integrating the uranium series and elemental diffusion geochronometers in mixed magmas from volcan quizapu central chile magma mixing is a ubiquitous process in silicic magmatic systems we present pre and post mixing time scales for a single magma mixing event associated with the 1846 1847 eruption of volcan quizapu we compare and contrast 226 ra 230 th crystal residence ages between the mixed lavas of the 1846 1847 effusive eruption and the largely homogeneous plinian dacite eruption of 1932 both eruptions are dominated by the same dacite magma whereas the ear lier eruption contains evidence for a single episode of mafic recharge and mixing the use of uranium series mineral separate dating on a mixed magma requires deconvolution of different crystal populations we present a four component mixing model for the crystal separates to obtain dacite derived plagioclase model ages as well as andesite derived recharge plagioclase ages plagioclase model ages average 3 6 ka for dacite derived plagioclase from the mixed 1846 1847 eruption 1 4 kyr older than average plagioclase model ages of the 1932 eruption suggesting that magma mixing and reheating led to some resorption of young crystal rims in the 1846 1847 magmatic episode and or that some growth of plagioclase rims occurred during the repose time of 86 years the andesite derived plagioclase residence ages are younger than the corresponding dacite derived plagioclase residence ages but they are still of the order of thousands of years in addition we use mg diffu sion in plagioclase to constrain time scales of magma mixing we show that the 1846 1847 eruption was triggered by large volume mafic recharge magma that mixed and mingled with the resident dacite within probably days to weeks of the ensuing eruption

evaluating diatom derived holocene ph reconstructions for arctic lakes using an expanded 171 lake training set inference models from diatoms preserved in lake sediments can be used to reconstruct long term ph changes to better understand the process of lake ontogeny an expanded diatom training set was developed using taxonomically harmonized modern assemblages in surface sediments of 171 lakes spanning a variety of geological and climatic settings across the canadian arctic lake water ph emerged as a significant variable and the most influential in structuring diatom assemblages the resulting two component weighted averaging partial least squares ph inference model performs strongly even after identifying effects of spatial autocorrelation at distances 20km the model was then applied to three dated holocene diatom stratigraphies from arctic regions of contrasting bedrock geology and buffering capacity and the significance of the ph reconstructions was assessed at lake cf3 in a poorly buffered catchment a gradual but significant ph decline begins 5000 years after lake inception coincident with regional late holocene cooling reconstructions for two well buffered more alkaline sites were not significant probably due to poor analogues and other factors driving changes in diatom assemblages due to sparse soil and vegetation in these and other arctic basins bedrock composition is the most important regulator of holocene ph and only in poorly buffered lakes does ph primarily represent a climate signal copyright 2014 john wiley sons ltd

microwave backscatter modeling of erg surfaces in the sahara desert the sahara desert includes large expanses of sand dunes called ergs these dunes are formed and constantly reshaped by prevailing winds previous study shows that saharan ergs exhibit significant radar backscatter spl sigma spl deg modulation with azimuth angle f we use spl sigma spl deg measurements observed at various incidence angles and f from the nasa scatterometer nscat the seawinds scatterometer the ers scatterometer escat and the tropical rainfall measuring mission s precipitation radar to model the spl sigma spl deg response from sand dunes observations reveal a characteristic relationship between the backscatter modulation and the dune type i e the number and orientation of the dune slopes sand dunes are modeled as a composite of tilted rough facets which are characterized by a probability distribution of tilt with a mean value and small ripples on the facet surface the small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at bragg angles only longitudinal and transverse dunes are modeled with rough facets having gaussian tilt distributions the model results in a spl sigma spl deg response similar to nscat and escat observations over areas of known dune types in the sahara the response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere this analysis provides a unique insight into scattering by large scale sand bedforms

timing of abrupt climate change a precise clock 1 many paleoclimatic data reveal a 1 500 year cyclicity of unknown origin a crucial question is how stable and regular this cycle is an analysis of the gisp2 ice core record from greenland reveals that abrupt climate events appear to be paced by a 1 470 year cycle with a period that is probably stable to within a few percent with 95 confidence the period is maintained to better than 12 over at least 23 cycles this highly precise clock points to an origin outside the earth system oscillatory modes within the earth system can be expected to be far more irregular in period

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

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

millennial scale temperature variations in north america during the holocene 1 a mean continental july temperature reconstruction based on pollen records from across north america quantifies temperature variations of several timescales for the past 14 000 cal yr bp in north america temperatures increased nearly 4 c during the late glacial reaching maximum values between 6000 and 3000 cal yr bp after which mean july temperatures decreased superimposed on this orbital scale trend are millennial scale temperature variations that appear coherent in structure and frequency with highresolution ice marine and other terrestrial paleoclimate records of the holocene during the holocene climate in north america appears to have varied periodically every 1100 years rather than the 1500 year cycle found during the last glacial period coherence at frequencies between 900 and 1100 years between land ice and ocean records suggests a common forcing associated with widespread surface impacts during the holocene these results provide important insight to the global warming debate as the observed twentieth century temperature increase appears unprecedented compared to our mean north american temperature reconstruction of the past 14 000 years

influences of forested and grassland vegetation on late quaternary ecosystem development as recorded in lacustrine sediments geosphere biosphere interactions are ubiquitous features of the earth surface yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail to assess the nature rate and magnitude of vegetation influence on parent material and sediment delivery we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern united states over time terrigenous inputs declined at both sites with increasing amounts of organic inputs toward present the similarities between sites were striking given that the grassland sequence began in the early holocene and the forested sequence began after the last glacial maximum multiple mechanisms of chemical weathering hydrologic transport and changes in source material potentially contribute to this pattern although there were strong links between vegetation composition and nitrogen cycling at each site it appears that changes in forest type or from oak woodland to grassland did not exert a large influence on elemental k ti si ca fe mn and s abundance in the sedimentary sequences rather other factors in the catchment lake system determined the temporal sequence of elemental abundance

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

widespread evidence of 1500 yr climate variability in north america during the past 14 000 yr there is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation existing evidence is largely restricted to the north atlantic and adjacent landmasses the spatial extent magnitude and effects of these climate variations within the terrestrial environment during the holocene have not been established we show that millennial scale climate variability caused changes in vegetation communities across all of north america with a periodicity of 1650 500 yr during the past 14 000 calendar years cal yr times of major transitions identified in pollen records occurred at 600 1650 2850 4030 6700 8100 10 190 12 900 and 13 800 cal yr b p consistent with ice and marine records we suggest that north atlantic millennial scale climate variability is associated with rearrangements of the atmospheric circulation with far reaching influences on the climate

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

a 1600 year diatom record of hydroclimate variability from wolf lake new york a high resolution diatom record from wolf lake a minimally disturbed heritage lake provides insights into the hydroclimatic history of the adirondack mountains of northern new york during the last c 1600 years three pronounced dry periods occurred during c ad 490 610 780 870 and 1010 1080 and low precipitation generally prevailed during the warm medieval climate anomaly c ad 950 1350 a finding that fills an important gap in knowledge of the spatial extent of droughts across north america during that period during the cooler little ice age interval c ad 1350 1800 inferred water balance was generally more positive seven peaks in charcoal abundance represent fire events during both wet and dry periods unusually high charcoal and inorganic sediment deposition c ad 1700 could reflect human activity in the watershed as might an abrupt rise in the relative abundances of planktonic and tychoplanktonic diatoms in wolf lake during the ad 1860s the diatom record displays periodicities of c

azimuth variation in microwave scatterometer and radiometer data over antarctica while designed for ocean observation scatterometer and radiometer data have proven very useful in a variety of cryosphere studies over large regions of antarctica ice sheet and bedrock topography and the snow deposition drift and erosional environment combine to produce roughness on various scales roughness ranges from broad basin scale ice sheet topography at spl sim 100 km wavelengths to large spatially coherent dune fields at spl sim 10 km wavelength to erosional features on the meter scale known as sastrugi these roughness scales influence the microwave backscattering and emission properties of the surface combining to introduce azimuth angle dependencies in the satellite observation data in this paper the authors explore the use of nasa scatterometer nscat data european remote sensing ers advanced microwave instrument ami scatterometer mode data and special sensor microwave imager ssm i data to study surface roughness effects in antarctica all three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and results in a katabatic wind flow regime due to its broad azimuth coverage nscat data appears to be the best suited for azimuth angle observations a simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from nscat data at a fine scale is presented results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small scale roughness relative to the sensor look direction

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

rapid and widespread vegetation responses to past climate change in the north atlantic region ongoing anthropogenic perturbations to the atmosphere and biosphere increase the risk of future abrupt changes in the climate system and generate concern about the ability of natural ecosystems to respond to rapid climate change study of past climatic events and biotic responses can inform us about potential future change qualitatively fast local responses of plant taxa to abrupt late glacial climate oscillations have been reported from individual records and attributed to short migration distances in areas of high topographic relief by using quantitative time series analyses we show that vegetation responses to late glacial climate change around the north atlantic were rapid and widespread and occurred in areas of differing relief cross correlation analysis of 11 high resolution lacustrine records in eastern north america and europe indicates vegetation response times consistently of 200 yr and often 100 yr despite regional differences in physiography and species composition vegetation lags of 200 yr confirm theoretical predictions and the apparently tight coupling between vegetation and atmosphere suggests that recent climatic trends may already have begun to affect plant population abundances and distributions

spatial and temporal variability of lake ontogeny in south western greenland abstract holocene palaeolimnological records of diatoms and carotene a proxy for aquatic production from four lakes in the low arctic region of south western greenland were used to investigate the role of climate on lake ontogeny two of the lakes are located in the maritime coastal region near sisimiut and two inland close to the head of kangerlussuaq fjord where there is a more continental climate diatom records from the four lakes at1 at4 ss1381 ss8 had similar long term ontogeny trends independent of climatic setting and the changes are interpreted as responses to first order weathering controls on catchment lake chemistry short term excursions from these broad trends occurred in one coastal site at4 caused by intense erosion of the steep catchment and at inland sites where temporary hydrological closure and lake level decline occurred during the mid holocene 8000 5000 cal a bp algal production as carotene was more closely and consistently correlated with climatic changes it peaked during the mid holocene the warmest period of the holocene at all sites and there were transient increases in production in inland lakes during the medieval climate anomaly and little ice age because of fertilization through increased aeolian dust deposition a synthesis of seven palaeolimnological records from this region identified that only the mid holocene was correlated with diatom stratigraphic zones and there was considerable among site variability in later holocene lake response to climate forcing in this area comparable long term trends in species assemblage turnover dca ca axis 1 scores clearly demonstrate that lakes have predictable ontogeny trends in this region characterised by maximum alkalinity and nutrient availability in the first few millennia followed by progressive oligotrophication and alkalinity loss however individual lake and catchment characteristics lake morphology catchment geomorphology when modified by climatic change vegetation cover erosion weathering rates aeolian dust deposition lake level can diverge from this ontogeny template leading to complex ecological transitions in lakes from this region

the recent eutrophication of baldeggersee switzerland as assessed by fossil diatom assemblages diatom analyses with an annual resolution were carried out on varves of the hypertrophic baldeg gersee central swiss plateau for the timespan ad 1885 to 1993 they reveal seven major changes in the dominant planktonic diatoms as a result of progressive nutrient enrichment baldeggersee changed in the 1910s from a cyclotella to a tabellaria fenestrata dominated assemblage and eventually in the 1950s to a stephanodiscus parvusdominated diatom assemblage the timing and direction of diatom assemblage changes in the varved sediment compare well with sedimentological and limnological observations partitioning of the variance in the diatom data revealed that tp is a stronger explanatory variable than temperature for these changes a diatom inferred total phosphorus tp reconstruction indicates three major steps in eutrophication occurring at 1909 the mid 1950s and the mid 1970s comparison with tp measurements in the water column demonstrates that the diatom tp inference model used is able to hindcast past tp concentrations reliably the major steps in eutrophication led to decreases in diatom diversity and also resulted in a progressive increase of calcite grain size the lake restoration programme established since 1982 shows no direct impact on the composition of the diatom assemblages however the decrease in phosphorus loads since the mid 1970s is reflected in the diatom assemblages and in decreasing diatom inferred tp concentrations

evolution of crystal sizes in the series of dissolution and precipitation events in open magma systems article i nfo we propose a model that describes the evolution of crystal sizes and crystal size distributions csd of igneous phenocrysts in a sequence of dissolution and crystallization events this model is based on the assumption that crystal dissolution is rate limited by diffusion in melt while crystal growth is controlled by the slower kinetic of new nucleation and growth as a result the dissolution rate is inversely proportional to crystal size coming into effect through the curvature of the crystal s surface but the growth rate does not depend on the crystal size closed form analytical solution of equation for csd is obtained we apply results of modeling to quartz and zircon two prime minerals in silicic igneous systems that are widely used in geochemical and isotopic investigations the time series of multiple solution reprecipitation episodes generate concave downward csds and this result fits well with experimental and natural observations on the abundant concave down csd in silicic igneous rocks we suggest that maturation of crystal populations with sizes above several micrometers can not be caused by a size effect on the solubility of the crystals ostwald ripening but is rather driven by thermal oscillations in experiments and in nature the model predicts that mean crystal size increases with time proportionally to t 0 20 which is very close to the published experimental results for quartz maturation with the exponent of 0 19 0 22 our proposed model gives an opportunity to use natural csds for interpretation of pre eruptive magma history when solubilities and diffusion data are available for constituent elements of the dissolving mineral in particular we present time estimates for maturing zircon populations in large volume ignimbrites and estimate that it takes 100 1000 yrs to mature an initially exponential csd to a lognormal csd

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

unraveling the presence of multiple plagioclase populations and identification of representative two dimensional sections using a statistical and numerical approach many plagioclase phenocrysts from volcanic and plutonic rocks display quite complex chemical and textural zoning patterns understanding the zoning patterns and variety of crystal populations holds clues to the processes and timescales that lead to the formation of the igneous rocks however in addition to a true natural complexity of the crystal population the large variety of plagioclase types can be partly artifacts of the use of two dimensional 2d petrographic thin sections and random cuts of three dimensional 3d plagioclase crystals thus the identification of the true number of plagioclase populations and the decision of which are representative crystal sections to be used for detailed trace element and isotope analysis is not obvious and tends to be subjective here we approach this problem with a series of numerical simulations and statistical analyses of a variety of plagioclase crystals zoned in 3d we analyze the effect of increasing complexity of zoning based on 2d chemical maps e g backscattered electron images bse we first analyze the random sections of single crystals and then study the effect of mixing of different crystal populations in the samples by quantifying the similarity of the compositional histogram of about a hundred 2d plagioclase sections it is possible to identify the so called reference and ideal sections that are representative of the real 3d crystal populations these section types allow filtering out the random cut effects and explain more than 90 of the plagioclase compositional data of a given sample our method allows the identification of the main crystal populations and representative crystals that can then be used for a more robust interpretation of magmatic processes and timescales

soil mineral depletion drives early holocene lake acidification in recent decades explanations for post glacial lake acidification have focused on changing climate and biotic factors here we present a unique lake sediment data set combining diatom inferred acidity reconstruction with detailed quantitative assessment of soil base dynamics that challenges this view we show at krakenes lake in norway that historical development of soil mineral depletion inferred from the lake sediment record is consistent with the extent and timing of early holocene acidification the lake water acidification can be fully accounted for by abiotic soil mineral depletion suggesting a lesser role for alternative acidifying mechanisms such as direct climate impacts and successional changes in organic acid production there are at present few comparable data sets but those that exist suggest similar rates of soil base depletion as this acidification is not confined to water abiotic mineral depletion is likely also to impact terrestrial ecosystems and dynamic vegetation models that exclude irreversible mineral depletion will fail to capture an important element of global ecology

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

aquatic ecosystem responses to holocene climate change and biome development in boreal central asia boreal ecosystems are highly vulnerable to climate change and severe ecological impacts in the near future are virtually certain to occur we undertook a multiproxy study on an alpine lake esm 1 at the modern tree line in boreal southern siberia steppe and tundra biomes were extensive in eastern sayan landscapes during the early holocene boreal forest quickly expanded by 9 1 ka bp and dominated the landscape until c 0 7 ka bp when the greatest period of compositional turnover occurred at this time alpine meadow landscape expanded and picea obovata colonised new habitats along river valleys and lake shorelines because of prevailing cool moist conditions during the early holocene chironomid assemblages were dominated by cold stenotherms diatoms for much of the holocene were dominated by alkaliphilous fragilarioid taxa up until 0 2 ka bp when epiphytic species expanded indicative of increased habitat availability c n mass ratios ranged between 9 5 and 13 5 11 1 15 8 c n atomic ratios indicative of algal communities dominating organic matter contributions to bottom sediments with small persistent contributions from vascular plants however 13c values increased steadily from 34 9 during the early holocene 9 3 ka bp to 24 8 by 0 6 ka bp this large shift in magnitude may be due to a number of factors including increasing within lake productivity increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically mature and declining soil respiration linked to small but distinct retreat in forest biomes the influence of climatic variables on landscape vegetation was assessed using redundancy analysis rda a linear direct ordination technique changes in july insolation at 60 n significantly explained over one fifth of the variation in species composition while changes in estimates of northern hemisphere temperature and ice rafted debris events in the north atlantic were also significant but considerably less important the potential importance of climate and biome development tundra steppe cold deciduous forest and taiga on different trophic levels i e chironomid and diatom communities in lake esm 1 was also assessed using rda climate predictors had a more significant influence on holocene chironomid assemblages especially july insolation at 60 n estimates of regional precipitation and estimates of northern hemisphere temperature while only the development of the taiga biome had a significant impact on these primary consumers diatom communities also had a small but significant influence on holocene chironomid populations perhaps linked to variation in faunal feeding strategies in contrast climatic and biome predictors explained similar amounts of variation in the holocene diatom assemblage approximately 20 each while chironomids themselves as predictors explained just under 7 of diatom variation lake acidity was inferred using a diatom inference model results suggest that after deglaciation the lake did not undergo a process of gradual acidification most likely due to the presence of continuous permafrost and low levels of precipitation preventing base cations and dissolved organic carbon entering the lake except for the period between 1 7 and 0 7 ka bp we conclude that lakes in continental boreal regions undergo different models of lake ontogeny than oceanic boreal regions unlike other regions discussed climate is a more important driver of ecosystem change than catchment changes we also demonstrate that the start of the period coincident with the onset of the little ice age resulted in important thresholds crossed in catchment vegetation and aquatic communities

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

last glacial maximum environmental conditions at andoya northern norway evidence for a northern ice edge ecological hotspot abstract andoya on the nw coast of norway is a key site for understanding the last glacial maximum lgm in northern europe controversy has arisen concerning the local conditions especially about the timing and extent of local glacial cover maximum july temperatures and whether pine and or spruce could have grown there we reviewed all existing data and add newly analysed ancient sedimentary dna sedadna pollen macrofossils geochemistry and stable isotopes from three lake sediment cores from ovre aerasvatnet a total of 23 new dates and age depth modelling suggests the lake has been ice free since gi2 14 7 cal ka bp data recorded 94 vascular plant taxa of which 38 have a northern limit in shrub tundra or more southern vegetation zones this unusual assemblage likely stems from a combination of proximity to ice free water in summer geographical isolation linked with stochastic long distance dispersal events and the presence of bird fertilized habitats the environmental reconstruction based on all records from the area does not preclude local growth of tree species as the local climate combined with high nutrient input may have led to periodically suitable environmental hotspot conditions

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

multiangle backscattering observations of continental surfaces in ku band 13 ghz from satellites understanding the signals particularly in arid regions backscattering in ku band 13 ghz over continen tal surfaces is analyzed with the tropical rainfall measurement mission precipitation radar instruments incidence angles from 0 to 18 along with observations from the topex poseidon nadir looking altimeter and the quikscat scatterometer inci dence angles around 50 the signals from the three instruments are very consistent the backscattering tends to decrease with increasing vegetation density as expected making it possible to classify vegetation density with active microwaves over the northern african desert a very large spatial variability of the backscattering is observed with both surface and volume scatter ings contributing to the signals the use of multiangle observations does help characterizing the desert types but in some areas the ambiguity of the signals is still unexplained the french chinese joint mission chinese french oceanic satellite will carry two active microwave instruments with a large range of incidence angles from 0 to 50 we show that the combined use of ob servations at low and high incidence angles adds information particularly over desert surfaces

vegetation dynamics in relation to late holocene climate variability and disturbance outaouais quebec canada a pollen diagram from lac brule in southwestern quebec 45 43 09 n 75 26 32 w 270 m provides a late holocene history of the vegetation the presence of varved sediments permitted the development of a high resolution 10 year cross dated chronology with an estimated error of approximately 1 during the last 1400 years the forests were dominated by tsuga fagus betula acer and pinus a peak in microcharcoal and evidence of post fire succession suggest that the changes in the pollen assemblages around ad 1375 were a consequence of a fire in the region there was a decrease in pollen influx of several deciduous taxa and tsuga between ad 1600 and 1700 suggesting a rapid climate change that was significant enough to have affected pollen production of these taxa this change associated with the beginning of the little ice age in the region affected the forest composition for the subsequent centuries a detailed comparison of this pollen record with that from a nearby pollen diagram also prepared at high temporal resolution shows the ability of pollen records to record short period climate variations and disturbances

envisat radar altimeter measurements over continental surfaces and ice caps using the ice 2 retracking algorithm abstract this study presents the first results obtained with the envisat satellite radar altimeter ra 2 over lands and ice caps as radar altimetry was firstly devoted to ocean study this paper starts with a detailed description of the radar altimetry principle over continental surfaces a general formulation of the radar altimeter echoes according to different surface types is given and the retracking procedure ice 2 specially implemented on the envisat satellite ground segment to provide output parameters over continents is clearly presented the envisat ra 2 datasets processed with the ice 2 procedure are then mapped given an overall description of the output parameters over various surfaces the behaviour of these envisat altimetric parameters are analysed and related to main land surface characteristics such as surface volume echo specularity roughness apart from few unexpected signals which will need to be further investigated the new envisat dataset confirms the potential of inland altimetry and provides a new opportunity to monitor continental surfaces the ku band measurements confirm previous results recently obtained with the altimeters on board ers or topex poseidon and offer a temporal continuity the s band altimeter measurements are in accordance with theoretical expected ones and confirm previous topex poseidon observations in c band the s band and the use of the dual frequency thus bring new capabilities for altimetric applications with important deliveries for temporal evolution survey for instance s band will be used over continents to better detect wetlands located under vegetated areas or to better quantify wave penetration in terrestrial snowpack to accurately retrieve snow depth evolution over ice sheets the dual frequency s and ku band waveforms parameters will provide a more accurate height estimation as it will be possible to quantify the error on height measurements induced by snowpack structure change over time this will then provide a more confident survey of the ice sheets surface topography evolution the combination and complementarities with the other altimetry missions such as ers topex poseidon and jason look already promising and offer a 10 year span dataset for continental altimetry applications

mafic monogenetic vents at the descabezado grande volcanic field 35 5 s 70 8 w the northernmost evidence of regional primitive volcanism in the southern volcanic zone of chile in the andean southern volcanic zone svz the broad distribution of mafic compositions along the recent volcanic arc occurs mainly south of 37 s above a comparatively thin continental crust 35 km and mostly associated with the dextral strike slip regime of the liquine ofqui fault zone lofz north of 36 s mafic compositions are scarce this would be in part related to the effect resulting from protracted periods of trapping of less evolved ascending magmas beneath a thick meso cenozoic volcano sedimentary cover that lead to more evolved compositions in volcanic rocks erupted at the surface here we present whole rock and olivine mineral chemistry data for mafic rocks from four monogenetic vents developed above a svz segment of thick crust 45 km in the descabezado grande volcanic field 35 5 s whole rock chemistry mgo 8 wt and compositional variations in olivine 92 fo 88 and ni up to 3650 ppm indicate that some of the basaltic products erupted through these vents e g los hornitos monogenetic cones represent primitive arc magmas reaching high crustal levels the combined use of satellite images regional data analysis and field observations allow to recognize at least 38 mafic monogenetic volcanoes dispersed over an area of about 5000 km2 between 35 5 and 36 5 s a link between ancient structures inherited from pre andean tectonics and the emplacement and distribution of this mafic volcanism is suggested as a first order structural control that may explain the widespread occurrence of mafic volcanism in this andean arc segment with thick crust

frank oldfield and his contributions to environmental change research frank oldfield s immense contribution to palaeoenvironmental science is summarized in relation to pollen analysis vegetation history and peat stratigraphy palaeolimnology and 210pb dating environmental magnetism catchment lake relationships and soil erosional history multiproxy approaches pages and editing the holocene the tribute includes an introduction to the 14 other papers in this special issue which were inspired in diverse ways by this remarkable scientist

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

direct and indirect effects of holocene climate variations on catchment and lake processes of a treeline lake sw china sedimentary records of inorganic elements and pigments over the last 12 000 years are used to assess major changes in limnological conditions of tiancai lake a small treeline lake sw china in response to holocene climate variations algal communities shifted from the dominance of cyanobacteria and cryptophytes in the early holocene towards siliceous algae in the mid holocene and chlorophytes in the late holocene algae responded to a combination of climate mediated vegetation and soil development associated with allochthonous inputs of dissolved nutrients and organic matter and sediment infilling decreases in al pb cu and zn from the early holocene probably resulted from soil podsolization and the sequestration of these elements within soils changes in mn and fe were likely linked to redox condition in catchment soils and water column synchronous peaks in ti ba ca sr na k and mg median grain size and magnetic susceptibility coincided with the troughs in the chemical index of alteration indicating that episodic cold events enhanced upland bedrock erosion and transported unleached and coarse detritus into the lake these cold events broadly correlate with holocene ice rafting events in the north atlantic although the cold events altered the influx of minerogenic elements by regulating upland bedrock erosion climate mediated vegetation and soil development led to a muted impact on primary producers holocene algal community shifts were subtle reflecting the relative abundance of p derived from weathering and n derived from soils throughout the record with the most pronounced effects on the lake biota being benthic expansion which occurred in response to sediment infilling

comparison of north american pollen based temperature and global lake status with cccma agcm2 output at 6 ka abstract we present new paleoclimate reconstructions for the time period of 6000 yr bp 6 ka that permit a quantitative comparison to corresponding mapped patterns of the newest version of the canadian cccma agcm2 climate model july temperature reconstructions were estimated using the modern analog technique employing fossil pollen records from the north american pollen database we present a new method of optimizing critical choices within the application of the mat through modern calibration the pattern of 6 ka temperature anomalies generated by the cccma agcm2 generally agree with those of the pollen based reconstruction particularly in the presence of a band of positive temperature anomalies across the continent from the yukon through the great lakes region and along the st lawrence this agreement suggests that both the model and data are reconstructing a contraction in the polar vortex over north america at 6 ka major areas of disagreement between the pollen based reconstruction and model simulation are also areas where the data are sparse and edge effects produce less reliable reconstructions the cccma agcm2 simulates drier conditions in a west east band stretching from alaska through the canadian prairies and midwest united states in agreement with low lake level observations at 6 ka simulated and reconstructed precipitation evaporation are also in agreement over the southwest united states with the exception of north central africa the cccma agcm2 fails to capture the northward and eastern extension of the afro asian monsoon belt at 6 ka general agreement between cccma agcm2 p e anomalies and lake status change is found throughout europe at 6 ka

new insights from xrf core scanning data into boreal lake ontogeny during the eemian marine isotope stage 5e at sokli northeast finland biological proxies from the sokli eemian marine isotope stage 5e paleolake sequence from northeast finland have previously shown that unlike many postglacial records from boreal sites the lake

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

magmatic life at low reynolds number the extremely high viscosities of high silica liquids mean that intermediate and high silica magmas exist deep within the laminar range of fluid behavior many common interpretations of layering in plutonic rocks rely on analogies with sedimentation in water but for such high viscosity liquids including interstitial liquid in partially crystallized intermediate magmas these analogies cannot be correct particle reynolds numbers for high silica liquids are exceedingly small on the order of 10 6 or less in such a regime inertia is negligible and everyday experience is inapplicable layering and other pseudo sedimentary structures in granodiorites and granites likely arise from processes such as chemical diffusion self organization and crystal ripening

pre eruptive reheating during magma mixing at quizapu volcano and the implications for the explosiveness of silicic arc volcanoes effusive explosive transitions are observed in volcanoes erupting water rich magmas that lack mineralogical evidence of degassing suggesting that gas loss occurred rapidly and ascent was fast despite the high viscosity of rhyodacitic to rhyolitic melts here we show that pre eruptive heating of water rich silicic magma by mixing with hot recharge in subvolcanic chambers controls the effusive explosive transition volcan quizapu chile emitted a 5 km3 mingled dacite andesite lava flow in a d 1846 1847 that was 130 c hotter than the 5 km3 of the same dacite that lead to a plinian eruption in a d 1932 we explain the suppression of explosive fragmentation in the 1846 1847 lavas by enhanced syneruptive magma degassing as a consequence of late reheating following mixing with andesite recharge higher magma temperatures led to the transitioning into effusive eruptive behavior by significantly accelerating volatile diffusion and lowering melt viscosity which facilitated bubble nucleation growth and coalescence while also inhibiting brittle fragmentation thus recharge by mafic magmas in subvolcanic magma chambers may reduce the risk of explosive eruptions in cases where heat can be efficiently transferred to cold volatile rich silicic magmas

cyclic variation and solar forcing of holocene climate in the alaskan subarctic high resolution analyses of lake sediment from southwestern alaska reveal cyclic variations in climate and ecosystems during the holocene these variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides 14c and 10be as well as north atlantic drift ice our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high latitude environments they also provide evidence that centennial scale shifts in the holocene climate were similar between the subpolar regions of the north atlantic and north pacific possibly because of sun ocean climate linkages

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

lake ecosystem dynamics and links to climate change inferred from a stable isotope and organic palaeorecord from a mountain lake in southwestern china ca 22 6 10 5 cal ka bp abstract a detailed understanding of long term climatic and environmental change in southwestern china is hampered by a lack of long term regional palaeorecords organic analysis toc tn c n ratios and 13c values of a sediment sequence from lake shudu yunnan province ca 22 6 10 5 cal ka bp indicates generally low aquatic palaeoproductivity rates over millennial timescales in response to cold dry climatic conditions however the record is punctuated by two marked phases of increased aquatic productivity from ca 17 7 to 17 1 cal ka bp and from ca 11 9 to 10 5 cal ka bp we hypothesise that these shifts reflect a marked stepwise lacustrine response to asian summer monsoon strengthening during the last deglaciation

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

simulating loss of primary silicate minerals from soil due to long term weathering using allogen comparison with soil chronosequence lake sediment and river solute flux data this paper presents allogen a process model of soil mineral chemical weathering though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations the model is also applicable to more general questions about long term weathering and soil development the model is constructed around a generalised version of the mineral weathering submodel of profile modified to minimise the need for site specific data and to optimise performance for long term change comparison with observed weathering rate data river flux studies chronosequences and lake sediment chemical stratigraphy suggests that soil mineral depletion can be usefully simulated over timescales applicable to quaternary and holocene studies to illustrate this the plausibility of a weathering interpretation is demonstrated for sediment records at lake hope simpson and moraine lake and the lake chronosequence at glacier bay while long term soil mineral depletion appears predictable reliable simulation of past runoff quality is hampered by lack of a suitable long term model for soil carbon

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

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

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

azimuthal anisotropy of scatterometer measurements over land studies of the earth s land surface involving scatterometers are becoming an increasingly important application field of microwave remote sensing similarly to scatterometer observations of ocean waves the backscattering coefficient sigma0 response of land surfaces depends on both the incidence and azimuth angle under which the observations are made in order to retrieve geophysical parameters from scatterometer data it is necessary to account for azimuthal modulation effects of the backscattered signal in the present study this paper localizes the regions affected by a strong azimuthal signal dependence when observed with the european remote sensing satellite scatterometer and the seawinds scatterometer on quikscat qscat the possible physical reasons for the azimuthal effects relating the very detailed qscat azimuthal response to the spatial orientation of special topographic features and land cover within the sensor footprint were then discussed different methods for normalizing the backscattering coefficient with respect of observation azimuth angle were also proposed and evaluated first the mean local incidence angle of the sensor footprint using the shuttle radar topography mission digital elevation model dem were modeled and concluded that the resolution of the dem is too coarse to characterize most of the observed azimuthal effects a more effective way of normalizing the backscatter with respect to azimuth is then found to be by using historical backscatter observations to statistically determine the expected backscatter at each observation azimuth and incidence angle as well as time of the year the efficiency of this method is limited to the availability of past measurements for each location on the earth

loss of apatite caused irreversible early holocene lake acidification lakes created by retreating ice at the end of the last glaciation underwent rapid acidification during the first few thousand years of their existence a phenomenon attributed in part to progressive leaching of soil bases since it was discovered more than 80 yeas ago though a role for leaching is still acknowledged the most recent studies see this as subordinate to the effects of biological and climatic changes initiated by deglaciation chiefly primary vegetation succession and species immigration until now there has been no quantitative test of the relative importance of these different mechanisms here i use geochemical modelling of runoff acidity to show that the extent and timing of early holocene lake acidification in eight published palaeoecological records can be explained by leaching of the calcium phosphate mineral apatite from the granitic till soils of their catchments at a rate controlled by simple dissolution kinetic factors this shows that a single progressive abiotic process is capabl

radar backscatter characteristics of a desert surface satellite radar altimeter measurements have shown spatial and temporal variations in the backscattered signal from desert surfaces in order to understand these variations we have carried out extensive in situ measurements for the validation of a compilation of existing backscatter models the model predictions are in excellent agreement with ground and satellite based measurements of the radar backscatter coefficient and show that the altimeter backscatter measurements are strongly affected by variations in soil moisture following rainfall and by the presence of dew on the surface regional but time invariant differences in backscatter are attributed to variations in surface topography

the space and time complexity of chaotic mixing of silicate melts implications for igneous petrology abstract we present new experimental results on the study of the space and time modulation of compositional fields during chaotic mixing between mafic and felsic silicate melts the experimental strategy was planned using numerical simulations performed using the experimental geometry these mixing experiments were performed using a recently developed experimental apparatus which is capable of mixing high viscosity silicate melts at high temperatures and under precisely controlled conditions of fluid dynamics and strain the compositional variability produced by the mixing process was investigated both along linear analytical transects and on high resolution 2d x ray maps covering the mixing patterns our results indicate that chaotic flow fields represent very powerful dynamics to blend silicate melts even under laminar fluid dynamic conditions reynolds number ca 10 7 and for dissimilar melts with high viscosity ratios on the order of 103 the repetition of stretching and folding processes between the two melts induced a strong increase of contact interfaces thus favoring efficient chemical exchanges as a result the initial mafic composition is no longer detectable in the mixing system after ca 2 h i e the duration of the experiment a further important result is the observation of highly non linear patterns in inter elemental plots produced by the onset of diffusive fractionation processes this is contrary to common thinking that magma mixing should always produce linear trends between pairs of chemical elements a new measure the concentration variance is proposed to quantify chemical element mobility during the mixing process this measure is statistically robust and can be quantitatively used to measure chemical element mobility independently of the geometry in which the compositional variation i e transects areas etc is embedded or the local strain history of the mingling our results highlight concentration variance as a robust probe of the as yet poorly understood processes involved in the common petrological process of magma mixing

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

experimental study of igneous and sedimentary apatite dissolution control of ph distance from equilibrium and temperature on dissolution rates apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of ph temperature solution saturation state and on non carbonated and carbonated apatite compositions igneous fluorapatite fap and sedimentary carbonate fluorapatite cfa respectively from 2 8 5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of fap for the cfa compositions studied the dissolution rate decreased with increasing ph from 4 ph 7 during early stages of the dissolution reaction for both fap and cfa mineral components were released in non stoichiometric ratios with reacted solution ratios of dissolved ca p and ca f being greater than mineral stoichiometric ratios suggesting that ca was preferentially released compared to p and f from the mineral structure during the early stages of dissolution an increase in reacted solution ph accompanies this early elevated release of ca as the dissolution reaction proceeded to steady state dissolution became congruent when normalized to bet measured surface area fap dissolved faster from 4 ph 7 compared to cfa the apparent arrhenius activation energy ea of fap dissolution over the temperature range of 25 55 c at ph 3 0 i 0 1 and pco2 0 is 8 3 0 2 kcal mol 1 both the apparent exchange of solution h for solid bound ca at low ph in the early stage of dissolution and the ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for fap and cfa the degree of undersaturation of the solution gr with respect to fap was important in determining the dissolution rate at ph 3 0 i 0 1 and pco2 0 the dissolution rate of fap was 5 greater in the far from equilibrium region compared to the near equilibrium slope region a simple apatite weathering model incorporating the experimental results from this study was constructed and numerical calculations suggest that during the phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the p weathering flux from apatite dissolution it is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early to mid paleozoic resulted in elevated p weathering fluxes which along with climatic evolutionary pressures of the neoproterozoic facilitated the radiation of multicellular organisms large scale phosphorite deposition and abundance of calcium phosphate shelled organisms during the early cambrian

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

magmatic processes under quizapu volcano chile identified from geochemical and textural studies quizapu is part of a linear system of active volcanos in central chile the volcanic petrology and geology have been used to infer the plumbing system beneath the volcano the 1846 1847 eruption 5 km3 started with small flows of dacite then changed to a range of andesite dacite compositions and finally terminated with large flows of dacite andesitic enclaves 10 occur in some of these flows activity restarted explosively in 1932 4 km3 dre with an initial andesite dacite ash followed by uniform dacite ash and then a terminal andesite ash all samples including the enclaves have chemical compositions that lie on an almost perfect mixing line with a few exceptions the abundant plagioclase macrocrysts in the matrix were divided into five petrographic classes on the basis of colour in cold cathode cathodoluminescence images and zonation in visible light all populations of macrocrysts have csds characteristic of coarsening although they differ in detail two classes can be ascribed to growth in andesite and dacite magmas but the three other classes are associated with particular magma batches a model is developed which started with ponding of andesite magma in the crust this differentiated to produce a dacite magma most of which probably solidified to make a granodiorite batholith activation of a n s fault enabled volcanism andesite magma traversed the dacite filled chamber heating and raising it up into storage areas hosted by the fault where it mixed to form a homogeneous magma a short time before the 1846 1847 eruption more andesite magma was injected into the shallow part of the system where it mingled with existing mixed magmas the first magma to be erupted from quizapu was a dacite but soon other storage areas along the fault started to feed the system first mixed magmas then back to dacites the eruption then terminated until 1932 when renewed injection of andesite into the system created a conduit that tapped an undegassed dacite chamber and resulted in a strong explosive eruption the whole story is one of continual andesite magmatism modulated by storage degassing and mixing

spaceborne altimetry and scatterometry backscattering signatures at c and ku bands over west africa abstract this study presents a comprehensive comparison of radar signatures acquired over west africa between latitudes 0 25 n and longitudes 5 w 25 e at both c and ku bands using nadir looking altimeters 35 day orbital period envisat ra 2 over 2003 2010 and 10 day orbital period jason 2 over mid 2008 2011 and side looking scatterometers quikscat over 2003 2009 and ascat over mid 2008 2011 that covers the major bioclimatic zones soil and vegetation types encountered in this region the backscattering coefficient s time series measured by both radar instruments are generated over regional transects and local sites meridian transects from the wet tropics to the arid regions of the sahara desert demonstrate the spatial and temporal changes of the radar response over the west african bioclimatic gradient in terms of surface roughness land cover and soil wetness nadir looking altimetry appears more sensitive to variations of surface soil moisture than side looking scatterometry at both c and ku bands in contrast the impact of vegetation on the backscattered signals is found to be lower for nadir looking instruments compared to side looking ones

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

late holocene climate changes in eastern north america estimated from pollen data well dated pollen profiles from six sites from maine to minnesota record vegetation changes indicative of summer temperature and annual precipitation variations over the past 2000 yr laminations in the sediment provide accurate time control multiple regression techniques were used to calculate calibration functions from a spatial network of modern pollen and climate data when applied to the six pollen diagrams these calibration functions yielded estimates that show a long term trend toward lower summer temperature superimposed on this long term trend are short term fluctuations that are frequently in phase at the sites departures from the long term cooling trend are positive around 1500 yr ago indicating relative warmth and negative between 200 and 500 yr ago indicating relative cold annual precipitation showed a slight increase at several sites during the past 1000 yr relative to the previous 1000 yr

a 7500 year peat based palaeoclimatic reconstruction and evidence for an 1100 year cyclicity in bog surface wetness from temple hill moss pentland hills southeast scotland analyses of plant macrofossils peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog temple hill moss in southeast scotland the plant macrofossil data were subjected to detrended correspondence analysis dca which modelled effectively the significant wet shifts within the record a mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes the three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation two tephra horizons glen garry and lairg a were used in conjunction with radiocarbon dates to construct an age depth model producing a robust geochronology from which a time series was calculated the palaeoclimatic reconstruction identified major wet shifts throughout the holocene with specific events occurring around cal 6650 5850 5300 4500 3850 3400 2800 2450 1450 1350 and 250 150 bp spectral analysis of the plant macrofossil dca and colorimetric humification data produced a millennial scale periodicity of 1100 years the same periodicity has also been found in a palaeoclimatic reconstruction from a site in cumbria walton moss and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf