stratigraphy amino acid geochronology and correlation of quaternary sea level and glacial events broughton island arctic canada raised marine and glaciomarine terraces on broughton island record regional isostatic adjustments and eustatic sea level changes previous workers proposed three alternative glacial and sea level chronologies of the region these conflicts are resolved by the stratigraphic control provided by amino acid ratios d allo isoleucine l isoleucine in marine molluscs collected form cliff exposures amino acid ratios radiometric dates and relative weathering measurements on geomorphological features provide a basis for regional correlations based upon amino acid ratios the coastal sedimentary sequences all part of the broughton island formation can be subdivided into six units to which informal member names have been assigned these units delimit at least four glacial episodes during which local ice advanced around broughton island to the outer coast the youngest advance is correlative with deposits that are dated 54 000 bp and the absolute ages of older events have been estimated from minimum uranium s

10be signature of the matuyama brunhes transition from the heqing paleolake basin abstract we present a new 10be record spanning the matuyama brunhes m b reversal from the heqing paleolake basin in southern china it provides a robust proxy for past geomagnetic variations that can be compared with paleomagnetic records the m b transition is identified as a pronounced maximum of authigenic 10be 9be ratio between 768 6 and 778 5 ka that is consistent with all other available 10be proxy records from marine ice and loess archives however it is offset by approximately 0 60 cm depth from the magnetic signature of the polarity transition recorded in the same sediments we attribute this offset to the lock in effect of the remanence acquisition process which is similar to the phenomenon that exists in marine sediments we suggest that after eliminating the climatic hydrological signal the heqing sediments may be used as an archive for atmospheric 10be production rate changes the combination of magnetic remanence measurements and the cosmogenic 10be allows for a more precise geochronology of geomagnetic polarity reversals

the pleistocene succession of the severn estuary a revised model based upon amino acid racemization studies this paper reports the results and stratigraphic implications of amino acid racemization studies of fresh and or inter tidal molluscs from i the important pleistocene sequences of kenn church new blind yeo drain yew tree farm and kenn pier avon county ii the previously undescribed pleistocene beach deposits beneath the llanwern steel mill south wales and iii re prepared and re analysed shells from the th u series dated beach deposits in belle houge cave jersey channel islands these studies indicate the complexity of sea level change in the area in amino acid group ii oxygen isotope stage 5e 120 000 130 000 years bp sea level reached 4 5 m od and possibly 12 m od this episode is correlated with similar group ii beach deposits on the gower coast and freshwater deposits in sw and se britain the data suggest these group ii deposits are different in age from the ipswichian interglacial inter tidal deposits at selsey a group iv age is attributed to freshwater deposits at yew tree farm and kenn pier which collected just above a contemporary sea level or included re worked earlier inter tidal rocky shore faunas these are provisionally correlated with the group iv deposits in the thames estuary at purfleet c 400 000 600 000 years bp since these deposits are thought at post date glacial deposits previously identified at kenn and court hill avon this glacial episode is now regarded as being much older than the wolstonian glacial stage with which it had been correlated previously

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

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

10be and9be in south atlantic dsdp site 519 relation to geomagnetic reversals and to sediment composition a high resolution10be profile has been measured on dsdp site 519 central south atlantic in order to search for changes in the flux of10be into a pelagic sediment during geomagnetic reversals as compared with times of constant magnetic polarity the decay corrected10be concentrations range from 1 to 9 108 at g the average10be flux rate is 5 108 at cm 2 kyr 1 9be and caco3 were measured on the same samples the10be vs depth curve is overall similar to the9be vs depth curve while the caco3 vs depth curve anticorrelates the beryllium isotope curves closely implying that be is carried mainly by the non caco3 phases of the sediment the positive correlation between10be and9be along with the fact that the average 10be 9be ratio of 5 5 10 8 is within the range of 10be 9be ratios reported for deep ocean water leads us to conclude 1 that the beryllium isotopes come close to an equilibrium in the open ocean and 2 that the 10be 9be in deep sea sediments with a low detrital component monitors the 10be 9be of deep ocean water through time relative increases of the 10be 9be ratio are observed in the vicinity of the geomagnetic reversals but the relationship between reversals and higher 10be 9be remains doubtful other mechanisms which could alter the 10be 9be ratio are discussed input of10be by melting of glacial ice changing input of9be due to changes in continental erosion changing deep ocean circulation changing scavenging activity at ocean margins but as yet no conclusive explanation for the observed behavior of the beryllium isotopes can be given

sensitivity and response of beryllium 10 in marine sediments to rapid production changes geomagnetic events a box model study the response and the sensitivity of the marine beryllium 10 flux to abrupt production changes e g caused by a geomagnetic event are investigated by using a simple box model the effect of mixing processes in the water column on the 10be flux is simulated and the influence of bioturbation on the sedimentary record is studied while the effect of the oceanic residence time is found to be small bioturbation can drastically change the shape and the amplitude of the modeled 10be peak the simulations indicate that 10be production peaks persisting for more than 1500 years are recorded well in deep sea sediments if bioturbation induced integration times are small tbio 1000 years while sediment cores with tbio 1000 years are found to be not well suited for stratigraphic purposes the results further show that the sedimentary 10be peak lags initial signal this time lag is almost independent of the event duration for tbio 1000 years ranging between about 400 and 600 years therefore the model results support the idea that marine 10be peaks corresponding to geomagnetic events can be used as a global time marker to match marine terrestrial and ice core chronologies on the millennial and if the time lag of 500 100 years is considered the submillennial timescale

a pseudo thellier relative palaeointensity record and rock magnetic and geochemical parameters in relation to climate during the last 276 kyr in the azores region summary in the pseudo thellier method for relative palaeointensity determinations tauxe et al 1995 the slope of the nrm intensity left after af demagnetization versus arm intensity gained at the same peak field is used as a palaeointensity measure we tested this method on a marine core from the azores spanning the last 276 kyr we compared the pseudo thellier palaeointensity record with the conventional record obtained earlier by lehman et al 1996 who normalized nrm by sirm the two records show similar features intensity lows with deviating palaeomagnetic directions at 40 45 ka and at 180 190 ka the first interval is associated with the laschamps excursion while the 180 190 ka low represents the iceland basin excursion channell et al 1997 the pseudo thellier method in combination with a jackknife resampling scheme provides error estimates on the palaeointensity spectral analysis of the rock magnetic parameters and the palaeointensity estimates shows orbitally forced periods particularly 23 kyr for climatic precession this suggests that palaeointensity is still slightly contaminated by climate fuzzy c means cluster analysis of rock magnetic and geochemical parameters yields a seven cluster model of predominantly calcareous clusters and detrital clusters the clusters show a strong correlation with climate for example samples from detrital clusters predominantly appear during rapid warming although both the pseudo thellier palaeointensity m a and fuzzy clusters show climatic influences we have not been able to find an unambiguous connection between the clusters and m a

response of benthos to stress factors in holocene arctic fjord settings maktak coronation and north pangnirtung fjords baffin island canada maktak coronation and north pangnirtung fjords are situated on cumberland peninsula baffin island canada having a common freshwater source from the penny ice cap bottom photographs were examined to identify epifaunal trails and shallow endobenthic burrow openings exposed on the seafloor surface these were compared to biogenic sedimentary structures revealed through x radiograph images and direct observations of lehigh gravity core samples intermediate and deep tier structures characterize the ichnofabrics of the glaciomarine sediments extensive bioturbation by the shallow tier and epibenthic tracemakers most notably ophiuroid echinoderms brittlestars and other organisms has destroyed much of the primary sedimentary fabric i e lamination resulting in homogenous silty clay sediments the dominant deep tier structure consisting of an open three dimensional boxwork burrow system is the most pervasive biogenic structure observed within the core samples interestingly although proximal distal trends in benthic macrofaunal composition are evident in the bottom photographs ichnofabrics remain relatively constant along the length of the fjords environmental factors influencing the biological community in these modern high latitude fjords differ from conditions described in paleozoic and cenozoic fjord environments an increasing number of recent studies are expanding significantly on the fjord ichnology database and provide the basis for the revision of the currently proposed fjord trace fossil model accommodating the complexity and diversity of fjord settings

evidence for an increase in cosmogenic 10be during a geomagnetic reversal reversals in the geomagnetic field which occur every few hundred thousand years represent a dramatic change in the earth s environment although there is no satisfactory theory for such reversals it is generally accepted that the dipole field intensity decreases to 20 of its normal value for a few thousand years during the change in direction1 because the galactic and solar cosmic rays which impinge on the earth s atmosphere are charged a significant fraction about half of them are deflected by the geomagnetic field2 at the time of a reversal this magnetic shielding is greatly reduced and it has been suggested that the increased flux of high energy particles could have effects on evolutionary3 or climatic4 processes for example the statistically significant coincidence in levels of some marine faunal extinctions and reversal boundaries in ocean sediments5 could be caused directly or indirectly by the decreased geomagnetic intensity during the reversal we report here evidence in marine sediments for an increase in cosmogenic 10be production in the earth s atmosphere during the brunhes matuyama reversal 730 000 yr ago in addition to confirming an increase in cosmogenic isotope production the results provide information on the magnitude and duration of the geomagnetic intensity decrease during such an event and the depth at which rmanent magnetism is acquired in marine sediments

relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the acores area abstract relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the acores area one core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain size distribution in the pseudo single domain range for the three cores changes in the amount of magnetite do not exceed a factor of 10 therefore these cores appear to be suitable for relative palaeointensity determinations two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation nrm but the power at these frequencies is not significant at the 95 level for the normalised remanence records for each core normalisation of the nrm using different normalising parameters yields virtually identical results using saturation isothermal remanent magnetisation sirm as the normalising parameter the results of the three cores were then combined into a stacked curve squared coherence analysis between this stacked curve and bulk mineral magnetic parameters reveals that the 18 kyear component is still present in the record but that the power spectrum is barely above noise level at this frequency some of the features of this north atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records for instance distinct periods of low intensity are observed around 40 120 and 190 kyears and periods of high intensity at 50 and 80 kyears because of the uniformity of the mineral magnetic characteristics of the three cores we suggest that this record may be a suitable palaeointensity reference curve for the central north atlantic ocean region

multiple 10be records revealing the history of cosmic ray variations across the iceland basin excursion abstract cosmogenic 10be is a proxy of cosmic ray flux and its natural records provide vital information about the past intensity variability of the geomagnetic field and solar activity 10be records also serve as powerful tools for global synchronization among a variety of paleoarchives and for elucidating sedimentary processes on natural remanent magnetization acquisition however high resolution multi decadal to multi centennial records of 10be are scarce especially those older than several tens of thousands of years here we present multiple high resolution 10be records of the iceland basin geomagnetic excursion interval ca 170 200 kyr ago obtained from sediment cores authigenic 10be 9be ratio and an ice core atmospheric 10be flux comparing sedimentary 10be records with relative paleointensity from the same cores we found differences in the magnetic lock in depth even between adjacent cores the 10be proxy records from the sediment and ice cores exhibit common characteristics an asymmetric large scale variation a 7 kyr quasi plateau around the maximum with a characteristic mid term depression and multi millennial fluctuations in cosmic ray flux during this interval minimal synchronized and stacked 10be records show that maximum cosmic ray flux occurred 188 5 190 0 kyr ago and was double the present flux a wavelet analysis of the stacked curve reveals dominant 4 kyr and secondary 8 kyr periodicities both of which can be interpreted as intrinsic geomagnetic cycles the wavelet spectrum of the high resolution ice core record shows a periodicity of 1 7 kyr and somewhat intermingled multi centennial cycles around the maxima of 10be which likely represent solar cycles in this period high resolution 10be records from multiple paleoarchives provide both a robust proxy record of cosmic ray flux and a valuable tool for detailed global synchronization based on cosmic ray variations

40ar 39ar dating of latest pleistocene 41 ka marine tephra in the mediterranean sea implications for global climate records abstract fifty one 40 ar 39 ar laser heating analyses of sanidine crystals in the c 13 tephra layer recovered out of a piston core raised from 3000 m depth in the tyrrhenian sea yielded apparent ages between 25 and 112 ka twenty four of these measurements define an age probability maximum and generate an isochron of 41 1 2 1 ka 2 with a 40 ar 36 ar intercept of 288 21 that is indistinguishable from the modern atmosphere however the entire population is skewed toward older apparent ages with smaller peaks at 48 ka 55 ka 67 ka and 110 ka the composition of glass shards in the c 13 tephra overlaps that of the sio 2 rich phase of the 150 km 3 campanian ignimbrite which erupted from the campi flegrei caldera 130 km northwest of the core site although the 41 1 2 1 ka isochron is 15 older than k ar and 14 c ages for the campanian ignimbrite it is indistinguishable from recent 40 ar 39 ar age determinations the campanian ignimbrite eruptions were also chemically similar to and correlated with the y 5 ash layer the most voluminous and widely dispersed late pleistocene tephra in the mediterranean region the age of the y 5 layer was constrained originally at 38 0 2 5 ka on the basis of astronomical dating of o isotope stages the 40 ar 39 ar ages astronomical dating plus chemical similarities permit correlation of the c 13 tephra layer with both the campanian ignimbrite and the y 5 tephra layer the older ages preserved in the c 13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the campi flegrei caldera 41 ka the c 13 tephra layer is correlated with a 10 be peak in an adjacent marine core o isotope stage 3 12 and immediately preceded a cooling episode corresponding to heinrich event 4 thus the age of these features is constrained by radioisotope dating the 41 ka peak in 10 be deposition is a global phenomenon whose age matches that of the laschamp geomagnetic excursion thus our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr precise age information independent of radiocarbon dating can be recovered from latest pleistocene marine tephra using the 40 ar 39 ar laser heating method despite the presence of multiple components that may have been incorporated during or after its deposition

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

enhanced cosmic ray production of 10be coincident with the mono lake and laschamp geomagnetic excursions the cosmogenic isotope 10 be total be and al were measured in partly varved sediments from the upper 50 m of core 480 leg 64 dsdp gulf of california the concentration of 10 be from 1 to 50 kyr is in general agreement with estimates of the geomagnetic dipole moment obtained from archaeomagnetic and marine core research 10 be anomalies were also found at 32 kyr and 43 kyr contemporaneous with the mono lake and laschamp excursions respectively the production of 10 be required to explain these anomalies is too high particularly for the mono lake excursion to be produced by a combination of decreased geomagnetic field and unprecedented long term solar activity we conclude that the cause is a change in the galactic cosmic ray flux consistent with a supernova event the coincidence with the two excursions remains a paradox

application of in situ produced cosmogenic 10be and 26al to the study of lateritic soil development in tropical forest theory and examples from cameroon and gabon abstract depth profiles of in situ produced cosmogenic nuclides including 10 be t 1 2 1 5 10 6 years and 26 al t 1 2 0 73 10 6 years in the upper few meters of the earth s crust may be used to study surficial processes quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations in this paper we discuss the fundamentals of the method and apply it to two lateritic sequences located in african tropical forests

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

palynostratigraphy and chronostratigraphy of baffin bay deep sea cores climatostratigraphic implications abstract palynostratigraphic considerations and 14c dates ams accelerator mass spectrometry on foraminifera samples from piston cores suggest sedimentation rates as high as ca 8 11 cm ka in deep baffin bay during the late pleistocene throughout this interval baffin bay experiences rigorous conditions and probably the extension of a dense sea ice cover unfavourable to phytoplanktonic productivity the dinocyst microflora indicates only brief episodes of higher productivity related to arctic conditions and to moderately low salinites ca 30 31 the abundance of reworked pre quaternary palynomorphs in the deposits is interpreted as a response to glacial and glacio marine activity in the northernmost areas surrounding baffin bay the dinocyst stratigraphy spanning approximately over the last ice age ca 100 ka reveals that baffin bay constituted a confined basin isolated from the north atlantic ocean prior to the present interglacial

quaternary stratigraphy of the fladen area central north sea a multidisciplinary study based on detailed stratigraphic investigations on a 200 6m long core bgs borehole no 81 26 from the fladen ground area british sector core material from the sleipner field norwegian sector and shallow seismic profiles between the core sites the following conclusions are drawn 1 the north sea was glaciated sometime during th elaterpart of matuyama reversed period a complete glacial interglacial glacial cycle is recorded in these sediments 2 in a period of marine sedimentation in the middle pleistocene a transgression regression cycle under boreal arctic regime is recorded 3 the fladen area has subsided between 0 9 and 0 6 m ka through the later parts of the quaternary 4 a major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81 26 this till which was deposited by ice moving from the southwest scotland probably represents a period when the scandinavian and british ice sheets coalesced in the north sea 5 based on the seismic data and the stratigraphy of the sleipner core an ice free open embayment dry land is favoured for the central north sea during the late weichselian 6 from the amino acid data it is shown that there has been an episodic style of sedimentation through the quaternary 7 of the investigated sediments which span the last 1 mill year ca 98 have been deposited under arctic to boreal arctic conditions

laurentide ice sheet meltwater and abrupt climate change during the last glaciation 1 a leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the north american laurentide ice sheet lis which may have routed fresh water between the gulf of mexico gom and the north atlantic affecting north atlantic deep water variability and regional climate paired measurements of 18o and mg ca of foraminiferal calcite from gom sediments reveal five episodes of lis meltwater input from 28 to 45 thousand years ago ka that do not match the millennial scale dansgaard oeschger warmings recorded in greenland ice we suggest that summer melting of the lis may occur during antarctic warming and likely contributed to sea level variability during marine isotope stage 3

evidence for enhanced 10be deposition in mediterranean sediments 35 kyr bp in this letter we report the profiles 160 samples of 10be 9be zn in a mediterranean sediment core spanning the last 60 kyr we show the existence of a 10be peak whose absolute age is estimated to be 34 3 kyr bp based on its stratigraphic position between two tephra layers originating from two volcanic eruptions campanian ignimbrite and citara dated by k ar 40ar 39ar and 14c methods this peak is similar to the increase in the 10be concentration observed in vostok and dome c ice cores at the same age the increase with approximately similar amplitude in both ice and sediment cores at different latitudes and hemispheres cannot be explained by changes in the archives the present result supports the view of a well defined global enhancement of the 10be flux related to an increase of the 10be production rate and not to a redistribution of the 10be fallout between different latitudes

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

a high resolution authigenic 10be 9be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the portuguese margin a high resolution study of authigenic be isotopes 10be and 9be combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the portuguese margin n e atlantic covering the past 300 ka in order to assess relationships between geomagnetic moment variations and 10be production rate variations a carefull examination of the various ways of taking into account environmental disturbing effects on the authigenic 10be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10be 9be ratio eight intervals of significant authigenic 10be 9be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions some being already admitted others being proposed as new geomagnetic features since contrarily to sedimentary magnetic remanence the authigenic 10be 9be records dipole moment variations without significant acquisition delay it provides better constraints on their timing comparison of 10be 9be and benthic 18o records from the same cores suggests that dipole moment lows preferentially occured during or at the end of interglacial episodes with a quasi period of 100 ka

new data on the pleistocene of mallorca abstract stratigraphic geomorphologic and isoleucine epimerization studies at 15 sites in mallorca define four aminozones a c e and f g of increasing age that are related to transgressive regressive marine cycles from the holocene to the mid pleistocene calibration of aminozone e glycymeris aile ile mean from all sites 0 41 0 03 n 38 is provided by a 129 7 ka u series coral age on cladocora caespitosa from son grauet of the younger aminozones a relates to the holocene transgression and aminozone c to a mid to late isotopic stage 5 event 90 15 ka revealed only by supralittoral eolianites assigning an age to the older poorly resolved aminozones f and g called f g in this case is uncertain without supporting radiometric data but an age of 180 ka can be assigned to these aminozone s f g based on a kinetic model and other examples in the mediterranean several deposits previously dated u series molluscs between 75 and 300 ka appear to belong to the last interglacial complex stage 5 and aminozone e a proposed revision of the positive sea level history of mallorca shows multiple minor oscillations during the major last interglacial cycle stage 5 and two mid pleistocene sea levels one lower than present and the other at about 14 m a s l

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

a geomagnetic chronology for antarctic ice accumulation the curve of 10be flux versus age in the vostok ice core largely covaries with a synthetic curve calculated assuming that a large fraction of 10be production rate is modulated by changes in the geomagnetic field intensity with this assumption it is also possible to derive a precise chronology for the vostok core this chronology is in good agreement with a very recent glaciological chronology obtained for vostok ice core and improves the correspondence of climate events recorded in antarctic ice with correlative events recorded in deep sea sediments therefore the idea that changes in the 10be flux at vostok may arise from variations in earth s geomagnetic dipole field has to be seriously considered this would imply that a large portion of the 10be deposited there is derived from lower latitudes

constancy of oceanic deposition of 10 be as recorded in manganese crusts recent developments in the use of nuclear accelerators as high energy mass spectrometers1 2 has renewed interest in the study of cosmogenic 10be half life 1 5 myr as a geophysical time tracer the accelerator techniques enable us to measure 10be with a sensitivity of 107 atoms or less the potential age dating span with 10be is extended back to at least 15 myr bp providing that the 10be production and deposition rates remain constant or nearly constant over that time period a knowledge of the long term constancy in the 10be deposition rate is thus very important we report here the first detailed measurements of 10be and 9be in two ferromanganese oxide crusts from the sea floor of the equatorial atlantic sample no k 9 21 and the north pacific schw 1d each representing 10 myr of accumulation history we have found in these crusts that the deposition of 10be and 10be 9be during the past 7 9 myr has been constant averaged over time intervals of 1 myr the variation is within 6 before that time both crusts show similar significant deviations the 7 9 myr demarcation may be related to the reported late miocene global abyssal circulation change in the ocean3

calibration of the 14c time scale to 40 ka by 234u 230th dating of lake lisan sediments last glacial dead sea a new comparison of 14c dates with 234u 230th ages is presented of aragonites from lake lisan the last glacial dead sea between 20 52 cal ka bp the lisan data are coincident with the coral based 14c calendar age calibration through the continuous portion of the curve to 23 5 cal ka bp and with the additional checkpoints at 30 and 40 cal ka bp the agreement with the corals provides evidence for the accuracy of the u th and 14c ages and indicates that lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14c variations through this crucial time interval the lisan data are compared with other records older than 25 cal ka bp from lake suigetsu japan north atlantic foraminifera south african cave deposits and tufa from spain over some age intervals the records show broad agreement over other intervals they diverge all agree that 14c ages were 2 5 0 5 ka younger than calendar ages between 20 32 cal ka bp for ages 32 cal ka bp the lake suigetsu data indicate small differences between 14c ages and calendar ages of less than 1 5 ka the other records broadly agree that 14c ages are too young by 3 1 ka from 32 39 cal ka bp at 40 cal ka bp the foraminifera show equal 14c and calendar ages while the corals lisan aragonites and the spanish tufa indicate a large age difference of 4 5 ka a recent paleomagnetic study of the lisan formation indicates that the high calendar 14c age difference at 40 cal ka bp may be associated with the laschamp paleomagnetic excursion

10be and 9be in marine sediments and their potential for dating using sequential leaching experiments we have measured the fraction of the cosmogenic isotope 10be half life 1 5 my and its stable isotope 9be co extracted with the following phases in marine sediments exchangeable calcium carbonate fe and mn oxyhydroxides organic opal and detrital the extraction of the authigenic phases typically release 70 of the 10be but only 40 of the 9be in order to test its potential for dating marine sediments we have measured the authigeniccally associated 10be 9be in 17 surface sediment samples from different ocean basins the observed spatial variability which appears to be influenced by proximity to continental input of 9be precludes the general and precise applications of leached 10be 9be for dating however the relatively constant value observed in surface sediments over large areas of the pacific indian and southern atlantic oceans shows considerable promise for approximate dating of open oceans sediments in order to test temporal variability a profile of the authigenically associated 10be 9be ratio has been measured in the independently dated central pacific core rc12 65 the observed variation in 10be 9be over the past nine my is approximately twice that expected on the basis of 10be decay alone several possible explanations for such behavior and their potential consequences for the use of leached 10be 9be for dating are discussed

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

the goldilocks dilemma big ice little ice or just right ice in the eastern canadian arctic our conceptions of the ne sector of the laurentide ice sheet lis at the last glacial maximum lgm have evolved through three major paradigms over the past 50 years until the late 1960s the conventional view was that the eastern canadian arctic preserved only a simple deglacial sequence from a lis margin everywhere at the continental shelf edge flint paradigm glacial geologic field studies began in earnest in this region in the early 1960s and within the first decade field evidence documenting undisturbed deposits predating the lgm led a pendulum swing to a consensus view that large coastal stretches of the eastern canadian arctic remained free of actively eroding glacial ice at the lgm and that the most extensive ice margins occurred early in the last glacial cycle this minimalist paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated lgm ice at least locally reached the continental shelf within the past decade the marine data coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the eastern canadian arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence collectively these lines of evidence indicate that all of southern baffin island was glaciated at the lgm but that some coastal uplands north of cumberland sound remained above the limit of actively eroding glacial ice even though outlet glaciers reached the continental shelf in front of most fiords and sounds the most plausible explanation for the observed glacial limits is that low gradient relatively fast moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain slow moving ice frozen to its bed would have had steeper surface gradients hence would have terminated inland from the coast this scenario is consistent with observations indicating high elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf lgm summer temperatures were apparently much lower than present as lakes in the ice free regions were permanently frozen

depth of post depositional remanence acquisition in deep sea sediments a case study of the brunhes matuyama reversal and oxygen isotopic stage 19 1 although post depositional magnetization pdrm in deep sea sediments appears to be acquired during the earliest stages of sediment compaction the natural variability of the pdrm lock in depth in deep sea sediments is poorly understood and as yet unquantified here we consider variations in the relative stratigraphic positions of oxygen isotopic interglacial stage 19 1 and the brunhes matuyama b m chronozone reversal for eight deep sea sediment cores results from a similar study of the displacement between a widespread microtektite layer and the b m boundary are also included 1 the pdrm lock in depth and the temporal relationships between the b m and stage 19 1 datums can be determined from the offsets between the paleomagnetic and the isotopic and microtektite stratigraphies for cores with sedimentation rates greater than 1 cm kyr a the depth offset between the paleomagnetic and isotopic datums is a linear function of sedimentation rate a simple model r 2 0 77 demonstrates that 1 pdrm acquisition occurs 16 cm below the sediment surface and 2 the b m reversal occurs 6 kyr 4 2 kyr after the stage 19 1 datum and the stage 19 1 datum occurs 9 kyr 4 3 kyr after the deposition of the australasian microtektite strewnfield this example argues against simple geophysical models linking geomagnetic field reversals to climate change or impact events the b m boundary is anomalously deep 30 50 cm in very low accumulation rate sediments 1 cm kyr 1 and this may reflect the unusual physical properties of these sediments a review of the geotechnical literature suggests that very low accumulation rate sediments have sufficient time to develop enhanced interparticle rigidity structural strength which inhibits early compaction and hence pdrm acquisition

lithologic controls on osmium isotopes in the rio orinoco abstract the seawater 187 os 188 os ratio has been increasing over the last 50 ma and at present is 1 06 reflecting that about 80 of os in the oceans is derived from the continents that provide os with an average 187 os 188 os ratio of about 1 26 whether the past variations in seawater os isotopes record changes in the bulk os flux with an average isotopic composition or the changes in the average 187 os 188 os ratio of the continental inputs or a combination of these two pathways is not clear the fundamental importance of lithology in controlling continental weathering rates and dissolved ion yields has been well established for the major cations it is dramatically manifested in the sr isotopes of rivers that are affected by selective dissolution of carbonates accordingly for os isotopes it has been proposed that disproportionate contributions of os with extremely high 187 os 188 os ratio come from weathering of organic rich black shales here we examine the effect of the weathering of specific lithologies on osmium isotopic composition and concentration in water samples of the orinoco river basin a major river basin draining both black shales exposed in the northern andes and granites of the precambrian guyana shield the northern andes was uplifted 17 ma which corresponds to the time of a dramatic rise in 187 os 188 os ratio the osmium isotopic composition and concentrations vary considerably in the tributaries and the main stem of the orinoco the highest os concentrations are observed in the rivers draining the andes however waters draining the andes are not highly radiogenic 187 os 188 os 187 os 188 os ratio of seawater during the last 17 million years

increased production of cosmogenic 10be during the last glacial maximum beryllium 10 half life 1 5 myr is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere its production rate is proportional to the flux of cosmic rays which is modulated by solar activity and the strength of the earth s magnetic field1 2 weakening of the magnetic field allows more cosmic rays to impinge on the earth s atmosphere thereby increasing 10be production here we report that the ocean wide average accumulation rate of 10be in pacific sediments which reflects the global average production rate of 10be ref 3 was at least 25 greater during the height of the most recent ice age 24 000 16 000 yr ago than during the holocene the past 10 000 yr the higher production rate of 10be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14c ages of fossil corals compared with ages obtained by u th dating4 these results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides

wisconsinan and early holocene glacial dynamics of cumberland peninsula baffin island arctic canada abstract three glacier systems an ice sheet with a large marine based ice stream an ice cap and an alpine glacier complex coalesced on cumberland peninsula during the late wisconsinan we combine high resolution mapping of glacial deposits with new cosmogenic nuclide and radiocarbon age determinations to constrain the history and dynamics of each system during the middle wisconsinan oxygen isotope stage 3 ois 3 the cumberland sound ice stream of the laurentide ice sheet retreated well back into cumberland sound and the alpine ice retreated at least to fiord head positions a more significant recession than previously documented the advance to maximal ois 2 ice positions beyond the mouth of cumberland sound and beyond most stretches of coastline remains undated partial preservation of an over ridden ois 3 glaciomarine delta in a fiord side position suggests that even fiord ice was weakly erosive in places moraines formed during deglaciation represent stillstands and re advances during three major cold events h 1 14 6 ka younger dryas 12 9 11 7 ka and cockburn 9 5 ka distinctly different responses of the three glacial systems are evident with the alpine system responding most sensitively to bolling allerod warming whereas the larger systems retreated mainly during pre boreal warming while the larger ice masses were mainly influenced by internal dynamics the smaller alpine glacier system responded sensitively to local climate effects asymmetrical recession of the alpine glacier complex indicates topoclimatic control on deglaciation and perhaps migration of the accumulation area toward moisture source

the laschamp geomagnetic dipole low expressed as a cosmogenic 10 be atmospheric overproduction at 41 ka authigenic 10be 9be ratiomeasurementswere performed at high resolution along a portuguese margin deep sea core 37 48 n 10 09w spanning the 20 50 ka time interval in order to reconstruct variations in atmospheric cosmogenic 10be production rates and derive the related geomagnetic dipole moment modulation a complementary approach consisting in 230thxs normalized 10be deposition rate determination on selected samples confirmed the reliability of the authigenic 10be 9be record this study constitutes the first successful comparison of the two widely used normalization techniques of 10be concentrations for both methods the presented results herein evidence a factor of 2 cosmogenic nuclide overproduction linked to a minimum dipole moment associated with the laschamp excursion the latter is stratigraphically constrained beneath heinrich event 4 its age is estimated at 41 ka on the basis of direct correlation between the series of rapid paleoclimatic events recorded in the portuguese margin sediments and in the greenland ice sheet and is confirmed by calibrated radiocarbon dating carried out on the same sediments the remarkable agreement between the authigenic 10be 9be and the greenland ice cores 10be deposition rate records attests to their global significance this new authigenic 10be 9be record has been combined with that previously obtained at the same site to produce a stacked record that is calibrated using absolute values of virtual dipole moment determined on lava flows this provides a reconstruction of dipole geomagnetic moment variations over the 20 50 ka interval independent frompaleomagnetically constrainedmethods that documents the laschamp dipole low but fails to express any dipole low related to t e mono lake excursion this high resolution record responds to the necessity of supplementing the knowledge of the atmospheric 14c variations in the 30 45 ka interval during which the 14c calibration curve suffers from a lack of accurate data and during which a discrepancy of about 5500 yr between the 14c and u th ages is due to the laschamp geomagnetic dipole low such new high resolution datasets from records obtained from different latitudes will be required to make significant advances in understanding the causes of atmospheric 14c variations

geomagnetic modulation of the 36cl flux in the grip ice core greenland geomagnetic field strength is expected to affect the production rate of cosmogenic isotopes such as beryllium 10 carbon 14 or chlorine 36 chlorine 36 data from the greenland ice core project grip ice core agree well with a production rate calculation based on a paleomagnetic reconstruction for the past 100 000 years over both long and short term variations a chlorine 36 peak at 38 000 years ago previously found in the beryllium 10 record from the vostok ice core can be explained by a period of low geomagnetic field intensity

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

nuclide production by cosmic rays during the last ice age carbon dating is an extremely important method for determining the age of ancient organic matter the method relies on measurements of radioactive carbon 14 produced by cosmic rays and incorporated into the bodies of animals and plants as bard discusses in his perspective the accuracy of the technique depends on quantifying the production rates of cosmogenic isotopes over time results presented in the same issue by plummer et al shed light on the past history of the important chlorine 36 isotope which in turn offers clues on how the geomagnetic field has influenced cosmic ray production of other isotopes

glacial geology and quaternary marine stratigraphy of the robeson channel area northeastern ellesmere island northwest territories glacial and marine deposits associated with two phases of glaciation are exposed along a 60 km corridor on ellesmere island that borders robeson channel the oldest sediments tentatively dated at 70 000 bp were deposited during a major advance of the northwest greenland ice sheet across robeson channel during subsequent retreat of this ice mass glaciomarine sediments containing a high arctic macro and microfauna were deposited in the isostatic downwarp on ellesmere island this marine unit was radiocarbon dated at 31 300 900 and 32 000 bp mean aile ile ratios are 0 218 0 03 for the free fraction and 0 063 0 011 for the total acid hydrolysate the last ice advance late wisconsin early holocene did not extend into the field area from either interior ellesmere island or northwest greenland the ice marginal sea transgressed to the marine limit 116 m and overlapped the deposits of the previous maximum greenland advance local plateau ice caps did however spill over into one major valle

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

geomagnetic field control of 14c production over the last 80 ky implications for the radiocarbon time scale we have used a recent estimate of the geomagnetic dipole field strength over the last 80 ky to examine the extent to which changes in geomagnetic field intensity have affected the radiocarbon time scale the magnetic record was converted into a 14c production signal which was then used to produce a synthetic atmospheric 14c record using a two box model for the carbon cycle this calibration suggests that the geomagnetic field has been the main factor governing the production of cosmogenic 14c atoms over the period of time considered and that 14c changes due to other causes such as climatic changes have been of lesser importance the results indicate that the radiocarbon ages are 2 to 3 ky younger than true age in the interval 18 40 ky b p in good agreement with recent u th and 14c age comparisons moreover the results predict that a negligible difference between true and 14c ages should be observed around 45 50 ky

palaeoclimate of baffin bay from 300 000 year record of foraminifera dinoflagellates and pollen several different models1 5 have attempted to relate quaternary marine and terrestrial records of ice sheet growth in the north atlantic region the models are derived from either discontinuous terrestrial records including marine fossils in raised shorelines1 2 or from deep sea calcareous microfossils3 4 this study correlates arctic marine and terrestrial data directly by comparing 18o foraminiferal dinoflagellate and pollen records from a core taken in baffin bay the core contains an almost continuous sequence of sediments deposited during isotope stages 1 10 subarctic foraminifera and atlantic dinoflagellates in early isotope stages 2 4 6 and 8 show that subarctic water entered southern baffin bay before the glacial maxima boreal subarctic pollen suggest that atlantic air flowed into baffin bay during the ice sheet growth phases these data support models which postulate that open water in the labrador sea had an important role in supplying moisture to laurentide and greenland ice sheets

land ocean correlations during the last interglacial glacial transition baffin bay northwestern north atlantic a review abstract evidence from terrestrial sections ice cores and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest north atlantic during marine isotope stages 5 and 4 the critical physical link between the landbased glacial chronology and marine events in baffin bay is the presence of carbonate rich drift along the baffin bay coast of bylot island and a detrital carbonate facies facies b in baffin bay sediments cores from baffin bay labrador sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards one occurrence of facies b is dated between late stage 5 and stage 4 and we correlate this event with the eclipse glaciation of bylot island and the ayr lake stade of the foxe glaciation of baffin island kogalu aminozone in contrast on west greenland amino acid racemization evidence suggests that the greenland ice sheet developed throughout stage 4 and reached a maximum in stage 3 svartenhuk advance 40 ka the oxygen isotope record in the devon island ice cap northwest baffin bay indicates that baffin bay was largely open during marine isotope stage 5 analyses of shallow water molluscan and foraminiferal assemblages deep water foraminifera pollen from iand sections and deep sea cores and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage 5 4 glaciation

timing and warmth of the last interglacial period new u series evidence from hawaii and bermuda and a new fossil compilation for north america abstract the timing and duration of the last interglacial period have been controversial with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing new high precison thermal ionization mass spectrometric tims u series ages of last interglacial corals from hawaii and bermuda test these competing hypotheses waimanalo formation corals from slowly uplifting oahu hawaii range in age from 134 to 113 ka with most ages between 125 and 115 ka combined with published u series ages from nearby lanai the data suggest a long last interglacial period that may have occurred from 136 to at least 115 ka the results indicate that orbital forcing may not have been the only control on ice sheet growth and decay because sea level would have been high at times of relatively low northern hemisphere summer insolation on tectonically stable bermuda deposits from the 200 ka penultimate interglacial period 120 ka peak last interglacial period and 80 ka late last interglacial period high sea stands have been newly dated fossil corals on bermuda are derived from patch reefs that likely were catch up responses to sea level rise it is expected that u series ages of last interglacial corals on bermuda should overlap with but not be as old as the range of corals on oahu last interglacial corals on bermuda give a range of 125 113 ka which supports this hypothesis a large number of emergent marine deposits on hawaii bermuda and along coastal north america have now been dated to the last interglacial period both oahu and bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks suggesting warmer than present waters during the last interglacial period warmer waters are also suggested for last interglacial localities around most of north america from florida to canada and greenland and baja california to alaska these observations are consistent with similar warm water faunas of last interglacial age reported from japan the mediterranean basin and western australia it is likely that significant changes in ocean currents took place during the last interglacial period with a movement of relatively warm waters to higher latitudes than is the case today

10 be and delta 2 h in polar ice cores as a probe of the solar variability s influence on climate and discussion by using the technique of accelerator mass spectrometry it is now possible to measure detailed profiles of cosmogenic cosmic ray produced 10 be in polar ice cores recent work has demonstrated that these profiles contain information on solar activity via its influence on the intensity of galactic cosmic rays arriving in the earth s atmosphere it has been known for some time that as a result of temperature dependent fractionation effects the stable isotope profiles delta 2 o and delta 2 h in polar ice cores contain palaeoclimate information thus by comparing the 10 be and stable isotope profiles in the same ice core one can test the influence of solar variability on climate and this independent of possible uncertainties in the absolute chronology of the records we present here the results of such a comparison for two antarctic ice cores one from the south pole covering the past ca 1000 years and one from dome c covering the past ca 3000 years

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

seismic hazard reappraisal from combined structural geology geomorphology and cosmic ray exposure dating analyses the eastern precordillera thrust system nw argentina because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture paleoseismological estimation of their associated seismic hazard is a difficult task to improve the seismic hazard assessments in the andean foreland of western argentina san juan province this paper proposes a novel approach that combines structural geology geomorphology and exposure age dating the eastern precordillera of san juan is probably one of the most active zones of thrust tectonics in the world we concentrated on one major regional active reverse structure the 145 km long villic um pedernal thrust where this methodology allows one to 1 constrain the quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes 2 analyse the geometry and the geomorphic characteristics of the villic um pedernal thrust and 3 estimate uplift and shortening rates through determination of in situ produced 1 0 be cosmic ray exposure cre ages of abandoned and uplifted alluvial terraces from a structural point of view the villic um pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique n40 e trending fault branches along the three segments inversion of fault slip data shows that the development of the eastern precordillera between 31 s and 32 s latitude is dominated by a pure compressive reverse faulting stress regime characterized by a n110 10 e trending compressional stress axis 1 a geomorphic study realized along the 18 km long las tapias fault segment combined with cre ages shows that the minimum shortening rate calculated over the previous 20 kyr is at least of the order of 1 mm yr 1 an earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation this analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three times greater than the shortening rate we determined for the las tapias fault i e 3 mm yr 1 suggesting that the san juan region may have experienced a seismic crisis during the 20th century moreover the ramp that controls the development of the eastern precordillera appears to be one of the main seismic sources in the san juan area particularly the 65 km long villic um las tapias segment a first order evaluation of the seismic hazard parameters shows that this thrust segment can produce a maximum earthquake characterized by a moment magnitude of 7 3 0 1 and a recurrence interval of 2 4 1 5 kyr this part of the villic um pedernal ramp may have ruptured during the ms 7 4 1944 san juan earthquake producing very few surface ruptures and only distributed flexural slip deformation on to the neogene foreland bedding planes between the eastern precordillera and pie de palo

palaeointensity in the pelagic realm marine sediment data compared with archaeomagnetic and lake sediment records summary four box cores collected from the ontong java plateau during the eurydice expedition have been used to make relative geomagnetic palaeointensity measurements rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy and that they are suitable for relative intensity estimates these are obtained by normalizing the nrm by an arm imparted in a low dc bias field the palaeoceanographic event known as the preservation spike is used to establish a crude time scale for the record so that it may be compared with other data from the same region and also with global palaeointensity estimates the marine sediment data are quite similar to australian intensity data from lake sediments and archaeomagnetic sources but as might be expected exhibit some obvious differences from the global record

the relationship between 10be and geomagnetic field strength records in central north atlantic sediments during the last 80 ka abstract a profile of leached 10 be 9 be has been measured in an 80 ka sediment core from the northeast atlantic ocean this profile shows a significant inverse correlation with the palaeomagnetic intensity profile inferred from nrm arm measurements in the same core particularly between 40 and 50 ka where a rapid decrease in field intensity is accompanied by a rapid increase in 10 be 9 be the extent to which this increase in 10 be 9 be at 40 ka is associated with a 10 be peak seen in polar ice cores at about the same time remains speculative