Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central–Southern Italy)     

Jacopo Cabassi  Franco Tassi  Orlando Vaselli  Jens Fiebig  Matteo Nocentini  Francesco Capecchiacci  Dmitri Rouwet  Gabriele Bicocchi 《Bulletin of Volcanology》2013,75(1):1-19

This paper focuses on the chemical and isotopic features of dissolved gases (CH₄ and CO₂) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH₄ and CO₂. The δ¹³C-CH₄ and δD-CH₄ values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH₄ is mainly produced by microbial activity. The δ¹³C-CO₂ values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO₂ contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO₂ source feeding the regional thermal and cold CO₂-rich fluid emissions. In contrast, the relatively low δ¹³C-CO₂ values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO₂. Chemical and isotopic compositions of dissolved CO₂ and CH₄ at different depths are mainly depending on (1) CO₂ inputs from external sources (hydrothermal and/or anthropogenic); (2) CO₂–CH₄ isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO₂ and CH₄ concentrations. In the hypolimnion, where the δ¹³C-CO₂ values progressively increase with depth and the δ¹³C-CH₄ values show an opposite trend, biogenic CO₂ production from CH₄ using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ¹³C-CO₂ values, and measured δ¹³C_TDIC values are not consistent, indicating that CO₂ and the main carbon-bearing ion species (HCO₃ ^?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO₂ and CH₄. This study demonstrates that the vertical patterns of the CO₂/CH₄ ratio and of δ¹³C-CO₂ and δ¹³C-CH₄ are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO₂ input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.  相似文献   

Seasonality in the North Sea during the Allerød and Late Medieval Climate Optimum using bivalve sclerochronology     

Bernd R. Schöne  Jens Fiebig 《International Journal of Earth Sciences》2009,98(1):83-98

Seasonal temperature patterns may have changed through time in response to current global warming. However, the temporal resolution of available proxy records is not sufficient to quantify paleotemperature seasonality prior to anthropogenic forcing of the climate. In the present study, we reconstructed seasonal and inter-annual temperature patterns of the North Sea during the last 140 years, the Allerød Interglacial and the Late Medieval Climate Optimum using sclerochronological and δ¹⁸O_aragonite data from bivalve shells, Arctica islandica. On average, the climate during 1278–1353 AD was ca. 1.1°C colder and seasonality was ca. 60% less than today. During the Allerød, long-term temperatures remained about 3.2°C below present values, and absolute summer and winter anomalies were ca. ?4 and ?2.7°C, respectively. However, seasonality was statistically indistinguishable from today. Long-term average temperatures compare well with existing data for the Late Medieval and Allerød, but detailed information on seasonality during the studied time intervals has never been presented before. Our data also demonstrated that annual instrumental and δ¹⁸O_aragonite-derived temperatures did not always match. This difference is explained by (1) NAO-driven salinity changes, which influence the temperature estimation from δ¹⁸O_aragonite and (2) food-driven changes in growth rates; portions of the shell that formed more rapidly are overrepresented in carbonate samples. Our study indicated that individual bivalve shells can open discrete, near-century long, ultra-high-resolution windows into the climate past. Such information can be vital for testing and verifying numerical climate models.  相似文献   

Re‐interpretation of the Meikirch pollen record,Swiss Alpine Foreland,and implications for Middle Pleistocene chronostratigraphy     

Frank Preusser  Ruth Drescher‐Schneider  Markus Fiebig  Christian Schlüchter 《第四纪科学杂志》2005,20(6):607-620

The Meikirch drilling site in the Swiss Midlands north of Bern is re‐interpreted using a combination of sedimentological logging, pollen analyses and luminescence dating. The sedimentary sequence comprises about 70 m of lacustrine deposits, overlain by about 39 m of coarse glacial outwash interpreted to represent at least two independent ice advances. Pollen analyses of the apparently complete limnic sequence reveal a basal late glacial period followed by three warm phases that are interrupted by two stadial periods (Meikirch complex). The warm periods were previously correlated with the Holsteinian and Eemian Interglacials. According to luminescence dating, and with consideration of evidence for Middle Pleistocene climate patterns at other central European sites, a correlation of the Meikirch complex with marine isotope stage (MIS) 7 is now proposed. If this correlation is correct, it implies the presence of three intervals with interglacial character during MIS 7. However, the late Middle Pleistocene vegetational features of the Meikirch complex show significant differences when compared with the pollen record from the Velay region, central France. Possible explanations for this discrepancy are distinct Middle Pleistocene patterns of atmospheric circulation over central Europe and a different distribution of vegetation refugia compared to the Eemian Interglacial and the Holocene. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Model Simulations of the Boundary-Layer Evolution over an Arid Andes Valley   总被引：1，自引：1，他引：0  

Inge Bischoff-Gauß  Norbert Kalthoff  Samiro Khodayar  Melitta Fiebig-Wittmaack  Sonia Montecinos 《Boundary-Layer Meteorology》2008,128(3):357-379

The boundary layer of the Elqui valley in the arid north of Chile exhibits several interesting phenomena, such as a very shallow convective boundary layer (CBL) during the day. In the morning, warming is observed in and above the CBL, while the humidity decreases in the CBL. At midday, in and above the CBL of the valley, the temperature stagnates. In the afternoon in the CBL the temperature decreases and humidity increases, although the latent heat flux is very low. Because the characteristic features of the valley atmosphere are hard to interpret from observations alone, model simulations were applied. The simulations indicate that all components of the budget equations, i.e. the turbulent flux divergences, advection via the sea breeze, the upvalley and upslope wind systems, as well as subsidence, contribute to the evolution of the valley atmosphere.  相似文献   

Further Characterisation of the 91500 Zircon Crystal   总被引：28，自引：2，他引：28  

Michael Wiedenbeck  John M. Hanchar  William H. Peck  Paul Sylvester  John Valley  Martin Whitehouse  reas Kronz  Yuichi Morishita  Lutz Nasdala  J. Fiebig  I. Franchi  J.-P. Girard  R.C. Greenwood  R. Hinton  N. Kita  P.R.D. Mason  M. Norman  M. Ogasawara  P.M. Piccoli  D. Rhede  H. Satoh  B. Schulz-Dobrick  O. Skår  MJ. Spicuzza  K. Terada  A. Tindle  S. Togashi  T. Vennemann  Q. Xie  Y.-F. Zheng 《Geostandards and Geoanalytical Research》2004,28(1):9-39

This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses.  相似文献   

ENSO-coupled precipitation records (1959–2004) based on shells of freshwater bivalve mollusks (<Emphasis Type="Italic">Margaritifera falcata</Emphasis>) from British Columbia     

Bernd R. Schöne  Nicholas A. Page  David L. Rodland  Jens Fiebig  Sven Baier  Samuli O. Helama  Wolfgang Oschmann 《International Journal of Earth Sciences》2007,96(3):525-540

We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ ¹⁸O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available.  相似文献   

Natural evidence for rapid abiogenic hydrothermal generation of CH₄   总被引：1，自引：0，他引：1  

Jens Fiebig  Alan B. Woodland 《Geochimica et cosmochimica acta》2007,71(12):3028-3039

Although recent hydrothermal experiments imply that abiogenic methane (CH₄) generation from hydrothermal reduction of CO₂ can occur, evidence from natural systems was still lacking. Based on the chemical and isotopic equilibrium signatures of low-temperature fumarolic gas discharges, we are able to provide hard evidence for its natural occurrence, namely in three subduction-related bi-phase hydrothermal systems of the Mediterranean, whose temperatures range from 260 to 470 °C. The attainment of equilibrium and the time spans of recent volcanic dormancy allowed us to calculate minimum rates for chemical and isotopic equilibration. These are significantly higher than those previously reported and might be due to the presence of a saturated water vapor phase in the investigated systems. The fact that nature provides conditions enabling relatively fast production of hydrocarbons from CO₂ strongly supports the concerns that were recently raised from laboratory experiments. These address the use of the carbon isotope composition of reduced carbon in Archean sediments as a tracer of early life and the occurrence of CH₄ on extraterrestrial planets as a bioindicator. In view of the potential role of abiogenic CH₄ as a precursor of life, we also present an estimate of abiogenic hydrothermal CH₄ fluxes throughout the Archean. It is not expected that these fluxes exceeded 80 Mt/yr during the past 4.0 Ga. This, however, would have been enough to facilitate HCN production on the prebiotic Earth.  相似文献   

Luminescence dating of historical fluvial deposits from the Danube and Ebro     

Markus Fiebig  Frank Preusser  Damian Steffen  Edit Tham‐Bozs  Michael Grabner  Georg J. Lair  Martin H. Gerzabek 《Geoarchaeology》2009,24(2):224-241

The validity of optically stimulated luminescence (OSL) has been tested on known‐age (historical) fluvial deposits along the rivers Danube (Austria) and Ebro (Spain). As partial bleaching of the OSL signal prior to deposition can interfere with correct age estimates, different approaches to extracting the dose accumulated during burial are compared. Using the finite mixture model gave OSL ages that are internally as well as stratigraphically consistent and in agreement with independent age control. According to these results, fluvial deposition at the Danube River study site can be attributed to different periods ranging from Bronze Age to the 18th century A.D. Fluvial deposits of Roman age and of the late 17th or early 18th century A.D. were found at the Ebro River study site. This is consistent with the morphological subdivision of the valleys and encourages further investigation of the fluvial and archaeological history of the study areas using OSL. © 2009 Wiley Periodicals, Inc.  相似文献