a 14 000 year sediment yield record from western germany based on annually laminated lake sediments the reconstruction of sediment yield data for the catchment of lake holzmaar 205 8 ha in the eifel mountains western germany is based on high resolution geochemical and physical analyses of an absolutely dated sediment record this technique provides flux rates of allochthonous minerogenic deposition for the last 13 840 years the pleistocene holocene transition is characterized by instable soils and vegetation caused by adjustment of the catchment to interglacial climatic conditions these instabilities are the reason for elevated mean sediment yields in the catchment of 16 t km 2 yr 1 until 9800 cal bp during most of the holocene erosive processes are insignificant and sediment yields are very low 1 5 t km 2 yr 1 since humans cleared the forests for agriculture and early industrial purposes the natural environment has been disturbed and sediment yields increased to mean values of 14 t km 2 yr 1 during the last 2750 years comparisons of reconstructions from the eifel area with similar data from southern sweden and with measured data from lakes reservoirs and monitoring sites suggest that quantitative reconstructions based on lake holzmaar sediments may be regarded as reliable despite uncertainties related to the methods of reconstruction applied

a lateglacial and holocene organic carbon isotope record of lacustrine palaeoproductivity and climatic change derived from varved lake sediments of lake holzmaar germany abstract a composite varve dated 11 4 m long sediment sequence from lake holzmaar situated in the eifel region of western germany was investigated for total organic matter content total nitrogen content and stable organic carbon isotopes mean time resolution is 75 years for tn and 14 years for 13 c org on millennial time scales primary production of lacustrine algae strongly depends on the delivery of nutrients from the catchment the respective carbon isotope record is characterized by marked variations of 13 c org ranging from 36 0 to 27 0 and includes a number of pronounced shifts reactions of the lacustrine system and the catchment to changes of environmental parameters e g runoff solar radiation and temperature induce changes of algal associations and of lacustrine primary production which are reflected in the sediments as carbon isotope variations clear evidence of ecosystem reorganizations is detected by the carbon isotope record around 14 200 10 400 9600 5500 2700 1700 and 900 varve years bp in particular the holocene events of 9600 around 5500 and 2700 are interpreted as the expression of massive changes of the climate system the steady rise of 13 c org values during the mid holocene is interpreted as a continuous climatic amelioration reaching an optimum around 6500 varve years bp rapid and large changes of 13 c org values from 2700 varve years bp to the present indicate major disturbances in the catchment area these are most probably related to deforestation or reforestation and runoff changes presumably in conjunction with human impact carbon isotopes thus characterize the holzmaar ecosystem in time revealing lacustrine palaeoproductivity as well as providing palaeoenvironmental and palaeoclimatic information

numerical simulation of the stratus to cumulus transition in the subtropical marine boundary layer part i boundary layer structure abstract a stratus to cumulus transition sct that resembles observations occurred in lagrangian numerical simulations of the subtropical marine boundary layer over the northeastern pacific ocean southwest of california the lagrangian approach involves translating the domain along the climatological boundary layer trajectory at a rate equal to the observed surface wind speed the sst is increased at a corresponding rate the simulations did not include drizzle the diurnal cycle divergence changes or mesoscale circulations and thus demonstrate that these processes are not essential for an sct a 2d numerical cloud model that can explicitly represent large convective eddies is used turbulence at scales smaller than the large eddies is parameterized using a third moment turbulence closure this type of model requires no cloud regime specific input and is computationally economical for multiday simulations the results suggest that there are four stages in the transition from the stratus topped boundary

application of a textural geospeedometer to the late stage magmatic history of mil 03346 dynamic crystallization experiments performed on fe rich al poor basalt are employed as a textural calibration set to quantify the late stage igneous history of nakhlite miller range mil 03346 the ratio of crystal melt surface area to volume typifying morphologically distinct populations of ca pyroxene has been shown to vary as a strong function of cooling rate hammer 2006 furthermore a texture of phenocrysts surrounded by finer grained groundmass crystals arises by sequential nucleation events during constant rate cooling but multiple populations nucleate only if the cooling rate is 72 c h 1 textural analysis of meteorite mil 03346 reveals at least two distinct populations the ca pyroxene phenocryst and microphenocryst three dimensional 3d aspect ratios are 112 8 3 and 1530 160 mm 1 respectively by comparison with the calibration set the range of cooling rates consistent with 3d aspect ratios of both populations in mil 03346 is 20 c h 1 an additional experiment was performed approximating a conductive heat transfer profile in order to interpret and apply results of constant rate cooling experiments to the natural cooling of magma results suggest that the textures of constant rate experiments parallel the initial period of rapid cooling in natural magma initial cooling rates of 20 c h 1 in the lava hosting mil 03346 occur in conductively solidifying lava at depths of 0 4 m constraining the minimum total thickness to 0 8 m crystal accumulation beginning in a subsurface reservoir and continuing after lava emplacement as an inflated pahoehoe sheet satisfies all textural constraints on the late stage igneous history of mil 03346

timescales of convection in magma chambers below the mid atlantic ridge from melt inclusions investigations closed hopper and complex swallowtail morphologies of olivine microcrysts have been described in the past in both mid oceanic ridge basalts and subaerial tholeitic volcanoes and indicate fluctuations in magma undercooling we describe similar morphologies in a mid atlantic ridge pillow basalt sample rd87dr10 and in addition we estimate the duration of temperature fluctuations required to produce these textures as follows 1 pairs of melt inclusions are arranged symmetrically around the centre of hopper crystals and each pair represents a heating cooling cycle using the literature olivine growth rates relevant to the observed morphologies and measuring the distance between two successive inclusions we estimate the minimum time elapsed during one convection cycle 2 the major element composition of melt inclusions analysed by electron microprobe was found to be in the range of the boundary layer measured in the glass surrounding the olivines irrespective of their size several major elements demonstrate that this boundary layer results from rapid quenching on the seafloor and not from crystal growth at depth implying the inclusions had the same composition as the surrounding magma when they were sealed using diffusivity of slow diffusing elements such as al2o3 we estimate the minimum time required for inclusion formation these two independent approaches give concordant results each cooling heating cycle lasted between a few minutes and 1 h minimum thus these crystals probably recorded thermal convection in small magmatic bodies a dyke or shallow magma chamber during the last hour or hours before eruption

diatom and geochemical evidence of mid to late holocene climatic changes at lake holzmaar west eifel germany abstract changes in diatom assemblages geochemistry and stable carbon isotope composition of bulk organic matter in a varved sediment section from lake holzmaar west eifel germany were used to infer mid to late holocene climatic changes and human impact from 6340 to 1470 cal yr bp shifts in total lacustrine primary production were derived from 13 c org values changes in non siliceous algae biomass productivity were deduced from accumulation rates of organic matter diatom valve accumulation rates and biogenic opal accumulation rates were used as proxies for diatom productivity and for siliceous phytoplankton abundance respectively based on weighted averaging of relative diatom abundance in subsamples qualitative changes in past trophic status were inferred accumulation rates of minerogenic material and the toc tn molar ratio permitted the deduction of past changes in allochthonous matter influx diatom assemblage composition showed statistically significant changes around 5130 3660 and 2900 cal yr bp whereas planktonic diatom productivity was subject to distinct shifts around 5900 5130 4500 3600 2660 and approximately 1630 cal yr bp and siliceous phytoplankton biomass changed ca 6100 4500 2660 1900 and 1700 cal yr bp causally determined changes in diatom assemblage composition and productivity for example due to shifts in nutrient ratios and or concentrations invoked by changes in lake circulation patterns precipitation rates and or erosion rates are discussed glacier fluctuations and lake level changes reported from other study sites in western europe support the finding that reconstructed lacustrine processes are at least indirectly linked to climate palynological and archaeological evidence however has shown a strong superimposition of lacustrine processes with local regional anthropogenic activity since the iron age

wrf hindcasts of cold front passages over the arm eastern north atlantic site a sensitivity study abstractthe present study explores the ability of the weather research and forecasting wrf model to accurately reproduce the passage of extratropical cold fronts at the doe arm eastern north atlantic ena observation site on the azores an analysis of three case studies is performed in which the impact of the wrf domain size position of the model boundary relative to the ena site grid spacing and spectral nudging conditions are explored the results from these case studies indicate that model biases in the timing and duration of cold front passages change with the distance between the model domain boundary and the ena site for these three cases if the western model boundary is farther than 1500 km from the site the front becomes too meridional and fails to reach the site making 1000 or 1500 km the optimal distances in contrast integrations with small distances e g 500 km between the site and domain boundaries have inadequate spatial spinup i e the domain is too small for the model to pr

environmental response to climatic and volcanic events in central europe during the weichselian lateglacial this paper reviews major results of the recent german research priority program changes of the geo biosphere during the last 15 000 years a contribution to pages focussing on changes of the geo biosphere during the weichselian lateglacial different continental archives such as annually laminated lacustrine sediments floodplain sediments and speleothems were used to reconstruct environmental response to climatic changes and the laacher see eruption event at ca 12 900 cal bp special emphasis is paid to establish a reliable time control using varve counting high precision radiocarbon dating of tree ring series and ams radiocarbon dating of terrestrial plant macrofossils recovered from lacustrine sediments to correlate and synchronize large scale environmental changes and events in central europe

formation of spinifex texture in komatiites an experimental study the formation of platy olivine spinifex the texture that characterizes komatiite lavas has long been enigmatic a major problem is that the dendritic morphology of the olivine resembles that of crystals grown in laboratory experiments at high cooling rates 50 c h but at the position where these textures form up to several meters below the komatiite flow top the cooling rate cannot have been greater than 1 5 c h we performed experiments that demonstrate that the platy habit of spinifex olivine or pyroxene is a consequence of slow cooling of ultramafic magma in a thermal gradient 7 35 c cm the charges were cooled at rates between 2 and 1428 c h and even at the low cooling rates the thermal gradient led to constrained growth and the development of preferentially oriented dendritic crystals with orphologies like those in natural platy spinifex textured lavas under these conditions olivine starts to crystallize at temperatures well below the equilibrium liquidus temperature 37 c dt 56 c depending on the composition of the starting material when the cooling rate is high the thermal gradient has a negligible effect on the texture and the crystals have a random orientation like that in the upper parts of komatiite flows

dendritic crystallization a single process for all the textures of olivine in basalts the olivine macrocrysts found in oceanites picrites and magnesian basalts erupted at hotspot volcanoes are generally interpreted either as phenocrysts crystallized from the magma or as xenocrysts extracted from a deforming cumulate to constrain the origin of these crystals we studied their texture and composition at piton de la fournaise volcano la reunion we show that macrocrysts are organized and subdivided into parallel units this suggests a crystallization by dendritic growth and ripening rather than by a complex combination of paired nucleation crystal aggregation or synneusis dendritic growth is also evidenced by the occurrence of hollow faces p rich zones melt and cr spinel inclusions formed from the accumulation of slow diffusing impurities p cr al in the liquid at the contact with rapid growing olivine we suggest that early dendritic crystallization may even cause branch misorientations and lattice mismatches yielding subgrain boundaries dislocation lamellae and to a certain extent undulose extinction which have all been formerly interpreted in terms of plastic intracrystalline deformation we interpret olivine macrocrysts as phenocrysts crystallized under a strong degree of undercooling t 60 c and derived from a harrisitic mush formed on the cold walls of the magma reservoir given the growth shapes indicated by p zoning patterns and external faces the olivine macrocrysts which consist of groups of several subcrystals have grown in suspension within the liquid and were neither aggregated into a dense cumulate nor corroded shocked or deformed before or during their transport to the surface the major consequence of our study is that most olivine macrocrysts are not xenocrysts and very few of them if any have experienced intracrystalline deformation the importance of deforming creeping cumulate bodies thought to accommodate the spreading of basaltic volcanoes in la reunion and hawaii may hence have been overestimated

evidence for dendritic crystallization of forsterite olivine during contact metamorphism of siliceous dolostones alta stock aureole utah forsterite crystals produced during metamorphism of siliceous dolomites in the alta utah contact aureole were investigated in situ and with crystal separates to constrain their aureole scale textural and morphological variability as the contact is approached forsterite crystals increase in abundance but decrease in average size suggesting greater kinetic influence on forsterite nucleation and growth in the inner aureole crystal morphologies vary widely from dendritic to skeletal to euhedral shapes across both periclase and forsterite zones highly skeletal forms of forsterite preserve crystallographically controlled internal scaffolding reentrants and internal void boundaries scanning electron microscope imaging of texturally more mature forsterite crystals reveals the common occurrence of surface features such as hopper structures ridges and terraces features that have been linked to dendritic crystallization of olivine in igneous rocks near end member forsterite crystals fo99 from the middle to outer forsterite zone exhibit complex cathodoluminescence cl patterns which can be linked to grain scale heterogeneities in the trace elements li b p and ti these grain scale cl zoning patterns can be correlated to crystallographic forms typical of forsterite the textural trends morphological characteristics surface features and cl patterns suggest that euhedral forsterite crystals grew by a process of early dendritic crystallization hopper development and infilling of hopper reentrants these results caution against interpreting all grain scale zoning profiles preserved in metamorphic forsterites as simple core to rim time sequences consideration of the possible role of dendritic crystallization in the development of forsterite morphologies is required to interpret 2 d element or isotope zoning profiles preserved in individual forsterite grains

late quaternary environmental and climatic changes in central europe as inferred from the composition of organic matter in annually laminated maar lake sediments 1 geochemical elemental analysis bulk 13ctoc thermal degradation techniques molecular analysis of n alkanes and microscopic investigations maceral analysis vitrinite reflectance were performed 1 to characterize the organic matter om in sediments from two maar lakes in the westeifel volcanic field germany and 2 to discuss paleoenvironmental processes which have controlled the accumulation and preservation of om the annually laminated sediments show a wide range of organic carbon contents between 0 3 and 21 4 toc and hydrogen index values between 80 and 501 mg hc g toc well developed laminations mirror suboxic to anoxic bottom waters diagnostic compounds in the pyrolysates and microscopic analysis permit discrimination between the principal om sources and their variations over time provide important evidence for the reconstruction of the environmental histories of the lakes and their watershed the significance of terrigenous om is reflected by the occurrence of methoxyphenols in the insoluble as well as mid and long chain n alkanes in the soluble om which are indicative of land plant or macrophyte input to the lakes the relative abundance of certain homologues together with the amount of terrigenous macerals can be used to show differences in higher plant input and vegetation changes through time during the pleniglacial and younger dryas period high reflecting reworked om was introduced by soil erosion in an environment with relatively open vegetation the alkylphenols in the pyrolysates originate partly from the microbial reworking of proteinaceous tyrosine moieties and or reflect a direct contribution from cyanobacteria we assume that variations in the carbon isotopic composition of om are mainly due to changes in the lake s primary productivity with the exception of the pleniglacial various forms of land use are reflected by increasing amounts of terrigenous particles as well as chemical plant markers from 500 varve years b p until present the organic geochemical and microscopic data correlate well with other proxy information about climate dependent fluctuations in the ecosystem of the studied sites

melt to mush variations in crustal magma properties along the ridge crest at the southern east pacific rise the determination of along axis variations in melt properties within the crustal axial magma chamber beneath fast spreading axes is important for understanding melt delivery from the mantle eruption history along the ridge crest and the process of crustal accretion seismic reflection images1 2 3 4 have shown the molten sill to be continuous along the ridge crest for many tens of kilometres with varying widths 250 4 500 m but variations in its seismic properties and thickness have remained elusive despite several attempts to constrain these properties5 6 7 here we report that the melt sill along the southern east pacific rise which is about 50 m thick undergoes abrupt changes in its internal properties ranging from pure melt to mush the 60 km long ridge crest segment near 14 00 s is characterized by three 2 4 km sections containing pure melt embedded within a magma chamber rich in mush these small pure melt pockets may represent a fresh supply of magma from the mantle capable of erupting and forming the upper crust conversely the 80 90 of the magma chamber which is mushy is unlikely to erupt and may influence the lower crustal accretion

cloud top entrainment instability mixing processes at cloud boundaries are thought to play a critical role in determining cloud lifetime spatial extent and cloud microphysical structure high fidelity direct numerical simulations by mellado j fluid mech 2010 this issue vol 660 pp 5 36 show for the first time the character and potency of a curious instability that may arise as a result of molecular mixing processes at cloud boundaries an instability which until now has been thought by many to control the distribution of climatologically important cloud regimes

holocene wildfires related to climate and land use change over the weihe river basin china abstract charcoal particles preserved in the loess palaeosol profiles provide records of wildfires during the holocene total organic carbon magnetic susceptibility and charcoal analysis and osl dating were carried out in the holocene loess palaeosol profiles at two sites in the weihe river basin the analytical results show that natural wildfires occurred frequently during the last glaciation when climate was dominated by northwest continental monsoon and steppe vegetation expanded southerly to the weihe river basin wildfire occurrence decreased during climatic amelioration in the early holocene during the holocene climatic optimum between 8500 b p and 3100 b p natural wildfire occurrence was reduced greatly pedogenic alteration to the accumulated dust was intensified because of the humid warm climate brought on by southeast maritime monsoon localized fire events in connection with human activities of the neolithic occurred in several episodes over the region during the late holocene when climate become drier wildfire occurrence over the upland hills shows a pattern different from that in the guanzhong basin over the upland hills in the north charcoal concentrations show a decreasing trend in the recent loess and topsoil it indicates infrequent biomass burning during the last 3100 years this is attributable to nomadic occupation of the loess hills during the bronze age and the development of a land use pattern of livestock farming in most part of the history over the loess tableland in the guanzhong basin in the south abruptly increased charcoal concentrations in the recent loess and topsoil show very high level of biomass burning this is attributable to the increasingly intensified land reclamation for cereal cultivation from the bronze age this study provides new insights into wildfires over the semi arid and sub humid regions in connection with climate and land use change

gabbros from iodp site 1256 equatorial pacific insight into axial magma chamber processes at fast spreading ocean ridges the odp iodp multileg campaign at odp site 1256 cocos plate eastern equatorial pacific provides the first continuous in situ sampling of fast spreading ocean crust from the extrusive lavas through the sheeted dikes and down into the uppermost gabbros this paper focuses on a detailed petrographic and microanalytical investigation of the gabbro section drilled during iodp expedition 312 the marked patchy and spotty features that can be observed in many hole 1256d gabbros is mostly due to a close association of two different lithological domains in variable amounts 1 subophitic domains and 2 a granular matrix major and trace element mineral compositions geothermometry and petrological modeling suggest that subophitic and granular domains follow one single magma evolution trend formed by in situ fractionation the subophitic domains correspond to the relative primitive high temperature end member compositionally similar to the basalts and dikes from the extrusive unit upsection while the granular domains fit with a magma evolution by crystal fractionation to lower temperatures up to a degree of crystallization of 80 our results support the following scenario for the fossilization of the axial melt lens at odp site 1256 relatively primitive morb melts under near liquidus conditions fill the melt lens and feed the upper extrusive crust near the melt lens sheeted dike boundary at lower temperatures crystallization starts with first plagioclase before clinopyroxene in a mushy zone forming the subophitic domains at decreasing temperatures the subophitic domains continue to crystallize finally forming a well connected framework evolved residual melt is finally trapped within the subophitic network crystallizing at near solidus conditions to the granular matrix another important textural feature in hole 1256d gabbros is the presence of microgranular domains which are interpreted as relics of stoped assimilated sheeted dikes transformed to granoblastic dikes by contact metamorphism all these different domains can be observed in close association often at the thin section scale demonstrating the extremely complex petrological record of combined crystallization assimilation processes ongoing in the axial melt lens very similar gabbros with a marked spotty patchy appearance and bearing the same close association of lithological domains as observed at site 1256 are known in the so called varitextured gabbro unit from the oman ophiolite located at the same structural level between cumulate gabbros and granoblastic dikes the close petrological similarity of the gabbro dike transition between both iodp hole 1256d and the oman ophiolite suggests that in situ fractionation and dike assimilation contamination are major magmatic processes controlling the dynamics and fossilization of the axial melt lens at fast spreading oceanic ridges

mid mountain clouds at whistler during the vancouver 2010 winter olympics and paralympics a comprehensive study of mid mountain clouds and their impacts on the vancouver 2010 winter olympics and paralympics is presented mid mountain clouds were frequently present on the whistler alpine venue as identified in an extensive archive of webcam images over a 45 day period from february 5 to march 21 2010 these clouds posed serious forecast challenges and had significant impacts on some olympic and paralympic alpine skiing competitions under fair weather conditions a diurnal upslope anabatic flow can work in concert with a diurnal temperature inversion aloft to produce a localized phenomenon known as harvey s cloud at whistler two detailed case studies in this paper suggest that mid mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope flow descending from the mountaintop a southerly inflow through the sea to sky corridor can be channeled by the local topography into a westerly upslope flow toward whistler mountain resulting in orographic clouds on the alpine venue under favorable circumstances these clouds are trapped to the mid mountain zone by the leeward subsidence of an elevated southerly flow the presence of the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid mountain clouds in both cases it is the subsidence induced adiabatic warming that imposes a strong buoyant suppression to trap the mid mountain cloud on the other hand the subsidence induced dry layer has the potential to trigger evaporative instability to periodically breakup the mid mountain cloud

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

an annually resolved record of western european vegetation response to younger dryas cooling abstract the regional patterns and timing of the younger dryas cooling in the north atlantic realm were complex and are mechanistically incompletely understood to enhance understanding of regional climate patterns we present molecular biomarker records at subannual to annual resolution by mass spectrometry imaging msi of sediments from the lake meerfelder maar covering the allerod younger dryas transition these analyses are supported by conventional extraction based molecular isotopic analyses which both validate the imaging results and constrain the sources of the target compounds the targeted fatty acid biomarkers serve as a gauge of the response of the local aquatic and terrestrial ecosystem to climate change based on the comparison of our data with existing data from meerfelder maar we analyse the short term environmental evolution in western europe during the studied time interval and confirm the previously reported delayed hydrological response to greenland cooling however despite a detected delay of western european environmental change of 135 years our biomarker data show statistically significant correlation with deuterium excess in greenland ice core at annual resolution during this time transgressive cooling this suggests a coherent atmospheric forcing across the north atlantic realm during this transition we propose that western european cooling was postponed due to major reorganization of the westerlies that were intermittently forcing warmer and wetter air masses from lower latitudes to western europe and thus resulted in delayed cooling relative to greenland

in situ observation of crystal growth in a basalt melt and the development of crystal size distribution in igneous rocks to understand the solidification processes of natural magma and the texture evolution of igneous rocks we have carried out in situ observation of the crystallization of a high k basaltic melt cooling from 1 240 c in a moissanite cell in a series of experiments with different thermal history olivine or clinopyroxene cpx appeared as the liquidus phase before the formation of plagioclase during cooling at 100 c h the morphology of olivine and cpx transited from tabular to hopper habit to first order approximation crystal grow rate 2 10 9 to 7 10 9 m s for olivine and 6 10 9 to 17 10 9 m s for cpx probably limited by chemical diffusion is proportional to crystal size in one experiment dominated by olivine crystallization the good image quality allows the analysis of texture evolution over an extended period nucleation of olivine occurred only in a narrow temperature and time interval below the liquidus two dimensional length and area based crystal size distributions csds show counterclockwise rotation around axes of 8 m and 100 m2 which is consistent with the proportionate crystal growth both csds and direct observation show the dissolution of small crystals and ostwald ripening these data suggest that conventional analyses of crystal size distributions of igneous rocks may be in error the slope of the csd cannot be interpreted in terms of a uniform growth rate and the intercept with the vertical axis does not correspond to a nucleation density

origins of the reversed flow over the windward alpine foothills during map iop3 and iop8 the synoptic scale situations during the two intensive observing periods iops of the mesoscale alpine programme map characterized by persisting precipitation and down valley flow as observed by the doppler on the wheel radar dow over the two alpine valleys toce and ticino were investigated the first period iop3 24 27 september 1999 was characterized by a south westerly flow and convective precipitation whereas the second period iop8 20 21 october 1999 by a down valley flow and stratiform precipitation during iop3 the down valley northerly flow over the north western part of the po valley was confined within a thin layer of 200 300 m depth during iop8 the northerly flow extended from the alps foothills to the ligurian sea in a deep layer of 1 2 km height the meso nh numerical model with a 2 5 km horizontal mesh grid reproduced the characteristics of both cases from the valley scale to the meso scale sensitivity experiments were furthermore performed in order to highlight the relationships between wet or dry drainage flow channelled by the alpine orography mesoscale upstream flow blocked by the alps and a regional cold pool at the foothills inside the po valley during iop8 the diabatic processes were dominant at local scales in confirmation of steiner results based on the dow observations and they were significant at regional scales upstream of the alps by maintaining a cold pool over the po valley the iop3 low level flow reversal occurred as the flow began to cross over the alps instead of turning around a downslope flow is associated with the blocked regime period upstream of the alps copyright 2006 royal meteorological society

15 000 years of black carbon deposition a post glacial fire record from maar lake sediments germany abstract fires accompanied human development throughout the holocene leaving behind black carbon bc as residues from incomplete biomass burning here we used molecular fire markers benzene polycarboxylic acids bpcas to reconstruct fire history in two eifel maar lakes germany we hypothesized to find indications for i changes in bc related to ecosystem changes ii an increase in bc influx at the onset of agriculture until modern times and iii a change in bc quality due to technical progress in combustion e g at the beginning of agriculture and at the onset of the bronze age to calculate absolute bc influx into the maar lakes we multiplied bc contents with sedimentation rates the bc influx rates were elevated during tundra like vegetation in the late pleistocene up to 7 7 g bc m 2 a 1 followed by relatively constant 2 5 g bc m 2 a 1 from the bolling interstadial 13 7 kilo years before present ka bp until the early atlantic when forest began to develop thereafter bc influx increased with the onset of land use of neolithic cultures in the region from 7 5 ka bp to rates of 7 9 g bc m 2 a 1 noteworthy also the quality of bc changed higher ratios of five to six times carboxylated benzenes b5ca b6ca pointed at colder arable fires approximately 1000 years after first neolithic activity from 6 to 4 ka bp b5ca b6ca increased from 1 0 to 2 0 from 4 ka bp bronze age to modern times increasing burning temperatures as indicated by dropping b5ca b6ca ratios from 2 0 to 1 0 were related to metallurgy and industrialization between 2 5 and 1 ka bp maximum bc influx rates were reached with ca 15 g bc m 2 a 1 with increasing combustion efficiency and a reduction of wild fires during the last centuries total bc influx decreased suggesting that fossil fuel combustion contributed less to total bc input into the lake sediments than former vegetation fires

lateglacial calendar year chronology based on annually laminated sediments from lake meerfelder maar germany abstract annually laminated sediments from lake meerfelder maar mfm in the eifel germany provide an independent calendar year timescale for the last glacial interglacial transition changes in varve thickness and varve facies reflect significant environment variations during this period the general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes an exception is the significant increase in diatom blooms at the beginning of the younger dryas six lateglacial biozones have been defined by litt and stebich quaternary international 1999 the sediment record comprises two tephra layers as chronomarkers the laacher see tephra 12 880 varve years bp is a continent wide correlation horizon while the ulmener maar tephra provides regional chronological links the beginning of the lateglacial warming is dated at 14 450 varve years vyrs bp which is regarded as the minimum age three abrupt cold spells interrupted the lateglacial interstadial at 13 800 vyrs bp oldest dryas 13 540 vyrs bp older dryas and 12 680 vyrs bp younger dryas the oldest dryas 130 years and the older dryas 190 years were rather short while the younger dryas lasted much longer 1090 years the mfm chronology was compared with ice core timescales from gisp2 and grip there is a good agreement between these timescales with the grip model age ss09 providing the best match to the mfm chronology

cloudiness and marine boundary layer dynamics in the astex lagrangian experiments part i synoptic setting and vertical structure abstract a goal of the atlantic stratocumulus transition experiment astex southeast of the azores islands in the east central atlantic ocean during june 1992 was to examine the coupled evolution of cloud dynamical and thermodynamical vertical structure in a marine boundary layer mbl air mass as it advected from cold to warm water in the trade winds in two lagrangian observation periods during astex an unprecedentedly complete view of mbl and cloud evolution was achieved by nearly continuous aircraft coverage of such an air mass for 36 48 hours using three boundary layer aircraft supplemented by satellite ship and balloon observations during the first lagrangian period an accelerated stratocumulus to trade cumulus transition occurred in a clean marine air mass in the second lagrangian period a 200 hpa deep decoupled modified continental mbl persisted with almost no change in structure cumulus rising into intermittent stratocumulus were observed throughout the period the two contrasting a

pre eruption history of phyric basalts from dsdp legs 45 and 46 evidence from morphology and zoning patterns in plagioclase phyric basalts recovered from dsdp legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains megacrysts or aggregates glomerocrysts and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition almost all the plagioclase crystals are complexly zoned in most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts core mantle and rim the cores exhibit two major types of morphology tabular with a euhedral to slightly rounded outline or a skeletal inner core wrapped by a slightly rounded homogeneous outer core the mantle region is characterized by a zoning pattern composed of one to several spikes plateaus superimposed on a gently zoned base line with one large plateau always at the outside of the mantle and by in most cases a rounded internal morphology the inner rim is typically oscillatory zoned the width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow the presence of a skeletal inner core and the concentration of glass inclusions in low an zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount the resorption features at the outer margins of low an zones indicate superheating of the liquid with respect to the crystal

thermal interaction between lava lobes pahoehoe lava may be emplaced as lobes which flow on top of each other a cross section was investigated through two lava lobes from the active pu u o o vent kilauea hawaii consisting of a 6 6 cm thick top lobe and the upper part of a 3 2 cm thick underlying bottom lobe the top lobe cooled at the contact with air and has a quenched glassy margin which is almost 1 cm thick the underlying lobe although originally also in contact with air is entirely crystalline suggesting that the bottom lobe experienced crystallization during reheating by the top lobe based on published data experimental results on reheating show that crystallization of basalt glass requires temperatures above 920 c and knowing that the pu u o o melt is initially at about 1 160 c the minimum temperature of the bottom lobe should have been 700 c prior to emplacement of the top lobe crystal size distribution csd theory demonstrates an oscillation of grain size which is superposed on an overall increase in size with depth cooling rates estimated from simple modeling and growth rates derived from csd suggest a thermal interaction of the bottom lobe on the top lobe to about 2 cm from the contact

mid and late holocene vegetation dynamics and fire history in the boreal forest of european russia a case study from meshchera lowlands abstract climate fire and human activities strongly affected the development of vegetation communities during the holocene yet the relative importance of these individual factors remains unclear in many areas this paper presents new multi proxy records of environmental change for the meshchera lowlands the central part of the east european plain during the holocene changes in regional vegetation during the mid and late holocene were influenced by climate fire regime and human impact as indicated by pollen plant macrofossil charcoal and testate amoebae analysis from several peat cores along with reconstruction of tree cover from pollen assemblages since 8500 cal yr bp the vegetation history represented a series of consecutive phases of birch birch pine and pine broadleaf forests with introduction of spruce after 2500 cal yr bp maximal abundance of broadleaf tree species was detected from 4700 to 2000 cal yr bp vegetation dynamics were strongly influenced by human activity since 1400 cal yr bp high fire frequency was recorded for the periods 8500 4500 cal yr bp and 3500 2000 cal yr bp when the fire return interval varied from 40 to 80 years since 2000 cal yr bp the fire return period exceeded 500 years suggesting a significant decline in fire frequency during the last two millennia

evidence for accumulated melt beneath the slow spreading mid atlantic ridge the analysis of data from a multicomponent geophysical experiment conducted on a segment of the slowspreading 20 mm yr 1 midatlantic ridge shows compelling evidence for a significant crustal magm

systematics of modal phenocryst assemblages in submarine basalts petrologic implications phenocryst assemblages in ocean ridge basalts generally show an increasing proportion of plagioclase as the total amount of phenocrysts increases the variations in phase assemblages as well as most crystal liquid kd s are similar to variations equimodal trends predicted by low pressure laboratory experiments suggesting that many of these basalts have experienced varying degrees of low pressure cyrstallization prior to quenching with little sorting of crystals and liquid important exceptions include moderately to highly phyric basalts enriched either in plagioclase or olivine which lie well off the experimental trends in these basalts megacrysts and xenocrysts usually cited as evidence for magma mixing commonly represent a small proportion of the total crystalline phase assemblage however phase proportions for many of these basalts lie well outside the range that could be produced by simple mixing selective gravitative sorting either prior or subsequent to mixing appears to be the likely explanation for these phyric basalts a relation between spreading rate and phase proportions is neither supported nor refuted by the data which as yet do not adequately represent fast spreading ridges

dusty and honeycomb plagioclase indicators of processes in the uchino stratified magma chamber izu peninsula japan abstract two types of melt inclusion bearing plagioclase coexist in the uchino basalt izu peninsula japan 1 dusty plagioclase with an ab rich core mantled by a dusty zone consisting of more an rich plagioclase and fine melt inclusions and 2 honeycomb plagioclase with a central core containing larger melt inclusions the dusty plagioclase probably forms through partial dissolution of ab rich plagioclase as dusty zones truncate the concentric zonal structure of the ab rich inner core the honeycomb plagioclase is formed by skeletal growth under supercooling conditions this is indicated by the euhedral geometry of the boundary between the inner inclusion free and the outer inclusion bearing zones of the honeycomb plagioclase which has a concentric inner core bimodal distribution of the chemical compositions of phenocryst cores and assemblages in crystal clots suggest that hybridization of basaltic and andesitic magmas took place before crystallization of phenocryst rims the core rim boundaries of phenocrysts derived from the andesitic magma and the basaltic magma have a rounded and a euhedral geometry respectively this suggests the andesitic magma was heated and the basaltic magma was cooled prior to hybridization these features are consistent with the development of a thermal diffusive interface between overlying andesitic magma and underlying basaltic magma in a stratified magma chamber

cloud water in windward and leeward mountain forests the stable isotope signature of orographic cloud water 1 cloud water can be a significant hydrologic input to mountain forests because it is a precipitation source that is vulnerable to climate change it is important to quantify amounts of cloud water input at watershed and regional scales during this study cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward east maui the difference in isotopic composition between volume weighted average cloud water and rain samples was 1 4 18o and 12 2h for the windward site and 2 8 18o and 25 2h for the leeward site with the cloud water samples enriched in 18o and 2h relative to the rain samples a summary of previous literature shows that fog and or cloud water is enriched in 18o and 2h compared to rain at many locations around the world this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes an end member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds orographic cloud water input was 37 of the total precipitation at the windward site and 46 at the leeward site this represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation

simulating the transition from drizzling marine stratocumulus to boundary layer cumulus with a mesoscale model a case of coastal california summer season boundary layer cloud has been simulated with the u s navy coupled ocean atmosphere mesoscale prediction system and the results analyzed in the context of consistency with conclusions derived from large eddy simulation based les studies results show a pronounced diurnal cycle and fair agreement with satellite derived observations of liquid water path when drizzle processes are included a significant degree of mesoscale organization emerges in the form of cloud bands accompanied by a transition from a well mixed boundary layer topped by unbroken stratocumulus cloud into a more potentially unstable convective boundary layer regime the transition and the subsequent development of mesoscale variability is analogous to the drizzle induced cloud breakup produced in large eddy simulation studies the dynamics of the pure stratocumulus cloud are dictated by the model s subgrid parameterization while the more convective regime exhibits appreciable vertical velocities characteristic of an ensemble of cumulus updrafts the existence of convective updrafts is tied to a weak drizzle induced decoupling of the cloud and subcloud layer after which air of higher equivalent potential temperature ue can pool at the surface some similarities to the propagation of deep convection are also noted

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

the relationship between boundary layer stability and cloud cover in the post cold frontal region using nasa aqua modis and airs data the relationship between low level cloud cover cloud top below the 700 hpa level and boundary layer stability is explored in post cold frontal conditions a linear relationship is found between seasonal cloud cover and two separate measures of inversion strength the lower tropospheric stability lts and the estimated inversion strength eis for two specific regions in the north atlantic and pacific in quiescent and weakly subsiding conditions the relationship barely changes when considering dynamically active and subsiding post cold frontal conditions for the same regions to explore the generality of this result and increase sample size cold front centered composites of cloud cover and stability are constructed the northern and southern hemisphere seasonal cloud cover and stability distributions in the post cold frontal regions are then compared a fairly good correlation between cloud cover and eis is found in both hemispheres across all seasons suggesting that a linear relationship between cloud cover and inversion strength proposed for quiescent conditions exists also in more dynamically active subsiding post cold frontal conditions however for a given season and hemisphere the correlation between cloud cover and eis degrades in post cold frontal regions especially in the northern hemisphere at these scales other large scale factors tend to correlate better with cloud cover

the influences of inversion height on precipitation and airflow over the island of hawaii abstract both the daily rainfall on the windward side of the island of hawaii and the early morning 0200 hst hawaiian standard time trade wind inversion height at hilo varied substantially during the hawaiian rainband project harp in general the inversion was higher during the passage of a cold front to the north or during the approach of tropical disturbances from the east to the south the daily rainfall on the windward side is highly correlated with the 0200 hst inversion height at hilo with a maximum correlation greater than 0 7 in the hilo area the daily daytime 1100 1900 hst rainfall on the windward slopes nocturnal 1900 0300 rst showers an the windward lowland and coastal precipitation in the predawn and early morning hours 0300 1100 hst are also highly correlated with the inversion height with a maximum correlation greater than 0 7 0 7 and 0 5 respectively for the low high inversion days the median daily rainfall on the windward side is about one half more than twice of t

incorporation of seawater into mid ocean ridge lava flows during emplacement evidence for the interaction between seawater and lava during emplacement on the deep seafloor can be observed in solidified flows at a variety of scales including rapid quenching of their outer crusts and the formation of lava pillars through the body of the flow recently an additional interaction incorporation of heated seawater vapor into the body of a flow has been proposed large voids and vesicles beneath the surface crusts of mid ocean ridge crest lobate and sheet lava flows and lava drips found within those cavities have been cited as evidence for this interaction the voids resulting from this interaction contribute to the high porosity of the shallow ocean crust and play an important role in crustal permeability and hydrothermal circulation at mid ocean ridges and thus it is important to understand their origin we analyze lava samples from the fast spreading east pacific rise and intermediate spreading galapagos spreading center to characterize this process identify the source of the vapor and investigate the implications this would have on submarine lava flow dynamics we find that lava samples that have interacted with a vapor have a zone of increased vesicularity on the underside of the lava crust and a coating of precipitate minerals i e crystal fringe that are distinct in form and composition from those crystallized from the melt we use thermochemical modeling to simulate the reaction between the lava and a vapor and find that only with seawater can we reproduce the phase assemblage we observe within the crystal fringes present in the samples model results suggest that large scale contamination of the lava by mass exchange with the vapor is unlikely but we observe local enrichment of the lava in cl resulting from the incorporation of a brine phase separated from the seawater we suggest that high eruption rates are necessary for seawater incorporation to occur but the mechanism by which seawater enters the flow has yet to be resolved a persistent vapor phase may be important in inhibiting the collapse of lava flow roofs during natural waxing and waning of lava levels during emplacement allowing lava pathways to be maintained during long lived eruptions in addition we illustrate the potential for a persistent vapor layer to increase local flow rates within submarine flows by up to a factor of three thereby influencing how lava is distributed across the ridge crest

buoyancy reversal decoupling and the transition from stratocumulus to shallow cumulus topped marine boundary layers the transition in a marine boundary layer mbl from stratocumulus topped to shallow cumulus topped is investigated by using a large eddy simulation les model the experiments performed aim to examine the influence on the transition of 1 the probability of buoyancy reversal at the mbl top i e situations in which the mixture of two air parcels becomes denser than either of the original parcels due to phase change or other nonlinear processes involved in the mixing and 2 the degree of decoupling in the mbl i e the strength of a shallow stably stratified layer near cloud base our results suggest that a stratocumulus topped mbl is most likely to transit to a cumulus topped one when 1 there exists high probability of buoyancy reversal at the mbl top and 2 the mbl is decoupled due to large surface evaporation we argue that a parameterization that includes representation of those two effects combined has the potential to provide a simple way of predicting the mbl transition in climate models

direct geological evidence for oceanic detachment faulting the mid atlantic ridge 15 45 n from a detailed survey and sampling study of corrugated massifs north of the fifteen twenty fracture zone on the mid atlantic ridge we demonstrate that their surfaces are low angle detachment fault planes as proposed but not previously verified spreading direction parallel striations on the massifs occur at wavelengths from kilometers to centimeters oriented drill core samples from the striated surfaces are dominated by fault rocks with low angle shear planes and highly deformed greenschist facies assemblages that include talc chlorite tremolite and serpentine deformation was very localized and occurred in the brittle regime no evidence is seen for ductile deformation of the footwall synkinematic emplacement of diabase dikes into the fault zone from an immediately subjacent gabbro pluton implies that the detachment must have been active as a low angle fault surface at very shallow levels directly beneath the ridge axis strain localization occurred in response to the weakening of a range of hydrous secondary minerals at a very early stage and was highly efficient

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part ii regional simulations of marine boundary layer clouds abstract the impact of physical parameterizations on simulations of cloud topped marine boundary layers is investigated using the fifth generation pennsylvania state university ncar mesoscale model mm5 three month mm5 simulations of the northeast and southeast pacific during june august 1987 are boundary forced with time varying ecmwf analyses runs with four planetary boundary layer pbl parameterizations already implemented in mm5 are compared with runs using new parameterizations of boundary layer turbulence and shallow cumulus convection shcu described in a companion paper numerous modifications to the mm5 that allow it to be used as a regional climate model are described the simulated 3 month mean shortwave cloud radiative forcing swcf and vertical structure of cloud topped boundary layers in the northeast pacific are sensitive to the pbl shallow convection schemes all four current mm5 pbl schemes the blackadar medium range forecast mrf burk thompson and gayno seaman schemes produc

annually dated late weichselian continental paleoclimate record from the eifel germany a record extending back to 23 220 calendar yr b p was obtained from varved sediments from lake holzmaar germany by applying multiple dating methods and interlake comparison with meerfelder maar variations in the weichselian inorganic carbon content resulting from intensified eolian activities coincide with proxy parameters of dust accumulation in greenland the timing for the end of the last glacial maximum at holzmaar agrees with the greenland ice sheet project gisp2 data but suggests dating discrepancies with the greenland ice core project data grip assuming that periods of maximum dust deposition in the eifel and greenland coincide with ice advances in northeastern germany the holzmaar record provides a means of dating three late weichselian terminal moraines

cracking the olivine zoning code distinguishing between crystal growth and diffusion olivine composition and zoning patterns are widely used to reconstruct the evolution of mafic magmas from source to surface and to extract time scales of magmatic processes deciphering the olivine zoning code is challenging because the contributions of growth and diffusion may overlap a detailed multielement fe mg p al and ni examination of zoning in an exceptional olivine with skeletal morphology allows unequivocal discrimination between these two processes using simple but powerful geometrical arguments olivine crystals initially grow rapidly and diagonally from corner locations whereas diffusion effectively tracks mutually perpendicular crystal lattice orientations generating the zoning patterns for our case study olivine required at least 4 5 months of diffusive reequilibration of fe mg further demonstrating that crystal morphologies produced by rapid growth can survive at magmatic temperatures for extended periods no significant major element zoning is preserved after rapid growth lending further credibility to time scales retrieved via diffusion modeling extending multielement approaches to decoding olivine zoning patterns can help determine whether the kinetic relationship between growth and diffusion induced zoning recognized herein is widely applicable such studies will improve our understanding of time scales of magma storage solidification mixing and or transit toward the surface

crystal morphologies in pillow basalts implications for mid ocean ridge processes abstract we present the results of a detailed petrological study of a sparsely phyric basalt mapco ch98 dr11 dredged along the mid atlantic ridge 30 41 n the sample contains microphenocrysts of olivine that display four different rapid growth morphologies comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample the dendritic morphology swallowtail chain and lattice olivine is directly related to the final quenching during magma seawater interaction in contrast the three other morphologies namely the complex polyhedral crystal the closed hopper and the complex swallowtail morphology result from several cycles of cooling heating corresponding to a maximum degree of undercooling of 20 25 c during crystal growth these thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge the results suggest that the mid atlantic ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation aphyric basalts are emitted during eruptions controlled by the tectonic activity whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas

a 2600 year record of past polycyclic aromatic hydrocarbons pahs deposition at holzmaar eifel germany polycyclic aromatic hydrocarbons pahs are a proxy for climate and human related historical fire activity which has rarely been used beyond 1800 ad we explored the concentration and composition patterns of pahs together with other proxies charcoal c n s 13c 15n and 34s in a sediment core of holzmaar as indicators of variations in climate and anthropogenic activity over the past 2600 years the concentrations of pyrogenic pahs remained low 500 ng g 1 from the pre roman iron age 600 bc until the first significant increases to ca 1000 1800 ng g 1 between 1700 and 1750 ad related to regional iron production the highest increases in pyrogenic pah concentrations occurred with industrialization peaking in the 1960s pah concentrations in most recent sediments decreased to pre industrial levels because of emission control measures and the switch from coal to oil and gas as major fuel sources fluxes of pahs mg km 2 yr 1 increased in the order migration period and early middle ages pre roman iron ages roman era high middle ages and renaissance pre industrial modern period industrial modern period the changes of pahs fluxes in pre industrial times parallel known changes in local regional and continental anthropogenic activity and climatic variations or their interactions across these historical periods perylene a mainly biologically produced compound was the dominant pah in pre industrial times the migration period and the early middle ages witnessed the most profound and simultaneous changes to the sedimentary organic matter properties in the past 2600 years including the lowest pah fluxes because of reduced human activity and more negative 13c and 15n values probably in response to colder and wetter conditions

magmatic processes at superfast spreading mid ocean ridges glass compositional variations along the east pacific rise 13 23 s major and minor element analyses of 496 natural volcanic glass samples from 141 locations along the superfast spreading 150 mm yr east pacific rise epr 13 23 s and near ridge seamounts comprise 212 chemical groups we interpret these groups to represent the average composition of individual lava flows or groups of closely related flows groups slightly enriched in k2o t morb are distributed variably along the axis in contrast to the galapagos spreading center where t morb are extremely rare this result is consistent with the interpretation that t morb magmas arise from low melting temperature k rich heterogeneities in the subaxial epr mantle the galapagos spreading center which is migrating to the west in an absolute reference frame is underlain by mantle previously processed and depleted in the t morb component during melting events giving rise to earlier epr magmas excluding t morb there are nearly monotonic twofold increases in k ti and k p of axial lavas from 23 s to 13 s from 22 s to 17 s these gradients correlate with isotopic ratios but north of 17 s there is a reversal of isotopic gradients indicating recent decoupling of the isotopic and minor element ratios in the subaxial mantle a strong southward increase in degree of differentiation for approximately 200 km north of the large offset at 20 7 s correlates with a gradient in bathymetry consistent with previous interpretations that this offset is propagating to the south samples from recently abandoned ridges associated with this dueling propagator mainly carry the distinctive evolved fractionation signatures of rift propagation suggesting that propagating rift tips have been abandoned preferentially to failing rift tips glass compositional variations south of this offset are consistent with rift failure on the southern limb within 40 km of the offset and possibly also south of 22 s the latter region may be affected by deformation accompanying northward growth of the easter microplate near ridge seamounts on the pacific plate between 18 19 s comprise two distinct populations those aligned approximately parallel to the spreading direction are extremely variable in major element composition but consistently enriched in sr relative to nearby axial lavas smaller seamounts aligned approximately parallel to the direction of absolute plate motion are uniformly depleted in minor elements and sr relative to axial lavas the degree of differentiation of axial lavas between 18 19 s can be related to the structural development of the rift axis and or vigor of hydrothermal activity of individual segments glass compositional variations indicate that magmatic segmentation occurs on several different scales at the superfast spreading rate of this area primary magmatic segmentation mainly reflects mantle source variations the boundaries of which correlate with the largest physical offsets in the rise axis between the easter microplate and garrett transform zone a secondary magmatic segmentation defined by the along axis continuity of similar parental magma compositions or liquid lines of descent occurs with a length scale varying from 11 to 185 km with an average of 69 57 1 km the boundaries of these segments mainly occur at overlapping spreading centers all first second and third order physical offsets correspond to secondary magmatic segment boundaries but some secondary magmatic segment boundaries also occur at small fourth order ridge axis discontinuities the secondary magmatic segments define the length scale of mantle melting variations mainly variations in extent of melting but not the scale of melt extraction processes that feed the axis this scale must be smaller than that of the secondary magmatic segments and probably corresponds to the length scale of fourth order physical discontinuities along axis there is a good positive correlation of average secondary magmatic segment length with spreading rate for four well sampled areas varying from 20 to 150 mm yr secondary magmatic segments also become more variable in axial length with increasing spreading rate the average lengths of secondary magmatic segments are smaller than those predicted by gravitational instability considerations at all spreading rates superposed on the axial magmatic segmentation are variations reflecting subaxial magmatic temperature defined by extent of magmatic differentiation which bears little systematic relation to physical or other kinds of magmatic segmentation at 13 23 s the length scale of this variation is 217 60 1 km approximately corresponding to the wavelength of rolls in the gravity field observed off axis taken together the various kinds and scales of magmatic variations observed for this superfast spreading ridge suggest that regional temperature of the upwelling asthenosphere magma supply to the axis and crustal magmatic temperature reflect independent regionally decoupled processes

syn and post fragmentation textures in submarine pyroclasts from lō ihi seamount hawai i abstract the extent and timing of vesiculation and microlite formation in ascending basaltic melts are relatively well understood for subaerial eruptions but they have not been studied thoroughly for submarine eruptions this is largely due to a lack of samples of appropriate volume and grain size we present a quantitative textural evaluation of coarse lapilli from two cone forming deposits at 1 km depth on l ihi seamount hawai i collected during a sampling intensive submersible dive series in 2006 lapilli from the deposits named the northern and southern cones have modal bulk vesicularities of 55 and 42 respectively and vesicle populations dominated by sub spherical non interconnected vesicles with number densities on the order of 10 4 to 10 5 cm 3 clasts of modal vesicularity have margin parallel zonation with seawater quenched rims interpreted to preserve syn fragmentation magmatic textures in microlite free sideromelane glass enclosing post fragmentation tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim to core degassing scenarios are linked to syn fragmentation vesicle textures to demonstrate that both magmas degassed in dominantly closed systems diffusion controlled cooling rates of basaltic pyroclasts in contact with water are linked to post fragmentation evolution of vesicle and microlite textures to make inferences about transportation and dispersal of the pyroclasts in low submarine jets the textural analysis shows that the northern and southern cone eruptions were not strictly analogous to any classical subaerial eruption type they were uniquely submarine with ambient seawater playing a crucial role in the processes of degassing vesiculation crystallization and dispersal

textural evolution of polyhedral olivine experiencing rapid cooling rates dynamic crystallization experiments in the cao mgo al2o3 sio2 cmas system have been used to investigate the change in crystal shape when pre existing polyhedral olivine crystals are cooled rapidly 1 639 2 182 c h polyhedral olivines are crystallized initially in a first step using a slow cooling rate 2 c h then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event during this second episode small dendritic olivines also nucleate within the liquid phase observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence polyhedral hopper polyhedral dendritic polyhedral this evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by sunagawa bull miner 104 81 87 1981 morphology of crystals terra scientific publishing company 1987 is proposed

disequilibrium growth of olivine in mafic magmas revealed by phosphorus zoning patterns of olivine from mafic ultramafic intrusions abstract olivine from mafic ultramafic intrusions rarely displays growth zoning in major and some minor elements such as fe mg and ni due to fast diffusion of these elements at high temperatures these elements in olivine are thus not useful in deciphering magma chamber processes such as magma convection multiple injection and mixing high resolution x ray elemental intensity mapping reveals distinct p zoning patterns of olivine from two mafic ultramafic intrusions in sw china polyhedral olivine grains from lherzolite and dunite of the abulangdang intrusion show p rich dendrites similar to those observed in volcanic rocks rounded olivine grains from net textured fe ti oxide ores of the baima layered intrusion have irregular p rich patches bands crosscut and interlocked by p poor olivine domains p rich patches bands contain 250 to 612 ppm p much higher than p poor olivine domains with 123 to 230 ppm p in electron backscattered diffraction ebsd maps p rich patches bands within a single olivine grain have the same crystallographic orientation indicating that they were remnants of the same crystal thus both p rich patches bands and p poor olivine domains in the same grain show a disequilibrium texture and clearly record two stage growth the p rich patches bands are likely the remnants of a polyhedral olivine crystal that formed in the first stage whereas the p poor olivine domains containing rounded ti rich magnetite and fe rich melt inclusions may have formed from an fe rich ambient melt in the second stage the complex p zoning of olivine can be attributed to the dissolution of early polyhedral olivine and re precipitation from the fe rich ambient melt the early polyhedral olivine was in chemical disequilibrium with the ambient melt that may have been developed by silicate liquid immiscibility in a crystal mush our study implies that olivine crystals in igneous cumulates with an equilibrium appearance may have experienced disequilibrium growth processes during slow cooling therefore the crystallization sequence of mafic magmas based on textural relationships should be treated with caution

mixed layer mode simulation of eastern north pacific stratocumulus abstract the cloud topped mixed layer theory developed by lilly 1968 is employed in a slightly generalized form to simulate stratocumulus in the eastern north pacific the radiation parameterization involves cloud top longwave cooling and mixed layer shortwave heating long wave emissivity and shortwave absorption are functions of cloud thickness the model is integrated along climatological trajectories which traverse the area bounded by 145 w 115 w 20 n and 40 n the results of the integration include fields of cloud top and cloud base height mixed layer thermodynamic structure and convective and radiative fluxes where it is possible to compare model generated fields with the observations of neiburger et al 1961 general agreement is found the model predicted location of the southern limit due to cloud top instability of stratocumulus clouds is in agreement with observations

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

airflow within major alpine river valleys under heavy rainfall summary this study documents the aire ow within major alpine river valleys in the presence of precipitation the analysis seeks a conceptual understanding of the effect of rain on the valley e ow ground based and airborne doppler radar and surface data from the mesoscale alpine programme show that during persistent rainy periods the subsidence caused by melting and evaporation of precipitation particles contributes to the formation of a down valley e ow this down valley eow opposes moist southerly e ow aloft which is lifted over the topographic barrier and in which precipitation particles are formed

the late quaternary loess record of tokaj hungary reconstructing palaeoenvironment vegetation and climate using stable c and n isotopes and biomarkers abstract large areas of southeast europe are covered by pleistocene loess deposits with interbedded palaeosol layers reflecting interglacials or stadials these loess palaeosol sequences are valuable terrestrial archives for continuous palaeoclimatic and palaeoenvironmental information in recent years the traditional paradigm of treeless full glacial palaeoenvironments has increasingly been called into question as there is palynological anthracological and malacological evidence for the continuous presence of trees from loess palaeosol sequences in the carpathian basin this paper aims at contributing to this discussion by applying biogeochemical geophysical and sedimentological methods to a late quaternary loess palaeosol profile at tokaj ne hungary previous studies at the same location have focused on molluscs and charcoal while this study concentrated on stable c and n isotopes and lipid biomarkers long chain n alkanes c 23 c 33 which form major constituents of plant leaf waxes have successfully been used as biomarkers over the last years and allow for a reconstruction of palaeovegetation based on the differentiation of grassland vs shrubs and trees stable carbon isotopes were used to further differentiate between c 3 and c 4 palaeovegetation and stable n isotopes to reconstruct the n cycle and climatic variations magnetic susceptibility ms organic carbon and grain size distribution which may serve as proxies for e g the intensity of pedegenesis weathering and palaeowind strength were measured to complement the biogeochemical results and to establish a pedo and biostratigraphy although the results do not agree in every detail with previous studies there are surprising matches and similarities in the data alkane and stable n isotopic data indicate that pedogenesis occurred under productive fertile steppe grasslands probably in an intensified seasonal climate and during reduced sedimentation two short treeless steppe periods were found between 26 and 12 ka bp however periods characterised by a cooler climate in which trees and shrubs expanded were also found this interpretation is also supported by previous mollusc data that provide evidence for several periods of favourable conditions for tree growth

cumulate gabbros from the southwest indian ridge 54 s 7 16 e implications for magmatic processes at a slow spreading ridge a diverse volcanic and plutonic rock suite was recovered from the center of the 80 km long ridge segment of the southwest indian ridge 54 s 7 16 e between the islas orcadas and shaka fracture zones the cumulus nature of the gabbroic rocks in the suite is indicated by phase modal and cryptic layering igneous lamination and low incompatible element abundances we present a mass balance model for calculating the proportions and compositions of cumulus phases and crystallized intercumulus liquid from bulk rock major element compositions the model is based on the ability to define a compositional array of basaltic liquids and on the assumption that cumulus minerals are initially in equilibrium with trapped liquid calculated proportions of trapped liquid range from 3 15 values that are characteristic of adcumulates to mesocumulates models of postcumulus crystallization indicate significant enrichments of incompatible elements and buffering of compatible elements in residual trapped liquids thus explaining the high tio2 contents observed in magnesian clinopyroxenes cumulus phase assemblages and compositions suggest solidification in shallow level magma chambers but disequilibrium plagioclase compositions suggest some crystallization at greater depth furthermore basalt compositions projected onto the olivine clinopyroxenequartz pseudoternary suggest magma generation over a range of pressures from less than 10 to greater than 20 kb as well as polybaric fractional crystallization we suggest that the southwest indian ridge is characterized by low magma supply with small batches of melt that either ascend directly to the surface having undergone limited polybaric crystallization or are trapped in shallow crustal magma chambers where they evolve and solidify to form cumulate gabbros the adcumulus nature of the gabbros investigated here suggests slow cooling rates typical of large intrusions implying relatively large but ephemeral magma chambers below segments of the southwest indian ridge

dynamic crystallization studies on the grande ronde pillow basalts central washington dynamic crystallization experiments were performed to reproduce textural and mineralogic features of some grande ronde columbia river pillow basalts and thereby estimate cooling rates of the various pillow textural zones the essential petrographic features of these pillows can be experimentally duplicated by melting at the liquidus temperature 1140 c followed by isothermal drop crystallization at 1125 c and then linear cooling to subsolidus temperatures at rates between 2400 c hr to reproduce vitrophyric rims and 10o hr to reproduce the holocrystalline interiors in both cooling experiments and the pillows the al content of pyroxenes and the fe content of plagioclase display a systematic variation with respect to cooling rate or position within the pillow pyroxene grain size data derived from the cooling experiments display a linear relationship with cooling rate but are strongly influenced by the original melting temperature pyroxenes crystallized during experiments originally melted at liq

building the crust at the mid atlantic ridge the morphology of the sea floor at mid ocean ridge spreading centres provides a key to understanding how ocean crust is constructed images of the axial zone of the slow spreading mid atlantic ridge obtained at a range of spatial scales show that crustal construction is complex and highly variable reflecting an underlying three dimensional variability in magmatic tectonic and hydrothermal processes

testing climate proxy stationarity throughout the holocene an example from the varved sediments of lake meerfelder maar germany abstract lake meerfelder maar germany provides a varved record from the last glacial interglacial transition back to ca 1500 years bp this study shows results for the holocene sequence from new cores collected in 2009 based on varve counting microfacies and micro xrf analyses the main goal of combining those analyses is to provide a new approach for interpreting long term palaeolimnological proxy data and testing the climate proxy stationarity throughout the current interglacial period varve counting provides a new independent holocene chronology mfm2012 with an estimated counting error of 1 0 5 and supported by 14 c dating varve structure and thickness and geochemical composition of the varves give information about the main environmental processes that affect the lake and its catchment as well as the possible climate variability behind varves are couplets of i a spring summer laminae composed of monospecific diatom blooms and ii an autumn winter sub layer made of minerogenic material and reworked sediments thickness of the varves and sub layers reflect lake variability and allow seasons to be distinguished as well as seasonal proxies changes in the winter minerogenic influx into the lake are reflected by ti intensities and the si ti ratio as an indicator for diatom concentration which can be used as a proxy for water circulation during the early spring long term variability of geochemical composition shows a reduction of the detrital material input ti at 5000 varve yrs bp and a visible sensitivity to water mixing si ti during the late holocene variations of ti intensities during the early and mid holocene do not show a clear relationship with climate in contrast higher values of the si ti ratio together with thicker varves have been interpreted as wind stress phases which coincide with centennial variability of european cold wet episodes during the late holocene our findings show that a long term change in the lake and or variability of the climate system can influence proxy sensitivity of a lacustrine record

a magmatic origin for silica rich glass inclusions hosted in porphyritic magnesian olivines in chondrules an experimental study rare silica rich glass inclusions 69 sio2 82 wt are described within magnesian olivines of porphyritic type ia chondrules these glass inclusion compositions are clearly out of equilibrium with their host mg olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases we performed dynamic crystallisation experiments that demonstrate that these si rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a ci i e solar composition their silica rich compositions are the consequence of the small volumes of inclusions which inhibit the nucleation of secondary crystalline phase ca poor pyroxene but allow olivine to continue to crystallize metastably on the walls of the inclusions we suggest that si rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system exhibiting a ci i e non fractionated composition

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

summertime post cold frontal marine stratocumulus transition processes over the eastern north atlantic abstractmarine boundary layer mbl cloud morphology associated with two summertime cold fronts over the eastern north atlantic ena is investigated using high resolution simulations from the weat

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

a developmental model of olivine morphology as a function of the cooling rate and the degree of undercooling we performed dynamic crystallization experiments in the cmas system at 1 atm to investigate the evolution of the morphology of forsterite crystals as a function of cooling rate and degree of undercooling in sections parallel to the 010 plane we observed the evolution of the forsterite morphology from tablets to hopper skeletal crystals and then to swallowtail shapes dendritic morphology for increased degree of undercooling the other shapes described in the literature can be interpreted as particular sections of those three shapes the onset of dendritic growth is due to a competition between the growth of the faces of the initial hopper crystal and dendrite overgrowths the forsterite dendrites are formed by a succession of units which look like hopper shapes this result has been tested by an additional set of experiments

lateglacial to holocene pedogenesis and formation of colluvial deposits in a loess landscape of central europe wetterau germany abstract loess areas in central europe have been settled since ancient times and are therefore predestined to archive information about both the paleoenvironment with and without human activities in gentle rolling loess landscapes distinct short and shallow valleys so called dells are prominent landscape elements that act as sediment traps the loess paleosol colluvium lpc sequence of gambach wetterau germany can be regarded as an exceptional sequence for lateglacial holocene pedogenesis and human impact in dry loess landscapes with the lpc sequence of gambach reflects climate controlled pedogenesis from ca 15 ka to 4 7 ka with the formation of a cambisol having some properties related to chernozem soil forming processes during the lateglacial a chernozem is developed in the deposits of the laacher see tephra which still show the influence of periglacial climate in their lowermost part the upper part of these deposits was relocated by colluvial processes at around 6 7 ka chernozem soil forming processes were still ongoing until 4 7 ka when these shifted to luvisol formation which is still active today since 4 7 ka extended land use with indications of agricultural fire use since at least 2 3 ka led to the formation of colluvial deposits combined with a topographic leveling of upland positions on a landscape scale the results of the formative element of humans on loess landscapes from the wetterau can also be taken as representative for around 9400 km2 of dry loess landscapes in central europe

bio and chronostratigraphy of the lateglacial in the eifel region germany abstract in recent years enormous success has been achieved in varve counting of the eifel maar lakes but a detailed correlation with the biostratigraphy has been missing in this paper we present new palynological results of the lateglacial sequences from holzmaar lake and meerfelder maar lake based on annually laminated sediments in particular the meerfelder maar has great potential because in contrast to the holzmaar the sequence between the ulmener maar tephra 11 000 varve years bp and the laacher see tephra 12 880 varve years bp including the younger dryas is undisturbed and complete therefore we currently use the meerfelder maar chronology brauer et al 1999b as an independent varve calendar for the biostratigraphy of the lateglacial the palynological signals of both maar lakes are in good agreement and can easily be correlated with one another and with type sections type regions in northwestern germany and jutland the sequences of the eifel maar lakes have the quality of hypostratotypes with regional biozones based on an absolute time scale

changes in fire regimes on the chinese loess plateau since the last glacial maximum and implications for linkages to paleoclimate and past human activity abstract a high resolution black carbon bc record from 27 5 kyr bp to present was reconstructed using a chemical oxidation method on loess and paleosol samples from the lijiayuan section of the chinese loess plateau the black carbon mass sedimentation rates bcmsr and carbon isotopic record reveal a paleofire history and its relationship with climate and vegetation changes at the study site the bcmsr record was decomposed into two components background bcmsr and the bcmsr peaks the background bcmsr represents regional fires and shows high fire activities occurred contemporaneous with the younger dryas older dryas heinrich events and greenland stadials as registered in the loess grain size record this suggests a rapid response of regional fires on the loess plateau to abrupt climate changes spectral analysis of background bcmsr showed two meaningful periodicities of 1620 and 1040 years close to the cyclicity of the east asian monsoon as recorded in the stalagmite 18o record in central china this indicates a tight control of millennial scale wet dry changes in the monsoonal climate on regional fires on the loess plateau by contrast the bcmsr peaks are considered to reflect local fire episodes the occurrences of local fires were more frequent during the last glacial period with a maximum frequency of 6 episodes 1000 years during the last glacial maximum lgm 22 3 to 14 6 kyr bp when the climate was drier and more continuous grassy fuels existed on the landscape during the last glacial interglacial transition lgit period 14 6 to 11 0 kyr bp fire frequency was largely reduced due to an increase in precipitation and more woody vegetation if the lgit period is taken as an analog for the projected near future then future global warming alone may not produce large wildfires in northwestern china wildfires remained infrequent during the early to middle holocene biomass burning increased after 4 0 kyr bp when the climate became drier and land use was more intensive bc carbon isotope ratios may well reflect changes in the vegetation being burnt i e grasses versus trees yielding results consistent with the associated pollen data in the region

magmatic processes under mid ocean ridges a detailed mineralogic study of lavas from east pacific rise 9 30 n 10 30 n and 11 20 n 1 detailed petrologic study has been made for lavas from the northern east pacific rise epr 9 30 n 11 20 n and 10 30 n 9 30 n and 11 20 n have robust magma supply and a shallow melt lens while 10 30 n has nonrobust magma supply and no shallow melt lens lavas from all three localities are sparsely phyric and glassy containing plagioclase olivine pyroxene typically the lavas contain several to many up to seven distinct chemical groups of plagioclase that are not always distinct texturally the lavas may also contain up to three chemically distinct groups of olivine and two groups of pyroxene the lavas contain both individual crystals and groups comprising reticulate and dendritic clots that we interpret to represent bits of crystal networks forming in mushy zones of an axial magma chamber 21 of the 23 samples studied in detail have diverse crystal compositions and require mixing which most likely occurs when mostly liquid magma passes through mushy zones we find no significant systematic differences between robust and nonrobust segments in terms of their crystal content proportion of texturally distinct xenocrysts crystal size aspect ratio roundness modal abundance magma residence time number of diverse mineral chemical groups and characteristics of mixing like the total range of composition of disequilibrium minerals present and the magnitude of the chemical gaps between disequilibrium and equilibrium compositions this unexpected and remarkable similarity suggests that the presence or absence of a seismically imaged shallow melt lens has essentially no effect on the mineralogy of erupted lavas we conclude that the fundamentally important magmatic process under mid ocean ridges from slow to fast is the formation of crystal networks and their subsequent compaction the seismically detected shallow melt lenses likely contain highly evolved magma formed by expelled interstitial melt during crystal network compaction and play very little role in crustal accretion our conclusion implies that the thick 3 km low velocity zone near the base of the crust produces the thin 30 m shallow melt lenses not the other way around

chernozem relics in the hellweg loess belt westphalia nw germany natural or man made abstract chernozems and chernozem like soils are widespread e g in central germany but its formation is still controversially discussed clustered findings of luvic phaeozems and buried dark soil horizons in the westphalian hellweg loess belt north rhine westphalia are traditionally interpreted as relics of early holocene chernozems more recent research raised the question whether these soils are of pre historic anthropogenic origin field observations in the east of dortmund revealed the existence of buried black horizons in hillslope hollows the underlying stagnic luvisol was penetrated by darkish clay illuviation veins forming a polygonal pattern this feature was also found below the plough horizon in luvisols beyond the hillslope hollows a multi analytical approach was used in order to clarify whether the black soil horizons are natural relics or man made in order to identify fire derived black carbon microcharcoal benzenepolycarboxylic acids were used as molecular markers beside the position of the fossil black horizons on top of a well developed stagnic luvisol micromorphological thin section analysis confirmed the colluvial origin of the black horizons total organic carbon contents of the black horizons were only 1 whereas high black carbon concentrations indicate large amounts of fire derived organic matter high concentrations of black carbon were also found in the clay illuviation veins testifying to a formerly more widespread occurrence of black carbon enriched soils radiocarbon ages of charcoal particles from the black horizons prove fire activities during the late neolithic and bronze age e g slash and burn finally our results strongly indicate that the chernozem like soils in the study area are man made and natural chernozem formation can be excluded

conditions of magma storage degassing and ascent at stromboli new insights into the volcano plumbing system with inferences on the eruptive dynamics stromboli is known for its persistent degassing and rhythmic strombolian activity occasionally punctuated by paroxysmal eruptions the basaltic pumice and scoria emitted during paroxysms and strombolian activity respectively differ in their textures crystal contents and glass matrix compositions which testify to distinct conditions of crystallization degassing and magma ascent we present here an extensive dataset on major elements and volatiles co2 h2o s and cl in olivine hosted melt inclusions and embayments from pyroclasts emplaced during explosive eruptions of variable magnitude magma saturation pressures were assessed from the dissolved amounts of h2 oa nd co2 taking into account the melt composition evolution both pressures and melt inclusion compositions indicate that 1 ca basaltic melts entrapped in high mg olivines fo89 90 generate stromboli basalts through crystal fractionation and 2 the stromboli plumbing system can be imaged as a succession of magma ponding zones connected by dikes the 7 10 km interval where magmas are stored and differentiate is periodically recharged by new magma batches possibly ranging from ca basalts to basalts with a co2 rich gas phase these deep recharges promote the formation of bubbly basalt blobs which are able to intrude the shallow plumbing system 2 4 km where co2 gas fluxing enhances h2o loss crystallization and generation of crystal rich dense degassed magma chlorine partitioning into the h2o co2 bearing gas phase accounts for its efficient degassing 69 under the open system conditions of strombolian activity paroxysms however are generated through predominantly closed system ascent of basaltic magma batches from the deep storage zone in this situation crystallization is negligible and sulfur exsolution starts at 170 mpa chlorine remains dissolved in the melt until lower pressures only 16 being lost upon eruption finally we propose a continuum in explosive eruption energy from strombolian activity to large paroxysmal events ultimately controlled by variable pressurization of the deep feeding system associated with magma and gas recharges

correlation and synchronisation of lateglacial continental sequences in northern central europe based on annually laminated lacustrine sediments abstract the present study focusses on correlation and synchronisation of weichselian lateglacial varved lake sediments from western germany meerfelder maar eifel region northern germany hamelsee lower saxony central poland lake go ci a z and eastern poland lake perespilno by using varve chronology tephrochronology palynostratigraphy and stable isotopes comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi synchronously within the errors of the different chronologies during the younger dryas preboreal transition moreover there is a consensus about the length of the younger dryas cold stage of 1100 1150 varve years in the allerod the prominent laacher see tephra 12 880 varve years bp can be used to fix floating varve chronologies the relative duration of this biozone has been determined in meerfelder maar and hamelsee at between 625 and 670 varve years in the meerfelder maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire lateglacial the comparison between continental limnic sequences and greenland ice core records should be made on the basis of independent chronologies in both archives it is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the lateglacial for terrestrial european records in this respect annually laminated lacustrine sequences have a great potential

self mixing magma in the ruiz peak rhyodacite new mexico usa a mechanism explaining the formation of long period polytypes of mica abstract the rhyodacite of ruiz peak volcano new mexico usa is an exceptional rock because it contains both long period and short period polytypes of mica our petrographic study shows that this rhyodacite is characterized by numerous disequilibrium textures of phenocrysts mica amphibole clinopyroxene olivine and plagioclase contained within both dark grey and reddish coloured groundmass the presence of two groundmasses as well as of disequilibrium textures reaction rims resorption dendritic skeletal morphologies etc suggests a complex magmatic history these two types of groundmass are not due to a mixing of magmas but result from a degassing process during the magma ascent in the conduit the disequilibrium textures are interpreted to be the result of small short lived convection cells in the magmatic chamber which may allow crystal crystal crystal spiral and spiral spiral interactions to occur leading to the formation of long period polytypes of mica for the first time the relationships between the crystallographic features of mica and the host rock formation are underlined in this study it follows that long period polytypes of mica can be considered markers of the complex history of magmas

fire history reconstruction from black carbon analysis in holocene cave sediments at ifri oudadane northeastern morocco fire residues elucidate the where when and how of land use charcoal analysis provides insights into wood burning practices but is restricted by the size of identifiable particles the present paper is the first to apply a black carbon bc method to archaeological sediment deposits this method oxidizes charcoal and soot particles from the bulk sediment to benzene polycarboxylic acids bpcas independent of size our aim was to test the potential of bc analysis in order to elucidate the input from grass and wood fires and discuss the potential limitations of the method on sediments of the ifri oudadane rock shelter morocco sediments cover the cultural transition from hunter gatherers to food producing communities epipaleolithic to neolithic period 11 6 kyr cal bp which has previously been shown to affect the geochemical palynological and archaeological inventories of these sediments we found respective changes in bc specifically content was highest during the epipaleolithic with an avera

on the dynamics of hawaiian cloud bands island forcing abstract this study focuses on basic island scale forcing mechanisms for the formation and evolution of a band cloud typically present upwind of the island of hawaii by means of numerical experiments and verification of our results against observations and laboratory experiments reported in the literature we show that the band cloud is a complex three dimensional phenomenon which is inseparable from the airflow around the island in particular we demonstrate that the event needs to be analyzed in terms of the basic fluid dynamics of strongly stratified flow past a three dimensional obstacle the band cloud is found to arise primarily from the dynamic interaction of the trade winds with the island the upwind surface flow forms a separation line with an associated stagnation point a low level convergence zone forms along this line resulting in an updraft line if the updrafts are strong enough a band cloud forms formation and characteristics of such a system are mostly controlled by the environmenta

anthracology and taphonomy from wood gathering to charcoal analysis a review of the taphonomic processes modifying charcoal assemblages in archaeological contexts abstract a discussion on the representativeness of charcoal from archaeological contexts and their potential for palaeoecological reconstruction is presented the charcoal deposits studied are the result of human activities and natural processes difficult to separate on the basis of their effects only this is why taphonomy should not be limited to the study of charcoal after the extinction of fire as a result our questioning has been widened to include the entire succession of processes from past vegetation to the anthracological diagram we propose a review of the taphonomic processes affecting anthracological assemblages in archaeological contexts from wood gathering to the analysis of charcoal results human practices appear clearly as the first filter determining or conditioning the assemblage the combustion process can induce a double filter by limiting the taxonomic information and by falsifying the initial quantity of burned wood post depositional agents represent a third level of filters between the vegetation and the anthracological assemblage finally sampling and quantification methods can also induce a distortion of the assemblage the aim of this paper is to present the state of the discipline today the problems already solved and the questions that remain to be studied

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

vegetation dynamics and fire history at the southern boundary of the forest vegetation zone in european russia during the middle and late holocene climate and human activity affected significantly the eurasian on the forest vegetation zone through the holocene this paper presents new multi proxy records of environmental changes at the southern boundary of the mixed coniferous broadleaved forest zone in the east central part of the east european plain during the middle and late holocene palaeoecological analyses of a peat core for pollen charcoal peat humification plant macrofossils and testate amoebae with dating using radiocarbon have shown that climate appears to have been a dominant control on vegetation there is strong evidence for a reduced precipitation evapotranspiration ratio and high fire frequency during the holocene thermal maximum 6 9 5 3 ka bp leading to dominance of betula pinus forests by contrast subsequent climatic cooling led to the expansion of broadleaved forests and establishment of picea human activities influenced vegetation from the neolithic onwards but played a role which was secondary to climate until the recent past over the last century human impacts considerably increased because of harvesting of broadleaved trees and contributed to the formation of the current mixed coniferous broadleaved forests

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

observed lagrangian transition of stratocumulus into cumulus during astex mean state and turbulence structure aircraft measurements made during the first lagrangian of the atlantic stratocumulus transition experiment astex between 12 and 14 june 1992 are presented during this lagrangian experiment an air mass was followed that was advected southward by the mean wind five aircraft flights were undertaken to observe the transition of a stratocumulus cloud deck to thin and broken stratocumulus clouds penetrated by cumulus from below from the horizontal aircraft legs the boundary layer mean structure microphysics turbulence structure and entrainment were analyzed the vertical profiles of the vertical velocity skewness are shown to illustrate the transition of a cloudy boundary layer predominantly driven by longwave radiative cooling at the cloud top to one driven mainly by convection due to an unstable surface stratification and cumulus clouds during the last flight before the stratocumulus deck was observed to be broken and replaced by cumuli the total water flux the virtual potential temperature flux and the vertical velocity variance in the stratocumulus cloud layer were found significantly larger compared with the previous flights to analyze the cloud top stability the mean jumps of conserved variables across the inversion were determined from porpoising runs through the cloud top these jumps were compared with cloud top entrainment instability criteria discussed in the literature it is suggested that enhanced entrainment of dry air is a key mechanism in the stratocumulus cumulus transition

biogeochemical and micro facial fingerprints of ecosystem response to rapid late glacial climatic changes in varved sediments of meerfelder maar germany the response of a lacustrine ecosystem to climatic changes from 13 500 to 10 800 bp was studied in a varve dated sediment profile of lake meerfelder maar western germany bulk biogeochemical parameters stable carbon and nitrogen isotopes of sedimentary organic matter and micro facies analysis are used for a detailed investigation of the lake s development from the allerod interstadial al to the younger dryas stadial yd and into the early holocene preboreal varve micro facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones the respective responses of bulk proxy parameters bi decadal resolution indicate different sensitivities to diverse climatic changes a prominent transition took place within two decades at the al yd boundary 12 690 12 670 bp increased flux of nutrients released from redeposited littoral sediments and shorter yd summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13c high lacustrine primary production was further favored by relatively warm yd summer temperatures at 12 240 varve years bp from 1 year to the next a regular deposition of detrital layers in spring set in which is related to local hydrologic threshold processes amplifying the response to increased snowmelt discharge this distinct change in the middle of the yd is clearly detected by varve micro facies but not equally recorded in organic bulk proxy data especially carbon isotope ratios remain constant and indicate a negligible effect of this process on the productivity of lacustrine algae the yd preboreal transition 11 645 11 585 bp is marked by a characteristic change in micro facies throughout this transition stable carbon isotope ratios strongly decline while the accumulation of opal and organic matter om remained constant this is seen as an increasing importance of spring and autumn for gross primary production at the onset of the holocene

high resolution sediment and vegetation responses to younger dryas climate change in varved lake sediments from meerfelder maar germany abstract this work focuses on a 1900 year section of varved sediments from lake meerfelder maar mfm extending from the late allerod to the preboreal varve counting provides the chronological framework and determines the length of younger dryas to 1025 1090 years a strong relation between climate change environment response and depositional processes has been found in consequence varve microfacies variations are a sensitive proxy for environment changes these are reflected for example in erosion processes within the lake s catchment minerogenic input and lake productivity diatom blooms the observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate in addition high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval varve observations reveal that environment changes at the beginning and the end of the younger dryas occurred within 20 50 years furthermore sediment and vegetation changes were synchronous within the actual precision of the mfm and grip chronologies divergence of only a few decades terrestrial responses in western europe occurred quasi synchronous to temperature changes in greenland

holocene changes in fire frequency in the daihai lake region north central china indications and implications for an important role of human activity abstract black carbon bc content in a sediment core from daihai lake inner mongolia was analyzed to reconstruct a high resolution history of fires occurring in northern china during the holocene and to examine the impacts of natural changes and human activities on the fire regime the black carbon mass sedimentation rate bcmsr was disintegrated into two components the background bcmsr and the bcmsr peak with the bcmsr peak representing the frequency of fire episodes both the background bcmsr and the magnitude of the bcmsr peak display a close relation with the percentage of tree pollen from the same sediment core suggesting that regional vegetation type would be a factor controlling the intensity of fires the inferred fire episode frequency for the holocene exhibits two phases of obvious increases i e the first increase from