Interhemispheric anti-phasing of rainfall during the last glacial period

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts (<1‰) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere.We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ¹⁸O (wet periods, intense SAM) at our site are synchronous with maxima in δ¹⁸O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor's greenhouse properties.     

黄龙与黄石钙华微生物沉积作用比较研究

本文通过调查黄龙风景区水体的环境地质特征与微生物群落结构及多样性,并与黄石公园对比分析,探讨了两种特殊地理环境下的微生物群落结构和多样性及其对钙华沉积的影响.结果表明:黄龙沟泉水属于地下冷泉,且景区内覆盖着大量植被,水体中有大量藻类和细菌;黄石公园猛犸象温泉区泉水属于地下热泉,植被覆盖率很低,泉水中微生物多为嗜热菌,藻...     

Geochronology,sediment provenance,and fossil emplacement at Sumidouro Cave,a classic late Pleistocene/early Holocene Paleoanthropological site in eastern Brazil

Peter Wilhelm Lund's (1845a) heavily debated suggestion of a contemporaneity between Paleo‐Indians and extinct Pleistocene fauna at Sumidouro Cave was re‐examined through detailed sedimentological and geochronological analyses of sediment and both human and faunal remains. Sources of the cave's sediment include both entrances as well as ceiling fissures. Non‐human fossils, on the other hand, were probably carried by floodwater through the once more‐spacious swallet entrance. Seasonal flooding reworked and mixed these two highly asynchronous assemblages. U‐series and radiocarbon ages indicate that there are at least two distinct episodes of sediment input in the cave, at ˜240,000 yr B.P. and ˜8000 yr B.P. Human remains represent a later emplacement event, probably at ˜8400 cal yr B.P. Although the human remains are of considerable age, the cave's complex stratigraphy, flooding dynamics, and extensive removal of the cave's filling during earlier excavations do not allow the determination of an unequivocal co‐existence between Paleo‐Indians and extinct megafauna at the site. © 2005 Wiley Periodicals, Inc.     

The World Karst Aquifer Mapping project: concept,mapping procedure and map of Europe

Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.

     

The influence of bedrock‐derived acidity in the development of surface and underground karst: evidence from the Precambrian carbonates of semi‐arid northeastern Brazil

Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi‐arid climate. The caves in the area display many morphological features characteristic of deep‐seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross‐sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present‐day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep‐seated sources of acidity. Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate‐independent processes related to hypogenic sources of acidity. Copyright © 2003 John Wiley & Sons, Ltd.