Timing and nature of late Quaternary climate change from cave deposits, 2006, Edwards Rl, Yuan Dx, An Zs, Wang Yj, Auler As, Cheng H, Rowe H, Wang Xf, Kelly Mj, Dykoski Ca,

Sensitivity of ancient Lake Ohrid to local anthropogenic impacts and global warming, 2006, Matzinger A. , Spirkovski Z. , Patceva S. , Wuest A. ,

Human impacts on the few ancient lakes of the world must be assessed, as any change can lead to an irreversible loss of endemic communities. In such an assessment, the sensitivity of Lake Ohrid (Macedonia/Albania; surface area A = 358 km(2), volume V = 55 km(3), > 200 endemic species) to three major human impacts-water abstraction, eutrophication, and global warming-is evaluated. It is shown that ongoing eutrophication presents the major threat to this unique lake system, even under the conservative assumption of an increase in phosphorus (P) concentration from the current 4.5 to a potential future 9 mg P m(-3). Eutrophication would lead to a significant reduction in light penetration, which is a prerequisite for endemic, deep living plankton communities. Moreover, a P increase to 9 mg P m(-3) would create deep water anoxia through elevated oxygen consumption and increase in the water column stability due to more mineralization of organic material. Such anoxic conditions would severely threaten the endemic bottom fauna. The trend toward anoxia is further amplified by the predicted global warming of 0.04 degrees C yr(-1), which significantly reduces the frequency of complete seasonal deep convective mixing compared to the current warming of 0.006 degrees C yr(-1). This reduction in deep water exchange is triggered by the warming process rather than by overall higher temperatures in the lake. In contrast, deep convective mixing would be even more frequent than today under a higher temperature equilibrium, as a result of the temperature dependence of the thermal expansivity of water. Although water abstraction may change local habitats, e.g., karst spring areas, its effects on overall lake properties was shown to be of minor importance

Modelling of dripwater hydrology and hydrogeochemistry in a weakly karstified aquifer (Bath, UK): Implications for climate change studies, 2006, Fairchild Ij, Tuckwell Gw, Baker A, Tooth Af,

A better knowledge of dripwater hydrology in karst systems is needed to understand the palaeoclimate implications of temporal variations in Mg/Ca and Sr/Ca of calcareous cave deposits. Quantitative modelling of drip hydrology and hydrochemistry was undertaken at a disused limestone mine (Brown's Folly Mine) in SW England overlain by 15 m of poorly karstified Jurassic limestones, with sub-vertical fracturing enhanced by proximity to an escarpment. Discharge was monitored at 15 sites intermittently from the beginning of 1996, and every 10-20 days from later 1996 to early 1998. Samples for hydrochemical parameters (pH, alkalinity, cations, anions, fluorescence) were taken corresponding to a sub-set of these data and supplernented by bedrock and soil sampling, limited continuously logged discharge, and soil water observations. Three sites, covering the range of discharge (approximately 1 mu L s(-1) to 1 ml s(-1) maximum discharge) and hydrochemical behaviours, were studied in more detail. A quantitative flow model was constructed, based on two parallel unit hydrographs: responsive and relatively unresponsive to discharge events, respectively. The linear response and conservative mixing assumptions of the model were tested with hydrogeochemical data. Dripwaters at many of sites are characterized by evidence of prior calcite precipitation in the flowpath above the mine, which in the higher discharging sites diminishes at high flow. Also at low flow rates, dripwaters may access seepage reservoirs enriched in Mg and/or Sr, dependent on the site. The discharge at all three sites can be approximated by the flow model, but in each case, hydrochemical data show violations of the model assumptions. All sites show evidence of non-conservative mixing, and there are temporal discontinuities in behaviour, which may be stimulated by airlocks generated at low flow. Enhanced Mg/Ca and Sr/Ca often do relate to low-flow conditions, but the relationships between climate and hydrogeochemical response are non-linear. (c) 2005 Elsevier B.V. All rights reserved

A gray system model for studying the response to climatic change: The Liulin karst springs, China, 2006, Hao Yonghong, Yeh Tian Chyi, Gao Zongqiang, Wang Yanrong, Zhao Ying,

SummaryGray system theory uses a black-gray-white color spectrum to describe a complex system whose characteristics are only partially known or known with uncertainty. In this study, we use gray system theory to investigate the relation between precipitation and spring flows in a karst region in China. The gray incidence analysis was applied to the Liulin Springs, Shanxi Province, China to analyze the time-lag between spring flow and precipitation. The results showed that the average groundwater residence time at Liulin Spings is about 4 years. The gray system GM(1,2) model was subsequently used as a predictive tool for spring discharge. It was found that model predictions are in agreement with observed data. This study also shows that the discharge of the Liulin Springs primarily responds to climate change; anthropogenic impacts are secondary. The continuous decline of water level in the karst aquifer and waning of spring discharges in semi-arid regions of China might be largely a response of the groundwater system to the decline in regional precipitation over the past two decades

The co-evolution of Black Sea level and composition through the last deglaciation and its paleoclimatic significance, 2006, Major Candace O. , Goldstein Steven L. , Ryan William B. F. , Lericolais Gilles, Piotrowski Alexander M. , Hajdas Irka,

The Black Sea was an inland lake during the last ice age and its sediments are an excellent potential source of information on Eurasian climate change, showing linkages between regionally and globally recognized millennial-scale climate events of the last deglaciation. Here, we detail changes from the last glacial maximum (LGM) through the transition to an anoxic marginal sea using isotopic (strontium and oxygen) and trace element (Sr/Ca) ratios in carbonate shells, which record changing input sources and hydrologic conditions in the basin and surrounding region. Sr isotope records show two prominent peaks between ~18 and 16 ka BP cal, reflecting anomalous sedimentation associated with meltwater from disintegrating Eurasian ice sheets that brought Black Sea level to its spill point. Following a sharp drop in Sr isotope ratios back toward glacial values, two stages of inorganic calcite precipitation accompanied increasing oxygen isotope ratios and steady Sr isotope ratios. These calcite peaks are separated by an interval in which the geochemical proxies trend back toward glacial values. The observed changes reflect negative water balance and lake level decline during relatively warm periods (Bolling-Allerod and Preboreal) and increasing river input/less evaporation, resulting in higher lake levels, during the intervening cold period (the Younger Dryas). A final shift to marine values in Sr and oxygen isotope ratios at 9.4 ka BP cal corresponds to connection with the global ocean, and marks the onset of sedimentation on the Black Sea continental shelf. This date for the marine incursion is earlier than previously suggested based on the appearance of euryhaline fauna and the onset of sapropel formation in the deep basin

Solar forcing of Holocene climate: New insights from a speleothem record, southwestern United States, 2007, Asmerom Y, Polyak V, Burns S, Rassmussen J,

Holocene climate change has likely had a profound influence on ecosystems and culture. A link between solar forcing and Holocene climate, such as the Asian monsoon, has been shown for some regions, although no mechanism for this relationship has been suggested. Here we present the first high-resolution complete Holocene climate record for the North American monsoon region of the southwestern United States (southwest) in order to address the nature and causes of Holocene climate change. We show that periods of increased solar radiation correlate with decreased rainfall, the opposite to that observed in the Asian monsoon, and suggest that a solar link to Holocene climate is through changes in the Walker circulation and the Pacific Decadal Oscillation and El Nino-Southern Oscillation systems of the tropical Pacific Ocean. Given the link between increased warming and aridity in the southwest, additional warming due to greenhouse forcing could potentially lead to persistent hyperarid conditions, similar to those seen in our record during periods of high solar activity