uranium series ages of travertines and timing of the last glaciation in the northern yellowstone area wyoming montana uranium series age determinations by mass spectrometric methods were done for travertines and associated carbonate veins related to clastic deposits of the last glaciation pinedale in the northern yellowstone area dramatic variations in the hydrologic head are inferred from variations in the elevation of travertine deposition with time and are consistent with the expected hydrologic effects of glaciation we determine the following chronology of the pinedale glaciation with the key assumption that travertine deposits and associated carbonate veins perched high above present thermal springs were deposited when glaciers filled the valley below these perched deposits 1 the early pinedale outlet glacier advanced well downvalley between 47 000 and 34 000 yr b p 2 the outlet glacier receded to an interstadial position between 34 000 and 30 000 yr b p 3 an extensive pinedale ice advance occurred between 30 000 and 22 500 yr b p 4 a major recession occurred between 22 500 and 19 500 yr b p 5 a minor readvance deckard flats culminated after 19 500 yr b p and 6 recession from the deckard flats position was completed before 15 500 yr b p this chronology is consistent with the general trend of climatic changes in the northern hemisphere as revealed by recent high resolution ice core records from the greenland ice sheet

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

238u234u230th disequilibrium in hydrogenous oceanic femn crusts palaeoceanographic record or diagenetic alteration abstract a detailed tims study of 234uexc 238u 230th 232th and th u ratios have been performed on the outermost margin of ten hydrogenous fe mn crusts from the equatorial pacific ocean and west central indian ocean th u concentration ratios generally decrease from the crust s surface down to 0 5 1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in fe mn crusts from the peru basin and the west central indian ocean fe mn crusts from the same geographical area define a single trend in plots of ln 234uexc 238u vs ln 230th 232th and th u ratios vs age of the analysed fractions results suggest that l hydrogenous fe mn crusts remain closed systems after formation and consequently 2 the discrepancy observed between the 230th and 234u chronometers in fe mn crusts and the variations of the th u ratios through the margin of femn crusts are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation but rather to temporal variations of both th u and initial thorium activity ratios recorded by the fe mn layers implications of these observations for determination of fe mn crust growth rates are discussed variations of both th u and initial th activity ratios in fe mn crusts might be related to changes in particle input to seawater and or changes in ocean circulation during the last 150 ka

climatic influences on the growth rates of mn crusts during the late quaternary abstract the concentration of 230 th in mn crust va13 2 146 w 9 25 s 4830 m from the pacific ocean was measured with high depth resolution 0 02 mm to a depth of 1 4 mm corresponding to an age of 226 ka b p the mean growth rate estimated from these results is 6 2 0 4 mm ma however the exponential curve obtained shows two drastic events in the 230 th concentration record with durations of 41 4 ka and 37 6 ka which are interpreted as growth standstills the decay corrected 230 th concentration is inversely correlated with those of mn fe and co indicating that the 230 th flux into the crust has been constant throughout time and that the observed fluctuations in 230 th are due to dilution by the main components by applying a constant 230 th flux model high resolution growth rates were derived from every sample investigated a detailed comparison of the growth pattern with the specmap time table reveals that the va13 2 growth rates tend to be higher during interglacial than during glacial periods in particular the observed growth standstills are associated with glacial stages 6 and 8 further investigation of mn crust 72 dk 9 taken from shallower water 170 35 w 20 13 n 1550 m tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the late quaternary

hafnium and neodymium isotopes in seawater and in ferromanganese crusts the element perspective abstract hafnium and nd isotopes are increasingly used as paleoceanographic proxies comparing the mantle crust array and the seawater array in plots of e hf vs e nd it has been observed that for a given e nd value the corresponding e hf value is higher for seawater than it is for terrestrial rocks while this difference had initially been explained by significant hydrothermal input of mantle hf into seawater the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine hf input we here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese fe mn crusts we distinguish between a truly dissolved and a dissolved hf and nd pool the latter being comprised of truly dissolved and colloid bound colloidal hf and nd while there exists a hydrothermal pathway for colloid bound dissolved mantle hf into the oceans there is in marked contrast to nd no important riverine pathway for colloidal or truly dissolved continental hf owing to their respective chemical speciation in seawater there exists truly dissolved nd in the ocean while the amount of truly dissolved hf is insignificant neodymium is in exchange equilibrium between local seawater and both the hydrous fe and mn oxides hydrogenetic fe mn crusts are composed of due to continuous ad and desorption there is continuous isotopic re equilibration and the isotopic composition of nd in a fe mn crust reflects that of truly dissolved nd in local ambient seawater in contrast hf is only associated with the hydrous fe oxides on which it forms surface precipitates that do not exchange with seawater due to this lack of isotopic re equilibration the isotopic composition of hf in a fe mn crust is the average of that of all the hf scavenged during the lifetime of the hydrous fe oxide particles since the hf bearing hydrous fe oxides in a fe mn crust do not form from local ambient seawater at the crust s growth site but are advected as colloids or fine particles their hf isotopic composition depends on the origin and migration pathway of these colloids hence while nd isotopes in fe mn crusts provide reliable information on truly dissolved nd in local ambient seawater hf isotopes rather indicate the origin and pathway of hydrous fe oxide colloids and might differ from truly dissolved hf in local ambient seawater this may explain the occasional decoupling of nd and hf isotopes in fe mn crusts and supports the notion of a significant hydrothermal mantle signal of hf in seawater

u th chronology and paleoceanographic record in a fe mn crust from the ne atlantic over the last 700 ka hydrogenetic ferromanganese crusts fe mn crusts provide a secular record of the variations of seawater composition responding to changes in ocean circulation and erosion processes in this respect the acquisition of an absolute and reliable chronology in fe mn crusts is a prerequisite here we combine four different and complementary chronometers 10 be 230 thex 230 thex 232 th 234 u 238 u in a fe mn crust dredged at 2000 m depth in the east atlantic to first establish a reliable chronology over the quaternary period then we use eds chemical analysis to look for correlation between major element chemistry and climate changes 230 thex 230 thex 232 th and be data give very consistent growth rates in particular the good match between 230 thex and 230 thex 232 th data indicates that at the location of crust 121dk 230 th and 232 th fluxes in the water column change simultaneously and suggests that the normalization of 230 thex to 232 th makes 230 thex 232 th a better chronometer our best fit model suggests that crust 121dk experi enced changes in growth rates at 122 and 312 ka and a growth with a constant 230 th initial flux this chronology returns an age of 680 ka for the uppermost 1 5 mm the 234 u 238 u depth profile however was clearly affected by diffusion of 234 u in the porous crust and can therefore not be used to derive a reliable chronology one part of the crust seems isolated from pore water diffusion and can be physically recognized as a zone of very small porosity on the basis of the 230 thex 232 th chronology major element chemistry is shown to be linked to climate change mn fe variations compare well with those in a fe mn crust from the pacific showing systematic maxima during glacial stages 2 and 4 high mn fe are tentatively interpreted to reflect expansion of the oxygen minimum zone during glacial periods resulting from higher bioproductivity in addition we note that the surface 230 th 232 th activity ratio of crust 121dk is entirely consistent with advection of deep water from the western toward the eastern atlantic basin copyright 2005 elsevier ltd

deep sea corals off brazil verify a poorly ventilated southern pacific ocean during h2 h1 and the younger dryas abstract simultaneous 14 c and th u dating of deep sea corals are useful for reconstructing the intensity of deep ocean circulation in the past as they deliver the time between the gas exchange of the water with the atmosphere and the incorporation of the 14 c in the carbonates adkins and boyle 1997 adkins et al 1998 mangini et al 1998 th u ages of deep sea corals sampled in sediment cores from locations off the coast of brazil bathed by antarctic intermediate water at depths between 600 and 800 m group close to heinrich events h2 h1 and the younger dryas the 14 c of the water bathing the corals starts to decrease approximately 2 kyr before the heinrich events and decreases to values 400 lower than the corresponding back tracked atmospheric values the timing and the magnitude of the decrease is similar to that observed in intermediate water in the n pacific off baja california marchitto et al 2007 and in the eastern pacific stott et al 2009 high ventilation ages partly exceeding 4000 years are an unambiguous indication for a reduction of north atlantic deep water formation during h2 h1 and the yd as deduced from higher 231 pa 230 th activity ratios and from end in n atlantic ocean sediments mcmanus et al 2004 pahnke et al 2008 yu et al 1996 they also could indicate a poorly oxygenated southern pacific ocean at the end of the heinrich events

mesozoic and cainozoic rocks dredged from the south china sea reed bank area and sulu sea and their significance for plate tectonic reconstructions abstract outcrops of pre quaternary rocks were sampled by dredging and coring during two cruises of rv sonne in the south china sea and sulu sea 1982 1983 late triassic deltaic sandstones wih plant remains are the oldest sediments recovered late jurassic early cretaceous regional metamorphism is indicated by gneiss and garnet mica schists exposed in the northwestern flanks of reed bank these rocks and occurrences of gabbro diorite dacite rhyolite and siliceous shale prove that the dangerous grounds and reed bank are underlain by a continental fragment during the period of seafloor spreading in the south china see a late oligocene to early miocene carbonate platform developed on this southwards drifting continental fragment which subsided in the middle miocene middle miocene andesite and early to middle miocene reefal carbonates were recovered from the cagayan ridge in the sulu sea the new data are in accord with the plate tectonic history developed by taylor and hayes 1980 1983 and holloway 1981

spatial and temporal distributions of the late mesozoic volcanic successions and their controlling effects on the changling fault depression of the songliao basin northeast china volcanic successions including their spatial temporal tectonic and geochemical attributes were identified based on well data 2d and 3d seismic data u pb isotopic ages and major and trace element data from the changling fault depression of the songliao basin in northeastern china three eruption cycles developed in the changling fault depression k1h huoshiling formation 124 118 ma k1yc1 first member of the yingcheng formation 115 106 ma and k1yc3 third member of the yingcheng formation 106 102 ma these three eruption cycles comprised seven eruption stages the volcanic successions in every eruption cycle were bimodal and evolved from basic to acidic the magma of the basic and intermediate rocks in these cycles was derived from partial melting of the asthenosphere in k1yc1 and k1yc3 partial melting of the newly formed basic rocks in the lower crust formed the high sio2 acidic magma in addition fractional crystallization of basic magma formed the small scale intermediate acidic m

238u234u230th chronometry of femn crusts growth processes and recovery of thorium isotopic ratios of seawater abstract comparison of 234 u excess 238 u and 230 th 232 th activity ratios in oceanic fe mn deposits provides a method for assessing the closed system behaviour of 238u 234u 230th as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides this approach is illustrated using a fe mn crust from lotab seamount marshall islands west equatorial pacific here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botryoid of this crust and from two depth profiles of the outermost rim of the same botryoid the decrease of 234 u excess 238 u and 230 th 232 th activity ratio with depth in the two profiles gives mean growth rates for the last 238u 212th 150 ka of 7 8 2 mm ma and 6 6 1 mm ma respectively all data points surface and core samples but one define a linear correlation in the ln 230 th 232 th ln 234 u excess 238 u diagram this correlation indicates that for all points the u th system remained closed after the fe mn layer precipitated and that the different samples possessed the same initial uranium and thorium isotope ratios furthermore these results show that the preserved surface of this fe mn crust may not be the present day growth surface and that the thorium and uranium isotopic ratios of seawater in west equatorial pacific have not changed during the past 150 ka the initial thorium activity ratio is estimated from the correlation obtained between ln 230 th 232 th ln 234 u excess 238 u

a lead isotopic study of circum antarctic manganese nodules abstract lead isotope ratios in manganese nodules from the circum antarctic ocean display systematic geographical variations eastward in the direction of current movement from south of australia they progressively decrease in the pacific sector and into the western atlantic sector until 30 w from this longitude lead isotope ratios increase in the eastern atlantic sector and reach their highest values in the indian sector near 110 e south of western australia they abruptly decrease these two lead isotope domains correspond closely to the circum antarctic neodymium isotope domains previously recognized by albarede and goldstein 1992 however the intraocean isotopic variations are much clearer for pb than nd reflecting the shorter oceanic residence time of pb 102 y compared with nd 103 y and confirming that pb is a much more sensitive marine tracer throughout the circum antarctic ocean the lead isotopic changes follow the pattern of present day oceanic circulation the pb shows an overall continental signature which is strongest in the indian sector the most probable candidate as the source of the continental signal is north atlantic deep water nadw which enters the circum antarctic in the south atlantic as nadw mixes with circumpolar water lead isotope ratios increase eastward in the indian sector reflecting progressive loss of the pacific derived pb signal the abrupt decrease of lead isotope ratios between the indian and pacific sectors appears to be a consequence of addition of pacific seawater through the pacific lead isotope ratios gradually decrease eastward approaching values of east pacific rise metalliferous sediments ocean ridge basalts and south pacific mn nodules this trend results from an increasing influence of pacific ocean water containing a component derived from pacific volcanism the pacific signature persists into the argentine basin in the southwest atlantic ocean reflecting significant input of water from the drake passage northward into the atlantic the pacific pb component is seen in the atlantic and indian oceans near southern africa as well as in the atlantic and indian sectors of the circum antarctic lead and neodymium isotopes correlate in the atlantic indian sectors but not in the pacific sector reflecting differences in residence times and modes of water mass mixing the renewal of circum antarctic water occurs on a timescale which is short compared to the residence time of nd but long compared to pb as a result dissolved pb is subject to considerable changes over the timescale of circumpolar current movement while nd is less easily affected nadw is added locally in the south atlantic and moves eastward as a water mass as nadw mixes with circumpolar water cpw through the indian sector changes affecting nd pb in nadw and cpw occur in tandem and neodymium and lead isotopes are correlated through the pacific sector gradual addition of pacific seawater occurs over a large region and nd pb relationships are not coupled because simple isotopic mixing systematics are not conserved there neodymium and lead isotopes vary independently the consistency of lead isotope variations with present day ocean bottom water circulation is remarkable considering that the mn nodules as sampled reflect the integrated flux of pb over 105 106 y the oceanic mixing time is 103 y the residence time for pb is 102 y and the circulation time of the circumantarctic ocean is 30 y processes occurring over such different timescales can show such a relationship only if the system is stable over the longest time interval thus on average element sources and ocean circulation through the pleistocene have been similar to the present day despite significant perturbations during glacial periods

diffusion and supply rates of 10be and 230th radioisotopes in two manganese encrustations from the south china sea ages of two mn encrustations estimated by their 230th and 10be distributions are compared with k ar ages and micropaleontological datings of their nuclei to discuss possible diffusion and supply effects of the radioisotope distribution and their influence on the reliability of age determinations based on comparable results obtained by the different methods the effective diffusion coefficient of 10be can be calculated as d 1 0 10 8cm2 y this coefficient is 3 8 times smaller than the best estimates available at present in both nodules we observe lower 10be concentrations in the uppermost 2 3 mm 1 3 m y which suggests that 10be uptake has been reduced since the middle pleistocene the 2 7 fold increase of the growth rate starting 3 2 m y ago coincides with the initiation of the northern hemisphere glaciation

u th dating and post depositional alteration of a cold seep carbonate chimney from the campos basin offshore brazil abstract dating authigenic cold seep carbonates allows determining the timing of active seepage of hydrocarbon rich fluids at continental margins and ultimately the detection of the geological factors affecting it u th dating has been selected in this study the method having been successfully used before however incorporation of initial thorium in substantial amounts of detrital material due to the precipitation of carbonates within the seabed and post depositional alteration potentially pose a major problem violating the basic assumptions of the method here we report results from several samples from the campos basin off the coast of brazil they are unusual in their high 13 c values mean of 10 0 vpdb high detrital contents and being dominantly dolomite elevated 230 th 238 u activity ratios indicate that most of the carbonates lost uranium during diagenesis isochrones are obtained from the unaffected samples yielding an age of 140 4 3 1 ka vertical growth of the chimney must have been short and rapid since results from the top and bottom parts of the chimney concur within analytical uncertainties furthermore profiles of u th radioisotope specific activity 234 u and 232 th specific activity on two quarter slices of a carbonate chimney reveal the occurrence of three distinct diagenetic processes u loss u exchange with seawater and th gain

precise th u dating of small and heavily coated samples of deep sea corals marine carbonate skeletons like deep sea corals are frequently coated with iron and manganese oxides hydroxides which adsorb additional thorium and uranium out of the sea water a new cleaning procedure has been developed to reduce this contamination in this further cleaning step a solution of na2edta na2h2tb and ascorbic acid is used which composition is optimised especially for samples of 20 mg of weight it was first tested on aliquots of a reef building coral which had been artificially contaminated with powdered ferromanganese nodule applied on heavily contaminated deep sea corals scleractinia it reduced excess 230th by another order of magnitude in addition to usual cleaning procedures the measurement of at least three fractions of different contamination together with an additional standard correction for contaminated carbonates results in th u ages corrected for the authigenic component a good agreement between th u and 14c ages can be achieved even for extremely coated corals

recording changes in enadw composition over the last 340 ka using high precision lead isotopes in a fe mn crust we report high precision pb triple spike data and u th isotopic ages on a high resolution depth profile from a fe mn crust 121dk northeastern atlantic 24 n 21 w 2000 m our results bring important information particularly on the origin of the pb isotopic composition of the northeastern atlantic deep water and more generally on the use of pb isotopes as a paleo proxy to reconstruct weathering inputs to the north atlantic ocean growth rates determined using 230th ex and 230th 232th ex 2 9 0 2 and 3 0 3 mm ma respectively are found to be more reliable than 234uex sensitive to sea water contamination and are similar to the 10be results 3 0 3 mm ma very small variations in 206pb 204pb 18 942 18 964 208pb 204pb 39 057 39 083 and 207pb 204pb 15 696 15 701 are resolved defining linear trends in pb isotope diagrams high precision pb triple spike analysis of samples from crust bm1969 05 northwestern atlantic 39 n 61 w 1829 m are found to entirely reproduce the multi collector plasma source mass spectrometry data recently published this interlaboratory cross calibration establishes that the west north atlantic deep water wnadw does not represent a suitable pb contributor to the northeastern atlantic and rather suggests that the pb isotopic composition of wnadw is significantly altered before or during transport toward the northeastern atlantic basin the pb isotopic compositions of both suspended loads from the amazon mouth and offshore sediment cores are consistent on average with crust 121dk we therefore propose that the change in pb isotopic composition of wnadw may be caused by input of suspended particle loads from the amazon and possibly orinoco rivers or by interaction with sediments deposited by those rivers we speculate further that the short term compositional variations observed in this study may be caused by fluctuations in the relative contributions of amazon tributaries to the bulk composition supplied to the ocean because these tributaries sample terrains of drastically different ages phanerozoic andes and precambrian amazonian shield

holocene sea level determination relative to the australian continent u th tims and 14c ams dating of coral cores from the abrolhos islands u th tims and 14 c ams measurements are presented from two coral cores from the easter group of the houtman abrolhos islands between 28 s and 29 s on the western continental margin of australia the u th measurements on the morley core from morley island cover a depth interval from 0 2 m above present sea level to 24 4 m below present sea level and comprise eleven samples the ages vary between 6320 50 a at 0 2 m above sea level and 9809 95 a at 24 4 m below sea level all errors are 2 the mean growth rate is 7 1 0 9 m ka the 14 c dates of selected morley core corals show that the 14 c ages are 1000 a younger than their corresponding u th ages which agrees with previous results the main purpose of our 14 c measurements is to be able to compare them precisely with other coral cores where no u th measurements are available the u th measurements of the suomi core from suomi island cover a depth interval from 0 05 m to 14 2 m below present sea level and consist of four samples the ages vary between 4671 40 a at 0 05 m below sea level and 7102 82 a at 14 2 m below sea level with a mean growth rate of 5 8 0 2 m ka the growth history of both cores is explained by a simple model in which the growth rates of the morley core can be interpreted as reflecting local rates of sea level rise whereas the suomi core is interpreted as reflecting lateral growth during the past 6000 a our results indicate that sea level relative to the western margins of the australian continent was about 24 m lower than present at about 9800 a b p 14 c gives a date of 8500 a b p sea level then rose and reached a highstand slightly higher than the present position at about 6300 a b p 14c date 5500 a this highstand declined but was still higher than present at 4600 a b p this is in agreement with previous observations along the australian coastal margins and with observations from the huon peninsula papua new guinea our results are very similar to theoretical numerical models which take into consideration water loading and isostatic compensation and viscous mantle flow in contrast coral cores from barbados show that corals with a 14 c age of 5500 a b p are some 10 m b p s l we interpret the difference between the barbados core and the morley core as resulting from additional flooding of barbados by water redistribution due to changes in the earth s geoid but not reflecting global sea level rise or major addition of melt waters over the past 6000 a the difference in the geoid at barbados between 6000 a b p and the present will require a refinement in the geophysical models precise 230 th tims measurements on continental coasts will be required to provide an adequate data base for modelling deformation flow of mantle material and sea level height

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

primary u distribution in scleractinian corals and its implications for u series dating in this study we use microsampling techniques to explore diagenetic processes in carbonates these processes are important as they can affect the accuracy of u series chronometry fission track maps of deep sea scleractinian corals show a threefold difference between the minimum and maximum u in modern corals which is reduced to a factor of 2 in fossil corals we use micromilling and mc icp ms to make detailed analyses of the u and 234uinitial distributions in corals from 218 ka to modern within each fossil coral we observe a large range of 234uinitial values with high 234uinitial values typically associated with low u a simple model shows that this observation is best explained by preferential movement of alpha decay produced 234u atoms alpha recoil diffusion open system addition of 234u may occur when alpha recoil diffusion is coupled with a high u surface layer such as organic material this process can result in large whole coral 234uinitial elevations with little effect on the final age the diagenetic pathways that we model are relevant to both shallow water and deep sea scleractinian corals since both exhibit primary u heterogeneity and may be subject to u addition

10be and th isotopes in manganese nodules and adjacent sediments nodule growth histories and nuclide behavior abstract the concentration profiles of 9 be 10 be 230 th 232 th 231 pa via 227 th and 238 u have been measured in three manganese nodules one each from the north pacific a47 16 4 the south pacific tf 5 and the indian ocean r v vitiaz in addition the 10 be concentration in deep water from the geosecs reoccupation station 500 of the north pacific and in cores raised from the manganese nodule field in the north pacific have been measured the 10 be concentration in nodule and seawater samples was measured by the accelerator masss spectrometric technique employing the yale tandem van de graaff accelerator the concentrations of 10 be 230 th exc and 231 pa exc and ratios of 10 be 9 be and 230 th exc 232 th all decrease with depth in the nodules this decrease interpreted in terms of nodule growth yields average growth rates of a few millimeters per million years for the nodules the growth rates of the nodules exhibit temporal variations both on short time 50 000 years and long time several million years scales of the three nodules studied only in tf 5 is the short term average growth rate based on 230 th exc in the top 0 0 5 mm the same as the long term average rate based on be isotope data for the 0 5 17 mm interval for the other two nodules the recent average growth rates based on 230 th exc data differ significantly from the long term average growth rates based on be isotopes in a47 16 4 the 10 be based rate is less than the 230 th exc rate and in r v vitiaz the 10 be based rate is greater than the 230 th exc rate this observation coupled with measurable changes in growth rates even during the past few hundred thousand years suggests but does not prove that the discordant growth rates deduced from 230 th exc and 10 be profiles document changes in nodule growth rate with time rather than mixing effects on 230 th exc profiles the 10 be concentration in the geosecs north pacific deep water is 6100 1200 atoms g this value coupled with the average surface 10 be 9 be ratio of north pacific nodules predicts a 9 be concentration within the limits of measured values the inventory of 10 be and 230 th exc in the nodules is only 10 of the total the remaining being in sediments the 10 be concentrations in the upper portions of two adjacent cores studied are nearly the same but the deposition fluxes of both 10 be and 230 th based on 230 th dating vary by a factor of two this difference is attributable to local redistribution of sediment at the time of deposition prior to accumulation

explaining discrepant depth profiles of 234u 238u and 230thexc in mn crusts abstract manganese encrustations are an important archive for the reconstruction of deep ocean circulation in the past however because of discordant growth rates derived from the decrease of the activity ratios of 234 u 238 u and of 230 th exc with depth their dating via the measurement of depth profiles of 230 th and 231 pa has been recently put into question chabaux et al 1997 in this study we present high precision depth profiles of uranium and thorium isotopes tims of a hydrogenous mn crust from the south china sea indeed the depth profiles of 234 u 238 u and 230 th exc deliver very different growth rates of 8 80 1 20 and 2 64 0 12 mm ma respectively we solve this discrepancy with a simple model which assumes exchange of uranium adsorbed in the mn crust with uranium dissolved in the pore water the best agreement to the data is obtained applying an exchange coefficient of 5 x 10 6 a 1 application of this model to the data set of chabaux et al 1997 reproduces very well their profiles of the 234 u we conclude that 234 u 238 u dating of mn encrustations is not reliable because of open system conditions for uranium

uranium isotope systematics of ferromanganese crusts in the pacific ocean implications for the marine 238u 235u isotope system abstract variations of 238u 235u ratio 238u in sedimentary rocks have been proposed as a possible proxy for the paleo oceanic redox conditions although the marine 238u system is not fully understood here we investigate the spatial variation of 238u in modern ferromanganese fe mn crusts by analyzing u isotopes in the surface 0 3 mm depth layer of 19 fe mn crusts collected from 6 seamounts in the pacific ocean 238u values in the surface layers show little variation and range from 0 59 to 0 69 the uniformity of 238u values is consistent with the long residence time of u in modern seawater although the 238u values are lighter than that of present day seawater by 0 24 the light 238u values are consistent with the isotope offset observed in previously reported adsorption experiment of u to mn oxide these results indicate that removal of u from seawater to mn oxide is responsible for the second largest u isotope fractionation in the modern marine system and could contribute to isotopically heavy u to seawater depth profiles of u isotopes 234u and 238u in two fe mn crusts mr12 03 d06 r01 and mc10 cb07 b dated by os isotope stratigraphy were investigated to reconstruct the evolution of the oceanic redox state during the cenozoic the 238u depth profiles show very limited ranges 0 57 to 0 67 for mr12 03 d06 r01 and 0 56 to 0 69 for mc10 cb07 b and have values that are similar to those of the surface layers of fe mn crusts the absence of any resolvable variation in the 238u depth profiles may suggest that the relative amounts of oxic and reducing u sinks have not varied significantly over the past 45 myr however the 234u depth profiles of the same samples show evidence for the possible redistribution of 234u after deposition therefore the depth profile of 238u in fe mn crusts may have been also overprinted by later chemical exchange with pore water or seawater and may not reflect the paleo oceanic environmental changes to assess the potential role of u removal by mn oxides on seawater 238u we calculated seawater 238u with different u sink fluxes into mn oxides using a simple mass balance model the results of these calculations suggest that seawater 238u could have varied significantly throughout earth s history due to changes in the accumulation rate of mn oxides

simple models for the geochemical response of the ocean to climatic and tectonic forcing abstract simple models for the geochemical response of the ocean to periodic forcing are used as a framework to discuss the shortest periods of change resolvable by present analytical precision of elemental or isotopic ratio measurements of the chemical evolution of seawater for chemical properties whose budget is dominated by fluxes into and out of the ocean we show that the geochemical response to changing fluxes is strongly attenuated at periods shorter than the residence time and that the response at these periods is also phase shifted so as to lag the forcing by one quarter cycle the amplitude response as a function of period is used to estimate the periods of forcing resolvable by present analytical precision in measuring the 87sr 86sr and 234u 238u evolution of seawater and we find that the shortest periods resolvable are of the order of 1 myr if variations at periods shorter than this are found we would argue that these are very likely of local as opposed to global origin we illustrate the importance of phase shifts as a function of forcing period by discussing some recently published data that show a high degree of correlation over the last 300 kyr between changes in 87sr 86sr and 18o measured in the same sediment core at first sight this correlation might be taken as good evidence that both 87sr 86sr and 18o are responding to some common climatic forcing but given the long residence time of sr in the ocean sr and o should in fact have different phase shifts relative to any proposed common forcing thus the apparent correlation between 87sr 86sr and 18o over the past several 100 ma is not necessarily an indication that they are responding to a common cause amplitude response curves are also used to place limits on permissible global seawater 234u 238u variations and these are then compared with published data to identify local diagenetic effects application to 187os 186os and u records in seawater detectors is proposed