discontinuity structure of the mantle transition zone beneath the north china craton from receiver function migration 1 a better understanding of the significant phanerozoic tectonic reactivation and destruction of the north china craton ncc demands a detailed knowledge of the deep structural features of the region we applied the wave equation based poststack migration technique to a combined receiver function data set from more than 250 broadband seismic stations to construct the structural image of the mantle transition zone beneath the ncc our imaging results reveal a relatively simple and flat 410 km discontinuity but a structurally complicated 660 km discontinuity beneath the region double discontinuities and a 30 km depression of the 660 km discontinuity are observed locally in the southern part of the eastern ncc in contrast to the smoothly varying structure to the north and in the central and western parts of the craton distinctly rapid variations in both the 660 km discontinuity structure and mantle transition zone thickness were found across the northsouth gravity lineament nsgl near the boundary between the eastern and central ncc which probably reflects different thermal and probably chemical properties on the two sides of the nsgl these differences are possibly associated with the pacific slab which is imaged tomographically as a flat lying structure in the mantle transition zone under the region east of the nsgl the structural variation in the deep upper mantle appears to coincide with the sudden changes in surface topography gravity field and crustal and lithospheric structures as well indicating that the two domains may have tectonically deformed differently throughout the whole upper mantle during the phanerozoic cratonic destruction the mantle transition zone on the eastern side of the nsgl is up to 30 40 km thicker than the global average this thickness and the complex structure of the 660 km discontinuity in this region may reflect the strong influence that the deep subduction and stagnancy of the pacific slab and its possible sporadic penetration into the lower mantle have had on mantle dynamics and lithospheric reactivation in the eastern ncc since the mesozoic time on the other hand the less variable structure and normal to thin mantle transition zone imaged beneath the central and western ncc may indicate that the indiaeurasia collision has had a relatively weak effect on the cenozoic tectonics of these regions

postglacial paleoecological history of a cedar swamp manitoulin island ontario canada abstract a cedar swamp on manitoulin island ontario canada was chosen for a paleoecological study of pollen macrofossils and cladocera a new elevation of 316 7 m a s l is given for the position of main lake algonquin on northeastern manitoulin island based on a wave cut feature 4 7 m above the swamp immediately adjacent to the site deposits inferred to predate 10 500 yr b p are dominated by picea artemisia cyperaceae and other herbs likely derived from spruce parkland climate on the small proto manitoulin island group was cool and possibly dry the cladoceran assemblage includes alona lapidicola acroperus harpae and chydorus brevilabris which resembles the modern fauna of wave swept rocky shores of georgian bay this suggests that the site was an embayment of main lake algonquin local lake waters were cold and shallow pinus banksiana resinosa populus cupressineae artemisia pteridium and other herbs dominate pollen assemblages from 10 500 to 10 000 yr b p an open pine dominated woodland prevailed under a warming and dry climate and marked progression towards the holocene climatic optimum on manitoulin island glacial lake algonquin levels fell and the embayment was transformed into a small alkaline lake potamogeton filiformis hippuris vugaris and scirpus plants provided habitat for a diverse littoral and planktonic cladoceran fauna which included chydorus brevilabris c cf gibbus and bosmina longirostris waters in the swamp basin were rich in nutrients warm and possibly transparent from 10 000 to 8000 years b p picea returned as the dominant pollen type and was slightly more abundant than pinus banksiana resinosa toward the end of this period abies larix and betula increased in frequency picea forest with p banksiana resinova grew on shallow well drained soils climate became more continental winters more severe and summers drier and hotter as the moderating effects of the great lakes ceased during the lake stanley lake hough stage at the site a shallow pond with abundant submersed and emergent aquatic plants and a diverse littoral cladoceran community existed at 8000 yr b p pinus strobus replaced picea and pinus banksiana resinosa shortly after tsuga canadensis and larix become important this conifer dominated pollen assemblage persists to the present and reflects modern forests the presence of nyssa pollen and decodon verticillatus seeds contemporaneous with their range extensions elsewhere in the great lakes region implies that the hypsithermal maximum occurred about 6000 yr b p on manitoulin island when climate remained warmer than present but became humid after about 8000 yr b p by 5000 yr b p conditions became cooler prairie and cordilleran floristic elements in the modern manitoulin flora are probably remnants predating 10 000 yr b p the southern floristic element may represent late hypsithermal relicts fluctuating water levels and influence of mineral rich groundwater probably were key factors controlling hydroseral succession in cedar swamps on manitoulin island

sound velocities of majorite garnet and the composition of the mantle transition region the composition of the mantle transition region characterized by anomalous seismic wave velocity and density changes at depths of approximately 400 to 700 km has remained controversial some have proposed that the mantle transition region has an olivine rich pyrolite composition whereas others have inferred that it is characterized by pyroxene and garnet rich compositions piclogite because the sound velocities in pyrolite estimated from laboratory data are substantially higher than those seismologically observed although the velocities of the olivine polymorphs at these pressures wadsleyite and ringwoodite have been well documented those of majorite another significant high pressure phase in the mantle transition region with realistic mantle compositions have never been measured here we use combined in situ x ray and ultrasonic measurements under the pressure and temperature conditions of the mantle transition region to show that majorite in a pyrolite composition has sound velocities substantially lower than those of earlier estimates owing to strong nonlinear decreases at high temperature particularly for shear wave velocity we found that pyrolite yields seismic velocities more consistent with typical seismological models than those of piclogite in the upper to middle parts of the region except for the potentially larger velocity jumps in pyrolite relative to those observed at a depth of 410 km in contrast both of these compositions lead to significantly low shear wave velocities in the lower part of the region suggesting possible subadiabatic temperatures or the existence of a layer of harzburgite rich material supplied by the subducted slabs stagnant at these depths

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

the effect of soil hydrology on the oxygen and hydrogen isotopic compositions of plants source water abstract many studies have demonstrated that the isotopic composition of plants source water is the main factor affecting the isotopic composition of tree rings because of soil hydrological processes soil water as the source water for plants may isotopically differ from precipitation that contains climatic information such as surface temperature this study addresses the effects of soil hydrological processes on the isotopic compositions of soil water and discusses how these effects affect interpretations of tree ring data in isotopic dendroclimatology we collected precipitation soil gas at two depths 20 and 50 cm and twigs from a maple tree acer saccharum on a biweekly basis during the growing season in 1997 1999 at hanover nh usa water was extracted from the twig samples by vacuum distillation all water samples were analyzed for both d and 18 o soil co 2 was extracted from soil gas and measured for the 18 o values and using the soil temperature and assuming isotopic equilibrium between co 2 and h 2 o we calculated the 18 o values of soil water comparisons among the isotopic time series of each type of sample indicate the following 1 the isotopic composition of soil water is much less variable than that of precipitation suggesting isotopic mixing between waters of different precipitation events 2 in early spring soil water at all depths is isotopically similar to winter precipitation but with time the surface soil water becomes progressively enriched in deuterium and 18 o due to infiltration of summer rain and enrichment through soil water evaporation 3 the influence of summer precipitation decreases with increasing depth and soil at 50 cm can only receive water from large storms 4 replacement of old soil water with new infiltrating water is dependent upon frequency and intensity of growing season precipitation and it is generally more efficient in a wet year than in a dry year 5 the tree we studied uses water mainly from near surface soil layers 6 the d 18 o relationship in twig water indicates that soil water has experienced isotopic enrichment by evaporation these results have important implications for selecting sites for paleoclimatic studies using isotopic data of tree rings

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

elasticity of mgsio3 in the ilmenite phase abstract the single crystal elastic moduli of the ilmenite phase of mgsio 3 have been determined from brillouin spectroscopy they are c 11 472 c 12 168 c 33 382 c 13 70 c 44 106 c 14 27 c 66 152 and c 25 24 in gpa these elastic properties are consistent with a structural mechanical model where the silicon octahedra are very stiff under compression and shear this latter property yields an unexpectedly high shear modulus for the magnesium silicate ilmenite as compared with analogue compounds the further transformation to perovskite will probably be associated with a significant increase in elastic properties since the strong silicon polyhedra form a structural network in this phase the transformation of spinel and stishovite to ilmenite is associated with a slight density increase and a slight decrease in acoustic velocities this transformation will probably not produce a seismic discontinuity even if it does occur in the earth s mantle

a complex 660 km discontinuity beneath northeast china abstract we present a detailed seismic study of the 660 km discontinuity beneath northeast china using the receiver function technique we use seismic data collected from 24 broadband stations in northeast china analysis of these data shows that the 660 km discontinuity is locally depressed in the region from longitude 128 0 e to 130 5 e and latitude 40 0 n to 44 0 n and then it splits into multiple discontinuities in the surrounding regions the complexity of the 660 km discontinuity beneath the subduction zones is probably attributable to the interaction between the upper mantle and subducted slab we speculate that the flattening of the subducted lithosphere near the bottom of the upper mantle causes the multiple discontinuity structure and that the slab penetrating the 660 km discontinuity into the lower mantle causes the narrow 660 km depression area

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

holocene paleoclimate and paleoecology determined from fossil coleoptera at brampton ontario canada an unusually rich and extensive 5 m sequence of organic rich sediments ca 13 000 to ca 4500 bp from a drained glacial kettle near brampton ontario has produced a large and varied assemblage of fossil insects coleoptera beetles from the base include species typical of northern boreal or tree line habitats today approximately one metre above the base of the section ca 11 500 bp there is an abrupt appearance of numerous bark beetles family scolytidae and other coleoptera that inhabit boreal forests temperate species whose ranges are predominantly or totally south of the ontario border appear beginning at ca 9500 bp suggesting environmental conditions similar to modern ones younger dryas and pre boreal oscillation cold events may be evident in lower parts of the boreal sequence although considerations of temporal and climatic resolution make interpretation somewhat ambiguous

mid holocene warming in the northwest kola peninsula russia northern pine limit movement and stable isotope evidence a set of 40 subfossil scots pines pinus sylvestris l was sampled in small lakes beyond the modernpine limit in the northwest kola peninsula russia radiocarbon dating suggests that the pine exp

thermoelastic properties of ringwoodite fex mg1 x 2sio4 its relationship to the 520 km seismic discontinuity abstract we combine density functional theory dft within the local density approximation lda the quasiharmonic approximation qha and a model vibrational density of states vdos to calculate elastic moduli and sound velocities of fe x mg 1 x 2 sio 4 ringwoodite the most abundant mineral of the lower earth s transition zone tz comparison with experimental values at room temperature and high pressure or ambient pressure and high temperature shows good agreement with our first principles findings then we investigate the contrasts associated with the fe x mg 1 x 2 sio 4 transformation at pressures and temperatures relevant to the tz this information offers clearly defined reference values to advance the understanding of the nature of the 520 km seismic discontinuity

climatic and hydrologic variability during the past millennium in the eastern rocky mountains and northern great plains of western canada modelling of tree ring 13 c and 18 o data from the columbia icefield area in the eastern rocky mountains of western canada provides fuller understanding of climatic and hydrologic variability over the past 1000 yr in this region based on reconstruction of changes in growth season atmospheric relative humidity rhgrs winter temperature twin and the precipitation 18 o twin relation the little ice age ad 1530s 1890s is marked by low rhgrs and twin and a 18 o twin relation offset from that of the present reflecting enhanced meridional circulation and persistent influence of arctic air masses independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern rockies in contrast the early millennium was marked by higher rhgrs and twin and a 18 o twin relation like that of the 20th century consistent with pervasive influence of pacific air masses because of strong zonal circulation especially mild conditions prevailed during the medieval climate anomaly ad 1100 1250 corresponding with evidence for reduced discharge in rivers draining the eastern rockies and extensive hydrological drought in neighbouring western usa 2008 published by university of washington

oxygen isotopes in tree rings of abies alba the climatic significance of interdecadal variations we determined the 18o variations in the latewood of tree rings from four silver firs abies alba mill for the period 1840 1997 at a mountain site in switzerland establishing the longest available tree ring record for 18o in central europe the isotope ratios were determined on whole wood with a rapid continuous flow pyrolysis technique thus avoiding cellulose extraction we found significant correlations with 18o tree ring records from the same region although these involved different materials cellulose extracted from whole rings rather than latewood and different species this indicates that physical factors are more important than biological influences as a determinant of 18o in tree rings the isotope tree ring chronology was highly correlated with the oxygen isotope variations in the june july precipitation for the period 1972 1992 r 0 72 and 18o in whole wood of tree rings is therefore well suited for the reconstruction of 18o in precipitation we found a slow quasi periodic variation of the 18o series with a periodicity of 24 years which is correlated to variations in the july temperature this could be caused by fluctuations in the large scale atmospheric circulation over europe and the north atlantic which may result in a change in source and flow path of atmospheric moisture affecting the isotope ratio of precipitation in switzerland although a significant correlation with summer temperature was found p 0 01 the low correlation coefficient r 0 31 indicates that the 18o variations cannot be explained by temperature variations alone however even when considering that the factors influencing 18o in precipitation are not yet fully understood our study shows the potential of tree rings to provide long records of 18o in precipitation for continental areas which will improve our understanding of the causes of natural perturbations of the climate system

thermodynamic and elastic properties of pyrope at high pressure and high temperature by first principles calculations pyrope is an mg end member garnet which constitutes up to 15 of the upper mantle thermodynamic and thermoelastic properties of garnet at high pressure and high temperature are important for understanding the composition and structure of the earth here we report the first principles calculations of vibrational properties thermodynamic properties and elasticity of pyrope over a wide pressure and temperature range the calculated results exhibit good consistency with the available experimental results and provide values up to the pressure and temperature range that are challenging for experiments to achieve and measure pyrope is almost isotropic at high pressure the elastic moduli especially the shear modulus of pyrope exhibit nonlinear pressure and temperature dependences density and seismic velocities of pyrope along with piclogite pyrolite and eclogite are compared with seismic models along the normal upper mantle and the cold subducting lithospheric plate geotherms pyrope has the highest density and seismic velocities among the major minerals of the upper mantle along these geotherms eclogite with 30 pyrope and 70 clinopyroxene is denser than the surrounding mantle even along the normal upper mantle geotherm and becomes still denser along the cold slab geotherm seismic velocities of eclogite with 30 pyrope along the normal upper mantle geotherm are slower than the surrounding mantle but along the cold slab geotherm are faster than the surrounding mantle

morphological adaptations of the brachiopods from a late cretaceous rocky shore ivo klack southern sweden abstract in 1965 d v ager highlighted the concept of morphological adaptations of mesozoic brachiopods to different environments rocky shores were only indirectly included in his seven habitats undoubtedly due their rarity in the fossil record a diverse brachiopod fauna comprising 19 species lived on the late early campanian gneissic rocky shore at the palaeo island of ivo southern sweden the brachiopods show many different morphological adaptations to the contrasting local habitats in the turbulent and highly variable environment they are grouped into guilds and related to preferred habitats according to their morphology substrate strategies mode of life and preservation four main local habitats are recognized representing different energy and illumination conditions ranging from protected areas below and between gneiss boulders and hummocks to the most exposed areas on the vertical sides of these rocks medium sized delicate species preferred the protected habitats whereas large robust species occupied the most exposed habitats no small sized brachiopod species are known from ivo klack in marked contrast to contemporaneous faunas of the more basinal chalks the only observed direct indication of predation on the brachiopods is boreholes after carnivorous gastropods the brachiopod fauna is by far the richest in terms of species diversity compared not only to other late cretaceous rocky shore faunas worldwide but rocky shore faunas in the entire phanerozoic this difference is so remarkable that it cannot be explained by taphonomic factors alone and the density and diversity of the well preserved brachiopods at ivo klack and the great variety in shell morphologies gives a unique opportunity to examine the variety in attachment strategies used in such a highly variable environment

double seismic discontinuities at the base of the mantle transition zone near the mariana slab 1 we use p to s converted phases from teleseimic data recorded at island and ocean bottom stations in mariana to investigate the upper mantle structure in the region we find evidence for double seismic discontinuities at the base of the transition zone near the mariana slab a shallower discontinuity is imaged at depths of 650 715 km and a deeper interface lies at 740 770 km depth the large lateral extent at near constant depths for both features is consistent with horizontal interfaces rather than small scale scatterers the amplitude ratios of the seismic signals suggest that the shear velocity contrast across the two interfaces is comparable these characteristics support the notion that the discontinuities are the results of phase transformations in olivine ringwoodite to post spinel and non olivine component ilminite to perovskite respectively for the pyrolite model of mantle composition

winter precipitation isotope slopes of the contiguous usa and their relationship to the pacific north american pna pattern this study compares the synoptic dynamic relationship between two phases of the pacific north american pna pattern and winter precipitation isotopes at 73 sites across the contiguous usa we use the spatial pattern of isotope slope the rate of changes in precipitation isotope ratios with distance to identify features in the seasonal precipitation isotope fields related to climatic patterns pna positive and pna negative our results show relationships between zones of high isotope slopes and the spatial position of the polar jet stream and juxtaposition of air masses associated with the pna pattern during a positive pna winter zones of high isotope slope in the eastern usa shift southward this change is coincident with a southward displacement of the polar jet stream in this region which leads to a greater frequency of polar air masses and 18o depleted isotope values of precipitation in the region in the western usa zones of high slope shift eastward during the positive pna winter associated with more frequent penetration of tropical air masses that bring 18o enriched precipitation to the region differences in 18o temperature relationships between the pna positive and negative winters and contrasting 18o temperature behaviors in the eastern and western usa provide support for the role of variation in moisture source and transport as a control on the isotopic patterns these findings highlight the importance of synoptic climate driven by pna pattern in determining the spatial patterns of precipitation isotopes and provide constraints on paleo water isotope interpretation and modern isotope hydrological processes

13c and 18o of wood from the roman siege rampart in masada israel ad 70 73 evidence for a less arid climate for the region the isotopic ratios 13c12c and 18o16o of cellulose from tamarix trees which were used by the roman army as a groundwork of the siege rampart of masada ad 70 73 were compared with ratios measured in present day tamarix trees growing in the masada region and in central israel the ancient tamarix cellulose is depleted in both 13c and 18o compared to cellulose from trees growing in the masada region today similar trends were observed on comparing modern tamarix trees growing in the negev desert with those growing in the temperate climate of central israel considering the factors that can contribute to the observed changes in isotopic composition we conclude that the ancient trees enjoyed less arid environmental conditions during their growth compared to contemporary trees in this desert region this report demonstrates the potential in using combined 18o and 13c analyses of archeological plant material as independent indication of regional climatic change in desert areas where conventional isotopic analyses such as in tree rings are impractical

deglacial hydroclimate of midcontinental north america abstract during the last deglaciation temperatures over midcontinental north america warmed dramatically through the bolling allerod underwent a cool period associated with the younger dryas and then reverted to warmer near modern temperatures during the early holocene however paleo proxy records of the hydroclimate of this period have presented divergent evidence we reconstruct summer relative humidity rh across the last deglacial period using a mechanistic model of cellulose and leaf water 18o and d combined with a pollen based temperature proxy to interpret stable isotopes of sub fossil wood midcontinental rh was similar to modern conditions during the last glacial maximum progressively increased during the bolling allerod peaked during the younger dryas and declined sharply during the early holocene this rh record suggests deglacial summers were cooler and characterized by greater advection of moisture laden air masses from the gulf of mexico and subsequent entrainment over the mid continent by a high pressure system over the laurentide ice sheet these patterns help explain the formation of dark colored cumulic horizons in many great plains paleosol sequences and the development of no analog vegetation types common to the midwest during the last deglacial period likewise reduced early holocene rh and precipitation correspond with a diminished glacial high pressure system during the latter stages of ice sheet collapse

rocky shore taphonomy a comparative study of modern and late cretaceous analogues abstract rocky shores are rare in the fossil record due to erosion under both sea level rise and fall in contrast modern rocky shores are well studied but little is known about the evolution of their ecosystems due to the rarity of ancient counterparts reconstruction of these ancient ecosystems is thus essential to get an insight into their evolution a high diversity late cretaceous campanian rocky shore fauna is found in southern sweden the original composition of the shelly fauna cannot be interpreted by direct examination of the preserved fauna due to the effects of taphonomic processes life and death assemblages from a modern rocky shore fauna from thailand have previously been analysed and a hypothetical fossil assemblage was reconstructed in order to attempt an interpretation of the campanian life assemblage this study shows a low taxonomic agreement between the original campanian life assemblage and the fossil assemblage due to taphonomic processes and high environmental fidelity with only a few out of habitat species represented the modern life assemblage showed in an earlier study a high loss of species before onset of fossilisation this suggests that the faunal composition of the campanian life assemblage cannot be easily reconstructed and time averaging by generations of death assemblages makes this even more difficult the campanian aragonitic fauna is poorly represented and the rarity of moulds after aragonitic species is interpreted as due to taphonomic processes and not to lower richness of aragonitic species in the cretaceous this is supported by comparison with the high richness of aragonitic species found on a late cretaceous rocky shore in germany an originally high diversity gastropod fauna is thus interpreted to have dominated the intertidal zone in the campanian example and the rare moulds of each of the aragonitic species indicate a high taphonomic loss in spite of rapid burial calcitic species richness is higher in the campanian fauna than in the modern life death and constructed hypothetical fossil assemblages this is interpreted as reflecting time averaging of generations of calcitic species and low loss of calcitic species by taphonomic processes in the campanian fauna it is thus assumed that the original campanian fauna experienced a change in faunal composition from a gastropod dominated life assemblage to a bivalve dominated fossil assemblage due to dissolution of aragonite and excellent preservation of calcite reconstruction of ancient rocky shore shelly faunas can thus be considerably improved by comparison with analogous modern rocky shore faunas

isotopic evidence of sea surface freshening enhanced productivity and improved organic matter preservation during sapropel deposition in the tyrrhenian sea multiple layers of sapropels occur widely in the sedimentary record of the mediterranean sea and record repetitions of paleoclimatic conditions that favored increased production and preservation of marine organic matter a combination of hydrogen and carbon isotope analyses of pleistocene sapropels from the tyrrhenian sea reveals new aspects of the factors leading to their deposition organic matter dd values that are significantly more negative in sapropels than in adjacent marls indicate a combination of dilution of surface waters by meteoric waters and increased burial of lipid rich organic matter during periods of sapropel deposition organic 13 c values in sapropels that are less negative than those in marls suggest periods of markedly elevated marine biological production the opposite but concordant excursions of these two isotopic parameters imply that the sapropel layers formed from increased export of marine organic matter from the photic zone to the sea floor during periods of greater fluvial delivery of continental nutrients to the mediterranean sea furthermore the isotopic evidence indicates that periods of wetter climate were widespread in southern europe at the same times as in northern africa

interpreting paleoclimate from l8o and 2h in plant cellulose comparison with evidence from fossil insects and relict permafrost in southwestern ontario the oxygen isotope content of terrestrial plant cellulose is related to that of the source waters by a two step process involving evapotranspirative leaf water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide a combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data humidity is the dominant influence on variations in the cellulose 18o enrichment relative to the source water a good first order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment without explicit consideration of factors such as temperature 18o of atmospheric vapour and leaf boundary layer dynamics the value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at brampton ontario estimates of the past relative humidity

spatially dependent seismic anisotropy in the tonga subduction zone a possible contributor to the complexity of deep earthquakes abstract the deep part of the tonga subduction zone consists of two differently oriented slab segments the northern segment within latitudes 17 19 s and the southern segment within latitudes 19 5 27 s the orientation of the slab is strike dip 110 57 in its northern part and 210 46 in its southern part both segments are seismically active at depths from 500 to 700 km the mechanisms of deep focus earthquakes reported in the harvard moment tensor catalogue contain compensated linear vector dipole clvd components that behave differently in both segments the mean value of the clvd is 3 for the northern segment but 10 for the southern segment the mean absolute value of the clvd is 12 for the northern segment and 16 for the southern segment the complex behaviour of the clvd is explained by spatially dependent seismic anisotropy in the slab the inversion for anisotropy from the non double couple components of moment tensors points to orthorhombic anisotropy in the both slab segments the anisotropy seems to have a uniform strength of 5 7 for p waves and 9 12 for s waves and is oriented according to the orientation of each segment and the stress acting in it the spatial variation of velocities is roughly similar in both segments the retrieved anisotropy might have several possible origins it can be 1 intrinsic caused by preferentially aligned anisotropic minerals such as wadsleyite ringwoodite ilmenite or others 2 effective caused for example by intra slab layering or 3 partly apparent produced by systematic errors in the moment tensors due to neglecting 3d slab geometry and the slab mantle velocity contrast when calculating the green functions in the moment tensor inversion

metastability of enstatite in deep subducting lithosphere olivine and mg fe sio3 pyroxene the most abundant minerals in the earth s upper mantle are believed to transform to high pressure phases at 400 km depth1 5 the possible metastable persistence of olivine to greater depths in some subduction zones with consequences for the origin of deep focus earthquakes and the dynamics of subduction has been discussed extensively6 14 but the role of other mantle minerals has not been considered we report here an experimental study of the kinetic behaviour of the magnesian pyroxene enstatite mgsio3 at upper mantle conditions we find that whereas forsterite mg olivine mg2sio4 transforms rapidly to phase at 1 200 c and 16 gpa the transformation of enstatite to phase plus stishovite on the same timescale requires much higher temperatures at lower temperatures enstatite transforms directly to the ilmenite structure but only at pressures greater than 20 gpa enstatite should therefore persist metastably to greater depths than olivine in subduction zones transforming directly to the ilmenite structure the enstatite ilmenite transformation is accompanied by a large decrease in volume which should increase the stresses in subducting slabs change the buoyancy forces that drive subduction and might also contribute to the origin of deep focus earthquakes

the nature of the 660 kilometer discontinuity in earth s mantle from global seismic observations of pp precursors the 660 kilometer discontinuity which separates earth s upper and lower mantle has been detected routinely on a global scale in underside reflections of precursors to ss shear waves here we report observations of this discontinuity in many different regions using precursors to compressional pp waves the apparent absence of such precursors in previous studies had posed major problems for models of mantle composition we find a complicated structure showing single and double reflections ranging in depth from 640 to 720 kilometers that requires the existence of multiple phase transitions at the base of the transition zone the results are consistent with a pyrolite mantle composition

late glacial climate and ecology of a kettle section at brampton ontario canada as determined from fossil coleoptera a 5 m sequence of organic rich sediments ca 13 000 years bp to ca 4500 bp from a drained glacial kettle pond near brampton ontario has yielded a rich and varied assemblage of coleopteran foss

multiresolution imaging of mantle reflectivity structure using ss and p p precursors summary knowledge of the mantle reflectivity structure is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals among the various data types and techniques long period ss pp precursors and high frequency receiver functions are routinely utilized to increase the confidence of the recovered mantle stratifications at distinct spatial scales however low resolution and a complex fresnel zone are glaring weaknesses of ss precursors while over reliance on receiver distribution is a formidable challenge for the analysis of converted waves from oceanic regions a promising high frequency alternative to receiver functions is ppprecursors which are capable of resolving mantle structures at verticalandlateralresolutionof 5and 200km respectively owingtotheirspectralcontent shallow angle of incidence and near symmetric fresnel zones this study presents a novel processing method for both ss or pp and ppprecursors based on deconvolution stacking radon transform and depth migration a suite of synthetic tests is performed to quantify the fidelity and stability of this method under different data conditions our multiresolution survey of the mantle at targeted areas near nazca south america subduction zone reveal both olivine and garnet related transitions at depths below 400km we attribute a depressed 660 to thermal variations whereas compositional variations atop the upper mantle transition zone are needed to explain the diminished or highly complex reflected scattered signals from the 410km discontinuity we also observe prominent ppreflections within the transition zone and the anomalous amplitudes near the plate boundary zone indicate a sharp 10km thick transition that likely resonates with the frequency content of ppprecursors the migration of ss precursors in this study shows no evidence of split 660 reflections but potential majorite ilmenite 590 640km and ilmenite perovskite transitions 740 750km areidentifiedbasedonsimilarlyprocessedhigh frequencyppprecursors additionalfindings of severely scattered energy in the lithosphere and distinct lower mantle reflections at 800km could be potentially important but require further verifications overall our improved imaging methods and the strong sensitivity of ppprecursors to the existence depth sharpness and strengthofreflective structuresoffersignificant futurepromisefortheunderstanding ofmantle mineralogy and dynamics

multiple discontinuities near 660 km beneath tonga area 1 we study the discontinuities beneath tonga subduction zone using the deep earthquakes recorded by the pacific northwest seismic network pnsn the multiple discontinuities around 660 km beneath tonga subduction zone are found using converted phase sdp the amplitude ratios of the converted phase with the direct p wave ac ap are also determined the largest number of robust converted phases with large ac ap comes from the depth range of 660 690 km its peak is at 680 km the second one appears in the depth range of 700 745 km its peak is at 740 km the two discontinuities are obviously depressed by the subduction slab according to experimental and numerical studies a possible explanation of the observation is that the first discontinuity is formed by the transition of spinel to perovskite and magnesiowustite and the second is formed by the transition of ilmenite to perovskite

mid mantle anisotropy in subduction zones and deep water transport the earth s transition zone has until recently been assumed to be seismically isotropic increasingly however evidence suggests that ordering of material over seismic wavelengths occurs there but it is unclear what causes this we use the method of source side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe we find significant amounts of splitting 2 4 s confirming that the transition zone is anisotropic here however there is no decrease in the amount of splitting with depth as would be the case for a metastable tongue of olivine which thins with depth suggesting this is not the cause the amount of splitting does not appear to be consistent with processes in the ambient mantle such as lattice preferred orientation development in wadsleyite ringwoodite or mgsio3 perovskite we invert for the orientation of several mechanisms subject to uncertainties in mineralogy and deformation and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions we suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab implying significant water transport from the surface down to at least 660 km depth

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

can sedimentary leaf waxes record d h ratios of continental precipitation field model and experimental assessments abstract d h ratios of leaf waxes d wax derived from terrestrial plants and preserved in lake sediments can provide important information on past continental hydrology ideally d wax can be used to reconstruct precipitation d h ratios d p which is a well established paleoclimate proxy however many other factors such as vegetation and relative humidity rh also affect d wax variation how the combination of these factors affects sedimentary d wax is unclear here we use a transect of 32 lake surface sediments across large gradients of precipitation relative humidity and vegetation composition in the southwestern united states to study the natural factors affecting sedimentary d wax d values of c 28 n alkanoic acids show significant correlation with d p values r 2 0 76 with an apparent isotopic enrichment of 99 8 indicating that sedimentary d wax values track overall d p variation along the entire transect leaf waxes produced by plants grown under controlled conditions rh 80 60 40 show a small increase in d h ratios as rh decreases consistent with prediction from the craig gordon model however the isotopic effect of rh on d wax along the natural transect is partially countered by the opposing influence of vegetation changes the correlation between d wax and d p values is significantly higher r 2 0 84 in the drier portions of the transect than in the wetter regions r 2 0 64 this study suggests that d h ratios of sedimentary leaf waxes can be used as a proxy for precipitation d variations with particularly high fidelity in dry regions although more studies in other regions will be important to further test this proxy

oxygen isotope variations in post glacial lake ontario abstract the role of glacial meltwater input to the atlantic ocean in triggering the younger dryas yd cooling event has been the subject of controversy in recent literature lake ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the laurentide ice sheet lis to the atlantic ocean via the lower great lakes here we use the oxygen isotope compositions of ostracode valves and clam shells from three lake ontario sediment cores to identify glacial meltwater contributions to ancient lake ontario since the retreat of the lis 16 500 cal 13 300 14c bp differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime the average lakewater 18o of 17 5 determined from ostracode compositions indicates a significant contribution from glacial meltwater upon lis retreat from the st lawrence lowlands ancient lake ontario glacial lake iroquois lakewater 18o increased to 12 largely because of the loss of low 18o glacial meltwater input a subsequent decrease in lakewater 18o from 12 to 14 accompanied by a median sediment grain size increase to 9 m indicates that post glacial lake ontario received a final pulse of meltwater 13 000 12 500 cal 11 100 10 500 14c bp before the onset of hydrologic closure this meltwater pulse which is also recorded in a previously reported brief freshening of the neighbouring champlain valley cronin et al 2012 may have contributed to a weakening of thermohaline circulation in the atlantic ocean after 12 900 cal 11 020 14c bp the meltwater presence in the ontario basin continued to inhibit entry of champlain seawater into early lake ontario opening of the north bay outlet diverted upper great lakes water from the lower great lakes causing a period 12 300 8300 cal 10 400 7500 14c bp of hydrologic closure in lake ontario anderson and lewis 2012 this change is demarcated by a shift to higher 18olakewater 7 driven in part by strong evaporative conditions in the ontario basin and in part by increasing 18oprecipitation at this time the 18olakewater then fluctuated only slightly upon the eventual return of the upper great lakes water during the nipissing phase at 5800 cal 5090 14c cal bp anderson and lewis 2012 after which shelly fauna are no longer preserved in the sediment record

paleohydrology of a canadian shield lake inferred from 18o in sediment cellulose oxygen and carbon isotope analyses on cellulose in the postglacial sediment of weslemkoon lake southern ontario show that the cellulose came mainly from aquatic plants or algae rather than from terrestrial sources if a wholly aquatic source is assumed the oxygen isotope content permits inferences of lake water 18o values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis chronological control is provided by pollen analysis and six 14c dates our reconstruction shows lake water 18o fluctuated from about 5 lower than present in the early postglacial to 5 or more above present values during the mid postglacial these broad secular shifts reflect a combination of fluctuating mean annual 18o of local precipitation evaporative isotopic enrichment of surface waters and snowmelt bypass effects the first two factors reflect the changing paleotemperature and paleohydrology respectively whereas the third factor is a more speculative interp

seismic discontinuities in the mantle transition zone and at the top of the lower mantle beneath eastern china and korea influence of the stagnant pacific slab we have analyzed broadband data to identify and determine mantle discontinuities in the mantle transition zone mtz beneath eastern china where the pacific slab is stagnant the depths of the 410 and 660 km discontinuities are generally shallower and deeper respectively than the global averages in and near the pacific slab beneath eastern china the mtz is thicker in the slab than the global average this observation is consistent with the thermally controlled olivine to wadsleyite transformation for the 410 km discontinuity and the post spinel transformation for the 660 km discontinuity other discontinuities appear from 690 to 750 km in the lower mantle part of the pacific slab recent mineralogical experiments indicate that the most plausible interpretation of these deep discontinuities is that they represent the ilmenite to perovskite transformation in a cold environment such as that in the pacific slab

anisotropy of akimotoite a molecular dynamics study elastic constants of akimotoite at high temperatures and pressures are calculated by using molecular dynamics simulations to study the anisotropic properties of akimotoite we find that akimotoite becomes more anisotropic with increasing temperature but less with increasing pressure on the 0 0 1 face s wave splitting and azimuthal anisotropy will occur simultaneously while the p wave velocity remains almost constant polarization directions of the two s waves are neither strictly perpendicular nor parallel to the crystallographic face the polarization direction of the fast s wave is more parallel with the plane than that of the slow s wave for all wave propagation directions on the 1 0 0 face no s wave splitting will occur for waves passing along the crystallographic c axis and the p wave velocity along the axis is smaller than that in other directions polarization anisotropy changes its sign with the variation of wave propagation directions giving rise to the dependence of the relative magnitude of vsh and vsv on the seismic wave propagation directions we further calculate the anisotropic properties of a mineral assemblage containing ringwoodite akimotoite and ca perovskite to infer the effect that akimotoite may have on the anisotropy of the lower portion of the mantle transition zone we find that the mineral assemblage is much less anisotropic than akimotoite but possesses many anisotropy features of akimotoite comparison of the anisotropy features with seismological observations indicates that a vertical flow direction is required in areas close to the subduction zones which may be caused by the downward penetration of slabs to the lower mantle as well as upwelling of fluids and light materials in the mantle wedge associated with deep dehydration reactions of the slabs 2005 elsevier b v all rights reserved

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

a paleoenvironmental study of the molluscs from the don formation sangamonian don valley brickyard toronto ontario the don formation comprises 8 9 m of fossiliferous stratified sand and clay lying between glacial deposits of wisconsinan and presumed illinioan age it has yielded a diverse fossil flora and fauna indicating a climate as warm as or warmer than present and is considered to be of last or sangamonian interglacial age about 2 t of sediment were processed from the type section of the don formation at toronto ontario and yielded approximately 18 000 identifiable mollusc shells representing 45 taxa previously unpublished taxa include 11 freshwater gastropod species 12 pelecypod species sphaeriidae and 7 terrestrial gastropod species the molluscs are mainly concentrated in the lower two thirds of the formation and are dominated by valvata perdepressa with abundant valvata sincera probythinella lacustris amnicola limosa amnicola walkeri pleurocera acuta elimia livescens pisidium casertanum pisidium compressum pisidium fallax and sphaerium striatinum all the mollusc species are modern inhabitants of the great lakes region their known ecological tolerances suggest deposition in relatively shallow waters of a large temperate lake having substantial fluvial input nearby stratigraphic variations in the relative abundance of different aquatic taxa may reflect variations in water depth or fluvial activity stable isotope data from several mollusc species and a single wood specimen together with taxonomic paleoenvironmental interpretation are consistent with deposition during the climatic optimum of the sangamonian interglaciation environmental conditions and faunas are similar to those of the nipissing phase hypsithermal of the eastern great lakes

mesozoic and cenozoic tectonic evolution of scania southern sweden abstract triassic to early cretaceous transtensional sinistral tectonics induced the subsidence of fault bounded basins in scania late cretaceous dextral transpressional deformations induced the inversion of these basins and the uplift of major basement blocks the resulting structural relief is of the order of 2000 m

the effects of different methods of preparing cellulose nitrate on the determination of the d h ratios of non exchangeable hydrogen of cellulose abstract cellulose nitrate prepared by different methods was subjected to elemental isotopic and spectroscopic analysis cellulose nitrate prepared by nitration of wood powder was contaminated most likely by nitrated lignin cellulose nitrate prepared by nitration of wood cellulose did not contain this component and thus provides a more accurate measure of the d h ratios of non exchangeable hydrogen of cellulose however cellulose nitrate prepared directly from cellulose contained trace amounts of hemicellulose nitrates and was not completely nitrated these conditions will not cause significant errors in the d h ratios measured for most samples analysis of aliquots of the same samples nitrated by the two methods suggests that published d values of cellulose nitrate from wood may be in error by 6 8 in many cases and occasionally by as much as 15

synchronous climate anomalies in the western north pacific and north atlantic regions during the last 14 000 years abstract a peat cellulose 18 o record spanning around 14 000 years from the hani peat mire in northeastern china reveals several abrupt temperature anomalies in the period from the last deglaciation through the holocene the timing of these anomalies coincides well with the notable cooling events recorded respectively using the gisp2 ice core and ice rafted sediment of the north atlantic ocean such as the older dryas inter allerod younger dryas and the nine ice rafted debris events the results demonstrate that this repeating pattern of abrupt temperature deterioration is not limited to the north atlantic area at high latitude but also exists in the western north pacific region at middle latitude the synchronous temperature anomalies possibly are resulted from the joint effects of meltwater discharge into the north atlantic ocean and reduced solar activity in the period from around 8600 to 8200 cal yrs bp the hani peat record shows a broad 18 o peak that may reflect compound climate signals resulting from the two kinds of forcing factors the temperature drop related to reduced solar activity at around 8600 8250 cal yrs bp and the temperature anomaly attributed to the meltwater effect at around 8220 70 cal yrs bp this result may provide palaeo temperature evidence for existence of the sharp 8 2 k event in the western north pacific region in addition our results have revealed that in the period from the last deglaciation through the holocene the synchronous temperature anomalies before and after the 8 2 k event seem to be related to meltwater outflow and reduced solar activity respectively it is important that the all temperature anomalies whether because of reduced solar activity in the late holocene or from meltwater discharge in the early holocene are accompanied by an abrupt decline in the indian ocean summer monsoon and abrupt strengthening of the east asian summer monsoon it is likely that reduced solar activity and meltwater outflow appear to modulate earth system changes in the same direction the influences could be compounded reduced solar activity and meltwater outburst both appear to act as triggers for occurrence of the el nino phenomenon in the equatorial pacific ocean which may result in broad teleconnections between the temperature anomaly in the northern hemisphere and abrupt variation of the asian monsoon

east asian summer monsoon variability during marine isotope stage 5 based on speleothem δ18o records from wanxiang cave central china abstract speleothems from wanxiang cave china 33 19 n 105 00 e located near the northern limit of the east asian summer monsoon provide high resolution records of paleomonsoon variability we present a simple model for interpreting 18o shifts in speleothems from this region in which the 18o of speleothem calcite is inversely related to monsoon intensity in contrast to observations at higher latitudes atmospheric temperature has little effect on 18o of precipitation near wanxiang cave furthermore the temperature dependence of calcite water 18o fractionation acts in the opposite sense most likely canceling out the effect of local temperature variations on speleothem 18o given this the maximum 18o shift that could occur due only to changes in the composition of the oceanic source region the amount of rainfall and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5 5 accordingly it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7 range observed in fossil wanxiang cave speleothems two stalagmites wxsm 51 and wxsm 52 exhibit more positive 18o during stadial periods marine isotope stages mis 8 6 5d 5b and 2 than during interstadial periods mis 9 5a 5c 5e thus east asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods we present detailed 18o records from mis 5a 5b and 5c 5d during the mis 5d 5c transition summer monsoon intensity increased steadily from 117 6 ka with a peak in intensity occurring at 106 8 ka concurrent with greenland interstadial 24 during the mis 5b 5a transition monsoon intensity increased abruptly at about 85 7 ka when 18o decreased by approximately 4 in 200 years monsoon variability inferred from the mis 5c 5d and mis 5a 5b records closely coincides with global climate changes observed in the gisp2 vostok and specmap records and with the northern hemisphere insolation curve this suggests that east asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in northern hemisphere incident solar radiation the mis 5a 5b and 5c 5d paleomonsoon records from wanxiang cave also agree well with other records of asian monsoon variability indicating that 18o of speleothems from wanxiang cave is a valid proxy for past changes in monsoon intensity

elasticity of superhydrous phase b at the mantle temperatures and pressures implications for 800 km discontinuity and water flow into the lower mantle the thermodynamic properties and elasticity of superhydrous phase b shyb at high pressure and temperature are calculated using first principles calculations based on density functional theory the velocities and densities of shyb are significantly lower than those of bridgmanite and periclase the major minerals in the lower mantle the anisotropy of shyb is unremarkable at relevant mantle conditions the decomposition of shyb into bridgmanite periclase and water which can occur at a depth around 800 km at a cold slab will cause an increase of 7 5 15 0 and 12 on shear velocity compressional velocity and density respectively thus the decomposition of a small amount of shyb can produce a local discontinuity at the depth of 800 km the water released from the decomposition of shyb may rise upward and promote the partial melt which can further explain the low velocity zones just above 800 km discontinuity in western pacific subduction zones

pliocene climate variability northern annular mode in models and tree ring data the northern annular mode nam and its regional expression the north atlantic oscillation nao are the primary interannual oscillatory systems in the northern hemisphere in the modern climate nam has been linked with a number of weather extremes including large terrestrial temperature increases and extreme snowfalls its connection to climate is more controversial although a change in its behaviour between 1970 and 2000 coincided with rapid temperature increases in the northern hemisphere the north atlantic and nordic seas are a key component in pliocene climate showing the largest increases from modern sea surface temperature to understand these changes and the ability of climate models to reproduce them we must consider simulations of the nam here we show that existing mid pliocene simulations exhibit large changes to the mean state and variability in the north atlantic and a significant dampening of the nao through sensitivity experiments this change is primarily attributed to the impact of the lowering of the rocky mountains as the timing of rocky mountains uplift is still disputed simulations of the north atlantic region contain significant uncertainty particularly relating to interannual variability and its climate feedbacks new high temporal resolution climate proxy data is required to test these model reconstructions here we report new annual resolution data and an analysis of climate variability from fossil tree rings these fossils from sites in the canadian arctic provide support for a strong north atlantic oscillation during the pliocene

elastic properties of stishovite and the cacl2 type silica at the mantle temperature and pressure an ab initio investigation a b s t r a c t the elastic constant tensors of stishovite and the cacl2 type silica at the earth s mantle temperature and pressure were determined using first principles calculations with local density approximation the elastic properties of stishovite show not only strong pressure dependence but also temperature dependence by increasing temperature the shear instability of stishovite is shifted to an elevated pressure with a slope of 5 4 1 4m pa k the softening of the shear modulus and the positive clapeyron slope result in crossing of the sound velocities at different temperatures which leads to the unusual positive temperature dependence of the sound velocities around the phase boundary the transition from stishovite to the cacl2 type silica at the lower mantle s temperature occurs at a depth far deeper than 1200 km and is accompanied by a velocity jump of 0 98 0 08 km si n s wave velocity v s and 0 45 0 15 km s in p wave velocity v p this transition is likely related to the seismic discontinuity at the depth of 1670 km in the vicinity of mariana island the unusual positive temperature dependence of v s of stishovite and strong anisotropy of stishovite and the cacl2 type silica around the phase boundary

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

stagnation of subducting slabs in the transition zone due to slow diffusion in majoritic garnet subducting slabs of oceanic lithosphere often stagnate before reaching the lower mantle laboratory experiments under high pressures and temperatures show that pyroxene a common mineral in such slabs is transformed to its dense high pressure counterpart majorite garnet at a very slow rate temporarily keeping the slabs buoyant compared to the surrounding mantle

a model based determination of spatial variation of precipitation δ18o over china abstract many works show the dependence of precipitation 18o on altitude and latitude as a result of air temperature change the assumption that these quantitative relations can hold across a large geographical region can be used to give a rough estimation of local precipitation 18o where there is on direct observation of precipitation 18o although there truly exists uncertainty in the estimation an effect was made in this paper to establish the precipitation 18o pattern over the whole china based on regional topography and the 18o of meteoric precipitation this paper established a quantitative relationship between 18o in precipitation and latitude and altitude using the existing 18o data from 55 sites over china the model describes as 18oppt 0 0073lat2 0 3261lat 0 0015alt 9 7776 and was used to generate a higher resolution map of mean annual 18o for precipitation over china using geographic information system software integrating with latitude altitude and the moisture cycle this determination of the spatial distribution of 18o in modern precipitation of china provides important information for ancient climate and stable isotope hydrology studies

slow si al interdiffusion in garnet and stagnation of subducting slabs abstract si 4 m 2 2al 3 m mg fe ca interdiffusion rates in majoritic garnet have been determined at pressure of 17 gpa and temperatures of 1550 1700 c using a kawai type high pressure apparatus the diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope and the rate of the si 4 m 2 2al 3 interdiffusion was determined to be a d si al m 2 s 1 2 10 10 exp 364 kj mol 1 rt we found that the diffusion rate is low compared to the si diffusion rate in other silicate minerals relevant to the deep mantle slow kinetics of the pyroxene garnet transformation due to the low diffusion rate indicates that large low density metastable regions may exist in the slab greatly contributing to the slab stagnation around the transition region stagnant slabs possibly stay in this region over 10 8 yr because of the sluggish pyroxene garnet transformation but may eventually fall into the lower mantle after the completion of the transformation

an investigation of the common signal in tree ring stable isotope chronologies at temperate sites we observed a strong common high frequency interannual signal for thed 13 c chronologies whereas the low frequency decadal scale signal was more similar among thed 18 o chronologies for both carbon and oxygen isotopes we found significant positive relationships with annual and growing season temperatures and negative relationships with precipitation again of similar magnitude for all species except forfraxinus which contained only minor climatic information averaging of all chronologies resulted in an increase in the climatic signal of the mean chronology the combinedd 18 o record reflected decadal scale temperature variations remarkably well r 0 72 however the relationship between climate and carbon isotopes declined over the last 3 decades of the 20th century probably related to the steep increase in atmospheric co 2 concentrations resulting in strongly divergingd 13 c trends of the different chronologies our study indicates that combining chronologies from different species enhances the potential of isotope studies for extending climate reconstructions into areas of temperate climate

twentieth century summer temperature variability in the southern altai mountains a carbon and oxygen isotope study of tree rings the altai mountains southern siberia represent an area of significant scientific interest and exceptional palaeoecological potential to assess the influence of climate on the stable isotopic composition of tree ring cellulose and the potential of this record as a palaeoclimate proxy replicated stable oxygen and carbon isotope time series were developed for the twentieth century from four siberian pine pinus sibirica du tour trees growing near the settlement of aktash russian altai mountains southern siberia bootstrapped calibrations for the local instrumental period ad 1954 2000 reveal strong correlations between summer july august growing season temperatures and tree ring oxygen r2 0 55 and carbon r2 0 30 isotopes covariance observed between both carbon and oxygen isotope data suggest a common stomatal control the resulting empirical model was used to reconstruct regional summer temperatures for the twentieth century no divergence is observed between the non detrended tree ring isot

relative humidity recorded in tree rings a study along a precipitation gradient in the olympic mountains washington usa abstract humidity is one of the fundamental variables controlling the energy balance of the climate and thus its reconstruction represents a significant aspect of paleoclimate studies we here report a study of oxygen and hydrogen isotopic compositions of tree ring cellulose along a precipitation gradient in the olympic mountains of washington usa to examine whether and how the relative humidity is recorded in the cellulose according to the physically based model described in this paper the relationship between d and 18 o of cellulose should have the same slope as that in the relationship between d and 18 o in the source water 8 8 for the local meteoric water if there is no systematic variation in the mean relative humidity among study sites and no physiologic differences among trees however our isotopic analyses of cellulose yielded a slope of 17 4 significantly greater than the slope of the local meteoric water line we show that to produce such a slope a positive covariation between the relative humidity and the d and 18 o in the source water is required across the precipitation gradient this work suggests that the d vs 18 o relationship in tree rings can be a useful tool for paleohumidity reconstruction

estimating 14c groundwater ages in a methanogenic aquifer this paper addresses the problem of 14c age dating of groundwaters in a confined regional aquifer affected by methanogenesis increasing ch4 concentrations along the groundwater flow system and 13c and 14c isotopic data for dissolved inorganic carbon dissolved organic carbon and ch4 clearly show the effect of methanogenesis on groundwater chemistry inverse reaction path modeling using netpath indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite ion exchange methanogenesis and oxidation of sedimentary organic matter modeling of groundwater 14c ages using netpath indicates that a significant part of groundwater in the alliston aquifer is less than 13 000 years old however older groundwater in the range of 15 000 23 000 years is also present in the aquifer this paper demonstrates that 14c ages calculated using netpath incorporating the effects of methanogenesis on the carbon pools provide reasonable groundwater ages that were not possible by other isotopic methods

prospects for reconstruction of seasonal environment from tree ring δ13c baseline findings from the great lakes area usa abstract plant 13 c and discrimination 13 c air 13 c plant embody ecophysiological response to environmental conditions influencing rates of carbon fixation and stomatal conductance this study scrutinizes the seasonal variation of 13 c and in growth rings developed in 1990 as represented in trees of 11 species at three sites along a 5 latitude transect in illinois and wisconsin usa radial stem xylem growth of the trees was monitored with monthly punch cores and the resulting growth curves precisely identified the growth period represented in the five segments into which each growth ring was subdivided seasonal 13 c variation of cellulose was usually 1 1 5 and the seasonal patterns were similar among angiosperm and conifer trees at a site with angiosperms generally 13 c depleted by 0 5 1 5 seasonal 13 c and patterns was different among sites however and regression with several environmental parameters revealed most frequent significant correlation with soil moisture palmer drought severity index pdsi the site averaged seasonal patterns track each of their divergent local seasonal drought index chronologies very well even when isotopic curves of the different trees are simply averaged without adjustment for different growth rates seasonal tree ring 13 c analysis is affirmed as a valuable method for assessing seasonal moisture status furthermore results favor successful extension to ancient tree rings where different species and slope aspects may be represented in wood samples at a collection site and where rates of ring development and seasonal 13 c air are not likely to be known

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

stable isotope paleoclimate records for southern ontario canada comparison of results from marl and wood profiles of 18o in two marl cores from southern ontario canada are compared in detail with the records of meteoric water isotopic composition and photosynthetic humidity obtained from previous isotopic studies using wood cellulose at brampton ontario by accounting for the inferred changes in meteoric water composition and temperature the changes in the oxygen isotope content of the marl arising from fluctuations in the evaporative enrichment of the lakewater can be estimated the resulting synthetic profiles of relative evaporative enrichment from both marl cores exhibit strong correspondence to the photosynthetic humidity profile generated from the studies at brampton which substantiates the importance of evaporation in the water budgets of these two lakes a striking analogy exists between the isotopic evaporative enrichment response of such lakewaters and that of the waters in terrestrial plants both of the marl lakes approach close to isotopic steady state during the summer season when carbon

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at steel lake minnesota abstract middle holocene 8 to 4 ka bp warmth and aridity are well recorded in sediment archives from midcontinental north america however neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators for example an important challenge is to distinguish among the interacting effects of evaporation temperature or precipitation seasonality in existing 18 o records from the region here we combine hydrogen isotopes of palmitic acid and oxygen isotopes of carbonate to derive lake water isotopic values during the holocene at steel lake in north central minnesota in combination these data enable us to separate variations in evaporation from variations in the isotopic composition of input waters to lake variations in evaporation are used as a proxy for aridity and lake water input isotopic values are used as a proxy for the isotopic values of meteoric precipitation our results suggest that lake water input isotopic values were more negative during the middle holocene than at present to test whether these more negative values are related to temperature or precipitation seasonality we compare pollen inferred temperatures and the expected isotopic value of precipitation resulting from these temperatures to the reconstructed precipitation isotopic values results suggest that middle holocene warmth and aridity were associated with increased evaporation rates and decreased summer precipitation these inferences are consistent with climate simulations that highlight the role of seasonal insolation and sea surface temperatures in driving variations in precipitation seasonality during the holocene results also suggest that changes in holocene precipitation seasonality may have influenced the expansion of the prairie forest border in minnesota as well as regional variations in grassland community composition this study demonstrates the efficacy of the dual hydrogen and oxygen isotope approach for distinguishing changes in evaporation and precipitation seasonality in the paleolimnological record

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

elasticity of akimotoite under the mantle conditions implications for multiple discontinuities and seismic anisotropies at the depth of 600 750 km in subduction zones abstract the equation of state and elastic properties of akimotoite at simultaneously high pressures and high temperatures are obtained using first principles calculations based on the density functional theory dft the calculated results agree with the available experimental data combining our results with the elastic data of other minerals we estimated the v p v s and density contrasts caused by the akimotoite related transitions the velocity contrasts between akimotoite and bridgmanite are 4 6 and 8 3 for v p and v s respectively which are only about half of those between majorite and akimotoite moreover because both the akimotoite bridgmanite and majorite akimotoite transitions have broad phase boundaries these two phase transitions may not contribute to multiple discontinuities around 660 km depth in subduction zones as detected by seismic studies instead the decomposition of pyrope into bridgmanite and corundum which would occur in cold subduction zones with a sharp phase boundary and a large impedance contrast due to the inhibition of the pyroxene garnet transformation at relatively low temperatures could be a more reasonable explanation for the discontinuity at 700 750 km in subduction zones furthermore the transformation from high pressure clinopyroxene to akimotoite at the depth of 600 km can increase the v p v s and density by 10 1 14 8 and 9 9 respectively indicating that the phase transition may account for the local discontinuity at 600 km in some subduction zones in addition the anisotropies of akimotoite are significantly higher than those of other major minerals at the base of the mantle transition zone and could be the origin of the seismic anisotropies detected in some subduction zones