bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleoceanography and the diachrony of radiolarian events in the eastern equatorial Pacific
Authors: Moore T. C. , Skackleton N. J. , Pisias N. G.
Published: February 2008

The development of an orbitally tuned time scale for the ODP leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework. With this framework we are better able to define which of the first and last appearances of species appear to be synchronous. In addition, the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped. These maps not only provide information on the process of evolution, migration, and extinction, they can also be related to water mass distributions and near‐surface circulation of the ocean. Of 39 radiolarian events studied at 11 sites in the eastern equatorial Pacific, 28 were found to have a minimum range in their estimated age that exceeded 0.15 m.y. The temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 Ma. These changes in the locations of high gradient regions suggest that the South Equatorial Current (SEC) was north of its present position prior to approximately 7 Ma. There was a southward shift in the northern boundary of this current between approximately 6 and 7 Ma, and the development of a relatively strong gradient between the northeastern and northwestern sites. Between approximately 3.7 and 3.4 Ma, there was a very slight northward shift in the northern boundary of the SEC and the steep gradients between the northeastern and northwestern sites may have disappeared. This change is thought to be associated with the closing of the Isthmus of Panama. The temporal‐spatial patterns of diachronous events younger than 3.4 Ma are consistent with patterns of circulation in the modern ocean.
Biogenic flux of Al to sediment in the central equatorial Pacific Ocean: Evidence for increased productivity during glacial periods
Authors: Murray R. W. , Leinen M. , Isern A. R.
Published: February 2008

We examined the flux of Al to sediment accumulating beneath the zone of elevated productivity in the central equatorial Pacific Ocean, along a surface sediment transect at 135°W as well as downcore for a 650 kyr record at 1.3°N, 133.6°W. Across the surface transect, a pronounced, broadly equatorially symmetric increase in Al accumulation is observed, relative to Ti, with Al/Ti ratios reaching values 3–4 times that of potential detrital sources. The profile parallels biogenic accumulation and the modeled flux of particulate 234Th, suggesting rapid and preferential adsorptive removal of Al from seawater by settling biogenic particles. Normative calculations confirm that most Al is unsupported by the terrigenous fraction. The observed distributions are consistent with previous observations of the relative and absolute behavior of Al and Ti in seawater, and we can construct a reasonable mass balance between the amount of seawater‐sourced Al retained in the sediment and the amount of seawater Al available in the overlying column. The close tie between Al/Ti and biogenic accumulation (as opposed to concentration) emphasizes that biogenic sedimentary Al/Ti responds to removal‐transport phenomena and not bulk sediment composition. Thus, in these sediments dominated by the biogenic component, the bulk Al/Ti ratio reflects biogenic particle flux, and by extension, productivity of the overlying seawater. The downcore profile of Al/Ti at 1.3°N displays marked increases during glacial episodes, similar to that observed across the surface transect, from a background value near Al/Ti of average upper crust. The excursions in Al/Ti are stratigraphically coincident with maxima in both bulk and CaCO3 accumulation and the excess Al appears to not be preferentially affiliated with opaline or organic phases. Consistent with the similar behavioral removal of Al and 234Th, the latter of which responds to the total particle flux, the Al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits. These results collectively indicate that (1) Al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater. Therefore, the common tenet that Al is dominantly associated with terrestrial particulate matter, and the subsequent use of Al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment, needs to be reevaluated. (2) The Al/Ti ratio in biogenic sediment can be used to trace the productivity of the overlying water, providing a powerful new paleochemical tool to investigate oceanic response to climatic variation. (3) The close correlation between the Al/Ti productivity signal and carbonate maxima downcore at 1.3°N suggests that the sedimentary carbonate maxima in the central equatorial Pacific Ocean record increased productivity during glacial episodes.
A 135,000‐year Vostok‐Specmap Common temporal framework
Authors: Sowers Todd , Bender Michael , Labeyrie Laurent , Martinson Doug , Jouzel Jean , Raynaud Dominique , Pichon Jean Jacques , Korotkevich Yevgeniy Sergeevich
Published: February 2008

The object of the present study is to introduce a means of comparing the Vostok and marine chronologies. Our strategy has been to use the δ18O of atmospheric O2 (denoted δ18Oatm) from the Vostok ice core as a proxy for the δ18O of seawater (denoted δ18Osw). Our underlying premise in using δ18Oatm as a proxy for δ18Osw is that past variations in δ18Osw (an indicator of continental ice volume) have been transmitted to the atmospheric O2 reservoir by photosynthesizing organisms in the surface waters of the world's oceans. We compare our record of δ18Oatm to the δ18Osw record which has been developed from studies of the isotopic composition of biogenic calcite (δ18Oforam) in deep‐sea cores. We have tied our δ18Oatm record from Vostok to the SPECMAP timescale throughout the last 135 kyr by correlating δ18Oatm with a δ18Osw record from V19‐30. Results of the correlation indicate that 77% of the variance is shared between these two records. We observed differences between the δ18Oatm and the δ18Osw records during the coldest periods, which indicate that there have been subtle changes in the factors which regulate δ18Oatm other than δ18Osw. Our use of δ18Oatm as a proxy for δ18Osw must therefore be considered tentative, especially during these periods. By correlating δ18Oatm with δ18Osw, we provide a common temporal framework for comparing phase relationships between atmospheric records (from ice cores) and oceanographic records constructed from deep‐sea cores. Our correlated age‐depth relation for the Vostok core should not be considered an absolute Vostok timescale. We consider it to be the preferred timescale for comparing Vostok climate records with marine climate records which have been placed on the SPECMAP timescale. We have examined the fidelity of this common temporal framework by comparing sea surface temperature (SST) records from sediment cores with an Antarctic temperature record from the Vostok ice core. We have demonstrated that when the southern ocean SST and Antarctic temperature records are compared on this common temporal framework, they show a high degree of similarity. We interpret this result as supporting our use of the common temporal framework for comparing other climate records from the Vostok ice core with any climate record that has been correlated into the SPECMAP chronology.
Long time scale evolution of high‐power radio wave ionospheric heating: 1. Beam propagation
Authors: Keskinen M. J. , Chaturvedi P. K. , Ossakow S. L.
Published: February 2008

The long time scale evolution, that is, for times long compared to an electron collision period of high‐power radio wave ionospheric heating, is studied. Preliminary studies are made to model high‐power radio wave propagation in an ionosphere containing a dynamically produced electron density cavity. We show that high‐power radio wave‐induced plasma density depletions in the F region ionosphere will convect and steepen in the direction perpendicular to the geomagnetic field due to ionosphere‐thermosphere coupling effects. We treat high‐power radio wave propagation including nonlinear self‐induced thermal effects in the presence of a steepened density depletion. We find that the beam is distorted, shifts in direction, and changes its peak intensity due to nonlinear self‐induced thermal effects. For weak beams, we find a decrease in beam intensity while for strong beams we observe an increase in beam intensity.
A model for wideband HF propagation channels
Authors: Vogler L. E. , Hoffmeyer J. A.
Published: February 2008

Expressions to model the sky wave propagation conditions that occur in a HF communication link are presented. The model is intended not only for narrowband applications but also for wideband systems such as those using spread spectrum techniques. A discussion of the background leading to the present development effort is followed by a description of the method used to derive the model transfer function. Analytic expressions for the impulse response and the scattering function are given, and the introduction of random processes into the model is described. Comparisons of scattering functions from the model and from measurements are shown for spread‐Fconditions ranging from mild to intense and for both an auroral path and a midlatitude path.
Crustal‐scale thrusting and origin of the Montreal River monocline‐A 35‐km‐thick cross section of the midcontinent rift in northern Michigan and Wisconsin
Authors: Cannon W. F. , Peterman Z. E. , Sims P. K.
Published: February 2008

A structurally simple, 35‐km‐thick, north facing stratigraphic succession of Late Archean to Middle Proterozoic rocks is exposed near the Montreal River, which forms the border between northern Wisconsin and Michigan. This structure, the Montreal River monocline, is composed of steeply dipping to vertical sedimentary rocks and flood basalts of the Keweenawan Supergroup (Middle Proterozoic) along the south limb of the Midcontinent rift, and disconformably underlying sedimentary rocks of the Marquette Range Supergroup (Early Proterozoic). These rocks lie on an Archean granite‐greenstone complex, about 10 km of which is included in the monocline. This remarkable thickness of rocks appears to be essentially structurally intact and lacks evidence of tectonic thickening or repetition.

Tilting to form the monocline resulted from southward thrusting on listric faults of crustal dimension. The faults responsible for the monocline are newly recognized components of a well‐known regional fault system that partly closed and inverted the Midcontinent rift system. Resetting of biotite ages on the upper plate of the faults indicates that faulting and uplift occurred at about 1060 +/−20 Ma and followed very shortly after extension that formed the Midcontinent rift system.
Thermochronologic constraints on the tectonic evolution of active metamorphic core complexes, D'entrecasteaux Islands, Papua New Guinea
Authors: Baldwin Suzanne L. , Lister Gordon S. , Hill E. June , Foster David A. , McDougall Ian
Published: February 2008

Metamorphic core complexes in the D'Entrecasteaux Islands, Papua New Guinea, formed as the result of active extension at the western end of the propagating Woodlark Basin spreading center. Domes of high‐grade metamorphic rocks (i.e., amphibolites, eclogites, and migmatites), intruded by large granodiorite bodies, comprise the lower plate of the D'Entrecasteaux metamorphic core complexes. The domes are transected by kilometer‐scale shear zones. A thermochronologic study of the D'Entrecasteaux Islands utilizing K/Ar,40Ar/39Ar, and fission track techniques has documented the unroofing history of these active metamorphic core complexes. Gneisses in the cores of the domes cooled rapidly (≥100°C/m.y.) as indicated by hornblende and biotite40Ar/39Ar apparent ages of ∼2.7 to 3.0 Ma and ∼1.6 to 1.7 Ma, respectively, and apatite fission track ages of ∼0.4 to 0.9 Ma.40Ar/39Ar apparent ages on white mica, biotite, and potassium feldspar and fission track ages on apatites from shear zone gneisses indicate extremely rapid cooling (in some cases >500°C/m.y.) and suggest shear zones were active from 4.0 to 3.5 Ma and 1.9 to 1.4 Ma. In general,40Ar/39Ar mineral ages for retrogressed core zone gneisses, shear zone gneisses, and granodiorites are 2.0 to 3.0 Ma (amphiboles), 1.5 to 1.7 Ma (muscovites), and 1.4 to 1.8 Ma (biotites) and 1.0 to 2.0 Ma (K‐feldspars). Apatite fission track ages from core zone gneisses, shear zone gneisses and granodiorites range from 0.4 to 1.0 Ma. Thermochronologic results indicate that emplacement of granodiorites closely coincided with retrogression of the metamorphic basement and movement on the outer shear zones bounding the gneiss domes. The granodiorite bodies associated with the D'Entrecasteaux Islands domes represent syn‐kinematically emplaced granitoids intruded into an area of active continental extension.
new constraints on Red Sea rifting from correlations of Arabian and Nubian Neoproterozoic outcrops
Authors: Sultan M. , Becker R. , Arvidson R. E. , Shore P. , Stern R. J. , El Alfy Z. , Attia R. I.
Published: February 2008

New constraints on the mechanics of Red Sea opening were obtained by correlating Neoproterozoic outcrops of the Arabian and Nubian Shields along two thirds of the Red Sea coastlines. Using a mosaic of 23 Landsat thematic mapper scenes (5×105 km²) together with field, geochemical, and geochronological data, we identified and mapped lithologic units, mobile belts, and terranes within the Arabian and Nubian Shields. Features best align if Arabia is rotated by 6.7° around a pole at latitude 34.6°N, longitude 18.1°E. Implications of our reconstruction include (1) the amount of continental crust underlying the Red Sea is small because the restored Red Sea coasts are typically juxtaposed, (2) only a single pole is needed, implying that the Arabian and Nubian Shields were rigid plates during Red Sea rifting, (3) coastlines reorient to align with preexisting structures, suggesting the rift propagated in part along pre‐existing zones of weakness, (4) large sinistral displacements of up to 350 km along the Red Sea are not supported, (5) the pole is inconsistent with the Pliocene‐Pleistocene motion along the Dead Sea transform (pole: 32.8°N, 22.6°E +/− 0.5° [Joffe and Garfunkel, 1987]), indicating that more than one phase of motion is required to account for the Red Sea opening. However, our pole is similar to that for the total motion along the Dead Sea transform (pole: 32.7°N, 19.8°E +/− 2° [Joffe and Garfunkel, 1987]), suggesting that the motion between Arabia and Nubia was parallel to the total motion along the Dead Sea transform.
Comparison of deep structure along three transects of the western North American Continental Margin
Authors: Fuis G. S. , Clowes R. M.
Published: February 2008

Similarities in geology and potential field data that have in the past been noted among the regions of southern Alaska, southern Vancouver Island, and central California are now seen to be accompanied by similarities in deep crustal structure. A number of tectonic elements have been identified in the deep structure along transects in these three regions, although not all elements are present along each transect. These elements are (A) an actively subducting oceanic plate and (B) an overriding continental plate that consists of (1) a Cenozoic accretionary prism, (2) a Mesozoic accretionary prism, (3) a backstop to the Mesozoic prism, (4) a tectonically underplated body of oceanic rocks, and (5) a crustal root. The Mesozoic prism is in some cases an underthrust body (type 2a) but in other cases forms the principal component of a landward verging tectonic wedge (type 2b). The technically underplated body of oceanic rocks extends landward from the fault contact between the Cenozoic and Mesozoic prisms to a point beneath the backstop. The crustal root lies beneath the backstop and landward of the underplated body. All of these elements are interpreted to be present along the Alaskan and Vancouver Island transects. In Alaska the underplated body is interpreted to be fragments of the Kula plate; the same may be true at Vancouver Island. These two transects appear to differ in that, in Alaska, the Mesozoic prism, in one interpretation, is the principal component of a tectonic wedge (type 2b), whereas at Vancouver Island, it is an underthrust body (type 2a). Along the central California transect, active subduction is no longer taking place, and the San Andreas fault has removed the Cenozoic prism from this region of the North American plate. On the North American plate (i.e., east of the San Andreas fault), the Mesozoic prism, interpreted as the main component of a tectonic wedge (type 2b), and the backstop to the Mesozoic prism are present. There is, however, no clear evidence of tectonically underplated oceanic rocks, and the crust is thin (no root). In both Alaska and Vancouver Island, the Mesozoic prisms above the underplated bodies experienced low‐pressure/high‐temperature metamorphism at about the time of tectonic underplating; no such metamorphism is currently exposed in California. The metamorphism may have been caused by the underplating of young, hot oceanic crust, or, alternatively, by subduction of an oceanic ridge. The presence of a tectonic wedge (type 2b) in Alaska and California and the absence of such a wedge at Vancouver Island could arise either from the fact that in the former two locations the Mesozoic prisms were more voluminous, owing to either more rapid trench sedimentation or more rapid convergence, or to the possibility that at the latter location the Mesozoic prism was juxtaposed with the backstop primarily by strike‐slip faulting.
Seismic evidence for blind thrusting of the northwestern flank of the Venezuelan Andes
Authors: De Toni Bruno , Kellogg James
Published: February 2008

Surface geology and seismic and well data from the northwestern flank of the Venezuelan Andes indicate overthrusting of Andean basement rocks toward the adjacent Maracaibo Basin along a blind thrust fault. The frontal monocline is interpreted as the forelimb of a northwestward verging fault‐related fold deformed over a crustal‐scale ramp. The Andean block has been thrust 20 km to the northwest and uplifted 10 km on a ramp that dips about 20°–30° southeastward. The thrust fault ramps up through crystalline basement rocks to a decollement horizon within the shaly units of the Cretaceous Colon‐Mito Juan formations. Backthrusts in the monocline produce a wedge geometry and reduce the amount of blind slip required on the decollement northwest of the Andes. The rigid Andean uplift was caused by northwest‐southeast compressive tectonic forces related to the convergence of the Caribbean plate, the Panama volcanic arc, and northwestern South America. The thick (up to 6 km) molasse deposits accumulated in the foredeep basin indicate that the Venezuelan Andes started to rise as early as the early Miocene. However, a late Miocene intramolasse unconformity marks the beginning of the formation of the monocline and the greatest uplift. The crustal‐scale fault‐related fold model may explain structural features seen in other areas of basement‐involved foreland deformation.
Global litter production, pools, and turnover times: Estimates from measurement data and regression models
Authors: Matthews Elaine
Published: February 2008

Systematic and compatible databases to quantify composition, distribution, and turnover times of carbon in global litter were developed and evaluated. The study employs an integrated approach, estimating related litter pools and fluxes using a variety of data‐based and model‐based techniques. The analysis includes direct estimates and indirect, or proxy, estimates of litter production and pools; steady‐state turnover times are estimated from the two. Proxies for litter production include net primary productivity and root respiration‐soil respiration relationships. In addition to implementing a suite of regression models, >1100 published measurements of litter components, along with site characteristics, were integrated into a baseline data set and used to estimate litter production and pools. Historically, global estimates of litter production have ranged from 75 to 135 Pg dm/yr; several estimates from this study suggest values in the middle of this range, from 90 to 100 Pg dm/yr. The estimate of aboveground litter production from the compiled measurements, 39 Pg dm/yr, includes mainly forest, woodland, and wooded grassland; other grassland, shrubland, and xeromorphic communities that occupy ∼25% of the ice‐free land surface are unrepresented in the present compilation. Aboveground litter production may be 5–10 Pg dm/yr higher with the inclusion of these ecosystems, and the total, including belowground production, may approach 90–110 Pg dm/year. Two novel production estimates derived from soil‐ and root‐respiration relationships are 93 Pg and 100 Pg dm/yr. These estimates have the major advantage of accounting for both aboveground and belowground litter; the latter is rarely included and can account for a substantial fraction of total production. Production of coarse woody detritus may add ∼12 Pg dm/yr to the fine litter total. The global litter pool has previously been estimated at ∼100 to 400 Pg dm. The fine litter pool estimated here from the measurement compilation is 136 Pg dm. Although this partial estimate includes ecosystems covering just under half the ice‐free land surface, it encompasses forests and woodlands which have the largest pools. Inclusion of the remaining ecosystems may add ∼25 Pg, raising the total to ∼160 Pg dm. An additional ∼150 Pg dm is estimated for the coarse woody detrital pool. Global mean steady state turnover times of litter estimated from the pool and production data range from 1.4 to 3.4 years; mean turnover time from the partial forest/woodland measurement compilation is ∼5 years, and turnover time for coarse woody detritus is ∼13 years. By encompassing spatial distribution, composition, and magnitude, along with numerous field measurements, this integrated approach has begun to yield compositional and ecosystem constraints on modeled global and regional litter fields and NPP allocation schemes in ecosystem models.
Factors regulating ozone over the United States and its export to the global atmosphere
Authors: Jacob Daniel J. , Logan Jennifer A. , Gardner Geraldine M. , Yevich Rose M. , Spivakovsky Clarisa M. , Wofsy Steven C. , Sillman Sanford , Prather Michael J.
Published: February 2008

The factors regulating summertime O3 over the United States and its export to the global atmosphere are examined with a 3‐month simulation using a continental scale, three‐dimensional photochemical model. It is found that reducing NOx emissions by 50% from 1985 levels would decrease rural O3 concentrations over the eastern United States by about 15% under almost all meteorological conditions, while reducing anthropogenic hydrocarbon emissions by 50% would have less than a 4% effect except in the largest urban plumes. The strongly NOx‐limited conditions in the model reflect the dominance of rural areas as sources of O3 on the regional scale. The correlation between O3 concentrations and temperature observed at eastern U.S. sites is attributed in part to the association of high temperatures with regional stagnation, and in part to an actual dependence of O3 production on temperature driven primarily by conversion of NOx to peroxyacetylnitrate (PAN). The net number of O3 molecules produced per molecule of NOx consumed (net O3 production efficiency, accounting for both chemical production and chemical loss of O3) has a mean value of 6.3 in the U.S. boundary layer; it is 3 times higher in the western United States than in the east because of lower NOx concentrations in the west. Approximately 70% of the net chemical production of O3 in the U.S. boundary layer is exported (the rest is deposited). Only 6% of the NOx emitted in the United States is exported out of the U.S. boundary layer as NOx or PAN, but this export contributes disproportionately to total U.S. influence on global tropospheric O3 because of the high O3 production efficiency per unit NOx in the remote troposphere. It is estimated that export of U.S. pollution supplies 8 Gmol O3 d−1 to the global troposphere in summer, including 4 Gmol d−1 from direct export of O3 out of the U.S. boundary layer and 4 Gmol d−1 from production of O3 downwind of the United States due to exported NOx. This U.S. pollution source can be compared to estimates of 18–28 Gmol d−1 for the cross‐tropopause transport of O3 over the entire northern hemisphere in summer.
Rift processes at the Valles Marineris, Mars: Constraints from gravity on necking and rate‐dependent strength evolution
Authors: Anderson Scott , Grimm Robert E.
Published: February 2008

Recent spherical harmonic representations of the gravity field of Mars have sufficient resolution to examine the regional crustal and lithospheric structure of the Valles Marineris and are used as constraints for rift modeling. While gravity signatures of individual troughs are not evident, a broad 190–260 mgal low indicates that the central chasmata as a whole are compensated at a depth of 30–80 km, representing the thickness of crust surrounding the troughs. Furthermore, at the time large‐scale relief was established, the effective thickness of the elastic lithosphere was <30 km, corresponding to heat flow >20 m W m−2. The calculated range of crustal thickness and heat flow can be used to test two semianalytic models of rift formation. In the first model, the distinction between single (“narrow rift”) and multiple (“wide rift”) troughs is determined by the wavelength of necking instabilities. In the second model, narrow‐versus‐wide morphology is controlled by the evolution of lithospheric strength during rifting. The large‐scale, parallel, multiple troughs of the central Valles Marineris are morphologically similar to terrestrial wide rifts, but a lack of distinct faulting in some of the chasmata could imply that the faulted troughs may have formed as isolated narrow rifts. Our results are only marginally consistent with necking leading to a wide rift; allowable combinations of crustal thickness and heat flow lead to decoupling within the lithosphere resulting in a second principal necking wavelength that is smaller than the main trough spacing, for which evidence is equivocal. At high heat flow (>40 m W m−2), however, necking of the strong upper crust alone can yield a shorter wavelength characteristic of a single trough, allowing narrow‐rift origins of faulted chasmata. In contrast, the inferred range of crustal thickness and heat flow poorly match the narrow‐rift regime of the strength‐evolution model but are in good agreement with its predictions for wide rifting. Furthermore, the distinction between wide rift and core complex in this model places an upper bound on heat flow of 70 m W m−2.
Mediterranean nutrient balance and episodes of anoxia
Authors: Sarmiento Jorge L. , Herbert Timothy , Toggweiler J. R.
Published: February 2008

We examine the causes of anoxia in regions such as the Eastern Mediterranean, which have exchange over sills with adjacent basins. Box models show that the concentration of the limiting nutrient is the major determinant of deep oxygen levels. The most effective way of increasing nutrient concentrations to the point where anoxia occurs is to change the flow pattern across the sills ventilating the basins. With a sill exchange pattern such as that in the present Strait of Sicily, it is difficult to obtain anoxia in the Eastern Mediterranean without also driving the Western Mediterranean to low oxygen and high nutrient levels. Episodes of anoxia in the Eastern Mediterranean are associated with a freshening of surface waters. A reversal in flow directions, presumably resulting from the observed freshening, will inevitably lead to anoxia associated with increased sediment burial rates of the limiting nutrient and will leave the Western Mediterranean largely unaffected, in keeping with the observational evidence.
Semiannual losses of nitrogen as NO and N2O from unburned and burned chaparral
Authors: Anderson Iris Cofman , Poth Mark A.
Published: February 2008

Nitric oxide (NO), nitrous oxide (N2O), and carbon dioxide (CO2) measurements were made at unburned and burned sites within a semiarid chaparral ecosystem located in southern California. Some sites were burned during the dry season (July); others at the start of the wet season (December). This report primarily describes measurements of gas fluxes and soil parameters at unburned sites and sites burned in December. Burning greatly increased the concentrations of ammonium (NH4+), nitrate (NO3−) and potentially mineralizable nitrogen in soil. Nitrate concentrations at sites burned in December were much higher than those at sites burned in July, indicating active nitrification and decreased water stress. Irrigation usually produced immediate but short‐lived increases in NO flux; however, these increases were more moderate than those observed in July. Diurnal studies performed at irrigated and nonirrigated burned sites both in July and December indicated a high correlation of NO flux with temperature (r2> 0.81) at most sites, provided that the soil moisture was greater than 30%. Results of diurnal studies were used to normalize daily fluxes and to calculate semiannual losses of nitrogen from both burned and unburned sites. Over a six‐month period, 0.3 g N m−2was lost as NO from burned chaparral, representing 75% of the exchangeable nitrogen lost over the same period and 3.9% of the potentially mineralizable nitrogen present in the soil. From unburned soil, 0.1 g N m−2was lost as NO, representing 33% of the exchangeable nitrogen and 3.3% of the potentially mineralizable nitrogen in soil. These studies indicate that over a six‐month period following a burn, much of the NH4+produced by the burning of aboveground vegetation is lost to the atmosphere as NO. These emissions may be expected to persist for periods in excess of six months because of the increased mineralizable nitrogen available in soil as a result of the burn. Losses of nitrogen both during and following a burn may impact soil fertility, contribute to both air and water pollution, and yield significant inputs to the global atmospheric budgets of both NO and N2O.
Effect of model structure on the response of terrestrial biosphere models to CO2 and temperature increases
Authors: Harvey L. D. Danny
Published: February 2008

The sensitivity of a number of different globally aggregated models of the terrestrial biosphere to changes of atmospheric CO2 and temperature is investigated. Net primary production (NPP) or net photosynthesis (NP) is modeled as a logistic function, with enhancement due to increased CO2 using the β factor widely used in global carbon cycle models. NPP also increases with temperature using a Q10 of 1.4, while respiration and coefficients for translocation and for detritus to soil, and soil to soil, carbon transfers increase with a Q10 of 2.0. The pathway of carbon flow to the slowly overturning soil reservoir has a significant effect on equilibrium sensitivity of total carbon mass to temperature increases if the transfer coefficient from the rapidly to slowly overturning soil reservoir is fixed; maximum sensitivity occurs if all the carbon entering the slowly overturning reservoir first passes through the rapidly overturning reservoir. If the transfer coefficient increases in parallel with the increase of soil respiration coefficient, the carbon pathway has no effect on equilibrium sensitivity, although the transient response depends strongly on the subdivision of the soil reservoir. Allowing the detritus to soil transfer coefficient to increase in parallel with the coefficient for detrital respiration reduces the equilibrium sensitivity of total carbon mass to temperature increases by about half. The variation in model response to CO2 and temperature increases using different model structures is generally comparable to the variation resulting from uncertainty in feedback parameters.
The cause of the glacial to interglacial atmospheric CO2 change: A Polar Alkalinity Hypothesis
Authors: Broecker Wallace S. , Peng Tsung‐Hung
Published: February 2008

In an attempt to create a scenario for the cause of the glacial to interglacial CO2 change recorded in air trapped in polar ice, we call on an increase in the alkalinity of polar surface waters. In this way we circumvent a major deficiency of the polar nutrient scenarios of Sarmiento and Toggweiler (1984), Siegenthaler and Wenk (1984) and Knox and McElroy (1984). Namely, our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by Boyle (1988a, b) that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to Holocene time. The rise in alkalinity required by our model is a natural consequence of the demise, during glacial time, of North Atlantic Deep Water as a major force in ocean circulation and of the nutrient maximum deepening of Boyle (1988b). Rather than being original, our hypothesis builds on the concept basic to the polar nutrient hypotheses, namely that the CO2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean. It also requires the alkalinity increase in surface waters produced by Boyle's nutrient deepening.
Continental scale models of water balance and fluvial transport: An application to South America
Authors: Vörösmarty Charles J. , Moore Berrien , Grace Annette L. , Gildea M. Patricia , Melillo Jerry M. , Peterson Bruce J. , Rastetter Edward B. , Steudler Paul A.
Published: February 2008

A coupled water balance and water transport model (WBM / WTM) was constructed as part of a larger study of global biogeochemistry. The WBM / WTM provides critical hydrologic information to models of terrestrial primary production, organic matter decay, riverine nutrient flux and trace gas exchanges with the troposphere. Specifically, it creates high‐resolution data sets for monthly soil moisture, evapotranspiration, runoff, river discharge and floodplain inundation. As a first step toward eventual global coverage, the WBM / WTM was applied to South America, represented by more than 5700 1/2° (latitude / longitude) grid cells. The WBM transforms spatially complex data on long‐term climate, vegetation, soils and topography into predictions of soil moisture (SM), evapotranspiration (ET) and runoff (RO). For South America, field capacity in soils ranged from 27 to 582 mm of water, and computed values for mean annual SM, ET and RO were 284 mm, 1059 mm/yr and 619 mm/yr, respectively. There were large differences regionally and over the year. The transport model uses WBM‐derived runoff, information on fluvial topology, linear transfer through river channels and a simple representation of floodplain inundation to generate monthly discharge estimates for any cell within a simulated catchment. The WTM successfully determined the timing and magnitude of discharge at selected locations within the Amazon / Tocantins basin. It also demonstrated the importance of floodplain inundation in defining flow regime on the mainstem Amazon. Estimated mean annual discharge was 207,000 m3/s for the Amazon River and 17,000 m3/s for the Tocantins. In these basins, 45% of the incident precipitation emerges as river flow; 55% is lost to ET. The model described in this paper will be expanded to include the dynamics of carbon, major nutrients and sediments. It will serve as a semimechanistic tool to quantify the transport of materials from the landscape to the world's oceans. Such a capability becomes increasingly important as we seek to understand the impacts of climate and land use change on major river systems of the globe.
Nitrous oxide flux from dry tropical forests
Authors: Vitousek Peter , Matson Pamela , Volkmann Carol , Maass J. Manuel , Garcia Georgina
Published: February 2008

Fluxes of nitrous oxide were determined in several sites in drought‐deciduous tropical forest, an extensive but little‐studied biome. N2O‐N fluxes from eight sites within intact Mexican forest averaged 0.91 ng cm−2 h−1 during the wet season; they were virtually absent in the dry season. Two subsistence maize fields yielded increased soil N2O‐N fluxes, while five pastures were more variable. Watering during the dry season caused a substantial but short‐lived pulse of N2O. Similar fluxes were observed in less‐intensive sampling of dry‐forest sites in Hawaii and Costa Rica. Overall, N2O fluxes from soils of dry tropical forests appear to be similar to those from moist tropical forests during the wet season and very low during the dry season.
Aerosol optical depths over the Atlantic derived from shipboard sunphotometer observations during the 1988 Global Change Expedition
Authors: Reddy Patrick J. , Kreiner Fred W. , DeLuisi John J. , Kim Young
Published: February 2008

Aerosol optical depths and values for the Angstrom exponent, alpha, were retrieved from carefully calibrated sunphotometer measurements which were made during the Global Change Expedition (GCE) of the NOAA ship Mt. Mitchell in July, August, and September 1988. Sunphotometer observations were acquired at wavelengths of 380, 500, 675, and 778 nm. Optical depths and alphas have been segregated into five categories associated with probable air mass source regions determined through back trajectories at the 1000‐, 850‐, 700‐, and 500‐mbar levels. The results for the three most distinct air mass types are summarized here. The mean 500‐ nm aerosol optical depth for North American air is 0.56 (±0.32), the mean for Atlantic air is 0.16 (±0.02), and the mean for Saharan air is 0.39 (±0.12). Alpha for mean GCE aerosol optical depth data for predominantly North American air masses is 1.15 (± 0.11), alpha for Atlantic air is 1.00 (±0.40), and for Saharan air, alpha is 0.37 (±0.18). There is a significant difference between alpha for Saharan air and alpha for North American or Atlantic air. There is also a significant difference between the mean 500‐nm optical depth for North American aerosols and Atlantic aerosols.
Kinematics of sea breeze storms
Authors: Lhermitte R.
Published: February 2008

The paper is concerned with dual Doppler radar observations of the motion fields inside convective storms developing under sea breeze conditions in the area of Miami, Florida. At low altitudes, the storm kinematics are dominated by the eastern sea breeze inflow. At altitudes above 3 to 4 kms, the convective storm's circulation becomes increasingly important. At yet higher altitudes, there is a very strong interaction between the storm and the prevailing north westerly wind. Very strong velocity gradients are found in the upper levels of the storms which suggest a mechanism for high altitude formation of vorticity.
Temperatures Inside Mars: Is the core liquid or solid?
Authors: Young Richard E. , Schubert Gerald
Published: February 2008

If internal heating in the mantle of Mars is similar to that in the Earth, solid‐state convection is the mechanism preventing large scale melting of the Martian mantle. Convection is efficient enough in transporting heat to preclude the existence of a liquid core and hence a dynamo driven intrinsic magnetic field, if the viscosity of mantle material is lower than 1022‐1023 cm²/sec at temperatures in excess of about 1500°C. The Martian lithosphere is probably several hundred kilometers thick, intermediate in size between that of the Earth and Moon.
Clear air convection: A close look at its evolution and structure
Authors: Richter Juergen H. , Jensen Douglas R. , Noonkester V. Ray , Konrad Thomas G. , Arnold Abraham , Rowland John R.
Published: February 2008

A unique experiment using advanced remote and direct sensing techniques was designed to investigate the detailed evolution and structure of clear air convection. The measurements were performed at Wallops Island, Va. and involved a high‐power, narrow‐beam pulse radar, a frequency modulated, continuous wave (FM‐CW) radar, an acoustic echo sounder, and instrumented aircraft. The various probing methods when used together complement each other and give a compatible and comprehensive description of the spatial and temporal evolution of clear air convection.
Circulation on the New England Continental Shelf: Response to strong winter storms
Authors: Beardsley Robert C. , Butman Bradford
Published: February 2008

Current and sea level observations made on the New England continental shelf during several winter storms show that these short intense wind events dominate the circulation over the shelf, and account for most of the observed net flow. The observations show that large westward mass transports along the shelf were produced by strong easterly winds, while westerly winds produced little along‐shore flow. Significant cross‐shelf and along‐shelf surface pressure gradients occur during the storms. A simple conceptual model is proposed to explain the observations.
Measurements of H2O2+ in the D‐region and implications for mesospheric H2O2
Authors: Arnold F. , Krankowsky D.
Published: February 2008

The D‐region ion 34+ probably can be identified as H2O2+ in contrast to its previous interpretation as S+. Number densities of H2O2+ and of the cluster ions H2O2+ · H2O, and H2O2+ · CO2 measured by three rocket borne mass spectrometers are presented. The chemistry of H2O2+ and its cluster is discussed particularly with respect to its implications for neutral H2O2.
Experimental determination of mean Doppler‐reflectivity relationship with a vertically pointing Doppler radar
Authors: Pasqualucci F.
Published: February 2008

A pseudo noise coded continuous wave Doppler radar, operated at a frequency of 35 GHz, was used to measure drop‐size distributions and the mean Doppler for vertical velocities
. The data have been used to determine a relationship between,
and the radar reflectivity factor, Z. 95% of the
experimental data fall within ±0.3 m sec−1 of the
function
= 2.67 Z0.095 (
m sec−1).

The spread of the data may be attributed to a small contribution of unknown vertical air velocity in the low altitude (15 m to 25 m) scattering region.
Semiannual and solar‐cycle variation of sector structure
Authors: Sawyer C.
Published: February 2008

The complexity of the interplanetary magnetic‐field polarity pattern shows a semiannual variation, with more sectors per solar rotation in May and June, and again in November and December, times when the earth is close to the sun's equatorial plane. Complexity varies also through the solar activity cycle, in a manner consistent with contribution to the interplanetary field from both the polar field and long‐lived, large‐scale fields related to active regions.
Radioactivity of Nevada Hot‐Spring Systems
Authors: Wollenberg H. A.
Published: February 2008

Field gamma radiometry and laboratory gamma‐ray spectrometry of waters and spring deposits were accomplished for some hot‐spring systems in northern Nevada. Gamma‐ray exposure rates measured on‐site range from 2 to 500 µR/hr, and depend mainly on the amounts of the natural radioelements in the spring deposits. High radioactivities, primarily from 226Ra, are associated with hot‐spring systems dominated by CaCO3, while silica‐dominated systems are relatively low in radioactivity. Gamma spectrometry disclosed the enrichment of 226Ra with respect to its parent U in CaCO3 dominated systems. 226Ra preferentially associates with Ca; therefore, where tufa and siliceous sinter are present in a deposit, the calcareous material is highest in radioactivity. Spring deposits at fast‐flowing CaCO3 dominated systems are generally less radioactive than calcareous deposits at slower flowing springs.
The influence of air‐water interfacial conditions on turbulent transfer of latent and sensible heat
Authors: McIntosh D. A. , Street R. L. , Hsu E. Y.
Published: February 2008

Wind, temperature and humidity profiles obtained in a wind‐water‐wave channel with four variations of the interfacial conditions were analyzed in order to assess the influence that the free surface conditions have on the fluxes under near neutral stability conditions. The dimensionless humidity gradient remained essentially constant at 1.2 for all surface variations except for the case of suppressed waves where its value was 0.86. On the other hand, the dimensionless temperature gradient demonstrates a definite response to changes in surface conditions and ranges from 0.73 for the suppressed wave case to as high as 1.41 for the larger wind speed (11 m/s), wind‐wave cases. Comparing the results from the suppressed surface and wind‐wave cases for U∞ = 10 m/s it was observed that the total energy (sensible plus latent heat) transfer remained constant. However, sensible heat flux increased with the suppression of the wind waves whereas latent heat flux decreased.
Scanning electron microscopy of a pink inclusion from the Allende Meteorite
Authors: Grossman Lawrence , Fruland Ruth M. , McKay David S.
Published: February 2008

A scanning electron microscope study of a fine‐grained, pink Ca‐rich inclusion from the Allende meteorite has revealed strong evidence for direct condensation of its constituent minerals from a vapor. This observation extends to the alkali‐bearing phases in addition to the Ca‐, Al‐ silicates and suggests that the feldspathoids as well as the refractory silicates are solar nebular condensates.
The global solar wind and predictions for Pioneers 10 and 11
Authors: Suess S. T. , Nerney S. F.
Published: February 2008

The dependence on latitude of the azimuthal component of the interplanetary magnetic field generates a meridional pressure gradient which, in turn, generates a meridional flow. This flow has observable consequences in the equatorial plane, although the meridional velocity itself may be zero in this plane. Analytic estimates of these observables—the mass flux, azimuthal and radial magnetic flux, density, and spiral angle—are made in the range of 1 to 12 AU.
Is there an electrostatic field tangential to the dayside magnetopause and neutral line?
Authors: Heikkila W. J.
Published: February 2008

The question of possible energy dissipation that might be associated with the dayside magnetopause current requires consideration of the tangential component of the electric field. If the total current of 9 × 106 amperes flowed through the average magnetospheric dawn‐dusk potential difference of 6 × 104 volts the power dissipation would be 5 × 1011 watts. We might expect this energy to be carried away by energized particles, perhaps as increased thermal or flow energy at or near the magnetopause boundary layer or mantle. Satellite observations are available, but they do not provide evidence of such energization. This failure leads us to conclude that the magnetopause current does not flow through the magnetospheric potential difference, and that the magnetopause is approximately an equipotential surface. Because of the necessary continuity of the tangential component of the electric field, this conclusion implies that there is no steady state electric field along the neutral or X‐line that must be located near the dayside magnetopause in an open magnetospheric model (which is clearly supported by other evidence). Such an electric field is an essential part of the theory of merging or reconnection of magnetic field lines, and it is therefore concluded that the merging model for the electric field is not correct. This conclusion could be avoided if some evidence for the implied energy dissipation were found.