a fortran visualization program for spherical data on a yin yang grid a fortran 90 program to visualize data on the yin yang grid system is developed the purpose of this study is to provide simulation researchers with a source code as a starting point of their own custom made visualization tools a basic but sufficiently diverse set of visualization methods are implemented using a fortran 90 binding for opengl for scalar and vector fields defined or simulated on the yin yang grid

fluid flow and late diagenesis of fault infill carbonates in the aptian dolostones at jabel semmama kasserine area western central tunisia abstract in western central tunisia kasserine area dolomitization of jabel semmama aptian limestones of the serj formation fm led to the dolostones of the orbata fm these dolostones are cross cut by several generations of faulting and fracturing the current study focused on e w trending faults and fractures system incorporating carbonate infills and freshwater flows which have stimulated continental diagenetic processes the faulting fracturing and rock fluid interactions yielded nine fault infill diagenetic and tectonic sedimentary phases the purpose of studying the tectonic stresses and the nine phases was to elucidate their late impact on the aptian dolostone reservoir quality this enquiry was based on lithological tectonic microfacies and oxygen carbon o c isotopes investigations analyses of stable o c isotopes are performed on crushed and dedolomitized dolostones as well as on calcite cement laminae and spherulites c1 c2 the crushed and dedolomitized dolostones 18o and 13c data averages 4 0 v pdb 1 75 v pdb remain close to the moderately depleted results of the aptian replacive dolostone host rocks averages 3 6 v pdb 2 0 v pdb inversely calcite cement laminae and spherulites c1 c2 yielded strikingly depleted oxygen values 18o averages 7 77 v pdb 8 0 v pdb pointing out to freshwater controlled diagenesis the discrepancy between the two records 0 23 v pdb is ascribed to cooling during the precipitation of calcitic cement spherulites the divergence between the two depleted 13c values of the two cements c1 c2 averages 6 19 v pdb and 4 0 v pdb is attributed to climatic control wet dry alternations that controlled the micritization phenomenon the latter orchestered the release of ca12co3 being more mobile than ca13co3 this process is in agreement with the strong variation of fluid flow supplies vadose phreatic transcribed in the lithology as cement phases lamellar spherulites gelatinous vadose and granular the study series record two major climatic changes a wet period encompassing phases p1 p4 and a dry period extending on phases p5 p9 two short cool and wet episodes accompany this period the nine tectonic sedimentary and diagenetic phases occurred into two periods through the telogenetic stage uplift they started at the miocene pliocene during the atlasic foldings along e w faults and fractures phases p1 p6 and continued throughout the quaternary period villafranchian along a reactivation of the same direction phases p7 p9 we believe that the nine phases arose after the oae s organic matter maturity and thus had nearly no impact on any early oil migration while the earlier diagenesis phases remain the most useful for the reservoir quality

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

january and july simulations with a spectral general circulation model abstract we describe the results of january and july simulations carded out with a nine level spectral model employing a rhomboidal truncation at wavenumber 15 sea surface temperature sea ice distribution and solar zenith angle are held constant in each simulation the model includes interactive clouds and radiative processes after ramanathan et al 1983 selected fields are shown which highlight the model s strengths and weaknesses the latitude height distribution of the zonal wind is successfully simulated the model captures the separation between the wintertime westerly jets in the troposphere and stratosphere and thus simulates the sign reversal in the vertical wind shear across the jet axis in the upper troposphere in addition to the zonal wind we show also the zonally averaged temperature meridional wind and vertical velocity regional distributions of sea level pressure surface air temperature precipitation and a number of other fields defined at various pressure levels are compared in

compositional variations in calciturbidites due to sea level fluctuations late quaternary bahamas piston cores in tongue of the ocean bahamas revealed an alternating sequence of periplatform ooze and bankderived turbidites of the past 5 glacial and interglacial periods by using the point count method we have analyzed the composition of the turbidite sediment variations in the bank derived fraction are clearly linked to the glacial interglacial cycles nonskeletal components pellets ooids grapestones are most abundant in interglacial turbidites while skeletal components calcareous algae peneroplids and reef builders dominate in glacial turbidites we attribute this pattern to the exposure and flooding of the surrounding carbonate platforms during late quaternary sea level cycles because nonskeletal sediment is produced in the interior of the platforms its growth and subsequent export to the flanks are at a maximum when the banks are flooded i e during interglacial periods during glacials skeletal grains dominate because the banks are exposed and carbonate production is limited to a narrow belt of skeletal sands and fringing reefs the resulting compositional signal appeared to have a good correlation with aragonite variations in the periplatform ooze between the turbidites further compositional variation parallels the change in turbidite frequency described earlier highstand bundling frequency and composition of turbidites are both unaffected by diagenesis and therefore provide an excellent monitor of sealevel fluctuations

dynamic causes of the relation between area and age of the ocean floor estimates for the area and age of the ocean floor are at odds with assumptions for mantle convection which imply that an older sea floor rather than a new one would be preferentially subducted over time previous efforts to explain these relationships have been based on geologic evidence and simple models coltice et al p 335 1 created numerical three dimensional convection models representing more realistic physical boundaries including a spherical earth the existence of continents and supercontinents over time and realistic rheologies a combination of continents and plate like behavior of the ocean floor sufficed to produce the observed relationship between plate area and plate age which explains why some old oceanic crust still remains 1 lookup doi 10 1126 science 1219120

thermospheric wind during a storm time large scale traveling ionospheric disturbance 1 a prominent large scale traveling ionospheric disturbance lstid was observed in japan during the major magnetic storm dst 358 nt of 31 march 2001 it was detected as enhancements of the 630 nm airglow and fof2 gps tec variations and a decrease in f layer virtual height at 1700 1900 ut 0200 0400 lt it moved equatorward with a speed of 600 m s the decrease in the f layer height was also detected by the mu radar at shigaraki thermospheric wind variations were observed by the mu radar through ion drift measurement and by a fabry perot interferometer fpi through a doppler shift of the 630 nm airglow line at shigaraki the wind data show a turn of the meridional wind from 94 m s equatorward to 44 m s poleward during the lstid indicating that an intense poleward wind in the thermosphere passed over shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the lstid intense poleward wind was also detected at mesospheric altitudes 95 100 km by the mu radar through meteor echoes and by the fpi through the 558 nm airglow with a delay of 2 hours from the thermospheric wind indicating downward phase progression of the wave generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics amie technique we suggest that simple atmospheric heating and or the lorentz force in the auroral zone do not explain the observed poleward wind enhancement

temporal and spatial distribution of whitings on great bahama bank and a new lime mud budget analysis of 69 shuttle and satellite images of the northern bahamas taken from 1965 to 1993 allowed us to calculate the regional and temporal distribution and longevity of 888 whitings on the great bahama bank at any time whitings cover between 35 and 200 km 2 in the area centered at lat 25 n and 78 50 w the highest occurrences of whitings are in april and october suggesting a seasonal component using a measured average of 10 6 mg l suspended sediment in typical whitings we calculated that 1 35 10 6 metric tons of lime mud are suspended every year if the suspended carbonate is precipitated in the water column these phenomena account for 280 of all of the holocene accumulated bank top mud and more than 40 of the total bank top mud and periplatform mud that have accumulated on the west side of great bahama bank

to the islands born the research potential of submerged landscapes and human habitation sites from the islands of nw australia this paper focuses on the continental shelf of nw australia and on models for change in littoral and offshore environments of relevance to human occupation over the last 50 kyr major island groups occur on the shelf including the montebello and barrow islands and those of the dampier archipelago at lowest sea level around 22 ka these would have been uplands that then became progressively isolated by subsequent sea level rise by integrating archaeological and zooarchaeological records from excavations on these islands with the geology and geomorphology we interpret palaeoeconomic resource potential in relation to changing sea level and coastline morphology the preservation potential for submerged archaeological sites and features is also assessed current archaeological evidence from these offshore islands indicates that the submerged coastal landscape is likely to have been a potentially rich environment for resources and human occupation even at times of lowest sea level and regional aridity should any exploration of submerged archaeology be carried out in this region it is likely to be rewarding offering unique insights into late pleistocene coastal occupation

theoretical effects of geomagnetic activity on low latitude ionospheric electric fields 1 the influence of geomagnetic activity on middle and low latitude thermospheric winds and ionospheric electric fields is investigated using model results from the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model model runs are made for different levels of geomagnetic activity model results show that the equatorward ionospheric currents produced by disturbance winds develop positive charge accumulation at low latitudes that maximizes in the premidnight sector the local time of maximum electric potential perturbation depends significantly on universal time so that the local time of reversal of the equatorial zonal perturbation electric field varies with longitude by 2 to 3 hours depending on the intensity of geomagnetic activity the westward perturbation electric field in the postsunset period indicates that stronger geomagnetic activity will produce a lower driven height of the evening f region after geomagnetic activity ceases model results show that the zonal disturbance winds can last for many days in the postrecovery period while the meridional disturbance winds decay more rapidly the long lasting zonal winds through the pedersen currents they drive help maintain meridional disturbance potential drops that decay much more slowly than the zonal disturbance potential drops after the activity ceases

lateral variations in cmb heat flux and deep mantle seismic velocity caused by a thermal chemical phase boundary layer in 3d spherical convection article i nfo numerical simulations of thermo chemical multi phase compressible mantle convection in a three dimensional spherical shell are used to investigate the relationship between lateral variations in seismic shear wave velocity vs above the core mantle boundary cmb and lateral variations in heat flux across the cmb qcmb when compositional variations and the post perovskite phase transition are included for simple thermal convection the vs qcmb relationship is reasonably but not perfectly linear the post perovskite transition introduces a non linearity that amplifies fast vs anomalies in cold regions but there is still a unique mapping between vs and qcmb lateral variations in composition such as piles of dense material introduce another non linearity that affects hot upwelling regions and introduces a non uniqueness in vs qcmb if the dense material e g morb is seismically fast compared to the surrounding material in this case dense piles are ringed by sharp low vs anomalies if the cmb is covered by a global dense layer than variations in vs and qcmb are reduced but so is the mean value of qcmb in all cases the peak to peak lateral variation in qcmb is similar to or larger than twice the mean value which might create problems for generating a dynamo according to existing numerical dynamo simulations analytical scalings are developed to explain the observed trends

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

cat island platform bahamas an incipiently drowned holocene carbonate shelf analyses of high resolution seismic reflection profiles and surface sediment samples indicate that the cat island shelf is presently in an incipiently drowned state this small carbonate bank is characterized by a thin 4 m coarse grained relict sediment cover along with limited reef development and a relatively deep 20 30 m margin indicating that it has been unable to keep up with holocene sea level rise early flooding at relatively high rates of sea level rise 4 m kyr 1 5 8 103 yr bp in conjunction with small bank size and relatively low elevation led to a reduced rate of carbonate accumulation and incipient drowning the shelf edge currently lies beneath the zone of maximum carbonate production and exposes the interior shelf to open marine conditions which may result in permanent drowning if it is unable to catch up with continued sea level rise sediment facies patterns are largely oriented perpendicular or oblique to the shelf edge and appear to be controlled by shelf circulation patterns focused by bank margin reentrants in comparison with most of the northern bahamas the cat island shelf was flooded earlier and at relatively higher rates of holocene sea level rise which led to selective drowning implying that carbonate platforms need not drown synchronously over widespread areas as commonly thought the potential rock record of this incipient drowning event would be a thin open marine sand sheet of highly degraded cryptocrystalline and aggregate grains associated with poorly developed reefs

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

effects of low viscosity post perovskite on thermo chemical mantle convection in a 3 d spherical shell 1 numerical simulations of thermo chemical multi phase mantle convection in a 3 d spherical shell are performed to determine how a low viscosity of post perovskite affects dynamics and structures in the deep mantle low viscosity post perovskite weakens the deepest part of slabs allowing them to more effectively spread over the core mantle boundary cmb and it also results in a greater volume of basalt segregating both of which increase the size of dense chemical piles the horizontal lengthscale of regions of pooled slab material and the steepness of piles edges in composition and phase consistent with the existence of steep sharp sided edges found in seismic analyses cmb heat flux is strongly enhanced in regions of low viscosity post perovskite consistent with a theoretical prediction and both cmb and surface heat flux are increased on average by a low viscosity of post perovskite which could have important implications for the evolution of earth s core and mantle

loss of primary texture and geochemical signatures in speleothems due to diagenesis evidences from castanar cave spain geochemical signals from speleothems are commonly used in the investigation of palaeoenvironments in most cases however little attention is paid to whether or not these signals are primary or altered by diagenesis the speleothems of the castanar cave caceres spain which are initially formed of calcite or aragonite have undergone a variety of meteoric diagenetic processes such as micritization and neomorphism inversion that collectively modify their primary features textures mineralogy geochemical signals the mean 13c and 18o values of the aragonites in the cave are 8 66 and 4 64 respectively whereas the primary calcites have mean 13c and 18o values of 9 99 and 5 77 respectively following the diagenetic process of micritization the aragonite isotopic signals averaged 7 63 13c and 4 74 18o and the calcite micrite signals 9 53 13c and 5 21 18o where inversion took place some secondary calcites after the aragonite show preserved aragonite whereas others do not the secondary calcites without aragonite relics show isotopic values slightly higher than those of the primary calcite due to the inheritance of the aragonite signal where aragonite relics are preserved the isotopic signatures are very similar to those of the aragonite micrite in addition the stable isotopic values and sr and mg contents of the speleothems became also modified by micritization and or inversion these diagenetic processes were driven by the changes in composition of the cave waters over time and space but also in the case of aragonite by its initial unstable mineralogy the present results highlight how important diagenesis is in caves and how the initial features of cave minerals may be lost these changes alter the geochemical signals shown by speleothems which may have an impact on the interpretation of the results obtained in palaeoenvironmental studies

high energy inner shelf carbonate facies along a tide dominated non rimmed margin northwestern australia abstract high energy inner shelf carbonates occur within 1 to 2 km of the mainland along the southern part of the northwest shelf a non rimmed carbonate shelf along northwestern australia coarse grained sands and gravels are deposited on and adjacent to a chain of subtidal and intertidal rock platforms which lies oblique to regional ne sw directed tidal currents intertidal and subtidal sand sheets less than 50 cm thick predominate along the margins and interior of the chain and subtidal linear to sinuous sand bodies up to 10 m thick and 4 km in length form banner banks to the northeast of rock platforms and reefs other features include narrow fringing and patch coral reefs calcareous red algal reefs and intertidal through subtidal coral shingle ridges fleshy algae are abundant on open sand covered and bare rock platforms as well as forming a mantle on relict coral reef frameworks supratidal through subtidal sediments are comprised of skeletal molluscs foraminifera bryozoans corals calcareous red algae and rock fragments the latter derived from rock platforms calcareous chlorophytes e g penicillus and halimeda are not important sediment contributors in general sediments are not representative of the present day turbid and fleshy algal dominated subtidal environment the predominantly coarse grained lithofacies

on the utilization of ionosonde data to analyze the latitudinal penetration of ionospheric storm effects upper atmosphere science is placing increased emphasis on global coupling between the magnetosphere ionosphere and thermosphere systems particularly with regard to the penetration of dynamic chemical and electrodynamic effects from high to low latitudes during magnetically disturbed periods an emerging potential exists for latitudinal and longitudinal chains of ionosondes to contribute uniquely to this thrust in ways complementary to the capabilities and shortcomings of other ground based sensors and satellites here we illustrate a methodology whereby the fullest potential of such ionosonde data can be realized data from a chain of stations close to the 165 magnetic meridian and separated by about 5 in magnetic latitude are used to study the relationships between magnetic activity hmf2 fof2 and inferred meridional winds during 17 28 april 1979 hourly values are fit in latitude using legendre polynomials and variations from quiet time values are displayed in latitude u t coordinates using a color graphics method which provides an illuminating illustration of the penetration of ionospheric disturbances in latitude and their dependence on kp storm time and local time observed effects are interpreted in terms of plausible electric field neutral wind and neutral composition changes during the storm period for instance net depletions in fof2 occur over the entire disturbed interval down to about 25 30 latitude apparently due to such increased n2 densities that the resulting enhanced plasma loss rates overcompensate any positive storm effects whereby southward winds elevate the f layer peak to altitudes of reduced chemical loss positive storm effects are however observed at lower latitudes and may also reflect the influence of electric fields as well as winds interestingly besides reflecting the anticipated southward flows and equatorward extensions in conjunction with magnetically disturbed conditions the 24 hour average meridional winds exhibit a northward return flow after the magnetic disturbance has relaxed this is a new feature of thermosphere dynamics which should be further investigated using general circulation models and other means of inferring the wind field

super plasma fountain and equatorial ionization anomaly during penetration electric field 1 relative importance of diffusion electric field and neutral wind on equatorial plasma fountain and equatorial ionization anomaly eia during a strong daytime eastward prompt penetration electric field ppef event are evaluated using the sheffield university plasmasphere ionosphere model and the recorded ppef during the super geomagnetic storm of 9 november 2004 the fountain rapidly develops into a super fountain during the ppef event the super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces or stops the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss the eia crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the ppef event however the crests become stronger than normal only in the presence of an equatorward wind the results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during a daytime eastward ppef event the equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms

impact megadomes and the origin of the martian crustal dichotomy abstract we show that a sufficiently energetic impact can generate a melt volume which after isostatic adjustment and differentiation forms a spherical cap of crust with underlying depleted mantle depending on impact energy and initial crustal thickness a basin may be retained or impact induced crust may be topographically elevated retention of a martian lowland scale impact basin at impact energies 3 1028 3 1029 j requires an initial crustal thickness greater than 10 km formation of impact induced crust with size comparable to the martian highlands requires a larger impact energy 1 3 1030 j and initial crustal thickness

rapid burial diagenesis of deep water carbonates exuma sound bahamas well lithified deep water periplatform limestones of late miocene age occur at subsurface depths from 113 m to total depth of 283 m at ocean drilling program odp site 632 in exuma sound bahamas this occurrence marked by a dramatic increase in compressional wave velocities up to 5 0 km s represents the most rapid transformation of ooze to limestone yet discovered in either periplatform or open ocean settings the burial diagenetic pathway is similar to those for meteoric and deep burial diagenetic environments aragonite dissolves magnesian calcites exsolve or dissolve low mg calcite precipitates as cement and secondary moldic vuggy porosity develops stable isotope ratios suggest precipitation of low mg calcite from cold marine derived pore waters accelerated diagenesis is a response to the influx of large quantities up to 80 of bank derived metastable carbonates and rapid burial via high accumulation rates up to 210 m m y our findings 1 document carbonate mineral stabilization and lithification in a seawater mediated shallow burial diagenetic environment 2 highlight the very high diagenetic potential of periplatform carbonates and 3 call into question the use of seismic velocities as support for the bahama megabank hypothesis

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

new aspects of thermospheric and ionospheric storms revealed by champ 1 the neutral mass density n and electron density ne at 400 km height measured by champ during nine intense geomagnetic storms bring out some new aspects of the thermospheric and ionospheric storms the thermospheric storms increase of n develop with the onset of the main phases mp of the geomagnetic storms and reach their peak phases before or by the end of the mps the ionospheric storms change of ne in general undergo an initial negative phase with the equatorial ionization anomaly eia crests shifting poleward before turning positive and the positive storms reach their peak strengths or phases centered at 25 30 magnetic latitudes in some 4 cases the positive storms develop without an initial negative phase and with the eia crests shifting equatorward in all cases the positive storms reach their peak phases before the end of the mps and turn to conventional negative storms by the end of the mps the observations agree with the different aspects of a physical mechanism of the positive storms the observations also reveal that the halloween storms of 30 october 2003 with a short mp without fluctuations produced the strongest positive ionospheric storms through impulsive response and there is strong equinoctial asymmetry in the ionosphere and thermosphere during geomagnetic storms

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

the potential for discovery of new submerged archaeological sites near the dampier archipelago western australia abstract the islands of the dampier archipelago preserve a probable 30 000 year archaeological record that reflects the change from a continental to an island environment following post glacial sea level rise the geomorphological history of the dampier archipelago region in combination with preliminary hydrodynamic modelling of past tidal regimes provides the basis for a new model of how the shelf landscape may have developed between the last glacial maximum c 20 ka bp through the holocene marine transgression and up to the present day using first order geomorphological principles an assessment is made of the key late pleistocene and holocene sediment bodies that may preserve archaeological deposits we show that archaeology is most likely to be present in deposits associated with the early phases of inundation of the dampier archipelago dating from around 9 7 ka bp at this time relative sea levels were around 30 m to 15 m which was when coastal configuration was complex and the variety and scale of intertidal and shallow sub tidal environments wide in contrast we anticipate that coastal archaeology older than 12 ka bp when the post glacial sea levels were below 50 m will have been exposed to a phase of faster tidal currents on the continental shelf and hence eroded or poorly preserved our study aims to improve prospection for and later management of the as yet unknown submerged elements of west australia s rich archaeological heritage

whiting related sediment export along the middle miocene carbonate ramp of great bahama bank modern aragonite needles are present all along the modern leeward margin of great bahama bank odp leg 166 while middle miocene sediments contain needles only in more distal areas sites 1006 and 1007 in contrast to the rimmed flat topped platform topography during the plio pleistocene the miocene great bahama bank morphology is a carbonate ramp profile this might imply a different location and precipitation type for miocene aragonite needles in this study aragonite needles in miocene sediments were isolated using a granulometric separation method furthermore the isolation of the various carbonate components enables the identification of primary versus diagenetic components the miocene aragonite needles are concentrated in the finest granulometric sediment fractions 12 m the fraction specific geochemical analyses 13c 18o and sr elemental abundance represent useful tools to assess the possible sources of the aragonite mud the geochemical variation of the fractions rich in pristine aragonite needles and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component both components indicate shallow water environments as the main sediment source area ramp top related fine grained particles now present at distal sites were likely exported as suspended material similar to present day transport mechanisms the scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded the granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine grained components

yin yang grid an overset grid in spherical geometry 1 a new kind of overset grid named yin yang grid for spherical geometry is proposed the yin yang grid is composed of two identical component grids that are combined in a complemental way to cover a spherical surface with partial overlap on their boundaries each component grid is a low latitude part of the latitude longitude grid therefore the grid spacing is quasi uniform and the metric tensors are simple and analytically known one can directly apply mathematical and numerical resources that have been written in the spherical polar coordinates or latitude longitude grid the complemental combination of the two identical component grids enables us to make efficient and concise programs simulation codes for geodynamo and mantle convection simulations using finite difference scheme based on the yin yang grid are developed and tested the yin yang grid is suitable for massively parallel computers

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

sea level at the last glacial maximum evidence from northwestern australia to constrain ice volumes for oxygen isotope stage 2 new sea level information from the bonaparte gulf in northwestern australia is used to constrain the magnitude and rates of change of ice volumes during the last glacial maximum lgm the region is tectonically stable and far from the former ice covered regions the glacio hydro isostatic adjustment of the coast is therefore relatively small and the corrections for this evect are not sensitive to details of the rebound model microfossil analysis and ams radiocarbon dating of 11 gravity cores taken across the shelf and bonaparte gulf demonstrate that 1 the lgm sea levels were locally at 125 4 m 2 the lgm terminated abruptly at 19 000 cal yr bp with a rapid rise in sea level of about 15 m over the next 500 years and 3 the onset of the minimum sea levels occurred before 22 000 cal yr bp when corrected for the glacio hydro isostatic evects the increase of lgm ice volumes over the present day ice volume is 52 5 106 km3 the termination of the lgm is marked by a rapid ice discharge of 5 2 106 km3 2001 elsevier science b v all rights reserved

estimates of holocene precipitation for rajasthan india based on pollen and lake level data abstract a pollen profile obtained from lake sediments at lunkaransar rajasthan in northwest india was used along with a pollen climate calibration function to estimate past precipitation between 10 500 and 3500 yr b p the estimated precipitation was about 500 mm yr or about 200 mm yr above the modern value a model was used for the energy and hydrologic budget of a lake basin and lake at sambhar located 240 km se of lunkaransar to calculate that a 200 mm yr increase in rainfall above the modern amount would have raised the lake level about 20 m above the modern level topographic charts and satellite imagery provided some evidence in support of an enlarged paleolake of that elevation but field exploration would be required to confirm the size and date of a former lake after about 3500 yr b p the lunkaransar profile indicated a desiccated lake bed because no pollen was preserved the pollen climate calibration function was of no use for estimating the amount of the precipitation decline a reduction of precipitation of about 200 mm yr below the modern amount was estimated from the energy and hydrologic budget for paleolake sambhar by assuming that the lake was one tenth of its present size during the dry interval

impact origin for the martian crustal dichotomy half emptied or half filled 1 one possible mechanism for martian hemispherical dichotomy formation is excavation of the northern lowland basin in the existing crust by a single giant impact here we explore a related scenario in which the impact melt volume is sufficient to fill the excavated cavity produce a thickened crust and generate a topographic basin centered on the opposite side of the planet we investigate this mechanism by formulating a model for viscous spreading of a partially molten layer over a spherical surface we derive numerical solutions and calculate the final area of the spreading layer as a function of impactor size and shape of the layer boundary due to an initially asymmetric melt region results are compared with observations including lowland basin size shape of the dichotomy boundary age difference between crustal provinces and crustal thickness

the pilbara coast a riverine coastal plain in a tropical arid setting northwestern australia abstract the unifying feature of the pilbara coast of northwestern australia is that it is a sedimentary repository for a range of rivers that drains a high relief precambrian rocky hinterland and discharges sediments along a coastal plain which fronts a wave dominated environment in a tropical arid climate the combination of fluvial and shoreline accretion processes coastal cementation coastal erosion and ancestral landform architecture such as residual pleistocene limestone ridges and large outcrops of precambrian bedrock has produced a complex coastal system during the quaternary as a result the coast is dominated by active deltas beach dune shores inactive eroding parts of deltas and their barriers limestone barrier coasts bays associated with eroded limestone barriers and archipelago ria coasts quaternary sediments throughout the area while varied in their distribution and history at the smaller scales exhibit a recurring pattern of lithotopes and lithologies in the region there are three main quaternary suites pleistocene red siliciclastic sediments alluvium deltaic sediments and aeolian sand that form an inland zone pleistocene limestones that form local barriers and a holocene system within which are the sedimentary suites of deltas beach dunes tidal flats and tidal embayments

positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms has been investigated to determine the phenomenological differences between positive and negative ionospheric storm effects using fof2 observations from azimuthal chain of stations to better organize the disturbance signatures two ionospheric indices were introduced to describe the maximum positive dfu index and negative dfl index deviation observed during an ionospheric storm a systematic appearance of nighttime positive effects was determined with a 24 hour recurrence the thermospheric ionospheric view associated with positive and negative storm effects proposed by prolss 1993 was extended to encompass our observations this test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms nevertheless the prominent feature of large nighttime enhancements in the ionization density have yet to be explained

three dimensional seismic analysis of sediment waves and related geomorphological features on a carbonate shelf exposed to large amplitude internal waves browse basin region australia this study analyses the three dimensional geometry of sedimentary features recorded on the modern sea floor and in the shallow subsurface of a shelf to upper slope region offshore australia that is characterized by a pronounced internal wave regime the data interpreted comprise an extensive 12 500 km2 industrial three dimensional seismic reflection survey that images the northern part of the browse basin australian north west shelf the most prominent seismic morphological features on the modern sea floor are submarine terrace escarpments fault scarps and incised channels as well as restricted areas of seismic distortion interpreted as mass wasting deposits besides these kilometre scale sea floor irregularities smaller bedforms were discovered also including a multitude of sediment waves with a lateral extent of several kilometres and heights up to 10 m these sedimentological features generally occur in extensive fields in water depths below 250 m mostly at the foot of submerged terraces along the scarps of modern faults and along the shelf break between the outer shelf and the upper continental rise additional bedforms that characterize the more planar regions of the outer shelf are elongate north west south east oriented furrows and ridges the formation of both sediment waves and furrow ridge systems requires flow velocities between 0 3 m sec 1 and 1 5 m sec 1 which could be generated by oceanic currents gravity currents or internal waves in the studied setting these velocities can be best explained as being generated by bottom currents induced by internal waves an interpretation that is discussed against oceanographic background data and modelling results in addition to the documentation of three dimensional seismic geomorphological features of the modern sea floor it was also possible to map kilometre scale buried sediment wave fields in the seismic volume down to ca 500 ms two way time below the present sea floor indicating the general potential for the preservation of such bedforms in the sedimentary record

genesis and dispersal of carbonate mud relative to late quaternary sea level change along a distally steepened carbonate ramp northwestern shelf western australia abstract accumulation of carbonate mud is minor on the northwest shelf western australia a broad 200 300 km wide distally steepened tropical carbonate ramp it is negligible along most of the inner ramp 0 to 50 m water depth owing to siliciclastic riverine input it is also negligible along the mid from 50 to 120 m ramp and where the entire ramp narrows to 100 km owing to constant reworking by storm waves and ocean swell in these areas carbonate mud is derived mostly from mechanical degradation of skeletal fragments but this does not include calcified remains of calcareous green algae e g halimeda although these plants grow locally only along the outer 120 to 200 m water depth ramp and slope is there any relatively abundant accumulation of carbonate mud here the sediment consists of modern pelagic foraminifer pteropod and nannoplantkon ooze and aragonitic needle rich 2 m micrite the latter having an age based on ams 14c of 19 ka distribution of aragonite micrite defines an extensive 5 0 104 km2 yet relatively narrow 40 km tract running 600 km along the platform margin crystal morphology mineralogy and isotope c o composition identify the micrite to be a seawater precipitate its production and seaward export having occurred during the last glacial maximum when lowered sea level transformed the otherwise broad platform into a narrow epicontinental shelf margin now the modern distal slope today this sediment body lies stranded in deep water about 200 300 km seaward of the shallow inner ramp the volume of micrite produced appears equal to the present day production potential of the great bahama bank rapid postglacial rise in sea level and change in platform geometry climate and oceanography were very influential factors in addition to water depth and area of submergence in the production and distribution of aragonite micrite along the northwest shelf in general 1 epicontinental carbonate platforms can lack substantial micrite accumulation when oceanic current and wave energies sweep unimpeded across a platform and coastal clastics and absence of shoal barriers prevent development of protective lagoons and carbonate tidal flats 2 not all highstand carbonate systems are associated with significant amounts of micrite in shallow water environments nor do they necessarily export large volumes of micrite to the periplatform realm and 3 some lowstand systems can produce and export volumes of carbonate mud that rival highstand systems

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

average daytime f region disturbance neutral winds measured by uars initial results thermospheric neutral winds play important roles on the dynamics of the upper atmosphere we use extensive f region zonal and meridional wind data measured by the wind imaging interferometer windii instrument on board the upper atmosphere research satellite uars to study the mid and low latitude daytime average perturbation winds during magnetically disturbed periods we have determined the perturbation winds by subtracting the quiet time wind values along the satellite orbits our data indicate large changes in the latitudinal profiles of both the zonal and meridional disturbance winds from morning to afternoon hours the early morning zonal disturbance winds are eastward near the equator and at upper mid latitudes above 50o and westward at lower mid latitudes the mid morning and afternoon zonal disturbance wind patterns show very small amplitudes at low latitudes and increasing westward winds at mid latitudes these latitudinal profiles are in excellent agreement with the patterns derived from zonal wind measurements on board the de 2 satellite the meridional daytime perturbation winds are equatorward and have magnitudes increasing linearly with latitude with largest values in the early morning sector the

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

a statistical study of the response of the dayside equatorial f2 layer to the main phase of intense geomagnetic storms as an indicator of penetration electric field 1 the response of the dayside equatorial f2 layer to the main phases of the 22 intense geomagnetic storms dst 150 nt in 1998 2008 is investigated using the digital ionosonde data from the equatorial stations in brazilian indian and australian longitudes together with equatorial electrojet strength and imf bz the storms include 15 superstorms dst 200 nt the observations show that there is a period during all mps when the f2 layer peak rises and falls rapidly with large peak electron density nmax reduction the rise velocity strongly correlates with the intensity dst of the storms and the duration of the nmax reduction corresponds to that of strong eastward electrojet when imf bz remains highly negative the observations indicate the occurrence of strong eastward prompt penetration electric fields ppef during the rapid f2 layer response the ppef drives the f2 layer peak rapidly upward which reduces nmax due to vertical expansion and diffusion the results therefore suggest that the rapid f2 layer response rapid rise and fall of peak height hmax with large nmax reduction observed by ionosondes can be used to detect the occurrence of the daytime eastward ppef during intense geomagnetic storms irrespective of season and level of solar activity the data also show two rare events of strong daytime westward electric fields due to disturbance dynamo and or prompt penetration the results are important when radars are not available to monitor the occurrence of the ppef

accumulation of bank top sediment on the western slope of great bahama bank rapid progradation of a carbonate megabank high resolution seismic profiles and submersible observations along the leeward slope of western great bahama bank show large scale export of bank top sediment and rapid progradation of the slope during the holocene a wedge shaped sequence up to 90 m thick is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6 8 ka total sediment volume of the slope sequence is 40 80 that of holocene sediment currently retained on the bank maximum rates of vertical accumulation and lateral progradation are 11 15 m ka and 80 110 m ka respectively 10 to 100 times greater than previously known for periplatform muds slope deposition of exported mud during sea level highs appears to have been a major mechanism for the westward progradation of great bahama bank throughout the quaternary this may provide a critical modern analogue for ancient progradational margins

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

relationships between colour and diagenesis in the aragonite calcite speleothems in basajaun etxea cave spain abstract basajaun etxea cave north spain contains a wide morphological and colour variety of speleothems most of them are composed of aragonite but calcite speleothems are also found their most common colour is white but there are also pink green and turquoise speleothems in different areas of the cave mg rich dissolution waters from the cave s crystalline dolostone and magnesite host rock favour aragonite precipitation and drive important diagenetic changes in this paper we will discuss how diagenesis modifies speleothem texture mineralogy and geochemistry causing significant changes in the colour we also discuss how speleothems that have undergone diagenesis may also be useful indictors of paleoclimatic conditions our work shows that diagenesis changes the colour of the speleothems because of the mobility of the chromophore elements during this process along with this elemental alteration comes the loss of the primary isotopic signals of speleothems detailed petrological studies of speleothems should precede their analysis for palaeoclimatic reconstruction so that influence of areas affected by diagenesis can be eliminated in addition diagenetic signals also contain valuable information on the changes of the waters within the cave and the overall evolution of speleothems and the cave itself

a physical mechanism of positive ionospheric storms at low latitudes and midlatitudes 1 a physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi instrument observations theoretical modeling and basic principles according to the mechanism an equatorward neutral wind is required to produce positive ionospheric storms the mechanical effects of the wind 1 reduce or stop the downward diffusion of plasma along the geomagnetic field lines 2 raise the ionosphere to high altitudes of reduced chemical loss and hence 3 accumulate the plasma at altitudes near and above the ionospheric peak centered at around 30 magnetic latitudes daytime eastward prompt penetration electric field ppef if it occurs also shifts the equatorial ionization anomaly crests to higher than normal latitudes up to approximately 30 latitudes the positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind the mechanism agrees with the multi instrument observations made during the supergeomagnetic storm of 7 8 november 2004 with 18 h long initial phase ip and 10 h long main phase mp the observations which are mainly in the japanese australian longitudes where the mp onset was in the morning 0600 lt 2100 ut show 1 strong positive ionospheric storms in ne nmax hmax global positioning system total electron content gps tec and 630 nm airglow intensity in both northern and southern hemispheres started at the morning 0600 lt mp onset and lasted for a day 2 repeated occurrence of strong eastward ppef events penetrated after the mp onset and superposed with westward electric field started before the mp onset and 3 storm time equatorward neutral winds inferred from 1 and 2 repeated occurrence of an unusually strong f3 layer with large density depletions around the equator was also observed during the morning noon mp

early permian deep water allochthonous limestone facies and reservoir west texas conventional cores from six wells in southwest reagan and northern crockett counties texas recovered interbedded limestone conglomerate intraclast and bioclast limestone calcarenite and shale twenty one lithologies are grouped into six lithofacies based on study of slabbed core surfaces lithoclast rudstone floatstone porous bioclast lithoclast rudstone floatstone bioclast wackestone intraclast floatstone rudstone thin bedded grainstone packstone calcarenite and dark gray shale the limestone facies are interpreted on the basis of petrologic characteristics biota regional stratigraphic setting and facies stratigraphy as deep water and allochthonous biotic constituents within the lithoclasts and matrix indicate an early permian wolfcamp age the porous bioclast lithoclast rudstone floatstone facies contains a modest but geologically significant oil reservoir at gunnx field southwest reagan county production is from 10 ft 3 m of perforations in about 42 ft 13 m of pale yellow brown porous limestone with intercrystalline reduced and solution enlarged biomoldic intraskeletal fracture and possible intergranular porosity moldic porosity appears to be mainly within lithoclasts baroque dolomite is rare to common and partly to completely fills former void space in addition to calcite spar and micrite porosity generally ranges 7 18 the producing depth is about 9 450 ft 2 880 m and the trap is stratigraphic the cored sequence at gunnx is interpreted as a basin floor complex of debris flow sheets which contain the reservoir overlain by interbedded thin carbonate turbidites thin debris flow sheets and shale the lowermost debris flow at gunnx was deposited on a thin generally undated shale the lower part of which is late pennsylvanian at west world field the shale is interpreted as representing starved basin floor deposition and abruptly overlies shallow water strawn limestone in core at west world field carbonate detrital components in the limestone at gunnx were probably derived from a wolfcamp platform at least 10 mi 16 km west and were emplaced by various submarine gravity flow processes age and facies determinations from cores in the gunnx area significantly alter earlier stratigraphic interpretations made with wireline logs alone late paleozoic allochthonous carbonate facies may provide significant new reserves in the permian basin

isotope records c o sr of late pliensbachian early toarcian environmental perturbations in the westernmost tethys majorca island spain the late pliensbachian early toarcian early jurassic was a time of major environmental changes that culminated with the early toarcian oceanic anoxic event t oae ca 183 ma this period is marked by significant disturbances in the carbon cycle and rapid climatic changes to improve the understanding of the expression of these events in westernmost tethyan domains this study provides new belemnite and bulk carbonate c and o stable isotope records of a 5 myr upper pliensbachian to middle toarcian marine succession of the balearic basin es cosconar section majorca time resolution has been improved by combination of biostratigraphic ammonoids and brachiopods and geochronologic 87sr 86sr methods seawater paleotemperatures derived from 18o belemnite records reveal cooler paleotemperatures in the upper part of the spinatum zone the uppermost spinatum zone is characterized by the onset of a warming event that crosses the pliensbachian toarcian boundary culminating with the warmer temperatures up to 10 c of warming for the serpentinum zone of the lower toarcian this warming event has been detected contemporaneously in many other european and tethyan basins and is interpreted to represent generalized raised seawater temperatures linked to the t oae four significant 13c events have been recorded in belemnite and bulk carbonate records the first is a negative carbon isotope excursion cie around the pliensbachian toarcian boundary which is best represented in the belemnite record soon after the bulk carbonate record shows a positive shift in the lower tenuicostatum zone concomitant with a return to background values in the belemnite record suggesting strong water stratification or decoupling probably related with export of neritic carbonate to the basin the third is a negative cie represented in bulk carbonate across the tenuicostatum serpentinum zonal transition which could be correlated with the negative excursion characterizing the onset of the t oae in other sections the position of this excursion corresponds with a gap in the belemnite record finally in the lower toarcian both the bulk carbonate and belemnite carbon isotope records show pronounced positive cies in the lower middle part of the serpentinum zone these cies testify the impact of the t oae in the balearic basin

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

high production and highstand shedding from deeply submerged carbonate banks northern nicaragua rise abstract because the shallow isolated carbonate banks on the northern nicaragua rise the nicaragua honduras and southern jamaica carbonate shelves and many other modern carbonate banks worldwide are covered by an average of 20 to 30 m of water and by a thin blanket of coarse carbonate sediments other carbonate sedimentologists have considered these banks good examples of incipiently drowned or even drowned carbonate banks however based on recent research on the northern nicaragua rise we can demonstrate that these banks currently are healthy producers of large volumes of periplatform sediments fine aragonite and magnesian calcite which are exported almost entirely to the deep surrounding slopes these sediments which were deposited during the past 9000 10 000 years form peripl tform wedges on the middle and upper slopes which are seen clearly on 3 5 khz seismic profiles radiocarbon ages of the wedge surface sediment range between 230 and 610 ybp and provide clear evidence for the contemporaneous production of sediments on the shallow bank and shelf and their instantaneous export to the upper slopes for the last 5000 years sedimentation rates ranged from 2000 mm ky off pedro bank to 1300 mm ky off jamaica these rates are somewhat lower than but of the same order of magnitude as sedimentation rates on the western leeward slopes of great bahama bank deposition of the metastable carbonate sediments discussed in this paper occurred as soon as sea level rose to flood the bank and shelf which flank walton basin following the last glacial lowstand they com rise a wedge shaped package of transgressive and highstand sediments on the upper and middle slopes of pedro bank and the southern jamaica shelf

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

biochemical and ultrastructural evidence for the origin of whitings a biologically induced calcium carbonate precipitation mechanism we propose that bahamian whitings floating patches of lime mud are in part the result of biological precipitation of calcium carbonate induced by picoplankton and cellular components the cells may act as nucleation sites for crystallization from seawater supersaturated with caco3 our model represents a new hypothesis concerning bahamian whiting formation and is based on several lines of evidence biochemical data suggest that the macromolecules from carbonate suspended in bahama banks whitings are distinct from those found in the lime mud sediment producer penicillus and from bottom sediment direct ultrastructural evidence indicates that mineralization occurs on the surfaces of picoplankton cells and degrading organic cellular components the organic constituents include but are not restricted to whole and fragmented algal cells and composite structures 20 30 m in diameter the observed calcium carbonate crystals are distinct from skeletal debris because of the magnitude of the whiting phenomenon calculations of carbonate sediment production budgets should include the potential contribution of calcium carbonate produced by epicefular precipitation knowledge of carbonate mud genesis is critical to interpretation of ancient occurrences of lime mud as well as to understanding ancient and global carbon cycles

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

oligocene and miocene carbonate platform development in the browse basin australian northwest shelf abstract extensive 2d and 3d seismic reflection data calibrated by wells provide new insights into the lateral extent morphology internal architecture and age of carbonate platforms in the subsurface of the browse basin australian northwest shelf nws the oldest carbonate build ups are interpreted as a giant bryozoan build up complex of oligocene age 34 03 27 8 ma in the late burdigalian tropical reef growth began and numerous reef rimmed carbonate platforms progressively coalesced into an extensive barrier reef from the mid langhian to the early tortonian the browse basin contained an elongate along margin barrier reef system over 500 km long this barrier reef possibly extended in the southwest into the northern carnarvon basin after the early tortonian reefs on top or landward of this major barrier reef system were smaller and less connected this significant reduction in area covered by reef rimmed platforms likely resulted from cooling following the mid miocene climate optimum and relatively high subsidence rates the reef rimmed carbonate platforms that formed between the late burdigalian and the early tortonian are very similar throughout the browse basin platform development after the early tortonian was regionally diverse high subsidence rates in the northern browse basin are interpreted to have promoted the development of thick aggrading platforms lower subsidence in the south led to thinner more widespread platforms recurrently shifting location in response to eustatic change the final phase of reef decline around 6 ma coincides with an increase in current driven drift sedimentation current related winnowing of sediments from the lagoons and slopes of the remaining carbonate platforms likely contributed to their final drowning

zonal flow formation in the earth s core as zonal flows are common in turbulent convection regimes such as in the atmospheres of giant planets and the earth s oceans they might also be present in the earth s outer core which is thought to be in a turbulent state takehiro miyagoshi and colleagues have investigated numerical simulations of the earth s geodynamo with lower viscosities than most previous simulations have been able to use and have identified a new convection regime of core flow that exhibits a dual structure inner sheet like radial plumes surrounded by westward cylindrical zonal flow thus convection in the earth s outer core may therefore resemble that seen in planetary atmospheres and oceans more closely than was expected zonal jets are common in nature and are spontaneously generated in turbulent systems because the earth s outer core is believed to be in a turbulent state it is possible that there is zonal flow in the liquid iron of the outer core by investigating numerical simulations of the geodynamo with lower viscosities than most previous simulations have been able to use a convection regime of the outer core is now found that has a dual structure comprising inner sheet like radial plumes and an outer westward cylindrical zonal flow zonal jets are very common in nature well known examples are those in the atmospheres of giant planets and the alternating jet streams found in the earth s world ocean1 zonal flow formation in nuclear fusion devices is also well studied2 a common feature of these zonal flows is that they are spontaneously generated in turbulent systems because the earth s outer core is believed to be in a turbulent state it is possible that there is zonal flow in the liquid iron of the outer core here we report an investigation at the current low viscosity limit of numerical simulations of the geodynamo we find a previously unknown convection regime of the outer core that has a dual structure comprising inner sheet like radial plumes and an outer westward cylindrical zonal flow we numerically confirm that the dual convection structure with such a zonal flow is stable under a strong self generated dipole magnetic field

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

low holocene level 7700 to 3650 years ago of lake titicaca bolivia abstract preliminary results of sedimentological and paleontological analysis of two cores taken in lake titicaca bolivia indicate that between 7700 and 3650 yr b p the lake level was up to 50 m lower than at present evaporitic deposits occurred at the maximum low lake level

evidence for the equatorward penetration of electric fields winds and compositional effects in the asian pacific sector during the september 17 24 1984 ets interval data from a chain of eight ionosondes between 15 and 51 magnetic latitude near the 165 east magnetic meridian asian pacific sector are analyzed to illustrate the equatorward penetration of ionospheric storm effects during the september 17 24 1984 equinox transition study ets interval hourly values of measured f0f2 m 3000 f2 and f0e are used to infer the storm time deviations of f0f2 hmax and an effective meridional wind speed from their average magnetically quiet values at the beginning of the interval the latter parameters are subjected to a 5 hour running average and are fit with legendre polynomials in latitude to clarify the large scale dynamical features in a color coded display the method illustrates the equatorward penetration of several phenomena in response to changing magnetic conditions interpreted as follows 1 elevations in hmax of the order of 40 km occur down to 35 45 magnetic latitude during the first less intense magnetic storm occurring on september 19 and elevations of the order of 50 70 km penetrate to at least 15 magnetic latitude during the more intense storm at the end of the interval these effects are interpreted as primarily due to meridional winds driven by high latitude heating 2 daytime depressions in f0f2 occur on the following day storm negative phase of the order of 1 0 1 5 mhz 30 change between 30 and 40 magnetic latitude after the first storm and of the order of 2 0 2 5 mhz 45 change down to 15 20 magnetic latitude after the second storm due to decreased o n2 ratios connected with the global heating and dynamical transport 3 enhancements in f0f2 of the order of 2 0 3 0 mhz 30 40 change near 15 20 magnetic latitude are interpreted as originating from a pumping up of the fountain effect by eastward electric fields penetrating to low latitudes during the early phases of the storms and a secondary enhancement several hours later is consistent with the existence of an ionospheric disturbance dynamo 4 diurnal average meridional winds inferred from the changes in hmax illustrate disturbance mean meridional circulations of the order of 20 25 m s 1 and 30 50 m s 1 for the two disturbances whose equatorward penetration is sensitive to the energetic input at high latitudes this information forms one data set which numerical simulations of the ets interval should strive to reproduce

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

late quaternary shedding of shallow marine carbonate along a tropical mixed siliciclastic carbonate shelf great barrier reef australia the north east australian margin is the largest modern example of a tropical mixed siliciclastic carbonate depositional system with an outer shelf hosting the great barrier reef gbr and an inner shelf dominated by fluvially sourced siliciclastic sediment wedges the long term interplay between these sediment components and sea level is recorded in the queensland trough a 1 2 km deep n s elongate basin situated between the gbr platform and the queensland plateau in this paper 154 samples from 45 surface grabs and six well dated piston cores were analysed for total carbonate content carbonate mineralogy and sr concentration to establish spatial and temporal patterns of carbonate accumulation in the queensland trough over the last 300 kyr surface carbonate contents are lowest on the inner shelf 5 and in the trough axis 60 because of siliciclastic dilution carbonate on the shelf is mostly sr rich aragonite and high mg calcite hmc whereas that in the basin is mostly low mg calcite once normalized to remove the effects of siliciclastic dilution surface sr rich aragonite and hmc abundances decrease linearly to background levels 100 km seaward of the shelf edge core samples show that over time normalized aragonite and sr abundances are greatest during periods of shelf flooding and lowest when sea level drops below the shelf edge this is consistent with changes in the production of coral and calcareous algae and the shedding of their debris from the shelf interestingly normalized hmc concentrations on the slope peak during periods of major transgression perhaps because of maximum off shelf transport from inter reef areas or intermediate water dissolution after accounting for siliciclastic dilution there are strong similarities in both spatial and temporal patterns of carbonate minerals between slopes and basins of the north east australian margin and those of pure carbonate margins such as the bahamas a limited set of basic processes including the formation and breakdown of carbonate on the shelf the transport of carbonate off the shelf and eustatic sea level probably controls carbonate accumulation in slope and basin settings of tropical environments irrespective of proximal siliciclastic sediment sources

low latitude ionospheric disturbance electric field effects during the recovery phase of the 19 21 october 1998 magnetic storm 1 low latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity these perturbations can last for several hours after geomagnetic quieting we use incoherent scatter radar measurements from jicamarca and arecibo during 19 21 october 1998 to study for the first time the low latitude disturbance electric fields during the recovery phase of a large magnetic storm on 19 october the jicamarca data showed initially large and short lived time scale of about 10 20 min upward and westward drift perturbations in the early afternoon sector due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure following the decrease of auroral activity very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over jicamarca but surprisingly only small and sporadic perturbation drifts were present over arecibo the latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds the disturbance dynamo drifts also indicate significantly different local storm time and possibly latitudinal dependences for their vertical perpendicular and zonal drift components suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector in the next day during moderately disturbed conditions the daytime perturbation drifts were small but following transient increases in geomagnetic activity large upward perpendicular drifts were observed near dusk over jicamarca and arecibo where simultaneous westward perturbation drifts were also seen these perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator the measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models later at night under moderately disturbed conditions relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars our results illustrate the large variability of the low latitude perturbation electric fields relative to their climatological values after large storms probably due to the importance of additional disturbance processes they also indicate that a much deeper understanding of solar wind magnetospheric ionospheric processes is required for accurate predictions of these electric fields

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

mid latitude ionospheric irregularities persisting into late morning during the magnetic storm on 19 march 2001 1 post sunrise intense ionospheric irregularities at low to mid latitudes are reported for the first time a method based on spaced receiver technique is proposed to estimate the apparent drift velocity of the irregularities by using the correlation of the slant total electron content tec from 3 gps receivers the irregularities were detected at 23 45 n by the gps earth observation network geonet of japan from 0455 lt to 1051 lt on 21 march 2001 during the recovery phase of the magnetic storm at the corresponding time spread f was observed with 3 ionosondes located meridionally at okinawa 127 8 e 26 3 n 20 7 n magnetic latitude kokubunji 139 5 e 35 7 n 30 0 n magnetic latitude and wakkanai 141 7 e 45 4 n 40 5 n magnetic latitude while an intense negative ionospheric storm was processing and propagating from mid to lower latitudes the irregularities were seen as plasma bubbles by the defense meteorological satellite program dmsp in situ measurements westward drift with the speed of 100 m s was estimated by spaced receivers from geonet and confirmed by dmsp during the evolution of the irregularities the plasma bubbles at mid latitude sustained 1 5 hour after sunrise and at the lower latitudes they survived more than 4 hours after sunrise the observations suggested that the irregularities were generated by an eastward electric field associated with the disturbance dynamo and the long time existence of the irregularities after sunrise seemed to be related to the daytime intense negative ionospheric storm on 21 march

great bahama bank aragonitic muds mostly inorganically precipitated mostly exported sr concentrations in aragonitic muds on the banktop and leeward slope of great bahama bank gbb are greater than in the needles produced by codiacean green algae but the same as in precipitated sand size ooids and other nonskeletal grains results of two part and three part mixing models suggest that chemically precipitated aragonite contributes an average of 55 78 of the clay size aragonite individual samples contain as much as 95 chemically precipitated aragonite nonskeletal aragonitic needles apparently are precipitated ubiquitously over gbb but accumulate on the banktop only leeward of andros island much of the mud produced on the bank is exported to deeper waters the thickness of mud dominated holocene sediments on the leeward slope can reach 90 m and the aragonitic lysocline around the bahamas is depressed by nearly 1500 m

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

conditions for intense ionospheric storms expanding to lower midlatitudes 1 for studying conditions of intense ionospheric storms at lower midlatitudes several storms that occurred in march and april 2001 were compared in the two largest magnetic disturbances that occurred during this period the disturbance dst index reached 387 and 271 nt the two largest ionospheric storms occurred in response to other weaker magnetic disturbances in which dst reached 149 and 102 nt for the largest ionospheric storms on 21 march 2001 and 22 april 2001 a sequence of ionospheric and thermospheric disturbances was analyzed we found that a nighttime disturbance dynamo plays an important role in expanding ionospheric storms to lower latitudes when an eastward disturbance dynamo electric field forms after midnight the ionospheric layer is uplifted and the ion drag is reduced the storm time equatorward surge effectively reaches lower latitude regions without decaying under the condition of reduced ion drag the equatorward surge pushes up the ionosphere in turn and the ion drags might be further reduced the large event to event variation of ionospheric storms might be partly owing to such a positive feedback process in addition to the well known local time effect