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

no iron isotope fractionation between molten alloys and silicate melt to 2000 c and 7 7 gpa experimental evidence and implications for planetary differentiation and accretion abstract whether core mantle differentiation of terrestrial planets fractionates iron isotope is currently a debated issue melting experiments corresponding to the conditions inferred for core differentiation in an early silicate magma ocean were performed at 1750 and 2000 c and from 1 to 7 7 gpa to address this question the starting mixtures correspond to a devolatilized ci chondrite composition and oxygen fugacity conditions were 2 log units below the iron wustite buffer scanning electron microscopy observations electron microprobe chemical analyses and plasma source mass spectrometric isotope analyses of the experimental charges show that chemical and iron isotope equilibrium was reached at 2000 c within 100 s no fe isotope fractionation was found between the fe ni alloy and the ultramafic silicate melt at this temperature this result holds within the 2 7 7 gpa pressure range and is likely to remain valid at higher pressures and temperatures the addition of sulfur to the system does not alter this conclusion the compilation of all experiments conducted at 2000 c yields 57 fe metal silicate glass 0 047 0 063 our results suggest that significant iron isotope fractionation is unlikely during equilibration of molten core forming materials in a deep magma ocean this process therefore cannot explain the heavier fe isotope composition of the moon relative to the earth itself heavier than mars vesta and chondrite parent bodies

early stages of core segregation recorded by fe isotopes in an asteroidal mantle ureilites displays 56 fe values higher than average chondrite 29 segregation of fe sulfide melts explains the high 56 fe values in ureilites 30 formation of a core can begin at very low degrees of melting through the circulation of a fe s melt 31 through a silicate mantle 32 33 earth and planetary science letters in press 11 3 15 34 2 35 abstract 36 37 ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon they provide a unique opportunity to study the differentiation 39 processes of such a body we analyzed the iron isotopic compositions of 30 samples from the ureilite 40 parent body upb including 29 unbrecciated ureilites and one ureilitic trachyandesite alm a 41 which is at present the sole large crustal sample of the upb the 56 fe of the whole rocks fall within a 42 restricted range from 0 01 to 0 11 with an average of 0 056 0 008 which is significantly 43 higher than that of chondrites we show that this difference can be ascribed to the segregation of s 44 rich metallic melts at low degrees of melting at a temperature close to the fe fes eutectic and 45 certainly before the onset of the melting of the silicates 1100 c in agreement with the marked s 46 depletions and the siderophile element abundances of the ureilites these results point to an efficient 47 segregation of s rich metallic melts during the differentiation of small terrestrial bodies 48 49

iron and zinc isotope fractionation during magmatism in the continental crust evidence from bimodal volcanic rocks from hailar basin ne china abstract this study presents fe zn isotope data for a suite of well characterized bimodal volcanic rocks from hailar basin northeast china to understand the mechanism of fe isotope fractionation in highly differentiated igneous rocks the samples range from basaltic trachyandesites to trachytes rhyodacites and rhyolites the 56 fe values increase with increasing sio 2 contents with the rhyolites having the highest 56 fe up to 0 64 0 02 among the previously reported data for igneous rocks at a similar sio 2 the lack of correlation between 56 fe and rb la argues against the effect of fluid exsolution on fe isotopes the 56 fe do not show a clear correlation with 66 zn and radiogenic isotopes suggesting that thermal diffusion or crustal contamination cannot produce the high 56 fe in hailar volcanic rocks fe isotopic variation in hailar volcanic rocks can be explained by two steps of magmatism during the first step partial melting of basaltic trachyandesites with an average 56 fe of 0 09 0 14 produced trachytes rhyodacites with an average 56 fe of 0 24 0 27 modelling using rhyolite melts shows that fe isotopes can be fractionated by preferential partitioning of isotopically different fe 3 and fe 2 between the solid residue and partial melt the second step involves formation of rhyolites with significantly high 56 fe through partial melting or extensive crystallization of crust materials during which isotopically heavy fe preferentially partition into the rhyolitic melt therefore fractionation of fe isotopes between melts and minerals can result in high 56 fe in sio 2 rich igneous rocks and apparent fe isotope heterogeneity within the continental crust

iron isotope differences between earth moon mars and vesta as possible records of contrasted accretion mechanisms the iron isotope compositions of shergotty nakhla chassigny snc meteorites thought to come from mars eucrites and diogenites assumed to sample asteroid 4 vesta and rocks from the moon and earth have been measured using high precision plasma source mass spectrometry the means of eight samples from mars and nine samples from vesta are within error identical despite a range of rock types they are lighter by 0 1 in 57fe 54fe compared to the average of 13 terrestrial mantle derived rocks the latter value is identical within uncertainty with a previously published mean of 46 igneous rocks from the earth the average for 14 lunar basalts and highland plutonic rocks covering a broad spectrum of major element composition is heavier by 0 1 in 57fe 54fe relative to our estimate for the earth s mantle and therefore 0 2 heavier than the eucrites diogenites and snc meteorites however the data scatter somewhat and the apollo 15 green glass and apollo 17 orange glass are identical to samples from mars and vesta there is no clear relationship between petrological characteristics and fe isotope composition despite a wide spectrum of samples instead contrasted planetary isotopic signatures are clearly resolved statistically after evaluating alternative scenario it appears that the most plausible explanation for the heavier fe in the earth and moon is that both objects grew via processes that involved partial vaporisation leading to kinetic iron isotope fractionation followed by minor loss this is consistent with the theory in which the moon is thought to have originated from a giant impact between the proto earth and another planet combined with numerical simulations fe isotope data can offer the potential to provide constraints on the processes that occurred in planetary accretion

an fe isotope study of ordinary chondrites the fe isotope composition of ordinary chondrites and their constituent chondrules metal and sulphide grains have been systematically investigated bulk chondrites fall within a restricted isotopic range of 1 0 84 to 0 21 relative to the irmm 14 fe standard fe isotope compositions do not vary systematically with the very large differences in total fe concentration or oxidation state of the h l and ll chondrite classes similarly the fe isotope compositions of chondrules do not appear to be determined by the h l or ll classification of their host chondrite this may support an origin of the three ordinary chondrite groups from variable accretion of identical fe bearing precursors a close relationship between isotopic composition and redistribution of fe during metamorphism on ordinary chondrite parent bodies was identified the largest variations in chondrule compositions were found in chondrites of the lowest petrologic types the clear link between element redistribution and isotopic composition has implications for many other non traditional isotope systems e g mg si ca cr isotopic compositions of chondrules may also be determined by their melting history porphyritic chondrules exhibit a wide range in isotope compositions whereas barred olivine and radial pyroxene chondrules are generally isotopically heavier than the ordinary chondrite mean very large chondrules preserve the greatest heterogeneity of fe isotopes the mean fe isotope composition of bulk ordinary chondrites was found to be 0 06 0 12 2 sd this is isotopically lighter than the terrestrial mean composition and all other published non chondritic meteorite suites e g lunar and martian samples eucrites pallasites and irons ordinary chondrites though the most common meteorites found on earth today were not the sole building blocks of the terrestrial planets

late quaternary vegetation and climate of southern tierra del fuego vegetation and climate over approximately the past 13 000 yr are reconstructed from fossil pollen in a 9 4 m mire section at caleta robalo on beagle channel isla navarino 54 56 s 67 38 w southern tierra del fuego fifty surface samples reflecting modern pollen dispersal serve to interpret the record chronologically controlled by nine radiocarbon dates fossil pollen assemblages are empetrum gramineae gunnera tubuliflorae zone 3b 13 000 11 850 yr b p gramineae empetrum assorted minor taxa zone 3a 11 850 10 000 yr b p nothofagus gramineae tubuliflorae polypodiaceae zone 2 10 000 5000 yr b p nothofagus empetrum zone 1b 5000 3000 yr b p and empetrum nothofagus zone 1a 3000 0 yr b p assemblages show tundra under a cold dry climate zone 3 followed by open woodland zone 2 as conditions became warmer and less dry and later with greater humidity and lower temperatures by closed forest and the spread of mires zone 1 comparisons drawn with records from antarctica new zealand tasmania and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar southern hemisphere the influences of continental and maritime antarctic air masses were apparently considerable in tierra del fuego during cold late glacial time whereas holocene climate was largely regulated by interplay between maritime polar and maritime tropical air

multiproxy record of late pleistocene holocene climate and vegetation changes from a peat bog in patagonia abstract pollen assemblage changes and stable hydrogen isotope analysis of mosses sphagnum magellanicum and drepanocladus s l from a bog in tierra del fuego argentina provided independent proxies for reconstructing changes in effective moisture and temperature over the past 16 000 cal yr b p a deterministic model was used to reconstruct the stable hydrogen isotope composition of meteoric water from the d h ratios of bog mosses over the last 16 000 years abrupt changes in temperature as recorded in d h ratios of moss cellulose were accompanied by synchronous changes in vegetation composition during the late pleistocene and early and middle holocene when moisture levels were lower than today in contrast temperature variability during the late holocene was not accompanied by comparable vegetation changes in particular grass pollen poaceae increased during periodic cold spells between 15 000 and 11 000 cal yr b p but a cold spell of similar magnitude ca 2000 cal yr b p did not appear to affect vegetation during the late pleistocene the isotopic record from the peat core shows variations similar to the d h ratios in the antarctic taylor dome ice core however the timing of the changes in the harberton record is more in line with the timing of other southern hemisphere records

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

fuegian floating tree ring chronology from subfossil nothofagus wood the discovery of subfossil nothofagus wood buried in several peat bogs of argentine tierra del fuego is reported a provisional fragmented floating tree ring width chronology covering the last 1400 years has been obtained statistical and spectral analysis revealed no significant differences between the present and floating tierra del fuego tree ring chronologies some cyclical growth peculiarities found in both modern and floating chronologies are discussed

experimental evidence for the absence of iron isotope fractionation between metal and silicate liquids at 1 gpa and 1250 1300 c and its cosmochemical consequences abstract iron isotope fractionation during metal silicate differentiation has been proposed as a cause for differences in iron isotope compositions of chondrites iron meteorites and the bulk silicate earth stable isotope fractionation however rapidly decreases with increasing temperature we have thus performed liquid metal liquid silicate equilibration experiments at 1250 1300 c and 1 gpa to address whether fe isotope fractionation is resolvable at the lowest possible temperatures for magmatic metal silicate differentiation a centrifuging piston cylinder apparatus enabled quantitative metal silicate segregation elemental tin or sulphur was used in the synthetic metal oxide mixtures to lower the melting temperature of the metal the analyses demonstrate that eight of the 10 experimental systems equilibrated in a closed isotopic system as was assessed by varying run durations and starting fe isotope compositions statistically significant iron isotope fractionation between quenched metals and silicates was absent in nine of the 10 experiments and all 10 experiments yield an average metal silicate fractionation factor of 0 01 0 04 independent of whether graphite or silica glass capsules were used this implies that fe isotopes do not fractionate during low pressure metal silicate segregation under magmatic conditions in large bodies such as the earth fractionation between metal and high pressure 20 gpa silicate phases may still be a possible process for equilibrium fractionation during metal silicate differentiation however the 0 07 0 02 heavier composition of bulk magmatic iron meteorites relative to the average of bulk ordinary carbonaceous chondrites cannot result from equilibrium fe isotope fractionation during core segregation the up to 0 5 lighter sulphide than metal fraction in iron meteorites and in one ordinary chondrite can only be explained by fractionation during subsolidus processes

equilibrium high temperature fe isotope fractionation between fayalite and magnetite an experimental calibration abstract the iron isotopic fractionation factor between magnetite and fayalite was measured at high temperature in a piston cylinder apparatus for the first time the three isotope method matsuhisa j goldsmith j r and clayton r n 1978 mechanisms of hydrothermal crystallisation of quartz at 250 c and 15 kbar geochim cosmochim acta 42 173 182 has been used to determine equilibrium fractionation between two minerals directly the experimentally determined temperature dependent iron isotope fractionation between fayalite and magnetite is described by 10 3 ln 57 mag fa 57 fe mag fa 0 30 0 024 10 6 t 2 the equation predicts measurable fractionation at magmatic temperatures our work bears on the magnitude of fe isotope fractionation attending differentiation in magmatic systems and provides a new isotope thermometer for co existing fayalite and magnetite

an assessment of iron isotope fractionation during core formation abstract iron is a ubiquitous element in terrestrial and extra terrestrial settings and can provide clues as to the conditions during which planetary scale processes occurred one example of this is determining the conditions accompanying metal core formation in rocky planets and planetesimals for at least two decades there has been a growing database of experimental and natural data aimed at understanding whether iron isotopes fractionate during the separation of silicate and metal while it has been argued that the data are not in agreement with one another it is apparent that once criteria are established that prove equilibrated samples there is good agreement amongst the different studies when looked at as a function of the metallic composition proving equilibrium is critical in these types of experiments the three isotope experimental technique for establishing equilibrium is found to be both mathematically and fundamentally sound further it is clear that the question of whether there is an equilibrium iron isotope fractionation between metal and silicate is not straightforward and that it can vary significantly as a function of temperature pressure metallic composition oxygen fugacity and silicate composition

on the iron isotope composition of mars and volatile depletion in the terrestrial planets iron is the most abundant multivalent element in planetary reservoirs meaning its isotope composition expressed as 57fe may record signatures of processes that occurred during the formation and subsequent differentiation of the terrestrial planets chondritic meteorites putative constituents of the planets and remnants of undifferentiated inner solar system bodies have fe57 0 an isotopic signature shared with the martian shergottite nakhlite chassignite snc suite of meteorites the silicate earth and moon as represented by basaltic rocks are distinctly heavier fe57 0 1 however some authors have recently argued on the basis of iron isotope measurements of abyssal peridotites that the composition of the earth s mantle is fe57 0 04 0 04 indistinguishable from the mean martian value to provide a more robust estimate for mars we present new high precision iron isotope data on 17 snc meteorites and 5 mineral separates we find that the iron isotope compositions of martian meteorites reflect igneous processes with nakhlites and evolved shergottites displaying heavier fe57 0 05 0 03 whereas mgo rich rocks are lighter fe57 0 01 0 02 these systematics are controlled by the fractionation of olivine and pyroxene attested to by the lighter isotope composition of pyroxene compared to whole rock nakhlites extrapolation of the fe57 snc liquid line of descent to a putative martian mantle yields a 57fe value lighter than its terrestrial counterpart but indistinguishable from chondrites iron isotopes in planetary basalts of the inner solar system correlate positively with fe mn and silicon isotopes while mars and iv vesta are undepleted in iron and accordingly have chondritic 57fe the earth experienced volatile depletion at low 1300 k temperatures likely at an early stage in the solar nebula whereas additional post nebular fe loss is possible for the moon and angrites

on the iron isotope heterogeneity of lithospheric mantle xenoliths implications for mantle metasomatism the origin of basalts and the iron isotope composition of the earth with the aim to better understand the cause of the iron isotope heterogeneity of mantle derived bulk peridotites we compared the petrological geochemical and iron isotope composition of four xenolith suites from different geodynamic settings sub arc mantle patagonia subcontinental lithospheric mantle cameroon oceanic mantle kerguelen and cratonic mantle south africa although correlations were not easy to obtain and remain scattered because these rocks record successive geological events those found between 57fe mg some major and trace element contents of rocks and minerals highlight the processes responsible for the fe isotope heterogeneity while partial melting processes only account for moderate fe isotope variations in the mantle 0 9 the kinetic nature of rapid metasomatic exchanges between low viscosity melts fluids and their wall rocks peridotite in the mantle is the likely explanation for this large range there are a variety of responses of fe isotope signatures depending on the nature of the metasomatic processes allowing for a more detailed study of metasomatism in the mantle with fe isotopes the current database on the iron isotope composition of peridotite xenoliths and mafic eruptive rocks highlights that most basalts have their main source deeper than the lithospheric mantle finally it is concluded that due to a complex geological history fe isotope compositions of mantle xenoliths are too scattered to define a mean isotopic composition with enough accuracy to assess whether the bulk silicate earth has a mean 57fe that is chondritic or if it is 0 1 above chondrites as initially proposed

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

experimental quantification of the fractionation of fe isotopes during metal segregation from a silicate melt abstract fractionation of fe isotopes between a silicate melt and metallic alloys has been quantified experimentally at 1500 c the effects of oxygen fugacity and run duration have been investigated to distinguish between kinetic and equilibrium fractionations a new experimental setup is presented in which metallic fe is produced by reduction of oxidized iron from a silicate melt due to a change of redox conditions this metallic fe is physically removed from the silicate and sequestered as a pt fe alloy bulk analyses of the silicate and metallic fractions using multi collector icp ms methods are coupled with in situ analyses using an ion microprobe experimental results indicate that significant isotopic fractionation of fe occurs during metal segregation during the early stages of the experiments we find evidence for kinetic fractionation caused by faster diffusion of 54 fe along concentration gradients in the alloy this process leads to the formation of a metallic phase which is isotopically light compared to the residual silicate metal silicate fractionation up to 2 35 a m u the data are used to quantify the difference in diffusion coefficient of each isotope of iron providing a means to predict fe isotope fractionation during fe diffusion in metallic alloys on the other hand this state of affairs is transient in nature and at superliquidus temperature the systems rapidly reach a state of isotopic equilibrium in which the metal is isotopically heavier than the silicate melt by about 0 2 0 15 a m u these results are consistent with the range of variation observed in natural samples these kinetic and equilibrium data provide an experimental framework to understand the observed variability among igneous and meteoritic materials formed at high temperature particularly for iron and pallasite meteorites

chemical and isotopic kinship of iron in the earth and moon deduced from the lunar mg suite abstract the moon and the earth s mantle share many chemical and isotopic traits leading to the prevailing theory that they were formed from similar material iron is one element that shows apparent differences between the two bodies with models for the composition of the moon having 1 5 times more feo 12 14 wt relative to the earth s mantle 8 wt this difference is mirrored in their isotope compositions where lunar mare basalts have 57fe per mille deviation of the 57fe 54fe ratio from the irmm 014 standard 0 1 0 2 higher than peridotitic rocks representative of earth s mantle a feature initially attributed to loss of isotopically light fe following a giant impact however whether basaltic rocks are suitable analogues for the moon s composition is debatable in the light of their distinct source regions that reflect the extensive lithological stratification of the lunar mantle here we evaluate the iron isotope composition of the bulk moon through the study of igneous cumulate rocks of the lunar highlands magnesium suite mg suite the 57fe of mg suite rocks spans a limited range from 0 05 to 0 10 with an average 0 07 0 02 that overlaps with earth s mantle 0 05 0 01 similarities that extend to their mg s where both reach 0 9 numerical modelling of iron isotope fractionation during lunar magma ocean crystallisation shows that the mg suite should accurately reflect the composition of the bulk moon which is therefore 0 07 0 02 indistinguishable from earth s mantle but heavier than chondrites 0 01 0 01 iron thus behaves coherently with other elements that condense at temperatures higher than li in showing no isotopic difference between the earth and moon suggesting element depletion on the moon affected only the more volatile elements therefore there is no cosmochemical basis for iron enrichment or depletion in the bulk moon relative to the earth s mantle whose composition is an analogue for that of the moon

thermal equilibration of iron meteorite and pallasite parent bodies recorded at the mineral scale by fe and ni isotope systematics abstract in this work a femtosecond laser ablation la system coupled to a multi collector inductively coupled plasma mass spectrometer fs la mc icp ms was used to obtain laterally resolved 30 80 m high precision combined ni and fe stable isotope ratio data for a variety of mineral phases olivine kamacite taenite schreibersite and troilite composing main group pallasites pmg and iron meteorites the stable isotopic signatures of fe and ni at the mineral scale in combination with the factors governing the kinetic or equilibrium isotope fractionation processes are used to interpret the thermal histories of small differentiated asteroidal bodies as fe isotopic zoning is only barely resolvable within the internal precision level of the isotope ratio measurements within a single olivine in esquel pmg the isotopically lighter olivine core relative to the rim 56 54 fe rim core 0 059 suggests that the olivines were largely thermally equilibrated the observed hint of an isotopic and concentration gradient for fe of crudely similar width is interpreted here to reflect fe loss from olivine in the process of partial reduction of the olivine rim the ranges of the determined fe and ni isotopic signatures of troilite 56 54 fe of 0 66 to 0 09 and schreibersite 56 54 fe of 0 48 to 0 09 and 62 60 ni of 0 64 to 0 29 may result from thermal equilibration schreibersite and troilite likely remained in equilibrium with their enclosing metal to temperatures significantly below their point of crystallization the ni isotopic signatures of bulk metal and schreibersite correlate negatively with isotopically lighter ni in the metal of pmgs and isotopically heavier ni in the metal of the iron meteorites analyzed as such the light ni isotopic signatures previously observed in pmg metal relative to chondrites may not result from heterogeneity in the solar nebula but rather reflect fractionation in the metal schreibersite system comparison between the isotope ratio profiles of fe and ni determined across kamacite taenite interfaces 56 54 fe kam tae 0 51 to 0 69 and 62 60 ni kam tae 1 59 to 2 50 and theoretical taenite sub solidus diffusive isotopic zoning broadly constrain the cooling rates of esquel cms 04071 pmgs and udei station iab to between 25 and 500 c myr

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

dating raised bogs new aspects of ams 14c wiggle matching a reservoir effect and climatic change abstract high resolution ams dating of holocene raised bog deposits engbertsdijksvenen the netherlands shows natural 14c variations wiggles which can be matched with the dendrochronological calibration curve comparison of our results with other conventionally dated peat cores and the 14c record shows an unexpected and as yet unreported reservoir effect and a marked and sudden wetting of the bog surfaces coinciding with the advent of a sporer type solar minimum the homeric minimum the potential of ams dating to vastly improve the accuracy of holocene chronologies is demonstrated

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

a multi phase model of runaway core mantle segregation in planetary embryos abstract a classic scenario of core formation suggests that growing proto planets are heated by the impacts of accreting planetesimals at their surface until their shallow layers reach the melting temperature of their metallic components or even of the silicates in this partially molten shell metal and silicates differentiate and the metallic phase ponds on top of the still undifferentiated inner planet later a gravitational instability brings dense metallic diapirs to the center of the planet we test this multi phase scenario by using a formalism that self consistently accounts for the presence of solid silicates solid and liquid iron at each point of the mixture an average velocity and a separation velocity of the solid and liquid phases are defined the energy balance accounts from the changes in potential energy associated with the segregation we show that core formation starts before a significant melting of the silicates as soon as impact heating is large enough to reach the melting temperature of the metallic component segregation proceeds in a few thousand years by a runaway process due to the conversion of gravitational energy into heat that occurs necessarily in all undifferentiated embryos of moon to mars sizes the first metallic diapirs leave behind them a trailing conduit along which most of the further melting occurs the cores of large planets do not form at the end of accretion but must result from the merging of the already differentiated hot cores of embryos

planetary science a nickel for your planet s thoughts variability of iron isotopes among planetary bodies may reflect their accretion or differentiation histories experiments suggest nickel may be the ingredient controlling iron isotope signatures supporting fractionation during core formation

comparison of element and isotope diffusion of k and ca in multicomponent silicate melts recent experimental work has shown that the homogenization of elemental concentrations can be much slower than that of isotopic ratios when there are strong concentration gradients in sio 2 and al 2o 3 the ramifications of this result for magma homogenization and other petrological problems related to diffusion are significant we report here a comparison of experimental profiles of elemental concentrations and isotopic fractions of k and ca in rhyolite andesite large concentration gradients and rhyolite rhyolite small concentration gradients melt couples when the concentration profile and the isotopic profile of the same element in a single couple are compared the former is much shorter than the latter in the rhyolite andesite couple consistent with other recent studies however the lengths of both concentration and isotopic profiles are similar in the rhyolite rhyolite couple therefore diffusion of an element or oxide may be decoupled from or coupled with isotopic diffusion depending on whether large concentration gradients of major components are present when the two couples are compared the intrinsic effective binary diffusivities obtained from isotopic profiles are similar for each element in the two couples whereas the effective binary diffusivity of k obtained from the concentration profile in the rhyolite rhyolite couple is 37 times that in the rhyolite andesite couple therefore isotopic homogenization is roughly independent of elemental homogenization and the presence of sio 2 al 2o 3 and other concentration gradients whereas elemental homogenization is strongly affected by concentration gradients our experimental data isotopic and concentration profiles including uphill diffusion profiles can be modeled quantitatively to a good approximation using a modified effective binary diffusion model in which the flux of a component is assumed to be proportional to its activity gradient instead of its concentration gradient therefore the multicomponent diffusion effect in the silicate systems of our experiments seems to be largely due to contributions of non ideal mixing to the cross terms of the diffusivity matrix

the effect of core composition on iron isotope fractionation between planetary cores and mantles abstract we have conducted high pressure high temperature isotope exchange experiments between molten silicate and molten fe si c alloys to constrain the effect of si on equilibrium fe isotope fractionation during planetary core formation the values of 57 femetal silicate at 1850 c and 1 gpa determined by high resolution mc icp ms in this study range from 0 013 0 054 2se to 0 072 0 085 with 1 34 8 14 atom si in the alloy respectively these results although not definitive on their own are consistent with previous experimental results from our group and a model in which elements that substitute for fe atoms in the alloy structure i e ni s and si induce a fractionation of fe isotopes between molten silicate and molten fe alloys during planetary differentiation using in situ synchrotron x ray diffraction data for molten fe rich alloys from the literature we propose a model to explain this fractionation behavior in which impurity elements in fe alloys cause the nearest neighbor atomic distances to shorten thereby stiffening metallic bonds and increasing the preference of the alloy for heavy fe isotopes relative to the silicate melt this fractionation results in the bulk silicate mantles of the smaller terrestrial planets and asteroids becoming isotopically light relative to chondrites with an enrichment of heavy fe isotopes in their cores consistent with magmatic iron meteorite compositions our model predicts a bulk silicate mantle 57 fe ranging from 0 01 to 0 12 for the moon 0 06 to 0 33 for mars and 0 08 to 0 33 for vesta independent estimates of the 57 fe of primitive mantle source regions that account for fe isotope fractionation during partial melting agree well with these ranges for all three planetary bodies and suggest that mars and vesta have cores with impurity i e ni s si abundances near the low end of published ranges therefore we favor a model in which core formation results in isotopically light bulk silicate mantles for the moon mars and vesta the processes of magma ocean crystallization mantle partial melting and fractional crystallization of mantle derived melts are all likely to result in heavy fe isotope enrichment in the melt phase which can explain why basaltic samples from these planetary bodies have variable 57 fe values consistently heavier than our bulk mantle estimates additionally we find no clear evidence that fe isotopes were fractionated to a detectable level by volatile depletion processes during or after planetary accretion although it cannot be ruled out

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

core formation in earth s moon mars and vesta stimulated by new experimental results on metal silicate partitioning of elements at elevated temperatures and pressures we have revisited the question of core formation in earth s moon mars and vesta the probable source of the eucritic meteorites earlier studies suggested metal silicate equilibrium in mars but led to the paradox that mars accreted homogeneously while the earth accreted heterogeneously using new elevated pressure and temperature metal silicate partition coefficients we show that abundances of the moderately siderophile elements in the mantles of the moon mars and vesta are consistent with early magma oceans on these bodies the most successful model for explaining the lunar mantle siderophile element abundances requires a core of 5 of the mass of the moon 500 km radius siderophile element abundances in mars are consistent with intermediate pressure metal silicate equilibrium as has also been recently suggested for the earth the most successful model for explaining the martian siderophile element abundances requires a bulk planetary composition that has greater than ci chondritic abundances of the moderately siderophile elements and a core of 30 of the mass of mars siderophile element abundances in the mantle of vesta are consistent with low pressure liquid metal liquid silicate equilibrium as expected for an asteroid sized body and a core of 10 of the mass of vesta comparison of our best fit oxygen fugacities for vesta with thermodynamic calculations of oxygen fugacity for silicate bearing iron meteorites indicates that parts of the inner solar system were homogeneous with respect to redox state at 4 5 ga approximately 2 log fo2units below the fe feo buffer much higher than estimates for the solar nebula similar comparisons for mars and the earth indicate that these bodies have undergone oxidation since 4 5 ga because the oxygen fugacities associated with metal silicate equilibrium in both mars and the earth moon system are much lower than those recorded in martian and terrestrial basaltic and periodotitic samples the oxidation on mars is most likely due to atmospheric effects whereas earth s much wider range of oxygen fugacities must be due to both atmospheric and plate tectonic effects

correlated helium 3 and tungsten isotopes in iron meteorites quantitative cosmogenic corrections and planetesimal formation times abstract core formation in planetesimals can in principle be dated using the short lived 182 hf 182 w chronometer however it has been predicted that burnout and production of w isotopes by nuclear reactions can substantially modify the compositions in iron meteorites when exposed for several hundred million years myr to galactic cosmic rays this may severely limit the use of the hf w system for determining chronologies of metal segregation as recorded in iron meteorites here we present the first experimental evidence of cosmogenic effects on w isotopes in two magmatic iron meteorites carbo iid and grant iiiab the 182 w 184 w ratio near the pre atmospheric centre of the meteorites is lower by 0 5 epsilon compared to values near the pre atmospheric surface the 182 w 184 w ratio displays excellent correlations with the 3 he concentration which in turn provides a proxy for the fluence of the relevant cosmic ray particles using new nuclear physics parameters a first order correction for cosmic ray effects on w isotopes is proposed based on the 3 he concentration and on an independent exposure age of the meteorite this method is then applied to other magmatic iron meteorites negrillos cape of good hope navajo and arispe when corrected for cosmogenic effects the w isotopic compositions of carbo grant negrillos cape of good hope and navajo are similar to the initial composition recorded in allende cais this shows that at least some magmatic meteorites from groups iiab iid iiiab and ivb segregated within less than 1 2 myr of the hf w system closure in allende cais the isotopic variations among the samples indicate that the iron meteorites studied in this paper segregated over a time interval of 4 myr carbo being the oldest iron meteorites of this study

protactinium 231 dating of carbonates by thermal ionization mass spectrometry implications for quaternary climate change measurement of protactinium 231 231pa in carbonates by thermal ionization mass spectroscopy yields 231pa ages that are more than 10 times more precise than those determined by decay counting carbonates between 10 and 250 000 years old can now be dated with 231pa methods barbados corals that have identical 231pa and thorium 230 230th ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the astronomical theory two devils hole calcite subsamples record identical 231pa and 230th ages suggesting that the chronology of this climate record is accurate

experimental determination of the si isotope fractionation factor between liquid metal and liquid silicate abstract the conditions of core formation and the abundances of the light elements in earth s core remain debated silicon isotope fractionation provides a tool contributing to this subject we present experimentally determined si isotope fractionation factors between liquid metal and liquid silicate at 1450 c and 1750 c which allow calibrating the temperature dependence of si isotope fractionation experiments were performed in a centrifuging piston cylinder at 1 gpa employing both graphite and mgo capsules tin was used to lower the melting temperature of the metal alloys for experiments performed at 1450 c tests reveal that neither sn nor c significantly affects si isotope fractionation an alkaline fusion technique was employed to dissolve silicate as well as metal phases prior to ion exchange chemistry and mass spectrometric analysis the results show that metal is consistently enriched in light isotopes relative to the silicate yielding average metal silicate fractionation factors of 1 48 0 08 and 1 11 0 14 at 1450 c and 1750 c respectively the temperature dependence of equilibrium si isotope fractionation between metal and silicate can thus be described as 30 si metal silicate 4 42 0 05 10 6 t 2 the si isotope equilibrium fractionation is thus about 1 7 times smaller than previously proposed on the basis of experiments a consequence of this smaller fractionation is that the calculated difference between the si isotope composition of the bulk earth and that of the bulk silicate earth generated by core formation is smaller than previously thought it is therefore increasingly difficult to match the si isotope composition of the bulk silicate earth with that of chondrites for metal silicate equilibration temperatures above 2500 k this suggests that si isotopes were more sensitive to the early stages of core formation when low oxygen fugacities allowed significant incorporation of si into metal

high resolution records of late holocene climate change and carbon accumulation in two north west european ombrotrophic peat bogs the peat stratigraphy plant macrofossils colorimetric humification pollen non pollen microfossils carbon nitrogen ratios of three replicate cores from a raised peat bog in the uk walton moss and a single core from a raised peat bog in denmark lille vildmose were examined in an attempt to investigate the relation between long term climate change and changes in species composition of the peat forming vegetation nine wet shifts identified in the monoliths from walton moss and lille vildmose mainly occurred during periods of increasing atmospheric c 14 content because fluctuations in holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity the little ice age lia climatic deteriorations registered in both peat bogs were probably driven by changes in solar activity climatic deteriorations in the three replicate cores from walton moss are not all consistently registered and may reflect the internal variability in the extent of hollow lawn hummock microforms within raised peat bog ecosystems the lowest carbon accumulation values for the walton moss monoliths between ca cal ad 1300 and 1800 and between ca cal ad 1490 and 1580 for lille vildmose occurred during the course of lia climatic deteriorations peat bog primary productivity may have been reduced during the lia owing to lower spring summer temperatures and shorter growing seasons for the peat forming plants species specific higher decomposition rates may have also caused the lower carbon accumulation rates in the peat bogs during the lia c 2002 elsevier science b v all rights reserved

younger dryas in southernmost south america an update abstract high resolution pollen data from a peat section in southern tierra del fuego documents high paleoenvironmental variability between 11 ka and 9 ka detailed analysis of plant macro remains in the same section showed that the repeated high amplitude changes in pollen taxa were related to repeated fire disturbance burning at least once even the surface of the mire in many peat sections from southernmost patagonia and tierra del fuego charcoal particles have been found intermittently since about 13 ka and in great abundance especially after 11 ka this suggests that the environmental changes previously interpreted to imply a return to colder climates comparable to the north atlantic younger dryas event instead are in response to local and regional disturbances by fires

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

milankovitch theory viewed from devils hole variations in the oxygen isotope content 18o of late quaternary deep sea sediments mainly reflect changes in continental ice mass1 and hence provide important information about the timing of past ice ages because these sediments cannot yet be dated directly beyond the range of radiocarbon dating 40 50 kyr ages for the 18o record have been generated2 3 by matching the phase of the changes in 18o to that of variations in the earth s precession and obliquity adopting this timescale yields a close correspondence between the time varying amplitudes of these orbital variations and those of a wide range of climate proxies4 lending support to the milankovitch theory that the earth s glacial interglacial cycles are driven by orbital variations recently winograd et al 5 reported a record of 18o variations in a fresh water carbonate sequence from devils hole nevada dated by u th disequilibrium6 they concluded that the timing of several of the features in the record which reflects changes in the temperature of precipitation over nevada as well as changes in the isotopic composition of the moisture source5 7 showed significant deviations from that predicted by milanko vitch theory here we demonstrate that applying the devils hole chronology to ocean cores requires physically implausible changes in sedimentation rate moreover spectral analysis of the devils hole record shows clear evidence of orbital influence we therefore conclude that transfer of the devils hole chronology to the marine record is inappropriate and that the evidence in favour of milankovitch theory remains strong

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

climatic fluctuations in northern patagonia during the last 1000 years as inferred from tree ring records abstract millennium old alerce trees fitzroya cupressoides mol johnst have been used to develop a 1120 year reconstruction of the summer temperature departures for the andes of northern patagonia in argentina four main climatic episodes can be distinguished in this proxy paleoclimatic record the first a cold and moist interval from a d 900 to 1070 was followed by a warm dry period from a d 1080 to 1250 correlative with the medieval warm epoch of europe afterward a long cold moist period followed from a d 1270 to 1670 peaking around a d 1340 and 1650 these cold maxima are contemporaneous with two principal little ice age events registered in the northern hemisphere warmer conditions then resumed between a d 1720 and 1790 these episodes are supported by glaciological and palynological data in patagonia following a cold period in the early 1800s tree ring indices have oscillated around the long term mean except for a warmer period from a d 1850 to 1890 correlations between the rio alerce reconstruction and the regional weather stations indicate that the tree ring variations are correlated with a homogeneous summer weather pattern covering patagonia east of the andes from 38 to 50 s

a sensitive high resolution record of late holocene climatic change from a raised bog in northern england proxy climatic data in the form of plant macrofossils have been analysed from a 5 m core from bolton fell moss cumbria uk detailed analysis of peat from the upper 50 cm of this core is used to demonstrate a strong correlation between changes in the relative proportion of taxa and known climatic changes over the last 1000 years the record of changes in bog vegetation contained within the peat profile is used to reconstruct changes in bog surface wetness for the latter half of the holocene as bog surface wetness is directly controlled by the prevailing climatic conditions this reconstruction can be viewed as a proxy climate record twelve radiocarbon age estimates on the 5m core suggest that between 50 and 500 cm peat accumulated at a relatively constant rate of 12 4 yr cm 1 the regular sampling intervals thus provide a time series of past bog surface wetness spectral analyses of this series indicates that wetness changes are cyclic with a ca 800 year periodicity

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

the experimental calibration of the iron isotope fractionation factor between pyrrhotite and peralkaline rhyolitic melt abstract a first experimental study was conducted to determine the equilibrium iron isotope fractionation between pyrrhotite and silicate melt at magmatic conditions experiments were performed in an internally heated gas pressure vessel at 500 mpa and temperatures between 840 and 1000 c for 120 168 h three different types of experiments were conducted and after phase separation the iron isotope composition of the run products was measured by mc icp ms i kinetic experiments using 57 fe enriched glass and natural pyrrhotite revealed that a close approach to equilibrium is attained already after 48 h ii isotope exchange experiments using mixtures of hydrous peralkaline rhyolitic glass powder 4 wt h 2 o and natural pyrrhotites fe 1 x s as starting materials and iii crystallisation experiments in which pyrrhotite was formed by reaction between elemental sulphur and rhyolitic melt consistently showed that pyrrhotite preferentially incorporates light iron no temperature dependence of the fractionation factor was found between 840 and 1000 c within experimental and analytical precision an average fractionation factor of 56 fe 54 fe pyrrhotite melt 0 35 0 04 2se n 13 was determined for this temperature range predictions of fe isotope fractionation between fes and ferric iron dominated silicate minerals are consistent with our experimental results indicating that the marked contrast in both ligand and redox state of iron control the isotope fractionation between pyrrhotite and silicate melt consequently the fractionation factor determined in this study is representative for the specific fe 2 fe ratio of our peralkaline rhyolitic melt of 0 38 0 02 at higher fe 2 fe ratios a smaller fractionation factor is expected further investigation on fe isotope fractionation between other mineral phases and silicate melts is needed but the presented experimental results already suggest that even at high temperatures resolvable variations in the fe isotope composition can be generated by equilibrium isotope fractionation in natural magmatic systems

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

the iron isotope composition of enstatite meteorites implications for their origin and the metal sulfide fe isotopic fractionation factor abstract despite their unusual chemical composition it is often proposed that the enstatite chondrites represent a significant component of earth s building materials based on their terrestrial similarity for numerous isotope systems in order to investigate a possible genetic relationship between the fe isotope composition of enstatite chondrites and the earth we have analyzed 22 samples from different subgroups of the enstatite meteorites including eh and el chondrites aubrites main group and shallowater and the happy canyon impact melt we have also analyzed the fe isotopic compositions of separated magnetic and non magnetic phases from both enstatite chondrites and achondrites on average eh3 5 chondrites 56fe 0 003 0 042 2 standard deviation n 9 including previous literature data as well as el3 chondrites 56fe 0 030 0 038 2 sd n 2 have identical and homogeneous fe isotopic compositions indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite in contrast el6 chondrites display a larger range of isotopic compositions 0 180 enstatite achondrites aubrites also exhibit a relatively large range of fe isotope compositions all main group aubrites are enriched in the light fe isotopes 56fe 0 170 0 189 2 sd n 6 while shallowater is isotopically relatively heavy 56fe 0 045 0 101 2 sd n 4 number of chips we take this variation to suggest that the main group aubrite parent body formed a discreet heavy fe isotope enriched core whilst the shallowater meteorite is most likely from a different parent body where core and silicate material remixed this could be due to intensive impact induced shearing stress or the ultimate destruction of the shallowater parent body analysis of separated enstatite meteorite mineral phases show that the magnetic phase fe metal is systematically enriched in the heavier fe isotopes when compared to non magnetic phases fe hosted in troilite which agrees with previous experimental observations and theoretical calculations the difference between magnetic and non magnetic phases from enstatite achondrites provides an equilibrium metal sulfide fe isotopic fractionation factor of 56femetal troilite 56femetal 56fetroilite of 0 129 0 060 2 se at 1060 80 k which confirms the predictions of previous theoretical calculations

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

improving the time control of the subboreal subatlantic transition in a czech peat sequence by 14c wiggle matching to achieve an optimal time control for a late subboreal to early subatlantic peat sequence from pancavska louka in the czech republic different strategies are applied to convert a series of radiocarbon dates into a calendar time scale the methods of selection and preparation of the samples for ams 14c dating are presented the results of calibrating single radiocarbon dates are compared with a 14c wiggle match strategy as the accumulation rate of the peat was not constant the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes the resulting time control represents the best solution for this peat sequence with the methods currently available

late holocene climatic changes in tierra del fuego based on multiproxy analyses of peat deposits a ca 1400 yr record from a raised bog in isla grande tierra del fuego argentina registers climate fluctuations including a medieval warm period although evidence for the little ice age is less clear changes in temperature and or precipitation were inferred from plant macrofossils pollen fungal spores testate amebae and peat humification the chronology was established using a 14c wiggle matching technique that provides improved age control for at least part of the record compared to other sites these new data are presented and compared with other lines of evidence from the southern and northern hemispheres a period of low local water tables occurred in the bog between a d 960 1020 which may correspond to the medieval warm period date range of a d 950 1045 generated from northern hemisphere tree ring data a period of cooler and or wetter conditions was detected between ca a d 1030 and 1100 and a later period of cooler wetter conditions estimated at ca cal a d 1800 1930 which may correspond to a cooling episode inferred from law dome antarctica

a new approach to paleoclimatic research using linear programming abstract one of the most frequently attempted correlations in quaternary research is between insolation and paleoclimatic data yet there are a large number of insolation time series that could potentially explain a quaternary dataset individually or in combination we computed 342 insolation time series varying by latitude time of year and time of day for fitting to four different paleoclimatic records foraminiferal 18 o from specmap temperatures inferred from vostok antarctica ice cores marine accumulation rates of a freshwater diatom melosira originating from tropical africa lakebeds and 18 o variations in calcite at devil s hole nevada we developed two inductive linear programming models that solve for the weighted combination of insolation curves that minimize either the average or maximum residual from the proxy curve each of the four proxy records lagged and unlagged was solved by both model types on average our composite insolation curves fit the proxy records 48 76 better than does june daily insolation at 60 n the key insolation curve of the milankovitch paradigm globally high latitude insolation 60 70 n and s and insolation at specific times of day noon or non noon as opposed to daily dominated the results regionally the model tended to select insolation curves from absolute latitudes similar to those of the proxy records the fact that these results are plausible given known biophysical processes combined with the fact that a small number of curves repeatedly accounted for a disproportionate share of the explanation suggest strongly that the correlations found are not happenstance despite the inductive method used

reconciliation of the devils hole climate record with orbital forcing the driving force behind quaternary glacial interglacial cycles and much associated climate change is widely considered to be orbital forcing however previous versions of the iconic devils hole nevada subaqueous calcite record exhibit shifts to interglacial values 10 000 years before orbitally forced ice age terminations and interglacial durations 10 000 years longer than other estimates our measurements from devils hole 2 replicate virtually all aspects of the past 204 000 years of earlier records except for the timing during terminations and they lower the age of the record near termination ii by 8000 years removing both 10 000 year anomalies the shift to interglacial values now broadly coincides with the rise in boreal summer insolation the marine termination and the rise in atmospheric co2 which is consistent with mechanisms ultimately tied to orbital forcing

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

potential reconciliation of devils hole and deep sea pleistocene chronologies the standard model of pleistocene climate fluctuations being driven by orbital insolation changes has been challenged by results from a high precision radiometrically dated deposit from devils hole nevada although the devils hole record agrees with a previously derived ice volume record for most of the last 500 000 years clear indication of warming prior to the orbitally dated onset of the last interglacial forms the prime basis for this conclusion i suggest that early warming at devils hole needs to be understood in light of the prior very extensive glaciation at 150 000 b p marine records in both the north pacific and north atlantic from the same latitude as devils hole indicate that the subpolar fronts during the penultimate glaciation 150 000 years ago were 5 father south than during the last glaciation continental glaciation may also have been more extensive at this time the first phase of ice retreat 145 000 years ago is associated with a northward shift of these fronts which results in full interglacial sea surface temperatures in the north atlantic the early warming at devils hole may reflect the northward movement of the ice margins and associated fronts if so both the devils hole and deep sea chronologies may be correct with differences between 130 000 and 150 000 years ago reflecting a regionally varying response to climate shifts associated with a very extensive glaciation

quaternary of tierra del fuego southernmost south america an updated review abstract the quaternary of tierra del fuego is represented by glacial glaciofluvial glaciolacustrine marine and aeolian deposits six drift units have been described the oldest dating from the late pliocene these are starting from the oldest the rio grande sierra de los frailes cabo virgenes punta delgada primera angostura and segunda angostura drifts neoglacial and little ice age events are represented in cirques and higher mountain valleys marine deposits and raised beaches were formed during middle pleistocene late pleistocene and holocene interglacial stages after the definitive ice retreat 10 ka ago vegetation changed from tundra and cold steppe to subantarctic forest environments marine deposits reflect also colder conditions than the present ones aeolian processes prevailed in northern tierra del fuego where semiarid conditions and the frequent westerlies favoured the retransportation of finer materials coming from pre existing deposits before the opening of the magellan straits earliest human colonization occurred in northern tierra del fuego ca 11 ka bp in tundra like environmental conditions pedestrian hunters of camelids and foxes co existed with pleistocene fauna that became extinct during late glacial earliest holocene times the steppe area inland and atlantic coast was successively occupied since then until recent times on the other hand the beagle channel coasts were occupied since 6 ka bp by hunter gatherer groups adapted to maritime littoral conditions finally the easternmost area of the island was inhabited at least since 1 5 ka bp the human settlements in these latter areas occurred under environmental conditions similar to the present ones when the fuegian forest was definitively established

non chondritic magnesium and the origins of the inner terrestrial planets abstract high precision magnesium mg isotope data obtained using a large geometry high resolution mc icpms are reported for 9 carbonaceous and ordinary chondrites 9 eucrites and diogenites generally considered to originate from asteroid 4 vesta together with 4 martian meteorites and a variety of terrestrial and lunar materials the variation in mg isotopic composition found for mafic and ultramafic rocks mafic minerals and chondrites is smaller than reported previously the range of 26mg and 25mg of 0 6 and 0 3 defines a single mass dependent fractionation line consistent with a homogeneous mix of nucleosynthetic components data for the earth mars and vesta display no systematic mg isotopic differences despite large variations in the level of depletion in moderately volatile elements lunar mare basalts exhibit a significant range in 26mg 0 53 to 0 05 and 25mg 0 27 to 0 02 attributable to magmatic differentiation in the lunar magma ocean lmo lunar basalts derived from early segregated cumulates and thought to be the most primitive are on average slightly 0 17 26mg heavy relative to basalts from the earth mars and vesta however the difference is not well resolved more strikingly all differentiated planets and planetesimals as sampled have mg that is on average isotopically heavy compared with most chondrites analyzed thus far chondrules and cais also are generally heavy in terms of mg so this might reflect sorting of material in the proto planetary disk such an explanation would be similar to one previously proposed hewins r h and herzberg c t 1996 earth planet sci lett 144 1 7 to explain the non chondritic si mg of the earth in this model chondrule like objects separate from volatile rich planetary dust by accumulation in stagnant regions between eddies in the solar nebula small 1 km planetesimals formed by accumulation of such molten material then develop into planetary embryos and thence to larger terrestrial planets by combinations of runaway growth and collisions as such accumulation of molten chondrule like droplets provides an explanation that obviates some of the dynamic difficulties associated with the onset of planetary accretion the non chondritic mg isotopic composition of the earth is consistent with data for li and has important implications for earth s bulk composition and putative hidden reservoirs

climatic hydrologic oscillations since 155 000 yr b p at owens lake california reflected in abundance and stable isotope composition of sediment carbonate abstract sediment grain size carbonate content and stable isotopes in 70 cm long 1500 yr channel samples from owens lake core ol 92 record many oscillations representing climate change in the eastern sierra nevada region since 155 000 yr b p to first order the records match well the marine 18o record at owens lake however the last interglaciation appears to span the entire period from 120 000 to 50 000 yr b p according to our chronology and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate sediment proxies reveal that the apparent timing of glacial interglacial transitions notably the penultimate one is proxy dependent in the grain size and carbonate content records this transition is abrupt and occurs at 120 000 yr b p in contrast in the isotopic records the transition is gradual and occurs between 145 000 and 120 000 yr b p differences in timing of the transition are attributed to variable responses by proxies to climate change

a reassessment of the iron isotope composition of the moon and its implications for the accretion and differentiation of terrestrial planets abstract the fe isotope composition of planetary bodies may provide constraints on their accretion modes and or differentiation processes but to do so the fe isotope systematics of key planetary reservoirs needs to be determined to investigate this for the moon we measured the fe isotope compositions for a suite of 33 bulk lunar mare basalts and highland rocks combined with published data a compendium of 73 different lunar bulk rocks reveals a statistically significant fe isotope difference between low ti and high ti mare basalts yielding average 57fe 0 127 0 012 2se n 27 and 57fe 0 274 0 020 2 se n 25 respectively relative to the irmm 14 isotopic reference material as lunar basalts are thought to reflect the fe isotope composition of their respective mantle sources the estimated relative proportion of the low ti and high ti source mantle suggests that the lunar upper mantle 57fe value should be close to 0 142 0 026 whilst the composition of highland rocks ferroan anorthosites and mg suite rocks should provide a more global view of the moon the calculation of the mean 57fe value of 15 available highland rock analyses yields 57fe 0 078 0 124 such a value is not defined precisely enough to be of critical use for comparative planetology ferroan anorthosites and mg suite rocks also give unresolvable means it appears that fe isotope heterogeneity among the lunar highland rocks is caused by non representatively too small sample aliquots of coarse grained rocks it can also be the result of mixed lithologies for some when the kinetic effect of olivine tending towards low 57fe and feldspar with predominantly high 57fe is cancelled a more precise 57fe value of 0 094 0 035 is calculated it is indistinguishable from the mean 57fe of impact melts and is also similar to the upper lunar mantle estimate obtained from mare basalts collectively this newly determined fe isotope composition of the bulk moon is indistinguishable from that of the earth and heavier than those reported for other planetary bodies this planetary isotope relationship is only observed for silicon given the currently available mass dependent stable isotope database because both iron and silicon reside in the earth s metallic core in significant quantities this may point to the involvement of metallic cores of the earth and moon in the interplanetary fe and si isotope fractionation rather than via high pressure metal silicate fractionation at the core mantle boundary this would more likely be achieved by partial vaporization of the liquid outer metallic core in the aftermath of a moon forming giant impact

late quaternary climatic history of the chilean channels based on fossil pollen and beetle analyses with an analysis of the modern vegetation and pollen rain fossil beetles and pollen were examined from an intermorainal bog at puerto eden isla wellington chile latitude 49 08 s longitude 74 25 w wood from near the base of the section has an age of 12 960 150 yr bp occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia the assumption that the chilean channels were entirely ice covered is incorrect plants and insects that invaded the deglaciated terrain were those of an empetrum heathland in which patches of nothofagus forest were restricted to sheltered locations the climate supporting the heathland is inferred to have been windier and probably drier than that of the present day from 13 000 yr bp to 9500 yr bp nothofagus forest expanded possibly in response to less windiness and more available moisture neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr bp at the time of the younger dryas stade from 9500 to 5500 yr bp the climate was as wet as that of the present day based on an increased representation of the pollen of moorland plants and of aquatic beetle species from 5500 to 3000 yr bp the climate was drier as indicated by the expansion of empetrum heath and the reduction in mesic habitats from 3000 yr bp to the present day mesic habitats dominated as the climate returned to a wetter mode the alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of southern westerlies

late holocene glacier variations in the cordillera darwin tierra del fuego chile radiocarbon dates obtained on peat and macrofossils sampled both proximally and distally of a terminal moraine in the bahia pia area cordillera darwin tierra del fuego chile indicate that the glacier system reached maxima sometime before 3060 bp prior to 940 bp and between 940 bp and 675 bp the glacier retreated 4 km to a pinning point position where it dammed a lake before 2605 80 bp between 1950 75 and 1790 75 bp and some time shortly after 1790 75 bp by 250 bp the glacier system had receded more than 15 km towards the fjord head and probably reached close to its present position thus we obtained no evidence from bahia pia of any glacial advance occurring during the global little ice age maximum seventeenth to nineteenth centuries

multiproxy surface wetness records from replicate cores on an ombrotrophic mire implications for holocene palaeoclimate records ombrotrophic mires can provide records of palaeoclimate over the mid to late holocene in several areas of the world their potential is currently partly limited by difficulties with scaling indices based on plant macrofossils and humification and the need to account for the internal variability of the mire system this paper explores the use of testate amoebae analysis as a third technique and assesses the minimum within site variability by comparing results from two closely spaced cores reconstruction of surface wetness changes was carried out on cores from the centre of an intermediate raised blanket mire coom rigg moss northumberland by analysis of testate amoebae plant macrofossils and humification surface wetness changes were expressed as mean annual water table changes inferred from testate amoebae assemblages two separate indices based on plant macrofossils and percentage transmission of humification extracts comparisons between the proxies suggest good agreement of general trends in sphagnum peats but some differences in monocot and ericaceous peats the magnitude of surface wetness changes also differs within sphagnum peats the records from the separate cores converge over time and replicability between cores is best in the last 1000 yr changes over this period are similar to those shown by estimates based on documentary sources good agreement is obtained between a normalised plant macrofossil index and normalised reconstructed water table values and it is suggested that this approach could form the basis for improved composite multiproxy records from peatlands copyright 1999 john wiley sons ltd

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp

significance of iron isotope mineral fractionation in pallasites and iron meteorites for the core mantle differentiation of terrestrial planets abstract seven bulk chondrites with 57 fe 54 fe values between 0 1 and 0 relative to irmm 14 tend to be slightly lighter than 11 bulk iron meteorites which have 57 fe 54 fe values ranging from 0 04 to 0 2 at the mineral scale taenite from two iron meteorites cranbourne and toluca shows 57 fe 54 fe values heavier by up to 0 3 than their kamacite counterpart thus calling into question the significance of bulk iron meteorite data on three pallasites esquel marjalahti and springwater we measured a heavier iron isotope composition for the metal fractions compared to the coexisting olivines as previously observed on two other pallasites eagle station and imilac but the range of 57 fe 54 fe differences from 0 32 to 0 07 is larger than that originally found troilite from two pallasites appears to be even heavier than the metal fraction whereas schreibersite is lighter than its olivine counterpart there is thus a general tendency for minerals within a given rock to show a heavier fe isotope composition as the coordination number of fe increases although troilite is an exception to this rule iron meteorites are classically considered as remnants of asteroid cores and pallasites as core mantle interfaces the simultaneous finding that the metal fractions of pallasites have a higher 57 fe 54 fe signature than the coexisting olivines and that the iron meteorites are slightly heavier than chondrites could be taken as an indication that planetary core mantle differentiation is accompanied by sizeable iron isotope fractionation in this hypothesis mass balance constraints imply that resultant planetary mantles should be isotopically lighter than the chondritic starting material that is not observed however since all planetary mantles analyzed so far have 57 fe 54 fe values equivalent to or heavier than those of chondrites it thus appears that the moderate temperature and pressure metal silicate fractionation that occurred in pallasite and iron parent bodies is not readily transposable to planets as far as fe isotopes are concerned instead these mantle signatures could reflect equilibrium fractionation at a higher temperature or the lack of a global core mantle equilibration at the planetary scale overall these new results show that the mass dependent isotopic scatter observed among inner solar system bodies from the bulk rock to the planetary scale 0 3 57 fe 54 fe is more restricted than previously thought this likely confirms a homogenization process that occurred in the protoplanetary accretion disk between refractory inclusion condensation and chondrule formation

sulfur controlled iron isotope fractionation experiments of core formation in planetary bodies abstract a series of high pressure and temperature experiments were conducted to better constrain the fe isotope fractionation during core mantle differentiation in planetesimal and planetary bodies synthetic mixtures of oxides and metal having varying amounts of sulfur approximating terrestrial and martian compositions were melted at 1 2 gpa and 1650 c iron isotopic equilibrium between the resulting metal and glass run products was verified for all experiments using the three isotope technique purified fe from metal and glass was analyzed by multiple collector icp ms in high resolution mode iron alloy and silicate glass show a well resolved 57femetal silicate of 0 12 0 04 in a sulfur free system isotope fractionation increases with sulfur content to 0 43 0 03 at 18 wt sulfur in the metal these results cannot be easily interpreted within the context of known fe isotope ratios in most natural samples of planetary and asteroidal mantles and therefore suggest more complex processes affected the fe isotope fractionation therein however to reconcile martian meteorite iron isotopic signatures with geophysical models using this new experimental data requires a smaller amount of sulfur in the martian core than previous estimates with an upper limit of 8 wt