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Extreme Late Quaternary climatic events, sometimes of considerable continental extent, are being proposed as major contributors to ancestral human behaviour, particularly migration, in Africa. Most recently, a catastrophic drought in the Afro‐Asian monsoon region has been proposed for 16 000–17 000 years ago, driven by global impacts of the Heinrich event 1 (H1), with potentially significant consequences for Palaeolithic cultures. We provide a new analysis of the assertion and find, on examination of a wide set of palaeoenvironmental records, that the scale and extent of the proposed drought is not supported. While some parts of the African tropics, close to the equator, do appear dry at this time, data for the tropics as a whole suggest markedly variable terrestrial conditions, with some environmental systems experiencing very positive hydrological excursions during H1. We contend that in the quest for evidence of climate drivers of ancestral human behaviour, the variability associated with spatially and temporally complex climatic conditions is a significant factor in itself. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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KANG Shi chang QIN Da he YAO Tan dong PAUL A. Mayewski SALLIE Whitlow 《中国地理科学(英文版)》2000,10(3):218-225
Investigations of atmospheric composition in the Himalayas has been limited in both temporal and spatial scales, mainly due to difficult logistics. Ideal sites for monitoring atmospheric composition and its evolution should be free from local pollution and representative of the remote troposphere (HUEBERT et al., 1980). As the Himalayas are far removed from highly industrialized regions they provide suitable locations to monitor the chemistry of the remote troposphere and to study the evolu… 相似文献
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The δ13C and δ18O values of well-preserved carbonate rhizoliths (CRs) provide detailed insights into changes in the abundance of C3 and C4 plants in response to approximately decadal-scale changes in growing-season climate. We performed stable isotope analyses on 35-40 CRs sampled at 1-cm intervals from an 18-cm-thick paleosol formed in southern Illinois during Wisconsin interstadial 2. Minimum δ13C values show little variation with depth, whereas maximum values vary dramatically, and average values show noticeable variability; maximum δ18O values vary less than the minimum δ18O values. These findings indicate that a diverse and stable C3 flora with a limited number of C4 grass species prevailed during this interval, and suggest that the maximum growing-season temperatures were relatively stable, but minimum growing-season temperatures varied considerably. Two general patterns characterize the relationships between the δ13C and δ18O values obtained from the 1-cm samples. In some cases, low δ13C values correspond to low δ18O values and high δ13C values correspond to high δ18O values, suggesting that cooler growing-season temperatures favored C3 and warmer growing-season temperatures favored C4 plants. In other cases, low δ13C values correspond to high δ18O values, likely suggesting that wetter growing-season conditions were favorable to C3 plants. The high density of well-preserved CRs in this paleosol provides a unique opportunity to study detailed ecological responses to high-resolution variability in growing-season climate. 相似文献
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High-resolution multispectral images of main-belt asteroid 3 Juno were taken at visible and near-IR wavelengths with the 100-inch telescope at Mount Wilson Observatory equipped with an adaptive optics system. The images show spectral features that may represent a large relatively recent impact that deeply excavated the coarse-grained olivine-pyroxene-rich crust of the asteroid. 相似文献
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The Kalahari region has become a major source of Quaternary palaeoenvironmental data derived primarily from the analysis of geomorphological proxies of environmental change. One suite of data, from palaeolacustrine landforms, has recently provided a new record of major hydrological changes in the last 150 ka [Burrough, S. L., Thomas, D. S. G., Bailey, R. M., 2009. Mega-Lake in the Kalahari: A Late Pleistocene record of the Palaeolake Makgadikgadi system. Quaternary Science Reviews, in press.]. Here we present an improved analysis of the drivers and feedbacks of lake level change, utilising information from three main sources: data from the lake system itself, from analyses of other late Quaternary records within the region and from climate modelling. Simulations using the Hadley Centre coupled climate model, HadCM3, suggest that once triggered, the lake body was large enough to potentially affect both local and regional climates. Surface waters and their interactions with the climate are therefore an important component of environmental dynamics during the late Quaternary. Through its capacity to couple Middle Kalahari environments to distant forcing mechanisms and to itself force environmental change, we demonstrate that the existence or absence of megalake Makgadikgadi adds a new level of complexity to the interpretations of environmental proxy records in southern Africa's summer rainfall zone. 相似文献
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The previous paper in this series presented a one-dimensional stochastic nested model to account for superimposed sources of soil variation at various scales. This paper shows how the nested model can be fitted to experimental data using weighted or generalized least-squares methods that account for correlations between consecutive terms that had previously been neglected. This paper also presents a method of estimating effective degrees of freedom for each sampling interval and thus for estimating 90% confidence limits for the semivariogram of the nested model. 相似文献
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Sallie Yea 《Singapore journal of tropical geography》2004,25(2):180-197
Although the migration of Filipinas to the Republic of Korea has only a short history, some Filipinas have already begun to form incipient communities around the largest United States military bases there. These communities are formed by an increasing number of women who run away from the military camptown clubs where they work as entertainers, to marry or live in cohabitation/de facto relationships with the enlisted American army personnel (or GIs) whom they meet and develop relationships with while working as entertainers in the GI clubs. Drawing on ethnographic research and interviews with the women in one such camptown, this paper documents their experiences and the dynamics of their marriages as they attempt to negotiate their transition from “trafficked entertainers” to “runaway brides”. Their experiences illustrate the daily tribulations of women who wish to improve their prospects, or more ambitiously, transform their identity whilst abroad, by entering into marriages or similar arrangements, but who continue to be encumbered with the stigma attached to being trafficked entertainers. The discussion in this paper aims to contribute to the literature on Filipina migrants' anxieties about identity in the context of transnational migration. 相似文献
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We have analyzed the direct records of sunspot number between 1749 and 1990 with the same technique currently used in the study of stellar activity cycles observed with Mount Wilson Observatory's 60-inch telescope. In order to mimic the stellar time series, which span only two decades, we analyzed twenty- and fifty-year intervals of the sunspot data in comparison to the entire record. We also examined the reliability of the oldest (pre-1850) sunspot records. The mean solar cycle period determined from the entire record (1749–1990) is 11.04 yr with a computed precision of ± 0.01 yr, but an overall accuracy of only ±1.1 yr. The large uncertainty is caused by variation of the cycle period with time and not observational uncertainty.The correct sunspot period is found slightly more often (82%) in 50-year intervals compared to 20-year (74%). The cause is twofold: first, a more precise period results from the longer sample length, and second, other periodicities exist in the sunspot record, so that a more accurate determination of the dominant 11.0-year period results from the longer time series. As a guideline for cycle periodicities in other stars, the solar results indicate that the 50-year intervals would produce more precise and accurate periods than the 20-year time series. On the other hand, useful statistics concerning long-term activity could be obtained from a less-frequently sampled group of stars that is substantially larger than the group of 100 lower Main-Sequence stars currently observed at Mount Wilson, although knowledge of short-term variability would be sacrificed.Pre-doctoral fellow, Harvard-Smithsonian Center for Astrophysics. 相似文献
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