气候变暖条件下,中(高)亚洲地区不稳定型冻土的巨大挑战和创新解决方案:——来自首届亚洲冻土大会及会后青藏高原考察的总结报告

首届亚洲冻土大会于2006年8月5~16日在兰州、青藏线和拉萨顺利召开.大会讨论主要包括以下5个议题:1)冻土工程;2)山区和高原冻融灾害及冰缘环境;3)冰冻圈的气候与环境条件;4)冻土水文、寒区水资源及土地利用,和;5)冻土监测、制图及模拟.国内论文大多集中于青藏铁路各种科技创新和工程(示范)建设方面.中亚冻土分类、制图和监测研讨会明确了制定统一的中亚地区冻土图的计划和实施方案.会议期间,国内主要新闻媒体对全球15位著名冻土学家进行了联合采访.大约80位中外代表参加了青藏(公)铁路沿线考察,并于8月15日在拉萨举行青藏铁路工程和环境问题讨论会.专家一致认为,青藏铁路所采取的冻土工程措施基本上是恰当、有效的,能够保证青藏铁路路基的长期稳定性.但是,沿线寒区环境保护问题还任重道远,需要尽快进行综合管(治)理,以达到青藏地区社会经济和谐、持续发展的目标.     

Supernova remnants, planetary nebulae and the distance to NGC 4214

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.     

Insight to Ecosystem Based Approach (EBA) at Landscape Level Using a Geospatial Medium

Ecosystem based approach (EBA) for resource management is a concerted, environmentally tuned and an integrated framework that holistically addresses the ecological character of the natural resource, its societal benefit spectrum and its environmental functions. In this paper, the EBA concept is closely linked with the emerging concept of multiple use systems (MUS) while taking account of environmental, economic, and social factors that govern the ecosystems services and benefits. We elucidate a multi-scalar approach and multiple case studies to understand EBA particularly in context of a wetlandscape. At the global scale, Ramsar sites of international importance are geospatially analyzed with reference to their agro-ecology and biodiversity. At regional scale, the agrarian use of inland wetlands in India was re-evaluated taking account of database from a recent inland wetland inventory. At the local scale, drawing on the landscape characterization and the ecological economics for fresh water Lake Kolleru in India and the Muthurajawela Marsh-Negombo Lagoon coastal marsh in Sri Lanka, we illustrate some of the practical challenges in balancing wetland conservation, development needs and the overall well-being of local people. We also discuss how variability in the scale, geophysical characteristics of the site and the data availability confines the ability to simplify a single complete approach to address issues in complex ecosystem such as wetlands. All levels of the study are supported by a variety of earth observation data and the geographical information system (GIS) tools. The site level analysis also draws on socio-economic assessment tools.     

Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land–ocean interactions since AD 1660

We examine the relationship between three tropical and two subtropical western Indian Ocean coral oxygen isotope time series to surface air temperatures (SAT) and rainfall over India, tropical East Africa and southeast Africa. We review established relationships, provide new concepts with regard to distinct rainfall seasons, and mean annual temperatures. Tropical corals are coherent with SAT over western India and East Africa at interannual and multidecadal periodicities. The subtropical corals correlate with Southeast African SAT at periodicities of 16–30 years. The relationship between the coral records and land rainfall is more complex. Running correlations suggest varying strength of interannual teleconnections between the tropical coral oxygen isotope records and rainfall over equatorial East Africa. The relationship with rainfall over India changed in the 1970s. The subtropical oxygen isotope records are coherent with South African rainfall at interdecadal periodicities. Paleoclimatological reconstructions of land rainfall and SAT reveal that the inferred relationships generally hold during the last 350 years. Thus, the Indian Ocean corals prove invaluable for investigating land–ocean interactions during past centuries. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Three monthly coral Sr/Ca records from the Chagos Archipelago covering the period of 1950–1995 A.D.: reproducibility and implications for quantitative reconstructions of sea surface temperature variations

In order to assess the fidelity of coral Sr/Ca for quantitative reconstructions of sea surface temperature variations, we have generated three monthly Sr/Ca time series from Porites corals from the lagoon of Peros Banhos (71°E, 5°S, Chagos Archipelago). We find that all three coral Sr/Ca time series are well correlated with instrumental records of sea surface temperature (SST) and air temperature. However, the intrinsic variance of the single-core Sr/Ca time series differs from core to core, limiting their use for quantitative estimates of past temperature variations. Averaging the single-core data improves the correlation with instrumental temperature (r > 0.7) and allows accurate estimates of interannual temperature variations (~0.35°C or better). All Sr/Ca time series indicate a shift towards warmer temperatures in the mid-1970s, which coincides with the most recent regime shift in the Pacific Ocean. However, the magnitude of the warming inferred from coral Sr/Ca differs from core to core and ranges from 0.26 to 0.75°C. The composite Sr/Ca record from Peros Banhos clearly captures the major climatic signals in the Indo-Pacific Ocean, i.e. the El Niño–southern oscillation and the Pacific decadal oscillation. Moreover, composite Sr/Ca is highly correlated with tropical mean temperatures (r = 0.7), suggesting that coral Sr/Ca time series from the tropical Indian Ocean will contribute to multi-proxy reconstructions of tropical mean temperatures.     

Role of major terrestrial cratering events in dispersing life in the solar system

The larger and most energetic cratering events from comet and asteroid collisions with the Earth are probably associated with ejection of solid material faster than escape speeds every 100 Myr or so. Metre-sized boulders, we estimate, may have been ejected directly into Venus-crossing and perhaps Mars-crossing orbits from comet impacts at higher speeds and of larger mass, at least on 10 occasions in the last 3.5 Ga. Subsequent close encounters with Earth can also enable slower boulders to reach Mars-crossing orbits. Orbit perturbations from Mars and Jupiter would then have sent a fraction of the boulders to the outer planets and their icy satellite systems. In the so-called late bombardment epoch at 3.9 Ga, when primitive life was developing, ejection-causing impacts were much more frequent, at 30 per 0.1 Ga, yielding an increased probability of distributing seeds of terrestrial biology to the outer regions of the solar system.     

Precursory seismic quiescence

Seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromM _L=4.7 toM _S=8.0 are summarized. The amount of rate decrease ranges from 45% to 90%. The significance of these changes varies between 90% and 99.99%. The assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied. All quiescence anomalies seem to have abrupt beginnings, and the rate during the anomalous period is fairly constant. The duration of the precursors ranges from 15 to 75 months, and it is not clear what factors determine that time. At least three successful predictions have been based on seismic quiescence. These cases have shown that mainshocks can be predicted based on quiescence, but they have also shown that the interpretation of the data in real time is difficult and nonunique. If a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area, then we estimate, based on searches in four areas, that the false alarm rate may be on the order of 50%. Failure to predict may be expected in perhaps 50% of mainshocks, even in carefully monitored areas. Quiescence cannot be used as a precursor in tectonic environments with low seismic activity. Most characteristics of the phenomenon are still poorly defined, but data exist which probably permit at least a doubling of the presently available data on case histories.     

Reconstructing seawater δO from paired coral δO and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)

We compare several statistical routines that may be used to calculate δ¹⁸O_sw and SSS from paired coral Sr/Ca and δ¹⁸O measurements. Typically, the δ¹⁸O_coral-SST relationship is estimated by linear regression of coral δ¹⁸O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and δ¹⁸O_sw (SSS) often co-vary, and this will bias the estimate of the regression slope of δ¹⁸O_coral-SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the δ¹⁸O_coral-SST relationship has known, we propose to insert this value for γ₁ in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in δ¹⁸O_sw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral δ¹⁸O and Sr/Ca equal the amplitude of the seasonal cycle of δ¹⁸O_sw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed δ¹⁸O_sw (SSS) is lower than the magnitude of seasonal variations of δ¹⁸O_sw (SSS), and the seasonal cycle of δ¹⁸O_sw (SSS) can be resolved.