advances in global bioavailable strontium isoscapes abstract strontium isotope ratios 87sr 86sr are a popular tool in provenance applications in archeology forensics paleoecology and environmental sciences using bioavailable 87sr 86sr in provenance studies requires comparing the 87sr 86sr of a sample of interest to that of 87sr 86sr baselines historically these baselines required building empirical datasets from plants or local animals to characterize the 87sr 86sr available to local ecosystems bioavailable 87sr 86sr however researchers are increasingly relying on modeled bioavailable 87sr 86sr maps called isoscapes we review the advantages and limitations of existing approaches to mapping bioavailable 87sr 86sr for provenance studies and propose a globally applicable scalable and editable framework for creating bioavailable 87sr 86sr isoscapes this framework relies on 1 compiling global bioavailable 87sr 86sr data 2 mapping 87sr 86sr variability in rocks 3 leveraging global environmental covariates and 4 applying a random forest regression method that integrates these data to predict bioavailable 87sr 86sr when the random forest model is applied at the global scale it performs well explaining 60 of the variance of the global bioavailable 87sr 86sr dataset and accounts for geological geomorphological and atmospheric controls in data rich regions e g europe the global bioavailable 87sr 86sr isoscape can be successfully extrapolated to broad regions without bioavailable 87sr 86sr data however we also show that this extrapolation may not be valid in exceptionally geologically complex and data poor regions e g madagascar we suggest research directions to improve the accuracy of global bioavailable 87sr 86sr isoscapes which include 1 increasing the collection of bioavailable datasets in data poor regions 2 harmonizing data management practices and metadata collection for bioavailable 87sr 86sr data and 3 relying on advances in remote sensing and geological mapping techniques to improve geological covariates while significant potential to refine 87sr 86sr isoscapes remains the data products provided in this review form a basis for using 87sr 86sr data in large scale provenance studies opening new research avenues in a range of fields

magnetism and transmission electron microscopy of fe ti oxides and pyroxenes in a granulite from lofoten norway granulites from southwest lofoten norway often carry intense and stable components of natural remanent magnetization nrm coercivities in excess of 100 mt and blocking temperatures up to 580 645 c are common several phases in these rocks can carry stable components of nrm clinopyroxenes augite with exsolved pigeonite and orthopyroxene usually contain abundant fe ti oxides the majority of which are too small to be studied conclusively with visible light additionally these rocks typically contain coarse grained 100 1000 m exsolution intergrowths of rhombohedral fe ti oxides and coarse grained magnetite we have studied the magnetism and mineralogy of the titanohematite and the inclusion bearing augites in one granulite sample using transmission electron microscopy tem and magnetic experiments to understand better the remanence properties of naturally occurring fe ti oxides and their relationships to silicate minerals the coarse grained titanohematite has a coercivity of 350 mt and a laboratory saturation remanence that unblocks at 570 600 c the hysteresis characteristics of this titanohematite are typical of much smaller 10 m sized single domains which apparently reflects the presence of exsolved ilmenite lamellae as small as 10 nm in thickness these lamellae presumably inhibit 1 domain wall nucleation and 2 movement of walls that manage to nucleate the inclusions in the augites serve as carriers of lower coercivity remanence with blocking temperatures less than about 560 c magnetite hematite and ilmenite are present in the augite and intergrowth of the rhombohedral phases revealed by tem persists down to the 20 nm scale the distribution of the magnetite inclusions in the augite appears to be unrelated to any silicate microstructure while that of the rhombohedral fe ti oxides is strongly controlled by silicate microstructure with intergrowths of these oxides commonly decorating lamellae of pigeonite orthopyroxene and clinoamphibole within the augite the nrm of this sample possibly dates from the amphibolite facies metamorphism that the region experienced about 1000 m y ago paleomagnetic studies of these rocks could readily recover virtual geomagnetic poles dating from this event in addition to the included oxides the augites display a number of unusual features that probably result from the protracted polymetamorphic history of these granulites pigeonite lamellae are not parallel to the b crystallographic axis pigeonite lamellae cut across those of orthopyroxene and numerous included minerals occur rare earth elements are concentrated within inclusions that reside in the augite

seasonal variability of element fluxes in two central siberian rivers draining high latitude permafrost dominated areas in order to constrain the origin and fluxes of elements carried by rivers of high latitude permafrost dominated areas major and trace element concentrations as well as sr and u isotopic ratios were analyzed in the dissolved load of two siberian rivers kochechum and nizhnyaya tunguska regularly sampled over two hydrological cycles 2005 2007 large water volumes of both rivers were also collected in spring 2008 in order to perform size separation through dialysis experiments this study was completed by spatial sampling of the kochechum watershed carried out during summer and by a detailed analysis of the main hydrological compartments of a small watershed from element concentration variations along the hydrological cycle different periods can be marked out matching hydrological periods during winter baseflow period october to may there is a concentration increase for major soluble cations and anions by an order of magnitude the spring flood period end of may beginning of june is marked by a sharp concentration decrease for soluble elements whereas dissolved organic carbon and insoluble element concentrations strongly increase when the spring flood discharge occurs the significant increase of aluminum and iron concentrations is related to the presence of organo mineral colloids that mobilize insoluble elements the study of colloidal ree reveals the occurrence of two colloid sources successively involved over time spring colloids mainly originate from the uppermost organic rich part of soils whereas summer colloids rather come from the deep mineral horizons furthermore u and sr isotopic ratios together with soluble cation budgets in the kochechum river impose for soluble elements the existence of three distinct fluxes over the year a at the spring flood a surface flux coming from the leaching of shallow organic soil levels and containing a significant colloidal component b a subsurface flux predominant during summer and fall mainly controlled by water rock interactions within mineral soils and c a deep groundwater flux predominant during winter which enters large rivers through unfrozen permafrost paths detailed study of the kochechum watershed suggests that the contribution of this deep flux strongly depends on the depth and continuous nature of the permafrost

crustal large scale serpentinized mantle peridotite body in the sulu ultrahigh pressure metamorphic belt eastern china evidence from gravity and magnetic anomalies abstract from analysis of the geological and geophysical data gravity magnetic seismic and petrophysics we propose that geophysical anomalies are produced by a serpentinized mantle peridotite body smpb situated in the middle to lower crust in the sulu belt the smpb was formed by crustal emplacement of mantle peridotites accompanied by ultrahigh pressure uhp metamorphism our finding suggests an emplacement mechanism for the serpentinized mantle wedge smw early in the subduction process this is different from the classic view which holds that the serpentinized forearc mantle is formed by in situ hydration processes blakely et al 2005 the petrophysical properties of the smpb are similar to those of the serpentinized forearc mantle or smw in modern subduction zones worldwide but the formation mechanisms for smpb and smw are different this observation is important for understanding the geodynamic processes that operated in the large uhp metamorphic belt in the dabie sulu area eastern china

ultrahigh pressure texture inheritance during retrogression evidence from magnetofabrics in eclogites and ultramafic rocks chinese continental scientific drilling project abstract in order to contribute to a better understanding of exhumation related retrogression processes ultrahigh pressure uhp mafic and ultramafic rocks from the chinese continental scientific drilling ccsd in the maobei eclogite body of the sulu ultrahigh pressure metamorphic belt in eastern china were studied for their magnetofabrics variably retrogressed eclogites and serpentinized ultramafic rocks were retrieved from the depth interval of 100 to 1000 m of the borehole a vein network of irregular shaped veins with a retrograde metamorphic assemblage cuts across the eclogite foliation at both low and high angles sem imaging of the eclogites documents that magnetite associated with retrograde pargasitic amphiboles developed around shape preferred garnet sem imaging of the serpentinized ultramafic rocks documents that magnetite rims grew around shape preferred garnet and that magnetite formed within a mesh texture related to serpentinization syn serpentinization magnetite growth increased bulk susceptibilities but reduced anisotropy maximum susceptibility axes from both eclogites and serpentinized garnet peridotites trend n s i e parallel with the stretching lineation as defined by olivine and omphacite grains this implies that the magnetic fabric mimics the uhp fabric and survived retrogression and that the fabric is inherited from the uhp stage as a consequence retrogression was not associated with substantial ductile deformation and the mafic ultramafic maobei body behaved as a rigid body within a ductile deforming quartzo feldspathic matrix during exhumation internal strain is restricted to brittle fracturing associated fluid circulation and vein formation facilitating retrograde reactions in the mafic ultramafic rocks

serpentinization of oceanic peridotites 2 kinetics and processes of san carlos olivine hydrothermal alteration 1 the kinetics of the reaction mg fe olivine h 2 o serpentine magnetite brucite h 2 were investigated at 500 bars in the 250 350 c range using natural olivine san carlos fo 91 with grain sizes between 1 and 150 mm and for run durations up to 514 d the amount of magnetite produced which directly relates to reaction progress was accurately monitored using up to 24 time resolved magnetic measurements per experiment eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5 15 mm and after 500 d for grain sizes of 50 63 mm serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains they were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization related processes the nature of the serpentine mineral product depended on the initial olivine grain size igs for igs in the 5 150 mm range lizardite formed and olivine dissolution was the rate limiting process at igs below 5 mm chrysotile crystallized instead of lizardite and the relationship between olivine surface area and reaction kinetics no longer held we infer that for such small olivine grain sizes dissolution is no longer the rate limiting process serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes etch pits formation associated with dissolution and grain fracturing for igs above 20 mm interestingly fractures and etch pits with similar geometry and sizes were also observed for residual olivine with a typical grain size of 50 mm in serpentinized peridotite samples from the southwest indian ridge this suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems we therefore suggest that the new kinetic data set that we present here which encompasses a range of olivine grain sizes and reaction temperatures is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project i petrology and geochemistry of the main hole 0 2 050 m the main hole mh of the chinese continental scientific drilling project ccsd in southern sulu has penetrated into an ultrahigh pressure uhp metamorphic rock slice which consists of orthogneiss paragneiss eclogite ultramafic rock and minor schist recovered eclogites have a uhp metamorphic mineral assemblage of garnet omphacite rutile phengite kyanite coesite epidote ultramafic rocks contain garnet olivine clinopyroxene orthopyroxene ti clinohumite phlogopite gneisses and schists contain an amphibolite facies paragenesis but their zircons have coesite garnet omphacite or jadeite and phengite inclusions indicating that eclogites and gneisses have been subjected to in situ uhp metamorphism using available geothermobarometers p t estimates of 3 1 4 4 gpa and 678 816 c for eclogites were obtained if surface outcrops and neighboring shallow drill holes are considered together we suggest that a huge supracrustal rock slab 50 km long 100 km wide 5 km deep was subducted to a depth 100 km and then exhumed to the surface the depth interval 0 2 050 m of the ccsd mh can be divided into six lithological units unit 1 consists of alternating layers of quartz rich and rutile rich eclogites with thin interlayers of gneiss and schist eclogites of unit 1 are characterized by nb ta sr and ti depletions low mg number and general lree enrichment unit 2 comprises rutile and ilmenite rich eclogite and minor normal eclogite and is characterized by high tio2 total fe v co and sr and very low sio2 alkali zr ba nb ta and total ree contents and lree depleted ree patterns with slightly positive eu anomalies unit 3 contains ultramafic rock and minor mgo rich eclogite protoliths of uhp rocks from units 1 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth units 4 and 6 consist of interlayered eclogite and paragneiss the eclogites are characterized by th u nb ta and ti depletion and k enrichment and lree enriched ree patterns paragneisses show nb ta sr and ti depletions and lree enriched ree patterns occasionally with slightly negative eu anomalies indicating that their protoliths represent metamorphic supracrustal series unit 5 consists mainly of orthogneisses showing distinct nb ta sr and ti depletions and lree enriched ree patterns with pronounced negative eu anomalies suggesting granitic protoliths in conclusion it is proposed that the southern sulu uhp belt consists of a series of meta supracrustal rocks a layered mafic ultramafic complex and granites

paleomagnetism magnetic anisotropy and mid cretaceous paleolatitude of the duke island alaska ultramafic complex we report paleomagnetic results from layered igneous rocks that imply substantial post mid cretaceous poleward motion of the insular superterrane western canadian cordillera and southeast alaska relative to north america the samples studied are from the stratiform zoned ultramafic body at duke island which intruded rocks of the alexander terrane at the south end of the southeastern alaska archipelago at about 110 ma thermal and alternating field demagnetization experiments show that the characteristic remanence of the ultramafic rocks has high coercivity and a narrow unblocking temperature range just below the curie temperature of magnetite this remanence is likely carried by low ti titanomagnetite exsolved within clinopyroxene and perhaps other silicate hosts the duke island intrusion exhibits a well developed gravitational layering that was deformed during initial cooling but below 540 c into folds that plunge moderately to the west southwest the characteristic remanence clearly predates this early folding and is therefore primary the fisher parameter describing the concentration of the overall mean remanence direction improves from 3 to 32 when the site mean directions are corrected by restoring the layering to estimated paleohorizontal all samples exhibit a magnetic anisotropy that is strong but nonuniform in orientation across the intrusion and we show that it has no significant or systematic effect on the site mean directions of remanence at least some of the anisotropy derives from secondary magnetite formed during partial serpentinization the mean paleomagnetic inclination 56 10 corroborates paleomagnetic results from five coeval silicic plutons of the canadian coast plutonic complex to the south and southeast and implies 3000 km 1300 km of poleward transport relative to the north american craton between mid cretaceous and middle eocene time the insular superterrane and coast plutonic complex shared a common paleolatitude history with more poleward transport than coeval inboard terranes

multidecadal increases in the yukon river basin of chemical fluxes as indicators of changing flowpaths groundwater and permafrost the yukon river basin underlain by discontinuous permafrost has experienced a warming climate over the last century that has altered air temperature precipitation and permafrost we investigated a water chemistry database from 1982 to 2014 for the yukon river and its major tributary the tanana river significant increases of ca mg and na annual flux were found in both rivers additionally so4 and p annual flux increased in the yukon river no annual trends were observed for dissolved organic carbon doc from 2001 to 2014 in the yukon river mg and so4 flux increased throughout the year while some of the most positive trends for ca mg na so4 and p flux occurred during the fall and winter months both rivers exhibited positive monthly doc flux trends for summer yukon river and winter tanana river these trends suggest increased active layer expansion weathering and sulfide oxidation due to permafrost degradation throughout the yukon river basin

oriented inclusions of magnetite in clinopyroxene source of stable remanent magnetization in gabbros of the messum complex namibia 1 crystallographically oriented and highly elongate magnetite inclusions in clinopyroxene are the dominant source of highly stable remanent magnetization in gabbros of the early cretaceous messum complex namibia rock magnetic properties determined for individual pyroxene crystals indicate a high proportion of single domain magnetite consistent with the observed sizes and shape anisotropy of the magnetite inclusions as in previous studies of similar inclusions these are inferred to have formed by exsolution two arrays of inclusions are regularly present in the messum clinopyroxenes inclined at about 74 consistent with formation at about 800 c deduced from optimization of phase boundary orientations virtual geomagnetic poles from these rocks are consistent with reference data confirming that the magnetization is of thermoremanent origin bipolar magnetizations are recorded at one site as well in individual clinopyroxene crystals suggesting that remanence acquisition upon initial cooling of the gabbro spanned a geomagnetic polarity reversal

magnetic properties and opaque mineralogy of drilled submarine intrusive rocks summary measurements of natural remanent magnetization nrm curie temperature ferrimagnetic and paramagnetic susceptibility saturation induced and remanent magnetizations coercive forces alternating field properties and viscous magnetization are reported for 50 submarine intrusive rocks drilled during legs 30 37 and 45 of dsdp the collection includes doleritic sill rocks fresh and serpentinized cumulate gabbros and serpentinized cumulate peridotites and serpentinized lherzolites believed to have originated in layers 2b 3b and 4 respectively magnetite with a curie temperature between 520 and 580 c is the principal magnetic mineral in all samples there is no indication of maghemitization or of metamorphism to greenschist facies or above the magnetite in the doleritic and cumulate gabbros is a product of deuteric alteration of titanomagnetite and pyroxene the stable nrm is a primary trm the magnetite in the serpentinized rocks is a secondary product of serpentinization the stable nrm is a crm in most rock types the magnetite is of single domain or pseudo single domain size and soft components of nrm are small the magnetite grain size in some of the doleritic gabbros is much coarser these rocks acquire large viscous magnetizations which however are readily removed by alternating field cleaning the cleaned nrms of legs 30 and 45 rocks have approximately dipole inclinations but the nrms of most of the mutually intruded leg 37 units have been dispersed by tectonic rotations the doleritic gabbros and the serpentinized peridotites have stable directionally coherent nrms 10 3emu cm 3 in intensity their counterparts in layers 2b and 3b 4 are likely contributors to oceanic magnetic anomalies layer 3b cumulate gabbros and tectonic serpentinites in the middle and upper crust are less likely anomaly sources

the chemistry of river lake systems in the context of permafrost occurrence mongolia valley of the lakes part i analysis of ion and trace metal concentrations abstract this study provides a description of water chemistry in river lake systems located in central mongolia at the borderline of permafrost occurrence the analysis involved water samples collected from two river lake systems baydrag river boon tsagaan lake system and shargalyuut tuyn rivers orog lake system in the water samples ions and trace elements were detected and quantified additionally the parameters of ph electrical conductivity sec total dissolved solids tds and total organic carbon toc were determined principal component analysis pca was performed on the sample results water chemistry is mostly influenced by geochemical and hydrometeorological processes permafrost thawing could increase the concentration of nitrogen nh4 no3 as well as na and ca2 cl and so42 however it may also be an effect of other factors such as livestock farming seasonal drying out of lakes e g lake orog may also influence water chemistry by deflation of evaporites from exposed lake beds and at the same time with lower concentration of chemical compounds in water the pca shows that water samples can be divided into two groups the first group contains lake samples where water chemistry is shaped by prevailing evaporation processes whereas the second includes samples from rivers and springs water chemistry of the latter is predominantly influenced by geochemical and hydro meteorological processes

the role of serpentinization in exhumation of high to ultra high pressure metamorphic rocks abstract analysis of physical processes involved in serpentinization show that it can lead to a significant reduction in density huge volume increase and generate giant pressure within serpentinizing rocks combined together these factors make the serpentinization process a very important one for the start and support of exhumation of high and ultra high pressure rocks serpentinization can generate a significant buoyancy force as well as forces capable of horizontal displacing of an exhuming block exhumation of high grade rocks to the surface requires the presence of an external force and it cannot be accomplished by buoyancy alone intimate relationships between exhumation and serpentinization serpentinized peridotites and hp lt uhp lt rocks and co existence of eclogites and blueschists with thrusts and nappes containing peridotites serpentinites or ophiolites point to the significant role of serpentinization in exhumation formal analysis of the viscous properties of the lithosphere illustrates that exhumation within the continental crust is extremely slow that its velocity increases with an increase of slab size and that the velocity value during the subduction process should be greater than during exhumation generated by serpentinization process pressure can play an important role in both forcing an exhuming block up and or detaching the upper part of the subducting slab from its bottom part an absence of serpentinites of the archean age proves that serpentinization cannot play a significant role in exhumation of high grade rocks in the archean

unraveling the magnetic carriers of igneous cores from the atlantic pacific and the southern indian oceans with rock magnetic characterization previous rock magnetic investigations of oceanic basement samples have been mainly restricted by single drill holes of dredge collections in this study we present new and published data on the rock magnetic properties of igneous rock samples recovered during seven ocean drilling program odp legs in the atlantic pacific and the southern indian oceans the recovered igneous rocks from these legs are mainly basaltic flows both submarine and subaerial diabase sills and serpentinized peridotites with approximate ages of 140 000 years 10 12 34 69 100 108 and 110 121 ma which offers an opportunity to investigate magnetic properties and mineral changes attending alteration of basement rocks over a wide range of ages from variable tectonic settings titanomagnetite and titanomaghemite are commonly present in igneous rock samples of the ontong java plateau the kerguelen plateau broken ridge the eastern equatorial pacific the middle atlantic ridge trans atlantic geotraverse area and the newfoundland iberia rifted margins for basaltic rock samples three general groups a b and c respectively can be divided in terms of rock magnetic properties samples from group a have a single phase of ti poor titanomagnetite with curie temperatures ranging between 480 and 580 degrees c and exhibit a strong verwey transition in the vicinity of 110 k basalts from this group are most likely good paleomagnetic recorders and probably have preserved original and stable magnetic remanences group b is mainly observed in pillow lavas and is characterized by a curie temperature of 260 280 degrees c which is typical of low temperature oxidized titanomaghemite or titanium rich titanomagnetite the low temperature curves for group b do not show the verwey transition group c has more than one curie temperature which suggests the presence of multiple magnetic phases the thermomagnetic signature indicates the inversion of titanomaghemite to a strongly magnetized magnetite as shown by the irreversible cooling curves for the serpentinized peridotites recovered from both sides of the newfoundland iberia rifted margins results from low temperature measurements show that titano magnetites are present in the dark colored peridotites with a strong verwey transition in the vicinity of 110 k and with field and frequency dependent susceptibility curves that resemble those of synthetic tmo in contrast to the magnetic properties observed from the dark colored peridotites the low temperature curves for the yellow brown colored peridotites did not show any verwey transition thermomagnetic analysis also failed to show evidence for titanomagnetites the remanent magnetization is carried by a thermally unstable mineral that breaks down at about 420 degrees c probably maghemite the magnetic signatures of the serpentinized peridotites recovered from both sides of the newfoundland iberia rift appear not in conflict with the notion that conjugate margins will have generally similar crustal structure and evolution history our rock magnetic data indicate that the differences in the rock magnetic properties of basaltic rocks are mainly a function of mineralogy and alteration there is no apparent coincidence between the age of the rocks and the degree of low temperature alteration as suggested by the presence of nearly unoxidized titanomagnetite in the cretaceous aged basalts and by an examination of curie temperature versus sample age that does not unambiguously show a positive relationship between the degree of low temperature oxidation and crust ages c 206 elsevier b v all rights reserved less

small scale melange fabric between serpentinite block and matrix magnetic evidence from the mitsuishi ultramafic rock body hokkaido japan abstract the mitsuishi ultramafic rock body in hokkaido japan consists mainly of serpentinized peridotites that originated from a depleted mantle this study aims to show new evidence of small scale melange fabric of serpentinite matrix in the rock body each serpentinite block in the serpentine matrix shows large and stable intensities of natural remanent magnetization nrm however the directions of serpentinite blocks nrm in the matrix are randomly scattered a curie temperature tc of 580 c corresponding to pure magnetite was also observed additionally there is no evidence of heating over 580 c after serpentinization the blocks in the matrix must have obtained crystallization remanent magnetization crm during serpentinization the directions of the blocks characteristic remanent magnetization chrm are also scattered it shows that serpentinite blocks were magnetized prior to uplifting the results of the study indicate that the magnetic carrier of the serpentinite blocks in the matrix is mainly composed of magnetite and it can keep original magnetization before uplifting the results also imply that the scattering directions of nrm indicate the presence of small scale melange fabric of serpentinite matrix

magnetic properties opaque mineralogy and magnetic anisotropies of serpentinized peridotites from odp hole 670a near the mid atlantic ridge abstract magnetic mineralogy and magnetic properties of 16 samples of serpentinized peridotites harzburgites from odp hole 670a are studied the degree of serpentinization was determined by a new method which combines saturation magnetization and whole rock iron content a unique curie temperature t c of 580 c corresponding to pure magnetite was observed microprobe analyses whole rock metal content and curie temperatures indicate the absence of awaruite ni 3 fe or native metals hysteresis parameters reveal the contribution of pseudo single domain psd grains in samples with a low degree of serpentinization and large multi domain md grains in highly serpentinized samples with j rs j s 0 08 natural remanent magnetization nrm is mainly unstable and possibly composite particularly in the highly serpentinized samples the intensity j a of anhysteretic remanent magnetization arm in the geomagnetic field is much higher than j n intensity of nrm with j a j n averaging 2 4 the koenigsberger ratio q is low and susceptibility k depends on degree of serpentinization ranging from 1 2 to 51 5 10 6 m 3 kg 1 nrm inclinations are scattered with some tendency to lie near the horizontal plane which is close to the foliation plane anisotropies of susceptibility of arm and of saturation remanent magnetization srm were studied and compared with spinel foliation determined for three less serpentinized samples in these samples magnetic anisotropies seem to be mimetic of high temperature deformation before serpentinization when the degree of serpentinization is high later magnetic fabrics probably related to magnetite veins dominate previous anisotropies the temperature dependence of susceptibility and of viscous remanent magnetization vrm were studied the thermal variation of susceptibility shows a shallow hopkinson effect at about 300 400 c time dependence of induced and remanent magnetization increases with temperature reaching maximum values at about 300 400 c based on these observations induced magnetization and vrm of lower crustal and upper mantle rocks and their contribution to marine magnetic anomalies are discussed

carbon export and cycling by the yukon tanana and porcupine rivers alaska 2001 2005 1 loads and yields of dissolved and particulate organic and inorganic carbon doc poc dic pic were measured and modeled at three locations on the yukon river yr and on the tanana and porcupine rivers tr pr in alaska during 2001 2005 total yr carbon export averaged 7 8 tg c yr 1 30 as oc and 70 as ic total c yields 0 39 1 03 mol c m 2 yr 1 were proportional to water yields 139 356 mm yr 1 r2 0 84 at all locations summer doc had an aged component fraction modern fm 0 94 0 97 except in the permafrost wetland dominated pr where doc was modern poc had fm 0 63 0 70 doc had high concentration high aromaticity and high hydrophobic content in spring and low concentration low aromaticity and high hydrophilic content in winter about half of annual doc export occurred during spring dic concentration and isotopic composition were strongly affected by dissolution of suspended carbonates in glacial meltwater during summer

petrology of ultrahigh pressure eclogites from the zk703 drillhole in the donghai eastern china abstract the 558 m deep zk703 drillhole located near donghai in the southern part of the sulu ultrahigh pressure metamorphic belt eastern china penetrates alternating layers of eclogites gneisses jadeite quartzites garnet peridotites phengite quartz schists and kyanite quartzites the preservation of ultrahigh pressure metamorphic minerals and their relics together with the contact relationship and protolith types of the various rocks indicates that these are metamorphic supracrustal rocks and mafic ultramafic rock assemblages that have experienced in situ ultrahigh pressure metamorphism the eclogites can be divided into five types based on accessory minerals rutile eclogite phengite eclogite kyanite phengite eclogite quartz eclogite and common eclogite with rare minor minerals rutile eclogite forms a thick layer in the drillhole that contains sufficient rutile for potential mining two retrograde assemblages are observed in the eclogites the first stage is characterized by the formation of sodic plagioclase amphibole symplectite or symplectitic coronas after omphacite and garnet plagioclase biotite after garnet or phengite and plagioclase coronas after kyanite the second stage involved total replacement of omphacite and garnet by amphibole albite epidote quartz peak metamorphic p t conditions of the eclogites were around 32 to 40 kbar and 720 c to 880 c the retrograde p t path of the eclogites is characterized by rapidly decreasing pressure with slightly decreasing temperature micro textures and compositional variations in symplectitic minerals suggest that the decompression breakdown of ultrahigh pressure minerals is a domainal equilibrium reaction or disequilibrium reaction the composition of the original minerals and the diffusion rate of elements involved in these reactions controlled the symplectitic mineral compositions

magnetic properties of serpentinized peridotites from the dongbo ophiolite sw tibet implications for suture zone magnetic anomalies magnetic properties of a suite of variably serpentinized peridotites from the dongbo ophiolite sw tibet china have been investigated to determine the magnetic signatures of suture zones the degree of serpentinization s for these peridotites is mainly in the range of s 60 and s 20 30 serpentinized peridotites indicating that peridotites with such degrees of serpentinization contribute to the aeromagnetic anomalies within the yarlung zangbo suture zone in south tibet

magnetic properties of serpentinized garnet peridotites from the ccsd main hole in the sulu ultrahigh pressure metamorphic belt eastern china 1 magnetic properties of 14 serpentinized garnet peridotites from the interval of 603 20 683 53 m of the chinese continental scientific drilling ccsd hole in the sulu ultrahigh pressure uhp metamorphic belt eastern china were investigated and compared with those of ultramafic rocks from other tectonic settings to relate them to the uhp post metamorphic evolution serpentinized garnet peridotites are characterized by high susceptibility natural remanent magnetization nrm and q koenigsberger ratio nrm h where h is the intensity of the local geomagnetic field values the average nrm and q values are 299 65 10 7 m3 kg 1 19 15 10 3 am2 kg 1 and 16 59 respectively which are generally higher than those of other serpentinized peridotites in the world the serpentine concentration for most samples ranges from 40 to 60 suggesting that the peridotites are of obvious homogeneous serpentinization degree micro raman and x ray diffraction spectra of serpentine for representative samples indicate that lizardite is the only serpentine mineral opaque minerals in samples are mainly nonstoichiometric magnetite and cr spinel with or without minor ilmenite and fe sulfide magnetite occurs as rims around olivine and garnet as well as in clusters a chromian garnet further overgrew on the rims of the garnet the grain size of magnetite in rims is in the pseudo single domain region and favorable for development of high nrm high pressure uhp metamorphic processes possibly lead to enhanced concentrations of fe ti oxides in garnet peridotites and thus increase the magnetism of serpentinized garnet peridotites in the ccsd main hole integrated lizardite formation temperature 450 c and its relationships with the pressure temperature time evolution of the associated uhp rocks permit us to infer that serpentinization of garnet peridotites in the ccsd main hole occurred during late exhumation stages ca 200 215 ma ago under temperatures of 425 c however the exact relationship between magnetic properties of garnet peridotite and the uhp metamorphic process will require further studies

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

the effects of serpentinization on density and magnetic susceptibility a petrophysical model abstract new measurements are presented of initial magnetic susceptibility and density for serpentinized harzburgites from the josephine peridotite oregon an inverse correlation between density and susceptibility which is typical of these rocks and similar rocks from other localities is not explained by simple serpentinization reactions calculations of density and susceptibility as a function of reaction progress for reactions that produce magnetite show susceptibilities that are larger than those observed at low degrees of serpentinization susceptibilities of fe bearing serpentine and brucite are calculated from a molecular field model initially developed for the olivine and orthopyroxene solid solutions at high degrees of serpentinization susceptibilities that are lower than those observed are predicted by reactions where iron is sequestered by serpentine and brucite observed density susceptibility trends of serpentinized harzburgites fall between the values predicted by these limiting reactions the observed properties may be modelled by multiple reactions involved in multi stage serpentinization processes such that the production of magnetite increases with the degree of serpentinization the empirical and calculated properties provide a complementary characterization of density and susceptibility values of serpentinites

electron microscopy of iron oxides and implications for the origin of magnetizations and rock magnetic properties of banded series rocks of the stillwater complex montana the origins of multiple magnetizations of the archean stillwater complex have been investigated through scanning electron microscopy and scanning transmission electron microscopy observations of mineralogical relations using representative samples from nine sites in mafic banded series rocks on the basis of directional grouping and demagnetization behavior three magnetizations here labeled a b and c have been recognized the natural remanent magnetizaton nrm is lypically dominated by only one of these magnetizations and multicomponent behavior in individual specimens is rare the a remanence resides in magnetic grains of high median destructive fields and high discrete laboratory unblocking temperatures and is inferred to be a primary thermoremanent magnetization of circa 2 71 ga age the b and c magnetizations of lower median destructive fields and more distributed unblocking temperatures are inferred to be secondary and related to alteration including serpentinization involving limited moderate to low temperature fluid interaction perhaps in response to thermotectonic events e g mafic dike emplacement samples with nrm dominated by the a magnetization contain titanium free magnetite needles width 1 m and maximum dimension between about 2 and 50 m with preferred orientations in cumulus plagioclase crystals these oxides are interpreted to have formed during initial crystallization of cumulus phases in samples containing only b or c magnetizations such needles are absent in cumulus plagioclase whereas secondary fe bearing silicates particularly zoisite and chlorite are conspicuous the samples dominated by the b or c magnetizations contain anhedral low chromian magnetite fecr2 xfexo4 1 5 x 2 0 along fractures in both cumulus plagioclase and pyroxene and in zones of more pervasive alteration of pyroxenes the paragenesis of these oxides is consistent with an origin related to hydrothermal alteration hysteresis data show that plagioclase crystals containing magnetite needles have higher remanent coercivities hcr 60 to 100 mt whereas plagioclase crystals with anhedral chromian magnetite have remanent coercivities less than 60 mt consistent with their alternating field response because oxygen isotope data show no indication of appreciable alteration of host plagioclase we infer that the absence of magnetite needles and their associated a magnetization are caused by selective alteration of the magnetite needles to nonmagnetic phases in the remagnetized gabbros in this case rock magnetic and paleomagnetic data appear to be higher resolution indicators of fluid rock interaction than the stable isotope data anhedral chromian magnetite precipitated during hydrothermal alteration and therefore carries secondary magnetizations

tracing hydrologic flow paths in a small forested watershed using variations in 87sr 86sr ca sr ba sr and δ18o 1 natural variations in 87sr 86sr ca sr ba sr and 18o were used to investigate changing hydrologic flow paths during storm events in an 11 8 ha first order watershed of the hubbard brook experimental forest throughfall soil water and stream water were sampled during several storm events and a single snowmelt event throughfall had 87sr 86sr ca sr and 18o values that were distinct from other water types soil water was highly variable in composition but could be separated into three distinct elevation zones in the watershed with 87sr 86sr and ba sr both increasing with elevation in the watershed changes in 87sr 86sr ba sr and 18o of stream water during storm events yielded complementary information about watershed hydrologic flow paths traditional hydrograph separation using 18o values indicated that new water was only a small component of storm flow 9 18 whereas 87sr 86sr and ba sr ratios indicated that shallow subsurface flow soil water contributed significantly to storm flow in amounts up to 40 depending on soil moisture conditions

magnetism of biotite crystals abstract we report mossbauer spectra magnetic hysteresis acquisition and demagnetization of isothermal remanent magnetization irm and low temperature irm warming curves of biotite crystals as well as a summary of domain observations on magnetic extracts the biotites are from 1 0 to 1 2 ga gneisses and 1 85 ga plutons of the grenville churchill and bear provinces canada most have paramagnetic susceptibilities in the range 0 45 1 2 10 3 si similar to reported values for iron rich biotites magnetite identified by its 120 k verwey transition is an inclusion in all the biotites sizes and domain states of inclusions correlate with magnetite content as measured by saturation magnetization ms the higher ms is the lower are the domain state indicators mrs ms mrs is saturation irm and coercive force hc added to a base population 0 003 0 1 of pseudo single domain psd grains with mrs ms from 0 1 to 0 3 and hc from 7 to 20 mt is 1 in two exceptional cases 7 and 14 of coarse grained multidomain md magnetite with much softer hysteresis properties the underlying psd magnetite fraction in biotites potentially retains useful paleomagnetic remanence in the more magnetic micas this stable fraction may be swamped by md magnetite with less stable behavior

the magnetic properties of metaperidotitic rocks as a function of metamorphic grade implications for crustal magnetic anomalies seventeen samples from the malenco serpentinite in the swiss alps representing systematic prograde metamorphic conditions from prehnite pumpellyite to upper amphibolite are moderately to strongly magnetic average susceptibility of 6 61 10 2 si units due predominantly to the presence of a magnetite rich spinel some greenschist facies samples contain the metal alloy awaruite ni3fe these contain in addition much greater amounts of magnetite small amounts of pyrrhotite in about half the samples complete the contributions to the total magnetization susceptibilities generally decrease with increasing metamorphic grade because of the production of increasing amounts of chromerich spinel which dilutes the magnetite component these results indicate that significant magnetic anomalies should be generated in suture zones containing metamorphosed serpentinite and in areas where serpentinite is being actively subducted

the chemistry of river lake systems in the context of permafrost occurrence mongolia valley of the lakes part ii spatial trends and possible sources of organic composition abstract the chemistry of river lake systems located in central mongolia near the southern border of permafrost occurrence has not been well studied the main aim of this paper is to summarize patterns in water chemistry in supply springs rivers and lakes in relation to permafrost occurrence as well as other natural and anthropogenic impacts the analyses involved water samples taken from two river lake systems the baydrag river boon tsagaan lake system and the shargalyuut tuyn rivers orog lake system total organic carbon toc and polycyclic aromatic hydrocarbons pahs were detected and quantified other organic compounds such as organic halogen compounds phthalates and higher alkanes were also noted the main factors which influence differences in toc concentrations in the water bodies involve permafrost occurrence mainly because compounds are released during active layer degradation in the upper reach of the tuyn river and by intensive livestock farming in river valleys and in the vicinity of lakes in relation to the concentrations of pahs high variability between samples 300 ng l 1 indicates the influence of thermal water and local geology structures e g volcanic and sedimentary deposits as well as accumulation of suspended matter in lakes transported during rapid surface runoff events the monitoring of toc as well as individual pahs is particularly important to future environmental studies as they may potentially reflect the degradation of the environment therefore monitoring in the valley of the lakes should be continued particularly in the light of the anticipated permafrost degradation in the 21st century in order to collect more data and be able to anticipate the response of river lake water chemistry to changes in permafrost occurrence

permafrost carbon stock and decomposability of a globally significant carbon pool 1 the magnitude of future co2 induced climate warming is difficult to predict because of uncertainties in the role of ecosystems and oceans as co2 sources and sinks siberia has extensive areas 1 106 km2 of deep up to 90 m deposits of organic rich frozen loess wind blown silt that accumulated during the pleistocene but have not been considered in most global carbon c inventories similar deposits occur less extensively in alaska recent warming at high latitudes causes this permafrost permanently frozen ground to thaw raising questions about the fate of c in thawing permafrost here we show that siberian loess permafrost contains a large organic c pool 450 gt more than half the quantity in the current atmosphere that decomposes quickly when thawed and could act as a positive feedback to climate warming

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

exsolved magnetite inclusions in silicates features determining their remanence behavior submicroscopic needle shaped titanomagnetite inclusions exsolved in silicate minerals commonly occur in mafic intrusive rocks and are protected from alteration by their silicate hosts making them excellent candidates for paleomagnetic studies a suite of samples containing clinopyroxene and plagioclase hosted magnetite inclusions from five geologically diverse sites was examined using magnetic force microscopy to image the inclusions magnetic domain state alternating field demagnetization experiments indicate that some inclusions are more stable recorders than others the two factors controlling the remanence behavior of the inclusions are internal microstructures and inclusion dimensions magnetite ulvospinel unmixing within an inclusion subdivides the original titanomagnetite solid solution into a boxwork structure composed of 103 105 magnetite prisms separated by thin ulvospinel lamellae the conversion of multidomain sized needles into assemblages of interacting single domains increases the coercivity and hence relaxation time of the inclusions and results in a thermochemical magnetic remanence in samples without this exsolution microstructure the inclusions diameters determine coercivity and their magnetization is thermoremanent both styles of high coercivity inclusions successfully record paleomagnetic directions in mesozoic rocks and their ubiquity within silicate minerals clinopyroxene and plagioclase of mafic intrusive rocks indicates their value as chemically and magnetically stable tools for elucidating the ancient magnetic field marine magnetic anomalies and crustal kinematics

influence of pyroxene and spinel on the kinetics of peridotite serpentinization hydrothermal experiments were performed at 311 degrees c and 3 0 kbar on natural olivine and peridotite to investigate the kinetics of serpentinization the results show that the rates of reaction strongly depend on grain sizes of solid reactants with smaller grain sizes resulting in faster kinetics after 27 days of reaction the reaction extent was 99 for peridotite with grain sizes of 30 mu m and the reaction extent was 28 for grain sizes of 100 177 mu m compared to peridotite olivine is serpentinized at much slower rates e g 5 3 of reaction extent was achieved for olivine with grain sizes of 100 177 mu m after 27 days approximately five times lower than that reached during peridotite serpentinization such contrasting results are due to the presence of pyroxene and spinel an interpretation which is supported by a marked increase in reaction extents for experiments with the addition of pyroxene and spinel the reaction extent achieved in experiments with 3 wt spinel greatly increased to 98 after 27 days much higher than that achieved during olivine serpentinization these results appear to be related to pyroxene and spinel releasing al and cr during serpentinization as indicated by compositions of serpentine orthopyroxene lost similar to 60 of al at a reaction extent of 59 influence of al and cr is suggested by a dramatic increase in reaction extents with the addition of al2o3 and cr2o3 powders olivine in natural geological settings is commonly associated with pyroxene and spinel consequently serpentinization kinetics may be much faster than previously thought

subduction zone magnetic anomalies and implications for hydrated forearc mantle continental mantle in subduction zones is hydrated by release of water from the underlying oceanic plate magnetite is a significant byproduct of mantle hydration and forearc mantle cooled by subduction should contribute to long wavelength magnetic anomalies above subduction zones we test this hypothesis with a quantitative model of the cascadia convergent margin based on gravity and aeromagnetic anomalies and constrained by seismic velocities and find that hydrated mantle explains an important disparity in potential field anomalies of cascadia a comparison with aeromagnetic data thermal models and earthquakes of cascadia japan and southern alaska suggests that magnetic mantle may be common in forearc settings and thus magnetic anomalies may be useful in mapping hydrated mantle in convergent margins worldwide

strontium isotope variation and carbonate versus silicate weathering in rivers from across alaska implications for provenance studies abstract the characterization of strontium sr isotopic 87 sr 86 sr variation in surface waters of alaska ak has significant implications for provenance studies aiming to track movement patterns of animals this study presents 87 sr 86 sr ratios concentrations of sr ca mg na and k and selected molar ratios sr na ca na mg na and ca sr from 61 rivers from across ak to characterize regional patterns in i 87 sr 86 sr variation and ii carbonate versus silicate weathering influencing 87 sr 86 sr ratios 87 sr 86 sr ratios range from 0 70422 0 74041 0 00009 rivers north of the denali fault exhibit more radiogenic and variable 87 sr 86 sr ratios 0 70763 to 0 74041 than rivers to the south 0 70422 to 0 70895 reflecting the tectonic growth of southern ak via accretion of relatively young mafic rich exotic island arcs along north america s continental margin during the mesozoic within interior ak an east west gradient exists radiogenic 87 sr 86 sr ratios 0 725 in east central ak and relatively low ratios 0 711 than lowland rivers 87 sr 86 sr ratios in high relief watersheds north of the denali fault and in watersheds of south central ak elemental and 87 sr 86 sr ratios indicate silicate weathering is important across ak but is most influential in lowland basins north of the denali fault and in southwestern ak this study illustrates the large sr isotopic heterogeneity across ak on multiple spatial scales and provides necessary baseline information for provenance studies

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

strontium isotope compositions of river waters as records of lithology dependent mass transfers the garonne river and its tributaries sw france the relation of lithology in the drainage basin to the dissolved load of the garonne river and its main tributaries in southwestern france was evaluated by determining 87sr 86sr ratios and concentrations of major and trace elements during a 2 year long survey in the upper drainage basin the garonne river waters were isotopically varied at two observation points 0 71131 0 00030 2 for 84 18 ppb 2 and 0 71272 0 00044 for 86 10 ppb respectively in the lower drainage basin the garonne river waters were isotopically identical at three observation points at 0 71020 0 00024 for 125 22 ppb by contrast the tributaries lot truyere aveyron arriege gers and salat are widely varied in their 87sr 86sr ratios and sr concentrations from 0 70836 0 00049 to 0 71058 0 00057 and from 18 8 to 280 116 ppb the sr isotope ratios and concentrations suggest a dominant supply of two reservoirs of sr one of which is with low 87sr 86sr ratios and high sr contents that is typically characteristic of carbonate rocks and the other with high 87sr 86sr ratios and low sr concentrations that is characteristic of felsic rocks locally as in the lot waters draining the massif central and within the pyrenees mountains a third source of sr from mafic rocks may be involved mass balance calculations based on the mean 87sr 86sr ratios and contents of the dissolved sr and on the mean discharges integrating the 2 year survey suggest that contribution of the silicate reservoir amounts 3 8 of the total dissolved sr flux mass balance calculations also suggest that variation in the supply of sr from either of the two major reservoirs does not exceed the analytical uncertainty at about 5 the 87sr 86sr ratios of hcl and nh4cl leachates of suspended loads of the garonne river are different from that of the associated dissolved sr this leaching related supplementary sr represents less than 10 of the total amount of sr transported by the garonne waters the sr isotope characteristics of the leachates are probably records of an intermediate pedogenic episode in the weathering erosion process occurring in the garonne drainage basin

contribution of serpentinized ultramafics to marine magnetic anomalies at slow and intermediate spreading centres insights from the shape of the anomalies summary detailed characteristics of marine magnetic anomalies 33r and 20r suggest that the magnetization of the deeper magnetic layers including the lower crust and possibly the uppermost mantle is horizontally displaced with respect to that of the upper crust we examine the possibility that serpentinization of ultramafics in the lower crust and possibly the uppermost mantle delays the acquisition of magnetization and introduces a shift between the upper and lower crustal magnetization patterns thermal evolution models and the resulting magnetization patterns of the oceanic lithosphere are calculated for a wide range of physical parameters such as the nusselt number and the depth of hydrothermal circulation in the crust and the temperature range of serpentinization the models with moderate hydrothermal cooling of the whole crust and serpentinization temperatures ranging between 200 and 300 dc successfully explain the anomalous skewness and the hook shape of observed sea level magnetic anomalies created at slow and intermediate spreading rates

seasonal variations in strontium and carbon isotope systematics in the lower mississippi river implications for chemical weathering abstract multiple isotope systematics incorporating paired carbon isotopes 13c and 14c strontium isotopes 87sr 86sr and water isotopes 2h and 18o are used to investigate the coherent relationships among flow paths chemical weathering regimes and sr export fluxes from the lower mississippi river monthly water samples were collected at a site near baton rouge louisiana during 2006 2008 for measurements of water isotopic composition the concentration and isotopic composition of dissolved inorganic carbon dic and the concentration and isotopic ratio of sr along with other selected major elements both 2h and 18o followed a similar seasonal pattern with a steady increase from a minimum in march to a maximum in july indicating a shift of water sources from the snowmelt dominant uppermost upper mississippi river during spring freshet to rainfall induced midcontinent surface runoff and groundwater during other seasons values of 13c dic ranged from 8 67 to 5 96 while 14c dic varied from 56 8 to 27 9 corresponding to a 14c age from contemporary to 415 yr bp generally 14c dic increased with increasing 13c dic suggesting variations in bicarbonate sources in response to the shifts of flow paths and chemical weathering regimes depleted 14c dic and 13c dic values during the wet seasons are likely contributed by carbonate mineral dissolution involving soil derived co2 while the higher 14c and relatively enriched 13c dic values during the dry seasons mirror the atmospheric co2 signatures implying the supply by silicate weathering and a seasonal co2 exchange between riverwater and the atmosphere which is enhanced by high primary production sr concentrations and 87sr 86sr ratios averaged 1 80 0 26 mol l 1 and 0 709866 0 000248 respectively both sr concentrations and 87sr 86sr ratios show a significant correlation with 18o values supporting a hydrologic control of the sr provenance in the mississippi river basin indeed the radiogenic 87sr from the archean and early proterozoic terrain in the uppermost upper mississippi river the sr released from carbonate mineral dissolution and the radiogenic 87sr from silicate weathering are manifested in the lower mississippi river with modifications from the snowmelt flow rainfall induced surface runoffs and subsurface groundwater respectively overall our results suggest that different hydrological flow regimes play unique roles in regulating the chemical weathering processes and therefore the seasonal variations in isotope systematics and in the concentrations and export fluxes of both dic and sr from the mississippi river

spreading rate dependent magnetization of the oceanic lithosphere inferred from the anomalous skewness of marine magnetic anomalies summary the anomalous skewness of marine magnetic anomalies decreases with increasing spreading rate and becomes negligible above a spreading rate of about 50 km myr i previous magnetization models of the oceanic lithosphere fail to explain this observation we propose a new model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate anomalous skewness measurements for anomalies 33 reversed and 25 reversed at various spreading rates are in agreement with a magnetization model in which layer 3 and the uppermost mantle bear a similar saturation magnetization and the ratio of layer 3 over layer 2a saturation magnetizations varies linearly from about 0 4 at a spreading rate of 10kmmyr to about 0 at 55kmmyr i for spreading rates higher than 55 km myr layer 3 and uppermost mantle magnetizations are negligible recent advances concerning accretionary processes at mid ocean ridges suggest that the combined effect of variations with spreading rate of magma fractionation alteration of layer 2a and serpentinization of layer 3 and the uppermost mantle may account for the proposed variation of magnetization with spreading rate

sr isotope and major ion compositional evidence for formation of qarhan salt lake western china abstract qarhan salt lake qsl is the largest potash brine deposit in the continental qaidam basin qb of western china the origins of the qarhan brines whether from migration of qaidam mega paleolakes paleoriver capture or mixing of modern river water and ca cl spring water are controversial details about the origin hydrothermal diagenetic or both of the ca cl inflow waters entering qsl in the qb are unclear here we show from the strontium sr isotope ratios of river waters intercrystalline brines spring waters halite gypsum and corbicula shells from qarhan playa that 87 sr 86 sr increases from bieletan western qsl to huobuxun eastern qsl this trend verifies that river water spring water mixing has been operating at qsl for the past 50 000 years contributions of ca cl inflow waters to the qb have profoundly influenced the brine evolution and mineralogy of salt deposits mixing between low sr 2 concentration low 87 sr 86 sr value of river waters and high sr 2 concentration high 87 sr 86 sr value of ca cl spring inflow waters has produced various intercrystalline brines and salt deposits at qsl ca cl inflow waters and brines are enriched in sr 2 and ca 2 and depleted in mg 2 and so 4 2 these characteristics suggest brine sedimentary rock silicate interactions at burial diagenetic or hydrothermal conditions ca cl inflow waters and brines have a similar sr isotopic range as oilfield brines and celestite deposits in the qb which also suggests a diagenetic hydrothermal origin ca cl brines discharge as springs or seeps along fault zones in the qb they are interpreted to reach the surface of the northern margin of qarhan playa by topographically driven circulation

serpentinization of oceanic peridotites 1 a high sensitivity method to monitor magnetite production in hydrothermal experiments 1 a new method using the magnetic properties of magnetite fe 3 o 4 was developed to monitor experimental serpentinization the saturation remanent magnetization signal jrs was measured during the course of experiments designed to react san carlos olivine mg 0 91 fe 0 09 2 sio 4 with water at 250 to 350 c and 500 bars at the end of the experiments the ratio with saturation magnetization jrs js ratio allowed to convert each successive jrs measurement into an in situ amount of magnetite produced by the serpentinization reaction water weight loss was also measured on the end product to determine the final degree of serpentinization the application of this procedure to a series of experiments performed at 300 c 500 bars for various run duration 9 to 514 days and starting olivine grain size 1 to 150 mm shows a linear relationship between magnetite production and reaction progress this relationship can be safely transposed to other experimental conditions using thermochemical modeling and or the fe content of the product phases we show that this high sensitivity magnetic method is a powerful tool to precisely monitor serpentinization kinetics in fe bearing systems it represents in addition a new indirect mean for monitoring the production of hydrogen which is bound to magnetite production rate citation malvoisin b j carlut and f brunet 2012 serpentinization of oceanic peridotites 1 a high sensitivity method to monitor magnetite production in hydrothermal experiments

how widespread and important is n2 fixation in the north atlantic ocean the spatial extent of n2 fixation in the atlantic ocean is examined by determining the isotopic composition of n in suspended particulate organic nitrogen 15n ponsusp the samples were collected from zonal and meridional transects of the atlantic ocean during a 3 year period there is a consistent depleted 15n ponsusp signal extending over the center of the northern subtropical gyre which partly coincides with a region where the tracer n increases westward following the gyre circulation this nonconservative behavior of n implies that n2 fixation is responsible for the depleted 15n ponsusp a mixing model suggests that n2 fixation over parts of the northern gyre provides up to 74 of the n utilized by phytoplankton however since the ponsusp represents only a small fraction of the total n pool n2 fixation probably only plays a minor role in supplying new n to the euphotic zone in the surface waters of the northern subtropical gyre

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

high frequency variability in the circulation and hydrography of the denmark strait overflow from a high resolution numerical model abstractinitial results are presented from a yearlong high resolution 2 km numerical simulation covering the east greenland shelf and the iceland and irminger seas the model hydrography and circulation in the vicinity of denmark strait show good agreement with available observational datasets this study focuses on the variability of the denmark strait overflow dso by detecting and characterizing boluses and pulses which are the two dominant mesoscale features in the strait the authors estimate that the yearly mean southward volume flux of the dso is about 30 greater in the presence of boluses and pulses on average boluses pulses are 57 1 27 5 h long occur every 3 2 5 5 days and are more frequent during the summer winter boluses pulses increase decrease the overflow cross sectional area and temperatures around the overflow interface are colder warmer by about 2 6 c 1 8 c the lateral extent of the boluses is much greater than that of the pulses in both cases the along stra

strontium isotopes in otoliths of a non migratory fish slimy sculpin implications for provenance studies abstract heterogeneity in 87 sr 86 sr ratios of river dissolved strontium sr across geologically diverse environments provides a useful tool for investigating provenance connectivity and movement patterns of various organisms and materials evaluation of site specific 87 sr 86 sr temporal variability throughout study regions is a prerequisite for provenance research but the dynamics driving temporal variability are generally system dependent and not accurately predictable we used the time keeping properties of otoliths from non migratory slimy sculpin cottus cognatus to evaluate multi scale 87 sr 86 sr temporal variability of river waters throughout the nushagak river a large 34 700 km 2 remote watershed in alaska usa slimy sculpin otoliths incorporated site specific temporal variation at sub annual resolution and were able to record on the order of 0 0001 changes in the 87 sr 86 sr ratio 87 sr 86 sr profiles of slimy sculpin collected in tributaries and main stem channels of the upper watershed indicated that these regions were temporally stable whereas the lower nushagak river exhibited some spatio temporal variability this study illustrates how the behavioral ecology of a non migratory organism can be used to evaluate sub annual 87 sr 86 sr temporal variability and has broad implications for provenance studies employing this tracer

abrupt permafrost collapse enhances organic carbon co 2 nutrient and metal release into surface waters abstract thawing of frozen peat in discontinuous permafrost zones may significantly modify the environment at local slumps and engineering damages and global greenhouse gases regime scales we studied the aquatic geochemistry of co2 ch4 dissolved organic carbon doc p si and colloidal trace metal from hollows depressions permafrost subsidences and soil waters in the actively thawing discontinuous permafrost zone of western siberia lowland wsl this site of abrupt permafrost collapse is dominated by minerotrophic fens located within the flat mound peat bog the co2 doc major and trace metal concentrations decreased with the increase of the surface area of the water body along the hydrological continuum soil water hollows depressions and permafrost subsidences thaw ponds thermokarst lakes aqueous concentrations of co2 ch4 ca si p al fe nd and u were a factor of 4 to 10 higher in the site of catastrophic thaw compared to the steady thawing of a palsa peat bog that was previously studied in the same region the colloids 1 kda 0 45 m formed in hot spots were strongly enriched in fe al and trivalent and tetravalent hydrolysates relative to organic carbon because the increase in the thickness of the thawing depth intensifies the input of inorganic components from deep mineral horizons abrupt permafrost thaw enriches the surface waters in al rich colloids and low molecular weight organic complexes as a result the wsl s surface water colloidal composition may shift from dom rich and dom fe rich to dom al rich and the release of low soluble trivalent and tetravalent hydrolysates from the soil to the river will increase we hypothesize that in sites of abrupt permafrost thaw there is direct mobilization of soil waters to a hydrological network rivers and lakes and there is minimal transformation by autochthonous processes which is unlike the case of steady permafrost thawing therefore the change in physical factors such as water pathways and the water residence time within a given elementary landscape will likely control the overall impact of on going permafrost thaw on both the surface water chemistry and dissolved greenhouse gas pattern of the territory for this high resolution

causes of changes in the denmark strait overflow abstract the warming nordic seas potentially tend to decrease the overflow across the greenland iceland scotland ridge gisr system recent observations by macrander et al document a significant drop in the intensity of outflowing denmark strait overflow water of more than 20 over 3 yr and a simultaneous increase in the temperature of the bottom layers of more than 0 4 c a simulation of the exchange across the gisr with a regional ocean circulation model is used here to identify possible mechanisms that control changes in the denmark strait overflow and its relations to changed forcing condition on seasonal and longer time scales the authors establish links of the overflow anomalies to a decreasing capacity of the dense water reservoir caused by a change of circulation pattern north of the sill on annual and shorter time scales the wind stress curl around iceland determines the barotropic circulation around the island and thus the barotropic flow through denmark strait for the overlapping time sc

on the nature and variability of the east greenland spill jet a case study in summer 2003 abstractresults from a high resolution 2 km numerical simulation of the irminger basin during summer 2003 are presented the focus is on the east greenland spill jet a recently discovered component of the circulation in the basin the simulation compares well with observations of surface fields the denmark strait overflow dso and the hydrographic structure of typical sections in the basin the model reveals new aspects of the circulation on scales of o 0 1 10 days and o 1 100 km the model spill jet results from the cascade of dense waters over the east greenland shelf spilling can occur in various locations southwest of the strait and it is present throughout the simulation but exhibits large variations on periods of o 0 1 10 days the spill jet sometimes cannot be distinguished in the velocity field from surface eddies or from the dso the vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term the

geochronologic and thermobarometric constraints on the metamorphic history of the fairbanks mining district western yukon tanana terrane alaska this study presents new petrologic and thermochronologic information from the fairbanks district of east central alaska that indicate a complex metamorphic and structural history for the western yukon tanana terrane garnet biotite and garnet pyroxene thermometry and jadeite barometry yield prograde temperatures and pressures for the chatanika eclogite 523 c 14 15 kbar 1 kbar 100 mpa cooling from peak eclogitization is estimated from 40 ar 39 ar single grain geochronology at 210 180 ma secondary white mica ages of 140 115 ma along the fault contact between eclogite and underlying lower amphibolite facies rocks constrain the age of the event that placed the chatanika eclogite over the fairbanks schist based on observations from field mapping and diamond drill samples we interpret this structural contact as a thrust fault garnet biotite mineral pairs are reset by as much as 200 c within this fault zone biotite and white mica ages of 100 110 ma combined with jurassic amphibole ages in fairbanks schist samples indicate the fairbanks schist and chatanika eclogite cooled through biotite and white mica argon closure temperatures in the early cretaceous intrusion of mid cretaceous calc alkalic gold related granitic plutons in the fairbanks district are evidenced by loss of radiogenic argon in many of the 40 ar 39 ar age fractions eocene basalt is visible in six widely separated localities within the eastern part of the fairbanks district however the pervasiveness of a 50 ma resetting event in samples as far as 30 km from present day basalt localities indicates the eocene flows were either deposited throughout the fairbanks area or are associated with large plutons at depth

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

weathering processes catchment geology and river management impacts on radiogenic 87sr 86sr and stable δ88 86sr strontium isotope compositions of canadian boreal rivers abstract radiogenic 87sr 86sr and stable 88 86sr strontium isotope compositions spanning a calendar year are reported for rivers from across subarctic canada that drain contrasting lithologies ranging from precambrian bedrock koksoak great whale and la grande rivers of northern quebec to carbonate and clastic phanerozoic sedimentary rocks of the western interior platform nelson river of central and western canada the 87sr 86sr isotopic compositions of the river waters reflect the underlying geology with rivers draining the precambrian shield having higher 87sr 86sr ratios 0 727 0 734 than the phanerozoic dominated nelson river 0 713 the stable strontium isotope values 88 86sr range from 0 26 to 0 39 with the values for the nelson river overlapping those of the other three rivers that have not been developed for hydroelectric power show a seasonal variation in the 87sr 86sr ratios whereas those that have been diverted or dammed show little or no seasonal variation due to increased residence time of their water in hydroelectric reservoirs the three rivers from northern quebec show discrete ranges in their 87sr 86sr and 88 86sr isotope compositions that correlate with the ca sr and na sr ratios of the river water these correlations are interpreted to reflect differential chemical weathering of felsic versus mafic source rocks and or of surficial sediment vs bedrock sources

cenozoic remagnetization of the paleozoic rocks in the kitakami massif of northeast japan and its tectonic implications abstract secondary remanent magnetization is identified in the paleozoic igneous and sedimentary rocks of the kitakami massif the secondary nature is shown by a negative fold test for the permo carboniferous sedimentary rocks the northwesterly paleomagnetic declination with moderate inclination d 321 2 i 56 5 95 5 2 n 18 of this secondary remanent magnetization is almost parallel to the primary magnetization reported for the cenozoic welded tuffs of northeast japan indicating that the paleozoic rocks were subjected to remagnetization at any period between 62 and 16 ma the secondary magnetization of the serpentinized ultramafic rocks is carried by magnetite which grew in veins and mesh rims of serpentine whereas the carrier of the magnetization in limestones is fine grained pyrrhotite combining this with the previously reported remagnetization of the kitakami granitic rocks it is suggested that rocks in the kitakami massif were subjected to crystallization remanent magnetization at low temperature conditions since serpentinization requires fluid migration one of the most likely events is the eastward lateral migration of water into the kitakami massif we postulate a cenozoic suturing of the kitakami massif with the asian continent as a plausible tectonic event for this fluid migration

insights into combined radiogenic and stable strontium isotopes as tracers for weathering processes in subglacial environments this study reports stable and radiogenic strontium isotope behaviour in the dissolved load and suspended sediments from the subglacial outflow of the lemon creek glacier juneau ice field alaska over a single melt season in situ measurements discharge total alkalinity ph and conductivity are combined with elemental concentrations x ray diffraction xrd analysis and radiogenic strontium isotope measurements to interpret the variations observed in stable strontium isotopic ratios the stable sr isotope composition 88sr 86sr ratio expressed as 88 86sr of the dissolved load averages 0 31 0 05 and is heavier than both the suspended sediment 0 18 0 03 as well as local bedrocks 0 20 to 0 26 we attribute the enrichment of heavier isotopes in the dissolved load to the uptake of lighter sr isotopes by secondary weathering minerals driving the dissolved load to heavier values x ray diffraction xrd analysis confirms the presence of clays in the suspended sediments and thermodynamic modelling suggests the presence of iron oxy hydroxide phases although it is not possible to completely rule out the effect of dissolution of primary minerals in controlling sr isotopic compositions of the dissolved load our data indicate that the extent of secondary mineral formation likely plays a significant role the preferential weathering of minerals such as biotite consistent with the mineralogical assemblages found in the suspended sediments as well as the potential presence of radiogenic calcites from metacarbonates derived from the yukon tanana terrain may be driving the small seasonal shifts in 87sr 86sr of the dissolved load to more radiogenic compositions from 87sr 86sr dl 0 71048 to 0 710647 using the combination of stable and radiogenic strontium isotopes to investigate weathering processes shows that radiogenic sr isotopes provide information regarding weathering of primary phases while the stable sr isotope data appear to record information regarding the extent of secondary mineral formation where secondary minerals incorporate the light isotopes driving the dissolved load to heavy values

magnetic properties of variably serpentinized abyssal peridotites we have compiled new and published data on the magnetic properties of 245 serpentinized abyssal peridotites from seven deep sea drilling project and ocean drilling program sites the magnetic susceptibility k of these samples does not increase linearly with the degree of serpentinization s instead k remains modest in partially serpentinized samples s 75 peridotites in the oceanic crust moderately serpentinized peridotites s 75 have nrm values 5 a m and k 0 05 si low temperature oxidation of magnetite is found to lower the nrm and k values of seafloor samples and of cataclastically deformed drilled samples

hydrogeochemistry of seasonal flow regimes in the chena river a subarctic watershed draining discontinuous permafrost in interior alaska usa abstract thawing of permafrost and a shift in the timing of major seasonal transitions spring melt and fall freeze up are two anticipated effects of climate warming in northern regions these fundamental changes in terrestrial ecosystems could have major ramifications for the timing and fluxes of carbon and nutrient exports from watersheds and the geochemical signatures of northern rivers discontinuous permafrost which underlies watersheds in interior alaska usa is expected to degrade rapidly in response to climate warming and this will likely alter subsurface flows and flow paths water residence times water soil and water rock interactions this study of the chena river in interior alaska was undertaken to quantify dissolved organic carbon doc total dissolved nitrogen tdn major ion strontium isotope and stable oxygen and hydrogen isotope values during two year long time series sampling periods our goal was to identify the hydrogeochemical signatures associated with the major seasonal flow regimes periods of increased discharge such as spring melt and major summer precipitation events yielded elevated doc and tdn concentrations diluted major ion concentrations and shifted stable oxygen and hydrogen isotope ratios from base flow toward precipitation values during dry summer periods nutrient concentrations decreased and strontium isotope values were indicative of a higher proportion of silicate versus carbonate mineral dissolution winter base flow had a unique geochemical signal with a slight increase in tdn concentrations compared to typical summer conditions and a lower proportion of silicate versus carbonate mineral dissolution since flow paths in subarctic watersheds can change dramatically over the course of a year we interpreted our results within the context of a schematic model for subsurface flow to identify how permafrost degradation might affect nutrient exports and hydrogeochemical patterns in these watersheds

structure and variability of the denmark strait overflow model and observations we report on a combined modeling and observational effort to understand the denmark strait overflow dso four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution the observations reveal the mean path of the dense water as well as the presence of strong barotropic flows energetic variability and strong bottom friction and entrainment a regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes the model successfully reproduces the volume transport of dense water at the sill as well as the 1000 m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1 3 day intervals hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations in addition despite the differences in surface forcing both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom trapped baroclinic flow downstream indicating the dominant role of the overflow in determining the full water column dynamics

changes in surface area of the boon tsagaan and orog lakes mongolia valley of the lakes 1974 2013 compared to climate and permafrost changes abstract the main aim of the study is the analysis of changes in surface area of lake boon tsagaan 45 35 n 99 8 e and lake orog 45 3 n 100 44 e taking place in the last 40 years in the context of climate conditions and permafrost degradation the lakes located in central mongolia at the borderline of permafrost range are fed predominantly by river waters and groundwater from the surrounding mountain areas characterized by continuous and discontinuous permafrost occurrence mostly the khangai the analysis of the boon tsagaan and orog lake surface area in 1974 2013 was conducted based on satellite images whereas climate conditions were analysed using the noaa climate data and cru dataset principal component analysis pca was used to study the relationship patterns between the climatic factors and changes in the surface area of the lakes a tendency for a decrease in surface area intermittent with short episodes of resupply was observed in both studied lakes climate changes recorded in the analysed period had both direct and indirect impacts on water supply to lakes taking into account the results of pca analysis the most significant factors include fluctuation of annual precipitation increase in air temperature and thickness of snow cover the extended duration of snow cover in the last decades of the 20th century may constitute a key factor in relation to permafrost degradation

ca sr and 87sr 86sr ratios as tracers of ca and sr cycling in the rio icacos watershed luquillo mountains puerto rico abstract we investigated ca and sr cycling in a humid tropical forest by analyzing ca sr ratios and 87sr 86sr ratios in soil minerals soil exchangeable cations soil porewater and plant roots wood and leaves and calculating the relative contributions of sr from atmospheric inputs and weathering of local bedrock an unexpectedly large contribution of bedrock derived sr and presumably ca is cycled through the vegetation reflecting the important role of geological processes in controlling the cycling of base cation nutrients even in a system with intensely weathered soil this is surprising because over 99 of the ca and sr that was originally in the bedrock is leached out of the soil and saprolite during early stages of weathering at this site and because there are large atmospheric inputs to the site of both sea salt and saharan dust substantial differences in ca and sr cycling are seen on small spatial scales between a ridgetop and an adjacent steep hillslope site measured ca sr ratios reflect fractionation between these elements during biogeochemical cycling fractionation was particularly evident between wood and foliar tissue but fractionation during soil exchange processes is also likely in comparing the ca sr ratios of plants exchangeable cations and bulk soils we found that foliar ca sr ratios were greater than exchangeable cation ca sr ratios which in turn were greater than soil ca sr ratios similar to patterns observed at other highly weathered tropical sites

high frequency fluctuations in denmark strait transport 1 denmark strait ocean current transport exhibits quasi regular fluctuations immediately south of the sill with periods of 2 4 days the transport variability is similar to the mean transport itself using a circulation model we explore prospects to monitor the fluctuations the model has realistic transport and shows water leaving denmark strait in equivalent barotropic cyclones that are nearly geostrophic and correlate with sea surface height ssh existing satellite altimeter observations of ssh have adequate space time sampling to reconstruct the transport fluctuations using a regression developed from the model results but measurement error overwhelms the signal from the model results the pending surface water and ocean topography swot wide swath altimeter appears accurate enough and with good enough coverage to allow the transport fluctuations to be reconstructed bottom pressure recorders at the exit of the denmark strait can also reproduce the transport variability

increased groundwater to stream discharge from permafrost thawing in the yukon river basin potential impacts on lateral export of carbon and nitrogen 1 arctic and subarctic watersheds are undergoing climate warming permafrost thawing and thermokarst formation resulting in quantitative shifts in surface water groundwater interaction at the basin scale groundwater currently comprises almost one fourth of yukon river water discharged to the bering sea and contributes 5 10 of the dissolved organic carbon doc and nitrogen don and 35 45 of the dissolved inorganic carbon dic and nitrogen din loads long term streamflow records 30 yrs of the yukon river basin indicate a general upward trend in groundwater contribution to streamflow of 0 7 0 9 yr and no pervasive change in annual flow we propose that the increases in groundwater contributions were caused predominately by climate warming and permafrost thawing that enhances infiltration and supports deeper flowpaths the increased groundwater fraction may result in decreased doc and don and increased dic and din export when annual flow remains unchanged

magnetic properties of archean gneisses from the northeastern north china craton the relationship between magnetism and metamorphic grade in the deep continental crust

stream geochemistry as an indicator of increasing permafrost thaw depth in an arctic watershed the presence of permafrost has a strong influence on arctic hydrology ecology and engineering therefore understanding the response of permafrost to arctic warming is critical to predicting the regional effects of global climate change recent research suggests that thaw depth may be increasing in response to warming but physical thaw depth surveys in the alaskan arctic are often not sensitive enough to detect incremental increases and cannot measure increases in the permafrost thaw bulbs beneath lakes and streams here we assess the use of geochemical tracers in stream water to identify changes in thaw depth in an arctic watershed based on marked differences in geochemistry with depth in soils and permafrost on the alaskan north slope we used 87sr 86sr and elemental ratios in an arctic stream as tracers of increases in the maximum depth of soil water flow and therefore the integrated thaw depth in the watershed from 1994 to 2004 stream water 87sr 86sr ca na and ca ba at base flow showed significant trends with time consistent with increasing depth of soil water flowpaths although long time series will be necessary to identify long term trends stream geochemistry may be useful as a qualitative indicator of changes in thaw depth in other areas where permafrost and active layer soil geochemistry differs

seasonal hydrochemistry of a high arctic wetland complex the seasonal evolution in the hydrochemistry of four types of wetland pond ice wedge trough wet meadow and mesic site was studied in a 0 5 km2 wetland complex in the canadian high arctic on the fosheim peninsula ellesmere island in the spring a large influx of overland runoff from snowmelt quickly flushed away the solutes of the ice stored on the wetland surface over the winter and homogenized the hydrochemistry across the entire wetland complex as the surface flow receded various wetland patches became hydrologically disconnected and their hydrochemical characteristics evolved differently although underlain by marine sediments and saline permafrost solute concentrations in much of the wetland complex remained dilute compared with many arctic wetlands through continued evaporation melting of ground ice and localized thermokarst activities the hydrochemistry of different wetland types acquired their distinctive characteristics as the summer progressed this study demonstrates that large diversity in wetland hydrochemistry occurs even within a limited area indicating the need to caution against generalizations based on limited spatial and temporal samples copyright 2009 john wiley sons ltd

the 3100 bp eruption of the soufriere of guadeloupe a transmission electron microscopy study of the cryptodome andesite fragments of unaltered andesite found at all levels in the deposits of the catastrophic flank failure directed blast eruption of the soufriere of guadeloupe in 3100 bp are thought to be remnants of the cryptodome they were observed in analytical transmission electron microscopy for clues to the evolution of the intrusion prior to the eruption several features that could potentially be used as temperature markers were identified among which the angle between microexsolutions of magnetite in augite phenocrysts was used to find an upper boundary of the temperature of the intrusion before the eruption 600 700 c calculation of the time a dyke or sphere shaped intrusion may have taken to cool from the emplacement temperature down to the temperature of exsolution of the magnetite leads to an estimate of the time between emplacement of the intrusion and the eruption which could not have been less than a few tens of years it therefore seems probable that the emplacement of the magmatic intrusion was not the immediate cause of the flank destabilization and catastrophic eruption of the soufriere in 3100 bp

deep root of a continent continent collision belt evidence from the chinese continental scientific drilling ccsd deep borehole in the sulu ultrahigh pressure hp uhp metamorphic terrane china abstract the chinese continental scientific drilling ccsd deep borehole which reached a depth of 5158 m in the sulu ultrahigh pressure uhp metamorphic terrane provides a new window into the deep root of a continent continent collision belt and the tectonic processes by which supracrustal material is recycled into the mantle by subduction and then uplifted to the surface major research themes of the ccsd project were to 1 determine the three dimensional composition structure and geophysical character of the deep root of this orogenic belt 2 investigate the nature and timing of the uhp metamorphism 3 investigate the processes of crust mantle interaction involved in the formation and exhumation of the uhp rocks 4 study the process of fluid circulation and mineralization during subduction and exhumation 5 study the rheological properties of the various rocks during subduction and exhumation 6 develop and refine dynamic models for deep subduction and exhumation of crustal rocks and 7 establish a long term natural laboratory for the study of present day crustal dynamics e g stress strain fluid activity the ccsd has developed precise oriented profiles of the main borehole in terms of lithology geochemistry oxygen isotopes zircon shrimp u pb ages 40ar 39ar ages deformation rheology mineralization physical properties of the rocks petrophysical logs seismic reflections and underground fluids the present paper summarizes the integrated research results of this project especially the new findings concerning the deep root of a continent continent collision

observability of the irminger sea circulation using variational data assimilation this paper explores the prospects for constraining circulation and stratification estimates in the irminger sea and denmark strait using variational data assimilation a regional circulation model with 9 km horizontal grid spacing seven vertical levels and open boundaries is used the circulation it simulates is realistic in several important respects and includes a chaotic mesoscale eddy field pulsation of the outflow of dense water through the denmark strait is also reasonably realistic although entrainment and mixing of this water downstream is crudely represented identical twin assimilation experiments are performed to address the observability of the system with the existing in situ and satellite observing network in the absence of systematic errors that is the constraints exerted on the circulation and stratification by the data assimilation system are quantified synthetic data come from a reasonably realistic observing network that includes in situ hydrographic and current measurements and remotely sensed surface temperature and sea level over a 15 day assimilation period in summer the system fits all the observations to the relevant noise level largely by correcting the initial conditions only modest changes in the time dependent surface forcing and negligible changes to the open boundary conditions are needed the system can accurately estimate sea surface height and sea surface temperature correcting errors in the locations of surface fronts and eddies the mid depth salinity is almost completely unconstrained however whereas the velocity fields are somewhat constrained by the assimilation especially by the remote sensing data assimilation of satellite data enables us to accurately track the phase and amplitude of the overflow variability at the exit of denmark strait in the identical twin experiments at other model outflow transects the assimilated solution is contaminated with spurious inertial oscillations this is true even at a section offshore of angmagssalik where a current meter mooring array exists in our experiments and in the real ocean nevertheless improvement of the model dense outflow near the moorings is significant and propagates several hundred kilometres upstream and downstream copyright 2006 royal meteorological society

magnetic petrology of high fe ti eclogites from the ccsd main hole implications for subduction zone magnetism 1 the high fe ti eclogites with exsolved lamellar in 530 600 m depths from the chinese continental scientific drilling ccsd main hole in the sulu ultra high pressure uhp metamorphic belt eastern china record an anomalously high susceptibility natural remanent magnetization nrm and koenigsberger ratio q nrm ji ji is induced magnetization this provides us with a good opportunity to study the effects of magnetic minerals and exsolution lamellae on the magnetic properties of deep rocks in this paper we have measured systematically magnetic properties and mineral assemblage and structure for three special samples no 83 no 86 and no 89 results show that these fe ti rich eclogites are the result of the fine grained titano magnetite exsolution in pyroxene and lamellar structure consisting of finely interlayered ilmenite and hematite in exsolved hemo ilmenite we found that the dominant fe bearing oxide minerals in samples studied are ilmenite hematite hem ilm up to 25 little titano magnetite and pyrite the ferromagnetic susceptibility is mainly controlled by fine grained titano magnetite and nrm is closely related to the exsolved lamellar structure we hence propose that the anomalous magnetism of these eclogites observed in our samples is the result of exsolution from homogenous pyroxene and ilmeno hematite during cooling and decompression processes these fe ti rich eclogites might be one of the sources of high magnetic anomalies observed in the sulu subduction zone eastern china

a petrologic and rb sr isotopic study of intrusive rocks near fairbanks alaska epizonal granodiorite and granite plutons intrude the northwestern portion of the yukon crystalline terrane near fairbanks alaska mineralogic major oxide and trace element studies indicate that the plutons represent a comagmatic fractionation suite a rb sr whole rock isochron for one pluton yields an age of 90 9 0 9 ma in agreement with previous k ar dating of biotite and hornblende and an initial 87sr 86sr ratio of 0 71238 0 00014 the elevated initial 87sr 86sr ratio suggests that the plutons may have had a different source from that of the belt of subduction related mid cretaceous plutonic rocks found farther to the southeast in the yukon crystalline terrane in contrast they appear to have been formed at least in part by anatectic melting of late proterozoic or early paleozoic crustal rocks comparison of aplite dike compositions with the synthetic granite system estimates of average uplift rate and k ar cooling ages of surrounding schists all indicate that the magmas that formed the plu

petrologic evolution of plagioclase rich cumulates from the wichita mountains oklahoma effects upon magnetic remanence properties the glen mountains layered complex gmlc of the wichita mountains of oklahoma is a coarse grained analog to layer 3 gabbros of the sea floor the slowly cooled mafic layered complex developed in the site of an aulacogen which is interpreted as a failed intracontinental rift the remanent magnetism of rocks of the layered complex is extremely stable due to the presence of magnetic inclusions in the major phases primarily plagioclase the early formation of plagioclase facilitated the formation of these magnetically important inclusions petrologic processes that promote the formation of magnetically stable mineralogic inclusions in coarsegrained gabbros should be operative in oceanic slow spreading ridges therefore the contribution of magnetization of layer 3 gabbros should be greater in slower spreading ridges than in faster spreading ridges because of their differences in petrologic evolution

degrading permafrost mapped with electrical resistivity tomography airborne imagery and lidar and seasonal thaw measurements accurate identification of the relationships between permafrost extent and landscape patterns can help to develop airborne geophysical or remote sensing tools to map permafrost in remote locations or across large areas these tools will be particularly applicable in discontinuous permafrost where climate warming or disturbances such as human development or fire can lead to rapid permafrost degradation we have linked field based geophysical point scale and imagery surveying measurements to map permafrost at five fire scars 1930 1975 1988 2001 and 2010 on the tanana flats in central alaska ground based elevation surveys seasonal thaw depth profiles and electrical resistivity tomography ert measurements were combined with airborne imagery and light detection and ranging lidar to identify relationships between permafrost geomorphology and elapsed time since fire disturbance ert proved to be a robust technique for mapping the presence or absence of permafrost because of the marked difference in resistivity values for frozen versus unfrozen material there was no clear relationship between elapsed time since fire and permafrost extent at our sites however we have found that the transition zone boundaries between permafrost soils and unfrozen soils in the collapse scar bogs at our sites had complex and unpredictable morphologies this result suggested that attempts to quantify the presence or absence of permafrost using aerial measurements alone could lead to incomplete results taken in total the results from our study indicated that although ground based ert measurements were the most rapid means of mapping permafrost we were still limited in being able to apply airborne surveying measurements at the landscape scale toward accurately estimating permafrost extent

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes