climate and vegetation history of the midcontinent from 75 to 25 ka a speleothem record from crevice cave missouri usa four missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago ka the thorium 230 dated records reveal that between 75 and 55 ka the midcontinental climate oscillated on millennial time scales between cold and warm and vegetation alternated among forest savanna and prairie temperatures were highest and prairie vegetation peaked between 59 and 55 ka climate cooled and forest replaced grassland at 55 ka when global ice sheets began to build during the early part of marine oxygen isotope stage 3

stable isotope record and its palaeoenvironmental interpretation for a late middle pleistocene speleothem from victoria fossil cave naracoorte south australia abstract a speleothem from victoria fossil cave south australia provides a continuous stable isotope record from 185 to 157 ka oxygen isotope analysis indicates that at commencement of deposition mean annual temperatures were much lower than at present and that between 178 and 162 ka regional surface temperatures were similar to today such high temperatures during an interstadial are surprising but may be attributable to increased continentality due to low sealevels carbon isotope analysis indicates the presence of an active vegetation cover dominated by c3 plants during the interstadial while a sparse vegetation dominated by c4 grasses appears to have been dominant during full glacial conditions variations in moisture availability and vegetation productivity are probably closely related to stages in the precessional cycle

elevated and variable values of 13c in speleothems in a british cave system 13c isotope variations in speleothems have been investigated for samples from the british isles where plants which use the hatch slack or c4 photosynthetic pathway are not present the range of 13c expected in speleothem carbonate formed in isotopic equilibrium with soil co2 derived from the overlying c3 vegetation should thus fall in the range 12 to 6 forty one actively growing speleothem samples from low discharge sites were analysed from stump cross caverns yorkshire england ten percent have 13c greater than 6 in addition a large range of 13c was observed 8 06 1 38 a 1 variability of 17 with adjacent samples having 13c differing by a maximum of 4 74 similar findings were obtained from a review of analyses of late quaternary speleothem samples from the british isles with 75 of flowstone samples and 57 of high flow stalagmite samples exhibiting elevated 13c three possible processes are proposed as possible causes of elevated 13c in speleothems firstly fractionation may occur between the stalactite and stalagmite due to evaporation or degassing secondly degassing of the groundwaters may have occurred within the aquifer before reaching the cave void allowing release of some co2 from the water whilst remaining saturated in calcium finally the elevated 13c may be due to short water residence times in the soil such that equilibrium between soil water and soil co2 is not reached evidence presented here demonstrates that any one of these mechanisms may be important in the karst areas of the british isles caution is needed before interpreting the 13c signal within speleothems in terms of palaeovegetation

early mid holocene climatic variations in tasmania australia multi proxy records in a stalagmite from lynds cave mass spectrometric uranium series dating and c o isotopic analysis of a stalagmite from lynds cave northern tasmania australia provide a high resolution record of regional climate change between 5100 and 9200 yr before present bp combined delta 18 o delta 13 c growth rate initial u 234 u 238 and physical property color transparency and porosity records allow recognition of seven climatic stages stage i 9080 yr bp a relatively dry period at the beginning of stalagmite growth evidenced by elevated u 234 u 238 stage ii 9080 8600 yr bp a period of unstable climate characterized by high frequency variability in temperature and bio productivity stage 111 8600 8000 yr bp a period of stable and moderate precipitation and stable and high bio productivity with a continuously rising temperature stage iv 8000 7400 yr bp the warmest period with high evaporation and low effective precipitation rainfall less evaporation stage v 7400 7000 yr bp the wettest period with highest stalagmite growth and enhanced but unstable bio productivity stage vi 7000 6600 yr bp a period with a significantly reduced precipitation and bio productivity without noticeable change in temperature stage vii 6600 5100 yr bp a period of lowest temperature and precipitation marking a significant climatic deterioration overall the records suggest that the warmest climate occurred between 8000 and 7400 yr bp followed by a wettest period between 7400 and 7000 yr bp these are broadly correlated with the so called mid holocene optimum previously proposed using pollen and lake level records however the timing and resolution of the speleothem record from lynds cave are significantly higher than in both the pollen and lake level records this allows us to correlate the abrupt change in physical property delta 18 o delta 13 c growth rate and initial u 234 u 238 of the stalagmite at similar to8000 yr bp with a global climatic event at early mid holocene transition c 2001 elsevier science b v all rights reserved

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

annual trace element variations in a holocene speleothem high resolution secondary ionization mass spectrometry sims analysis along the growth axis of a holocene speleothem from northern scotland reveals high frequency oscillations and longer term trends in mg ca sr ca and ba ca at the scale of the high frequency oscillations mg ca and sr ca display a well defined anticorrelation while sr ca and ba ca are positively correlated imaging of elemental ratios in two dimensions reveals that the high frequency signal is well preserved and laterally continuous across the sample tims 230th ages and annual ultraviolet luminescence banding provide chronological control and demonstrate that the high frequency cyclicity is annual trace element variations in speleothem calcite are a reflection of hydrochemical processes in the unsaturated zone overlying the cave supply effects and partitioning at the water calcite interface mg partitioning between water and calcite is temperature dependent calculations suggest that the annual mg ca oscillations may be caused by seasonal temperature changes however the longer timescale variations in mg ca are too great to be explained by this mechanism seasonal variations in water residence time in the unsaturated zone which reflect effective precipitation provide a more probable explanation for the observed annual oscillations and also explain the inverse relationship between mg ca and sr ca this record suggests that trace elements in speleothems have the potential to provide the high resolution insights into interannual palaeoclimatic variability required for assessment of general circulation models

late pleistocene chronology and paleoclimate of vancouver island determined from cave deposits speleothems from four caves in south central vancouver island have been analysed by the 230th 234u method only speleothems from one cave cascade cave near port alberni contained sufficient uranium for them to be dated twenty seven ages determined for seven speleothems were found to cluster in two periods 67 28 ka corresponding to the olympia interstadial and 23 10 ka or 15 ka if corrected for detrital thorium contamination corresponding to the fraser late wisconsin deglaciation and holocene periods two speleothems were found to be deposited in isotopic equilibrium with their seepage waters profiles of variations in 18o of the calcite 18oc of each of the two deposits show a decrease of 1 3 over the growth period 64 28 ka at all times 18oc was less than 18o of modern calcite in the cave using modern cave temperature and the variation of 18o of seawater over the dated period the profiles of 18oc are interpreted in terms of a paleotemperature record for the olympia interstadial

tectonic stress controls on ascent and emplacement of magmas abstract the tectonic stresses can significantly affect the propagation of a magma filled crack it has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress however it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states we have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow the stress profiles were estimated by a simple model of lithospheric deformation we employed a three layer model of the lithosphere the upper crust the lower crust and the upper mantle have different rheological properties a constant horizontal force is applied to the lithosphere and the horizontal strain is assumed to be independent of depth when realistic tectonic forces 10 11 n m are applied the rheological boundaries mainly control the emplacement of magma the emplacement is expected at the moho the upper lower crust boundary and the brittle ductile boundary for lower tectonic forces 11 n m the tectonic stress no longer plays an important role in the emplacement of magmas when the tectonic stress controls the emplacement the roles of rheological boundaries strongly depend on the surface heat flow when the surface heat flow is relatively high 80 mw m 2 the stress in the mantle is quite low and the moho cannot trap ascending magmas for relatively low heat flow 2 on the other hand the moho acts as a magma trap and the upper lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high our results suggest that the emplacement depth can change responding to the change in the tectonic force and or that in the surface heat flow this may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and or thermal history

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

aeolian contribution to strontium and strontium isotope variations in a tasmanian speleothem abstract a speleothem from south central tasmania shows marked secular variations in its strontium content the element exhibits a striking bimodal distribution pattern with abrupt changes between two modal groups that is believed to be due to rapid changes in the direction of the dominant strong winds strontium isotope compositions in the speleothem range from 0 70865 to 0 70898 indicating derivation of sr from at least two distinct sources the first a persistent one from the overlying limestone the second a higher 87 sr 86 sr component probably representing input from terrestrial dust the speleothem record is unusual because it indicates a greater input of radiogenic sr dust flux during interstadial times than under full glacial conditions if an aeolian origin of some of the strontium contained in speleothems at other inland cave sites around the world can be confirmed variations in strontium isotope composition will provide high resolution records of how terrestrial dust flux has varied during the quaternary in near coastal sites significant amounts of strontium may be derived from seasalt and in those areas temporal variation of the element in speleothems may reflect at least in part changing distance from the coast due to changes in sealevel

a 3000 year high resolution stalagmitebased record of palaeoclimate for northeastern south africa high resolution stable isotope variations and growth structure analyses of the last three millennia of a 6600 year stalagmite record at cold air cave makapansgat valley south africa are presented growth layers which are measurable over the last 250 years are shown to be annual the correlation between the width of growth layers and precipitation is strongly positive changes in 18o and 13c are positively correlated and inversely correlated to changes in the colour of the growth layers in the stalagmite variations in colour are directly correlated with mean annual temperature dark colouration is the product of increased temperature and mobilization of organic matter from the soil and is associated with wetter summers and enhanced growth of c4 grasses darker colouring and enriched 18o and 13c reflect a warmer wetter environment whereas lighter colouring and depleted isotopic values are indicative of cooler drier conditions the dominant episode in the 3000 year record is the cool dry 500 year

continental oxygen isotopic record of the last 170 000 years in jerusalem abstract a long radiometrically dated oxygen isotopic record of continental climatic variations since the penultimate glaciation was obtained from a stalagmite deposited in a sealed cave in jerusalem this record shows that speleothems have the potential of assigning dates to long and short term climatic events with possible refining of milankovitch tuning of ice and marine records which themselves are not datable short term 1000 yr events are very significant in the region reaching 50 of glacial interglacial fluctuations the mediterranean sea was the most probable source of local precipitation throughout the last glacial cycle

paleoclimate implications of mass spectrometric dating of a british flowstone the timing of growth phases in a cave flowstone from yorkshire england has been precisely dated by thermal ionization mass spectrometric 238u 234u 230th dating six growth periods of both short duration and fast growth rate are separated by nondepositional hiatuses the ages of these phases were determined to be 128 8 2 7 103 1 1 8 84 7 1 2 57 9 1 5 49 6 1 3 and 36 9 0 8 ka there is a remarkably good correlation between the periods of active speleothem growth and the timing of solar insolation maxima derived from orbital parameters which has not previously been reported speleothem growth theory and evidence from other terrestrial paleoclimate records suggest that episodic rapid growth phases at the insolation maxima are most likely to be caused by changes in either precipitation intensity or volume which caused switching in the routing of water flow in the unsaturated zone above the cave such a result provides new evidence of the importance of variations in solar insolation for terrestrial paleoclimate and offers the potential for derivation of a paleowetness index from speleothem growth

orbital forcing of the marine isotope stage 9 interglacial milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records however the validity of this theory remains uncertain and independent sea level chronologies used to test its applicability have been restricted largely to the past approximately 135 000 years here we report u series ages for coral reefs formed on henderson island during sea level high stands occurring at approximately 630 000 and approximately 330 000 years ago these data are consistent with the hypothesis that interglacial climates are forced by northern hemisphere summer solar insolation centered at 65 degrees n latitude as predicted by milankovitch theory

annual growth banding in a cave stalagmite the presence of microscopic luminescence banding in cave calcite deposits speleothems has recently been reported1 3 the luminescence seems to be caused by excitation of humic and fulvic acids derived from the overlying soil and subsequently incorporated into the calcite3 4 we have tested whether such luminescence corresponds to annual growth layers using high precision thermal ionization mass spectrometric 238u 234u 230 th ages from banded sections of a holocene stalagmite we report here that the timespans yielded by counting bands on the assumption that they are annual agree within error limits with those obtained by our uranium thorium dating this demonstration that the banding is annual should make banded speleothems valuable resources for providing high resolution records of past climate in which precipitation can be estimated from growth rates5 6 and temperatures from stable isotope measurements7 and solar terrestrial correlations as the luminescence intensity can be related to the solar sunspot cycle1 3

500 ka precipitation record from southeastern australia evidence for interglacial relative aridity 230 th 234 u dating of speleothems from southeastern australia documents changes in effective precipitation over the past 500 k y at a temporal resolution not previously achieved results show that the highest effective precipitation for the southeastern interior of australia occurred during stadials and cool interstadials of the past four glacial cycles interglacials and warm interstadials as well as glacial maxima are comparatively arid we suggest that lower regional temperatures over the continent and changes in atmospheric circulation stronger walker circulation produced the observed periods of increased effective precipitation

evidence of younger dryas and neoglacial cooling in a late quaternary palaeotemperature record from a speleothem in eastern victoria australia a calcitic stalagmite collected from a limestone cave in the buchan area of eastern victoria has been dated by three mass spectrometric uranium series analyses two growth phases are represented the older from 13 4 to 10 6 ka and the younger from 3 2 to 2 1 ka oxygen isotope analysis reveals that temperatures were below present day values at all times but particularly cool conditions are indicated between 12 3 and 11 4 ka and neoglacial conditions occurred at about 3 ka the older cold climate event is clearly synchronous with the younger dryas in europe and this is the first time that strong evidence for this event has been found in australia carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall they indicate particularly high levels of plant productivity from 11 5 to 11 0 ka 1996 john wiley sons ltd

late quaternary lake level changes and climates of australia abstract spatial and temporal patterns in lake level data from 38 sites in australia and papua new guinea provide a basis for reconstructing changes in water balance and atmospheric circulation during the past 30 000 years the reconstructions are consistent with hydrological changes inferred from pollen analysis and palaeowind directions inferred from dunes generally wetter conditions between 30 000 and 24 000 bp are consistent with a strong walker circulation with the sta near its present position general aridity at the glacial maximum until 12 000 bp with higher than present lake levels in the southeastern interior of australia implies that the southern margin of the subtropical anticyclone belt was expanded southward and the southern westerlies were correspondingly displaced this southward shift appears in all gcm simulations of the 18 000 bp climate and may be a result of the increased vigour of the northern hemisphere circulation a northward migration of the belt of high lake levels between 11 000 and 6000 bp suggests that the sta shifted back equatorward to north of its present position relaxation to modern conditions occurred after 6000 bp interrupted by an unexplained dry phase 6000 5000 bp in tasmania and queensland

problems with inferring p t t paths in low p granulite facies rocks microstructural evidence commonly is used to infer metamorphic reactions which are used to infer pressure temperature time p t t paths however this approach in low p high t lpht granulite facies metamorphic terranes has two main problems 1 microstructural evidence may be inconclusive so that reactions cannot be inferred with confidence in particular relative timing of mineral growth inferred from inclusions moulding relationships and foliation porphyroblast relationships is commonly ambiguous or invalid the most reliable indicators of metamorphic reactions are partial pseudomorphs and corona structures especially if symplectic intergrowths indicating simultaneous growth of two or more minerals are involved 2 even reactions that can be inferred with confidence do not indicate unique p t trends owing to p t slopes of reaction curves where successive reactions can be shown to have occurred in the same rock a line or curve joining reaction curve intersections gives an apparent single event path however isotopic evidence is needed to prove that polymetamorphism involving more complex paths making fortuitous intersections with the apparent single event path did not occur although these problems are well known their importance is not always emphasized in metamorphic investigations the difficulties are illustrated by published work on p t t paths for proterozoic lpht granulite facies rocks of central australia and antarctica recent work in antarctica has shown that p t t paths may be episodic and more complex than the simple single event paths commonly inferred from microstructural evidence alone

spectral analysis of a 1000 year stalagmite lamina thickness record from shihua cavern beijing china and its climatic significance stalagmite laminae provide a high resolution geological record of climate change in this paper moving spectral analysis is used to analyse a stalagmite lamina thickness record to study climatic v

application of iversen s glacial interglacial cycle to interpretation of the late last glacial and holocene vegetation history of western tasmania abstract the iversen glacial interglacial cycle of vegetation change is modified and applied to glacial lateglacial and holocene age pollen records from western tasmania cryocratic conditions occurred at high altitude ca 500 m during glacial and lateglacial time transition from cold humid to cool humid climate occurred on the lowlands by 13 ka bp and in the mountains by 10 ka bp there is regional parallelism of vegetation development from grassland herbland sedgeland through alpine subalpine scrub and woodland to temperate rainforest dominated by nothofagus cunninghamii however radiocarbon dating shows that changes in the vegetation succession and nothofagus rainforest maximum were non synchronous although climate change from glacial to interglacial conditions directed the general succession variations in dates for similar vegetation changes show that biological and physical variables were important for local vegetation development some sites show late holocene vegetation changes that could be interpreted as revertance aboriginal fire and lake infilling were probably responsible there is no evidence for an allerod type warm phase between 13 and 11 ka bp or a younger dryas type cold phase between 11 and 10 ka bp the climate was cool temperate between 13 and 0 ka bp and neither temperature nor precipitation change was sufficient to cause vegetation change of regional significance

thermal ionization mass spectrometry u series dating of a hominid site near nanjing china mass spectrometric u series dating of speleothems from tangshan cave combined with ecological and paleoclimatic evidence indicates that nanjing man a typical homo erectus morphologically correlated with peking man at zhoukoudian should be at least 580 k y old or more likely lived during the glacial oxygen isotope stage 16 similar to 620 ka such an age estimate which is similar to 270 ka older than previous electron spin resonance and alpha counting u series dates has significant implications for the evolution of asian h erectus dentine and enamel samples from the coexisting fossil layer yield significantly younger apparent ages that of the enamel sample being only less than one fourth of the minimum age of nanjing man this suggests that u uptake history is far more complex than existing models can handle as a result great care must be taken in the interpretation of electron spin resonance and u series dates of fossil teeth

continuous early last glacial palaeoenvironmental record from a tasmanian speleothem based on stable isotope and minor element variations a columnar stalagmite from a limestone cave in the florentine valley tasmania has been dated by three 230th 234u age determinations continuous profiles of 170 18o and 13c values as well as magnesium and strontium concentrations are presented 18o values indicate temperatures lower than today with a gradual temperature decline in the basal part of the profile punctuated by two short cooling events and culminating in a double temperature minimum between 70 and 60 ka the profile shows marked similarities with the gisp ice core record from greenland which shows two short intense stadials centred on 74 and 70 ka preceding the last glacial temperature minimum they have been correlated with heinrich events in north atlantic marine cores which in turn have been attributed to periodic massive discharges of icebergs into the north atlantic the tasmanian speleothem record suggests that these events may also have affected climates in the southern hemisphere the 13c variations also appear to indicate periodic environmental change minor element variations were found to be significantly correlated with isotopic changes strontium concentrations show a bimodal distribution indicating control by a switching mechanism tentatively attributed to variations in calcitic dust supply to the ground surface above the site

u th isotope systematics from the soreq cave israel and climatic correlations precise 230 th 234 u ages were obtained on thirty one growth laminae in speleothem samples which are self consistent with the detailed layer stratigraphy samples with low 232 th 238 u ratios give ages with analytical uncertainties of 40 years at 2 ky and 1000 years at 90 ky some growth zones with high but variable 232 th 238 u were dated by intermal isochrons this permits the determination of the initial 230 th 232 th assuming equilibrium of 232 th and 238 u series in the source of the high 232 th component this shows initial 230 th 232 th in activity units of from 1 3 to 2 9 the calculated atomic ratios of 232 th 238 u for the high 232 th component range from 1 08 to 2 4 which is well below the average crustal value speleothem materials with high 232 th 238 u are found to exhibit clear correlations of 232 th with si al and fe while 238 u correlates with sr and ba analyses of soreq cave drip waters show that the particulates in the waters have high 232 th concentrations and a 232 th 238 u ratio much lower than that found in the high 232 th component in speleothems but with 230 th 232 th 1 0 to 2 4 we infer that the trapped high th component in speleothems is from particulate matter in water with a large concentration of adsorbed u and not simply from detrital material the speleothems have only small234u excess the initial 234 u 238 u 0 show a range of 1 02 to 1 14 that was found to correlate with age over the past 25 ky the youngest samples have values in the same range as the modern drip waters there appears to be a correlation of 234 u 238 u 0 with the 18 o values there is a drop of 18 o in the time interval 20 to 15 ky which then remains relatively constant to recent times as the high 18 o values have been related to rainfall and associated climatic conditions we suggest that the 234 u 238 u in the speleothem reflects the effects of rainfall and soil weathering conditions on drip water composition and may provide a proxy for climate change