The Austin Chalk-Taylor Clay succession in Texas and the Santonian-Campanian boundary     

P. Marks  B. Stam 《Cretaceous Research》1983,4(3):271-279

Re-evaluation of samples from several Texas localities over the Austin Chalk-Taylor Clay boundary for planktic Foraminifera, and comparison with recent work on European and North African successions confirms the general correlation of the Texan formations with the European Stage succession. The sedimentary hiatus indicated by Pessagno (1967) does not appear to be present: the Late Santonian-Early Campanian zonal marker Globigerinita elevata (Brotzen) occurs in the Lower Taylor Clay associated with late representatives of Marginotruncana. The Lower Taylor Clay may belong to the Late Santonian in some localities.  相似文献   

Declining Temporal Effectiveness of Carbon Sequestration: Implications for Compliance with the United National Framework Convention on Climate Change     

L. D. Danny Harvey 《Climatic change》2004,63(3):259-290

Carbon sequestration is increasingly being promoted as a potential response to the risks of unrestrained emissions of CO₂, either in place of or as a complement to reductions in the use of fossil fuels. However, the potential role of carbon sequestration as an (at-least partial) substitute for reductions in fossil fuel use can be properly evaluated only in the context of a long-term acceptable limit (or range of limits) to the increase in atmospheric CO₂ concentration, taking into account the response of the entire carbon cycle to artificial sequestration. Under highly stringent emission-reduction scenarios for non-CO₂ greenhouse gases, 450 ppmv CO₂ is the equivalent, in terms of radiative forcing of climate,to a doubling of the pre-industrial concentration of CO₂. It is argued in this paper that compliance with the United Nations Framework Convention on Climate Change (henceforth, the UNFCCC) implies that atmospheric CO₂ concentration should be limited, or quickly returned to, a concentration somewhere below 450 ppmv. A quasi-one-dimensional coupled climate-carbon cycle model is used to assess the response of the carbon cycle to idealized carbon sequestration scenarios. The impact on atmospheric CO₂ concentration of sequestering a given amount of CO₂ that would otherwise be emitted to the atmosphere, either in deep geological formations or in the deep ocean, rapidly decreases over time. This occurs as a result of a reduction in the rate of absorption of atmospheric CO₂ by the natural carbon sinks (the terrestrial biosphere and oceans) in response to the slower buildup of atmospheric CO₂ resulting from carbon sequestration. For 100 years of continuous carbon sequestration, the sequestration fraction (defined as the reduction in atmospheric CO₂ divided by the cumulative sequestration) decreases to 14% 1000 years after the beginning of sequestration in geological formations with no leakage, and to 6% 1000 years after the beginning of sequestration in the deep oceans. The difference (8% of cumulative sequestration) is due to an eflux from the ocean to the atmosphere of some of the carbon injected into the deep ocean.The coupled climate-carbon cycle model is also used to assess the amount of sequestration needed to limit or return the atmospheric CO₂ concentration to 350–400 ppmv after phasing out all use of fossil fuels by no later than 2100. Under such circumstances, sequestration of 1–2 Gt C/yr by the latter part of this century could limit the peak CO₂ concentration to 420–460 ppmv, depending on how rapidly use of fossilfuels is terminated and the strength of positive climate-carbon cycle feedbacks. To draw down the atmospheric CO₂ concentration requires creating negative emissions through sequestration of CO₂ released as a byproduct of the production of gaseous fuels from biomass primary energy. Even if fossil fuel emissions fall to zero by 2100, it will be difficult to create a large enough negative emission using biomass energy to return atmospheric CO₂ to 350 ppmv within 100 years of its peak. However, building up soil carbon could help in returning CO₂ to 350 ppmv within 100 years of its peak. In any case, a 100-year period of climate corresponding to the equivalent of a doubled-CO₂ concentration would occur before temperatures decreased. Nevertheless, returning the atmospheric CO₂concentration to 350 ppmv would reduce longterm sea level rise due to thermal expansion and might be sufficient to prevent the irreversible total melting of the Greenland ice sheet, collapse of the West Antarctic ice sheet, and abrupt changes in ocean circulation that might otherwise occur given a prolonged doubled-CO₂ climate. Recovery of coral reef ecosystems, if not already driven to extinction, could begin.  相似文献   

Endpiece: mapping changes and the 2001 census for the UK     

Bethan Thomas  Danny Dorling 《Area》2004,36(2):xxiii-xxxvi

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Fluid–rock interaction in autoliths of agpaitic nepheline syenites in the Ilímaussaq intrusion, South Greenland     

Johannes Schnenberger  Michael Marks  Thomas Wagner  Gregor Markl 《Lithos》2006,91(1-4):331-351

Within the 1.16 Ga old Ilímaussaq intrusion, up to 700 m large autoliths occur in one stratigraphic unit of the layered floor series of agpaitic nepheline syenites (kakortokites). These autoliths consist of two different rock types: augite syenite and naujaite (agpaitic nepheline syenite). All three rock types show a number of alteration features related to the entrapment of the autoliths in the kakortokite magma caused by the interaction with a fluid phase.

In the kakortokites, the oxidation of primary arfvedsonite to aegirine and fluorite is restricted to the close proximity to the autoliths. Close to the surrounding kakortokite, the primary mafic phases of the augite syenites (augite, fayalite, Fe–Ti oxides) are completely replaced by arfvedsonite, aenigmatite, biotite, aegirine and fluorite. The decomposition of primary hastingsite to spectacular aegirine–augite–nepheline–aenigmatite symplectites can be observed up to several meters inside the autoliths. Additionally, fluorite formed at grain boundaries of primary nepheline. In the naujaite autoliths, primary arfvedsonite is replaced by aegirine–biotite intergrowths and abundant aenigmatite is occasionally replaced by Ti-rich aegirine and Fe–Ti oxides.

The mineral reactions in the autoliths are used to decipher details of the late to post-magmatic processes in a peralkaline syenitic intrusion. Mineral equilibria record an evolution governed by falling temperature (620 to ca. 500 °C) and increasing relative oxygen fugacity from FMQ + 1 to above FMQ + 4. Quantification of the observed mineral reactions reveals the infiltration of the autoliths with an oxidizing fluid phase rich in Na and F and minor addition of K. Volatiles (H and F) and in some cases also Fe, Ti and Ca (± Mg) released from primary autolith phases were mainly just relocated within the autoliths.  相似文献   

Combining Ring Width, Density and Stable Carbon Isotope Proxies to Enhance the Climate Signal in Tree-Rings: An Example from the Southern French Alps   总被引：1，自引：0，他引：1  

Mary Gagen  Danny McCarroll  Jean-Louis Edouard 《Climatic change》2006,78(2-4):363-379

At present the most powerful tree-ring based climate reconstructions use high numbers of growth proxy series (ring width and density) to produce spatially smoothed estimates, such as average Northern Hemisphere summer temperatures. These single parameter reconstructions might be supplemented with regional climate reconstructions capable of capturing variability in more than one climate variable without lower replication compromising statistical quality, if multiple tree ring proxies were used. Pinus sylvestris and Pinus uncinata latewood density, width and δ¹³C series are presented from two sites in the French subalpine zone, east of Briançon. Where two proxies have the same dominant climate control their combination enhances that signal. Where proxies differ in dominant controlling climate variable, combining series allows access to bi-variable calibrations. Using this approach, multi-proxy reconstructions of both temperature and precipitation would better reflect complex synoptic variability in climate on spatially useful scales.  相似文献   

On the role of high latitude ice,snow, and vegetation feedbacks in the climatic response to external forcing changes     

L. D. Danny Harvey 《Climatic change》1988,13(2):191-224

A seasonal energy balance climate model containing a detailed treatment of surface and planetary albedo, and in which seasonally varying land snow and sea ice amounts are simulated in terms of a number of explicit physical processes, is used to investigate the role of high latitude ice, snow, and vegetation feedback processes. Feedback processes are quantified by computing changes in radiative forcing and feedback factors associated with individual processes. Global sea ice albedo feedback is 5–8 times stronger than global land snowcover albedo feedback for a 2% solar constant increase or decrease, with Southern Hemisphere cryosphere feedback being 2–5 times stronger than Northern Hemisphere cryosphere feedback.In the absence of changes in ice extent, changes in ice thickness in response to an increase in solar constant are associated with an increase in summer surface melting which is exactly balanced by increased basal winter freezing, and a reduction in the upward ocean-air flux in summer which is exactly balanced by an increased flux in winter, with no change in the annual mean ocean-air flux. Changes in the mean annual ocean-air heat flux require changes in mean annual ice extent, and are constrained to equal the change in meridional oceanic heat flux convergence in equilibrium. Feedback between ice extent and the meridional oceanic heat flux obtained by scaling the oceanic heat diffusion coefficient by the ice-free fraction regulates the feedback between ice extent and mean annual air-sea heat fluxes in polar regions, and has a modest effect on model-simulated high latitude temperature change.Accounting for the partial masking effect of vegetation on snow-covered land reduces the Northern Hemisphere mean temperature response to a 2% solar constant decrease or increase by 20% and 10%, respectively, even though the radiative forcing change caused by land snowcover changes is about 3 times larger in the absence of vegetational masking. Two parameterizations of the tundra fraction are tested: one based on mean annual land air temperature, and the other based on July land air temperature. The enhancement of the mean Northern Hemisphere temperature response to solar constant changes when the forest-tundra ecotone is allowed to shift with climate is only 1/3 to 1/2 that obtained by Otterman et al. (1984) when the mean annual parameterization is used here, and only 1/4 to 1/3 as large using the July parameterization.The parameterized temperature dependence of ice and snow albedo is found to enhance the global mean temperature response to a 2% solar constant increase by only 0.04 °C, in sharp contrast to the results of Washington and Meehl (1986) obtained with a mean annual model. However, there are significant differences in the method used here and in Washington and Meehl to estimate the importance of this feedback process. When their approach is used in a mean annual version of the present model, closer agreement to their results is obtained.  相似文献   

Erratum to Antonio C. Lasaga, Danny M. Rye, Andreas Lüttge, and Edward W. Bolton (2001), “Calculation of fluid fluxes in earth’s crust,” geochimica et cosmochimica acta65, 1161-1185.     

Danny M Rye  Andreas Lüttge 《Geochimica et cosmochimica acta》2003,67(9):1755

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Linking censuses through time: problems and solutions   总被引：1，自引：0，他引：1  

David Martin  Danny Dorling  & Richard Mitchell 《Area》2002,34(1):82-91

This paper reviews the difficulties encountered when attempting to study social change by comparing data from successive censuses, and describes a system designed to provide integrated online access to data from the 1971, 1981 and 1991 Censuses in Great Britain at http://census.ac.uk/cdu/lct/.  相似文献   

Sodic Pyroxene and Sodic Amphibole as Potential Reference Materials for In Situ Lithium Isotope Determinations by SIMS     

Michael A.W. Marks  Roberta L. Rudnick  Thomas Ludwig  Horst Marschall  Thomas Zack  Ralf Halama  William F. McDonough  Detlef Rost  Thomas Wenzel  Edward P. Vicenzi  Ivan P. Savov  Rainer Altherr  Gregor Markl 《Geostandards and Geoanalytical Research》2008,32(3):295-310

Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilímaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro‐drilled material analysed by MC‐ICP‐MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 ± 51 μg g^?1 (2s, n = 69, MC‐ICP‐MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 ± 3.6 μg g^?1 (2s, n = 33) as determined by SIMS. The seven micro‐drilled regions measured by solution MC‐ICP‐MS returned slightly lower concentrations (41–46 μg g^?1), but still overlap with the SIMS data within uncertainty. Based on MC‐ICP‐MS and SIMS analyses, the variation in δ⁷Li was about 1‰ in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC‐ICP‐MS and SIMS. The latter deviated from the MC‐ICP‐MS results by ?6.0 ± 1.9‰ (2s) for the amphibole and by ?3.9 ± 1.9‰ (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC‐ICP‐MS results, mean δ⁷Li values of +0.7 ± 1.2‰ (2s, n = 10) for the arfvedsonite crystal and of ?3.7 ± 1.2‰ (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request.  相似文献   

Pleistocene river systems in the southern peribaltic area as indication of interglacial sea level changes in the Baltic Basin     

Leszek Marks   《Quaternary International》2005,130(1):43

The modern drainage system of central Poland developed during the Holsteinian, but it originated from the Elsterian glacial tunnel valleys and deglacial residual overflow lakes. In spite of occupation of this area by the Wartanian ice sheet and the following formation of the landscape during deglaciation, a similar river network was renewed during the Eemian. During the Weichselian the Middle Vistula valley was subjected to widespread ice-dam deposition. This resulted in rise of the base level of erosion and in westward deflection of the runoff, connected with development of the Central European spillways. The presented reconstruction of the Middle and Late Pleistocene fluvial network shows that the Holstein and Eemian sea levels were the driving force for river system development in central Poland. The Holstein and Eemian sea levels were very close to the present water level of the Baltic Sea. They made interglacial fluvial patterns roughly similar to the contemporary one, and therefore the main watersheds have been only slightly modified since that time. However, due to the considerable southward extension of the sea during the Eemian and presumably also during the Holsteinian, buried interglacial river deposits in central Poland occur at present well beneath the Holocene alluvia.  相似文献