to solid CO(2) and water ice at temperatures above about 121 degrees K. Since this hydrate forms from finely divided ice and gaseous CO(2) in several hours at 150 degrees K, it is likely to be present in the martian ice cap. The ice cap can consist of water ice, water ice + CO(2) hydrate, or CO(2) hydrate + solid CO(2), but not water ice + solid CO(2). 相似文献