geomagnetic intensity and 14c abundance in the atmosphere and ocean during the past 50 kyr we have used a new sedimentary record of geomagnetic field intensity combined with published volcanic data to examine the extent to which geomagnetic changes have affected 14c production in the past the production record was then converted into an atmospheric 14c signal using a 4 box model of past oceanic circulation the results indicate that changes in geomagnetic field intensity account for at least 80 of the 14c shift documented by published u th data which are of the order of 500 per mil with respect to a constant production hypothesis model simulations show that changes in past oceanic circulation account for only 100 per mil of 14c variation which is within the uncertainty of the geomagnetic correction in terms of dating these results show that the radiocarbon ages have to be shifted by 2 to 3 5 kyr towards older ages during the 20 40 ka interval

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

process based one dimensional model for cyclic longshore bar evolution abstract a wave averaged process based one dimensional model for beach profile change was developed to predict the cyclic evolution of longshore bars the cross shore sediment transport was assumed to be composed of suspended load due to wave breaking and bed load due to velocity skewness acceleration skewness and beach slope the model s performance was investigated using the beach profile data obtained every weekday during a 12 year period from 1989 to 2000 along a 400 m long pier at the hazaki oceanographical research station located on the hasaki coast of japan where the mean duration of bar evolution is approximately 1 year the model was unable to reproduce bar development from a rather flat profile possibly because some sediment movement process was missing in the model however the model calibrated with a 1 year data set including the bar evolution cycle consisting of bar generation seaward migration decay and new bar generation can be used to predict the first cycles of bar evolution at hasaki

chlorine 36 evidence for the mono lake event in the summit grip ice core abstract a distinct peak has been discovered in the 36 cl data from the grip ice core between the dansgaard oeschger d o events 6 and 7 at approximately 32 kyr bp this peak can be attributed to a minimum of the geomagnetic dipole field associated with the mono lake event since the 36 cl peak reflects a higher production rate of all cosmogenic radionuclides it has an impact on the 14 c dating of the last ice age furthermore it provides an additional time marker similar to a peak found earlier corresponding to the laschamp event at approximately 39 kyr bp

correlation of late pleistocene glaciation in the western united states with north atlantic heinrich events a survey of the chronology of late pleistocene glaciers in the western united states indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing numerical dating of late pleistocene deposits from the puget lobe of the cordilleran ice sheet and alpine glaciers and ice caps in the rocky mountains and cascade range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the laurentide ice sheet associated with the north atlantic heinrich events specifically the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a heinrich event and retreated shortly thereafter because midlatitude glaciers respond relatively rapidly to climate change this complex record of glacial fluctuations suggests mechanisms of climate forcing in western north america that are in some way tied to heinrich events one possible mechanism involves southerly and northerly displacement of the jet stream across the western united states in response to growth and collapse of the laurentide ice sheet

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

chronology of latest pleistocene lake level fluctuations in the pluvial lake chewaucan basin oregon usa new accelerator mass spectrometer radiocarbon ages from gastropods in shore deposits within the pluvial lake chewaucan basin combined with stratigraphical and geomorpho logical evidence identify an abrupt rise and fall of lake level at ca 12 14 c ka the lake level high is coeval with lake level lows in the well dated records of palaeolakes bonneville and lahontan and with a period of relatively wet conditions in the more southerly owens lake basin this spatial pattern of pluvial lake levels in the western usa at 12 14 c ka indicates a variable synoptic response to climate forcing at this time copyright 2001 john wiley sons ltd

amplitude and timing of the laschamp geomagnetic dipole low from the global atmospheric 10 be overproduction contribution of authigenic 10 be 9 be ratios in west equatorial pacific sediments 1 authigenic 10be 9be ratios were measured along a sediment core collected in the west equatorial pacific in order to reconstruct cosmogenic 10be production variations near the equator where the geomagnetic modulation is maximum from 60 to 20 ka the single significant 10be production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the laschamp excursion no significant 10be overproduction signature is recorded at the age of the mono lake excursion 34 ka a compilation of authigenic 10be 9be records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged 10be flux record of greenland ice cores their remarkable similarity demonstrates that 10be production is globally modulated by geomagnetic dipole variations and redistributed by atmosphere dynamics after calibration using absolute values of the virtual dipole moment drawn from paleomagnetic database the authigenic 10be 9be stack allows reconstructing the geomagnetic dipole moment variations over the 20 50 ka time interval between 48 and 41 ka the dipole moment collapsed at a rate of 1 5 1022 a m2 kyr 1 which will be an interesting criterion for the assessment of the loss rate of the historical field and the comparison of dipole moment loss prior to excursions and reversals after a 2 kyr duration of the minimum dipole moment 1 1022 a m2 a slow increase started at 39 ka progressively reaching 5 1022 a m2 at 20 ka the absence of a significant dipole moment drop at 34 ka the age of the mono lake excursion suggests that the duration and amplitude of the dipole weakening cannot be compared with that of the laschamp this study provides a reliable basis to model the production of radiocarbon and in situ cosmogenic nuclides and to improve the calibration of these dating methods

temporal correspondence between pluvial lake highstands in the southwestern us and heinrich event 1 pluvial lakes were abundant in the southwestern united states during pleistocene glaciations particu larly in the great basin many of these lakes occupied closed basins therefore fluctuations of their water surface elevations are valuable sources of paleoclimate information histories of the largest lakes are well constrained whereas dozens of smaller lakes that were present in this region have received relatively little scientific attention given their dimensions these smaller lakes were climatically sensitive and can offer important information about quaternary climate variability here we present new ages for the highstands of three previously undated small lakes based on radiocarbon dating of gastropod shells recovered from beach ridges these results are combined with other published and unpublished 14 c ages to yield an extensive compilation of highstand shoreline ages for lakes of all sizes throughout the southwestern us the results indicate that although some lakes reached highstands during the last glacial maximum the strongest temporal correspondence is between highstands and heinrich event h1 these results are consistent with speleothem based reconstructions of effective moisture in the southwestern us which show increased precipitation during stadials of the last glacial cycle copyright 2012 john wiley sons ltd

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

interstadial climatic cycles a link between western north america and greenland during the interval 33 6 to 26 1 ka searles lake in southeastern california went through six major cycles of expansion and contraction a comparison of u th ages for these events with the chronologies for quasi cyclic interstadial episodes in the ice core from summit greenland suggests that the episodes of low water at searles lake are synchronous with the interstadial episodes at summit the two phenomena may be linked by variations in the strength of the global hydrological cycle driven by oscillations in the atlantic ocean thermohaline circulation

bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum abstract lacustrine shoreline depositional features in the bonneville basin western north america were investigated to chronicle paleolake expansion and contraction in response to climate change based on stratigraphy sedimentology geomorphology and radiocarbon dating this study identifies multiple intermediate to large lake intervals during marine isotope stage 3 and the last glacial maximum timing and magnitude of the bonneville basin lake size change are compared with those of hemispheric scale climate change events reported from the greenland ice sheet southwestern north america winter precipitation and east asian monsoon 18 o records the amount of precipitation received by surface water systems in the bonneville basin appears to have increased significantly during the greenland stades throughout the last half of mis 3 and early mis 2 the lake also underwent rapid large amplitude oscillations during the last glacial maximum

modelling teleconnections between the north atlantic and north pacific during the younger dryas evidence for a cooling event synchronous with the younger dryas 12 000 calendar years before present has been found in the north pacific ocean north of 30 n in records of surface1 5 and subsurface water properties6 7 these changes may be related to a temporary shut down of north atlantic deep water formation and associated surface cooling over the north atlantic it has remained unclear however whether this north atlantic cooling was communicated to the north pacific ocean through the atmosphere or the ocean here we report results of a sensitivity experiment with a coupled ocean atmosphere general circulation model that support a primarily atmospheric forcing of north pacific climate variations changes in wind strongly affect coastal upwelling at the north american west coast and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast pacific this effect is amplified by oceanic progagation to the pacific of the signal arising from collapse of north atlantic deep water formation these teleconnections may also explain earlier north pacific and western north american millenial scale cooling events of a similar nature8 12

transgressive stratigraphic record and possible oscillations of late pleistocene lake bonneville northern hogup mountains utah u s a abstract distinct mappable facies changes make the stratigraphic record of the shorezone of late pleistocene lake bonneville the most robust indicator for past lake level oscillations unfortunately clear stratigraphic evidence of transgressive and regressive deposits has been generally lacking new stratigraphic and chronological data within the lacustrine shorezone sediments of the hogup mountains of northwestern utah provide some of the best evidence yet for oscillations within the overall transgressive phase of the lake this study documents two previously unknown oscillations hereby named the lower hogup 22 cal ka and upper hogup 20 6 cal ka oscillations and provides further evidence for the previously proposed u2 oscillation 21 3 cal ka the study suggests that the water level of the lake changed dramatically up to 25 of the lake s total volume during the transgressive phase 30 15 cal ka with the additional oscillations documented in this study there are seven proposed oscillatory events during the transgressive phase of the lake these events likely correlate to rapid but short term regional climatic fluctuations during the broader climatic trends of the last glacial maximum however it is still unknown what specific climatic drivers are causing these oscillations and if these events can be correlated to other global climatic events

middle late pleistocene relative palaeointensity of the geomagnetic field from lacustrine sediments lake chewaucan western united states summary detailed palaeomagnetic and rock magnetic studies of a 15 m succession of middlellate pleistocene lacustrine sediments from ancient lake chewaucan southern oregon western united states indicate that the remanence bearing grains are sufficiently uniform to be applicable to relative palaeointensity studies we have used arm sirm and x for normalization of the nrm all three parameters give essentially identical results in their relative stratigraphic variations which indicates that the normalizations efficiently remove the effects of variation in magnetic mineral concentration patterns in grain size variation as indicated by small scale quasi cyclic fluctuations in hysteresis parameters may be due to environmental changes such as lake level variation however these fluctuations are within the acceptable range of grain sizes for palaeointensity studies and cannot be correlated with any of the features of the normalized remanence record we therefore conclude that the large scale variations in the normalized remanence record are due to geomagnetic palaeointensity fluctuations parts of the normalized remanence record where firm chronological constraints exist may correlate with features of relative palaeointensity records from deep sea sediments our results also confirm the observation that low geomagnetic field intensities dominate during geomagnetic excursions further studies of relative palaeointensity of the geomagnetic field may enable the development of an independent time scale which would make possible the direct correlation of palaeoclimate records from deep sea and continental environments

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

synchronous millennial scale climatic changes in the great basin and the north atlantic during the last interglacial stalagmites from goshute cave located in the great basin of the western united states preserve 20 000 yr of millennial scale oxygen isotopic variability during marine isotope stages 5c and 5b similar in timing and structure to dansgaard oeschger d o events 23 21 from the greenland ice sheet project 2 record that d o interstades 23 21 were of longer duration than many of the later d o events coupled with the asymmetric shape of the d o oxygen isotope curve and the direct u th dating of the goshute cave stalagmites allows for an improved understanding of the synchroneity of climatic changes between the western continental united states and the north atlantic eastern pacifi c atmosphere interactions are a likely mechanism for transmission of millennial scale climate variability into the great basin

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

evidence of synchronous climate change across the northern hemisphere between the north atlantic and the northwestern great basin united states from ca 50 to 20 ka summer lake oregon rose and fell in tune with north atlantic interstadial and stadial climatic oscillations respectively this record exhibits the complete morphology of the north atlantic millennial scale climate change signal including dansgaard oeschger oscillations heinrich events and bond cycles the phase relationship of these climate change records high summer lake during warm north atlantic low during cold is demonstrated at millennial scale resolution by the relative positions of the mono lake and laschamp paleomagnetic excursions in these records these results in conjunction with comparisons of historical climate records also presented here imply a direct temporal connection at the subcentury scale between the north atlantic and the northwestern great basin via an atmospheric teleconnection

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

late pleistocene to early holocene lake level and paleoclimate insights from stansbury island bonneville basin utah abstract this paper reports on recent multiproxy research conducted to determine the chronology of lake level fluctuations recorded in sediments from a natural exposure at a classic bonneville basin site grain size carbonate percentage magnetic susceptibility amount of charcoal and diatom community composition data were collected from the 16 lacustrine units that compose the 122 cm stratigraphic column in stansbury gulch trends observed in the measured proxies reveal several significant changes in lake level and thereby effective moisture over the approximately 14 500 yr time span represented by the sediments results 1 verify the effectiveness of the multiproxy approach in bonneville basin studies which has been underutilized in this region 2 reaffirm the double nature of lake bonneville s stansbury oscillation 3 suggest a previously undocumented post gilbert highstand of great salt lake and 4 identify possible teleconnections between climate events in the bonneville basin and events in the north atlantic at about 20 500 and 7500 14c yr bp

paleoclimatic context of geomagnetic dipole lows and excursions in the brunhes clue for an orbital influence on the geodynamo the hypothesis of an influence of the astronomical precession on the geodynamo energy budget was recently reappraised by theoreticians paleomagnetic indications of such an influence remain controversial because reconstructions of paleointensity variations from sediments are suspected to be contaminated by lithological paleoclimatically induced influences three sets of complementary indicators are however available 1 records of the direction of magnetization in sediments 2 records of magnetic anomalies of the deep sea floor basalts and 3 records of production variations of cosmogenic isotopes from sediment and ice cores these records confirm the genuine geomagnetic origin of paleointensity lows and their narrow link with excursions or short reversals recorded in various materials and often dated by radiometric methods the analysis of these time series and their comparison with 18o records of the paleoclimate suggest that such globally recorded geomagnetic dipole lows have preferentially occurred in the context of interglacial or transitional paleoclimates at the time of low or decreasing obliquity the dominant periods extracted with the complex continuous wavelet transform technique range from 40 to 125 ka further suggesting a link with orbital parameters these results encourage future efforts of research to improve the precision the resolution and the dating of the time series of geomagnetic dipole low in order to better decipher orbital signatures and understand their origin an important implication of this topic is that the next geomagnetic dipole low should be related with the present interglacial

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

multi proxy stalagmite records from northern california reveal dynamic patterns of regional hydroclimate over the last glacial cycle abstract despite its importance for california s water resources little is known about how precipitation has varied in far northern california beyond the historical record we present a new multi proxy paleoclimate record derived from two coeval stalagmites from lake shasta caverns lsc california that covers the end of marine isotope stage 3 through heinrich stadial 1 35 000 to 14 000 years bp at 40 8 n lsc is situated within the transition zone between regions in the northwestern and southwestern united states that demonstrate different precipitation responses to both modern and paleoclimatic drivers stable isotope and trace element proxies from lsc stalagmites indicate the region experienced wet conditions during interstadials warm periods associated with dansgaard oeschger cycles similar to proxy records from southern oregon and the northern great basin but in contrast to records from the desert southwest similar to the northern cascades and rocky mountains lsc was drier during the last glacial maximum however proxies indicate increased rainfall throughout heinrich stadial 1 similar to the great basin and southwest thus the lsc record demonstrates the non stationarity of the transition zone location and illustrates a complex pattern of precipitation response to global climate change in the western united states covariation of speleothem 18o an indicator of moisture source with 13c and trace elements indicators of moisture amount suggest a higher proportion of central pacific precipitation during the last glacial maximum despite the enhanced aridity in contrast periods characterized by increased precipitation amounts such as early heinrich 1 are associated with enhanced moisture from the northern pacific

directly dated mis 3 lake level record from lake manix mojave desert california usa abstract an outcrop based lake level curve constrained by 70 calibrated 14 c ages on anodonta shells indicates at least 8 highstands between 45 and 25 cal ka bp within 10 m of the 543 m upper threshold of lake manix in the mojave desert of southern california correlations of manix highstands with ice marine and speleothem records suggest that at least the youngest three highstands coincide with dansgaard oeschger d o stadials and heinrich events 3 and 4 the lake level record is consistent with results from speleothem studies in the southwest that indicate cool wet conditions during d o stadials notably highstands between 43 and 25 ka apparently occurred at times of generally low levels of pluvial lakes farther north as interpreted from core based proxies mojave lakes may have been supported by tropical moisture sources during oxygen isotope stage 3 perhaps controlled by southerly deflection of pacific storm tracks due to weakening of the sea surface temperature gradient in response to north atlantic climate perturbations

thermoluminescence dating of late pleistocene loess and tephra from eastern washington and southern oregon and implications for the eruptive history of mount st helens the first numeric dating of late pleistocene loess from the palouse region of eastern washington is reported this loess is interbedded with thin distal tephra layers some identified as mount st helens products both the interbedded tephra layers and thick paleosols that have developed in the loess have previously been correlated across the region a thicker correlative of one of these tephra layers mount st helens set c was collected from summer lake oregon for direct dating by thermoluminescence tl polymineral fine grain tl ages for loess from three chosen sections in washington range from 17 to 83 ka these imply ages for some tephra beds that are significantly older than implied by earlier radiocarbon 14c dating for example tl ages of 17 21 ka for loess bracketing a tephra layer correlated to mount st helens set s suggests a somewhat older age for this ash than the previously accepted 14c age of 15 5 0 5 ka cal yr corrected to calendar years tl ages of 46 6 1 ka and 57 7 ka for loess above and of 53 7 ka and 75 6 ka below a tephra bed correlated to a mount st helens set cw layer along with a tl age of 46 5 ka for fine silt sized glass from a mount st helens set cy bed in oregon revise upward from 38 ka cal yr 14c age is 36 ka b p to 50 ka the age of this regionally important marker ash set several tl ages taken together imply a much longer eruptive history for mount st helens than previously thought a tl age of 83 8 ka just below a previously undated tephra layer from mount st helens emsh ash suggests that the eruptive history of the mountain extends back to at least 80 ka furthermore age depth extrapolation through our sections to an ash wa 5c probably correlated to mount st helens suggests an eruptive history of at least 120 ka

overprinting of natural magnetic remanence in lake sediments by a subsequent high intensity field there has been considerable debate recently on how well sedimentary rocks record transitional field directions during a polarity reversal1 5 this has not been an easy question to answer because the input geomagnetic signal for a given sedimentary record is not known independently and because the process by which remanent magnetization is acquired by sediments is difficult to duplicate in the laboratory the geomagnetic excursion recorded by sediments outcropping around the shores of mono lake california6 8 offers an unusually good opportunity to examine this question we report here a study of the mono lake excursion mle at a new locality on the southeast shore where although the records satisfy usually applied standards of palaeomagnetic quality it is clear from comparison with records from other localities that the field directions during a time of low field intensity have not been faithfully preserved the distinctive directions of natural remanence in the discrepant part of the record show that the southeast shore sediments were overprinted by the ensuing higher intensity field acting on the still unconsolidated sediment apparently by realigning some magnetic grains that had previously been locked in

a record of holocene climate in the mineral magnetic record of alpine lakes sagistalsee and hinterburgsee the effect of climate variations on the magnetic properties of sediments from two small alpine lakes in the bernese alps switzerland was investigated although relatively similar in water volume and general environment sa gistalsee and hinterburgsee have different catchment vegetation and lithology due to their different elevation and geographic locations the climatic signal in the mineral magnetic parameters of the sediments was validated and interpreted with the aid of palynological and geochemical data the sediment age was determined with several accelerated mass spectrometry 14 c dates the results from the different lakes compare well on a common time scale and show that the influence of local conditions on the magnetic record is rather small a climatic influence on the mineral magnetism has been recognized at both studied sites this is interpreted as a consequence of the production of an authigenic mineral with particularly uniform magnetic properties during the warmer stages and the influx of heterogeneous detrital magnetic minerals during the colder stages the clearest climate record is found in sediments with no organic matter whereas the anoxic conditions found in highly organic sediment can completely obliterate the climate signal recorded in the sediment magnetic properties fl 2001 elsevier science b v all rights reserved

heat partitioning in terrestrial planets during core formation by negative diapirism article i nfo we investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets we model the dynamic evolution of an iron diapir sinking through a solid silicate proto mantle our calculations include viscous heating and strong temperature and composition dependence of viscosity we show that the diapir mean temperature evolves towards an asymptotic value td which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings and on the viscous rheology we derived a simple analytic model that captures the thermal evolution observed in our numerical experiments this model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs during their growth and early differentiation we show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs a large number of small sinking iron diapirs favors metal silicate heat exchange and leads to a relatively hot core which allows a sustainable dynamo as on earth a small number of large diapirs have the opposite effect and could correspond to a mars like planet with an early dynamo that is no longer active in all cases negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part which could trigger large amounts of melting in the early deep mantle

early holocene glacier advance southern coast mountains british columbia canada abstract terrestrial and lake sediment records from several sites in the southern coast mountains british columbia provide evidence for an advance of alpine glaciers during the early holocene silty intervals within organic sediments recovered from two proglacial lakes are bracketed by ams 14 c dated terrestrial macrofossils and mazama tephra to 8780 6730 and 7940 6730 14 c yr bp 10 150 7510 and 8990 7510 cal yr bp radiocarbon ages ranging from 7720 to 7380 14 c yr bp 8630 8020 cal yr bp were obtained from detrital wood in recently deglaciated forefields of sphinx and sentinel glaciers these data together with previously published data from proglacial lakes in the canadian rockies imply that glaciers in western canada advanced during the early holocene the advance coincides with the well documented 8200 yr cold event identified in climate proxy data sets in the north atlantic region and elsewhere

radiocarbon ages and environments of deposition of the wono and trego hot springs tephra layers in the pyramid lake subbasin nevada abstract uncalibrated radiocarbon data from core plc92b taken from wizards cove in the pyramid lake subbasin indicate that the trego hot springs and wono tephra layers were deposited 23 200 300 and 27 300 300 14 c yr b p uncorrected for reservoir effect sedimentological data from sites in the pyramid lake and smoke creek black rock desert subbasins indicate that the trego hot springs tephra layer was deposited during a relatively dry period when pyramid lake was at or below its spill point 1177 m to the winnemucca lake subbasin the wono tephra layer was deposited when lake depth was controlled by spill across emerson pass sill 1207 m to the smoke creek black rock desert subbasin 18 o data from core plc92b also support the concept that the trego hot springs tephra fell into a relatively shallow pyramid lake and that the wono tephra fell into a deeper spilling lake