diagenesis of the lower eocene thebes formation gebel rewagen area eastern desert egypt abstract the diagenesis of lower eocene shallow water carbonates with flint was studied in the gebel rewagen area eastern desert egypt the carbonates are mainly wackestones to packstones with benthic bioclasts embedded in a dark red luminescent micrite matrix the studied succession displays a complex diagenetic history that involves syngenetic and late diagenetic processes silica which exists either as persistent bands nodules and or silicified benthic bioclasts shows a distinctive pattern regarding its distribution source depositional environments and timing three lines of evidence support a syngenetic origin of the chert bands 1 they alternate in a cyclic manner within the host carbonates and 2 they exhibit noticeable lateral persistence throughout the investigated area following the strata boundaries and 3 there is a lack of any carbonate dissolution in limestone adjacent to chert bands the deposition of silica bands in association with shallow water carbonates is possibly related to eustatic sea level changes which were accompanied by episodic variations in silica and carbonate productivities with a relative sea level fall and the establishment of a lowstand period at the end of the early eocene a basinward shift of the groundwater zones is expected within the carbonate platform during this period some late diagenetic processes took place which involve 1 the formation of siliceous and carbonate concretionary growths 2 partial silicification of bioclasts 3 neomorphic stabilization of the caco3 bioclasts and 4 the formation of equant calcite cement siliceous and carbonate concretions are believed to have taken place within microenvironments created and controlled by sulphate reducing bacteria and physico chemical and kinetic factors near a marine meteoric water mixing zone this is inferred from the distribution of iron sulphides the non ferroan nature of all concretions and the depleted 13c 5 4 to 6 0 pdb and 18o 5 8 to 6 8 pdb values of the carbonate concretions the silica fabrics of all the partly silicified benthic bioclasts with abundant pyrite cubes argue for a delayed silicification process within the sulphate reduction zone the close and relatively depleted 18o values of the low mg calcite micrite matrix 3 0 to 4 4 pdb and benthic bioclasts 3 4 to 4 8 pdb indicate that both matrix and bioclasts have probably suffered neomorphic stabilization from freshwater dominated solutions the initial marine 13c values of both low mg calcite matrix 0 2 to 2 2 pdb and altered benthic bioclasts 0 2 to 0 9 pdb are retained and not affected by diagenesis the luminescence character and the extremely depleted oxygen values 8 3 to 10 1 pdb of the equant void filling calcite mosaics are consistent with their formation within a meteoric phreatic realm

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

estimating sea ice area flux across the canadian arctic archipelago using enhanced amsr e 1 enhanced resolution advanced microwave scanning radiometer amsr e imagery is used to estimate daily sea ice area fluxes between the canadian arctic archipelago and the arctic ocean and baffin bay for the period september 2002 to june 2007 over the period amundsen gulf and m clure strait exported 54 103 km2 of sea ice area or roughly 77 km3 of sea ice volume each year into the arctic ocean export import into the arctic ocean through the queen elizabeth islands is small and uncertain since no estimates for july and august could be made due to atmospheric attenuation of the microwave signal lancaster sound exported 68 103 km2 of sea ice area or roughly 102 km3 of ice volume into baffin bay this produced a net loss of sea ice area of about 122 103 km2 or roughly 174 km3 a 1 which is presumed to be generated from within the archipelago itself mainly through the stationary and transient polynyas and leads that form each winter daily ice area fluxes for amundsen gulf ag and lancaster sound ls were as high as 2500 km2 d 1 and were event driven depending on synoptic scale atmospheric circulation and the mobility of the sea ice mean sea level pressure difference across each gate is moderately correlated with daily sea ice area fluxes despite the fact that free ice drift conditions are not always met in the region cross gradient and daily sea ice area flux for lancaster sound show a large number of counter gradient ice flux occurrences suggesting that local mesoscale winds nongeostrophic and perhaps ocean currents play a role in transporting sea ice through this gate monthly ice fluxes for the ag and ms gate were positively correlated with the ao index indicating that a strong beaufort sea high pressure and gyre correspond to more export into the beaufort sea monthly fluxes for the ls gate were positively correlated with the nao index indicating that strong southerly atmospheric circulation over baffin bay increases ice export into baffin bay from lancaster sound

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

a modeling study of coastal circulation and landfast ice in the nearshore beaufort and chukchi seas using ciom this study investigates sea ice and ocean circulation using a 3 d 3 8 km ciom coupled ice ocean model under daily atmospheric forcing for the period 1990 2008 the ciom was validated using both in situ observations and satellite measurements the ciom successfully reproduces some observed dynamical processes in the region including the bering inflow originated coastal current that splits into three branches alaska coastal water acw central channel branch and herald valley branch in addition the beaufort slope current bsc the beaufort gyre the east siberian current esc mesoscale eddies and seasonal landfast ice are well simulated the ciom also reproduces reasonable interannual variability in sea ice such as landfast ice and anomalous open water less sea ice during the positive dipole anomaly da years vice versa during the negative da years sensitivity experiments were conducted with regard to the impacts of the bering strait inflow heat transport onshore wind stress and sea ice advection on sea ice change in particular on the landfast ice it is found that coastal landfast ice is controlled by the following processes wind forcing bering strait inflow and sea ice dynamics

origin of chondrule rims and interchondrule matrices in unequilibrated ordinary chondrites optical microscopy electron probe microanalysis scanning electron microscopy and analytical transmission electron microscopy were used to study the interchondrule matrix and opaque chondrule rims in bishunpur krymka semarkona chainpur all ll3 tieschitz and sharps both h3 the size distribution of grains in matrix in bishunpur obeys a power law rims around chondrules tend to be finer grained than matrix and may be layered all rims and matrices studied contain clasts of forsteritic olivine and low ca pyroxene in bishunpur the clasts may be cemented by amorphous glue rich in normative albite and partly altered to smectite rims in krymka sharps chainpur and tieschitz have a densely packed olivine groundmass with a grain size of about 0 1 m in krymka groundmass olivine is fo20 30 and forms interlocking dendrites various fe oxides are present in rims and matrices grain size distribution and chemical data indicate that clastic olivines and pyroxenes are derived from chondrules from analyses matrices rims in the ll group apparently are enriched in a feldspathic component tieschitz rims are slightly enriched but here the feldspathic component is present as white matrix sharps rims are not enriched in a feldspathic component opaque interchondrule matrices and chondrule rims probably formed from the products of fragmentation of chondrules partly induced by contraction of protopyroxene on inversion to clinopyroxene fragmented silica rich chondrule mesostases reacted with fe oxides and na to form the groundmass of fayalitic olivine and feldspathic glue a low temperature nebular or pre solar component is limited to 3 vol of each meteorite so equilibrium condensate was not the carrier of volatiles such as tl and bi

coexisting goethite and gibbsite from a high paleolatitude 55 n late paleocene laterite concentration and 13c 12c ratios of occluded co2 and associated organic matter abstract a late paleocene 60 ma bp lateritic soil from northern ireland the antrim paleosol herein referred to as nire contains coexisting goethite gibbsite phyllosilicate and hematite the fe iii oxides exhibit pisolitic and liesegang type morphologies that are mutually exclusive in hand specimens x ray diffraction xrd measurements of al substituted for fe in goethite indicate two populations 1 low al liesegang type goethites 0 mol al and 2 high al pisolitic goethites 9 to 24 mol al selective dissolution and incremental vacuum dehydration decarbonation were used to determine the concentration and 13c values of co2 occluded in the respective structures of the goethites and gibbsites in this complex mixture of nire lateritic minerals the fe co3 oh component in the high al goethites appears to retain a proxy carbon isotopic record of vadose zone co2 in the ancient soil the 13c values of co2 occluded in coexisting goethites and gibbsites indicate that these minerals did not form in equilibrium with the same environmental co2 the measured mole fractions x of fe co3 oh in the high al goethites range from 0 0059 0 0005 to 0 0077 0 0006 and correspond to soil co2 concentrations of 28 000 to 37 000 ppmv the average values of x and 13c for the four high al goethites are 0 0067 0 0007 and 20 1 0 5 respectively the 13c value of the organic matter undergoing oxidation in this midlatitude 55 n late paleocene soil appears to have been 28 2 taken together these data indicate an atmospheric co2 concentration of 2400 ppmv 1200 ppmv at 60 ma bp the inferred high concentration of atmospheric co2 would have been coincident with the warm global climate of the late paleocene and is consistent with the idea that co2 plays an important role in climate variation

stable isotope record in paleosol carbonates from the chinese loess plateau implications for late neogene paleoclimate and paleovegetation abstract stable carbon and oxygen isotope analyses were conducted on pedogenic carbonates collected from a continuous late neogene terrestrial sequence located in lantian in the chinese loess plateau the sequence consists of 300 m of fluvial deposits bahe formation with a basal age of ca 11 ma overlain by ca 50 m thick sequence of aeolian red clay lantian formation deposited between 6 8 and 2 6 ma pedogenic carbonates from the fluvial part of the sequence i e the bahe formation show only slight variation in 13 c and 18 o values suggesting that no marked change in plant photosynthetic pathway or climate took place during ca 10 6 8 ma the carbon isotope compositions imply a pure c 3 vegetation however most data are in the upper c 3 plant range suggesting that water stress conditions prevailed in the area a shift in both carbon and oxygen stable isotope curves occur at the boundary of the two formations where the sedimentation regime changed from fluvial to mainly aeolian the 13 c record shows more depleted values in the lantian formation with no indications of c 4 plant contribution in the soil carbonate except for the youngest sample at ca 2 7 ma the formation boundary marks a general rise in 18 o values moreover the 13 c and 18 o values scatter more in the lantian formation compared to those measured from the bahe formation as the shift in 13 c and 18 o values at the formation boundary is concurrent we hypothesize that the reason for the changes in both values are mostly interrelated the changes probably reflect increased summer precipitation related to the onset and or intensification of the asian monsoon system sedimentological and fossil vertebrate analyses suggest that stable environments with relatively dry conditions prevailed during the time when the bahe formation was laid down slightly below the formation boundary there is a faunal turnover event implying a marked change into more humid and closed habitats the paleoenvironmental patterns deduced from carbon and oxygen isotopes are in good agreement with the palaeoenvironments inferred from sedimentological and paleontological studies from the lantian area

late twentieth century northern hemisphere sea ice record from u s national ice center ice charts 1 arctic sea ice plays a key role in the climate system by acting as the interface between a warm ocean and a cold atmosphere establishing the true pattern of recent behavior of the sea ice in this region is critical to simulating the role of sea ice in future climate recently released operational ice charts from the u s national ice center provide insight into the late twentieth century behavior of northern hemisphere sea ice providing more reliable ice concentrations during summer and freeze up than those available from the passive microwave record the major winter and summer modes of ice concentration variability observed from empirical orthogonal function analysis covering the period 1972 1994 are shown to indicate respectively the 1 year lagged response of the sea ice to the north atlantic oscillation and the winter preconditioning of summer sea ice coverage in the eastern arctic by the north atlantic oscillation feedback to the atmosphere is suggested in each case by zero lag cyclone frequency relationships to these two sea ice modes of variability

variability of an under ice river plume in hudson bay observations of the great whale river plume in the coastal waters of hudson bay canada during late winter and early spring during four different years showed its area to vary as a power of the discharge the under ice plume area was much larger than plume area in open water for comparable discharges differences in plume geometry were related to elapsed time since ice formation and low frequency variability of the coastal circulation the strength and orientation of the coastal motion was weakly correlated with the cross hudson bay atmospheric pressure gradient the passage of low pressure systems over hudson bay is thought to generate a progressive edge wave in the absence of direct wind forcing the amplitude of the low frequency variations in coastal circulation decreased with the increasing spatial extent of the landfast ice in the study area

relict and other anomalous grains in chondrules implications for chondrule formation we have identified relict olivine and pyroxene grains in chondrules from ordinary and carbonaceous chondrites that probably did not crystallize in situ some of these olivines are clear but others contain fine grained fe ni dusty olivines and resemble previously described occurrences in ordinary chondrites there are also chondrules in which all olivine is dusty we conclude 1 not all relict olivines are dusty 2 not all dusty olivines crystallized outside the chondrule in which they occur and 3 some dusty olivines were produced during chondrule formation by a reduction process that affected the whole chondrule the occurrence of dusty olivines and relict pyroxenes and olivines in chondrules from carbonaceous as well as ordinary chondrites supports the argument that chondrules from all chondrites had similar origins and histories we propose that chondrules and mineral fragments were transported across f o2 gradients in the solar nebula while they were hot or were reheated in an environment different from the one in which they formed partially molten chondrules sometimes incorporated mineral grains or chondrules with different redox states producing compound chondrules and chondrules containing anomalous grains dusty olivines may also have formed when hot chondrules were transported to regions of lower oxygen fugacity

seasonal and interannual variability of fast ice extent in the southeastern laptev sea between 1999 and 2013 along with changes in sea ice extent thickness and drift speed arctic sea ice regime is characterized by a decrease of fast ice season and reduction of fast ice extent the most extensive fast ice cover in the arctic develops in the southeastern laptev sea using weekly operational sea ice charts produced by arctic and antarctic research institute aari russia from 1999 to 2013 we identified five main key events that characterize the annual evolution of fast ice in the southeastern laptev sea linking the occurrence of the key events with the atmospheric forcing bathymetry freezeup and melt onset we examined the processes driving annual fast ice cycle the analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season while the wind has a strong influence only on the first stages of fast ice development the maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals where fast ice is likely grounded the annual fast ice cycle shows significant changes over the period of investigation with tendencies toward later fast ice formation and earlier breakup these tendencies result in an overall decrease of the fast ice season by 2 8 d yr which is significantly higher than previously reported trends

on the relationship between isolated and chondrule olivine grains in the carbonaceous chondrite alha77307 abstract the origin of isolated olivine grains in carbonaceous chondrites has been suggested to be either by direct condensation or by fragmentation of chondrules in an attempt to resolve this debate isolated olivine grains in the carbonaceous chondrite alha77307 have been studied in detail zoning characteristics and minor element compositions of olivines from all isolated and chondrule occurrences are described the data show that a strong relationship exists between isolated olivines and the chondrule population chondrule olivine compositions and zoning properties are consistent with olivine crystallization from the molten chondrules because properties of isolated grains are very similar to chondrule olivines an igneous origin for most if not all isolated grains is proposed large isolated forsterite grains may be derived from fragmentation of macroporphyritic type i chondrules which contain one or very few large olivine grains relic forsterite grains in type ii chondrules and complex isolated olivine grains with forsteritic cores and fayalite rich rims provide evidence that fragmentation and recycling of chondrules and their components was a common and efficient process in the chondrule forming region

a basal stress parameterization for modeling landfast ice current large scale sea ice models represent very crudely or are unable to simulate the formation maintenance and decay of coastal landfast ice we present a simple landfast ice parameterization representing the effect of grounded ice keels this parameterization is based on bathymetry data and the mean ice thickness in a grid cell it is easy to implement and can be used for two thickness and multithickness category models two free parameters are used to determine the critical thickness required for large ice keels to reach the bottom and to calculate the basal stress associated with the weight of the ridge above hydrostatic balance a sensitivity study was conducted and demonstrates that the parameter associated with the critical thickness has the largest influence on the simulated landfast ice area a 6 year 2001 2007 simulation with a 20 km resolution sea ice model was performed the simulated landfast ice areas for regions off the coast of siberia and for the beaufort sea were calculated and compared with data from the national ice center with optimal parameters the basal stress parameterization leads to a slightly shorter landfast ice season but overall provides a realistic seasonal cycle of the landfast ice area in the east siberian laptev and beaufort seas however in the kara sea where ice arches between islands are key to the stability of the landfast ice the parameterization consistently leads to an underestimation of the landfast area

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

evidence in co3 0 chondrules for a drift in the o isotopic composition of the solar nebula several recent studies have shown that materials such as magnetite that formed in asteroids tend to have higher 17o 17o 0 52 x 18o values than those recorded in unaltered chondrules other recent studies have shown that in sets of chondrules from carbonaceous chondrites 17o tends to increase as the feo contents of the silicates increase we report a comparison of the o isotopic composition of olivine phenocrysts in low feo fa1 type i and high feo fa15 type ii porphyritic chondrules in the highly primitive co3 0 chondrite yamato 81020 in agreement with a similar study of chondrules in co3 0 alh a77307 by jones et al 2000 17o tends to increase with increasing feo we find that 17o values are resolved but only marginally between the two sets of olivine phenocrysts in two of the high feo chondrules the difference between 17o of the late formed high feo phenocryst olivine and those in the low feo cores of relict grains is well resolved although one of the relicts is interpreted to be a partly melted amoeboid olivine inclusion by yurimoto and wasson 2002 it appears that during much of the chondrule forming period there was a small upward drift in the 17o of nebular solids and that relict cores preserve the record of a different and earlier nebular environment

multiyear ice replenishment in the canadian arctic archipelago 1997 2013 in the canadian arctic archipelago caa multiyear ice myi replenishment from first year ice aging caamyi oct 1 and arctic ocean myi exchange caamyi exchange contribute to the caa s relatively heavy sea ice conditions at the end of the summer melt season we estimate these components using radarsat and the canadian ice service digital archive and explore processes responsible for interannual variability from 1997 to 2013 caamyi oct 1 52 36 103 km2 provides a larger contribution than caamyi exchange 13 11 103 km2 caamyi oct 1 represents 10 of the amount that occurs in the arctic ocean caamyi exchange represents 50 of nares strait myi export to baffin bay and 12 of fram strait myi export to the greenland sea caamyi oct 1 exhibits dependence on warmer cooler summers that increase decrease melt evident from strong relationships to surface air temperature sat albedo and total absorbed solar radiation qtotal caamyi exchange is influenced by summer sea level pressure slp anomalies over the beaufort sea and canadian basin which shifts the primary source of caamyi exchange between less obstructed m clure strait low slp anomalies and the more obstructed queen elizabeth islands high slp anomalies over the 17 record appreciable replenishment occurred for most years from 1997 to 2004 reduced replenishment from 2005 to 2012 and large replenishment in 2013 the reduced replenishment period was associated with positive sat negative albedo and positive qtotal anomalies that facilitated more melt and less caamyi oct 1 together with high slp anomalies that facilitated less caamyi exchange large replenishment in 2013 was primarily from caamyi oct 1 attributed to strongly negative sat and qtotal anomalies and strongly positive albedo that impeded melt

sedimentary record of late paleozoic to recent tectonism in central asia analysis of subsurface data from the turan and south kazak domains abstract the turan and south kazak domains tsk are in central asia between the caspian sea and the tien shan the area is covered by sediments deposited since the late permian during a series of tectonic events closely related to the history of two oceanic domains paleotethys and neotethys sedimentary basins on the tsk therefore provide constraints on the tectonic development of the southern margin of eurasia since the late permian our study is based on structure contour maps and isopach maps of five key stratigraphic markers of late permian to tertiary age isopach maps help locate major faults and delimit sedimentary basins providing information on vertical motions and in some instances horizontal motions subsidence associated with extension appears to have dominated the tsk from the late permian to the eocene the extension may have been of back arc type in southern eurasia next to the active margin where the paleotethys and neotethys successively subducted toward the north here sedimentary basins are both wide and deep up to 15 km during the mesozoic two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of eurasia the first one at the end of the triassic led to strong selective inversion of basins over the turan domain the second one during the late jurassic early cretaceous had weaker effects since the oligocene following collision of both india and arabia with eurasia inversion has become more generalized and compressional basins have formed on the tsk throughout the entire history of development of the tsk from the late permian to the tertiary structures of paleozoic and early mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters the south kazak domain has registered little subsidence in comparison with the turan domain where some basins have become very deep

mio pliocene monsoonal record from himalayan foreland basin indian siwalik and its relation to vegetational change carbon and oxygen isotope ratios of soil carbonate nodules and carbon isotope ratio of associated organic matter were measured from three indian siwalik stratigraphic successions in order to reconstruct vegetational history and change in contemporaneous precipitation 13c values of soil carbonates show that from 10 5 to 6 ma the vegetation was c3 type and around 6 ma c4 grasses appeared the 18o variations of soil carbonates suggest that the monsoon system intensified with one probable peak at around 10 5 ma and a clear onset at 6 ma with peak at 5 5 ma after 5 5 ma monsoon strength decreased and attained the modern day condition with minor fluctuations which is supported by marine proxy of upwelling in the arabian sea and sedimentary morphology in siwalik the covariation between 18o and 13c data suggests that a change in precipitation pattern was partly responsible for expansion of c4 grasses in a mixed c3 c4 environment estimation of abundance of c3 and c4 plants using soil carbonate in one case and residual soil organic matter in another may differ this can be explained by assuming that the plant respired co2 is the main contributor of carbon in soil carbonate and may have different isotopic composition from that of the residual organic matter in the soil in addition the abundance estimate of c3 c4 plants also shows variation with time probably caused by change in growing season conditions through time

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

improving the simulation of landfast ice by combining tensile strength and a parameterization for grounded ridges in some coastal regions of the arctic ocean grounded ice ridges contribute to stabilizing and maintaining a landfast ice cover recently a grounding scheme representing this effect on sea ice dynamics was introduced and tested in a viscous plastic sea ice model this grounding scheme based on a basal stress parameterization improves the simulation of landfast ice in many regions such as in the east siberian sea the laptev sea and along the coast of alaska nevertheless in some regions such as the kara sea the area of landfast ice is systematically underestimated this indicates that another mechanism such as ice arching is at play for maintaining the ice cover fast to address this problem the combination of the basal stress parameterization and tensile strength is investigated using a 0 25 pan arctic cice nemo configuration both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the kara sea but also in the laptev sea however the simulated landfast ice season for the kara sea is too short compared to observations this is especially obvious for the onset of the landfast ice season which systematically occurs later in the model and with a slower build up this suggests that improvements to the sea ice thermodynamics could reduce these discrepancies with the data this article is protected by copyright all rights reserved

stable isotopic composition of calcic paleosols of the early cretaceous hasandong formation southeastern korea abundant pedogenic carbonate nodules are present in the cretaceous non marine hasandong formation southeastern korea the oxygen isotope compositions of these pedogenic carbonates range from 14 2 to 18 0 pdb the meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the previous estimate this suggests that the oxygen isotope compositions of the hasandong pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the hasandong carbonates range from 2 4 to 9 3 pdb with an average of 5 6 pdb suggesting carbonate formation in soils dominated by c3 type of vegetation the estimated average composition of the vegetation is about 6 pdb enriched compared with the present day c3 vegetation this is probably due to atmospheric influence contributing about 35 of the total co2 in the soil an analysis of this contribution using the model of cerling 1991 indicates that the partial pressure of co2 in the early cretaceous hasandong atmosphere was about 2300 ppmv

changes in the thickness distribution of arctic sea ice between 1958 1970 and 1993 1997 1 submarine sonar data collected in the central arctic basin during middle and late summer were used to examine differences in the sea ice thickness distribution function g h between the periods 1958 1970 and 1993 1997 cruises during the former period were made in july and august whereas the 1993 1997 cruises were made in september and october seasonal correction was applied to adjust for the differences in thickness while ice drafts were from only seven submarine cruises and somewhat spatially limited results indicate that the fractional area covered by open water and first year ice increased from 0 19 to 0 30 during the time interval this was balanced by an 11 reduction of level multiyear and ridged ice substantial losses occurred in ice thicker than 2 m with an increase in the amount of 1 2 m ice the volume of ice less than 4 m thick remained nearly the same and the total volume decreased about 32 losses in the volume of thicker ice increased with increasing thickness part of the change in g h is likely caused by increased ice area export through fram strait in the late 1980s and early 1990s because decadal variations in the north atlantic oscillation and arctic oscillation indices correlate with ice export anomalies export induced changes in g h probably tend to be cyclical in nature however a substantial shift in the peak of g h suggests that changes in thermal forcing were also a major factor in the observed thinning

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

dynamic cyrstallization of chondrule melts of porphyritic olivine composition textures experimental and natural abstract melts of the same composition as has been defined for porphyritic olivine chondrules have been crystallized under controlled cooling conditions dynamic crystallization the full range of textures observed in such chondrules has been duplicated in the experimentally produced analogs the primary controlling factor in producing this range of textuures is the heterogeneous nucleation behavior in general if nuclei are present when cooling begins growth starts immediately at low degrees of supercooling and porphyritic textures result the shapes of the phenocyrsts depend on the growth rate which in turn depends on the cooling rate with high nucleation densities and modest to low cooling rates the textures are microporphyritic with generally equant euhedral phenocrysts as the nucleatio density decreases the phenocrysts become larger and as the cooling rate increases they become increasingly skeletal if nuclei are not present when cooling begins growth is delayed until subcritical sized embryos graduate to supercritical nuclei growth usually begins at some significant degree of supercooling depending on the cooling rate and how long it takes the embryos to become nuclei the shapes of the crystals depend on the degree of supercooling when growth is initiated and on the subsequent cooling rate the resulting textures vary from plate dendrites barred olivine chondrules to randomly oriented elongated skeletal crystals as the degree of supercooling and cooling rates decreases the results of a matrix of experiments set limits on the maximum melting temperatures of chondrule forming materials and the subsequent cooling rates based primarily on crystal shape the porphyritic textures develop best for this composition at melting temperatures less than 1590 c and cooling rates near 100 c hr and definitely less than 1000 c hr at cooling rates significantly less than 100 c hr the phenocrysts are generally larger than observed in chondrules and as cooling rates approach 1000 c hr they become more skeletal barred olivine chondrule textures form best from materials melted at higher temperatures and cooling rates in the range 1000 to 3000 c hr

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

oxygen isotopic compositions of low feo relicts in high feo host chondrules in acfer 094 a type 3 0 carbonaceous chondrite closely related to cm with one exception the low feo relict olivine grains within high feo porphyritic chondrules in the type 3 0 acfer 094 carbonaceous chondrite have 17o 17o 0 52 18o values that are substantially more negative than those of the high feo olivine host materials these results are similar to observations made earlier on chondrules in co3 0 chondrites and are consistent with two independent models 1 nebular solids evolved from low feo low 17o compositions towards high feo more positive 17o compositions and 2 the range of compositions resulted from the mixing of two independently formed components the two models predict different trajectories on a 17o vs log fe mg olivine diagram but our sample set has too few values at intermediate fe mg ratios to yield a definitive answer published data showing that acfer 094 has higher volatile contents than co chondrites suggest a closer link to cm chondrites this is consistent with the high modal matrix abundance in acfer 094 49 vol acfer 094 may be an unaltered cm chondrite or an exceptionally matrix rich co chondrite chondrules in acfer 094 and in co and cm carbonaceous chondrites appear to sample the same population textural differences between acfer 094 and cm chondrites are largely attributable to the high degree of hydrothermal alteration that the cm chondrites experienced in an asteroidal setting

ubiquitous low feo relict grains in type ii chondrules and limited overgrowths on phenocrysts following the final melting event type ii porphyritic chondrules commonly contain several large 40 m olivine phenocrysts furnace based cooling rates based on the assumption that these phenocrysts grew in a single stage melting cooling event yield chondrule cooling rate estimates of 0 01 1 k s 1 because other evidence indicates much higher cooling rates we examined type ii chondrules in the co3 0 chondrites that have experienced only minimal parent body alteration we discovered three kinds of evidence indicating that only minor 4 10 m olivine growth occurred after the final melting event 1 nearly all 90 type ii chondrules in co3 0 chondrites contain low feo relict grains overgrowths on these relicts are narrow in the range of 2 12 m 2 most type ii chondrules contain some feo rich olivine grains with decurved surfaces and acute angles between faces indicating that the grains are fragments from an earlier generation of chondrules the limited overgrowth thicknesses following the last melting event are too thin to disguise the shard like nature of these grains 3 most type ii chondrules contain many small 40 m high feo phenocrysts are relicts from earlier generations of chondrules and that cooling rates after the last melting event were much more rapid than indicated by models based on a single melting event these observations are thus inconsistent with the classic igneous model of formation of type ii porphyritic chondrules by near total melting of a precursor mix followed by olivine nucleation on a very limited number of nuclei say 10 and by growth to produce the large phenocrysts during a period of monotonic and roughly linear cooling our observations that recycled chondrule materials constitute a large component of the phenocrysts of type ii chondrules also imply that this kind of chondrule formed relatively late during the chondrule forming period

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

oxygen isotopes in chondrule olivine and isolated olivine grains from the co3 chondrite allan hills a77307 we have measured o isotopic ratios in a variety of olivine grains in the co3 chondrite allan hills alh a77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites oxygen isotopic ratios of olivines in this chondrite are variable from delta 17 o 15 5 to 4 5 parts per thousand and delta 18 o 11 5 to 3 9 parts per thousand with delta 17 o varying from 10 4 to 3 5 parts per thousand forsteritic olivines fa 1 are enriched in o 16 relative to the bulk chondrite whereas more feo rich olivines are more depleted in o 16 most ratios lie close to the carbonaceous chondrite anhydrous minerals ccam line with negative values of delta 17 o although one grain of composition fa 4 has a mean delta 17 o of 1 6 parts per thousand marked o isotopic heterogeneity within one feo rich chondrule is the result of incorporation of relic o 16 rich mg rich grains into a more o 16 depleted host isolated olivine grains including isolated forsterites have similar o isotopic ratios to olivine in chondrules of corresponding chemical composition this is consistent with derivation of isolated olivine from chondrules as well as the possibility that isolated grains are chondrule precursors the high o 16 in forsteritic olivine is similar to that observed in forsterite in cv and ci chondrites and the ordinary chondrite julesburg and suggests nebula wide processes for the origin of forsterite that appears to be a primitive nebular component

morphology and isotope heterogeneity of late quaternary pedogenic carbonates implications for paleosol carbonates as paleoenvironmental proxies abstract stable isotope values and radiocarbon ages were determined for pedogenic carbonate microsamples from relict soils and palaeosols from the rio grande rift region of new mexico carbonate nodules and clusters were sampled from fluvial and piedmont soils and palaeosols with widely varying exposure durations 7 900 ky pedogenic carbonates from individual soils exhibited irregular relationships between age and depth ranging in radiocarbon age by 13 ky at individual depths 18 o values and to a lesser extent 13 c values likewise had wide ranges within soils however comparing the stable isotope values of carbonates with similar radiocarbon ages within and between soils revealed consistent trends in stable isotope values over time 18 o values of pedogenic carbonates tended to decrease with decreasing age 25 17 radiocarbon ka and increased with decreasing age 13 c values with either depth or age although the oldest palaeosol piedmont carbonates radiocarbon ages of 24 5 19 2 ka are 1 more negative than the younger piedmont palaeosol carbonates pedogenic carbonates in the relict fluvial soil which has by far the longest exposure period showed the greatest range in 13 c values comparing the 13 c values of samples of similar radiocarbon age from the relict fluvial soil indicates a transition from a mixed c 3 c 4 ecosystem at 11 ka to an effectively pure c 3 ecosystem at 9 ka followed by a return to mixed vegetation by 5 ka thus although c 4 vegetation persisted in southern new mexico through the last glaciation drought resistant c 3 vegetation became dominant at 9 ka prior to significant strengthening of the summer monsoon this study illustrates that the stable isotope values of carbonate nodules and clusters from relict soils and or slowly buried palaeosols can be used for palaeoenvironmental reconstructions in the context of a detailed chronologic framework

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

atmospheric pco2 and depositional environment from stable isotope geochemistry of calcrete nodules barremian lower cretaceous wealden beds england abstract nodular soil carbonates calcretes are present in overbank facies of lower cretaceous non marine wealden beds wessex formation of southern england field evidence suggests that these calcretes formed mostly under semi arid mediterranean type climatic conditions typical calcrete fabrics identified petrographically include floating detrital grains corroded grain margins and circumgranular cracks defining peds localized alteration of primary micrites is mainly associated with large cracks where early non ferroan diagenetic cementation and neomorphism was focused diagenetic ferroan calcites occur as void fills and yield relatively light carbon isotope and oxygen isotope compositions 13 c 15 0 18 o 6 3 compared to well preserved micrite 13 c 10 2 18 o 4 0 precise definition of 13 c values for well preserved micrites allow estimation of partial pressure of atmospheric co 2 p co 2 for the early barremian of 560 ppmv using a published diffusion reaction model the data suggest that atmospheric co 2 was low during the mid early cretaceous before rising to a previously defined mid cretaceous high data from calcretes in the weald clay highlight the need for selection of appropriate material and careful evaluation before p co 2 calculations are attempted the weald clay samples come from marshy palaeoenvironments where ingress of atmospheric co 2 into the soil zone was either reduced or prevented

kara sea freshwater transport through vilkitsky strait variability forcing and further pathways toward the western arctic ocean from a model and observations siberian river water is a first order contribution to the arctic freshwater budget with the ob yenisey and lena supplying nearly half of the total surface freshwater flux however few details are known regarding where when and how the freshwater transverses the vast siberian shelf seas this paper investigates the mechanism variability and pathways of the fresh kara sea outflow through vilkitsky strait toward the laptev sea we utilize a high resolution ocean model and recent shipboard observations to characterize the freshwater laden vilkitsky strait current vsc and shed new light on the little studied region between the kara and laptev seas characterized by harsh ice conditions contrasting water masses straits and a large submarine canyon the vsc is 10 20 km wide surface intensified and varies seasonally maximum from august to march and interannually average freshwater volume transport is 500 120 km3 a 1 0 53 0 08 sv with a baroclinic flow contribution of 50 90 interannual transport variability is explained by a storage release mechanism where blocking favorable summer winds hamper the outflow and cause accumulation of freshwater in the kara sea the year following a blocking event is characterized by enhanced transports driven by a baroclinic flow along the coast that is set up by increased freshwater volumes eventually the vsc merges with a slope current and provides a major pathway for eurasian river water toward the western arctic along the eurasian continental slope kara and laptev sea freshwater transport is not correlated with the arctic oscillation but rather driven by regional summer pressure patterns

the character and genesis of calcrete in late quaternary alluvial deposits gujarat western india and its bearing on the interpretation of ancient climates late quaternary deposits in mainland gujarat contain sediments deposited in subhumid and semi arid climates the 30 35 m succession shows the presence of vertisols at the base and a red bed horizon ferric calcisol when pedogenic in origin that roughly bisects the succession a widespread development of calcretes is observed throughout the succession the various varieties of calcrete include pedogenic calcrete groundwater calcrete calcrete conglomerate transported calcrete and rhizogenic calcrete pedogenic calcrete nodules associated with vertisols and the red soil show marked differences in morphology dimensions and the distribution of microscopic features these differences arise due to contrasting climate controlled physicochemical environs under which they formed pedogenic calcrete nodules associated with vertisols acquire large 5 10 cm dimensions and are characterised by either showing the presence of a nucleus of soil matter or showing a dense micritic groundmass cut by thick sparitic veins in contrast calcrete nodules that formed in the red soil are 3 cm in size and do not exhibit dense networks of sparitic veins calcretes associated with vertisols and the ferric calcisol also exhibit differences in the morphology of rhizoliths these differences also show up in the distribution of microfabrics of calcretes grain coats are present in rhizogenic and pedogenic calcretes but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes clotted micrite is present in all types except groundwater calcretes sparitic veins however are observed in each type but are relatively less developed in groundwater calcretes a similar distribution of displacive and replacive textures is also seen although some grains in groundwater calcretes showed signs of corrosion the vertisol associated calcretes represent a subhumid 500 700 mm climate whereas the red soil calcretes suggest a semi arid 100 500 mm climate calcretes from the vertisol association show a range in 13c composition constrained between 9 and 5 whereas the red soil calcretes exhibit the whole spectrum of values from 9 to 1 based on mineralogical associations calcretes usually taken to reflect semi arid episodes in the earth s history may be classified further calcretes when associated with sepiolite palygorskite suggest an arid climate mean annual rainfall 50 100 mm when associated with smectite haematite and the absence of hydromorphism a semi arid climate mean annual rainfall 100 500 mm and when found in smectitic vertisols subhumid climates mean annual rainfall 500 700 mm

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

paleosols trace fossils and precipitation estimates of the uppermost triassic strata in northern new mexico abstract this study provides a detailed pedogenic evaluation of two upper triassic late norian through rhaetian stratigraphic intervals in new mexico in order to assess the climate and ecology of the latest triassic which ended in a mass extinction the two study areas are located in north central and east central new mexico and are separated by 200 km each section contains abundant paleosols of varying maturity with features that reflect an arid to semiarid climate there is little pedogenic variation throughout the strata at each location and a typical paleosol profile is about 1 m thick and has an ab bw bk bc horizon succession bkm bss bssk or bssg horizons are present in some paleosols micromorphological features suggest dominantly well drained sola e g abundant carbonate nodules illuviated clay with minor periods of moist or saturated conditions e g femn concretions femn coatings and hypocoatings sepic plasmic fabrics trace fossils are abundant in these strata and are dominated by taenidium serpentinum and root traces depth to carbonate functions estimate that mean annual precipitation was between 200 and 450 95 mm relative to location 1 eastern new mexico location 2 north central new mexico produced higher paleo precipitation estimates and has stronger and more abundant sepic plasmic fabrics in thin sections the presence of a gleyed paleosol camborygma eumnkenomos and slickensides at location 2 also suggests conditions wetter than at location 1 taxonomically all of the paleosols in this study appear to be entisols or aridisols and can be grouped into seven representative pedotypes of varying maturity by comparing these paleosols to modern soils this study demonstrates that the late triassic western interior during the late norian to rhaetian was arid to semiarid and supported a desert shrub environment that had localized and periodic moist or saturated soil conditions

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

origin of metallic fe ni in renazzo and related chondrites abstract the anomalous positive co ni correlation among metal grains from the renazzo and al rais chondrites reported in previous studies has two components 1 1 a chondrule trend that extends up to 120 145 mg g ni probably reflects the mixing of fe rich and fe poor nebular metal and 2 2 a weak extrachondrule trend that spans a ni range from 40 70 mg g reflects fe introduction during mild metamorphism to assess the formation of this metal we determined ni and co zoning profiles in metallic fe ni from different petrographic sites chondrule interiors chondrule margins chondrule rims and matrix in renazzo al rais and the related chondrite macalpine hills 87320 metal from chondrule interiors shows flat ni and co concentrations and profiles moderately large grain to grain compositional variations even within chondrules and generally high ni and co nickel concentrations extend above the kamacite stability limit etching such martensite shows high ni domains in some cases but observed ni concentrations do not exceed 190 mg g metal from chondrule margins adjacent to matrix shows convex inverted u shaped ni and co zoning profiles the highest ni and co concentrations are at grain centers although the mean central ni and co concentrations in margin grains are much lower than those in metal from chondrule interiors about half of the matrix metal shows flat co and ni profiles like those from chondrule interiors the remainder are convex the differences in mean co and ni contents between chondrules and extrachondrule materials may reflect differential sampling of nebular metal grains having compositions that varied with particle size we interpret the low co and ni contents at the edges of grains in chondrule margins to reflect dilution by fe produced by feo reduction the reduction seems not to have occurred in the nebula but rather during a brief period of parent body metamorphism reduction of fine grained feo produced metallic fe that plated onto nearby metal grains although diffusive exchange between pentlandite and metal could produce the observed ni gradient it is doubtful that it could produce the similar gradient of co metal from chondrule interiors was inaccessible during the reduction event and retained the flat profiles established during chondrule formation

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

meteorological forcing of sea ice concentrations in the southern beaufort sea over the period 1979 to 2000 1 northern hemisphere sea ice areal extent and perhaps thickness have shown a detectable reduction over the past several decades this situation is particularly apparent in the southern beaufort sea the region encompassing the mackenzie shelf the cape bathurst polynya and the canada basin mobile pack ice all occur in a region referred to here as the canadian arctic shelf exchange study area cases in this paper we present results from an analysis of atmosphere sea ice and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the cases research network operating over the period 2001 2005 results show that the cape bathurst polynya complex can be considered as a recurrent polynya particularly the flaw leads associated with the early opening of the polynya the polynya appears to be a consequence of the beaufort sea gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling the sea ice average areal extent has been decreasing in this region over the period 1979 to 2000 large regional reductions are found i north of the yukon and alaska coasts in the region between the canada basin pack ice and the landfast sea ice and 2 at the eastern limit of the cape bathurst polynya in amundsen gulf the meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales at hemispheric scales a statistical cross correlation analysis between weekly sea ice concentration anomalies and the arctic oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the canadian archipelago coast at local scales positive and negative concentration anomaly periods can be explained through local scale advective processes associated with regional scale sea level pressure 500 hpa geopotential heights and surface temperature anomalies

stable isotope record in pedogenic carbonates in northeast iran implications for early cretaceous berriasian barremian paleovegetation and paleoatmospheric p co2 levels abstract the shurijeh formation early cretaceous consists of siliciclastic evaporate and carbonate facies with associated calcareous paleosols in the kopet dagh basin these calcareous paleosols pedogenic carbonate nodules include specific macromorphological and micromorphological features based on macroscopic and microscopic properties the shurijeh calcareous paleosols are divided into pedogenic and non pedogenic ground water types that are each formed under specific conditions estimated 13c values of plant co2 for shurijeh vegetation range from 20 75 to 22 14 with an average 21 31 these values are consistent with plant type c3 the contribution of atmospheric co2 in 13c values of plant co2 of studied calcareous paleosols was 25 to 30 the neocomian berriasian barremian paleoatmospheric pco2 gap was reconstructed by interpretation from measured carbon isotopic compositions of the shurijeh formation pedogenic carbonates the paleoatmospheric co2 levels of the shurijeh formation are estimated to be 1226 2196 ppmv the general trend of early cretaceous estimates matches the modeled value trends for these times

sea ice of the northern canadian arctic archipelago 1 existing information concerning the pack ice and relevant climate variables of the canadian arctic archipelago north of parry channel is summarized this knowledge is enhanced by newly available data on ice thickness derived from 123 703 drill holes completed during the 1970s pack ice in this area is a mix of multiyear second year and first year ice types with the latter subordinate except in the southeast ice remains land fast for more than half the year and summertime ice concentration is high 7 9 tenths in a typical year less than 20 of the old ice and 50 of the first year ice melt there are large interannual fluctuations in ice coverage and some suggestion of a decadal cycle the average ice thickness in late winter is 3 4 m but subregional means reach 5 5 m the pack is a mix of two populations one consisting largely of multiyear ice imported from the zone of heavy ridging along the periphery of the beaufort gyre and the other consisting of a mix of relatively undeformed first year second year and multiyear ice types that grow and age within the basin the ice of the sverdrup basin is strongly influenced by a flux of heat approximately 10 w m 2 that originates in the atlantic derived waters of the arctic ocean the drift of ice through the basin is controlled in the present climate by the formation of stable ice bridges across connecting channels the drift is episodic relaxation of these controls in a warmer climate may cause deterioration in ice conditions in canadian arctic waters

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous

lower eocene carbonate cemented chimneys varna ne bulgaria formation mechanisms and the a biological mediation of chimney growth abstract in the area of pobiti kamani varna northeast bulgaria massive carbonate cemented columns chimneys up to 1 5 m diameter and 8 m high and horizontal interbeds 1 5 m thickness occur in dispersed outcrops over an area of 70 km2 within loose lower eocene sands field observations and petrographical and stable isotope geochemical characterisation of four studied locations reveal a relationship between these structures and processes of ancient hydrocarbon seepage column and interbed structures both consist of similar well sorted silt to sand sized nummulitic host sediments predominantly cemented by early diagenetic low magnesium calcite filamentous textures about 10 m in diameter and 80 650 m long are only locally detected within interparticle calcite cement of columns column samples from two sites reveal a similar linear and inverse covariant trend of 13c 18o values which was interpreted as a mixing trend between two end member fluid precipitation conditions i e 1 a methane and or higher hydrocarbon derived carbon member characterised by 13c values as low as 43 and marine controlled precipitation conditions with 18o of 1 0 5 v pdb and 2 a member with less contribution of methane which was mixed most likely with less depleted carbon sources explaining 13c values ranging up to 8 v pdb the corresponding depleted 18o values with many samples clustering around 8 v pdb are interpreted in terms of precipitation at elevated temperatures this suggests the venting system was not a true cold seep sensu stricto furthermore column cross transects often document an internal pattern consisting of concentric zones with distinct isotopic signatures which vary between the two end members the mixing and internal pattern of column isotopic data together with petrographical observations are qualitatively interpreted as evidence of alternating precipitation conditions controlled by varying seepage rates of a single fluid source at depth during build up of individual chimney pipes near the sediment surface based on several field observations migration of the hydrocarbon charged fluids in lower eocene times was possibly channelled along ne oriented faults isotopic signatures of calcite cemented horizontal interbeds with depleted 18o ratios as low as 8 88 v pdb and variable 13c 1 to 16 mainly around 5 to 7 suggest that ascending fluids contributed to their cementation or resetted the calcite cement isotopic signature predominantly during periods of active seepage of warmer fluids only few petrographical and preliminary lipid biomarker evidence has been found pointing to the presence or possibly former activity of microbiota involved in carbon cycling and calcite precipitation typical of cold seep settings this may result from diagenetic alteration of organic components however considering the processes of chimney formation a cementation process governed by the inorganic oxidation of hydrocarbons in which interstitial oxygen is rapidly consumed without bacterial mediation is considered

landfast ice affects the stability of the arctic halocline evidence from a numerical model landfast ice covers large surface areas of the winter siberian seas the immobile landfast ice cover inhibits divergent and convergent motion hence dynamical sea ice growth and redistribution decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore in spite of the potentially large effects state of the art numerical models usually do not represent landfast ice in its correct extent a simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated arctic ocean are demonstrated the simulations suggest that the siberian landfast ice impacts the arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by redirecting river water to the canadian basin these processes strengthen the halocline in the canadian basin but erode its stability in the makarov and eurasian basins

sedimentology and diagenesis of tertiary carbonates on the mangkalihat peninsula borneo implications for subsurface reservoir quality abstract combined field and laboratory studies of surface exposures on the mangkalihat peninsula borneo provide new constraints on the chronostratigraphy sedimentology and diagenesis of tertiary carbonate deposits the reservoir characteristics of carbonate facies are described providing an analogue model for carbonate reservoirs in the subsurface of this region a mixed carbonate siliciclastic shelf with intervening probably fault bounded deeper water areas developed on the eastern part of the mangkalihat peninsula in the late eocene to oligocene during the oligo miocene shallow water platform carbonates accumulated over much of the area of the mangkalihat peninsula this platform had a steep reef rimmed or possibly locally faulted northern margin where high energy conditions prevailed and marine cements were pervasive in contrast the platform interior was a low energy area affected by leaching of aragonitic bioclasts the best reservoir quality on the platform occurs in moderate energy grainstones and packstones tens to hundreds of metres towards the platform interior from the platform margin where a combination of primary intergranular and secondary mouldic porosity results in good porosity and permeability

stable isotopic composition of pedogenic carbonates of the early cretaceous shimonoseki subgroup western honshu japan abstract abundant pedogenic carbonate nodules are present in the shimonoseki subgroup in the kanmon basin of kyushu and honshu japan the oxygen isotope compositions of these pedogenic carbonates range from 20 1 to 22 8 pdb which is 7 lower than those of the septarian crystallaria in the carbonate nodules the meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the estimate from other sources this suggests that the oxygen isotope compositions of the shimonoseki pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the shimonoseki carbonates range from 5 4 to 7 0 pdb with an average of 6 7 pdb suggesting carbonate formation in soils dominated by c 3 type of vegetation an analysis of these values using cerling s model cerling t e wright v p vanstone s d 1992 further comments on using carbon isotopes in paleosols to estimate the co 2 content of the palaeo atmosphere j geol soc london 148 1991 945 947 149 673 676 indicates that the partial pressure of co 2 in the early cretaceous shimonoseki atmosphere was about 1700 3200 ppmv

the valanginian carbon isotope event a first episode of greenhouse climate conditions during the cretaceous lower cretaceous pelagic carbonates outcropping along the southern alps of northern italy provide a record of tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle the carbonate c isotope stratigraphy established at five selected localities in the southern alps allows an accurate picture to be drawn of the duration and amplitude of the valanginian c isotope event 13c values near 1 25 1 50 determined in berriasian and lower valanginian sediments are replaced by more pdsitive 13c values near 3 in the late valanginian the carbonate c isotope excursion ends in the early hauterivian with values fluctuating between 1 5 and 2 the carbonate c isotope excursion is accompanied by a positive excursion in the total organic carbon c isotope curve the valanginian c isotope excursion identified in tethyan sediments correlates with a c isotope excursion recorded in the western north atlantic in the gulf of mexico and in the central pacific dsdp sites 534 391 535 and 167 by analogy with the aptian stage also marked by a significant positive c isotope excursion the time of positive 13c values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments a warm and humid climate possiblycoupled with a high atmospheric co2 content and a high global sea level may have triggered the acceleration of the global carbon cycling in this case the valanginian c isotope event would reflect a first episode of greenhouse earth conditions during the cretaceous

regional dependence in the timing of onset of rapid decline in arctic sea ice concentration arctic sea ice concentration from satellite passive microwave measurements is analyzed to assess the form and timing of the onset of decline of recent ice loss and the regional dependence of the response the timing of the onset is estimated using an objective method and suggests differences of up to 20 years between the various subregions a clear distinction can be drawn between the recent onset times of the atlantic sector beginning in 2003 and the much earlier onset times associated with the pacific sector where the earliest transition to rapid loss is found in 1992 rates of decline prior to and following the transition points are calculated and suggest that the postonset rate of loss is greatest in the barents sea and weakest in the pacific sector covariability between the seasons is noted in the sic response both at interannual and longer time scales for two case regions potential mechanisms for the onset time transitions are briefly analyzed in the barents sea the onset time coincides with a redistribution of the pathways of ice circulation in the region while along the alaskan coast the propagation of the regional signal can be traced in the age of the sea ice the results presented here indicate a series of spatially self consistent regional responses and may be useful in understanding the primary drivers of recent sea ice loss

elemental composition of calcites in late quaternary pedogenic calcretes from gujarat western india abstract pedogenic calcretes commonly exhibit clotted micrite circum granular calcite grain coats and microspar spar veins the three calcite types with different dimensions were analyzed for their magnesium content to determine the relationship between crystal elongation and magnesium incorporation the results show a very low mgo content for grain coats and microspars and high values for clotted micrite indicating that the ideal kinetic model does not hold true and several variables govern the end composition of calcites the magnesium concentrations of meteoric calcites are genetically linked to the evolutionary history of the soil and climate grain coats which are elongated calcites contain the least amount of mg and is related to the initial stages of pedogenesis wherein the limiting factor is the mg ca ratio of the parent fluid lower magnesium contents arise due to smaller quantities of mg being released during incipient weathering micrite morphology and composition is controlled by the greater availability of mg ions through weathering higher pco2 in soil due to increased time dependent soil respiration which causes a rise in calcite precipitation rates and clay authigenesis this in turn exerts a physical control on morphology by occluding pore space and providing numerous nuclei for calcite precipitation the wide variability in spar cements is inherently controlled by inhomogeneties in parent fluid compositions with lower than micrite values on account of slower precipitation rates

fine nickel poor fe ni grains in the olivine of unequilibrated ordinary chondrites abstract fine 2 m ni poor 10 mg g fe ni grains are common inclusions in the olivine in porphyritic chondrules in unequilibrated ordinary chondrites the olivine grains appear to be relicts that survived chondrule formation without melting the most common occurrence of this dusty metal is in the core of olivine grains having clear fe poor rims and surrounded either by small euhedral clear olivine grains zoned with feo increasing toward the border of the grains or by large elongated fe poor orthopyroxenes oriented parallel to the chondrule surface and enclosing small round olivine grains various amounts of ca al rich glass are always present the dusty metal is occasionally found in the rims of olivine grains either isolated in the matrix or included in chondrules a rare occurrence is as bands in highly deformed olivines this dusty metal appears to be the product of in situ reduction of feo from the host olivine among the possible reductants h2 or carbonaceous matter ch2 n seem the most likely hydrogen may have been implanted by solar wind or solar flare irradiation but this requires that dissipation of nebular gas occurred before the end of the chondrule formation process carbonaceous matter may have been implanted by shock less likely reductants are nebular co or c dissolved in the olivine lattice the large relict olivine grains may be nebular condensates or more likely fragments broken off earlier generations of chondrules

oblique to orthogonal convergence across the turan block in the post miocene the 2 17 km thick post triassic sediments of the turan continental block accumulated in a south dipping basin characterized by fault controlled facies and thickness variations since the late miocene the thickest part of the basin fill on the southern margin of the turan block has been folded and uplifted as the kopet dag range in response to the iran turan convergence the apsheron sill which separates the northern continental from the southern oceanic caspian sea basins links the kopet dag greater balkan ranges turkmenistan to the caucasus azerbaijan the large scale east west to west northwest east southeast oriented arrays of periclinal folds of the kopet dag range which indicate a north south oriented compression were generated by a fault propagation mechanism the migration and accumulation of hydrocarbons has been controlled by the deformation pattern the 75 km of north south shortening in the western kopet dag greater balkan area can be resolved into 70 km of pure compression orthogonal to the n120 oriented ashgabat fault and 35 km of dextral slip along this fault the north south iran asia relative motion has produced the oblique convergent northwest southeast structures along the dextral ashgabat fault and the pure convergent east west structures in the western kopet dag greater balkan region the orientation of the structures has been controlled by the angular relationship between the relative motion of two blocks and the orientation of their boundaries the ashgabat fault as a major crustal anisotropy has concentrated the deformation into a narrow fold and thrust belt whereas in the west the deformation is distributed over a wider area the pattern of deformation has been controlled by the iran turan boundary conditions

paleovegetation and paleoatmospheric p co2 levels during the early cretaceous examples from the hasandong formation korea and the shimonoseki subgroup japan abstract stable carbon isotope compositions of pedogenic carbonates occurring in two lower cretaceous non marine deposits the hasandong formation korea hauterivian barremian and the shimonoseki subgroup japan aptian provide a record of past pedogenic environments and are used to infer paleovegetation and co 2 pressure p co 2 of the early cretaceous atmosphere the carbon isotopic compositions 5 6 to 6 7 of pedogenic carbonates from both strata suggest soils dominated by c 3 type of vegetation atmospheric co 2 contributed generally less than 30 of the carbon isotopes to these pedogenic carbonates the early cretaceous atmosphere is unlikely to have contained more than about 4500 ppm v by volume of co 2 high concentrations of carbon dioxide in the early cretaceous atmosphere are in good agreement with the modeled atmospheric p co 2 estimation of berner american journal of science 294 1994 56 91 the fact that paleo p co 2 levels during shimonoseki time 1900 3200 ppm v were lower than those of hasandong time 2400 4500 ppm v indicates that the paleo p co 2 levels in the atmosphere were lower than the early cretaceous high which fits well with a trend of decreasing carbon dioxide levels in the paleoatmosphere during the cretaceous

core concepts of paleopedology abstract the current renaissance of scientific interest in paleosols has brought a variety of views and approaches to paleopedology two main approaches have emerged for the description and labelling of paleosols geosols are ancient land surfaces consisting of laterally connected suites of paleosols used for stratigraphic subdivision of sedimentary deposits pedotypes are individual kinds of paleosols named after localities like geosols pedotypes are used for mapping and describing individual profiles usually for the purpose of paleoenvironmental interpretation both pedotypes and geosols are field based labels for which genetic or interpretive considerations are at a minimum they can be interpreted using at least three distinct approaches taxonomic uniformitarianism is based on the assumption that a paleosol is formed in a similar environment to a surface soil of the same type the factor function approach interprets specific aspects of paleoenvironments from measured features of paleosols by comparison with paleoenvironmentally related variation of that feature in surface soils finally the process model approach seeks to recreate soil forming processes mathematically with input from measurable features of paleosols each approach has limitations such as the need for proxy features to classify paleosols in systems designed for surface soils the attainment of similar appearance of a paleosol by different pathways and the mathematical uncertainty of model assumptions the approaches of classification experimentation and modelling are not unique to paleopedology being widespread among other sciences fundamental to paleopedology however are the concepts of profiles and soilscapes of the past

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

evidence for glacial control of rapid sea level changes in the early cretaceous lower cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves strontium data from an interval spanning 7 million years in the berriasian valanginian imply that global sea level fluctuated about 50 meters over time scales of 200 000 to 500 000 years which is in agreement with the exxon sea level curve oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes if glaciation caused all the rapid sea level changes in the cretaceous that are indicated by the exxon curve then an antarctic ice sheet may have existed despite overall climatic warmth

a relict grain bearing porphyritic olivine compound chondrule from ll3 0 semarkona that experienced limited remelting chondrule d8n in ll3 0 semarkona is a porphyritic olivine po chondrule 1300 1900 m in size with a complicated thermal history the oldest recognizable portion of d8n is a moderately high feo po chondrule that is modeled as having become enmeshed in a dust ball containing a small intact low feo porphyritic chondrule and fine grained material consisting of forsterite kamacite troilite and possibly reduced c the final chondrule melting event may have been a heat pulse that preferentially melted the low feo material and produced a low feo opaquerich exterior region 45 140 m in thickness around the original chondrule at one end of the exterior region a kamacite and troilite rich lump 960 m in length formed during the final melting event the coarse moderately ferroan olivine phenocrysts within the original chondrule appear to have been partly resorbed these relict phenocrysts have the highest concentrations of feo mno and cr2o3 7 5 0 20 and 0 61 wt respectively in d8n narrow olivine overgrowths crystallized around the phenocrysts following final chondrule melting their compositions seem to reflect mixing between melt derived from the exterior region and the resorbed margins of the phenocrysts during the melting event feo in the relict phenocrysts was reduced producing numerous small blebs of ni poor metallic fe along preexisting curvilinear fractures the reduced olivine flanking the trails of metal blebs has lower feo than the phenocrysts but virtually identical mno and cr2o3 contents subsequent parent body aqueous alteration in the exterior region of the chondrule formed pentlandite and abundant magnetite

isotopic tracers of the origin of ca in a carbonate crust from the middle atlas morocco abstract carbonate crusts developed on basalt were studied at tazouta in the moroccan middle atlas the chosen representative weathering profile is 2 8 m thick and is composed from base to top of a fresh basalt overlain by a coherent saprolite a friable saprolite and a surface soil carbonate crust genesis occurs by replacement of primary and secondary clay minerals by low mg calcite the 14 c dates of the calcite range from 15 to 14 ka in the coherent saprolite and from 12 to 8 5 ka in the friable saprolite smectitic weathering and replacement of si bearing minerals by carbonate are coupled processes leading to a strong calcium net gain 300 kg m 3 within the friable saprolite the low weathering rate of basalt compared to the calcrete genesis rate and the high mobility of calcium in supergene weathering mantles limit the basaltic ca contribution to calcrete genesis the contribution of the triassic sediment is also limited by the mineralogical unavailability of ca the 87 sr 86 sr ratios confirm the low contribution of basalt and indicate an external origin of ca the sr isotope ratios of calcrete are different from those of the adjacent liassic carbonates and are close to rainfall values the carbon isotope compositions of carbonates 8 to 9 vs pdb imply a significant contribution of c3 dominated organic carbon during carbonate precipitation oxygen isotopic compositions of carbonates average 5 24 vs pdb show that carbonates are 18 o enriched compared to meteoric waters 4 to 3 5 vs smow

rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates the elevation of earth s surface is among the most difficult environmental variables to reconstruct from the geological record here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters constrained by measurements of abundances of 13 c 18 o bonds in soil carbonates we use this approach to show that the altiplano plateau in the bolivian andes rose at an average rate of 1 03 0 12 millimeters per year between 10 3 and 6 7 million years ago this rate is consistent with the removal of dense lower crust and or lithospheric mantle as the cause of elevation gain

the upper valanginian early cretaceous positive carbon isotope event recorded in terrestrial plants our understanding of the ancient ocean atmosphere system has focused on oceanic proxies however the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs we have analyzed carbon isotope ratios from fossil plant material through the valanginian and lower hauterivian from a shallow marine ammonite constrained succession in the crimean peninsula of the southern ukraine in order to determine if the upper valanginian positive carbon isotope excursion is expressed in the atmosphere d 13 cplant values fluctuate around 23x to 22x for the valanginian hauterivian except during the upper valanginian where d 13 cplant values record a positive excursion to 18x based upon ammonite biostratigraphy from crimea and in conjunction with a composite tethyan marine d 13 ccarb curve several conclusions can be drawn 1 the d 13 cplant record indicates that the atmospheric carbon reservoir was affected 2 the defined ammonite correlations between europe and crimea are synchronous and 3 a change in photosynthetic carbon isotope fractionation caused by a decrease in atmospheric pco2 occurred during the upper valanginian positive d 13 c excursion our new data combined with other paleoenvironmental and paleoclimatic information indicate that the upper valanginian was a cool period icehouse and highlights that the cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought d 2005 elsevier b v all rights reserved

the impact of tides on simulated landfast ice in a pan arctic ice ocean model the impact of tides on the simulated landfast ice cover is investigated pan arctic simulations are conducted with an ice ocean cice nemo model with a modified rheology and a grounding scheme the reference experiment without tides indicates there is an overestimation of the extent of landfast ice in regions of strong tides such as the gulf of boothia prince regent inlet and lancaster sound the addition of tides in the simulation clearly leads to a decrease of the extent of landfast ice in some tidally active regions this numerical experiment with tides is more in line with observations of landfast ice in all the regions studied thermodynamics and changes in grounding cannot explain the lower landfast ice area when tidal forcing is included we rather demonstrate that this decrease in the landfast ice extent is dynamically driven by the increase of the ocean ice stress due to the tides plain language summary landfast ice is sea ice that is immobile near a coast for a certain period of time this coastal ice can stay at rest because it is attached to the coast and or anchored to the sea floor in shallow water to study landfast ice we used a numerical model that represents the physical interactions between the atmosphere the ocean and the sea ice we compared two simulations done with this model one without ocean tides and one that includes the tides the experiment with tides exhibits a lower extent of landfast ice which is more in line with the observations this decrease in the landfast ice extent when adding the tides is a dynamical process the strong tidal currents constantly set the sea ice in motion preventing it to become landfast