bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport into the south polar vortex in early spring
Authors: Hartmann D. L. , Heidt L. E. , Loewenstein M. , Podolske J. R. , Vedder J. , Starr W. L. , Strahan S. E.
Published: February 2008

Data collected during the Airborne Antarctic Ozone Experiment during August and September 1987 show conclusively that a photochemical sink and not transport caused the ozone decline during that time. During the period August 23 to September 22, 1987, mixing ratios of trace constitutents with long lifetimes remained relatively constant for fixed potential temperature and latitude. Over the same period the ozone mixing ratio declined by more than 50% inside the polar vortex near 18 km altitude. This observation alone requires a substantial photochemical sink of ozone. The conservative tracer data indicate that the Lagrangian mean vertical velocity cannot have been upward inside the polar vortex where the ozone hole appeared. Tracer and ozone gradients in the region from 54° to 72°S imply that ozone could be transported into the polar vortex during the spring season. Observed gradients of conserved tracers with respect to latitude and potential temperature are used to deduce a relationship between meridional mixing on potential temperature surfaces and mean diabatic descent in the vortex. The observed gradients and time tendency of ozone are then used to infer the magnitude of the effect of ozone transport in mitigating the springtime ozone decline, using an assumed best guess heating rate of 0.2 K d−1. It is estimated that ozone transport increased the requirement for a photochemical sink by about 20%±10% near the 425‐K potential temperature level during the period of the 1987 experiment, so that transport from other latitudes or heights had a relatively weak influence on the development of the ozone hole in 1987. This estimate is also consistent with inferences based on the magnitude of the ozone gradient at the edge of the region of chemical depletion. The sharpness of the observed ozone drop with latitude at the edge of the ozone hole suggests relatively weak lateral mixing there. The tracer data also suggest that the amounts of lateral mixing and subsidence are strong functions of altitude, with more efficient mixing below about 400 K.
Laboratory studies of heavy ozone
Authors: Morton J. , Barnes J. , Schueler B. , Mauersberger K.
Published: February 2008

Dissociation of ozone in the Chappuis bands has been used as an O atom source to study isotope effects occurring in the O(3P)+O2(3∑g) recombination reaction. The ozone produced was found to be enriched in both of its heavy isotopes. The pressure dependence (5–1000 torr) and temperature dependence (127–360 K) of this isotope effect have been investigated. The enrichment is approximately constant from 5 torr to 100 torr and decreases at higher pressures. It increases with temperature, with 50O3 showing a slightly faster rate of increase than 49O3. The results of this experiment have clearly isolated the source of the isotope effect to the gas phase O(3P) + O2(3∑g) recombination reaction. For comparison, we also present isotope ratios of ozone formed in an electric discharge. None of the results, however, have shown the large enhancement of 40% or more in mass 50 observed in some stratospheric measurements.
The sensitivity of ozone to nitrogen oxides and hydrocarbons in regional ozone episodes
Authors: Sillman Sanford , Logan Jennifer A. , Wofsy Steven C.
Published: February 2008

We examine the sensitivity of ozone concentrations in rural areas of the United States to emissions of NOx and hydrocarbons using a regional photochemical model. Ozone production in rural areas appears to be limited by the availability of NOx. Rural ozone is strongly dependent on emission rates for NOx but is almost independent of hydrocarbons. This relationship is quite different from that in urban air, where ozone levels depend on both NOx and hydrocarbons. The predicted relationship between ozone and nitrogen oxides appears to be consistent with observations in rural air. For the low NOx regime (< 2 ppb) in rural areas, increases in NOx lead to increases in OH and to corresponding increases in the oxidation rate of hydrocarbons and in levels of ozone. Ozone concentrations in urban plumes appear to be related to regional scale production in addition to production within the plume.
On the radiation field turn‐on term associated with traveling current discontinuities in lightning
Authors: Rubinstein Marcos , Uman Martin A.
Published: February 2008

We show that the mathematical expression for the radiation field associated with a traveling lightning current discontinuity given by Uman and McLain (1970) is an approximation, and we derive a generalized formulation for the discontinuity‐associated radiation.
Time variations of CO and O3 concentrations in a region subject to biomass burning
Authors: Kirchhoff V. W. J. H. , Rasmussen R. A.
Published: February 2008

Carbon monoxide (CO) and ozone (O3) concentrations have been observed in the Brazilian Amazon region, at a site strongly affected by biomass burning (Cuiabá, 16°S, 58°W). Time variations are described for the first long‐term program of studying the effect of biomass burning on O3 and CO over a complete seasonal cycle, including the seasonal maxima of 1987 and 1988. Concentrations of O3 are measured continuously, and CO samples are collected three times a week. In order to obtain elements for comparison, an identical observational program was maintained at a site totally outside of the direct influence of biomass burning (Natal, 6°S, 35°W). The biomass burning contribution to the Cuiabá concentrations of CO and O3 is very large. Diurnal maximum concentrations exceeded 90 ppbv (parts per billion by volume) O3 in 1987 and 120 ppbv O3 in 1988, in September. For the wet season, the monthly average ozone concentration in March–April is about 10 ppbv. During the month of maxima, September, the O3 concentration average was 41 ppbv for 1987 and 71 ppbv for 1988. The CO concentrations are about 90 ppbv in the wet season. In September, 460 ppbv and 660 ppbv of CO were observed for 1987 and 1988, respectively. At Natal the seasonal variation is of the order of a factor of 2. For the biomass burning site this factor is 4 for 1987 and almost 7 for 1988. In contrast, during the wet season, the concentrations of CO and O3 at both stations are about the same.
Nitrous oxide emissions from fossil fuel combustion
Authors: Linak William P. , McSorley Joseph A. , Hall Robert E. , Ryan Jeffrey V. , Srivastava Ravi K. , Wendt Jost O. L. , Mereb Jamal B.
Published: February 2008

The role of coal combustion as a significant global source of nitrous oxide (N2O) emissions was reexamined through on‐line emission measurements from six pulverized‐coal‐fired utility boilers and from laboratory and pilot‐scale combustors. The full‐scale utility boilers yielded direct N2O emission levels of less than 5 ppm. The sub‐scale combustor test data were consistent with full‐scale data, and also showed N2O emission levels not exceeding 5 ppm, although these levels increased slightly when various combustion modifications to lower NO emissions were employed. These on‐line emission measurements are very different from previously published data. The discrepancy is shown to be due to a sampling artifact by which significant quantities of N2O can be produced in sample containers which have been used in establishing the previously employed N2O data base. Consequently, we conclude that N2O emissions bear no direct relationship to NO emissions from these combustion sources, and that this direct source of N2O is negligible. Other indirect routes for the conversion of NO into N2O outside the combustor and other combustion sources not examined by this study, however, cannot be ruled out.
Contribution of organic nitrates to the total reactive nitrogen budget at a rural eastern U.S. site
Authors: Buhr Martin P. , Parrish David D. , Norton Richard B. , Fehsenfeld Frederick C. , Sievers Robert E. , Roberts James M.
Published: February 2008

Measurements of ambient levels of PAN (peroxyacetyl nitrate or, more properly, peroxyacetic nitric anhydride), C2–C5 alkyl nitrates, NOx (NO+NO2), HNO3, and NO3− particulates were made concurrently with a measurement of total reactive nitrogen species (NOy) at Scotia, Pennsylvania, from July 16 to August 31, 1988. Each of the organic nitrates exhibited a marked diurnal variation. The concentration of PAN varied from 0.05 to 3 ppbv (parts per billion by volume). The sum of the alkyl nitrate concentrations varied from less than 2 to 200 pptv (parts per trillion by volume). The NOy levels varied from 1 to 30 ppbv. During periods of high photochemical activity the contributions to NOy were 30–45% from HNO3, 20–25% from PAN, 15–25% from NOx, 5% from NO3−, and an additional 1.5% from the C2–C5 alkyl nitrates, on average. During these periods, about 15% of the measured NOy could not be accounted for by the sum of the individually measured species. The unidentified species that constitute this 15% exhibit behavior similar to that of the measured organic nitrates.
Use of lidar measurements and numerical models in air pollution research
Authors: Beniston M. , Wolf J. P. , Beniston‐Rebetez M. , Kölsch H. J. , Rairoux P. , Wöste L.
Published: February 2008

This article presents the present‐day capability of three‐dimensional analysis of air pollution, by both differential absorption lidar and advanced numerical models. These two techniques exhibit numerous similarities, both at the level of spatial resolution and on a working scale. Two measurement campaigns have been performed to determine emission characteristics and concentrations of sulfur dioxide (SO2) in order to illustrate these similarities. The results of the intercomparisons are satisfactory, and differences are usually within 20%.
The sensitivity of a coupled atmospheric‐oceanic model to variations in the albedo and absorptivity of a stratospheric aerosol layer
Authors: Walsh K. , Pittock A. B.
Published: February 2008

Considerable uncertainty exists regarding the precise physical parameters of a smoke or aerosol cloud that would be injected into the lower stratosphere by a catastrophic event such as a nuclear war, a major volcanic eruption, or an asteroid impact. In this paper, the sensitivity of the sea surface temperature of a one‐dimensional coupled atmospheric‐oceanic model to variations in the albedo and absorptivity of an aerosol cloud introduced into the lower stratosphere is examined. Zonally averaged results are produced for two latitudes in the southern hemisphere. The temperature response of the oceans to forcings by a cloud with realistic aerosol properties is examined, with particular emphasis on the impact on the surface climate on time scales of 6 months to 2 years.
A tunable diode laser system for aircraft measurements of trace gases
Authors: Schiff H. I. , Karecki D. R. , Harris G. W. , Hastie D. R. , Mackay G. I.
Published: February 2008

The advantages of tunable diode laser absorption spectrometry (TDLAS) for measuring trace atmospheric gases are universality, positive identification, good sensitivity, and rapid response time. A TDLAS system is described which is capable of making measurements on board an aircraft. The instrument was employed during the Chemical Instrumentation Test and Evaluation (CITE) 2 program to measure NO2, on 11 flights and HNO3, on five flights. Detection limits were determined to be 25 parts per trillion by volume [pptv] for NO2 and 75 pptv for HNO3 with response times of 3 min. This was sufficient to permit measurements of NO2 in the free troposphere and HNO3, in the continental boundary layer a significant fraction of the time.
The dependence of constituent transport on chemistry in a two‐dimensional model of the middle atmosphere
Authors: Smith Anne K. , Brasseur Guy P.
Published: February 2008

The transport of trace species by waves is affected by their production and/or destruction by photochemical processes. For this reason the transport or “diffusion” matrices used in two‐dimensional models should be different for each constituent. This paper describes a method for altering the meridional and vertical dynamical transport coefficients for use with photochemically active species. The transport represents the net meridional eddy flux by planetary waves and the net vertical eddy flux by gravity waves. Output from integrations using the control (species independent) and chemical eddy transport coefficients are compared. The change in the meridional (planetary wave) transport results in modest, but nevertheless significant, changes in the distribution of trace species. In many cases, for example odd oxygen and nitric acid, the model changes bring the distributions closer to those observed. In contrast, the incorporation of the chemical eddy effect into the gravity wave transport has almost no effect on any of the model fields.
Ozone variability in the equatorial middle atmosphere
Authors: Sun Chi‐Rong , Leovy Conway
Published: February 2008

Ozone variability in the equatorial middle atmosphere is investigated and related to temperature and zonal wind variations using data from the Nimbus 7 and Solar Mesosphere Explorer (SME) satellite. The dominant component of the seasonal variability at most levels from the middle stratosphere to the lower thermosphere is the semiannual oscillation (SAO) which has maxima near 10,3, 0.07, 0.01 mbar, and near or above 0.0024 mbar. There is evidence that the 10‐mbar peak is due to vertical advection of odd nitrogen (NOy) by the semiannually varying residual mean circulation, while temperature dependependence of chemical reactions coupled with the thermal SAO near the stratopause and in the upper mesosphere is responsible for the peaks near 3 and 0.07 mbar. The seasonal dependence suggests a contribution from gravity wave modulated vertical mixing of water vapor near the 0.01 mbar level, and we speculate that semiannually modulated mixing of atomic oxygen by the (1,1) mode of the thermal tide contributes to the SAO ozone peak above 0.0024 mbar. The negative correlation between temperature and ozone is so strong in the 7‐ to 0.5‐mbar layer that ozone is a useful proxy for temperature variability on time scales from a few days to many months. A preliminary look at annual and interannual variations shows that differing patterns of winter high latitude Rossby wave variability in the two hemispheres are reflected in the signatures of equatorial ozone and temperature in the same layer.
Measurements of CH4, N2O, CO, H2O, and O3 in the middle atmosphere by the Atmospheric Trace Molecule Spectroscopy experiment on Spacelab 3
Authors: Gunson M. R. , Farmer C. B. , Norton R. H. , Zander R. , Rinsland C. P. , Shaw J. H. , Gao B.‐C.
Published: February 2008

The volume mixing ratios of five minor gases (CH4, N2O, CO, H2O, and O3) have been retrieved through the middle atmosphere from the analysis of 0.01 cm−1 resolution infrared solar occultation spectra recorded near 28°N and 48°S latitudes with the Atmospheric Trace Molecule Spectroscopy instrument, flown on board Spacelab 3 (April 30 through May 6, 1985). The results, which constitute the first simultaneous observations of continuous profiles through the middle atmosphere for these gases, are in general agreement with reported measurements from ground‐, balloon‐, and satellite‐based instruments for the same seasons. In detail, the vertical profiles of these gases show the effects of the upper and middle atmospheric transport patterns dominant during the season of these observations. The profiles inferred at different longitudes around 28°N suggest a near‐uniform zonal distribution of these gases, for conditions corresponding to late spring. Although based on fewer observations, the sunrise occultation measurements (southern hemisphere early winter) point to a larger longitudinal variability in the vertical distribution of these gases at 48°S.
Submicron desert dusts: A sandblasting process
Authors: Gomes Laurent , Bergametti Gilles , Coudé‐Gaussen Genevieve , Rognon Pierre
Published: February 2008

Mass size distributions of the major elements of the mineral aerosol of northern Sahara were obtained from measurements carried out with an inertial cascade impactor. A fitting procedure by data inversion was applied to these data. This technique considers the major mechanisms of nonideal behavior such as particle bounce‐off, wall losses and cross sensitivity which affect the accuracy of impactor measurements of aerosol size distribution. Accurate size distributions of Saharan aerosol (range 0.1–20 μm) were so obtained for different conditions of soil mobilization. These measurements, coupled with wind speed information, show the shape of the size distribution for desert aerosols in the considered range to be characterized by a similar pattern with a common mode of particles having diameter between 1 and 20 μm whatever the weather conditions. A second mass peak of submicron particles appears when the wind speed increases above the threshold value for erosion. Scanning electron microscope photographs indicate that the whole granulometric spectrum of the sampled aerosol between 0.1 and 20 μm mainly consists of clay easily disaggregated by sandblasting. The common origin of submicron particles with those between 1 and 20 μm is established by showing the similar composition of dusts in the both modes. The results suggest that the presence of submicron mineral particles during dusty and sandstorm conditions is consistent with a sandblasting process.
Seasonal dynamics in methane emissions from the Amazon River floodplain to the troposphere
Authors: Devol Allan H. , Richey Jeffrey E. , Forsberg Bruce R. , Martinelli Luiz A.
Published: February 2008

Methane fluxes to the troposphere from the three principal habitats of the floodplain of the Amazon River main stem (open waters, emergent macrophyte beds, and flooded forests) were determined along a 1700‐km reach of the river during the low‐water period of the annual flood cycle (November–December 1988). Overall, emissions averaged 68 (±20) mg CH4 m−2 d−1 and were significantly lower than similar emissions determined previously for the high‐water period, 184 (±41) mg CH4 m−2 d−1 (July–August 1986). This difference was due to significantly lower emissions from floating macrophyte environments. Low‐water emissions from open waters and flooded forest areas were not significantly different than at high water. A monthly time series of methane emissions from eight lakes located in the central Amazon basin showed similar results. Average annual emission from the lakes was 125 (±28) mg CH4 m−2 d−1. Methane emissions from lakes were significantly higher during the high water period, again primarily due to an increase in emissions from macrophyte habitats. The data were used to calculate a seasonally weighted annual emission to the troposphere from the Amazon River main stem floodplain of 5.1 Tg yr−1, which indicates the importance of the area in global atmospheric chemistry.
Ozone measurements in Amazonia: Dry season versus wet season
Authors: Kirchhoff V. W. J. H. , da Silva I. M. O. , Browell E. V.
Published: February 2008

The concentration of atmospheric ozone was measured in the Amazonian rain forest. Observations were made almost continuously at the surface, and in addition, 20 ozone profiles were obtained in the troposphere and stratosphere. These ozone measurements were part of a field expedition to the Brazilian Amazon region, the ABLE 2B mission, a joint American‐Brazilian effort to measure local concentrations of several species relevant to atmospheric chemistry. The time period of this expedition was April–May 1987, during the local wet season. For the surface ozone data the measurement technique used was UV absorption. Ozone profiles were obtained with electrochemical concentration cell sondes, launched on balloons. The major site of operation was set up near Manaus (3°S, 60°W). The results are presented and compared with a previous dry season experiment. Surface ozone mixing ratios show diurnal variations that have maxima in the daytime and minima at night. The diurnal maximum at noontime, considered very low (12 ppbv) in the dry season was even lower in this wet season period (6 ppbv). A significant difference can be seen between clearing and forest data, and between different height levels above the surface, showing the existence of a large positive gradient of ozone with height. The ozone profiles in the troposphere show that there is less ozone not only at the surface but in the whole troposphere, with the wet season average showing between 6 and 12 ppbv less ozone. This difference is much smaller in the stratosphere, where there is slightly more ozone in the region of the peak, during the wet season. An isolated shower or thunderstorm in the dry season could produce transient ozone variations (mixing ratio increases or decreases) that were not observed in the wet season.
Radiosonde observations of large‐amplitude gravity waves in the lower and middle stratosphere
Authors: Kitchen M. , Shutts G. J.
Published: February 2008

Radiosondes ascending near to mountainous areas in the United Kingdom occasionally encounter very large‐amplitude gravity waves in the stratosphere. These ascents are characterized by large perturbations in the temperature (∼5 K) and vertical velocity (2–10 m s−1) on vertical scales of about 2 km. Some of the profiles suggest a large vertical flux of horizontal momentum (order 1 Nm−2). Examples of these waves are illustrated, and the situations in which they are observed are described. Simple linear wave theory has been used to diagnose many of the important wave properties.
Carbon kinetic isotope effect in the oxidation of methane by the hydroxyl radical
Authors: Cantrell Christopher A. , Shetter Richard E. , McDaniel Anthony H. , Calvert Jack G. , Davidson James A. , Lowe David C. , Tyler Stanley C. , Cicerone Ralph J. , Greenberg James P.
Published: February 2008

The reaction of the hydroxyl radical (HO) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The measured ratio of the rate coefficients for reaction with 12CH4 relative to 13CH4 (k12/k13) was 1.0054 (±0.0009 at the 95% confidence interval), independent of temperature within the precision of the measurement, over the range studied. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere through the use of carbon isotope measurements.
Search for Milankovitch patterns among oolitic ironstones
Authors: Van Houten F. B.
Published: February 2008

The stratigraphic record of about 175 oolitic ironstones is sparse, yet it portrays several meaningful patterns. Repeated ironstone episodes occurred in only about 10 major sedimentary basins which were marked by relative tectonic stability or subdued orogeny. Intervals between episodes varied but were mostly a few to several million years long. Repetitions on this scale are commonly construed as global rise and fall of sea level. The pattern persisted for a few tens of million years in fore deeps, several tens of million years on unstable cratons and microcontinents, and more than 100 m.y. in intracratonic basins. Within the congenial habitats an ironstone developed locally between each of several successive shallow marine upward shoaling detrital sequences. These asymmetric units, normally a few meters to a few tens of meters thick, recurred on average every 250 to 500 kyr. Commonly, fewer than 10 ironstone‐bearing sequences are involved. During a very long lapse in normal sedimentation between such sequences stacked ironstones accumulated on the same short‐time scale. Speculation about short‐time scale patterns is poorly constrained, but several other repetitive stratigraphic successions with a several hundred thousand year cadence have been attributed tentatively to the 400,000‐year Milankovitch climate cycle. It is unclear how this would exert a eustatic control without the waxing and waning of continental glaciers.
Rhythmic bedding produced in Cretaceous pelagic carbonate environments: Sensitive recorders of climatic cycles
Authors: Bottjer David J. , Arthur Michael A. , Dean Walter E. , Hattin Donald E. , Savrda Charles E.
Published: February 2008

Various types of rhythmic bedding are prominent features of Cretaceous pelagic carbonates. These bedding rhythms are the primary depositional result of variations in carbonate productivity, terrigenous dilution, redox conditions and/or the energy of bottom currents. Each bedding cycle type is different in its expression in the stratigraphic record but ultimately was caused by rhythmic climatic variations related to variations in receipt of solar insolation as the result of the earth's orbital characteristics, the so‐called Milankovitch cycles. Stratigraphic sequences may contain a single bedding cycle type or a composite of several types. Although sediment type and sedimentary structures were influenced by variations in local climatic, oceanographic, tectonic, and diagenetic parameters, pelagic carbonate environments during the Cretaceous were particularly sensitive recorders of orbitally induced changes in worldwide climate.
Organic geochemical character of opal‐rich sediments in light‐dark cycles near the Pliocene‐Pleistocene boundary in Deep‐Sea Drilling Project Site 532, Walvis Ridge
Authors: Meyers Philip A. , Dunham Keith W. , Rau Greg H.
Published: February 2008

Geochemical studies have been done on organic matter from biogenic sediments from Deep‐Sea Drilling Project site 532, which is under the seaward edge of the Benguela upwelling system and has light‐dark color cycles resulting from variations in sediment properties. Cyclical fluctuations in opal, organic carbon, and calcium carbonate accompany the color changes. Examination of early Pleistocene sediments taken at 10‐cm intervals from section 532B‐17‐2 reveals that high carbonate concentrations coincide with lower organic carbon percentages. Carbon and nitrogen isotope contents of organic matter remain essentially constant through the color cycles. Geolipid contents show somewhat better retention of original character in darker sediments than in lighter portions of this section and reflect variations in the degree of preservation of organic matter. The origin of the light‐dark cycles may be fluctuations in the Benguela Current caused by variations in the earth's obliquity.
Barium, equatorial high productivity, and the northward wandering of the Indian continent
Authors: Schmitz Birger
Published: February 2008

High concentrations of biologically precipitated barite characterize the deep‐sea sediments underlying the equatorial high‐productivity belt of the Indian Ocean. By studying the barium distribution in five Deep Sea Drilling Project cores (213–217), drilled in the eastern Indian Ocean north of and below the present high‐productivity zone, it is possible to determine the times when the different coring sites passed beneath the zone. From this information, net northward spreading rates of the Indian plate can be deduced. The results suggest that northward movement was very rapid during the early and middle Paleogene, slow during the mid‐Cenozoic, and then rapid again from the Late Miocene onwards. The Late Miocene revitalization of active seafloor spreading south of the Indian continent coincides with the main phase of the Himalayan uplift.

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North American Paleozoic oceanography: Overview of progress toward a modern synthesis
Authors: Johnson Markes E.
Published: February 2008

Three fundamental questions have confronted paleoceanographers from the beginning of their North American explorations. What was the size and timing of ancient epicontinental seas: large and long‐lasting or small and brief? What characterized the distribution of biotas and sediments at any one point in time: a multitude of complex facies patterns or a more spacially homogeneous cover? What promoted continental foundering: eustatic changes in sea level or relative changes in sea level brought about by regional tectonics? These questions have been debated by North Americans since the middle 1800s in response to various new insights, usually coming from abroad but often elaborated into substantial contributions of equal standing. Contemporary facies zones in Mediterranean biota found by the Englishman E. Forbes attracted the notice of geologists as early as 1844. C. Whittlesey was among the first to apply the bathymetric scheme of Forbes to the interpretation of American Paleozoic strata in 1851. The outstanding “native” innovation of the period was J. Hall's geosyncline concept, which is reflected in the earliest map of Paleozoic North America made by T. C. Chamberlin in 1881. Another wave of influence spread from the late 19th century work on stratigraphic facies patterns by the German J. Walther. A. W. Grabau is best remembered as Walther's foremost American champion against the formidable layer‐caker E. O. Ulrich in the first decades of the 20th century, but he also made pioneering contributions of his own on Paleozoic sea level studies and global paleogeographic reconstructions. Charles Schuchert was the consummate paleogeographer of this period. Meanwhile, the term “cyclothem” was coined by J. Marvin Weller in 1930 for recurrent Carboniferous strata in Illinois. Controversy fast erupted over a glacial as opposed to tectonic mode of origin for these cycles. In 1964, A. B. Shaw restimulated interest in Paleozoic oceanography through his reformulation of Walther's ideas. Novel additions included a model for epeiric sea carbonates and the methodology for graphic correlation. Invoking studies by C. G. J. Petersen on recent communities in Danish waters, A. M. Ziegler added new emphasis to paleobathymetry based on fossil communities. As was in Grabau's case, this interest eventually led to larger concerns with global paleogeography. Although the same questions are still debated today, the foregoing periods set the stage for a modern, more interdisciplinary approach to Paleozoic oceanography.
The chronology of the last Deglaciation: Implications to the cause of the Younger Dryas Event
Authors: Broecker W. S. , Andree M. , Wolfli W. , Oeschger H. , Bonani G. , Kennett J. , Peteet D.
Published: February 2008

It has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions. This extraordinary event, referred to by European palynologists as the Younger Dryas, was centered in the northern Atlantic basin. Evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern Atlantic Ocean. Further, it appears that these mode changes may have been triggered by diversions of glacial meltwater between the Mississippi River and the St. Lawrence River drainage systems. We report here Accelerator Mass Spectrometry (AMS) radiocarbon results on two strategically located deep‐sea cores. One provides a chronology for surface water temperatures in the northern Atlantic and the other for the meltwater discharge from the Mississippi River. Our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern Atlantic basin with the meltwater history for the Laurentian ice sheet.
Tertiary paleoceanic chemical variability: Unintended consequences of simple geochemical models
Authors: Delaney Margaret Lois , Boyle Edward A.
Published: February 2008

Five lines of concrete, quantitative evidence about oceanic chemical composition during the past 65 m.y. can provide insights into the controlling processes and their temporal variations, but the system constraints are not yet fully understood. The calcium carbonate compensation depth, mean carbon isotopic ratio, and strontium isotopic ratio have all changed significantly during this time, while changes in lithium‐to‐calcium and strontium‐to‐calcium ratios have been much smaller. When these tracers are considered separately, simple scenarios of changes in geochemical and geological factors can be used to explain the historical records. These factors include: (1) increases in continental chemical weathering rates and net continental fluxes to the oceans, (2) changes in the isotopic composition of material weathered from continents to the oceans, (3) decreases in the proportion of calcium carbonate deposited on continental shelves, (4) changes in the deposition or weathering rates of certain types of sediments, and (5) changes in hydrothermal circulation. Because these geochemical cycles are linked to each other (and to others, such as nutrients and global atmospheric carbon dioxide), an explanation invoked for one tracer must satisfy the direction, magnitude, and timing of the patterns for all the tracers. Several simple scenarios for geochemical variations have been evaluated for their consequences (both intended and unintended) and compared to the historical records. Despite the attractiveness and possible justifications of some simple hypotheses, for example, decreases in organic carbon burial rates, increases in carbonate weathering rates on the continents, or increases in all continental weathering rates, no one simple scenario appears to be consistent with both the timing and magnitude of the changes observed during the past 65 m.y. for all tracers considered. The contradictions uncovered can be useful in defining what knowledge is crucial to further understanding of oceanic chemical history. Better knowledge is needed of absolute deep‐ocean sediment accumulation rates and their temporal variability, of the extent and time scale of variability in the net carbon isotope input to the ocean from continental weathering, of steady state fluxes for oceanic mass balances and the extent to which these mass balances approach steady state behavior, and of the links and interactions between the geochemical cycles of various elements.
A new mechanism for decreasing North Atlantic Deep Water production rates during the Pleistocene
Authors: Crowley Thomas J. , Häkkinen Sirpa
Published: February 2008

Geological data suggest that North Atlantic Deep Water (NADW) production rates decreased during the Pleistocene. We apply a coupled ice‐mixed layer model for vertical overturn in the marginal ice zone (Häkkinen, 1987a) to propose an explanation for such a decrease. The model predicts that prevailing wind direction is important in preconditioning of the water column along the marginal ice zone (MIZ) because it affects rates of upwelling and mixing of surface and subsurface waters, processes that result in deep ‐water formation. At present, prevailing wind directions during the winter in the Greenland Sea are northeasterly. Because ice has a larger drag coefficient than water, Ekman transport is greater under the ice than in open water. This configuration causes divergence along the MIZ, mixing of surface and subsurface waters, and vertical overturn. During the glacial maximum, however, the prevailing winds along the MIZ (polar front) were predominantly westerly. Modeling studies suggest that ice‐age changes in the prevailing winds would have significantly increased the depth of the mixed layer and decreased entrainment (equal to mixing) rates, in agreement with geological data. Mixing changes due to westerly winds are greater than mixing changes due to a lower ‐salinity layer under the present wind regime. Changes due to winds are so large that further changes in boundary conditions (low ‐salinity surface layer) result in only minor additional reductions in vertical mixing. Still, the maximum reduction occurs when the two processes are considered together, a situation that may be applicable to the Younger Dryas event during the last deglaciation, when a meltwater lid may have developed in the subpolar North Atlantic. Our study suggests that wind‐induced changes in mixed ‐layer depth along the MIZ represent a viable mechanism for decreasing past NADW production rates.
Germanium/silicon fractionation during biogenic opal formation
Authors: Murnane R. J. , Stallard R. F.
Published: February 2008

Model results and empirical data show that germanium is fractionated from silica during biogenic opal formation. In a two‐box model of the ocean, particulate Ge/Si can vary between the average ocean Ge/Si and the average ocean ratio times the Ge fractionation coefficient. The two‐box model requires a Ge fractionation coefficient near 0.48 to reproduce Si and Ge concentrations similar to the ocean. Analysis of paired water and opal samples yields a Ge fractionation coefficient of 0.51. As a consequence of this fractionation, the Ge/Si of opal can be an upwelling indicator. Small shifts of opal Ge/Si in adjacent centimeter‐scale lighter and darker layers in the Miocene Monterey Formation are consistent with other sedimentologic indicators of productivity and upwelling variations. Opal Ge/Si are lower in lighter layers and are consistent with interpretations that the lighter layers were formed by increased productivity in overlying waters.
Paleoenvironmental changes in the Norwegian Sea and the northeast Atlantic during the last 2.8 m.y.: Deep Sea Drilling Project/Ocean Drilling Program Sites 610, 642, 643 and 644
Authors: Jansen E. , Bleil U. , Henrich R. , Kringstad L. , Slettemark B.
Published: February 2008

Sedimentological, isotopic and magnetostratigraphic investigations of Ocean Drilling Program and Deep Sea Drilling Project sites 642, 643, 644 and 610 document the oceanographic and climatic evolution of the Norwegian Sea and the northeastern Atlantic over the last 2.8 m.y.. The results show that a major expansion of the Scandinavian Ice Sheet to the coastal areas took place at about 2.56 Ma. Relatively severe glacials appeared until about 2 Ma. The period 2.6 ‐ 1.2 Ma experienced in general cold surface water conditions with only a weak influx of temperate Atlantic water as compared with late Quaternary interglacials. The Norwegian Sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the Holocene. Deep water formed by other mechanisms than it does today. Between 2 and 1.2 Ma the glaciations in Scandinavia were small. A transition toward larger glacials took place during the period 1.2 to 0.6 Ma, corresponding to warmer interglacials and reduced calcite dissolution. Only during the last 0.6 m.y. has the oceanographic and climatic system of the Norwegian Sea varied in the manner described in previous studies of the late Quaternary. A strong thermal gradient was present between the Norwegian Sea and the northeastern Atlantic during the Matuyama (2.5–0.7 Ma). This is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation.
Preliminary estimates for the radiocarbon age of deep water in the glacial ocean
Authors: Broecker W. S. , Andree M. , Bonani G. , Wolfli W. , Oeschger H. , Klas M. , Mix A. , Curry W.
Published: February 2008

Radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two Atlantic and two Pacific cores are reported. The differences for benthic‐planktonic pairs suggest that the radiocarbon age for deep Atlantic water was somewhat larger than today's (i.e., 600±250, as opposed to 400 years) and that the radiocarbon age for deep Pacific water was also slightly larger than today's (2100±400, as opposed to 1600, years). Our results suggest that during glacial time, the deep Pacific was, as it is today, significantly depleted in radiocarbon relative to the deep Atlantic. As many questions remain unanswered regarding the reliability of this approach, these conclusions must be considered to be preliminary.
Late Cenozoic Ge/Si record of marine biogenic opal: Implications for variations of riverine fluxes to the ocean
Authors: Shemesh A. , Mortlock R. A. , Froelich P. N.
Published: February 2008

We have determined germanium/silicon ratios in purified diatoms and radiolarians from siliceous sediments in Holocene core tops, one late Pleistocene piston core, and four high‐latitude Southern Ocean Deep Sea Drilling Project (DSDP) sites ranging in age from Holocene to Oligocene. High‐latitude Holocene diatoms in the 10‐ to 38‐µm size fraction ([Ge/Si]opal = 0.693 ± 0.039 × 10−6) faithfully record the present oceanic ratio ([Ge/Si]seawater = 0.699 ± 0.004 × 10−6). This confirms that diatoms from siliceous oozes are monitors of seawater Ge/Si and may record past changes in rates of delivery of weathering products to the sea from continental and seafloor weathering. Large diatoms and radiolarians display ratios much lower than (Ge/Si)seawater, suggesting that (Ge/Si)opal, to some extent, displays the effects of biological fractionation. From 0 to 2.5 m.y.B.P., (Ge/Si)opal in diatoms from DSDP sites ranges from about 0.54 to 0.70 × 10−6, similar to the range observed in one late Pleistocene piston core over the last 25 kyr. From 2.5 to 6 m.y.B.P., the ratio is more variable, while prior to 10 m.y.B.P., ratios are clearly higher, averaging about 0.9 × 10−6 in the early to middle Miocene. Low values of the ratio are consistent with global weathering regimes dominated by river silica input to the sea, while higher ratios suggest periods of enhanced hydrothermal input or reduced fluvial contribution. Nevertheless, an oceanic one‐box model with variable river and hydrothermal inputs and biogenic opal output cannot adequately account for the magnitude or the timing of changes observed in the record, suggesting the existence of other sources/sinks for inorganic germanium and/or silicon to or from the sea.
An organic geochemical assessment of oceanographic conditions at Manop Site C over the past 26,000 years
Authors: Prahl F. G. , Muehlhausen L. A. , Lyle M.
Published: February 2008

Eleven sediment samples taken downcore and representing the past 26 kyr of deposition at MANOP site C (0°57.2′N, 138°57.3′W) were analyzed for lipid biomarker composition. Biomarkers of both terrestrial and marine sources of organic carbon were identified. In general, concentration profiles for these biomarkers and for total organic carbon (TOC) displayed three common stratigraphic features in the time series: (1) a maximum within the surface sediment mixed layer (≤4 ka); (2) a broad minimum extending throughout the interglacial deposit; and (3) a deep, pronounced maximum within the glacial deposit. Using the biomarker records, a simple binary mixing model is described that assesses the proportion of terrestrial to marine TOC in these sediments. Best estimates from this model suggest that ≈20% of the TOC is land‐derived, introduced by long‐range eolian transport, and the remainder is derived from marine productivity. The direct correlation between the records for terrestrial and marine TOC with depth in this core fits an interpretation that primary productivity at site C has been controlled by wind‐driven upwelling at least over the last glacial/interglacial cycle. The biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr B.P. Diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr.
Foraminiferal reconstruction of barium distributions in water masses of the glacial oceans
Authors: Lea David W. , Boyle Edward A.
Published: February 2008

Foraminiferal Ba can be used to reconstruct the distribution of deeply regenerated chemical components in past oceans. The Ba contents of benthic foraminifera recovered from cores in the Atlantic Ocean indicate that waters deeper than 2900 m had ∼30–60% higher Ba during the last glacial maximum (LGM). These changes are consistent with previously observed glacial nutrient enrichments based on foraminiferal Cd and δ13C. Increases in deepwater nutrient contents in the Atlantic can be explained by reductions in North Atlantic Deep Water formation during the LGM. Ba/Ca of benthic foraminifera from the glacial sections of intermediate depth Atlantic cores are equal to or lower than Holocene values. This Ba evidence argues against the Mediterranean as a greatly increased source to Atlantic intermediate waters during the LGM, since the Mediterranean is enriched in Ba today and apparently remained enriched during the LGM. Benthic foraminiferal Ba from the glacial sections of cores from the eastern equatorial Pacific suggest that deep waters of the Glacial Pacific were about 25% lower in Ba (at ∼3000 m). Taken together, the foraminiferal evidence indicates that the Ba content of deep waters of the Atlantic, Antarctic, and Pacific were similar at the LGM. Since foraminiferal Cd distributions indicate that Cd remained significantly lower in the deep Atlantic relative to the Pacific at the last glacial maximum, a seven‐box ocean model is used to explore several scenarios for reconciling LGM Ba and Cd distributions. While the changed distribution of both tracers suggests diminishment in the flux of nutrient depleted waters to the deep Atlantic during the LGM, increased Atlantic upwelling rates and consequently enhanced Ba particle fluxes can account for the the lack of Ba fractionation between the deep Atlantic and Pacific. The model suggests that Ba can be transferred efficiently to the deep Atlantic by enhanced upwelling because the vast majority of the Ba is regenerated in the deep Atlantic box.
Advances in the theory of anisotropic elastic wave propagation
Authors: Kraut Edgar A.
Published: February 2008

The qualitative effects of anisotropy on elastic waves propagating in a solid medium were well known to Lord Kelvin. Having been recognized, however, these effects were neglected as being of secondary importance in the dynamics of elastic mediums. This relegation of anisotropy to a secondary role in the dynamics of elastic mediums was undoubtedly justified, particularly in view of the relatively primitive state of experimental elasticity and seismology during Kelvin's time. It was not until after World War 2 that the effects of anisotropy again received serious attention. This was primarily because of the development of ultrasonic techniques for the measurement of dynamic elastic constants of pure crystals. In such experimental problems anisotropy no longer plays a secondary role. The study of how a disturbance, generated by a transducer on the surface of a crystal, spreads through the crystal led to the discovery, by Musgrave, that the wave surface, which forms the boundary of the spreading disturbance, could have cuspidal singularities. This had not been previously predicted, although it could have been predicted by Kelvin had he been more familiar with algebraic geometry. In another area of research (seismology), the post World War 2 years also saw a rise of interest in anisotropy, particularly in the effect of possible continental anisotropy on the propagation of Rayleigh waves. The increased experimental activity in crystal dynamics and the improvement of experimental seismology to the point where secondary effects became important resulted in a number of theoretical investigations into the propagation of plane, time harmonic waves in anisotropic mediums. By 1959 the state of the theoretical and experimental understanding of anisotropic elastic wave propagation had advanced to the point where rigorous wave theoretical calculations were in order. All the simple, solvable problems of isotropic dynamic elasticity, i.e. the initial value problem for an unbounded homogeneous medium, the mixed initial and boundary value problem for a surface line source on a half‐space, the normal mode problem for an elastic wave guide, etc., can be formulated and solved in detail in the anisotropic case. Furthermore, the solutions can be obtained by extensions of the usual transform methods used in isotropic problems. The results can be physically interpreted by means of classical differential geometry. This review summarizes those anisotropic problems treated since 1959 and the techniques developed to solve them.