bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainties in global terrestrial biosphere modeling, Part II: Global constraints for a process‐based vegetation model
Authors: Knorr Wolfgang , Heimann Martin
Published: February 2004

The terrestrial biosphere is one of several key components of the global carbon cycle. Because the mechanisms by which climate determines terrestrial biosphere carbon fluxes are not well understood, significant uncertainties concerning model results exist even for the current state of the system, with important consequences for our ability to predict changes under future climate change scenarios. We assess how far this uncertainty can be reduced by constraining a global mechanistic model of vegetation activity, either with global satellite‐derived vegetation index data or with measurements of the seasonal CO2 cycle in the atmosphere. We first show how constraining the model with satellite data from the National Oceanic and Atmospheric Administration advanced very high resolution radiometer reduces the sensitivity to estimated uncertainties in model parameters, and thus the estimated error range of net primary productivity. Regionally, the satellite data deliver the largest constraint for vegetation activity in boreal and arctic as well as in tropical water‐limited environments. In a second analysis through an atmospheric tracer transport model, we check the consistency of those results with the measured seasonal cycle of CO2 at various remote monitoring sites. While before including the satellite data into model calculations, some simulations within the error range lead to a CO2 seasonal cycle outside the observations, there is a good agreement with the additional constraint. The conclusion is that the constraint delivered by the satellite data is at least as significant as that delivered by atmospheric CO2 measurements. We also show that the CO2 data mainly reflect the activity of northern vegetation, in particular conifers and C3 grasses. This suggests that satellite measurements provide the most useful global data currently available for checking and improving terrestrial vegetation models and that consistency with CO2 measurements is a necessary but not a sufficient requirement for their realism.
Stratospheric BrO profiles measured at different latitudes and seasons: Instrument description, spectral analysis and profile retrieval
Authors: Ferlemann F. , Camy‐Peyret C. , Fitzenberger R. , Harder H. , Hawat T. , Osterkamp H. , Schneider M. , Perner D. , Platt U. , Vradelis P. , Pfeilsticker K.
Published: February 2004

Measurements of stratospheric BrO profiles are reported using a novel DOAS instrument (Differential Optical Absorption Spectrometry) operated on the LPMA/DOAS balloon gondola (LPMA/Laboratoire de Physique Moléculaire et Applications) during three flights (León, Nov. 23, 1996, Kiruna, Feb. 14, 1997, and Gap, June 20, 1997). BrO was detected by its vibrational bands (4–0 at 354.7nm; 5–0 at 348.8nm) of the A(²π)←X(²π) transition in direct sunlight spectra from balloon ascent, descent and during solar occultation at maximum (float) altitude. We show that our accuracy is about ±18% (1 σ) during balloon ascent (solar zenith angles, SZA < 88°), and about ±25% for solar occultation measurements. For altitudes above the balloon float our observations indicate average BrO mixing ratios of (14.4±2.5)ppt, (15.6±2.8)ppt, and (15.3±2.8)ppt above 30.6km, 30.0km, and 39.8km, respectively.
The in‐flight sensitivity of Gold‐Tube NOy converters to HCN
Authors: Weinheimer A. J. , Campos T. L. , Ridley B. A.
Published: February 2004

In‐flight measurements of the HCN conversion efficiency of three gold‐tube NOy converters were made during the recent TOTE/VOTE and SUCCESS aircraft projects. While sampling ambient air and with the upstream addition of 500 ppmv H2O, two converters had HCN conversion efficiencies averaging about 5%. The H2O addition was a routine part of the NOy measurement procedure for these projects. A third converter showed much higher HCN conversion, about 30%. Conversion efficiencies determined while sampling synthetic air were significantly higher than those measured while sampling ambient air. The dependence of conversion efficiency on ambient H2O and O3 was minimal, at least with respect to the variability of the measured values over the course of the missions.
Climate variability of the coupled Tropical‐Extratropical Ocean‐Atmosphere System
Authors: Wang Chunzai , Weisberg Robert H.
Published: February 2004

Observations show that tropical and extratropical Pacific SST anomalies vary out‐of‐phase, and that the atmospheric meridional Hadley and zonal Walker Circulations are related to these variations. A tropical‐extratropical model is constructed to show oscillations consistent with observations. The positive feedback introduced by the Walker Circulation causes tropical warming so that the air rises and flows toward the subtropics where it sinks. When the sinking air approaches the sea surface, it flows both equatorward and poleward enhancing tropical easterly and extratropical westerly winds, respectively. Enhanced extratropical westerlies increases wind speed and hence evaporation, resulting in extratropical cooling. The Walker and Hadley Circulations thus result in tropical warming and extratropical cooling, respectively. The tropical warming and extratropical cooling increase the meridional SST difference and hence the meridional heat transport which erodes the tropical warming and extratropical cooling. Enhanced tropical easterlies due to the Hadley Circulation cools the tropical ocean through ocean dynamics. These negative feedbacks help the system to switch from warm to cold phases, and vice versa.
A note on record‐high temperatures at the northern polar stratopause in winter 1997/98
Authors: von Zahn U. , Fiedler J. , Naujokat B. , Langematz U. , Krüger K.
Published: February 2004

A series of lidar temperature soundings from the ALOMAR observatory in northern Norway indicated an extreme warming of a descending stratopause in February 1998. The maximum temperature recorded during this event was +49°C at 40 km altitude. This stratospheric warming is described by means of SSU satellite radiance data and of stratospheric analyses from the Free University Berlin. Comparisons are made to a number of historical events with similar temperature observations from rocket soundings and to results from the Berlin general circulation model. It turns out that in all cases the highest stratopause temperatures occur close to the 40 km altitude level.
The MOLA Topographic signature at the crustal dichotomy boundary zone on Mars
Authors: Frey Herbert , Sakimoto Susan E. , Roark James
Published: February 2004

MOLA data collected during the aerobraking hiatus provide good longitudinal sampling of the crustal dichotomy boundary zone in eastern Mars and reveal a significant topographic signature associated with the transition from cratered highlands to lowland plains. Total relief between the two major units is always >2.5 km and sometimes >6 km; median elevation differences are about 4 km. Regional slopes are very low (<0.02°) in both cratered terrain south and in lowland plains north of the boundary. Within the transition zone where cratered terrain changes to detached plateaus, mesas and knobby terrain, slopes are 50–100 times steeper and over a few hundred kilometers average about 1°. The topographic signature of the boundary zone is best described as a 2–4 km step function between two nearly flat surfaces, similar in slope and amplitude to some terrestrial passive margins. This supports previous conclusions of a significant difference in crustal properties (thickness, composition, or both) between the lowland plains and cratered terrain, and suggests this difference occurs over a relatively short distance of a few to several hundred kilometers.
Change of stress field in Beta‐Atla‐Themis Region on Venus, estimated from surface geometry of dike swarms, lava stratigraphy and crater density
Authors: Nagasawa Chiaki , Sasaki Sho , Koyama Masato
Published: February 2004

We estimate the orientations of crustal stress on Venus from surface geometry of dike swarms associated with volcanoes. The inferred stress field sometimes has various orientations even in the same region. Using lava stratigraphy, volcanoes in the Beta‐Atla‐Themis (BAT) region are classified into three groups: volcanoes before, during and after the formation of corona chains. Dike swarms in each group show a similar stress orientation. Between the first two groups, the compressional stress orientation had changed from a N‐S trend to a trend parallel to the strike of the corona chains. The stress fields during and after the corona chain formation are similar. The crater densities of the two volcano groups are 1.67±0.94 × 10−6 and 0.86±0.36 × 10−6 km−2, respectively, which indicates a probable age difference (>108yr). The stress field and volcanic activity before the corona chain formation in the BAT are probably associated with adjacent rift activity in Beta Regio. Those during the corona chain formation may be attributed to a mantle upwelling centered at Atla Regio.
A possible link between El Niño and precipitation in Israel
Authors: Price Colin , Stone Lewi , Huppert Amit , Rajagopalan Balaji , Alpert Pinhas
Published: February 2004

Various data sets related to precipitation in Israel have been analysed to see whether any statistical relationships exist between the El Niño phenomenon and weather in Israel. An understanding of patterns of precipitation in Israel is extremely important given the limited water resources in the Middle East. The authors have analysed seasonal rainfall, streamflow, snowfall and lake level data, and all of these data sets indicate enhanced precipitation during the winter seasons associated with El Niño years. One intriguing finding is that the statistically significant correlations appear only in the last 25 years.
Ballooning instability in the tail plasma sheet
Authors: Lee D.‐Y.
Published: February 2004

Numerical computations of the ideal MHD ballooning mode are performed for the 2‐D tail plasma sheet model. The computations are done for the analytic model equilibria that include the Earth's 2‐D dipole field, as well as for those that do not. It is found that the ballooning mode can be unstable in some class of plasma sheet equilibria where the field lines are not too much stretched but when the plasma beta still exceeds some critical value. The instability is more easily triggered in the equilibria where the Earth's dipole field is fully included.
Teleconnections between tropical pacific sea surface temperature anomalies and North Carolina precipitation anomalies during El Niño events
Authors: Roswintiarti Orbita , Niyogi Devdutta S. , Raman Sethu
Published: February 2004

Linear teleconnections of El Niño events and precipitation over a regional coastal land mass were analyzed. Two statistical techniques were used. First, the Empirical Orthogonal Function extracted major variances of the monthly tropical Pacific sea surface temperature anomalies and coastal North Carolina precipitation anomalies. Second, the Canonical Correlation Analysis calculated the linear combinations of the anomaly data sets that were highly correlated. The results show that El Niño‐related precipitation anomalies along the North Carolina coast were positive from November to May and negative between June and October consistent with large‐scale studies. Results indicate simple, linear statistical techniques can be effectively adopted to determine teleconnections on a local scale.
Stress and temperature dependence of recrystallized grain size: A subgrain misorientation model
Authors: Shimizu Ichiko
Published: February 2004

The steady‐state grain size of Earth materials undergoing solid state flow is estimated based on a nucleation‐and‐growth model of dynamic recrystallization. Assuming a nucleation mechanism of subgrain rotation, the mean diameter d of recrystallized grains is obtained as d/b = A(σ/µ)−p exp[‐((Qgb ‐ Qv)/mkT)], where b is the length of the Burgers vector, σ is differential stress, µ is the shear modulus, Qgb is the activation energy for the jump of an atom across the grain boundary, Qv is that for self‐diffusion in the grain volume, k is the Boltzmann constant, T is temperature, A is a constant, p = 1.25 and m = 4 for intracrystalline nucleation, and p = 1.33 and m = 3 for grain‐boundary nucleation. The exponent p = 1.25 ∼ 1.33 agrees well with available data for high‐ temperature dislocation creep of rock‐forming minerals. A weak negative dependence of grain size on temperature is expected from this theory.
Above cloud electrical discharges: The effect of aerosol transport
Authors: Shaw Glenn E.
Published: February 2004

Upward‐propagating discharges from thunderstorms, called “blue jets” and “blue starters” and high altitude near‐cloud top discharges have been reported over strong convective storm systems. The electrodynamics involved in these high altitude electrical phenomena are not clarified, though several models have been proposed, including initiation by run‐away high energy electron beams and breakdowns related to quasi‐electrostatic fields. We suggest that the occurrence of such high altitude discharges may, under some conditions, be instigated by decreases in electrical conductivity (and therefore increases in electric field strength) near and above cloud tops, the conductivity decrease resulting from the presence of large ions. We hypothesize that the large ions are pollution aerosols which are systematically transported to the lower stratosphere/upper troposphere from the lower troposphere by convective currents. In addition we propose that large ion production in the region above cloud is further enhanced by: 1. creation of new large ions by photolytic gas‐to‐particle conversion; and 2. by the upward transport of cloud top ions across the tropopause into the lower stratosphere.
Estimation of surface actinic flux from satellite (TOMS) ozone and cloud reflectivity measurements
Authors: Mayer B. , Fischer C. A. , Madronich S.
Published: February 2004

Recently, a method has been proposed to estimate ultraviolet (UV) spectral irradiances at the Earth's surface, from satellite‐based measurements of ozone and cloud reflectivity. Here, we extend this method to the determination of spectral actinic fluxes needed for the calculation of photodissociation rate coefficients. It is shown that the modification of actinic flux by clouds is closely approximated by the cloud reduction factor applicable to the irradiance, if considering averages over area or time instead of instantaneous point data. The conversion of irradiance estimates into actinic flux estimates introduces additional errors, but for most practical situations these fall below 10 to 20% in the UV spectral region, where the relevant photolytic reactions have their maximum sensitivity. Based on these results, large satellite‐derived data sets (e.g., ozone column and cloud reflectivity from the Total Ozone Mapping Spectrometer, TOMS) can be utilized to estimate near‐surface photolysis rate coefficients on a global scale.
Coronal mass ejections associated with interplanetary ejecta
Authors: Bravo Silvia
Published: February 2004

In a previous work we have shown that interplanetary ejecta, which sometimes appear behind transient shocks and sometimes appear alone, are related to coronal mass ejections (CMEs) associated with some kind of near‐surface solar events (Hα flares or prominence eruptions). In this paper we study the characteristics of these particular CMEs by taking the list of interplanetary shocks with and without ejecta from the Solwind/Helios combined study of CMEs and transient interplanetary shocks. From the same list and the Solwind CME Catalogue we obtained the characteristics of their associated CMEs and compared them. We find that the mean velocity of ejecta‐associated CMEs is higher than that of CMEs associated with shocks without ejecta, and belong to different structural classes. We also find that the CMEs of ejecta cases are almost always associated with near surface solar activity, while CMEs of no‐ejecta cases are rarely accompanied by this kind of activity. Also, the duration of the associated near‐surface events is much longer for CMEs related to interplanetary ejecta.
Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter
Authors: Garvin James B. , Frawley James J.
Published: February 2004

The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power‐law relationship for these craters is: d = 0.14 D0.90 for simple varieties, and d = 0.25 D0.49 for complex structures. The simple‐to‐complex transition diameter is 8 km (+/−0.5 km). The cross‐sectional “shape” of the crater cavities was determined by fitting a power‐function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.
Observations of the 1997–98 warm ENSO event at the Manus Island ARM site
Authors: Jensen Michael P. , Mather James H. , Ackerman Thomas P.
Published: February 2004

The 1997–98 warm ENSO event is one of the strongest on record. There are several signatures of this event which have been observed in at the Manus Island ARM site. These signatures have been observed in several different data streams including the solar radiation, water vapor column and rainfall measurements. These observations are presented along with a look ahead at what can be expected at forthcoming ARM TWP sites.
A master equation study of laser‐generated interference in the detection of hydroxyl radicals using laser‐induced fluorescence
Authors: Zeng Guang , Heard Dwayne E. , Pilling Michael J. , Robertson Struan H.
Published: February 2004

Concentrations of OH in the atmosphere are extremely small, and for any quantitative measurement technique it is imperative that the observed signal originates solely from ambient OH. A master equation model has been formulated to calculate the contribution to the OH concentration from laser photolysis of O3 and the subsequent reaction of O(¹D) with H2O, for conditions typical of instruments designed to measure OH by laser‐induced fluorescence. The model incorporates the quantum state specific production of OH from the O(¹D)+H2O reaction and rotational energy transfer, and calculates the temporal behaviour of all rotational states. For detection at 308 nm and 282 nm, whilst probing the lowest rotational level, N”=1, the model predicts that interference from laser generated OH accounts for 0.4% and ∼10% respectively, of the total LIF signal, for [OH]=106 molecules cm−3, [O3]=50 ppb, 40% relative humidity, and typical operating temperatures, pressures and laser parameters.
Wind‐driven effects on the Yellow Sea Warm Current
Authors: Mask Andrea C. , O'Brien James J. , Preller Ruth
Published: February 2004

The Yellow Sea is a shallow basin writh an average depth of 44 m located between China and the Korean Peninsula. One of the dominant ocean circulation features of the Yellow Sea is a warm wrater intrusion known as the Yellow Sea Warm Current. This feature is present throughout the year but reaches its farthest northward extension in winter. The circulation of the Yellow, East China, and Bohai Seas was modeled using the Princeton Ocean Model to better understand the dynamics of the Yellow Sea Warm Current. The horizontal resolution of the model varies from 8 km in the Yellow Sea to 25 km in the East China Sea. Twenty‐four sigma levels are used to define the vertical structure. The model uses daily atmospheric forcing from the Navy Operational Global Atmospheric Prediction System for 1993. Open boundary conditions are applied at the Taiwan Strait, the Tsushima (Korea) Strait, an area south of Taiwan, and the Tokara Strait, with a closed boundary south of the Ryukyu Islands. The model results are examined to determine the effect of the wind on the northward extension of the warm water intrusion, using both water mass characteristics and northward velocity components. Sensitivity tests and spectrum analyses, performed to study the influence of the wind on the Yellow Sea Warm Current, show that winds modify the pathway and extent of the Yellow Sea Warm Current. The current's origin, however, appears to be due to external forcing from the current systems developed in the East China Sea.
Anthropogenic forcing on tropospheric ozone and OH since preindustrial times
Authors: Wang Yuhang , Jacob Daniel J.
Published: February 2004

A global three‐dimensional model of tropospheric chemistry is used to investigate the changes in tropospheric O3 and OH since preindustrial times as a result of fuel combustion and industry, biomass burning, and growth in atmospheric CH4. Model results indicate a 63% increase of the global tropospheric O3 burden from preindustrial times to present (80% and 50% in the northern and southern hemispheres, respectively). Anthropogenic emissions of NOx and of CO and hydrocarbons make comparable contributions to the global O3 increase (60% and 40% respectively), even though the local rate of tropospheric O3 production is generally NOχ limited. The rise in O3 production parallels closely the rise in the emissions of CO and hydrocarbon because the O3 yield per mole of CO or hydrocarbon oxidized has remained constant at 0.7–0.8 mol/mol since preindustrial times. In contrast, the O3 production efficiency per mole of NOχ emitted has decreased globally by a factor of 2. We find a 9% decrease in the global mean OH concentration (mass‐weighted) since preindustrial times. A linear relationship is found in the model between the global mean OH concentration and the SN/SC3/2 ratio, where SN and SC are the sources of NOχ and of CO and hydrocarbons, respectively. The relative constancy of the global mean OH concentration since preindustrial times reflects the conservation of the SN/SC3/2 ratio despite large increases in both SN and SC. Comparisons of model results with reconstructed nineteenth century observations of O3 at continental sites indicate a systematic overestimate of about 5 ppbv. Correcting this overestimate would require either a large missing chemical sink for O3 or a downward revision of the natural NOχ source from lightning (3 Tg N yr−1 in our model). The nineteenth century observations of O3 over France show no vertical gradient between the boundary layer and the free troposphere, which is inconsistent with our current understanding of tropospheric O3. The model underestimates preindustrial CO concentrations derived from polar ice cores; these measurements are difficult to reconcile with any reasonable CO emission inventories.
On the stability of the atmosphere‐vegetation system in the Sahara/Sahel region
Authors: Brovkin Victor , Claussen Martin , Petoukhov Vladimir , Ganopolski Andrey
Published: February 2004

A conceptual model has been developed for the analysis of atmosphere‐vegetation interaction in subtropical deserts. The model can exhibit multiple stable states in the system: a “desert” equilibrium with low precipitation and absent vegetation and a “green” equilibrium with moderate precipitation and permanent vegetation cover. The conceptual model is applied to interpret the results of two climate‐vegetation models: a comprehensive coupled atmosphere‐biome model and a simple box model. In both applications, two stable states exist for the western Sahara/Sahel region for the present‐day climate, and the only green equilibrium is found for the mid‐Holocene climate. The latter agrees well with paleoreconstructions of Sahara/Sahel climate and vegetation. It is shown that for present‐day climate the green equilibrium is less probable than the desert equilibrium, and this explains the existence of the Sahara desert as it is today. The difference in albedo between the desert and vegetation cover appears to be the main parameter that controls an existence of multiple stable states. The Charney's mechanism of self‐stabilization of subtropical deserts is generalized by accounting for atmospheric hydrology, the heat and moisture exchange at the side boundaries, and taking into account the dynamic properties of the surface. The generalized mechanism explains the self‐stabilization of both desert and vegetation in the western Sahara/Sahel region. The role of surface roughness in climate‐vegetation interaction is shown to be of secondary importance in comparison with albedo. Furthermore, for the high albedo, precipitation increases with increasing roughness while, for the low albedo, the opposite is found.
An ozone climatology based on ozonesonde and satellite measurements
Authors: Paul J. , Fortuin F. , Kelder Hennie
Published: February 2004

An ozone climatology is presented, based entirely on ozone observations over the target period 1980–1991. The climatology gives zonal mean ozone values, as well as the corresponding interannual standard deviation, for 17 zonal bands (80°S–S0°N) at 19 pressure levels (1000–0.3 hPa), for each month of the year. It is intended mainly for climate simulations with general circulation models (GCMs). For the troposphere and lower stratosphere (1000–10 hPa) the climatology is compiled from ozonesonde observations of 30 ozonesonde stations located around the world. To account for tropospheric longitudinal variability within a zonal band, a data set giving tropospheric total ozone values between 50°S and 50°N is used. For stations within this latitude range the tropospheric profile is scaled with a factor derived from this data set to make it more representative of the zonal mean. Consequently, the corrected profiles of the individual stations are combined within each zonal band, using weighted averaging. These zonal profiles are then attached to zonal monthly mean SBUV‐SBUV/2 (solar backscattered ultraviolet) observations in the stratosphere (30–0.3 hPa). Three overlap layers, at 30, 20, and 10 hPa, give an indication of how well these two data sets match. Where possible, the integral of the combined ozone profiles is made consistent with total ozone mapping (TOMS) profiles, by applying a correction factor to the ozonesonde part of the profile, derived from TOMS minus the integrated SBUV‐SBUV/2 profile. The resulting climatology is compared with three other ozone climatologies: the predecessor of this one, a climatology compiled by the State University of New York, and a climatology used in the GCM at the Max Planck Institute in Hamburg, Germany. Apparent improvements are better consistent with TOMS (compared with the first climatology) and more realistic ozone values in the tropics and polar regions (compared with the first and second climatologies). There is an overall strong improvement compared with the third climatology, which was generated from an analytical formula and old ozone observations in the 1970s. A unique further advantage of the current climatology is the accompanying standard deviation climatology, giving an indication of the natural variability and reliability of the mean ozone values.
The background aerosol size distribution in the free troposphere: An analysis of the annual cycle at a high‐alpine site
Authors: Nyeki S. , Li F. , Weingartner E. , Streit N. , Colbeck I. , Gäggeler H. W. , Baltensperger U.
Published: February 2004

Measurements during free tropospheric (FT) and planetary boundary layer (PBL) conditions were conducted over an annual cycle at the Jungfraujoch high‐Alpine research station (3454 m), Switzerland, in order to establish diurnal and seasonal cycles of the background continental aerosol over central Europe. Using a condensation nucleus counter (TSI 3025) and an optical particle counter (PMS Las‐X) from June 1996 to May 1997, the following were determined: (1) accumulation mode lognormal parameters and (2) number concentrations for the nucleation (diameter d < 0.1 μm), accumulation (0.1 ≤ d ≤ 1.0 μm), and part of the coarse (1.0 < d ≤ 7.5 μm, designated “coarse”) modes. Lognormal parameters were found to be similar for FT and PBL conditions, and exhibited a weak seasonality in geometric median diameter dGN =0.13 and 0.10 μm, and standard deviation σG = 1.73 and 1.64 for summer and winter, respectively. Aerosol number concentrations in each mode exhibited a more pronounced seasonality, with FT concentrations being lower than those for PBL. Summer and winter FT median concentrations for the nucleation, accumulation, and “coarse” modes were 405 and 195 cm−3, 114 and 26 cm−3, and 0.052 and 0.014 cm−3, respectively. These results provide tentative support of other long‐term observations that the FT background aerosol mode appears to vary mainly in concentration rather than accumulation mode shape. Further analysis indicated that only the total concentration in each mode varied with weather type and a classification between that of a remote continental and polar aerosol model was found for the Jungfraujoch.
Dissolved oxygen transfer at the sediment‐water interface in a turbulent flow
Authors: Hondzo Midhat
Published: February 2004

Laboratory experiments have been conducted in an effort to elucidate the details of the dissolved oxygen transfer mechanism at the sediment‐water interface. Near‐bed liquid turbulence and dissolved oxygen concentrations were measured for a range of Reynolds numbers from 2700 to 10,600 over a smooth bed. The results show that the shear stress velocity controls the dissolved oxygen diffusive layer thickness and therefore the local mass transfer coefficient at the sediment‐water interface. From a dynamic point of view the results suggest the possibility that streamwise vortices control the interfacial dissolved oxygen transfer process. The research results will provide an opportunity to validate the existing conceptual models as well as enhance the development of new models that can improve our ability to predict dissolved oxygen and transport related parameters in lakes, reservoirs, coastal waters, and rivers.
Simultaneous measurement of capillary pressure, saturation, and effective permeability of immiscible liquids in porous media
Authors: Dane J. H. , Hofstee C. , Corey A. T.
Published: February 2004

In many studies involving a liquid and air, the effective permeability of the wetting phase (kw) is determined from the capillary pressure (Pc)–saturation (S) relation and a corresponding, measured kw value. The movement, and therefore the effective permeability, knw, of air in an air‐liquid system is often ignored, especially by those who consider only the flow of water in soils. However, if a wetting and a nonwetting liquid coexist (two immiscible liquids), the effective permeability function of the nonwetting liquid must be determined as well. Rather than using some indirect method to determine the knw (Pc) or knw (S) relationship of the nonwetting liquid, we propose a direct measurement technique by using a permeameter which allows for steady state flow of the nonwetting liquid over a range of Pc and S values. During each steady state flow condition of the nonwetting liquid, Pc and S are constant and uniform throughout the permeameter, while the wetting liquid is at rest. The nonwetting liquid can either be a dense non–aqueous phase liquid (DNAPL) or a light non–aqueous phase liquid (LNAPL). The knw values are calculated as a function of Pc and S from the measured flow rates and the density difference between the wetting and nonwetting liquid. The proposed technique can be applied during drainage as well as imbibition. The S values are determined by recording the amount of water being displaced from the cell each time the Pc is changed. Results are discussed for the DNAPL perchloroethylene (PCE) and the LNAPL Soltrol.
Trace gas exchange in a high‐Arctic valley: 1. Variationsin CO2 and CH4 Flux between tundra vegetation types
Authors: Christensen T. R. , Friborg T. , Sommerkorn M. , Kaplan J. , Illeris L. , Soegaard H. , Nordstroem C. , Jonasson S.
Published: February 2004

Ecosystem exchanges of CO2 and CH4 were studied by chamber techniques in five different vegetation types in a high arctic valley at Zackenberg, NE Greenland. The vegetation types were categorized as Cassiope heath, hummocky fen, continuous fen, grassland and Salix arctica snowbed. Integrated daytime fluxes for the different vegetation types of the valley showed that the fen areas and the grassland, were significant sources of CH4 with a mean efflux of 6.3 mg CH4 m−2 hr−1 and sinks for CO2, with almost ‐170 mg CO2 m−2 hr−1. The heath and snowbed areas had much lower carbon sequestration rates of about −25 mg CO2 m−2 hr−1 and were also sinks for CH4. Methane emissions from the valley dominated in the hummocky fens. Computation of area integrated mean daytime flux values across all vegetation types of the entire valley bottom revealed that it was a sink of CO2 in the order of −96 ± 33 mg CO2 m−2 hr−1 and a source of 1.9 ± 0.7 mg CH4 m−2 hr−1. These values were in accordance with eddy correlation measurements reported elsewhere in this issue and reflect a high‐carbon exchange despite the high arctic location. In the fens, where the water table was at or above the soil surface, methane emissions increased with net ecosystem CO2 flux. In places with the water table below the soil surface, such as particularly in the hummocky parts of the fen, oxidation tended to become the dominant controlling factor on methane efflux.
Anthropogenic CO2 invasion into the northeast Pacific based on concurrent δ13CDIC and nutrient profiles from the California Current
Authors: Ortiz J. D. , Mix A. C. , Wheeler P. A. , Key R. M.
Published: February 2004

The stable isotopic signature of dissolved inorganic carbon (δ13CDIC) in the northeast Pacific Ocean is lower in near‐surface waters by ≈1.1‰ relative to values predicted from global oceanic trends of δ13CDIC versus nutrients. A combination of anthropogenic carbon uptake from the atmosphere and thermodynamic, air‐sea gas exchange processes in different water mass source areas account for the isotopic depletion. Here we evaluate the efficacy of using a concurrent nutrient‐δ13C strategy to separate these two effects, with the goal of improving estimates of anthropogenic carbon uptake over the course of the Industrial Revolution. In depth profiles from the sea surface to 2500 m at four stations across the California Current (42°N), nitrate, rather than phosphate, is best correlated to δ13CDIC providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000–2500 m depth (potential densities, σθ ∼ 27.3–27.7), the “anthropogenic— preanthropogenic” carbon isotope shift (Δδ13Ca−p) in near‐surface waters of the northeast Pacific is inferred to be −0.62 ± 0.17‰, while the thermodynamic air‐sea gas exchange signature is estimated at −0.48 ± 0.17‰. Values of Δδ13Ca−p (similar to the regional patterns of Δ14C and Tritium penetration) approach zero for σθ > 26.8, indicating little penetration of anthropogenic carbon into the North Pacific Intermediate Water or the upper North Pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic carbon over the past ∼200 years that is ∼40% greater than that estimated for the interval between ∼1970 and ∼1990 by Quay et al., [1992]. Our estimate of the North Pacific inventory of anthropogenic carbon, added to published estimates from the North Atlantic and Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the deep sea via the Southern Ocean.
Space and time variation of δ18O andδD in precipitation: Can paleotemperature be estimated from ice cores?
Authors: Hendricks M. B. , DePaolo D. J. , Cohen R. C.
Published: February 2004

A one‐dimensional model of meridional water vapor transport is used to evaluate the factors that control the spatial and temporal variations of oxygen (δ18O) and hydrogen (δD) isotopic ratios in global precipitation. The model extends Rayleigh descriptions of isotopes in precipitation by including (1) effects of recharge to air masses by evaporation and (2) horizontal transport by both eddy fluxes and advection. Globally, spatial variations in precipitation δ18O and δD depend on the ratio of evaporation to the product of horizontal moisture flux and horizontal temperature gradient. At low latitudes, where this ratio is large, precipitation δ18O and δD are closely tied to the isotopic ratios of oceanic evaporation. At high latitudes the ratio is small, and δ18O and δD are controlled by the ratio of advective transport to eddy transport. Transport by eddy fluxes induces less fractionation than transport by advection, resulting in a smaller gradient of isotopic ratios with temperature. The model‐predicted temporal relationships between δ18O (or δD) of Antarctic precipitation and temperature do not necessarily coincide with the modern spatial relationship and depend strongly on the proximity of the precipitation site to the ocean evaporation source. Sensitivity of δ18O to temporal changes in local surface temperature is low at coastal sites and increases with distance inland. These results suggest a possible explanation of the apparent discrepancy between borehole temperature inversion estimates of glacial temperatures and temperatures inferred from the modern spatial δ18O—surface temperature relationship.
Temperature effects on export production in the open ocean
Authors: Laws Edward A. , Falkowski Paul G. , Smith Walker O. , Ducklow Hugh , McCarthy James J.
Published: February 2004

A pelagic food web model was formulated with the goal of developing a quantitative understanding of the relationship between total production, export production, and environmental variables in marine ecosystems. The model assumes that primary production is partitioned through both large and small phytoplankton and that the food web adjusts to changes in the rate of allochthonous nutrient inputs in a way that maximizes stability, i.e., the ability of the system to return to steady state following a perturbation. The results of the modeling exercise indicate that ef ratios, defined as new production/total production = export production/total production, are relatively insensitive to total production rates at temperatures greater than ∼25°C and lie in the range 0.1‐0.2. At moderate to high total production rates, ef ratios are insensitive to total production and negatively correlated with temperature. The maximum ef ratios are ∼0.67 at high rates of production and temperatures of 0°−10°C. At temperatures less than ∼20°C, there is a transition from low ef ratios to relatively high ef ratios as total production increases from low to moderate values. This transition accounts for the hyperbolic relationship often presumed to exist between ef ratios and total production. At low rates of production the model predicts a negative correlation between production and ef ratios, a result consistent with data collected at station ALOHA (22°45′N, 158°W) in the North Pacific subtropical gyre. The predictions of the model are in excellent agreement with results reported from the Joint Global Ocean Flux Study (JGOFS) and from other field work. In these studies, there is virtually no correlation between total production and ef ratios, but temperature alone accounts for 86% of the variance in the ef ratios. Model predictions of the absolute and relative abundance of autotrophic and heterotrophic microorganisms are in excellent agreement with data reported from field studies. Combining the ef ratio model with estimates of ocean temperature and photosynthetic rates derived from satellite data indicates that export production on a global scale is ∼20% of net photosynthesis. The results of the model have important implications for the impact of climate change on export production, particularly with respect to temperature effects.
Interannual variation of soil respiration in two New England forests
Authors: Savage K. E. , Davidson E. A.
Published: February 2004

Soil respiration is an important component of the annual carbon balance of forests, but few studies have addressed interannual variation in soil respiration. The objectives of this study were to investigate the seasonal and interannual variation in soil respiration, temperature, precipitation, and soil water content in two New England forest soils and to develop and evaluate empirical models for predicting variations in soil respiration using temperature and soil moisture content. We have been measuring soil respiration, using dynamic chambers in well‐drained upland sites and poorly drained wetland sites since 1995 at the Harvard Forest, Massachusetts, and since 1996 at the Howland Forest, Maine. The upland sites had consistently greater rates of respiration than wetlands. Prolonged drought periods in 1995, 1998, and 1999 at the Harvard Forest resulted in decreased soil respiration rates in the uplands, particularly once soil moisture contents decreased below about −150 kPa. In contrast, wetland respiration increased upon drying. The interannual variation in soil respiration at the Harvard Forest, 0.23 kg C m−2 yr−1, exceeds the interannual variation in net ecosystem exchange (NEE), 0.14 kg C m−2 yr−1 previously measured for this forest, indicating that interannual variation in soil respiration can have an important influence on NEE. Interannual variation was lower at the Howland Forest, and the effects of low soil moisture content on respiration rates were more subtle. The onset of spring was variable among years at both forests, owing to variation in both temperature and precipitation, and contributed to 33–59% of the annual variability in total carbon release. At the upland sites, parameterization of empirical regression models for respiration as a function of soil temperature was inconsistent among years, indicating an important effect of interannual variation in soil water content. The negative residuals of the Harvard Forest temperature regression model were best explained by drought conditions (soil matric potentials ≤−150 kPa). This function was only applicable during severe drought and did not account for less severe dry periods that also reduced soil moisture and soil respiration. An empirical regression model for the wetlands as a function of temperature was significantly improved with the addition of a soil moisture function, which increased respiration rates under dry conditions and decreased it under wet conditions. Climatic changes resulting in drier conditions will likely decrease soil respiration rates in uplands and increase soil respiration in wetlands.
Evaluation and analysis of a dynamic terrestrial ecosystem model under preindustrial conditions at the global scale
Authors: Friend Andrew D. , White Andrew
Published: February 2004

The ability of a mechanistically based dynamic terrestrial ecosystem model, Hybrid v4.1, to predict the global distribution of vegetation, primary productivity, biomass carbon, and soil carbon under preindustrial conditions of climate, atmospheric CO2, and nitrogen deposition is evaluated. This model predicts the dynamic global distribution of eight Plant Functional Types (PFTs) by treating the interactions between individual trees, an herbaceous layer, and their physical environment at independent points on the land surface. Carbon, water, and nitrogen flows are simulated on a daily, or subdaily, basis resulting in dynamic predictions of productivity, biomass, and plant and soil carbon and nitrogen contents. Hybrid v4.1 successfully predicts the major global patterns of preindustrial vegetation, primary productivity, biomass carbon, and soil carbon. When not subject to competition, single PFTs have much broader distributions across climatic gradients than when allowed to compete with one another, demonstrating the importance of competition in determining vegetation distribution. Trade‐offs between the avoidance of frost and drought damage, growing season length, and foliage nitrogen allocation determine the relative performance of tree PFTs along climatic gradients. Six areas of disagreement between prediction and reality are noted: (1) African savanna, (2) South American grassland, (3) an area of desert in Amazonia, (4) Southern Chinese evergreen forest, (5) Siberian larch forest, and (6) tundra. These discrepancies provide useful information for future model development.
Extrinsic controls on the evolution of Hawaiian ocean island volcanoes
Authors: Clague David A. , Dixon Jacqueline E.
Published: February 2004

Extrinsic parameters that affect the evolution of magmatic systems within and beneath ocean island volcanoes include physical variables such as confining pressure, which controls magma degassing, and temperature of the underlying lithosphere and crust, which controls magma crystallization during ascent. Other extrinsic parameters are environmental variables coupled to the hydrosphere and atmosphere such as hydrothermal circulation systems and even rainfall. All these extrinsic factors interact with intrinsic parameters, such as magma supply rates or composition, to modulate the evolution of magma chambers and the petrologic processes that take place within them.
Petrology and Sr, Nd, and Pb isotope geochemistry of mid‐ocean ridge basalt glasses from the 11°45′N to 15°00′N segment of the East Pacific Rise
Authors: Castillo P. R. , Klein E. , Bender J. , Langmuir C. , Shirey S. , Batiza R. , White W.
Published: February 2004

Basaltic glasses from the geophysically well‐studied section of the East Pacific Rise (EPR) between 11°45′N to 15°00′N range from normal mid‐ocean ridge basalts (MORB) to transitional MORB and their major element variations correlate with isotopic and trace element indices of enrichment. To first order, basalts enriched in Na8.0, incompatible elements, 87Sr/86Sr, and 206Pb/204Pb but low in Fe8.0 and 143Nd/144Nd are more prevalent along the shallow portions of the ridge axis. In detail, the samples can be divided into two chemical and geographical Groups: the southern bathymetric dome, extending from the 11°45′N overlapping spreading center to ∼14°10′N, and the northern Group, extending from ∼14°10′N to the Orozco transform. The boundary between these two Groups is apparent in a change in isotopic composition. Results indicate that there are three mantle source components that produce the compositional variability observed among samples from the 11°45′N to 15°00′N segment of the EPR: a depleted mantle component, a seamount‐type enriched mantle component, and an Indian MORB‐like mantle component. South of ∼14°10′N, the geochemical variability is dominated by binary mixing between a depleted mantle component and an enriched component similar to near‐ridge seamounts. North of ∼14°10′N, the low 206Pb/204Pb, high 207Pb/204Pb Indian MORB‐like component exerts a major influence on the geochemical variability of the axial lavas. Regional averages of major element composition (e.g., Na8.0 and Fe8.0) show relatively limited variability consistent with the restricted range in depth for this region and plot within the Pacific field of the previously defined global trends. Major element variations among individual samples, however, parallel the global array, and their correlation with indices of mantle enrichment supports the idea that the “Pacific‐type local trend” results from small‐scale heterogeneities in the mantle beneath the EPR. Our results also indicate that tectonic segmentation and magmatic boundaries are probably not causally related in this study area and that the sizes of the present magma chambers are not a dominant factor in determining the compositional variability of erupted lavas.