holocene climatic and environmental changes inferred from midge records diptera chironomidae chaoboridae ceratopogonidae at lake berkut southern kola peninsula russia a radiocarbon dated sediment sequence from lake berkut in the southern part of the kola peninsula northwest russia was investigated by means of midge analysis in order to reconstruct the holocene climatic and environmental history of the region past mean july air temperatures at the study site and hypolimnetic oxygen contents of the lake water were inferred from chironomid based transfer functions the early holocene c 10 100 8400 cal yr bp is characterized by summer temperatures and hypolimnetic oxygen concentrations broadly similar to present day conditions the midge records give evidence of a lake level fall at c 7000 cal yr bp resulting in weakened thermal stratification of the lake water and improvement of the hypolimnetic oxygen conditions after c 4000 cal yr bp midge assemblages suggest a lake level rise related to increased effective moisture a secondary mid holocene climatic optimum with inferred mean july air temperatures of c 12 1 degrees c was recorded between 6000 and 4400 cal yr bp followed by minimum values c 11 3 degrees c between 3500 and 1500 cal yr bp accompanied by the onset of natural acidification of the lake the late holocene midge assemblages suggest weakly acidic conditions low hypolimnetic oxygen contents and a general warming trend during the last c 1500 years although paludification and natural acidification may have influenced the temperature reconstruction at this stage however the modern chironomid inferred mean july air temperature 12 5 degrees c is consistent with meteorological data from a nearby station in general the midge records reflect relatively warm and moist conditions at lake berkut before c 7000 cal yr bp a relatively warm and dry climate at c 7000 4000 cal yr bp and a shift to cooler and wetter climatic conditions in the region after c 4000 cal yr bp less

parametric representation of the primary hurricane vortex part i observations and evaluation of the holland 1980 model although numerical models are essential to hurricane forecasting many other applications require only statistical depiction of the wind distribution in holland s 1980 parametric profile radius of maximum wind maximum wind and a measure of the profile width describe the radial variation of the axisymmetric wind variants of the holland profile are used to predict insurance underwriting risk ocean response and storm surge inundation since these calculations guide high stakes financial and emergency managment decisions it is logical to test them against observations the hurricane research division s flight level database archives observations were obtained by noaa and u s air force reserve aircraft the data considered here are winds and geopotential heights observed during 606 lower and midtropospheric flights into atlantic and eastern pacific tropical cyclones during 1977 2000 the 493 profiles that meet quality control criteria are seasonally geographically representative least squares fits of the holland model to these data provide evaluation of the parameters distributions and critical examination of the profile s realism individual fitted profiles differ from the observations in a consistent pattern the areas of strong winds in the eyewall and of nearly calm winds at the vortex center are too wide beyond 2 or 3 times the eye radius the wind decreases too rapidly with distance from the center although the average bias in fitted profiles is 1ms 21 the root mean square error is 4 2 m s 21 5 2 m s21 for independent data maximum winds estimated from the fitted holland profile height wind relation average 2 5 m s 21 too strong with an rms error of 6 5 m s 21 the pattern of too strong wind spread over too much real estate exaggerates the occurrence of winds stronger than 50 m s 21 by 50

directional analysis of sar images aiming at wind direction currently the retrieval of wind fields from synthetic aperture radar sar images suffers from inadequate knowledge of the wind direction state of the art spectral analysis works fine on open seas but is limited in spatial resolution the method described here is based on the local gradients computed with standard image processing algorithms it handles image features not caused by wind and can be applied to irregularly shaped regions the new method has already been applied to many images from the european remote sensing satellite sars and radarsat 1 scansar usually supplying reasonable wind fields the spatial sampling most frequently used was 20 spl times 20 and 10 spl times 10 km sup 2 in some cases samplings down to 1 spl times 1 km sup 2 were tested this paper describes the local gradients method including the filtering of nonwind generated image features and gives some application examples

new constraints on the 138la β decay constant based on a geochronological study of granites from the yilgarn block western australia abstract the decay constant of 138 la has been geochronologically determined using archean granites from the yilgarn block western australia rb sr and sm nd mineral isochron ages were obtained for the two granite samples which are nearly identical with the ion microprobe u pb zircon ages this agreement indicates that the closure date for these samples is the same within analytical error making them suitable for geochronological estimation of the decay constant for 138 la applying a new method of ce isotope analysis with analytical reproducibility of 0 008 la ce isotope data for the studied samples resulted in precise mineral isochrons based on these internal mineral isochrons and ages determined by other geological clocks the decay constant for 138 la was estimated to be 2 33 0 24 10 12 a 1 2

holocene climate variability on the kola peninsula russian subarctic based on aquatic invertebrate records from lake sediments sedimentary records of invertebrate assemblages were obtained from a small lake in the khibiny mountains kola peninsula together with a quantitative chironomid based reconstruction of mean july air temperature these data provide evidence of holocene climate variability in the western sector of the russian subarctic the results suggest that the amplitude of climate change was more pronounced in the interior mountain area than near the white sea coast a chironomid based temperature reconstruction reflects a warming trend in the early holocene interrupted by a transient cooling at ca 8500 8000 cal yr bp with a maximum drop in temperature ca 1 c around 8200 cal yr bp the regional holocene thermal maximum characterized by maximum warmth and dryness occurred at ca 7900 5400 cal yr bp during this period july temperatures were at least 1 c higher than at present the relatively warm and dry climate persisted until ca 4000 cal yr bp when a pronounced neoglacial cooling was initiated minimum temperatures ca 1 2 c lower than at present were inferred at ca 3200 3000 cal yr bp faunal shifts in the stratigraphic profile imply also that the late holocene cooling was followed by a general increase in effective moisture

a new geochronometer using lanthanum 138 we have applied a new geochronometer based on the decay of 138la to 138ba to a sample of amitsoq gneiss from west greenland using a value for the electron capture decay constant ec of 4 44 10 12 yr 1 the resulting age 2 408 24 myr is in good agreement with that from sm nd systematics 2 410 54 myr application of this geological clock is limited to ree rare earth element rich minerals but its merit is that for archaean rocks the age can be evaluated from one specimen on the assumption that the initial ba isotope ratios are effectively constant

tropical cyclone intensity estimated from wide swath sar images due to the relatively small amount of in situ data available for the open oceans remote sensing techniques take an important role in the retrieval of geophysical information particularly during extreme events the work presented here aims at the improvement of prediction of cyclone intensity using synthetic aperture radar sar images a new method to measure the hurricane intensity using sar images in combination with a parametric holland type model of wind speed is presented the algorithm is based on a least square minimization of the difference between the parametric model results and the sar measurement the radius of the maximum wind speed required as input for the minimization procedure is estimated from the sar image using wavelet analysis information on wind direction is extracted from the sar image through analysis of image features caused by boundary layer rolls the root mean square error of the suggested method has been validated to be equal to 3 9 m s the study is based on a data set of wide swath sar images of about 400 km 400 km coverage acquired by the european envisat satellite over tropical cyclones as a case study hurricane katrina is investigated in detail a total of five tropical cyclone images will be used to validate the results of the new algorithm

can synthetic aperture radars be used to estimate hurricane force winds 1 we compare wind fields retrieved from a radarsat i synthetic aperture radar sar image acquired over hurricane ivan on september 10 2004 using the c band geophysical model functions cmod4 and its newest version cmod5 cmod4 has previously been shown to yield very good wind field estimates under low and moderate wind conditions wind directions obtained from streaks imaged by the sar that are well aligned with the mean surface wind direction are used to invert both algorithms to obtain estimates of the wind speed on scales of 1 km these estimates are compared with predictions from a high resolution tropical cyclone model as well as local in situ data it is found that the sar wind speeds using cmod5 agree reasonably well while those from cmod4 significantly under predict the measured wind speeds near the hurricane eye wall that reach values as high as 60 m s 1

the distribution of late quaternary woody taxa in northern eurasia evidence from a new macrofossil database we present a database of late quaternary plant macrofossil records for northern eurasia from 23 to 180 e and 46 to 76 n comprising 281 localities over 2300 samples and over 13 000 individual records samples are individually radiocarbon dated or are assigned ages via age models fitted to sequences of calibrated radiocarbon dates within a section tree species characteristic of modern northern forests e g picea larix tree betula are recorded at least intermittently from prior to the last glacial maximum lgm through the lgm and lateglacial to the holocene and some records locate trees close to the limits of the scandinavian ice sheet supporting the hypothesis that some taxa persisted in northern refugia during the last glacial cycle northern trees show differing spatio temporal patterns across siberia deciduous trees were widespread in the lateglacial with individuals occurring across much of their contemporary ranges while evergreen conifers expanded northwards to their range limits in the holocene

mid holocene warming in the northwest kola peninsula russia northern pine limit movement and stable isotope evidence a set of 40 subfossil scots pines pinus sylvestris l was sampled in small lakes beyond the modernpine limit in the northwest kola peninsula russia radiocarbon dating suggests that the pine exp

origin of storm footprints on the sea seen by synthetic aperture radar spaceborne synthetic aperture radar can detect storm footprints on the sea coastal weather radar from cape hatteras provides evidence that the echo free hole at the footprint core is the result of wave damping by rain the increased radar cross section of the sea surrounding the echo free hole results from the divergence of the precipitation forced downdraft impacting the sea the footprint boundary is the gust front its oriention is aligned with the direction of the winds aloft which are transported down with the downdraft and its length implies downdraft impact 1 hour earlier at a quasi stationary impact spot the steady localized nature of the storm remains a mystery

ion microprobe 232th 208pb ages from high common pb monazite morefield mine amelia county virginia implications for alleghanian tectonics monazite ce th po4 from a pegmatite in the morefield mine of the eastern piedmont of central virginia has unusually high and variable amounts of common pb leading to problematic interpretations of its u th pb ages and how the monazite relates to nearby granite intrusions and faults to address these issues we analyze a single large monazite grain from the pegmatite using electron microprobe analysis empa n 64 laser ablation inductively coupled plasma mass spectrometry la icp ms n 58 and secondary ion mass spectrometry sims n 59 the monazite study grain exhibits compositional variations in proximity to microcracks consistent regions of secondary alteration and recrystallization although the compositions of these regions fit the ideal stoichiometry of monazite they have lower si th u and y and higher p rare earth element ree and ca concentrations compared to visibly unaltered portions of the grain la icp ms and sims analyses demonstrate that common pb as proxied by 204pb is enriched in proximity to microcrack regions and correlates with 137ba sims 232th 208pb analysis from grain regions with lowest contents of common pb 208pb comprises 99 of pb isotopes yields two sets of ages 263 5 3 0 ma 1 mswd 1 7 n 11 and 234 1 3 3 ma 1 mswd 0 4 n 13 regionally the ages are similar to the youngest appalachian pegmatite bodies emplaced during the terminal alleghanian laurentia africa collision however the monazite ages are younger than locally surrounding intrusions the closest intrusive in distance 30 km and age is the petersburg granite 296 33 0 11 ma zircon 238u 206pb the emplacement of which coincided with activity along the hylas fault because the fault experienced a brittle ductile transition in the late permian 262 ma coeval with the older 232th 208pb monazite age group we postulate that the hylas fault may have operated as a fluid migration system between the petersburg granite and morefield mine pegmatite the younger monazite age coincides with triassic normal and or sinistral faulting linked to the development and deformation of local rift basins

medieval climate warming and aridity as indicated by multiproxy evidence from the kola peninsula russia data obtained from the low elevation khibiny mountains ca 67 68jn 33 34je on the kola peninsula northwest russia indicate a period of exceptionally warm and dry conditions commenced at ca ad 600 and was most pronounced between ca ad 1000 and 1200 warmer summer temperatures during this period coeval with the medieval warm period observed in other parts of europe are evident in a 100 140 m upward shift in the pine pinus sylvestris l limit in the khibiny mountains on average the cellulose of pine trees that grew between ca ad 1000 and 1300 is enriched by y 13 c values of around 1xcompared to the modern trees from the region further suggesting warmer summer climate than at present the medieval warm period was also accompanied by a steady decline in avalanche activity and the resulting formation of soils on the current avalanche cones in the khibiny mountains suggesting lower winter precipitation and thinner snow cover lower precipitation is also evident by currently submerged tree stumps dating to the medieval period that indicate lower lake levels on the kola peninsula in the middle of the peninsula at about ad 1000 the level of small closed basin lakes was f1 m lower than the modern time at some sites drier conditions may be attributable to decreased cyclonic activity the medieval warm and dry episode was followed at ca ad 1300 by the development of a colder climate with increased precipitation resulting in a decline in the alpine pine limits increased avalanche activity and higher lake levels that phase corresponds to the modern aeolian episode reconstructed in subarctic finland our results indicate that the medieval warm period on the kola peninsula

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

cross polarization geophysical model function for c band radar backscattering from the ocean surface and wind speed retrieval the wind speed sensitivity of cross polarization cross pol radar backscattering cross section vh from the ocean surface increases toward high winds the signal saturation problem of vh if it exists occurs at a much higher wind speed compared to the copolarization copol vv or hh sea returns these properties make vh a better choice over vv or hh for monitoring severe weather combined with high spatial resolution of the synthetic aperture radar sar the development of hurricane wind retrieval using vh is advancing rapidly this paper describes a cross pol c band radar backscattering geophysical model function gmf with incidence angle dependence for the full wind speed range in the available data sets up to 56 m s the gmf is derived from radarsat 2 r2 dual polarization dual pol scansar modes with 300 and 500 km swaths the proposed gmf is compared to other published algorithms the result shows that the simulated vh cross section and the retrieved wind speed with the proposed gmf is in better agreement with measurements with careful treatment of noise the vh retrieved wind speeds may extend to mild or moderate conditions the higher fraction of non bragg contribution in vh can be exploited for analysis of surface wave breaking

wave glider observations of surface winds and currents in the core of typhoon danas simultaneous monitoring of surface winds and currents is essential to understand oceanic responses to tropical cyclones we used a new platform a wave glider liquid robotics to observe air sea processes during a typhoon equivalent to a category 4 hurricane at peak strength near okinawa japan surface winds showed strong asymmetry in both speed and direction faster fore than aft rotations of surface winds and currents were not coupled currents rotated clockwise in the wake of the typhoon eye after passage of rapid wind rotations wind work was mostly done ahead of the eye amplifying prior inertial motions with a phase shift wind induced energy was nearly balanced with an increase in estimated kinetic energy of the upper ocean current relative to prior inertial oscillations this study provides a newer more complete view of actual atmosphere ocean interactions in a typhoon

mesoscale and convective scale characteristics of mature hurricanes part i general observations by research aircraft abstract the analysis of instrumented aircraft data from four recent mature hurricanes reveals common mesoscale and convective scale features the structure and organization of the convection precipitation and wind flow are studied by combining the airborne observations using basic instrumentation with quantitative radar measurements three predominant precipitation features seen are 1 the eyewall 2 a stratiform rain region adjacent to and outside the eyewall and 3 rainbands that contain both convective and stratiform regions the eyewall is so named because it surrounds the rain free eye but several additional features distinguish it from other convective bands in the hurricane in particular the updraft tangential wind maximum and highest rainfall have preferred locations relative to each other with the updraft being radially inward from the rain and wind maxima the 10 dbz radar reflectivity contour indicative of the inner edge slopes substantially outward with height and there is evide

holocene climate of the kola peninsula evidence from the oxygen isotope record of diatom silica holocene climate variability was studied in a lake sediment record covering the last c 9000 years from lake chuna on the kola peninsula north west russia using the oxygen isotope composition of diatom silica 18odiatom the evaporation of the lake waters is likely to be minimal and thus the isotopic composition of the lake waters recorded by the 18odiatom reflects the isotopic composition of summer precipitation overall the 18odiatom signal seems to record a predominance of the polar arctic air mass bringing cold summer air temperatures immediately after the last glaciation and again after 4000 years to present time the atlantic maritime air mass is likely to have supplied warm summer rainfall especially in the mid holocene the pattern is broadly consistent with a quantitative pollen reconstruction from chuna lake which suggests higher mean july temperatures from deglaciation to 5500 years bp with a rather steep decline to lower temperatures after 4000 years bp our results support the general regional scenario of a mid holocene warm period deduced from the higher tree line vegetation changes and glacier fluctuations in fennoscandia however the 18odiatom record from the kola peninsula suggests a relatively cold early holocene with a gradual shift to warmer conditions to a maximum at around 5000 4000 years bp assuming that the modern precipitation temperature relationship has been constant throughout the holocene

mediaeval climatic warming recorded by radiocarbon dated alpine tree line shift on the kola peninsula russia studies of the tree line history in northern fennoscandia provide useful evidence about the holocene environment and the region s climatic history here we report on late holocene alpine tree line movement in the khibiny low mountains on the kola peninsula northwestern russia a highly representative collection of subfossil woods above the modern tree line was obtained and 49 pine samples were radiocarbon dated their radiocarbon ages range from c 1400 to 3000 yr bp with a distinct maximum between c 800 and 1000 yr bp about cal ad 1000 to 1300 we conclude that especially during the mediaeval climatic optimum pine forests grew at least 100 140 m above the modern pine tree line in the khibiny mountains

on the use of doppler shift for sea surface wind retrieval from sar the synthetic aperture radar sar doppler centroid has been used to estimate the scatter line of sight radar velocity in weak to moderate ocean surface current environment the sar doppler centroid is dominated by the directionality and strength of wave induced ocean surface displacements in this paper we show how this sea state signature can be used to improve surface wind retrieval from sar doppler shifts of c band radar return signals from the ocean are thoroughly investigated by colocating wind measurements from the ascat scatterometer with doppler centroid anomalies retrieved from envisat asar an empirical geophysical model function cdop is derived predicting doppler shifts at both vv and hh polarization as function of wind speed radar incidence angle and wind direction with respect to radar look direction this function is used into a bayesian inversion scheme in combination with wind from a priori forecast model and the normalized radar cross section nrcs the benefit of doppler for sar wind retrieval is shown in complex meteorological situations such as atmospheric fronts or low pressure systems using in situ information validation reveals that this method helps to improve the wind direction retrieval uncertainty of the calibration of doppler shift from envisat asar hampers the inversion scheme in cases where nrcs and model wind are accurate and in close agreement the method is however very promising with respect of future sar missions in particular sentinel 1 where the doppler centroid anomaly will be more robustly retrieved

tree ring and summer temperature response to volcanic aerosol forcing at the northern tree line kola peninsula russia potential linkages between volcanic activity and a 403 year record of pinus sylvestris l scots pine growth and summer temperatures estimated from tree ring widths are evaluated from an arctic tree line site on the kola peninsula northwestern russia the joint occurrence of volcanic eruptions and severe negative ring width values is more than four times that expected by chance a composite average of temperatures indicates that a 0 72 c temperature reduction is typical for the year immediately following volcanic eruptions while tree growth is reduced for up to two decades the greenland ice sheet project 2 gisp2 volcanic sulphate record shows a small but significant correlation with summer temperatures volcanic aerosols originating at low and middle latitudes appear to cause the greatest ring width reduction and cooling

on solar forcing of holocene climate evidence from scandinavia the focus of this study is the possible correlation between changes in the climate of scandinavian and changes in solar irradiation reliable information about holocene climatic change in sweden and norway is currently available from two main sources the 14c dating of pine wood retrieved from above the present pine tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines the reconstructed alpine tree limit reveals that summer temperature in general was warmer during the early holo cene than it was during the late holocene superimposed on this general trend are several fluctuations of a few hundred years duration relatively cold periods with a duration of the order of 300 600 years occurred frequently during the holocene in this paper dates of the major climatic events are compared with an index of solar activity the so called 14c anomalies for most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in scandi

hurricane sea surface inflow angle and an observation based parametric model abstractthis study presents an analysis of near surface 10 m inflow angles using wind vector data from over 1600 quality controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes the mean inflow angle in hurricanes is found to be 22 6 2 2 95 confidence composite analysis results indicate little dependence of storm relative axisymmetric inflow angle on local surface wind speed and a weak but statistically significant dependence on the radial distance from the storm center a small but statistically significant dependence of the axisymmetric inflow angle on storm intensity is also found especially well outside the eyewall by compositing observations according to radial and azimuthal location relative to storm motion direction significant inflow angle asymmetries are found to depend on storm motion speed although a large amount of unexplained variability remains generally the largest storm relative inflow angles 50 are found in the fas

holocene tree line permafrost and climate dynamics in the nenets region east european arctic pollen stomata and macrofossils in a lake core with a basal date of 9700 14 c bp were used to reconstruct past changes in climate and vegetation in the arctic tree line area northeast european russia a palsa peat profile was investigated to establish a chronology of mire initiation and permafrost development during the holocene macrofossils show that tree birch was present in the study area at the beginning of the holocene and stands of spruce became established shortly thereafter however pollen evidence suggests that almost 400 years passed before the area was occupied by a mixed spruce birch forest which lasted until ca 5000 bp subsequently the area reverted to forest tundra paludification began ca 9000 bp continuing at least until 5700 bp the conditions were permafrost free at least until 4500 bp the latest permafrost aggradation phase is dated to the little ice age we interpret summer temperatures to have been ca 3 4 c higher between ca 8900 and 5500 bp than at present and the lowest temperature regime of the holocene to have occurred between 2700 and 2100 bp resume du pollen des stomates et des macrofossiles dans une carotte de fond de lac ayant une date de base de 9700 14 c avant le present ont ete utilises pour reconstruire d anciens changements dans le climat et la vegetation dans

a statistical analysis of the effects of vertical wind shear on tropical cyclone intensity change over the western north pacific abstractthe effect of vertical wind shear vws between different pressure levels on tc intensity change is statistically analyzed based on the best track data of tropical cyclones tcs in the western north pacific wnp from the joint typhoon warning center jtwc and the ecmwf interim reanalysis era interim data during 1981 2013 results show that the commonly used vws measure between 200 and 850 hpa is less representative of the attenuating deep layer shear effect than that between 300 and 1000 hpa moreover the authors find that the low level shear between 850 or 700 and 1000 hpa is more negatively correlated with tc intensity change than any deep layer shear during the active typhoon season whereas deep layer shear turns out to be more influential than low level shear during the remaining less active seasons further analysis covering all seasons exhibits that a tc has a better chance to intensify than to decay when the deep layer shear is lower than 7 9 m s 1 and the low level shear is below

cerium isotope geochemistry of ocean island basalts the source of ocean island basalts is one of geology s major problems and many different models have been proposed one of these involves recycling of continental and oceanic crustal material into the mantle source of ocean island basalt magmas1 2 island arc basalts are an important link in the chain of evidence that supports this model as they display isotope signatures in common with both ocean floor sediment2 4 and ocean island basalts1 5 but hafnium isotope data6 appear either to place severe restrictions on the quantity of sedimentary material recycled into the mantle or to demand very thorough homogenization of this material during the subduction process the lanthanum cerium isotope method7 offers a prospect of applying similar constraints to the recycling of different sediment types into the mantle based on cerium and neodymium isotope systematics here i report cerium isotope ratios for eight ocean island basalts when plotted against published neodymium isotope data these form a mantle array of compositions which indicates coherent behaviour of the two elements during mantle differentiation this precludes the recycling into the deep mantle of ocean floor sediments with a large net cerium anomaly

holocene temperature changes in northern fennoscandia reconstructed from chironomids using bayesian modelling the recently developed bayesian multinomial calibration model bummer was applied to the fossil chironomid assemblages of a lake situated at the present tree line in northern fennoscandia to reconstruct patterns in holocene climates the results are compared with inferences derived using non bayesian weighted averaging partial least squares regression the reconstruction exhibits both long term trends as well as a series of shorter term oscillations abrupt climatic excursions were particularly characteristic for the early holocene period with cooling episodes around 9200 8600 and 8200 cal yr bp the interval from ca 8000 to 5800 cal yr bp appeared to be warm and stable but was followed by a pronounced climatic cooling around 5800 cal yr bp leading to a relatively long lasting mid holocene temperature minimum between ca 5800 and 4000 cal yr bp the reconstruction during the latter part of the holocene is relatively featureless which may partly be due to gradual shallowing of the lake by sedimentation that may have affected chironomid compositions thereby masking the climate signal the major climatic patterns in our reconstruction agree well with inferences from greenland ice and marine sediments and are also in line with the previous reconstructions based on diatoms and pollen from the same core although the finer scale variations reflected by the three proxies do not always match the overall results provide evidence for climatic complexity during the holocene epoch and demonstrate that bayesian modelling is highly suitable for reconstruction purposes

la ce dating of lewisian granulites to constrain the 138la β decay half life the isotope 138la makes up 0 089 of natural lanthanum and exhibits a branched decay by to 138ce and electron capture to 138ba the la ce isotope scheme is a potentially powerful adjunct to the sm nd method for petrogenetic studies but the best determination by counting of the decay half life of la 3 02 x 1011 yr 1 is in conflict with geological half life determinations based on la ce and sm nd mineral isochrons2 4 to test these alternatives i determined a six point la ce isochron on whole rock samples of lewisian granulite facies archaean gneiss from nw scotland here i report based on a half life of 3 02 1011yr a la ce age of 2 990 400 myr 2 which falls very well within the error of a whole rock sm nd date on lewisian granulites of 2 895 100 myr 2 this half life equivalent to a la decay constant of 2 30 10 12 yr 1 is therefore recommended for geological application of the ce isotope method

a hurricane wind speed retrieval model for c band radarsat 2 cross polarization scansar images a hybrid backscattering model is built to provide a consistent description for c band vh and vv polarized normalized radar cross sections nrcss ocean surface co and cross polarized nrcs are both treated as a sum of bragg and non bragg scattering components to better understand the synthetic aperture radar sar observed nrcs signals under high wind conditions five c band radarsat 2 dual polarization sar hurricane images and the collocated wind vectors measured by the airborne stepped frequency microwave radiometer sfmr are collected based on the match up data we add a non bragg term in the composite bragg theory to explain the discrepancy between the measurements in the cross polarization channel and the existing theory results the non bragg scattering to bragg scattering ratio b r is found to be a constant we build the hybrid backscattering model with b r and establish a relationship between the cross polarization nrcs and the radar incidence angle under different wind conditions the nrcs dependence on incidence angle is simulated by the hybrid backscattering model finally a c band cross polarization coupled parameters ocean c 3po model is developed to retrieve hurricane winds using vh polarized scansar by including the radar incidence angle the collocated sar and sfmr data sets are separated into two parts data set a for hybrid backscattering model derivation and c 3po model coefficients tuning and data set b for hurricane wind validation c 3po model validation results show that the model is suitable for ocean surface wind mapping from radarsat 2 cross polarization scansar images the retrieval has a root mean square error less than 3 m s for wind speed up to 40 m s

footprints of storms on the sea a view from spaceborne synthetic aperture radar synthetic aperture radar sar on board seasat observed images of stormlike echoes on the sea in 1978 the core of these images is usually an echo free hole which is attributed to the damping of the short 30 cm radar detectable gravity waves by the intense rain in the storm core although the beating down of waves by rain is consistent with observations by seafarers and with the first scientific explanation of the phenomenon by reynolds 1875 neither theory nor experiment has provided definitive support one experiment appears to provide the key it shows that the kinetic energy of the rain produces sufficient turbulence in a thin fresh water layer to damp 30 cm waves in 10 20 s thus producing the echo free hole a sequence of positive feedbacks then serves to damp the longer waves the angular dependence of the sea surface echo cross sections seen by seasat sar outside the echo free hole indicates winds diverging from the downdraft induced by the intense rain core the wind generated waves and associated echoes extend out to a sharply defined gust front the sea surface footprint thus mimics the features of a storm microburst the variations in surface radar cross section due to a combination of rain and wind effects impacts spaceborne measurements of surface winds by scatterometry and rainfall measurements by radar portions of this synthesis remain speculative but serve as hypotheses for further research

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

dopscat a mission concept for simultaneous measurements of marine winds and surface currents a radar scatterometer operates by transmitting a pulse of microwave energy toward the ocean s surface and measuring the normalized per unit surface radar backscatter coef cient r8 the primary application of scatterometry is the measurement of near surface ocean winds by combining r 8 measurements from different azimuth angles the 10 m vector wind can be determined through a geophys ical model function gmf which relates wind and backscatter this paper proposes a mission concept for the measurement of both oceanic winds and surface currents which makes full use of earlier c band radar remote sensing experience for the determination of ocean currents in particular the novel idea of using two chirps of opposite slope is introduced the fundamental processing steps required to retrieve surface currents are given together with their associated accuracies a detailed description of the mission proposal and comparisons between real and retrieved surface currents are presented the proposed ocean doppler scatterometer can be used to generate global surface ocean current maps with accuracies better than 0 2 m s at a spatial resolution better than 25 km i e 12 5 km spatial sampling on a daily basis these maps will allow gaining some insights on the upper ocean mesoscale dynamics the work lies at a frontier given that the present inability to measure ocean currents from space in a consistent and synoptic manner repre sents one of the greatest weaknesses in ocean remote sensing

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

geochemistry of ce and nd isotopes and ree abundances in the amitsoq gneisses west greenland abstract ce and nd isotope ratios and rare earth element ree abundances were determined on the archean amitsoq gneisses west greenland samples used were four grey gneisses two white gneisses and one banded gneiss from the isukasia area and one banded grey gneiss from the godthaab area all of the amitsoq gneisses studied here have negative e nd and positive e ce values for the present nd and ce isotopic compositions calculated initial values of e nd and e ce give the following evolution histories of the ree patterns the grey gneiss in the godthaab area is considered to have been derived from a chondritic source with la ce n and nd sm n ratios of 1 1 0 4 and 0 99 0 02 in the chondrite normalized values on the other hand it is concluded that the grey gneisses and the banded gneiss in the isukasia area were formed from a light ree depleted source with la ce n 0 6 0 1 and nd sm n 0 97 0 03 furthermore it is suggested that the white gneisses in the isukasia area may have been produced from a source with a convex ree pattern our study on ce and nd isotopes and ree abundances provides further evidence that fractionated ree patterns were established already in the very early stages of the archean

radiocarbon dated pinus sylvestris l wood from beyond tree line on the kola peninsula russia radiocarbon dates were obtained from 24 samples of pinus sylvestris l scots pine wood recovered from sites beyond the modern conifer tree line on the kola peninsula of russia twenty one of the samples came from the shallow waters and eroding peats at the edges of two small lakes at 68 439n 35 109e located north of the modern conifer tree line three samples came from a small pond located above the modern elev ational limits of pinus sylvestris at 68 259n 35 199e the radiocarbon dates indicate that pine trees grew approximately 20 km north of the mapped modern limits of the species from 6680 bp to 3830 bp pine trees were also growing some 40 m above their modern elevational limits between 5890 bp and 3450 bp nineteen of the samples date from 6680 bp to 5070 bp suggesting that the density of trees north of the modern tree line was greatest between 7000 and 5000 bp the timing of tree line advance and greatest density on the kola peninsula are in agreement with the results of similar studies from northern fennoscandia which indicate that maximum northern and elevational extension of tree line occurred between 7000 bp and 4000 bp the general agreement between tree line reconstructions suggests that the climatic changes that promoted mid holocene tree line extension along the north atlantic margins in northern fennoscandia propagated eastward to the kola peninsula the late timing of initial pine expansion on the kola and in adjacent northern fennoscan dia remains problematic and may relate to lower winter insolation temperature regimes in the adjacent oceans or slow rates of migration

late quaternary summer temperature changes in the northern european tree line region abstract we present two new quantitative july mean temperature t jul reconstructions from the arctic tree line region in the kola peninsula in north western russia the reconstructions are based on fossil pollen records and cover the younger dryas stadial and the holocene the inferred temperatures are less reliable during the younger dryas because of the poorer fit between the fossil pollen samples and the modern samples in the calibration set than during the holocene the results suggest that the younger dryas t jul in the region was 8 0 10 0 c being 2 0 3 0 c lower than at present the holocene summer temperature maximum dates to 7500 6500 cal yr bp with t jul about 1 5 c higher than at present these new records contribute to our understanding of summer temperature changes along the northern european tree line region the holocene trends are consistent in most of the independent records from the fennoscandian kola tree line region with the beginning of the holocene thermal maximum no sooner than at about 8000 cal yr bp in the few existing temperature related records farther east in the russian arctic tree line the period of highest summer temperature begins already at about 10 000 cal yr bp this difference may reflect the strong influence of the atlantic coastal current on the atmospheric circulation pattern and the thermal behaviour of the tree line region on the atlantic seaboard and the more direct influence of the summer solar insolation on summer temperature in the region east of the kola peninsula

holocene vegetation history and climate change on the northern kola peninsula russia a case study from a small tundra lake abstract a sediment core from lake kp3 unofficial name located near the coastline on the northern kola peninsula 100 km east south east from murmansk russia 69 04 19 n 36 00 40 e provides palynological evidence for the vegetation and climate history of the last 14 000 years during the younger dryas time the climate was cold and vegetation cover around the lake consisted of a shrub birch willow tundra with warming during the early holocene birch forest expanded across the kola peninsula and by 9500 cal yr bp a dense birch tree forests likely extended as far north as the modern barents sea coastline by about 7800 cal yr bp alnus incana was present as an admixture to birch in wet places as far north as the barents sea shoreline scots pine expanded to north of its modern limits on the kola peninsula between 7900 and 3700 cal yr bp with its maximum northward progress and abundance at 7300 6200 cal yr bp although scattered pines may have grown near the coastline pine forests did not reach the barents sea coastal area and the region remained covered with birth forest tundra as much as during earlier holocene the expansion of birch forest and pine forest in the early to mid holocene likely reflects the impact of higher amounts of summer radiation due to milankovitch forcing and warmer temperatures in the north atlantic ocean and barents sea the mid holocene summer warming in the barents sea coastal area likely ranged from 1 c to 1 5 c above modern conditions following 5900 cal yr bp shrub tundra communities began to replace birch forest and pines on the northernmost kola peninsula the modern tundra which occupies the coastal region near lake kp3 was established at about 3100 cal yr bp the vegetation and climatic changes evident on the northern kola peninsula are similar to those evident in northernmost fennoscandia

rain footprints on c band synthetic aperture radar images of the ocean revisited abstract it is well known that rain leaves footprints on the sea surface that sometimes become visible on synthetic aperture radar sar images rain cells can easily be detected on sar images at all radar frequencies when they are associated with a downdraft pattern but rain cells are not always associated with downdraft and rain can also occur in other forms as stratified rain rain bands and squall lines it turns out that radar signatures of rain at c band are much more complex than at l or x band radar and that it is particularly difficult to identify unambiguously rain events on c band sar images acquired over the ocean this is because c band lies in the transition region where raindrops impinging onto the sea surface can increase usually or decrease the backscattered radar power and where volume scattering and attenuation by rain drops in the atmosphere are not always negligible at very high rain rates in order to get an insight into the physical mechanisms causing the c band radar signatures of rain we first revisit results obtained from historic laboratory and field experiments and multi frequency multi polarization sar data acquired during the sir c x sar spaceshuttle mission in 1994 then we analyze several c band sar images acquired by the european satellites envisat and sentinel 1a and the canadian satellite radarsat 2 and compare them whenever possible with quasi coincident and collocated weather radar images the observational data show that at low to medium rain rates the main physical mechanism causing c band radar signatures of rain is bragg scattering at ring waves generated by the rain drops impinging onto the sea surface which increase the radar backscatter however areas of increased radar backscatter are often accompanied by adjacent areas of decreased radar backscatter which is due to attenuation of the bragg waves by turbulence also generated by the impinging rain drops furthermore we present a full polarimetric radarsat 2 sar image of a rain cell together with a polarimetric decomposition analysis which shows that the c band radar signature of a rain cell is caused by surface scattering the observation show that radar signatures of rain cells often contain segments where the co polarized as well the cross polarized radar backscatter are strongly enhanced which indicates non bragg scattering contributions to the scattering process furthermore the polarimetric decomposition analysis shows that the c band radar signature of a rain cell is dominated by surface scattering possible mechanisms like scattering at splash products are discussed whether the normalized radar cross section nrcs due to rain is increased or decreased depends on rain rate wind speed incidence angle and history of the rain event at low to moderate wind speeds 10 m s 1 and low to high rain rates but

a revised model for radial profiles of hurricane winds abstract a revision to the holland parametric approach to modeling the radial profile of winds in hurricanes is presented the approach adopted uses information readily available from hurricane archives or in hurricane warning information and the profile can be readily incorporated into existing parametric models of the hurricane surface wind field the original model utilized central and environmental surface pressures maximum winds and radius of maximum winds in the revision a capacity to incorporate additional wind observations at some radius within the hurricane circulation was included if surface observations are used then a surface wind profile will result obviating the need for deriving a boundary layer reduction from the gradient wind level the model has considerably less sensitivity to data errors compared to the original and is shown to reproduce hurricane reconnaissance and surface wind profiles with high accuracy

effect of varying oceanicity on early to mid holocene palaeohydrology kola peninsula russia isotopic evidence from treeline lakes the stable isotope stratigraphy of sedimentary organic matter and algal cellulose in cores from two lakes near treeline on the kola peninsula indicate changes in water and nutrient balance that correlate with inferred expansion of pinus sylvestris during the early to mid holocene trends in cellulose inferred lakewater 18o values for both lakes suggest that moist conditions after deglaciation were followed by progressive drying from about 9500 to between 8000 and 7500 14c yr bp although pine appeared in the area by 8000 14c yr bp the maximum density of trees locally as suggested by stomate evidence occurred during subsequent moistening between 7500 and 6000 14c yr bp this is c 1000 years later than in other regions of northern russia and is possibly attributable to limitations on seedling establishment and survival due to root desiccation during dry winters changes in nutrient balance and productivity in the lakes as inferred from variations in sediment carbon and nitrogen elemental abundances an

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

a multiproxy record of holocene environmental changes in the central kola peninsula northwest russia a sediment core from chuna lake kola peninsula northwest russia was studied for pollen diatoms and sediment chemistry in order to infer post glacial environmental changes and to investigate responses of the lake ecosystem to these changes the past ph and dissolved organic carbon doc of the lake were inferred using diatom based transfer functions between 9000 and 4200 cal yr bp slow natural acidification and major changes in the diatom flora occurred in chuna lake these correlated with changes in regional pollen the arrival of trees in the catchment changes in erosion sediment organic content and doc during the past 4200 yr diatom based proxies showed no clear response to changes in vegetation and erosion as autochthonous ecological processes became more important than external climate influences during the late holocene the pollen stratigraphy reflects the major climate patterns of the central kola peninsula during the holocene i e a climate optimum between 9000 and 5400 5000 cal yr bp when climate was warm and dry and gradual climate cooling and an increase in moisture during the past 5400 5000 yr this agrees with the occurrence of the north south humidity gradient in fennoscandia during the holocene copyright 2002 john wiley sons ltd

mid and late holocene tree population density changes in northern fennoscandia derived by a new method using megafossil pines and their tree ring series changes in tree density are estimated for the northern forest limit region of finnish lapland over the past seven and a half millennia this is done using dendrochronologically dated scots pine megafossils and their tree ring series direct and indirect estimates of past tree density are derived from chronology sample size css and growth trend modelling gtm respectively the latter is a new method where the past levels of growth competition the influence of nearby trees are extracted from the behaviour of growth trends in cross dated tree ring series trends that are expected to be driven by tree density control two records constructed from the same original data set but by different means independently correlate significantly both records show a tree density maximum around 3000 1750 bc indicating relative warmth during that time another positive tree density anomaly occurred in accordance with the medieval warm period preceding the thinning at the forest limit due to the little ice age copyright 2005 john wiley sons ltd

a ce nd isotope study of crustal contamination processes affecting palaeocene magmas in skye northwest scotland twelve138ce 136ce isotope determinations 31 nd isotope analyses and 31 ree profiles are presented for tertiary basic to intermediate igneous rocks from the isle of skye nw scotland the aim of this work is to precisely identify the contamination mechanisms of basic magmas emplaced through old crust and to test the effectiveness of ce isotope analysis as a petrogenetic tool

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

the la ce geochronometer a new dating method the isotope 138la 0 089 of natural lanthanum decays by and electron capture to 138ce and 138ba with a long half life we present here the first age determination using la ce dating an internal la ce isochron of a gabbro from the upper zone of the bushveld south africa yields an age of 2 390 480 2 myr based on the partial decay constant 2 58 10 12 yr 1 this age agrees with the sm nd isochron age 2 050 90 2 myr which was obtained from an aliquot of the same sample solution within the uncertainties of 138la half life and isotopic measurement