bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of an ocean eddy with an ice edge ocean jet in a marginal ice zone
Authors: Smith David C. , Bird Arlene A.
Published: February 2008

Remotely sensed images in the East Greenland Current marginal ice zone region indicate a variety of mesoscale motions. These range from isolated monopoles and dipoles to multiple eddy fields. Recent observations indicate that many of the eddies may be advected into the region from the West Spitsbergen Current region. They then interact with the East Greenland Current marginal ice zone and its associated along‐ice‐edge jet. In this paper we illustrate how the ice floe fields can evolve during the interaction of an ocean eddy with an along‐ice‐edge ocean jet. The effects of eddy sense of rotation, flow strength, and bottom topography are considered in barotropic and baroclinic, two‐layer numerical experiments. Initially, barotropic experiments involve the combined effects of flat‐bottom eddy‐jet interactions and eddy‐topography interactions. Over a flat bottom, anticyclones interact with the cyclonically sheared side of the jet and move seaward, exporting ice away from the ice edge in a dipolar distribution. Cyclones move toward the jet and are advected downstream. A second dipole formation mechanism is associated with eddy‐topography interaction and is a consequence of the shallow pycnocline depth of the region. Rapid topographic Rossby wave radiation in the lower layer spreads energy along slope and upslope (downslope) for cyclones (anticyclones). The upper ocean response to this process is a dipole which propagates parallel to the ice edge with shallow water to the left (topographic eastward). Jet‐induced and topography‐induced eddy propagation tendencies combine to enhance cyclone‐jet interaction and limit anticyclone‐jet interactions. The dipole formation associated with eddy‐topography interaction is weakened by the presence of the jet but not eliminated. Eddy‐induced distortions in the ice edge are suppressed by the stabilizing effect of topography on the jet. Sensitivity of the initially barotropic results to variation in the Rossby number and degree of topographic slope illustrates that eddies are more efficient in producing ice edge distortions for stronger flows and weaker topographic slopes. For initially baroclinic simulations over topography, results are comparable to flat‐bottom cases. Strong upper layer eddy‐jet interactions can occur independent of topographic effects which are constrained to the lower layer.
The Arctic front in the Greenland Sea during February 1989: Hydrographic and biological observations
Authors: van Aken Hendrik M. , Quadfasel Detlef , Warpakowski Andrea
Published: February 2008

High‐resolution hydrographic and biological observations in the Arctic frontal regime were made in February 1989 along 74°45′N. The frontal zone was found to contain four individual frontal interfaces. These fronts were a result of the large‐scale convergence of the currents around the Greenland Sea gyre, bringing together Arctic and Polar surface waters and two modes of Atlantic Surface Water. The distribution of Arctic and Atlantic copepod species as well as the composition of their developmental stages showed a strong correlation with the distribution of water masses whereby the frontal interfaces acted as biogeographic boundaries. Whereas the fronts bounding the Polar Water reached only to a depth of about 100 m, the fronts bordering the Atlantic water masses could be observed to depths of 600 m. At subsurface levels a core of Atlantic Intermediate Water from the Jan Mayen Current was observed. The properties of this water type can be explained quantitatively from double‐diffusive exchange with the overlying water. The mixing across the fronts was found to be dominated by fluxes of heat, salt, and copepods toward the central Greenland Sea gyre.
The sea ice thickness distribution in the northwestern Weddell Sea
Authors: Lange M. A. , Eicken H.
Published: February 2008

We present new data on distribution of snow and sea ice thicknesses in the northwestern Weddell Sea. The data were obtained through direct measurements along 19 profiles, each approximately 100 m long on 17 different floes located between 54°–46°W and 59°–64°S. The overall probability density functions (PDFs) for ice thicknesses reflect the complex mixture of first‐, second‐, and multi‐year ice to be expected in the outflowing branch of the Weddell Gyre. Further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered. These classes (I–IV) represent strongly deformed first year ice, less deformed first‐ and second‐year ice, and deformed second‐ or multi‐year ice, respectively. Each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct PDFs for snow and ice thicknesses. In addition, geometric surface and bottom roughness characteristics differ significantly for each of the floe classes.
Photochemical free radical production rates: Gulf of Maine and Woods Hole‐Miami transect
Authors: Zafiriou Oliver C. , Dister Brian
Published: February 2008

The total free radical fluxes generated by illumination of surface water samples with a solar simulator were measured in a variety of coastal surface waters along the east coast of the United States in summer 1987. Photochemically generated free radicals were scavenged with a known excess of added nitric oxide, and the nitric oxide losses were measured by difference using a semiautomated, computer‐controlled system coupled to the ship/s clean surface water intake system. This first large free radical flux data set shows that radical production occurs at significant rates that are relatively uniform over large regions. However, at the time of this cruise a strong photoreactivity front divided coastal waters north of Cape Cod (3.85±0.82 nmol L−1 min−1 sun−1, n=8 sites) from coastal waters south to northern Florida (1.67±0.32 nmol L−1 min−1 sun−1, n = 20). The mean flux on an areal basis is estimated to be ∼0.7 mmol−2 d−1, or about 50 mmol m−2 for the summer season. These values are sufficiently large to produce interesting but unknown geochemical consequences. The regional uniformity and wavelength dependence of the rates are consistent with the concept that the principal mechanism of radical production is photolysis of long‐lived dissolved chromophores of unknown structure, such as fulvic and humic acids. A vertical profile shows strong near‐surface depletion of reactive materials under calm conditions. The dependence of total radical production rates on irradiation time, light intensity, concentration of added NO, and wave‐length range of polychromatic radiation is also reported. The results support the conclusion that the method produces an operationally consistent, well‐behaved estimate of photochemical free radical production potential that is not strongly affected by biological processes.
A model of evaporating spray droplet dispersion
Authors: Rouault Mathieu P. , Mestayer Patrice G. , Schiestel Roland
Published: February 2008

A model with a discrete droplet size distribution has been built in order to investigate the fate and influence of marine spray droplets dispersed by atmospheric turbulence as they evaporate. In its present state the Couche Limite Unidimensionelle Stationnaire d'Embruns (CLUSE) model considers freshwater droplets between 5 and 105 μm in radius that are ejected from a water surface by bursting air bubbles. The droplets are then diffused in a fully developed atmospheric surface layer. The droplet population is separated into 10 categories according to their size. The mass concentration of each category is treated as a scalar field, like sensible heat and water vapor concentration. Diffusion by air turbulence is modeled by K diffusivities. In addition, specific droplet surface processes (i.e., ejection and deposition) and the effects of inertia and gravity are explicitly modelled. The effects of evaporation (i.e., droplet shrinking, production of water vapor, and absorption of sensible heat) are modeled by local source‐sink functions that couple all 12 budget equations. The model is adjusted for comparison with measurements of turbulence statistics and droplet distributions taken in the Institut de Mécanique Statistique de la Turbulence air‐water tunnel. The influence of evaporating droplets on the humidity and sensible heat fields and fluxes, as well as the coupling of turbulent diffusion and evaporation is demonstrated.
Velocity and temperature fluctuations in a buoyancy‐driven current off Vancouver Island
Authors: Hickey B. M. , Thomson R. E. , Yih H. , LeBlond P. H.
Published: February 2008

An experiment to study buoyancy driving of the poleward flowing coastal current off the west coast of Vancouver Island was carried out from June to November 1984. The experiment consisted of two hydrographic surveys and a three‐dimensional instrumented array that included 51 current/temperature sensors distributed on 18 moorings. Moorings were maintained across the mouth of the Strait of Juan de Fuca (to monitor the fluctuating buoyant source/sink) and along three cross‐shelf transects roughly 40, 90, and 130 km north of the mouth of the strait. To detect possible incoming propagating coastal‐trapped waves (CTWs), moorings were also located ∼10 and ∼30 km south of the mouth of the strait.The main thrust of the experiment was to attempt to identify signals specifically associated with buoyant outflow from the Strait of Juan de Fuca. Four such signals were identified. (1) A seasonally varying mean poleward flow over the mid and inner shelf. (2) Velocity and temperature fluctuations associated with buoyant plumes over the shelf. The plumes, which occur at roughly monthly and bimonthly intervals, are driven by anomalously strong freshwater pulses from the strait, and the associated fluctuations in the along‐isobath component of velocity accounted for about 20% (10%) of the variance during summer (fall) in the region within about 50 km of the mouth of the strait. (3) Positive temperature anomalies (∼3°C) related to the cessation of strait outflow. These anomalies, which are strongest at and south of the mouth of the strait, occur during periods of regional southwesterly winds and have a south‐to‐north lag consistent with poleward advection of the pre‐existing (usually cold) plume water at about 30 km d−1. (4) Phase modification of the wind‐driven CTW and local wind‐driven velocity signals across the mouth of the strait: a south to north phase difference of about 90° is observed across the mouth of the strait at low (<0.12 cpd) frequencies during both summer and fall. Statistical analysis as well as application of a first‐mode wind‐driven CTW model demonstrated that the dominant variance over the Vancouver Island shelf is related primarily to the first‐mode wind‐driven CTW (summer, ∼55%) or local wind forcing (fall, ∼80%). This being the case, and also because of the rugged shelf topography in the area, the analysis proved insufficient to identify definitively more subtle results of plume and strait processes such as the local generation of CTWs.
Can meddies be detected by satellite altimetry?
Authors: Stammer Detlef , Hinrichsen Hans‐Harald , Käse Rolf H.
Published: February 2008

Geosat Exact Repeat Mission altimeter data have been used to estimate the sea surface height anomaly relative to a 2‐year mean reference surface in the eastern North Atlantic Ocean. Horizontal maps of the sea surface height anomaly for various periods were constructed by means of an objective analysis procedure. The mean sea level was approximated by the dynamic topography from climatological hydrographic data. Results were compared to the dynamic topography calculated from hydrographic ground truth data sampled during March 1988 on an eddy‐resolving station network in the Iberian Basin. Despite the low signal‐to‐noise ratio of the altimeter data in this part of the ocean, the agreement of the altimeter signal with hydrographic measurements is found to be significant. Individual cyclonic and anticyclonic eddies in the Mediterranean outflow are identified in the altimetric maps. The information visible in the sea surface height is significantly correlated with the dynamic topography of the layer 500/3000 dbar containing the core of the Mediterranean outflow and maximum velocities of the baroclinic eddies. The successive development of the identified eddies as studied from a sequence of sea surface height maps indicates a slight westward drift of the most pronounced feature with approximately 1.9 cm/s propagation velocity. The inferred path of that feature is consistent with additional information from moored current meter data.
Solar radiative line‐by‐line determination of water vapor absorption and water cloud extinction in inhomogeneous atmospheres
Authors: Ramaswamy V. , Freidenreich S. M.
Published: February 2008

The complete available spectral features (line‐by‐line, or LBL) of the water vapor molecule in the solar spectrum and a precise treatment of particulate scattering are employed to obtain and analyze the solar radiative fluxes and heating rates in plane‐parallel, vertically inhomogeneous model atmospheres containing vapor only, water cloud only, and vapor‐plus‐cloud present simultaneously. These studies are part of the Intercomparison of Radiation Codes in Climate Models (ICRCCM) project and constitute useful benchmark computations against which results from simpler radiation algorithms can be compared. The “exact” solution of the radiative transfer equation for cloudy atmospheres with the cloud in a single model layer consumes an exorbitant amount of computational resources (∼100 hours on a Cyber 205). Two other techniques that are considerably more economical are also investigated. These techniques, too, are based on the LBL spectral features of the H2O molecule but consist of an approximation in either the vapor optical depth or in the multiple‐scattering process. The technique involving the “binning” of the vapor optical depths yields extremely accurate fluxes and heating rates for both the vapor and vapor‐plus‐cloud cases; in particular, it is a practical alternative for obtaining benchmark solutions to the solar radiative transfer in overcast atmospheres (3.8 hours). In contrast, the multiple‐scattering approximation technique does not yield precise results; however, considering its computational efficiency (0.5 hours), it offers a rapid means to obtain a first‐order approximation of the spectrally integrated quantities. The analyses of the alternate techniques suggest their potential use for high spectral resolution sensitivity studies of the radiative effects due to various types of clouds.
Temporal variability of atmospheric lead concentrations and fluxes over the northwestern Mediterranean Sea
Authors: Remoudaki Emmanouela , Bergametti Gilles , Buat‐Ménard Patrick
Published: February 2008

Beginning in 1985, daily 24‐hour aerosol samples were collected on 0.4‐pm pore size filters at a coastal location in northwestern Corsica. Total atmospheric deposition (wet + dry) were sampled between February 1985 and October 1987 with a collection period of about 15 days. As indicated by three‐dimentional air mass trajectories, lead aerosol particles collected at this site are primarily derived from European continental source regions. The variability of lead aerosol concentrations on both daily and seasonal time scales is primarily due to the scavenging of lead aerosol particles by rain rather than to changes in source regions. Our results suggest that the ratio between the total atmospheric deposition of Pb and the corresponding mean daily precipitation (mdp) rate is not constant. This ratio reaches a maximum during the Mediterranean summer. We attribute this difference to wet scavenging processes which wash a more loaded atmosphere during the dry season than during the wet season. The precipitation frequency (FP) is a major factor influencing seasonal variability of the total atmospheric deposition of lead over the western Mediterranean. An intermediate value of FP allows sufficient reloading of the atmosphere with long‐range transported Pb aerosol particles as well as efficient scavenging by precipitation events.
Clouds‐radiation interactions in a general circulation model: Impact upon the planetary radiation balance
Authors: Smith Laura D. , Vonder Haar Thomas H.
Published: February 2008

The unique multimonth set of simultaneous Earth radiation budget observations and cloud amount estimates taken during the Nimbus 7 satellite mission from June 1979 to May 1980 was used to validate a long‐term climate simulation obtained with the latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model. The comparison focused on the temporal variability of the model‐generated cloud and radiation fields versus satellite data with the aim to (1) test the model's ability to simulate short‐term fluctuations; and (2) examine the impact of the treatment of the interactions between clouds, radiation, and the hydrologie cycle on the model's performance. The Nimbus 7 data set comprised broad‐spectral‐band observations of the outgoing infrared radiation and planetary albedo taken by the Earth radiation budget scanners and total cloud amount estimates derived from radiances measured by the Temperature Humidity Infrared Radiometer and Total Ozone Mapping Spectrometer using a bispectral threshold method. Model‐simulated northern hemisphere summer and winter seasons were obtained from a 15‐year time integration including a seasonal cycle. The comparison helped identify a major difficulty in the simulation of climate with the NCAR Community Climate Model. Although the global distributions of the seasonal average and standard deviation of the model‐generated cloud and radiation fields agreed reasonably well with those obtained from satellite observations, the magnitude of the standard deviation of both fields was overestimated by about a factor of 2 over the whole globe. The high frequency of occurrence of clouds is responsible for the increased temporal variability in the model and partially results from reduced interactions between clouds and the hydrologic cycle. In view of the impact of clouds on the atmospheric circulation and its temporal variability, increased fluctuations in cloudiness may affect the sensitivity of the model‐simulated climate to external forcings and it is desirable to implement stronger couplings between the various physical processes in the NCAR Community Climate Model.
A nested grid mesoscale atmospheric chemistry model
Authors: Pleim Jonathan E. , Chang Julius S. , Zhang Kesu
Published: February 2008

A nested grid version of the Regional Acid Deposition Model (RADM) has been developed. The horizontal grid interval size of the nested model is 3 times smaller than that of RADM (80/3 km = 26.7 km). Therefore the nested model is better able to simulate mesoscale atmospheric processes while maintaining consistency with larger‐scale features. The nested model uses dynamic boundary conditions along inflow boundaries which are interpolated from coarse grid model (RADM) results. Since the nesting is one‐way, the outflow boundary conditions are specified to minimize numerical reflections. Three‐day wet deposition amounts of sulfate and nitrate simulated by the nested grid version of RADM as well as the coarse grid version were compared to measurements made by the regional scale network during the Oxidizing and Scavenging Characteristics of April Rains (OSCAR) IV experiment. Both models were able to predict wet depositions of sulfate to within a factor of 2 for over 80% of the sampling sites. Nitrate predictions were slightly worse with just over 70% of the pairs within a factor of two for both models. Although the nested grid model showed no improvement over the coarse grid model in terms of point by point comparisons, it did demonstrate the ability to predict a more realistic range and spatial variability of wet deposition amounts. Plots of predicted deposition fields show that the nested model predicted values similar to the observations in their vicinity more often than did the coarse grid model. Nested model simulations of wet deposition were also compared to measurements made by a high density sampling network over a 110×110km area of northeastern Indiana. Most of the spatial features of the observed distribution were well simulated by the model demonstrating the nested model's ability to resolve processes on scales which are subgrid to the coarse grid model. The predictions of wet depositions by both models were in better agreement with observations than were predictions of precipitation. Since the OSCAR IV experiment was characterized by very efficient washout, the rate of wet deposition was often primarily controlled by the rate of supply of airborne material to the precipitating system rather than aqueous oxidation and precipitation processes. Therefore, errors in precipitation rate had little impact on wet deposition predictions.
Ions in oceanic and continental air masses
Authors: Tanner D. J. , Eisele F. L.
Published: February 2008

Measurements of tropospheric ions and several trace atmospheric neutral species have been performed at Cheeka Peak Research Station and at Mauna Loa Observatory. Two new positive ion species at masses 114 and 102 have been identified as protonated caprolactam and a saturated 6‐carbon primary amine, respectively. In the negative ion spectrum, methane sulfonic acid (MSA) has been identified as the parent species responsible for an ion commonly observed at mass 95 during these two studies. The diurnal variations of gas phase H2SO4 and MSA were also measured at Cheeka Peak and have typically been found to be present in the sub‐ppt range. Ion assisted measurements at Mauna Loa Observatory of pyridine and ammonia indicate concentrations of 2.5 and 70 ppt, respectively, with at least a factor of 2 uncertainty. Interesting variations and potential sources of several of the observed ions are also discussed.
Tropospheric nitrogen: A three‐dimensional study of sources, distributions, and deposition
Authors: Penner J. E. , Atherton C. S. , Dignon J. , Ghan S. J. , Walton J. J. , Hameed S.
Published: February 2008

We simulate the global cycle of reactive nitrogen in a three‐dimensional model of chemistry, transport, and deposition. Our model is based on the Lagrangian tracer model described by Walton et al. [1988] and uses winds and precipitation fields calculated by the Livermore version of the NCAR Community Climate Model. The model includes the basic chemical reactions of NO, NO2, and HNO3. For this study, we use prescribed OH and O3 concentrations and calculate the concentrations of NO, NO2, and HNO3 for a perpetual January and a perpetual July. The sources of reactive nitrogen due to fossil‐fuel combustion (22 Mt N/yr), lightning discharges (3 Mt N/yr), soil microbial activity (10 Mt N/yr), biomass burning (6 Mt N/yr), and the oxidation of N2O in the stratosphere (1 Mt N/yr) are included. Model‐predicted concentrations of NO, NO2, and HNO3 are compared to available measurements. In general, we find reasonable agreement between model predictions and measurements except for concentrations of HNO3 in the remote Pacific. At these latter locations, we require a larger source of reactive nitrogen to fit the observations. This may be supplied by lightning discharges, although increasing this source degrades our agreement with measured HNO3 abundances in the free troposphere. Alternatively, a local marine source could contribute to the measured abundances. Predictions for nitrate deposition by precipitation are within a factor of 2 of measured deposition rates in the northern hemisphere in the summer and in both seasons at remote locations. The model underpredicts nitrate deposition in winter in Europe, due primarily to the excessively strong winds generated by the general circulation model. Model simulations for NOx and HNO3 surface mixing ratios from calculations including only the fossil‐fuel source, only natural sources, and all sources acting together, are compared. Anthropogenic sources have substantially increased the concentrations of NOx and HNO3 throughout all continents during both January and July. Fossil‐fuel sources are responsible for most of this increase in the northern hemisphere, while both biomass burning and fossil‐fuel combustion contribute in the southern hemisphere.
Satellite observations of polar mesospheric clouds by the solar backscattered ultraviolet spectral radiometer: Evidence of a solar cycle dependence
Authors: Thomas Gary E. , McPeters Richard D. , Jensen Eric J.
Published: February 2008

Measurements from space of the Earth's ultraviolet albedo are affected by scattering of sunlight from polar mesospheric clouds (PMC). We have examined 8 years of solar backscattered ultraviolet (SBUV) albedo data and find evidence of an annual occurrence of PMC in the summertime polar cap regions of both hemispheres. We have devised a cloud selection algorithm based upon the expected spectral properties of PMC scattering and show that the albedo residuals selected by this algorithm, at least above some threshold brightness, possess the basic properties of PMC with regard to their brightness levels, their seasonal characteristics, and latitude variation. Because of the uniform sampling of the polar caps, particularly in the southern hemisphere, it is possible to examine year‐to‐year variations in PMC activity. We find that a significant trend is present in the PMC occurrence frequency values over the period 1978 to 1986. The increase (up to a factor of 10 at some brightness levels) in the occurrence frequency from solar maximum to solar minimum conditions indicates an anticorrelation with solar activity, an effect that also appears to be present in noctilucent cloud sightings over the past several decades. Garcia [1989] suggested that PMC should be modulated by changes in the solar Lyman‐alpha (121.6 nm) flux through its strong photodissociation control of upper mesospheric water vapor. Solar Lyman‐alpha underwent a significant (50%) variation during this period. Our results confirm this expectation, and thus indirectly support the current theories of PMC formation. However, other influences such as long‐term changes of mesopause temperature or dynamics cannot be ruled out. We have identified two kinds of hemispherical asymmetries: the first, that PMC in the northern hemisphere is significantly brighter than in the south is consistent with previous results derived from Solar Mesosphere Explorer data; and the second, that the solar cycle response in the south is more pronounced than in the north. We show that if PMC scattering is not taken into account in the SBUV ozone retrieval algorithm, systematic errors of order 10% can occur in derived ozone concentration in the 40–50 km region of the summer polar cap.
Lidar search for atmospheric atomic mercury in Icelandic geothermal fields
Authors: Edner H. , Faris G. W. , Sunesson A. , Svanberg S. , Bjarnason J. Ö. , Kristmannsdóttir H. , Sigurdsson K. H.
Published: February 2008

A search for atmospheric atomic mercury as a possible tracer gas for geothermal energy exploration was performed in three Icelandic geothermal fields using the differential absorption lidar technique. Contrary to expectations, concentrations basically only at the Atlantic background value of about 2 ng/m3 were found in Iceland.
Gravity waves in the middle atmosphere observed by Rayleigh lidar: 2. Climatology
Authors: Wilson R. , Chanin M. L. , Hauchecorne A.
Published: February 2008

A large data set obtained by Rayleigh lidars during 4 years has been analyzed in order to describe the gravity wave climatology in the 30‐ to 75‐km altitude range at mid‐latitude. The lidar data were collected in two sites different with respect to orography, both located in the south of France (44°N). The seasonal variability of the wave activity, the vertical growth of potential energy density per unit mass, and the power spectral density versus vertical wave number are shown. The seasonal variability of the wave activity is found to be mainly annual, the maximum of activity occurring during winter. A semiannual component, with a secondary maximum in summer, is superposed to the annual cycle above 60‐km altitude. The power spectral density increases from the stratosphere to the mesosphere in the entire spectral range. A significant positive correlation is found between the wave activity and the wind intensity in the stratosphere. Finally, some simple hypotheses, in terms of wave sources and wave transmission, are advanced in order to get an insight into the causes of the observed seasonal and geographical variability of the wave activity.
A new self‐calibration method applied to TOMS and SBUV backscattered ultraviolet data to determine long‐term global ozone change
Authors: Herman J. R. , Hudson R. , McPeters R. , Stolarski R. , Ahmad Z. , Gu X.‐Y. , Taylor S. , Wellemeyer C.
Published: February 2008

The currently archived (1989) total ozone mapping spectrometer (TOMS) and solar backscattered ultraviolet (SBUV) total ozone data (version 5) show a global average decrease of about 9.0% from November 1978 to November 1988. This large decrease disagrees with an approximate 3.5% decrease estimated from the ground‐based Dobson network. The primary source of disagreement was found to arise from an overestimate of reflectivity change and its incorrect wavelengths dependence for the diffuser plate used when measuring solar irradiance. Both of these factors have led to an overestimate of the rate of atmospheric ozone depletion by SBUV and TOMS. For total ozone measured by TOMS, a means has been found to use the measured radiance‐irradiance ratio from several wavelengths pairs to construct an internally self consistent calibration. The method uses the wavelength dependence of the sensitivity to calibration errors and the requirement that albedo ratios for each wavelength pair yield the same total ozone amounts. Smaller errors in determining spacecraft attitude, synchronization problems with the photon counting electronics, and sea glint contamination of boundary reflectivity data have been corrected or minimized. New climatological low‐ozone profiles have been incorporated into the TOMS algorithm that are appropriate for Antarctic ozone hole conditions and other low ozone cases. The combined corrections have led to a new determination of the global average total ozone trend (version 6) as a 2.9±1.3% decrease over 11 years (October 1978 to November 1989). Version 6 data are shown to be in agreement within error limits with the average of 39 ground‐based Dobson stations and with the world standard Dobson spectrometer 83 at Mauna Loa, Hawaii. The global average ozone trend from version 6 data shows the presence of varying short‐period trends (1979 to 1983, −0.33%/yr; 1983 to 1986, −0.91% yr, and 1986 to 1990, +0.16%/yr) that are partially masked in the original version 5 trends.
Atmosphere‐biosphere exchange of carbon dioxide in boreal forests
Authors: Bonan Gordon B.
Published: February 2008

An ecophysiological model of photosynthesis and respiration by forest ecosystems was used to examine CO2 fluxes in 23 mature boreal forests near Fairbanks, Alaska. Simulated soil respiration, photosynthesis, decomposition, and moss and tree productivity were consistent with observed data. Monthly ecosystem CO2 flux and net photosynthesis, averaged over the 23 sites, were correlated with atmospheric CO2 concentrations and δ13 ratios, respectively, at Barrow, Alaska, suggesting the boreal forests of Alaska play an active role in the seasonal dynamics of atmospheric CO2 at Barrow. Only one of the 23 stands was a source of CO2, and the 23 stands absorbed (mean ± SE) 1173±211 g CO2 m−2 yr−1. Observed productivity in these forests spans the range of productivity in the circumpolar boreal forest, suggesting the simulated CO2 fluxes are representative of the circumpolar boreal forest. If so, metabolic activity in the circumpolar boreal forest results in a significant annual uptake of CO2.
Atmospheric fate of CF3Br, CF2Br2, CF2ClBr, and CF2BrCF2BR
Authors: Burkholder James B. , Wilson Robert R. , Gierczak Tomasz , Talukdar Ranajit , McKeen Stuart A. , Orlando John J. , Vaghjiani Ghanshyam L. , Ravishankara A. R.
Published: February 2008

The temperature dependent UV absorption cross sections of the haloalkanes CF3Br, CF2ClBr, CF2Br2, and CF2BrCF2Br are reported. The UV absorption cross sections were measured over the temperature range 210 to 296 K and the wavelength range 190 to 320 run. Upper limits of the rate coefficients for the reactions of OH with CF3Br, CF2Br2, CF2ClBr, and CF2BrCF2Br were also determined using both pulsed photolysis and flow tube techniques. The rate coefficients at 296 K were found to be <1.2×10−16, <1.5×10−16, <5.0×10−16, and <1.5×10−16 cm3 molec−1 s−1 for CF3Br, CF2ClBr, CF2Br2, and CF2BrCF2Br, respectively. The UV absorption cross‐section data and OH reaction rate coefficients of these species were combined with a one‐dimensional model to yield atmospheric lifetimes of 65, 16, 3.2, and <20 years for CF3Br, CF2ClBr, CF2Br2, and CF2BrCF2Br, respectively.
Benthic foraminiferal δ18O in the ocean's temperature‐salinity‐density field: Constraints on Ice Age thermohaline circulation
Authors: Zahn Rainer , Mix Alan C.
Published: February 2008

Benthic δ18O data from 95 core sites are used to infer possible temperature‐salinity (T‐S) fields of the Atlantic and Pacific oceans at the Last Glacial Maximum (LGM). A constraint of stable density stratification yields logically consistent scenarios for both T and S. The solutions are not unique but are useful as a thinking tool. Using GEOSECS data, we solve for the modem relationship between δ18Owater (δw) and salinity in the deep sea: δw (SMOW) = 1.529 * S ‐ 53.18. As a starting point, we assume that the slope of this equation applies to LGM conditions and predict δ18Ocalcite (δc) gradients in equilibrium with probable T‐S fields of LGM deep and bottom waters. Benthic foraminiferal δ18O data from the deep Pacific (2–4 km depth), and the bottom Atlantic (> 4 km depth), are 0.1–0.2‰ lower than from the deep Atlantic (2–4 km depth) at the LGM. If the modern δw‐S slope applies, Atlantic deep and bottom waters were more dense than Pacific deep waters. This assumption would imply bottom waters both fresher (ΔS >0.5) and colder (ΔT ∼3°C) than overlying deep waters, in conflict with other data, suggesting ice age deep water much colder than at present. It is also possible that the observed δc gradients are an artifact of laboratory intercalibration. If Atlantic deep and bottom water δc values were similar to deep Pacific values, this would be consistent with the hypothesis of a stronger southern ocean versus North Atlantic source for deep‐ocean ventilation at the LGM. Taking the observed gradients at face value, however, a solution could be that the LGM δw‐S slope in deep and bottom waters was higher than at present, conceivably because of a stronger contribution of salt to the deep ocean via more intense sea ice freezing. This would allow Pacific deep waters and Atlantic bottom waters to have a common source, again in the Antarctic. Both would be more dense than Atlantic deep waters, even though the deep waters were much colder than at present. To better constrain these inferences drawn from the spatial distribution of benthic δ18O, we must reduce scatter in the δ18O data with more high‐quality measurements in high sedimentation rate cores. This is especially true at bottom water sites. Also, we must intercalibrate mass spectrometers at different isotope laboratories more accurately, to insure our isotope data are compatible.
Late Pleistocene Paleoclimatology of the Central Equatorial Pacific: Flux Patterns of Biogenic Sediments
Authors: Rea David K. , Pisias Nicklas G. , Newberry Teresa
Published: February 2008

High‐resolution records of the concentration and mass accumulation rate (MAR, or flux) of biogenic sediments from core RC11‐210 in the central equatorial Pacific are compared for the entire late Pleistocene. The fluxes of calcium carbonate and organic carbon correlate well. The opal flux pattern shows no direct correlation with the other two; rather, opal flux maxima correlate with slopes of (i.e. both precede and follow) the organic carbon and carbonate MAR peaks. Organic carbon and calcite therefore may both be better indicators of past productivity than opal, which is an indicator of transition at this location. We interpret the sequence low biogenic fluxes, high opal fluxes, high carbonate, carbon, and opal fluxes as representing the transition from low to high sea surface biological productivity. The phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume, the ice core CO2 record, the Pacific Δδ13C record, the deep nutrient (Cd/Ca) record, and the eolian grain‐size record of wind intensity. We find that starting from maximum ice volume (phase angle of 0°) the phase relationships of the 100,000‐year periodicity show, in the first quadrant, maximum wind intensity (30°) and maximum calcite and carbon flux (45°) occurring first, followed by maximum opal flux (75°) and then maximum deep nutrients (95°). Minimum Pacific Δδ13C occurs at a phase angle of 155°, the maximum CO2 in the Vostok record and minimum ice volume is at 180°. Thus, in the eccentricity climate cycle, glacial conditions lead to stronger wind‐driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume.
On the Life History of Planktonic Foraminifera: Lunar Reproduction Cycle in Globigerinoides Sacculifer (Brady)
Authors: Erez Jonathan , Almogi‐Labin Ahuva , Avraham Sophie
Published: February 2008

Detailed plankton sampling in the Gulf of Elat, Red Sea, demonstrates a lunar periodicity in the abundance of the foraminifer Globigerinoides sacculifer in surface water as well as below the photic zone. Shell size distribution coupled with abundance changes and laboratory observations suggests the following scheme for the life cycle of this spinose foraminifer: Young individuals of roughly 200 µm (average diameter) are found in surface water 7–8 days after the full moon. During the course of 1 week they grow rapidly to an average size of 300–400 µm. The larger and mature individuals, many of which having a saclike chamber, start to sink down below the photic zone. They add a final chamber, shed their spines, thicken their shell, continue to sink well within the main thermocline, digest their symbionts, and eventually reproduce via gametogenesis at the full moon. We do not have information about the fusion of the gametes, the embryonic growth stages, and the vertical migration of the young foraminifera. However, 1 week after the full moon, small individuals appear again in surface waters and the cycle repeats itself. Although the mechanism by which the moon is synchronizing the reproduction cycle is not clear, it obviously offers better chances for the gametes to fuse. Sinking to deeper water may provide the following advantages: avoidance of predators at the crucial stage of their life cycle when they are without their spine protection; synchronization of reproduction by triggering gametogenesis due to the change from light/dark cycle to complete darkness; better chances for the gametes to concentrate and fuse on a narrow sigma‐t surface at the zone where the pycnocline is steeper; and finally, better chances for survival for the young unprotected foraminifera who start their growth in an environment that contains fewer potential predators.
The layered character of snow covers
Authors: Colbeck S. C.
Published: February 2008

Snow studies have generally ignored the layered nature of snow covers. Having achieved a good understanding of the properties and processes in homogeneous snow, snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response. Many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium. The various mechanisms by which layers are generated, their effects, and some of the outstanding research problems are described here.
Paleozoic and Grenvillian Structures in the southern Appalachians: Extended interpretation of seismic reflection data
Authors: Hubbard Susan Sharpless , Çoruh Cahit , Costain John K.
Published: February 2008

Interpretive reprocessing of seismic reflection data has elucidated Paleozoic and Grenvillian structures in the southern Appalachians. The seismic data include a 7500‐km² grid of ADCOH, Seisdata, and COCORP reflection profiles that traverse the Blue Ridge and Inner Picdmont geologic provinces of North Carolina, South Carolina, and Georgia. Surface geology and potential field data were used to constrain the interpretation. The reprocessed seismic reflection data have delineated the internal and external geometry of the crystalline Blue Ridge‐Inner Piedmont allochthon, including the locations of the Blue Ridge master décollement, Haycsville fault, and Brevard fault zone. On the basis of the reprocessed data, all of the major faults within the allochthonous upper crust sole in the Blue Ridge master décollement. Reflections extending to the southeast from beneath the surface location of the Hayesville fault to the Blue Ridge thrust might be the seismic signature of a high strain zone. This implies that internal deformation of the Blue Ridge allochthon associated with the Alleghanian orogeny might have occurred farther to the west than has been previously documented from field studies. Relative amplitude seismic data enabled the discrimination between Blue Ridge‐Inner Piedmont crystalline rocks and underlying lower Paleozoic shelf strata, thereby delineating the Blue Ridge thrust. The interpreted geometry constrains the top of the shelf sequence beneath the Blue Ridge to depths of less than 3 km. This relatively shallow depth of the shelf strata together with the presence of duplex structures and bright spots that are imaged within the sequence might imply favorable conditions for hydrocarbon exploration beneath the Blue Ridge. Midcrustal reflections from within the upper‐to‐Iower crust are interpreted to originate from preserved Grenvillian structures that were reactivated at the basement surface during Late Proterozoic‐Early Cambrian extension. Reflection continuity is occasionally disrupted by interpreted post‐Grenvillian, pre‐Early Cambrian low‐density intrusions. Topography at the basement surface, possibly caused by the intrusions, is interpreted to have controlled the formation of some of the structures within the overlying allochthon, including Blue Ridge and Brevard fault zone ramps. Correlation of seismic time‐structure contour maps with available gravity data and two‐dimensional gravity modeling suggest that anomalies in the gravity field can be attributed to low‐density sources within the autochthonous crust. Discontinuous reflection packages from depths of 36–42 km are interpreted to originate from the Mohoroviĉiĉ discontinuity. The reflectors trend about N15°E with a true dip of approximately 15°NW.
Well‐documented travel history of Mesozoic pelagic chert in Japan: From remote ocean to subduction zone
Authors: Matsuda Tetsuo , Isozaki Yukio
Published: February 2008

The Mino‐Tanba belt in southwest Japan, a segment of the Cordilleran‐type orogenic chain of Jurassic east Asia, is composed mainly of a Middle‐Upper Jurassic subduction‐accretion complex in which Triassic and Lower Jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with Middle‐Upper Jurassic clastic rocks. High‐resolution microfossil (conodont and radiolaria) research has identified very low average sedimentation rates of about 0.5 g/cm²/1000 yr in the chert units, similar to those of modern pelagic sediments accumulated in open ocean environments. Judging from the low average sedimentation rate, high purity of biogenic silica, long duration of continuous deposition (>50 m.y.), and wide along‐strike extent (>1000 km), the bedded radiolarian cherts in the Mino‐Tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments; accordingly, the alleged origin in smaller marginal basins is untenable. Upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench. The tectonic interlayering of these cherts and coarse‐grained terrigenous elastics is a secondary feature that was added through duplexing‐underplating in the subduction zone. On the basis of the primary stratigraphy and field occurrence of Triassic bedded chert in the Mino‐Tanba belt, newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a Cordilleran‐type bedded chert from its birth at a mid‐oceanic ridge to its demise at a subduction zone.
Localized rotation during Paleogene Extension in east central Idaho: Paleomagnetic and geologic evidence
Authors: Janecke Susanne U. , Geissman John W. , Bruhn Ronald L.
Published: February 2008

We collected paleomagnetic data from 137 sites in middle Eocene volcanic rocks of the northeastern Basin and Range province in order to characterize the three‐dimensional kinematics of continental extension in the Lost River and Lemhi ranges, Idaho, and to test previous block rotation models. Statistically significant flattening of directions at three of 10 localities reflects either insufficient averaging of paleosecular variation or erroneous tilt corrections. Five of the seven remaining locality means are statistically indistinguishable from the middle Eocene reference direction. This indicates that vertical axis rotation did not accompany post‐50 Ma normal faulting. Discordant declinations from two localities in the northern Lost River Range indicate 30°–40° of counterclockwise rotation of a large domain of NNW striking volcanic rocks. Inclination flattening at one of the two rotated localities is moderate but statistically significant (F±ΔF=9.9°±6.5°). In total, the paleomagnetic data conflict with earlier predictions of uniform clockwise rotation in response to right lateral transtension adjacent to the eastern Snake River Plain. There is a close correspondence between counterclockwise rotated localities and domains of NNW striking volcanic rocks and between unrotated localities and domains of north striking volcanic rocks. New mapping shows that counterclockwise rotated localities are all in the hanging wall of a major west dipping low‐angle normal fault, the Donkey fault (named for the first time). This fault loses displacement southwards, was active in Eocene‐Oligocene time and is probably a tilted high angle fault. The spatial distribution of rotated and unrotated localities is best explained by counterclockwise rotation of the hanging wall of the Donkey fault during opening of a southward tapering half graben. According to this hanging wall rotation model the footwall of the Donkey fault remained fixed relative to its rotating hanging wall. Our proposed kinematic model is generally applicable to extending continental lithosphere and provides a mechanism for coeval crustal thinning and vertical axis rotation. Thus vertical axis rotation may occur in the absence of strike‐slip faults in extensional orogens.