Showing papers on "Speleothem published in 2011"

Chinese stalagmite δ 18 O controlled by changes in the Indian monsoon during a simulated Heinrich event

Abstract: Carbonate cave deposits in India and China are assumed to record the intensity of monsoon precipitation, because the 18 O of the carbonate tracks the isotopic signature of precipitation. These records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial-scale climate variations known as Dansgaard‐Oeschger events and during the Heinrich cooling events. Here we use a numerical climate model with an embedded oxygen-isotope model to assess what caused the shifts in the oxygen-isotope signature of precipitation during a climate perturbation designed to mimic a Heinrich event. Our simulations show that a sudden increase in North Atlantic sea-ice extent during the last glacial period leads to cooling in the Northern Hemisphere, reduced precipitation over the Indian basin and weakening of the Indian monsoon. The precipitation is isotopically heavier over India and the water vapour exported to China is isotopically enriched. Our model broadly reproduces the enrichment of 18 O over Northern India and East Asia evident in speleothem records during Heinrich events. We therefore conclude that changes in the 18 O of cave carbonates associated with Heinrich events reflect changes in the intensity of Indian rather than East Asian monsoon precipitation.

Mid-Holocene climate variations revealed by high-resolution speleothem records from Soreq Cave, Israel and their correlation with cultural changes

Abstract: Mid-Holocene (7000—4000 yr BP) paleoclimate conditions were reconstructed for the eastern Mediterranean region through a high-resolution (3—20 yr) oxygen and carbon isotopic record in a speleothem ...

Pleistocene water intrusions from the Mediterranean and Caspian seas into the Black Sea

Abstract: The hydrological balance of the Black Sea is governed by riverine input and by the exchange with the Mediterranean Sea. A speleothem record from a cave in northern Turkey that tracks the isotopic signature of Black Sea surface water suggests an open connection to the Mediterranean Sea in at least twelve periods in the past 670,000 years.

Abrupt variations in South American monsoon rainfall during the Holocene based on a speleothem record from central-eastern Brazil

Abstract: Well-dated high-resolution oxygen isotope records of speleothems in central-eastern Brazil spanning from 1.3 to 10.2 kyr B.P. reveal that the occurrence of abrupt variations in monsoon precipitation is not random. They show a striking match with Bond events and a significant pacing at ∼800 yr, a dominant periodicity present in sea surface temperature records from both the North Atlantic and equatorial Pacific Oceans that is possibly related to periods of low solar activity (high 14 C based on the atmospheric Δ 14 C record). The precipitation variations over central-eastern Brazil are broadly antiphased with the Asian and Indian Monsoons during Bond events and show marked differences in duration and structure between the early and late Holocene. Our results suggest that these abrupt multicentennial precipitation events are primarily linked to changes in the North Atlantic meridional overturning circulation (AMOC). Anomalous cross-equatorial flow induced by negative AMOC phases may have modulated not only the monsoon in South America but also affected El Nino–like conditions in the tropical Pacific during the Holocene.

Speleothem-derived Asian summer monsoon variations in Central China, 54–46 ka

Abstract: The oxygen isotope signature (delta O-18) of stalagmite SI3 collected from Shizi Cave in north-east Sichuan Province provides an Asian Summer Monsoon (ASM) record in Central China for the period 54-46 ka. The SI3 delta O-18 record clearly shows a negative delta O-18 excursion centred around 49.4 ka, which was reported in Hulu Cave in East China but not identified in the speleothem records from South-west China. As a whole, this record displays a higher coherence with the two Hulu records from East China than with the speleothem delta O-18 records from South-west China, suggesting that at 54-46 ka, Central China was influenced more by the East Asian Summer Monsoon than by the Indian Summer Monsoon. It also displays a significant negative delta O-18 excursion at 47.5-46.6 ka, which is not clearly documented in two other speleothem delta O-18 records previously reported from South-west China. This suggests that details of the Greenland interstadial 12 warrant further investigations in future in monsoonal China. The SI3 delta O-18 record displays more significant centennial-scale variations than the other four speleothem delta O-18 records from East and South-west China, which may be due to the fact that the study site is closer to the north-west boundary of the ASM and more sensitive to variations of the ASM than East and South-west China. Copyright (C) 2011 John Wiley & Sons, Ltd.

Origin and palaeoenvironmental significance of lamination in stalagmites from Katerloch Cave, Austria

Abstract: The origin and environmental dependencies of lamination in stalagmites from Katerloch, common in speleothems from other cave sites, are examined in detail. Petrographic observations and chemical analyses (including isotopes) of stalagmites and modern calcite were combined with multi-annual cave monitoring. All investigated stalagmites are composed of low-Mg calcite and show white, porous laminae and typically thinner, translucent dense laminae. The binary lamination pattern results from changes in the calcite fabric: white, porous laminae are characterized by a high porosity and abundant fluid inclusions and also by enhanced vertical growth and thinning towards the flanks. Translucent, dense laminae exhibit a compact fabric and constant thickness of individual growth layers. U-Th dating supports an annual origin of the lamination and the seasonally changing intensity of cave ventilation provides a robust explanation for the observed relationships between lamination, stable C isotopic compositions and trace elements (Mg, Sr and Ba). The seasonally variable air exchange, driven by temperature contrasts between the cave interior and outside atmosphere, modulates the rate and amount of CO2 degassing from the drip water and affects the hydrochemistry and consequently the fabric of the precipitating calcite. Although cave air composition and drip rate are both major variables in controlling CO2 degassing from the drip water, the seasonally changing ventilation in Katerloch exerts the primary control and the results suggest a secondary (amplifying/attenuating) influence of the drip rate. Drip rate, however, might be the controlling parameter for lamina development at cave sites experiencing only small seasonal cave air exchange. Importantly, the seasonally variable composition of drip water does not reflect the seasonal cycle of processes in the soil zone, but results from exchange with the cave atmosphere. The alternating porous and dense calcite fabric is the expression of a variable degree of lateral coalescence of smaller crystallites forming large columnar crystals. The white, porous laminae represent partial coalescence and form during the warm season: low calcite δ13C values are linked to low δ13C values of cave air and drip water during that time. This observation corresponds to times of reduced cave ventilation, high pCO2 of cave air, low drip water pH, lower calcite supersaturation and typically high drip rates. In contrast, the translucent, dense laminae represent more or less complete lateral coalescence (inclusion-free) during the cold season (high calcite, drip water and cave air δ13C values), i.e. times of enhanced cave ventilation, low cave air pCO2, increased drip water pH, relatively high calcite supersaturation and typically low drip rates. In essence, the relative development of the two lamina types reflects changes in the seasonality of external air temperature and precipitation, with a strong control of the winter air temperature on the intensity of cave-air exchange. Thick translucent, dense laminae are favoured by long, cold and wet winters and such conditions may be related closely to the North Atlantic Oscillation mode (weak westerlies) and enhanced Mediterranean cyclone activity during the cold season. Studies of speleothem lamination can thus help to better understand (and quantify) the role of seasonality changes, for example, during rapid climate events.

Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake, Shanxi, North China

Abstract: Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (28 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP The results demonstrate that the main magnetic mineral is magnetite The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon The variations in the χ and S −300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments

Humid Medieval Warm Period recorded by magnetic characteristics of sediments from Gonghai Lake, Shanxi, North China

Abstract: Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the χ and S −300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.

Bacterial and Archaeal Community Structure of Two Adjacent Calcite Speleothems in Kartchner Caverns, Arizona, USA

Abstract: Information concerning the bacterial and archaeal communities present on calcite speleothems in carbonate caves is of interest because the activity of these microbes has been implicated as a potential biogenic component in the formation of secondary mineral deposits. In addition, these speleothems may harbor unique, previously unidentified microbes. The current study presents a comparative analysis of the superficial bacterial and archaeal community structure of multiple stalactites from two different cave formations located in close proximity to each other in a nonhuman-impacted area of Kartchner Caverns, Arizona, USA. PCR-denaturing gradient gel electrophoresis analysis (PCR-DGGE) revealed that microbial communities sampled from stalactites of a single speleothem are more similar to each other than to the communities sampled from stalactites of an adjacent speleothem, suggesting that both bacterial and archaeal communities are speleothem-specific. SR-XRD analysis confirmed that both speleothems sampled ...

Using the 14C Bomb Pulse to Date Young Speleothems

Abstract: Three modern speleothems were sampled at high resolution for radiocarbon analysis to identify their bomb-pulse signatures and to construct chronologies. Each speleothem exhibited a different 14C response, presumed to be related to site characteristics such as vegetation, temperature, rainfall, depth below the surface, and water pathway through the aquifer. Peak 14C activity for WM4 is 134.1 pMC, the highest cited thus far in the literature and suggestive of a lower inertia at this site. Dead carbon fractions for each stalagmite were calculated and found to be relatively similar for the 3 speleothems and lower than those derived from Northern Hemisphere speleothems. An inverse modeling technique based on the work of Genty and Massault (1999) was used to estimate soil carbon residence times. For each speleothem, mean soil 14C reservoir ages differed greatly between the 3 sites, ranging from 2-6.5 to 32-46 yr.

Secondary halite deposits in the Iranian salt karst: general description and origin

Abstract: This paper summaries 12 years of documentation of secondary halite deposits in the Iranian salt karst. A variety of secondary halite deposits was distinguished and classified into several groups, on the basis of the site and mechanism of their origin. Deposits formed: i) via crystallization in/on streams and pools, ii) from dripping, splashing and aerosol water, iii) from evaporation of seepage and capillary water, and iv) other types of deposits. The following examples of halite forms were distinguished in each of the above mentioned group: i) euhedral crystals, floating rafts (raft cones), thin brine surface crusts and films; ii) straw stalactites, macrocrystalline skeletal and hyaline deposits, aerosol deposits; iii) microcrystalline forms (crusts, stalactites and stalagmites, helictites); iv) macrocrystalline helictites, halite bottom fibers and spiders, crystals in fluvial sediments, euhedral halite crystals in rock salt, combined or transient forms and biologically induced deposits. The occurrence of particular forms depends strongly on the environment, especially on the type of brine occurrence (pool, drip, splashing brine, microscopic capillary brine, etc.), flow rate and its variation, atmospheric humidity, evaporation rate and, in some cases, on the air flow direction. Combined or transitional secondary deposits can be observed if the conditions changed during the deposition. Euhedral halite crystals originate solely below the brine surface of supersaturated streams and lakes. Macrocrystalline skeletal deposits occur at places with rich irregular dripping and splashing (i.e., waterfalls, places with strong dripping from the cave ceilings, etc.). Microcrystalline (fine grained) deposits are generated by evaporation of capillary brine at places where brine is not present in a macroscopically visible form. Straw stalactites form at places where dripping is concentrated in small spots and is frequent sufficient to assure that the tip of the stalactite will not be overgrown by halite precipitates. If the tip is blocked by halite precipitates, the brine remaining in the straw will seep through the walls and helictites start to grow in some places. Macrocrystalline skeletal deposits and straw stalactites usually grow after a major rain event when dripping is strong, while microcrystalline speleothems are formed continuously during much longer periods and ultimately (usually) overgrow the other types of speleothems during dry periods. The rate of secondary halite deposition is much faster compared to the carbonate karst. Some forms increase more than 0.5 m during the first year after a strong rain event; however, the age of speleothems is difficult to estimate, as they are often combinations of segments of various ages and growth periods alternate with long intervals of inactivity. Described forms may be considered in many cases as the analogues of forms found in the carbonate karst. As they are created in a short time period the conditions of their origin are often still visible or can be reconstructed. The described halite forms can thus be used for verification of the origin of various carbonate forms. Some of the described forms bear clear evidence of the paleo-water surface level (transition of the skeletal form to halite crystals and vice versa). Other kinds of deposits are potential indicators of the microclimate under which they developed (humidity close to the deliquescence relative humidity).

Intra‐annual variation of the calcite deposition rate of drip water in Shihua Cave, Beijing, China and its implications for palaeoclimatic reconstructions

Abstract: Monthly in situ monitoring of the calcite deposition rate, drip-water chemistry and surrounding cave environment was carried out at Shihua Cave, Beijing, China, through two hydrological years (from January 2006 to February 2008) to determine the seasonal variability and mechanisms of stalagmite growth in Shihua Cave. Calcite deposition rates exhibit significant intra-annual variation, with the lowest values during the summer monsoonal rainy season (July-August) and peak values from autumn to spring. The temporal change in the calcite deposition rate is negatively correlated with the drip rate, cave-air PCO(2) (CO(2) partial pressure) and Ca concentration, and positively correlated with the pH of the feeding drip water. The seasonal recharge regime of drip water is likely to be the primary control on the drip-water quality and quantity, which, in turn, control the calcite deposition rate in Shihua Cave. During the summer rainy season, periodic and intense rainstorms increase the drip rate and cave-air PCO(2), leading to drip water with a lower pH and saturation index of calcite, thereby reducing the calcite precipitation. It seems that the high cave-air PCO(2) is the dominant control on the calcite deposition rate during the rainy season. Our previous study on the dissolved organic carbon of drip water concluded that the thin luminescent bands in stalagmite laminae from Shihua Cave form during the rainy season. The lower calcite deposition rate during the rainy season further supports this suggestion. The significant intra-seasonal variability of the calcite deposition rate implies that the seasonal bias of delta(18)O of stalagmites should be considered when stalagmite delta(18)O is used as a high-resolution palaeoclimatic archive.

Milankovitch‐paced Termination II in a Nevada speleothem?

Abstract: [1] The Devils Hole (DH) calcite record from the Great Basin, Nevada, provided the first radiometrically dated time series of late-Pleistocene climate fluctuations, In doing so, DH suggested that the penultimate deglaciation, Termination II (T-II), occurred at 142 ± 3 ka, which is ∼10 kyr before the associated rise in summer insolation, helping to launch the “causality problem” for Milankovitch The interpretation of the DH record has been subject to considerable discussion ever since We present the first attempt to reproduce the DH record of an early T-II in the Great Basin based on a stalagmite from Lehman Caves, Nevada, which is ∼400 km northeast of Devils Hole Our speleothem records at least the latter part of T-II over its period of growth from ∼133–129 ka, which appears to disagree with the early timing of T-II in DH DH also exhibits important differences from many other paleoclimate records over the past two deglaciations, though these are reduced somewhat after ice-volume correcting DH δ18O We suggest that the climatic signal in the DH record remains to be fully explained