bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen constituents of the mesosphere inferred from positive ions: H2O, CH4, H2CO, H2O2, and HCN
Authors: Kopp E.
Published: February 2008

Positive ion compositions from one mid‐latitude and four high‐latitude rocket flights were used to infer the H2O, CH4, H2CO, H2O2, and HCN concentrations in the mesosphere. The water vapor mixing ratio was highly variable between 0.1 and 5 ppmv. Only partial agreement is obtained with the ground‐based microwave measurements and/or model prediction by Garcia and Solomon (1985). The observed methane concentration varied between 70 and 4 ppb in daytime and 900 and 100 ppbv at night, respectively. Unexpectedly high H2CO concentrations have been determined with [H2CO]/[H2O] ratios between 6×10−4 and 0.1. Additional CH4 oxidation in heterogeneous chemical processes or an unknown direct local formaldehyde production is proposed to account for the high H2CO concentration. A mean HCN volume mixing ratio of 6×10−10 was inferred. A local source, CH3 + N → HCN + H2, may explain the HCN increase from 0.15 ppb in the stratosphere to 0.6 ppb in the auroral mesosphere.
Momentum and eddy kinetic energy transports by a multiple microburst‐producing storm
Authors: Lin Yeong‐jer , Coover John A.
Published: February 2008

A comprehensive study of the structure and internal dynamics was made for a multiple microburst‐producing storm for August 5, 1982, in Colorado during the Joint Airport Weather Studies (JAWS) Project at Denver's Stapleton International Airport. The analysis levels were contained between 0.25 and 2 km. The horizontal and vertical grid spacings were 0.5 and 0.25 km, respectively. These fields were subjected to internal consistency checks to determine the level of confidence before interpretation. Results show that the combined effects of misocyclone circulations, perturbation‐pressure gradients, melting, buoyancy, and precipitation loading contribute to the maintenance of the microburst downdrafts in the atmospheric boundary layer (ABL). At low levels where the microbursts dominate, the presence of microburst gust fronts and diverging outflow enhances the vertical transport of horizontal momentum and eddy kinetic energy. The misocyclones located above the microbursts largely determine the transport of horizontal momentum and eddy kinetic energy there. In the microburst subdomain, a net transport of horizontal momentum and eddy kinetic energy is downward from the misocyclone to the surface. Its magnitude is directly proportional to the strength of a microburst at low levels and the misocyclone aloft. Budget studies of horizontal momentum flux and eddy kinetic energy within the storm domain and the microburst subdomain have added to a further understanding of the storm's structure and internal dynamics. The pressure and buoyancy effects are two main contributors to the generation/decay of horizontal momentum fluxes and eddy kinetic energy at the microburst levels.
Measurement and interpretation of concentrations of H2O2 and related species in the upper midwest during summer
Authors: Daum Peter H. , Kleinman Lawrence I. , Hills Alan J. , Lazrus Allan L. , Leslie Alistair C. D. , Busness K. , Boatman J.
Published: February 2008

Measurements of H2O2 and related species were made by aircraft on 18 flights over 11 days during June 1987 over Ohio. Measurements typically encompassed an altitude range from the surface to 5.5 km above mean sea level and were conducted under a variety of meteorological conditions, but focussed on conditions conducive to the formation of convective storms. Concentrations of H2O2 ranged from <0.2 to 7 ppb and exhibited as much as a factor of 10 variability even on a given day at fixed altitude, as well as between days. Hydrogen peroxide concentration typically was low near the surface, rose to a maximum near the top of the boundary layer, then slowly decreased with altitude. In contrast, SO2 and NOy were largely confined to the surface layer. A simple photochemical calculation shows that where NOx concentrations are low, [H2O2] is strongly influenced by the water vapor concentration. The [H2O2] tracked changes in dew point, and measured and calculated H2O2 concentrations were in general agreement. The low [H2O2] in the boundary layer is ascribed to consumption of radicals by reactions other than combination reactions, and to loss of H2O2 by dry deposition. Comparison of the profile shapes for H2O2 and SO2 suggests that mixing processes will have a large influence on the extent to which these two species will react in convective systems.
Meteorological conditions during the summer 1986 CITE 2 flight series
Authors: Shipham Mark C. , Bachmeier A. Scott , Cahoon Donald R.
Published: February 2008

An overview of meteorological conditions during the NASA Global Tropospheric Experiment/Chemical Instrumentation Testing and Evaluation (GTE/CITE 2) summer 1986 flight series is presented. Computer‐generated isentropic trajectories are used to trace the history of air masses encountered along each aircraft flight path. The synoptic‐scale wind fields are depicted based upon Montgomery stream function analyses. Time series of aircraft‐measured temperature, dew point, ozone, and altitude are shown to depict air mass variability. Observed differences between maritime tropical and maritime polar air masses are discussed.
An airborne compatible photofragmentation two‐photon laser‐induced fluorescence instrument for measuring background tropospheric levels of NO, NOx, and NO2
Authors: Sandholm S. T. , Bradshaw J. D. , Dorris K. S. , Rodgers M. O. , Davis D. D.
Published: February 2008

Reported on is a photofragmentation two‐photon laser‐induced fluorescence (PF/TP‐LIF) sensor with a demonstrated capability for making simultaneous measurements of NO/NOx/NO2. This instrumental technique is based on the direct spectroscopic detection of NO via the TP‐LIF methodology. The measurement of NOx (NO+NO2), and subsequently NO2, is accomplished by the photofragmentation of NO2 at 353 nm via a XeF excimer laser. The resultant NO photofragment is then quantitatively detected using the TP‐LIF technique. The laser photolysis efficiency for NO2 is typically 60% for NO2 photolysis cell residence times of less than 0.5 s. The limit of detection (S/N=2) for the described PF/TP‐LIF instrument is 3.5 pptv for NO (2 min integration time) and 10 pptv for NO2 (6 min integration time). An assessment of chemical interferences in this system revealed no significant problems. The extension of the PF/TP‐LIF methodology to the simultaneous detection of multiple NxOy, species is discussed.
A note on the improvement of TIROS operational vertical sounder temperature retrievals above the Antarctic snow and ice fields
Authors: Lutz Hans J. , Smith William L. , Raschke Ehrhard
Published: February 2008

In this paper we deal with the problem of retrieving temperature and moisture profiles in the Antarctic regions using radiance observations from the TIROS operational vertical sounder (TOVS). The high‐resolution infrared sounder (HIRS) data are calibrated with the internal cold and warm blackbodies in order to alleviate apparent calibration discrepancies resulting from using the space as a cold reference. Significant improvements of the simultaneous retrieval results have been achieved in using a climatological first guess and selected channels of HIRS as a result of this change in calibration procedure. The retrieval results of the orbit at December 21, 1987 (2345 UT) are compared with radiosonde data and analyses of the European Center of Medium Range Weather Forecasts (ECMWF) of December 22, 1987 (0000 UT).
Acid precursor concentrations above the northeastern United States during summer 1987: Three case studies
Authors: Boatman J. F. , Laulainen N. , Ray J. , Van Valin C. , Gunter L. , Lee R. , Luecken D. , Busness K.
Published: February 2008

Two aircraft measured the spatial distribution of SO2, H2O2, O3, and NOy above the northeast United States during summer. The aircraft flew three missions between Columbus, Ohio and Saranac Lake, New York. The sulfur dioxide concentration averaged 1–2 ppbv within the planetary boundary layer (pbl) and <1 ppbv in the free troposphere. Superimposed on this background concentration were surface source regions with elevated concentrations as high as 14 ppbv. The hydrogen peroxide concentration averaged 2–4 ppbv, with the highest values found above the top of the planetary boundary layer. The H2O2 pattern increased in both size and intensity above the top of the pbl during the afternoon. The ozone concentration varied between 30 and 110 ppbv. The concentration of O3 increased by as much as 30 ppbv during the day. Nitrogen oxide concentrations were in the range <1–8 ppbv. The pattern of SO2 and Noy concentrations remained substantially the same during the daytime hours. The O3 and NOy concentrations were linked to surface emissions and photochemical processes. The ratio between H2O2 and SO2 was >1, except in the lower pbl and near surface SO2 source regions.
A model of stratospheric chemistry and transport on an isentropic surface
Authors: Austin John , Holton James R.
Published: February 2008

First results from a new type of photochemical model are presented. The model has an Eulerian grid with latitude and longitude coordinates on a single isentropic surface, which in this work is specified at a potential temperature of 846.6 K. The photolysis rates in the model are determined using a specified distribution of the total ozone column above the surface. The model contains 107 reactions and 40 species whose concentrations are solved for explicitly with an algorithm that fully accounts for diurnal variations. Species are advected implicitly using a semi‐Lagrangian technique in which 12 hour air particle trajectories are computed and then the particles are reinitialized back onto the Eulerian grid. The photochemical model is integrated for 12 days with winds and temperatures supplied from a three‐dimensional model integration of an idealized wavenumber one disturbance. The results for the long‐lived model tracers such as N2O show excellent correlation with the potential vorticity distribution, providing confidence in the transport scheme. The distribution of the tracers and the night‐time distribution of the reservoir species show the effect of the wave disturbance in enhancing gradients at the edge of the vortex region and in low to mid‐latitudes where a tongue of low potential vorticity air is advected. The effect of the photochemistry is to produce ringed structures surrounding the vortex in reservoir species such as HNO3 and ClONO2. For the radical species, the differences in the steepness of the gradients at the nighttime terminator and the daytime terminator are clearly apparent. Steep high‐latitude gradients in NO2 (the Noxon cliff) are also seen in the results. The results demonstrate the highly complex nature of the photochemistry resulting from the movement in the dynamical vortex and its interaction with the diurnal variation near the terminator. The model provides an interesting way of viewing the full complexity of the photo‐chemistry in the presence of large‐scale advection. Calculations with zonally averaged wind and temperature fields reveal discrepancies in the calculation of the zonal mean of less than 10% for O3 and HNO3 compared with the zonal mean of the previous results. However, the discrepancies for NO2 and N2O5 were much larger, especially in high latitudes. This suggests the need to exercise caution in the interpretation of the results of some species calculated by latitude‐height models.
Micrometeorological measurements in Amazon forest during GTE/ABLE 2A mission
Authors: Viswanadham Y. , Molion L. C. B. , Manzi A. O. , Sá L. D. A. , Filho V. P. Silva , André R. G. B. , Nogueira J. L. M. , Santos R. C. dos
Published: February 2008

As part of the Global Tropospheric Experiment/Amazon Boundary Layer Experiment 2A, micrometeorological measurements were made using a 45 m scaffolding tower located in the Ducke Reserve Forest site (2°57′S, 59°57′W) 26 km northeast of Manaus, Amazonas, Brazil. We report the daily variation within and above the forest of several meteorological parameters such as temperature, humidity, winds, radiation exchange, and energy partition into latent and sensible heat fluxes. Estimates of eddy diffusivity coefficients for momentum, heat, and water vapor were made using the observed profiles. These results provide information on the physical processes involved in the exchange of momentum, heat, and water vapor between the forest and the air layer above. To account for the anomalies in eddy diffusivities, a brief discussion is presented based on turbulent transport processes.
In situ measurement of water vapor in the stratosphere with a cryogenically cooled Lyman‐alpha hygrometer
Authors: Schwab J. J. , Weinstock E. M. , Nee J. B. , Anderson J. G.
Published: February 2008

In situ measurements of water vapor in the stratosphere with a new instrument are reported. The instrument has been designed to observe daytime water vapor from a multi‐instrument balloon gondola that simultaneously measures free radicals such as OH, HO2, and O3 in the stratosphere up to 40 km. Lyman‐alpha photofragment fluorescence is used to measure water molecules in a flowing sample of ambient air. Outgassing from the interior walls of the instrument is avoided by cooling the walls with liquid nitrogen to a temperature near or below the dewpoint of the environment and by drawing air through the instrument with a fan. A brief description of the instrument is given, followed by the results of the first four balloon flights. Because frost formation in the scattering chamber resulted in a large and variable background, the data from July 15, 1987, have a relatively modest signal‐to‐noise ratio. The measured mixing ratio for this flight varies from 3.0–5.5 ppmv over the altitude range of 17–34 km. Adjustments in the cooling protocol for the flights of July 6, 1988, July 28, and August 25, 1989, result in a much higher signal‐to‐noise ratio. Profiles from these three flights are similar to, but somewhat higher, than the 1987 profile, The July 1988 and August 1989 profiles exhibit the highest mixing ratios, reaching peak values of about 6.5 ppmv near 35 km. Implications of these four measurements are discussed, as are the issues of short‐ and long‐term variability of stratospheric water vapor.
Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica 7. OClO diurnal photochemistry and implications for ozone destruction
Authors: Solomon S. , Sanders R. W. , Miller H. L.
Published: February 2008

Observations of the ratio between the change in slant column abundance of OClO and that of ozone as a function of solar zenith are used to deduce the diurnal cycle of the daytime OClO column abundance above Anarctica during September 1987. This approach effectively normalizes other factors such as air mass factor changes and allows study of the photochemical variations of OClO during twilight. The data exhibits a marked increase in OClO at large solar zenith angles in the evening twilight (near 90°–93°), in agreement with model predictions. The increase is likely caused primarily by the attenuation of the OClO photolysis rate in the twilight. Knowledge of both the full diurnal and daily variations of OClO deduced from the data can be used to evaluate the destruction of the ozone column due to coupled chlorine‐bromine chemistry. The inferred ozone loss above McMurdo Station assuming presently accepted photochemistry is
Dobson units over the entire month of September, or about
of the observed total column decline. This value is in general agreement with inferences drawn from in‐situ measurements of ClO and BrO. In mid‐September, available OClO and HOCl column measurements suggest that the chlorine‐bromine and chlorine‐hydrogen cycles respectively contribute about 22–28% and 3–4% of the observed rate of column ozone decrease at that time of the month. Model calculations constrained by ClO, BrO, and OClO measurements suggest that these mechanisms combined with photolysis of the ClO dimer can account for much, and possibly all, of the total ozone destruction rate observed in mid‐September 1987.
On the structures, binding energies and entropies of the complex ions NO+ · N2, NO+ · O2 and NO+ · CO2
Authors: Zinn J. , Sutherland C. D. , Hay P. J.
Published: February 2008

This paper describes ab initio computations of the molecular structures, binding energies, entropies, and specific heats of the complex ions NO+ · N2, NO+ · O2, and NO+ · CO2. The computed binding energies are 0.23, 0.15, and 0.42 eV, respectively; the standard entropies at 298 K are 74.0, 79.8, and 77.5 cal/deg mol, and the molar heat capacities Cp(298 K) are 15.6, 15.8, and 17.2 cal/deg mol. For the case of NO+ · N2 the computed heat capacity is used in conjunction with previously published equilibrium data to obtain a revised experimentally determined value for the binding energy, namely, 0.21 eV, in fairly good agreement with the computed value. The computed binding energies for the other ions are compared with other previously published estimates. Applications of these results to the chemistry of the ionospheric D region are discussed.
Evolution of the total ozone field during the breakdown of the Antarctic circumpolar vortex
Authors: Bowman Kenneth P.
Published: February 2008

Nine years of total ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7 are used to study the evolution of the southern hemisphere total ozone field during the breakdown of the Antarctic circumpolar vortex. The TOMS data provide detailed maps of the morphology of the ozone field and reliable estimates of the vertically integrated meridional transport of ozone during the springtime period when the breakdown occurs (September, October, November). In estimating the ozone transport, chemical effects, including those thought to be responsible for the Antarctic ozone hole, are neglected. This approximation appears to be valid for times scales of a few days to a week. On this time scale, local ozone changes are primarily due to transport. Planetary‐scale waves, especially zonal wave numbers 1 and 2 dominate the eddy variance and ozone transport. Wave number 1 is quasistationary, while wave number 2 is eastward moving with a period of ∼10 days. Before the breakdown the planetary‐scale waves transport ozone poleward (equatorward) as their amplitude increases (decreases). During the vortex breakdown and filling of the ozone hole, when poleward ozone transport is large, planetary wave amplitudes generally decrease.
Nitric acid uptake by sulfuric acid solutions under stratospheric conditions: Determination of Henry's law solubility
Authors: Reihs Christa M. , Golden David M. , Tolbert Margaret A.
Published: February 2008

A Knudsen cell flow reactor is used to study the uptake of nitric acid by sulfuric acid solutions representative of stratospheric particulate. Henry's law solubility constants are determined using the time dependence of the measured nitric acid uptake efficiencies. Solubilities are reported for sulfuric acid solutions ranging from 58 to 87 weight percent sulfuric acid over a temperature range from 188 to 240 K. In general, the solubility of nitric acid increases with decreasing sulfuric acid concentration and decreasing temperature. Over the reported temperature range the solubilities are cast in the form H* = A exp(B/T), where A = 7.47 × 10−8 M/atm, B = 7.16 × 103 K for 58% H2SO4; A = 0.202 M/atm, B = 3.19 × 103 K for 66% H2SO4; A = 8.54 × 10−3 M/atm, B = 3.55 × 103 K for 74% H2SO4; and A = 3.56 × 10−3 M/atm, B = 3.32 × 103 K for 87% H2SO4. The measured solubilities indicate that nitric acid in the global stratosphere will be found predominantly in the gas phase. The ratio of condensed to gas phase nitric acid is less than 10−4 even under conditions of highly elevated sulfuric acid loading.
Atmospheric peroxyacetyl nitrate measurements over the Brazilian Amazon Basin during the wet season: Relationships with nitrogen oxides and ozone
Authors: Singh H. B. , Herlth D. , O'Hara D. , Salas L. , Torres A. L. , Gregory G. L. , Sachse G. W. , Kasting J. F.
Published: February 2008

Aircraft measurements of peroxyacetyl nitrate (PAN) were performed for the first time over the Brazilian Amazon Basin during the wet season (April–May 1987) as part of the NASA Atmospheric Boundary Layer Experiment (ABLE 2B) expedition. In addition to tropical measurements, free tropospheric latitudinal profiles were also obtained during transit flights to and from Manaus, Brazil. Complementing PAN were measurements of NO, O3, CO, C2Cl4, radon, and a variety of other chemical and meteorological parameters. Over the Amazon Basin, PAN was present at a mixing ratio of 5 to 125 ppt. Despite strong local and regional convective activity, a distinct vertical structure with highest mixing ratios aloft was observed. Median PAN mixing ratios of 12, 20, and 48 ppt were present in the 0‐ to 2‐, 2‐ to 4‐, and 4‐ to 6‐km height intervals, respectively. Data collected during the cross‐basin flights showed that the PAN mixing ratio was highest over the rain forest and declined eastward toward the Atlantic Ocean. Over the Atlantic, PAN was low and appeared to be uniformly distributed with height. Above the Amazon forest, PAN was as much as 5 times more abundant than NOx with the largest PAN/NOx ratios occurring at the highest altitudes. Both PAN and possibly the PAN/NOx ratio showed a latitudinal dependence, with decreasing values from the northern midlatitudes to the tropics. Free tropospheric (4–6 km) PAN mixing ratios were found to be strongly correlated with those of O3. Preliminary modeling results indicate that a sizeable fraction of NOx and HNO3 in the free troposphere could result from PAN decomposition alone. The primary source of free tropospheric PAN observed over the Amazon Basin is not well understood. Large‐scale transport from the upper tropospheric PAN reservoir present at the higher northern latitudes, and precursor emissions of nonmethane hydrocarbons from the forest and NOx from soil and lightning clearly play an important role.
On the relevance of OClO photodissociation to the destruction of stratospheric ozone
Authors: Lawrence W. G. , Clemitshaw K. C. , Apkarian V. A.
Published: February 2008

The gas phase photodissociation of chlorine dioxide has been examined to elucidate its role in the destruction of stratospheric ozone. The existence of the photodissociation channel, OClO + hv → Cl + O2, which could in principle catalyze the destruction of ozone, has recently been reported (E. Rühl et al., 1990). We establish here that the quantum yield of this process, in the spectral range 359–368 nm is less than 5×10−4 and therefore too small to significantly perturb the stratospheric ozone budget.
Exchange of momentum among atmosphere, ocean, and solid earth associated with the Madden‐Julian oscillation
Authors: Gutzler David S. , Ponte Rui M.
Published: February 2008

We investigate coherences among time series of tropical zonal winds, total atmospheric angular momentum (M), the length of day of Earth rotation (LOD), and near‐equatorial sea level, all of which exhibit a broad intraseasonal spectral density peak. We seek to ascertain how the wavy, eastward propagating “40–50 day” or “Madden‐Julian” oscillation (MJO) in near‐equatorial zonal winds is related to intraseasonal fluctuations of the zonally averaged zonal wind in the tropics [u] and global momentum M. It is found that 40–50 day upper tropospheric zonal wind fluctuations at western Pacific stations (where the MJO signal is pronounced) are mostly incoherent with fluctuations of M and [u] in the tropics, but lower tropospheric fluctuations at the same stations are significantly coherent. The observed phase lags between variations of near‐surface wind and M are consistent with the hypothesis that fluctuations of surface stress on the Pacific Ocean associated with the MJO are the primary agent for deposition and removal of momentum into and out of the atmosphere. We then examine whether equatorial sea level variability at the South American coast represents a continental torque coupling the ocean and solid Earth on the 40–50 day time scale, thereby accounting for the high coherence observed between M and LOD. Coherence between sea level and LOD is not significant, however, suggesting that oceanic baroclinic wave activity, which is the primary cause of 40–50 day sea level fluctuations, does not contribute significantly to the exchange of momentum between the ocean and solid Earth. On the other hand, the results support the conjecture that barotropic ocean waves provide the required transport and exchange of momentum, and the potential importance of such waves is briefly discussed.
Absorption cross sections of ozone in the 590‐ to 610‐nm region at T = 230 K and T = 299 K
Authors: Amoruso Antonella , Cacciani Marco , Di Sarra Alcide , Fiocco Giorgio
Published: February 2008

Measurements of the ozone absorption cross section in the 590‐ to 610‐nm region of the Chappuis bands have been carried out at the temperatures T = 230 K and T = 299 K. Ozone is produced with an electrical discharge and stored cryogenically. Differential absorption measurements are obtained in a slowly evolving mixture of ozone and molecular oxygen. Previous results by other authors indicate a certain disagreement on the temperature dependence of the absorption cross section. Our data at each wavelength show no significant dependence of the absorption coefficient on the temperature, within experimental errors. The statistical consistency of the results is discussed.
Beryllium‐7 and Lead‐210 in the atmosphere and surface snow over the Greenland ice sheet in the summer of 1989
Authors: Dibb Jack E.
Published: February 2008

The concentrations of 7Be and 210Pb were measured in surface air and fresh and aging snow samples from Summit (72°20′N, 38°45′W) and Dye 3 (65°10′N, 44°45′W) Greenland, during June and July 1989. The aerosol concentrations of these radionuclides showed rapid variations at both sites, but were nearly twice as high, on average, at Summit. Concentrations in the 16 fresh snowfall events that were sampled also showed wide variability, but the averages were the same at the two sites. The apparent difference in air‐snow fractionation and the lack of coherence in the concentration in air time series between the two sites indicate previously unsuspected complexity in atmospheric dynamics over the ice sheet. Improved understanding of atmospheric processes, and how the results of those processes are recorded in snow and ice, is crucial for full interpretation of the information about past atmospheric chemistry and climate contained in the snow and ice of glaciers around the world.
Fourier transform infrared studies of model polar stratospheric cloud surfaces: Growth and evaporation of ice and nitric acid/ice
Authors: Tolbert Margaret A. , Middlebrook Ann M.
Published: February 2008

Fourier Transform Infrared (FTIR) surface studies have been used to probe the microphysical properties of nitric acid trihydrate (NAT) and ice films representative of type I and II polar stratospheric clouds (PSCs), respectively. The infrared spectra of NAT and nitric acid monohydrate (NAM) are obtained by dosing calibrated 3:1 and 1:1 mixtures of water and nitric acid onto a support at −90°C. The spectra, along with previously reported spectra for NAT and NAM, are used to monitor growth, transformation, and evaporation of ice and NAT films. Under our experimental pressure and temperature conditions, NAT is observed to grow at temperatures around 5°C higher than the ice frost point. This is in agreement with the conclusions drawn by Hanson and Mauersberger (1988a,b) from vapor pressure studies over ice and NAT solids. At temperatures 2°C warmer than NAT appearance, we observe growth of a film recently assigned by Ritzhaupt and Devlin (1990) as nitric acid dihydrate (NAD). Because it is formed at the highest temperatures, it is possible that NAD plays a role in PSC formation. However, the differences between the pressures used in the present study and atmospheric pressures, as well as uncertainties in measurements of absolute temperature, could explain NAD formation in our experiment that may not occur in the atmosphere. FTIR surface studies have also been used to probe the condensed products that result from the interaction of ice with gaseous nitric acid. The experiments indicate that upon initial exposure of ice to 1.8×10−6 torr of HNO3, a layer of ice is quantitatively converted to NAT. However, conversion of ice to NAT does not proceed indefinitely, but rather the system reaches saturation. For longer exposures or higher HNO3 pressures, NAM becomes the dominant nitric acid containing species on the surface. Evaporation studies were performed to test the feasibility of a recent denitrification mechanism proposed by Wofsy et al. (1990). The results indicate that ice coated with 0.02 μm of NAT evaporates at a temperature about 4°C higher than uncoated ice. This is consistent with the mechanism for stratospheric denitrification proposed by Wofsy et al. (1990).
The Cretaceous/Tertiary Boundary Event in the North Pacific: Planktonic foraminiferal results from Deep Sea Drilling Project Site 577, Shatsky Rise
Authors: Gerstel Jennifer , Thunell Robert C. , Zachos James C. , Arthur Michael A.
Published: February 2008

A detailed micropaleontologic analysis of sediments from Deep‐Sea Drilling Project site 577 from the Shatsky Rise, North Pacific, was undertaken to describe extinction and radiation patterns of plank‐tonic foraminifera in a continuous carbonate sequence spanning the Cretaceous/Tertiary (K/T) boundary. A 15‐m section containing the boundary was closely sampled and contained planktonic foraminiferal assemblages characteristic of the late MaastrichtianAbathomphalus mayaroensiszone through the DanianGloborotalia uncinatazone. The Cretaceous/Tertiary boundary was placed at the abrupt disappearance of almost all Maastrichtian planktonic foraminifera. Coincident with these extinctions was the presence of a large number of “microtektitelike” spherules. The most important faunal change in the late Maastrichtian was an abrupt increase in the relative abundance of the high‐latitude speciesHedbergella monmouthensis, together with the appearance of diminutive populations ofGuembelitria cretaceaandGlobigerina eugubinaapproximately 20,000 years before the boundary. These changes are interpreted as indicating a cooling of surface water conditions.Globigerina eugubinaandG. cretaceawere the only planktonic foraminiferal species to survive the Cretaceous/Tertiary boundary event at this locality. The δO‐18 and δC‐13 values ofG. eugubinafrom below the K/T boundary are nearly the same as those from above the boundary, but in both cases the δO‐18 values indicate relatively cooler paleotemperatures than those from other coexisting planktonic foraminiferal species. In addition, the δC‐13 values ofG. eugubinaare lighter than those of the other planktonic foraminifera. Such a relationship might suggest thatG. eugubinalived in cooler, shallow intermediate water masses advected from higher latitudes during a latest Maastrichtian cooling episode. Better preservation of planktonic foraminifera, a progressive change in the δC‐13 of benthic foraminifera, and a brief positive excursion in δC‐13 of the carbonate fine fraction and of planktonic foraminifera within 20 to 30 cm below the K/T boundary all suggest important paleoceanographic changes that preceded the extinction event. A large population of aberrantG. eugubinaandEoglobigerinawas observed in the earliest Danian. These forms are characterized by the development of secondary apertures, bullae, and abnormal final chambers. These abnormal morphotypes are considered to be ecophenotypic variants reflecting ecologic stress or instability in the earliest Cenozoic marine environment.
Pleistocene calcite lysocline and paleocurrents of the central Arctic Ocean and their paleoclimatic significance
Authors: Morris Thomas H. , Clark David L.
Published: February 2008

Most previous references to the depth of the Arctic Ocean calcite lysocline have been based on comparison with the known North Atlantic carbonate compensation depth. Foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central Arctic Ocean. These data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past ˜1.5 m.y., interrupted by 300‐m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions. Most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past ˜1.5 m.y. Low abundances commonly occur in coarse‐textured sediment and are interpreted to represent low productivity during major deglaciations. Within certain equivalent lithostratigraphic units representing the past ˜1.5 m.y. there is an absence of foraminifera in cores from depths greater than 2450 m. This absence of foraminifera is interpreted to be due to dissolution. Dissolution intervals are associated with fine‐grain sediments interpreted to represent interglacial and early glacial climate conditions. The interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the Atlantic Ocean but is complementary with the hypothesis that formation of Norwegian‐Greenland Sea Deep Water (NGDW) and cold Canada Basin Deep Water occurs during interglacials. Paleocurrent data from the Lomonosov Ridge and the adjacent Makarov Basin are interpreted to indicate that during periods of increased glacial ice influx into the Arctic Ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present. This is in accord with the idea that NGDW affects intermediate and deep water circulation in the central Arctic Ocean and hence the calcite lysocline level.
History of atmospheric CO2: Constraints from the deep‐sea record
Authors: Berger W. H. , Spitzy A.
Published: February 2008

The carbon chemistry of deep ocean water is quantitatively reflected in carbonate preservation and in the δ13C values of foraminifera. By using benthic δ13C ranges to estimate total dissolved CO2 and correcting for the aging effect of deep water (“back‐aging”) the pCO2 of the atmosphere can be reconstructed. Data at hand are insufficient for detailed studies, but allow the calculation of an upper limit of pCO2 for selected periods within the last 100 million years. The limit is probably near a factor of 2.5 times present atmospheric CO2 for post‐Eocene time, and below a factor of 10 for the late Cretaceous.
Eustasy and epeirogeny of continents on time scales between about 1 and 100 M.Y.
Authors: Harrison C. G. A.
Published: February 2008

Eustatic changes are believed to be the cause of the extensive flooding of the continents by shallow marine seas during the Cretaceous and much of the Paleozoic. The possible causes of eustatic change which can be easily quantified over the past 100 m.y. have been estimated in order to arrive at a value for the freeboard decrease of the continents. These causes, in order of decreasing importance, are ridge crest volume, thermal uplift associated with excessive volcanism in the Pacific during the Cretaceous, formation of continental ice sheets, the collision of India with Asia, and the cooling of the oceans. Several effects act in the opposite direction, and they can be grouped together because they are all due to there being larger quantities of sediments in the ocean basins today than there were 100 m.y. ago. Another effect causing a freeboard increase is the thinning of continental masses, during continental breakup and the formation of new ocean basins. The total change in sea level (after having allowed for isostatic response) is 202 m during the last 80 m.y. Flooding of the continents can also be used to determine sea level changes with help from modern hypsographic curves. When this is done it is found that the freeboard decrease is considerably less than that calculated from volume estimates. Although the inaccuracy of the various data would allow these estimates to be not significantly different, it is likely that the estimate of freeboard decrease using flooded areas and modern hypsographic data is an underestimate, due to the probability that the hypsographic curve has become less steep with time. Individual estimates of flooding from continents require considerably different amounts of freeboard change. The common signal is usually assumed to be the eustatic signal, whereas when this common signal is removed from the freeboard estimate for an individual continent, the remaining signal is the epeirogenic signal. Epeirogenic movements can be as large as 150 m and can occur on time scales of a few tens of millions of years. Other examples of epeirogenic variations are also discussed. We have developed a rough power spectrum for epeirogenic movements of the continents. This appears to have 1/f² variation. We suggest that the spectrum could be produced by temperature changes at the bottom of the lithosphere.
A link between paleoceanography, early diagenetic cementation, and shear strength maxima in Late Quaternary deep‐sea sediments?
Authors: Kassens H. , Sarnthein M.
Published: February 2008

Near‐surface sediments from the equatorial east Atlantic and the Norwegian Sea exhibit pronounced shear strength maxima in profiles from the peak Holocene and Pleistocene. These semi‐indurated layers start to occur at 8–102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments. However, scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets, which are clearly restricted to (undisturbed) samples from indurated layers and form a manifest explanation for their origin. The minerals precipitated comprise calcite, aragonite, and in samples more proximal to the African continent SiO2 needles, and needles of as yet unidentified K‐Mg‐Fe‐Al silicates, crusts of which dominate the indurated layers in the Norwegian Sea. By their stratigraphic position in deep‐sea sediments the carbonate‐based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early Holocene and hence to short‐lived no‐analogue events of early diagenesis. Possibly, they have been controlled by a reduced organic carbon flux, leading to increased aragonite preservation in the deep sea.
Stable isotope stratigraphy of Latest Miocene sequences in northwest Morocco: The Bou Regreg section
Authors: Hodell David A. , Benson Richard H. , Kennett James P. , Rakic‐El Bied Kruna
Published: February 2008

Oxygen and carbon isotopic ratios of foraminifers were measured from outcrop and drill core sequences from the Bou Regreg Section, northwest Morocco. This composite section was located at the western end of the Rifian Corridor during the late Miocene and thus potentially contains a record of water exchange between the Atlantic and Mediterranean during the late Tortonian and Messinian stages. Here we correlate isotopic and sedimentologic events in the Bou Regreg Section with Mediterranean and deep‐sea sequences during the time leading up to and including the deposition of the Messinian evaporites. The late Miocene chron 6 carbon shift was identified in two Moroccan sequences, providing a valuable 6.3‐Ma datum level. In both sections, the carbon shift coincides with the first occurrence of Globorotalia conomiozea and the Tortonian/Messinian boundary. Near this boundary, a major faunal turnover occurred in ostracod, planktonic foraminiferal, and nannofossil assemblages that indicates a cooling of surface and deep water in the Rifian Corridor. At 6.1 Ma, just above the Tortonian/Messinian boundary, mean ∂18O values of benthic foraminifers increased by 0.4‐0.5‰ suggesting decreased temperature and/or increased continental ice volume. The faunal and isotopic changes are interpreted as reflecting a reversal in the direction of deep water flow through the Rifian Corridor that occurred between 6.3 and 6.1 Ma. At this time, cold, nutrient‐rich waters filled the Mediterranean basins from intermediate depths of the Atlantic, and the production of Mediterranean Outflow Water ceased. The upwelling of nutrient‐rich Atlantic intermediate water stimulated productivity in the Mediterranean, which led to the deposition of organic‐rich strata such as those found in the Tripoli Formation. At ∼5.5 Ma, coincident with a coiling shift in Neogloboquadrina acostaensis, the variability of the benthic ∂18O signal increased markedly, and strong color variations appeared in the sediments (alternating between red and blue marls). These isotopic and sedimentologic changes at Bou Regreg represented markedly fluctuating oceanographic conditions in the Rifian Corridor between 5.5 and 4.8 Ma. We speculate that these cycles were related to sea level variations that controlled the periodic influx of marine water into the Mediterranean during the time of evaporite deposition. The onset of these cycles occurred at 5.5 Ma and is correlated to a eustatic fall in sea level at the base of the Caliza Tosca Formation in Carmona, Spain, and to the base of the lowermost evaporite unit in the Mediterranean (e.g., Calcare di Base in Sicily). In this proposed scenario, the duration of the Messinian salinity crisis was 700,000 years and lasted between 5.5 and 4.8 Ma.
The Last Deglaciation in the Southern Ocean
Authors: Labracherie Monique , Labeyrie Laurent D. , Duprat Josette , Bard Edouard , Arnold Maurice , Pichon Jean‐Jacques , Duplessy Jean‐Claude
Published: February 2008

The isotopic and micropaleontological deglacial records of three deep‐sea cores from 44°S to 55°S have been dated by accelerator mass spectrometry. The available records did not allow accurate dating of the initiation of the deglaciation. By 13,000 years B.P., sea surface temperatures reached values similar to the present values. A cool oscillation abruptly interrupted this warm phase between 12,000 and 11,000 years B.P. Initiation of this cooling therefore preceded the northern hemisphere Younger Dryas by approximately 1000 years. Complete warming was reached by 10,000 years B.P., more or less synchronous with the northeast Atlantic Ocean.
Nonlinear response in the global climate system: Evidence from benthic oxygen isotopic record in core RC13‐110
Authors: Pisias Nicklas G. , Mix Alan C. , Zahn Rainer
Published: February 2008

The Milankovitch theory of climate change predicts that variations of the climate system should match the dominant frequencies of the orbital forcing in the 41 and 23 kyr−1 frequency bands. Such a linear theory would predict that the amplitude variations of the climate response in these bands should match amplitude variations in orbital forcing. Here we compare amplitude variations of the marine oxygen isotope record with orbital forcing in these bands over the last 700,000 years and find systematic changes through time. We express these amplitude mismatches as variations in the glacial response time, a measure of the climate system's sensitivity to orbitally induced insolation changes. Variations in the glacial response time occur in all frequencies bands without strong concentration of variance in any given band, and have a “red” spectrum with larger variations at the longer periods. The response time is coherent with δ18O at periods of 100 and 41 kyr, which suggests that the variations in glacial response time in part reflect internal feedback mechanisms of the global climate system. The phase relationship between the estimated glacial response time and the δ18O (ice volume) record is very different at these two frequencies, which suggests at least two separate feedback mechanisms. The first mechanism enhances the 100,000‐year climate cycle by increasing rates of change during major glacial terminations. Candidates for this feedback include lithospheric depression and rebound, enhanced ice calving from large marine based ice sheets, and possibly others. A second set of mechanisms, which is detected in the response to the 41,000‐year orbital cycle of Earth's obliquity, accelerates ice growth events and slows glacial melting. Some models which include feedbacks between ice sheets, sea ice, and deep ocean temperatures predict early rapid ice growth, followed by slower growth, and this general feature is consistent with our analysis. While we can not at present identify the specific feedbacks leading to asymmetry of growth and decay rates at different frequency bands, the finding of this ice‐growth acceleration mechanism in the 41,000‐year frequency band suggests that high‐latitude processes, where insolation varies most strongly at this rhythm, may be involved. Our finding of systematic changes in climate sensitivity has implications for orbitally tuned chronologies in Pleistocene sediments. Instead of a constant phase shift within a frequency band between orbital forcing and glacial response, as has been assumed in the past, we suggest a variable phase. The largest changes in age estimates for isotopic events are at the glacial terminations, which in our chronology are as much as 3500 years older that estimated previously.
A phase sensitive algorithm for detection of short‐lived events in stable isotope records
Authors: Yu Z. , Lerche I. , Williams D. F.
Published: February 2008

This study provides a first attempt at using a phase sensitive detection algorithm to detect short‐lived events, such as glacial meltwater events, in stable oxygen isotope records. Pertinent parameters such as the decay time and oscillation frequency of such rapid events are determined. A comparative study has been made from δ13C data and δ18O data using the phase sensitive detection technique. Common events are identified in the two types of records, with a decay time of 7±5 kyr and with an angular oscillation frequency ωr=1.5±0.2 (ky)−1 (correspondingly, a cycle frequency fr = ωr/2π ≈ 0.4±0.03 ky−1, or a cycle time T=1/f = 2.5 kyr), likely corresponding to rapid glacial meltwater effects.
Quaternary planktonic foraminiferal assemblage zones of the northeast Gulf of Mexico, Colombia Basin (Caribbean Sea), and tropical Atlantic Ocean: Graphic correlation of microfossil and oxygen isotope datums
Authors: Martin Ronald E. , Johnson Glenn W. , Neff Eric D. , Krantz David W.
Published: February 2008

Sediments of Ocean Drilling Program's hole 625B (northeast Gulf of Mexico) represent a virtually continuous record of Pleistocene paleoceanographic development associated with the Florida Loop Current. Utilizing relative abundances of the Globorotalia menardii complex and G. inflata, supplemented by left‐ and right‐coiling varieties of G. truncatulinoides, we have subdivided the prezone W Pleistocene of core 625B into 17 subzones, resulting in an average duration of approximately 100,000 years per unit. This is substantially better resolution than for the Ericson and Wollin [1968] zones alone (average duration ∼300,000 years per unit). The subzones recognized in core 625B can be recognized in Eureka core E67‐135 (northeast Gulf of Mexico) and extended to cores 502B (Colombia Basin, Caribbean Sea) and V16‐205 (tropical Atlantic). Subzonal boundaries are largely coeval between sites based on graphic correlation of paleomagnetic, biostratigraphic, and oxygen isotope datums. The subzonation reveals relatively abrupt changes in sediment accumulation rate which probably decrease the signal to noise ratio in spectral analysis and tuning of oxygen isotope curves. In some cases, accumulation rate changes correspond to core breaks. Abundances of Globorotalia inflata and G. truncatulinoides are damped in the tropical cores (V16‐205 and 502B) but amplified in the subtropical Gulf of Mexico (625B), an observation which is consistent with previously published biogeographic models.