bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the changing lunar orbit on the astronomical frequencies of pre‐Quaternary insolation patterns
Authors: Berger A. , Loutre M. F. , Dehant V.
Published: February 2008

The sensitivity of the frequencies of the Earth's orbital elements, involved in the astronomical theory of paleoclimates (obliquity and climatic precession), to the Earth‐Moon distance and consequently to the length of the day and to the dynamical ellipticity of the Earth is investigated for the last billions of years. But the new frequencies have been computed for the last 440 million years only, a time interval over which data and a model of the Earth were available. Moreover, we consider only the impact of the changing precessional parameter, assuming that the fundamental frequencies of the planetary motion are steady at the geological time scale. Under such hypotheses, the shortening of the Earth‐Moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for obliquity and precession, a shortening that is larger for longer periods.
Deep circulation changes in the South Atlantic Ocean: Response to initiation of northern hemisphere glaciation
Authors: Turnau Rene , Ledbetter Michael T.
Published: February 2008

Particle size statistics (coarsest 1 percentile and mean) of the nonbiogenic silt fraction of samples from Deep Sea Drilling Project sites 514, 516A, 517, 518, and 548 were used to infer relative changes in paleospeed of deep water masses in the Atlantic Ocean during the late Pliocene initiation of northern hemisphere glaciation. Grain size statistics were integrated with previous studies of geochemical and faunal assemblages to examine how climatic forcing regulates deepwater mass paleospeed and stratification. On the basis of between‐site comparison of particle size, the late Pliocene was divided into four intervals of deepwater activity: 3.2 to 2.9 Ma, 2.9 to 2.6 Ma, 2.6 to 2.5 Ma, and 2.5 to 2.3 Ma, with pulses of increased paleospeed occurring at 3.15–3.10, 2.85, 2.7, 2.6, and 2.4 Ma. Except for a brief increase in paleospeeds at 3.1 Ma, the first time interval is characterized by low inferred Antarctic Bottom Water (AABW) paleospeed corresponding to depleted δ13C and enriched δ18O values in all but the shallowest core. Enriched δ13C and depleted δ18O values in the shallowest core correspond to coarse grain sizes and are inferred to represent a deep and intense Antarctic Intermediate Water (AAIW). The expansion of AABW and AAIW precludes a significant North Atlantic Deep Water (NADW) incursion to 30°S at this time. The interval from 2.9 to 2.6 Ma is dominated by climatic cooling and an influx of deep waters originating in the North Atlantic. The introduction of significant volumes of Mediterranean Outflow Water (MOW), as demonstrated by increased inferred paleospeed at site 548, and an expanding glaciation beginning at 2.9 Ma, resulted in increased paleospeed and an expansion of NADW in the South Atlantic. A pulse of increased inferred paleospeed at 2.7 Ma resulted in the temporary deepening of NADW to the depth of site 518 (presently 3944 m). From 2.9 to 2.6 Ma AABW velocity remained low, but AAIW deepened and intensified. The 2.6‐to 2.5‐Ma interval represents the retreat of deep water, originating in the North Atlantic, from the depth of site 518 to the depth of site 517 (presently 2963 m). Increased inferred paleospeed at site 518 corresponds with depleted δ13C values and a northward shift in the polar front, thus suggesting the reintroduction of Circumpolar Water to the depth of site 518 and the establishment of a deepwater stratification similar to today's. A continuing trend toward a modern stratification continued into the latest time interval (2.5–2.3 Ma) as inferred deepwater paleospeed at all depths increased in response to the formation of extensive northern hemisphere ice sheets.
Paleoceanographic modeling of temperature‐salinity profiles from stable isotopic data
Authors: Railsback L. Bruce , Anderson Thomas F. , Ackerly Spafford C. , Cisne John L.
Published: February 2008

Temperature‐salinity (T‐S) profiles in ancient seawater can be estimated from oxygen isotopic compositions of well‐preserved calcitic fossils sampled from known paleodepth gradients. The proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition (given estimates of average salinity, isotopic composition, and net global hydrologic fractionation for ancient oceans). Increasing density with depth constrains those combinations to narrow ranges. This graphic method superposes curves for density and isotopic composition in T‐S space, to reveal possible ancient T‐S profiles. Application of this method to oxygen isotope data from Ordovician brachiopods deposited on the eastern continental slope of North America demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer, more saline deep waters.
The Oligocene marine microfossil record: Age assessments using strontium isotopes
Authors: Hess Jennifer , Stott Lowell D. , Bender Michael L. , Kennett James P. , Schilling Jean‐Guy
Published: February 2008

A strontium isotope record for the latest Eocene to earliest Miocene has been produced for two well‐preserved, deep‐sea sequences from the Atlantic, (Deep Sea Drilling Project sites 516F and 563) which have magnetostratigraphic age control and four sequences from the Pacific (sites 77B, 292, and 593) and Atlantic (site 529) which lack magnetostratigraphy. The composite87Sr/86Sr age record of sites 516F and 563 forms a comprehensive, composite standard for the Oligocene against which other sequences can be correlated. Unlike previously published87Sr/86Sr Oligocene sea water curves which have suggested that the sea water isotopic composition changed monotonically during the latest Paleogene, we note a distinct change in slope between the early Oligocene (36 to 27 Ma) and the late Oligocene to earliest Miocene (27 to ∼20 Ma). The slope of the early Oligocene segment is less steep than that of the late Oligocene to earliest Miocene. We have fit two linear regression curves to the Oligocene to early Miocene seawater δ87Sr data of sites 516F and 563, which we use to establish Sr isotope‐age relationships for the Oligocene. The δ87Sr age equations were used to evaluate the synchroneity of specific planktonic and calcareous nannofossil datum levels used to correlate Oligocene sections. Although some datum levels appear to be synchronous between the Atlantic and Pacific, our results show that others are diachronous along longitudinal gradients. This is most evident in several last appearance datums that occurred earlier in the western equatorial Pacific than in the eastern equatorial Pacific. This diachroneity extends into the Atlantic where last occurrences were later than in the eastern equatorial Pacific.
Late Neogene paleoceanography and paleoclimatology of the Gulf of Aden region based on calcareous nannofossils
Authors: Rahman A. , Roth P. H.
Published: February 2008

Quantitative study of climatically sensitive nannofossils in the sediments of the Gulf of Aden has provided a climatic and oceanographic scenario for the northwestern Indian Ocean during the late Neogene. The surface water temperature was relatively cold during the latest middle Miocene to late Miocene (10.7 to 6.32 Ma) with a probable warm interval in the early late Miocene (9.82 to 8.49 Ma). This cooling is attributed to increased upwelling in the northwestern Indian Ocean. The surface water was relatively warm from the latest late Miocene to the middle of the late Pliocene (6.32 to 2.59 Ma). The most intense cooling took place during the late Pliocene to early Pleistocene (2.59 to 1.69 Ma). Intense upwelling during this interval coincides with worldwide climatic deterioration. A probable short warm interval (1.69 to 1.59 Ma) followed this cold interval. In the Pleistocene the surface water was cold from 1.59 to 1.00 Ma and from 0.61 to 0.24 Ma and warm from 1.00 to 0.61 Ma and after 0.24 Ma.
Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity: Eolian records from the lithogenic component of deep‐sea sediments
Authors: Clemens Steven C. , Prell Warren L.
Published: February 2008

The modern Indian Ocean summer monsoon is driven by differential heating between the Asian continent and the Indian Ocean to the south. This differential heating produces a strong pressure gradient which drives southwest monsoon winds during June, July, and August. Satellite and meteorological observations, aerosol measurements, sediment trap studies, and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest Arabian Sea. Analyses of lithogenic grain size and mass accumulation rate (MAR) records from the Owen Ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr. Visual inspection shows that the MAR record is positively correlated with global ice volume as indicated by the marine δ18O record. In contrast, the grain‐size record varies at a much higher frequency, showing little correlation to either the MAR or the δ18O records. Spectral analyses confirm these relationships, indicating that the lithogenic grain‐size and MAR records are coherent only over the precession band whereby the grain size leads the MAR by 124° (∼8 kyr). We conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and MAR with independent eolian records. We use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic MAR as a paleoclimatic indicator of source‐area aridity. These interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength (Globigerina bulloides upwelling record) and aridity (a loess record from central China). Such comparisons indicate high coherence and zero phase relationships. Our work supports the findings of previous studies which have documented the link between monsoon strength and the Earth's axial precession cycles. Both the lithogenic MAR and the grain‐size records have high coherency with precessional insolation. Maximum lithogenic MAR (source‐area aridity) is in phase with δ18O (global ice volume) and leads maximum precessional insolation by 88° (∼6 kyr). We attribute this lead to the influence of glacial conditions on the aridity, and therefore the deflation potential, of the source areas. Maximum lithogenic grain size (summer monsoon wind strength) lags maximum precession by 148° (∼9 kyr). We attribute this lag both to the influence of global and/or local ice volume and to the availability of latent heat from the southern hemisphere Indian Ocean, the two of which combine to determine the strength of the Indian Ocean monsoon.
Variability in upwelling fields in the northwestern Indian Ocean 1. Model experiments for the past 18,000 years
Authors: Luther Mark E. , O'Brien James J. , Prell Warren L.
Published: February 2008

A nonlinear reduced gravity ocean model is used to assess the effects of changes in the monsoon winds during glacial and interglacial conditions on the seasonal circulation in the northwestern Indian Ocean. Winds from the National Center for Atmospheric Research Community Climate Model simulations for 18 kyr B.P. (the most recent glacial maximum and a period of weaker monsoon winds), 9 kyr B.P. (near the beginning of the present interglacial and a period of stronger monsoon winds), and present‐day (0 kyr B.P.) conditions are used to drive the model to a steady seasonal cycle. Strength of upwelling fields are inferred in each case by integrating upward displacements of the model pycnocline over the primary upwelling season of mid‐April to mid‐August. In both the 0 kyr B.P. and the 9 kyr B.P. cases, a broad band of upwelling and decreased model upper layer thickness extends along the coast of the Arabian Peninsula out 350–500 km offshore during the southwest monsoon. This upwelling is driven by the strongly positive wind stress curl beneath the cyclonic side of the atmospheric Findlater Jet, located to the north and west of the jet axis. Farther offshore, in the anticyclonic region to the south and east of the jet axis, the negative wind stress curl drives downwelling and increased upper layer thickness. In the 9 kyr B.P. case, the atmospheric jet is much stronger and narrower than in the 0 kyr B.P. case, with stronger values of both positive and negative curl to the northwest and southeast, respectively, of the jet axis. This drives much stronger upwelling to the northwest of the jet axis and downwelling to the southeast. In the 18 kyr B.P. case, the Findlater Jet is very weak, and upwelling patterns are uniformly weak across the basin. The spatial distribution and temporal variation of the upwelling fauna in the sediment record is consistent with the model upwelling fields in all three cases. The ocean model thus provides the link between the climate model and the sedimentation data, verifying the hypothesis that variations in upwelling driven by variations in the strength of the monsoon jet are responsible for the observed variations in the sediment record.
High‐resolution planktic stable isotope record and spectral analysis for the last 5.35 M.Y.: Ocean Drilling Program Site 625 northeast Gulf of Mexico
Authors: Joyce J. Edward , Tjalsma Leonard R. C. , Prutzman John M.
Published: February 2008

Planktic δ18O, δ13C, and biostratigraphy are presented from a nearly complete Pliocene and Quaternary sequence from Ocean Drilling Program hole 625B, northeast Gulf of Mexico. A high‐resolution chronology is derived for the last 5.35 m.y. by tuning the δ18O record to variations in orbital obliquity. Most ages derived for biostratigraphic datums in hole 625B are similar to the same events based on magnetobiochronologies from outside the basin. The δ18O record indicates that Pliocene and early Pleistocene temperature decrease/ice buildup in the northern hemisphere was nonlinear, occurring via a series of steps and gradual shifts beginning about 3.8 Ma. Late Pliocene (2.30–1.66 Ma) and early Pleistocene (1.66–0.73 Ma) δ18O anomalies with magnitudes of −1.4 to −2.0‰ indicate glacial meltwater discharge from the Mississippi River implying that an ice sheet has been present at mid‐latitudes in North America periodically since 2.3 Ma. Spectral analysis of the δ18O signal indicates that the 100‐kyr period dominated during approximately the last 0.5 m.y. and the 41‐kyr period was dominant during the early Pleistocene and entire Pliocene. A contour plot of the δ18O spectrum indicates that the early to mid‐Pleistocene climate transition commenced about 1.0 Ma with the first occurrence of a strong low‐frequency component to the climate system. This low‐frequency component gradually became the 100‐kyr frequency by about 0.6 Ma. Between 0.7 and 0.6 Ma, the 41‐kyr period decayed and via intermediate frequencies gave way to near‐100‐kyr periodicities. The magnitude of glacial‐interglacial δ13C variation during the middle to late Pleistocene at site 625 is greater than observed in open‐ocean records and may have resulted from increased flux of isotopically light, terrestrial organic carbon into the basin during glacial lowstands of sea level.
The Younger Dryas Cool Episode in the Gulf of Mexico
Authors: Flower B. P. , Kennett J. P.
Published: February 2008

Data are presented from Orca Basin piston core EN32‐PC4 in the Gulf of Mexico that confirm the existence of surface water cooling during the Younger Dry as chronozone (11–10 ka). Late glacial planktonic foraminiferal species made a reappearance between 11.4 and 9.8 ka, an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer Globigerinoides ruber. The presence of the Younger Dryas event in the gulf at 27°N demonstrates that surface water cooling extended to mid‐latitude regions in the North Atlantic. The cool surface water interval is bracketed by rapid shifts in δ18O related to changes in the influx of meltwater to the Gulf of Mexico. A chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a ∼500 year period and ended in less than 200 years. These results are among the first deep‐sea sediment data documenting the climatic transitions bracketing the Younger Dryas with a rapidity observed in ice core records. A rapid decrease in δ18O values measured in the white form of Gs. ruber at 10.2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures. Surprisingly, a similar decrease is not observed in the pink form of Gs. ruber, a summer surface water dweller in the gulf. This discrepancy may be explained by continued meltwater influx throughout the Younger Dryas during the summers only, such that there was no change in the δ18O of the pink form at the end of the episode. An additional possibility is that warming at the end of the Younger Dryas raised year‐average temperatures and summer temperatures remained constant. The coincidence of rapid shifts in δ18O with the Younger Dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the Younger Dryas cooling based on changes in the routing of Laurentide glacial meltwater.
The growth of our knowledge of the Earth's outer radiation belt
Authors: Farley T. A.
Published: February 2008

The development of our knowledge of the outer Van Allen radiation zone is surveyed. In general, the approach within each topic is historical. The early discoveries of the gross features of the radiation belt, the difficulties encountered in determining the electron energy spectrum, and the misinterpretation of geomagnetic storm intensity changes due to inadequate knowledge of the electron spectrum are discussed. Also considered are the equatorial pitch angle distributions of electrons, the presence of protons in the outer zone, and the question of a ‘slot’ between the inner and outer zones. The calculations of the neutron albedo contribution of electrons to the outer zone are reviewed; the contribution appears to be inadequate, because the resulting energy spectrum is incorrect, the intensity inadequate, and the required lifetime too long. Observations of electron precipitation into the atmosphere are briefly reviewed, and several possibilities for the connection of such observations to the intensity and lifetimes of trapped electrons are listed.
The escape of helium from the Earth's atmosphere
Authors: MacDonald Gordon J. F.
Published: February 2008

The rate of influx of helium 4 from the earth's crust into the atmosphere is about 2 × 106 atoms cm−2 sec−1. The average rate of thermal escape averaged over the last solar cycle is 6 × 104 atoms cm−2 sec−1. The present abundance of helium in the atmosphere would accumulate in about two million years. Either some nonthermal mechanism permits at present a greater rate of escape of helium or the rate of escape has varied in time. This paper is concerned with an examination of possible changes in the escape rate due to variations in the earth's magnetic field. Problems associated with the heat balance in the upper atmosphere are reviewed. Statistical analysis of drag on satellites and solar decimeter flux establishes that the 27‐day variation in atmospheric density results from fluctuations in the intensity of the solar wind. It is considered likely that a heat source over and beyond that provided by ultraviolet radiation is required to account for both the day‐night variations in upper atmosphere densities and the 27‐day variation. Various mechanisms by which energy density in the solar wind can be transferred into the upper atmosphere are considered. It is suggested that, if the additional heat source is indeed due to the solar plasma, historical fluctuations in the earth's magnetic field could result in a greater escape rate for helium. The establishment and identification of the additional heat source is necessary for a full understanding of the escape of helium. The terrestrial economy of helium 3 is reviewed. The contribution by solar cosmic rays to the abundance of helium 3 remains a major problem. The rate of influx of helium 3, about 10 atoms cm−2 sec−1, is greater than the escape rate averaged over the last solar cycle, about 4 atoms cm−2 sec−1, if solar cosmic rays contain about 10 per cent helium 3.
Seismological evidence pertaining to the structure of the Earth's upper mantle
Authors: Nuttli Otto
Published: February 2008

This review is concerned with the variation of compressional and shear‐wave velocities with depth in the earth's upper mantle. Information about the compressional velocities is obtained from a study of body waves of the P type. Most P‐wave studies have been limited to continental regions. These studies suggest that there is no pronounced shadow zone for P waves resulting from a low‐velocity channel in the upper mantle, except in tectonically active regions such as California‐Nevada, Japan, Andes, etc. Information about the shear velocities is obtained from studies of body waves of the S type and of Rayleigh and Love surface waves. Surface‐wave studies have been made for both continental and oceanic regions. The surface‐ and S‐wave studies suggest that there is an earth‐encircling, low‐velocity channel for shear waves in the upper mantle. The shear velocities in this channel are lower than average in oceanic regions, and higher than average in continental shield regions.
The variation of the deuterium content of natural waters in the hydrologic cycle
Authors: Friedman Irving , Redfield Alfred C. , Schoen Beatrice , Harris Joseph
Published: February 2008

Exploratory data from more than 1000 analyses of the distribution of deuterium in waters of the North American continent and the surface oceans contiguous to the continent are presented. The elementary theory of the processes that appear to explain the changes in the deuterium content of natural waters is developed. Quantitative expressions of the deuterium fractionation that can be expected to occur are presented for all phases of the hydrologic cycle from the evaporation of water from the oceans, its precipitation as rain and snow, and its travel back to the sea. Processes such as the freezing of water under equilibrium and nonequilibrium conditions, the evaporation of water from closed lakes and from lakes with an outlet, the formation of fog, frost, and dew are also discussed. The regional characteristics of the surface waters of North America are described and interpreted as reflecting the history of the water in the course of the hydrologic cycle.
The solar wind geomagnetic field boundary
Authors: Beard David B.
Published: February 2008

The theory of the boundary of the cavity surrounding a magnetic dipole immersed in a steadily flowing stream of plasma is reviewed, and the various results are compared with satellite observations of the termination of the geomagnetic field. The shape on the solar side as roughly hemispherical with an indentation near the poles; the shape on the antisolar side is probably that of a raindrop, but it depends critically on the direction and relative magnitude of the interplanetary magnetic field and possible nonadiabatic processes in the boundary transition layer.
Interference phenomena in mediums having spherical interfaces
Authors: Buldyrev V. S. , Yanson Z. A.
Published: February 2008

Phase and group velocities are computed for several of the lowest modes of Love waves for a homogeneous spherical annulus overlying a homogeneous sphere. The solution is obtained by evaluating the contour integrals in p space by a variety of asymptotic methods, each appropriate in a different range of frequency; p is the index of Bessel functions. Comparison is made with the corresponding solutions in a flat layer over a half‐space. Extension of the formalism is made to the case in which the inner sphere is inhomogeneous.
A proposed basis for geographical and seismic regionalization
Authors: Flinn Edward A. , Engdahl Eric R.
Published: February 2008

A computer‐oriented system of geographical and seismic regionalization is proposed in which the surface of the earth is divided into geographical regions along integral values of latitude and longitude. Boundaries of the geographical regions follow established geographical and political divisions as closely as possible; geographical region names follow the U. S. Coast and Geodetic Survey usage. Seismic regions are defined as combinations of the geographical region and are based on Gutenberg and Richter's region definitions. The proposed system is intended to provide uniformity of geographical description, speed up the regular publication of epicenter information, and aid in seismicity studies.
Seismic digital data acquisition systems
Authors: Smith Stewart W.
Published: February 2008

Two digital seismograph systems in current operation are described. Together they provide high quality data for experimental studies of earth tides, free oscillations, surface waves, and teleseismic body waves. A broad‐band system sampling three components 10 times per sec covers the frequency range between 0.003 and 3.0 cps, and a long‐period system sampling each of ten channels every 15 sec covers the range between 0.0 and 0.01 cps. The broad‐band system can be used to simulate any desired standard seismograph and provides greater dynamic range and more flexibility than most existing seismographs. The long‐period system is currently being used for a free oscillation experiment in which strain and pendulum seismographs record together.
Statistical models for data processing in seismology and magnetic prospecting
Authors: Goltzman F. M.
Published: February 2008

The problems of geophysical data processing are reducible to those of maximizing certain likelihood functions in which the parameters of the likelihood functions are the parameters of the geophysical model. Examples are given from travel‐time seismology and magnetic prospecting.
Engineering applications of nuclear explosives: Project Plowshare
Authors: Johnson Gerald W. , Higgins Gary H.
Published: February 2008

The exploration of possible engineering uses of nuclear explosives, begun in 1957, has continued and has resulted in substantial progress. Major advances have been achieved in development of much cleaner explosives that will extend the range of possible use and will lead to lower costs. Several nuclear experiments have been carried out which provide an improved technological base from which to assess both cost and feasibility of various projects. The effect of the additional knowledge has been to increase confidence in the feasibility and economic advantage of nuclear excavation, certain underground mining applications, and isotope production for research.
Use of arrays for acoustic transmission in a noisy ocean
Authors: Clay C. S.
Published: February 2008

The ocean can be regarded as a horizontally stratified waveguide for the transmission of acoustical signals. The use of transducer arrays in the ocean presents special problems that are not present in an infinite homogeneous medium. For example, the signal at the receiver is the sum of many arrivals and each arrival is dispersive. In the normal mode formalism, the solution for a single frequency source can be expressed as the product of spectrum functions. Each spectral component is the horizontal component of wave number κ. The responses of waveguide transmission function, transmitting arrays, and receiving array can be expressed as functions of κ. Because of the horizontal stratification, horizontal and vertical arrays have quite different properties and are considered separately. The horizontal array is much less critical in design and operates more as it would in homogeneous space. The vertical array operates as a mode filter and is extremely sensitive to the depth and phase adjustment of the transducers. The signal output of the receiving array filter is the product of source, transmission, and receiver functions of κ. The maximum signal‐to‐noise ratio is obtained when the receiver array amplitude and phase response are the complex conjugate of the signal field at the receiver divided by the noise power. The condition is analogous to the matched filter condition of electrical circuit theory. The effect of fluctuations of the stratification of the ocean on sound transmission is included in an approximate treatment. The radiation in a mode is assumed to be trapped, and the radiation scattered by inhomogeneities can be ignored. The average signal transmission was found to depend on the correlation functions and distribution functions of the irregularities. The maximum signal‐to‐noise ratio is obtained when all modes or arrivals can be added coherently; i.e., no phase fluctuations exist. The performance of the arrays decreases as the phase fluctuation increases. Upper and lower limits of the signal‐to‐noise ratio are given for small and large phase fluctuations. The degree of coherence of the modes has been related to the reproducibility of the signal transmission between a single source and a single receiver.
Insolation changes, ice volumes, and the O18 record in deep‐sea cores
Authors: Broecker Wallace S. , van Donk Jan
Published: February 2008

A detailed curve of ice volume versus time is needed in order to test the validity of the hypothesis that changes in the earth's orbital parameters are the cause of oscillations in Pleistocene climate. Although absolute ages available for glacial moraines and raised coral reefs provide a number of key points, they by no means allow a continuous curve to be drawn. Those points that exist, however, are entirely consistent with the hypothesis that the O18/O16 curves from deep‐sea cores provide good approximations to the ice volume record. If so, then the primary glacial cycle must be sawtoothed in character; gradual glacial buildups over periods averaging 90,000 years in length are terminated by deglaciations completed in less than one tenth this time. Modulating this primary cycle are secondary oscillations. Those recognized during glacial growth phases average 20,000 years in length and those during the retreats about one thousand years in length. When the ice volume curve obtained in this way is compared with the summer insolation curve for the northern hemisphere, it is seen that the rapid deglaciations occur during times of unusually great seasonal contrast and that the secondary cycles modulating the glacial buildups closely parallel the insolation variations. Although these findings provide convincing evidence for the influence of orbital changes on climate, the cause of the primary sawtoothed cycle is still an open question. In conjunction with this study, we have determined the O18/O16 record for Caribbean core V12‐122 and find it to be compatible with those given by Emiliani for cores P6304‐8 and P6304‐9. Our dating of this core by Pa231‐Th230 and by magnetic reversals, however, strongly suggests that the absolute time scale adopted by Emiliani for deep‐sea cores must be increased by 25%.
Propagation of cosmic rays in the solar wind
Authors: Jokipii J. R.
Published: February 2008

This paper presents a coherent exposition of the modern statistical theory of the transport of fast charged particles (cosmic rays) in the solar wind. Observations are discussed only as they illustrate the phenomena under discussion. A brief introductory section surveys the historical development of the theory. The dominant effect on the motion of cosmic rays in the solar wind is the interplanetary magnetic field, which is irregular and which is therefore best treated statistically, using random functions. The magnetic irregularities scatter the cosmic rays in pitch angle, so that to a good approximation the cosmic rays diffuse through the irregular magnetic field. Using a statistical analysis of the equations of motion, one may relate the diffusion tensor to the power spectrum of the magnetic field, which is in principle measurable. The resulting general transport theory relates the motion of cosmic rays, statistically, to the solar‐wind velocity and magnetic field. Application of the theory both to the modulation of galactic cosmic rays by the solar wind and to the propagation of solar cosmic rays is discussed in detail. It is concluded that the present theory explains the principal phenomena quite well. Future theoretical work will probably be devoted to obtaining better solutions of the equations, to obtaining better values of the parameters, and to studying higher‐order or more subtle effects.
Clear‐air turbulence, aviation, and atmospheric science
Authors: Dutton John A.
Published: February 2008

Clear‐air turbulence (CAT) presents a scientific problem of considerable importance to aviation and to attempts to understand atmospheric processes that must be incorporated in a long‐range numerical prediction model. Present knowledge about CAT is reviewed briefly, and the fact that the requirements of both aviation and atmospheric science for new information necessitate a measurement program whose objective is increased understanding of the physical mechanisms of CAT is emphasized. Specific investigations that should be a part of such a measurement program are presented, and the importance of the energy budget of CAT is stressed both for its scientific value and for its potential as a method of verifying accuracy of measured data. A new approach to determining the required accuracy of turbulence instrumentation, utilizing root‐mean‐square error techniques, is presented. Some aspects of the management of a large measurement program are also considered.
Evolutionary model for lead isotopes in conformable ores and in ocean volcanics
Authors: Russell R. D.
Published: February 2008

Recently, absolute isotopic ratios have been published for lead standards. This makes possible for the first time a meaningful comparison of published isotopic ratios of lead from conformable ores with those from oceanic rocks. Such a comparison is interesting because these classes of material exhibit isotopic patterns that may be of worldwide significance. A preliminary study has been made of the adjusted ratios of 18 conformable ores and 22 oceanic volcanic‐rock leads. Each group shows a recognizable pattern such that leads from one regime cannot be obtained by any simple mixture of leads from the other. One widely recognized difference between the patterns is the considerable variation of isotopic ratios for oceanic volcanic samples of similar age, indicative of a heterogeneous source. This contrasts sharply with conformable ores for which isotopic ratios are similar for samples of the same age. Another characteristic, considered to be of equal importance, is the significant deficiency of 207Pb in the oceanic volcanic leads. This paper shows that both characteristics can be reproduced by a model in which uranium, thorium, and lead are transferred between two reservoirs. The transport of uranium and thorium must occur more quickly than for lead, and for all elements transport must be sufficiently rapid to reach quasi‐steady state in a time much shorter than the age of the earth. The close relationship between this model and bidirectional transport between the systems is discussed. Two forms of the model are presented. In each, the time‐varying concentrations of 204Pb approach asymptotic values exponentially with time. Model A, in which the transport of uranium and thorium is very rapid, provides the most recent beginning of differentiation, at a time 2500 m.y. ago. Model B, in which the transport of uranium and thorium is also exponentially related to time, corresponds to a differentiation beginning 3000 m.y. ago. These seem to be extreme times for the form of the model used. It is suggested that lead‐isotope measurements might be used to identify characteristically oceanic materials now in continental areas as the result of tectonic plate movement.
Recent satellite measurements of the morphology and dynamics of the plasmasphere
Authors: Chappell C. R.
Published: February 2008

The very low energy thermal plasma (∼1 eV or several thousand degrees Kelvin) is often overlooked in reviews of magnetospheric plasma populations, usually as a result of energy considerations in which thermal particles are believed unimportant. In reality this cold plasma, which surrounds the earth in a region known as the plasmasphere, has an important direct influence on the characteristics of the ionospheric F region and on the location of regions of plasma turbulence in the magnetosphere, and it is an excellent indirect measure of the intensity of magnetospheric convection. The characteristic morphology and dynamics of the plasmasphere vary with local time and with geomagnetic conditions. On the nightside the plasmapause position changes predictably with changing magnetic activity. Once established at a specific L‐shell value, the steep density gradient on the nightside corotates into the dayside, where filling from the ionosphere takes place. In the duskside bulge region the characteristic density profile inside the plasmapause displays a smooth decrease proportional to 1/R4, where R is radial distance. Plasmasphere morphology and dynamics can be understood in terms of a time‐varying convection electric‐field model of the magnetosphere that includes the bulge region as part of the main circulation pattern of the plasmasphere.
The auroral oval—A reevaluation
Authors: Eather R. H.
Published: February 2008

The auroral oval represents a region of auroral occurrence where particular spectral features have sufficient integrated intensity to exceed all‐sky camera thresholds. It has been argued that this is not a good representation of the characteristics of particle precipitation or of energy deposition. Consequently, the auroral oval concept may not be a good one to use to order diverse auroral data on a 24‐hour basis. Rather, the precipitation patterns for specific energy classes of protons and electrons should form the basis for the interpretation of high‐latitude geophysical measurements.
Dynamical models for sea floor spreading
Authors: Richter Frank M.
Published: February 2008

Fluid dynamic models of the lithosphere‐asthenosphere system are studied. These models provide a basis for understanding driving mechanisms involved in sea floor spreading. The asthenosphere is represented as a highly viscous Newtonian fluid that is nonrotating, Boussinesq, incompressible, and nondissipative. A sequence of two‐dimensional model problems is considered in an effort to understand the dynamic role of various energy sources available in the upper mantle. The first models investigate the role of vertical temperature gradients and find these incapable of generating flows in the asthenosphere that move overlying lithospheric plates by viscous traction. By considering the combined effect of horizontal and vertical temperature gradients, a mechanism for effecting the original breakup of large continental masses is suggested. The dynamic role of phase changes is investigated in a series of finite‐amplitude model problems. The olivine‐spinel phase transition is found to increase the amplitude of convection by a factor of about 2, and the depth at which the phase change occurs is influenced by the convection. A final class of problems explicitly consider the lithosphere coupled to the underlying asthenosphere and the mass flux into and out of the asthenosphere implied by moving surface plates. It is found that if the subducted lithosphere has a negative buoyancy of the order of present estimates, the lithospheric plates will move at velocities of 1–10 cm yr−1.
Major variations in solar luminosity?
Authors: Cameron A. G. W.
Published: February 2008

One possible explanation for the failure to detect neutrinos emitted from the solar interior is that the core of the sun may be in a temporarily expanded state. If so, the solar luminosity is currently much less than its normal value, which may account for the fact that the earth is now in the middle of a major glacial period. The astrophysical background of this situation is described, and the terrestrial consequences are discussed.
Laboratory studies of collisions of energetic H+ and hydrogen with atmospheric constituents
Authors: McNeal R. J. , Birely J. H.
Published: February 2008

Laboratory studies of ionization and excitation of atmospheric gases in collisions with 0.1‐ to 1000‐kev protons and hydrogen atoms are reviewed. Recent measurements of the mixed flux of H+ and H that penetrates the auroral zone atmosphere during a hydrogen aurora indicate that particles with energies less than 10 kev are most important, which implies that energetic hydrogen atoms cause most of the observed ionization and light emission. Both H+ and H produce free electrons by collisional ionization of atmospheric constituents, and stripping of energetic H is an additional source of electrons. Reliable data are available for the cross section for production of electrons in collisions of H+ and H with all important target gases, except atomic oxygen, over the full range of auroral energies. Excitation of atmospheric gases has been widely studied for H+ collisions in the range above 10 kev, but cross sections for H+ below 10 kev and H in any energy range are still largely unknown. Data are available for calculation of expected auroral emissions in the υ′ = 0 bands of the N2+ first negative system and in the υ′ = 0 bands of the N2 second positive system. The ratio of the cross section for electron production by ionization to the cross section for emission of the 391.4‐nm band of the N2+ first negative system is found to be about 20 for energies above 10 kev and then to rise to more than 100 at 1 kev. In the case of the hydrogen emissions, laboratory data are adequate for auroral calculations of Lyman α radiation. Collisional excitation of energetic H to the 2p level, rather than charge transfer excitation involving fast H+, is the major source of Lyman α in the hydrogen aurora. Data on the production of the Balmer α line are lacking at energies below 10 kev. The available Balmer α data suggest a broad peak near 10 kev in the effective auroral cross section that is nearly an order of magnitude smaller than the peak in the Lyman α cross section, which occurs at energies less than or equal to 1 kev. Insufficient laboratory data exist for meaningful calculations of auroral Hβ intensities.
Structure and constitution of the lower oceanic crust
Authors: Christensen Nikolas I. , Salisbury Matthew H.
Published: February 2008

Any petrologic model of the lower oceanic crust must be consistent with three sets of data: (1) the seismic structure of the oceanic crust, (2) the petrology of oceanic dredge samples, and (3) laboratory measurements of seismic velocity through such samples. A review of these data indicates that within the framework of earlier three‐layer models of oceanic seismic structure the crust is internally complex and varies markedly with age, azimuth, and tectonic province. Mantle compressional wave velocities Vp are anomalously low under the ridge (7.2–7.7 km/s) but increase to 8.0–8.3 km/s beyond 15 m.y.; layer 3 thickens by 2 km within 40 m.y. of formation and decreases in Vp from 6.8 to 6.5 km/s within 80 m.y.; both the mantle and layer 3 are statistically anisotropic. Dredge lithologies consist predominantly of serpentinized ultramafics and mafic igneous rocks ranging from basalt to gabbro, the gabbro often showing evidence of fractionation. Metamorphism of mafic rocks from zeolite to amphibolite facies grade is common. Velocities in oceanic serpentinites and basalts are generally lower than layer 3 refraction velocities. Unaltered gabbros have compressional wave velocities of approximately 7.0 km/s, which is high for layer 3, together with shear wave velocities Vs of 3.8 km/s and values of Poisson's ratio σ of 0.30. Metabasites containing hornblende and plagioclase have values of Vp = 6.8 km/s, Vs = 3.8 km/s, and σ = 0.28, in good agreement with those of layer 3. On the basis of petrology and velocity it is suggested that layer 3 is composed of hornblende metagabbro underlain by normal gabbro. In a model consistent with geophysical observations of heat flow, seismicity, gravity, and seismic structure at the ridge it is proposed that layer 2 and the upper levels of layer 3 form near the median valley but that deeper levels of layer 3 thicken for 40 m.y. by intermittent offridge intrusion fed from the underlying anomalous mantle. Ophiolites in such a model represent segments of thin immature ridge crest obducted onto continental margins during subduction of a spreading ridge.
Dynamics of lunar origin and orbital evolution
Authors: Kaula William M. , Harris Alan W.
Published: February 2008

The considerable differences in bulk composition of the moon and the earth have led most investigators to favor the capture hypothesis of lunar origin. However, upon closer examination all forms of the hypothesis still seem much less plausible dynamically than formation by accretion, i.e., acquisition of the moon in many small pieces rather than as predominantly one body. Models of accretion do suggest that the proto‐lunar matter had a significantly different history from the proto‐earth matter. A better understanding of collisions is needed to infer the compositional consequences of this history. Recent work on the acceleration of the moon's orbit exacerbates the time scale problem of orbital evolution. However, it now is much clearer that the locus of tidal dissipation is in the oceans and hence that the solution to the time scale problem lies in differing oceanic configurations in the past.
Marine gravimetry
Authors: Dehlinger Peter
Published: February 2008

This report summarizes marine gravity activities undertaken by universities, research institutions, government laboratories, and meter manufacturers but does not include proprietary work such as that undertaken by the petroleum industry. All nonproprietary gravity data are eventually place on file at either the National Geophysical and Solar‐Terrestrial Data Center (NGSDC) of the National Oceanic and Atmospheric Administration (Washington, D.C.) or the Defense Mapping Agency Aerospace Center (DMAAC) Gravity Library (St. Louis) or both.

Sea gravity measurements made by U.S. organizations and obtained since the time of the previous International Union of Geodesy and Geophysics report [Dehlinger, 1971] are generally more accurate than those obtained in prior years. The improved measurements result from the combined effects of refinements made on the design and operation of the sea gravity meters and the use of a satellite navigation system to determine ship positions. The satellite systems now in common use make it possible to calculate Eötvös corrections well within 1 mGal [e.g., Chiburis and Dehlinger, 1974b]. The gravity meters are capable of accuracies of 1 mGal in all but severe seas.
Earthquake prediction
Authors: Kisslinger Carl , Wyss Max
Published: February 2008

Vigorous efforts in earthquake prediction research have been under way in the United States only during the last 4 yr. A primary result of this research is the growing confidence that at least some earthquakes, shallow ones located on continents, including near offshore regions, are, in fact, predictable. Diagnostic premonitory phenomena, mostly discovered before 1971, have been tested further. The synthesis of laboratory and field observations has been crucial in the development of theories of the earthquake process that account for these precursors. Prediction technology is still in the early research and development stage, but a few successful predictions have been made by U.S. and other investigators.