evidence of lateglacial and holocene climatic change and human impact in eastern anatolia high resolution pollen charcoal isotopic and geochemical records from the laminated sediments of lake van turkey annually laminated sediments from lake van spanning about 13000 varve years were sampled for stable isotopic geochemical pollen and charcoal analyses in order to find evidence of past regional climatic changes and human impact in the semi arid region of eastern anatolia turkey the lateglacial period was cold and dry with steppe vegetation and saline lake water during the younger dryas the lake level dropped dramatically and the vegetation turned to a semi desert geochemical and isotopic records indicate a strong increase in moisture at the onset of the holocene and artemisia chenopod steppes were partly replaced by grass steppe and pistachio scrub a delay of about 3000 years in the expansion of deciduous oak woodlands and high steppe fire frequencies suggest dry spring and summer weather during the early holocene at 8200 yr bp a shift in the regional climate regime facilitated the transport of more moisture into the interior areas of the taurus mountains and caused a change in the seasonal distribution of precipitation the steppe forests dominated by quercus advanced and reached their maximum extention at about 6200 yr bp all the proxy data indicate optimum climatic conditions low water salinity and high lake level between 6200 and 4000 yr bp after 4000 yr bp aridity increased again and the modern climatic situation was established human impact in the catchment of lake van started at 3800 yr bp and was intensified during the last 600 years

improved age modelling approaches as exemplified by the revised chronology for the central european varved lake soppensee abstract one of the key factors in understanding past climate change is the development of robust age models that have sufficient chronological precision for comparing different palaeoclimate archives while retaining accuracy recent developments in bayesian age modelling are applied here to the swiss varve lake soppensee we develop revised age models for this sequence using the available stratigraphic information to constrain the calibrated radiocarbon ages we begin by using stratigraphical order as the only constraint and then sequentially increase the information incorporated into the model using relative varve age sample depth and varying depositional models within this bayesian framework we develop internally robust models that significantly improve the dating precision and are applicable to both varved and non varved sequences we then compare the model output to wider chronological information such as the age of the laacher see tephra in order to test the model accuracy the results of this exercise suggest that these methods can be used to build very reliable improved age models in a variety of records

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

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

evolution and environmental impacts of the eruption of laacher see volcano germany 12 900 a bp abstract laacher see volcano lsv 40 km south of bonn explosively erupted ca 6 3 km 3 of chemically strongly zoned phonolite magma probably during spring 12 900 years ago the resulting eruption column having reached at least 20 km in height the bulk of the laacher see tephra lst was deposited east of the volcano within the neuwied basin lst ashes form the most important stratigraphic marker in lateglacial deposits over much of central europe a minimum of 2 mt total s was calculated to have been released during the eruption by comparing pre and posteruptive volatile concentrations in glass inclusions and pumice matrix glasses because a separate s bearing vapor phase was probably present in the magma prior to eruption as indicated by the high melt h 2 o contents close to saturation level the actual amount of s released during the eruption could have significantly exceeded 2 mt the sulfuric acid aerosol layer resulting from the massive stratospheric s input probably resided in the stratosphere for years and most likely had a significant impact on climate and thus the environment increased precipitation in central europe and or impairment of the vegetation cover for several years is suggested by several proxies especially increased sediment supply into lakes proximal to the eruptive center major environmental impacts include an initial blast that felled trees up to 4 km away from vent fast deposition of huge tephra volumes led to the complete disruption of rhine river within the lower neuwied basin and the damming up of a lake ca 140 km 2 in areal extent sudden collapse of the temporary tephra dam caused a catastrophic flood wave downstream whose deposits are recognized as far north as bonn reworking of unconsolidated tephra deposits over several 100 km 2 was widespread and extensive generating abundant lahars and flood plain deposits a braided river system established in neuwied basin probably persisted up to several years recent reports for a second eruption of lsv are not confirmed

the disturbance regime of an early holocene swamp forest in the czech republic as revealed by dendroecological pollen and macrofossil data abstract a unique remnant of forest dating back to the period 9733 7897 yr bc and consisting of hundreds of tree bases was discovered in the czech republic we aimed to reveal the complex disturbance history of this sub fossil forest using dendrochronology and to describe its detailed plant species composition changes using palaeobotanical techniques analysing such early holocene forest dynamics should help us understand the ability of the forest community to actively adapt to climate change and generally to understand the role of dynamic instability in ecosystem evolution we anatomically identified woody species in 488 samples and determined the ages growth suppressions releases and fire scars in 116 well preserved tree ring series using a modern boundary line approach this image of the forest structure and dynamics was supplemented with analyses of pollen spectra and plant macrofossils in excavated profiles in order to achieve accurate dating we dated 87 samples using 14c and synchronized tree ring series and compared them with an existing pinus sylvestris chronology the developmental trajectory of the forest was unique and did not match the general trend of postglacial pine growth in central europe palaeobotanical proxies indicated that during the circa 2000 years the forest persisted this early holocene ecosystem passed through several phases reflected in the species composition of the vegetation as well as in habitat conditions nevertheless the dominance of pine and the complex fine scale disturbance regime were relatively robust and did not change fundamentally low severity fires and short term changes in soil moisture regime were crucial disturbance agents in the ecosystem stand replacing disturbances were not found up to the gradual collapse of the forest around 8300 yr bc replaced by a swamp community the disturbance regime was relatively stable suggesting a mitigating effect of changing climate due to the predominance of pine in the forest

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

environmental and climatic conditions at a potential glacial refugial site of tree species near the southern alpine glaciers new insights from multiproxy sedimentary studies at lago della costa euganean hills northeastern italy abstract it has been hypothesized that refugia of thermophilous tree species were located in northern italy very close to the alps though this hypothesis has yet to be tested thoroughly in contrast to central and southern italy with its relative wealth of data only a few fragmentary records are currently available from northern italy for the last glacial wurm weichselian our new study site lago della costa lies adjacent to the catchment of the megafans of the alpine forelands and the braided rivers of the northeastern po plain that have so far inhibited the recovery of continuous glacial and late glacial records we analyze pollen plant macrofossils charcoal and ostracods to reconstruct the vegetation fire and lake history for the period 33 000 16 000 cal bp we compare our data with glacial records from southern europe to discuss similarities and dissimilarities between these potential refugial areas a comparison with independent paleoclimatic proxies allows to assess potential linkages between environmental and climatic variability new macrofossil and pollen data at lago della costa unambiguously document the local persistence of boreal tree taxa such as larix decidua and betula tree species around the study site during the last glacial the regular occurrence of pollen of temperate trees in the organic lake sediments fine detritus calcareous gyttja suggests that temperate taxa such as corylus avellana quercus deciduous tilia ulmus fraxinus excelsior carpinus abies alba and fagus sylvatica most likely survived the last glacial maximum lgm at favorable sites in the euganean hills the percentage values of temperate trees are comparable with those from southern europe e g monticchio in southern italy we conclude that the euganean hills were one of the northernmost refugial areas of temperate taxa in europe however the relative and absolute abundances of pollen of temperate trees are highly variable pollen inferred declines of temperate tree communities e g quercetum mixtum and low ostracod inferred water levels at lago della costa correspond to the cold heinrich events h 2 lgm 23 000 19 000 cal bp and h 3 around 28 000 cal bp as recorded in the marine sediments of the north atlantic similar patterns of significant temperate tree population collapses during cold heinrich events are recorded at southern mediterranean sites e g monticchio and the alboran sea these findings suggest close linkages between northern atlantic and south central european climates during the past glacial

implications of the mechanical and frictional behavior of serpentinite to seismogenic faulting the widespread occurrence of serpentinite along major strike slip seismogenic faults warrants systematic investigation to determine how its frictional characteristics may affect slip along the fault different locations along the motagua fault zone in guatemala were sampled to investigate the sliding mode as a function of composition and texture confining pressure and displacement rate air dried right circular cylinders 7 1 cm in length and 3 3 cm in diameter with a precut 35 to the cylinder and load axes were deformed at confining pressures up to 200 mpa room temperature and displacement rates of 10 4 and 10 7 cm s compositional analyses of specimens cored from five blocks of serpentinite that were tested show that the serpentinite can be divided into two groups one is a mesh textured serpentinite containing up to 70 serpentine mostly lizardite 11 enstatite phenocrysts 19 oxides and minor amounts of olivine and carbonate undifferentiated the other is a flare textured serpentinite containing up to 84 serpentinte mostly antigorite 10 oxides 6 magnesite and dolomite and almost no enstatite or olivine the flare serpentinite undergoes the transition from stable sliding to stick slip sliding at confining pressures as low as 10 mpa the mesh serpentinite results only in stable sliding up to confining pressures of 200 mpa and a displacement rate of 10 4 cm s at a displacement rate of 10 7 cm s only one of the three mesh blocks exhibits stick slip the shear stress required to initiate sliding for the flare textured serpentinites is given by 0 77 n for the mesh textured serpentinites at a displacement rate of 10 4 cm s it is given by 0 56 n and at a displacement rate of 10 7 cm s by 0 50 n differences in fracture strength between the five specimen blocks correlate with differences in frictional strength differences in the sliding behavior and in the deformation observed along the sliding surfaces can be related to the mineralogical components of each serpentinite type extensive deformation occurs in the mesh serpentinites as a result of hard oxide and enstatite indenters ploughing through a soft lizardite substrate lizardite lizardite contacts prevail and these deform by plastic flow the stick slip behavior in the flare textured serpentinites is explained by brittle failure of antigorite antigorite contacts the smaller grain size of the flare serpentinites relative to the mesh serpentinites may also contribute to the higher frictional strength of the flare serpentinites we discuss the implications of the antigorite rich flare textured serpentinite to seismogenic faulting in particular we consider the case of antigorite forming by shear heating induced progressive metamorphism of lizardite chrysotile serpentinites if serpentine dehydration temperatures are approached talc may form having a lower coefficient of friction than serpentine talc may act as a lubricant along the fault plane

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

rapid changes in ocean circulation and atmospheric radiocarbon a latitude depth coupled global ocean ice atmosphere model is extended to include a simple biosphere component a physically reasonable adjustment of runoff into the north atlantic is invoked to achieve a transient response to glacial meltwater perturbations which closely resembles the younger dryas climate event we then investigate the evolution of the isotopic ratio of atmospheric radiocarbon 14c due to the rapid changes of deep ocean circulation when the north atlantic branch of the conveyor belt circulation is interrupted the oceanic uptake of radiocarbon is reduced resulting in an increase of atmospheric 14c by about 35 the reduction of ventilation in the north atlantic is partly compensated by an increase of the 14c ratios of the biosphere the southern ocean and the upper ocean above 1000 m depth a plateau of the 14c year calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years it is hence significantly shorter than that found by analyzing tree rings during the termination of younger dryas longer than 400 years a sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150 300 years if changes of pco2 or sea ice coverage are taken into account

a model for the development of crenulations in shear zones with applications from the southern appalachian piedmont abstract two sets of crenulations are associated with a major alleghanian dextral shear zone which deformed stratigraphic and structural boundaries in the eastern piedmont of south carolina both sets of crenulation planes are oblique to the boundaries of the shear zone the morphologies and orientations of the crenulation sets and their spatial distributions indicate that they are related to slip along foliation planes and that they serve to compensate for displacement components of foliation slip normal to the overall movement direction in the shear zone the crenulations act to maintain the initial thickness of the shear zone our evaluation of the recent literature on shear zones suggests that crenulations related to foliation slip are abundant and constitute a reliable sense of shear indicator

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

domainal failure of serpentinite in shear zones state line mafic complex pennsylvania u s a abstract deformation within 0 2 1 4 km wide dextral strike slip shear zones in the serpentinite portion of the state line mafic complex pennsylvania maryland is partitioned into two types anastomosing throughgoing mylonitic faults experienced a long relatively simple deformational history of unidirectional dextral transcurrent shearing the relatively less deformed lenticular shaped areas between these faults deformed in a complex sequence of faulting the lenticular pods contain early e striking extensional veins and brittle reverse faults with north strikes northeast striking dextral strike slip faults deformed the veins and reverse faults east striking shear bands developed in both the throughgoing faults and the mylonitic dextral faults within the lenticular pods northwest striking sinistral strike slip faults transected the lenticular pods and earlier faults the sinistral mylonites formed shear bands late in their movement history a similar sequence of faulting occurred in microscopic lenticular pods within mylonitic serpentinite these faults exhibit the same orientation and sequence as their larger counterparts but are clearly not synchronous with them each lenticular pod may have acted as a separate system and therefore like faults between pods of any size may not have been synchronous

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

high resolution climate signals in the bolling allerod interstadial greenland interstadial 1 as reflected in european tree ring chronologies compared to marine varves and ice core records abstract lateglacial and holocene tree ring chronologies are unique archives which provide various information on past environments on a true annual time scale changes in ring width can be related to past climate anomalies and dendrodated wood provides an ideal source for radiocarbon calibration we present a 1051 year tree ring chronology from the late glacial built from subfossil scots pines pinus sylvestris that grew in different regions of central and southern europe through a series of high precision radiocarbon measurements we obtained a floating radiocarbon chronology which allowed accurate wiggle matching to the intcal98 calibration curve the trees show a coherent pattern in ring width variations throughout central europe and extending into the mediterranean which indicates a strong external climatic factor most probably temperature during the growing season we identified major growth events which appear synchronous with events seen in isotopic and tracer signals in the greenland ice cores and with changes in the strength of upwelling in the cariaco basin

experimental constraints on the chemical evolution of large icy satellites abstract we derive experimental constraints on the interior structure and mineralogy of large icy satellites by reacting material of chondritic chemistry with water at a pressure of 1 5 gpa temperatures between 300 c and 800 c and a range of oxygen fugacities our results document the existence of three chemical processes that probably occur in large icy satellites as a result of high pressure hydrothermal processing 1 the formation of low density hydrated silicates 2 the alloying of iron and sulfur to form fes dominated cores and 3 the instability of organic material relative to carbonates we construct new internal models of the thermal and structural state of ganymede and infer that the magnetic field of this body arises from convection within a mostly iron sulfide core simple thermochemical calculations are conducted to further explore the likely effects of composition and oxygen fugacity on the high pressure chemistry undergone by organic material within icy satellites both experimental and calculated results show that primordial organics are likely to have been largely oxidized to carbonates through hydrothermal processing early in ganymede s history potentially sterilizing ganymede s h 2 o layer

mantle phase transitions and postglacial rebound the short term response of a univariant or divariant isochemical phase boundary to a pressure change is studied the pressure change can be caused by vertical displacement of material in response to surface loading the aim is to determine if the density discontinuity is nonadiabatic i e will affect fluid flow or adiabatic for the basic state both a quasi static mantle with a smooth thermal structure in the transition region and the case of a steady convection current through the boundary are considered in the latter case the peculiar temperature distribution near the boundary affects significantly the response to additional loading a univariant transition behaves fully nonadiabatic at low convective velocities below the verhoogen limit but increasingly adiabatic above a divariant transition behaves partly adiabatic already in a static mantle and the adiabatic character is strongly enhanced with increasing velocity of convection with realistic combinations of the relevant parameters for a divariant mantle phase change the response will be hardly more than 10 nonadiabatic and probably less than 1 this result affects especially the interpretation of the gravity anomaly above formerly glaciated areas in terms of mantle viscosity and layering of mantle convection

varve chronology and palynology of the lateglacial in northwest germany from lacustrine sediments of hamelsee in lower saxony abstract the hamelsee is a dolina from a collapse over permian salt that occurred at the end of the pleniglacial it is more than 21 m deep and contains 18 m of lacustrine sediments the lateglacial sediments in the central part of the lake consist of 2 7 m from 15 to 17 7 m of sapropelic and silty muds which are mostly laminated and partly bioturbated minor slumps occur mainly during colder phases the subdivision of the lateglacial is based on pollen zones multidisciplinary studies of the microfacies from thin sections geochemistry pollen analysis and rotifer analysis allow environmental and palaeoclimatological interpretations to be made the biozones of the lateglacial and their boundaries are marked by rapid climatic changes though covering comparatively short periods of time they are not monotonous but characterized by minor internal climatic fluctuations the sediments of the meiendorf and oldest dryas are not laminated the allerod sediment is seasonally varved without interruption and encompasses 625 yr the eruption of the laacher see volcano 12 900 cal bp had an impact on the climate during the following 10 yr the transition from the allerod to the younger dryas took some 50 yr and it occurred 200 yr after the eruption of the laacher see volcano the abrupt change at the end of the lateglacial 11 560 cal bp occurred within less than 10 yr however many proxies reacted with a time lapse of 15 to 30 yr

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

millennial scale paleoclimate cycles recorded in widespread palaeozoic deeper water rhythmites of north america rhythmically interbedded limestone and shale or limestone and chert rhythmites are a common feature of many deep water phanerozoic carbonate marine deposits seventeen different palaeozoic rhythmite successions from across north america 8 studied in detail 9 studied in reconnaissance are described and summarized individual rhythmite couplets 4 20 cm thick are composed of fine grained laminated to massive detrital limestone alternating with shale or marl or laminated spiculitic chert stratigraphic and primary depositional features within rhythmites and associated facies indicates that the carbonate rich and carbonate poor interbedding is the result of repetitive changes in sediment input primary rather than due to diagenetic redistribution of calcareous material secondary the average duration of individual rhythmite couplets is calculated using spectral analysis to determine couplet thickness combined with biostratigraphically calibrated undecompacted average sediment accumulation rates the duration of rhythmite couplets from the eight well studied successions ranges between 150 and 4900 yrs with the majority lying between 1000 and 3000 yrs i e millennial scale the paucity and low diversity of skeletal and trace fossils preserved suspension laminae lack of sediment reworking and facies associations indicate rhythmite accumulation was favored by 1 deposition below storm wave base which limited reworking by currents 2 dysaerobic bottom waters which restricted bioturbation and intermixing of interbedded lithologies and 3 proximity to nearshore carbonates supplying abundant fine grained detrital carbonate these combined conditions were best met along flooded subtropical continental shelves or epeiric seas during my scale 3rd order sealevel rises the rhythmic alternation between carbonate rich and carbonate poor layers is interpreted to represent millennial scale paleoclimatic changes related to 1 wet dry climate cycles which influenced the amount of continent derived eolian and or fluvial sediment input 2 variations in offshore transport via storm generated or density currents of nearshore derived terrigenous or carbonate sediments and or 3 changes in wind driven upwelling and availability of recycled biogenic silica the various rhythmite successions accumulated under dramatically different paleoenvironment and paleogeographic conditions including active to passive tectonic settings equatorial to subtropical latitudes long term icehouse through greenhouse climatic conditions calcite versus aragonitic seas variable atmospheric co2 concentrations before and after land plant and animal evolution and across widely varying ocean basin configurations if our short term paleoclimatic interpretations for the rhythmites are correct then it is apparent that millennial scale climate changes occurred over a very wide spectrum of paleoceanographic paleogeographic paleoclimatic tectonic and biologic conditions and over time periods from the cambrian to the quaternary given this it is difficult to invoke models of internally driven thermohaline oceanic oscillations or continental ice sheet instabilities to explain their origin instead we suggest that

plastic deformation and development of antigorite crystal preferred orientation in high pressure serpentinites we have inferred the deformation mechanisms of antigorite by high resolution ebsd mapping of samples from cerro del almirez ultramafic massif betic cordillera se spain textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600 630 c and 1 6 1 9 gpa deformation was followed by static annealing of antigorite at ca 680 c the crystal preferred orientation cpo of antigorite is characterised by a strong alignment of 001 poles normal to the foliation plane and a weaker but clear parallelism between 100 axes and the macroscopic lineation defined by the elongation of magnetite aggregates analysis of misorientations across subgrains shows predominance of 010 rotation axis consistent with activation of the 100 001 slip system however tilt subgrain boundaries subparallel to 100 probably formed by edge dislocations of this system are subsidiary most subgrain boundaries are subparallel to 001 planes they are interpreted as 001 twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins modelling of the evolution of the antigorite cpo using a lower bound approach and considering different deformation regimes and sets of basal and non basal slip systems has shown that intensities of 100 and 010 maxima reflect the relative strength of the antigorite 100 001 and 010 001 systems activation of other basal or non basal slip systems does not change significantly the cpo patterns but results in less concentrated cpo 3d transpression models better reproduce the cpo of natural antigorite serpentinites we propose that the widespread occurrence of strong cpo in high pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on hk0 001 together with the activation of twinning implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge

dating synthesis and interpretation of palaeoclimatic records of the last glacial cycle and model data integration advances by the intimate integration of ice core marine and terrestrial records cost action es0907 since 2010 the intimate integration of ice core marine and terrestrial records network has been operating as a cost action designated es0907 this paper outlines the accomplishments of the intimate cost action in the context of how the intimate ideas have evolved during the network s twenty year life span and highlights a number of challenges that can guide further work in the second part of the paper the contributions that comprise this intimate special issue are introduced

comparison of the natural deformation of the state line serpentinite u s a with experimental studies abstract lizardite rich serpentinite dominantly underwent ductile deformation whereas antigorite rich serpentinite underwent brittle deformation during dextral strike slip shearing in the state line serpentinite pennsylvania piedmont metamorphic reactions within the shear zones constrain the temperature of deformation to between 350 and 500 c at 2 5 kbar pressure comparison with the temperature pressure limits determined by the experimental serpentinite deformation studies of raleigh and paterson 1965 indicates that the mechanical response should have been the opposite under these conditions antigorite should have been ductile and lizardite brittle the differences between the experimental and natural deformation responses is proposed to reflect the poor dependence of the mechanical response of serpentine to temperature and pressure as well as the presence or absence of fluid during deformation the shear zones in the state line serpentinite served as a fluid conduits during deformation the fluid drove retrograde reactions in the serpentinite and allowed it to undergo reaction enhanced ductility the experimental studies that concentrate on deformation during prograde metamorphism may not be completely applicable to retrograde shear zones

the younger dryas cooling in northeast germany summer temperature and environmental changes in the friedlander groβe wiese region a lake sediment record from the friedlander gro e wiese in northeast germany was studied to reconstruct summer temperature changes associated with changes in vegetation development during the weichselian lateglacial the record was analysed for pollen chironomids and oxygen and carbon isotopes of lake marl the combination of radiocarbon dates the presence of the laacher see tephra and correlation of lithological and palynological changes with other records from the region indicated that the record encompassed the allerod to the early holocene pollen assemblages reflect development of birch and later pine dominated forests during the allerod comparable to other sites in the region chironomid inferred mean july air temperatures c it for this period range between 14 0 and 14 8 c a temporary decrease in c it of 1 c a negative shift in the isotope records and a minor decline of birch may correspond to greenland interstadial 1b even though the transition to the younger dryas appears to be affected by reworking and redeposition processes a drop in c it to 11 1 c is reconstructed for the later part of the younger dryas while it appears that pine locally persisted in the region comparison with a nearby pollen record further indicates a local expansion of wetland grasses during this period at the transition to the holocene c it increased to 15 7 c while birch and pine forests re expanded copyright 2012 john wiley sons ltd

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

stable carbon and hydrogen isotope ratios of subfossil oaks in southern germany methodology and application to a composite record for the holocene the d ad values exist for the time interval 6470 bc to ad 905 not all records have the same time resolution and not all of them were prepared in the same way for isotope analysis however investigations on the influence of the preparation technique on the isotope values and on the isotope composition of different wood compartments latewood and earlywood respectively allowed us to homogenize the records the comparison of d values of wood with different cambial ages showed that hydrogen isotoperatios were affected by growth tre

microstructure of serpentinite mylonites from the josephine ophiolite and serpentinization in retrogressive shear zones california the josephine peridotite has experienced deformational episodes over a wide range of temperatures deformation within the stability field of a serpentine group mineral appears invariably accompanied by retrogressive metamorphism serpentinization two general types of deformed serpentinites have been identified 1 incohesive serpentinites most common which appear to have experienced low temperature predominantly brittle deformation and 2 serpentinite mylonites which have experienced plastic flow near the upper limit of antigorite stability the distinction between these two is based on textural and mineralogical criteria serpentinite mylonites are cohesive homogeneously foliated and typically strongly lineated rocks composed primarily of antigorite and magnetite they occur in planar bounded zones enclosed within the josephine peridotite that were the loci of both noncoaxial deformation and serpentinization we discuss the development of two important shear sense indicators porphyroclast systems and oblique shear band foliations as observed in these rocks porphyroclast systems in serpentinite mylonites are often comprised of cores and mantles of different mineralogy cores are usually composed of primary pyrogenetic minerals whereas mantles including tails are composed of products of the serpentinization reaction these systems are therefore termed porphyroctasts with neocrystallization tails oblique shear bands are common micro structures in serpentinite mylonites shear bands which offset the mylonitic foliation along narrow discrete fractures are termed f type whereas those which offset the mylonitic foliation along narrow ductile micro shear zones are termed d type the latter are considered more reliable for shear sense determinations strains accomplished by movement on shear bands are probably small strain resulting from a volume increase dur ing serpentinization while holding the shear zone width constant is sufficient to produce the shear bands therefore we suggest that oblique shear bands may develop to accom modate volume increases associated with deformation

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

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

a stable isotope tree ring timescale of the late glacial holocene boundary late glacial and holocene tree ring chronologies like deep sea sediments or polar ice cores contain information about past environments changes in tree ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere we have established a 9 928 year absolutely dated dendrochronological record of holocene oak quercus robur quercus petraea and a 1 604 year floating late glacial and early holocene chronology of pine pinus sylvestris from subfossil tree remnants deposited in alluvial terraces of south central european rivers the pine sequence provides records of dendro dated 14c 13c and 2h patterns for the late younger dryas and the entire preboreal 10 100 9 000 yr bp through the use of dendrochronology radiocarbon age calibration and stable isotope analysis we suggest that the late glacial holocene transition may be identified and dated by 13c and 2h tree ring chronologies

dehydration reactions and micro nanostructures in experimentally deformed serpentinites high t torsion experiments on lizardite chrysotile serpentinites produced mineralogical and micro nanostructural changes with important implications in rheological properties high resolution tem showed that specimens underwent ductile by microkinking and 001 interlayer glide and brittle deformation by microfracturing together with dehydration and break down reactions lizardite is affected by polytypic disorder and microkinking kink axial planes at high angle with respect to 001 planes that were not present in the initial ordered 1t lizardite chrysotile fibres are deformed resulting in elliptical cross sections with strong loss of interlayer cohesion both lizardite and chrysotile break down to a fine intergrowth of olivine up to 200 nm talc up to 30 nm and poorly crystalline material lizardite out reaction preferentially occurs at kink axial planes representing sites of preferential strain and enhanced reactivity conversely chrysotile break down is a bulk process resulting in large healed olivine aggregates up to micrometric in size overall observations suggest that dehydration and break down reactions are more advanced in chrysotile than in lizardite

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

boundary conditions for damming of a large river by fallout during the 12 900 bp plinian laacher see eruption germany syn eruptive rhine damming ii abstract the rhine river germany the largest river in western europe was dammed by pyroclastic material multiple times during the major plinian laacher see eruption 12 900 bp dams formed both upstream and downstream of the broad tectonic lower neuwied basin lnb which interrupts the narrow rhine canyon here we document upstream damming of the rhine river at the entrance to the lnb close to the present city of koblenz due to overloading with tephra fall into the rhine and its major tributaries the moselle and the lahn the dam was formed repeatedly during rapid pumiceous tephra fall events and breached during breaks in eruptive activity causing extensive high energy flooding throughout the entire basin the ephemeral koblenz dams differed significantly from normal volcanically induced dams by consisting principally of washed together pumice clasts and some driftwood the porous nature of pumice and its ability to absorb water were crucial factors thus a large volume percentage of the tephra that had fallen into the rhine floated submerged within the upper part of the water column or swam at the surface moreover the absorption of the river water by the pumice clasts increased the sediment water ratio of the two phase flow considerably we here present a model of dam formation resembling the formation of ice jams we visualize the koblenz dams to have been elongate partly floating and partly grounded permeable plugs many kilometers long and rising no higher than the flood plain damming was most plausibly initiated in the lnb within the area of maximum tephra loading and propagated upstream in a chain reaction comparable to the formation of traffic jams a major dam was finally accumulated at the bottleneck entrance to the lnb a site combining several favorable conditions the upstream multi channel rhine was confined to a single channel change of flow direction by 125 extremely low gradient 0 19 starting already 24 km upstream of the bottleneck constant decrease of flow velocity over many kilometers towards the bottleneck and the moselle river largest tributary of the rhine within the lnb and an important conveyor of additional tephra masses entered the rhine only 700 m upstream of the bottleneck we assume that the koblenz dams could only have formed and been stabilized by an extremely long foot region that extended many kilometers downstream and that was possibly connected to one or several low rise secondary jams dams the backwater of lake brohl that was dammed by pyroclastic flows 7 km downstream of the lnb about halfway through the eruption extended further and further upstream into the lnb during the second plinian stage of the laacher see eruption and was probably a major factor contributing to the formation and large size of koblenz dam no 4 the koblenz dams were probably not completely sealed most of the time this way the major pre eruptive rhine channel received some water an equilibrium condition was established that enabled the dams to remain stable as long as tephra fell into the rhine relatively continuously

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

ams radiocarbon dating of annually laminated sediments from lake holzmaar germany ams radiocarbon ages have been determined on terrestrial macrofossils selected from the annually laminated sediments of lake holzmaar germany the radiocarbon chronology of this lake covers the last 12 6 ka comparison of the radiocarbon dated varve chronology with tree ring data shows that an additional 878 years have to be added to the varve chronology the corrected c 14 varve chronology of holzmaar reaches back to ca 13 8 ka cal bp and compares favourably with the results from soppensee switzerland hajdas et al 1993 the corrected ages for the onset and the end of the younger dryas biozone are 11 940 cal bp and 11 490 cal bp respectively the ash layer of the laacher see volcanic eruption is dated at 12 201 224 cal bp and the ulmener tephra layer is dated at 10 904 cal bp

shear zone control on mineral deposits in the state line serpentinite pennsylvania piedmont the secondary redistribution and in some cases the primary formation of mineral deposits in the state line serpentinite were controlled by shear zone processes the state line serpentinite is a layered mafic intrusion with a basal serpentinized peridotite with cumulate chromite layers rhythmically layered gabbro and quartz diorite in the upper section there are three generations of shear zones that have affected the serpentinite including early thrust faults conjugate high angle reverse faults and late dextral strike slip faults with complex temporal spatial and angular relations the thrust faulting emplaced the state line serpentinite onto the peters creek metasediments and represents the major faulting event the conjugate reverse faulting may have been a late feature of the thrust faulting or related to the strike slip faulting the strike slip faulting produced extensive mylonitization in the serpentinite and is the latest deformation in the area chromite is the most economic mineral resource in the state line serpentinite most of the cumulate chromite deposits are lenticular to lensoidal in shape as the result of physical reorientation in thrust and strike slip shear zones talc and magnesite were also mined from the state line serpentinite talc occurs adjacent to pegmatite dikes but both talc and magnesite formed in mylonite where magnesite also fills the matrix of late stage cataclasite and extensional veins some of the long fiber variety of asbestos formed in cross fiber veins and slip fiber slickensides in all brittle faults the asbestos was mined from a few small prospects the metamorphic reactions within the active shear zones during talc and magnesite mineralization reflect fluid evolution to lower temperatures and higher concentrations of co2 comparison with experimental results on the metamorphism of serpentinite indicates a decrease in temperature from approximately 500 to 350 c and an increase in co2 content from 0 to 3 the shear zones acted as fluid conduits during deformation recorded the evolution of metamorphic conditions in their mineralogies and controlled the distribution of talc and magnesite deposition

tree rings and ice cores reveal c 14 calibration uncertainties during the younger dryas the younger dryas interval during the last glacial termination was an abrupt return to glacial like conditions punctuating the transition to a warmer interglacial climate despite recent advances in the layer counting of ice core records of the termination the timing and length of the younger dryas remain controversial also a steep rise in the concentration of atmospheric radiocarbon at the onset of the interval recorded primarily in the cariaco basin has been difficult to reconcile with simulations of the younger dryas carbon cycle here we discuss a radiocarbon chronology from a tree ring record covering the late glacial period that has not been absolutely dated we correlate the chronology to ice core timescales using the common cosmic production signal in tree ring 14c and ice core 10be concentrations the results of this correlation suggest that the cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the younger dryas climate reversal in the cariaco basin this bias in the marine record may also affect the accuracy of a widely used radiocarbon calibration curve over this interval our tree ring based radiocarbon record is easily reconciled with simulated production rates and carbon cycle changes associated with reduced ocean ventilation during the younger dryas attaching a floating tree ring chronology to ice core records that cover the abrupt younger dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly the chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean which may affect the accuracy of a popular radiocarbon calibration program during this interval

a revised 10 4 c magnitude of the abrupt change in greenland temperature at the younger dryas termination using published gisp2 gas isotope data and air thermal diffusion constants abstract we revisit the portion of nature 391 1998 141 devoted to the abrupt temperature increase reconstruction at the younger dryas preboreal transition the original estimate of 5 to 10 c abrupt warming is revised to 10 4 c the gas isotope data from the original work were employed combined with recently measured precise air thermal diffusion constants geochim cosmochim acta 67 2003a 345 j phys chem 23a 2003b 4636 the new constants allow a robust interpretation of the gas isotope signal in terms of temperature change this was not possible at the time of the original work when no air constants were available three quasi independent approaches employed in this work all give the same result of a 10 c warming in several decades or less the new result provides a firm target for climate models that attempt to predict future climates