bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of climate variability in general circulation models: Comparison with observations and changes in variability in 2xCO2 experiments
Authors: Mearns L. O. , Schneider S. H. , Thompson S. L. , McDaniel L. R.
Published: February 2008

This study concerns analysis of climatic variability in general circulation models, first to determine how faithfully the models reproduce measures of the present variability, and then to examine how variability changes in CO2 perturbed cases. The control run output of three different versions of the NCAR Community Climate Model is examined for selected regions of the United States including the Great Plains, the Southeast, the Great Lakes region, and the upper West Coast. Mainly temperature and precipitation are analyzed, but some preliminary analysis of relative humidity is also included. Inter annual variability is analyzed in one version (Chervin) for only the present day climate. Results indicate that this version underestimates the interannual variability of temperature, but generally successfully reproduces the relative variability of precipitation. Two versions of the CCM tend to overestimate daily temperature variability while the third (Dickinson) accurately reproduces or underestimates it. Reasons for these differences are discussed. Daily precipitation variability is overestimated by two model versions (Chervin and Dickinson) but fairly well reproduced by the Washington version. The CO2 perturbed run of one version (Washington) produces mixed results for changes in daily temperature variability and tends to produce increased daily variability for precipitation.
Stratospheric ClONO2, HCl, and HF concentration profiles derived from Atmospheric Trace Molecule Spectroscopy Experiment Spacelab 3 observations: An update
Authors: Zander R. , Gunson M. R. , Foster J. C. , Rinsland C. P. , Namkung J.
Published: February 2008

Updated volume mixing ratio profiles of ClONO2, HCl, and HF are reported from a reanalysis and reinterpretation of solar infrared absorption spectra obtained with the Atmospheric Trace Molecule Spectroscopy instrument on board Spacelab 3 (April 29 to May 6, 1985). These analyses incorporate improved spectroscopic parameters as well as instrumental and observational corrections made to this series of infrared spectra. While the HCl and HF results and their precisions reflect changes essentially below 30 km from the use of smaller pressure‐broadened half‐widths, the ClONO2 profiles have changed significantly as a consequence of adopting improved sets of line parameters which include a more realistic temperature dependency appropriate for stratospheric studies. The new ClONO2 results have an overall accuracy of ±20%; when expressed in terms of vertical column abundances above their altitude span, they are in satisfactory agreement with values derived from airborne and ground based investigations.
Methane fluxes in wetland and forest soils, beaver ponds, and low‐order streams of a temperate forest ecosystem
Authors: Yavitt J. B. , Lang G. E. , Sexstone A. J.
Published: February 2008

Studies in tropical and boreal regions suggest that wetlands and forest soils are important sources and sinks, respectively, for atmospheric methane. This study was conducted to determine whether temperate wetlands and forests play important roles in the global balances of atmospheric methane. Flux measurements for methane in several different wetland, forest, and open‐water (e.g., beaver pond and low‐order stream) sites were determined using collection chambers placed over the soil‐ or water‐air interface. All of the sites were located in the Appalachian Mountain region of West Virginia and western Maryland. Between June 1987 and April 1989 the wetland sites acted as small sources of atmospheric methane, with emission rates for methane usually < 200 mg CH4 m−2 d−1 consumption of atmospheric methane in the wetland soils was observed frequently. The forest sites were mostly atmospheric methane sinks, even though emission rates (< 40 mg m−2 d−1) were observed sporadically. Open‐water sites were large sources of atmospheric methane, with emission rates often exceeding 1000 mg CH4 m−2 d−1. Methane fluxes were poorly correlated with environmental variables including soil moisture, soil and air temperature, and cloud cover, thereby making it difficult to determine the factors controlling methane fluxes in these sites. Scenarios of future global climate warming due to an increasing greenhouse effect suggest that wetlands and forests in the southern boreal forest will begin to resemble present‐day temperate wetlands and forests. The results of our studies suggest that methane emissions from these “temperatelike” ecosystems will not result in a large positive feedback that might exacerbate the rate of global climate warming.
Global three‐dimensional simulations of ozone depletion under postwar conditions
Authors: Kao Chih‐Yue Jim , Glatzmaier Gary A. , Malone Robert C. , Turco Richard P.
Published: February 2008

Oxides of nitrogen (NOx) produced in nuclear fireballs could catalytically destroy stratospheric ozone. Since the NOx would be deposited in the upper troposphere and lower stratosphere below the level of maximum ozone concentration, earlier one‐dimensional model results showed that the potential ozone destruction rate was limited by the slow rate of vertical diffusion of NOx into the stratosphere. In the current study, the presence of a massive amount of smoke which absorbs solar energy in the upper atmosphere introduces three important changes. First, solar‐driven lofting of smoke‐filled air displaces ozone‐rich stratospheric air with ozone‐poor air from the troposphere; at the same time ozone from the northern hemisphere is shifted into the southern hemisphere. Secondly, the modified large‐scale circulation rapidly pushes NOx upward, which mixes NOx into the ozone layer much more quickly than previously thought. Finally, the heating of the stratosphere caused by the solar heating of the rising smoke increases the rates of catalytic chemical reactions that destroy ozone. Thus, NOx acts as a chemical catalyst and smoke acts as a thermal catalyst for ozone destruction. The results of simulation using general circulation model (GCM) suggest a rapid ozone depletion in the northern hemisphere. The smoke‐induced transport alone can reduce the O3 column by 15–20 Dobson units between the tropics and 60°N after 20 days of simulation. With the chemical reactions included,∼15% of ozone is depleted between 25°N and 75°N after 20 days.
Chemical loss of polar vortex ozone inferred from UARS MLS measurements of ClO during the Arctic and Antarctic late winters of 1993
Authors: MacKenzie I. A. , Harwood R. S. , Froidevaux L. , Read W. G. , Waters J. W.
Published: February 2008

A computationally cheap, and easily initialized photochemical model utilizing UARS MLS measurements of ClO to calculate ozone destruction rates within the polar vortices due to the ClO + ClO, ClO + BrO, and ClO + O catalytic cycles is developed. The method involves calculating local reactive chlorine concentrations from individual ClO retrievals, and then inferring the diurnal cycle of ClO from a quadratic expression using the relevant kinetic parameters. In test integrations this simple treatment is shown to give good agreement with more detailed model calculations. Analysis of the late Arctic and Antarctic winters of 1993 yields similar vortex‐averaged ozone loss rates at 465 K of ∼1% per day in both hemispheres, while the reactive chlorine remains enhanced. Net ozone destruction in the north is less, largely because the elevated ClO and Cl2O2 concentrations are less persistent. The estimated chemical destruction on isentropic surfaces in the lower stratosphere is broadly similar to the observed change in ozone distribution, implying that the change is dominated by chemical destruction.
Paleoclimatic constraints on the maintenance of possible ice‐shelf cover in the Norwegian and Greenland seas
Authors: Lindstrom Dean R. , MacAyeal Douglas R.
Published: February 2008

We examine the controversial issue of whether or not an integrated ice shelf existed in the Norwegian and Greenland seas during glacial events of the Pleistocene. Our method consists of testing for equilibrium ice shelf configurations with the use of a finite element model that predicts ice shelf evolution under a variety of atmospheric and oceanic forcing conditions. Ice flow at the margins of the simulated hypothetical ice shelf is determined from one of Denton and Hughes' (1981) reconstructions of continental glaciation applicable to the last glacial maximum. Our results suggest that the existence of the ice shelf, and possibly surrounding marine‐based ice sheets, depends most sensitively on oceanic heat flux. A heat flux of approximately 4.80 J m−2 s−1, corresponding to an area‐average basal melting rate of 0.50 m a−1 (ice equivalent), is near the upper limit allowing ice shelf equilibrium. Greater heat flux is found to cause an initial 450‐m‐thick ice shelf to rapidly collapse. The equilibrium ice shelf configurations examined provide effective buttressing support for the marine ice sheet grounded in the Barents Sea 18 kyr B.P. Tests confirming the existence of ice shelf cover in the Norwegian and Greenland seas are possible through a comparison of the sedimentary record of ice‐rafted debris with ice shelf flow patterns deduced from our simulations.
Rainy periods and bottom water stagnation initiating brine accumulation and metal concentrations: 1. The Late Quaternary
Authors: Rossignol‐Strick Martine
Published: February 2008

A working hypothesis is proposed to account for the present accumulation of brines in isolated pockets of the ocean floor and for the formation of the underlying organic and metal‐rich sediments. These are the Tyro and Bannock basins in the East Mediterranean, the Red Sea Deeps, and the Orca Basin in the northern Gulf of Mexico. Initiation of brine‐derived deposition in the Red Sea Deeps and Orca Basin occurred between 12,000 and 8000 years B.P. This time bracket also encompasses the formation of the latest East Mediterranean sapropel and the wettest global climate since the last glacial maximum. This wet period first appeared in the tropics around 12,000 years B.P, then in the subtropical and middle latitudes. During the same period, the 23,000 year precession cycle brought the summer insolation of the northern hemisphere to its peak at 11,000 years B.P. with retreating northern hemisphere ice sheets. The Red Sea Deeps and the Orca Basin became anoxic during this humid period, and metal‐rich sapropel deposition then began. In contrast, the Tyro and Bannock basins began accumulating a brine long before and persisted beyond this climatic stage. The hypothesis involves two propositions: (1) As in the Eastern Mediterranean Sea, marine anoxia was mainly the consequence of the large influx of continental runoff and local precipitation. Longer residence time of bottom waters, so‐called “stagnation,” in silled rimmed basins would have resulted from lower salinity at the sea surface in areas of deep water formation in the Eastern Mediterranean, the Red Sea, and the Gulf of Mexico and (2) Miocene or older evaporites underlie these basins or outcrop on their flanks. Leaching from these evaporites was an ongoing process before the quasi‐stagnation phase, but the initial leachate, much less saline than the present brines, was continuously flushed by bottom circulation. The climate‐induced quiescence of bottom waters in these basins enabled the leachate to accumulate. The feedback of stagnation by increased density progressively raised the salinity of entrapped bottom waters to the present brine concentration. The high density has resisted brine removal by bottom circulation until present time, long after cessation of the initiating wet period. The brines therefore are stagnant, fossil waters.
Late Quaternary sediment pathways through the deep ocean, east of New Zealand
Authors: Carter Lionel , Mitchell John S.
Published: February 2008

Late Quaternary sediment pathways through the deep ocean, east of New Zealand, were determined using sand‐sized mica tracers in conjunction with physical oceanographic, seismic, and stratigraphic data. Results indicate that in glacial times, micaceous sediment, derived mainly from low‐grade metamorphic rocks of the eastern South Island, was delivered by rivers directly to Bounty Trough. Here turbidity currents transferred the sediment 1000 km eastward to the Bounty Fan on the 4500 m deep Southwest Pacific Basin. A western boundary current (WBC), flowing over the fan, redirected the sediment 1000 km to the north and northwest where it eventually accumulated as a drift deposit near Hikurangi Trough. The drift also received mica that had been transported 700 km along Hikurangi Trough from mainly plutonic sources on the northwestern South Island. Interglacial episodes witnessed a major change in transport paths. River‐borne sediment was diverted away from Bounty Trough which became a site of predominantly calcareous pelagic sedimentation. Denied the lateral injection of terrigenous sediment, the WBC nevertheless continued to supply small quantities of mica to the drift through erosion of existing glacial deposits on the Bounty Fan. The paucity of interglacial mica on the drift indicates it is also receiving little terrigenous sediment by way of Hikurangi Trough.
Toward a high‐resolution chronology for latest Miocene paleoceanographic events
Authors: Keigwin L. D.
Published: February 2008

It is now widely accepted that expansion of continental glaciers is one manifestation of profound paleoenvironmental change in latest Miocene time. The oxygen isotopic record in deep‐sea cores is inferred to document brief pulses in glaciation, based on covariance of δ18O in benthic and planktonic foraminifera, which probably lowered latest Miocene sea level by a minimum of 60 m. Additional evidence of glacial activity in the oxygen isotope record is obscured by the small signal amplitude. Before further details of paleoenvironmental change can be investigated it is essential to have a high‐resolution stratigraphy and chronology. This has not been achieved previously because most studies of the latest Miocene have had a sampling interval greater than the duration of events they seek to resolve. A high‐resolution stable isotope record from the north Atlantic (Deep Sea Drilling Project (DSDP) 552) is correlated with a second record from the southwest Pacific (DSDP 588). Each core has magnetostratigraphy, but there are two possible interpretations of magnetic results in the Atlantic core. By assuming that brief events of 18O enrichment and 13C depletion in each core are synchronous it is possible to assign the most likely age model to the Atlantic core. Results of this exercise indicate that two δ18O maxima occurred at 4.8 and 5.2 Ma. If these events reflect continental glaciation, and if sea level was lowered enough to contribute to isolation and desiccation of the Mediterranean, then the Miocene/Pliocene boundary must be close to 4.8 Ma in age because Messinian deposits are latest Miocene in age. This interpretation is consistent with biostratigraphy at DSDP 552; magnetostratigraphy, biostratigraphy, and isotope stratigraphy at a site commonly referred to because of its proximity to the Mediterranean (DSDP 397, northwest African continental margin); and recent work on land in the Mediterranean region.
Late Pleistocene paleoclimatology of the central equatorial Pacific: Sea surface response to the southeast Trade Winds
Authors: Pisias Nicklas G. , Rea David K.
Published: February 2008

Proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data, and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late Pleistocene: All indicators fluctuate at higher frequencies than the 100,000‐year glacial‐interglacial cycle, display reduced amplitude variations since 300,000 years ago, exhibit a change in the record character at about 300,000 years ago (the mid‐Brunhes climatic event), and have higher amplitude variations in sediments 300,000–850,000 years old. Time series analyses were conducted to determine the spectral character of each record (δ18O of planktonic foraminifer, sea surface temperature values, equatorial divergence indicators, and wind intensity indicators) and to quantify interrecord coherence and phase relationships. The record was divided at the 300,000‐year clear change in climatic variability (nonstationarity). The δ18O‐based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402,000–774,000 years. The δ18O spectra show 100,000‐ and 41,000‐year power in the younger portion, 0–300,000 years, and 100,000‐, 41,000‐ and 23,000‐year power in the older interval, all highly coherent and in phase with the SPECMAP average stacked isotope record. Unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31,000 years. This period is also important in the sea surface temperature signal where the dominant spectral peak is 100,000 years. The 31,000‐year spectral component is coherent and in phase between the eolian and divergence records, confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record. Since the 31,000‐year power appears in independent data sets within this core and also appears in other equatorial records [J. Imbrie personal communication, 1987], we assume it to be real and representative of both a nonlinear response to orbital forcing, possibly a combination of orbital tilt and eccentricity, and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component. The mid‐Brunhes climatic event is an important aspect of these records, but its cause remains unknown.
Ocean heat transport during the Last Glacial Maximum
Authors: Miller James R. , Russell Gary L.
Published: February 2008

The annual mean oceanic poleward heat transport during the last ice age is calculated using surface heat fluxes from a global atmospheric general circulation model. The atmospheric model is used to simulate the climate 18,000 years ago using Climate: Long‐Rang Investigation, Mapping and Prediction data for the model's seasonally varying sea surface temperature and ice cover. Heat transport is obtained by assuming that there is no net heat storage in the ocean over an annual cycle and by calculating the required converged ocean heat transport for each latitude band. Ocean heat transports for the present‐day climate have been calculated with this model and are in good agreement with other studies. The results indicate that the global transports are similar for the present climate and the ice age except for the northern high latitudes where the present climate has significant poleward transport. The maximum transports occur at the same latitudes in both cases, are about the same magnitude in the northern hemisphere, and are somewhat larger during the ice age in the southern hemisphere. The maximum northward transport in the North Pacific is about twice as large for the ice age as for the present climate. For the present climate in the Atlantic there is a net northward transport of heat at all latitudes and hence a net transport of heat into the Atlantic from other basins. For the ice age in the Atlantic there is a reduced northward transport in the northern hemisphere, a southward transport in the southern hemisphere, and a net transport of heat out of the Atlantic into the other ocean basins.
Processes controlling the accumulation of diatoms in sediments: A model derived from British Columbian fjords
Authors: Sancetta Constance
Published: February 2008

The transformation of biocoenosis to taphocoenosis of diatom assemblages was examined using monthly sediment traps over a 3‐year period at four sites in the fjords of British Columbia. The fjords were chosen as a natural laboratory where productivity is high and seasonally variable and where geological rates of sediment accumulation approach the biological rates of production and flux. The composition of trap samples from different depths was quantified and compared with the surface sediment, recovered by box cores. Fragmentation caused by zooplankton grazing preferentially destroys 20–50% of the early spring and 50–75% of the late spring and early summer production. Grazing activity and incorporation into pellets does not otherwise affect preservation. Differential dissolution occurs during settling through the water column; taxa with a high surface‐to‐volume ratio are preferentially lost. Low‐level lateral advection tends to concentrate heavy, robust taxa, while strong advection affects all particles equally and has no net biasing effect. The interaction of these processes results in a sediment assemblage in which winter and fall taxa are more common than they are in the plankton, while the early spring bloom is badly underrepresented. Multivariate analyses indicate that the sediment is dominated by the early summer bloom, but caution must be exercised in this interpretation, because the bloom is characterized by a species (Skeletonema costatum) which is common at all seasons of the year and therefore is not a reliable indicator of a single period of production. The end result is a decrease in seasonal contrast and at some sites a reordering of seasonal proportion in the sediment. While the seasonal composition can still be identified, there is also evidence of homogenization of sediment assemblages, with some of the original spatial variability obscured. Taken to an extreme, a unique fossil assemblage may be produced which cannot be statistically related to any combination of seasons of production. Three factors which might affect preservation of deep‐sea assemblages (water depth, accumulation rate, and degree of bioturbation) do not have a measurable effect in fjord environments. Strong modification of assemblages can occur within the upper 500 m; deep‐sea monitoring programs which do not include this interval may lead to erroneous conclusions concerning production and flux to the sediments.
A record of past ocean‐Atmosphere radiocarbon differences from the northeast Pacific
Authors: Southon J. R. , Nelson D. E. , Vogel J. S.
Published: February 2008

A record of the 14C age differences between atmosphere and the mixed layer of the northeast Pacific Ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in British Columbia. This series of mixed layer reservoir ages spans the Holocene and extends into the period of the Younger Dryas cold event in the North Atlantic and surrounding regions. The data reflect the extent of upwelling in the northeast Pacific and thus constrain models of carbon cycling and ocean circulation. Most of the reservoir ages are only slightly less than than the present (preindustrial) value of about 800 years, and may be identical when probable sampling errors are taken into account. Either the North Pacific reached a state close to its present mode of circulation at or before the end of the Younger Dryas or a different circulation fortuitously produced a similar reservoir age. Our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the Holocene arose from 14C production rate changes. Data corresponding to a radiocarbon age of around 6400 years B.P. give a reservoir age of 1200 years. If this result is confirmed, it indicates a much greater variability for the Holocene ocean circulation than was previously believed possible.
The correspondence between water temperature and coiling direction in Bulimina
Authors: Collins Laurel S.
Published: February 2008

The influence of temperature on the direction of coiling in the benthic foraminifera Bulimina marginata d'Orbigny and B. aculeata d'Orbigny is investigated by direct comparison of specimens and temperature data measured at or near the sites of collection. Nine samples from the Gulf of Mexico and 16 samples from the Gulf of Maine south to New Jersey are used. These areas include cold temperate and subtropical regions, the continental shelf, slope, and a semirestricted gulf. Complicating factors of life cycle stage and possible ontogenetic change are eliminated. Dextrality is strongly associated with warm temperatures, but cold temperatures do not produce predominantly sinistrally coiled individuals. This is the first demonstration of an unambiguous correlation between temperature and coiling direction in benthic foraminifera.
Miocene benthic foraminiferal Cd/Ca records: South Atlantic and western equatorial Pacific
Authors: Delaney M. L.
Published: February 2008

Cadmium‐to‐calcium records in benthic foraminifera, interpreted in conjunction with carbon isotope records, reflect oceanic circulation patterns and oceanic inventories of Cd, carbon 13/carbon 12, and indirectly, phosphorus. Cd/Ca ratios have been determined in benthic foraminifera Cibicidoides spp. for the late, middle, and early Miocene from a site in the South Atlantic (Deep Sea Drilling Project (DSDP) site 525, leg 74, ∼2500 m, Walvis Ridge) and from a site in the western equatorial Pacific (DSDP site 289, leg 30, ∼2200 m, Ontong‐Java Plateau). Both sites have well‐established carbon isotope records for benthic foraminifera typical of the global record dominated by inventory changes. Cd/Ca ratios and carbon isotope values were averaged for the Miocene in time intervals substantially longer than estimated oceanic residence times of Cd, C, or P. Oceanic mean Cd/Ca and carbon isotopes were estimated as weighted means of the values from both sites using weighting factors based on replicating modern oceanic means; this may tend to underestimate oceanic inventories earlier than the late Miocene because of changing water mass dominance at the South Atlantic site. From these means, the oceanic Cd inventory appears relatively stable during the Miocene, while there are large changes in carbon isotope inventories. Miocene Cd inventory estimates are at least 20% lower than published estimates for Quaternary stages 1 and 2. Increasing oceanic Cd inventories over the past 10 m.y. are consistent with hypotheses of increased river fluxes in the recent geologic past. Cd/Ca differences between sites may be indicative of the extent of basin‐basin fractionation from bottom water circulation, although the validity of this comparison depends on how representative each of these two sites is through time for its respective ocean basin. The Pacific‐Atlantic Cd/Ca difference based on these two sites was larger in the late Miocene compared to the middle and early Miocene. The relationship between Cd/Ca and carbon isotope inventories and intersite gradients for these sites suggests that either oceanic phosphorus inventories or parameters related to marine organic matter composition must have been different in the Miocene than at present. Large changes in the carbon isotope balance, reflected as both positive and negative excursions in the carbon isotope inventories, occurred with little effect on Cd inventories. Changes in phosphorus fluxes associated with these carbon isotope flux changes may have been compensated for by changing deposition fluxes to other phosphorus sinks. Phosphorus inventories may have increased from the middle to late Miocene with increasingly negative oceanic carbon isotope inventories. However, confirmation of these suggestions depend on collecting more Cd/Ca (and δ13C) data throughout the Miocene oceans and on developing the application of other constraints for these interpretations.
Cryosphere/ocean interactions at the margin of the Laurentide Ice Sheet during the Younger Dryas Chron: SE Baffin Shelf, northwest Territories
Authors: Andrews J. T. , Evans L. W. , Williams K. M. , Briggs W. M. , Jull A. J. T. , Erlenkeuser H. , Hardy I.
Published: February 2008

Cores HU82‐034‐057 and HU84‐035‐008, Resolution Basin, SE Baffin Shelf, contain 200 and 450 cm, respectively, of sediment that spans the Younger Dryas chron. In both cores the interval is bracketed by 14C dates on foraminifera or molluscs. These sites were close to the margin of the late Wisconsin (Foxe) ice sheet as it flowed toward the Labrador Sea. Prior to 11 ka, both cores record moderate to high accumulations of foraminifera, relatively high del 18O values in planktonic foraminifera, and low values of detrital carbonate. The diatom and percent opal records imply occasional seasonally open water conditions. During part of the Younger Dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production, suggesting surface water conditions affected by increased sea ice and/or reduced nutrients. In addition, the Younger Dryas interval is marked by an increase in coarse sand and detrital carbonate, a decrease in total organic carbon and foraminifera, and high rates of sediment accumulation. The inferred environment during the Younger Dryas is ice‐proximal. In HU82‐034‐057, the foraminifera and other data suggest a change in conditions during the middle part of the Younger Dryas chron.
Tidal dissipation by solid friction and the resulting orbital evolution
Authors: Kaula William M.
Published: February 2008

Dissipation of tidal energy in the earth's mantle and the moon was calculated assuming a dissipation factor 1/Q constant throughout both bodies. In the mantle the dissipation varies from about 2 × 10−6/Q erg cm−3 sec−1 near the pole at the bottom of the mantle to about 0.02 × 10−6/Q erg cm−3 sec−1 near the surface. The effects of compressibility and inhomogeneity are less than 3%. In a homogeneous moon the dissipation varies from a maximum of about 0.03 × 10−6/Q erg cm−3 sec−1 near the center to a minimum of about 0.4 × 10−9/Q erg cm−3 sec−1 at the surface. A theory of orbital evolution is developed in which the disturbing function is expressed in a Fourier series with respect to time, so that the effects of variation of dissipation factor 1/Q, or lag angle ϵ, with amplitude and frequency can be examined. Comparisons with results of other authors are made.
Ocean acoustics: An evaluation
Authors: Tolstoy I. , Clay C. S.
Published: February 2008

The past two decades have seen a number of successful applications of the theory of wave propagation in stratified mediums to ocean acoustics, having the straightforward objective of comparing an observed acoustical field, in as much detail as possible, with that calculated under suitable simplifying assumptions. But this approach has intrinsic limitations due to the fact that the ocean is not the fixed, simply stratified medium assumed in the theory. It is an irregular, fluctuating medium; therefore a completely deterministic attitude toward it is impossible. It appears that future advances in our understanding of ocean acoustics must rely heavily on statistical and stochastic theory and on the considered use of modern data‐processing methods. In this spirit, we suggest a fundamentally new approach to long‐range, low‐frequency acoustic propagation experiments, consisting of spectrum‐analyzing the square of the acoustical pressure versus range for interference wavelength lines.
Quenching of metastable states of atomic and molecular oxygen and nitrogen
Authors: Hunten D. M. , McElroy M. B.
Published: February 2008

The quenching (or deactivation) of metastable states by atmospheric particles is studied by means of a combination of laboratory and observational data. The observational data come mainly from recent rocket measurements of the dayglow. The laboratory results of Kvifte and Vegard are considered in detail, and it is found that the quenching coefficients of O2 for both metastable states of atomic oxygen are very small. The strong atmospheric quenching of the O red lines ( ¹D state) is found to be produced by N2, with a coefficient approaching the gas‐kinetic value. The auroral data that gave a lower quenching rate disagree with the dayglow results and must be rejected; the difficulty is traced to contamination of low‐altitude spectra by light from higher altitudes. Only less detailed treatment of other atoms, molecules, and ions can be made; however, some conclusions are possible. Quenching coefficients seem to range from large to very small in a totally unpredictable fashion. Quenching by electrons is important in only a few special cases. The quenching of vibrationally excited O2 and N2 is slow enough so that significant concentrations can be built up, especially for N2 in aurora.
Escape of atmospheric helium by nonthermal processes
Authors: Patterson T. N. L.
Published: February 2008

Several nonthermal mechanims have been proposed to resolve the discrepancy between the rate at which helium is released from the earth's crust and the average rate of thermal escape of the gas. The various mechanisms are examined critically. Loss of its ions from the polar ionosphere appears to be the most likely mechanism controlling the escape of helium.
Equations of state and crystal structures of high‐pressure phases of shocked silicates and oxides
Authors: Ahrens Thomas J. , Anderson Don L. , Ringwood A. E.
Published: February 2008

Shock‐wave data are now available for a variety of rocks, minerals, and oxides of geophysical interest in the pressure range appropriate for the lower mantle. These data are analyzed to obtain equation‐of‐state parameters with emphasis on the shock‐induced high‐pressure phases. Of twenty‐four materials for which Hugoniot data are analyzed, all but MgO, Al2O3, and MnO2 undergo at least one shock‐induced phase change below 800 kb. Birch‐Murnaghan parameters for the raw Hugoniots, metastable Hugoniots, adiabats, and 25°C isotherms are obtained for the high‐pressure phases. On correcting the raw Hugoniot data for MgO and Al2O3 for strength effects, we find that the calculated adiabatic equations of state are in good agreement with recent ultrasonic data. The zero‐pressure densities of high‐pressure phases are obtained by constraining the adiabats calculated from the Hugoniot data such that the zero‐pressure densities and the zero‐pressure slopes of the adiabats satisfy Anderson's seismic equation of state.

Probable crystallographic structures of the high‐pressure phases are inferred from the classical laws of crystal chemistry and, in some cases, from static high‐pressure recovery experiments on analog compounds. Shock data for SiO2 (stishovite) indicate that transformation to the fluorite‐type structure (observed in TiO2) does not take place under shock, at least to ∼2000 kb. Fe2O3 probably transforms to either the perovskite or B rare earth structure with a zero‐pressure density of 5.96 g/cm³. MgAl2O4 (spinel) may transform to the CaFe2O4 structure with a zero‐pressure density of 4.19 g/cm³. Feldspars transform to the hollandite structure (density, of ∼3.85 g/cm³). Olivine‐rich rocks containing greater than 10% FeO either disproportionate to the ilmenite and rock salt structure or transform to a new post‐spinel polymorph having the Sr2PbO4 structure. Pyroxenes containing greater than 10% FeO probably transform to the ilmenite structure. High‐pressure forms of sillimanite and andalusite have calculated densities of 4.00 and 3.95 g/cm³, respectively. This probably represents disproportionation reaction products, Al2O3 + SiO2 (stishovite), which would give a density of 4.09 g/cm³. The Birch‐Murnaghan second‐order parameter ξ is nearly zero for MgO and Al2O3. 0.73 for stishovite, and ∼1 for the high‐pressure phases of the olivines and pyroxenes. The values of K′ = dK/dP are calculated along the Hugoniots and adiabats and are found to decrease at a rate of −0.5 to −1.6 cm³/g when the density is increased either by compression or by iron substitution.
The Gegenschein
Authors: Roosen Robert G.
Published: February 2008

A comprehensive review is made of the observational history of the gegenschein with emphasis on its physical parameters: size, shape, brightness, spectrum, position, and parallax. The theories that have been considered tenable until recently are critically discussed. The libration point, gas tail, and dust tail hypotheses can be disproved, whereas the heliocentric dust cloud hypothesis is consistent with all evidence available. At present the asteroid belt seems to be the most likely source of the material producing the gegenschein. A short discussion of the false zodiacal light is included.
Numerical simulation of turbulent flows
Authors: Fox Douglas G. , Lilly Douglas K.
Published: February 2008

Numerical simulation of turbulent flow is of practical importance in geophysics and is useful as a test of turbulence theory. From a basic scale analysis of turbulent flow it is shown that complete simulation is only practicable for two‐dimensional or marginally turbulent three‐dimensional flows. Some examples of such simulations are described. A more useful approach for practical applications is to directly simulate the larger scales of motion and only consider the small unresolved scales with respect to their gross statistical interactions with the larger scales. A variable eddy viscosity model has proved useful for this purpose, although better approximations can be devised. Methods of discretization and numerical integration are discussed, and it is proposed that Galerkin methods are preferred when feasible in order to avoid truncation and aliasing errors.
Paleomagnetism of deep‐sea cores
Authors: Opdyke Neil D.
Published: February 2008

This review is intended to cover the principal developments that have occurred within the last six years in the paleomagnetic study of marine sediments. Recent work utilizing the reflecting‐light microscope indicates that detrital high‐temperature Fe‐Ti oxides are probably responsible for most of the magnetic remanence in marine sediments. These minerals possess a spectrum of coercivities that makes it necessary to use alternating‐field—demagnetization techniques to isolate stable components. It is possible to use the standard magnetic stratigraphy for the last 4 m.y. of earth history derived from terrestrial lavas. Using the ages of the magnetic boundaries from this time scale it is possible by extrapolation and interpolation to better determine the ages of the major events. The ages of these events in increasing age are Jaramillo, 0.87 to 0.92 m.y.; Olduvai, 1.71 to 1.86 m.y.; Kaena, 2.82 to 2.90 m.y.; Mammoth, 3.0 to 3.085 m.y.; Cochiti, 3.72 to 3.82 m.y.; Nunivak, 3.97 to 4.14 m.y.; ‘c’ event of the Gilbert series, 4.33 to 4.65 m.y. Through the use of long cores from the central Pacific and through correlation using fossil datums, it has been possible to extend the magnetic stratigraphy back to the upper middle Miocene to magnetic epoch 5. It is concluded that very short magnetic events are probably short‐term excursions of the field and not true magnetic events. It is shown that the field of the earth averages to an axial‐dipole field within a period of 27,000 years and that the field over the last two million years has acted as a geocentric axial dipole. The evidence shows that when reversals of the dipole occur, the values of the reversed inclination are not significantly different from the normal values. The use of magnetic stratigraphy in marine geology has opened up a new era in study of sedimentary processes and evolution of marine organisms.
Solar energetic particles and the configuration of the magnetosphere
Authors: Lanzerotti L. J.
Published: February 2008

Since the original study of PCA riometer measurements, solar energetic particles have been increasingly employed as test particles in the magnetosphere. The characteristics of the access of these particles to the magnetosphere are studied to determine if substantial connection exists between the earth’s dipole field and the solar‐generated interplanetary field. Satellite measurements over the polar caps indicate strong north pole‐south pole proton flux asymmetries that may be related to existing interplanetary particle anisotropies. High‐latitude measurements indicate significant pseudo‐trapping of the solar fluxes on closed magnetospheric field lines. Particle flux comparisons between satellites in interplanetary space and within the magnetosphere suggest that the particle access point is probably not greater than 1000 RE (earth radii) behind the earth in the magnetotail.
Rotation of solid bodies in the solar system
Authors: Peale S. J.
Published: February 2008

The effects of elastic distortion, nonprincipal axis rotation, precessing orbits, and internal dissipation on the rotation of a solid solar system body, which is in the gravitational field of an exterior body, are relatively easily analyzed by a Hamiltonian theory developed here. Examples of applications include the Chandler wobble, wobble of the moon, spin‐orbit coupling, generalized Cassini laws, and tidal evolution.
Aeronomy of the lower atmosphere of Mars
Authors: Hunten Donald M.
Published: February 2008

Recent models and observations relevant to Martian aeronomy are discussed. The stability of the CO2 atmosphere against photodissociation into CO and O2 has finally been accounted for. The basic mechanism is catalysis by odd hydrogen, aided by very rapid downward mixing, photolysis of H2O2, or some combination. The low abundance of ozone at low latitudes is readily explained, and its higher abundance in cold regions is accounted for by the freezing out of H2O, H2O2, and possibly HO2. The system seems likely to be unstable, and major changes of the CO and O2 abundances may be expected on a time scale of 1 year.
Developments in seismic source theory
Authors: Archambeau Charles
Published: February 2008

The basic stimulus for the development of a quantitative theory of seismic or earthquake sources is simply the desire to achieve some depth of understanding of this complex phenomenon. Beyond this intrinsic desire to unify and understand, a variety of applications of that understanding can be made which have considerable practical importance.

In particular, the most important current applications of seismic source theory are to earthquake‐explosion discrimination and to earthquake prediction and control. Indeed, perhaps the greatest stimulus to theoretical work in seismic source theory in recent years has come from the diverse, and sometimes contradictory, observational data obtained in studies related to these particular problems. Thus while a large number of empirical relationships have been defined from the data, it is clear that a general theoretical framework is needed to unify the empirical results and to provide predictions outside the range and resolution of current observations as well as to provide deeper understanding of the meaning of the observations.
Water quality
Authors: Hem John D. , Steele Timothy Doak
Published: February 2008

In this report we will attempt to highlight significant contributions in the broad area of water quality over the quadrennium 1971–1974. The diversity of subject areas that might be considered within this topic heading and the large volume of published research results necessitated the selection of representative indicator contributions made during this period. The references that are cited are believed to be indicative of general trends in research and of the more important developments during this period. Many additional citations could have been made.
The West Antarctic Ice Sheet: Instability, disintegration, and initiation of Ice Ages
Authors: Hughes T.
Published: February 2008

An ice age model is proposed in which glacial‐interglacial global climatic cycles are controlled by interactions between the cryosphere, hydrosphere, and atmosphere in the Atlantic environment. In the model, climatic change results from instabilities which develop in the snowfields or ice sheets of North America, Europe, and Antarctica. Disintegration of the West Antarctic ice sheet (that portion of the Antarctic ice sheet lying in the western hemisphere) initiates a chain of events which culminates in a global ice age. Ten independent bodies of data can be interpreted as evidence that the West Antarctic ice sheet has been and is disintegrating. The dynamics of the Ross Sea ice drainage system of Antarctica is examined to determine what controls disintegration and recovery of the West Antarctic ice sheet. It is concluded that disintegration is controlled by ice streams which drain the inherently unstable West Antarctic ice sheet and recovery is controlled by outlet glaciers which drain the inherently stable East Antarctic ice sheet. Glacial stability in both cases is determined by the degree of coupling between the ice sheet and its bed. Ice drainage channels develop when this coupling is weakened normal to the margin of an ice sheet and can lead to surges in ice streams or outlet glaciers. Ice shelves develop when this coupling is weakened parallel to the margin of an ice sheet and can lead to a rapid grounding line retreat of floating ice tongues or ice shelves. An inflection maximum on the ice sheet surface migrates inland during a surge and migrates seaward after the surge is spent. A transition zone between the ice sheet and the ice shelf widens during a grounding line retreat inland and narrows during a grounding line advance seaward. Inflection line and grounding line migrations combine to give the ice sheet a concave surface during retreat and a convex surface during advance. A train of surging segments in an ice stream lowers the ice sheet in stages, creating a terraced ice stream surface which causes rapid discontinuous retreats of the grounding line. Rapid glacial recovery following a surge can truncate the advancing ice sheet‐ice shelf boundary. Today at least one West Antarctic ice stream is terraced and at least one East Antarctic outlet glacier is truncated in the Ross Sea ice drainage system. If this condition is general, the West Antarctic ice sheet is disintegrating along the Siple Coast as a result of surging ice streams and is recovering along the Transantarctic Mountains as a result of thickening outlet glaciers. The competition between these processes will provide a critical test of the ice age model, which predicts that progressive disintegration of the West Antarctic ice sheet results in progressive growth of adjacent parts of the East Antarctic ice sheet.
Cosmic ray propagation in interplanetary space
Authors: Völk Heinrich J.
Published: February 2008

The validity of the test particle picture and the approximation of static fields, as well as the spatial diffusion approximation, are discussed in a general way before specific technical assumptions are introduced. It is argued that the spatial diffusion equation for the intensity per unit energy has a much wider range of applicability than the kinetic (Fokker‐Planck) equation it is derived from. This gives a strong weight to the phenomenological propagation theory. Its general success (and possible failure at small energies) for the modulation of galactic cosmic rays and solar events is described. Apparent effects like the ‘free boundary’ are given disproportionate weight, since through them the connection to the detailed plasma physics of the solar wind is established. Greatest attention in detail is paid to the pitch angle diffusion theory. A general theory is presented that removes the well‐known secularities of the quasi‐linear approximation. The possible breakdown of any pitch angle diffusion theory at very small energies is perhaps connected to the observed ‘turn up’ of the spectrum at low energies. A first attempt to derive the spatial dependence of the diffusion coefficient in the solar cavity, using such a divergence free scattering theory, is described and compared with recent observations out to 5 AU.
Crystal chemistry of silicate minerals of geophysical interest
Authors: Papike J. J. , Cameron Maryellen
Published: February 2008

Recent crystal chemical research on rock‐forming silicate minerals has focused on the accurate refinement of room temperature and high‐temperature crystal structures. The data are of sufficient accuracy to allow detailed examination of structural topology and intracrystalline equilibria and to provide some insight into exsolution phenomena, chemical bonding, and phase transitions. This paper summarizes the results of recent research on olivines, humites, garnets, aluminosilicates, pyroxenes, pyroxenoids, amphiboles, micas, silica minerals, feldspars, feldspathoids, and scapolites.