bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of the nitric acid to NOx ratio in the troposphere
Authors: Huebert B. J. , Vanbramer S. E. , Lebel P. J. , Vay S. A. , Torres A. L. , Schiff H. I. , Hastie D. , Hubler G. , Bradshaw J. D. , Carroll M. A. , Davis D. D. , Ridley B. A. , Rodgers M. O. , Sandholm S. T. , Dorris S.
Published: February 2008

Nitric acid concentrations, measured by both teflon/nylon filter packs (FP) and the tungstic oxide denuder (DEN), are compared with the average NOx concentrations from laser‐induced fluorescent and chemiluminescent methods. The HNO3/NOx ratio based on filter packs ranged from 0.8 to 10.4, with a mean of 3.4. The DEN nitric acid concentrations produced ratios ranging from <0.3 to 9.8, with a mean of 2.6. Average marine ratios were larger than those from continental regions, in part due to continental anthropogenic sources of NOx. Although we collected very few boundary layer samples, their average ratios were smaller than those in the free troposphere, apparently because of the effect of dry surface removal of nitric acid. The nitric acid to NOx ratio was greatest when the NOx/NOy ratio was smallest, such that the nitrogen photochemistry was nearing completion.
Aircraft measurements of NOx over the eastern Pacific and continental United States and implications for ozone production
Authors: Carroll M. A. , Hastie D. R. , Ridley B. A. , Rodgers M. O. , Torres A. L. , Davis D. D. , Bradshaw J. D. , Sandholm S. T. , Schiff H. I. , Karecki D. R. , Harris G. W. , Mackay G. I. , Gregory G. L. , Condon E. P. , Trainer M. , Hubler G. , Montzka D. D. , Madronich S. , Albritton D. L. , Singh H. B. , Beck S. M. , Shipham M. C. , Bachmeier A. S.
Published: February 2008

Measurements of NO, NO2, O3, and CO are presented from 13 aircraft flights made over the eastern Pacific Ocean and the continental United States in August and September 1986 during the NASA GTE/CITE 2 program. Measurements of NO by three different groups (two different techniques) and of NO2 by three different groups (three different techniques) are presented and examined along with calculated NOx (NO+NO2) for correlations with O3, CO, and dew‐point temperature (DPT) primarily as a function of air mass category. Median values of NO and NO2 in the marine boundary layer were 4.0 and 10.4 pptv, respectively, and 12.4 and 18.0 pptv in the marine free troposphere. In the continental boundary layer, median values of NO and NO2 were 34.5 and 75.0 pptv, respectively, and 13.0 and 36.0 pptv at altitudes above 3 km in air masses having continental influence. In the maritime NOx data set a negative correlation is often observed between NOx and DPT, while positive correlations were typically observed between NOx and O3 and between NOx and CO. As expected, then, negative correlations were often observed between O3 and DPT and between CO and DPT, along with positive correlations between CO and O3. In the continental data set, positive correlations were typically observed between NOx and DPT, O3, and CO. Additionally, the various air masses were examined with respect to regions of net ozone production or net ozone destruction. In all but one case in the marine boundary layer, model calculations indicate that there is significant ozone destruction. In the continental boundary layer, however, calculations indicate significant ozone production. In the middle free troposphere at 5±1 km, the in situ ozone formation was most often nearly in balance with ozone destruction.
Vapor pressures in the ternary system water‐nitric acid‐sulfuric acid at low temperatures
Authors: Jaecker‐Voirol A. , Ponche J. L. , Mirabel P.
Published: February 2008

The partial vapor pressures over liquid or supercooled solutions of water and nitric acid and of water and sulfuric acid are calculated for temperatures below 0°C. From these results the partial vapor pressures over the ternary system water‐nitric acid‐sulfuric acid (liquid or supercooled) have been estimated and compared with the available experimental data of Vandoni at 0°C. Some possible implications for the formation of stratospheric aerosols are also discussed.
Column ozone measurements from Palmer Station, Antarctica: Variations during the Austral Springs of 1988 and 1989
Authors: Lubin Dan , Frederick John E.
Published: February 2008

The National Science Foundation scanning spectroradiometer at Palmer Station, Antarctica (64°46′S, 64°04′W), provides hourly ground‐based measurements of solar ultraviolet (UV) irradiance. In addition to defining the UV radiation environment of the region, these measurements allow the derivation of the column density of atmospheric ozone above the station nearly every daylight hour. This hourly time resolution, not generally available from other methods of monitoring Antarctic ozone abundances, enables the detection of large and rapid changes in total column ozone and UV surface irradiance associated with the dynamics of the polar vortex. Column ozone abundance is derived from a ratio of measured irradiances at 300 and 313.5 nanometers (nm) by means of theoretical calculation of this ratio as a function of total ozone amount. Noontime ozone abundances over Palmer Station obtained from this method agree with those obtained by the Total Ozone Mapping Spectrometer (TOMS) instrument aboard Nimbus 7 to within about 10% throughout the austral spring of 1988. Ozone recovery at Palmer Station, associated with the breakup of the polar vortex as indicated by TOMS satellite ozone observations, occurred rapidly within a 24‐hour period beginning in midafternoon on November 15. Over the Antarctic Peninsula, the 1989 ozone depletion was slightly greater than in 1988, the minimum noontime ozone abundances over Palmer Station as measured by the spectroradiometer being 194 and 166 Dobson units for October 14, 1988, and October 14, 1989, respectively. The 1989 ozone depletion however ended by November 5 over the Antarctic Peninsula, 10 days earlier than the 1988 event.
The second generation regional acid deposition model chemical mechanism for regional air quality modeling
Authors: Stockwell William R. , Middleton Paulette , Chang Julius S. , Tang Xiaoyan
Published: February 2008

A state‐of‐the‐art gas phase chemical mechanism for modeling atmospheric chemistry on a regional scale is presented. The second generation Regional Acid Deposition Model (RADM2) gas phase chemical mechanism, like its predecessor RADM1, is highly nonlinear, since predicted ozone, sulfate, nitric acid and hydrogen peroxide concentrations are complicated functions of NOx and nonmethane hydrocarbon concentrations. The RADM2 chemical mechanism is an upgrade of RADM1 in that (1) three classes of higher alkanes are used instead of one, (2) a more detailed treatment of aromatic chemistry is used, (3) the two higher alkene classes now represent internal and terminal alkenes, (4) ketones and dicarbonyl species are treated as classes distinct from aldehydes, (5) isoprene is now included as an explicit species, and (6) there is a more detailed treatment of peroxy radical‐peroxy radical reactions. As a result of these improvements the RADM2 mechanism simulates the concentrations of peroxyacetyl nitrate, HNO3, and H2O2 under a wide variety of environmental conditions. Comparisons of RADM2 mechanism with the RADM1 mechanism predictions and selected environmental chamber experimental results indicate that for typical atmospheric conditions, both mechanisms reliably predict O3, sulfate and nitric acid concentrations. The RADM2 mechanism gives lower and presumably more realistic predictions of H2O2 because of its more detailed treatment of peroxy radical‐peroxy radical reactions.
Intercomparison and interpretation of climate feedback processes in 19 atmospheric general circulation models
Authors: Cess R. D. , Potter G. L. , Blanchet J. P. , Boer G. J. , Del Genio A. D. , Déqué M. , Dymnikov V. , Galin V. , Gates W. L. , Ghan S. J. , Kiehl J. T. , Lacis A. A. , Le Treut H. , Li Z.‐X. , Liang X.‐Z. , McAvaney B. J. , Meleshko V. P. , Mitchell J. F. B. , Morcrette J.‐J. , Randall D. A. , Rikus L. , Roeckner E. , Royer J. F. , Schlese U. , Sheinin D. A. , Slingo A. , Sokolov A. P. , Taylor K. E. , Washington W. M. , Wetherald R. T. , Yagai I. , Zhang M.‐H.
Published: February 2008

The need to understand differences among general circulation model projections of CO2‐induced climatic change has motivated the present study, which provides an intercomparison and interpretation of climate feedback processes in 19 atmospheric general circulation models. This intercomparison uses sea surface temperature change as a surrogate for climate change. The interpretation of cloud‐climate interactions is given special attention. A roughly threefold variation in one measure of global climate sensitivity is found among the 19 models. The important conclusion is that most of this variation is attributable to differences in the models' depiction of cloud feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as reliable climate predictors. It is further emphasized that cloud feedback is the consequence of all interacting physical and dynamical processes in a general circulation model. The result of these processes is to produce changes in temperature, moisture distribution, and clouds which are integrated into the radiative response termed cloud feedback.
Liquid water content and precipitation characteristics of stratiform clouds as inferred from satellite microwave measurements
Authors: Curry Judith A. , Ardeel Christopher D. , Tian Lin
Published: February 2008

In this paper we present an analysis of the integrated liquid water content and precipitation characteristics of stratiform clouds using data from the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) for January 1979, over the North Atlantic Ocean (40°–60°N). Concurrent analysis of the SMMR data with the U.S. Air Force 3‐Dimensional Nephanalysis (3DNEPH) allows the interpretation of the SMMR‐derived liquid water paths and precipitation characteristics in terms of cloud type, cloud fraction, and cloud height. Combining the initialized analyses from the European Center for Medium‐Range Weather Forecasting (ECMWF) with the 3DNEPH enables vertical temperature and humidity profiles to be incorporated into the retrievals. The interpretation and presentation of our results are guided by their implications for the parameterization of liquid water content of layer clouds in largescale atmospheric models. The average liquid water paths for middle and low clouds were determined to be 115 and 102 g m−2, respectively, with a maximum value of 1070 g m−2. A comparison of the SMMR‐derived values of the liquid water path with the adiabatic liquid water path determined from the 3DNEPH cloud data and the ECMWF temperature profiles indicated that these clouds were for the most part substantially diluted by a combination of precipitation, freezing, and entrainment. Analysis of the liquid water path as a function of temperature showed that clouds with average temperature below 246 K had little liquid water and were inferred to be predominantly crystalline. There was little evidence that cloud liquid water path increases with temperature for cloudiness on a large scale, suggesting that cloud thickness plays the dominant role in determining cloud liquid water path. A total of 8.5% and 4.4% of the total middle and low clouds, respectively, were determined to be raining. Liquid water paths of 350 g m−2 and 500 g m−2 for middle and low clouds, respectively, were determined to be average thresholds for the onset of precipitation. Maximum rain rates for these clouds were determined to be 7 mm h−1. The autoconversion of cloud water to rain water was determined to occur at a rate of 0.001 s−1.
Case studies of the oxidation of sulphur dioxide in a hill cap cloud using ground and aircraft based measurements
Authors: Gallagher M. W. , Downer R. M. , Choularton T. W. , Gay M. J. , Stromberg I. , Mill C. S. , Radojevic M. , Tyler B. J. , Bandy B. J. , Penkett S. A. , Davies T. J. , Dollard G. J. , Jones B. M. R.
Published: February 2008

Two case studies are presented which investigate the aqueous phase oxidation of sulfur dioxide (SO2) within a cap cloud on the summit of Great Dun Fell (847 m above sea level) in England. Data gathered by aircraft showed that hydrogen peroxide (H2O2) concentrations in the free troposphere were much greater than near the ground and that entrainment of air containing H2O2, into the cap cloud could provide a significant supply of oxidant. These findings suggest that the entrainment of H2O2 into cloud systems may be important to the oxidation of SO2, particularly in the absence of large concentrations of ammonia gas, which may favor oxidation by ozone. It is also shown that the apparent reaction rate of H2O2 within the cloud is consistent with our previous estimates made and were substantially larger than would be predicted from laboratory studies in bulk solutions (Chandler et al., 1988b). Sulphate, (SO42−), production was observed when significant concentrations of SO2 were present. The measured concentrations of the principal species involved in one of the case studies were consistent with model predictions which take account of SO2 oxidation by H2O2 and O3 and an enhanced H2O2‐SO2 reaction rate.
Product study of the gas‐phase reactions of monoterpenes with the OH radical in the presence of NOx
Authors: Arey Janet , Atkinson Roger , Aschmann Sara M.
Published: February 2008

Hydroxyl radical reactions play an important role in the removal of monoterpenes from the troposphere during daytime hours, but there are few data available to date concerning the products of these reactions. From the gas‐phase reactions of β‐pinene and d‐limonene with the OH radical in the presence of NOx, the predicted products, 6,6‐dimethylbicyclo[3.1.1]‐heptan‐2‐one and 4‐acetyl‐1‐methylcyclohexene, respectively, were observed with formation yields of 30.0±4.5% and 17.4±2.8%. On the basis of mass spectral data a number of ketone and keto‐aldehyde products were tentatively identified in irradiated CH3ONO–NO–air–monoterpene mixtures of d‐limonene, α‐pinene, Δ3‐carene, sabinene, and terpinolene. The estimated formation yields of the observed products range from a low of ∼29% for α‐pinene to a high of ∼45% for d‐limonene. No significant products were observed from the OH radical‐initiated reaction of myrcene. Certain of these monoterpene reaction products, such as the 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one observed from β‐pinene, are less reactive than the parent monoterpene and are formed in sufficient yield that they may serve as markers for the monoterpene emissions. These gas‐phase products should be amenable to analysis by the techniques used for ambient air sampling of monoterpenes.
Interpretation of aircraft measurements of NO, ClO, and O3 in the lower stratosphere
Authors: Kawa S. R. , Fahey D. W. , Solomon S. , Brune W. H. , Proffitt M. H. , Toohey D. W. , Anderson D. E. , Anderson L. C. , Chan K. R.
Published: February 2008

Results are presented from an October 17, 1988, flight of the NASA ER‐2 stratospheric research aircraft. The flight sampled a nearly constant air mass at 20 km altitude, near 39°N latitude, from before sunrise until near noon. The instrumentation on board simultaneously measured NO, ClO, O3, temperature, and pressure. The measurements are combined with modeled photodissociation coefficients and known reaction kinetics to infer abundances of other important species, and the results are compared to previous estimates as a test for consistency in our understanding of the photochemical processes governing the species distributions. NO and ClO are observed to increase after sunrise, consistent with photolysis of nighttime reservoirs. The derived values for NO2, ClONO2, and N2O5 near midday are 320 (±190) pptv, 170 (±120) pptv, and 200 (±150) pptv, respectively, and are in good agreement with most previous measurements and model estimates. The slope of the NOx (= NO + NO2) change with time is a sensitive function of the shape of the JNO2 versus zenith angle curve at zenith angles above about 75°. This makes the derived value for N2O5 dependent on the model method used to compute the solar flux, with a detailed treatment of multiple scattering required for good results. Subtracting the sum of the measured and derived values for the nitrogen species from the average of measurements of total reactive nitrogen (NOy) on other flights, we obtain an estimate for the mixing ratio of HNO3 of 3.3 (±1.7) ppbv. This value for HNO3 and the HNO3/NOy fraction are in good agreement with values measured by the ATMOS experiment. The HNO3 and NO2 values are further used to estimate a daytime average OH mixing ratio of 0.6 pptv, which is consistent with extrapolation of previous measurements at higher altitudes.
Length bounds for connecting discharges in triggered lightning subsequent strokes
Authors: Idone Vincent P.
Published: February 2008

Highly time resolved streak recordings from nine subsequent strokes in four triggered flashes have been examined for evidence of the occurrence of upward connecting discharges. These photographic recordings were obtained with superior spatial and temporal resolution (0.3 m and 0.5 μs) and were examined with a video image analysis system to help delineate the separate leader and return stroke image tracks. Unfortunately, a definitive determination of the occurrence of connecting discharges in these strokes could not be made. The data did allow various determinations of an upper bound length for any possible connecting discharge in each stroke. Under the simplest analysis approach possible, an “absolute” upper bound set of lengths was measured that ranged from 12 to 27 m with a mean of 19 m; two other more involved analyses yielded arguably better upper bound estimates of 8–18 m and 7–26 m with means of 12 and 13 m, respectively. An additional set of low time‐resolution telephoto recordings of the lowest few meters of channel revealed six strokes in these flashes with one or more upward unconnected channels originating from the lightning rod tip. The maximum length of unconnected channel seen in each of these strokes ranged from 0.2 to 1.6 m with a mean of 0.7 m. This latter set of observations is interpreted as indirect evidence that connecting discharges did occur in these strokes and that the lower bound for their length is about 1 m.
Chemical fluctuations associated with vertically propagating equatorial Kelvin waves
Authors: Salby Murry L. , Callaghan Patrick , Solomon Susan , Garcia Rolando R.
Published: February 2008

Satellite retrievals of ozone and nitrogen dioxide from the Nimbus‐7 Limb Infrared Monitor of the Stratopshere (LIMS) reveal distinct spectral features which are collocated in frequency with Kelvin wave temperature fluctuations. These features represent a significant component of the unsteady variance in retrievals of O3 and nighttime NO2 in the tropics and are very similar to Kelvin wave temperature disturbances. Chemical fluctuations occur symmetrically about the equator, in phase across the tropics, and propagate downward, all consistent with the behavior of equatorial Kelvin waves. The phase structure of ozone perturbations mirrors that of temperature fluctuations in the upper stratosphere and mesosphere, only shifted 180°. The regular phase tilt with altitude disappears in the middle to lower stratosphere, where it is replaced by more or less barotropic behavior. That change in phase structure marks a transition from photochemical control in the upper stratosphere and mesosphere to dynamical control in the lower stratosphere. Fluctuations in NO2 propagate downward throughout the observed region, with a constant shift of 180° from temperature fluctuations. Only a slight indication of equatorial Kelvin waves is found in nitric acid, in accord with the weaker temperature sensitivity, relatively long lifetime, and small vertical gradient of HNO3 in the tropics. Fluctuations in ozone are consistent with dynamical and chemical mechanisms operating on that species. The response of ozone in a detailed photochemical calculation driven by observed temperature variability locks into agreement with the observed ozone variability above about 4 mbar, where O3 is under photochemical control. At lower altitudes, vertical transport is able to explain both the magnitude and phase of the observed fluctuations in ozone. The same considerations have only mixed success in explaining the observed variability of nitrogen dioxide. The amplitude of nighttime NO2 fluctuations is underestimated in the photochemical calculation by about a factor of 2. Although large enough to explain the discrepancy, contributions from vertical transport have the wrong phase. Observed fluctuations in daytime NO2, which have a much smaller signal‐to‐noise ratio, are at odds with both chemical and dynamical explanations. Contamination in the NO2 channel of LIMS by water vapor may be responsible for these discrepancies.
N2O and NO emissions from soils of the northern part of the Guayana Shield, Venezuela
Authors: Sanhueza Eugenio , Hao Wei Min , Scharffe Dieter , Donoso Loreto , Crutzen Paul J.
Published: February 2008

Soil fluxes of N2O and NO were measured in a scrub grass savanna and a nearby semideciduous forest in the savanna climatic region of Venezuela, during October 1988. The forest soil produces significantly larger emissions of N2O (ranging from 5.7 to 25.0×109 molecules cm−2 s−1) than the savanna soil (−3.6 to 14.0×109 molecules cm−2 s−1). This suggests that “long‐term” deforestation could produce a reduction of the N2O emissions to the atmosphere. In comparison with previous results from another site in the Venezuelan savanna region, very low emissions of NO, of the order of 1 to 2×109 molecules cm−2 s−1, were recorded. Considering that the NO/N2O emission ratio was much lower than 1, that practically no changes in the emission were observed after the fertilization with NH4Cl, and that very low concentration of NO3− is found in the natural soil, it is likely that under undisturbed conditions N2O and NO are mainly produced by denitrification and that there is a lack of nitrifying bacteria in these soils. Both N2O and NO emissions increased after application of NaNO3. Since the emission of NO remained larger than the N2O emission (with a ratio of ∼4/1), a significant change in the production pattern must have occured after fertilization with nitrate.
A significant correlation between fluctuations in seafloor spreading rates and evolutionary pulsations
Authors: Rich James E. , Johnson G. Leonard , Jones Janet E. , Campsie John
Published: February 2008

This report presents the results of a detailed correlation analysis which reveals a remarkable correspondence between variations in seafloor spreading rates and marine taxonomic diversity. The implications of this analysis are that the evolution of some biota was influenced by tectonic processes operative in the ocean basins. Such a conclusion suggests the need to seek a terrestrial explanation for extinction crises. An indirect link via tectonism, rise axis hydrothermal activity and the carbon dioxide cycle may provide a partial explanation.
Interregional model for deposition of Upper Cretaceous pelagic rhythmites, U.S. western interior
Authors: Hattin Donald E.
Published: February 2008

The Bridge Creek Member of the Greenhorn Limestone and Fort Hays Member of the Niobrara Chalk comprise rhythmic sequences of bioturbated pelagic limestone or chalk beds that alternate with generally shaly interbeds. Within each member individual couplets are time parallel and can be traced with great precision for hundreds of kilometers. Certain of the Bridge Creek beds can be traced from northeastern Kansas to the Four Corners area, a distance exceeding 1000 km. Regional stratigraphic analysis of these remarkable bedding sequences permits integration of concepts generated by several students of pelagic sedimentary sequences into a comprehensive model. In the basin center, Bridge Creek rhythms resulted from dilution cycles wherein a background of pelagic sedimentation was punctuated by episodes of increased siliciclastic influx and water column stratification. Consequent development of oxygen‐depleted bottom waters created high potential for preservation of laminae and organic matter in shaly interbeds. Within a given couplet, predominating influence of western siliciclastic source areas is evident in westward decrease of carbonate content in both bioturbated limestones and shaly interbeds, disappearance of one and then another of the limestone beds, and increase in abundance of the coarse detrital fraction. Toward the east, both bioturbated limestones and shaly interbeds grade progressively into chalky lithotypes. At some point where effects of detrital‐dilution episodes were minimal and the water was probably shallower, stratification of the water column was not possible, and interbeds are not only thinner but also bioturbated. Because of erosion this facies is not preserved in the Bridge Creek interval of Kansas, but it is exemplified there by the Fort Hays Member. Still farther eastward, where detrital influx was negligible, most of the Bridge Creek equivalent comprises a massive, bioturbated chalk sequence that lacks interbeds. This facies is preserved in northwestern Iowa. In condensed sections, the Bridge Creek Member contains considerable skeletal grainstone that bespeaks improved benthic circulation, even during deposition of shaly interbeds. The condensed sections developed on seafloor highs that apparently presaged the Laramide orogeny. The foregoing interpretation of regional variations in the Bridge Creek Member is generally applicable to the less widespread Fort Hays rhythmic sequence, in which simple dilution cycles seem to have predominated.
Antarctic marine temperatures: Late Campanian through Early Paleocene
Authors: Barrera Enriqueta , Huber Brian T. , Savin Samuel M. , Webb Peter‐Noel
Published: February 2008

An oxygen isotope paleotemperature study of benthic foraminifera from the upper Campanian through lower Paleocene section at Seymour Island, near the coast of Antarctica, was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation. The isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that Campanian through Paleocene high‐latitude shelf waters near Antarctica had temperatures between approximately 4.5° and 10.5°C. Temperatures during early and middle Maastrichtian time were slightly higher than those of either the late Campanian or late Maastrichtian. The inference of temperate climatic conditions in Antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera, as well as with published conclusions based upon paleobotanical evidence. The Maastrichtian and Campanian water temperatures at Seymour Island are similar to those inferred from published isotope ratios of Pacific Late Cretaceous benthic foraminifera from low latitudes, indicating that Campanian through early Paleocene deep ocean waters, at least in the Pacific and perhaps elsewhere as well, could have formed by sinking of surface waters in polar regions.
The analysis and interpretation of stratification cycles
Authors: Schwarzacher W.
Published: February 2008

Beds in carbonate successions often form regular patterns. Either there is a cyclic repetition of beds with different thicknesses, or bundles of beds occur separated from each other by some distinct layer. Any such group will be called a stratification cycle. Cycles of this type are from 0.5 m to several meters in thickness, and they seem to be present throughout the geological column. The analysis of sedimentary cycles involves three stages.

(1) Regional mapping is necessary to understand the facies of the sediment. Establishing the lateral persistence of bedding eliminates the possibility that bedding is caused by diagenetic processes.

(2) Petrographic examination and, in particular, analyses of primary structures are used to reconstruct the sedimentation conditions during cycle formation. Such conditions are extremely important for judging the time content of individual beds.

(3) The quantitative analysis of vertical sections using power spectral methods can find superimposed cycles and enables one to judge their degree of regularity. The latter approach is illustrated using lower Carboniferous limestone sections from NW Ireland as an example. Spectral analysis finds a stratification cycle of 1 to 3 m in thickness. Each cycle consists of between five to seven limestone beds. Upper Jurassic limestone marl successions from southern Germany and late Cretaceous and early Tertiary successions from Italy show a very similar cyclic pattern. The scale of the cycles and their regularity suggest that they are ultimately caused by variations in the earth's orbit, possibly by climatic cycles as was postulated by Milankovitch. However, the exact mechanism which links sedimentation with orbital variations is not known.
Models for circulation patterns in epicontinental seas applied to Paleozoic facies of North America craton
Authors: Witzke Brian J.
Published: February 2008

Circulation in epicontinental seas develops in response to thermohaline, wind‐driven, and tidal motions in various climatic, geographic, and bathymetric settings. Mass balance relations in a seaway are established by the relative rates of outflow, inflow (freshwater and ocean water), and evaporation, which constrain two contrasting styles of epicontinental circulation. Quasietuarine circulation (QEC) is established where rates of freshwater influx exceeds evaporation. Surface outflow from a seaway with QEC typically is balanced by inflow of oceanic water at depth. A density stratification can be established below the limits of vertical mixing. A bottom layer of oxygen poor or anoxic water may develop in a seaway with or without an entrance sill if the bottom waters are derived from the oxygen minimum zone of the open ocean or if organic productivity exceeds the limits of aerobic respiration. Upwelling may be promoted in specific epicontinental settings with QEC. Antiestuarine circulation (AEC) is developed in arid climates where evaporation exceeds freshwater influx. Evaporative concentration in the surface layer causes oxygenated water to sink. Bottom outflow of denser, more saline water is balanced by surface inflow from the open ocean. A sill or barrier may inhibit bottom circulation in seas with AEC, permitting development of a basal brine layer. Stagnation in the brine layer may lead to oxygen depletion. Seas with AEC commonly are characterized by extensive carbonate‐evaporite facies. Geographic and stratigraphic syntheses of lithofacies and biofacies provide the empirical basis for interpretations of seaway dynamics in ancient epicontinental settings. Examples from the Upper Ordovician (Maquoketa formation) and Upper Devonian (Lime Creek‐Sweetland Creek formations) of cratonic North America are interpreted in the context of stratified QEC patterns. In each case, oxygen poor to anoxic waters appear to have impinged along the basin slope below the margin of an oxygenated carbonate shelf. Upwelling along the shelf margin in the Maquoketa example helps explain the distribution of phosphatic sediments. A stratified AEC pattern is interpreted for the Gower formation (Silurian) of eastern Iowa. A barrier to bottom circulation at the mouth of an embayment in the epicontinental sea resulted in a basal layer of hypersaline water devoid of shelly benthos. Surface water salinities increased progresively shoreward within the embayment, but benthic organisms flourished where carbonate mounds built upward into the oxygenated layer.
Stable isotopic fractionation among particles in Quaternary coccolith‐sized deep‐sea sediments
Authors: Paull Charles K. , Thierstein Hans R.
Published: February 2008

Oxygen and carbon isotopic ratios of individual grain size splits of the <38 µm fraction of deep‐sea carbonate particles vary systematically with size over a range of 1.25 – 4.0‰. Most splits are dominated by just a few coccolith taxa and other types of particles. The ∂18O and ∂13C values of individual splits are linearly related to each other with a slope of 1.5 ∂13C/∂18O in all Holocene and Glacial samples analyzed. Although the observed variability is less than predicted from culture experiments of individual components, compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction.
Fluctuations in the trophic resource continuum: A factor in global diversity cycles?
Authors: Hallock Pamela
Published: February 2008

The trophic resource continuum (TRC) in euphotic zones of the world's oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas. That spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved, as oceanic circulation rates changed, and in response to oceanic‐mixing events. Reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy, that is, TRC expansion. Because oceanic waters as a whole are relatively nutrient rich, increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing, causing TRC contraction. Global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments. Nutrient deficient waters are more stable and more transparent than richer waters, permitting higher degrees of specialization. Sparse nutrient supplies necessitate smaller phytoplankton and longer, more complex food chains. Preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved. Fluctuations in the TRC should profoundly affect diversity of habitats within the euphotic zone of the oceans. The evolutionary response to a TRC expansion, diversification, would occur in a geologic time frame of millions of years, while evolutionary responses to a TRC contraction, including extinction, could occur in a biological time frame of generations. A simple model indicates that a reduction in the trophic resource continuum, from expansion during a major marine transgression, down to modern levels could result in loss of 40% of the euphotic habitats. How fluctuations in the TRC control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles, as well as taxonomically selective extinctions, changes in species dominance, and some morphologic trends.
The temporal distribution of evolutionary and migrational events in pelagic systems: Episodic or continuous?
Authors: Kitchell Jennifer A.
Published: February 2008

The evolutionary and ecological dynamics of origination/immigration and extinction/emigration patterns of two pelagic groups (planktic foraminifera and calcareous nannofossils) within two paleoceanographic regions over the past 40 m.y. are compared with predictions of the turnover‐pulse hypothesis that speciation, extinction, and migration are pulsed or episodic and synchronous with change in the physical environment. The specific species dynamics examined of the records of 918 species include expected time to extinction, origination/‐immigration as a function of geologic time, extinction/emigration as a function of biologic age and geologic time, and the interactive effects of time of origination/immigration and geologic time on the probability of extinction/emigration. Overall, there is little empirical support for times of evolutionary quiescence or ecological stability. Rather, the dominant pattern is one of continuous rather than episodic evolutionary and ecological activity. There is little evidence of synchroneity of response among cohorts or with major change in the physical environment. Coeval species experience the same time periods differently in terms of the probability of speciation/immigration and extinction/emigration. The empirical patterns support the hypothesis that at this taxonomic and temporal resolution the controlling factors on evolutionary and ecological turnover are more omnipresent than pulsed or episodic.
Atlantic sediments: Glacial/interglacial comparisons
Authors: Balsam William L. , McCoy Floyd W.
Published: February 2008

To assess the regional effects of glaciation on sedimentation in the Atlantic Ocean we compare sediment types, distributions, and rates between Recent (core top) and last glacial maximum (LGM: ∼18,000 years B.P.) stratigraphic levels. Based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than Recent. During both the Recent and LGM, carbonate content shows an east/west asymmetry with western basins exhibiting lower carbonate values. Input of ice‐rafted detritus into the North Atlantic during LGM time interrupts this topographic control on carbonate distribution considerably farther south than at present; in the South Atlantic this effect is minor. Comparison of LGM and Recent sediment distributions indicates that the LGM seafloor was dominated by biogenic oozes, calcareous clays, and clays, while the Recent is dominated by biogenic oozes and marls. Coarse‐grained detritus is much more prevalent in LGM sediments, derived not only from glacial input but also from fluvial and aeolian sources. Sedimentation rates, calculated from LGM to Recent sediment thickness in cores, are <4 cm/1000 yr for most of the ocean. Higher rates are typical of the continental margin off the Amazon River, the North American Basin, and a small region off west equatorial Africa.
Event stratigraphy and paleoceanography in the Fortuna Basin (southeast Spain): A scenario for the Messinian salinity crisis
Authors: Müller Daniel W. , Hsü Kenneth J.
Published: February 2008

The timing and duration of evaporitic deposition during the Messinian in the Mediterranean is poorly known. To assist with this problem, we have correlated sedimentological events at widely separated locations in the Mediterranean and dated paleoceanographic events in the world ocean (event stratigraphy). Our working hypothesis is as follows: The Messinian Salinity Crisis caused the formation of evaporites in a deep desiccated basin which implies that (1) the evaporites were deposited during a steady marine influx, (2) multiple intervals of isolation led to drastic changes in the sediments and in the fauna of the Mediterranean, (3) the sea level of the Mediterranean Sea was mostly several hundreds of meters below that of the Atlantic Ocean, and (4) the seaways (Betic and Rif Strait) connecting the Mediterranean with the Atlantic during the late Miocene were affected by eustatic sea level changes caused by Antarctic glaciation. We found supporting evidence in the sedimentological and paleoceanographic records in the Betic Strait (Fortuna and Sorbas basins) which was one of the sites of major inflow into the late Miocene Mediterranean Sea. Drastic sea level changes and fluctuations during the late Tortonian and Messinian caused chronologically: (1) the deposition of brackish sediments overlying marine deposits, (2) the progradation of deltas, (3) reef growth at lower levels and their destruction by erosion and coverage by conglomerates, (4) evaporite deposition alternating with marine marls containing Atlantic diatom assemblages, and (5) five marine/terrestrial cycles associated with coral reefs. Based on event stratigraphy the following scenario for the Messinian “Salinity Crisis” is proposed: The Tripoli Formation (Chron 6R1/5N2: 5.93–5.7 Ma), the Lower Evaporites (Chron 5N2, 5R: 5.7–5.5 Ma), and the Upper Evaporites (lowermost Gilbert c: 5.25–5.15 Ma) were deposited during influx of Atlantic water into the Mediterranean. During this time, a unidirectional circulation dominated from the Atlantic through the Betic Strait. Only during the intra‐Messinian inundation (Chron 5N1 into lowermost Gilbert c: 5.4–5.25 Ma) that occurred after a short intra‐Messinian erosional event (Chron 5N1: 5.5–5.4 Ma) was a normal bidirectional circulation pattern established. This is reflected in the diatomites of the Chicamo Formation and the Mediterranean (site 124) as well as most likely in a reef on Cyprus. The marine record of the Pliocene filling of the Mediterranean is missing in these basins. Overall, marine water inflow into the Mediterranean through the Betic Strait dominated during the Messinian. The threefold marine/terrestrial cyclicity with severe paleoceanographic changes in the Fortuna and Sorbas basins favor the “deep, desiccated basin” model.
Pleistocene fluctuations in the western boundary undercurrent on the Blake Outer Ridge
Authors: Johnson Thomas C. , Lynch Elizabeth L. , Showers William J. , Palczuk Nicholas C.
Published: February 2008

The mean grain size of the detrital silt fraction was analyzed in two piston cores from the crest of the Blake Outer Ridge using electronic particle analysis. The resultant profiles in the two cores are highly correlatable and are interpreted to reflect the paleospeed of the Western Boundary Undercurrent (WBUC) for the past 90 kyr. The record can be divided into three periods. The first encompasses the past 12,000 years and begins with an abrupt acceleration marking the transition from slow, glacial to more vigorous, Holocene conditions. The later Holocene is a period of strong but variable flow. The second period extends from 30 to 12 × 10³ years and is characterized by a steady reduction of WBUC strength through the last ice age. The current continued to decelerate until 12 × 10³ years when the polar front finally retreated northward past the passages connecting the Norwegian Sea to the north Atlantic. The third period, from 30 to about 90 × 10³ years, was a time of strong and variable flow that was independent of the glacial/interglacial signal that is seen in the oxygen isotope record. During this time, the core of maximum flow appears to have shifted up and down the flank of the Blake Outer Ridge and may have been influenced as much by salinity as by temperature variations in the source areas of the WBUC.
Upper Eocene to Oligocene isotope (87Sr/86Sr, δ18O, δ13C) standard section, Deep Sea Drilling Project Site 522
Authors: Miller Kenneth G. , Feigenson Mark D. , Kent Dennis V. , Olsson Richard K.
Published: February 2008

We improved upper Eocene to Oligocene deep‐sea chronostratigraphic control by integrating isotope (87Sr/86Sr, δ18O, δ13C) stratigraphy and magnetostratigraphy. Most previous attempts to establish the timing of isotope fluctuations have relied upon biostratigraphic age estimates which have uncertainties of 0.5 to over 4.0 m.y. Deep Sea Drilling Project (DSDP) Site 522 contains the best available upper Eocene to Oligocene magnetostratigraphic record which allows first‐order correlations of isotope records (87Sr/86Sr, δ18O, δ13C) to the Geomagnetic Polarity Time Scale (GPTS). Empirical calibrations between the 87Sr/86Sr of foraminifera and magnetochronology at Site 522 allow more precise correlation of “unknown” samples with the GPTS. For example, shallow water and high‐latitude sections may be tied into the deep‐sea record. Sr‐isotope stratigraphic resolution for the latest Eocene to Oligocene is approximately 2 m.y.
Aliasing of the geologic record and the search for long‐period Milankovitch cycles
Authors: Pisias N. G. , Mix A. C.
Published: February 2008

Aliasing of a time series shifts high‐frequency variance into lower frequencies. It is caused by sampling at an interval too broad to resolve true high‐frequency signals. This effect is well understood in classical time series analysis, where sample intervals are known and constant, but in a geologic context, where sample intervals may vary, aliasing remains poorly known. We address here the aliasing problem relevant to the search for orbital variations recorded in sedimentary sections. Our example is aliasing of the 23,000‐year period orbital precession rhythm which is common in late Quaternary paleoclimatic records. We illustrate three cases of aliasing. First, we sample precession at a constant interval of 25,000 years. This is a typical target for many “high‐resolution” studies of Neogene sections. This sampling interval translates precessional variance into predictable spectral peaks near 400 ka and 100 ka, which could be mistaken for the longer‐period eccentricity rhythms. Second, random variations in the sampling interval around the 25,000‐year target spread the aliased variance over a range of frequencies. This induces either unpredictable long‐period spectral peaks or, in the extreme, a white noise spectrum. In the third case, variations of the sampling interval are autocorrelated. This simulates a section with long‐period variations in sedimentation rate sampled at constant depth intervals. Here the single aliased peaks of case 1 are split into two or more peaks of slightly higher and lower frequencies. In all three cases, for long enough time series, the total variance recorded is the same. We compare these numerical experiments to a Miocene oxygen isotope record from Deep Sea Drilling Project site 577, sampled at ∼25,000‐year intervals. With these data it is impossible to tell whether the long‐period variations are due to the direct effects of eccentricity or the aliased effects of precession. In theory it should be possible to test for eccentricity signals at low resolution by randomizing the sampling intervals. In practice, however, it is only through high‐density sampling that we can define intervals well enough to assess the effects of aliasing.
A simple evolutionary model for water and salt in the Black Sea
Authors: Boudreau Bernard P. , Leblond Paul H.
Published: February 2008

This paper presents a time‐dependent variable‐size box model for the total fluid and salinity balances of the Black Sea. In addition to the advective flows due to riverine and Mediterranean inputs of water, the model accounts for entrainment flows which are parameterized using the theory of Ellison and Turner (1959) and employs a modified version of the Gargett (1984) formulation for eddy diffusivity in describing cross‐pycnocline mixing flows. The variable volume of the boxes permits explicit simulation of the replacement of the preexisting late Pleistocene lake water by the inflow of denser Mediterranean water. Our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less. Because of the effects of mixing, the salinity of both the surface and deep waters requires a greater time interval to obtain present‐day values, i.e., ∼4000 years if the inflow of Mediterranean water is constant in time at its present value and ∼6000 years if this input changes with time in approximation to the rate of sea level rise. The occurrence of the marine coccolithophorid Emiliania huxleyi in the Holocene sapropel layer requires a minimum surface salinity of 11‰, which takes some 1600 to 3100 years to develop. This range is a result of the uncertainty in the history of the Mediterranean water input. The model is also employed to investigate the freshening of the Black Sea after cutoff of Mediterranean input. The salinity of both surface and deep waters is found to fall below 11‰ in less than 3000 years, and the freshening process is complete in ∼9000 years.