on the 1470 year pacing of dansgaard oeschger warm events 1 the oxygen isotope record from the greenland ice sheet project 2 gisp2 ice core was reanalyzed in the frequency and time domains the prominent 1470 year spectral peak which has been associated with the occurrence of dansgaard oeschger interstadial events is solely caused by dansgaard oeschger events 5 6 and 7 this result emphasizes the nonstationary character of the oxygen isotope time series nevertheless a fundamental pacing period of 1470 years seems to control the timing of the onset of the dansgaard oeschger events a trapezoidal time series model is introduced which provides a template for the pacing of the dansgaard oeschger events statistical analysis indicates only a 3 probability that the number of matches between observed and template derived onsets of dansgaard oeschger events between 13 and 46 kyr b p resulted by chance during this interval the spacing of the dansgaard oeschger onsets varied by 20 around the fundamental 1470 year period and multiples thereof the pacing seems unaffected by variations in the strength of north atlantic deep water formation suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period

warm atlantic surface water inflow to the nordic seas 34 10 calibrated ka b p a number of short lasting warm periods interstadials interrupted the otherwise cold climate of the last glacial period these events are supposedly linked to the inflow of the warm atlantic surface water to the nordic seas however previous investigations of planktonic foraminifera from the nordic seas have not been able to resolve any significant difference between the interstadials and intervening cold stadials as the faunas are continuously dominated by the polar species neogloboquadrina pachyderma s here we examine the planktonic foraminifera assemblages from a high resolution core link17 taken at 1500 m water depth off northern scotland below the warmest part of the inflowing atlantic water the core comprises the time period 34 10 calibrated ka b p the coldest period of the last glaciation and the deglaciation the results reveal a hitherto unknown faunistic variability indicating significant fluctuations in both surface water inflow and in summer sea surface temperatures during the interstadials relatively warm atlantic surface water 4 7 c flowed north into the eastern norwegian sea during the stadials and heinrich events the surface inflow stopped and the temperatures in the study area dropped to 2 c the last glacial maximum was nearly as warm as the interstadials but the inflow was much more unstable the data reveal two previously unrecognized warming events each lasting more than 1600 years and preceding heinrich events he3 and he2 respectively by destabilizing the ice sheets on the shelves the warmings may have played a crucial role for the development of heinrich events he2 and he3

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

comment were last glacial climate events simultaneous between greenland and france a quantitative comparison using non tuned chronologies m blaauw b wohlfarth j a christen l ampel d veres k hughen f preusser and a svensson 2009

an artificial recharge experiment in the san jacinto basin riverside southern california lee t c williams a e and wang c 1992 an artificial recharge experiment in the san jacinto basin riverside southern california j hydrol 140 235 259 during a 3 month recharge experiment related to conjunctive use of water resources 1 5 x 106 t of imported water were percolated through a pond of 128 m by 128 m in the san jacinto basin the infiltration rates which declined with time averaged 1 9mday equivalent to four times the lowest laboratorymeasured hydraulic conductivity of the fluvial deposits ponding altered the unimodal grain size distribution at the ground surface to types without a dominant mode but this redistribution did not always lead to reduction in conductivities which varied over at least three orders of magnitude the water table 80 m downstream from the ponding edge began to rise slowly 1 month after the start of ponding it leveled off at 8 m above the pre recharge water table depth of 75 m and did not recede 2 months after termination of ponding water levels in wells bottomed in the original vadose zone suggested that an inverted water table migrated downward to meet the rising water table minor local perching occurred at 14m depth as indicated by the presence of moist ground near one monitoring well and by hydraulic responses during a 20 day intermission in percolation as it percolated through the sediments the imported northern california water gained ca but lost mg so that the mg ca ratio resembled that of local ground water such cation exchange has also been demonstrated by leaching experiments in the laboratory however the characteristics of the original source waters appear to be retained by d h isotope ratios and c1 concentrations as well as cross plots of so 4 vs c1 and b vs c1 such unreactive tracers could serve to monitor transport and mixing of the chemically diverse water used in future recharge programs in the san jacinto basin

composition and origin of ash zones from marine isotope stages 3 and 2 in the north atlantic abstract the composition and distribution of four north atlantic ash zones from the faroe islands margin is presented including the widespread north atlantic ash zone ii naaz ii 52 53 ka bp and three mainly basaltic ash zones here referred to as the faroe marine ash zones fmaz i ca 15 4 14 c ka bp ii ca 23 14 c ka bp also referred to as the fugloyarbanki tephra and iii ca 33 14 c ka bp one core from the south east labrador sea was also analysed naaz ii was found in all investigated cores indicating very large eruption events in the early marine isotope stage mis 3 detailed investigations of naaz ii in high resolution cores show that two separate layers can be distinguished a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra the main component of the basaltic fmaz ii was found in all cores from the faroe island margin and the labrador sea indicating that this tephra is the most widespread tephra from mis 2 in the north atlantic discovered so far we discuss the possibility to use these tephra layers for exact correlations between marine records and land sections such as the greenland ice cores and terrestrial records on the european mainland

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

the age and chronostratigraphical significance of north atlantic ash zone ii rhyolitic tephra with the geochemical characteristics of north atlantic ash zone naaz ii are described from the giant piston core md95 2006 from the northeast atlantic ocean shard size distribution indicates that the tephra represent a wind sorted primary air fall deposit but with a mode close to 200 m they are too coarse to be air fall deposits at the core site which lies ca 1000 km from the possible tephra source randomly sampled shards reveal a single geochemical population belonging to the icelandic transitional alkali magma series suggesting that they are unlikely to represent ice rafted debris derived from icelandic icebergs the tephra probably represent air fall deposits transported to the core site by sea ice within the northeast atlantic gyre the naaz ii peak coincides with the rapid climate transition cooling at the end of interstadial 15 which can be assigned an age of 53 260 2660 yr bp from direct correlation with the greenland ice core gisp2 record a comparison of the md95 2006 neogloboquadrina pachyderma sinistral relative abundance and gisp2 18o records relative to the naaz ii isochron suggests that this climatic event was synchronous across the north atlantic by direct correlation of interstadial maxima between the two records the gisp2 time scale is transferred to md95 2006 comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the gisp2 ages at the same stratigraphical horizon suggest major age differences these probably result from large variations in atmospheric 14c concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3 copyright 2004 john wiley sons ltd

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

magnetic characterisation and correlation of a younger dryas tephra in north atlantic marine sediments a technique for identifying non visible basaltic tephra rich horizons of younger dryas yd greenland stadial gs 1 age in northeast atlantic sediments using rapid non destructive magnetic measurements is presented three high resolution marine sediment cores have been studied in an e w transect across the hebridean margin st kilda basin md95 2007 barra fan md95 2006 and rockall trough md04 2822 magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments in all three cores an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard 250 m counts which can be constrained to the early part of the yd gs1 based on faunal climate proxies electron microprobe analyses of the magnetically distinct basaltic tephra interval in all three cores displays the same major element geochemistry as published for the vedde basaltic i tab 1 i e sourced from the icelandic volcano katla the identification of transitional alkalic basaltic tephras within marine sediments could potentially be facilitated by magnetic analysis as a useful chronostratigraphic screening tool copyright 2009 john wiley sons ltd

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

recharge from an ephemeral stream following wetting front arrival to water table after the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table the rate of recharge which is also that of infiltration is affected by the development of a groundwater mound the effect is practically immediate if the water content behind the wetting front is close to saturation an approximate analytical solution is developed in that case which predicts the time dependence of the recharge rate comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations as long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2 5 the analytical solution is essentially exact under most field conditions these ratios are largely exceeded consequently the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications

evaluating recharge to an ephemeral dryland stream using a hydraulic model and water chloride and isotope mass balance summary dewatering associated with mining below water table to achieve dry mining conditions may exert significant pressure on water balance in terms of lowering the water table and change in the dynamics of interactions between surface water and groundwater the discharge of surplus mine water into ephemeral streams may also affect the water balance by elevating groundwater levels and altering the exchange rate between streams and underlying aquifers however it is unclear whether volumes and recharge processes are within the range of natural variability here we present a case study of an ephemeral creek in the semi arid hamersley basin of northwest australia that has received continuous mine discharge for more than six years we used a numerical model coupled with repeated measurements of water levels chloride concentrations and the hydrogen and oxygen stable isotope composition 2h and 18o to estimate longitudinal evapotranspiration and recharge rates along a 27 km length of weeli wolli creek we found that chloride increased from 73 to 120 mg l across this length while 18o increased from 8 2 to 7 00 groundwater is directly connected to the creek for the first 13 km and recharge rates are negligible below this point the creek flows over a highly permeable aquifer and water loss by recharge increases to a maximum rate of 4 4 mm d which accounts for 65 of the total water discharged to the creek evapotranspiration losses account for the remaining 35 the calculated recharge from continuous flow due to surplus water discharge is similar to that measured for rainfall driven flood events along the creek groundwater under the disconnected section of the creek is characterised by a much lower cl concentration and more depleted 18o value than mining discharge water but is similar to flood water generated by large episodic rainfall events our results suggest that the impact of recharge from continuous flow on the water balance of the creek has not extended beyond 27 km from the discharge point our approach using a combination of hydrochemical and isotope methods coupled with classical surface flow hydraulic modelling allowed evaluation of components of the water budget otherwise not possible in a highly dynamic system that is mainly driven by infrequent but large episodic floods

unconfined aquifer response to infiltration basins and shallow pump tests summary we measure and model the unsteady axisymmetric response of an unconfined aquifer to delayed arbitrary recharge water table drainage follows the initial elastic aquifer response as modeled for uniform instantaneous recharge by zlotnik and ledder zlotnik v ledder g 1992 groundwater flow in a compressible unconfined aquifer with uniform circular recharge water resources research 28 6 1619 1630 and delayed drainage by moench moench a f 1995 combining the neuman and boulton models for flow to a well in an unconfined aquifer ground water 33 3 378 384 we extend their analyses with a convolution integral that models the delayed response of an aquifer to infiltration from a circular infiltration basin the basin routes the hydrograph to the water table with a decay constant dependent on a brooks and corey brooks r h corey a t 1966 properties of porous media affecting fluid flow journal of the irrigation and drainage division asce 92 2 61 88 unsaturated permeability exponent the resulting closed form model approaches neuman s neuman s p 1972 theory of flow in unconfined aquifers considering delayed response of the water table water resources research 8 4 1031 1045 partially penetrating pump test equation for a small source radius instantaneous uniform drainage and a shallow screen section irrigation pump data at a well characterized part of the plymouth carver aquifer in southeastern massachusetts calibrate the small source model while infiltration data from the closed drainage system of state route 25 calibrate the infiltration basin model the calibrated permeability elasticity specific yield and permeability exponent are plausible and consistent for the pump and infiltration data sets

an oceanic origin for the increase of atmospheric radiocarbon during the younger dryas 1 variations in carbon 14 to carbon 12 ratio in the atmosphere 14catm provide a powerful diagnostic for elucidating the timing and nature of geophysical and anthropological change the atlantic marine archive suggests a rapid 14catm increase of 50 at the onset of the younger dryas yd cold reversal 12 9 11 7 kyr bp which has not yet been satisfactorily explained in terms of magnitude or causal mechanism as either a change in ocean ventilation or production rate using earth system model simulations and comparison of marine based radiocarbon records from different ocean basins we demonstrate that the yd 14catm increase is smaller than suggested by the marine archive this is due to changes in reservoir age predominantly caused by reduced ocean ventilation

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

high resolution stalagmite δ18o records of asian monsoon changes in central and southern china spanning the mis 3 2 transition abstract high resolution oxygen isotope records of three stalagmites from sanbao central china wulu southern china and dashibao southern china caves based on 876 oxygen isotope measurements and 25 precise 230 th dates provide a detailed asian monsoon am history from 32 5 to 20 8 ka b p spanning the shift between marine isotope stages 3 and 2 the calcite 18 o records although geographically widespread about 1000 km between them including the previously reported hulu record are similar in timing shape and amplitude these observations support the idea that changes in speleothem 18 o largely represent variations of precipitation isotopic composition associated with large scale summer monsoon circulation over a large portion of china these profiles show four centennial to millennial scale strong summer monsoon events analogous in timing and structure to greenland interstadials 5 through 3 gis 5 3 chronology of the events refines the hulu record and broadly supports the ngrip gicc05 timescale five weak monsoon events are identified at 31 2 30 1 28 1 25 7 and 24 2 ka b p all of which correspond to stadial events in greenland the 30 1 and 24 2 ka events correlate with heinrich stadials 3 and 2 furthermore these events correlate to warm episodes in antarctic ice cores indicating that the climatic response to north atlantic cooling is similar in china and in antarctica but in an opposite sense these observations are consistent with the bi polar seesaw hypothesis the strong coupling between am circulation and climate at both high latitudes at the centennial scale indicates that atmospheric circulation changes are important in transmitting abrupt climate signals globally

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

the synchronization of palaeoclimatic events in the north atlantic region during greenland stadial 3 ca 27 5 to 23 3 kyr b2k two high resolution marine sediment cores located 83 km apart in the ne atlantic have been studied md95 2006 barra fan 57 01 82 n 10 03 48 w 2120 m water depth and md04 2822 rockall trough 56 50 54 n 11 22 96 w 2344 m water depth the records are anchored to the ngrip ice core stratigraphy and gicc05 chronology by the presence of geochemically characterized fugloyarbanki tephra and further tested by radiocarbon age control replicated sea surface temperature sst records show evidence for an abrupt and short lived warming within greenland stadial gs 3 to which we tentatively assign an age of ca 25 6 24 8 kyr gicc05 b2k based on these and another marine palaeoclimate record link17 from the faroe shetland channel we propose a new three fold event stratigraphy for gs 3 within the north east atlantic region the recognition of this warming event within gs 3 in ne atlantic sst records demonstrates that such events may not readily be identified within the coldest stadials of the greenland ice cores highlights the need for carefully constructed event stratigraphies independently tested by the use of tephra isochrones and radiocarbon and illustrates pervasive millennial scale climate variability of the north atlantic region dansgaard oeschger d o events is deeply embedded in the dynamics of atlantic meridional overturning circulation amoc

identification of the fugloyarbanki tephra in the ngrip ice core a key tie point for marine and ice core sequences during the last glacial period a visible tephra horizon in the ngrip ice core has been identified by geochemical analysis as the fugloyarbanki tephra a widespread marker horizon in marine cores from the faroe islands area and the northern north atlantic an age of 26 740 390 yr b2k 1 uncertainty is derived for this tephra according to the new greenland ice core chronology gicc05 based on multi parameter counting of annual layers detection of this tephra for the first time within the ngrip ice core provides a key tie point between marine and ice core records during the transition between mis 3 and 2 identification of this volcanic event within the greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time copyright 2008 john wiley sons ltd

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

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

on sharp spectral lines in the climate record and the millennial peak the existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order thus the appearance of such a spectral peak with a q 20 near 1500 years period in the physical properties of the greenland ice core is intriguing bandwidth less than two cycles in 110 000 years apparently similar phenomena exist in some deep sea cores it is shown however that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately under the nyquist criterion sampled at integer multiples of the common year if this peak is therefore discounted climate variability appears as expected to be a continuum process in the millennial band more generally however aliasing of high frequencies must be a concern in any core analysis

geophysical constraints on lunar bulk composition and structure a reassessment theoretical lunar mantle seismic velocity and density profiles are calculated for a series of proposed bulk compositions present day selenotherms and models for early differentiation and evolution the seismic velocity profiles are compared to the most recent observational model derived from the complete apollo data set to evaluate compositional implications the mantle density profiles are compared to mean density moment of inertia and crustal density thickness constraints to evaluate the need for a metallic core the calculated seismic velocity profiles are in qualitative agreement with the observational model in two general respects 1 a quasicontinuous velocity decrease occurs in the upper mantle due to the large thermal gradients that characterize all three of the considered thermal models 2 a discontinuous velocity increase occurs at the spinel to garnet transition approximately 500 km depth due mainly to the higher garnet velocities as compared to olivine and orthopyroxene in the upper mantle all four of the considered bulk compositions spanning a range of plausible feo and al2o3 contents are allowed when uncertainties in the temperature profile and depth of differentiation are taken into account however in the middle mantle depths 500 km the most aluminous models those with larger garnet abundances consistently produce larger velocity increases that are most nearly in accord with the observational model in general models that assume differentiation of the upper mantle only that are more aluminous in bulk composition and that have strong thermal gradients in the upper mantle but smaller gradients in the middle mantle result in calculated velocity profiles that most nearly agree with the observational velocity model an alternate differentiation model in which the middle mantle is dominated by mgo rich mafic silicates is also in accord with the observational seismic velocity model but results in density decreases that appear to violate stability arguments in every case calculated mantle density increases are insufficient to match the one standard deviation upper limit on the moment of inertia even when the most favorable combinations of allowed crustal thickness and density are assumed agreement with the moment of inertia upper limit is obtained if metallic cores representing 1 4 of the lunar mass are added to the bulk composition such cores are larger than needed to explain the observed depletions of lunar siderophile elements if the moon formed entirely from terrestrial mantle material

a reductionist physical approach to unsaturated aquifer recharge from a circular spreading basin in this paper the process of aquifer recharge from a circular area through the unsaturated zone is investigated the same basic methodology described previously by the authors for the case of a long strip recharging area morel seytoux et al 1988 is applied an approximate solution to the three dimensional problem is obtained by matching two unidimensional flows a vertical and a radial one the mathematical formulation is obtained first for the case of a constant infiltration rate and then for a time dependent rate through the unsaturated zone the formulation leads to an integrodifferential equation whose solution is obtained numerically using the discrete kernel approach morel seytoux et al 1973 morel seytoux and daly 1975 in both cases concrete examples illustrate the influence of the parameters on the discharge into the saturated zone and on the water table level also a criterion to evaluate the efficiency of the recharge is provided for practical purposes this criterion allows comparison between different recharge designs