oxygen and hydrogen isotope ratios in tree rings how well do models predict observed values we have measured annual oxygen and hydrogen isotope ratios in the cellulose of the latewood of oak quercus robur l growing on well drained ground in norfolk uk we compare the observed values of isotope ratios with those calculated using equations that allow for isotopic fractionation during the transfer of oxygen and hydrogen from source water taken by the tree to cellulose laid down in the cambium the equations constitute a model in which isotopic fractionation occurs during evaporative enrichment within the leaf and during isotopic change between carbohydrates and water in the trunk during cellulose synthesis from the relationship between isotope ratios in precipitation and cellulose we deduce that the source water used by the tree comprises a constant mixture of groundwater and precipitation chiefly from the months of may june and july of the growth year by selection of isotopic fractionation factors and the degree of isotope exchange within the trunk we are able to model the observed annual values of oxygen isotope ratios of cellulose to a significant level r 0 77 p 0 01 when we apply the same model to hydrogen isotope ratios however we find that although we can predict the average value over the time series we can no longer predict the year to year variation we suggest that this loss of environmental signal in the hydrogen isotopes is caused by differences in the kinetic isotope effects of the biochemical reactions involved in the fixation of hydrogen in different positions of the glucose molecule owing to these effects the hydrogen isotope ratios of cellulose can vary in a way not anticipated in current models and hence may induce non climatic noise in the hydrogen isotope time series

model evaluation for reconstructing the oxygen isotopic composition in precipitation from tree ring cellulose over the last century the oxygen isotope composition of tree rings is controlled by many factors including temperature amount of precipitation and changes in relative humidity in this study we present a modified leaf water model from dongmann et al radiation and environmental biophysics 11 1974 41 that can be used to calculate the isotopic composition of the source water and thus of precipitation that a tree used during the growing season the calibration of the model was accomplished by comparing a previously measured oxygen isotope tree ring chronology from central switzerland with the swiss network for isotopes in the hydrologic cycle station at bern from 1971 to 1995 and integrating temperature relative humidity data and ring width in particular our efforts focused on understanding the significance of the dampening factor f which we relate to changes in humidity and its variability over both the calibration period 1971 to 1995 and the study period 1913 to 1995 our results indicate that f ranging between 0 27 to 0 49 is variable based on correlation with relative humidity average daily temperature and ring width index using this model we have constructed a record of the oxygen isotope composition of precipitation during the growing season may through september for the last century in central western europe this approach can be potentially used in other locations where isotopic and meteorological data are available to extend records of the isotopic composition of precipitation back in time beyond observational records

climate variability in the early pliocene arctic annually resolved evidence from stable isotope values of sub fossil wood ellesmere island canada abstract tree ring analyses have contributed significantly to investigations of past climate stable isotope climate proxies 18o d and 13c values enhance traditional ring width data although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the holocene and the late pleistocene here we apply stable isotope techniques to wood that represent the remains of mixed coniferous boreal vegetation preserved in early pliocene 4 5 ma deposits at strathcona fiord ellesmere island canada ca 78 n four well preserved tree trunks identified through wood anatomical characteristics as larix larch from this high arctic site provide annually resolved sequences of up to 250 years from which we developed a high resolution record of pliocene climate stable oxygen isotope values in conjunction with ring width measurements were used to derive annually resolved temperature records for this site our ring width and isotope based reconstructions provide an annually resolved record up to 250 years of temperature and indicate growing season jj temperatures 15 8 5 0 c 11 8 5 1 c and mean annual temperatures mat 1 4 4 0 c 18 3 4 1 c warmer than present estimated isotope values of precipitation of 16 3 2 18o and 150 1 8 9 d were calculated from the isotopic values of wood cellulose relative humidity estimated from both 13c and d records ranged from 60 to 80 paleotemperature source water and humidity estimates are comparable to those of a modern boreal forest growing ca 15 20 south of modern ellesmere island

geomagnetic field intensity and reversals during the past four million years a long and continuous record of the geomagnetic field intensity shows that intensity variations are dominated by two modes major episodes of field regeneration prevail on timescales of a few thousand years immediately after most reversals whereas stable polarity states are characterized by a slow 0 5 myr relaxation process reversals can be seen as the consequence of a progressive degradation of the dipole field

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

identifying bias in cold season temperature reconstructions by beetle mutual climatic range methods in the pliocene canadian high arctic abstract well preserved beetle elytra from the fossil and subfossil record are used by palaeoclimatologists to estimate past temperatures beetle derived estimates of temperature across the pliocene arctic are consistently lower than those derived from other palaeoclimate proxies here we test if that pattern is attributable to either the modern dataset or specific mutual climatic range method mcrm we used a global dataset of observations global biodiversity information facility for modern beetles as opposed to a north american regional dataset and a consistent mcrm for comparison to vegetation derived estimates termed cracle climate reconstruction analysis using coexistence likelihood estimation rather than different mcrm methods for each analysis beetle derived estimates from one site beaver pond are consistently much lower than the vegetation derived estimates stable isotope results from flora and fauna and summer temperatures from bacterial tetraethers the reanalysis of beetle data produced a small reduction in proxy estimate mismatch overall we found good agreement among proxy estimates of maximum temperature of the warmest month for two of the three sites in the canadian arctic but increasingly poorer agreement for warmest quarter coldest quarter and minimum temperature of the coldest month this pattern may be due to beetles avoidance mechanisms and a climate space different from modern calibration sets during the pliocene beetle derived temperature estimates especially cold season should be interpreted with caution when reconstructing palaeoclimates

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

paleointensity in the quaternary west eifel volcanic field germany preliminary results abstract preliminary paleointensity results are presented from 36 sites with virtual geomagnetic pole vgp latitudes of about 30 90 normal polarity in the quaternary west eifel volcanic field a strong correlation between vgp latitude and the earth s virtual magnetic dipole moment vdm is observed with low intensities for low vgp latitudes indicating possibly an emplacement during an excursion or event of the brunhes epoch the age distribution of the west eifel volcanics is as yet poorly known also the mean vdm value for sites with high vgp latitudes is considerably lower than the present day dipole moment of the earth

pliocene and early pleistocene paleoenvironmental conditions in the pannonian basin hungary slovakia stable isotope analyses of fossil proboscidean and perissodactyl teeth abstract stable carbon and oxygen isotope values of structural carbonate 13c 18oco3 and phosphate 18opo4 in bio apatite were measured for fossil mammalian teeth from slovakia and hungary oxygen isotope compositions of enamel provide new quantitative records of the pliocene and early pleistocene paleoclimate in the pannonian basin pb the 18opo4 values were used to study the temporal variations in the oxygen isotope compositions of precipitation and the changes in temperature over the pb the new o isotope data suggest that surface air temperatures between 4 5 and 2 0 ma were 1 to 4 c warmer with about 700 mm yr more precipitation compared to the present c isotope analyses of samples from proboscideans anancus sp mammut sp and perissodactyls stephanorhinus sp tapirus sp from the pliocene mn15 mn16 and early pleistocene mn17 suggest that they were primarily c3 browsers the mean 13c value is high at 4 5 to 3 7 ma mn14 15 during the pliocene warm period and decreases at about 3 5 to 3 0 ma mn16 mid pliocene warm period with the onset of more humid conditions in europe the 13c values return to higher values from 2 5 ma onwards mn17 most likely reflecting more arid conditions as a consequence of the onset of the northern hemisphere glaciation

a contourite drift system on the baffin bay west greenland margin linking pliocene arctic warming to poleward ocean circulation terrestrial records from the canadian arctic archipelago indicate that a temperate and moist climate prevailed during the pliocene i e before the intensification of northern hemisphere glaciations but the controlling factors causing these conditions remains elusive here we present marine seismic reflection evidence of contiguous kilometer scale sedimentary drifts or contourites buried below the west greenland shelf which relates high latitude pliocene warmth to intense geostrophic currents along the eastern baffin bay margin seismic to borehole correlation indicates that enhanced current induced deposition began during the middle miocene ca 17 15 ma and terminated during the late pliocene onset of global cooling the transition from along slope sediment transport to trough mouth fan progradation designates the onset of greenland ice sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in baffin bay and the nordic seas from 3 3 to 2 7 ma our results suggest that the baffin bay west greenland margin formed a late neogene passageway for persistent ocean boundary currents and we infer that the pliocene high latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the arctic regions attenuation of the poleward heat flux conveyed by the paleo current system may have been critical for allowing glacial buildup in the canadian arctic and northern greenland during the late pliocene we further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation which eventually caused the demise of meridional ocean circulation through baffin bay

a cold supergene zinc deposit in alaska the reef ridge case the reef ridge deposit is a typical supergene nonsulfide zinc mineralization located in the yukon koyukuk region of west central alaska usa it is hosted in sedimentary rocks of the farewell terrane a continental fragment sandwiched between the siberian and laurentian cratons during the early paleozoic the mineralization occurs in lower middle devonian shallow water dolomite of a paleozoic carbonate platform succession belonging to the nixon fork tectonic unit the mineralization consists of oxidized minerals associated with minor remaining sulfides pyrite marcasite and sphalerite in the oxidation zone smithsonite is the predominant mineral mixed with fe hydr oxides goethite and hematite a complete petrographic and mineralogical study was performed samples were analyzed by x ray diffraction inductively coupled plasma mass spectrometry and emission spectrometry energy dispersive scanning electron microscopy and qemscan quantitative evaluation of minerals by scanning electron microscopy the most abundant mineral in the nonsulfide ore is smithsonite similar to other nonsulfide zn deposits worldwide the first generation of smithsonite has replaced both primary sphalerite and the host carbonates a second smithsonite generation precipitated as cement in vugs cavities and fractures minor zinc amounts also occur in the fe hydr oxides and zinc traces have been identified in clay minerals the carbon and oxygen isotope values of smithsonite at reef ridge vary from 0 7 to 2 1 relative to vienna peedee belemnite vpdb and 19 1 to 21 9 relative to vienna standard mean ocean water vsmow the 13 c values are similar to those of the host rock suggesting that the predominant carbon source for smithsonite was the host carbonates with only a limited contribution from organic carbon the oxygen isotope ratios of reef ridge smithsonite are more depleted in 18 o compared to supergene nonsulfides from other parts of the world formed under warm humid temperate or semiarid climates the oxygen isotope fractionation between water and smithsonite which relates the 18 o value of the mineralizing solution the formation temperature of smithsonite and its 18 o composition indicates that the 18 o composition of reef ridge smithsonite is related to very low formation temperatures 10 c and strong depletion in 18 o of the precipitating waters the 18 o smithsonite composition the strong 18 o depletion and the relationship of the formation of the reef ridge nonsulfide deposit with the development of the sleetmute upland surface which started in the late tertiary and continues to the present indicate that the formation of the reef ridge nonsulfide deposit is probably related to cold humid weathering episodes during a period comprised between late tertiary and holocene the traditional interpretation on the genesis of zn nonsulfide deposits in warm humid temperate or semiarid conditions should be questioned where other climate zones are indicated

isotopic composition δ13c δ18o in wood and cellulose of siberian larch trees for early medieval and recent periods 1 we related tree ring width trw and isotopic composition 13c 18o of wood and cellulose from four larch trees larixcajanderi mayr to climate parameters the material was sampled in northeastern yakutia 70 n 148 e for the recent ad 1880 2004 and early medieval ad 900 1000 periods during the recent period june july and august air temperatures were positively correlated with 13c and 18o of wood and cellulose while july precipitation was negatively correlated furthermore the vapor pressure deficit vpd of july and august was significantly correlated with 13c of wood and cellulose but vpd had almost no influence on 18o comparative analyses between mean isotope values for the ad 900 1000 and ad 1880 2004 periods indicate similar ranges of climatic conditions with the exception of the period ad 1950 2004 while isotopic ratios in cellulose are reliably related to climatic variables during some periods those in whole wood showed even stronger relationships strong positive correlations between 18o of cellulose and greenland ice core gisp2 data were detected for the beginning of the medieval period r 0 86 p 0 05 indicating the reliability of isotope signals in tree rings for large scale reconstructions

aluminium loss during sandstone diagenesis petrographical observations from a sandstone buried to between 3 2 and 5 7 km in the north sea central graben suggest a significant change in bulk chemistry during burial the sand contained 35 or more feldspar upon deposition but due to extensive dissolution only 5 remains in the deep sandstones this has released much more al than is currently contained as authigenic minerals up to 1460 mol cm 3 of al have been exported this deep secondary porosity is economically important but its recognition by petrographic textures is unreliable as are bulk chemical provenance studies of deeply buried sedimentary and metamorphic strata

thermal history model for the south central graben north sea derived using both tectonics and maturation abstract the thermal history modelling of basins is essential for petroleum systems analysis the methodology involves the derivation of the heat flow history by calibration using a kinetic model to match the predicted and observed vitrinite reflectance values in wells although this method is almost universally used by basin modellers a simple check using two independent methods with tectonic subsidence history being the second method shows that the thermal histories derived from the subsidence history do not match those predicted by the vitrinite reflectance method for any point in a basin there can only be one thermal history and the derivation of two different thermal histories indicates that there is a problem that has been ignored by geochemists and basin modellers the thermal history must predict the tectonic subsidence history and this heat flow history must also account for the maturation data e g vitrinite reflectance sediments subside under the action of forces and energy e g heat is a function of force during subsidence the downward force exceeds the upward force and the heat flow supplied to the basin must be reduced as the upward force is reduced while force and heat flow must be increased during uplift applying this relationship to the central graben north sea a heat flow history is derived that accounts for the rifting and subsequent subsidence tectonic history of two wells the british 23 26 2z and the danish lulu 1 the vitrinite reflectance predicted by this thermal history and the easy ro kinetic vitrinite reflectance model are higher than the measured values in both wells both wells are overpressured and the problem with the vitrinite reflectance calibration method is that the kinetic parameters used do not correctly account for the retardation produced by pressure le chatelier s principle without the pressure retardation effect incorporated into the kinetic parameters the modeller has to use lower temperatures to simulate retardation using the presro vitrinite reflectance model which incorporates pressure retardation as required by thermodynamics the thermal history derived from the rifting subsidence history can also be used to model the vitrinite reflectance data in the british 23 26 2z and danish lulu 1 wells this method of deriving an unknown e g thermal history using two independent models is widely used in physical sciences as an essential check on any prediction and this scientific rigor has to be followed by geoscientists modelling the thermal history of basins

environment and paleoecology of a 12 ka mid north american younger dryas forest chronicled in tree rings abstract until now availability of wood from the younger dryas abrupt cooling event yde in n america ca 12 9 to 11 6 ka has been insufficient to develop high resolution chronologies for refining our understanding of yde conditions here we present a multi proxy tree ring chronology ring widths events evidenced by microanatomy and macro features stable isotopes from a buried black spruce forest in the great lakes area liverpool east site spanning 116 yr at ca 12 000 cal yr bp during this largely cold and wet period the proxies convey a coherent and precise forest history including frost events tilting drowning and burial in estuarine sands as the laurentide ice sheet deteriorated in the middle of the period a short mild interval appears to have launched the final and largest episode of tree recruitment ultimately the tops of the trees were sheared off after death perhaps by wind driven ice floes culminating an interval of rising water and sediment deposition around the base of the trees although relative influences of the continental ice sheet and local effects from ancestral lake michigan are indeterminate the tree ring proxies provide important insight into environment and ecology of a n american yde boreal forest stand

multiple brunhes chron excursions recorded in the west eifel germany volcanics support for long held mantle control over the non axial dipole field volcanic records of excursional geomagnetic field behavior in particular paleointensity estimates are fragmentary for the pleistocene the west eifel volcanic field is unique in that 12 of 66 measured lava flow sites record virtual geomagnetic poles vgps clustered between 34 45 n latitude and 30 50 e

stability of climate signal in carbon and oxygen isotope records and ring width from scots pine pinus sylvestris l in finland four hundred year long records of carbon and oxygen stable isotope ratios and ring width were measured from scots pine pinus sylvestris l from sites in northern and eastern finland responses of isotope ratios to temperature and precipitation were analysed for the 20th century carbon isotope ratios responded strongly to summer temperature at both sites whereas an influence of precipitation on the record was observed only at the site in eastern finland oxygen isotope ratios were less responsive to climatic variation than carbon at the high frequency level to shed light on the role of the possible divergence problem during last decades the climate responses were studied separately in the first and in the second half of the 20th century the responses to temperature were stable in the north but in eastern finland the significant period of summer occurred earlier during the later half of the century relationships between records were studied during the 400 a period all proxies correlated positively with each other although temporal changes occurred common forcing discovered in northern finland between carbon isotope and ring width records was weaker in the earlier period studied three climate reconstructions were created temperature reconstruction for northern finland and temperature and precipitation reconstructions for eastern finland copyright 2009 john wiley sons ltd

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

stratospheric modulation of the boreal response to pliocene tropical pacific sea surface temperatures variations in the sea surface temperature of the eastern equatorial pacific usually associated with the el nino southern oscillation have a global impact previous work has shown that the stratosphere modulates the northern hemisphere response to these temperature anomalies here we show that the stratosphere also plays a major role in modulating the response to tropical sea surface temperature anomalies representative of the mean state of the pliocene era approximately four million years ago key to the response is a predominance of sudden stratospheric warmings during boreal winter which cause a large anomalous surface pressure response over the north atlantic ocean the stratospheric modulation results in relatively cold winter spring eurasian surface temperatures and relatively warm surface temperatures in greenland and north america the implications of these results for simulating and understanding the climate of the pliocene era are discussed

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

humidity estimate for the middle eocene arctic rain forest the exquisite preservation of fossilized metasequoia trees that grew near 808n latitude during the middle eocene ca 45 ma in nunavut canada allowed for dd and d 18 o analyses of cellulose techniques previously restricted to wood 30 000 yr old from the isotopic results we determined that the middle eocene arctic atmosphere contained 23 the water found in the region s atmosphere today this water vapor contributed to a middle eocene greenhouse effect that insulated the polar region during dark polar winters

glaciation of north america in the james bay lowland canada 3 5 ma glaciers expanded in the northern hemisphere during the middle pliocene however whether they extended into the midlatitude lowlands remains unknown a pliocene sequence from a buried deep bedrock trench in the midlatitude james bay lowland canada 52 49 5 n 83 52 5 w contains a till and an overlying lacustrine deposit rich in fossil pollen magneto stratigraphy together with pollen derived biostratigraphy constrains it to a time span from 3 6 to 3 0 ma based on multiple lines of evidence we are able to prove the deposition of the till by an early ice sheet and hence glaciation of the lowland at ca 3 5 ma 3 6 3 4 ma after glaciation rapid warming permitted thermophilic trees now exotic to this area to grow which include oak sweetgum and cypress furthermore pollen analysis indicates alternating carolinian deciduous and boreal evergreen forests under a climate that oscillated and cooled gradually during a prolonged postglacial period from 3 5 to 3 0 ma

spatial and temporal oxygen isotope trends at the northern tree line in eurasia 1 the oxygen isotope ratio of ice cores and sea sediments is an extremely useful source of information on long term climatic changes a similar approach has been applied to the oxygen isotope ratio of tree rings to enable a pattern based reconstruction of the isotope variations on the continents we present an oxygen isotope map for northern eurasia spanning from norway to siberia that reflects the isotope distribution in the late 19th century and compare it with an equivalent map for the present day situation the average isotope values of 130 trees show a large east to west gradient and are highly correlated with the isotope distribution of precipitation surprisingly the 18o 16o ratio of the wood has been decreasing in the interior of the continent since the late 19th century in contrast to the strong temperature increase recorded by meteorological data from this isotope trend over time a change in the seasonality of precipitation can be inferred

annually resolved temperature reconstructions from a late pliocene early pleistocene polar forest on bylot island canada abstract here we use 18o ratios measured in tree rings of crossdated sub fossil wood to reconstruct an annually resolved record of temperature and 18o of meteoric water for an interglacial late pliocene early pleistocene fossil forest found on bylot island nunavut canada our record represents the first crossdated record of pliocene wood mean annual temperatures determined in this study average 3 4 3 8 c which is 11 4 4 4 c warmer than present day bylot island 14 8 2 2 c june july temperatures average 13 5 1 1 c approximately 12 6 1 6 c warmer than present day meteoric water 18o values average 15 5 2 9 2 6 more enriched than present values of precipitation 18o our temperatures are comparable to mid pliocene modeled temperatures for the arctic 3 5 c warmer than present suggesting that interglacial warm periods in the late pliocene early pleistocene may have been as warm as the mid pliocene warm period that both the bylot island forest deposit and the kap kobenhavn deposit represent the remains of northern tree line vegetation that lived during warm interglacial periods within the overall cool plio pleistocene suggests that forest deposits in the arctic capture a snapshot of interglacial conditions during the plio pleistocene rather than the average pliocene climate and may not be suitable records to study pliocene cooling

tree ring growth curves as sources of climatic information abstract regional growth curves rgcs have been recently used to provide a new basis for removing nonclimatic trend from tree ring data here we propose a different use for rgcs and explore their properties along two transects one meridional and the other elevational rgcs consisting of mean ring width plotted against cambial age were developed for larch samples from 34 sites along a meridional transect 55 72 n in central siberia and for 24 sites on an elevational gradient 1120 and 2350 m a s l in tuva and neighboring mongolia at approximately 51 n there are systematic gradients of the parameters of the rgcs such as i 0 maximum tree ring width near pith and i min the asymptotic value of tree ring width in old trees they are smaller at higher latitude and elevation annual mean temperature and mean may september temperature are highly correlated with latitude here and hence rgc parameters are correlated with these climatic variables correlations with precipitation are more complex and contradictory between meridional and elevational transects the presence of a similar gradient in the elevational transect is consistent with temperature being the causal factor for both gradients rather than for example latitude dependent patterns of seasonal photoperiod change taking ring measurements from collections of relict and subfossil wood the rgc latitude and rgc temperature relationships are used to estimate paleo temperatures on centennial time scales these estimates are consistent with earlier traditional dendroclimatic approaches and with independent information on the northern extent of forest growth in the early mid holocene it may be possible to use this same approach to make estimates of century scale paleo temperatures in other regions where abundant relict wood is present

asymmetrical saw tooth pattern of the geomagnetic field intensity from equatorial sediments in the pacific and indian oceans abstract a record of relative paleointensity from marine sediments in the equatorial indian ocean spanning the last 4 ma completes a previous dataset from ocean drilling program odp leg 138 sites in the equatorial pacific 1 the timescale was defined with a precision better than 20 kyr with different and independent methods most of the features present in the record from the equatorial pacific are confirmed the overall saw tooth pattern is observed across every field reversal and the short term fluctuations superimposed on the slow intensity decrease preceding the reversals appear to be similar at both sites the global character of these features reinforces their interpretation in terms of changes in dipole field intensity and provides new important constraints on models of the geodynamo a synthetic curve of field intensity changes during the last 4 ma is proposed as a first paleointensity timescale for future stratigraphic studies

arctic north american seasonal temperatures from the latest miocene to the early pleistocene based on mutual climatic range analysis of fossil beetle assemblages late tertiary and early quaternary fossil beds in the arctic regions of north america have yielded abundant well preserved remains of plants and arthropods documenting the existence of coniferous forests in the high arctic latitudes nearly all of the beetle coleoptera specimens in these fossil assemblages represent extant species we have applied the mutual climatic range mcr method of paleotemperature analysis to fossil beetle assemblages from 11 sites to estimate mean summer t max and winter t min temperatures we found that arctic t min values during the latest miocene and pliocene were substantially warmer than they are today the mcr estimates therefore support the scenario derived from the paleobotanical data namely that arctic pliocene climates were far less continental several pliocene age assemblages from the high arctic yielded t max estimates 9 10 c warmer than modern values at the sites this is the same degree of warming required to allow coniferous forests to grow in the high arctic by 3 million years bp a cooling trend is marked in the paleobotanical and fossil beetle evidence from alaska all assemblages dating between 5 7 and 2 million years bp yielded calibrated t max values between 12 4 and 13 8 c regardless of location thus the insect fossil data support the theory that there was far less latitudinal gradation in temperatures during the late pliocene than there is today our reconstructions suggest regional climatic cooling especially winter temperatures began by at least 2 million years bp

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

estimates of arctic land surface temperatures during the early pliocene from two novel proxies during the pliocene 2 6 to 5 ma ago atmospheric co 2 levels have been estimated as similar to or slightly above present levels tripati et al 2009 pagani et al 2010 and yet earth s climate was considerably different recent evidence suggests that although global temperatures were 2 3 c warmer than pre industrial arctic warming may have been amplified during the pliocene thus precise temperature records of this interval are required to assess the sensitivity of earth s climate to persistent levels of co 2 between 365 and 415 ppm we present records of two independent proxies for terrestrial growing season temperatures at the early pliocene beaver pond site on ellesmere island 18 o values of cellulose from well preserved peat constrain the 18 o values of meteoric water to 20 7 0 3 which we combined with 18 ovalues of aragonitic freshwater molluscs found within the peat in order to calculate mollusc growth temperatures this approach results in an average growing season temperature of 14 2 1 3 c temperatures were independently derived by applying carbonate clumped isotope thermometry to mollusc shells from the same site indicating an average growing season temperature of 10 2 1 4 c a one way anova indicates that the differences between the two techniques are not significant as the difference in mean temperatures between both methods is no different than the difference between individual shells using a single technique both techniques indicate temperatures 11 16 c warmer than present may sept temperature 1 6 1 3 c and represent the first thermodynamic proxy results for early pliocene ellesmere island

determination of geomagnetic palaeointensities from the quaternary west eifel volcanic field germany summary determination of geomagnetic palaeointensities has been attempted for 418 specimens from 51 volcanic units of the quaternary west eifel volcanic field this paper describes the measuring procedure using a modification of the thellier method the analysis of the derived data points the determination of linear segments and the quality of the individual palaeointensity values calculated from the corresponding slopes according to a series of acceptance and rejection criteria finally 312 reliable individual palaeointensity results have been obtained about 73 per cent of the accepted regression lines have correlation coefficients better than 0 990 and less than 10 per cent of the accepted thellier experiments have quality factors less than 1 0 the carriers of magnetization of the west eifel volcanic rocks are titanomagnetites with a broad range of titanium contents and oxidation states in a more or less unweathered mostly foiditic rock matrix accompanying rock magnetic experiments allowed a rough classification of the specimens corresponding to the oxidation state of the titanomagnetites specimens with highly oxidized titanomagnetites have been the most successful candidates for the thellier experiments however a prediction of the suitability of the specimens for the thellier experiments by sample selection according to this classification was not always appropriate instead for most volcanic units pilot specimens were first measured to determine the suitability of a specific sample type the temperature interval from which the evaluation of palaeointensity was possible and the best laboratory field intensity to keep the slope errors of the thellier experiments to a minimum palaeointensity determination was not possible for 14 volcanic units because only unsuitable specimens were available for each of the 37 remaining volcanic units at least five successful thellier experiments have been carried out leading to a final mean palaeointensity result these 37 values have relative standard errors of between 4 and 23 per cent mostly around 10 per cent specimens with differing rock magnetic properties from the same volcanic unit yielded consistent palaeointensity values therefore all west eifel palaeointensity results have to be regarded as reliable estimates of the earth s magnetic palaeofield strength mean palaeointensities range from 7 to 62 pt with an unexpectedly large number of palaeointensity values less than 30 pt about half of the low palaeointensity values are associated with intermediate virtual geomagnetic pole latitudes which may be due to a geomagnetic excursion

oxygen isotope ratios in fossil wood cellulose isotopic composition of eocene to holocene aged cellulose abstract we measured the 18 o of cellulose 18 o cel extracted from fossil wood collected at 9 sites in the northern and southern hemispheres as a potential source of information about precipitation 18 o 18 o ppt in the past and paleotemperatures the samples had been buried in fluvial sediments for periods of time ranging from ca 45 million to 250 years at the oldest localities high latitude eocene through pliocene age sites in canada and russia mean annual temperature mat estimates derived from the modern relationship between mat and 18 o cel are 6 16 c lower than the mat estimates derived from other biological proxies estimates of pleistocene and holocene mean annual temperatures are close to the modern values at those sites these results are consistent with other recent findings that the mat 18 o ppt relationship across north america was not constant throughout the cenozoic paleo 18 o ppt estimates derived from fossil cellulose and the modern north american relationship between 18 o cel and 18 o ppt are within the current annual range of 18 o ppt values at all locations the middle eocene 18 o ppt we determined from arctic cellulose samples 21 9 is consistent with river water 18 o determined in two other studies 19 1 to 22 these findings provide some evidence that a precipitation 18 o signal may be retained in wood cellulose during millions of years of burial and that latitudinal patterns in 18 o ppt may not have changed much during the past 45 ma these interpretations depend of course on the assumption that the isotopic composition of the cellulose has not changed during burial an assumption for which it is difficult to gather direct evidence xrd analysis shows that the crystalline form of the fossil cellulose we used to estimate paleoprecipitation 18 o and paleo mat is the same as that of modern cellulose and that the samples are free of quartz and iron oxide contaminants that result in negative errors in measured 18 o cel

oxygen isotope ratios of oak in east england implications for reconstructing the isotopic composition of precipitation annual latewood 18o values from oak quercus robur l are presented for the period 1895 1994 for four trees growing in eastern england we demonstrate using the 18o values of precipitation from wallingford 1982 1994 and the longer time series from groningen 1965 1994 that the 18o values of winter precipitation had the strongest influence on the 18o values of tree ring cellulose the influence of winter precipitation on the spring summer formed latewood may be explained by several factors most soil water is replenished during the winter water may take several months to penetrate the unsaturated zone and oaks may sample water from lower in the profile during times of water stress the 18o values of oak latewood cellulose were also significantly p 0 01 correlated with summer relative humidity therefore although precipitation 18o values may be altered by partial isotopic exchange with xylem water and the influence of stomatal conductance upon evapotranspiration some of the original 18o signature remains

pliocene arctic temperature constraints from the growth rings and isotopic composition of fossil larch instrumental records reveal that the current rate of arctic warming greatly exceeds mean global warming however arctic temperatures during the pliocene were considerably warmer than present making it an excellent time period for investigating potential consequences of current warming trends here we focus on an early pliocene 4 to 5 ma peat deposit from ellesmere island characterized by a remarkable fossil assemblage representative of a modern boreal forest among the fossils are wellpreserved samples of an extinct larch larix groenlandii which were exploited as an archive of paleoclimatic information we reconstruct pliocene terrestrial temperatures in the high arctic using a novel approach that combines measurements of ring width and oxygen isotopes this technique was calibrated by analyzing modern analog larch growing at the northern extent of their range and accounting for biotic fractionation of oxygen isotopes using a global database of modern trees based on this approach we estimated mean annual temperature in the arctic during the pliocene to be 5 5 1 9 c indicating that arctic temperatures were 14 2 c warmer than today this more precise multi proxy estimate is slightly warmer than previous estimates derived from empirical evidence and general circulation models our results also demonstrate that the biotic fractionation of oxygen isotopes in cellulose is non linear and dependent upon regional factors affecting aridity such as latitude and elevation therefore the simultaneous measurement of oxygen isotopes and morphological characteristics in paleovegetation can be useful in constraining climatic variables of earth s past

twentieth century trends in tree ring stable isotopes δ13c and δ18o of larix sibirica under dry conditions in the forest steppe in siberia 1 tree ring width density and ratio of stable isotopes 13c 12c and 18o 16o in wood and cellulose were determined for larch larix sibirica ledeb growing under water deficit conditions in the forest steppe zone in central siberia 54 24 n 89 57 e for the period 1850 2005 dendroclimatic analysis of the chronologies indicated precipitation to be the most important factor determining indicated parameters precipitation of june is significantly correlated with tree ring width and maximum density r 0 36 and 0 43 p 0 05 respectively relations of 13c and 18o to precipitation are similar but the most important month is july r 0 47 p 0 05 for 13c r 0 29 p 0 05 for 18o further 18o is positively related to the mean temperatures of july r 0 30 p 0 05 carbon and oxygen isotope ratios in wood and cellulose showed strong negative trends for the last 100 years the reason for this decrease could be the observed shift of the beginning of the vegetation period to earlier dates up to 1 week in spring and the increased use of precipitation water stored in the soil from october of the previous year although other explanations cannot be excluded in particular the physiological effect of increasing atmospheric co2 also responsible for lower 13c values thus an earlier start of the vegetation period could lead to tree ring formation during a period with higher water availability resulting in stronger isotopic fractionation and 13c depletion also reflected in a higher earlywood to latewood ratio at the same time highly 18o depleted water from october precipitation of the previous year is absorbed the incorporation of this isotopically lighter water during photosynthesis is reflected in the wood and cellulose of tree rings

dating and palaeoenvironmental reconstruction of the sediments around the miocene pliocene boundary in yermak plateau odp hole 911a using marine palynology abstract the late neogene evolution of the arctic to subarctic region is poorly understood due to few available records and poor age control at the margin of the arctic ocean yermak plateau ocean drilling program odp hole 911a is strategically located for establishing a stratigraphic framework for the arctic here we present dinoflagellate cyst and acritarch data from 24 stratigraphic levels in the lower part 474 26 505 64 metres below the seafloor of odp hole 911a the marine palynomorphs indicate a latest miocene to earliest pliocene age between 5 8 and 5 0 ma for the base of the hole based on the co occurrence of the dinoflagellate cyst barssidinium evangelineae and acritarch lavradosphaera crista our age estimate can possibly be further refined to 5 0 5 33 ma based on the presence of achomosphaera andalousiensis suttonensis which apparently has a range restricted to the pliocene an age close to the miocene pliocene boundary agrees with the planktonic foraminifer data together with recently available magnetostratigraphic data the base of the hole is likely to be placed at 5 2 ma this new chronostratigraphy is a first step towards a better understanding of the late neogene palaeoenvironment for the yermak plateau and also for the wider arctic to the subarctic region the terrestrial and fresh water palynomorphs were most likely redistributed and or displaced from the shelf towards deeper parts of the basin during contourite deposition under the influence of the west spitsbergen current the in situ marine dinoflagellate cyst assemblage contains a mixture of cool water and thermophilic taxa indicating sea ice free cool temperate and warmer than present conditions at the yermak plateau rivers were likely the source for the freshwater influence warmer than present conditions may have occurred due to northward warm water transport via the west spitsbergen current but also the absence of sea ice and consequent lower albedo could have played a role

extraction of α cellulose from mummified wood for stable isotopic analysis abstract stable isotope ratios of carbon 13c and oxygen 18o from tree ring cellulose can provide valuable paleoclimatic information at annual and subannual resolution from time periods long before instrumental climate records recently mummified non permineralized wood was discovered within canadian subarctic kimberlites inviting paleoclimatic investigations of the time in which the trees grew in the mummified wood polysaccharides hemicellulose cellulose are frequently preferentially degraded in the low silica anaerobic burial environment of the kimberlites resulting in a lignin rich material however some samples from the ekati panda kimberlite pipe ca 53 3 ma contain remnant cellulose demonstrating the extraordinary preservation potential of kimberlites preservation of cellulose is important because it allows for the construction of stable isotopic proxy records of deep time paleoclimates at annual to subannual resolution established cellulose extraction methods i e using a 17 5 sodium hydroxide naoh solution were unsuitable for this material because all holocelluloses were dissolved therefore we tested variants of two cellulose extraction methods i e brendel et al 2000 and jayme wise leavitt and danzer 1993 loader et al 1997 to optimize a procedure for extraction of a consistent yield of mummified wood cellulose for stable isotopic analysis stable carbon 13c and oxygen 18o isotopes were measured from cellulose from each extraction method as well as extractive free wood and unextracted mummified wood vitrinite reflectance used to assess thermal alteration of the unextracted material to estimate post burial temperatures within the kimberlite suggested low post burial peak temperatures tpeak 60 c we detected no mineral contaminants i e iron oxides in the material using energy dispersive x ray spectroscopy edx despite low cellulose yield

paleoclimatic implications of the relationship between oxygen isotope ratios of moss cellulose and source water in wetlands of lake superior abstract groundwater dominated wetlands contain abundant peat deposits but few studies have addressed the potential of using the oxygen isotopic composition 18 o of fen peat cellulose to evaluate past changes in climate here we investigated the relationship between 18 o values of pond water and those of moss cellulose from species inhabiting different micro environments in three different swales near lake superior united states isotope results over two growing seasons indicate a negligible effect of evaporation on the studied fens and the strong control of groundwater on the isotopic composition of swale water isotopic values for groundwater show a small seasonal variability and their low values suggest the influence of snowmelt our results show a consistent offset of 27 1 between average swale water 18 o and cellulose 18 o values for hollow sphagnum species reflecting the fractionation associated with cellulose biosynthesis when sphagnum species from hummocks are included the offset shows a larger variability 27 3 pointing to evaporative effects affecting hummock species this evaporative effect is more pronounced in emerged mosses which show the largest difference 30 relative to their source water the smaller variability associated with hollow species points to the possibility of performing species specific analyses from peat cellulose for improved paleoclimatic reconstructions

cross bedded woody debris from a pliocene forested river system in the high arctic beaufort formation meighen island canada abstract cross bedding the inclined internal stratification that records the migration of certain transverse sedimentary bedforms is nearly ubiquitous in current transported bedload sediments although examples of the structure are known from inorganic clastic sediments and sedimentary rocks from practically all depositional environments and intervals of geologic history here we report cross bedded lenses that are composed wholly or significantly of woody debris in pliocene alluvium of the beaufort formation in the canadian high arctic the uniqueness of cross bedded woody debris has hitherto been overlooked but we demonstrate that in the entire phanerozoic record it is apparently restricted to alluvium deposited during a warm climatic interval that permitted the growth of boreal type forests within 10 latitude of the north pole the marked spatiotemporal restriction of cross bedded woody debris implies that there may be environmental factors unique to polar forests which promote the subaqueous transport of large amounts of fine woody debris as fluvial bedload we propose a non uniformitarian conceptual model for the formation of cross bedded woody debris in forested polar rivers whereby an exceptional abundance of woody debris could accumulate and become saturated and denser than water due to reduced decomposition on forest floors that were subject to prolonged periods of darkness and subzero temperatures

the relationship between the magnitude and direction of the geomagnetic field during the late tertiary in eastern iceland summary during the late tertiary well over 1000 lavas were extruded in eastern iceland potentially they each record an instantaneous description of the palaeomagnetic field we have systematically attempted to determine the palaeofield magnitude from one specimen from each lava about one in every four studied has yielded a palaeomagnitude value to go with the palaeofield direction value previously obtained there is a slight preference for reversely magnetized specimens to yield results results from 106 lavas indicate an arithmetic mean value for the virtual dipole moment vdm of 8 2 0 5 1022 am2 the data suggest an asymmetry whereby the normal polarity field was maintained in magnitude over a wider range of directions than was the reversed polarity field possibly indicating its greater stability

combined paleointensity and 40ar 39ar age spectrum data from volcanic rocks of the west eifel field germany evidence for an early brunhes geomagnetic excursion results of virtual geomagnetic pole position paleointensity and isotopic age determinations have been derived from lavas of the quaternary west eifel volcanic field germany the characteristic remanent magnetization carm directions and corresponding positions of virtual geomagnetic poles vgp have mainly been determined by bohnel et al they are exclusively of normal polarity the vgps form a strongly non fisherian distribution characterized by about 30 pole positions with latitudes below 60 n which are mainly confined to the longitude sector from 20 w to 120 e eight independent poles are clustered at 40 n and 45 e geomagnetic paleointensity values from 37 volcanic units of the west eifel have been determined paleointensities range from 7 to 62 t with an unexpectedly large number of paleointensity values below 30 t about half of the low paleointensity values are associated with intermediate vgp latitudes isotopic age determinations from west eifel volcanic rocks have been published fuhrmann and lippolt additional isotopic ages are presented here the west eifel volcanic field is usually devided into an older part in the nw and a younger one in the se based on petrological models and geological evidence all available isotopic ages of the west eifel volcanic rocks which are exclusively from the northwestern part of the field lie in the interval between 460 and 660 kyr for seven of the clustered low latitude vgps it was possible to determine paleointensities and 40ar 39ar ages within their error limits six poles have identical virtual dipole moments vdm at 3 5 1022a m2 furthermore the individual isotopic age intervals of the 40ar 39ar data overlap the assigned age of 510 30 kyr is considered to be the age of a geomagnetic excursion for higher latitude vgp positions 45 n vdm values range from 2 to 10 1022a m2 the mean vdm value about 7 5 1022a m2 of the younger volcanoes ages estimated to be below 100 kyr is not remarkably different from the present dipole moment of the earth in contrast the older volcanoes with higher latitude vgp positions yielded a mean value of only 5 3 1022a m2 and a bimodal frequency distribution of the vdm values isotopic ages determined for two of these volcanic units are close to the inferred excursion age suggesting a decrease of the geomagnetic dipole moment during a time interval which surpassed the duration of the excursion

on the temperature correlation of δ18o in modern precipitation reevaluation of modern precipitation temperature and isotope data permits reconciliation of previous disparate values for the correlation between 18o of modern precipitation and surface temperature past analysis has used the mean surface temperature over the time interval of sample collection e g mean weekly monthly or annual temperature to calculate temperature coefficients and different approaches at mid latitudes yield different temperature coefficients 18o t spatial correlations among geographically distinct sites yield 0 55 k seasonal variations at single sites yield 0 2 0 4 k and 12 month running averages yield 0 5 1 k however there are systematic differences in temperature during precipitation events vs time averaged surface temperature means correction for this bias using hourly weather and monthly isotope data from u s sites yields a single value of 0 55 k for all three approaches revised temperature coefficients based on surface observations are also commensurate with coefficients obtained using cloud base temperatures and with theoretical distillation models 0 5 0 7 k these coefficients provide a consistent basis for validation of general circulation models that incorporate stable isotopes of precipitation and for comparison to independent estimators of the isotopic response to climate change

climate signals in tree ring width density and δ13c from larches in eastern siberia russia abstract we present the first and longest 413 years dataset on stable carbon isotope ratios in tree ring cellulose 13c tree ring width trw and maximum latewood density mxd obtained from larch trees growing on permafrost under continental climate in the suntar khayata mountain ridge in eastern siberia russia with this first study we calibrate tree ring parameters against climate quantities and based on these results assess the potential added value of mxd and especially of 13c complementing trw analysis for future climate reconstruction purposes 13c chronologies were corrected for human induced changes in atmospheric co2 since ad 1800 two different approaches were compared i a correction referring merely to the decline in atmospheric 13c 13catm and ii a correction additionally accounting for the increase in atmospheric partial pressure of co2 13c chronologies are characterized by strong signal strength with only 4 trees representing the population signal at the site mean inter series correlation 0 71 and eps 0 90 13c variation shows low similarity to trw and mxd while correlation between trw and mxd is highly significant correlation analysis of tree ring parameters with gridded instrumental data climate research unit cru ts 2 1 over the ad 1929 2000 calibration period demonstrates that trw and mxd react as reported from other sites at cold and humid northern latitudes precipitation plays no significant role but strong dependencies on monthly mean maximum and minimum temperatures particularly of the current summer june to august are found up to r 0 60 p

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

a 500 year record of summer near ground solar radiation from tree ring stable carbon isotopes tree ring stable carbon isotope ratios d13c in environments of low moisture stress are likely to be controlled primarily by photosynthetic rate therefore sunshine rather than temperature represents the more direct controlling factor temperature reconstructions based on tree ring d13c results thus rest on the assumption that temperature and sunshine are strongly coupled this assumption is tested using a d13c series from pine trees in nw norway where there are long 100 yr records of both summer temperature and cloud cover it is demonstrated that when summer temperature and d13c diverge summer temperature and cloud cover also diverge and that cloud cover sunshine may provide a stronger and more consistent parameter with which to calibrate tree ring d13c series in this area when a 500 year reconstruction of summer cloudiness is compared with a published reconstruction of summer temperatures in northern sweden based on tree ring maximum densities the two time series are largely parallel with

mafic potassic lavas of the quaternary west eifel volcanic field major and trace element analyses for 103 volcanoes of the quaternary west eifel volcanic field show the lavas to be dominantly primitive mgo 7 wt and potassic na2o k2o 1 the rocks are divided into 1 a foidite f suite volumetrically dominant and consisting of four types leucitites and nephelinites melilite bearing foidites olivine free foidites sodalite bearing melilite free foidites and 2 a younger olivine nephelinite and basanite onb suite concentrated in the southeastern part of the field dominantly cpx phyric f suite magmas differ from the dominantly ol phyric onb suite mainly in higher k2o na2o and cao al2o3 ratios higher rb cu h2o co2 and lree concentrations and slightly lower sr ni and y contents most magmas have fractionated small amounts of olivine clinopyroxene and minor phlogopite systematic compositional variations within volcanoes or volcano groups are rare five more differentiated volcanoes 2 tephrites 3 phonolites occur in the center of the field their magmas are interpreted to have formed by fractionation within crustal magma chambers

pockmark formation by porewater expulsion during rapid progradation in the offshore taranaki basin new zealand abstract after the first discovery of seabed pockmarks in the 1960s and 1970s many examples of both modern and ancient pockmarks have been reported from sedimentary basins around the world the exact mechanisms and fluids involved in pockmark formation are still subject to debate with many studies inferring that pockmark formation is a direct indication of hydrocarbon expulsion this study provides the first description of a buried pliocene paleo pockmark field in the offshore taranaki basin new zealand the paleo pockmarks are located approximately 1 2 1 3 km below the seabed and are well imaged by three dimensional seismic data their spatial density and size increases towards the distal portions of the fan and they vary in size between 45 and 580 m in diameter and 2 35 ms twt pockmark size is inversely correlated with the fan thickness in the study area detailed analysis rules out any links with faulting while the relationship with fan variations in the depositional thickness suggests porewater expulsion during overburden progradation as the most likely cause of the paleo pockmarks a model is proposed in which rapid sediment loading generated overpressure which was greatest on the proximal fan due to the lateral gradient in the sediment load imposed by clinoform progradation fluids were consequently forced towards the distal fan where eventually the pore pressure exceeded the fracture gradient of the seal the implications of this study are that not all pockmarks can be used as evidence for hydrocarbon expulsion in frontier regions and care should be taken to examine the subsurface context plumbing systems and any associated acoustic anomalies before concluding on the pockmark origin

climate in southwestern ontario canada between ad 1610 and 1885 inferred from oxygen and hydrogen isotopic measurements of wood cellulose from trees in different hydrologic settings abstract oxygen and hydrogen isotopes were measured in wood cellulose and cellulose nitrate from trees that grew in different hydrologic settings in southwestern ontario canada an isotope model that accounts for isotopic fractionations associated with photosynthesis in plants was applied to the stable isotope data to infer past meteoric water isotopic composition and seasonal air moisture variations the model inferred climate data was rationalized in terms of the trees hydrologic environment and weather characteristics of the great lakes region the result is an account of summer and winter conditions in southwestern ontario for 275 years 1610 to 1885 prior to instrumental climate records conditions between 1610 and 1750 are inferred to have been cooler and drier than present this was followed by a warm moist climate interval between 1750 and 1885 during which there was an increase in winter precipitation cool dry conditions were recorded instrumentally in this region at the end of the nineteenth century

late jurassic half graben control on the siting and structure of hydrocarbon accumulations uk norwegian central graben abstract the late jurassic structure of the central graben is discussed both in terms of the extensional features developed at this time and their subsequent controls on younger inversion structures the regional kinematics of the north sea rift suggest that during the late jurassic the central graben opened approximately orthogonally to the main nnw sse fault trend within the basin some evidence that triassic extensional faults were reactivated at this time is seen towards the basin margins and a significant triassic extensional history is inferred the late jurassic basin comprises the axial c 100 km of the central graben s l the basin axis is offset progressively to the se by both transfer zones and discrete transfer faults footwall uplift of the basin margins during extension provided the source for the upper jurassic reservoir sands encountered by exploration drilling these sands were probably preferentially fed into the basin at transfer zones in the margins salt structures are ubiquitous within the central graben and their siting is everywhere controlled by the underlying fault block topography salt structures form preferentially towards the crests of half graben or buttressed against their boundary faults inversion structures in the norwegian sector reactivated with a reverse sense of displacement late jurassic extensional faults a model is proposed which shows the two main inversion structures feda graben norway tail end graben denmark to be detached on antithetic reverse faults riding in the salt these faults terminate at tip folds within major salt walls the geometry of the inversion structures can be understood only when considered together with the geometry of the underlying late jurassic half graben

influence of poroelastic behavior on the magnitude of minimum horizontal stress sh in overpressured parts of sedimentary basins in many sedimentary basins of the world the minimum hori zontal stress s h is greater in overpressured zones than in normally pressured zones at equivalent depths a common explanation is that the frictional slip on listric normal faults keeps the difference between vertical stress s v and s h within certain bounds and the difference is smaller under lower effective stress i e higher pore pressure p p however in the overpressured parts of the central north sea graben united kingdom and the sable subbasin of the scotian shelf canada conventional friction envelopes underestimate the magnitude of s h these data instead indicate that s h increases at a rate proportional to but less than the rate of increase of p p a condition consistent with a p p induced deformation of the rock called poroelastic behavior this paper argues that whereas friction may govern s h in normally pressured basins poroelastic behavior is responsible for the unusually high s h in the overpres sured parts of these same basins data on the p p and s h gradients from these basins suggest that s h p p 0 7

organic geochemical indicators of dynamic fluid flow processes in petroleum basins a variety of preliminary geophysical geochemical and geological observations anderson et al geophysics 12 17 april 1991a b anderson oil gas j 85 91 26 april 1993 along with well production data schumacher aapg ann conv abstr april 1993 have led to the hypothesis that fluid injection into eugene island block 330 ei 330 in the u s louisiana gulf coast may be a continuing episodic process with the most recent injections having occurred on short geologic time scales 10 000 yr or less organic geochemical evidence presented here suggests these processes may occur on very short time scales years a process called dynamic fluid injection was proposed to explain these observations and is envisioned as episodic pressure build up followed by rapid escape of gas and oil through geopressure and injection into overlying reservoirs

carbon and oxygen isotopes of lakeshore black spruce trees in northeastern canada as proxies for climatic reconstruction abstract in the boreal zone of northeastern canada paleoclimatic reconstructions of millennial length are rare and long isotopic climatic records are unavailable however millennial tree ring series could be constructed within the region by cross dating sub fossil stems preserved in the littoral part of lakes thus there is a need to evaluate the potential of using stable isotopes of lakeshore black spruce trees picea mariana mill b s p as proxies for climatic reconstruction we collected four living riparian black spruce trees and we investigated the inter and intra tree correlations for four trees at two different sampling heights 1 and 4 m for their carbon 13c and oxygen 18o isotopes as a test for potential long term reconstruction a significant correlation pearson coefficient for the isotopic series was found for the two sampling heights r 0 92 for 13c 0 65 for 18o and between the four trees we further assessed the climatic significance of the mean of the four trees the strongest correlation of the 13c series was with the mean of june to august vapor pressure deficit vpd r 0 50 and the 18o values with the june to august climatic index and june to july maximal temperature r 0 61 and 0 55 respectively this study suggests that 18o series of riparian black spruce trees and eventually their sub fossil counterparts can be used as proxies for reconstructing long climatic series in northeastern canada

coupling of co2 and ice sheet stability over major climate transitions of the last 20 million years the co2 content of the atmosphere has varied cyclically between 180 and 280 ppmv over the last 800 000 years closely coupled with temperature and sea level for earlier periods in earth s history pco2 is much less certain and the relationship between pco2 and climate remains poorly constrained we use boron calcium ratios in foraminifera to estimate pco2 during major climate transitions of the last 20 million years myr during the middle miocene when temperatures were 3 to 6 c

significantly warmer arctic surface temperatures during the pliocene indicated by multiple independent proxies temperatures in the arctic have increased by an astounding 1 c in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades the pliocene 2 6 5 3 ma is of particular interest as an analog for future warming because global temperatures were signifi cantly warmer than today for a sustained period of time with continental confi gurations similar to present here we estimate mean annual temperature mat based upon three independent proxies from an early pliocene peat deposit in the canadian high arctic our proxies including oxygen isotopes and annual ring widths mat 0 5 1 9 c coexistence of paleovegetation mat 0 4 4 1 c and bacterial tetraether composition in paleosols mat 0 6 5 0 c yield estimates that are statistically indistinguishable the consensus among these proxies suggests that arctic temperatures were 19 c warmer during the pliocene than at present while atmospheric co 2 concentrations were 390 ppmv these elevated arctic pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo these results indicate that arctic temperatures may be exceedingly sensitive to anthropogenic co 2 emissions