fractionation of sulfur isotopes during bacterial sulfate reduction in deep ocean sediments at elevated temperatures abstract a numerical model of sulfate reduction and isotopic fractionation has been applied to pore fluid so 4 2 and 34 s data from four sites drilled during ocean drilling program odp leg 168 in the cascadia basin at 48 n where basement temperatures reach up to 62 c there is a source of sulfate both at the top and the bottom of the sediment column due to the presence of basement fluid flow which promotes bacterial sulfate reduction below the sulfate minimum zone at elevated temperatures pore fluid 34 s data show the highest values 135 yet found in the marine environment the bacterial sulfur isotopic fractionation factor is severely underestimated if the pore fluids of anoxic marine sediments are assumed to be closed systems and rayleigh fractionation plots yield erroneous values for by as much as 15 in diffusive and advective pore fluid regimes model results are consistent with 1 077 0 007 with no temperature effect over the range 1 8 to 62 c and no effect of sulfate reduction rate over the range 2 to 10 pmol cm 3 d 1 the reason for this large isotopic fractionation is unknown but one difference with previous studies is the very low sulfate reduction rates recorded about two orders of magnitude lower than literature values that are in the range of mol cm 3 d 1 to tens of nmol cm 3 d 1 in general the greatest 34 s depletions are associated with the lowest sulfate reduction rates and vice versa and it is possible that such extreme fractionation is a characteristic of open systems with low sulfate reduction rates

delta progradation and neoglaciation laguna paron cordillera blanca peru the history of holocene glaciation serves as an important record of glacier mass balance and therefore of climatic change the moraine record of holocene glaciation in the tropical andes however is fragmentary and poorly dated in contrast increases in the rate of accumulation of inorganic sediment in glacier fed lakes have been linked to periods of neoglaciation in many mountain regions the interpretation of such a record of neoglaciation from sediment cores in glacier fed lakes in the tropical andes can provide the continuity and chronologic control that is lacking in the existing moraine record unusual exposures of glacial lacustrine sediment in the cordillera blanca peru provide a rare opportunity to assess the link between climatic change glaciation and lacustrine sedimentation intentional lowering of water levels in laguna paron 9 s 77 44 w 4200 m a s l in 1985 resulted in the incision and exposure of at least 20 m of deltaic deposits at the eastern end of the lake three deltaic units can be identified horizontal topset beds steeply dipping and deformed foreset beds and horizontally laminated fine grained sediment six radiocarbon ages ranging from 1800 210 to 465 95 14c yr bp on wood indicate that the average rate of delta progradation in the late holocene has been approximately 290 m per 1000 yr the lake formed during deglaciation at least 10 000 yr ago and if such a rate of progradation of the delta had prevailed over the entire holocene then the delta would be at least three times as extensive as it is today thus the rate of delta progradation has varied significantly over the holocene we suggest that the rate of delta progradation was at least three times greater when glaciers were in advanced positions these positions are clearly delimited by neoglacial moraines which are within 1 2 km of the exposures studied and within 1 km of modern ice limits the most recent increase in the rate of delta progradation is evidenced by an increase in sedimentation rate ca 575 90 14c yr bp coincident with the onset of the little ice age copyright 2005 john wiley sons ltd

tropical glacier fluctuations in the cordillera blanca peru between 12 5 and 7 6 ka from cosmogenic 10be dating we report cosmogenic surface exposure 10be ages of 21 boulders on moraines in the jeullesh and tuco valleys cordillera blanca peru 10 s at altitudes above 4200 m ages are based on the sea level at high latitude reference production rate and scaling system of lifton et al 2005 addressing solar modulation and long term uncertainties in scaling secondary cosmic rays for in situ cosmogenic nuclide applications earth and planetary science letters 239 140 161 in the cronus earth online calculator of balco et al 2008 a complete and easily accessible means of calculating surface exposure ages or erosion rates from 10be and 26al measurements quaternary geochronology 3 174 195 using the lifton system large outer lateral moraines in the jeullesh valley have a 10be exposure age of 12 4 ka inside of which are smaller moraine systems dated to 10 8 9 7 and 7 6 ka large outer lateral moraines in the tuco valley have a 10be exposure age of 12 5 ka with inner moraines dated to 11 3 and 10 7 ka collectively these data indicate that glacier recession from the last glacial maximum lgm in the cordillera blanca was punctuated by three to four stillstands or minor advances during the period 12 5 7 6 ka spanning the younger dryas chronozone ydc 12 9 11 6 ka and the cold event identified in greenland ice cores and many other parts of the world at 8 2 ka the inferred fluctuations of tropical glaciers at these times well after their withdrawal from the lgm indicate an increase in precipitation or a decrease in temperature in this region although palaeoenvironmental records show regional and temporal variability comparison with proxy records lacustrine sediments and ice cores indicate that regionally this was a cold dry period so we ascribe these glacier advances to reduced atmospheric temperature rather than increased precipitation

assessment study of lichenometric methods for dating surfaces in this paper we discuss the advantages and drawbacks of the most classical approaches used in lichenometry in particular we perform a detailed comparison among methods based on the statistical analysis of either the largest lichen diameters recorded on geomorphic features or the frequency of all lichens to assess the performance of each method a careful comparison design with well defined criteria is proposed and applied to two distinct data sets first we study 350 tombstones this represents an ideal test bed because tombstone dates are known and therefore the quality of the estimated lichen growth curve can be easily tested for the different techniques secondly 37 moraines from two tropical glaciers are investigated this analysis corresponds to our real case study for both data sets we apply our list of criteria that reflects precision error measurements and their theoretical foundations when proposing estimated ages and their associated confidence intervals from this comparison it clearly appears that two methods the mean of the n largest lichen diameters and the recent bayesian method based on extreme value theory offer the most reliable estimates of moraine and tombstones dates concerning the spread of the error the latter approach provides the smallest uncertainty and it is the only one that takes advantage of the statistical nature of the observations by fitting an extreme value distribution to the largest diameters

stable isotope analysis of the cretaceous sulfur cycle we report the sulfur and oxygen isotope composition of sulfate 34sso4 and 18oso4 respectively in coexisting barite and carbonate associated sulfate cas which we use to explore temporal variability in the marine sulfur cycle through the middle cretaceous the 34sso4 of marine barite tracks previously reported sulfur isotope data from the tropical pacific the 18oso4 of marine barite exhibits more rapid and larger isotopic excursions than the 34sso4 of marine barite these excursions temporally coincide with ocean anoxic events oaes neither the 34sso4 nor the 18oso4 measured in marine barite resembles the 34sso4 or the 18oso4 measured in coexisting cas culling our data set for elemental parameters suggestive of carbonate recrystallization low sr and high mn sr improves our record of 18oso4 in cas in the cretaceous this suggests that the cas proxy can be impacted by carbonate recrystallization in some marine sediments a box model is used to explore the response of the 34sso4 and 18oso4 to different perturbations in the marine biogeochemical sulfur cycle we conclude that the 34sso4 in the middle cretaceous is likely responding to a change in the isotopic composition of pyrite being buried coupled possibly with a change in riverine input on the other hand the 18oso4 is likely responding to rapid changes in the reoxidation pathway of sulfide which we suggest may be due to anoxic versus euxinic conditions during different oaes

lichenometric and radiocarbon dating of holocene glaciation cordillera blanca peru hfeasurements of rliizocurpoii subgenus rliizocurpo r thalli on moraines the ages of which are constrained by six radiocarbon dates two pre colombian structures and one historically dated flood dep6sit indicate that lichenometry can be used to estimate the age of stabilization of glacial deposits that date to the last c 7 ka on the west side of the cordillera blanca perlj 8 40 9040 s 77 00 77 40 w the preliminary growth curve for subgenus rtiizocurpan resembles those derived for alpine areas in alaska and colorado and can be subdivided into an initial rapid phase of growth c 0 4 mm yr that lasts c 100 years a c 500 to 1000 year long phase of decelerating growth and a period of slow linear growth 0 016 mm yr that commences after c loo0 years size clustering of subgenus riiizocurpoir thalli supports a four fold subdivision of cirque moraines at altitudes between 4200 and 4650 m the oldest moraines stabilized between c 7000 and 6ooo bp and the three younger groups between c 3350 and 1600 bp between c 1250 and 400 bp and within the last 100 years this subdivision is supported by limiting radiocarbon dates from the cordillera blanca and from several cordilleras in southern peni and indicates that the holocene glacial chronology of the cordillera blanca is the most complete heretofore recognized in the tropical andes

holocene glacier advances in the headwaters of sredniaya avacha kamchatka russia abstract holocene glacial deposits in sredniya avacha headwaters are subdivided into three age groups events a b and c based upon geomorphic features tephrochronology and lichenometry tephras of opala volcano 1400 1500 yr b p ksudach volcano 1700 1800 and 6000 yr b p and zavaritskiy volcano 2800 yr b p are used as stratigraphic markers rhizocarpon geographicum l dc and rhizocarpon section alpicola growth curves are established using tephrochronologically dated and historical surfaces the age of event a pre hypsitermal moraines is constrained by an age of 6000 yr b p for overlying ksudach 2 tephra and an age of 7200 lichenometric l yr b p event b neoglaciation had a multiple nature with the most prominent advances at 4300 3500 3300 2800 2600 2100 1800 1400 and 1300 1100 l yr b p the culmination occurred before 2800 yr b p as suggested by a date for zavaritskiy volcano tephra found on the glacial and outwash deposits less extensive glacier advances of event c little ice age occurred at 800 600 500 200 180 110 and 90 40 l yr b p the ela depression was 200 250 100 150 30 70 m during the culmination of events a b and c respectively

on the coupling between the harang reversal evolution and substorm dynamics a synthesis of superdarn dmsp and image observations 1 the harang reversal is a prominent feature frequently observed in the electric and magnetic field patterns in the high latitude auroral zone and plays an important role in substorm dynamics a comprehensive set of instruments including super dual auroral radar network superdarn defense meteorological satellite program dmsp and imager for magnetopause to aurora global exploration image is used to investigate the relationship between the harang reversal and substorms on the basis of nine events that have been analyzed we find that the harang reversal forms and becomes well defined during the growth phase azimuthal flows equatorward of the harang reversal a majority of which are in the subauroral region enhance during the growth phase the observations indicate that subauroral polarization streams saps and the harang reversal evolve together as part of the growth phase development of the region 2 current system furthermore the substorm auroral onset is seen to occur quite near the center of the harang flow shear which suggests that the substorm upward field aligned current develops there after onset the evolution of convection flows in the vicinity of the harang region depends strongly on their location relative to that of the onset saps flows equatorward of the harang reversal suddenly increase at the substorm onset flow shear east of the auroral onset relaxes after the onset and poleward flows part of a clockwise vortex are observed west of the auroral onset after the onset these observations demonstrate the strong coupling between the harang reversal evolution and substorm dynamics and suggest that the nightside region 2 physics is closely related to substorm dynamics

development of unusual rock weathering features in the cordillera blanca peru abstract mylonite textures in granodiorite boulders are responsible for higher rates of surface denudation of host rocks and the progressive development of unusual rock weathering features termed weathering posts these textures are characterized by smaller grain sizes higher biotite content and a higher biotite axial ratio in host rocks relative to weathering posts elemental concentrations do not show a significant difference between weathering posts and the host rocks in which they are found and this reflects the absence of a weathering residue on the rock surfaces chemical weathering loosens the bonds between mineral grains through the expansion of biotite and the loosened grains fall off or are blown off the boulder surface and continue their chemical alteration in the surrounding soil the height of weathering posts on late quaternary moraines increases at a linear rate of 1 45 0 45 cm 1000 yr 1 until post heights reach the diameter of host rocks such a rate of boulder denudation if unrecognized would generate significant errors 20 in cosmogenic exposure ages for pleistocene moraines given the paucity of boulders with diameters that significantly exceed 1 5 m the maximum age of utility of weathering posts as a numeric age indicator is 100 ka

proglacial lacustrine sediments from el altar ecuador evidence for late holocene climatic change late holocene glacier variations on el altar ecuador have been reconstructed from proglacial lacustrine sediments variations in bulk density and organic content in sediment cores from laguna verde are interpreted as representing a record of the neoglacial activity of the obsipo glacier two sedimentological units of laminated silt and clay represent two late holocene episodes of glacier expansion which probably occurred during the last millennium and tentatively suggest a double little ice age signal reconstructed equilibrium line altitudes on the obispo glacier seem to reflect changes in both precipitation and temperature and the glacial fluctuations documented on el altar are consistent with other evidence of environmental change from northern south america

application and validation of the spherical elementary currents systems technique for deriving ionospheric equivalent currents with the north american and greenland ground magnetometer arrays 1 with data from the canadian magnetic observatory system canadian array for real time investigations of magnetic activity geophysical institute magnetometer array greenland time history of events and macroscale interactions during substorms themis and magnetometer array for cusp and cleft studies ground magnetometer arrays we applied the state of art technique on the basis of spherical elementary currents systems secs developed by amm and viljanen 1999 in order to calculate maps of ionospheric equivalent currents over the whole north american auroral region this study is the first to apply the secs technique to a large nonrectangular area with widely separated ground magnetometers 350 km for this study we will first demonstrate the validity of the technique using synthetic data and then examine equivalent ionospheric currents associated with a harang discontinuity for a case study on 10 december 2007 the results show in detail the dynamic evolution of the currents over the entire north american ground magnetometer network equivalent ionospheric current eic maps inferred at the minimum resolution of the database in this case 10 s can thus be analyzed further in conjunction with near simultaneous images of the themis all sky imager mosaics and super dual auroral radar network radar data the eic maps represent a value added product from the raw magnetometer database and can be used for contextual interpretation as well as help with our understanding of magnetosphere ionosphere coupling mechanisms using the ground arrays and the themis spacecraft data

the use of dithiothreitol for the quantitative analysis of elemental sulfur concentrations and isotopes in environmental samples abstract determining the concentration and isotopic composition of elemental sulfur in modern and ancient environments is essential to improved interpretation of the mechanisms and pathways of sulfur utilization in biogeochemical cycles elemental sulfur can be extracted from sediment or water samples and quantified by converting to hydrogen sulfide alternatively elemental sulfur concentrations can themselves be analyzed using hplc and other methodologies however the preparation and analysis times can be long and these methods are not amenable to stable isotopic analysis current reduction methods involve the use of costly and specialized glassware in addition to toxins such as chromium chloride or cyanide to reduce the sulfur to hydrogen sulfide the novel reduction method presented here uses dithiothreitol dtt as a less toxic reducing agent to obtain both elemental sulfur concentrations and isotopic composition from the same sample the sample is dissolved in an aqueous or organic liquid medium and upon reaction with dtt the elemental sulfur is volatilized as hydrogen sulfide and collected in a sulfide trap using an inexpensive gas extraction apparatus the evolved sulfide concentrations can easily be measured for concentration by absorbance spectrophotometery or voltammetry techniques and then analyzed for sulfur isotopic composition the procedure is quantitative at 93 recovery to dissolved elemental sulfur with no observed sulfur isotope fractionation during reduction and recovery controlled experiments also demonstrate that dtt is not reactive to sulfate sulfite pyrite or organic sulfur

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

subdivision of late pleistocene moraines in the cordillera blanca peru based on rock weathering features soils and radiocarbon dates abstract the progressive development of unusual rock weathering features and soils and minimum limiting radiocarbon dates provide a basis for subdividing four groups of late pleistocene moraines on the west side of the cordillera blanca northern peru 9 20 1 000 s 77 10 77 30 w boulders on the youngest late pleistocene moraines have 10 to 14 cm tall weathering posts soils on these moraines yield mean profile development index pdi values of 0 05 0 04 1 these moraines date between ca 13 500 and 9700 500 yr b p older than previously postulated the next older moraines have boulders with weathering post heights between 20 and 25 cm and soils with pdi values of 0 08 0 07 and were deposited prior to 13 280 190 yr b p probably during the last glacial maximum marine isotope stage 2 moraines from an older glaciation have boulders with weathering posts between 39 and 50 cm high soils that yield pdi values of 0 21 0 07 and are older than 19 700 340 yr b p boulders on moraines from a still older glaciation have lost ca 50 of their above ground volume and have weathering posts between 62 and 70 cm high pdi values for soils on these moraines are 0 32 0 06 linear and logarithmic models of weathering post and soil development with time are used to estimate minimum and maximum ages for the two oldest moraine groups linear models suggest that the second oldest moraines are between ca 20 500 and 46 500 yr b p and that the oldest moraines are between ca 29 000 and 72 000 yr b p in contrast logarithmic models suggest ages of greater than ca 75 500 yr b p and greater than ca 500 000 yr b p respectively

nightside ionospheric electrodynamics associated with substorms pfisr and themis asi observations 1 observations from the newly available poker flat incoherent scatter radar have been used to study the ionospheric electrodynamics during the substorm expansion phase substorm events selected have been divided into three categories based on onset location relative to the radar and repeatable features have been identified west of onset westward flows increased in response to the passage of the westward traveling surge wts poleward of them the enhanced flows occurred within the sub auroral polarization streams region of downward region 2 currents which extend equatorward from near the equatorward boundary of electron precipitation strong e region ionization increase associated with the wts occurred poleward of the enhanced westward flows suggesting that poleward pedersen currents fed by the downward region 2 field aligned current fac further equatorward contribute at least partially to closure of the upward fac of the wts an enhanced eastward flow channel developed east of onset e region ionization decreased poleward of this flow peak implying formation of downward fac and further increased equatorward of the flow peak suggesting strengthening of preexisting region 2 upward fac these observations indicate that the downward fac formed at onset at least partially closes via the upward region 2 currents the enhanced eastward flows decreased after passage of the auroral bulge and the reduced e region ionization increased again when onset occurred within the radar fov the thin breakup arc of onset occurred at the center of the harang reversal while if the optical onset was poleward of the radar fov the harang reversal was observed after the onset a 2 d picture of the evolution of ionospheric electrodynamics was generated by synthesizing observations from the three categories which provides a schematic description of the relationship between region 2 and substorm expansion electrodynamics

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

sulfate reduction related to the early diagenetic degradation of organic matter and black spot formation in tidal sandflats of the german wadden sea southern north sea stable isotope 13c 34s 18o and other geochemical results abstract a stable isotope geochemical investigation 34 s 32 s 13 c 12 c 18 o 16 o has been carried out to study the development of anoxic surface sediments black spots in the backbarrier tidal area of spiekeroog island southern north sea microbial sulfate reduction related to the degradation of mainly marine organic matter under anaerobic conditions led to the accumulation of hydrogen bisulfide up to 8 mm in the interstitial waters of the sandy sediments while the carbon isotopic composition of organic matter reflected the downcore preferential degradation of labile marine organic matter sulfur and oxygen isotope variations in the dissolved sulfur species provided information about the microbiologically mediated complex interactions between the sulfur carbon and oxygen cycles

oxygen 18 oxygen 16 and d h studies of plutonic granitic and metamorphic rocks across the cordilleran batholiths of southern british columbia hydrogen and oxygen isotope ratios of 500 samples mainly from granitic plutons were measured along a 700 km e w traverse across the accreted terranes of southern british columbia latitudes 49 52 n despite the geological complexity and range of intrusive ages late triassic to tertiary and although there are steps in the isotopic values at some geologic boundaries e g across the strait of georgia two clear patterns emerge 1 the 18 o 16 o and d h ratios of the waters involved in hydrothermal interactions with the granitic rocks show a regular eastward trend of depletion in d and 18 o enormous areas were affected by the hydrothermal processes but the most intense alteration is localized along major north trending lineaments e g okanagan lake 2 independent of the hydrothermal effects the primary 18 o values of the granitic rocks also change systematically eastward from 7 0 to 8 5 in vancouver island reaching a minimum of 5 5 to 7 0 in the western and central coast plutonic complex then increasing progressively from the eastern coast batholith to the okanagan batholith and attaining a maximum of 10 0 to 12 0 in the nelson batholith two groups of samples are unique in their high d values the first group is represented by two geographically isolated batholiths guichon and thuya that were not affected by the tertiary meteoric hydrothermal systems and that have therefore preserved their early jurassic to triassic k ar ages the second group is represented by the jurassic plutons of vancouver island there the hydrothermal fluids were both d rich and 18 o rich 18 o 0 as evidenced by the fact that feldspars in the altered granites are enriched in 18 o relative to coexisting quartz both anomalies can be explained if these terranes were located closer to the equator and or in a maritime environment at the time of intrusive and hydrothermal activity in agreement with available paleomagnetic data excluding these anomalous areas two distinct ages of meteoric hydrothermal activity can be identified cretaceous in the west and early to mid tertiary in the east the isotopic trends in the rocks are similar to the present day patterns of meteoric waters in the region with one primary difference the paleowaters are enriched in d by about 20 compatible with a northward translation of these terranes a climatic change or both the similarities of the patterns suggest a topography similar to that of the present day a mountain chain along the coast during the early tertiary the whole rock 18 o values of the granitic rocks determined by extrapolation of the trends of 18 o quartz versus 18 o feldspar to correct for hydrothermal alteration effects suggest that the main part of the coast plutonic complex formed from magmas similar to those in oceanic island arcs derived from basaltic crust or from an upper mantle source toward the east an increasingly larger component of sedimentary rocks must be present in the source regions of the granitic magmas it may be significant that right at the edge of the north american craton there is a drop in the 18 o of the plutons from 11 down to 9 5 suggesting involvement of old granitic crust instead of sedimentary rocks these new data from southern british columbia confirm and amplify previous studies that have documented 1 the existence of widespread and pervasive hydrothermal effects throughout the north american cordillera and 2 regular west to east asymmetries in the amounts of different kinds of parent rocks in the source regions from which these mesozoic and cenozoic granitic magmas were derived

sulfur and oxygen isotope tracing of sulfate driven anaerobic methane oxidation in estuarine sediments we use multiple stable isotope measurements in two highly stratified estuaries located along the mediterranean coast of israel the yarqon and the qishon to explore the consumption of sulfate through the anaerobic oxidation of methane sulfate driven aom at both sites pore fluid sulfate is rapidly consumed within the upper 15 20 cm although the pore fluid sulfate and dissolved inorganic carbon dic concentration profiles change over a similar range with respect to depth the sulfur and oxygen isotopes in the pore fluid sulfate and the carbon isotopes in the pore fluid dic are fundamentally different this pore fluid isotope geochemistry indicates that the microbial mechanism of sulfate reduction differs between the studied sites we suggest that in the yarqon estuary sulfate is consumed entirely through aom whereas in the qishon both aom and bacterial sulfate reduction through organic matter oxidation coexist these results have implications for understanding the microbial mechanisms behind sulfate driven aom our data compilation from marine and marginal marine environments supports the conclusion that the intracellular pathways of sulfate reduction varies among environments with sulfate driven aom the data can be used to elucidate new pathways in the cycling of methane and sulfate and the findings are applicable to the broader marine environment

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

sulfur and oxygen isotopic compositions of dissolved sulfate in the orca basin implications for origin of the high salinity brine and oxidation of sulfides at the brine seawater interface abstract analysis of sulfur and oxygen isotopic compositions of dissolved sulfate from a vertical water profile in the anoxic hypersaline orca basin provides important constraints upon the provenance of the sulfate results support a dissolution origin of the brine from a jurassic evaporitic salt however mass balance considerations and the observed minima in the vertical 18o sulfate profile at the brine seawater interface are not reconcilable with only a simple two box brine seawater mixing model instead the data imply contributions from the oxidation of sulfides

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

climate in the western cordillera of the central andes over the last 4300 years abstract the distichia peat core obtained in the carhuasanta valley near nevado mismi cordillera chila provides information on climatic and environmental conditions over the last 4300 years the relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the western cordillera of the southern peruvian andes these temperature variations can be additionally linked with the changes in precipitation patterns by analysing c and c n ratio in the core relatively warm and moist conditions prevailed from 4280 to 3040 cal yrs bp bc 2330 1090 with a short colder dry episode around 3850 cal yrs bp bc 1900 the most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal yrs bp bc 1090 800 when the initial warming turned to a rapid cooling to temperatures at least 2 c lower than the mean for the late holocene initially drier conditions within this event turned to a short wet phase after 2780 cal yrs bp bc 830 when the temperature increased again this event coincides with significant changes in peat and ice core records in the central andes matching the timing of the global climate event around 2 8 cal ka bp climatic conditions in the study area became relatively dry and stable after the event for about 800 years highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal yrs bp ad 1310 1795 followed by predominantly colder and drier conditions the established 13 c peat record represents the first continuous proxy for the temperature in the southern peruvian andes dated by the ams 14 c distichia peat is wide spread in the andes and the proposed approach can be applied elsewhere in high altitudes where no other traditional climate proxies are available

rcm e and amie studies of the harang reversal formation during a steady magnetospheric convection event this paper presents the results of a modeling study on the formation of the harang reversal hr during a steady magnetospheric convection event the harang reversal is identified as the boundary of the northward and southward electric field in the nightside auroral zone using the assimilative mapping of ionospheric electrodynamics amie procedure we simulate the event with the rice convection model equilibrium rcm e by adjusting its boundary conditions to approximately match time history of events and macroscale interactions during substorms themis and goes observations in the nightside magnetosphere our results show that the hr is collocated with an upward region 1 field aligned current where converging ionospheric currents cause a southward northward electric field on the poleward equatorward side of the hr our results also indicate that the electric field reversal is slightly poleward of the ionospheric east west current reversal and is to the northeast of the ground magnetic reversal which is consistent with previous observations we also test the sensitivity of the hr formation to a variety of parameters in the rcm e simulations we find that 1 the reduction of the flux tube entropy parameter pv5 3 near the midnight sector plays a major role in the formation of the hr 2 a run carried out assuming uniform conductance produced the same major features as the run with more realistic precipitation enhanced conductance and 3 the detailed pattern of the polar cap potential distribution plays a minor role but its dawn dusk asymmetry significantly controls the location of the hr with respect to midnight the rcm e simulations also predict pv5 3 and flow distributions associated with the magnetospheric source of the hr in the plasma sheet which can be further tested against observations

a chronology of the little ice age in the tropical andes of bolivia 16 s and its implications for climate reconstruction dating moraines by lichenometry enabled us to reconstruct glacier recession in the bolivian andes since the little ice age maximum on the 15 proglacial margins studied we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries moraines were dated by performing statistical analysis of lichen measurements based on the extreme values theory like glaciers in many mid latitude mountain areas bolivian glaciers reached their maximal extent during the second half of the 17th century this glacier maximum coincides with the maunder minimum of solar irradiance by reconstructing the equilibrium line altitude and changes in mass balance we think the glacier maximum may be due to a 20 to 30 increase in precipitation and a 1 1 to 1 2 c decrease in temperature compared with present conditions in the early 18th century glaciers started to retreat at varying rates until the late 19th to early 20th century this trend was generally associated with decreasing accumulation rates by contrast glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity these results are consistent with observations made in the study region based on other proxies

proglacial lake sediment records of holocene climate change in the western cordillera of peru abstract sediment records from proglacial lakes between 9 and 10 s in the western cordillera of the peruvian andes document the waxing and waning of alpine glaciers since the end of the lateglacial stage these records from the southern tropical andes provide supporting evidence that the early holocene between 12 and 8 ka was relatively warm and dry and the middle holocene between 8 and 4 ka was marked by a shift to cooler and possibly wetter conditions in certain regions leading to glacial advances although there were multiple periods of brief ice advances that interrupted the overall trend glaciers in multiple valleys generally retreated from 4 0 ka through the medieval climate anomaly 1 0 0 7 ka this late holocene pattern of ice retreat occurred during a period when lake level studies and both lacustrine and speleothem stable isotopic records indicate wetter conditions relative to the middle holocene suggesting that higher temperatures contributed to the pattern of ice retreat following this period of glacial retreat multiple proxy records suggest that the start of the little ice age 0 6 0 1 ka was a colder and wetter time throughout much of the tropical andes there appear to be two primary synoptic scale climatic controls on temperature and precipitation linked to insolation dynamics that drive changes in ice cover in the southern tropical andes during the holocene 1 the strength of the south america summer monsoon which is linked to northern hemisphere temperatures and the mean position of the intertropical convergence zone over the atlantic and 2 sea surface temperature distributions in the tropical pacific ocean and its influence on atmospheric temperature precipitation and circulation patterns

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

seasonal succession and microlamina formation in a meromictic lake displaying varved sediments in a small meromictic lake near toronto canada a mass mortality of photosynthetic bacteria followed the ventilation of the chemocline during fall autumn and resulted in 3 8 g m 2 day 1 of organic matter being deposited as a dark layer in sediment traps which were suspended in the permanently anaerobic zone this mass mortality of photosynthetic bacteria occurred in late autumn following the annual thermal destratification of the lake s mixolimnion wind mixing during this period of homeothermy resulted in the introduction of low levels of dissolved oxygen into the lake s chemocline the ensuing mass mortality of photosynthetic bacteria resulted in the release of elemental sulphur as the sulphur rich bacteria decomposed and sank to the bottom of the lake the ferrous ions in the water below a depth of 15 m in crawford lake reacted with this sulphur to form black ferrous sulphides and pyrite which formed a dark microlamina on the lake floor each dark microlamina was overlain by a light coloured calcite rich layer which was deposited each spring and summer during the 3 yr period of this study the mechanism of microlamina formation elucidated here has been based on the examination of bi weekly sediment trap information this approach has permitted an explanation of the mechanisms by which specific events such as calcite precipitation and phytoplankton seasonal succession are transcribed into the sediment record

seasonal changes in sulfur biogeochemistry of a dilute dimictic arctic lake implications for paired sulfur isotope records from ancient oceans abstract calibration of ancient marine sulfate levels has been done largely using experimental studies of the kinetic isotope effect associated with microbial sulfate reduction and work from modern ocean basins or high sulfate lakes that are largely restricted and meromictic the sulfur isotope record of sulfates and sulfides from sedimentary sequences have been used to reconstruct sulfate levels throughout the geologic record and indicate that sulfate concentrations were low relative to modern oceans 28 mm for most of earth s history despite the higher potential for modern low sulfate systems to be a better analog for ancient oceans there are few sulfur isotope studies that have been carried out in these environments here we present 34s systematics of a modern low sulfate 330 600 m euxinic lake on the ice free margin of southwestern greenland we find large isotope fractionations 20 between water column sulfate and sulfides with this fractionation increasing from 23 9 during open water conditions to 42 0 under annual ice cover while these large kinetic isotope effects associated with microbial sulfate reduction esr are expressed in the water column of this lake the underlying sedimentary sulfides preserve a notably smaller range of 34s values 13 0 26 6 geochemical modeling of our data suggests that the 34s of water column sulfate and sulfides along with sedimentary sulfides are primarily controlled by esr and a reservoir effect established under strong thermal stratification during open water conditions under ice covered conditions esr appears to be the dominant control on 34s values and when combining both seasonal data sets esr increases as a function of sulfate levels in the lake sulfur isotopic data presented here highlight the complexity of seasonal biogeochemical cycling of sulfur in low sulfate systems and how system openness affects 34s fractionations in modern euxinic depositional environments specifically a reservoir effect is only documented in the water column 34s data under open water conditions however a reservoir effect is apparent from sedimentary sulfides under both ice cover and open water conditions due to time averaging pyrite 34s values our results add to the growing body of work on modern low sulfate systems to help further constrain the use of ancient 34s records for paleoenvironmental reconstructions

influence of glacial sediments on the chemical quality of surface water in the ulta valley cordillera blanca peru the rio santa ancash peru and its tributaries are an essential source of drinking and irrigation water its discharge relies on glacial meltwater which is diminishing due to the rapid decrease in glacial extent as a secondary effect water quality can be compromised e g ph 3 and high concentrations of so42 and trace metals although this has previously been attributed to pyrite rich chicama bedrock exposed by glacial retreat little is known about the occurrence of chicama fragments in quaternary glacial sediments and its influence on water quality this research aims at elucidating this effect by relating observed changes in water quality in streams to presence and chemical composition of morainic ridges in the quebrada ulta in the rio santa basin changes in water quality before and after contact with a morainic ridge were assessed using carbonate alkalinity titration ion analysis and elemental analysis moreover relative contributions of glacial meltwater and precipitation were assessed qualitatively using stable water isotope analysis we used a novel method to explain the provenance of contaminated glacial sediments using a reconstruction of their source area the mineralogical composition of a morainic ridge was strongly related to the geology of the source area indicating that mineralogical composition of tills may be predicted using this technique effects of glacial sediments in morainic ridges on water quality were minimal but depended on their mineralogical composition morainic ridges with a high content of chicama shales tended to increase solute loads of mg and so42 additionally isotope signatures suggest that during the dry season moraines may act as reservoirs for precipitation derived shallow groundwater clear trends in water quality were observed along the whole flow path of the rio buin which could potentially be explained by increased groundwater contribution downstream and shifts in dominant weathering mechanisms future research should focus on disentangling these various drivers of water quality in glacial catchments

a comprehensive sulfur and oxygen isotope study of sulfur cycling in a shallow hyper euxinic meromictic lake abstract mahoney lake is a permanently anoxic and sulfidic euxinic lake that has a dense plate of purple sulfur bacteria positioned at mid water depth 7 m where free sulfide intercepts the photic zone we analyzed the isotopic composition of sulfate 34 s so4 and 18 o so4 sulfide 34 s h2s and the water 18 o h2o to track the potentially coupled processes of dissimilatory sulfate reduction and phototrophic sulfide oxidation within an aquatic environment with extremely high sulfide concentrations 30 mm large isotopic offsets observed between sulfate and sulfide within the monimolimnion 34 s so4 h2s 51 and within pore waters along the oxic margin 34 s so4 h2s 50 are consistent with sulfate reduction in both the sediments and the anoxic water column given the high sulfide concentrations of the lake sulfur disproportionation is likely inoperable or limited to a very narrow zone in the chemocline and therefore the large instantaneous fractionations are best explained by the microbial process of sulfate reduction pyrite extracted from the sediments reflects the isotopic composition of water column sulfide suggesting that pyrite buried in the euxinic depocenter of the lake formed in the water column the offset between sulfate and dissolved sulfide decreases at the chemocline 34 s so4 h2s 37 a trend possibly explained by elevated sulfate reduction rates and inconsistent with appreciable disproportionation within this interval water column sulfate exhibits a linear response in 18 o so4 34 s so4 and the slope of this relationship suggests relatively high sulfate reduction rates that appear to respond to seasonal changes in the productivity of purple sulfur bacteria although photosynthetic activity within the microbial plate influences the 18 o so4 34 s so4 relationship the biosignature for photosynthetic sulfur bacteria is restricted to the oxic anoxic transition zone and is apparently minor relative to the more prevalent process of sulfate reduction operative throughout the light deprived deeper anoxic water column and sediment pore waters

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

late quaternary glacial chronology on nevado illimani bolivia and the implications for paleoclimatic reconstructions across the andes 10be terrestrial cosmogenic nuclide surface exposure ages from moraines on nevado illimani cordillera real bolivia suggest that glaciers retreated from moraines during the periods 15 5 13 0 ka 10 0 8 5 ka and 3 5 2 0 ka late glacial moraines at illimani are associated with an ela depression of 400 600 m which is consistent with other local reconstructions of late glacial elas in the eastern cordillera of the central andes a comparison of late glacial elas between the eastern cordillera and western cordillera indicates a marked change toward flattening of the east to west regional ela gradient this flattening is consistent with increased precipitation from the pacific during the late glacial period

late quaternary glacier response to humidity changes in the arid andes of chile 18 29 s abstract today no glaciers exist between 18 30 s and 27 s even on mountains much higher than 6000 m these dry high mountain environments are very sensitive to changes in climatic boundary conditions particularly humidity since temperatures are far below freezing here we present a reconstruction of climatic changes since the last glacial maximum for the chilean dry andes of the southern hemisphere we reconstructed regional equilibrium line altitudes ela for three different moraine stages representing extensive past glaciations in this currently unglaciated region comparison of the regional pattern of the ela with modern climate conditions allows us to draw implications about the paleoclimatic conditions during the best preserved moraine stage ii glaciations in the northern as well as in the southern part of the research area our results suggest humid conditions in the northern part 18 24 s during late glacial times with strongly increased convective precipitation during austral summer the temporal coincidence of glaciers in the mountains and high lake levels on the altiplano tauca phase is evident to the south no simple shift of the westerlies is implied by our glacier reconstructions the northern limit of effective moisture for glacier formation did not shift significantly but stayed in the area of the present day northernmost glaciers of the westerlies at about 27 s but further south precipitation increased significantly accompanied by at least 2 3 c colder conditions the age of this glaciation is uncertain but probably of late glacial or last glacial maximum lgm times overall glaciers in the dry andes of south america clearly responded to large changes in the humidity not primarily the temperature regime with all its consequences on the environment hydrology vegetation etc illustrating the different regional responses to global climatic change

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

rhizocarpon calibration curve for the aoraki mount cook area of new zealand development of rhizocarpon growth curve from the aoraki mount cook area of new zealand provides a means to assess little ice age glacier behaviour and suggests approaches that have wider application employing a sampling strategy based on large populations affords the oppor tunity to assess which of various metrics e g single largest average of five largest mean of an entire population best characterise rhizocarpon growth patterns the 98 quantile from each population fitted with a quadric curve forms a reliable representation of the growth pattern since this metric does not depend on the original sample size comparisons are valid where sample strategy must be adapted to local situations or where the original sample size differs for the aoraki mount cook area a surface 100 years old will have a 98 quantile lichen diameter of 34 3 mm whereas a 200 year old surface will have a lichen diameter of 73 7 mm in the southern alps constraints from the age range of calibration points the flattening of the quadric calibration curve and ecological factors limit the useful age range to approximately 250 years copyright 2005 john wiley sons ltd

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

late glacial and late holocene moraines in the cerros cuchpanga central peru abstract small ice fields on the western cordillera northeast of lima were expanded to three times their present size in the recent past and the regional snow line was probably about 100 m lower than it is today outwash from the expanded glaciers formed deltas of silt in valley bottom lakes when the ice lobes retreated the reduced outwash was trapped behind recessional moraines and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools the delta surfaces then became covered with peat and radiocarbon dates for the base of the peat 1100 70 and 430 70 yr b p for two different deltas indicate that the maximum ice advance was older than those dates and thus older than the little ice age of many north temperate regions much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys which had previously been inundated by the cordilleran ice field the cordilleran deglaciation and this expansion of local glaciers probably occurred between 12 000 and 10 000 yr ago on the basis of slightly contradictory radiocarbon dates

coordinated superdarn themis asi observations of mesoscale flow bursts associated with auroral streamers 1 nightside auroral zone localized flow channels typically associated with auroral poleward boundary intensifications and streamers are an important component of high latitude ionospheric plasma dynamics we investigate the structure of these flow channels using two dimensional line of sight flow observations from the super dual auroral radar network superdarn radars and auroral images from the time history of events and macroscale interactions during substorms themis ground based all sky imager asi array radar echoes captured 500 km horizontal distance from the radars were mainly used to detect small scale flow structures that would otherwise be missed or poorly resolved in long range radar echoes after identifying 135 auroral streamers in the asi images at close radar capture locations we examined the associated ionospheric flow data in the radar echoes flow bursts and streamers are invariably correlated in all events the flow bursts are often directed equatorward and appear simultaneously with the streamers equatorward flows are located just to the east of the streamers less frequently 10 of the time a poleward flow enhancement was detected even when a streamer propagated equatorward the poleward flow enhancement being located to the west of the auroral streamer or to the east of the equatorward flow enhancement consistently with the spatial relationship between flow shear and upward field aligned currents in plasma sheet flow bursts the azimuthal width of the flow channel is on average 75 km and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is 57 km eastward this study demonstrates the capability of radar imager pairs for identifying the 2 d structure of localized flows associated with plasma sheet flow bursts

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

oxidative sulfur cycling in the deep biosphere of the nankai trough japan the existence of oxidative microbial sulfur cycling in the deep biosphere has been postulated but it is difficult to identify because isotope effects of reductive sulfur cycling generally overprint those of oxidative sulfur cycling in the sediments at integrated ocean drilling program iodp site c0007 holes a c drilled and sampled during iodp expedition 316 at the nankai trough japan sulfur and oxygen isotope compositions of dissolved and solid phase sulfur compounds show evidence for a discrete zone of deep oxidative sulfur cycling the sulfate concentration profile and isotope values show two distinct sulfate reduction regimes one for downward diffusing sulfate in the uppermost 36 m of sediment unit i and another zone below 90 m where sulfate diffuses upward from a deep subsurface fluid the sulfur and oxygen isotope composition of sulfate and a dramatic change in solid phase iron geochemistry indicate that oxidative sulfur cycling occurs at depth the highly dynamic sedimentary and tectonic regime at nankai trough has created an environment in the subsurface where geochemical gradients can sustain deep oxidative sulfur cycling over long durations of time

two dimensional ionospheric flow pattern associated with auroral streamers 1 we present direct two dimensional flow observations and auroral images from the super dual auroral radar network superdarn radar and wideband imaging camera onboard imager for magnetopause to aurora global exploration image wic imager to investigate the ionospheric flow pattern associated with auroral streamers for four events using the superdarn observations allows us to observe the flow associated with the streamers in the context of the larger scale background convection for all four cases studied streamers developed from preexisting east west ew arcs that initiated from bead like or small scale auroral intensifications around the auroral poleward boundary we find a vortex like flow pattern with clockwise sense surrounding both the initial auroral forms and the ensuing streamers we also found in three cases signatures of flow bifurcations at the equatorward end of the streamers which suggests a double vortex like flow pattern with the counterclockwise vortex east of the clockwise one our results are consistent with the double vortex flow structure that results from interchange convection associated with a plasma sheet bubble predicted by different numerical simulations this supports several previous studies and offers more complete observational evidence that the observed flow pattern may be the ionospheric manifestation of interchange instability in the plasma sheet

a late holocene 2600 bp glacial advance in the south central andes 29 s northern chile radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late holocene 2600 bp readvance of glaciers in the western part of the arid andes at 29 s the glacier in the encierro valley northern chile reached about 60 of its late pleistocene extent the equilibrium line altitude ela during this advance remained between 4250 and 4500 m which is above the modern 0 c isotherm of the free atmosphere during summer it is suggested that given the specific climate at high elevations in the extremely arid andes a substantial increase in effective moisture is sufficient to explain this advance whereas no significant temperature depression was needed this compares favourably with the regional late holocene climatic history when lake levels were higher and effective moisture greater than today between 3000 and 1800 bp judging from regional palaeodata we suggest that this late holocene humid spell was most likely related to increased westerly moisture sources from the pacific

rcm e simulation of substorm growth phase arc associated with large scale adiabatic convection 1 substorm auroral breakup often occurs on a longitudinally elongated arc at the end of a growth phase we present an idealized high resolution simulation with the rice convection model equilibrium rcm e to investigate how large scale adiabatic convection under equilibrium conditions can give rise to an auroral arc we find that a thin arc that maps to the magnetic transition region at r 8 re emerges in the late growth phase the simulation implies that the arc in the premidnight sector is associated with a sheet of additional region 1 sense field aligned current fac just poleward of the main region 2 fac while the arc in the postmidnight sector is associated with the poleward portion of the main upward region 2 fac explanations for the location and the thickness of the arc are proposed based on the simulation

a superposed epoch study of superdarn convection observations during substorms 1 case studies of flow patterns during substorms have revealed characteristic patterns in the period leading to expansion onset velocities in the premidnight region have been observed to become strongly sheared and the premidnight convection reversal has been observed to extend across the midnight meridian at expansion onset the shear decreases and flow at midnight becomes meridional out of the polar cap the study presented here superposes flow patterns from 10 substorm intervals to determine the average flow patterns the study confirms the findings of the case studies and extends them to additional local time sectors in addition changes to the flow pattern after expansion onset are examined

tertiary meteoric hydrothermal systems and their relation to ore deposition northwestern united states and southern british columbia tertiary meteoric hydrothermal systems have altered the rocks exposed over more than 5 of the land surface of the northwestern united states and southern british columbia including at least 25 000 km 2 in idaho the systems typically involved convective circulation of fluid derived from ordinary meteoric groundwaters around crystallizing calc alkaline epizonal plutons emplaced into coeval volcanic cover rocks these individual systems had widely ranging lifetimes of 10 3 to 10 6 years and operated locally throughout the cenozoic although the most profound development of such activity occurred during eocene time individual systems varied in size from a few tens of square kilometers yankee fork idaho or less to several thousand square kilometers sawtooth and castro ring zones idaho typically regional propylitization aacompanied the fluid circulation although the higher temperature alteration assemblages were developed locally as were intense alteration effects e g silicification sericitization etc near some veins and in mining districts a significant amount probably 25 50 of the mineral production and potential in the region is closely related to tertiary meteoric hydrothermal systems oxygen and hydrogen isotopic data clearly demonstrate the close geologic association of meteoric hydrothermal systems and mineralization in 1 the paleocene cu zn pb mn main stage mineralization at butte montana 2 numerous eocene epithermal deposits principally valued for au and ag but also including significant deposits of cu pb zn f sb etc as at republic washington and in several mining districts in the idaho batholith and the challis volcanic field 3 several eocene skarn deposits valued for w ima idaho and cu mackay idaho 4 important lead silver vein and replacement deposits of tertiary bluebell british columbia and of probable cretaceous and early tertiary age wood river idaho 5 several potentially economic mo be and u bearing eocene porphyry plutons and 6 miocene epithermal deposits most prominently the au and ag bearing veins at silver city and delamar idaho the hg deposits at the mcdermitt caldera nevada and oregon and at weiser idaho and au deposits in the western cascade range and lake county oregon a close spatial association has been demonstrated between ore deposits and rocks having anomalous 18 o values and low d values the most important deposits are associated with relatively small generally 5 300 km 2 zones of low 18 o values and they are particularly closely linked with zones of very steep 18 o 16 o gradients in the altered rocks these associations hold much promise for the use of 18 o and d contour maps in future exploration efforts

holocene environmental change resets lichen surface dates on recess peak glacial deposits in the sierra nevada california abstract development of an accurate chronology for glacial deposits in the sierra nevada has long been problematic given the lack of suitable organic material for radiocarbon dating lichenometry initially appeared promising as ages showed an increase from cirque headwalls to down canyon moraines however while recess peak lichen age estimates range from 2 to 3 ka recent work shows these deposits to be at least 10 ka older here we present evidence for a late holocene reset of recess peak lichen ages by significant post depositional climate change following late pleistocene deposition of recess peak moraines warming through the mid holocene allowed forests to advance into shallow basins eliminating local inverted tree lines this produced a partial canopy where shading killed the original post pleistocene crustose lichen colonies late holocene cooling resulted in forest retreat from these basins as alpine tree line fell lichens then recolonized the re exposed recess peak deposits we conclude that while recess peak lichen ages are accurate to within the dating uncertainty of the technique existing lichen ages actually date the timing of post mid holocene cooling and recolonization and not the original emplacement of these deposits thus applications of lichenometry should consider post depositional environmental change when interpreting the meaning of these dates

large scale current systems and ground magnetic disturbance during deep substorm injections 1 we present a detailed analysis of the large scale current systems and their effects on the ground magnetic field disturbance for an idealized substorm event simulated with the equilibrium version of the rice convection model the objective of this study is to evaluate how well the bubble injection picture can account for some classic features of the substorm expansion phase the entropy depletion inside the bubble is intentionally designed to be so severe that it can penetrate deep into geosynchronous orbit the results are summarized as follows 1 both the region 1 sense and region 2 sense field aligned currents facs intensify substantially the former resembles the substorm current wedge and flows along the eastern and western edges of the bubble the latter is connected to the enhanced partial ring current in the magnetosphere associated with a dipolarization front earthward of the bubble in the ionosphere these two pairs of facs are mostly interconnected via pedersen currents 2 the horizontal ionospheric currents show a significant westward electrojet peaked at the equatorward edge of the footprint of the bubble the estimated ground magnetic disturbance is consistent with the typical features at various locations relative to the center of the westward electrojet 3 a prominent harang reversal like boundary is seen in both ground h disturbance and plasma flow pattern appearing in the westward portion of the equatorward edge of the bubble footprint with a latitudinal extent of 5 and a longitudinal extent of the half width of the bubble 4 the dramatic dipolarization inside the bubble causes the ionospheric map of the inner plasma sheet to exhibit a bulge like structure which may be related to auroral poleward expansion 5 the remarkable appearance of the westward electrojet harang reversal like boundary and poleward expansion starts when the bubble reaches the magnetic transition region from tail like to dipole like configuration we also estimate the horizontal and vertical currents using magnetograms at tens of ground stations for a deep injection substorm event occurred on april 9 2008 resulting in a picture that is qualitatively consistent with the simulation based on the simulations and the observations an overall picture of the ionospheric dynamics and its magnetospheric drivers during deep bubble injections is obtained

rcm e simulation of a thin arc preceded by a north south aligned auroral streamer the time history of events and macroscale interactions during substorms themis all sky imager data have recently revealed a repeatable sequence that occurs during many auroral substorms in which a newly formed thin arc is preceded by an equatorward propagating streamer the paper aims at modeling this sequence using the rice convection model equilibrium the simulation shows a thin arc arising when a plasma sheet bubble with its pv5 3 reduced to the transition region value arrives at the magnetic transition region the modeled thin arc consists of two parts the one east of the streamer is the result of the bubble pushing high pv5 3 flux tubes ahead of it strengthening the upward region 2 current and the one west of the streamer is associated with westward drifting bubble particles sliding along the transition region the model predicts that 1 the westward and eastward leading edges of the thin arc propagate azimuthally at a speed of 0 5 2 7 km s and 2 the streamer induced thin arc is accompanied by classic signatures of bubble injections

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

glacier fluctuations during the past 2000 years abstract a global compilation of glacier advances and retreats for the past two millennia grouped by 17 regions excluding antarctica highlights the nature of glacier fluctuations during the late holocene the dataset includes 275 time series of glacier fluctuations based on historical tree ring lake sediment radiocarbon and terrestrial cosmogenic nuclide data the most detailed and reliable series for individual glaciers and regional compilations are compared with summer temperature and when available winter precipitation reconstructions the most important parameters for glacier mass balance in many cases major glacier advances correlate with multi decadal periods of decreased summer temperature in a few cases such as in arctic alaska and western canada some glacier advances occurred during relatively warm wet times the timing and scale of glacier fluctuations over the past two millennia varies greatly from region to region however the number of glacier advances shows a clear pattern for the high mid and low latitudes and hence points to common forcing factors acting at the global scale globally during the first millennium ce glaciers were smaller than between the advances in 13th to early 20th centuries ce the precise extent of glacier retreat in the first millennium is not well defined however the most conservative estimates indicate that during the 1st and 2nd centuries in some regions glaciers were smaller than at the end of 20th early 21st centuries other periods of glacier retreat are identified regionally during the 5th and 8th centuries in the european alps in the 3rd 6th and 9th centuries in norway during the 10th 13th centuries in southern alaska and in the 18th century in spitsbergen however no single period of common global glacier retreat of centennial duration except for the past century has yet been identified in contrast the view that the little ice age was a period of global glacier expansion beginning in the 13th century or earlier and reaching a maximum in 17th 19th centuries is supported by our data the pattern of glacier variations in the past two millennia corresponds with cooling in reconstructed temperature records at the continental and hemispheric scales the number of glacier advances also broadly matches periods showing high volcanic activity and low solar irradiance over the past two millennia although the resolution of most glacier chronologies is not enough for robust statistical correlations glacier retreat in the past 100 150 years corresponds to the anthropogenic global temperature increase many questions concerning the relative strength of forcing factors that drove glacier variations in the past 2 ka still remain

holocene fluctuations of a meromictic lake in southern british columbia abstract holocene deposits of mahoney lake a meromictic saline lake located in a closed basin in the semi arid okanagan valley contain evidence of frequent and marked changes in lake depth up to 12 m 10014c yr probably caused by short term changes in effective precipitation we studied a 5 45 m long core comprising a basal layer of inorganic mud overlain by a succession of layers of calcareous laminated and nonlaminated organic mud marl and sand we used mazama tephra to adjust nine radiocarbon ages for the hardwater effect meromixis developed ca 900014c yr b p and the lake has been episodically meromictic for about half the time since because of close linkages between sediments and depositional environments in meromictic and saline lakes we infer that laminated sediments indicate meromictic conditions and high lake levels ca 12 m water depth whereas thick marl layers and nonlaminated sediments indicate nonmeromictic conditions and thus low lake levels

lateglacial and holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold based glaciers at nevado sajama bolivia comparisons of palaeo equilibrium line altitudes between the western and eastern cordilleras in the central andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the western cordillera date to the last glacial maximum lgm however field investigation and geomorphic mapping at nevado sajama bolivia indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them 36cl exposure ages from the shorter moraines suggest that they date to lateglacial times ca 16 9 10 2 ka although lateglacial deposits have been found throughout the central andes the extent of these deposits relative to lgm deposits varies both between the western and eastern cordilleras and north to south along the western cordillera in the western cordillera in the zone of easterly winds the lateglacial appears to be the most extensive glacial advance of the last glacial cycle geomorphic evidence also suggests that some lateglacial moraines were deposited by cold based ice a previously unreported finding in the tropical andes retreat from other glacial features occurred at about 7 0 4 4 ka and 4 7 3 3 ka these are the first directly dated holocene glacial deposits in the western cordillera of bolivia and their presence suggests that the mid holocene may not have been as warm and dry as previously thought copyright 2008 john wiley sons ltd

glacial stratigraphy of stough creek basin wind river range wyoming abstract multiparameter relative age ra techniques identify four post pinedale morphostratigraphic units in each of three cirque valleys tributary to stough creek basin wind river range wy soil development lichenometry boulder weathering characteristics and the geomorphic relations among morphostratigraphic units indicate glacial deposits here correspond to the sequence previously described in the temple lake valley arct alp res 6 1974 301 cirque deposits in stough creek basin correspond to the temple lake alice lake black joe and gannett peak alloformations gsa abs prog 32 2000 a 16 10 be ages from moraine boulders and polished striated bedrock assoc am geogr annu mtg abs 2000 155 support recent numeric age estimates from temple lake and titcomb basin that indicate the temple lake alloformation corresponds to the younger dryas climate episode geogr phys quat 41 1987 397 geology 23 1995 877 science 268 1995 1329 gsa abs prog 31 1999 a 56 soils described from pinedale recessional deposits here represent the first systematic description of pinedale alpine deposits in the wrr

recent glacial history and paleoclimate of the peruvian bolivian andes abstract radiocarbon dates of glacial deposits in the peruvian bolivian andes are used to place the observed phases of glaciation in a common chronological framework the climatic conditions that may determine modern snowline are examined in order to understand the types of climatic forcing to which glaciers may have been sensitive in the past also considered are independent proxies of climatic change including pollen sequences lake level history and ice core data late pleistocene glaciation in central peru between 24 ka and 12 ka bp appears to have occurred during colder and perhaps drier conditions in bolivia a glacial maximum is dated to phases of late holocene glaciation in peru that correspond in part to the little ice age in the northern hemisphere appear to have been caused by a combination of colder and wetter conditions an overall warming trend may be the cause for the retreat of many glaciers in the region since the mid 19th century

quaternary glacial history of nw garhwal central himalayas a first account of the quaternary glacial history is presented for northwest garhwal central himalaya on the basis of sediments and landforms one glacial stage has been recognised this is called the bhagirathi glacial stage when extensive valley glaciers advanced down the bhagirathi valley to jhala 40 5 km from the snout of gangotri glacier the ela depression during this stage was ca 640 m the bhagirathi glacial stage is constrained by optically stimulated luminescence dates of ca 63 ka and 5 ka bp and this glaciation is considered equivalent to the last glaciation elsewhere in the world the maximum extent of ice occurred ca 63 ka bp this however does not correlate with the last glacial maximum for the northern hemisphere ice sheets 20 18 ka bp a series of sharp crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers these moraines formed during the mid holocene 5 ka bp termed here the shivling glacial advance small moraines are inset into these and are dated at about 200 to 300 bp the bhujbas glacial advance ca 300 to 200 bp and considered equivalent to the little ice age in other parts of the world ela depressions of between 40 100 m and 20 60 m occurred during the shivling and bhujbas glacial advances respectively since the bhujbas glacial advance there has been progressive retreat of glaciers initially by downwasting and retreat and then by simple retreat this retreat has accelerated during the last few decades impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat

recalibration of the yellow rhizocarpon growth curve in the cordillera blanca peru and implications for lia chronology abstract a new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the cordillera blanca peru during the little ice age lia our results reveal that an early lia glacial advance occurred around ad 1330 29 however a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers hence this second glacial stage dated from ad 1630 27 is considered as the lia maximum glacial advance in the cordillera blanca during the 17th 18th centuries at least three glacial advances were recorded synchronously for the different glaciers ad 1670 24 1730 21 and 1760 19 the moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18 in the total length of the glacier from the lia maximum extent to the beginning of the 20th century the 24 glaciers have retreated a distance of about 1000 m corresponding to a reduction of 30 in their length this rate is comparable to that observed during the 20th century estimates of palaeo equilibrium line altitudes show an increase in altitude of about 100 m from the lia maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century because long time series are not available for precipitation and temperature this glacial retreat is difficult to explain by past climate changes however there is a fair correspondence between changes in glacier length and the 18 o recorded in the quelccaya ice core at a century timescale our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet lia to the drier conditions of today finally a remarkable synchronicity is observed with glacial variations in bolivia suggesting a common regional climatic pattern during the lia

clastic sediment flux to tropical andean lakes records of glaciation and soil erosion we developed records of clastic sediment flux to 13 alpine lakes in peru ecuador and bolivia and compared these with independently dated records of regional glaciation our objectives are to determine whether a strong relationship exists between the extent of ice cover in the region and the rate of clastic sediment delivery to alpine lakes and thus whether clastic sediment records serve as reliable proxies for glaciation during the late pleistocene we isolated the clastic component in lake sediment cores by removing the majority of the biogenic and authigenic components from the bulk sediment record and we dated cores by a combination of radiocarbon and tephrochronology in order to partially account for intra basin differences in sediment focusing bedrock erosivity and sediment availability we normalized each record to the weighted mean value of clastic sediment flux for each respective core this enabled the stacking of all 13 lake records to produce a composite record that is generally representative of the tropical andes there is a striking similarity between the composite record of clastic sediment flux and the distribution of 100 cosmogenic radionuclide crn exposure ages for erratics on moraine crests in the central peruvian and northern bolivian andes the extent of ice cover thus appears to be the primary variable controlling the delivery of clastic sediment to alpine lakes in the region which bolsters the increasing use of clastic sediment flux as a proxy for the extent of ice cover in the region the crn moraine record and the stacked lake core composite record together indicate that the expansion of ice cover and concomitant increase in clastic sediment flux began at least 40 ka and the local last glacial maximum llgm culminated between 30 and 20 ka a decline in clastic sediment flux that began 20 ka appears to mark the onset of deglaciation from the llgm at least one millennium prior to significant warming in high latitude regions the interval between 20 and 18 ka was marked by near holocene levels of clastic sediment flux and appears to have been an interval of much reduced ice extent an abrupt increase in clastic sediment flux 18 ka heralded the onset of an interval of expanded ice cover that lasted until 14 ka clastic sediment flux declined thereafter to reach the lowest levels of the entire length of record during the early middle holocene a middle holocene climatic transition is apparent in nearly all records and likely reflects the onset of neoglaciation and or enhanced soil erosion in the tropical andes

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

glaciation in the andes during the lateglacial and holocene this review updates the chronology of andean glaciation during the lateglacial and the holocene from the numerous articles and reviews published over the past three decades the andes which include some of the world s wettest and driest mountainous regions offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68 degree meridional transect the geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad scale atmospheric circulation and consequent regional moisture patterns glaciers in the tropical andes and in the mid latitude andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical andes broad scale temporal and spatial patterns of glaciation during the lateglacial are apparent in the southernmost andes the lateglacial chronology appears to have a strong antarctic signature with the best dated moraines correlating closely with the antarctic cold reversal the southernmost andes do not appear to have experienced a significant ice advance coeval with the younger dryas yd climatic reversal at the other end of the andes from w 0t o 9 n a stronger yd connection may exist but critical stratigraphic and geochronologic work is required before a yd ice advance can be fully demonstrated in the central andes of peru well dated moraines record a significant ice readvance at the onset of the yd but ice was retreating during much of the remaining yd interval the spatial temporal pattern of holocene glaciation exhibits tantalizing but incomplete evidence for an early to mid holocene ice advance s in many regions but not in the arid subtropical andes where moraines deposited during or slightly prior to the little ice age lia record the most extensive advance of the holocene in many regions there is strong evidence for neoglacial advances in the interval between 1 0 and 2 5 ka moraines that correlate with the lia of the northern hemisphere are seen in all presently glacierized mountain ranges most of these date to within the past 450 years outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the lia priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies for the lateglacial these gaps include the arid regions of northern chile and argentina the southern peruvian andes between 11 5 and 13 5 s and the andes of northern peru and

high isotope fractionations during sulfate reduction in a low sulfate euxinic ocean analog a detailed record of the early earth sulfur s cycle is chronicled by the s isotope values of sulfide and sulfate preserved in the rock record interpretation of this record rests on our understanding of sulfur cycling in modern systems experiments and the resulting isotopic signatures very large fractionations in 34s of 70 are commonly measured between sulfide and sulfate in modern systems and in ancient sediments theoretical calculations suggest that sulfate reducing prokaryotes are capable of producing such large fractionations during the reduction of sulfate to sulfide although they have only been demonstrated to generate fractionations up to 48 here we report the first direct determination of 60 70 fractionations by natural populations of sulfate reducers these high fractionations occur under the relatively low sulfate conditions 1 1 2 mm of meromictic lago di cadagno in switzerland the major and minor isotopic composition of sulfide and sulfate in the lake water is consistent with sulfide produced by sulfate reduction with little evidence for modification by further oxidative sulfur cycling these observations help us to constrain the evolution of seawater sulfate concentrations

ionospheric signatures of a plasma sheet rebound flow during a substorm onset 1 magnetic reconnection in earth s magnetotail produces fast earthward flows in the plasma sheet tailward flows are often observed associated with the earthward flows both return flow vortices at the flanks of an earthward flow channel and rebound of the earthward flow from the intense dipolar magnetic field of the inner magnetosphere have been shown to explain tailward flows observed near earth we combine plasma sheet measurements from cluster with conjugate ground based magnetic and auroral data to examine the development of earthward and tailward flow signatures during a substorm onset we show for the first time observations of ionospheric signatures that appear to be associated with rebound flows because of the highly dynamic magnetotail configuration special care is taken with the satellite footprint mapping the ionospheric footprints produced by the event oriented am02 model drift equatorward and poleward in response to tail magnetic field stretching and dipolarization respectively the footprint motion matches that of the ambient ionospheric structures and the plasma flow measured by cluster agrees with that inferred from the conjugate ionospheric observations confirming the validity of the am02 mapping the ionospheric signatures of fast earthward flows during a substorm onset are shown to resemble the known signatures of quiet time flows including equatorward propagating auroral streamers inside a channel of enhanced poleward equivalent current however the large scale dipolarization results in additional poleward expansion of the signatures as has been predicted by simulations

the imprint of methane seepage on the geochemical record and early diagenetic processes in cold water coral mounds on pen duick escarpment gulf of cadiz abstract the diagenetic history and biogeochemical processes in three cold water coral mounds located in close proximity to each other on pen duick escarpment in the gulf of cadiz were examined the influence of ascending methane rich fluids from underlying sediment strata delineated two mound groups alpha and beta mound showed evidence for the presence of a sulfate methane transition zone smtz at shallow depth whereas gamma mound appeared to lack a shallow smtz in the methane influenced alpha and beta mound upward diffusion of hydrogen sulfide from the shallow smtz caused extensive pyritization of reactive iron phases as indicated by values for the degree of pyritization 0 7 this secondary pyritization overprinted the sulfur isotope composition of sulfides formed during organoclastic sulfate reduction the almost complete consumption of reactive iron phases by upward diffusing sulfide limited dissimilatory iron reduction to the top layer in these mounds while organic matter in the pyritized zones below was primarily degraded by organoclastic sulfate reduction hydrogen sulfide produced during sulfate reduction coupled to the anaerobic oxidation of methane aom diffused upward and induced aragonite dissolution as evidenced in strongly corroded corals in alpha mound this mound has been affected by strong fluctuations in the depth of the smtz as observed by distinct layers with abundant diagenetic high mg calcite with a 13 c depleted carbon isotope composition in the non methane influenced gamma mound low sulfate reduction rates elevated concentrations of dissolved iron and solid phase iron speciation indicated that organic matter mineralization was driven by dissimilatory iron reduction and organoclastic sulfate reduction coupled to oxidative sulfur cycling the latter process led to 34 s depletion in pyrite of up to 70 relative to pore water sulfate