comparison between active sensor and radiosonde cloud boundaries over the arm southern great plains site 1 in order to test the strengths and limitations of cloud boundary retrievals from radiosonde profiles 4 years of radar lidar and ceilometer data collected at the atmospheric radiation measurements southern great plains site from november 1996 through october 2000 are used to assess the retrievals of wang and rossow 1995 and chernykh and eskridge 1996 the lidar and ceilometer data yield lowest level cloud base heights that are on average within approximately 125 m of each other when both systems detect a cloud these quantities are used to assess the accuracy of coincident cloud base heights obtained from radar and the two radiosonde based methods applied to 200 m resolution profiles obtained at the same site the lidar ceilometer and radar cloud base heights agree by 0 156 0 423 km for 85 27 of the observations while the agreement between the lidar ceilometer and radiosonde derived heights is at best 0 044 0 559 km for 74 60 of all cases agreement between radar and radiosonde derived cloud boundaries is better for cloud base height than for cloud top height being at best 0 018 0 641 km for 70 91 of the cloud base heights and 0 348 0 729 km for 68 27 of the cloud top heights the disagreements between radar and radiosonde derived boundaries are mainly caused by broken cloud situations when it is difficult to verify that drifting radiosondes and fixed active sensors are observing the same clouds in the case of the radar the presence of clutter e g vegetal particles or insects can affect the measurements from the surface up to approximately 3 5 km preventing comparisons with radiosonde derived boundaries overall wang and rossow 1995 tend to classify moist layers that are not clouds as clouds and both radiosonde techniques report high cloud top heights that are higher than the corresponding heights from radar

cloud vertical structure and its variations from a 20 yr global rawinsonde dataset abstract a global cloud vertical structure cvs climatic dataset is created by applying an analysis method to a 20 yr collection of twice daily rawinsonde humidity profiles to estimate the height of cloud layers the cvs dataset gives the vertical distribution of cloud layers for single and multilayered clouds as well as the top and base heights and layer thicknesses of each layer together with the original rawinsonde profiles of temperature humidity and winds the average values are cloud top height 4 0 km above mean sea level msl cloud base height 2 4 km msl cloud layer thickness 1 6 km and separation distance between consecutive layers 2 2 km multilayered clouds occur 42 of the time and are predominately two layered the lowest layer of multilayered cloud systems is usually located in the atmospheric boundary layer below 2 km height msl clouds over the ocean occur more frequently at lower levels and are more often formed in multiple layers than over land latitudinal variations o

rayleigh fractionation of iron isotopes during pedogenesis along a climate sequence of hawaiian basalt abstract we measured iron isotopic composition of surface 10 20 cm and subsurface 50 70 cm basaltic soil horizons from the island of maui along a climate gradient mcg ranging from 2 2 to 4 2 m mean annual precipitation map all soil forming factors except climate were conserved the mcg has a documented decrease in fe with increasing rainfall that is highly correlated with decreasing mean annual eh values we found that increasing map from 2 8 to 4 2 m resulted in a surface plus subsurface average increase of 0 56 0 09 56fe with the subsurface consistently 0 33 0 06 56fe greater than the surface horizons based on loss of fe relative to nb rayleigh fractionation was observed with 103ln lost retained values of 0 37 0 03 and 0 34 0 04 for the surface and subsurface respectively equivalent 103ln lost retained values for the surface and subsurface soils suggests fe loss is driven by similar mechanisms throughout the soil profile our calculated fractionation factor is about 1 3 the magnitude of laboratory determined fractionation factors for fe reduction suggesting other processes organic complexation fe re precipitation modulate the net fe loss along the mcg these results offer field scale confirmation of laboratory experiments on model systems that show anoxic weathering reactions produce materials enriched in heavy fe isotopes

iron isotope constraints on fe cycling and mass balance in oxygenated earth oceans the fe isotope composition of proterozoic to modern clastic sedimentary rocks and aerosols defines a range ind 56 fe values that is only slightly more variable than the range of fe isotope com positions measured in terrestrial igneous rocks indicating that chemical weathering sedimentary transport and diagenesis play only a minor role in producing fe isotope variations in environ ments where fe redox conditions have been controlled by current levels of atmospheric oxygen in contrast the fe isotope composi tions of hot fluids 300 8c from mid ocean ridge mor spread ing centers define a narrow range that is shifted to lower d 56 fe values by 0 2 0 5 as compared to igneous rocks these new data allow a conceptual model for the fe isotope composition of the oxic oceans that predicts large ranges in fe isotope composition under conditions of changing aerosol and mor fe fluxes such as during periods of major worldwide glaciation

copper isotopic zonation in the northparkes porphyry cu au deposit se australia abstract significant systematic cu isotopic variations have been found in the northparkes porphyry cu au deposit nsw australia which is an orthomagmatic porphyry cu deposit copper isotope ratios have been measured in sulfide minerals chalcopyrite and bornite by both solution and laser ablation multi collector inductively coupled plasma mass spectrometry mc icp ms the results from both methods show a variation in 65cu of hypogene sulfide minerals of greater than 1 relative to nist976 significantly the results from four drill holes through two separate ore bodies show strikingly similar patterns of cu isotope variation the patterns are characterized by a sharp down hole decrease from up to 0 8 0 29 0 56 1 n 20 in the low grade peripheral alteration zones phyllic propylitic alteration zone to a low of 0 4 0 25 0 36 1 n 30 at the margins of the most mineralized zones cu grade 1 wt in the high grade cores of the systems the compositions are more consistent at around 0 2 0 19 0 14 1 n 40 the cu isotopic zonation may be explained by isotope fractionation of cu between vapor solution and sulfides at high temperature during boiling and sulfide precipitation processes sulfur isotopes also show an isotopically light shell at the margins of the high grade ore zones but these are displaced from the low 65cu shells such that there is no correlation between the cu and s isotope signatures fe isotope data do not show any discernable variation along the drill core this work demonstrates that cu isotopes show a large response to high temperature porphyry mineralizing processes and that they may act as a vector to buried mineralization

the copper isotope geochemistry of rivers and the oceans abstract we present the first extensive dataset for copper cu isotopes in rivers as well as preliminary data for estuaries and seawater rivers exhibit a range in dissolved 65 cu relative to nist srm 976 of 0 02 to 1 45 per mil the discharge weighted average dissolved 65 cu and cu concentration for the studied rivers representing around 25 of the global riverine water discharge are 0 68 and 18 8 nmol kg 1 respectively isotopic data for the dissolved phase in two small estuaries in se england exhibit relatively minor variation through the salinity gradient 0 42 to 0 94 and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths analyses of the particulate phase in the estuaries reveal a complementary light pool 0 24 to 1 02 the isotopic composition of the total cu inventory is however close to that of the crustal source these data along with published constraints suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by cu bound to strong organic complexes open ocean seawater samples generally exhibit even heavier dissolved cu isotopic compositions than the riverine input 65 cu 0 9 to 1 5 the heavy isotopic composition of seawater is inferred to originate from intra oceanic processes the small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom perhaps reflecting the relative importance of scavenging and thus the sequestration of light cu to particulate material at different depths

copper and iron isotope fractionation during weathering and pedogenesis insights from saprolite profiles abstract iron and copper isotopes are useful tools to track redox transformation and biogeochemical cycling in natural environment to study the relationships of stable fe and cu isotopic variations with redox regime and biological processes during weathering and pedogenesis we carried out fe and cu isotope analyses for two sets of basalt weathering profiles south carolina usa and hainan island china which formed under different climatic conditions subtropical vs tropical unaltered parent rocks from both profiles have uniform 56 fe and 65 cu values close to the average of global basalts in the south carolina profile 56 fe values of saprolites vary from 0 01 to 0 92 in the lower reduced part and positively correlate with fe 3 fe r 2 0 90 whereas 65 cu values are almost constant by contrast 56 fe values are less variable and negatively correlate with fe 3 fe r 2 0 88 in the upper oxidized part where large 4 85 65 cu variation is observed with most samples enriched in heavy isotopes in the hainan profile formed by extreme weathering under oxidized condition 56 fe values vary little 0 05 0 14 whereas 65 cu values successively decrease from 0 32 to 0 12 with depth below 3 m and increase from 0 17 to 0 02 with depth above 3 m throughout the whole profile 65 cu positively correlate with cu concentration and negatively correlate with the content of total organic carbon toc overall the contrasting fe isotopic patterns under different redox conditions suggest redox states play the key controls on fe mobility and isotope fractionation the negative correlation between 56 fe and fe 3 fe in the oxidized part of the south carolina profile may reflect addition of isotopically light fe this is demonstrated by leaching experiments which show that fe mineral pools extracted by 0 5 n hcl representing poorly crystalline fe hydr oxides are enriched in light fe isotopes the systematic cu isotopic variation in the hainan profile reflects desorption and downward transport of isotopically heavy cu leaving the organically bound cu enriched in light isotope as supported by the negative correlation of 65 cu with toc r 2 0 88 the contrasting mostly positive vs negative cu isotopic signatures in the upper parts of these two profiles can be attributed to the different climatic conditions e g high rainfall at a tropical climate in hainan favors desorption and the development of organism whereas relatively dry climate in south carolina favors cu re precipitation from soil solutions and adsorption onto fe hydr oxides our results highlight the potential applications of fe and cu isotopes as great tracers of redox condition ancient climate and biological cycling during chemical weathering and pedogenic translocation

routine isotopic analysis of iron by hr mc icpms how precise and how accurate abstract high temperature isotopic variations documented in natural materials span a narrow range and call for precise and accurate isotopic analyses precisions better than 0 03 95 confidence interval for 56 fe have been obtained by high resolution multi collector inductively coupled plasma mass spectrometry hr mc icpms whether these uncertainties encompass all sources of error has not been carefully evaluated the current study examines all parameters that can affect accuracy and precision of fe isotopic measurements by hr mc icpms it is demonstrated that accurate 56 fe measurements can be routinely achieved within the quoted uncertainties

fe cycling in the shale hills critical zone observatory pennsylvania an analysis of biogeochemical weathering and fe isotope fractionation abstract during weathering fe in primary minerals is solubilized by ligands and or reduced by bacteria and released into soil porewaters such fe is then removed or reprecipitated in soils to understand these processes we analyzed fe chemistry and isotopic composition in regolith of the shale hills watershed a critical zone observatory in central pennsylvania overlying iron rich shale of the rose hill formation elemental concentrations were measured in soil from a well drained catena on a planar hillslope on the south side of the catchment based upon x ray diffraction and bulk elemental data loss of fe commences as clay begins to weather 15 cm below the depth of auger refusal more fe iii was present than fe ii in all soil samples from the ridge top to the valley floor both total and ferrous iron are depleted from the land surface of catena soils relative to the bedrock loss of ferrous fe is attributed mostly to abiotic or biotic oxidation loss of fe is most likely due to transport of micron sized particles that are not sampled by porous cup lysimeters but which are sampled in stream and ground waters the isotopic compositions 56 fe relative to irmm 014 of bulk fe and 0 5 n hcl extracted fe operationally designed to remove amorphous fe oxyhydr oxides range between 0 3 and 0 3 with 56 fe bulk extractable values between 0 2 and 0 4 throughout the soils along the catena 56 fe signatures of both bulk fe and hcl extracted fe become isotopically lighter as the extent of weathering proceeds the isotopic trends are attributed to one of two proposed mechanisms one mechanism involves fe fractionation during mobilization of fe from the parent material due to either fe reduction or ligand promoted dissolution the other mechanism involves fractionation during immobilization of fe oxyhydr oxides if the latter mechanism is true then shale which comprises one quarter of continental rocks could be an important source of isotopically heavy fe for rivers

variations of sr nd hf isotopic systematics in basalt during intensive weathering abstract the sr nd hf isotopic compositions of both saprolites and parent rocks of a profile of intensively weathered neogene basalt in hainan south china are reported in this paper to investigate changes of isotopic systematics with high masses the results indicate that all these isotopic systematics show significant changes in saprolites compared to those in corresponding parent rocks the 87 sr 86 sr system was more seriously affected by weathering processes than other isotope systems with e sr drifts 30 to 70 away from those of the parent rocks in the upper profile 2 2 m the sr isotopes of the saprolites show an upward increasing trend with e sr changing from 50 at 2 2 m to 70 at 0 5 m accompanying a upward increasing of sr concentrations from 10 g g to 25 g g as nearly all the sr of the parent rock has been removed during intensive weathering in this profile the upward increasing of sr concentrations in the upper profile suggests import of extraneous sr rainwater in this region which enriches in sr up to 139 g l from seawater may be the important extraneous source thus the sr isotopes of the saprolites in the upper profile may be mainly influenced by import of extraneous materials and the sr isotopic characteristics may not be retained in contrast the e nd and e hf of the saprolites drift only 0 2 6 and 0 3 7 away from the parent rocks respectively the negative drifts of the e nd and e hf are coupled with nd and hf losses in the saprolites i e larger proportions of nd and hf loss correspond to lower e nd and e hf compared with the relative high nd and hf concentrations of the saprolites the contributions of extraneous nd and hf both from wet and dry deposits of aeolian input are negligible thus the e nd and e hf changes in the profile are mainly resulted from consecutive removal of the nd and hf calculation indicates that the 143 nd 144 nd and 176 hf 177 hf ratios in saprolites are all significantly lower than their initial values in the parent rock simply removing part of the nd and hf by incongruent decomposing some of the minerals may not account for this fractionation should be happen which 143 nd and 176 hf may be preferentially removed from the profile relative to 144 nd and 177 hf during intensive chemical weathering resulting in lower 143 nd 144 nd and 176 hf 177 hf ratios in saprolites relative to the parent rock even though details for this process is not known a positive correlation is observed between the e nd and e hf of the saprolites interestingly the saprolites with a net loss of nd and hf in the upper profile show good positive correlation and the regression line parallels the terrestrial array by contrast saprolites with a net gain of nd and hf in the lower profile generally show higher e hf values at a given e nd value and the regression line between these e nd and e hf appears to parallel the seawater array this supports the hypothesis that the contribution of continental hf from chemical weathering release is the key to the obliquity of the seawater array away from the terrestrial array of the global e nd and e hf correlation our results also indicate that caution is needed when using e sr e nd and e hf to trace provenances for sediments and soils

experimental determination of fe isotope fractionation between aqueous fe ii siderite and green rust in abiotic systems abstract iron isotope fractionation between aqueous iron and siderite has been measured using abiotic synthesis experiments at 20 c applying a rayleigh distillation model to three experiments in which siderite feco3 was continuously precipitated from solutions over the course of tens of hours the derived fractionation factor is 103ln fe ii siderite 0 48 0 22 2 this experimentally determined fractionation factor is significantly smaller by 1 5 than that calculated from vibrational frequencies and mossbauer shifts geochim cosmochim acta 64 2000 849 865 geochim cosmochim acta 65 2001 2487 2497 and lies on the high end of that inferred from natural mineral assemblages where the fe ii aq siderite fractionation factor was inferred to lie between 1 7 and 0 3 contrib mineral petrol 144 2003 523 547 the measured fe ii aq siderite fractionation from this study suggests that siderite from archean and proterozoic rocks which have moderately negative 56fe values 1 5 to 0 5 may reflect precipitation from fe ii aq whose origin was hydrothermal in contrast natural siderites that have higher 56fe values apparently require non hydrothermal sources of fe and or different pathways of formation or may reflect the effects of cation substitution on the fe ii aq carbonate fractionation factor

iron stable isotopes beyond biosignatures abstract the stable isotope geochemistry of fe has attracted intense interest in the past five years this interest was originally motivated by the possible use of fe isotopes in biosignature applications particularly in sediments from the ancient earth or mars this application is still being developed with particular attention to fractionation mechanisms understanding such mechanisms should also provide new insights into the environmental biogeochemistry of fe at the same time the fe isotope system holds promise for other exciting frontiers including applications in oceanography solid earth geochemistry and biomedicine such applications will be increasingly attractive as fe isotope analysis becomes routine

cloud layer thicknesses from a combination of surface and upper air observations abstract cloud layer thicknesses are derived from base and top altitudes by combining 14 years 1975 1988 of surface and upper air observations at 63 sites in the northern hemisphere rawinsonde observations are employed to determine the locations of cloud layer top and base by testing for dewpoint temperature depressions below some threshold value surface observations serve as quality cheeks on the rawinsonde determined cloud properties and provide cloud amount and cloud type information the dataset provides layer cloud amount cloud type high middle or low height classes cloud top heights base heights and layer thicknesses covering a range of latitudes from 0 to 80 n all data comes from land sites 34 are located in continental interiors 14 are near coasts and 15 are on islands the uncertainties in the derived cloud properties are discussed for clouds classified by low mid and high top altitudes there are strong latitudinal and seasonal variations in the layer thickness only for high

iron speciation and isotope fractionation during silicate weathering and soil formation in an alpine glacier forefield chronosequence abstract the chemical weathering of primary fe bearing minerals such as biotite and chlorite is a key step of soil formation and an important nutrient source for the establishment of plant and microbial life the understanding of the relevant processes and the associated fe isotope fractionation is therefore of major importance for the further development of stable fe isotopes as a tracer of the biogeochemical fe cycle in terrestrial environments we investigated the fe mineral transformations and associated fe isotope fractionation in a soil chronosequence of the swiss alps covering 150 years of soil formation on granite for this purpose we combined for the first time stable fe isotope analyses with synchrotron based fe exafs spectroscopy which allowed us to interpret changes in fe isotopic composition of bulk soils size fractions and chemically separated fe pools over time in terms of weathering processes bulk soils and rocks exhibited constant isotopic compositions along the chronosequence whereas soil fe pools in grain size fractions spanned a range of 0 4 in 56 fe the clay fractions 56 fe for all soils the lightest isotopic composition was observed in a 1 m nh 2 oh hcl 25 acetic acid extract targeting poorly crystalline fe iii hydr oxides compared with easily leachable fe in primary phyllosilicates 0 5 m hcl extract and fe in residual silicates the combination of the fe isotope measurements with the speciation data obtained by fe exafs spectroscopy permitted to quantitatively relate the different isotope pools forming in the soils to the mineral weathering reactions which have taken place at the field site a kinetic isotope effect during the fe detachment from the phyllosilicates was identified as the dominant fractionation mechanism in young weathering environments controlling not only the light isotope signature of secondary fe iii hydr oxides but also significantly contributing to the isotope signature of plants the present study further revealed that this kinetic fractionation effect can persist over considerable reaction advance during chemical weathering in field systems and is not only an initial transient phenomenon

fe isotope variations in the modern and ancient earth and other planetary bodies iron the fourth most abundant element in the earth s crust has four naturally occurring stable isotopes 54fe 5 84 56fe 91 76 57fe 2 12 and 58fe 0 28 and the natural mass dependent isotope variations of fe in the rock record span a range of 4 per mil in 56fe 54fe ratios fig 1 the field of fe isotope geochemistry is relatively new but has received considerable attention because it may allow us to gain a better understanding of how fe is cycled in different environments iron typically occurs as either reduced ferrous fe in oxygen poor environments or as oxidized ferric iron in oxygen rich environments notably only the reduced species is soluble in oxygenated aqueous solutions unless the ph is low in the archean and early proterozoic the earth may have been relatively oxygen poor e g kasting et al 1979 grandstaff 1980 holland 1994 suggesting that there may have been significant quantities of fe 0 9 millimolar dissolved in the oceans as fe ii aq e g ewers 1983 sumner 1997 the extensive iron formations of archean to early proterozoic age may have been deposited from such fe ii rich oceans e g beukes and klein 1992 in the modern oxic oceans however fe contents are exceedingly low 1 nanomolar in the open oceans e g martin and gordon 1988 bruland et al 1991 martin 1992 johnson et al 1997 and it is now recognized that marine productivity is fe limited in parts of the open oceans e g martin and fitzwater 1988 martin et al 1989 1994 the differences in the behavior of fe with redox state and the significant isotope fractionations 1 or more in 56fe 54fe that are associated with redox conditions suggests that fe isotope studies will be extremely useful for tracing

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

fractionation of cu fe and zn isotopes during the oxidative weathering of sulfide rich rocks abstract we measured the fe cu and zn isotopic compositions of the fluids generated during leaching experiments with pyrite chalcopyrite and sphalerite rich rocks and with a sphalerite mineral separate our study demonstrates that the oxidative weathering of sulfide rich rocks can produce substantial variations in fe 1 75 to 1 0 56 fe solution pyrite rock and cu 0 0 to 2 0 65 cu solution chalcopyrite rock isotopes and small variations in zn isotopes 0 0 to 0 2 66 zn solution sphalerite in the fluid phase relative to the rock for the fe and cu systems we suggest that isotopic fractionation is caused by electron exchange driven e g fe ii fe iii and cu i cu ii redox reactions at the surfaces of the sulfide minerals that occur during air and aqueous chemical reactions under acidic conditions these reactions tend to enrich the fluid phase in the heavier fe and cu isotopes however under circumneutral ph conditions the fe isotopic composition in solution was controlled by the precipitation of fe iii oxide phases which enriched the solution in the lighter fe isotopes this investigation provides a preliminary framework for interpreting the impact of sulfide oxidation reactions on the distributions of stable fe cu and zn isotopes in natural waters

biogeochemical cycling of iron in the archean paleoproterozoic earth constraints from iron isotope variations in sedimentary rocks from the kaapvaal and pilbara cratons abstract iron isotope compositions of low metamorphic grade samples of archean paleoproterozoic sedimentary rocks obtained from fresh drill core from the kaapvaal craton in south africa and from the pilbara craton in australia vary by 3 in 56 fe 54 fe ratios reflecting a variety of weathering and diagenetic processes depositional ages for the 120 samples studied range from 3 3 to 2 2 ga and fe c and s contents define several compositional groups including samples rich in fe organic carbon carbonate and sulfide the 56 fe values for low c org low c carb and low s sedimentary rocks are close to 0 the average of igneous rocks this range is essentially the same as that of c org poor late cenozoic loess aerosol river loads and marine sediments and those of c org poor phanerozoic proterozoic shales that these 56 fe values are the same as those of igneous rocks suggests that fe has behaved conservatively in bulk sediments during sedimentary transport diagenesis and lithification since the archean these observations indicate that if atmospheric o 2 contents rose dramatically between 2 4 and 2 2 ga as proposed by many workers such a rise did not produce a significant change in the bulk fe budget of the terrestrial sedimentary system if the archean atmosphere was anoxic and fe was lost from bedrock during soil formation any isotopic fractionation between aqueous ferrous fe fe aq 2 and fe bearing minerals must have been negligible in contrast if the archean atmosphere was oxic fe would have been retained as fe 3 hydroxides during weathering as it is today which would produce minimal net isotopic fractionation in bulk detrital sediments siderite rich samples have 56 fe values of 0 5 0 5 and experimentally determined fe aq 2 siderite fractionation factors suggest that these rocks formed from fe aq 2 that had similar or slightly higher 56 fe values the 56 fe values calculated for fe aq 2 overlaps those of modern submarine hydrothermal fluids but it is also possible that fe aq 2 had 56 fe values higher than those of modern hydrothermal fluids depending upon the fe aq 2 fe carbonate fractionation factor that is used in contrast c org rich samples and magnetite rich samples have strongly negative 56 fe values generally between 2 3 and 1 0 and available fluid mineral fractionation factors suggest that the fe bearing minerals siderite and magnetite in these rocks formed in the presence of fe aq 2 that had very low 56 fe values between 3 and 1 reduction of fe 3 hydroxide by sulfide precipitation of sulfide minerals or incongruent dissolution of silicate minerals are considered unlikely means to produce significant quantities of low 56 fe fe aq 2 we interpret microbial dissimilatory fe 3 reduction dir as the best explanation for producing such low 56 fe values for fe aq 2 and our results suggest that dir was a significant form of respiration since at least 2 9 ga

the cu isotopic signature of granites from the lachlan fold belt se australia abstract this contribution reports our preliminary work to determine cu isotope ratios for various granite rocks and examine the cu isotope systematics within granite suites a chemical procedure modified from marechal marechal c n telouk p and albarede f 1999 precise analysis of copper and zinc isotopic compositions by plasma source mass spectrometry chemical geology 156 1 4 251 273 was used to separate cu from rock matrix quantitative recovery 100 6 1 6 with a low total procedural blank 2 65 0 66 ng for cu has been achieved allowing cu isotopic measurements on samples with as little as 10 ppm cu the cu isotope ratios 65cu relative to nist srm 976 of 32 rock samples ranging from mafic to felsic compositions from 3 batholiths 2 i type 1 s type from the lachlan fold belt in southeastern australia vary from 0 46 to 1 51 most of them cluster around zero with mean values for the i type and s type granites of 0 03 0 15 and 0 03 0 42 2 sigma respectively these data together with cu isotope ratios of two loess samples provide preliminary evidence that the baseline cu isotopic composition of the crystalline part of upper continental crust is close to zero the tight clustering of cu isotope ratios of rocks from the i type suites suggests that high temperature magmatic processes do not produce significant cu isotope fractionation however two granites with abnormally heavy cu isotope signatures up to 1 51 appears to be the result of localized hydrothermal alteration measurable variation in cu isotopic composition of the s type granite may reflect isotopic heterogeneity in the sedimentary source region as a result of redox processes or may be due to hydrothermal overprinting thus cu isotope geochemistry may be a useful tracer for studying hydrothermal alteration and source heterogeneity of granitic rocks

explicit simulation of cumulus ensembles with the gate phase iii data budgets of a composite easterly wave the mass heat and moisture budgets of a composite easterly wave over the eastern tropical atlantic are analysed from simulations of a convection resolving model crm the large scale data from the garp global atmospheric research program atlantic tropical experiment gate phase iii are used to drive the crm simulations the simulated composite easterly wave is reasonably comparable with the observed except for the lack of shallow convection embedded in the simulated easterly waves the mesoscale stratiform precipitation processes are found to be an inseparable component of cumulus convection embedded in the easterly waves their main differences from convective processes are twofold 1 the distinct vertical structures of the budget components due to mesoscale updraughts and downdraughts and 2 the phase lags relative to the convective processes in the temporal evolution of the easterly waves thus theoretical studies should include both convective and mesoscale stratiform precipitation processes in order to further understanding of diabatic processes in the dynamics of the easterly waves and possibly other waves in the tropics in addition the budget analysis presented in this study also provides some details for improving parametrizations of cumulus convection

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

limited iron isotope variations in recent lateritic soils from nsimi cameroon implications for the global fe geochemical cycle laterites are oxidized fe rich soils covering one third of the continents and are drained by half of the continental waters they therefore represent a key component of the iron geochemical cycle at the earth s surface yet no iron isotope study has been conducted on recent laterites so far building on previous integrated morpho pedological studies of soils located in an equatorial rainforest southern cameroon we have undertaken a mineralogical elemental and isotopic study of iron in two lateritic profiles one is a borehole 3620 cm deep going to the parent granodioritic rock located at the top of a hill whereas the other is 675 cm deep and is located downhill mossbauer spectroscopy reveals that typically geq 96 of the soil s iron is held in nanocrystalline hematite and goethite iron isotope measurements performed by plasma source mass spectrometry show that fe isotopic equilibrium was rarely reached between these iron oxide and hydroxide despite their small size overall it is found that most samples display iron isotope signatures very close to the mean crustal value with a maximum range of 0 2 in delta 57 fe given that lateritic soils evolve over millions of years show large variations in fe concentrations and mineralogical abundances this range is surprisingly small when compared to other fe isotope studies of soils from different climatological contexts that can easily show delta 57 f e ranges in excess of 1 at the bulk sample scale the most likely explanation of this finding is that despite notable vertical and lateral fe mobility in the studied laterites from cameroon as computed using the open system mass fraction transport function tau fe w iron remained mostly in the oxidized form as shown by mossbauer pectroscopy this probably results from the strong bioturbation and pedoturbation of these lateritic soils that lead them to remain porous over a large thickness and facilitated the flow of oxygenated waters from the surface down to the saprolite horizon this study therefore reveals that soils that remained as an open system for iron do not necessarily show large fe isotopic variations it is suggested that the fe drained from such lateritic soils should have delta 57 fe values within sim 0 1 of that of the continental crust this is in contrast with previous soil studies notably from sites located at higher latitudes that imply that these soils should release isotopically more variable fe to surface waters such possible contrasted isotopic signatures from different surface waters will likely lead to an isotopically heterogeneous ocean given the short residence time of fe in seawater

analysis of progressive deformation of the edmonton convention centre excavation a finite element analysis was performed of the deformations observed during the excavation of the edmonton convention centre local geology in the edmonton area consists of layers of shale with weak bentonite seams overlain by glacial deposits the presence of the bentonite seams which possess strain softening characteristics controls the stability of the excavation which is located in a valley wall to simulate the influence of the bentonite seams a strain softening finite element model is used to estimate the amount of deformation in the foundation of the excavation field measurements indicated that localized progressive straining had occurred during the excavation process and substantial heave of the foundation floor was observed the finite element results show progressive deformation of the excavation and propagation of shear zones good agreement between the finite element results and the field observations is obtained key words progressive failure strain softening finite element analysis

iron isotopes in the seawater of the equatorial pacific ocean new constraints for the oceanic iron cycle abstract this study presents the isotopic compositions and concentrations of dissolved and particulate iron from two seawater profiles of the western and central equatorial pacific ocean sampled during the eucfe cruise most of the 56 fe values are positive relative to irmm 14 from 0 01 to 0 58 in the dissolved fraction dfe and from 0 02 to 0 46 in the particulate fraction pfe the mean measurement uncertainty of 0 08 2sd allows the observation of significant variations most of the isotope variations occur in the vertical and not in the horizontal direction implying that each isotope signature is preserved over long distances within a water mass the thermocline waters of the papua new guinea png area mostly influenced by sedimentary inputs display a mean 56 dfe value of 0 37 0 15 2sd this isotopic signature suggests that the process releasing dissolved iron into the seawater in this area is a non reductive dissolution of sediments discharged by local rivers and likely re suspended by strong boundary currents rather than dissimilatory iron reduction dir within the sediment characterized by negative 56 dfe these positive 56 dfe values seem to be the result of a mean isotopic fractionation of 56 fe dfe pfe 0 20 0 11 2sd produced by the non reductive dissolution at 0 n 180 e the fe isotope signature of the equatorial undercurrent euc waters is identical to that of the png station within the range of the uncertainty this suggests that the dissolved iron feeding the euc and ultimately the eastern pacific high nutrient low chlorophyll area is of png origin likely released by a non reductive dissolution of terrigenous sediments significant fe removals are observed within the thermocline and the intermediate waters between the png and the open ocean stations the corresponding isotopic fractionations appear to be small with 56 fe removed sw fe values of 0 30 0 31 to 0 18 0 12 2sd for dfe removal and of 0 10 0 04 to 0 05 0 31 2sd for pfe removal in the chlorophyll maximum of the open ocean station the isotopic fractionation associated with biological uptake is estimated at 56 fe phyto dfe 0 25 0 10 to 0 13 0 11 2sd although these fractionations are based on a limited dataset and need to be further constrained they appear to be small and to limit the transformations of the iron source signatures within the ocean

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

the structure water budget and radiational features of a high latitude warm front abstract on 30 september 1994 an arctic low pressure system passed over the southern beaufort sea area of northern canada and research aircraft observations were made within and around the warm front of the storm this study is unique in that the warm front contained subzero centigrade temperatures across the entire frontal region the overall structure of the warm front and surrounding region was similar to midlatitude storms however the precipitation rates liquid water content magnitudes horizontal and vertical winds vertical wind shear turbulence and thermal advection were very weak in addition a low level jet and cloud bands were aligned parallel to the warm front near neutral stability occurred within and around the front and conditional symmetric instability was likely occurring a steep frontal region resulted from strong coriolis influences that in turn limited the amount of cloud and precipitation ahead of the system the precipitation efficiency of the storm was high 60 but is beli

adsorption and desorption controlled magnesium isotope fractionation during extreme weathering of basalt in hainan island china magnesium isotopic compositions of a set of clay rich saprolites developed on the neogene tholeiitic basalt from hainan island in southern china have been measured in order to document the behavior of mg isotopes during continental weathering compared with unaltered basalts 26mg 0 36 the overlying saprolites are strongly depleted in mg i e th mg 99 1 to 92 9 and display highly variable 26mg ranging from 0 49 to 0 40 magnesium concentration and 26mg value of the saprolites display a general increasing trend upwards in the lower part of the profile but a decreasing trend towards the surface in the upper part the variations of mg concentration and isotopic composition in this weathering profile can be explained through adsorption and desorption processes 1 adsorption of mg to kaolin minerals kaolinite and halloysite with preferential uptake of heavy mg isotopes onto kaolin minerals and 2 desorption of mg through cation exchange of mg with the relatively lower hydration energy cations in the upper profile evidence for adsorption is supported by the positive correlation between 26mg and the modal abundance of kaolin minerals in saprolite of the lower profile while negative correlations between 26mg and concentrations of lower hydration energy cations e g sr and cs in the upper profile support the desorption process our results highlight that adsorption and desorption of mg on clay minerals play an important role in behavior of mg isotopes during extreme weathering which may help to explain the large variation in mg isotopic composition of river waters

the major ion δ44 40ca δ44 42ca and δ26 24mg geochemistry of granite weathering at ph 1 and t 25 c power law processes and the relative reactivity of minerals abstract we dissolved boulder creek granodiorite in a plug flow reactor for 5794 h at ph 1 and t 25 c the primary purpose of the experiment was to identify controls on dissolved 44 40ca 44 42ca and 26 24mg values during granite weathering herein we also examine the origin of ca and mg isotopic variability among minerals composing the boulder creek granodiorite and we constrain fundamental characteristics of granite weathering important for quantifying the elemental and isotopic geochemistry of the reactor output nine ca bearing minerals display an 8 80 range of 44 40ca values and a 0 51 range of 44 42ca values three mg bearing minerals display a 1 53 range of 26 24mg values these ranges expressed at the mineralogical scale are higher than the ranges thus far reported for bulk igneous rocks most of the 44 40ca variability reflects 40ca enrichment in k feldspar and to a lesser extent biotite due to the radioactive decay of 40k over the 1 7 ga age of the rock whereas the entire range of 44 42ca values reflects mass dependent isotope fractionation during igneous differentiation and crystallization the range of 26 24mg values may represent either fractionation during the chloritization of biotite or interaction of the boulder creek granodiorite with mg rich metamorphic fluids having low 26 24mg values the elemental and isotopic composition of the reactor output varied substantially during the experiment we synthesize the mineralogical and fluid data using coupled mass conservation equations solved at non steady state model calculations reveal an intricate balance between increasing specific surface area and decreasing mineral concentrations while surface area normalized dissolution rate constants were time invariant specific surface area increased as a power law function of time through positive feedbacks between mechanical disaggregation chemical dissolution and mineral depletion variations in dissolved 44 40ca 44 42ca and 26 24mg values reflect conservative mixing rather than fractionation apatite and calcite initially control 44 40ca and 44 42ca values followed by biotite titanite epidote hornblende and plagioclase the release of radiogenic 40ca clearly defines the period where biotite dissolution dominates the brucite layer of chlorite initially controls 26 24mg values followed by biotite the tot layer of chlorite and hornblende through direct isotopic tracking these results demonstrate that trace minerals such as apatite and calcite in the case of ca and brucite in the case of mg dominate elemental release during the incipient stages of granite weathering the results further show that biotite dissolution dominates the middle stages of granite weathering and that plagioclase dissolution only becomes important during relatively late stages the ca and mg isotope variations associated with these stages are distinct and potentially resolvable in soil mineral weathering studies

iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids abstract transport of iron fe within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex polyminerallic rocks understanding the isotope fractionation mechanisms during this process is key for any application of the fe isotope system to biogeochemical studies here we reacted biotite granite and tholeiite basalt with 0 5 m hydrochloric acid and 5 mm oxalic acid solutions at ambient temperature solution aliquots were recovered over a seven day period and analysed for major and trace element concentrations and fe isotopic compositions in all experiments fe initially released into solution was isotopically lighter with 56fesolution rock as low as 1 80 in the granite hydrochloric acid system the oxalic acid experiments showed similar patterns but smaller fractionation in all experiments the 56fesolution rock reduced over time which would be in line with the formation of a leached layer as proposed before brantley s l liermann l j guynn r l anbar a icopini g a and barling j 2004 fe isotopic fractionation during mineral dissolution with and without bacteria geochim cosmochim acta 68 15 3189 3204 granite and basalts reacting with hydrochloric acid reached apparent steady state values of 0 60 0 15 and 0 40 0 20 respectively whilst experimental values with oxalic acid were 1 0 0 15 and 0 50 0 15 during the granite experiments alteration of biotite to chlorite followed by dissolution of chlorite were likely the dominant processes whilst in the basalt experiments dissolution of pigeonite was likely the principal source of fe variations in ph during the hydrochloric acid experiments were minimal remaining below 0 5 at all times in oxalic acid solutions the ph increased to over 4 leading likely to precipitation of secondary minerals and adsorption co precipitation of fe onto mineral surfaces these processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments our results highlight the importance of mineralogy and fluid composition on the fe isotope systematics during weathering the fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils sediments groundwater and hydrothermal deposits and from laboratory studies of single mineral leaching

cu isotopes and concentrations during weathering of black shale of the marcellus formation huntingdon county pennsylvania usa abstract the complex weathering processes which govern the production of soil from bedrock have proven difficult to understand for many lithologies weathering of black shale is of particular interest because it releases organic carbon and heavy metals as solutes and therefore impacts the health of terrestrial and aquatic ecosystems to understand black shale weathering a geochemical survey was initiated for soils developed on shales of the marcellus formation at a zero order catchment at a satellite site of the susquehanna shale hills critical zone observatory located in jackson corner pennsylvania this formation is an organic and metal rich carbonaceous shale that underlies much of new york pennsylvania ohio and west virginia in this paper we focus on the effects of weathering on variations of cu isotopes in the shale cu concentration data for soil were normalized using ti concentrations to document the mobility of cu relative to bedrock at both the ridgetop and valley floor depletion profiles for cu are documented in the soils the cu in the soils is depleted in 65 cu average 65 cu 0 5 0 2 compared to the parent material average 65 cu 0 03 0 15 consistent with loss of cu from soils the pore waters contain 10 ppb cu on average and are enriched in the heavy isotope average value 65 cu 1 14 0 44 rayleigh fractionation models using the concentration and isotope data of the soils are consistent with pyrite weathering and loss of cu from the ridgetop but downslope transport and cu re precipitation at the valley floor

fractionation of fe isotopes by soil microbes and organic acids small natural variations in fe isotopes have been attributed to biological cycling however without understanding the mechanisms of fractionation it is impossible to interpret such variations here we show that the d 56 fe of fe dissolved from a silicate soil mineral by siderophore producing bacteria is as much as 0 8 lighter than bulk fe in the mineral a smaller isotopic shift is observed for fe released abiotically by two chelates and the magnitude of the shift increases with affinity of the ligand for fe consistent with a kinetic isotope effect during hydrolysis of fe at the mineral surface fe dissolved abiotically without chelates shows no isotopic shift the d 56 fe of the exchange fraction on soil grains is also lighter by 0 6 1 than fe from both hornblende and iron oxyhydroxides the kinetic isotope effect is therefore preserved in open systems such as soils when recorded in the rock record fe isotopic fractionation could document fe transport by organic molecules or by microbes where such entities were present in the geologic past

variability of cloud vertical structure during astex observed from a combination of rawinsonde radar ceilometer and satellite the macroscale cloud vertical structure cvs including cloud base and top heights and layer thickness and characteristics of multilayered clouds is studied at porto santo island during the atlantic stratocumulus transition experiment astex by using rawinsonde radar ceilometer and satellite data the comparisons of cvs parameters obtained from four different approaches show that 1 by using the method developed by wang and rossow rawinsonde observations raob s can sample all low clouds and determine their boundaries accurately but oversample low clouds by about 10 mistaking clear moist layers for clouds 2 cloud base heights less than 200 m in the radar data are ambiguous but can be replaced by the values measured by ceilometer and 3 the practical limit on the accuracy of marine boundary layer cloud top heights retrieved from satellites appears to be about 150 300 m mainly due to errors in specifying the atmospheric temperature and humidity in the inversion layer above the cloud the vertical distribution of clouds at porto santo during astex is dominated by low clouds below 3 km a cloud free layer between 3 and 4 km and 20 high clouds with a peak occurrence around 7 8 km low clouds have mean base and top heights of 1 0 km and 1 4 km respectively and occur as single layers 90 of the time for double layered low clouds the tops of the uppermost layers and the bases of the lowermost layers have similar distributions as those of single layered clouds the temporal variations of low clouds during astex are apparently dominated by advecting mesoscale 20 200 km horizontal variations coherent time variations are predominately synoptic timescale 4 5 6 8 days and diurnal variability on the diurnal timescale all cloud properties show maxima in the early morning around 0530 lst decreasing to minima in the late afternoon diurnal variations appear to be altered when high clouds are present above low clouds the general characteristics of cvs in three astex and the first isccp regional experiment fire87 regions derived from a 20 yr rawinsonde dataset are also presented the results suggest that cvs characteristics obtained from data collected at porto santo during astex june 1992 are not representative of other marine stratiform cloud regions

element mobility patterns record organic ligands in soils on early earth considerable mobilization of fe without mobilization of al in precambrian paleosols has been documented and attributed to either anoxic or ligand promoted dissolution to elucidate these mechanisms basalt was dissolved under oxic and anoxic conditions with and without citrate and the mobility of several elements was analyzed the extent of release of fe and p was minor in citrate free conditions or considerable with citrate regardless of oxygen pressure release of al was minor in all cases whereas release of cu was minor in anoxic conditions or considerable in oxic conditions release of cu was enhanced by citrate in comparison in the weathered surface of two of the oldest known basalt derived paleosols the mount roe 2 76 ga and the hekpoort 2 25 ga fe and p were considerably depleted and al retained consistent with the presence of organic ligands cu retained in the mount roe paleosol but considerably mobilized in the hekpoort paleosol documents formation under an anoxic atmosphere and an oxic atmosphere respectively as inferred by others on the basis of fe mobility the immobility of al in both paleosols is consistent with formation under conditions in which the annual volume of rainwater was lower than the topsoil pore volume mobilization of p in such paleosols developed under low rainfall conditions provides a new proxy for identification of ligands secreted by terrestrial organisms on early earth