plagioclase mantles on sanidine in silicic lavas clear lake california implications for the origin of rapakivi texture at clear lake california mixed dacite lavas contain sanidine mantled by oligoclase that closely resemble rapakivi feldspars in granites resorption and mantling of sanidine by plagioclase is one of many disequilibrium textures in these lavas resulting from maficfelsic magma interaction mantling of sanidine by plagioclase may occur directly in mixed magmas due to shifts in composition and temperature or indirectly in crystal rich silicic magmas influenced by thermal under plating or mafic felsic hybridization in adjacent regions of the magmatic system other silicic laves containing mantled sanidine also show evidence for mafic felsic magma interaction textural and compositional similarities between rapakivi texture in extrusive and intrusive rocks suggest that they have a common origin moreover modification of early formed textures due to protracted crystallization subsolidus reactions and metasomatic hydrothermal alteration in the plutonic environment accounts for most of the observed differences between extrusive and intrusive examples the association of coeval mafic rocks and evidence for mafic felsic magma interaction in many plutons containing rapakivi exture confirm that magma mixing plays a key role in its formation in some intrusive texamples evidence for a compositional control and multiple episodes of mantle formation are also compatible with repeated cycles of recharge and mixing regardless of the exact cause of k feldspar instability textural evidence from volcanic rocks and experiments indicates that development of rapakivi texture is controlled by cation diffusion in a dissolution boundary layer developed on k feldspar mantles appear to form in a two stage process that involves initial epitaxial nucleation of plagioclase on sanidine followed by simultaneous dissolution of sanidine and inward growth of plagioclase

marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

fracturing and diking in incompletely crystallized granitic plutons abstract dikes in granitic plutons commonly have mineralogic and textural characteristics indicating a genetic relation to their host the contact between the dike and the host is marked signifcantly by interlocking unfractured crystals rather than by truncations and overgrowths although megascopically the contacts between dike and host pluton may be exceedingly sharp and planar an explanation of these relationships by fracturing an incompletely crystallized host rather than by entirely post magmatic fracturing with subsequent diking is postulated to be consistent with experimental date and certain petrologic observations published experimental research indicates that fracturing of crystal melt systems may occur if there is at least 70 crystals in the system at which point the system is capable of transmitting compressive and shear stresses via a crystalline framework dilatancy pumping of melt into fracture zones and subsequent hydraulic fracturing is thought to be one possible way late stage fluids of granitic systems evolve into dikes in granitic plutons such as leucogranites aplites and pegmatites interlocking textures between dike and host may also develop if magma from some distant source is interjected along the plane of fracturing in crystal melt systems

magma mingling and melt modification between granitic pipes and host diorite guernsey channel islands within the northern igneous complex of guernsey cylindrical pipe intrusions 20 40 cm in diameter developed by buoyant emplacement of granite magma into overlying denser diorite magma the high viscosity of the partially crystallized magmas and lack of mechanical stirring inhibited physical mixing and mesoscopically sharp well defined interfaces developed the granitic pipes are surrounded by aureoles up to a metre in diameter which exhibit changes in bulk chemical composition and partial mineralogical re equilibration these formed in response to the modification of interstitial melt in the partially crystallized host resulting from residual melt migration and or melt interdiffusion across the pipe host interface such processes between partially crystallized magmas may in part provide an explanation for textural mineralogical and chemical compositional features commonly exhibited by mafic enclaves within granites

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

the transition from temperate phases to stadials in the long upper pleistocene sequence from les echets france abstract from two sections of the long sequence of les echets corresponding to the end of the eemian and to the end of st germain ii interstadial respectively detailed pollen diagrams have been established which provide information about the climatic conditions prevailing during the transitions from very temperate periods to the following cold stadials

modest summer temperature variability during do cycles in western europe abrupt climatic shifts between cold stadials and warm interstadials termed dansgaard oeschger do cycles occurred frequently during the last glacial their imprint is registered in paleorecords

a 13 000 year paleolimnological record from the uinta mountains utah inferred from diatoms and loss on ignition analysis paleolimnological research in mountainous regions of the western united states provide baseline understanding of how these lake systems will respond to ongoing climate change fossil diatom assemblage and loss on ignition data were investigated from a 13 000 year lake sediment core from the uinta mountains northeastern utah usa results indicate the presence of three major zones of environmental change 1 from 12 9 10 9 cal ka modern lake formation began temperatures were cool and water was turbid 2 from 10 9 3 5 cal ka conditions were warmer than present and the lake stratified during the summer and 3 beginning approximately 3 5 cal ka temperatures decreased relative to the previous zone and the lake appears to have become increasingly alkaline shifts in diatom taxa relative abundances within the middle zone ca 8 2 6 5 and 5 0 3 5 cal ka are probably caused by precipitation driven decreases in alkalinity and increases in lake depth this record reflects evolution of the lake system and suggests that currently rising temperatures will reduce ice cover and enhance lake stratification and internal nutrient cycling any future changes in precipitation patterns may also impact lake ecology through shifts in alkalinity and or depth

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

deglaciation shore displacement and early holocene vegetation history in eastern middle sweden the sedimentary record at lake vibysjo lake basin is situated close to the narke strait where the main water exchange occurred between the vanern basin and baltic basin during the middle and late phases of the yoldia sea stage of the baltic sea c 10 000 9500 14c years bp the area was deglaciated in a glaciomarine environment as reflected by the occurrence of benthic calcareous fossils foraminifera ostracods and the mollusc portlandia arctica gray in the lower most clay units the estimated date of deglaciation 10 440 clay varve years bp suggests that a saline bottom water current entered the baltic basin shortly after the high areas south of lake vibysjon became free of ice the brackish water fauna occurs during a regional betula empetrum hippophae pollen zone which in southern sweden is correlated with the early preboreal the isolation of the lake vibysjon basin is dated to 8100 14c years bp and occurred during the last part of the ancylus lake stage based on investigations of other bas

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

short term soil formation events in last glacial east european loess evidence from multi method luminescence dating here we provide a robust luminescence chronology for stayky ukraine a reference profile in european late pleistocene loess stratigraphy based on optically stimulated luminescence osl dating on quartz 4 11 m 63 90 m and post infrared infrared stimulated luminescence pir irsl on polymineral fine grains for the bug loess unit the equivalent of marine isotope stage mis 2 results are in agreement between methods demonstrating that the suite of embryonic soils previously interpreted as reflecting climate variability similar to greenland interstadials gi actually date to 29 27 15 ka with most emplaced around or after 20 ka this temporal span is further confirmed by age depth modelling of available data apart from gi 2 no interstadial type climate events are recorded in greenland ice core data for that time interval as short term pedogenetic phases are also documented in records from central western europe there is a need for more research into the european mid latitude terrestrial environments response to mis 2 hydroclimate variability the dating of vytachiv paleosol previously debatably linked to various gi events within mis 3 resulted in ages of 40 4 ka and 53 4 ka at the lower transition and 26 2 ka to 30 2 ka in the overlying loess these ages indicate that the truncated vytachiv paleosol is either not continuous or that it encompasses a broader age range within mis 3 than previously considered in both cases data would not allow for an unambiguous linking of this paleosol with specific gi events as previously attempted the pir irsl290 dating of the loams immediately underneath pryluky unit in the range of 120 ka to 168 ka and of the pryluky mollisol from 90 ka to 126 ka confirm the broad correspondence of this unit with mis 5 although poor dose recovery results open the possibility for further testing on the degree these ages provide overestimated results quartz data severely underestimate the pir irsl290 ages for these samples the application of pir irsl290 dating for the underlying dnieper till previously linked to the saalian glaciation resulted in natural signals at the level of laboratory saturation yielding minimum ages of c 700 ka for the same sample the natural sar osl signals for 4 11 m quartz were found significantly below laboratory saturation level resulting in finite ages of 250 270 ka interpreted here as underestimates while coarse quartz 63 90 m signals reached about 85 of the laboratory saturation level these data suggest extreme caution must be taken when dating such old samples using quartz osl results from our high resolution luminescence dating raises important implications for the chronological representativeness of stayky as a key loess site in eastern europe beyond mis 2

were last glacial climate events simultaneous between greenland and france a quantitative comparison using non tuned chronologies several large abrupt climate fluctuations during the last glacial have been recorded in greenland ice cores and archives from other regions often these dansgaard oeschger events are assumed to have been synchronous over wide areas and then used as tie points to link chronologies between the proxy archives however it has not yet been tested independently whether or not these events were indeed synchronous over large areas here we compare dansgaard oeschger type events in a well dated record from southeastern france with those in greenland ice cores instead of assuming simultaneous climate events between both archives we keep their age models independent even these well dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi centennial time scales if possible comparisons between proxy archives should be based on independent non tuned time scales copyright 2009 john wiley sons ltd

diatom community response to multiple scales of holocene climate variability in a small lake on victoria island nwt canada abstract a lake sediment core spanning 9900 years collected from a small lake on western victoria island nwt canada provides a high resolution record of diatom community dynamics over the holocene ten radiocarbon dates and 210 pb dating provided the core chronology loss on ignition loi magnetic susceptibility biogenic silica content and diatom concentrations provided information on changes in the sedimentary environment loi gradually increased over the holocene whereas magnetic susceptibility showed an inverse trend biogenic silica content showed three distinct peaks spaced approximately 3000 years apart major shifts in diatom assemblages occurred at 8100 8000 5800 5700 and 3800 3500 cal yr bp there is evidence of diatom community response to centennial scale variations such as the medieval warm period 1000 700 cal yr bp little ice age 800 150 cal yr bp and recent warming although recent changes in diatom community composition productivity and species richness are apparent they were surpassed at other periods throughout the holocene variations of the taxa within the genera staurosira pseudostaurosira fragilaria and staurosirella usually combined into one genus in arctic lake sediment studies suggest these taxa provide useful insight into paleonvironmental questions

paleolimnological records of climatic change in north america lacustrine fossil records provide long time series of data on limnological and climatic conditions these data are useful for establishing natural patterns of climate variability and for generating testable hypotheses about atmospheric circulation and climate ecosystem linkages shoreline features can indicate past lake level fluctuations that may reflect changes in moisture balance but often these records are discontinuous and are evidence of only extreme conditions the organisms geochemistry and sedimentology of lake sediments may provide a more continuous sequence of direct and indirect lake climate interactions in the past the most clearly interpretable paleolirnnological records of climatic change are those that use several lines of evidence to corroborate a climatic hypothesis and are from sites near an ecotone or in regions of extreme climate in all cases hydrologic setting mediates a lake s response to climate and must be considered in interpreting sedimentary sequences discussion of the impact of recent and future climatic changes necessitates a baseline against which the magnitude of observed or predicted changes can be measured commonly we look to recent history as a reference point for comparison however the landscape of recent decades or in some cases even centuries has been altered greatly by human activities thus to determine whether recent or future climatic change is unique or unusual we need long natural preanthropogenic time series against which observed or predicted climatic states and variability can be compared paleolimnological archives are a tool for looking at environmental patterns prior to anthropogenic impact and show a range of climatic states far greater than those documented by written records former strand lines of pluvial lakes bonneville and lahontan in the western u s for example testify to moisture extremes unsurpassed in recent centuries or even millennia in addition one can us the paleolimnological record as an independent climatic proxy against which patterns and rates of terrestrial response to climatic change can be compared here i present a broad overview of paleoclimatic reconstruction in north america from lacustrine records with a focus on the late quaternary the review is limited to climatic inference from paleolirnnological records a term i use in a restrictive sense to refer to records of past lake states physical biological and geochemical as opposed to records of past stream hydrology e g ely et al 1993 knox 1993 or terrestrial conditions i summarize paleolimnological tools available for reconstruction of past climate the capabilities and limitations of these tools

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

ecological thresholds and patterns of millennial scale climate variability the response of vegetation in greece during the last glacial period the regional expression of millennial scale climate variability during the last glacial is examined with particular reference to the vegetation response in greece inspection of three pollen records from contrasting bioclimatic areas suggests that differences in the magnitude of cold events as recognized in the north atlantic and western mediterranean are expressed in terms of tree population changes only in areas with a range of favorable habitats by contrast records from sites where populations approach their tolerance threshold do not appear to resolve differences in the amplitude of the climate oscillations understanding the importance of local factors in modulating the biological response to climate change is critical when attempting to establish the spatial pattern of millennial variability

a 2200 yr record of hydrologic variability from foy lake montana usa inferred from diatom and geochemical data abstract a 2200 yr long high resolution 5 yr record of drought variability in northwest montana is inferred from diatoms and 18o values of bio induced carbonate preserved in a varved lacustrine core from foy lake a previously developed model of the diatom response to lake level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data high frequency decadal fluctuations in the de trended 18o record mirror variations in wet dry cycles inferred from banff tree rings demonstrating the sensitivity of the oxygen isotope values to changes in regional moisture balance low frequency multi centennial isotopic changes may be associated with shifts in the seasonal distribution of precipitation from 200 b c to a d 800 both diatom and isotope records indicate that climate was dry and lake level low with poor diatom preservation and high organic carbon nitrogen ratios subsequently lake level rose slightly although the climate was drier and more stable than modern conditions at a d 1200 lake level increased to approximately 6 m below present elevation after which the lake fluctuated between this elevation and full stage with particularly cool and or wetter conditions after 1700 the hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake s outlet spectral analysis of the 18o data indicates that severe droughts occurred with multi decadal 50 to 70 yr frequency

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

late pleistocene climatic variations as recorded in two italian maar lakes lago di mezzano lago grande di monticchio abstract sediment profiles from two maar lakes lago di mezzano central italy and lago grande di monticchio southern italy were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20 000 yr of the last glaciation the chronological framework is provided by calibrated radiocarbon ages varve counting calculation of sedimentation rates and tephrochronology in the time slice between 34 000 and 14 000 cal bp periods of increased minerogenic input are observed in both lacustrine records interrupted by periods of low minerogenic input these cyclic variations have an average recurrence time of 1785 yr for lago di mezzano and 2875 yr for lago grande di monticchio comparing well with marine and ice core data explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff the higher precipitation evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from lago grande di monticchio show a contemporary development of steppe vegetation an indicator for cool dry climatic conditions this may be connected with a southward shift of the westerlies and a reinforced jet stream agreement of lacustrine data from italy with late pleistocene glacial events in central italy with events recorded in marine archives from the north atlantic heinrich events and with oxygen isotope data from greenland ice cores is interpreted as evidence for the late pleistocene climate in europe being influenced by north atlantic climatic forcing which may be related to dansgaard oeschger cycles

multidecadal drought and holocene climate instability in the rocky mountains time series analysis of a diatom inferred drought record suggests that holocene hydroclimate of the northern rocky mountains has been characterized by oscillation between two mean climate states the dominant climate state was initiated at the onset of the holocene ca 11 ka under this climate state drought was strongly cyclic recurring at frequencies that are similar to twentieth century multidecadal phase changes of the pacific decadal oscillation this pattern remained consistent throughout much of the midholocene continuing until ca 4 5 ka after this time the mean climate state changed and drought recurrence became unstable periods of cyclic drought alternated with periods of less predictable drought the timing of this shift in climate was coincident with widespread severe drought in the mid continent of north america overall the strongest periodicity in severe drought occurred during the mid holocene when temperatures in the northern rocky mountains were warmer than today

the response of nw iberian vegetation to north atlantic climate oscillations during the last 65 kyr pollen and oceanographic data from deep ocean core md95 2039 provide a centennial to millennial scale record of conditions offshore and of the vegetation of north west iberia for the period 10 65 ka the planktonic oxygen isotope record of this core reflecting predominantly sea surface temperature sst shows a pattern of millennial scale oscillations that is very similar to climatic changes recorded by the greenland ice core records over the same interval in turn tree populations show a pattern of rapid expansions and contractions that follow the pronounced and abrupt isotopic shifts recorded offshore through marine isotope stage mis 3 this millennial scale pattern of vegetation change alternating between steppe and open woodland is superimposed on a longer term pattern of shrinking ericaceous heathland and decreasing size of successive interstadial tree populations trees persisted during the last glacial maximum lgm at greater abundance than during many of the coldest episodes of mis 3 this agrees with the marine data which indicate that lgm sea surface temperatures here were significantly warmer than the minima recorded in mis 3 our combined marine terrestrial record together with data from nearby sequences provides a stepping stone between terrestrial sequences and the greenland ice core and north atlantic marine records this will permit a better understanding of the behaviour of vegetation across different regions at several scales of climatic forcing

paleolimnological response to millennial and centennial scale climate variability during mis 3 and 2 as suggested by the diatom record in les echets france a 27 m long sediment sequence retrieved from the central part of the les echets basin in france has been analysed in sub centennial resolution for biogenic silica and fossil diatom remains the sequence corresponds to the later part of marine isotope stage mis 3 and to most of mis 2 distinct changes in diatom productivity diversity and taxonomic composition between 36 2 and 31 7 kyr bp appear to relate to dansgaard oeschger do climate variability intervals characterized by low diversity productivity and small sized benthic diatom taxa are most likely a response to colder conditions in relation to do stadials in contrast higher diversity productivity and a high abundance of planktonic taxa indicate a response to warmer temperatures during do interstadials the time interval between 30 3 and 15 7 kyr bp is characterized by continuous low diatom productivity and a benthic dominated community with intermediate species richness suggesting a transition to more stable conditions three time intervals with extremely low concentrations of diatom valves 46 1 36 2 31 7 30 3 and 26 3 23 6 kyr bp overlap with ages reported for heinrich h events 4 3 and 2 we speculate that the lake at les echets suffered from severe ecological stress as a response to h events this is the first detailed study exemplifying the response of a lake based on diatoms to climate variability during late part of mis 3 and most of mis 2 in europe

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

centennial scale surface hydrology off portugal during marine isotope stage 3 insights from planktonic foraminiferal fauna variability 1 the marine isotopic stage 3 mis3 at ocean drilling program odp site 1060 gulf stream shows both sharp onset and end of interstadials the existence of very short lived warm events during stadials and points to differences in detail between the sea surface temperature sst record from the western north atlantic and the atmospheric temperature record inferred from 18o in greenland ice investigating mis3 and obtaining comparable data from other locations appears crucial the eastern atlantic provides well documented records of climate changes we have selected a core from off portugal and use it to examine dansgaard oeschger events d o at centennial scale resolution 139 years on average between two data points we have obtained a faunal data set for core md01 2444 37 n 10 w 2600 m water depth and use a group of species globigerina bulloides globigerinita glutinata as a proxy of upwelling intensity driven by trade winds intensity changes we tentatively relate the variation of this group to a north atlantic oscillation like phenomenon nao off portugal we observe that it resembles the rainfall index in the caribbean as recorded at odp site 1002 cariaco basin which traces the intertropical convergence zone itcz location through changes of terrigenous inputs the driest intervals itzc to the south at site 1002 correspond to intervals of increased upwelling in md01 2444 as well as the driest periods identified during stadials on similar cores in the area because the itzc to the south is consistent with an el nino southern oscillation enso situation our study suggests a positive correlation between enso like conditions and nao like conditions at a millennial timescale during interstadial intervals when increased wetness over cariaco is recorded itcz to the north and the upwelling in md01 2444 is decreased we see from both ssts and faunal tropical indicators that md01 2444 site is warm in addition interstadials are equally warm through each so called bond cycle this contrasts with the greenland ice core project grip record where interstadial peaks are successively cooler through each bond cycle this record confirms a link between tropical climate linked to itcz position and the climate of southern europe at millennial timescales in spite of showing a very good correlation with polar latitudes grip through 18o on globigerina bulloides in addition because the warmest ssts and the 18o on g bulloides are so remarkably different our work points to changes in seasonality as a strong control over the climatic pattern of the north atlantic area and the marked influence of winter conditions

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

methane seepage effects on biodiversity and biological traits of macrofauna inhabiting authigenic carbonates abstract authigenic carbonate rocks at methane seeps are recognized as hosting diverse and abundant invertebrate assemblages with potential forcing from fluid seepage and hydrography mensurative studies of carbonate macrofauna 0 3 mm at hydrate ridge or revealed little effect of water depth and overlying oxygenation at 600 m and 800 m but a large influence of seepage activity on density taxonomic composition diversity and biological traits feeding lifestyle motility size and calcification rocks exposed to active seepage had 3 4 higher total macrofaunal densities than under inactive conditions assemblages exhibited higher species richness and reduced evenness greater dominance under active seepage than inactive conditions but no difference in h or rarefaction diversity actively seeping sites were characterized by errant motile bacterial grazing small and medium sized heavily calcified species whereas inactive sites exhibited a greater diversity of feeding modes and more burrowers sessile large and lightly calcified species active rocks supported more exogonid syllidae ampharetid and cirratulid polychaetes provannid snails pyropeltid limpets nemerteans and sponges whereas inactive rocks supported higher densities of ophiuroids isopods gammarid amphipods hydroids typosyllis syllidae and tanaids transplant experiments in which rocks were transferred between active and inactive sites at hydrate ridge north 600 m revealed that assemblages respond within 13 months to increase or cessation of seepage taking on the feeding size and calcification characteristics of the background fauna at the new site lifestyles and motility patterns shifted more slowly as the sessile attached species did not track seepage as quickly provannid snails and pyropeltid limpets rapidly colonized rocks transplanted to active sites and disappeared when transplanted to inactive sites given the known variability of fluid fluxes and rapid community response a mosaic of communities changing in space and time is hypothesized to generate the relatively high species diversity at methane seeps

submillennial environmental fluctuations during marine oxygen isotope stage 2 a comparative analysis of diatom and pollen evidence from lago grande di monticchio south italy high temporal resolution pollen and diatom analyses carried out on sediments from lago grande di monticchio span the interval 23 700 21 200 calendar yr bp a brief interstadial during marine oxygen isotope stage 2 both records exhibit marked changes that are interpreted as responses to climatic changes the diatoms and terrestrial vegetation appear to respond at the same time any relative lag in the response of the vegetation was less than the ca 60 yr resolution of the two records the interval coincides at least in part with the campo imperatore stade when the gran sasso ice sheet reached its maximum extent and water level was high in the fucino lake correlation of the marked environmental oscillation with one of the dansgaard oeschger events recorded by stable oxygen isotope records from the greenland ice cap is proposed this follows an interval interpreted as having a cold dry climate and correlated with a heinrich event in the north atlantic together the two records enable a multifactorial interpretation of the palaeoclimate changes that characterise the oscillation providing additional insight to that obtained from studies of ice and ocean sediment cores especially with respect to the seasonality of temperature and precipitation copyright 1999 john wiley sons ltd

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

diatom shifts as evidence for recent subarctic warming in a remote tundra lake nwt canada abstract changes in diatom assemblage composition were examined from the sediments of slipper lake an isolated tundra lake located 50 km north of current treeline in canada s northwest territories diatom shifts over the last ca 5600 years were related to the response of this ecosystem to climatic and environmental change during the late holocene with particular emphasis on the last few hundred years to date a detailed diatom analysis for this recent time frame has not been undertaken for the central canadian subarctic the first ca 5400 years of the sediment record was marked by modest shifts between benthic alkaliphilous diatom taxa e g fragilaria achnanthes and navicula species and heavily silicified tychoplanktonic aulacoseira species in the 19th century abrupt changes were delineated by a marked shift to a diatom assemblage characteristic of more planktonic habitats consisting of the cyclotella stelligera complex c stelligera c pseudostelligera which was absent in earlier sediments several possible mechanisms for these recent changes are examined including atmospheric deposition of acidifying compounds and anthropogenically derived nutrient enrichment however we conclude that climatically induced limnological changes associated with shorter duration of ice cover and a longer growing season can best explain the direction and magnitude of changes in our diatom record

rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka we present a high resolution and independently dated multiproxy lake sediment record from the paleolake at les echets in southeastern france that displays synchronous changes in independent limnic and terrestrial ecosystem proxies in concert with millennial scale climate oscillations during the last glacial period distinct lake level fluctuations low lake organic productivity and open treeless vegetation indicate cold and dry conditions in response to heinrich events alternating phases of higher and low lake organic productivity stratified surface waters and long lasting lake ice cover decreased or increased catchment erosion and tree dominated or herb dominated vegetation resemble dansgaard oeschger interstadialstadial variability transitions between different ecological states occurred in as little as 40 230 yr and seem to have been controlled by the position of the polar front ecosystem response after 30 ka suggests that local climate conditions became more important our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with dansgaard oeschger and heinrich events and that regional factors modulated ecosystem response

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

geochronological osl and geomorphological investigations at the presumed frankfurt ice marginal position in northeast germany abstract the weichselian frankfurt ice marginal position in northeast germany has been critically discussed in the past owing to weak morphological evidence and a lack of clear sedimentological records this study aims to contribute to this discussion with new geochronological and geomorphological results apart from very few cosmogenic exposure ages the time frame is to date still based on long distance correlation with radiocarbon chronologies we selected a study site in a key position regarding the classic location of the frankfurt ice marginal position and the recently described arcuate ridge structures on the barnim plateau for the first time we present optically stimulated luminescence osl ages of quartz from glaciofluvial deposits for this weichselian phase our results indicate an advance of the scandinavian ice sheet sis at around 34 1 4 6 ka this is in agreement with osl ages from sandur deposits at the brandenburg ice marginal position located farther south and could also be correlated with the klintholm advance in denmark the subsequent meltdown phase lasted until around 26 3 3 7 ka during the meltdown phase a minor oscillation of the sis caused the formation of the recently described arcuate ridges on the barnim till plain recalculated surface exposure ages of glacigenic boulders with an updated global production rate indicate a landscape stabilization phase at around 22 7 1 6 ka which is in agreement with our ages a phase of strong aeolian activity has been dated with osl to 1 0 1 ka this may have been triggered by human activities that are documented in this region for the medieval period

the origin of small scale geochemical and mineralogic variations in a granite intrusion a crystallization and mixing model a post tectonic unzoned granite intrusion in the meatiq dome a late proterozoic metamorphic complex in the central eastern desert of egypt shows significant chemical and mineralogic heterogeneity on the scale of sampling 5 kg whole rock analyses of 21 samples indicate small variations in sio2 al2o3 na2o and k2o and larger systematic variations in the less abundant major elements such as feo tio2 cao mno and mgo and trace elements such as sc cr co rb sr zr la ce nd sm tb yb lu ta th and u these variations cannot be accounted for by processes such as marginal accretion assimilation alteration by late stage fluids or multiple intrusion instead we proposed a model involving 35 percent solidification of the granite magma followed by partial solid liquid segregation during emplacement resulting in rocks containing 7 71 volume percent early formed solids such randomly distributed local segregation could have been caused by filter pressing flow differentiation and possibly gravity segregation either singly or in combination thus each sample is interpreted as a mixture of two end members with nearly constant compositions an early formed solid assemblage of crystals and a complementary residual liquid early formed solids are enriched in tio2 feo cao p2o5 sc co cr sr la ce and depleted in sio2 rb yb lu ta th and u while the residual liquid has complementary enrichments and depletions this simple mixing model is consistent with field and petrographic observations experimental studies pertaining to the crystallization sequence in the system ab or qtz h2o at 1 kb and physical properties of silicic magmas furthermore it is quantitatively supported by trace element data for minerals computed endmember compositions at 35 crystallization using mineral analyses and reasonable kd values and internal consistency in the percent solid for each sample computed from each of 17 elements in the inferred end members we suggest that this model might also apply to other small epizonal granite intrusions that show small scale chemical heterogeneities

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

laboratory investigations of viscous effects in replenished magma chambers abstract some laboratory experiments are described which investigate the dynamical effects of replenishment of a magma chamber containing high viscosity magma by hotter denser and much more fluid magma in the experiments a layer of hot kno3 solution is emplaced beneath cold glycerine which has a viscosity 3000 times greater less dense fluid is released immediately and continuously from the interface as a result of crystallization in the lower layer and rises as plumes through the overlying glycerine further crystallization occurs in the plumes and the crystals fall out but there is little mixing between the two fluids and a layer of depleted kno3 solution forms at the top the experiments demonstrate that interfacial processes begin to dominate where there are large viscosity differences between adjacent fluid layers as would be the case in a rhyolitic magma chamber replenished by basaltic magma

extensional pluton emplacement models do they work for large plutonic complexes shallow crustal to mid crustal magma emplacement models commonly rely on local or regional extension to solve the room problem we argue that existing extensional models explain the emplacement of sheeted dike complexes or internally layered plutons but are not as easily reconciled with the emplacement of elliptically shaped plutons or batholiths for the following reasons 1 rock strengths and crustal stresses prevent large voids from existing at depth and therefore require wall rock extension to be balanced by magma influx 2 rates of extension are controlled by fault slip rates of millimetres to centimetres per year and thus require numerous small injections of magma and 3 because of their sheetlike shapes and small thicknesses these small magma injections will cool rapidly and form sheeted plutons or dike swarms extension may however facilitate emplacement of elliptically shaped plutons in concert with other mechanisms if certain kinematic constraints are satisfied

diatom responses to limnological and climatic changes at ribains maar french massif central during the eemian and early wurm abstract high resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at ribains maar french massif central during the late pleistocene 131 105 ka bp with a focus on the eemian interglacial in particular numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation as represented by pollen data diatom based quantitative reconstructions of the past limnological conditions as well as a comprehensive literature review on the auto ecological requirements for the principal diatom taxa were used to interpret the record an absolute time scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in italian stalagmites this study shows that at ribains maar the transition from the riss saalian glacial to the eemian interglacial was marked by a gradual increase in the contribution of spring blooming diatom species indicating a longer growing season and milder winter spring conditions at that time a short cooling event interrupts this trend and may correspond to a stadial at the start of the eemian a peak in benthic taxa and the suppression of spring blooming flora probably reflects the effects of deglaciation on the catchment during the eemian interglacial itself three main phases were distinguished within the diatom record the first phase 8000 years in duration was dominated by stephanodiscus minutulus which suggests that intense mixing in the water column took place during spring the pollen record was simultaneously dominated by quercus and corylus that typify this phase as the climatic optimum of the eemian the second phase almost equal in duration to the first phase 7000 years is generally dominated by cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase in the pollen diagram this corresponds to an interval dominated by carpinus picea abies that indicates a cooler and wetter climate the third and last phase of the eemian 2000 year long saw the return to stephanodiscus dominated assemblages indicating a warming that may correspond to the dansgaard oeschger event 25 identified in the greenland ice core record in the early stage of the wurm glacial weichselian assemblages in the melisey i stadial 3000 year long were dominated by either aulacoseira subarctica or asterionella formosa which suggest colder spring conditions than during the late eemian but not as cold as the ones indicated by the pollen record stephanodiscus spp again dominate during the saint germain ia interstadial 5000 year long suggesting a return to the conditions that prevailed before the melisey stadial in agreement with the pollen record the record ends with the montaigu cold event which is characterised by a pinus peak in the pollen record and corresponds to a large abundance of a subarctica in the diatom sequence throughout the eemian the abundance of stephanodiscus spp which is thought to be driven by winter conditions show cyclic fluctuations that most likely match the cooling events identified in a pollen record from germany variation in insolation throughout the eemian may have been the driving factor behind the species succession observed in the diatom sequence while this study demonstrates that diatom analysis of lake sediment can provide very detailed information on long term climate change a review of the few other diatom investigations published on european eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern europe

mixing between granitic and dioritic crystal mushes guernsey channel islands uk abstract the contact zone between the cobo granite and bordeaux diorite complex of guernsey channel islands uk displays numerous features which result from the interaction of these two penecontemporaneously emplaced intermediate to felsic magmas initial interaction resulted in the formation of chilled mafic enclaves in granite magma as thermal equilibrium was approached some physical mixing took place to produce a heterogeneous marginal facies continued interaction resulted in incorporation of previously mixed magma into intruding magma the early mixed material is locally preserved as enclaves but more commonly underwent disaggregation promoted by its incompletely crystallised nature the mineral components becoming distributed as xenocrysts and often as microenclaves or glomeroxenocrysts into surrounding magma further modification within the contact zone was brought about by the infiltration of melt through the interconnected pore space of the magma mushes on the scale of centimetres to hundreds of metres these processes produced geochemical profiles which do not exhibit perfect mixing trends the petrographic and geochemical features described not only demonstrate the efficacy of mixing between partially crystallised magma mushes of broadly similar composition but also provide criteria by which such interaction may be recognised elsewhere many features in particular mineral scale disequilibria and small scale modal heterogeneity bear striking similarities to those which occur widely in granite plutons where obvious evidence for magma mixing is absent as such it is possible that many granite bodies preserve a subtle record of hitherto overlooked mixing events

late glacial to holocene climate change and human impact in the mediterranean the last ca 17ka diatom record of lake prespa macedonia albania greece lake prespa macedonia albania greece occupies an important location between mediterranean and central european climate zones although previous multi proxy research on the late glacial to holocene sequence core co1215 320 cm ca 17 cal ka bp to present has demonstrated its great value as an archive of quaternary palaeoclimate data some uncertainty remains in the interpretation of climate change with the exception of oxygen stable isotope data previous palaeolimnological interpretation has relied largely on proxies for productivity here existing interpretation is strengthened by the addition of diatom data results demonstrate that shifts in diatom assemblage composition are driven primarily by lake level changes and thus permit more confident interpretation of shifts in moisture availability over time while corroborating previous interpretation of catchment and climate induced productivity shifts an inferred cold arid shallow lake phase between ca 17 1 and 15 7 cal ka bp is not only followed by a high productivity phase from ca 15 7 cal ka bp with late glacial warming but also is the first evidence for a gradual increase in lake level in line with other regional records clear evidence for a younger dryas climate reversal between ca 13 1 and 12 3 cal ka bp is followed by an unusually gradual transition to the holocene and deeper oligotrophic mesotrophic lake conditions are reached by ca 11 0 cal ka bp in contrast to the arid episode from ca 10 0 to 8 0 ka inferred from positive 18 ocalcite values rapid diatom inferred lake level increase after the start of the holocene suggests high moisture availability in line with palynological evidence but with only very subtle evidence for the impact of an 8 2 ka cold event the maintenance of high lake levels until 1 9 cal ka bp and the peak of inferred humidity from ca 7 9 to 6 0 cal ka bp matches the oxygen stable isotope profile and confirms that the latter is driven primarily by evaporative concentration rather than reflecting regional shifts in precipitation sources over time during the late holocene progressive eutrophication is inferred between 1 9 and present two shallow phases at ca 1 0 cal ka bp and at ca 100 years ago probably represent an aridity response which is added to increase human impact in the catchment overall the study is important in confirming previous tentative inferences that late glacial to holocene moisture availability has strong affinity with other sites in the eastern mediterranean it also tracks the pattern of north atlantic forcing

the last climatic cycle at la grande pile vosges france a new pollen profile a new pollen diagram has been made from an old unanalyzed core from la grande pile gp xx correlations with the previous work of woillard 1975 1978 leads to the following conclusions the end of the eemian was marked by a minor climatic change prior to the melisey i stadial the ognon ii and ognon iii interstadials are not consistent and correspond to the level of reworking of mesophilous taxa during the last pleniglacial the limitations of the botanical interpretation of pollen spectra from the last pleniglacial are underlined lastly bruckenthalia and larix are identified for the first time at la grande pile the respective roles of these taxa following the eemian are additional arguments for correlating the st germain i and ii with the early weichsel interstadials in the north of middle europe

a compilation of western european terrestrial records 60 8 ka bp towards an understanding of latitudinal climatic gradients terrestrial records of past climatic conditions such as lake sediments and speleothems provide data of great importance for understanding environmental changes however unlike marine and ice core records terrestrial palaeodata are often not available in databases or in a format that is easily accessible to the non specialist as a consequence many excellent terrestrial records are unknown to the broader palaeoclimate community and are not included in compilations comparisons or modelling exercises here we present a compilation of western european terrestrial palaeo records covering entirely or partially the 60 8 ka intimate time period the compilation contains 56 natural archives including lake records speleothems ice cores and terrestrial proxies in marine records the compilation is limited to include records of high temporal resolution and or records that provide climate proxies or quantitative reconstructions of environmental parameters such as temperature or precipitation and that are of relevance and interest to a broader community we briefly review the different types of terrestrial archives their respective proxies their interpretation and their application for palaeoclimatic reconstructions we also discuss the importance of independent chronologies and the issue of record synchronization the aim of this exercise is to provide the wider palaeo community with a consistent compilation of high quality terrestrial records to facilitate model data comparisons and to identify key areas of interest for future investigations we use the compilation to investigate western european latitudinal climate gradients during the deglacial period and despite of poorly constrained chronologies for the older records we summarize the main results obtained from nw and sw european terrestrial records before the lgm

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

rock magnetic detection of distal ice rafted debries clue for the identification of heinrich layers on the portuguese margin abstract high resolution measurements of concentration and grain size dependent magnetic parameters along a sedimentary sequence deposited on the portuguese margin 38 n during the last 120 ka allowed the detection of multiple thin layers slightly enriched by a coarse lithogenic fraction sizes mineralogy shapes and mode of deposition identify the material as ice rafted detritus ird the four most recent events dated by calibrated radiocarbon ages are contemporaneous with heinrich events he1 he4 older events can be identified as he5 he6 or with minor ird that occurred during stage 5 the resolution and sensitivity obtained with rock magnetic methods enable the detection of multiple secondary events showing that iceberg delivery was a frequent phenomenon directly linked to temperature variations over ice caps heinrich events representing the extreme cases

mixing basaltic and dacitic magmas by forced convection although magma mixing is an old concept which has been applied to many magma types recent petrographic studies have revived interest in the theory by suggesting that it may account for the origin of calk alkaline magma1 6 and mid ocean ridge basalt7 9 there has been no previous experimental investigation into how two magmas with different properties can mix to form a homogeneous magma of andesitic composition or to produce textures such as observed in banded dacite we present here the results of experiments demonstrating that basaltic and dacitic magmas can be easily mixed by forced convection to form both banded dacite and homogeneous andesite in less than a few hours

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

timing of the late vistulian weichselian glacial phases in poland abstract the lower vistula region in northern poland is a stratotype area for the vistulian weichselian glaciation and during last glacial maximum lgm the southernmost extension of the scandinavian ice sheet occurred in western poland and in eastern germany reinterpretation of the available geochronological data radiocarbon 36 cl and 10 be ages supplied with new field geological evidence mostly for the late vistulian ice sheet limits and movement directions was focused in three key regions in poland during the late middle vistulian there was one or two ice sheet advances in the lower vistula region the late vistulian maximum ice sheet limit in poland was time transgressive and occurred at 24 19 kyrs bp generally the younger to the east ice sheet limits during the leszno phase occurred at 24 cal 10 be 36 cl kyrs the poznan phase ice sheet limit was dated to 19 10 be 36 cl kyrs and the pomeranian phase ice sheet limit about 16 17 10 be 36 cl kyrs every late vistulian glacial phase in poland was preceded by an ice sheet retreat

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

millennial scale oceanic climate variability off the western iberian margin during the last two glacial periods high resolution palaeoclimate records recovered from the iberian margin in core md95 2040 exhibit large fluctuations in oceanographic conditions over the last 190 ka large scale cooling of the surface ocean is indicated by the presence of the polar planktonic foraminifer neogloboquadrina pachyderma sinistral and in some instances the occurrence of ice rafted debris ird ice rafting episodes were prevalent in both of the last two glacials with greater intensity in stages 2 through 4 than in stage 6 the six youngest heinrich events are well defined during the last glacial but detrital carbonate is absent from heinrich layers hl6 hl5 and hl3 dansgaard oeschger stadial equivalent sub millennial ird deposition events have been detected in particular during stage 3 allowing a good match with the cooling displayed in the greenland ice core gisp2 sea surface temperature off portugal in stage 6 was in general warmer than during the last glacial pointing towards a weaker southward influence of polar water masses ice rafting occurred mainly in mid mis marine isotope stage 6 between 173 and 153 kyr as a group of poorly differentiated short duration quasi continuous events mainly marked by the high abundance of sinistral n pachyderma differences exist in ird composition relative to the last glacial with a reduced canadian derived detrital carbonate component combined with an important contribution of volcanic particles the lower magnitude and higher frequency of these events suggest that the higher temperatures would have induced iceberg waning closer to the source areas

microstructural evidence of orders of crystallization in granitoid rocks experimental melting studies of granitoid rocks have documented variations in the order of crystallization of minerals depending on the melt composition total pressure and the activity of water and other volatiles in the melt microstructural criteria for independent determination of the order of crystallization are needed to permit application of the experimental data to the evaluation of the conditions of crystallization unfortunately few criteria can be reliably applied to infer either the order of initial crystallization on the order in which minerals cease to crystallize in granitoid rocks most microstructures of granitoid rocks record simultaneous rather than sequential crystallization of minerals grain size criteria e g phenocrysts vs groundmass can be used to infer a partial order of crystallization in many volcanic rocks but the presence of extremely large phenocrysts of k feldspar that from experimental data must be the last mineral to crystallize highlights the dangers inherent in the use of grain size criteria providing it can be determined that included minerals did not form subsequently along cracks or from entrapped melt inclusions those inclusions that are demonstrably and consistently only near the centre of large grains must have ceased to crystallize before the host mineral where the host mineral occurs only as rims on the early formed mineral it is possible to infer both the order of cessation and initiation of crystallization common examples are provided by the rimming produced by a discontinuous reaction relationship most other examples of inclusion relationships could result from simultaneous crystallization microstructures involving moulding and impingement relationships are unreliable as the microstructure is produced only after the minerals have begun to crystallize in the melt or on the melt solid interface as most minerals continue to crystallize right to the solidus they cease to crystallize simultaneously new criteria perhaps involving detailed chemical zoning patterns need to be developed before the orders of crystallization can be reliably determined for granitoid rocks

climate induced changes as registered in inorganic and organic sediment components from laguna potrok aike argentina during the past 51 ka total organic carbon total inorganic carbon biogenic silica content and total organic carbon total nitrogen ratios of the laguna potrok aike lacustrine sediment record are used to reconstruct the

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints