bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of reactive nitrogen oxides (NOy) within and above a tropical forest canopy in the wet season
Authors: Bakwin Peter S. , Wofsy Steven C. , Fan Song‐Miao
Published: February 2008

Measurements of ambient concentrations of reactive nitrogen oxides (NOy) were made in the Amazon rain forest, near Manaus, Brazil, contiuously at 39 m (above the canopy), and on several days and nights at 19 m (within the canopy). Concentrations were very low, typically 100–700 pptv, except for brief periods when up to 5000 pptv of NOy was observed, indicating polluted air from the urban area of Manaus. The forest was a net sink for NOy with the NOy, flux = −7.6 (±5.0) × 109 molecules cm−2 s−1 in unpolluted periods, even though soils emitted NO at a significant rate (8.9±1.5 × 109 molecules cm−2 s−1). The deposition rate for NOy appeared to be much larger during the daytime than at night, suggesting that uptake was controlled either by plant processes (stomatal opening) or by supply of reactive components of NOy (e.g., HNO3) during the daytime. Implications for regional and global atmospheric chemistry are discussed.
The atmospheric sulfur cycle over the Amazon Basin: 2. Wet season
Authors: Andreae M. O. , Berresheim H. , Bingemer H. , Jacob D. J. , Lewis B. L. , Li S.‐M. , Talbot R. W.
Published: February 2008

We determined the fluxes and concentrations of atmospheric sulfur species at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of hydrogen sulfide (H2S) were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmospheric sulfur cycle over the Amazon Basin. Using the gradient‐flux approach, we estimated the flux of DMS at the top of the tree canopy. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values. The sulfate concentration in rainwater, on the other hand, was lower by about a factor of 5 during the wet season. Due to the higher precipitation rate, however, the wet deposition flux of sulfate was not significantly different between the seasons. The measured fluxes and concentrations of DMS, H2S, and SO2 were consistent with a model describing transport and chemistry of these sulfur species in the boundary layer. The concentrations of aerosol and the sulfate deposition rate, on the other hand, could only be explained by import of significant amounts of marine and anthropogenic sulfate aerosol into the Amazon Basin.
Amazon Basin ozone and aerosol: Wet season observations
Authors: Gregory Gerald L. , Browell Edward V. , Warren Linda S. , Hudgins Charles H.
Published: February 2008

The tropical environment is recognized as having a major impact on global tropospheric chemistry. In particular, the Amazon Basin, with its emissions and an abundance of moisture and sunlight, provides favorable conditions for the production of hydroxyl radical and subsequent chemical and photochemical reactions which generate or consume key atmospheric trace species. Wet season convection provides a mechanism for efficient mixing between the surface and the free troposphere, and thus provides the means for integrating Amazon Basin events into the global circulation processes. The data show that the wet season Amazon Basin is an effective sink for ozone and a net source for aerosols. Mixed layer ozone at 150‐m altitude averaged 8.5 ppbv compared to about 18 ppbv at 3‐km altitude. In addition, a negative ozone gradient (decreasing value to the surface) was observed within the mixed layer. The averaged wet season mixed layer ozone was about 7 ppbv lower than observed during the dry season. This is attributed to the enhanced convective activity associated with the wet season and the change in mixed layer photochemistry from net ozone production (dry season) to a net destruction (wet season). The net sink characteristics of the wet season mixed layer are seen throughout the troposphere of the Amazon Basin in that ozone (3‐ to 4‐km altitude) is typically 15–25 ppbv as compared to dry season values of 30–35 ppbv. In terms of the aerosol source characteristics of the Amazon Basin, mixed layer aerosols (0.1‐ to 0.4‐μm diameter) are a factor of 5–10 higher than observed in the troposphere with mixed layer values of 100–200 aerosols/cm3. Analyses of both tropospheric and mixed layer aerosol samples show aerosols which are multisource. Tropospheric samples have size distributions which are trimodal and show modes at aerosol diameters which suggest the aerosols are (1) of lifetimes <1 hour, (2) of lifetimes of days, and (3) mechanically generated elements (e.g., wind‐blown dust). Mixed layer data show two of the three modes with no mode which represent aerosols with lifetimes of days.
Estimates of daily rainfall over the Amazon Basin
Authors: Martin David W. , Goodman Brian , Schmit Timothy J. , Cutrim E. C.
Published: February 2008

Five geostationary satellite rain estimation techniques were tested over Amazonia. Individually, the techniques explained ¼ to ⅓ of the variance of daily gage rainfall. Based in large part on cost, one technique, which involves a nonlinear relation in temperature, was selected to provide a mapping of daily Amazonia rainfall between May 6 and 12, 1987. Accumulated over the 7 days, rainfall by this technique averaged 40 mm. It varied from zero in the southeast to more than 150 mm in the northwest. To the southwest the predominantly convective pattern of the rain image was overlaid by a streakiness, implying some baroclinic influence. In maps combining gage observations with satellite estimates, rainfall varied significantly from day to day. Only over the largest scale did a trend emerge: a tendency for rain to withdraw from south to north.
Third‐generation FAGE instrument for tropospheric hydroxyl radical measurement
Authors: Chan C. Y. , Hard T. M. , Mehrabzadeh A. A. , George L. A. , O'Brien R. J.
Published: February 2008

We have constructed a single‐stage, frequency‐doubled, copper vapor laser‐pumped dye laser to be used in the measurement of atmospheric hydroxyl radical concentrations. This laser can be tuned to either the 1←0 or 0←0 vibrational transition in the electronic transition 2Σ←2Π. A new photon counting instrument is used for HO fluorescence detection. Theoretical and experimental studies of instrument performance show better sensitivities and reduced photolytic interferences than have been possible with previous systems based upon Nd:YAG pumping.
The space shuttle's impact on the stratosphere
Authors: Prather Michael J. , García María M. , Douglass Anne R. , Jackman Charles H. , Ko Malcolm K. W. , Sze Nien Dak
Published: February 2008

Launch of spacecraft using solid rocket motors leads to release of gaseous and particulate matter in the stratosphere. Concern over these emissions, particularly chlorine, goes back to the Climatic Impact Assessment Program (Hoshizaki, 1975). The buildup of these exhaust products and their perturbation to stratospheric ozone is followed with two‐ and three‐dimensional atmospheric chemical transport models. Chlorine enhancements due to the current rate of shuttle launches is small, on average less than 0.6% above the current background. Other gases emitted from the solid rockets appear to have even smaller global effects, although the impact of particulate alumina remains uncertain.
K and M changes in close lightning ground flashes in Florida
Authors: Thottappillil Rajeev , Rakov Vladimir A. , Uman Martin A.
Published: February 2008

Electric field changes produced by K and M processes in Florida lightning ground flashes at distances within 12 km are analyzed and compared. The geometric‐mean time durations were similar: 0.7 ms for 135 K changes and 0.9 ms for 80 M changes. The geometric‐mean time intervals between events were dissimilar: 12.5 ms for 93 K change intervals and 2.1 ms for 48 M change intervals. Our geometric mean K change interval is about twice the median value observed by Kitagawa et al. (1962) in New Mexico who used a somewhat different measurement technique, while our geometric mean M change interval is about one‐third the New Mexico median value although Kitagawa et al. (1962) apparently excluded from their statistical data those M components occurring within 15 ms of the return stroke initial peak field, and we included these. The K electric field changes were not always simple ramps superimposed on the slower interstroke J or final F field changes, but, rather, could be grouped into four general waveshape categories. All M field changes had relatively similar hooked shapes. We argue that the hypothesis proposed by Kitagawa et al. (1962) that K and M processes are essentially the same physical phenomenon is not supported by our data, although it cannot be positively ruled out; and, additionally, that the conclusion of Kitagawa and Brook (1960) that the net interstroke field change (J change) is essentially the sum of the individual K changes is also not supported by our data. Further, our data suggest that there is a significantly higher upper limit for the moment change associated with K processes in ground flashes than the 1 to 2 C‐km reported by Brook and Kitagawa (1960) and Ogawa and Brook (1964).
Soil fluxes and atmospheric concentration of CO and CH4 in the northern part of the Guayana Shield, Venezuela
Authors: Scharffe Dieter , Hao Wei Min , Donoso Loreto , Crutzen Paul J. , Sanhueza Eugenio
Published: February 2008

Soil fluxes and atmospheric concentrations of CH4 and CO were measured in a scrub grass savanna in Venezuela, during October 1988. Soil flux measurements were also made in a nearby semideciduous forest. Emission of CH4 was observed from the “dry ” savanna soils; emissions do not show any significant trend with the time of day and have an average of 3.5±5.0×1010 molecules cm−2 s−1. CO fluxes show a strong diurnal variation, with net emission during daytime and consumption during nighttime. Twenty‐four‐hour integrated soil fluxes give a small net emission of CO of 5.6×109 molecules cm−2 s−1 this result contrasts with previous net sink estimates given in the literature. Forest soils consume both CH4 and CO at rates of −5.0×1010 and −2.4×1011 molecules cm−2 s−1 respectively. Therefore, long‐range forest degradation should produce an increase in the emission of CO and CH4 from these tropical soils. At the savanna site, higher atmospheric concentrations of CH4 and CO were observed during nighttime. Minimum concentrations, representative of boundary layer conditions, were observed during hours of high solar irradiation with values of 1.78±0.04 ppm and 224±61 ppb for CH4 and CO, respectively. Using the methane concentration increase inside the nocturnal mixing height, a total methane source of 4.9×1011 molecules cm−2 s−1 from the surface was calculated, showing that a significant dispersed source, likely from termites and/or small tracts of flooded soils, is present in the tropical savanna region. Extrapolating this value to the world savanna regions, an emission of 61 Tg CH4 is estimated, this is about 10% of the global source of methane. From chamber measurements a distinct nighttime soil consumption of CO was observed; however, the concentration remained fairly constant during the night, indicating a surface source of CO of the order of 5×1010 molecules cm−2 s−1. Even though anthropogenic sources cannot be ruled out completely, termites and vegetation emission are, most likely, the dispersed sources of CO in the savanna region.
Precipitation in the southern High Plains: Meteorologic and isotopic features
Authors: Nativ Ronit , Riggio Robert
Published: February 2008

The meteorologic characteristics and isotopic composition of precipitation events in the Southern High Plains, Texas and New Mexico, were monitored during 1 full year to estimate the natural recharge potential of the region's major aquifer. Precipitation events during spring and summer derive their moisture from the Gulf of Mexico. Temperature effects account for the isotopically enriched rainwater during this period, offsetting possible amount effects. During fall and winter, precipitation events acquire moisture from the eastern Pacific Ocean. Temperature as well as continental and altitude effects produce isotopically depleted precipitation during this period. Precipitation during events throughout the year that lasted for several days became depleted in both chloride concentration and isotopic composition, thus displaying a front effect.
Paleoceanography of the Cretaceous/Tertiary Boundary Event: Inferences from stable isotopic and other data
Authors: Zachos J. C. , Arthur M. A.
Published: February 2008

We report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction, whole rock, and benthic foraminifers, CaCO3and coarse fraction percentage determinations, and trace element (Sr) analyses on carbonate constituents across the Cretaceous/Tertiary (K/T) boundary in Deep Sea Drilling Project (DSDP) sites 47.2, 356, 384, and 577 and compare them with published results from K/T boundary sections in other DSDP sites. We used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study. The ∂18O data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late Maestrichtian followed by somewhat fluctuating temperatures in the early Paleocene. However, there is no indication of either a significant warming or cooling at or following the K/T boundary. Several sites do exhibit somewhat heavier ∂18O values by about 0.5‰ across the boundary, which might suggest a 2‐3°C cooling at most. However, we interpret these somewhat heavier ∂18O values as reflecting slightly better preservation of ∂18O of carbonate constitutents in relatively clay‐rich intervals (e.g., lower diagentic potential) characteristic of the K/T boundary. The ∂13C values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary. The surface water and deepwater ∂13C values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest Paleocene are consistent with a major decrease in productivity across the K/T boundary. The decrease in CaCO3accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters. The low‐productivity episode lasted at least 1 m.y. beyond the K/T boundary crisis, suggesting that hypothesized catastrophic events alone, such as impact of an apollo object, are not the only explanation for the observed long‐term decrease in productivity. There is also an indication in the ∂13C curves from several sites that the surface water ∂13C decrease began in the latest Maestrichtian, suggesting that the decrease in productivity may have been independent of a hypothesized impact event.
Reducing power of ferrous iron in the Archean Ocean, 1. Contribution of photosynthetic oxygen
Authors: François Louis M. , Gérard Jean‐Claude
Published: February 2008

A quantitative model of the Archean ocean is developed in order to estimate the oxidation rate of dissolved ferrous iron, a key process for the deposition of banded iron formations. The continuity equation including chemical reactions and vertical transport is solved for O2 and Fe II. The oxidation rate depends on the oceanic pH profile, which is calculated as a function of the atmospheric CO2 pressure. In this first part, the oxidation due to the reaction with photosynthetic oxygen is considered. The results are presented as a function of the oxygen concentration in the mixed layer which was varied between 10−10 and 10−6 mol kg−1. It is shown that this Fe II oxidation by O2 is very efficient and that relatively low O2 levels are required for the oxidation rate to be limited by upward transport of iron to the surface ocean. Possible evolutionary paths for the Archean ocean‐atmosphere system are discussed by an analysis of the balance of the iron input flux.
Diatom record of Late Quaternary climatic change in the eastern equatorial Atlantic and tropical Africa
Authors: Pokras Edward M.
Published: February 2008

Over the last 160,000 years, diatom productivity in the equatorial Atlantic has been high during glacial stages 2, 4, and 6, and moderate during parts of substages 5b and 5d (approximately 96,000 and 117,000 years B.P.). Productivity of diatoms is particularly low in substage 5e and in the middle of stage 1. Higher productivity implies more vigorous trade winds during glacial intervals, leading to stronger upwelling and enhanced lateral advection of surface waters. The influence of the Benguela Current near the equator was strongest during stage 2; a separate regime of coastal upwelling may have existed in the Gulf of Guinea at this time. Upwelling and advection may not always respond to the same forcing as sea surface temperature. Results support the hypothesis that Ethmodiscus rex oozes result from high diatom productivity. Runoff from the Zaire and Niger rivers was highest at the stage 2/1 transition and just prior to the stage 6/5 transition, due to intensification of the African Monsoon. Several other times of increased runoff are indicated. Periods of increased surface water circulation in the eastern equatorial Atlantic appear to correspond to times of aridity in tropical Africa. Conversely, intervals of decreased circulation in the eastern equatorial Atlantic coincide with times of humidity in tropical Africa. Precessional forcing of continental climate is suggested; however, precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here. Influx of Antarctic Bottom Water to the eastern equatorial Atlantic has been insignificant throughout the last 160,000 years.
The δ13C of equatorial Atlantic surface waters: Implications for Ice Age pCO2 levels
Authors: Curry William B. , Crowley Thomas J.
Published: February 2008

Carbon isotopic records of nutrient‐depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pCO2 levels. The best records of nutrient‐depleted δ13C are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical Atlantic Ocean. We have produced a composite, stacked Globigerinoides sacculifer δ13C record from the equatorial Atlantic, which exhibits significant spectral power at the 100,000‐ and 41,000‐year Milankovitch periods, but no power at the 23,000‐year period. Similar to the record presented by Shackleton and Pisias [1985], surface‐deep ocean Δδ13C produced with the G. sacculifer record leads the δ18O ice volume record. However, the glacial‐interglacial amplitudes of Δδ13C differ between our record and Shackleton and Pisias [1985] record. Although large changes in Δδ13C occur in the equatorial Atlantic during early stages of the last three glacial cycles, surface‐deep Δδ13C at glacial maxima (18O stage 2, late stage 6, and late stage 8) was only about 0.2‰ greater than during the subsequent interglacial. Our results imply that nutrient‐driven pCO2 changes account for about one third of the pCO2 decrease observed in ice cores, and consequently, Δδ13C should not be used as a proxy pCO2 index. Enough variance in the ice core pCO2 records remains to be explained that conclusions about pCO2 and ice volume phase relationships should also be reexamined. As much as 40 ppm pCO2 change still has not been accounted for by models of past physics and chemistry of the ocean.
Benthic isotope evidence for changes of the Mediterranean outflow during the Late Quaternary
Authors: Zahn Rainer , Sarnthein Michael , Erlenkeuser Helmut
Published: February 2008

A suit of sediment cores close to and south of the Strait of Gibraltar (12°‐36°N, 500–2800 m water depth) were analyzed for stable isotopes in epibenthic foraminifers Cibicidoides wuellerstorfi and Planulina ariminensis. During peak glacial times, the data exhibit higher δ13C values of up to 1.6‰ at intermediate depths near the Strait of Gibraltar (36°N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38°N (in Duplessy et al. [1987]). Thus, the distribution pattern of δ13C provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the δ18O fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5°C. During glacial times and during Termination I the maximum δ13C values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and vice versa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.
Changes in the distribution of δ13C of deep water ΣCO2 between the Last Glaciation and the Holocene
Authors: Curry W. B. , Duplessy J. C. , Labeyrie L. D. , Shackleton N. J.
Published: February 2008

Carbon isotopic measurements on the benthic foraminiferal genus Cibicidoides document that mean deep ocean δ13C values were 0.46 ‰ lower during the last glacial maximum than during the Late Holocene. The geographic distribution of δ13C was altered by changes in the production rate of nutrient‐depleted deep water in the North Atlantic. During the Late Holocene, North Atlantic Deep Water, with high δ13C values and low nutrient values, can be found throughout the Atlantic Ocean, and its effects can be traced into the southern ocean where it mixes with recirculated Pacific deep water. During the glaciation, decreased production of North Atlantic Deep Water allowed southern ocean deep water to penetrate farther into the North Atlantic and across low‐latitude fracture zones into the eastern Atlantic. Mean southern ocean δ13C values during the glaciation are lower than both North Atlantic and Pacific δ13C values, suggesting that production of nutrient‐depleted water occurred in both oceans during the glaciation. Enriched 13C values in shallow cores within the Atlantic Ocean indicate the existence of a nutrient‐depleted water mass above 2000 m in this ocean.
Radiocarbon‐based chronology for the 18O/16O record for the Last Deglaciation
Authors: Broecker W. S. , Oppo D. , Peng T. ‐H. , Curry W. , Andree M. , Wolfli W. , Bonani G.
Published: February 2008

A radiocarbon‐calibrated box model for today's ocean suggests that a lag of about 1750 years should exist between the arrival of the midpoint of the deglaciation 18O signal in the deep Atlantic Ocean and its arrival in the deep Pacific Ocean. In order to assess the actual lag, we have carried out accelerator radiocarbon measurements on two cores from the Atlantic Ocean and one core from the Pacific Ocean. Although the results are not definitive, there is a suggestion that the actual time lag was about 1000 years.
Ocean circulation and atmospheric CO2 changes: Coupled use of models and paleoceanographic data
Authors: Lyle Mitchell , Pisias Nicklas
Published: February 2008

We have perturbed a simple model of oceanic circulation in a series of sensitivity tests to determine how circulation changes associated with the last glacial maximum could affect observable or potentially observable paleoceanographic parameters. Ultimately, we want to use such paleoceanographic data to construct models of glacial ocean circulation. We have found that the different circulation patterns that we imposed in our sensitivity tests have dramatically different responses for the distribution of PO4, O2, and ∂13C contents of the oceans. They also produce different levels of low‐latitude productivity. By comparing the coupled responses of several of these paleoceanographic parameters to the responses from the sensitivity tests it is possible to constrain the possible glacial circulation scenarios to a relatively small number. We give, as one example, a case where intermediate turnover is significantly higher than the present and deep ocean turnover has dropped. In addition, exchange of waters between the intermediate‐ and high‐latitude surface ocean is much lower. The result of this scenario is an atmosphere with 60 ppm lower atmospheric CO2, low latitudes with about 40% higher productivity, and a change in the planktic/benthic ∂13C contrast of about 0.3‰. When we compare our model to other independent paleoceanographic data, we find that the major point of disagreement is in the distribution of surface water ∂13C in the Antarctic region. We believe that somewhat more complex box models which take open system effects into account will resolve this discrepancy.
Late Quaternary paleoceanography of the South China Sea: Glacial‐interglacial contrasts in an enclosed basin
Authors: Wang Luejiang , Wang Pinxian
Published: February 2008

The sea surface paleotemperature of the South China Sea (SCS) is estimated quantitatively, based on the quantitative analysis of planktonic foraminiferal faunas recovered from piston cores V36‐06‐3, V36‐06‐5, and SO49‐KL8 on the northern continental slope. The results lead to a reconstruction of the history of paleocirculation patterns during the last 200,000 years. The postglacial and interglacial transbasinal circulation pattern was replaced by a semienclosed basin flow pattern during glacial episodes. Lowered sea level transformed the SCS into a semienclosed basin with the only passageway to the open ocean in its northeastern corner. The East Asian Monsoon, which governs circulation patterns in the SCS both today and during the late Quaternary, created both clockwise (summer) and counterclockwise (winter) surface gyres during glacials. The inflow of tropical surface water‐masses from both the Pacific and Indian oceans decreased or was completely cut off from this marginal sea, causing a greater decrease in glacial sea surface temperature than in the open ocean of the same latitude. Inferred increased influence of Pacific Temperate Waters and decreased influence of Tropical‐Subtropical Waters are confirmed by changes in the planktonic foraminiferal assemblages. Glacial‐interglacial fluctuation in sea surface temperature (SST) (6.8–9.3°C for winter and 2–3°C for summer), as well as the seasonality (4–6°C for postglacial and interglacials and 9–10°C for glacials), are much greater than the adjacent open western Pacific, reflecting the amplification of the climatic signal in the marginal sea.
Nonlinear response of Pliocene climate to orbital forcing: Evidence from the eastern equatorial Pacific
Authors: Hagelberg Teresa K. , Pisias Nicklas
Published: February 2008

A high‐resolution radiolarian record from the eastern equatorial Pacific is used to examine paleoceanographic events during the Pliocene, from 1.8 to 4.9 Ma. These data provide a means to evaluate the response of the equatorial Pacific to the onset of northern hemisphere glaciation near 2.47 Ma and to the closure of the Isthmus of Panama near 3.2 Ma. Responses are recorded both as long‐term trends and as variations within the Milankovitch band (104 to 105 years). Radiolarian‐based sea surface temperature (SST) estimates indicate a mean cooling from lower to upper Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation, and no abrupt changes are observed before or after the closure of the isthmus. Spectral and cross‐spectral analyses of this SST time series indicate concentrations of variance within the precession (23‐kyr) and obliquity (41‐kyr) bands in several but not all time intervals. Variance is commonly concentrated at lower frequencies. Cross spectral analysis of SST time series and calculated orbital variations indicates that the SST record is not coherent with, and therefore not linearly related to, orbital variations. Detailed time series analysis of the SST and δ18O time series indicates the absence of a direct linear relationship but rather the presence of a strongly nonlinear relationship between Pliocene climatic variables and Earth's orbit. High coherence is seen between the amplitude of the 23‐kyr component of SST and the amplitude modulation of precession. The amplitude modulation of the 41‐kyr component of the SST record is dissimilar to the amplitude modulation of obliquity but is extremely similar to and coherent with the amplitude of the 23 kyr component of SST. The amplitude modulations of SST and δ18O at a range of frequency bands have the same features, features that roughly follow the modulation of precession. This suggests a strongly nonlinear response of equatorial Pacific SST and planktonic δ18O to orbital forcing in the Pliocene. Such a response, extending over a number of frequency bands, has not previously been seen in a paleoclimatic data set but may be consistent with proposed models describing paleoclimatic variability. Although the reasons for this response are still unclear, it is evident that strong nonlinearities in climate are present during this time.
Tracers of ocean paleoproductivity and paleochemistry: An introduction
Authors: Elderfield H.
Published: February 2008

New developments in ocean paleoproductivity and paleochemistry have involved the application of tracers that record seawater composition, that document sedimentary fluxes, and that may be used to infer oceanic processes. These include the use of Cd/Ca and Ba/Ca ratios in benthic foraminifera, rare earth element patterns of chemical sediments, uranium‐series nuclides in carbonate sediments and studies of the origins of chemical fluxes and anomalies in sedimentary profiles.
Meltwater cooling of the Gulf of Mexico: A GCM simulation of climatic conditions at 12 ka
Authors: Maasch Kirk A. , Oglesby Robert J.
Published: February 2008

Marine and terrestrial evidence indicate that at least two major glacial meltwater discharges into the Gulf of Mexico occurred during the last deglaciation. Based on radiocarbon dates, the time interval between these two meltwater events appears to coincide with the Younger Dryas, roughly 10–11 ka. We have used an atmospheric general circulation model, the National Center for Atmospheric Research Community Climate Model version 1 (NCAR CCM1), to investigate possible effects of reduced Gulf of Mexico sea surface temperatures (SST), assumed due to the meltwater discharges, on regional and hemispheric climates. We conducted six numerical experiments: (1) perpetual January (wintertime) and (2) July (summertime) sensitivity experiments using present‐day boundary conditions except for an imposed gulfwide SST cooling of 6°C; (3) perpetual January and (4) July control simulations using 12 ka boundary conditions for continental ice, sea surface temperature (no reduction due to meltwater cooling), sea ice, and radiative forcing; and (5) perpetual January and (6) July 12 ka simulations with a 6°C SST cooling of the Gulf of Mexico. In both of the January simulations with a cooled Gulf of Mexico, a significant reduction in the North Atlantic storm track intensity occurred, with higher surface pressures over the North Atlantic indicating a reduction of the Icelandic low. In the January 12 ka control there are large changes in surface pressure over the Atlantic Ocean and Greenland relative to the present‐day control. However, these changes are almost completely offset when the Gulf of Mexico is cooled. In the July simulations with a cool Gulf of Mexico, the Atlantic subtropical high is strengthened and expanded to the west. This results in stronger trade winds across the Caribbean and southwest Atlantic. There is also an enhanced monsoonal flow of moisture over northwest Mexico, and the American southwest and Rocky Mountain regions, leading to increased precipitation. Unlike the winter situation, in summer the Gulf of Mexico cooling serves to enhance the effects of the other 12 ka boundary conditions.
A statistical analysis of the generation of microseisms
Authors: Hasselmann K.
Published: February 2008

Theories of the origin of microseisms have in the past generally been expressed in terms of the Green functions of the elastic systems considered. An alternative approach based on spectral transfer functions and the local energy‐balance equation of the seismic field is proposed. The method enables a rigorous analysis of the statistical aspects of the problem, which could be treated only approximately and under restrictive conditions in terms of the far‐field representations used previously. Three suggested origins of microseisms are considered: (1) the action of ocean waves on coasts, originally proposed by Wiechert; (2) atmospheric pressure fluctuations, as suggested by Gherzi, Scholte, and others; and (3) nonlinear interactions between ocean waves as proposed by Longuet‐Higgins. In all cases appreciable microseisms are generated only by Fourier components of the random exciting fields that have the same phase velocities as free modes of the elastic system. The effect of pressure fluctuations associated with turbulence in the atmosphere is found to be negligible. The theory for Wiechert's and Longuet‐Higgins' mechanisms is in good agreement with recent measurements by Haubrich et al.
Theory of two‐dimensional mountain waves
Authors: Krishnamurti T. N.
Published: February 2008

The governing equations for the steady two‐dimensional mountain wave problem are presented with both heightzand entropysas vertical coordinates. Some intrinsic advantages of usingsare discussed. A formal scaling of the equations for a wide mountain is shown. Some of the classical problems in isothermal atmospheres and multilayer models are reviewed. A discussion of the time‐dependent linear problem is presented as a problem of wave motion on an interface. The final part of the paper contains a brief review of the recent numerical work on the steady two‐dimensional problem. Some suggestions for further work in theoretical and numerical finite amplitude problems are made.
Propagation of a compressional pulse in a layered solid
Authors: Pekeris C. L. , Alterman Z. , Abramovici F. , Jarosch H.
Published: February 2008

In this investigation we solve the problem of propagation of a compressional pulse in a solid half‐space which is overlain by a solid layer of different properties. The point source is situated at the depth ½H, H denoting the thickness of the layer. Theoretical seismograms of the vertical displacement w at the surface are evaluated out to ranges r = 20H. The solution is obtained by the exact ray theory. The displacement Wo due to the source was assumed to have a shape which at large distances reduces to a sawtooth. The once‐reflected waves from the interface, PP and PS, are strongly marked. The Rayleigh wave is already recognizable at r = 5H and is fully developed at r = 20H. The method of ‘ray theory’ was applied here far into the region where the normal mode theory converges well. The theoretical seismograms are illustrated. The properties assumed for the layer (1) and for the half‐space (2) are λ1 = μ1 μ2 = 2μ1cs2 ≡ c2 = 1.1cs1 ≡ 1.1c1cp2 > cp1 > c2 > c1
Propagation of an SH‐torque pulse in a sphere
Authors: Alterman Z. , Kornfeld P.
Published: February 2008

An exact solution is obtained for the displacement of the surface of a uniform solid sphere of radius a due to an impulsive SH‐torque pulse from a point source situated at a distance b from the center. The duration of the source was varied from 0.05a/c to 0.5a/c, keeping the time variation of the torque such that the surface displacement stays finite when the time tends to infinity. c is the shear‐wave velocity. Theoretical seismograms have been computed at several distances from a surface source and from buried sources at b = 7a/8, a/2, 0.3a, and 0. Arrival times of reflected pulses coincide with arrival times of reflected rays, where the latter are obtained according to geometrical optics. The solution for buried sources reveals diffracted pulses. They are connected with the two cases in which reflected rays are disallowed by geometrical optics: (1) owing to distance of observer from source and (2) owing to depth of source. In these cases the arrival time as obtained from the ‘steepest descent’ analysis of Jeffreys and Lapwood is complex. The real part of the complex arrival times lies in the time interval during which diffracted pulses occur. There are no diffracted pulses for the surface source.
Pressure and CO2 content of the Martian atmosphere: A critical discussion
Authors: Chamberlain Joseph W. , Hunten Donald M.
Published: February 2008

This article reviews the principal techniques that have been used to estimate the surface pressure on Mars. The basic physics behind each technique is outlined and illustrated with simplified examples. An attempt is made to evaluate the reliability of each technique and its use to date. The problem is outlined in section 1; the older techniques (polarimetry and photometry) are examined in section 2; the spectroscopic method, wherein at least two CO2 absorption bands are used to derive both the CO2 abundance and the surface pressure, is reviewed in section 3. The conclusions, summarized in section 4, are principally (1) that the polarimetric and photometric techniques are not nearly so reliable as has been generally supposed, and (2) that, although the spectroscopic method should ultimately settle the problem, the data thus far available do not yield good accuracy in either the CO2 content or the total pressure.
Feynman diagrams and interaction rules of wave‐wave scattering processes
Authors: Hasselmann K.
Published: February 2008

The energy transfer due to weak nonlinear interactions in random wave fields is reinterpreted in terms of a hypothetical ensemble of interacting particles, antiparticles, and virtual particles. In the particle picture, the interactions can be conveniently described by Feynman diagrams, which may be regarded either as branch diagrams of the perturbation expansion or as collision diagrams. The derivation of the transfer expressions can then be reduced to a few general rules for the construction of the diagrams and the associated collision cross sections. The representation follows closely the standard treatment of nonlinear lattice vibrations, but the particle picture differs from the usual phonon interpretation of lattice waves. It has the unrealistic property that the energies and number densities of antiparticles are negative. This is offset by simpler interaction rules and a closer correspondence between the perturbation graphs and collision diagrams. The method is illustrated for scattering processes in the oceanic wave guide involving surface and internal gravity waves, horizontal currents (turbulence), seismic waves, and bottom irregularities.
Advances in ionospheric physics in the rocket and satellite era
Authors: Schmerling E. R.
Published: February 2008

With the systematic use of rockets and satellites, a great deal of progress has been made in increasing our knowledge and understanding of the ionosphere and the interaction of radio waves with a magnetoplasma. This paper attempts to summarize the major results obtained during the last six years. During this period, helium was found to be an important atmospheric constituent; topside sounders produced the first survey of the electron distribution above the peak of the F region; several types of plasma resonance were discovered; electron temperatures were observed to be systematically in excess of neutral temperatures, even at night; and new types of whistlers were observed. Steady progress was made in establishing the sources of ionization, from the cosmic rays effective below 70 km to the particular regions in the solar X‐ray and UV emissions responsible for ionization at greater altitudes. Less progress has been made in understanding the mechanisms of electron loss, since uncertainties still exist about reaction rates, the role of minor constituents, and the contributions of electrodynamic transport. As a result of the observations made during the past six years, a new picture of the ionosphere is emerging which is very different from the old one of layers produced in an isothermal atmosphere by monochromatic radiation. Although the new picture is much more complicated, it is firmly based on observation, and it holds out a real hope that the solution of some outstanding problems is now within reach.
Theory of statistical analysis of data distributed over a sphere
Authors: Kaula W. M.
Published: February 2008

The problem of obtaining a representation of a variable on a sphere from irregularly distributed observations is divided into two topics (1) Spectral representation: the relationships between covariances, spherical harmonic coefficients, power spectra, etc.; and (2) statistical analysis: extrapolation, power spectrum, and coefficient determination, etc., under the assumption of stationarity. The relationships of various techniques are discussed.
A review of digital pass filtering
Authors: Wood Lawrence C.
Published: February 2008

This paper discusses the design and application of numerical pass filters. Pass filtering is a general term encompassing low‐pass, high‐pass, band‐pass, and band‐reject (notch) filtering. These filters are zero phase, and they can provide roll‐offs of almost any desired amount. Truncation effects are reduced with Fejer weights. Relatively short time‐domain operators are obtained through a combined use of parabolic rounding, linear attenuation, and Fejer weighting. These operators decay with an approximate 7/2 power law, as compared with the 2/2 decay of the sin x/x function. The emphasis in this paper is on applications rather than theory. Examples illustrate data processing with pass filters. Examples of digital‐alias filters are given, Applications include synthetic data as well as actual field examples. The applications relate to exploration seismology; however, these filters are quite general, applying equally well to other geophysical, geological, and scientific problems.
Time series regression of sea level on weather
Authors: Groves Gordon W. , Hannan E. J.
Published: February 2008

Analysis of sea‐level and weather records by frequency is done by the usual methods of spectrum analysis, whereupon a regression analysis is performed in each frequency band. The very complete array of existing statistical procedures, for testing hypotheses and allocating confidence intervals, is then available, suitably modified to take account of the fact that the regression coefficients are complex numbers. Associated statistics, such as partial and multiple coherences and residual spectral matrices, may be treated similarly. The combination of estimates from neighboring frequency bands is also discussed.

These methods are used to study records of sea level, surface atmospheric pressure, and wind components at Kwajalein and Eniwetok in the Marshall Islands. An 8 × 8 spectral matrix of these variables covering the frequency range of 0 to 0.85 cycles per day is the starting point for the study. The spectra are characteristic of other sea‐level and weather spectra at islands in low latitudes. There is good coherence between the two islands, especially in sea level and atmospheric pressure. At each island there is the usual strong coherence between sea level and pressure, with moderate coherence between sea level and wind at each island. Several regression models of sea level on the weather records are considered in order to study oceanic influences on the sea‐level records free from local weather noise. However, the spatial coherence of the residual sea level is less than that of the original sea‐level records, apparently because most of the original spatial coherence results from coherent weather patterns and not from coherent water motions. If the computed statistical relations are taken as the true relations, the results are not compatible with a simplified theory of free planetary barotropic waves on the surface of an ocean of constant depth. Because of statistical uncertainty, however, little can be deduced regarding the presence or absence of planetary waves.
Coherence and band structure of inertial motion in the sea
Authors: Munk Walter , Phillips Norman
Published: February 2008

It is now well established by observation that a peak in the spectrum of horizontal motion should be anticipated everywhere in the ocean near the local inertia frequency, 2ω sine (latitude). The theory of wave motion in a weakly stratified, rotating ocean of constant depth explains this observation either by the existence of a frequency condensation point in wave‐number space or, alternatively, by the vanishing of the meridional group velocity. This explanation is independent of a specific generating mechanism, such as tidal forcing. The details of the wave structure and dispersion relation are readily obtained when, as seems both likely and desirable, it is permissible to ignore the discrete normal‐mode‐producing effects of distant lateral boundaries.

This theory predicts a spectral peak slightly above the inertia frequency, and this displacement depends on the zonal and vertical wave numbers. The peak frequency in the North Atlantic measurements by Fofonoff and Webster implies vertical modes of O(10) and a zonal wave number of O (several hundred cycles per earth circumference). When these numbers are applied to a simple coherence model, assuming phase independence between different wave numbers, one can account for the observed lack of coherence between stations separated in depth or longitude. This theory also defines a latitudinal scale; for vertical wave number 10 this is, typically, of O(25 km), which is in qualitative agreement with Hendershott's observations in the eastern North Pacific.

The present theoretical model is appropriate for random distributed sources. The observations, however, indicate a higher degree of intermittency than is implied by this model. We conclude that both random distributed sources and intermittent discrete sources must be taken into account for a satisfactory description of the phenomena.
Some elastic constant data on minerals relevant to geophysics
Authors: Anderson Orson L. , Schreiber Edward , Liebermann Robert C. , Soga Naohiro
Published: February 2008

Measurements of the elastic constants and related pressure and temperature derivatives of ten compounds of interest to geophysical and geochemical theories are reported and analyzed. We discuss the corrections that are expected from effects of anisotropy and porosity and conclude that polycrystalline samples with porosities of 4% are not adequate for reliable acoustic measurements. We find that two anharmonic parameters, γth and δS, are independent of temperature at high temperature, and we use this result to estimate the temperature derivative of the bulk modulus at high temperatures. We present a number of correlations between the elastic constants and illustrate their use by attempting to predict the unmeasured elastic properties of fayalite.