role of corrosion by h2so4 fallout in cave development in a travertine deposit evidence from sulfur and oxygen isotopes abstract 18o and 34s values for spring water dissolved sulfates and sulfides air borne sulfur species and gypsum found on the walls of two caves in the travertine deposit of the cave and basin hot springs in banff national park alberta canada suggest that the caves are developing at least in part via a chemical corrosion process microbiological reduction of dissolved sulfate with positive 18o and 34s values produces reduced sulfur species hs h2s with negative 34s values upon escape from the spring water the h2s is converted to h2so4 fallout h2so4 attacks the calcite in the travertine leading to the formation of gypsum the gypsum on the walls of the caves has negative 34s values similar to those of the reduced sulfur species and negative 18o values that reflect incorporation of an appreciable proportion of oxygen derived from spring water vapor during h2s oxidation hydrolysis isotopically similar gypsum in spring pools at the site represents gypsum that has fallen off the walls exposing fresh travertine to attack by sulfuric acid

turbulent heat flux in the upper ocean under sea ice turbulence data from three arctic drift station experiments demonstrate features of turbulent heat transfer in the oceanic boundary layer time series analysis of several w t records shows that heat and momentum flux occur at nearly the same scales typically by turbulent eddies of the order of 10 20 m in horizontal extent and a few meters in vertical extent probability distribution functions of w t have large skewness and kurtosis where the latter confirms that most of the flux occurs in intermittent events with positive and negative excursions an order of magnitude larger than the mean value an estimate of the eddy heat diffusivity in the outer ekman part of the boundary layer based on measured heat flux and temperature gradient during a diurnal tidal cycle over the yermak plateau slope north of fram strait agrees reasonably well with the eddy viscosity with values as high as 0 15 m2 s 1 an analysis of measurements made near the ice ocean interface at the three stations shows that heat flux increases with both temperature elevation above freezing and with friction velocity at the interface it also reveals a surprising uniformity in parameters describing the heat and mass transfer e g the thickness of the transition sublayer from a modified version of the yaglom kader theory is about 10 cm at all three sites despite nearly a fivefold difference in the under ice roughness z0 which ranges from approximately 2 to 9 cm a much simplified model for heat and mass transfer at the ice ocean interface suggested by the relative uniformity of the heat transfer coefficients at the three sites is outlined

turbulence beneath sea ice and leads a coupled sea ice large eddy simulation study the importance of leads sea ice motion and frazil ice on the wintertime ocean boundary layer was examined by using a large eddy simulation turbulence model coupled to a thermodynamic slab ice model coupling was achieved through exchange coefficients that accounted for the differing diffusion rates of heat and salinity frazil ice concentrations were modeled by using an ice crystal parameterization with constant crystal size and shape stationary ice without leads produced cellular structures similar to atmospheric convection without winds ice motion caused this pattern to break down into a series of streaks aligned with the flow eddy fluxes were strongly affected by ice motion with relatively larger entrainment fluxes at the mixed layer base under moving ice whereas stationary ice produced larger fluxes near the top of the boundary layer opening of leads caused significant changes in the turbulent structure of the boundary layer leads in stationary ice produced concentrated plumes of higher salinity water beneath the lead ice motion caused the lead convection to follow preexisting convective rolls enhancing the roll circulation salinity and vertical velocity under the lead comparison of model time series data with observations from the arctic leads experiment showed general agreement for both pack ice and lead conditions simulated heat flux carried by frazil ice had a prominent role in the upper boundary layer suggesting that frazil ice is important in the heat budget of ice covered oceans

an arctic ocean cold core eddy detailed physical and chemical observations were obtained during september 1997 of a cold core eddy situated in the southern central canada basin of the arctic ocean the eddy was about 20 km in diameter had maximum current speeds exceeding 20 cm s 21 and extended from the base of the upper mixed layer near 40 m down to 400 m excess salt in the eddy core was consistent with addition of brine from 1mo f ice formation core tracer distributions indicated a lifetime exceeding 1 year and were consistent with an origin as near surface pacific water with some admixed terrestrial runoff the eddy was probably formed in association with a polynya along the alaskan chukchi sea coast through local water densification from surface ice formation followed by development of frontal instabilities formation and subsequent migration of such eddies which may have lifetimes of several years provide a mechanism for transporting water from the beaufort and chukchi sea coastal and shelf regions into the interior canada basin and for contributing to maintenance of the permanent halocline present light ice conditions throughout the arctic ocean favor the formation of such eddies and may contribute to enhanced ventilation of the halocline waters

sulfur isotope geochemistry of gypsiferous aridisols from central iran abstract gypsum accumulation is one of the prominent pedogenic processes occurring in many and regions of the world gypsiferous soils occur in large areas of the iranian central plateau the origin of gypsum in the aridisols of central iran and its distribution in different landscapes were studied using sulfur and oxygen isotopic composition of both solid and dissolved sulfates the results strongly support the hypothesis that the area was cut off from the tethys seaway at the end of the mesozoic era and as a result the lower cretaceous sulfate has controlled the s geochemistry of the younger sediments including the soils studied the mean values of 34 s and 18 o of the soil gypsum and of dissolved sulfate match with the average isotopic values of the marine sediments which are the most common soil parent materials the results also confirm that s and o in dissolved so 4 and so 4 in gypsum have not undergone any reduction and re oxidation reactions dissolution and reprecipitation appear to be the possible mechanisms responsible for the observed minimal isotope fractionation both 34 s and 18 o values of the soil gypsum decrease slightly with decreasing elevation in the study area these findings are important for understanding the landform evolution in this arid region

arctic ocean mixed layer eddy generation under leads in sea ice 1 convection in the arctic ocean mixed layer occurs under openings in sea ice where new sea ice is formed the process of brine rejection during ice formation creates negatively buoyant fluid at the surface of ice leads when the fluid convects downward the ocean mixed layer below the lead is stirred vertically and through planetary rotational effects along lead flows at the lead edges are induced these vertical and lateral motions have been previously studied using two dimensional numerical ocean models and observed in field programs such as leadex in this paper the generation of arctic ocean eddies through dynamic instabilities is investigated using a three dimensional nonhydrostatic ocean model results suggest that salt enriched vortices can develop at the base of the mixed layer as a consequence of brine rejection but the vortex formation requires a time period of several days a time long enough that the progenitor lead would likely have closed the scale of the eddies is found to depend on the magnitude of the buoyancy forcing the width of the lead and the duration of the buoyancy forcing the number of vortices produced depends on lead width and duration of buoyancy forcing but is less sensitive to the magnitude of the buoyancy forcing vortex sizes scaled appropriately and vortex numbers are compared with those found in recent laboratory studies of convectively driven flows from line segment sources

34s and 18o abundances differentiate upper cambrian and lower devonian gypsum bearing units district of mackenzie n w t an update previous sulfur isotope data for the lower devonian bear rock formation and the upper cambrian saline river formation in the district of mackenzie n w t have been supplemented by additional sulfu

coloured mineral coatings on monument surfaces as a result of biomineralization the case of the tarragona cathedral catalonia successive coloured coatings on the taragona cathedral catalonia were analyzed using chemical microbiological and mineralogical techniques the coatings consist of mainly biogenic minerals calcite several oxalates phosphates and their fabric and composition is independent of the underlying rock the origin of the crusts or patinas is attributed to bygone sub fossil microflores which formed biofilms and microbial mats on and within the surface of the limestones and marbles of the cathedral the staining of the patina layers is not related to the mineral colours nor to anthropogenic dust or fly ashes the colours are most probably organic pigments embedded between the crystals and fe and mn organic compounds remaining from bioactivity a sequential hypothesis of the origin s of the patina layers is given

origin of radioactive barite sinter flybye springs northwest territories canada cold springs emerging a long the contact between devonian limestone and shale units in the northwestern canadian cordillera are presently depositing a radium enriched barite sinter a geological cross section through the springs area shows that groundwaters could circulate through a mainly limestone aquifer to depths of approximately 2 km some shales and volcanic rocks associated with the aquifer contain barium bound in feldspars barite pyrite and organic matter hosted in shale and radium in feldspars or produced by the radioactive decay of uranium associated with organic matter hosted in shale spring waters are of the type characteristic of water that has equilibrated with clay minerals a subsurface equilibration temperature of 34 c was determined by silica geothermometry and 31 c by magnesium corrected na k ca2 geothermometry emerging waters are partly mixed with surface runoff and therefore these temperatures represent only minimum values assuming a normal geothermal gradient these tem

variability in sulfur isotope records of phanerozoic seawater sulfate the s of seawater sulfate reflects processes operating at the nexus of sulfur carbon and oxygen cycles however knowledge of past seawater sulfate s values must be derived from proxy materials that are impacted differently by depositional and post depositional processes we produced new timeseries estimates for the s value of seawater sulfate by combining 6710 published data from three sedimentary archives marine barite evaporites and carbonate associated sulfate with updated age constraints on the deposits robust features in multiple records capture temporal trends in the s value of seawater and its interplay with other phanerozoic geochemical and stratigraphic trends however high frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints the amount of noise quantified from the variograms of each record increases with age for all s proxies indicating that post depositional processes obscure detailed knowledge of seawater sulfate s s value deeper in time

sedimentology of perennial ice covered meromictic lake a ellesmere island at the northern extreme of canadapolar continental shelf program contribution 00109 the sedimentology of coastal meromictic lake a ellesmere island 83 00 n 75 30 w was investigated to understand the linkages between the extreme lake environment and its sedimentary features four facies were identified within the sedimentary record that represent stages of the lake s development from a marine embayment to a meromictic lake despite low ecosystem productivity both clastic and biogenic materials contribute substantially and highly seasonal sedimentation pervasive ice cover and anoxia in the saline bottom water monimolimnion act to preserve annual sedimentary units varves within the upper part of the sedimentary record sediment texture is predominantly silt and clay but the irregular presence of sand indicates past episodes of higher energy stream discharge to the lake oxygen incursions into the chemocline likely cause bacteria mortality and provide elemental sulphur for iron sulphides that are deposited in the sediments millimetre scale sedimentary pellets are also a consp

origin and evolution of the thermal waters from the pamukkale geothermal field denizli basin sw anatolia turkey insights from hydrogeochemistry and geothermometry abstract the pamukkale geothermal field pgf of the denizli basin sw turkey is one of the most distinguished active geothermal fields known in the world the thermal waters from the pgf are subdivided into two groups group 1a ca hco3 and group 1b ca so4 types the cold waters are also classified into two groups group 2a ca hco3 and group 2b mg hco3 types the hydrogeochemical properties of the pgf thermal waters suggest interactions with the basal metamorphic rocks of the menderes massif tectonically overriding by the carbonate rocks of the lycian nappes and sedimentary rocks of the neogene formations the bedrock units are stratigraphically overlain by the neogene sedimentary units of the denizli group the thermal springs of the pgf are affected by several hydrothermal processes including mixing water rock interaction and input of mantle volatiles the thermal water plots of the pgf deviate from the full equilibrium line indicating a low water maturity and or mixing processes mixing models and na k mg ternary diagram suggest mixing between meteoric and thermal waters during the uprising of the deep originated fluids the water rock interaction leads saturation of calcite and induces travertine precipitation in the discharge area low tritium this study proposes a conceptual hydrogeological hydrogeochemical tectonic model for the pgf the thermal waters are derived from the infiltration of rainwater through fractures and faults in high recharge areas to the deep hot reservoir heating produced by the high geothermal gradient is interpreted in relation with the regional crustal thinning thermal waters upwell along wnw ese trending deep faults and fractures the pamukkale fault system that act as hydrothermal pathways favouring migration of a huge amount of co2 rich gas from deep geothermal reservoir the geochemical and isotopic data of the thermal waters and gas indicate that the degassing of both metamorphic co2 and mantle derived co2 occurs in the pgf helium isotope data indicate that mantle volatiles produce possibly an upwelling into asthenosphere and ascent along these tectonic discontinuities in this context the pgf is one of the best example of geothermal fields as an interaction of active magmatism in the actively extending crustal setting

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

travertine formation in plitvice national park yugoslavia chemical versus biological control hydrochemical studies of the plitvice lakes and their tributaries croatia yugoslavia were coupled with micromorphological investigations on carbonate lake sediments and recent travertines karst springs discharge water from aquifers in triassic and jurassic dolomites and limestones and collect in lakes which are ponded behind accreting travertine dams waters at springs have a high co2 partial pressure greater than 7000 ppm and are slightly undersaturated with respect to calcite saturation index less than 0 03 co2 partial pressure is quickly reduced in swift running streams leading to very high supersaturation with carbonate minerals saturation indices between 0 74 and 0 53 calcite deposition however is restricted to the lake bottoms formation of lake marl and to the tufa dams the annual carbonate precipitating capacity of the system based on water balance and downstream loss of dissolved ions is estimated to be on the order of 10 000 t caco3 as cascade deposits tufa dams or as micrite in lakes behind the travertine dams the initial stages of travertine formation as a result of morphological biological and chemical factors are i moss settling on small ridges in the creek courses ii epiphytes diatoms and cyanobacteria settling on the moss surface iii micrite particles resuspending from lake bottoms and being trapped on mucous excretions from bacteria and diatoms and iv inorganic calcite precipitating as sparite at nucleation sites provided by these crystal seeds geochemical studies of the lake marl and tufa dams show that amino acids are dominated by aspartic acid carbohydrates come from structural polysaccharides of diatoms the sticky excretions rich in aspartic acid are necessary for the initiation of calcite precipitation they may be a response of algal and bacterial metabolism to environmental stress by either nutrient depletion or high calcium concentrations in ambient waters the formation of tufa and micrite lake marl appears to be initiated by localized biological factors and is not governed by mere calcite supersaturation of the water oligotrophy may be an essential precondition for the formation of fresh water carbonate deposits

an investigation of the link between lead induced thermohaline convection and arctic eddies a recent laboratory study indicates that a turbulent buoyant line plume discharging into a rotating stratified fluid provides a natural mechanism for generating a series of anticyclonic geostrophic vortices bush and woods 1999 here we examine the implications of these experimental results in the context of the thermohaline convection which develops when saline water is released as leads freeze over in the polar oceans using the experimental results in conjunction with a simple numerical model of plume dynamics in a non uniformly stratified environment we develop a model which characterizes the geometry of the eddies which would develop owing to lead induced convection the model predicts that in the absence of strong currents lead induced thermohaline convection may generate anticyclonic geostrophic vortices of characteristic radius 2 10 km at the base of the mixed layer however this mechanism cannot account for the arctic eddies observed at substantial depths beneath the mixed layer cyclonic or strongly ageostrophic eddies

sulfur and oxygen isotopes in the gypsum deposits of the provalata sulfuric acid cave macedonia abstract sulfur stable isotopes from cave sulfates mainly gypsum have been used in a number of studies to trace the source of sulfur in caves formed by sulfuric acid but only few studies apply combined use of sulfur and oxygen stable isotopes to further understand the processes operating in sulfuric acid speleogenesis sas here we present results of a detailed study of the distribution of sulfur and oxygen stable isotopes within the gypsum deposits formed during sulfuric acid speleogenesis of provalata cave macedonia the 18o vs vsmow values range between 3 9 and 8 2 and the 34s vs cdt values between 7 5 and 0 7 we found a strong positive correlation between the 18o and 34s values with a 0 5 increase in the 34s for every 1 increase in the 18o indicating that both oxygen and sulfur isotopes were concurrently affected during the oxidation process we attribute these effects to be either due to environmental control concentrations of h2s and o2 or due to isotope fractionation during multi step microbial oxidation also affected by the environmental conditions additionally a shift of 1 85 in the 34s values prior to the h2s oxidation is found indicating evolution of the h2s 34s in the sas system the wide range of both 18o and 34s values in the gypsum deposits of the small provalata cave show that both the number of samples and their location can be an important factor for the understanding of sulfuric acid speleogenesis using stable isotopes

hydrochemical characterization of pamukkale travertines denizli turkey for remediative measures the unesco world heritage snow white travertines in pamukkale w turkey are discolored as a consequence of algae growth at the surface the first act to restore the travertines was to abandon the activities and facilities that found to provide nutrients discoloration has continued after the pollution sources were abandoned because the nutrients were sorpted onto the travertine material the subsurface water was found to be contaminated by desorption of the nutrients sorption desorption characteristics of the travertines had to be quantified in order to achieve an effective remediation and restoration this study was carried out to determine the sorption desorption characteristics of the travertines by batch and column experiments batch experiments revealed that the sorption isotherms of the pamukkale travertine fit a linear model for nitrate and freundlich isotherm model for phosphate the distribution coefficients k d for nitrate and phosphate were calculated from the isotherms as 24 1 and 181 l kg respectively incorporating k d values the retardation factors were calculated as 142 for nitrate and 1553 for phosphate thus the relative velocity of nitrate and the phosphate was calculated as 7 3 10 2 and 6 7 10 3 m day respectively the data obtained from the column experiment evaluated by fitting a theoretical curve the results from the column experiment were then interpreted in terms of flushing of nitrate by pore volumes and suggested that the travertines can be cleaned up by flushing at least four pore volumes

ice ocean interactions during shallow convection under conditions of steady winds three dimensional numerical studies abstract a three dimensional hydrodynamic ocean model coupled to a thermohydrodynamic model for young sea ice is applied to study shallow haline convection in the central greenland sea with an emphasis on sub mesoscale ice ocean interactions two types of young sea ice are distinguished i e frazil and pancake ice both acting different on surface heat salt and momentum fluxes two scenarios are considered a continued frazil ice production during steady winds and b the same scenario but with the intermittent formation of pancake ice during a short intervening period of low winds brine release due to new ice production creates shallow convection in both cases under conditions of continued frazil ice production ice streaks develop at the sea surface finally becoming oriented roughly parallel to the wind these streaks are the result of convective plumes that induce organized patterns of convergent and divergent surface currents frazil ice is herded into convergence zones where it becomes as thick as 6 m within 24 h the studies suggest a strong relationship between streak spacing and the penetration depth of convection given by an aspect ratio in the range of 2 3 after pancake ice has been formed however the organized ice streaks vanish developing into complex patterns of pancake ice this finding is in agreement with recent field observations in the greenland sea is odden ice tongue with the existence of pancake ice moreover the surface averaged buoyancy flux decreases and is determined from the integral of local sub mesoscale ice ocean interactions

oxygen and sulfur isotope geochemistry of acidic groundwater discharge in british columbia yukon and district of mackenzie canada the paint pots in kootenay national park british columbia appear to derive the fe zn pb and contents of their water from sulfide mineralization in lower and middle cambrian carbonates the fe zn ni and contents of groundwater discharging into a tributary of engineer creek yukon are likely derived from sulfide mineralization in devonian or ordovician black shales exposed in the area the high fe and contents of a natrojarosite deposit northeast of fort norman northwest territories are probably derived from pyritiferous cretaceous shales in that area isotope analyses of water and of dissolved and precipitated sulfur species from these three sites where acidic heavy metal bearing groundwater is being discharged revealed that between 38 and 74 of the oxygen used in the subsurface oxidation of metal sulfides is supplied by h2o molecules rather than by molecular dissolved oxygen the available data also suggest that lower percentages of water oxygen in the secondary sulfates reflect increasing

sem imaging of bacteria and nannobacteria in carbonate sediments and rocks abstract bacteria and nannobacteria 0 1 m dwarfed forms are abundant in both non etched and gently etched travertines deposited by hot springs in viterbo italy they are also plainly visible in bahama ooids and hardgrounds and in great salt lake aragonite ooids and cements in addition nannobacteria are found in paleozoic and mesozoic rocks because of their extraordinary abundance in some specimens they probably play a prominent role in catalyzing the precipitation of carbonate materials

isotope geochemistry of dissolved precipitated airborne and fallout sulfur species associated with springs near paige mountain norman range n w t 34s values determined for dissolved sulfate in water discharged by sulfurous springs near paige mountain identify gypsum beds in the lower devonian bear rock formation as the sulfate source whereas relatively low 18o values show that as much as 30 of the sulfate may have gone through a reduction re oxidation cycle reduced sulfur species in the spring water have negative 34s values as a result of microbiological isotope fractionation during sulfate reduction airborne sulfur species h2s so2 h2so4 and gypsum formed through reaction of h2so4 fallout with exposed carbonate rocks show similar negative 34s values negative 18o values for the sulfate radical in h2so4 fallout and in the alteration product indicate that more than half of the oxygen reacting with airborne h2s is derived from water vapour

perennial spring occurrence in the expedition fiord area of western axel heiberg island canadian high arctic this paper documents perennial spring activity at expedition fiord on western axel heiberg island in the canadian high arctic two groups of mineralized springs occur near the mcgill university axe

a geochemical evaluation of perennial spring activity and associated mineral precipitates at expedition fjord axel heiberg island canadian high arctic abstract two groups of perennial springs are observed in the canadian high arctic at expedition fjord on axel heiberg island at colour peak and gypsum hill saline discharge 1 3 2 5 molal nacl produces a variety of calcite travertine and gypsum rich precipitates saturation index calculations of the spring waters at colour peak suggest co 2 degassing from the waters causes calcite precipitation gypsum precipitation dominates at gypsum hill where spring waters have lower alkalinity and higher so 4 concentrations mineral accumulations form both channel and rimstone pool morphologies as a result of varying slope conditions at colour peak confined flow in steep slope areas develop massive structures in contrast to more friable porous accumulations in areas where waters fan out on shallower slopes these morphological variations lead to corresponding varying apparent rates of mineral precipitation mineral precipitation at gypsum hill is far less notable as a result of lower discharge rates and annual degradation by icing formation microscopic observations and geochemical analyses of the channel precipitates at colour peak reveal alternating light calcite spar and dark anhedral microcrystalline calcite combined with organic matter and non carbonate minerals laminae rimstone pools forming in lower sections of spring discharge are composed of accumulations of large euhedral calcite crystals interbedded with allochthonous inputs high concentration of dissolved solids is responsible for slow travertine precipitation rates which occurs during winter this precipitation is further retarded during summer months by the introduction of crystal growth inhibitors such as fe 3 and deposition of organic matter and soil sediments

solidification of leads theory experiment and field observations thin sea ice plays a central role in the surface heat and mass balance of the arctic ocean in order to develop understanding of these balances we describe and analyze highly resolved temperature data taken through the air sea ice interface during the transition from an ice free to an ice covered arctic ocean surface the data were taken to observe the thermodynamic evolution of a lead a process that has previously only been accessible to measurement techniques confined to the lead edge our detailed analysis of the field data is guided by recent theoretical and experimental advances in understanding the phase dynamics of directionally solidified alloys because of the dearth of direct observations we also present time series of the relevant heat fluxes inferred from our data and demonstrate the controlling influence that the internal phase evolution has on these quantities we have previously examined the stability of the brine trapped in a growing sea ice matrix both theoretically and experimentally and now find that haline convection driven from within the growing layer is consistent with this previous work and with the nature of direct turbulence measurements the importance of this process is that although ice growth is continuous the local brine flux commences abruptly only after some time in contrast to what had previously been supposed hence the ice growth process itself is a source of intermittency in oceanic boundary layer turbulence furthermore we find that in this particular situation the sea ice growth is not simply a square root function of time in contrast to the model typically used in numerical simulations by far the most practical methods of studying lead convection are numerical simulations and laboratory models and a strong conclusion of this study is the importance of the proper treatment of the boundary conditions describing the buoyancy flux

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

convection beneath freezing leads new observations compared with numerical model results vertical distributions of temperature salinity and horizontal and vertical current speed were measured along the edges of a number of rapidly freezing leads in the southern central beaufort sea during march april 1992 these observations were restricted to cases having sufficiently small ice water relative speeds that brine driven convection was expected based on scaling arguments to dominate shear turbulence generated by the relative ice water motion the observed salinity and current features were consistent with an existing conceptual model for sublead convection consequent to brine rejection from ice formation and with the results of a numerical model which assumes two dimensionality in the cross lead direction and uses a brine input consistent with the field observations these models predict convection of brine enriched plumes beneath the lead downward to the pycnocline where they then spread outward away from the lead volume continuity is satisfied by horizontal inflow of water to the lead at the surface observed mean downward convection speeds varied from 0 2 to 0 7 cm s 1 and had maxima up to about 2 cm s 1 consistent with the numerical model salinities associated with the convecting parcels were about 0 001 practical salinity units psu above ambient which was an order of magnitude less than predicted by the model while plumes of water flowing away from the lead on the pycnocline had salinities as high as 0 004 psu above ambient these similarities and discrepancies are discussed within the context of a steady state model versus a nonsteady field situation and it is concluded that the steady convection cell concept is probably valid if viewed as a time averaged sequence of discrete convective plumes or thermals

isotope geochemistry of stratified lake a ellesmere island n w t canada ionic composition salinity temperature ph tritium and stable isotope compositions of water and ions were determined for samples collected in 1969 and 1982 from different depths of stratified lake a on ellesmere island tritium contents and ionic and stable isotope compositions were diagnostic of recent fresh water overlying older deeper trapped seawater a temperature maximum occurs at 15 m in the freshwater seawater transition zone salinity 18o and d data suggest that the lake evaporated slightly and acquired about 12 fresh water prior to stratification individual ion concentrations reveal a slightly modified cation composition and marked depletions in sulphate and enrichments in dissolved carbonate compared with modern ocean water the 34s 18o and 13c data for and attest to extensive anaerobic reduction during the lake s history

manetoe facies a gas bearing megacrystalline devonian dolomite yukon and northwest territories canada the manetoe facies is a broadly stratiform and regionally developed 38 000 km2 or 15 000 mi2 body of white sparry dolomite hosted in lower and middle devonian strata and is the northwestward continuation of the similar but better known presqu ile facies dolomite several large gas fields have been discovered within anomalously thick developments of the manetoe dolomite close to the northwest limit of the devonian elk point basin of alberta the external geometry of the manetoe facies indicates that it may have been a cavern or karst system excavated in the late middle devonian by a large vertically confined coastal aquifer the local regions of anomalously thick manetoe facies may have developed where the aquifer stoped upward into strata above the confining aquiclude of the headless formation shale dolomite cementation may have occurred during any of three possible episodes of large scale fluid movement fluid inclusion and strontium isotope data favor the hypothesis that manetoe dolomites precipitated from heated 150 210 c or 300 410 f hypersaline evaporitic brines that have interacted with the underlying precambrian crust probably in the late devonian lead isotope data support the general concept of pre mesozoic dolomite cementation and largely preclude a late early tertiary deep burial setting spectacular zones of detrital dolomite cement within the manetoe are most readily accommodated by a near surface very early middle devonian aquifer mixing model origin but the presence of these zones does not preclude the other possible origins carbon and xygen isotope data from the manetoe facies support the concept that the presqu ile and manetoe facies are physically continuous and had a common origin

naturally precipitating vaterite μ caco3 spheres unusual carbonates formed in an extreme environment vaterite a rare hexagonal caco3 polymorph was identified in precipitates forming at a supra glacial sulfur spring in borup fiord pass northern ellesmere island canadian high arctic vaterite occurs in a precipitate mound along with calcite gypsum and native sulfur the unusual conditions of the site including an extremely cold climate supersaturated alkaline waters and the presence of gypsum mimics conditions used to grow vaterite in laboratory experiments stable isotope data suggest that vaterite may preferentially form during colder periods of the year vaterite found at the site is characterized by 2 to 10 m rounded to spherical shaped particles comprising smaller 0 5 to 2 m spheres as both individuals and in chainlike structures the spherical habit of vaterite resembles carbonate structures that have been interpreted to be organic however 13 c values are indicative of an inorganic origin the thick permafrost and the extreme cold and dry environment make this site a good terrestrial analog for carbonate precipitates that might be expected at potential deposits associated with water discharge on other planetary bodies copyright 2003 elsevier science ltd

aragonite laminae in hot water travertine crusts rapolano terme italy small 5 30 m aggregates of aragonite needles occur in calcite crystal crusts of present day hot water slope travertines at rapolano terme in tuscany italy the aggregates are mainly concentrated in irregular wispy and dark laminae which cross cut calcite crystal feathers to create a pervasive millimetre scale banded appearance in the deposit they also occur less commonly scattered irregularly through the calcite layers the aragonite needle aggregates are in the form of crosses fascicles sheaf shaped bundles or dumbbell shaped rosettes and spherulites locally irregular masses of needles also occur the fascicles rosettes and spherulites have hollow centres which resemble microbial components fungal spores bacterial colonies and pollen suggesting that the aragonite crystals are biotically nucleated the lamination is interpreted to reflect diurnal control stimulation of microbial activity during daylight concentrates cells in laminae and promotes aragonite calcification calcite feather crystals although traversed by the aragonite aggregate laminae have a clear appearance under the light microscope they form more or less continuously through the diurnal cycle by abiotic precipitation the constant association of aragonite with organic nuclei irrespective of whether the latter are in laminae or scattered through the calcite layers supports a biotic control on aragonite formation lamination in pleistocene travertines is superficially similar to that in the present day deposits but is diagenetically altered in the pleistocene deposits the calcite feathers appear dark under the light microscope and the aragonite aggregates where they are not altered to dark calcite are dissolved together with parts of the adjacent spar calcite and therefore appear light coloured

origin and diagenesis of quaternary travertine shrub fabrics rapolano terme central italy millimetre to centimetre sized arborescent shrub like calcite precipitates are common constituents of hot water travertine shallow pool deposits of quaternary age at rapolano terme tuscany italy in the presently forming travertines the shrubs consist of apparently random associations of i micrite aggregates and ii subhedral to euhedral rhombic spar crystal aggregates in thin section the micrite aggregates appear dark and the spar rhomb aggregates light giving the shrubs a mottled appearance travertines are basically produced by caco3 precipitation due to degassing and evaporation of the spring waters although biological influence may also stimulate precipitation the formation of masses of erect shrubs rather than dense crystal crusts that form on slopes is probably due to limited water flow in the pool environments microbes including bacteria and diatoms are important influences on shrub microfabric and external shape the micrite aggregates are associated with bacteriform bodies seen as tiny rods and spheres the micrite precipitates around these bodies and in adjacent biofilm spar rhomb precipitation appears to be external to the biofilm and may be related to the presence of diatoms which are locally closely associated with the spar rhombs although an essentially inorganic origin particularly for the more euhedral rhombs cannot be ruled out in the older quaternary travertines the original microfabric of the shrubs has been diagenetically altered the original mottled appearance of the shrubs has become uniformly dark and micritic and the evidence for the dual micritic and spar rhomb origin of the shrubs is obscured or destroyed spar micritization of the shrubs is probably due to abiotic and locally biotic dissolution previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity

origin of annual laminations in tufa deposits southwest japan abstract laminated tufas and a tufa depositing stream in sw japan shirokawa ehime prefecture were studied monthly over a 3 yr period a series of samples from the tufa clearly reveals the pattern of annual laminations the annual layering pattern was primarily controlled by changes in the rate of calcite precipitation as calculated from water chemistry the concentration of dissolved caco 3 which correlates with the precipitation rate was high in summer autumn and low in winter spring owing to changes in the partial pressure of co 2 in underground air regular seasonal changes in underground pco 2 probably resulted from two temperature dependent processes the diffusion of soil co 2 and the ventilation of underground air these changes in addition to water temperature changes altered the precipitation rate which has a clear seasonal pattern especially in the lower stream the seasonal precipitation rate was high in summer autumn and low in winter spring which is consistent with the seasonal lamination pattern seen in the tufas the textures of collected samples show that the laminations consist of densely calcified summer autumn june october laminae and lightly calcified winter spring november may laminae we infer that the increased precipitation rate stimulated thick calcite encrustation on cyanobacterial filaments to produce the dense textures this interpretation is supported by the lowered organic inorganic carbon production ratio in summer autumn seasonal variations in cyanobacterial assemblages are present but do not reflect the seasonal lamination pattern because the relevant processes are temperature dependent the seasonal lamination pattern at shirokawa is thought to generally apply to other laminated tufas deposited in temperate climates however a reversed pattern can result from local and climatic circumstances dense laminae were deposited in winter near the source of the spring at shirokawa because calcite precipitation was high owing to low underground pco 2 in winter reversed patterns reported from northwestern europe were probably influenced by seasonal rainfall which is reflected in hydrological conditions

the chemical evolution of a travertine depositing stream geochemical processes and mass transfer reactions this field study focuses on quantitatively defining the chemical changes occurring in falling spring creek a travertine depositing stream located in alleghany county virginia the processes of co sub 2 outgassing and calcite precipitation or dissolution control the chemical evolution of the stream the observed chemical composition of the water was used with the computerized geochemical model wateqf to calculate aqueous speciation saturation indices and co sub 2 partial pressure values mass balance calculations were performed to obtain mass transfers of co sub 2 and calcite reaction times estimated from stream discharge were used with the mass transfer results to calculate rates of co sub 2 outgassing and calcite precipitation between consecutive sampling points the stream which is fed by a carbonate spring is supersaturated with respect to co sub 2 along the entire 5 2 km flow path outgassing of co sub 2 drives the solution to high degrees of supersaturation with respect to calcite metabolic uptake of co sub 2 by photosynthetic plants is insignificant because the high supply rate of dissolved carbon dioxide and the extreme agitation of the stream at waterfalls and rapids causes a much greater amount of inorganic co sub 2 outgassing to occur calcite precipitation is kinetically inhibited until near the crest of amore 20 m vertical waterfall calcite precipitation rates then reach a maximum at the waterfall where greater water turbulence allows the most rapid escape of co sub 2 physical evidence for calcite precipitation exists in the travertine deposits which are first observed immediately above the waterfall and extend for at least 1 0 km below the falls net calcite precipitation occurs at all times of the year but is greatest during low flow conditions in the summer and early fall less

seasonal formation of ikaite caco3 6h2o in saline spring discharge at expedition fiord canadian high arctic assessing conditional constraints for natural crystal growth abstract spring discharge at expedition fiord pollard et al 1999 on axel heiberg island in the canadian high arctic produces a variety of travertine forms in addition to a diverse collection of mineral precipitates this paper focuses on clusters of thermally unstable crystals believed to be the mineral ikaite caco3 6h2o growing seasonally along two spring outflows at colour peak this form of calcium carbonate mineral occurs along small sections of discharge outflow as white euhedral crystals up to 0 5 cm in length difficulty in sampling storage and transport of the samples for analysis has hampered attempts to confirm the presence of ikaite by x ray diffraction however various field observations and the remarkable instability of these crystals at normal ambient temperatures strengthens our argument this paper provides a description of these particular caco3 6h2o crystals and their environmental surroundings and attempts to determine the validity of ikaite precipitation at this site by theoretical geochemical modeling these results are compared with other reported observations of ikaite to both understand their occurrence and help delineate their geochemical characteristics it is believed that the restrictive combination of spring water chemistry and long periods of low temperatures characteristic of arctic climates are necessary for ikaite growth at this site the fact that ikaite is not forming at a second group of saline springs 11 km away allows us to more specifically outline conditions controlling its presence

lead convection measured with an autonomous underwater vehicle the winter lead experiment leadex was conducted during 1992 in the beaufort sea there the autonomous conductivity temperature vehicle actv was operated under and around leads these are the first measurements of this kind measurements of temperature salinity and turbulence parameters were also made at lead edges with sensors fixed to rigid masts by combining information from the fixed measurements and the actv an inertial dissipation method is used to derive horizontal profiles of salt flux from actv salinity measurements comparisons also show that turbulent vertical velocity perturbations can be estimated from the vertical motion of the actv with these velocity estimates horizontal profiles of the turbulent fluxes of heat w t and salt w s are also computed directly data from a wide 1000 m wide lead with rapid ice motion indicate stronger turbulence under the lead than downstream but the character of the flow is that of a convective boundary layer modified by a change in surface buoyancy flux the convection is characterized by multiple intermittent plumes that scale in size with the mixed layer depth at a medium sized 100 m wide lead with slower ice motion the convective circulation set up by the lead is more apparent convective plumes are stronger and more prevalent at the lead edges particularly the downstream edge the comparison between the horizontal profiles from the actv and time series from fixed sensors suggests that lead convection is a combination of a near surface convective boundary layer and a deeper quasi stationary convection pattern

kinetics of weathering and diagenesis weathering and diagenesis are discussed from a kinetic standpoint such a discussion depends upon an intimate interplay between field measurements laboratory experiments and mathematical theory because of the accessibility of soils and sediments models based on laboratory measurements and theoretical calculations can be used along with field data to calculate rate parameters which are otherwise difficult to measure in the laboratory also theoretical models can be tested in the field ways in which chemical kinetics can be applied to geological problems in the surficial environment are discussed and the author recomends extensive future study of such problems jmt

hydrogeology of the central mackenzie valley abstract more than 100 springs seeps and mineralized ponds in the central mackenzie valley have been investigated using chemistry field observations and a general knowledge of the geology in conjunction with environmental isotopes 2 h and 18 o values indicate precipitation primarily snowmelt as the source for all groundwaters sampled chemical analyses of the waters indicate that there are three major components ca 2 so 4 2 dominates followed by na cl and ca 2 mg 2 hco 3 the chemical data in combination with 34 s data indicate that the devonian bear rock formation is the major aquifer throughout the valley other important bedrock aquifers include the mt kindle franklin mountain and saline river formations recharge is directly into bedrock through solution channels or karst systems within the franklin mountains discharge from the bedrock units is controlled by fold and fault structures permafrost is a major factor controlling groundwater recharge but does not significantly affect the location of groundwater discharge

initial model results for arctic mixed layer circulation under a refreezing lead at the temperatures in the arctic ocean mixed layer during lead induced surface water cooling convection is primarily salinity controlled owing to continuous brine expulsion from newly forming ice a nonlinear time dependent convective model has been developed that simulates existing field data obtained on the circulation characteristics under and near a refreezing lead the model uses typical arctic ocean ambient conditions as initial input and allows for imposition of varying geostrophic currents the zero geostrophic current free convective case model output for typical lead surface salt input resulted in maximum horizontal current velocities of 0 05 m s 1 eddy viscosities on the order of 0 01 m2 s 1 average salt fluxes beneath the lead of 3 3 10 5 kg m 2 s 1 and a subsequent increase in the depth of the mixed layer the circulation cells are symmetric with respect to the lead axis imposition of a cross lead constant geostrophic current shows a resultant circulation cell asymmetry associated with increased salt advection in a forced convective regime

isotopic composition and origin of lacustrine brines in the arctic meromictic lakes in the arctic archipelago were analyzed to determine whether the isotope content of the water molecule might confirm their oceanic origin the 25 m bottom layer of lake garrow on little cornwallis island is filled with a homogeneous sodium chloride solution with 2 6 times the chloride concentration of seawater 52 g l 1 its 18o value is around 10 with respect to v smow and its 2h is eight times the oxygen value 85 in lake sophia on cornwallis island the deep stratum 25 m thick is less concentrated 35 g l 1 cl 1 and shows slightly higher 18o and 2h values 9 and 75 respectively chemocline and surficial waters result from mixing between bottom waters and meteoric waters the chemical and isotopic signals are interpreted as evidence of diagenesis through subpermafrost or intrapermafrost freezing of aquifers once filled with seawater at some time during postglacial emergence

processes affecting groundwater chemistry in a zone of saline intrusion into an urban sandstone aquifer abstract samples have been collected from inflows into railway tunnels in the triassic sandstone aquifer beneath liverpool and the mersey estuary england u k these provide a profile through a saline freshwater mixing zone analyses were made of major anions and cations 34s and 18o in so4 13c in dissolved inorganic c and 87sr 86sr the data demonstrate that the presence of a low permeability fault exerts a strong control on the local groundwater chemistry on the estuary side of the fault groundwater chemistry is dominated by mixing of intruding estuary water which is modified by so4 reduction and calcite dissolution with fresh groundwater the environment of so4 reduction in the tidal estuary is one of repeated reduction and re oxidation of s in an open system and has resulted in virtually no change in s isotopic composition but an enrichment in residual so4 18o of 1 5 groundwater chemistry on the landward side of the fault is primarily the result of recharge in an urban environment there is also evidence that saline water has been present in this region of the aquifer in the past and that this has now been flushed by fresh groundwaters this saline water was either transported along the landward side of the fault from nearer the estuary or more probably transmitted across the fault both mechanisms would have been driven by large landward head gradients caused by heavy industrial abstraction earlier this century this has produced a zone of groundwaters depleted in ca and radiogenic sr and enriched in na as a result of ion exchange between the fresh groundwaters and the aquifer previously occupied by more saline water sulphur isotopic composition however shows no variation since so4 does not undergo significant ion exchange a tracer test from a borehole to the tunnels showed multiple breakthroughs to some locations indicating a number of different flow paths through the aquifer the maximum flow velocity recorded in this test was 140 m d suggesting flow along fractures

effects of loss of perennial lake ice on mixing and phytoplankton dynamics insights from high arctic canada perennially ice covered lakes are well known from antarctica and also occur in the extreme high arctic climate change has many implications for these lakes including the thinning and disappearance of their perennial ice cover the goal of this study was to consider the effects of transition to seasonal ice cover by way of limnological observations on a series of meromictic lakes along the northern coastline of ellesmere island nunavut canada conductivity temperature profiles during a rare period of ice free conditions august 2008 in these lakes suggested effects of wind induced mixing of their surface freshwater layers and the onset of entrainment of water at the halocline sampling of the mixed layer of one of these meromictic lakes in may and august 2008 revealed a pronounced vertical structure in phytoplankton pigments and species composition with dominance by cyanobacteria green algae chrysophytes cryptophytes and dinoflagellates and a conspicuous absence of diatoms the loss of ice cover resulted in an 80 fold increase in water column irradiance and apparent mixing of the upper water column during a period of higher wind speeds zeaxanthin a pigment found in cyanobacteria was entirely restricted to the 3 mm cell fraction at all depths and increased by a factor of 2 17 with the greatest increases in the upper halocline region subject to mixing consistent with the pigment data picocyanobacterial populations increased by a factor of 3 with the highest concentration 1 65 10 8 cells l 1 in the upper halocline chlorophyll a concentrations and the relative importance of phytoplankton groups differed among the four lakes during the open water period implying lake specific differences in phytoplankton community structure under ice free conditions

the oceanography of winter leads leads in pack ice have long been considered important to the thermodynamics of the polar regions a winter lead affects the ocean around it because it is a density source as the surface freezes salt is rejected and forms more dense water which sinks under the lead this sets up a circulation with freshwater flowing in from the sides near the surface and dense water flowing away from the lead at the base of the mixed layer if the mixed layer is fully turbulent this pattern may not occur rather the salt rejected at the surface may simply mix into the surface boundary layer in either event the instability produced at the surface of leads is the primary source of unstable buoyancy flux and as such exerts a strong influence on the mixed layer here as many as possible of the disparate and almost anecdotal observations of lead oceanography are assembled and combined with theoretical arguments to predict the form and scale of oceanographic disturbances caused by winter leads the experimental data suggest the velocity disturbances associated with lead convection are about 1 5 cm s 1 these appear as jets near the surface and the base of the mixed layer when ice velocities across the lead are less than about 5 cm s 1 the salinity disturbances are about 0 01 to 0 05 psu scaling arguments suggest that the geostrophic currents set up by the lead density disturbances are also of the order of 1 5 cm s 1 the disturbances are most obvious when freezing is rapid and ice velocity is low because the salinity and velocity disturbances in the upper ocean are not smeared out by turbulence in this vein lead convection may be characterized at one extreme as free convection in which the density disturbance forces the circulation at the other extreme lead convection may be characterized as forced convection in which the density disturbance is mixed rapidly by boundary layer turbulence the lead number lo which is the ratio of the pressure term to the turbulence term in the momentum equation and the turbulent lead number lot which is the ratio of buoyant production to shear production in the turbulent kinetic energy equation define the boundary between the free and forced regimes for lo and lot less than one both the large scale circulation and the turbulence are forced by surface stress for lo and lot greater than one both the large scale circulation and the turbulence are forced by the buoyancy flux the magnitudes of velocity and salinity disturbances from a model developed elsewhere suitable to free convection agree with what few observations we have the results of a forced convection model developed here suggest salinity disturbances of the order of 0 01 0 02 practical salinity units with the maximum occurring at the surface of the lead and decreasing substantially below 5 10 m this unstable gradient is a unique characteristic of lead convection though the salinity disturbances may be small when ice velocities are large the buoyancy flux in leads has a major effect on the boundary layer turbulence

the phase evolution of young sea ice sea ice forms as a porous matrix consisting of pure ice crystals in equilibrium with brine we present an experimental and theoretical study that reveals that the brine expelled by growing sea ice initially remains trapped within the crystalline interstices but that drainage into the underlying water is ultimately triggered abruptly due to the onset of buoyancy driven convection the onset is quantified by a critical porous medium rayleigh number and we present an empirical marginal stability diagram that defines the transition

the chemical development of a hypersaline coastal basin in the high arctic we investigated a hypersaline seasonally isolated marine basin simb in the canadian high arctic to elucidate the role of brine rejection tidal forcing and groundwater input over the formation of hypersalinity analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near shellabear point melville island northwest territories 75 n 113 w observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice free season which lasts substantially longer than the period of freshwater inflow from the catchment an ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water and that the current hypersalinity may have formed in less than a decade modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers a tidal connection is a critical consideration in lake evolution and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation by contrast in some coastal lakes marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop hence the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the high arctic

controls on δ 34 s and δ 18 o of dissolved sulfate in aquifers of the murray basin australia and their use as indicators of flow processes the usefulness of stable isotopes of dissolved so4 34s and 18o to study recharge processes and to identify areas of significant inter aquifer mixing was evaluated in a large semi arid groundwater basin in south eastern australia the murray basin the distinct isotopic signatures in the oxidizing unconfined murray group aquifer and the deeper reducing renmark group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections 34s values in the unconfined murray group aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20 8 to 0 3 the concomitant increasing so4 cl ratios as well as relatively low 18oso4 values suggest that vertical input of biogenically derived so4 via diffuse recharge is the predominant source of dissolved so4 to the aquifer further along the hydraulic gradient towards the discharge area near the river murray 34s values in the unconfined murray group aquifer increase and so4 cl ratios decrease due to upward leakage of waters from the confined renmark group aquifer which has a distinctly low so4 cl and high 34s 14 9 56 4 relatively positive 34s and 18oso4 values and low so4 cl in the renmark group aquifer is typical of so4 removal by bacterial reduction the s isotope fractionation between so4 and hs of 24 estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation 70 even though the confined groundwater residence time is 300 ka years mapping the spatial distribution of 34s and so4 cl of the unconfined murray group aquifer provides an indicative tool for identifying the approximate extent of mixing however the poorly defined end member isotopic signatures precludes quantitative estimates of mixing fractions

coupled landscape lake evolution in high arctic canada we profiled five ice covered lakes and two ice covered fiords of ellesmere island at the northern limit of high arctic canada to examine their environmental characteristics and to evaluate the long term limnological consequences of changes in their surrounding landscape through time landscape evolution all of the ecosystems showed strong patterns of thermal chemical and biological stratification with subsurface temperature maxima from 0 75 to 12 15 c conductivities up to 98 1 ms cm 1 twice that of seawater in some bottom waters pronounced gradients in nitrogen phosphorus ph dissolved inorganic and organic carbon manganese iron and oxygen and stratified photo synthetic communities these ecosystems form an inferred chronosequence that reflects different steps of landscape evolution including marine embayments open to the sea inlets blocked by thick sea ice disraeli fiord taconite inlet perennially ice capped saline lakes isolated from the sea by isostatic uplift lakes a c1 c2 and isolated lakes that lose their ice cover in summer the latter are subject to entrainment of saline water into their upper water column by wind induced mixing lake romulus lake a in 2000 or complete flushing of their basins by dilute snowmelt lake c3 and char lake which lies 650 km to the south of the ellesmere lakes region this chronosequence illustrates how changes in geomorphology and other landscape properties may influence the limnology of coastal high latitude lakes and it provides a framework to explore the potential impacts of climate change resume cinq lacs et deux fjords recouverts de glace ont ete profiles sur l ile ellesmere a la limite nord de l extreme arctique canadien afin d examiner leurs caracteristiques environnementales et d evaluer les consequences limnologiques a long terme des changements dans le temps des paysages voisins evolution du paysage tous les ecosystemes montraient de forts patrons de stratification thermique chimique et biologique avec des temperatures maximales sous la surface de 0 75 a 12 15 oc des conductivites atteignant 98 1 ms cm 1 deux fois celle de l eau de mer dans certaines

isotopic study of the source and cycle of sulfur in the yamdrok tso basin southern tibet china abstract this study focuses on the inland drainage basin of yamdrok tso tso means lake in the tibetan language which lies at altitudes between 4394 and 4989 m in southern tibet the basin is located in the tethys himalayan zone and consists of seven lakes with different hydrological characteristics the main purpose of the study was to investigate the source of dissolved so42 and the sulfur cycle in the groundwater river lake system we measured the hydrogeochemical composition 18oh2o 34sso4 and 18oso4 of sulfate in river spring and lake water the total sulfur content stotal and 34stotal of total sulfur in a lake sediment core and the 34spyrite of pyrite in the bedrock the results indicate that most of the rivers in the study area are characterized by a high sulfate content with values of up to 270 mg l in addition the 34spyrite of pyrite in the bedrock ranges between 4 31 and 5 77 while the sulfate in river and spring waters has mainly negative values of 34sso4 7 14 to 2 02 and 18oso4 13 2 to 4 04 in contrast the waters of closed lakes in the study basin have high values of 34sso4 3 44 8 58 and 18oso4 7 26 10 3 the negative 34sso4 and 18oso4 dual isotopic composition of sulfate indicates that pyrite weathering controls the dissolved sulfate and other solutes in rivers and spring water while the anthropogenic pollutant sulfur flux is negligible water is the main oxygen source for sulfate derived from the oxidation of pyrite while fe3 is the main direct agent of pyrite s oxidation the lake water and sediments in the study basin are important sinks stores of sulfur the 34stotal values of total sulfur in a sediment core from a closed and holomictic lake ranges between 8 5 and 44 9 as evidenced by the strong 34s and 18o enrichment in the residual pool of so42 in the lake waters and the marked depletion of 34s in the sediment core the dissimilatory microbial sulfate reduction msr in the lake sediments generally results in the preferential sequestration of sulfur enriched in 32s in addition the magnitude of 34s 32s fractionation between sulfate in the lake water and sedimentary total sulfur can reach up to 48 3 this abnormally high fractionation value can be explained mainly by the reoxidation of reduced inorganic sulfur compounds together with the dispropotionation pathway in the sediments caused by lake level fluctuations the changes in stotal and 34stotal values with depth in the sediment core can also be explained by the same mechanism

the paint pots kootenay national park canada a natural acid spring analogue for mars1 2 the paint pots are a natural fe so4 acid spring system along the kicking horse rim a major geological feature that has controlled fluid flow and mineralization over geologic time the very low ph 3 and extremely high trace metal concentrations of the springs are anomalous and greatly exceed health limits zn 35 8 mg l pb 0 461 mg l as 82 7 ppb sulphur isotopes 34s and 18o in sulphate equal to 11 4 and 12 1 respectively are consistent with sulphide oxidation mass balance calculations indicate that the springs must have derived their acidity and metal content from natural weathering of a pyrite rich ore deposit in the vicinity several ore deposit types occur along the kicking horse rim with the mississippi valley type mvt style being the most consistent with the source of the spring waters at the spring outlet fe rich waters oxidize forming large cone features of fe o precipitates predominantly goethite a diverse microbial community has been identified in the site that is di

sulfur isotope signatures in gypsiferous sediments of the estancia and tularosa basins as indicators of sulfate sources hydrological processes and microbial activity abstract in order to reconstruct paleo environmental conditions for the saline playa lakes of the rio grande rift we investigated sediment sulfate sources using sulfur isotope compositions of dissolved so 4 2 ions in modern surface water groundwater and so 4 2 precipitated in the form of gypsum sediments deposited during the pleistocene and holocene in the tularosa and estancia basins the major sulfate sources are lower and middle permian marine evaporites 34s of 10 9 14 4 but the diverse physiography of the tularosa basin led to a complex drainage system which contributed sulfates from various sources depending on the climate at the time of sedimentation as inferred from sulfur isotope mass balance constraints weathering of sulfides of magmatic hydrothermal and sedimentary origin associated with climate oscillations during last glacial maximum contributed about 35 50 of the sulfates and led to deposition of gypsum with 34s values of 1 2 to 2 2 which are substantially lower than permian evaporates in the estancia basin microbial sulfate reduction appears to overprint sulfur isotopic signatures that might elucidate past groundwater flows a rayleigh distillation model indicates that about 3 18 of sulfates from an inorganic groundwater pool 34s of 12 6 13 8 have been metabolized by bacteria and preserved as partially to fully reduced sulfur bearing minerals species elemental sulfur monosulfides disulfides with distinctly negative 34s values 42 3 to 20 3 compared to co existing gypsum 3 8 to 22 4 for the tularosa basin microbial sulfate reduction had negligible effect on 34s value of the gypsiferous sediments most likely because of higher annual temperatures 15 33 c and lower organic carbon content median 0 09 in those sediments leading to more efficient oxidation of h2s and or smaller rates of sulfate reduction compared to the saline playas of the estancia basin 5 28 c median 0 46 of organic carbon the white sands region of the tularosa basin is frequently posited as a hydrothermal analogue for mars high temperatures of groundwater 33 3 c and high 18o h2o values 1 1 in white sands however are controlled predominantly by seasonal evaporation rather than the modern influx of hydrothermal fluids nevertheless it is possible that some of the geochemical processes in white sands such as sulfide weathering during climate oscillations and upwelling of highly mineralized waters might be considered as valid terrestrial analogues for the sulfate cycle in places such as meridiani planum on mars

causes and spatial distribution of anomalous magnetization in hydrocarbon seepage environments in diagenetic environments containing hydrocarbons the most important magnetic minerals formed appear to be magnetite and pyrrhotite whereas the most important magnetic mineral dissolved or replaced is hematite hence hydrocarbon seepage and migration may result in positive absent or negative anomalous magnetization magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending on the amounts of magnetite and pyrrhotite formed relative to the amounts of hematite destroyed where anomalous magnetization is formed by hydrocarbon seepage the magnetic contrasts are located in relatively reducing geochemical plumes such plumes are located above leaking subsurface hydrocarbon accumulations if buoyancy is the predominant driving force for hydrocarbons commonly however migration of the escaping hydrocarbons is dominated by advection hydrocarbon seepage therefore may be vertical or may have any direction other than vertical depending on the position of the leaking hydrocarbon accumulation in the prevailing flow system and on the distribution of high permeability pathways such as carrier beds and faults in these cases magnetic contrasts are deflected or displaced and they are not likely to be vertically above the hydrocarbon source anomalous magnetization magnetic contrasts has been documented from some hydrocarbon seepage environments and can be used for hydrocarbon exploration in association with other surface exploration methods similar magnetic contrasts should also be detectable in core and could be used for evaluation of subsurface proximity to hydrocarbon traps the magnitude and spatial distribution of such magnetic contrasts whether at the surface or in the subsurface depend on geochemical microbial geophysical sedimentologic and hydrogeologic processes these factors must be taken into consideration in aeromagnetic and ground based prospecting for hydrocarbons in particular the use of anomalous magnetization as an exploration tool should always be accompanied by a hydrogeologic study the results of this study suggest that magnetic contrasts could also be used in environmental studies for example to detect hydrocarbons leaking from storage tanks or waste disposal sites on the other hand magnetic contrasts may be generated also by natural and anthropogenic processes that have no genetic relationships to hydrocarbons consequently anomalous magnetization may or may not be genetically related to natural or anthropogenic hydrocarbon accumulations

ice ocean turbulent exchange in the arctic summer measured by an autonomous underwater vehicle the first ever observed horizontal profiles of summertime ice ocean boundary layer fluxes were obtained using vertical water velocity temperature and salinity collected by an autonomous underwater vehicle during the surface heat balance of the arctic ocean sheba experiment of 1998 scalars and their vertical fluxes as well as vertical stability varied in the horizontal direction with correspondence to changes in the overlying surface in early summer fresh meltwater was trapped at the upper ice surface and only entered the ocean through leads a highly stable fresh layer was formed in the sheba lead which eventually grew to depths greater than the mean draft of the local first year ice near the end of july a storm removed this layer via shear generated turbulence supercritical hydraulic flow speeds and ice divergence the mixed layer freshened and deepened at this time particularly strong fluxes were observed under and downstream of rough ridged ice and properties changed rapidly with distance downstream of leads the location and signs of the fluxes are suggestive of a mechanism of instability in which fresh surface water is forced under salty water downstream of leads and or ridges simulations from a two dimensional unsteady model suggest that both mechanical forcing from ice topography and a dynamic instability near downstream lead edges may enhance vertical mixing particularly when ice velocity is large the horizontal variability in interfacial fluxes observed at sheba may explain the difference between the observed melt rates and those calculated using a bulk relationship because this relationship may not adequately parameterize the large lateral heat fluxes at lead edges and basal heat fluxes under ridge keels

travertine mounds of the cave and basin national historic site banff national park the cave and basin national historic site is a fan shaped travertine deposit associated with four thermal spring outlets tentative age dating of the travertine mound indicates growth initiated with onset of the late holocene shift to more humid and cool climate conditions and suggests that the flow of thermal waters was limited during the hypsithermal which in turn places constraints on the evolutionary biology of endemic species in the spring system two large caves and one collapsed cave structure are developed within the deposit cave development is in response to both physical erosion of till underlying the travertine and acid gas attack of calcite that makes up the deposit this process is buffered by formation of reaction crusts of gypsum on the interior cave walls only minor modern travertine growth occurs due to historic flow control measures understanding the flow of water through the historic site is critical for long term preservation

the skewness of temperature derivatives in oceanic boundary layers abstract the skewness of the derivative of temperature measured by sensors in the upper ocean boundary layer in convective conditions has been measured and is observed to have a sign opposite to that found in conditions of stable heating this is consistent with observations in the atmospheric boundary layer high resolution measurements in the benthic boundary layer on a continental rise show a variation of skewness during the m2 tidal cycle which dominates the motion with negative skewness consistent with conditions favoring convection occurring during the upslope phase of the motion the observations are compared with laboratory studies of the reflection of internal waves from a slope we suggest that information about the gross features of a turbulent oceanic boundary layer flow may be derived from relatively simple measurements

digital terrain mapping of the underside of sea ice from a small auv 1 in april 2007 the first three dimensional digital terrain mapping of the underside of sea ice to be done from an ice launched autonomous underwater vehicle auv was carried out at an ice camp in the beaufort sea using the gavia vehicle which could be launched and recovered through 3 1 m holes gavia was equipped with a geoswath 500 khz interferometric sonar system which yielded swaths of typical width 80 m the imagery showed the morphological distinctions between first year fy and multi year my ice undersides the contrast between the shapes of fy and my ridges and the appearance of refrozen leads ice drafts were validated by drilling and it was found that ridge slope statistics and local probability density functions pdfs of draft could be derived with high precision the special opportunities offered by access to 3 d mapping are pointed out

evaluation of hydrological and biological influences on co2 fluxes from a karst stream carbon dioxide exchange is the fundamental process that drives calcite precipitation in a spring fed travertine depositing stream located in augusta county virginia groundwater issuing at the surface springs that feed the stream is supersaturated with respect to atmospheric co2 co2 flux along the stream is attributed to physical outgassing caused by the steep concentration gradient between co2 dissolved in the stream water and its partial pressure in the atmosphere the stream water is so rich in co2 that biological cycling does not significantly alter the mass flux outgassing is enhanced by hydrological agitation at the cascades the local flux of co2 from the stream is greatest during the summer and fall during those times outgassing is driven by high dissolved co2 concentrations in the springs warm temperatures and low stream discharge seasonally variations in the net flux of co2 from falling spring run are minor outgassing drives the solution to high degrees of supersaturation with respect to calcite yet calcite precipitation does not occur until the solution attains concentrations near five times supersaturation high enough to overcome kinetic inhibition precipitation is greatest along the cascades where 1 hydrological agitation drives rapid loss of co2 and 2 benthic algal and moss mats and the travertine itself provide fresh surfaces for crystal growth calcite precipitation is greatest in the summer and fall when the local co2 flux is greatest

hydrogeochemistry stable isotope composition and geothermometry of co2 bearing hydrothermal springs from western iran evidence for their origin evolution and spatio temporal variations abstract this study aims to hydrochemically characterise three co2 bearing springs representing distinct hydrofacies in nw gorveh western iran and interpret them in the light of their geological setting the results of laboratory measurements of elemental concentrations stable oxygen carbon and hydrogen isotopes dissolved and particulate organic and inorganic carbon dic doc poc pic and alkalinity are combined with in situ measurements of ph and temperature parameters such as alkalinity dic ca2 and pco2 concentration display strong positively correlated values with systematic decrease from the spring vent in down flow direction for the three spring systems the inverse correlation of ph and 13cdic is caused by co2 degassing the 18o and d values show no significant variation related to minor or no evaporation due to normal ambient temperatures the low concentration of poc pic and doc compared to that of dic and the lack of correlation between them reflect predominant inorganic carbon in these fluids spring i is oversaturated in calcite with additional dissolution of co2 and despite high concentrations of na and cl undersaturated in halite indicating a fluid of geothermal origin and or reflecting steady state dissolution this is related to water rock interaction processes with carbonate and evaporitic rocks that affected the isotopic signature of 18o which is shifted to the right of the global meteoric water line spring i also represents a partially equilibrated and mature deep chloride type water spring ii and iii are less saline and represent a different fluid circulation and or shorter residence time the two latter springs are characterized by peripheral shallow dilute chloride bicarbonate type waters decreasing key parameters especially in spring iii during the winter suggest that superficial mixing with rain and meteoric water results in high temporal variations cation and stable carbon isotope geothermometry applied to the studied springs reveals an average reservoir temperature of 210 110 and 90 c for spring i and ii and iii respectively the geochemical and isotopic data allowed to depict a conceptual model where the hydrothermal reservoir for spring i is residing in carbonate and evaporitic rocks most likely the qom formation situated at a depth of 3 4 km whereas those of spring ii and iii are likely sourced from a shallower depth 1 2 km in correspondence with carbonate and porous and permeable volcanic rocks integration of hydrofacies with conceptual hydrological and geological models forms the base towards a proper understanding of water circulation patterns increasingly important for sustainable water management and geothermal applications

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

east west asymmetry in surface mixed layer and ocean heat content in the pacific sector of the arctic ocean derived from amsr e sea surface temperature abstract deep greater than 25 m and anomalously warm surface mixed layer sml has been evident in the pacific sector of the arctic ocean since 2007 this warm sml contributes to the formation of maximum near surface temperature which act as the sea ice formation inhibitor after freeze up season in this study we attempt to estimate the ocean heat content ohc in the sml of the pacific sector of the arctic ocean the surface mixed layer depth smld and ohc from 2007 to 2010 were estimated from sst measured by the microwave radiometer amsr e and ncep derived net heat budget based on the assumption that changes of heat content within sml can be explained by the air sea heat exchange only estimated smld and ohc were well comparable with the in situ ctd measurements especially in the western canada basin smld greater than 25 m up to 40 m and ohc greater than 300 mj were estimated at southern northwind ridge area 73 75 n 168 150 w where the catastrophic reduction of sea ice has been reported while less ohc was estimated at the eastern side of the canada basin although anomalous high sst has uniformly been captured over the northern chukchi sea and the northwind ridge area since 2007 our results indicate the nonuniformity of surface ohc distribution in the canada basin with relatively large amount in the northwind ridge area conversely we can assume that the northwind ridge area is the plausible candidate for the near surface temperature maximum formation area recent thin ice condition is probably responsible for deepening smld efficient ocean heat uptake and delayed onset of sea ice formation in the pacific sector of the arctic ocean our results also indicate oceanic horizontal or vertical heat flux along the sea ice edge which will promote the suppression of sea ice growth during freeze up season

the carbon isotopic composition of dissolved inorganic carbon in perennially ice covered antarctic lakes searching for a biogenic signature the stable isotopic signature of dissolved inorganic carbon dic has been routinely used in temperate lake systems to investigate the biogeochemical dynamics of carbon we studied seven perennially ice covered lakes in the mcmurdo dry valleys antarctica to ascertain how carbon cycling affects the d 13 c of dic in water columns of these systems unlike temperate lakes and in fact most polar lake systems the permanent ice covers of these lakes eliminate physical mixing turnover and hence redistribution of dic in the lakes as well as minimize co2 exchange with the atmosphere these important and unique physical constraints have significant impact on carbon dynamics in the lakes and important consequences for the d 13 c distribution the geochemistry in these lakes is influenced in varying amounts by landscape position hydrologic input and their evolutionary history five of these lakes both lobes of lake bonney and lakes fryxell miers and vanda have surface water d 13 c ratios of 0 4 lake hoare has more negative values while lake joyce the highest elevation lake has a much higher value 10 5 all of the lakes have upper to mid depth d 13 c maxima reflecting biological uptake of 12 c only four of the lakes lakes vanda joyce hoare and fryxell have deep waters with negative values of d 13 c implying rigorous remineralization of 12 c at depth lake miers the only lake that is not closed basin has the smallest d 13 c variation with depth indicating that hydrologic exchange greatly influences the d 13 c signal

autumn snowfall and hydroclimatic variability during the past millennium inferred from the varved sediments of meromictic lake a northern ellesmere island canada abstract we examined the hydroclimatic signal in a record of annual lamina varve thickness from high arctic lake a ellesmere island 83 00 00 n 75 30 00 w in this unglacierized catchment nival melt is the dominant source for meltwater and transport of sediment to the lake and autumn snowfall is highly influential on varve thickness through the amount of snow available for melt in the following year for the period during which climatic data are available varve thickness in lake a was significantly correlated r 0 50 p r 0 39 p