bluuebunny/crossref_metadata_2025 huggingface dataset:
Methane and carbon monoxide emissions from asphalt pavement: Measurements and estimates of their importance to global budgets
Authors: Tyler S. C. , Lowe D. C. , Dlugokencky E. , Zimmerman P. R. , Cicerone R. J.
Published: February 2008

We measured emissions of methane from asphalt surfaces used in pavement for roadways. Maximum emissions were 22 mg/m2/hr for 1‐ to 4‐week‐old pavement during maximum sunlight intensity. Emissions were much smaller at low sunlight intensity and dropped off to negligible amounts at night. Smaller emissions were observed for asphalt pavement of 2.5 to 3 years approximate age under similar conditions. Companion measurements of carbon monoxide emissions resulted in maximum emissions of about 2.6 mg/m2/hr for 1‐week‐old pavement. These findings indicate that emissions of CH4 and CO are a function of both sunlight and temperature. Based on our results, methane emissions from asphalt pavement cannot be a significant source of atmospheric methane as compared to other identified methane sources. Therefore, although asphalt methane emissions are a form of fossil fuel methane, they cannot explain the relatively high fraction of 14C‐depleted methane in the atmosphere.
Smokes from the burning of aviation fuel and their self‐lofting by solar heating
Authors: Radke Lawrence F. , Lyons Jamie H. , Hobbs Peter V. , Weiss Ray E.
Published: February 2008

The emission factors and optical properties of smokes produced by the burning of aviation fuel were determined from airborne measurements. These rather large fires (30 m in diameter and containing as much as 4.5×104 L of fuel) produced dark columns of smoke. On several occasions the smoke was observed to continue to rise slowly after its initial stabilization at a temperature inversion. This rise was evidently due to the absorption of solar radiation by the smoke.
Long‐term trends in the concentrations of SF6, CHClF2, and COF2 in the lower stratosphere from analysis of high‐resolution infrared solar occultation spectra
Authors: Rinsland C. P. , Goldman A. , Murcray F. J. , Blatherwick R. D. , Kosters J. J. , Murcray D. G. , Sze N. D. , Massie S. T.
Published: February 2008

Long‐term trends in the concentrations of SF6, CHClF2 (CFC‐22), and COF2 in the lower stratosphere have been derived from analysis of ca. 1980 and more recent infrared solar occultation spectra recorded near 32°N latitude at ∼0.02‐Cm−1 resolution. Consistent sets of line parameters and spectral calibration methods have been used in the retrievals to minimize systematic error effects. Quoted error limits are 1 sigma estimated precisions. The SF6 and CHClF2 results are based on spectra recorded by balloon‐borne interferometers in March 1981 and June 1988 and a comparison of these results with the Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment/Spacelab 3 measurements obtained in May 1985 near 30°N latitude. In the 13–18 km altitude range the mean measured SF6 mixing ratio in parts per trillion by volume (pptv) increased from 1.17±0.21 in March 1981 to 2.02±0.20 pptv in June 1988, and the CHClF2 mixing ratio below 15 km altitude increased from 51±8 pptv in March 1981 to 102±10 pptv in June 1988. The CHClF2 retrievals used new empirical CHClF2 line parameters derived from 0.03‐Cm−1 resolution laboratory spectra recorded at six temperatures between 203 and 293 K; the derived mixing ratios are ∼30% higher than obtained with earlier sets of line parameters, thereby removing a large discrepancy noted previously between IR and in situ measurements of CHClF2. Assuming an exponential growth model for fitting the trends, SF6 and CHClF2 mean increase rates of 7.4% ±1.9% and 9.4% ±1.3% year−1, are obtained, respectively, which correspond to cumulative increases by factors of ∼1.7 and ∼2.0 in the concentrations of these gases over the 7.2‐year measurement period. Analysis of spectra recorded in October 1979 and April 1989 yields COF2 volume mixing ratios that are respectively 0.44±0.17 and 1.21±0.24 times the ATMOS/Spacelab 3 values, from which an average COF2 increase rate of 10.3±1.8% year−1 over this time period has been estimated. The present results are compared with previously reported observations and trends and with one‐dimensional model calculations. The model calculated trends are in reasonably good agreement with the observations.
The Amazon Boundary Layer Experiment: Wet season 1987
Authors: Harriss R. C. , Garstang M. , Wofsy S. C. , Beck S. M. , Bendura R. J. , Coelho J. R. B. , Drewry J. W. , Hoell J. M. , Matson P. A. , McNeal R. J. , Molion L. C. B. , Navarro R. L. , Rabine V. , Snell R. L.
Published: February 2008

The Amazon Boundary Layer Experiment (ABLE 2B) used data from aircraft, ground‐based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during wet season (April–May 1987) conditions. This paper reports the experimental design for ABLE 2B and a brief summary of the results for the combined ABLE 2A and ABLE 2B. The detailed results of ABLE 2B are presented in a series of papers in this issue. The chemical composition of the atmospheric mixed layer over the Amazon Basin ecosystem during both wet and dry seasons reflects interacting influences from biogenic gas and aerosol sources and sinks, photochemistry, exchange with the free troposphere, influx of marine air from the tropical Atlantic, and long‐range transport of pollutants from distant industrial and agricultural activities. The signature of human activities on undisturbed regions of the Amazon Basin is most pronounced during the dry season due to meteorological conditions which favor the transport to and accumulation of regional pollution from biomass burning in the troposphere over the region. During the wet season, the northern hemisphere becomes a source of pollution to the Amazon as a result of episodic inputs associated with changes in the large‐scale atmospheric circulations associated with subtropical anticyclones. Seasonal variations in biogenic emissions are important in determining the photochemical characteristics of the Amazon mixed layer. The undisturbed regions of the Amazon are potentially a globally significant sink for ozone during wet‐season conditions. The region is an important source of both methane and nitrous oxide. The extensive area of undisturbed tropical forests in the Amazon Basin and the relatively pristine atmospheric chemical conditions during much of the wet season are an important resource for understanding the role of biosphere‐atmosphere interactions in global atmospheric chemistry.
Measurements of soil and canopy exchange rates in the Amazon rain forest using 222Rn
Authors: Trumbore S. E. , Keller M. , Wofsy S. C. , da Costa J. M.
Published: February 2008

Measurements of the emission of 222Rn from Amazon forest soils, and profiles of 222Rn in air were used to study the ventilation of the soil atmosphere and the nocturnal forest canopy. The emission of 222Rn from the yellow clay soils dominant in the study area averaged 0.38±0.07 atom cm−2 s−1. Nearby sand soils had similar fluxes, averaging 0.30 ± 0.07 atom cm−2 s−1. The effective diffusivity in the clay soil (0.008±0.004 cm2 s−1), was lower than that for the sand soil (0.033±0.030 cm2 s−1). Profiles of 222Rn and CO2 in air showed steepest concentration gradients in the layer between 0 and 3 m above the soil surface. Aerodynamic resistances calculated for this layer from 222Rn and CO2 varied from 1.6 to 18 s cm−1, with greater resistance during the afternoon than at night. Time averaged profiles of 222Rn in the forest canopy measured during the evening and night were combined with the soil flux measurements to compute the resistance of the subcanopy to exchange with overlying air. The integrated nocturnal rate of gas exchange between the canopy layer (0 to 41 m) and overlying atmosphere based on 222Rn averaged 0.33±0.15 cm s−1. An independent estimate of gas exchange, based on 13 nights of CO2 profiles, averaged 0.21±0.40 cm s−1. These exchange rates correspond to flushing times for the 41 m canopy layer of 3.4 and 5.5 hours, respectively. Comparison of 222Rn and CO2 profiles show that the nocturnal production of CO2 by above‐ground vegetation was about 20% of the soil emission source, consistent with data from eddy‐correlation experiments (Fan et al., this issue).
Surface carbon monoxide measurements in Amazonia
Authors: Kirchhoff V. W. J. H. , Marinho E. V. A.
Published: February 2008

The concentration of atmospheric carbon monoxide, CO, was measured in the Amazonian rain forest. Air samples were collected at least three times a day during a continuous sequence of 36 days, from a height of 1.5 m above the ground. These surface CO measurements were part of a large binational 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 experiment was April–May of 1987, in the local wet season. The measurement technique used was Chromatographic separation followed by mercury vapor detection. The surface CO measurements obtained represent a comprehensive CO data set, unique in that the concentrations were measured immediately after collection, by a measurement system installed next to the sampling sites. The CO lab was set up at Ducke Forest Reserve, some 30 km north of the city of Manaus (3°S, 60°W). The results show a small but consistant diurnal variation of the CO concentration, with a maximum around noon. The average CO mixing ratio for the period was 102.9±11.4 parts per billion by volume (ppbv), with most samples giving concentrations between 95 and 105 ppbv. On six occasions in April, large CO concentrations were observed during relatively short periods, and these were classified as pollution episodes associated with unusual wind conditions which probably brought air into the forest that had contact with the city of Manaus. No such episodes were seen during May. Simultaneous sampling inside the forest, under the canopy, and in the Ducke Forest clearing, show larger concentrations in the forest, by a few ppbv. This result is consistent with the direct measurement of the CO profile below the forest canopy, which gave a concentration gradient consistent with an upward flux of 4×1011 CO molecules cm−2 s−1.
Precipitation chemistry in central Amazonia
Authors: Andreae M. O. , Talbot R. W. , Berresheim H. , Beecher K. M.
Published: February 2008

Rain samples from three sites in central Amazonia were collected over a period of 6 weeks during the 1987 wet season and analyzed for ionic species and dissolved organic carbon. A continuous record of precipitation chemistry and amount was obtained at two of these sites, which were free from local or regional pollution, for a time period of over 1 month. The volume‐weighted mean concentrations of most species were found to be about a factor of 5 lower during the wet season compared with previous results from the dry season. Only sodium, potassium, and chloride showed similar concentrations in both seasons. When the seasonal difference in rainfall amount is taken into consideration, the deposition fluxes are only slightly lower for most species during the wet season than during the dry season, again with the exception of chloride, potassium, and sodium. Sodium and chloride are present in the same ratio as in sea salt; rapid advection of air masses of marine origin to the central Amazon Basin during the wet season may be responsible for the observed higher deposition flux of these species. Statistical analysis suggests that sulfate is, to a large extent, of marine (sea salt and biogenic) origin, but that long‐range transport of combustion‐derived aerosols also makes a significant contribution to sulfate and nitrate levels in Amazonian rain. Organic acid concentrations in rain were responsible for a large fraction of the observed precipitation acidity; their concentration was strongly influenced by gas/liquid interactions.
Nonmethane hydrocarbon chemistry in the remote marine boundary layer
Authors: Donahue Neil M. , Prinn Ronald G.
Published: February 2008

We present a photochemical model of the remote marine boundary layer, focusing on the role of reactive nonmethane hydrocarbons (NMHCs). Current observations constrain total NMHC atmospheric concentrations in the remote marine boundary layer only to within a factor of 25, with the major uncertainty lying in the heavier alkenes. Using our model, we deduce air‐sea fluxes of NMHCs from these observations by demanding a balance between oceanic evasion fluxes and atmospheric loss rates for these species. The total NMHC air‐sea flux so deduced lies between 1×1010 and 2×1011 molec cm−2 s−1, with the range representing either true variability or uncertainty. This is inconsistent with the total NMHC air‐sea flux ((1‐6) × 109 molec cm−2 s−1) derived using a diffusive microlayer model together with the few existing oceanic NMHC observations. Diurnally averaged OH concentrations in our model range between 1.2×106 and 4.0×105 molec cm−3; our preferred model run, with a total NMHC flux of 5.4×1010 molec cm−2 s−1, produces a diurnally averaged OH concentration of 8.4×105 molec cm−3. This agrees well with OH concentrations derived from inversions of methyl chloroform data. Our model results imply a possibly significant role for NMHCs in determining OH concentrations in the remote marine boundary layer. Definitive conclusions about the role of NMHCs are prevented, however, both by inconclusive data on the NMHCs themselves and by large chemical uncertainties, particularly that in the O(1D) quantum yield.
Tropospheric OH in a three‐dimensional chemical tracer model: An assessment based on observations of CH3CCl3
Authors: Spivakovsky C. M. , Yevich R. , Logan J. A. , Wofsy S. C. , McElroy M. B. , Prather M. J.
Published: February 2008

The three‐dimensional global distribution of OH over a year is calculated as a function of temperature, ultraviolet irradiance, and densities of H2O, CO, O3, CH4, and NOt, (defined as NO + NO2 + NO3 + 2N2O5 + HNO2 + HNO4). The concentration of OH is computed within a chemical tracer model (CTM) with an accuracy comparable to that of a detailed photochemical model. Distributions of CO, NOt, O3, CH4, and the density of O3 column were specified on the basis of observations. Meteorological fields were derived from the general circulation model developed at the Goddard Institute for Space Studies. The numerical method for parametrization of chemistry is described in Spivakovsky et al. (this issue). The CTM is used to simulate the global distribution of CH3CCl3. The computed distribution of OH implies a lifetime of 5.5 years for CH3CCl3 (obtained by relating the global burden of CH3CCl3 to the global loss, integrated using simulated three‐dimensional distributions). Analysis of the long‐term trend in CH3CCl3 as defined by observations suggests a lifetime of 6.2 years (consistent with Prinn et al. (1987)), indicating that model levels of OH may be too high by about 13%. This estimate for the lifetime depends on industry data for global emissions and on the absolute calibration of observations. It is argued that seasonal variations of CH3CCl3 provide an independent test for computed OH fields that is insensitive to the uncertainties in the budget of CH3CCl3. The annual cycle of CH3CCl3 from about 25°S to the South Pole is dominated by seasonal changes in OH. Observed seasonal variations of CH3CCl3 indicate that the OH field south of 20°S±4° should be scaled by 0.75±0.25 from computed values, consistent with the result based on long‐term trends. Reactions involving non‐methane hydrocarbons were not included in the current model. These reactions could account for lower concentrations of OH than computed. Seasonal variations of CH3CCl3 in the tropics and in the northern mid‐latitudes are dominated by effects of transport. If use of CH3CCl3 is phased out (as envisioned by the Montreal protocol), the dynamically driven seasonal variations of CH3CCl3 will decrease dramatically, whereas the chemically driven variations will remain proportional to the concentration of CH3CCl3; then the annual cycle of CH3CCl3 in northern mid‐latitudes will provide a measure of OH as does at present the annual cycle in southern mid‐latitudes. The influence of chemistry on the latitudinal distribution of CH3CCl3 is small and at present does not provide a constraint for the globally averaged OH or for the latitudinal distribution of OH. However, if emissions of CH3CCl3 were to cease, the tropical depression in the concentration of CH3CCl3 caused by high levels of OH in the tropics may provide an additional means to test OH models.
Depletion of lower tropospheric ozone during Arctic spring: The Polar Sunrise Experiment 1988
Authors: Bottenheim Jan W. , Barrie Leonard A. , Atlas Elliot , Heidt Leroy E. , Niki Hiromi , Rasmussen Reinholt A. , Shepson Paul B.
Published: February 2008

Results are presented from the 2‐month Polar Sunrise Experiment 1988, which was undertaken to further investigate the cause of ozone destruction during spring in the lower Arctic atmosphere. A strong anticorrelation between the decrease in ozone and concurrent increase in bromine compounds collected on filters observed during a 21‐day period in 1986 was confirmed. It is shown that the reason for this observation is a meteorological modulation which alternately brings to the sampling location lower boundary layer air, depleted in ozone and enriched in filterable bromine, and free tropospheric air with abundant ozone and few bromine compounds. Several other compounds that may have a bearing on the chemical reactions leading to ozone depletion were measured. Bromoform, a potential source for Br atoms, was found to be present at levels between 1 and 10 parts per trillion by volume (pptv); good evidence was obtained that, as with filterable bromine, it had increased in ozone depleted boundary layer air. The mean NO2 level was 85 pptv with an estimated uncertainty of a factor less than 2. However, this measurement of NO2 may have been the sum of NO2+N2O5. The possibility that Br atoms are formed from an N2O5+NaBr interaction is therefore not ruled out. There was a good indication that apparent NO2 was depleted during episodes of low ozone. An upper limit for the mixing ratio of formaldehyde was found to be 39 pptv, while acetaldehyde was observed at mixing ratios of ca. 65 pptv. Ethylene and acetylene were also found to be depleted concurrently with O3. These compounds do react with Br radicals in air (as do the aldehydes) and it is speculated that they may create a link with HOx. chemistry. Data on several other chemical compounds are also presented. Their participation in the O3 depletion chemistry is less clear. The implications of the measurements with respect to the hypothesis that the ozone depletion are due to a BrOx‐O3 destruction cycle are explored.
On the relation between polar continentality and climate: Studies with a nonlinear seasonal energy balance model
Authors: Hyde William T. , Kim Kwang‐Yul , Crowley Thomas J. , North Gerald R.
Published: February 2008

The seasonal cycle of surface temperature is largely controlled by the land‐sea distribution. Previous studies with a two‐dimensional, seasonal energy balance model (EBM) suggested that large annual cycles on supercontinents could produce sufficiently high summer temperatures to melt summer snow, even when the continents were located in polar regions. The above calculations were done with a linear model. In this paper we test the sensitivity of these conclusions to seasonally varying snow albedo feedback by developing a new nonlinear two‐dimensional, seasonal EBM. The model satisfactorily reproduces the present annual and semiannual cycles, plus snow and sea ice margins; its sensitivity is ≈ 25% greater than that of the linear model and comparable to a number of general circulation model (GCM) studies for altered CO2 levels. Experiments are described for a series of idealized supercontinent configurations; in addition we examine the effect of changing land‐sea distributions on the climate of Greenland and Antarctica. Supercontinent model simulations are similar to the previously published linear model results and provide further support for the hypothesis that ice‐free states could occur on polar supercontinents. However, some of our results for smaller land masses differ from the earlier study. Although temperatures are systematically lower for the nonlinear run, we simulate >15°C decrease in summer temperatures over Greenland during the last 100 million years in both the linear and nonlinear models. However, there is only a weak suggestion of a long‐term trend in the southern hemisphere. Revised reconstructions of southern hemisphere geography further obscure any long‐term trend in this region. Overall, model simulations provide further support for the proposition that changes in seasonality have played an important role in climate change over the past few hundred million years.
Microphysics in an oceanic mesoscale convective system during the Taiwan area mesoscale experiment
Authors: Liu Chung‐Ming , Lo K. Kenneth
Published: February 2008

The microphysical processes in both the melting layer and the warm‐rain region of an oceanic mesoscale convective system observed during the Taiwan Area Mesoscale Experiment (TAMEX) are studied using airborne observations. Two flight cases are used, one flown in the transitional region and the other in the stratiform region. In the melting layer the particle number density decreases by an order of magnitude from the top to the bottom of the layer. This is caused by the sharp increase of particle fall speed as snowflakes melt into rain. The ice water content is higher in the transitional region, thus cooling the environment more efficiently during melting. In the warm‐rain region the microphysical process is dominated by coalescence process. Large raindrops are generated and the corresponding median diameter of all raindrops increases by a factor of 2 to 3 from the bottom of the melting layer to the ground level. The breakup process is more efficient in the transitional region.
Lidar observations of ozone changes induced by subpolar air mass motion over Table Mountain, California (34.4°N)
Authors: McGee Thomas J. , Newman Paul , Ferrare Richard , Whiteman David , Butler James , Burris John , Godin Sophie , McDermid I. Stuart
Published: February 2008

Between October 15 and November 8, 1988, the Goddard Space Flight Center mobile stratospheric lidar was in place at the (JPL) Table Mountain Facility (located at 34.4°N, 117.7°W) for the purpose of intercomparing with the JPL lidar permanently stationed at the observatory. During the course of the intercomparison both lidar systems detected a significant change in the vertical profile of ozone lasting for several days. An analysis of meteorological data available from the National Meteorological Center has shown this change to be dynamical in origin due to the transport of subpolar air over Table Mountain.
Two approaches to determining the sea‐to‐air flux of dimethyl sulfide: Satellite ocean color and a photochemical model with atmospheric measurements
Authors: Thompson Anne M. , Esaias Wayne E. , Iverson Richard L.
Published: February 2008

Two estimates of the ocean‐to‐atmosphere flux of dimethyl sulfide (DMS) are presented to determine the feasibility of using remotely sensed data to map the marine sources of a photoreactive trace gas. First, an empirical relationship between chlorophyll a and DMS in surface seawater (Andreae and Barnard, 1984) is used with NASA coastal zone color scanner (CZCS) data for chlorophyll a pigment to derive a mean DMS flux for a region in the tropical North Atlantic for October 1980. This is compared with the sea‐to‐air flux derived from a one‐dimensional photochemical model that reproduces boundary layer concentrations of O3, CO, NO, and hydrocarbons measured on a cruise at the same location and time (Meteor 56/1). Both evaluations of DMS fluxes are in the range (2–7)×109 molecules DMS cm−2 s−1 and agree well with fluxes based on the seawater DMS concentration given by Barnard et al. (1982) for the Meteor cruise. The applicability of the results to strategies for satellite remote sensing of the tropospheric sulfur cycle is discussed. For some species (e.g., DMS) surface sensing of sources is feasible, but only in regions and seasons where phytoplankton pigment is a meaningful marker for biogenic emissions. The general applicability of ocean color to DMS determination awaits the development of an algorithm that can extract distributions of DMS emitting species from the optical signal. For other sulfur constituents (e.g., SO2, COS) atmospheric measurements are appropriate for determining tropospheric distribution. Wind, moisture, cloud, precipitation, and temperature data are also required for complete characterization of the marine sulfur cycle.
Synoptic situation in the Atlantic Ocean region during ANT V/5
Authors: Behr H. D. , Gravenhorst G.
Published: February 2008

During a 4‐week Atlantic Ocean cruise from March 21 to April 15, 1987, along 30°W between 40°S and 40°N, several investigations on trace substances in the air and in the sea were made on board the German R/V Polarstern (ANT V/5). Some of them are discussed in this issue. To better understand these results and to put them into a framework of the general atmospheric situation, daily and long‐term mean meteorological data were combined to characterize the atmospheric conditions during this cruise. First, continuous record of surface and rawinsonde data (sea and air temperature, humidity, wind direction and speed, and pressure) was evaluated. Then, as the cruise traversed several climatological zones of the Atlantic Ocean, meridional distributions of surface and upper air data could be worked out; they do not differ significantly from long‐term means of this area.
Sulfur in particles in Arctic hazes derived from airborne in situ and lidar measurements
Authors: Brock Charles A. , Radke Lawrence F. , Hobbs Peter V.
Published: February 2008

Quantitative information is needed on arctic hazes in order to determine their effects on the radiation budget, clouds, the albedo and chemical properties of the arctic snowpack, and on ecosystems in the Arctic. Using airborne observations from lidar, and in situ measurements of particle light‐scattering coefficients, aerosol size distributions and meteorological parameters, we have related backscattering measured by the lidar to the mass concentrations of particles in two mesoscale haze layers encountered in the North American Arctic. Assuming that the haze particles were composed of H2SO4 in thermodynamic equilibrium with the ambient air, good agreement is obtained between sulfur concentrations measured on filters and those derived from the particle size distributions and lidar measurements. Time‐height cross sections are shown of the airborne concentrations of sulfur in particles derived from lidar backscatter measurements in a haze layer. The average concentrations of sulfur in accumulation mode particles in the two haze layers were 0.3 and 0.4 μg m−3, and the maximum concentration was ∼3 μg m−3, with substantial horizontal and vertical variability. We estimate lower limits for the total sulfur in particles in the two haze layers to be ∼3x;104 and ∼1x105 kg, respectively.
Cretaceous black mud from the central Arctic Ocean
Authors: Clark David L. , Byers Charles W. , Pratt Lisa M.
Published: February 2008

Perhaps the oldest sediment yet recovered from the central Arctic Ocean is a black, organic carbon‐rich mud of late Campanian or Maastrichtian age. The sediment is known in a single piston core, F1‐533, taken from the eastern Alpha Ridge. The black mud has an average organic carbon content of 14 wt % and contains abundant woody plant fragments and pollen in addition to amorphous organic matter in a marine dinoflagellate‐rich matrix. Moderate hydrogen and high oxygen indices determined by Rock‐Eval pyrolysis suggest a substantial contribution of terrestrial plant debris to the marine sediment. The black mud is younger than organic‐rich strata deposited during the Oceanic Anoxic Events proposed for Aptian‐Albian and late Cenomanian to early Turonian times in the Atlantic and Pacific oceans. The high content of organic carbon and the abundance of terrestrial organic matter in the Arctic black mud suggest a marine setting influenced by an abundant supply of organic detritus rather than by a low level of oxygenation in the water column. Sediment in this core demonstrates that the central Arctic Ocean may have been in existence by the late Campanian to Maastrichtian and that the area of core F1‐533 probably was adjacent to an eroding vegetated land mass.
Late Quaternary paleoceanography of the tropical Atlantic, 2: The seasonal cycle of sea surface temperatures, 0–20,000 years B.P.
Authors: Mix Alan C. , Ruddiman William F. , McIntyre Andrew
Published: February 2008

Foraminiferal species abundances are used to estimate seasonal variability of late Quaternary sea surface temperatures in the tropical Atlantic Ocean. Empirical orthogonal functions analysis of 28 time series isolates two patterns (modes) of variation. The dominant mode 1 reflects seasonal temperature contrast of the South Equatorial Current region 5°–6°C higher at the glacial maximum than at present, probably indicating larger seasonal variations of the southern trade winds. Forcing for this pattern may have come from equatorward compression of glacial climate zones due to high‐latitude cooling in both hemispheres and/or suppression of meridional monsoonal circulation via feedback from northern hemisphere ice cover. When compared with CLIMAP estimates of lower seasonal variations of glacial age sea ice fronts in Antarctica, mode 1 suggests decoupling of low‐ and high‐ latitude seasonal cycles in the southern hemisphere on a glacial‐interglacial scale. Mode 2 variations reflect seasonal contrast in sea surface temperature of 2°–3°C less 9000 to 14,000 years B.P. than at present along the equator and in the eastern subtropical Atlantic, perhaps related to an equatorial position of the Intertropical Convergence Zone, weakened trade winds, and/or strengthened monsoonal circulation during deglaciation. Our findings emphasize the need to isolate spatially coherent (and thus dynamically linked) patterns of climate change from a complex record of multiple climatic effects. Only then can effective tests of hypotheses be made with a coupled strategy of data acquisition and climate modeling.
Symmetrical and upward shallowing cycles in the Middle Devonian of New York State and their implications for the punctuated Aggradational Cycle Hypothesis
Authors: Brett Carlton E. , Baird Gordon C.
Published: February 2008

The Middle Devonian (Eifelian and Givetian) Hamilton Group in western and central New York, composed largely of fossil‐rich marine shelf and slope facies, is subdivisible into repetitive facies sequences of varying thicknesses. Minor cycles include 1‐ to 3‐m‐thick, upward coarsening shale to siltstone hemicycles, resembling sixth‐order punctuated aggradational cycles (PACs), in central New York; probably correlative (0.5‐1.0 m) shale to argillaceous, nodular limestone couplets occur in western areas.

Major cycles in western New York include subsymmetrical 3‐ to 5‐m‐thick packages with medial limestone beds, analogous to “upper limestones” of Pennsylvanian cyclothems. The center of each cycle marks a regressive maximum and grades vertically, above and below, into black shale or dark gray mudstone, corresponding, in a facies sense, to cyclothemic “core shales” in the midcontinent Pennsylvanian. These widespread units appear to be allocyclic in nature and approximate fifth‐order transgressive‐regressive cycles, based upon average unit thickness relative to the encompassing, well‐zoned, Hamilton sequence. Correlations show that most key regressive events marked by limestones in western New York are expressed by equivalent siltstone or fine sandstone units in central New York. Most cycles, which are nearly symmetrical in western New York, grade eastward into 5‐ to 20‐m upward coarsening (PAC motif) hemicycles. These asymmetric cycles apparently reflect rapid sediment aggradation to limits imposed by wave energy in a region of abundant sediment supply. Further minor shallowing was accompanied by winnowing and bypass of fine‐grained sediments, generating condensed, capping deposits of coarser silt and sand, reworked shells and, commonly, phosphatic nodules. Ensuing sea level rises were accompanied by initial sediment starvation followed by sedimentation in deeper water. Hence asymmetrical, upward shallowing hemicycles (PACs) appear to grade offshore into thin but symmetrical cycles. Both PAC and symmetrical motifs are local responses to the same, probably allocyclic, sea level fluctuations. We suggest that the PAC motif is partially facies controlled, being largely restricted to shallow shelf settings with relatively high rates of sediment accumulation.
Pulsation tectonics as the control of long‐term stratigraphic cycles
Authors: Sheridan Robert E.
Published: February 2008

A new theory of pulsation tectonics involving the cyclic eruption of thermal plumes from the D″ layer in the lowermost mantle explains the long‐term cycles of marine stratigraphy. Heating of the mantle changes conditions at the core/ mantle boundary that result in the quiescence of the earth's magnetic field. The rising plumes, after a phase lag, later induce faster plate spreading and widespread intraplate volcanism. Subsequently, colder rock returning to the lower mantle reestablishes the D″ thermal boundary layer and sets up conditions for more turbulent core convection and frequent magnetic reversals. Meanwhile, lower‐ mantle plumes cease erupting, and the plates spread more slowly. The cycles of fast and slow plate spreading and quiet and reversing magnetic field have a duration of 60–100 m.y. Global changes in spreading rate are one of the main causes of large‐scale (100–300 m) eustatic sea level changes and variations in output of volcanic gases. Consequential changes in albedo, global temperature, humidity, forestation, atmospheric and oceanic CO2, oceanic acidity, and oxygenation lead to variations in the preservation of organic carbon in the oceans and epicontinental seas and in the level of the calcite compensation depth. During rising sea levels, there is an increase in organic carbon preservation and relatively little calcite is preserved; with falling sea levels less organic carbon and more calcite are preserved in the deep sea. The long‐term cycles in carbon and calcite‐bearing sediments correspond generally to the pulsations of Grabau (1934), the long‐term rhythms which nearly equal the lengths of geologic time periods.
Hierarchal genetic stratigraphy: A framework for paleoceanography
Authors: Busch R. M. , West R. R.
Published: February 2008

A detailed, genetic stratigraphic framework for paleoceanographic studies can be derived by describing, correlating, interpreting, and predicting stratigraphic sequences relative to a hierarchy of their constituent time‐stratigraphic transgressive‐regressive units (“T‐R units”). T‐R unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data, but correlations can be enhanced or “checked” (tested to confirm or deny) with objective biostratigraphic, magnetostratigraphic, or chemostratigraphic data. Such chronostratigraphies can then be bracketed by radiometric ages, so that average periodicities for T‐R units can be calculated and a hierarchal geochronology derived. T‐R units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening‐shallowing units because the latter are noncorrelative intrabasinally. Boundaries between T‐R units are conformable or unconformable “genetic surfaces” of two types: transgressive surfaces and “climate change surfaces”. The latter are useful for correlating minor transgressive phases through nonmarine intervals, thereby deriving information linking paleoclimatic and paleoceanographic processes. Permo‐Carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic T‐R units having periodicities of 225–300 m.y. (first order), 20–90 m.y. (second order), 7–13 m.y. (third‐order), 0.6–3.6 m.y. (fourth order), 300–500 × 10³ years (fifth order), and 50–130 × 10³ years or less (sixth‐order). Paleogeographic maps for the time of maximum transgression (“transgressive apex”) of successive fifth‐order T‐R units (5–25 m thick) in the Glenshaw Formation (Upper Pennsylvanian, Northern Appalachian Basin) delineate delta lobes, embayments, islands, and linear seaways. Relative extent of marine inundation on the fifth‐order maps was used to delineate fourth‐order T‐R units, and the fourth‐order T‐R units constitute the transgressive half of a third‐order T‐R unit. This third‐, fourth‐, and fifth‐order hierarchy is correlated more than 1200 km (750 miles) to the Western Interior “Basin,” and is confirmed with limited objective biostratigraphy.
Rainy periods and bottom water stagnation initiating brine accumulation and metal concentrations, 2. Precambrian gold‐uranium ore beds and banded iron formations
Authors: Rossignol‐Strick Martine
Published: February 2008

I previously suggested that heavy runoff during the 12,500–7000 years B.P. tropical pluvial period generated bottom water quiescence and reducing conditions making possible sapropel formation, accumulation of brine originating at the sea bottom, and long‐term preservation of hydrothermal sulfides in the Red Sea Deeps. I hypothesized the same process to account for two Precambrian strata‐bound ores. In the Upper Witwatersrand paleoplacers, South Africa, gold and uranium eroded by running water from upstream greenstones, reached highest concentrations in association with organic matter in carbonaceous seams, and deposited in the distal end of fluvial fans during transgressive phases. I propose that the deep waters over these fans became anoxic when large, sudden floods stratified the water column. The organic matter thus locally preserved concentrated gold and uranium from the partial dissolution of the detrital metallic grains. In the Hamersley basin of Western Australia, banded iron formations (BIF) of the Dales Gorge Member are a major source of iron ore. Regularly fluctuating environmental conditions are shown by repetitious BIF and black shale macrobands. I propose that they were deposited in a confined, silled, deep basin connected with the open ocean. Before initiation of the lowest BIF deposition the active regional thermohaline circulation flushing the deep waters under a rather arid climate diluted and oxidized the Fe2+‐rich hydrothermal effluents exhaling from the basin floor. Then, during a strong wet period, heavy runoff scavenging volcanoclastics from the land surface lowered the basin surface water salinity and prevented deepwater renewal. The hydrothermal effluents began to accumulate and progressively concentrated in the quiescent and progressively oxygen‐depleted deep water. During this wet initial phase, the massive black, organic‐rich pyritic shale at the top of the Mount McRae Shale Member was deposited immediately and conformably underlying the lowest BIF macroband. When aridity returned, the quiescent deep water filling the basin to sill depth had become sufficiently dense to resist its displacement by reactivated vertical circulation. From Fe2+‐rich anoxic brine, Fe3+ was precipitated at the anoxic‐oxic interface near the photic zone base by biogenic photosynthesis or Fe2+ photooxidation and partially reduced to Fe2+ during its settling through the anoxic water mass. Thus the lowest BIF macroband of the Dales Gorge Member was formed. Once high bottom water density became established, black shale macrobands were formed during recurrent wet periods and BIF macrobands during the intervening arid intervals. The macrobands' wet‐arid periodicity is suggestive of control by Milankovitch‐type insolation variation. Mesobands and microbands point to shorter climatic cycles. Termination of the system is achieved only by tectonic movements.
A rock‐magnetic study of giant piston core LL44‐GPC3 from the central North Pacific and its paleoceanographic implications
Authors: Doh Seong‐Jae , King John W. , Leinen Margaret
Published: February 2008

Previous magnetostratigraphic studies of nonfossiliferous pre‐Pliocene age pelagic clay cores from the central north Pacific have proven unsuccessful because of the unstable behavior of the natural remanent magnetization. The inability to obtain a reliable magnetostratigraphy has severely limited the temporal resolution that can be achieved in paleoceanographic studies of these nonfossiliferous pelagic clays. We carried out a rock‐magnetic study of core LL44‐GPC3, which spans the interval 0‐70 m.y. ago, to determine whether rock‐magnetic parameters can be used to construct a high‐resolution stratigraphic framework for paleoceanographic studies of central north Pacific pelagic clays despite the instability of the natural remanence. In addition, we tested the ability of rock‐magnetic methods to detect and characterize the paleoceanographic changes that are recorded in the sediments of LL44‐GPC3. Stratigraphic variations in rapid and nondestructive rock‐magnetic parameters and related ratios reflect changes in the concentration, mineralogy, and grain size of the magnetic minerals within the sediments. Rock‐magnetic parameters exhibit coherent fluctuations within both the stable and unstable sections of LL44‐GPC3. This result suggests the potential use of these parameters for regional correlation and relative dating of the nonfossil‐bearing pelagic clays of the central north Pacific gyre. Major fluctuations in rock‐magnetic parameters plotted as accumulation rates correspond to intervals of paleoenvironmental change that have been previously detected by other paleoceanographic methods. In addition, variations in a parameter proportional to the concentration of goethite/hematite correlate remarkably well with the mass accumulation rate of the total eolian component, suggesting that in some situations it can be used as a proxy indicator for eolian activity.
The response of benthic foraminifera to productivity cycles in the eastern equatorial Pacific: Faunal and geochemical constraints on glacial bottom water oxygen levels
Authors: Pedersen Thomas F. , Pickering Mark , Vogel John S. , Southon John N. , Nelson D. Erle
Published: February 2008

The Stage 2 glacial maximum in eastern equatorial Pacific Ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved O2 in glacial bottom water. Several lines of evidence are presented, based on data from two gravity cores collected from the central Panama Basin, which support the former interpretation. First, both the abundance and the size of benthic foraminifera of the genus Uvigerina increase in Stage 2, coincident with the increase in organic carbon concentration, most probably because of the greater availability of organic detritus during the glacial period. The increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where Uvigerina spp. are thought to live. Second, the number of meiofaunal faecal pellets increases markedly during the Stage 2 maximum, indicating a more populous and active infauna, which again argues against oxygen depletion. Third, there is no significant decrease in the iodine:organic carbon (I:Corg) ratio in the Stage 2 sediments. Because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments, the absence of a depletion in the I:Corg ratio in Stage 2 is evidence that bottom water remained oxygen‐ replete during the last glacial. Fourth, molybdenum is not enriched in sediments deposited in Stage 2; the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of Mo to the sediments via coprecipitation with authigenic iron sulphides. The combined faunal and geochemical data are consistent with the notion that Panama Basin deep waters remained oxygen‐replete during the last glacial maximum. It is concluded that the late Stage 2 carbon enrichment in the eastern equatorial Pacific more probably reflects higher productivity rather than enhanced preservation.
The extraterrestrial component in marine sediments: Description and interpretation
Authors: Kyte Frank T.
Published: February 2008

The influx of extraterrestrial matter to the Earth is dominated by two size‐fractions: sub‐millimeter interplanetary dust and impacting asteroids and comets. Over geologic time the major contribution of extraterrestrial matter is from the largest impactors. Interplanetary dust is largely vaporized by atmospheric entry, but some surviving material is found in sediments as cosmic spherules. Impacting asteroids and comets can produce fallout layers either regionally or globally which may contain a significant fraction of meteoritic material as well as shock‐metamorphosed and shock‐melted terrestrial material. Iridium is a sensitive tracer of extraterrestrial matter. Although high concentrations of Ir in marine sediments probably have an extraterrestrial origin, they do not necessarily indicate the presence of a major impact event. Of the thousands of impact horizons which must be resolvable in the sedimentary record, to date only seven probable impact horizons have been identified in the entire Phanerozoic. The marine geochemistry and occurrence of Ir is still poorly understood, but the thousands of Ir analyses performed in the last several years have demonstrated that the global occurrence high Ir (>10 ng/g) concentrations in Cretaceous‐Tertiary boundary sediments is a truly anomalous phenomenon.
Global variations of surface ocean productivity in low and mid latitudes: Influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years
Authors: Sarnthein Michael , Winn Kyaw , Duplessy Jean‐Claude , Fontugne Michael R.
Published: February 2008

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic δ13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low‐ and mid‐latitude upwelling cells started to decline by more than 2‐4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large‐scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic δ13C by 0.4–0.5‰. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high‐latitude insolation, i.e., to orbital forcing as primary cause.