Similar morphological and chemical variations of Gloeocapsomorpha prisca in Ordovician sediments and cultured Botryococcus braunii as a response to changes in salinity     

S. Derenne  P. Metzger  C. Largeau  P.F. Van Bergen  J.P. Gatellier  J.S. Sinninghe Damst  J.W. de Leeuw  C. Berkaloff 《Organic Geochemistry》1992,19(4-6)

Most Ordovician source rocks consist of accumulation of a colonial marine microorganism, Gloeocapsomorpha prisca (G. prisca) whose nature, ecology and affinity with extant organisms have been in dispute for years. Furthermore, recent studies have shown major differences in phenol moieties between two G. prisca-rich samples. Examination of five G. prisca-rich kerogens by electron microscopy and pyrolysis studies revealed (i) the occurrence of two markedly distinct “morpho/chemical” types: a “closed/phenol-rich” type (Baltic samples) and an “open/phenol-poor” one (North American samples) and (ii) the selective preservation of the resistant micromolecular material building up the thick cell walls in the original organism. Comparison with extant Botryococcus braunii (a widespread green microalga) grown on media of increasing salinity suggests that G. prisca is likely to be a planktonic green microalga related to B. braunii, which can adapt to large salinity variations which, in turn, control its polymorphism. The large differences in colony morphology and in the content of phenol moieties observed in fossil G. prisca and the resulting occurrence of two “morpho/chemical” types, should therefore reflect depositional environments with different salinities. The presence of thick, highly aliphatic, resistant walls in G. prisca selectively preserved during fossilization, accounts for the major contribution of this organism to Ordovician organic-rich sediments and for the resulting typical signature of Ordovician oils.  相似文献   

Aqueous Phase Reaction of HNO4: The Impact on Tropospheric Chemistry     

Frank Dentener  Jason Williams  Swen Metzger 《Journal of Atmospheric Chemistry》2002,41(2):109-133

We use a global atmospheric chemistry transport model to study the possible influence of aqueous phase reactions of peroxynitric acid (HNO₄) on the concentrations and budgets of NO_x, SO_x, O₃ and H₂O₂. Laboratory studies have shown that the aqueous reaction of HNO_4aq withHSO^– _3aq, and the uni-molecular decomposition of the NO₄ ^– anion to form NO₂ ^– (nitrite) occur on a time scale of about a second. Despite a substantial contribution of the reaction of HSO^– _3aq with HNO_4aq to the overall in-cloud conversion of SO₂ to SO₄ ^2–, a simultaneous decrease of other oxidants (most notably H₂O₂) more than compensated the increase in SO₄ ^2– production. The strongest influence of heterogeneous HNO₄ chemistry was found in the boundary layer, where calculated monthly average ozone concentrations were reduced between 2% to 10% andchanges of H₂O₂ between –20% to +10%compared to a simulation which ignores this reaction. Furthermore, SO₂ was increased by 10% to 20% and SO₄ ^2–depleted by up to 10%. Since the resolution of our global model does not enable a detailed comparison with measurements in polluted regions, it is not possible to verify whether considering heterogeneous HNO₄ reactions results in a substantial improvement of atmospheric chemistry transport models. However, the conversion of HNO₄ in the aqueous phase seems to be efficient enough to warrant further laboratory investigations and more detailed model studies on this topic.  相似文献   

Radiocarbon calibration beyond 20,000 C yr B.P. by means of planktonic foraminifera of the Iberian Margin     

Edouard Bard  Frauke Rostek  Guillemette Ménot-Combes 《Quaternary Research》2004,61(2):204-214

We present a new set of ¹⁴C ages obtained by accelerator mass spectrometry (AMS) on planktonic foraminifera from a deep-sea core collected off the Iberian Margin (MD952042). This site, at 37°N, is distant from the high-latitude zones where ¹⁴C reservoir age is large and variable. Many independent proxies — alkenones, magnetic susceptibility, ice-rafted debris, foraminifera stable isotopes, abundances of foraminifera, pollen, and dinoflagellates — show abrupt changes correlative with Dansgaard-Oeschger and Heinrich events of the last glacial period. The good stratigraphic agreement of all proxies — from the fine to the coarse-size fractions — indicates that the foraminifera ¹⁴C ages are representative of the different sediment fractions. To obtain reliable ¹⁴C ages of foraminifera beyond 20,000 ¹⁴C yr B.P., we leached the shells prior to carbonate hydrolysis and subsequent analysis. For a calendar age scale, we matched the Iberian Margin U₃₇^K′ profile with that of Greenland Summit δ¹⁸O. Both are proxies for temperature, which in models varies synchronously in the two areas. The match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points. Except for ages older than 40,000 ¹⁴C yr B.P., Greenland's GISP2 and GRIP records yield similar calendars. The ¹⁴C and imported calendar ages of the Iberian Margin record are then compared to data — from lacustrine annual varves and from corals and speleothems dated by U-Th — previously used to extend the calibration beyond 20,000 ¹⁴C yr B.P. The new record follows a smooth pattern between 23,000 and 50,000 cal yr B.P. We find good agreement with the previous data sets between 23,000 and 31,000 cal yr B.P. In the interval between 33,000 and 41,000 cal yr B.P., for which previous records disagree by up to 5000 cal yr, the Iberian Margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the Lake Suigetsu and the Bahamian speleothem data sets.  相似文献   

Sea-level estimates during the last deglaciation based on δO and accelerator mass spectrometry C ages measured in Globigerina bulloides     

Edouard Bard  Richard Fairbanks  Maurice Arnold  Pierre Maurice  Josette Duprat  Jean Moyes  Jean-Claude Duplessy 《Quaternary Research》1989,31(3)

Coupled measurements of δ¹⁸O and accelerator mass spectrometry (AMS) ¹⁴C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by δ¹⁸O measurements of modern shells (core tops, plankton tows). Isotopic (δ¹⁸O, AMS-¹⁴C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas of the last deglaciation. Based upon Globigerina bulloides data, four δ¹⁸O-based sea-level estimates were calculated: −67 ± 7 m at 12,200 yr B.P. and −24 ± 8 m at about 8200 yr B.P. for core SU 81-18; −83 ± 10 m at 12,200 yr B.P. and −13 ± 11 m at about 8500 yr B.P. for core SU 81-14. Using a second working hypothesis concerning the seasonability of G. bulloides growth, it is suggested that the sea-level rose by about 40 m during the millennium which followed 14,500 yr B.P.  相似文献   

Using a maximum simplicity paleoclimate model to simulate millennial variability during the last four glacial periods     

Mark Siddall  Thomas F. Stocker  Thomas Blunier  Renato Spahni  Jerry F. McManus  Edouard Bard 《Quaternary Science Reviews》2006,25(23-24):3185

Many studies have documented the existence of millennial-scale variability in the Earth system during the last glacial period. An increasing number of studies document the occurrence of similar millennial variability during glacial periods previous to the last one. Here we use the simplest possible thermal-bipolar seesaw model to consider this variability for the last four glacial periods. We invert this model and use the high-pass filtered Vostok stable isotope records to make a first, tentative, attempt to estimate high-latitude N. Hemisphere temperature variability over the last four glacial periods, beyond the reach of Greenland ice-core records. The model result is compared against the Vostok methane record, which shows rapid variations in parallel to Greenland temperature records during the last glacial period. A further comparison is carried out against the planktonic oxygen isotope of north Atlantic core ODP 980. There is agreement between the records on the existence of similar millennial-scale variability during the last three glacial periods with very similar characteristics to the variability during the last glacial cycle.  相似文献   

Sources of high-chloride water and managed aquifer recharge in an alluvial aquifer in California,USA     

David R. O’Leary  John A. Izbicki  Loren F. Metzger 《Hydrogeology Journal》2015,23(7):1515-1533

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Corrosion of cast iron pipelines buried in Fraser River silt subject to climate-induced moisture variations     

Azoor  Rukshan  Asselin  Edouard  Deo  Ravin  Kodikara  Jayantha  Wijewickreme  Dharma 《Acta Geotechnica》2021,16(3):873-884

Acta Geotechnica - Experiments were carried out to characterise the influence of soil water retention properties on the corrosion of a cast iron specimen buried in Fraser River silt. The corrosion...  相似文献   

Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)     

George W. Luther III  Brian T. Glazer  Shufen Ma  Robert E. Trouwborst  Tommy S. Moore  Edouard Metzger  Chareonkwan Kraiya  Tim J. Waite  Gregory Druschel  Bjrn Sundby  Martial Taillefert  Donald B. Nuzzio  Timothy M. Shank  Brent L. Lewis  Paul J. Brendel 《Marine Chemistry》2008,108(3-4):221-235

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.  相似文献   

Simulated and observed circulation in the Indonesian Seas: 1/12° global HYCOM and the INSTANT observations     

E.J. Metzger  H.E. Hurlburt  X. Xu  Jay F. Shriver  A.L. Gordon  J. Sprintall  R.D. Susanto  H.M. van Aken 《Dynamics of Atmospheres and Oceans》2010

A 1/12° global version of the HYbrid Coordinate Ocean Model (HYCOM) using 3-hourly atmospheric forcing is analyzed and directly compared against observations from the International Nusantara STratification ANd Transport (INSTANT) program that provides the first long-term (2004–2006) comprehensive view of the Indonesian Throughflow (ITF) inflow/outflow and establishes an important benchmark for inter-basin exchange, including the net throughflow transport. The simulated total ITF transport (−13.4 Sv) is similar to the observational estimate (−15.0 Sv) and correctly distributed among the three outflow passages (Lombok Strait, Ombai Strait and Timor Passage). Makassar Strait carries ∼75% of the observed total ITF inflow and while the temporal variability of the simulated transport has high correlation with the observations, the simulated mean volume transport is ∼37% too low. This points to an incorrect partitioning between the western and eastern inflow routes in the model and is the largest shortcoming of this simulation. HYCOM simulates the very deep (>1250 m) overflow at Lifamatola Passage (−2.0 Sv simulated vs. −2.5 Sv observed) and indicates overflow contributions originating from the North (South) Equatorial Current in boreal winter–spring (summer–autumn). A new finding of INSTANT is the mean eastward flow from the Indian Ocean toward the interior Indonesian Seas on the north side of Ombai Strait. This flow is not robustly simulated at 1/12° resolution, but is found in a 1/25° version of global HYCOM using climatological forcing, indicating the importance of horizontal resolution. However, the 1/25° model also indicates that the mean eastward flow retroflects, turning back into the main southwestward Ombai Strait outflow, and in the mean does not enter the interior seas to become part of the water mass transformation process. The 1/12° global HYCOM is also used to fill in the gaps not measured as part of the INSTANT observational network. It indicates the wide and shallow Java and Arafura Seas carry −0.8 Sv of inflow and that the three major outflow passages capture nearly all the total Pacific to Indian Ocean throughflow.  相似文献   

The local impacts of climate change in the Ferlo, Western Sahel     

Lars Hein  Marc J. Metzger  Rik Leemans 《Climatic change》2009,93(3-4):465-483

Recent increases in the accuracy of climate models have enhanced the possibilities for analyzing the impacts of climate change on society. This paper explores how the local, economic impacts of climate change can be modeled for a specific eco-region, the Western Sahel. The people in the Sahel are highly dependent on their natural resource base, and these resources are highly vulnerable to climate change, in particular to changes in rainfall. Climate models project substantial changes in rainfall in the Sahel in the coming 50 years, with most models predicting a reduction in rainfall. To connect climate change to changes in ecosystem productivity and local income, we construct an ecological–economic model that incorporates rangeland dynamics, grazing and livestock prices. The model shows that decreased rainfall in the Sahel will considerably reduce local incomes, in particular if combined with increases in rainfall variability. Adaptation to these climate change projections is possible if reductions in rainfall are followed by destocking to reach efficient grazing levels. However, while such a strategy is optimal from the perspective of society, the stocking rate is determined by individual pastoralists that face few incentives to destock.  相似文献