bluuebunny/crossref_metadata_2025 huggingface dataset:
Waveforms of first and subsequent leaders in negative lightning flashes
Authors: Rakov Vladimir A. , Uman Martin A.
Published: February 2008

Statistics on the occurrence of different categories of leader electric field wave shapes are presented as a function of stroke order and distance for 286 strokes in 73 flashes. Electric field records of 71 first strokes and 182 subsequent strokes in 74 flashes are analyzed for leader duration. At distances closer than 5 km, 92% of 38 leader waveforms are hook‐shaped with a net negative field change regardless of stroke order (1 through 18). For strokes of order 8 through 13, 90% of 49 leader waveforms are hook‐shaped with a net negative field change regardless of distance (3 through 14 km). Sixteen percent of 270 subsequent leaders exhibited a marked inactive final portion characterized by a flattening in their field waveforms, the overwhelming majority (84%) of these leaders being associated with early strokes in a flash (2 through 4). In 77% of cases in which this electric field flattening was observed, the leaders were preceded by strokes creating a new termination on ground. The geometric mean leader duration for 71 first strokes was found to be 35 ms, while that mean for 154 subsequent strokes following the same channel as the preceding stroke was 1.8 ms. Twenty‐eight subsequent strokes creating a new termination on ground showed a geometric mean leader duration of 15 ms. The geometric mean leader duration for strokes following the same channel as the preceding stroke exhibited a tendency to increase with stroke order.
Electric charge acquired by airplanes penetrating thunderstorms
Authors: Jones J. J.
Published: February 2008

Three airplanes—a sailplane, a piston powered sailplane, and a twin turboprop—have been instrumented to measure electric fields inside electrified clouds and the net electric charge on the airplanes. In unelectrified clouds the powered airplanes become negatively charged during collisions with liquid cloud water droplets whereas the sailplane does not. In thunderstorm clouds, several airplane charging mechanisms are found to operate. These involve collisions with liquid water droplets of the cloud and the shedding of polarization charge in the presence of strong electric fields. For these charging processes, the sign of the acquired charge depends on the sign of the component of the atmospheric electric field along the direction of flight. When the amounts of charge on the powered airplanes are small, the engine exhaust acts to discharge the airplane, while for larger charges, corona emission becomes the predominant mechanism of discharge.
Annual and interannual variations of absorbed solar radiation based on a 10‐year data set
Authors: Smith G. Louis , Rutan David , Charlock Thomas P. , Bess T. Dale
Published: February 2008

Annual and interannual variations of absorbed solar radiation (ASR) are studied using the 10‐year Earth radiation budget data set from the Nimbus 6 and 7 Earth radiation budget instruments in the form of monthly averaged maps of ASR. Empirical orthogonal functions (EOFs) are computed for the global distribution of ASR. Six EOFs are found which have physical significance and which account for 97.8% of the spatial variance of the data set. The first EOF describes the annual cycle and is primarily a latitudinal variation which is driven by the incident solar radiation. The second and fourth EOFs are semiannual cycles. EOFs 3 through 6 are strongly longitudinally dependent. EOF 3 describes the spring/fall part of the annual cycle, and EOF 4 describes the part of the semiannual cycle which is out of phase with EOF 2. EOF 5 is the response of the ASR to El Niño. The annual cycle and its harmonics account for 97.6% of the variance with time. When the data set is deseasonalized, the first two EOFs of the resulting set are found to correspond closely to EOFs 5 and 6 of the data set with season included. As with outgoing longwave radiation, most of the interannual variation is found over the tropical oceans.
Visible and infrared spin scan radiometer atmospheric sounder water vapor and wind fields over Amazonia
Authors: Schmit Timothy J. , Brueske Kurt F. , Smith William L. , Paul Menzel W.
Published: February 2008

Both the mass and motion fields for Amazonia have been depicted using almost exclusively geostationary satellite data. Derived parameters include satellite retrievals of atmospheric temperature and dewpoint temperature, total precipitable water vapor, and cloud and water vapor winds. The capabilities of geostationary satellite data have been demonstrated at least four times a day for the period of May 5–8, 1987, during the Global Tropospheric Experiment/Amazon Boundary Layer Experiment. The satellite‐derived information is able to resolve synoptic‐scale atmospheric trends in space and time.
A one‐dimensional numerical model to simulate formation and balance of sulfate during radiation fog events
Authors: Forkel Renate , Seidl Winfried , Dlugi Ralph , Deigele Erika
Published: February 2008

A one‐dimensional numerical model of the atmospheric boundary layer is coupled with a bulk phase aqueous chemistry model to simulate meteorological conditions, sulfate production, and pH values during radiation fog events. The boundary layer model includes prognostic equations for atmospheric temperature, specific humidity, liquid water content, wind speed, and the concentrations of the gas phase and liquid phase chemical reactants. Within the soil, temperature and liquid water content are predicted. A hybrid equilibrium and kinetic aqueous chemistry model is used to predict reactant concentrations in the fog water. The model is used to investigate the influence of soluble aerosol material and of trace gases on SO2 oxidation, on fog water pH, and on deposition fluxes due to sedimentation. As the meteorological conditions have an influence on fog height, liquid water content, and duration, not only the initial aerosol composition and the trace gas concentrations but also thermodynamic and dynamic conditions of the atmosphere and soil properties have an impact on liquid phase sulfate production during the fog event. With the exception of the dissipation stage, the turbulent transport of oxidants from aloft into the fog layer has only a small influence on the production of sulfate within a fog layer. An important mechanism for downward supply of fresh material is the rise of the fog top, followed by sedimentation of droplets. Sedimentation also results in the removal of a considerable amount of aerosol material from the fog layer.
Rate of reaction of IO radicals with dimethylsulfide
Authors: Daykin E. P. , Wine P. H.
Published: February 2008

The kinetics of the title reaction have been investigated at 298 K using time‐resolved long‐pathlength absorption spectroscopy to monitor the temporal behavior of IO following 351‐nm laser flash photolysis of NO2/I2/CH3SCH3(DMS)/N2/O2 mixtures. We obtain an upper limit bimolecular rate constant for the IO+DMS reaction of 3.5×0−14 cm3 molecule−1 s−1; this upper limit is nearly 3 orders of magnitude slower than two previously reported measurements. Our results suggest that coupling of the marine sulfur and iodine cycles via the IO+DMS reaction is negligible.
The Effect of summer tropical heating on the location and intensity of the extratropical westerly jet streams
Authors: Yang Song , Webster Peter J.
Published: February 2008

The role of the summer hemisphere tropical diabatic heating on the location and magnitude of the winter hemisphere subtropical and extratropical westerly jet streams is studied. In particular, the relationships between the extratropical zonal wind, the subtropical meridional wind and the tropical outgoing longwave radiation (OLR) patterns are examined. It is found that the heating field, the cross‐equatorial meridional wind, and the winter zonal wind maxima are closely linked on annual and interannual time scales. These factors indicate that the adjacent hemisphere heating is at least as important as the northern hemisphere orography in determining the location and magnitude of the westerly jet streams. Credence is added to this conclusion by noting the similar associations between the northern hemisphere heating pattern and the location and variations of the southern hemisphere jet streams which are less clearly associated with orography. Furthermore, interannual changes in the location and magnitude of the westerly jet streams are closely related to the El Niño/Southern Oscillation (ENSO) phenomenon. Thus, in addition to the well known relationship between ENSO and the near‐equatorial or symmetric zonal circulation, there is a strong association on the same time scale in the cross‐equatorial flow or asymmetric components about the equator.
The interhemispheric distribution and the budget of acetonitrile in the troposphere
Authors: Hamm Stephan , Warneck Peter
Published: February 2008

Gas chromatography in conjunction with a thermionic nitrogen‐specific detector was used to determine mixing ratios of acetonitrile in air samples collected in Europe and over the Atlantic Ocean. In the city of Mainz, values of the order of 340 pptv were observed with large variations indicating the vicinity of sources. In the rural community of Deuselbach the average mixing ratio was 147±28 pptv; over the North Sea the range was 65–196 pptv depending on wind direction, with the lowest values occurring for northerly winds from the open ocean. The distribution of CH3 CN with geographic latitude over the Atlantic Ocean was explored between 30°S and 50°N on board R/V Polarstern during the cruise ANT V/5 in March–April 1987. Over the open ocean, maximum mixing ratios were observed near 4°S with values of 175 pptv. At latitudes near 30°S the mixing ratio averaged 90.4 pptv, whereas at 30°N the average was 52.1 pptv. The lowest mixing ratios of 21 pptv were found near 50°N. The tropical maximum is attributed to the advection with the trade winds of continental air from Africa, enriched with acetonitrile from biomass burning. The mixing ratios north and south of the maximum correlate well with the surface temperature of seawater, indicating a gas‐liquid equilibrium for CH3 CN dissolved in seawater. From the observations and with the further assumption that CH3 CN is vertically well mixed, its total mass content in the troposphere was estimated as 0.37–0.57 Tg. Global emission rates for various sources were estimated as follows: automobiles 0.27 Tg/year, oil‐fired power stations 0.0035 Tg/year, and biomass burning 0.80 Tg/year. The total estimated source strength is 1.1±0.5 Tg/year. The tropospheric residence time of acetonitrile was calculated from these data as 0.23–0.90 year with a probable value of 0.45 year. Wet precipitation and reaction with OH radicals are known sinks for tropospheric CH3 CN, but they can take up only 30% of the global emission rate. We suggest absorption in the ocean to be the major sink.
Comparison of field, laboratory, and theoretical estimates of global nitrogen fixation by lightning
Authors: Liaw Y. P. , Sisterson D. L. , Miller N. L.
Published: February 2008

The various theoretical, laboratory, and field estimates reported in the literature for global nitrogen fixation by lightning have been calculated by using different lightning frequency values, channel lengths, and energy values. We have recalculated each of the individual estimates by using values of 7 km for channel length, two equivalent return strokes per lightning flash, and 100 flashes per second for global frequency, and a lightning energy input of 5×109 per flash. The adjusted mean value is 72.2±96.2 Tg N yr−1 for the theoretical category, 19.1±10.0 Tg N yr−1 for the laboratory category, and 152±59.9 Tg N yr−1 for the field category. Each of the three category adjusted mean NOx global production rates is larger than previously reported contributions to the global N budget, making lightning potentially the single largest source.
Atmospheric response to Ice Age conditions: Climatology near the Earth's surface
Authors: Lautenschlager M. , Herterich K.
Published: February 2008

We present a 6‐year simulation of the ice age atmosphere using the T21 Atmospheric General Circulation Model (AGCM) of the European Centre for Medium‐Range Weather Forecasts (ECMWF). The lower boundary conditions (18 kyr B.P.) were taken from CLIMAP Project Members (1981). The analysis is restricted to the surface climatology for two reasons: The surface fields are the test data derived from the geological record on land, and they define the upper boundary conditions for simulating the glacial ocean. Model results are shown for the mean annual surface fields of temperature, wind, and precipitation. In the global average the surface temperature was 4.7°C cooler compared to the present temperature. The wind strength increased in mid‐latitudes and decreased in tropical trade wind regions. Precipitation did not change significantly in the global average; however, precipitation decreased over land and increased over the ocean. Most of the difference patterns between the present conditions and the ice age climate were statistically significant. The simulated surface climatology is roughly consistent with the paleogeological evidence and with numerical AGCM simulations of other authors. This suggests that presently available AGCMs, including the ECMWF model (T21), are able to describe climates far away from the present, although internal parameterizations were tuned to present data sets.
Variable marine productivity and high eolian input recorded by rhythmic black shales in Mid‐Cretaceous pelagic deposits from central Italy
Authors: Pratt Lisa M. , King J. David
Published: February 2008

Rhythmic interbedding of dark gray to black, laminated, calcareous shale (black shale) with lighter colored limestone, marlstone, or mudstone is a prominent feature of the Aptian‐Albian Scisti a Fucoidi in the Italian Apennines. Organic carbon contents of most black shales in the Scisti are less than 1.5%. Sedimentary structures and levels of bioturbation indicate that periods of poorly oxygenated benthic conditions alternated with more extended periods of well‐oxygenated benthic conditions during deposition of the Scisti. Geoochemical, isotopic, and visual studies of organic matter indicate variable marine productivity (generally low) and relatively high input of eolian dust during deposition of the Scisti black shales. One organic‐rich black shale near the middle of the formation may represent a brief period of stimulated marine fertility and high productivity coincident with benthic stagnation. Production of warm saline brines in evaporitic coastal settings, sinking of these brines into deepwater basinal settings, and development of stable salinity stratification is suggested as a causal linkage between arid climate, strong winds, and poorly oxygenated bottom waters in the Alpine‐Mediterranean Tethys during mid‐Cretaceous time.
An initial study of the sensitivity of modeled Cretaceous climate to cyclical insolation forcing
Authors: Glancy T. J. , Barron E. J. , Arthur M. A.
Published: February 2008

Some Cretaceous rhythmic sedimentation, such as the Colorado Greenhorn Formation deposited in the western interior seaway (U.S.), may have been produced by cyclic precipitation intensity change, responding to orbitally produced insolation forcing. To test this hypothesis, a general circulation model was forced with the seasonal maximum and minimum insolation calculated from assumed Cretaceous orbital parameters. Geographic comparisons for July and January of surface temperature, surface pressure, and precipitation were prepared. For January, maximum land‐sea contrast produced an increase of more than 6 mm/day precipitation over the interior seaway. However, the July maximum simulation did not produce precipitation increase despite an anticipated monsoonlike circulation over the region. North America appears to be very arid during Cretaceous northern hemisphere summer.
A 420,000‐year record of cyclicity in oceanic and atmospheric processes from the eastern equatorial Pacific
Authors: Rea David K. , Chambers Lucy W. , Chuey John M. , Janecek Thomas R. , Leinen Margaret , Pisias Nicklas G.
Published: February 2008

Samples from the upper portion of a cyclic pelagic carbonate sediment sequence in Deep‐Sea Drilling Project (DSDP) hole 503B (4.0°N, 95.6°W) are the first group to be analyzed for paleoceanographic and paleoclimatic proxy‐indicators of ice volume, deep ocean and surface water circulation, and atmospheric circulation in order to resolve the complex origin of the cyclicity. Temporal resolution is taken from the δ18O time scale, most other parameters are calculated in terms of their mass flux to the seafloor. CaCO3 percent in the sediments fluctuates in the well‐known Pacific pattern and is higher during glacial times. The fluxes of opal and organic carbon have patterns similar to each other and show a variability of a factor of 2.5 to 4. The longer organic carbon record shows flux maxima during both glacial and interglacial times. The accumulation patterns of both opal and organic carbon suggest that the variability in surface water productivity and/or seafloor preservation of those materials is not simply correlated to glacial or interglacial periods. Eolian dust fluxes are greater during interglacial periods by factors of 2 to 5, indicating that eolian source regions in central and northern South America were more arid during interglacial periods. The record of eolian grain size provides a semiquantitative estimation of the intensity of the transporting winds. The eolian data suggest more intense atmospheric circulation during interglacial periods, opposite to the anticipated results. We interpret this observation as recording the southerly shift of the intertropical convergence zone to the latitude of hole 503B during glaciations.
Atlantic Eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography
Authors: Boersma Anne , Silva Isabella Premoli , Shackleton N. J.
Published: February 2008

Reconstruction of Atlantic Ocean vertical and meridional water characteristics is based on combined synoptic fossil census data, stable isotope records, and measurements of individual planktonic foraminiferal species. Correlations between planktonic foraminiferal indices and specific water types and/or chemical conditions are used to trace seven stages in the history of Atlantic circulation during Eocene climatic changes: (1) warm, equable, probably saline, productive ocean of the early Eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water, (2) early middle Eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters, (3) maximal partitioning of water types, faunas, and bioprovinces in middle Eocene Zone P11 accompanying maximum planktonic foraminiferal diversity, accelerated near‐surface and deepwater cooling, and intensified upwelling, (4) latest middle Eocene (Zone P14) maximal planktonic foraminiferal evolutionary overturn during accelerated cooling, deep and surface water ventilation, and transformation of tropical, surface water habitat with the expansion of temperate water types and faunas; this accompanied the reduction of meridional heat transport in boundary currents, (5) late Eocene bottom water and middle‐latitude cooling, broadening of meridional temperature gradients, and expanded oxygen‐minimum, but faunal homogenization following the decreased import of Mediterranean water ourflow, (6) weakening and/or shoaling of the nutricline, an oxygen minimum, and the thermocline preceding a diminution of primary productivity at the Eocene‐Oligocene boundary, and (7) earliest Oligocene low‐productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small‐sized individuals. The increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic‐forcing mechanism in the latest middle and late Eocene.
Reducing power of ferrous iron in the Archean Ocean, 2. Role of FEOH+ photooxidation
Authors: François L. M.
Published: February 2008

A chemical and dynamical model of the Archean ocean is proposed to investigate the consequences of FeOH+ photooxidation in the surface mixed layer. The calculation assumes the presence of small amounts of photosynthetic oxygen, from negligible values to surface concentrations of 10−6 mol kg−1. Photooxidation releases hydrogen atoms which can recombine into H2 molecules, reduce some ferric compounds or react with O2 to form HO2. The results are presented for various atmospheric CO2 pressures (corresponding to different pH profiles) and for Fe II concentrations in the deep ocean varying from 10−7 to 10−4 mol kg−1. In spite of the uncertainties concerning the description of the Archean world the model indicates that Fe III reduction by hydrogen atoms would have been a minor process, except for unlikely small deepwater Fe II concentrations. Another significant result is that the FeOH+ photooxidation rate was probably limited by upward transport (upwelling and diffusion) of ferrous iron. Thus in the model this rate only depends on the deepwater Fe II content and on the dynamical parameters associated to upwelling and diffusion. It is also shown that two mixed layer O2 concentrations ([O2]o) are critical. First, for [O2]o ≲ 10−13 mol kg−1 the hydrogen atoms produced by photooxidation recombine to form H2. By contrast, for [O2]o ≳ 10−13 mol kg−1, these atoms are consumed by reaction with O2, and the HO2 molecule which is released generates three additional oxidations of Fe II ions. The second critical concentration is [O2]o ≃ 10−8 mol kg−1, for which the photosynthetic oxygen invades the deep layers of the ocean. In such a case, the photooxidation rate is rapidly decreased, and the direct reaction with O2 becomes the main oxidation process for Fe II.
Mesozoic calcareous nannofossil evolution: Relation to paleoceanographic events
Authors: Roth Peter H.
Published: February 2008

The taxonomic evolution of Jurassic and Cretaceous calcareous nannofossil species is described using the following indices: species diversity, rate of speciation, rate of extinction, rate of diversification, rate of turnover, survivorship, and species accretion. The Jurassic prior to the late Oxfordian is characterized by positive diversification rates, that is, rates of speciation exceeded rates of extinction. Highest rates of diversification occurred in the late Lias and early Oxfordian. During the generally regressive latest Jurassic, diversification rates remained low and rates of extinctions exceed rates of speciation. In the early Cretaceous, rates of diversification are positive and peak in the early Valanginian, early Aptian, and middle Albian, after which time rates of extinction generally exceed rates of speciation. Such peaks in rate of evolution coincide with times of increased accumulation of organic carbon in the ocean (“anoxic events”). Peaks in rates of extinction result in very high rates of turnover during times of major regressions, in particular, in the Tithonian and Maastrichtian. Survivorship analyses for three datum planes (74.5, 144, and 160 Ma) show relatively constant extinction rates with some stepping in the older part; they are best explained by a temporally fluctuating abiotic environment causing changes in the probability of extinction. Species accretion curves are also relatively linear with some indication of changing rates of speciation. The coincidences of major changes in evolutionary rates with major paleoceanographic events are indicative of a predominantly abiotic control of nannoplankton evolution. Relationships of evolutionary rates of calcareous nannoplankton with deep ocean ventilation, sea level, and ocean fertility indicates that global tectonic processes are the ultimate causes of evolutionary change.
Deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation
Authors: Duplessy J. C. , Shackleton N. J. , Fairbanks R. G. , Labeyrie L. , Oppo D. , Kallel N.
Published: February 2008

The degree of similarity of the ∂13C records of the planktonic foraminiferal speciesN. pachydermaand of the benthic foraminiferal genusCibicidesin the high‐latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle. Whereas continuous formation of deep water is recognized in the southern ocean, the Norwegian Sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation. However, deep water formed in the north Atlantic south of the Norwegian Sea during the last climatic cycle as early as isotope substage 5d, and this area was also the only active northern source during stages 4–2. A detailed reconstruction of the geographic distribution of ∂13C in benthic foraminifera in the Atlantic Ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean, whereas the Glacial North Atlantic Deep Water cannot be traced south of 40°N. At shallower depth an oxygenated13C rich Intermediate Water mass extended from 45°N to 15°S. In the Pacific Ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700–2600 m and is best explained by stronger formation of Intermediate Water in high northern latitudes.
Late Quaternary changes in Mediterranean intermediate water density and formation rate
Authors: Rohling Eelco J. , Gieskes Winfried W. C.
Published: February 2008

Three recently acquired eastern Mediterranean cores containing Late Quaternary sediments display a marked faunal contrast between the Holocene and older sapropels. It is suggested that the absence of neogloboquadrinids in the Holocene sapropel and their abundance in older sapropels reflect differences in food availability related to the extent of development of a deep chlorophyll maximum layer (DCM) and the intensity of “new” primary production associated with this layer. The depth of such a layer, which consists of phytoplankton with a characteristic taxonomic composition, is determined by the vertical hydrodynamical structure. During deposition of the older sapropels, the pycnocline was apparently positioned well above the base of the euphotic layer, a situation that favors a pronounced DCM and an associated relatively high rate of new production. Shallowing of the pycnocline implies a relatively low density of the Mediterranean Intermediate Water (MIW). On the other hand, during deposition of the Holocene sapropel the pycnocline had apparently vanished due to termination of MIW formation.
Estimates of sea surface temperature in the Coral Sea at the Last Glacial Maximum
Authors: Anderson D. M. , Prell W. L. , Barratt N. J.
Published: February 2008

The CLIMAP [1981] reconstruction of the Coral Sea found relatively little cooling (2°C) in the low latitudes (10°S) but a warming off Australia at about 25°S. The small low‐latitude changes are of interest because terrestrial pollen and snowline data from the New Guinea highlands imply that surface temperatures may have been 6° to 9°C colder at the last glacial maximum (LGM). The purpose of this paper is to evaluate these conclusions on the basis of additional core sites, new oxygen isotope stratigraphy, and new sea surface temperature (SST) estimates using the modern analog technique (MAT). In the northern Coral Sea, planktonic foraminifer assemblages consist of tropical‐subtropical species that show little change over the past 20 kyr. Quantitative estimates of SST using the modern analog technique (MAT) confirm the CLIMAP [1981] conclusion that little or no temperature change occurred in this tropical region at the LGM, thus reinforcing the conflict with terrestrial evidence. In the southern region (25°S), two cores indicate that foraminifer faunas became more subtropical at the LGM. The MAT estimates for the LGM are 3° to 4°C colder than modern, producing a steeper thermal gradient in the southern Coral Sea. These data remove the warm SST anomaly along the eastern coast of Australia and indicate that during the LGM, cool high‐ latitude waters were displaced northward along the coast of Australia into the southern Coral Sea.
Glacial‐interglacial CO2 change: The Iron Hypothesis
Authors: Martin John H.
Published: February 2008

Several explanations for the 200 to 280 ppm glacial/interglacial change in atmospheric CO2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients. An hypothesis is presented herein in which arguments are made that new productivity in today's southern ocean (7.4 × 1013g yr−1) is limited by iron deficiency, and hence the phytoplankton are unable to take advantage of the excess surface nitrate/phosphate that, if used, could result in total southern ocean new production of 2−3 × 1015 g C yr−1. As a consequence of Fe‐limited new productivity, Holocene interglacial CO2 levels (preindustrial) are as high as they were during the last interglacial (≈ 280 ppm). In contrast, atmospheric dust Fe supplies were 50 times higher during the last glacial maximum (LGM). Because of this Fe enrichment, phytoplankton growth may have been greatly enhanced, larger amounts of upwelled nutrients may have been used, and the resulting stimulation of new productivity may have contributed to the LGM drawdown of atmospheric CO2 to levels of less than 200 ppm. Background information and arguments in support of this hypothesis are presented.
Late Pleistocene Southern Ocean δ13C variability
Authors: Oppo D. W. , Fairbanks R. G. , Gordon A. L. , Shackleton N. J.
Published: February 2008

Variations in the contribution of North Atlantic Deep Water (NADW), relative to North Pacific Deep Water (NPDW), to the Southern Ocean, are assessed by comparing δ13C records from the mid‐depth North Atlantic, deep Southern Ocean, and deep equatorial Pacific Ocean. In general, the relative contribution of NADW was greater during interglaciations than glaciations of the past 550,000 years. An increase in the NADW flux to the Southern Ocean since the last glaciation was proposed to have resulted in higher atmospheric CO2 in the Holocene (Broecker and Peng, 1989). Glacial‐interglacial variations in the proportion of NADW in the Southern Ocean may have also influenced atmospheric CO2 levels over the past 550,000 years. The greatest relative flux of NADW to the Southern Ocean occurred during interglacial stage 11. Faunal data suggest that the North Atlantic polar front and southern Indian Ocean subtropical convergence zone were located farthest poleward during stage 11. Warmth in these locations and a strong southward flux of NADW during stage 11 may be causally linked by the NADW formation process/warm water return route (Gordon, 1986). Time series analysis indicates that δ13C variations in the deep Southern Ocean occur at the same frequencies as the Earth's orbital variations and are coherent and in phase with δ18O. At most, 50% of the glacial‐interglacial δ13C amplitude in the Southern Ocean is due changes in the contribution of NADW. The remainder is probably due to mean ocean δ13C changes.
Miocene history of the Benguela Current and Antarctic ice volumes: Evidence from rhythmic sedimentation and current growth across the Walvis Ridge (Deep Sea Drilling Project Sites 362 and 532)
Authors: Diester‐Haass Liselotte , Meyers Philip A. , Rothe Peter
Published: February 2008

The history of the northward growth and of the fluctuations of the Benguela Current from the middle Miocene (ca. 14 Ma) to the uppermost late Miocene (ca. 5 Ma) has been reconstructed from analyses of the coarse and clay fractions and geochemical analyses of the organic matter in sediments from Deep Sea Drilling Project Sites 362 and 532. In the middle Miocene the Benguela Current had not yet reached the Walvis Ridge, and consequently, no local upwelling occurred. Carbonate preservation was good during this period of low productivity. Rhythmic changes related to Antarctic ice volumes were weak, leading to slightly higher organic matter concentrations and higher montmorillonite/illite (M/I) ratios in sediments deposited during times of greater continental ice. Montmorillonite was carried north from the Orange River by the Benguela Current, whereas illite originated from the nearby Namib Desert. In the early late Miocene the Benguela Current reached the Walvis Ridge in colder periods and led to well‐developed rhythmic increases in opal, which was transported from near‐coastal upwelling areas. Organic matter concentration, carbonate dissolution, and M/I ratios were also enhanced during periods of greater ice volume. During the late Miocene, farther northward migration of the Benguela Current led to a change in the uppermost Miocene sediments: opal contents and M/I ratios were high during times of low ice volume rather than in colder times. During the cold periods, local winds from the Namib desert increased the illite supply to the Walvis Ridge and depressed the M/I ratio. In these periods, the Benguela Current flowed farther to the north, reaching the Angola Basin as it did in Quaternary glacial periods. Throughout these changes, sediment organic carbon content was always enhanced in high‐ice‐volume periods from near‐bottom downslope transport of organic matter from shelf regions during regressions, and carbonate dissolution in the sediments was increased as a result of oxidation of this organic matter.
Evidence for seasonal low‐salinity surface waters in the Gulf of Mexico over the last 16,000 years
Authors: Spero Howard J. , Williams Douglas F.
Published: February 2008

Oxygen isotopic analyses of individual Orbulina universa from Orca Basin core EN32‐PC6 document the presence of low salinity surface waters in the northern Gulf of Mexico over the past 16 kyr. Isotopic data from an interval immediately following the Younger Dryas Event indicate the rapid decrease in δ18O values at the conclusion of the Younger Dryas was due to a year‐round return of meltwater to the Gulf of Mexico. Data indicate periodic or seasonal low‐salinity waters existed over the region of the Orca Basin prior to the initiation of the meltwater spike. Estimates suggest O. universa grew its shell in salinities at least 4.5 ‰ below ambient. Since O. universa may have calcified deep in the mixed layer during periods of low salinity, surface salinities could have been even lower. Comparison of the average of individual O. universa oxygen isotopic values with data from multiple shell samples of white Gs. ruber from the same core samples demonstrates that the two species record similar values during the late Holocene. In contrast, O. universa records lower oxygen isotopic values during the late glacial/deglacial intervals, possibly due to differences in seasonal distribution or shell ontogeny between the two species.
The record of deglaciation in the Sulu Sea: Evidence for the Younger Dryas Event in the tropical western Pacific
Authors: Linsley Braddock K. , Thunell Robert C.
Published: February 2008

A high‐resolution, accelerator mass spectroscopy 14C dated sediment record from the Sulu Sea clearly indicates that the Younger Dryas event affected the western equatorial Pacific. Planktonic foraminiferal δ18O and abundance data both record significant changes during Younger Dryas time. In particular, a 0.4‰ increase in the δ18O value of Globigerinoides ruber and the reappearance of the cool water planktonic foraminifera, Neogloboquadrina pachyderma, occur during the Younger Dryas at this location. These isotopic and faunal changes are a response to either surface water temperature or salinity changes, or some combination of the two. Changes in surface salinities could have been accomplished through either local or global processes. Intensification of the monsoon climate system and increased precipitation at approximately 11 ka is one mechanism that may have resulted in local changes in salinity. A meltwater pulse derived from the Tibetan Plateau is another mechanism which may have caused local changes in salinity. The presence of the Younger Dryas in the tropical western Pacific clearly indicates that this climatic event is not restricted to the North Atlantic or high latitudes, but rather is global in extent.
Confidence regions and error determinations for seismic event location
Authors: Flinn Edward A.
Published: February 2008

A digital computer program has been written to locate seismic events and to determine the standard errors and joint confidence regions for the focal coordinates. Modified Jeffreys‐Bullen travel times are used, with surface focus travel times based on Nevada explosions. Results for eleven nuclear explosions in Nevada show a mean computed depth of focus of 39 ± 2 km. For these events, the displacement of the computed epicenter from the known epicenter is less than 20 km for all but three explosions when the Jeffreys‐Bullen travel times are used. The epicenter displacement is less than 15 km for all but the same three explosions when surface focus travel times are used. Linearized joint confidence regions for latitude and longitude were computed for all events; for all the Nevada explosions the semimajor axis of the 75% confidence region was less than 14 km. Exact confidence regions can be constructed for the focal coordinates. In a small neighborhood of the computed epicenter (10 to 20 km being sufficiently small), the linearized confidence region has the same statistical behavior as the exact confidence region. The axis ratio and orientation of the confidence region for latitude and longitude depends only on the distribution of the stations in distance and azimuth around the epicenter; the size of the confidence region depends also on the station residuals and the confidence level required. A quality factor for station distribution, varying between zero and unity, can be used to measure the capability of a given station network with respect to a given epicenter. This quality factor is related to the generalized variance of the estimates of focal coordinates. The statistical model used for earthquake location can be modified in several ways to take into account station time corrections, regional time corrections, travel time bias, etc., without basically altering the procedure for computing the confidence regions.
Dynamics of the motion of a phase change boundary to changes in pressure
Authors: O'Connell Richard J. , Wasserburg G. J.
Published: February 2008

Because of the significance of both shallow and deep phase changes to geophysical problems, the dynamical response of a phase change to pressure loading was investigated. It was found that the characteristic behavior of the system may be analyzed in terms of simple parameters of the system by using analytic expressions that apply for the initial part and the final part of the motion of the phase boundary. These expressions are obtained from approximations based on generalizations of Neumann's solution for melting at a constant temperature or from simple physical approximations based on the over‐all geometry of the model. The range of applicability of the approximations can be obtained from the approximations themselves. The analytic results compare very favorably with exact numerical solutions. The distribution of heat sources and convective heat transport are shown to be generally of minor importance on the motion of the phase boundary; the effect of convective heat transport can be estimated from the analytic approximation. The important parameters are the latent heat of the phase change and the difference in slope between the Clapeyron curve and the temperature distribution in the earth. In addition, the long‐term motion depends primarily on the over‐all geometry of the model and the boundary condition at depth. The analytic results indicate the time at which thermal blanketing by sediments becomes important and the effect of the rate of sedimentation on the response of the system; they also define slow and fast sedimentation and secular equilibrium. The effect of isostasy in conjunction with a shallow phase change is shown to be of major importance, and for certain cases the sediment thickness that can accumulate in a sedimentary basin may depend only on the sedimentation rate and not the initial depth of the basin. The analytic results permit a more physical discussion of the problem, since the functional dependence of the solution on the parameters may be seen. In addition, important results for a variety of models can be obtained by relatively simple calculations, without resorting to separate numerical solutions for each model considered.
Particles and fields: Significant achievements
Authors: Schardt Alois W. , Opp Albert G.
Published: February 2008

Space observations during 1964 and 1965 have led to discoveries in the physics of cosmic rays, the solar wind, and the magnetosphere. These results are particularly pertinent to a period of minimal solar activity. A regular sector structure, persisting for many solar rotations, was found to modulate the solar wind and its embedded magnetic field. Energetic protons up to about 10 Mev are emitted continuously from the sun in streams along certain magnetic field lines that corotate with the sector structure. The solar modulation of the propagation of galactic and solar cosmic rays was studied extensively, and theoretical explanations of this phenomenon have been derived on the basis of a diffusion model. It was discovered that low energy electrons (about 40 kev) are emitted by some solar flares, and substantial progress has been made in measuring the electron component of galactic cosmic rays. The existence of a neutral sheet in the geomagnetic tail has been demonstrated, and substantial progress was made in defining its properties as well as those of the transition region between the solar wind and the magnetopause. A short summary of spacecraft operation in 1965 is also given.
The long‐period tides
Authors: Wunsch Carl
Published: February 2008

Among the periodic terms expressing the disturbance of the geoid by the sun and moon are those that have no longitudinal dependence and are characterized by periods exceeding two weeks. These long‐period tides have amplitudes of less than 1 cm and have generally been thought, on theoretical grounds, to approximate to static equilibrium in the ocean. A static equilibrium long‐period tide is of great interest to the geophysicist, permitting determination of the elastic Love numbers, and to the oceanographer for determining low frequency oceanic dynamics. The equilibrium hypothesis was tested by computing peridograms for the fortnightly and monthly tides on islands of the Pacific. Despite high noise levels, substantial deviations from equilibrium were found, with fluctuations over distances of about 3000 km. An approximate analytic solution to the Laplace tidal equations shows the measurements to be consistent with the hypothesis that the tides excite the Rossby wave modes of the ocean. Dissipation requires the lower frequency tides to cause ‘Gulf‐Stream‐like’ westward intensification of motion. Previous measurements of the 14‐month pole tide are also consistent with the Rossby wave hypothesis.
Observations of inertial‐period motions in the deep sea
Authors: Webster Ferris
Published: February 2008

Inertial‐period oscillations have been observed by numerous investigators at deep‐sea locations ranging from subtropical to polar latitudes. Although observational techniques have favored surface‐layer measurement, there is evidence for the existence of inertial motions at all depths. There is, however, no strong evidence that the amplitude of inertial motions is strongest near the surface. The character of inertial motions has been described more fully by recent observations with moored current meters. Inertial motions have a transient nature, with generation and decay times of a few days. An analysis of the data from a single simple experiment shows that the inertial motions are coherent horizontally over much greater scales than they are coherent vertically. Thus the picture that emerges is one of transient phenomena, of thin vertical extent, and of apparent possible occurrence anywhere in the oceans.
Polar auroras, polar substorms, and their relationships with the dynamics of the magnetosphere
Authors: Feldstein Y. I.
Published: February 2008

Comparison is made between the position of the auroral oval during both night and day and that of the boundaries of trapped radiation according to observations from the satellite Alouette 2. We show that visual auroras are located on the poleward side of the boundary of smoothly closed field lines. From the data on auroral dynamics, information is obtained on some parameters of the geomagnetic field, i.e., field intensity in the magnetospheric tail, cross‐sectional dimensions of the tail at various geocentric distances, and the length of the tail. The density of low‐energy plasma at geocentric distances of 5 to 9 RE is estimated for various periods of the solar activity cycle. The influence of the magnetospheric ring current on the position of the auroral oval is considered. On the basis of polar auroral observations, estimates are made of variations in ring current parameters at times of ring current enhancement. DP and DPC magnetic field variations at high latitudes, linked with the structure of the geomagnetic field in the magnetosphere, are also discussed.

DPvariations are characterized by current electrojets, a western one within the auroral oval and an eastern one in the evening hours at Φ ∼ 65°, where Φ is the invariant latitude. The DPC variations of greatest intensity are noted on the daytime side of the earth. The field variations are due to a counterclockwise current. We show that the current system of Chapman's SD variations is a superposition of two different types of variations, DP and DPC.
Propagators of atmospheric motions 2. Excitation by switch‐on sources
Authors: Dickinson Robert E.
Published: February 2008

The excitation of various atmospheric wave motions by switch‐on sources is investigated. An asymptotic description of the propagation of the transient forerunners and the stationary forced motion contained within a Brillouin front is given. Three‐dimensional Rossby waves generated in an unbounded atmosphere by a traveling point source and several kinds of oscillating point sources are discussed. Also given is the solution for the switch‐on of a horizontally traveling gravity wave or vertically traveling atmospheric acoustic wave. Various one‐dimensional switch‐on Rossby wave problems in a periodic domain are solved in terms of image sources.
Polar ion flow: Wind or breeze?
Authors: Donahue T. M.
Published: February 2008

A review of the theories of light ion flow from the polar cap in their hydrodynamic and evaporative forms is offered. Both types of theories should be able to provide correct treatments of the phenomenon. Some difficulties with the hydrodynamic theory are mainly interpretative and should disappear if the so‐called pressure gradient force term in the equations of motion is recognized as really inertial in nature. An important new insight has been provided recently in an evaporative theory by the realization that the electric field in the exosphere required to balance electron and ion fluxes is quite different from the electric field of gravitational separation usually used in ionospheric theory. However, an evaporative theory that is based on realistic boundary conditions as well as an acceptable electric field remains to be worked out. The situation in the polar ionosphere is sufficiently complex that experimental studies will undoubtedly be needed to establish the actual conditions that exist there.