germanium silicon fractionation in the weathering environment abstract we present a detailed study of germanium behavior in the soil weathering environment as an important step toward using the ge si system as a tracer of silicate weathering processes in both modern and ancient environments intensely weathered soils developed on hawaiian basalts have bulk soil ge si ratios 2 to 10 times higher than fresh basalt e g 10 to 25 mol mol vs 2 5 mol mol soil ge concentrations increase with si and decrease with fe suggesting that ge sequestration is related to accumulation of secondary soil silicates rather than retention in soil fe oxy hydroxides sequential extractions of these soils suggest that ge si fractionation takes place by ge sequestration during the initial precipitation of secondary soil aluminosilicates principally allophane further si loss and changes in mineralogy as these soils age result in little additional ge si fractionation ge si ratios in granitic soils and saprolites are strongly influenced by relative weathering rates of primary minerals kaolinite has a ge si ratio 5 9 mol mol higher than the plagioclase from which it forms 3 1 mol mol whereas accumulation of primary quartz ge si 0 5 mol mol prevents granitic soils from attaining high ge si ratios laboratory synthesis of allophane confirms that ge is preferentially partitioned into the solid phase upon precipitation of secondary aluminosilicates from solution

tracing mechanisms controlling the release of dissolved silicon in forest soil solutions using si isotopes and ge si ratios the terrestrial biogenic si bsi pool in the soil plant system is ubiquitous and substantial likely impacting the land ocean transfer of dissolved si dsi here we consider the mechanisms controlling dsi in forest soil in a temperate granitic ecosystem that would differ from previous works mostly focused on tropical environments this study aims at tracing the source of dsi in forest floor leachates and in soil solutions under various tree species at homogeneous soil and climate conditions using stable si isotopes and ge si ratios relative to granitic bedrock clays minerals were enriched in si 28 and had high ge si ratios while bsi from phytoliths was also enriched in si 28 but had a low ge si ratio such a contrast is useful to infer the relative contribution of silicate weathering and bsi dissolution in the shallow soil on the release of dsi in forest floor leachate solutions the delta si 30 values in forest floor leachates 1 38 parts per thousand to 2 05 parts per thousand are the lightest ever found in natural waters and ge si ratios are higher in forest floor leachates relative to soil solution these results suggest dissolution of si 28 and ge enriched secondary clay minerals incorporated by bioturbation in organic rich horizons in combination with an isotopic fractionation releasing preferentially light si isotopes during this dissolution process ge si ratios in soil solutions are governed by incongruent weathering of primary minerals and neoformation of secondary clays minerals tree species influence si isotopic compositions and ge si ratios in forest floor leachates through differing incorporation of minerals in organic horizons by bioturbation and to a lesser extent through differing si recycling c 2010 elsevier ltd all rights reserved

provenance shallow to deep diagenesis and chemical mass balance in supermature arenites and pelites ordovician simpson group oklahoma and kansas u s a abstract this study considering original detrital compositions and diagenetic alterations relates sandstone and shale mineral and chemical composition to provenance and mass balance between the sedimentary assemblage and its provenance mature quartz rich sandstones and siltstones with clay rich shales in cores at depths of 60 m 5 2 km and burial temperatures of 150 c from over 50 wells were utilized in this work these provide the material for analysis of compositions and alterations in coastal and shallow marine clastic sedimentary rocks of the middle ordovician simpson group in oklahoma and kansas u s a mineral and geochemical data were obtained by optical petrography x ray diffraction scanning electron microscopy electron microprobe and whole rock x ray fluorescence and icp ms analyses results of the study show significant progressive diagenetic changes with increased burial depth and temperature mineralogically and chemically less altered rocks are comparable to modern quartz rich sands and kaolinitic muds in siliciclastic sediments developed during humid tropical weathering in crystalline basement shield provenance in africa and south america by analogy to modern tropical cases muds composed of major kaolinite with minor smectite and illite at deposition were diagenetically transformed to illite rich rocks by possible microbial action at surface to shallow 20 in sandstone buried 3 km during deep burial high temperature 110 c calcite cement from deep basin sources was precipitated in sandstones geochemical mass balance estimates physical and chemical evidence suggest quartz cement was sourced from within clastic rocks of the simpson group with minor external contribution of sio2 na is in low abundance due to loss in solution during weathering in the provenance rare earth elements ree have typical abundances and distributions in shales with enrichment in light ree littoral environment siltstones and matrix rich sandstones display enrichment of heavy ree in phosphatic brachiopod shell fragments

mechanisms controlling the silicon isotopic compositions of river waters it has been proposed that silicon si isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions in this study the first seasonal variations of stable isotope compositions of dissolved riverine si are reported and compared with concomitant changes in water chemistry four different rivers in switzerland were sampled between march 2004 and july 2005 the unique high resolution multi collector icp ms nu1700 has been used to provide simultaneous interference free measurements of 28si 29si and 30si abundances with an average limiting precision of 0 04 on 30si this precision facilitates the clarification of small temporal variations in isotope composition the average of all the data for the 40 samples is 30si 0 84 0 19 1 sd despite significant differences in catchment lithologies biomass climate total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved si in each river is strikingly similar with means of 0 70 0 12 for the birs 0 95 0 22 for the saane 0 93 0 12 for the ticino and 0 79 0 19 for the verzasca however the 30si undergoes seasonal variations of up to 0 6 comparisons between 30si and physico chemical parameters such as the concentration of dissolved si and other cations the discharge of the rivers and the resulting weathering fluxes permits an understanding of the processes that control the si budget and the fate of dissolved si within these rivers the main mechanism controlling the si isotope composition of the mountainous verzasca river appears to be a two component mixing between the seepage of soil ground waters with heavier si produced by clay formation and superficial runoff associated with lighter si during high discharge events a biologically mediated fractionation can be excluded in this particular river system the other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment in these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of si contributed by biological processes as opposed to abiotic weathering the presence of seasonal variations in si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved si delivered to the oceans the oceanic si isotope composition is very sensitive to even small changes in the riverine si isotope composition and this parameter appears to be more critical than plausible changes in the si flux therefore concurrent changes in weathering style may need to be considered when using the si isotopic compositions of diatoms sponges and radiolaria as paleoproductivity proxies

87sr 86sr ca sr and ge si ratios as tracers of solute sources and biogeochemical cycling at a temperate forested shale catchment central pennsylvania usa plant uptake and biological cycling processes are commonly the largest flux of nutrients in terrestrial ecosystems hydrologic and other losses are offset by inputs from atmospheric deposition and weathering this multi tracer study investigates these effects using 87sr 86sr ca sr and ge si ratios from solid soil profiles and bedrock biological leaves and sap waters and water pore ground stream waters samples to study ca sr ge and si sources and cycling in a forest catchment underlying gray shale in the temperate climate of central pennsylvania leaves and sap waters were found to have similar ge si ratios 1 mol mol which is consistent with biological fractionation occurring at the root soil water interface ge si ratios in soil porewaters were higher near the surface and increased over the growing season suggesting plant preferential uptake of si over ge ca sr ratios in oak leaves 1360 40 mol mol were significantly higher than those in maple leaves 650 20 mol mol ca sr ratios were also generally higher in leaves than in sap waters which are consistent with preferential sr adsorption or sr uptake during transpiration 87sr 86sr ratios in both leaves and sap waters were similar for a given site implying that trees access similar pools of sr and ca although there are site to site differences additionally 87sr 86sr ratios in plant tissues were most similar to shallow pore waters 0 50 cm suggesting that mineral nutrients are obtained by trees from the near sub surface 87sr 86sr ratios in soil solutions from ridgetop and swale sites are best explained by mixing sr derived from shale and atmospheric deposition valley bottom soil reservoirs and stream and groundwater samples include sr and ca derived from dissolution of two isotopically distinct generations of carbonates a preliminary estimate of the sr and ca stream fluxes and isotopic mass balances imply propagation of a carbonate weathering front of ca 300 m myr 1 a value larger than previously reported for regolith weathering advance rates calculated based on cosmogenic nuclides and u series isotopes the data for ca sr si and ge in soil soil solutions and stream waters reflect the interaction of slower weathering processes with rapid biologically driven cycling between soils and biomass

biomarker proxy shows potential for studying the entire quaternary arctic sea ice history recently a novel and promising biomarker proxy for reconstruction of arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons ip25 so far ip25 records have been restricted to the last 150 kyr bp here we present a biomarker record from ocean drilling program odp site 912 going back to the pliocene pleistocene boundary and indicating that sea ice of variable extent occurred in the fram strait southern yermak plateau area at least since about 2 2 ma furthermore our data support the idea that a combination of ip25 and open water phytoplankton biomarker data pip25 index may give more reliable and quantitative estimates of past sea ice cover at least for the study area this study reveals that the novel ip25 pip25 biomarker approach has potential for semi quantitative paleo sea ice studies covering the entire quaternary and motivate to carry out further detailed high resolution research on odp iodp material using this proxy

three levels of compartmentation within the overpressured interval of the anadarko basin deep basin pressure compartments can be classified on the basis of their size stratigraphy and pressure regimes detailed investigations of the geologic setting and pressure gradients of numerous reservoirs in the anadarko basin reveal the presence of three distinct levels of compartmentation level 1 is a basinwide feature known as the megacompartment complex mcc this complex is an overpressured volume of rocks that is completely enclosed by seals it is approximately 241 km 150 mi long 113 km 70 mi wide and has a maximum thickness in excess of 4877 m 16 000 ft gas reserves of the overpressured reservoirs within the mcc are speculated to be approximately 20 tcf the other two compartmentation levels are further subdivisions of the internal volume of the mcc level 2 compartmentation consists of multiple district or field sized configurations within a particular stratigraphic interval these compartments are 32 to 49 km 20 to 30 mi long 19 to 32 km 12 to 20 mi wide and 122 to 183 m 400 to 600 ft thick their reserve estimates can exceed 2 tcf examples of this type are the upper morrowan chert conglomerate reservoirs in the cheyenne reydon field area level 3 consists of a single small field or a particular reservoir nested within level 2 these compartments are generally 3 to 6 km 2 to 4 mi long the hierarchical classification of compartments has important implications for petroleum exploration and development recognizing the upper and lower boundaries of the mcc is essential to safe drilling practices the similar pressures within level 2 compartments allow the prediction of approximate reservoir pressures across trend size areas of the basin tens to

insights into circum arctic sea ice variability from molecular geochemistry abstract geological records of past sea ice such as those contained in arctic marine sediments offer an opportunity to strengthen our understanding of long term sea ice variability provided unambiguous paleo sea ice proxies can be developed one such recently proposed proxy is ip25 a highly branched isoprenoid alkene biosynthesized exclusively by sea ice dwelling diatoms haslea spp which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea ice extent however little is known about regional scale controls on ip25 production in sea ice limiting its wider applicability as a paleo sea ice proxy to address this issue we examined the distributions of ip25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the arctic we find a statistically significant logarithmic relationship between ip25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the pacific n 96 r2 0 67 p

germanium silicon fractionation in a tropical granitic weathering environment abstract germanium silicon ge si ratios were determined on quartz diorite bedrock saprolite soil primary and secondary minerals phytolith soil and saprolite pore waters and spring water and stream waters in an effort to understand ge si fractionation during weathering of quartz diorite in the rio icacos watershed puerto rico the ge si ratio of the bedrock is 2 mol mol with individual primary mineral phases ranging between 0 5 and 7 mol mol the ratios in the bulk saprolite are higher 3 mol mol than values measured in the bedrock the major saprolite secondary mineral kaolinite has ge si ratios ranging between 4 8 and 6 1 mol mol the high ge si ratios in the saprolite are consistent with preferential incorporation of ge during the precipitation of kaolinite bulk shallow soils have lower ratios 1 1 1 6 mol mol primarily due to the residual accumulation of ge poor quartz ge si ratios measured on saprolite and soil pore waters reflect reactions that take place during mineral transformations at discrete depths spring water and baseflow stream waters have the lowest ge si ratios 0 27 0 47 mol mol reflecting deep initial weathering reactions resulting in the precipitation of ge enriched kaolinite at the saprolite bedrock interface mass balance calculations on saprolite require significant loss of si and al even within 1 m above the saprolite bedrock interface higher pore water ge si ratios 1 2 mol mol are consistent with partial dissolution of this ge enriched kaolinite pore water ge si ratios increase up through the saprolite and into the overlying soil but never reach the high values predicted by mass balance perhaps reflecting the influence of phytolith recycling in the shallow soil

tracing silicon cycling in the okavango delta a sub tropical flood pulse wetland using silicon isotopes chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction potentially confounding estimates of silicate weathering rates silicon isotopes d30si may be a useful tool to investigate these processes here we present 82 d30si measurements from surface waters pore waters biogenic silica bsi clays sand and vegetation from the okavango delta botswana a freshwater sub tropical flood pulse wetland hydrologically the okavango is dominated by evapotranspiration water losses to the atmosphere it receives an annual pulse of water that inundates seasonal floodplains while river baseflow is sufficient to maintain a permanent floodplain d30si in dissolved silica dsi in surface waters along a 300 km transect at near peak flood show a limited range 0 36 1 19 imply ing the delta is well buffered by a balance of processes adding and removing dsi from the surface water a key control on dsi concentrations is the uptake production of bsi and recycling of si by aquatic vegetation although the net isotopic effect is necessarily small since all bsi re dissolves on short timescales in the sediments bsi d30si n 30 ranges from less

silicon isotope variations accompanying basalt weathering in iceland abstract this study presents the si isotope compositions of the dissolved phase of twenty rivers from across iceland the high resolution nu plasma 1700 mc icp ms was used to provide interference free 30 si 28 si ratios with an average limiting precision of 0 04 30 si the si isotope composition ranges from 0 08 to 1 46 30 si averaging 0 63 0 38 1 sd this is only slightly lighter than the recently reported mean of 0 84 0 19 for high precision measurements of swiss rivers but is significantly lighter than compositions reported for some other rivers the si isotope composition varies slightly with the amount of glacial cover which provides evidence that the continental si input to the oceans may be climatically controlled and thus likely to vary over glacial interglacial cycles after correction for the dissolution of trace amounts of calcite in one region a correlation is found between 30 si and ca si this is consistent with the measured basaltic composition and indicates isotopic fractionation during si removal from the dissolved phase by calculating the fraction of si that is removed from the dissolved phase into secondary phases it is possible to use the riverine si flux si denudation rate to calculate the initial dissolution rate of si within these catchments from this study we estimate that the total amount of si being dissolved by primary weathering of iceland is 3 million tons per yr however only 50 of this si is released into the rivers and contributes to denudation using the si isotope composition and the si fraction removed it is possible to model the si isotope fractionation as either a rayleigh type fractionation or a steady state system both yield similar fractionation factors of about 1 5 30 si implying only one underlying fractionation process that is controlled by external parameters such as runoff furthermore rivers that follow a steady state fractionation model are associated with higher si dissolution rates and lower 30 si values indicating an inverse relationship between weathering rates and dissolved riverine si isotope composition

identification of contrasting seasonal sea ice conditions during the younger dryas abstract a palaeo sea ice reconstruction for northern norway for the interval ca 13 8 7 2 cal ka bp has been performed using a combined organic geochemical proxy based study of a marine sediment core jm99 1200 obtained from andfjorden 69 15 95 n 16 25 09 e and the outcomes compared with a series of other palaeoclimate studies carried out previously within this study particular emphasis has been placed on the identification of the sea ice conditions during the younger dryas and the application of different biomarker based proxies to both identify and quantify seasonal sea ice conditions firstly the appearance of the specific sea ice diatom proxy ip 25 at ca 12 9 cal ka bp in the sedimentary record has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the younger dryas stadial the near continuous occurrence of ip 25 for the next ca 1400 yr demonstrates seasonal sea ice during this interval although variable abundances suggest that the recurrent conditions in the early mid younger dryas ca 12 9 11 9 cal ka bp changed significantly from stable to highly variable sea ice conditions at ca 11 9 cal ka bp and this instability in sea ice prevailed for the subsequent ca 400 yr during which an extremely short interval of permanent or near permanent sea ice was observed at ca 11 75 cal ka bp at ca 11 5 cal ka bp ip 25 disappeared from the record indicating ice free conditions that signified the beginning of the holocene the ip 25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate p b ip 25 data from which more quantitative measurements of sea ice were determined p b ip 25 data were consistent with consecutively seasonal then infrequent sea ice cover for the early mid and late younger dryas while further comparisons of the p b ip 25 data with the outcomes of previous correlations with modelled sea ice concentrations suggested that these intervals were characterised by ca 60 90 and ca 0 60 sea ice cover respectively both qualitative and quantitative sea ice records were also consistent with sea surface temperature and other palaeoclimate estimates derived previously from various other proxy studies the contrasting seasonal sea ice conditions during the younger dryas were further verified through a comparison of the concentrations of ip 25 with those of another highly branched isoprenoid hbi alkene that is di unsaturated and believed to also be produced by sea ice diatoms the ratio of the hbi diene to ip 25 termed dip 25 is believed to provide a useful indicator of stability or variability in sea ice conditions and complements the outcomes from the ip 25 and p b ip 25 index data the identification of contrasting seasonal sea ice conditions during the younger dryas will likely contribute to the debate regarding the climatic impacts that took place during this intriguing interval

weathering dust and biocycling effects on soil silicon isotope ratios abstract silicon isotope ratios 30si of bulk mineral materials in soil integrate effects from both silicon sources and processing here we report 30si values from a climate gradient of hawaiian soils developed on 170 ka basalt and relate them to patterns of soil chemistry and mineralogy the results demonstrate informative relationships between the mass fraction of soil si depletion and 30si in upper 1 m deep soil horizons generally correlate with the isotope fractionation predicted by a study of dissolved si in basalt watershed rivers and driven by preferential 28si removal from the dissolved phase during precipitation in contrast after correcting for the influence of dust secondary mineral si depletion and 30si values in shallow

sea ice variations in the central canadian arctic archipelago during the holocene abstract a sea ice record for barrow strait in the canadian arctic archipelago caa is presented for the interval 10 0 0 4 cal kyr bp this holocene record is based primarily on the occurrence of a sea ice biomarker chemical ip25 isolated from a marine sediment core obtained from barrow strait in 2005 a core chronology is based on 14c ams dating of mollusc shells obtained from ten horizons within the core the primary ip25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers stable isotope composition of bulk organic matter benthic foraminifera particle size distributions and ratios of inorganic elements the combined proxy data show that the palaeo sea ice record can be grouped according to four intervals and these can be contextualised further with respect to the holocene thermal maximum htm spring sea ice occurrence was lowest during the early mid holocene 10 0 6 0 cal kyr bp and this was followed by a second phase 6 0 4 0 cal kyr bp where spring sea ice occurrence showed a small increase between 4 0 and 3 0 cal kyr bp spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the htm elevated spring sea ice occurrences continued from 3 0 to 0 4 cal kyr bp although they were more variable on shorter timescales within this fourth interval we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the mediaeval warm period and the little ice age respectively comparisons are made between our proxy data with those obtained from other palaeo climate and sea ice studies for the caa

seeking a holocene drift ice proxy non clay mineral variations from the sw to n central iceland shelf trends regime shifts and periodicities quantitative x ray diffraction analysis of the 2 mm sediment fraction was carried out on 1257 samples from the seafloor and 16 cores from the iceland shelf west of 18 w all but one core b997 347pc were from transects along troughs on the nw to n central shelf an area that in modern and historic times has been affected by drift ice the paper focuses on the non clay mineralogy of the sediments excluding calcite and volcanic glass quartz and potassium feldspars occupy similar positions in an r mode principal component analysis and oligoclase feldspar tracks quartz these minerals are used as a proxy for ice rafted detritus ird accordingly the sum of these largely foreign minerals q k to icelandic bedrock is used as a proxy for drift ice a stacked equi spaced 100 a record is developed which shows both low frequency trends and higher frequency events the detrended stacked record compares well with the flux of quartz mg cm 2 a 1 at md99 2269 off n iceland the multi taper method indicated that there are three significant frequencies at the 95 confidence level with periods of ca 2500 445 and 304 a regime shift analysis pinpoints intervals when there was a statistically significant shift in the average q k weight and identifies four ird rich events separated by intervals with lower inputs there is some association between peaks of ird input less dense surface waters from 18o data on planktonic foraminifera and intervals of moraine building copyright 2009 john wiley sons ltd

climate induced changes in sedimentary regimes for organic matter supply on the continental shelf off northern norway abstract with this study i suggest that changes in biogeochemical processes in northern norwegian fjords during the last glacial interglacial transition 14 3 to 6 3 ka b p are predominantly climate induced variable strength in atlantic water inflow intrusion of arctic waters and sea ice coverage various nutrient supply as well as several re advances of continental ice sheets are recorded by both bulk organic and selected biomarkers in sediments of the andfjord stable isotope 13corg 15n and rock eval pyrolysis data indicate a strong supply of terrestrial organic matter during stadials e g younger dryas older dryas whereas enhanced input of marine organic matter prevailed during the interstadials bolling allerod profiles of selected biomarkers of marine origin show a characteristic climate induced variation during the whole time interval where relatively low concentrations of dinosterols and c37 alkenones may indicate similar to today a minor contribution of their respective plankton groups coccolithophorids dinoflagellates the prevalence of arctic waters and seasonal sea ice coverage during the younger dryas is indicated by a single maximum of 24 methylenecholesterol probably indicating the dominance of sea ice diatoms and or the prevalence of diatoms of thalassiosiraceae in surface waters the sediments of the allerod in contrast show a pronounced maximum in dinosterols indicating a better adaptation of dinoflagellates to an oceanic regime that is characterized by incipient intrusion of atlantic water highly variable sea surface temperatures and well stratified water masses the concentration of higher molecular weight n alkanes however follows the deglacial early holocene trend of climate amelioration from the last deglaciation to the middle holocene with maxima during ice advances stadials and minima during the middle holocene warm period these new results significantly improve the understanding of climate induced response on organic matter supply in fjords and provide a better knowledge of past variations of biogeochemical processes in high latitude coastal environments

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

using artificial neural networks to predict the presence of overpressured zones in the anadarko basin oklahoma many sedimentary basins throughout the world exhibit areas with abnormal pore fluid pressures higher or lower than normal or hydrostatic pressure predicting pore pressure and other parameters depth extension magnitude etc in such areas are challenging tasks the compressional acoustic sonic log dt is often used as a predictor because it responds to changes in porosity or compaction produced by abnormal pore fluid pressures unfortunately the sonic log is not commonly recorded in most oil and or gas wells we propose using an artificial neural network to synthesize sonic logs by identifying the mathematical dependency between dt and the commonly available logs such as normalized gamma ray gr and deep resistivity logs reid the artificial neural network process can be divided into three steps 1 supervised training of the neural network 2 confirmation and validation of the model by blind testing the results in wells that contain both the predictor gr reid and the target values dt used in the supervised training and 3 applying the predictive model to all wells containing the required predictor data and verifying the accuracy of the synthetic dt data by comparing the back predicted synthetic predictor curves grnn reidnn to the recorded predictor curves used in training gr reid artificial neural networks offer significant advantages over traditional deterministic methods they do not require a precise mathematical model equation that describes the dependency between the predictor values and the target values and unlike linear regression techniques neural network methods do not overpredict mean values and thereby preserve original data variability one of their most important advantages is that their predictions can be validated and confirmed through back prediction of the input data this procedure was applied to predict the presence of overpressured zones in the anadarko basin oklahoma the results are promising and encouraging

distinct silicon and germanium pathways in the soil plant system evidence from banana and horsetail plants strongly impact the continental silicon cycle by taking up si and precipitating opal phytoliths which are recycled into the soil studying ge incorporation a chemical analog of si relative to si may provide a useful tracer of si pathways however ge uptake and transport through plants and the impact on ge si of phytoliths remain poorly understood here we report ge uptake and accumulation and ge si fractionation in all plant parts and solutions from 1 hydroponic banana 2 in situ sampled banana and 3 horsetails we further combine these data with delta si 29 from banana plants our data reconcile opposite conclusions drawn from previous studies on ge uptake and pathways no discrimination of ge occurred at the root solution interface banana and horsetails were shown to accumulate ge in roots a previous study provided evidence of low ge si ratios in root phytoliths which contrasts with high bulk ge si ratios in roots we report here this suggests that ge is organically trapped in roots consequently shoots display lower ge si ratios without fractionation between shoot parts since ge would follow transpiration stream as silicon and is not discriminated between shoot parts this contrasts with the two step discrimination against heavy si isotopes at the root solution interface and then within the shoots the soil composition clays versus fe oxides has a leading role on the ge si signatures of plants which may in turn impact on the si and ge fluxes to the global ocean

δ30si systematics in a granitic saprolite puerto rico granite weathering and clay mineral formation impart distinct and interpretable stable si isotope 30 si signatures to their solid and aqueous products within a saprolite clay minerals have 30 si values 2 0 more negative than their parent mineral and the 30 si signature of the bulk solid is determined by the ratio of primary to secondary minerals mineral specific weathering reactions predominate at different depths driving changes in differing 30 si pore water values at the bedrock saprolite interface dissolution of plagioclase and hornblende creates 30 si pore water signatures more positive than granite by up to 1 2 these reactions are the main contributor of si to stream water and determine its 30 si value throughout the saprolite biotite weathering releases si to pore waters but kaolinite overgrowth formation modulates its contribution to pore water si the influence of biotite on 30 si pore water is greatest near the bedrock where biotite derived si mixes with bulk pore water prior to kaolinite formation higher in the saprolite biotite grains have become more isolated by kaolinite overgrowth which consumes biotite derived si that would otherwise influence 30 si pore water because of this isolation which shifts the dominant source of pore water si from biotite to quartz 30 si pore water values are more negative than granite by up to 1 3 near the top of the saprolite

biogenic and pedogenic controls on si distributions and cycling in grasslands of the santa cruz soil chronosequence california abstract biogenic and pedogenic processes control silica cycling in grasslands growing on a soil chronosequence and dominated by strong seasonal variabilities of a mediterranean climate shallow pore water si in spite of significant annual uptake and release by plant growth and dieback exhibits only moderate seasonal fluctuations reflecting strong buffering from labile biogenic si dominated by phytoliths and by secondary pedogenic silicates long phytolith residence times 340 900 yrs reflect the seasonally dry climate and high solute si concentrations water extractable si is closely associated with al indicating seasonal precipitation and dissolution of a highly labile 1 1 hydroxyaluminosilicate has probably allophane which transforms in deeper soil into fine grained poorly crystalline kaolinite shallow plant roots extract greater proportions of biogenic si and deeper plant roots larger amounts pedogenic si high pore water ge si in late winter and spring reflects the reinforcing effects of plant fractionation and concurrent dissolution of ge enriched has the same processes produce pore waters with depleted 30 si 28 si in the summer and fall ge si declines and 30 si 28 si increases reflecting the cessation of plant uptake continued dissolution of soil phytoliths and re precipitation of less soluble has si inputs from weathering 2 90 mmol m 2 yr 1 and losses from pore water discharge 18 68 mm m 2 yr 1 are comparable for individual soils decline with soil age and are significantly less than amounts of si annual cycled through the vegetation 42 171 mm m 2 yr 1 mobile si is generally balanced in the soils with upward bio pumping by the shallow rooted grasses efficiently competing against downward leaching and pore water discharge small net annual increases in si in the present day soils could not have been maintained over the time scale represented by the chronosequence 65 225 yrs implying past changes in environmental conditions

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

silicon isotope study on rice plants from the zhejiang province china silicon isotope compositions of 16 rice plants from the zhejiang province were studied and potential applications of silicon isotope study to agriculture and biogeochemistry were discussed it is found that the sio2 contents in ignited rice plant samples increased generally from roots through sl stem and leaves to husks large and systematic silicon isotope fractionation was observed among different organs of individual rice plants their 30si values show a generally increasing trend from roots and sl through husks to grains which can be explained by kinetic isotope fractionation in a rayleigh process a 30si value of 6 1 was obtained from two samples of rice grains which is much greater than the highest value 3 4 observed in terrestrial samples before it is inferred that monosilicic acid is the major silicon bearing component taken up by rice roots passive uptake of silicon is important for rice and evapotranspiration may be the major mechanism for the transportation and precipitation of silicon in rice plants it is suggested that silicon isotope study has a potential application to agriculture and biogeochemistry

the arctic sea ice biomarker ip25 a review of current understanding recommendations for future research and applications in palaeo sea ice reconstructions in recent years a novel proxy for the past occurrence of arctic sea ice has been proposed that is based on the variable marine sedimentary abundance of an organic geochemical lipid derived from sea ice diatoms in the spring this lipid termed ip25 ice proxy with 25 carbon atoms is a highly branched isoprenoid mono unsaturated alkene that appears to be sufficiently stable in sediments to permit meaningful palaeo sea ice reconstructions to be carried out over short to long term timescales since the first proposed use of ip25 as a proxy for palaeo sea ice by belt et al 2007 a number of laboratories have measured this biomarker in arctic sediments and it is anticipated that research activity in this area will increase further in the future the content of this review is divided into a number of sections firstly we describe the scientific basis for the ip25 proxy and its initial discovery in arctic sea ice sedimenting particles and sediments secondly we summarise the relatively few studies that have to date concentrated on examining the factors that influence the production and fate of ip25 and we identify some areas of future research that need to be addressed in order to improve our understanding of ip25 data obtained from sedimentary analyses what is clear at this stage however it that the presence of ip25 in arctic marine sediments appears to represent a proxy measure of past seasonal sea ice rather than permanent or multi year ice conditions thirdly we highlight the importance of rigorous analytical identification and quantification of ip25 especially if measurements of this biomarker are going to be used for quantitative sea ice reconstructions rather than qualitative analyses alone presence absence fourthly we review some recent attempts to make the interpretations of ip25 biomarker data more detailed and quantitative by combining sedimentary abundances with those of phytoplankton and other sea ice derived biomarkers thus the bases for the so called pip25 and dip25 indices are described together with an overview of potential limitations concluding that investigations into the use of these indices needs further research before their full potential can be realised in the final section we provide a summary of ip25 based palaeo sea ice reconstruction case studies performed to date these case studies cover different arctic regions and timescales spanning decades to tens of thousands of years

unstable younger dryas climate in the northeast north atlantic the younger dryas stadial greenland stadial 1 has long been recognized in proxy records throughout the north atlantic region as a stable cool period that started and ended abruptly however modeling experiments in which the younger dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records here we present evidence of a climatically unstable younger dryas based on a decadal resolution marine proxy record from the norwegian continental shelf this record shows that the north atlantic was characterized in the early younger dryas by arctic water and an increasing accumulation of fresh surface water that peaked at 12 500 calendar yr b p for 300 yr during the late younger dryas the sea surface temperatures fluctuated between glacial values 2 c and interglacial values 10 c on a subdecadal to multidecadal time scale this period of extreme instability preceded the more stable and warm holocene starting ca 11 500 calendar yr b p these results are consistent with modeling experiments that link the younger dryas climate changes to fluctuations of the north atlantic thermohaline circulation

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

new data on geology and germanium mineralization in the hunchun basin northeastern china abstract the geochemistry and mineralogy of palaeogene coals from the hunchun coalfield jilin province northeastern china have been studied using x ray fluorescence spectrometry inductively coupled plasma mass spectrometry scanning electron microscopy in combination with energy dispersive x ray spectrometry and x ray diffraction analysis of the low temperature ash the 22a coal from the banshi mine is of subbituminous a to high volatile bituminous rank 0 53 0 56 ro ran and has a low sulfur content 0 74 on average the 22a coal consists mainly of kaolinite quartz illite and to a lesser extent plagioclase siderite and pyrite as compared with the average world low rank coals the 22a coal is enriched in as sb ge cs and w combined with the geochemical features of six other coal seams from the hunchun coalfield the terrigenous materials of the hunchun coals were dominantly from mesozoic mostly lower cretaceous volcanic rocks and paleozoic granites and associated metamorphic rocks surrounding the coal basin a minor source was the paleogene volcaniclastics including some adakitic rocks which are characterized by higher sr y and la yb ratios the ge enrichments that are detected in some individual coal benches from the hunchun coalfield were related to tectonic uplift of the crystalline rocks surrounding the basin and their following denudation the oxidized meteoric waters episodically influenced by volcanic related hot springs might extract ge from the source rocks and then precipitate it as a result of bio chemical reduction forming the mineralization disseminated in the coals

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

mobilization of aluminium and magnesium by roots of banana musa spp from kaolinite and smectite clay minerals banana plants musa spp are very sensitive to al which is mobilized in acid soil conditions these plants may however contribute to their own intoxication because their roots can excrete protons in large quantities the authors studied the mobilization of al by banana roots from clay minerals in experimental designs exacerbating the root mineral contact the plants were grown on agarose gel or sand substrates previously mixed with smectite montmorillonite and kaolinite as sole source of al the ph and the ion concentrations in the aqueous and exchangeable phases of the substrates were determined as concentrations of al ca mg and k in plants in both agarose and sand substrates ph significantly decreased in the close vicinity of roots relative to the bulk substrate this root induced acidification involved a preferential mobilization of al in kaolinite substrates and of mg in smectite substrates and thereby a significant plant uptake of al and mg from these respective substrates root induced weathering of kaolinite and montmorillonite thus suggests that the mobilization of respectively al and mg are the limiting steps in the dissolution of these respective minerals just as demonstrated in previous chemical weathering studies c 2003 elsevier ltd all rights reserved

identification of paleo arctic winter sea ice limits and the marginal ice zone optimised biomarker based reconstructions of late quaternary arctic sea ice abstract analysis of 100 surface sediments from across the barents sea has shown that the relative abundances of the mono unsaturated sea ice diatom derived biomarker ip 25 and a tri unsaturated highly branched isoprenoid hbi lipid hbi iii are characteristic of the overlying surface oceanographic conditions most notably the location of the seasonal sea ice edge thus while ip 25 is generally limited to locations experiencing seasonal sea ice with higher abundances found for locations with longer periods of ice cover hbi iii is found in sediments from all sampling locations but is significantly enhanced in sediments within the vicinity of the retreating sea ice edge or marginal ice zone miz the response of hbi iii to this well defined sea ice scenario also appears to be more selective than that of the more generic phytoplankton biomarker brassicasterol the potential for the combined analysis of ip 25 and hbi iii to provide more detailed assessments of past sea ice conditions than ip 25 alone has been investigated by quantifying both biomarkers in three marine downcore records from locations with contrasting modern sea ice settings for sediment cores from the western barents sea intermittent seasonal sea ice and the northern norwegian sea ice free high ip 25 and low hbi iii during the younger dryas ca 12 9 11 9 cal kyr bp is consistent with extensive sea cover with relatively short periods of ice free conditions resulting from late summer retreat towards the end of the yd ca 11 9 11 5 cal kyr bp a general amelioration of conditions resulted in a near winter maximum ice edge scenario for both locations although this was somewhat variable and the eventual transition to predominantly ice free conditions was later for the western barents sea site ca 9 9 cal kyr bp compared to nw norway ca 11 5 cal kyr bp for both locations coeval elevated hbi iii but absent ip 25 potentially provides further evidence for increased atlantic water inflow during the early holocene but this interpretation requires further investigation in contrast ip 25 and hbi iii data obtained from a core from the northern barents sea demonstrate that seasonal sea ice prevailed throughout the holocene but with a gradual shift from winter ice edge conditions during the early holocene to more sustained ice cover in the neoglacial a directional shift that has undergone a reverse in the last ca 150 yr according to observational records our combined surface and downcore datasets suggest that combined analysis of ip 25 and hbi iii can provide information on temporal variations in the position of the maximum winter arctic sea ice extent together with insights into sea ice seasonality by characterisation of the miz combining ip 25 with hbi iii in the form of the previously proposed pip 25 index yields similar outcomes to those obtained using brassicasterol as the phytoplankton marker importantly however some problems associated with use of a variable balance factor employed in the pip 25 calculation are potentially alleviated using hbi iii

a global ge isotope budget we present measurements of ge isotope composition and ancillary data for samples of river water low and high temperature hydrothermal fluids and seawater the dissolved 74ge composition of analyzed rivers ranges from 2 0 to 5 6 which is significantly heavier than previously determined values for silicate rocks 74ge 0 4 0 7 escoube et al geostand geoanal res 36 2 2012 from which dissolved ge is primarily derived an observed negative correlation between riverine ge si and 74ge signatures suggests that the primary 74ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products high temperature 150 c hydrothermal fluids analyzed in this study have 74ge of 0 7 1 6 most likely fractionated during fluid equilibration with quartz in the reaction zone low temperature 25 63 c hydrothermal fluids are heavier 74ge between 2 9 and 4 1 and most likely fractionated during ge precipitation with hydrothermal clays seawater from the open ocean has a 74gesw value of 3 2 0 4 and is indistinguishable among the different ocean basins at the current level of precision this value should be regulated over time by the isotopic balance of ge sources and sinks and a new compilation of these fluxes is presented along with their estimated isotopic compositions assuming steady state non opal ge sequestration during sediment authigenesis likely involves isotopic fractionation 74gesolid solution that is 0 6 1 8

desilication in archean weathering processes traced by silicon isotopes and ge si ratios abstract the influence of continental weathering on oceanic seawater compositions in the precambrian is poorly understood here we combine si isotopes and ge si ratios of a mesoarchean paleosol 2 95 ga and overlying shales as proxies for weathering processes and si mass transfer at the early earth s surface results show that as with modern soils neoformation of secondary clay minerals in the paleosol was associated with the fractionation of si isotopes and ge si ratios in response to chemical weathering and soil desilication furthermore the loss of fe bearing minerals most likely fe bearing smectites produced additional controls on si and ge mobility through the coupled dissolution and re precipitation of clay minerals under reductive conditions opposite fractionation behaviors are observed neoformed secondary clay minerals acted as a 28 si and ge sink whereas the leaching of fe bearing minerals released 28 si and ge into soil solutions an attempt to estimate 30 si and ge si signatures of released dissolved elements into soil solution provided 30 si and ge si signatures of about 0 1 and 1 4 mol mol respectively furthermore shales deposited shortly after paleosol formation display 30 si and ge si compositions that may be explained as mixtures of the recognized paleosol components the shale record suggests that weathering induced desilication and leaching of fe bearing minerals to a lesser extent might have been widely effective during the mesoarchean for the transfer of si from the continents to the hydrosphere comparison of si isotopes recorded in detrital sediments and chemical precipitates over time might thus provide a useful supplementary tool to decipher the impact of putative increases in continental weathering and desilication relative to changes in hydrothermal and continent derived solute inputs to ocean and ocean cooling

germanium silicon as a flow path tracer application to the rio icacos watershed 1 we use dissolved silicon together with its geochemical twin germanium for the first time as a hydrologic tracer to study water delivery to the stream during storm events in the rio icacos watershed puerto rico ge and si were measured on base flow stormflow springwater and soil water samples compositions of all of these waters appear to reflect varying contributions from three components which we attribute to solutes released from bedrock weathering groundwater from short term soil water interaction quick soil water and longer term soil water interaction matrix soil water base flow stream waters have high si and moderate ge ge si ratio 0 29 mol mol consistent with a predominantly bedrock weathering source as indicated by their similarity with water sampled from springs emerging from the saprolite bedrock boundary on a hillslope landslide scar during storm events there is a shift toward more dilute compositions but higher ge si ratios similar to those measured on water samples from temporary depression storage and overland flow quick soil water geochemical mass balance shows that 80 90 of the stream chemistry can be explained by mixing groundwater with this quick soil water composition which we infer to reflect new water traveling as shallow throughflow stream water 18o values decrease to more negative values typical of precipitation supporting rapid delivery of rainwater to the stream channel during stormflow the third component with a ge rich composition characteristic of soil matrix water sampled by tension lysimeters is required to explain higher stream water ge si ratios measured during hydrograph recession we infer from this an additional slower and less dominant pathway for delivery of soil water to the stream channel

dissipation of anomalous pressures in the subsurface 1 zones of anomalous pressure higher and lower than hydrostatic pressure have been observed in many sedimentary basins around the world these normally consist of groups of pressure compartments volumes of higher permeability rock surrounded on all sides by lower permeability barriers knowledge of the timescales over which these abnormal pressures are maintained and the mechanisms by which they dissipate is critical for understanding how fluids such as oil and gas move in the subsurface existing analytic solutions investigate pressure dissipation through low permeability barriers on top of or underneath an isolated pressure compartment there are no analytic solutions describing pressure dissipation through lateral barriers such as faults or investigating the impact of groups of pressure compartments on the rate of pressure dissipation this paper presents simple analytic models to investigate pressure dissipation through barriers such as faults forming the sides of pressure compartments the timescales are compared with a solution for pressure dissipation through barriers on top of and underneath the compartment it also investigates analytically the rate of pressure dissipation from groups of pressure compartments lateral seal permeabilities of 10 19 m2 may delay pressure equilibration for millions of years provided the compartment has a sufficiently high fluid storage capacity factors contributing toward a high fluid storage capacity include a high fluid compressibility as is the case in hydrocarbon reservoirs and a high porosity the grouping of abnormally pressured compartments into megacompartment complexes may delay pressure dissipation for hundreds of millions of years

mapping recent sea ice conditions in the barents sea using the proxy biomarker ip25 implications for palaeo sea ice reconstructions abstract an analysis of the sea ice proxy ip 25 and the open water phytoplankton indicator brassicasterol has been carried out for 93 surface sediments collected from the barents sea and some additional data from previous studies have been included to augment the analysis further consistent with a specific and selective sea ice diatom origin for ip 25 this biomarker was identified in virtually all sediments from seasonally ice covered locations but was absent from the majority of sites beyond the maximum sea ice extent msie for the period 1983 2002 in contrast brassicasterol was detected in virtually all sediments from the region and concentrations were not at all associated with the msie instead more localised regions of brassicasterol concentrations were identified and these likely reflect different influences on production and deposition when the ip 25 and brassicasterol concentrations were combined together in the form of the previously proposed p b ip 25 index the aforementioned association between ip 25 occurrence and the msie was clarified further and in addition provided more detailed descriptions of sea ice cover in particular p b ip 25 data indicated seasonal sea ice or marginal ice zone conditions for the region of the barents sea within the msie according to previously defined p b ip 25 ranges we also amalgamated the biomarker data from the current study with those derived previously by muller et al 2011 and compared these larger datasets with satellite derived mean spring sea ice concentrations significantly although the correlation between the combined ip 25 concentration dataset with the satellite data was very similar to that reported previously by muller et al 2011 the corresponding correlation using the p b ip 25 values was poorer with the larger dataset and some possible reasons for this are discussed finally in a small number of cases ip 25 was identified in sediments somewhat distal from the msie and it is hypothesised that the occurrence of ip 25 in these sediments results from allochthonous input following sediment advection between shelf and trough environments this is the first reported example that provides evidence for the allochthonous input of ip 25 into marine sediments and it is recommended that this should be considered carefully when carrying out palaeo sea ice reconstructions based on the occurrence of this biomarker in the future

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

germanium sequestration by soil targeting the roles of secondary clays and fe oxyhydroxides abstract germanium is a trace element that behaves similarly to silicon and shows promise as a tracer of silicate weathering processes sequestration of ge by clay minerals is thought to be the dominant mechanism responsible for ge si fractionation during weathering in some environments ge may be sequestered by iron oxyhydroxides we examine ge behavior in soils along a well characterized climate gradient on the hawaiian island of maui to clarify the relationship between fe geochemistry and soil ge si ratios all of the sites are developed on basaltic lavas and tephras approximately 400 ky old are highly si depleted and have ge si ratios higher than parent material sites experiencing less than 3300 mm rain yr host oxidized highly weathered basaltic soils in which fe is present as secondary fe oxyhydroxide minerals in contrast the wetter sites 3340 mm yr show extensive fe reduction mobilization and loss we show that ge sequestration is independent of fe redox behavior along the gradient and thus precipitation of fe oxyhydroxides is not a major factor contributing to ge si fractionation during weathering instead elevated soil ge si ratios reflect partitioning of ge into secondary clay minerals plus additional retention of ge by refractory non silicates

characterization of a weathering sequence of soils derived from volcanic ash in cameroon taxonomic mineralogical and agronomic implications the characteristics of eight pedons developed in quaternary basaltic pyroclasts in western cameroon under humid tropical conditions are reported the soil weathering sequence consists of an andept tropept udalf udult association andic properties physico chemical characteristics and weathering stage clearly distinguish the taxonomic units the total reserve in bases trb and the clay content measured after adequate h2o dispersion with na resins both appear to be suitable weathering indices clay mineralogy of non andic soils shows direct relationships between interstratified halloysite smectite content cec of the clay fraction and weathering stage the weathering stage of the investigated soils is reflected not only in their components and classification but also in their nutrient status and banana crop performance

sea ice in the paleoclimate system the challenge of reconstructing sea ice from proxies an introduction sea ice is an important component of the earth system with complex dynamics imperfectly documented from direct observations which are primarily limited to the last 40 years whereas large amplitude variations of sea ice have been recorded especially in the arctic with a strikingly fast decrease in recent years partly attributed to the impact of anthropogenic climate changes little is known about the natural variability of the sea ice cover at multi decadal to multi millennial time scales hence there is a need to establish longer sea ice time series to document the full range of sea ice variations under natural forcings to do this several approaches based on biogenic or geochemical proxies have been developed from marine ice core and coastal records the status of the sea ice proxies has been discussed by the sea ice proxy sip working group endorsed by pages during a first workshop held at geotop in montreal the present volume contains a set of papers addressing various sea ice proxies and their application to large scale sea ice reconstruction here we summarize the contents of the volume including a table of various proxies available in marine sediments and ice cores with their possibilities and limitations

plant impact on the biogeochemical cycle of silicon and related weathering processes abstract the contribution of plants to the biogeochemical cycle of si and related weathering processes was studied in an equatorial rainforest ecosystem congo where the biologic turnover of si is high 58 to 76 kg ha y litterfall leaves a soil profile and groundwaters were analysed phytoliths and organic matter have a similar distribution with depth in the soil profile the model of a bicompartmental distribution of organic matter is applied to phytolith distribution and shows that about 92 of the biogenic silica input is rapidly recycled while about 8 of the biogenic silica input supplies a stable pool of phytoliths with a lower turnover reprecipitation of silica was observed at the base of the soil profile indicating a local geochemical environment that is oversaturated with respect to amorphous silica a balance in biogeochemical cycle of si requires that the vegetation absorb dissolved silicon released from weathering of minerals which otherwise would be available for mineral neoformation or export from the profile towards regional drainages plant uptake of si increases the chemical weathering rate without increasing the denudation rate this study shows that the uptake storage and release of si by the vegetation have to be taken into account when using dissolved si for tracing chemical weathering dynamics

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

identification and characterisation of a novel mono unsaturated highly branched isoprenoid hbi alkene in ancient arctic sediments abstract the occurrence of a novel c 25 highly branched isoprenoid hbi mono unsaturated hydrocarbon in arctic marine sediments from the fram strait is described the structure was determined following synthesis from a closely related diene and nmr spectroscopic analysis the position of the double bond was confirmed by oxidation ruo 4 and comparison of the mass spectrum of the resulting c 19 ketone with that of an authentic sample synthesised previously the same c 19 ketone was also present following oxidation of the fram strait sediment extracts the source of the novel hbi monoene biomarker is not known but is believed to be certain marine diatoms on the basis of structural similarities with other hbis from such sources it does not however appear to be biosynthesised by arctic sea ice diatoms unlike its regio isomer ip 25 an established proxy for arctic sea ice alternatively it may represent a diagenetic product of the sea ice diatom biomarker ip 25 this seems unlikely however on the basis of their respective structures since the new hbi monoene and ip 25 possess similar gas chromatographic and mass spectral properties but probably have contrasting sources we suggest that future paleo sea ice reconstruction studies based on the occurrence of ip 25 should pay further attention to the rigorous assignment of this biomarker in marine sediment extracts some suggestions for achieving this based on analytical purification and mass spectrometric measurements are provided

variations of δ30si and ge si with weathering and biogenic input in tropical basaltic ash soils under monoculture in soils silicon released by mineral weathering can be retrieved from soil solution through clay formation si adsorption onto secondary oxides and plant uptake thereby impacting the si isotopic signature and ge si ratio of dissolved si dsi exported to rivers here we use these proxies to study the contribution of biogenic si bsi in a soil plant system involving basaltic ash soils differing in weathering degree under intensive banana cropping delta si 30 and ge si ratios were determined in bulk soils 2 mm sand 50 2000 mu m silt 2 50 mu m amorphous si asi 2 50 mu m and clay 2 mu m fractions delta si 30 by mc icp ms nu plasma in medium resolution operating in dry plasma with mg doping delta si 30 vs nbs28 0 12 parts per thousand 2 sigma sd ge si computed after determination of ge and si concentrations by hr icp ms and icp aes respectively components of the asi fraction were quantified by microscopic counting phytoliths diatoms ashes compared to fresh ash delta si 30 0 38 parts per thousand ge si 2 21 mu mol mol 1 soil clay fractions 2 mu m were enriched in light si isotopes and ge with increasing weathering degree delta si 30 decreased from 1 19 to 2 37 parts per thousand and ge si increased from 4 10 to 5 25 mu mol mol 1 sand and silt fractions displayed delta si 30 values close to fresh ash 0 33 parts per thousand or higher due to saharian dust quartz deposition whose contribution was evaluated by isotopic mass balance calculation si isotopic signatures of bulk soils 2 mm were strongly governed by the relative proportions of primary and secondary minerals the bulk soil si isotopic budget could be closed indicating that all the phases involved were identified microscopic counting highlighted a surface accumulation of banana phytoliths and a stable phytolith pool from previous forested vegetation delta si 30 and ge si values of clay fractions in poorly developed volcanic soils isotopically heavier and ge depleted in surface horizons support the occurrence of a dsi source from banana phytolith dissolution available for si sequestration in clay sized secondary minerals clay minerals formation and si adsorption onto fe oxide in the soil plant system delta si 30 and ge si are thus highly relevant to trace weathering and input of dsi from phytoliths in secondary minerals although not quantifying the net input of bsi to dsi c 2009 elsevier ltd all rights reserved

river fluxes of dissolved silica to the ocean were higher during glacials ge si in diatoms rivers and oceans two centric marine diatom species thalassiosira oceanica and thalassiosira antarctica were grown in batch cultures to determine the incorporation of germanium ge and silicon si into siliceous shells opal the results were modeled as ge si isotope fractionation during exponential growth diatoms take up and incorporate ge si from solution without major discrimination against ge during stationary phase growth near silica limitation the antarctic species t antarctica discriminates slightly against ge but integrated ge si opal produced over the latter portion of the growth cycle is indistinguishable from the initial solution ratio these results confirm experiments using radioactive 68ge that showed absence of fractionation during diatom silica uptake azam and volcani 1981 in contrast to two box ocean models that invoke 50 ge discrimination by diatoms to explain the observed excess surface ocean germanium concentration murnane and stallard 1988 froelich et al 1989 and late pleistocene ocean sediment ge si opal records mortlock et al 1991 runs of a 10 box ocean ge and si model pandora with 50 discrimination reproduce the excess surface ocean ge but introduces curvature into the deep ocean ge versus si relationship that is not observed in the oceans thus 50 fractionation is not supported by either cultures or models if diatoms do not fractionate ge si then late pleistocene ge si opal variations in piston cores are caused not by changes in local biosiliceous production and silica utilization mortlock et al 1991 but rather by whole ocean changes in ge si seawater the marine ge si opal record of the last 450 kyr can be modeled as transient oceanic responses to instantaneous continental climate transitions consistent with the chemical weathering model of murnane and stallard 1990 glacial periods are characterized by lower continental weathering intensity lower ge si riv and two fold higher dissolved silica river fluxes marine ge si opal records thus contain a history of ocean silica chemistry that reflect rapid global changes in continental weathering

early holocene temperature variability in the nordic seas the role of oceanic heat advection versus changes in orbital forcing received 7 january 2011 revised 15 july 2011 accepted 21 july 2011 published 22 october 2011 1 the separate roles of oceanic heat advection and orbital forcing on influencing early holocene temperature variability in the eastern nordic seas is investigated the effect of changing orbital forcing on the ocean temperatures is tested using the 1dice model and the 1dice results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of atlantic water from the faroe shetland channel in the south to the barents sea in the north the stronger early holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures however ocean temperatures underneath the summer mixed layer did not increase significantly the absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka bp representing the holocene thermal maximum in the eastern nordic seas in contrast maximum in northward oceanic heat transport through the norwegian atlantic current occurred approximately 10 ka bp the maximum in oceanic heat transport at 10 ka bp occurred due to a major reorganization of the atlantic ocean circulation entailing strong and deep rejuvenation of the atlantic meridional overturning circulation combined with changes in the north atlantic gyre dynamic causing enhanced transport of heat and salt into the nordic seas

terrestrial ecosystems and the global biogeochemical silica cycle 1 most research on the global si cycle has focused nearly exclusively on weathering or the oceanic si cycle and has not explored the complexity of the terrestrial biogeochemical cycle the global biogeochemical si cycle is of great interest because of its impact on global co2 concentrations through the combined processes of weathering of silicate minerals and transfer of co2 from the atmosphere to the lithosphere a sizable pool of si is contained as accumulations of amorphous silica or biogenic silica bsi in living tissues of growing plants known as phytoliths and after decomposition of organic material as remains in the soil the annual fixation of phytolith silica ranges from 60 200 tmol yr 1 and rivals that fixed in the oceanic biogeochemical cycle 240 tmol yr 1 internal recycling of the phytolith pool is intense with riverine fluxes of dissolved silicate to the oceans buffered by the terrestrial biogeochemical si cycle challenging the ability of weathering models to predict rates of weathering and consequently changes in global climate consideration must be given to the influence of the terrestrial bsi pool on variations in the global biogeochemical si cycle over geologic time and the influence man has had on modifying both the terrestrial and aquatic biogeochemical cycles