late pleistocene sea level change in the bahamas from mass spectrometric u series dating of submerged speleothem abstract the dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change sea level change and milankovitch cycles dating of fossil corals and submerged speleothem provides such independent information results of thermal ionization mass spectrometric u series dating on layers of flowstone speleothem from lucayan caverns grand bahama island indicate that multiple sea level events have passed through a depth of 10 to 15 m below modern sea level during the last 300 000 years these data are used to constrain the magnitude and timing of sea level fluctuations during the late pleistocene the new sea level curve constructed from these data correlates closely with the marine isotopic record sea level peaks occurred at around 233 215 125 and 100 ka bp there is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks there is also no evidence of a double rise around the 125 ka 5e peak although such an oscillation could have occurred above 10 m leaving no record in the lucayan caverns speleothem

a 200 000 year δ18o record of closed basin lacustrine calcite death valley california abstract a modified method from mccrea mccrea j m 1950 the isotopic chemistry of carbonates and a paleotemperature scale j chem phys 18 849 857 has been developed for analyzing carbon and oxygen isotopic compositions of lacustrine calcite in bulk saline lake sediments a two level climatic fluctuation model is suggested based on a continuous 200 000 year 18 o record of lacustrine calcite from a 186 m sediment core from badwater basin death valley california this record provides new approaches to the debate on the timing and driving forces of late quaternary climatic changes excursions in calcite 18 o track those of 18 o in sulfate in the death valley core as well as to those in marine carbonate specmap and polar ice in the summit ice core grip greenland the death valley record shows periodicities of 96 000 39 000 21 000 14 000 and 8000 years the longer term 96 000 39 000 and 21 000 years fluctuations match milankovitch orbital forcing and are thus likely to be global in origin the shorter term 14 000 and 8000 years fluctuations probably reflect regional climatic and or hydrologic forcing

a new model for the origin of the anomalous radioactivity in niue island south pacific soils abstract the anomalous natural radioactivity of niue island is due to large excesses of both 230 th and 231 pa compared with their parent radionuclides it is suggested that material in niue island soils consisting mainly of goethite and gibbsite partially trapped within porous calcite was exposed to seawater a few hundred thousand years b p and the u content of the seawater adsorbed onto the soil minerals the island then rose and remained essentially above sea level until present the daughter products of the u isotopes grew into radioactive equilibrium with the u parents but then the u parents were leached away some time in the span 100 70 ka b p leaving large amounts of orphan daughters in the soils without supporting parents

spring related carbonate rocks mg clays and associated minerals in pliocene deposits of the amargosa desert nevada and california the amargosa desert of nevada california is a spring fed structural basin containing large amounts of pliocene carbonate rocks and mg clays deposited in playas marshland ponds and flood plains pliocene basin fill deposits dated at 2 4 to 3 2 ma are subdivided into three lithofacies designated tpa tld and tpl tpa is chiefly limestone and was deposited in marshland and ponds tld consists chiefly of limestone and montmorillonite claystone that were deposited in varied environments including ponds and flood plains tpl is almost entirely mg clays limestone and dolomite which were deposited in playas and associated marshland the largest area of playa sediments termed east playa is in the east central part of the basin limestone and dolomite seepage mounds and caliche breccia musses were formed along zones of ground water leakage within east playa chemically precipitated mg smectite and sepiolite form large deposits in tpl sepiolite was formed in water of low salinity whereas mg smectite was formed in water of higher salinity authigenic celadonitic illite and k feldspar are commonly associated with mg smectite and are very likely reaction products of montmorillonite in saline alkaline water silicic vitric ash layers were locally altered to phillipsite and k feldspar in saline alkaline water and to montmorillonite as a result of leaching by water of low salinity carbonate rocks are locally silicified along seepage zones carbonate minerals of the pliocene deposits have stable isotopic compositions that vary with their lithofacies tpa limestones deposited in or near areas of spring discharge have low 18o values averaging 16 6 tld limestones recrystallized in the vadose zone have higher 18o values averaging 18 1 carbonate minerals of tpl are the most 18o rich with calcite averaging 20 3 and dolomite 24 3 reflecting evaporative concentration in playas much of the dolomite is of replacement origin yet is in approximate isotopic equilibrium with the calcite it replaces relatively pure sepiolite has lower 18o values than do mg smectite clays which fits with the lower salinity inferred for sepiolite precipitation sepiolite and mg smectite disseminated in limestone fall outside the oxygen isotopic limits of the relatively pure clays possibly because of diagenetic recrystallization the pliocene climate was wetter than that of the present and springs were more widespread in the amargosa basin this dolomite may have formed in water isotopically and chemically about the same as that of the calcite and dolomitization may have been chiefly a result of the differing crystallization kinetics of calcite and dolomite and of fluctuating water chemistry in a playa environment the saline alkaline water of east playa resulted from evaporation of a mixture of alkali bicarbonate runoff from the volcanic terrane to the north with ca mg bicarbonate water discharged in springs from the ash meadows ground water system whose recharge area is principally in paleozoic carbonate rocks to the east and northeast seepage along fault zones in east playa was initially of ash meadows type low in silica and changed to siliceous water derived from volcanic rocks resulting in silicification of carbonate deposits caliche breccias along the western margin of the basin record a similar change in the composition of ground water seepage which may be attributed to a period of decreased precipitation about 2 5 ma which reduced recharge from nearby carbonate rocks relative to that from more distant volcanic rocks to the north and northwest

soil water flux in the southern great basin united states temporal and spatial variations over the last 120 000 years the disposal of hazardous and radioactive waste in arid regions requires a thorough understanding of the occurrence of soil water flux and recharge soil water chemistry and isotopic data are presented from three deep vadose zone boreholes 230 m at the nevada test site located in the great basin geographic province of the southwestern united states to quantify soil water flux and its relation to climate the low water contents found in the soils significantly reduce the mixing of tracers in the subsurface and provide a unique opportunity to examine the role of climate variation on recharge in arid climates tracing techniques and core data are examined in this work to reconstruct the paleohydrologic conditions existing in the vadose zone well beyond the timescales typically investigated stable chloride and chlorine 36 profiles indicate that the soil waters deep in the vadose zone range in age from approximately 20 000 to 120 000 years secondary chloride bulges that are present in two of the three profiles support the concept of recharge occurring at or near the last two glacial maxima when the climate of the area was considerably wetter and cooler the stable isotopic composition of the soil water in the profiles is significantly more depleted in heavy isotopes than is modern precipitation suggesting that recharge under the current climate is not occurring at this arid site past and present recharge appears to have been strongly controlled by surface topography with increased incidence of recharge where runoff from the surrounding mountains may have been concentrated the data obtained from this detailed drilling and sampling program shed new light on the behavior of water in thick vadose zones and in particular show the sensitivity of arid regions to the extreme variations in climate experienced by the region over the last two glacial maxima

climatic effects and bedrock control on rapid fluctuations of chhota shigri glacier northwest himalaya india active tectonism in the himalaya and the long fault lineament controlling the east west river valleys play an important role in melt at the snouts of glaciers or their fluctuations during the year lower glacier limits are controlled by high winds from the indian plains flowing along the valleys fluctuations of the chhota shigri glacier depend on temperature variations at the junction with the chandra river valley and in the unconsolidated morainic debris below the glacier ice high flow rates in the ablation zone indicate that basal sliding is the main movement mechanism melt takes place mainly from advection and this process of melting during the summer season occurs both day and night

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

stable isotopic evidence for a pedogenic origin of carbonates in trench 14 near yucca mountain nevada layered carbonate and silica encrust fault fractures exposed in trench 14 near yucca mountain site of the proposed high level nuclear waste repository in southern nevada comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate their isotopic composition differs markedly from that of carbonate associated with nearby springs the regional water table therefore remained below the level of trench 14 during the time that the carbonates and silica precipitated a period probably covering parts of at least the last 300 000 years

heat generated by cutting ice in deep ice core drilling in order to understand and solve the warm ice problem in deep ice core drilling we applied the metal cutting theory to ice and estimated the heat generated during ice coring taking into account the mechanical and thermal properties of the ice and cutters we found that 1 most of the heat in cutting is generated by shear deformation at the shear plane of ice and the heat could increase the chip temperature by several degrees 2 the rake angle of the cutter has more influence on the temperature increase in chips than the barrel rotation speed and penetration pitch 3 if the cutter is made of a material with larger thermal conductivity the temperature increase in the chips can be reduced and 4 if the density of the liquid is less than the density of ice the cutting chips sink to the bottom and the friction heat generated by the drill head and slush can raise the ambient temperature of the drill head by several degrees

severity and speed of northern hemisphere glaciation pulses the limiting case a brief pulse of ice sheet growth of enormous amplitude predicted by the theory of milankovitch is confirmed by oxygen isotopic and other evidence in pacific and north atlantic cores this glaciation bisected interglacial isotopic stage 7 lasted no more than 23 000 yr from inception to end and resulted in a very large ice volume buildup and a full glacial climatic response of the north atlantic ocean this pulse along with other episodes of rapid and large scale ice growth does not conform to the conventional sawtooth model of slow ice accumulation and rapid ice decay ice growth rates on such pulses can approach the mean ice decay rates on isotopic glacial terminations

high precision mass spectrometric uranium series dating of cave deposits and implications for palaeoclimate studies calcite deposits in caves known as speleothem can provide valuable palaeoenvironmental information1 4 in particular because speleothem are deposited only in air filled caves gaps in deposition in coastal caves record high stands of sea level here we report the use of isotope dilution mass spectrometry to date speleothem by the uranium series method the use of mass spectrometry in uranium series dating was first applied to corals5 and has greatly improved the precision of this dating method the speleothem dated here a flowstone from 15 m below modern sea level in a bahamian cave records changes in sea level over the past 280 000 years the dated hiatuses in deposition indicate high sea level stands that are in general agreement with data from deep sea oxygen isotope stratigraphy6 and other estimates for the timing of high stands and glacial minima1 3 7

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

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

a 24 000 year period climate signal in 1 7 2 0 million year old death valley strata continental records of plio pleistocene climatic fluctuations are often confined to fragmentary localized basins and not easily dated one exception is the confidence hills of southern death valley in this study we present a detailed description of a plio pleistocene section of interfingering alluvial fan and saltpan sediments from the confidence hills southern death valley this well exposed section accumulated with an average deposition rate of 25 cm 1000 yr with no bioturbation permitting more precise paleomagnetic dating than in oceanic records 1 we interpret the sequence of facies changes in the olduvai normal polarity zone of the confidence hills to represent alternations between wetter and drier regional climatic regimes the frequency of this variation 24 000 yr appears to correspond to the milankovitch precessional cycle 23 000 yr we believe this section records a milankovitch driven climatic variation in the death valley basin annual precipitation about 1 7 2 0 ma this is the first report of the precessional cycle in continental sediments of this age in the united states

tectonic speleogenesis of devils hole nevada and implications for hydrogeology and the development of long continuous paleoenvironmental records devils hole in southern nevada is a surface collapse into a deep planar steeply dipping fault controlled fissure in cambrian limestone and dolostone the collapse intersects the water table about 15 m below land surface and the fissure extends at least 130 m deeper below water most of the fissure is lined with a 30 cm thick layer of dense maxillary calcite that precipitated continuously from groundwater for 500 000 yr the thick mammillary calcite coat implies a long history of calcite supersaturated groundwaters which combined with the absence of dissolutional morphologies suggests that devils hole was not formed by karst processes devils hole is located in a region of active extension its tectonic origin is shown by evidence of spreading of its planar opening along a fault and by the orientation of its opening and others nearby perpendicular to the northwest southeast minimum principal stress direction of the region most quaternary tectonic activity in the area including seismicity and quaternary faults and fractures occurs on or parallel to northeast striking structures the hydrogeologic implications of this primarily structural origin are that fracture networks and caves opened by extensional tectonism can act as groundwater flowpaths functionally similar to those developed by karst processes and that during active extension transmissivity can be maintained despite infilling by mineral precipitation such extensional environments can provide conditions favorable for accumulation of deposits preserving long continuous paleoenvironmental records the precipitates in devils hole store chronologies of flow system water level fluctuations hydrochemistry a half million yr proxy paleoclimate record evidence of devils hole s tectonic origin and probably atmospheric circulation

oxygen isotopes sea level changes and the temperature history of a coral reef environment in new guinea over the last 105 years abstract coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of huon peninsula new guinea seven coral reef units i vii from the coast landwards spaced at about 20 kyr interval provide a rather complete record of sea levels oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle the systematic sampling of the coral reefs was restricted to the massive tridacna gigas species the giant clam which are about 0 7 0 enriched in 18o relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the 18o of their aragonitic skeleton sea levels rose rapidly to 5 6 5 m above present during the last interglacial which on stratigraphic grounds and 18o compositions can be separated into an early phase whose 18o is similar to modern reef viia dated at 138 kyr and a late phase that is 0 6 0 heavier reef viib dated at 118 kyr fringing reefs vi v iv iii and ii record short lived high sea levels stands at 107 85 60 45 to 40 and 31 kyr respectively that stopped short of the present sea level 12 19 28 32 to 42 m the general decline of the high sea level stands corresponds to an average 18o enrichment of 1 7 0 measured between the early interstadials of isotope stage 5 vi and v and the late interstadials of isotope stage 3 iv iiia iiib and ii the maximum 18o enrichment of 1 7 0 relative to present was registered during a regressive phase of reef iiia stratigraphic evidence indicates that sea level lows in the range of 37 to 55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle sea levels and 18o ddta pair offer important clues regarding the partitioning of ice volume and temperature in 18o records the results suggest that the ice volume effect accounts for the observed 18o changes during the early interstadial culminations but only for 29 46 during the late interstadial culminations sea water cooling beyond the threshold limit of coral reef growth 18 c did not occur during the last glacial cycle the temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3 c below present during the later interstadials of isotope stage 3

the last interglacial high sea level in the granitic seychelles indian ocean abstract in the granitic seychelles islands widely scattered remnants of marine limestones of late pleistocene age are found over a range of elevations within about 9 m with respect to present sea level these exposures can be subdivided into coralgal buildups and rubbly conglomerates 230 th 234 u dating from corals indicates that the limestones were deposited during the last interglacial stage 140 120 kyr b p in order to understand the sea level history for this time range various fabrics related to sequences of rock forming processes i e frame building bioerosion internal sedimentation cementation other depositional and diagenetic processes have been identified and used as possible indicators of paleosea level datum at their time of formation detailed examination of the rock fabric sequences in combination with radiometric dating reveals that sea level overstepped its present position around 140 kyr ago and reached its maximum altitude 135 kyr ago before retreating there were presumably two distinct events in sea level rise separated by a gap of about 10 kyr comparison between elevations of high sea stands of a similar age on a regional scale supports the contention that the seychelles area has been relatively instable since at least the late pleistocene either hydro isostatic uplift of the seychelles granitic bank or volcanic subsidence of nearby atolls are assumed to be responsible for such differences in paleosea level records

experimental studies in natural groundwater recharge dynamics the analysis of observed recharge events abstract the amounts and time distribution of groundwater recharge from precipitation over an approximately 19 month period were investigated at two instrumented sites in south central kansas precipitation and evapotranspiration sequences soil moisture profiles and storage changes water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths soil temperatures water table hydrographs and water level changes in nearby wells clearly depict the recharge process antecedent moisture conditions and the thickness and nature of the unsaturated zone were found to be the major factors affecting recharge although the two instrumented sites are located in sand dune environments in areas characterized by shallow water table and subhumid continental climate a significant difference was observed in the estimated effective recharge the estimates ranged from less than 2 5 to approximately 154 mm at the two sites from february to june 1983 the main reasons for this large difference in recharge estimates were the greater thickness of the unsaturated zone and the lower moisture content in that zone resulting from lower precipitation and higher potential evapotranspiration for one of the sites effective recharge took place only during late winter and spring no summer or fall recharge was observed at either site during the observation period of this study

repeating waveform initiated by a 180 190 ka geomagnetic excursion in western north america implications for field behavior during polarity transitions and subsequent secular variation new paleomagnetic lithologic and stratigraphic data are presented from the sediments of lake chewaucan in the summer lake basin oregon the new data place better age constraints on the sediments and improve the accuracy of the previously published paleomagnetic record from this locality a complex yet distinct waveform is observed in all three components of the paleomagnetic vector the waveform begins as the 180 190 ka pringle falls long valley summer lake ii geomagnetic excursion and continues for two cycles after the excursion until the record is interrupted by an unconformity that we correlate to the oxygen isotope stage 6 5e boundary the waveform s directional morphology in virtual geomagnetic pole vgp space is defined by two clockwise loops followed by a distinctive counterclockwise clockwise counterclockwise looping sequence the vgp paths of the two cycles after the excursion are rotated 180 about earth s spin axis with respect to the vgp paths of the excursion cycle the waveform also consists of a relative paleointensity variation which repeats during the two cycles after the excursion the average paleointensity of the postexcursion waveform repetitions is high relative to the extremely low values that occur during the excursion this observation indicates that excursion initiated secular variations can occur after the field fully recovers from the low intensities which commonly typify excursions because of the similarities noted previously between this excursion and full polarity transitions trie et al 1991 our new observations constrain models for a wide range of field behavior including polarity transitions excursions and secular variation

a diatom record of climate and hydrology for the past 200 ka from owens lake california with comparison to other great basin records abstract diatoms from lake sediments beneath owens lake playa inyo county california document a nearly continuous paleolimnological record of climate and hydrologic change since the penultimate glacial interglacial cycle based on a chronology established by radiocarbon tephrochronology and paleomagnetic control freshwater planktic diatoms especially species of stephanodiscus plagioclase feldspar rich sediments with high magnetic susceptibility and juniperus type pollen characterized the penultimate glaciation at owens lake saline diatoms dominated in the following interglacial period and there are several episodes during which freshwater planktic diatoms became abundant between 100 and 50 ka that may represent interstadial climatic conditions saline diatoms fell to low values after 50 ka but warm season aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of owens lake prior to the last glacial maximum by 25 ka glacial environments were again characterized by abundant juniperus plagioclase feldspar and stephanodiscus species generally arid holocene climates were recorded in owens lake by short term fluctuations of saline and freshwater diatoms desiccation and oolitic sediments barren of diatoms comparison to paleoclimate records both north and south of owens lake suggest a southerly displacement of storm tracks originating from the aleutian low during glacial episodes

the distribution of 230th234u ages in corals and the number of last interglacial high sea stands abstract the 104 available 230 th 234 u analyses of unrecrystallized corals from stable emerged terraces indicate that the last interglacial period occurred approximately 125 000 yr ago an estimate is made of the exact duration of this period by accounting for the surprisingly small distribution width observed among the 80 most reliable analyses this distribution width is compared with those obtained for model populations generated by assuming various characteristic analytical errors and various lengths of the last interglacial period the results show that 1 if there was only a single rise in sea level it probably lasted no more than 12 000 yr in agreement with previous estimates and 2 if there were two separate rises of sea level the gap between them must have been less than 7500 yr and not 12 200 as proposed by some authors

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

two million year record of deuterium depletion in great basin ground waters fluid inclusions in uranium series dated calcitic veins from the southern great basin record a reduction of 40 per mil in the deuterium content of ground water recharge during the pleistocene this variation is tentatively attributed to major uplift of the sierra nevada range and the transverse ranges during this epoch with attendant increasing orographic depletion of deuterium from inland bound pacific storms

deep water formation and quaternary glaciations a large fraction of climatic varability on the quaternary time scale can be explained by nonlinear interactions between the radiation balance of the global atmosphere ocean system and the mass balance of northern hemisphere ice sheets recent analyses of paleoclimatic proxy data indicate a further important contribution to this variability from changes in deep water formation occurring in the north atlantic subpolar sea we study the effects of these changes on variations in global temperature and ice volume characteristic of the late quaternary the novel framework of boolean delay equations bdes is used to formulate a conceptual model of the climatic system under study and to analyze this formal model selfsustained oscillations in the intensity of the atlantic ocean s thermohaline circulation result from the interaction of sea ice formation with the waxing and waning of continental ice sheets the comparison of model results with paleoclimatic records suggests a considerable slowing down of the abyssal circulation during glacial episodes

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

late quaternary u series speleothem growth record from southeastern minnesota southeastern minnesota contains an extensive karst developed in limestones and dolomites ranging in age from early ordovician to middle devonian preliminary results from u series dated speleothems from caves within the karst show cyclic deposition of secondary calcium carbonate that coincides with cycles of late pleistocene glaciation peak intervals of deposition which broadly correlate with interglacial or interstadial climates occur from the present to 13 000 yr b p from 35 000 to 70 000 yr b p from 90 000 to 170 000 yr b p and an undivided interval from 170 000 to 350 000 yr b p intervals of little or no deposition are thought to reflect glacial climates the youngest growth intervals can be interpreted in terms of known glacial records in the midwest but for the older intervals where the glacial record is not well defined and beyond the range of radioactive dating it becomes more difficult to correlate speleothem deposition to glacial cycles although the groups of ages are in general agreement with sea level curves the correlation is not exact local climatic conditions seem to have had as much importance in determining when deposition occurred as did the major climatic cycles recorded in the marine record

87sr 86sr and sr ca in speleothems for paleoclimate reconstruction in central china between 70 and 280 kyr ago limestone cave deposits speleothems provide archives for past changes in regional climates over a range of timescales while 18o and 13c in speleothem calcite have been commonly used for reconstruction of paleoclimates we report here further efforts in the use of 87sr 86sr and sr ca signals in speleothem calcite to deduce paleomonsoon variability near the loess plateau of central china a two end member mass balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the 87sr 86sr ratio in sediments overlying a limestone cave we show that this ratio reflects climate driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments the measurements of 87sr 86sr made on a well dated stalagmite sfl from buddha cave 33o40n 109o05 e show ratios of 0 71092 to 0 71133 0 00001 as 2 during relatively cold periods e g marine isotope stage mis 5b 5d and 8 lower than ratios of 0 71133 to 0 71194 during relatively warm periods e g mis 5a 5c 5e and 7 as changes in the sr ca ratio may affect speleothem 87sr 86sr we show that the direct use of speleothem 87sr 86sr is less ideal than our modeled 87sr 86sr for the exogenic sr source above the cave as a paleomonsoon proxy using the 18o 13c sr ca and 87sr 86sr records of the stalagmite we reconstruct the variability of the east asian monsoon for the time period between 70 and 280 kyr ago the results show that summer monsoons were more intense during interglacial periods than during glacial periods

devils hole paleotemperatures and implications for oxygen isotope equilibrium fractionation subaqueous calcite in devils hole nevada was growing continuously from slightly super saturated groundwater providing a 570 kyr long o18 paleoclimate record due to its very slow growth it has been assumed to have grown under conditions of isotopic equilibrium however its holocene o18 value is 1 5 higher than predicted by laboratory precipitation based oxygen isotope thermometer calibrations the suggestion that devils hole calcite anchors the isotope thermometer to more 18o enriched values has stirred a debate as to which paleothermometer calibration is relevant for paleoclimate and casts doubt on the validity of o18 based paleotemperatures we used clumped isotopes to test the assumptions of the devils hole alternative 18o thermometer carbonate clumped isotopes are a temperature proxy that measures the abundance of 13c18o bonds in caco3 this proxy is independent of the water composition and therefore gives independent estimates of temperatures when calcite forms at thermodynamic and isotopic equilibrium we find that devils hole water paleotemperatures were constant at 30 6 2 6 c between 27 and 180 ka similarly to the modern groundwater temperature of 32 8 34 3 c the proximity of the devils hole clumped isotope data to values expected based on modern groundwater temperatures supports the notion that devils hole calcite grew under equilibrium conditions therefore the commonly used laboratory based o18 temperature calibrations should be reconsidered the constant water temperature over the glacial interglacial cycles indicates that the long devils hole o18 record reflects only variations in the groundwater o18 values and as such represents a valuable archive of paleoclimate and isotope paleohydrology

uranium series dating of sediments from searles lake differences between continental and marine climate records one of the major unresolved questions in pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial 18 o marine record searles lake in california now a dry salt pan is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10 6 years uraniumseries dates on the salt beds range from 35 x 10 3 to 231x 10 3 years this range of dates allows identification of lake sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3 4 boundary back to the 8 9 boundary the 5 6 boundary coincided with a deepening of the lake but the analogous 1 2 boundary coincided with desiccation the 3 4 4 5 6 7 7 8 and 8 9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate these hydrologic results demonstrate that the continental paleoclimate record at this mid latitude site does not mimic the marine record

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

pleistocene paleoclimate of the arid region of israel as recorded in calcite deposits along regional transverse faults and in veins abstract the 18o and 13c values of the calcites associated with e w and ne sw transverse faults in the negev israel indicate that calcite was deposited from meteoric water a regional change in the 18o and 13c values was observed the 18o content in the calcite increases from the southwestern 18 o 17 8 to the northeastern 18 o 2 9 part of the region the 13c values show the opposite trend of the 13c content decrease from 2 in the south to 10 in the northeast these trends had to reflect changes in regional paleoclimate suggesting a change in the isotopic composition of the solution from which the calcite was deposited in different periods the variations in the 18o values reflect shifts in the 18o values of precipitation and are associated with a change in the source of moist air masses which came from the equatorial atlantic in the early pleistocene and from the mediterranean during a later period variations in 13c values reflect changes from humid to arid conditions two modes of calcite deposition are suggested 1 precipitation of calcite minerals in the unsaturated zone following the dissolution in the soil or 2 calcite deposition that occurred as co2 was lost during emergence of paleogroundwater from lower cretaceous and jurassic aquifers

palaeoclimate determination from cave calcite deposits calcite deposits formed in limestone caves have been found to be an excellent repository of palaeoclimatic data for terrestrial environments the very presence of a relict deposit indicates non glacial conditions at the time of formation and both 14c and uranium series methods can be used to date the deposit and hence the age of these climatic conditions variations in 13c and 18o content of the calcite in 2h and 18o content of fluid inclusions in trace element concentrations and more recently in pollen assemblages trapped in the calcite are all potentially available as synchronous palaeoclimatic indicators previous work has tended to concentrate mainly on abundance of deposits as a palaeoclimatic indicator for the last 300 000 years this literature is briefly reviewed here together with the theory and methods of analysis of the u series and stable isotopic techniques the combined use of u series ages and 13c and 18o variations in cave calcites illustrates the potential for palaeoclimate determination previously unpublished results of stable isotopic variations in dated calcites from caves in northern england indicate the level of detail of stable isotopic variations and time resolution that can be obtained and the complexity of interpretation that may arise tentative palaeoclimatic signals for the periods 90 125 ka and 170 300 ka are presented more comprehensive studies are needed in future work especially in view of the difficulty in obtaining suitable deposits and the ethics of cave deposits conservation

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

modeling of the thermo hydro mechanical chemical response of sedimentary rocks to past glaciations abstract thermo hydro mechanical chemical thmc coupled processes that have resulted from long term past climate changes and glaciation cycles in the sedimentry rocks of southern ontario are investigated a conceptual numerical model has been developed to solve four coupled partial differential equations pdes which represent hydraulic thermal mechanical and chemical processes the finite element method is used to solve the pdes under transient surface boundary conditions imposed by past glaciation cycles to predict the hydraulic mechanical thermal and geochemical responses of the geological system the results show that past glaciations have a significant impact on the hydraulic gradient and pressure vertical effective stress and salinity profiles and a limited effect on the permafrost depth the predicted results show good agreement when compared with the field data for the total dissolved solid rock strength and quality the results show relatively good agreement with the anomalous pore water pressure profile in the field the modeling results indicate that the infiltration depth of glacial melted water is less than 300 m and are consistent with the field observation of total dissolved solids at the level of a deep geological repository dgr for low and intermediate level radioactive wastes being planned in these rock formations a safety factor of 6 9 is predicted against failure by using hoek brown failure envelopes while a low safety factor of 0 83 is predicted at the shallower level of the silurian salina formation it is found that solute transport at the middle and upper ordovician formations are diffusion dominated at depths of 300 m or more and controlled by diffusion advection above 300 m based on the results obtained the modeling of a past glaciation can be used with reasonable confidence in predicting the impact of future glaciations related to the long term safety and stability of the proposed dgr in the sedimentry formation however for site specific conditions thmc modeling is very sensitive to material properties and sensitivity analysis is required for future model development