life on mars evaluation of the evidence within martian meteorites alh84001 nakhla and shergotty abstract analyses both support and are in opposition to the hypothesis that the martian meteorite alh84001 contains evidence for possible biogenic activity on mars new observations in two additional martian meteorites nakhla 1 3 ga old and shergotty 300 165 ma old indicate possible biogenic features features in the three martian meteorites compare favorably with the accepted criteria for terrestrial microfossils and evidence for early life on the earth there is strong evidence for the presence of indigenous reduced carbon biogenic magnetite and the low temperature formation of carbonate globules the morphological similarities between terrestrial microfossils biofilms and the features found in the three martian meteorites are intriguing but have not been conclusively proven every investigation must recognize the possibility of terrestrial contamination of the meteorites whether or not the meteorites are martian the search for evidence of ancient life in martian meteorites has emphasized the difficulties confronting the scientific community with the respect to the positive identification of evidence of past biogenic activity

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

r selected benthic foraminifera with associated bacterial colonies in upper pleistocene sediments of the ross sea antarctica implications for calcium carbonate preservation investigations on foraminifera from upper pleistocene holocene sediments cored in the continental slope of the western ross sea 2383 m water depth revealed that the record of calcareous assemblages was restricted to a limited time interval approximately 6 kyr and characterized by a dominance of phytodetritus exploiting taxa such as alabaminella weddellensis and epistominella exigua rod shaped calcified fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces either as clusters or as isolated cells suggesting that significant changes from underto oversaturated conditions with respect to calcium carbonate in the chemistry of the seawater developed before the final burial of the foraminiferal tests we postulate that bacterial activity on a microenvironmental scale interface and pore water in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities 1999 elsevier science b v all rights reserved

eddies in the labrador sea as observed by profiling rafos floats and remote sensing abstract data from profiling rafos floats topex poseidon altimetry and the alongtrack scanning radiometer atsr aboard ers 1 have been used to describe the spatial and seasonal patterns of eddy variability in the labrador sea peaks in sea surface height ssh variability appear in two regions off the west greenland shelf near 61 5 n 52 w where the 3000 m isobath separates from the shelf and in the center of the basin at 58 n 52 w both locations show seasonal ranges in ssh variability of up to 40 mm with the greenland site having largest variability in january march leading the central site by 50 days a sea surface temperature image from the atsr at the greenland site shows numerous eddies both cyclonic and anticyclonic being formed by injection of west greenland current water into the labrador sea interior data from profiling rafos floats launched in 1997 as part of the labrador sea deep convection experiment are used to describe three of the west greenland current eddies in detail one of

multi scale study of the role of the biofilm in the formation of minerals and fabrics in calcareous tufa abstract three sites of actively forming tufa two barrage systems and one terraced slope system located in northern calabria italy and in north east england have been investigated with the purpose of studying the neo formed carbonate minerals at the interface with the organic components that compose the associated biofilms several depositional facies are distinguished notably peloidal to aphanitic laminar and dendrolitic fabrics composed of micrite and microsparite and isolated botryoids and continuous crusts composed of sparite all fabrics occurring in all depositional facies are organized into layers with a more or less well developed seasonal cyclicity low mg calcite precipitates more or less constantly during all seasons within the active depositional zone this extends for a few hundred microns upon the external surface of the deposits where the biofilm occurs the latter is composed of a heterogeneous community of green algae filamentous cyanobacteria and other types of prokaryotes actinobacteria and fungi with a variable amount of extracellular polymeric substances eps porous micro columns 50 to 150 m in size separated by interstitial spaces characterize the active depositional zone here precipitation always begins with organomineral nanospheres 10 to 20 nm diameter both along the external surfaces and within internal cavities of the micro columns by replacing degraded organic matter and at point sites suspended within living cyanobacterial tufts along the external surface of their sheaths indicating that the biological activities of the biofilm are crucial with its living organisms and non living organic matter organomineral nanospheres successively agglutinate to form irregular to rod shaped crystal aggregates 100 200 nm in size that with their further agglutination create two basic types of larger more ordered crystal structure polyhedrons in the range of 1 2 m and minute triads of calcite fibres varying in length from 0 4 short triads to 1 m long triads basic crystal structures coalesce to form larger crystals mainly tetrahedrons tens of microns in size that constitute the micro columns

biomimetic properties of minerals and the search for life in the martian meteorite alh84001 the existence of extraterrestrial life was heralded by controversial claims made in 1996 that the martian meteorite alh84001 harbored relics of ancient microorganisms we review here the accumulated evidence for and against past extraterrestrial life in this martian meteorite the main pro life arguments the presence of polycyclic aromatic hydrocarbons magnetite crystals carbonate globules and structures resembling terrestrial life forms known as nanobacteria can be deemed ambiguous at best although these criteria are compatible with living processes each one of them can be explained by nonliving chemical processes by undergoing amorphous to crystalline transformations and binding to multiple substrates including other ions and simple organic compounds minerals especially those containing carbonate have been shown to display biomimetic properties producing forms that resemble bacteria this simple and down to earth explanation can account fully for the existence of mineral entities resembling put

origin of highly elongate calcite cemented concretions in some italian coastal beach and dune sands abstract highly elongate vertical and horizontal calcite cemented concretions in pleistocene shallow marine and coastal eolian sandstones are mixtures of terrigenous sand and carbonate biogenic grains cemented to various degrees by low mg calcite petrographic and stable carbon and oxygen isotopic data support the earlier hypothesis of mazzanti and parea 1979 that vertically oriented concretions formed by the precipitation of vadose meteoric water percolating downward toward the water table and that horizontal concretions were precipitated from phreatic groundwater flowing toward the coast many vertical concretions started growth as rhizocretions composed of micrite but enlarged and coalesced when equant sparry calcite was precipitated from percolating vadose water horizontal concretions cemented entirely by subequant calcite spar have coalesced into nearly completely cemented beds decimeter scale domains of curved horizontal concretion elements reflect the influence of adjacent phreatic flow domains each with their own particular flow paths aragonite and high mg calcite shells in the sands were the main source of carbon in calcite cement isotopically depleted 13c values of bulk samples 6 to 8 5o oo v pdb however require the input of a light carbon source probably soil co2 18o values of bulk samples are compatible with cementation chiefly by meteoric water at temperatures between 7 and 22 c the values are typical of air and inferentially groundwater temperatures today

on the dynamics and water mass transformation of a boundary current connecting alpha and beta oceans abstracta subpolar marginal sea like the nordic seas is a transition zone between the temperature stratified subtropics the alpha ocean and the salinity stratified polar regions the beta ocean

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

microbes and ooids abstract the bahamian archipelago is one of the few locations in the world where ooid formation is actively occurring ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14c 18o 13c mg ca and sr ca ratios ooids were examined under sem after each step in the incremental analyses to characterize the nature of dissolution radiocarbon dating indicates that ooids presently at the sediment water interface began forming across the archipelago between 1000 and 2800 yr bp and continue to form today the ooids have the same pattern of microboring alteration across the region the surface and outer cortex of the ooids are punctuated with unfilled microborings whereas the inner cortex contains two morphologies of aragonite cement filling the microborings the two morphologies of cement form in association with two different species of cyanobacteria one is solentia sp the other is interpreted to be hyella sp the chemistry of ooids from across the region is remarkably similar 18o and 13c values for all samples vary directly having a slope of approximately 1 the outer cortex has low 18o and 13c values of 3 4 and 0 2 respectively whereas the 18o and 13c values of the inner cortex are high with values of 1 9 and 6 8 respectively the presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid causing it to appear close to equilibrium with seawater the isotopic variation in 18o and 13c within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings the most exterior portion of the ooid has very high mg ca values and is interpreted as an amorphous calcium carbonate acc coating there are two other phases in the cortex both being aragonite the outer cortex has a higher mg ca ratio and lower sr ca ratio than the inner cortex this difference in chemistry is a result of the presence of aragonite cement in the inner cortex stable isotopic and trace element results coupled with sem investigations indicate that microbes do not play a role in ooid formation but instead alter the texture and chemistry of ooids after they have formed a new model of ooid formation is proposed whereby a veneer of acc precipitates on an ooid while it is at the sediment water interface the active phase this veneer of acc later recrystallizes to aragonite needles and a new cortex layer is formed the stationary phase observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis which allow a better understanding of paleoenvironments hosting ooid formation

impact of labrador sea convection on the north atlantic meridional overturning circulation abstract the overturning and horizontal circulations of the labrador sea are deduced from a composite vertical section across the basin the data come from the late spring early summer occupations of the world ocean circulation experiment woce ar7w line during the years 1990 97 this time period was chosen because it corresponded to intense wintertime convection the deepest and densest in the historical record suggesting that the north atlantic meridional overturning circulation moc would be maximally impacted the composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass the analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux i e the transformation of light water to labrador sea water the mean overturning cell is calculated to be 1 sv 1 sv 106 m3 s 1 as compared with a horizontal gyre of 18 sv the

nannobacteria as a by product of enzyme driven tissue decay spheroidal features 50 to 200 nm in size and found in sedimentary rocks have been described as nannobacteria the idea that they are minute fossilized life forms and especially the discovery of such features in martian meteorite alh84001 sparked a lively debate with regard to identification of ancient microbial life because biologists consider 200 300 nm to be the lower viable size limit for microorganisms an alternative explanation is needed for features that have been described as nannobacteria by geologists we report here on tissue decay experiments that produced abundant proteinaceous spheroids in the size range of nannobacteria described as nannoballs in the remainder of this paper experimental conditions were comparable to those found in earth9s surface sediments and diagenetic mineralization of these spheroids may be a common process for preservation of nannoballs that are observed in the rock record

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

aerobic microbial dolomite at the nanometer scale implications for the geologic record microbial experiments are the only proven approach to produce experimental dolomite under earth s surface conditions although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics the involvement of microbes in the dolomite nucleation process is poorly understood in particular the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored herein we demonstrate that halomonas meridiana and virgibacillus marismortui two moderately halophilic aerobic bacteria mediate primary precipitation of dolomite at low temperatures 25 35 c this report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale we describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface a combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be 1 the initial step for dolomite nucleation 2 preserved in the geologic record and 3 used as microbial tracers through time and or as a proxy for ancient microbial dolomite as well as other carbonate minerals

on the role of eddies and surface forcing in the heat transport and overturning circulation in marginal seas the factors that determine the heat transport and overturning circulation in marginal seas subject to wind forcing and heat loss to the atmosphere are explored using a combination of a high resolution ocean circulation model and a simple conceptual model the study is motivated by the exchange between the subpolar north atlantic ocean and the nordic seas a region that is of central importance to the oceanic thermohaline circulation it is shown that mesoscale eddies formed in the marginal sea play a major role in determining the mean meridional heat transport and meridional overturning circulation across the sill the balance between theoceaniceddyheatfluxandatmosphericcooling ascharacterizedbyanondimensionalnumber isshownto be the primary factor in determining the properties of the exchange results from a series of eddy resolving primitive equation model calculations for the meridional heat transport overturning circulation density of convective waters and density of exported waters compare well with predictions from the conceptual model over a wide range of parameter space scaling and model results indicate that wind effects are small and the mean exchange is primarily buoyancy forced these results imply that one must accurately resolve or parameterize eddy fluxes in order to properly represent the mean exchange between the north atlantic and the nordic seas and thus between the nordic seas and the atmosphere in climate models

influences of time dependent precipitation on water mass transformation heat fluxes and deep convection in marginal seas abstractinfluences of time dependent precipitation on water mass transformation and heat budgets in an idealized marginal sea are examined using theoretical and numerical models the equations proposed by spall in 2012 are extended to cases with time dependent precipitation whose form is either a step function or a sinusoidal function the theory predicts the differences in temperature and salinity between the convective water and the boundary current as well as the magnitudes of heat fluxes into the marginal sea and across the sea surface moreover the theory reveals that there are three inherent time scales relaxation time scales for temperature and salinity and a precipitation time scale the relaxation time scales are determined by a steady solution of the theoretical model with steady precipitation the relaxation time scale for temperature is always smaller than that for salinity as a result of not only the difference in the form of fluxes at the surface but also the variation in the eddy transpor

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

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

dynamics of downwelling in an eddy resolving convective basin the mean downwelling in an eddy resolving model of a convective basin is concentrated near the boundary where eddies are shed from the cyclonic boundary current into the interior it is suggested that the buoyancyforced downwelling in the labrador sea and the lofoten basin is similarly concentrated in analogous eddy formation regions along their eastern boundaries use of a transformed eulerian mean depiction of the density transport reveals the central role eddy fluxes play in maintaining the adiabatic nature of the flow in a nonperiodic region where heat is lost from the boundary current the vorticity balance in the downwelling region is primarily between stretching of planetary vorticity and eddy flux divergence of relative vorticity althougha narrowviscous boundarylayeris ultimately importantin closingtheregionalvorticitybudget this overall balance is similar in some ways to the diffusive viscous balance represented in previous boundary layer theories and suggests that the downwelling in convective basins may be properly represented in lowresolution climate models if eddy flux parameterizations are adiabatic identify localized regions of eddy formations and allow density to be transported far from the region of eddy formations

consistent fluctuations in intermediate water temperature off the coast of greenland and norway during dansgaard oeschger events abstract rapid warmings epitomize the dansgaard oeschger events that are recorded in greenland ice cores and imprinted in ocean sediment cores while the abrupt climate changes appear connected to perturbations in sea ice and ocean circulation it is unclear how the water masses within the nordic seas responded and were influenced by the inflowing atlantic water in the absence or presence of sea ice high resolution reconstructions of benthic mg ca together with stable isotopes of carbon and oxygen 13c and 18o show a recurring warming 2 5 0 5 c occurring consistently at the inflow and outflow of the nordic seas at intermediate depths down to 1500 m during greenland stadials 9 6 using idealized numerical simulations with an eddy resolving ocean model we investigate the impact of an isolating sea ice cover and freshwater lid in the nordic seas with the presence of an extensive sea ice cover the warm atlantic water entering the nordic seas in the east retains its heat as it exits in the west the depth of the recirculating warm atlantic water increases when including an external freshwater source at the surface of the nordic seas these findings support the view that cold stadials are accompanied by pervasive intermediate water warming across the nordic seas given the current rates of arctic sea ice loss these results provide a potential mechanism for water column destabilization and inception of abrupt climate change

influences of precipitation on water mass transformation and deep convection abstractthe influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses making explicit their dependence on both geometric parameters such as basin area sill depth and latitude as well as on the strength of atmospheric forcing in addition to the properties of the convective water the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode high resolution numerical model calculations compare well with the theory for the properties of the convective water mass the strength of the meridional overturning circulation and also the shutdown of deep convection however the numerical model also shows that for precipitation levels that exceed this critical threshold the circulat

large changes in sea ice triggered by small changes in atlantic water temperature abstractthe sensitivity of sea ice to the temperature of inflowing atlantic water across the greenland scotland ridge is investigated using an eddy resolving configuration of the massachusetts inst

the contrasting dynamics of the buoyancy forced lofoten and greenland basins abstractthe nordic seas are commonly described as a single basin to investigate their dynamics and sensitivity to environmental changes when using a theoretical framework here we introduce a conc

bacteria in the tatahouine meteorite nanometric scale life in rocks we present a study of the textural signature of terrestrial weathering and related biological activity in the tatahouine meteorite scanning and transmission electron microscopy images obtained on the weathered samples of the tatahouine meteorite and surrounding soil show two types of bacteria like forms lying on mineral surfaces 1 rod shaped forms rsf about 70 80 nm wide and ranging from 100 nm to 600 nm in length 2 ovoid forms ovf with diameters between 70 and 300 nm they look like single cells surrounded by a cell wall only na k c o and n with traces of p and s are observed in the bulk of these objects the chemical analyses and electron diffraction patterns confirm that the rsf and ovf cannot be magnetite or other iron oxides iron hydroxides silicates or carbonates the rites of the rsf and ovf are below those commonly observed for bacteria but are very similar to some bacteria like forms described in the martian meteorite alh84001 all the previous observations strongly suggest that they are bacteria or their remnants this conclusion is further supported by microbiological experiments in which pleomorphic bacteria with morphology similar to the ovf and rsf objects are obtained from biological culture of the soil surrounding the meteorite pieces the present results show that bacteriomorphs of diameter less than 100 nm may in fact represent real bacteria or their remnants c 2000 elsevier science b v all rights reserved

multiple equilibria as a possible mechanism for decadal variability in the north atlantic ocean decadal climate variability in the north atlantic has received increased attention in recent years because modeling results suggest predictability of heat content and circulation indices several years ahead however determining the applicability of these results in the real world is challenging because of an incomplete understanding of the underlying mechanisms here the authors show that recent attempts to reconstruct the decadal variations in one of the dominant circulation systems of the region the subpolar gyre spg are not always consistent a coherent picture is partly recovered by a simple conceptual model solely forced by reanalyzed surface air temperatures this confirms that surface heat flux indeed plays a leading role for this typeofvariability ashasbeensuggestedinpreviousstudies theresultsfurthersuggestthatlargevariationsin the spg correspond to the crossing of a bifurcation point that is predicted from idealized experiments and an analytical solution of the model used herein performance of this conceptual model is tested against a statistical stochastic model hysteresis and the existence of two stable modes of the spg circulation shape its response to forcing by atmospheric temperatures the identification of the essential dynamics and the reduction to a minimal model of spg variability provide a quantifiable basis and a framework for future studies on decadal climate variability and predictability

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

microbial biscuits of vaterite in lake issyk kul republic of kyrgyzstan abstract microbial biscuits of vaterite a polymorph of caco3 were found in lake issyk kul republic of kyrgyzstan four sections were defined from the inner part to the outer part of these microbial biscuits 1 a nucleus made up of coated discrete bacterial forms 2 a massive coating attributed to the calcification of the mucilaginous sheath of the bacterial community 3 a thick lamina composed of large fibers of vaterite and 4 a discontinuous external coating incorporating foreign elements such as diatoms the origin of these microbial biscuits is attributed to bacterial activity the vaterite formation seems to be related to the hexagonal structure of the mucilaginous sheath and to the inhibitor role of the phosphorous present in the water during calcite precipitation

thermally forced transients in the thermohaline circulation abstractthe response of a convective ocean basin to variations in atmospheric temperature is explored using numerical models and theory the results indicate that the general behavior depends strongly on the frequency at which the atmosphere changes relative to the local response time to air sea heat flux for high frequency forcing the convective region in the basin interior is essentially one dimensional and responds to the integrated local surface heat flux anomalies for low frequency forcing eddy fluxes from the boundary current into the basin interior become important and act to suppress variability forced by the atmosphere a theory is developed to quantify this time dependent response and its influence on various oceanic quantities the amplitude and phase of the temperature and salinity of the convective water mass the meridional overturning circulation the meridional heat flux and the air sea heat flux predicted by the theory compare well with that diagnosed from a series of numerical model

occurrence and significance of microbialites in the uplifted tasmaloum reef sw espiritu santo sw pacific abstract in the sw pacific ocean subduction of the d entrecasteaux ridge system has caused rapid uplift of the central new hebrides island arc the maximum uplift rate of 6 mm yr 1 occurs along the southwest coast of espiritu santo island near tasmaloum the tasmaloum uplifted reef sequence internal structure which is strongly linked to its tectonic context was investigated through a series of drill holes to depths up to 42 m although a stable tropical coast would undergo approximately 120 m of post glacial sea level rise the net relative sea level rise on such a rapidly uplifting coast is only about 20 m colonization of the tasmaloum fringing reef occurred by 24 ka upon a pre reef substrate composed of a thick bioclastic sand formation accumulated during the last glacial period during the post glacial sea level rise the vertical succession of reef assemblages reflects environmental and bathymetric variations controlled by the interplay of rapid but variable rates of sea level rise and more or less constant uplift of 5 6 mm yr 1 microbialite crusts composed of high magnesian calcite laminae occur in the tasmaloum reef from 20 to 6 ka and are particularly abundant from 16 to 10 ka the development of microbialite crusts is related to nutrient enrichment of interstitial waters through mixing with meteoric groundwater after 6 ka when sea level ceased rising in the region and continuing uplift caused rapid emergence of the reef microbialites disappear within the subtidal assemblages several explanations can be put forward for their disappearance in particular nutrient input changes are a likely cause a new hydrologic and oceanographic regime was established when sea level ceased rising this change was accompanied by warming of tropical waters

dense water formation around islands 1 basic constraints on the dense water formation rate and circulation resulting from cooling around an island are discussed the domain under consideration consists of an island surrounded by a shelf a continental slope and a stratified ocean atmospheric cooling over the shelf forms a dense water that penetrates down the sloping bottom into the stratified basin strong azimuthal flows are generated over the sloping bottom as a result of thermal wind thermally direct and indirect mean overturning cells are also forced over the slope as a result of bands of convergent and divergent reynolds stresses associated with the jets the coriolis force associated with the net mass flux into the downwelling region over the slope is balanced by these nonlinear terms giving rise to a fundamentally different momentum budget than arises in semienclosed marginal seas subject to cooling a similar momentum balance is found for cases with canyons and ridges around the island provided that the terms are considered in a coordinate system that follows the topography both eddy fluxes and the mean overturning cells are important for the radial heat flux although the eddy fluxes typically dominate the properties of the dense water formed over the shelf temperature diapycnal mass flux are predicted well by application of baroclinic instability theory and simple heat and mass budgets it is shown that each of these quantities depends only on a nondimensional number derived from environmental parameters such as the shelf depth coriolis parameter offshore temperature field and atmospheric forcing

observations of water mass transformation and eddies in the lofoten basin of the nordic seas abstractthe lofoten basin of the nordic seas is recognized as a crucial component of the meridional overturning circulation in the north atlantic because of the large horizontal extent of atlantic water and winter surface buoyancy loss in this study hydrographic and current measurements collected from a mooring deployed in the lofoten basin from july 2010 to september 2012 are used to describe water mass transformation and the mesoscale eddy field winter mixed layer depths mlds are observed to reach approximately 400 m with larger mlds and denser properties resulting from the colder 2010 winter a heat budget of the upper water column requires lateral input which balances the net annual heat loss of 80 w m 2 the lateral flux is a result of mesoscale eddies which dominate the velocity variability eddy velocities are enhanced in the upper 1000 m with a barotropic component that reaches the bottom detailed examination of two eddies from april and august 2012 highlights the variability of the e

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

marine saline ponds as sedimentary archives of late holocene climate and sea level variation along a carbonate platform margin lee stocking island bahamas a 1500 year late holocene history of coastal and lacustrine carbonate sedimentation is preserved in shallow ponds on lee stocking island exuma cays bahamas details of environmental change have been extracted by integrating lithostratigraphy biostratigraphy macrobiota foraminifers ostracodes and chemical stratigraphy c o isotopes of foraminiferal and molluscan skeletal carbonate mgo wt of ostracode calcite with a well defined 14 ca ms radiocarbon chronology carbonate deposition began within physically restricted euryhaline coastal embayments with several pronounced changes in salinity defined by biotic and calculated salinity variation from mgo wt in shells of cyprideis americana by about 700 740 yr b p embayment closure occurred possibly related to changed longshore deposition associated with sea level rise and or regional change in climate previously documented with closure the initial euryhaline foraminifer assemblage was replaced by a predominant hypersaline biofacies e g triloculina sp with progressive basin fill ostracode assemblages calculated salinities and variation in abundance of the gastropod cerithidea sp may resolve higher order and some extreme salinity fluctuations throughout the remaining history of saline pond development foraminiferal isotope stratigraphy is compatible with that expected for hydrologically closed lake basins carbonate accumulation was effectively shut down 200 years ago replaced by stromatolitic growth present day salinities vary according to water balance governed by rainfall and evaporation a centuries scale 300 400 year flux of abraded reworked marine derived bioclasts admixed with skeletal remains of indigenous biota is also preserved in these ponds allochthonous sediment was transported by hurricane storm surges or related to abrupt transgressive events superimposed on an overall gradual rise in global sea level we discuss evidence for both as controls on sedimentation our study illustrates that saline ponds on bahamian islands are excellent sedimentary archives of local regional and possibly global paleoclimatic events of late holocene age 1999 elsevier science b v all rights reserved

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

coherent eddies in the labrador sea observed from a mooring abstract during june november 1994 a mooring in the central labrador sea near the former ocean weather station bravo recorded a half dozen anomalous events that prove to be two different types of coherent eddies comparisons with simple analytical models are used to classify these events as coherent eddies on the basis of their velocity signatures the first clear examples of long lived convectively generated eddies are reported these four small radius 5 15 km eddies are exclusively anticyclonic with cold fresh middepth potential temperature and salinity s cores surrounded by azimuthal currents of 15 cm s 1 their s properties identify them unambiguously as the products of wintertime deep convection in the interior labrador sea compared with eddies in other regions these anticyclones are unusual for their strong surface expressions and composite s cores two warm cyclones are also seen these are larger radius 15 km than the anticyclones and about as energetic currents 15 cm s 1

aerobic biomineralization of mg rich carbonates implications for natural environments we studied the formation of mg rich carbonate in culture experiments using different aerobic bacterial strains and aqueous mg ca ratios 2 to 11 5 at earth surface conditions these bacteria promoted the formation of microenvironments that facilitate the precipitation of mineral phases dolomite huntite high mg calcite and hydromagnesite that were undersaturated in the bulk solution or kinetically inhibited dolomite huntite high mg calcite hydromagnesite and struvite precipitated in different proportions and at different times depending on the composition of the medium the mg content of dolomite and calcite decreased with an increasing ca concentration in the medium the stable carbon isotope composition of the mg rich carbonate precipitates reflected the isotope composition of the organic compounds present in the media suggesting that microbial metabolism strongly influenced the carbon isotope composition of biomediated carbonates we observed that ca enriched carbonate precipitates have relatively low carbon isotope composition these results provide insights into the mechanism s of carbonate formation in natural systems and they are of fundamental importance for understanding modern environments in which carbonate minerals form as a window into the geologic past

enhancement of leaf fossilization potential by bacterial biofilms terrestrial leaf fossils often form through authigenic preservation in which the leaf surface is coated by a variety of minerals especially iron oxides the mechanism of this fossilization is unclear because the largely hydrophobic leaf surfaces do not readily bind metal ions previously proposed mechanisms for mineral encrustation include precipitation of minerals in sediment pore space and precipitation of iron oxides at the surface by decay produced co 2 here we demonstrate that diverse bacterial species rapidly colonize leaf surfaces and form a biofilm within days of the leaf9s entry into a stream environment experimental mineralization of fresh and biofilm coated leaves indicates that leaves without biofilm do not mineralize but leaves with biofilms rapidly adsorb metal ions such as fe 3 onto the anionic biofilm surface where the ions form ferrihydrite once these mineralized leaves are buried by the sediment they are more likely to be converted to fossils than non mineralized leaves examination of a fossil leaf surface by scanning electron microscopy shows bacteria sized structures resembling those found in biofilms these experimental data imply that bacterial colonization of leaves may be an essential prerequisite for authigenic preservation

downwelling in basins subject to buoyancy loss abstractrecent observational theoretical and modeling studies all suggest that the upper part of the downwelling limb of the thermohaline circulation is concentrated in strong currents subject to buoyancy loss near lateral boundaries this is fundamentally different from the traditional view that downwelling takes place in regions of deep convection even when resolving the buoyant boundary currents coarse resolution global circulation and climate models rely on parameterizations of poorly known turbulent mixing processes in this study the first direct measurements of downwelling occurring within a basin subject to buoyancy loss are obtained downwelling is observed near the basin s vertical wall within the buoyant boundary current flowing cyclonically around the basin although the entire basin is cooled large scale mean downwelling is absent in the basin interior laboratory rotating experiments are conducted to explicitly resolve the turbulent mixing due to convective plumes and the baroclinic ed

bacterially induced mg calcite formation role of mg2 in development of crystal morphology abstract the production of several morphologies of magnesian calcite crystals by the soil bacterium myxococcus xanthus is reported for the first time mg calcite crystallization occurred in agar agar gel culture media in the presence of the live bacteria the agar agar used to solidify the nutritive microbial solution acted as a porous system that allowed slow counterdiffusion of cations and anions and of the bacterial metabolites produced under these conditions crystal nucleation and growth occurs apparently as a consequence of the localized ion supersaturation produced by the microbial metabolites and by microbial supply of heterogeneous nuclei for crystallization several morphologies of mg calcite typical of those formed under biotic and abiotic conditions developed simultaneously the crystals produced were not compositionally zoned and showed no significant variation in mg content probably as a consequence of the sponge like character of the precipitates

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

multiple equilibrium states in combined thermal and saline circulation abstract structure and stability of the multiple equilibria of the thermohaline circulation am studied using 2 2 and 3 2 box models thermohaline catastrophe is a shallow phenomenon and its time evolution consists of three stages the search stage the catastrophic stage and the adjustment stage a 3 2 box model is introduced to permit fitting a somewhat less truncated form of freshwater forcing although the total number of possible modes of circulation increases quickly as the number of boxes is increased the grand thermal mode and grand saline mode remain some multiple solutions are found to be statistically improbable and they belong to the so called minor modes with the more realistic freshwater forcing appropriate for the present day north atlantic our simple 3 2 model predicts that the thermohaline cimulation is near a critical mate because a small increase in freshwater flux can cause the system to collapse from the present thermally dominated circulation to an intermediate mode of

microbial structures and possible bacterial sulfide fossils in the giant jinding zn pb deposit yunnan sw china insights into the genesis of zn pb sulfide mineralization abstract the jinding zn pb sulfide deposit lanping yunnan china is one of the youngest sediment hosted giant zn pb deposit in the world it is also a well known deposit in china the large scale of the mineralization and especially the huge volume of h 2 s that was required to precipitate the zn pb sulfide are of great interest to ore geologists ore microscopy shows microbial structures such as framboidal sphalerite spherical aggregates of galena sphalerite oolite sphalerite dendritic colloidal sphalerite pyrite metacolloidal sphalerite pyrite multinuclear metacolloidalring like sphalerite pyrite botryoidal sphalerite pyrite framboidal pyrite and bacterial plate like of galena sphalerite detailed observations and analyses of the microbial structures at micron to nanometer scales by field emission scanning electron microscopy fesem and energy dispersive spectrometry eds reveal that the bacteria fossils are composed of sphalerite galena or pyrite or of multiple sulfide minerals with calcite and that they are distributed in bacterial colonies in the ore the individual bacteria fossils are spherical botryoidal or ring like with a diameter of 200 500 nm filamentous mucoid and tubular extracellular polymeric substances eps are commonly observed that are closely associated with and have the same composition as the bacteria fossils secondary ion microprobe analysis sims by in situ sulfur micro isotopic analysis of the microbial sulfide structures and bacteria fossils yield 34 s v cdt values varying from 48 6 to 9 5 per mil indicating that there was a high percentage of sulfate reducing bacteria in the zn pb sulfide mineralization process previous analyses have shown that the zn pb mineralization was formed at a shallow depth and low temperature with barely visible hydrothermal alteration the presence of evaporitic sulfate layers and paleo oil reservoir characteristics the authors believe that bacterial sulfate reduction might be the key h 2 s production mechanism in the jinding dome that was required to form this giant pb zn sulfide ore body

precipitation and growth morphology of calcium carbonate induced by myxococcus xanthus implications for recognition of bacterial carbonates abstract it is thought that morphologies of bacterial carbonates can be used to identify microbial fossils and or precipitates in sediments and rocks this study shows that calcite and vaterite formed in a gel medium in the presence of myxococcus xanthus display a range of morphologies that depend on whether the bacteria are live or dead metabolic activity of the bacteria induced 1 aggregates of calcified bacteria formed at maximum supersaturation 2 vaterite spheres final growth stage of dumbbell fibrous radiated aggregates and 3 dipyramid and disphenoid like calcite crystals combination of 011 and 0001 forms morphologies 2 and 3 developed at a lower supersaturation and are typically found in gel like media dipyrimidal like calcite crystals were also obtained abiotically in gel medium dead m xanthus cells induced heterogeneous precipitation of calcite with rhombohedral morphologies at low supersaturation a growth mechanism resulting from self assembly of calcium carbonate nanocrystals may account for the observed morphologies crystal microstructure and crystallite size measurements all of the above mentioned morphologies of bacterial carbonate have been observed in other laboratory experiments and in continental and marine environments however all of them have also been produced abiotically with the exception of calcified bacterial cells this may make it more difficult to identify bacterial activity in the rock record nonetheless bacterially induced alkalinization appears to be a prerequisite for the development of spherulitic and dipyramid or disphenoid like forms in natural mucilaginous biofilms and microbial mats the morphologies reported here may facilitate the recognition of early and recent marine and continental microcrystalline bacterial carbonates and cements

tem analysis of microbial mediated sedimentation and lithification in modern marine stromatolites three sedimentary processes are involved in the growth of living stromatolites at highborne cay bahamas 1 trapping of oolitic sands 2 formation of surface micritic crusts and 3 formation of fused grain laminae the microbial role in each process was investigated by examining the stromatolites using transmission electron microscopy species composition and physiological state of the bacteria were discerned by ultrastructure a well dispersed population of schizothrix gebeleinii was observed in rapidly accreting surface layers their filaments produce copious quantities of amorphous exopolymer and condensed sheath that surround individual and pairs of cells both fresh and degraded sheaths are however devoid of carbonate precipitates this suggests that the primary roles of s gebeleinii are the trapping and binding of unconsolidated sediment and the production of extra cellular polymeric secretions surface micritic layers are composed primarily of needle shaped crystals of aragonite the uppermost surface of the micritic crust is coated with a biofilm comprised primarily of small gram negative bacteria i e sulfate reducing bacteria that range in size from 250 to 500 nm in diameter and up to 1 m in length empty cyanobacterial sheaths and occasional gram positive spores were also observed thin sections through resin casts of ooid microborings in the fused grain laminae show cells of the endolithic cyanbacterium solentia sp and evidence of an organic matrix the micritic crusts and fused grain layers became lithified laminae that were preserved at depth although the organisms that formed them were not this suggests that morphological remains of these organisms i e microfossils in ancient stromatolites should not be expected

bacterially induced mineralization of calcium carbonate in terrestrial environments the role of exopolysaccharides and amino acids this study stresses the role of specific bacterial outer structures such as glycocalix and parietal polymers on calcium carbonate crystallization in terrestrial environments the aim is to compare calcium carbonate crystals obtained in bacterial cultures with those obtained during abiotically mediated synthesis to show implications of exopolysaccharides and amino acids in the mineralogy and morphology of calcium carbonate crystals produced by living bacteria this is done using various amounts of purified exopolysaccharide xanthan eps and l amino acids with a range of acidities amino acids and increasing xanthan content enhance sphere formation in calcite and vaterite regarding calcite the morphology of crystals evolves from rhombohedral to needle shape this evolution is characterized by stretching along the c axis as the amino acid changes from glutamine to aspartic acid and as the medium is progressively enriched in eps regarding vaterite the spherulitic habit is preserved throughout the morphological sequence and starts with spheres formed by the agglomeration of short needles which are produced in a xanthan free medium with glutamine monocrystals forming spheres increase in size as xanthan is added and the acidity of amino acids glutamic and aspartic acids is increased at high xanthan concentrations amino acids and mainly aspartic and glutamic acids induce vaterite precipitation the role of the carboxyl group is also probably critical because bacterial outer structures associated with peptidoglycan commonly contain carboxyl groups this role combined with the results presented here clearly demonstrate the influence of bacterial outer structure composition on the morphology and mineralogy of bacterially induced calcium carbonate this point should not be neglected in the interpretation of calcite cements and carbonate accumulations in terrestrial environments

autogenic microbial genesis of middle miocene palustrine ooids nullarbor plain australia abstract miocene palustrine ooids located in the nullarbor plain southern australia illustrate the importance of microbes and soil processes in the formation of these spherically laminated grains in pedogenic settings these particles are composed of dense minimicrite and include a wide assortment of microbially produced structures such biogenicity includes interpreted extracellular polymers eps algal filaments palygorskite and sepiolite nano fiber mats bacterial spores and meniscate fabrics ooid nuclei are peloids that are interpreted to have formed via microbial binding of lacustrine sediment in a subsequent palustrine environment both at the surface and inside underlying karst cavities the peloids are encapsulated in multigenerational micrite laminations that form the spherical cortex individual cortical laminae are made up of degraded minimicrite crystals and complex encrusting mats of palygorskite and sepiolite nano fibers cortex generation is interpreted to have been an annual process involving alternating soil hydration states in this conceptual model during the wet season ooids were covered in bacterial mucus that bound ions from solution and produced hydrated mg si gels that evenly surrounded the entire ooid gel dehydration during the following dry season resulted in precipitation of fibrous palygorskite and sepiolite succeeding seasonal variations in moisture produced numerous laminae that ultimately resulted in a multigenerational ooid cortex this annual microbial process provides a new mechanism involving an autogenic formation of ooids that may be applied to a wide variety of pedogenic sediments unlike the more common marine ooids that require constant movement to achieve cortical precipitation the process of grainification combined with microbially mediated mineral precipitation under different soil hydration states results in the in place formation of terrestrial ooids

rock varnish in new york an accelerated snapshot of accretionary processes abstract samples of manganiferous rock varnish collected from fluvial bedrock outcrop and erie barge canal settings in new york state host a variety of diatom fungal and bacterial microbial forms that are enhanced in manganese and iron use of a dual beam focused ion beam scanning electron microscope to manipulate the varnish in situ reveals microbial forms that would not have otherwise been identified the relative abundance of mn fe enriched biotic forms in new york samples is far greater than varnishes collected from warm deserts moisture availability has long been noted as a possible control on varnish growth rates a hypothesis consistent with the greater abundance of mn enhancing bioforms sub micron images of incipient varnish formation reveal that varnishing in new york probably starts with the mortality of microorganisms that enhanced mn on bare mineral surfaces microbial death results in the adsorption of the mn rich sheath onto the rock in the form of filamentous networks clay minerals are then cemented by remobilization of the mn rich material thus the previously unanswered question of what comes first clay mineral deposition or enhancement of mn can be answered in new york because of the faster rate of varnish growth in contrast very slow rates of varnishing seen in warm deserts of microns per thousand years make it less likely that collected samples will reveal varnish accretionary processes than samples collected from fast accreting moist settings

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

interactions between geomorphology and ecosystem processes in travertine streams implications for decommissioning a dam on fossil creek arizona travertine deposits of calcium carbonate can dominate channel geomorphology in streams where travertine deposition creates a distinct morphology characterized by travertine terraces steep waterfalls and large pools algae and microorganisms can facilitate travertine deposition but how travertine affects material and energy flow in stream ecosystems is less well understood nearly a century of flow diversion for hydropower production has decimated the natural travertine formations in fossil creek arizona the dam will be decommissioned in 2005 returning carbonate rich spring water to the natural stream channel should promote travertine deposition how will the recovery of travertine affect the ecology of the creek to address this question we compared primary production decomposition and the abundance and diversity of invertebrates and fish in travertine and riffle run reaches of fossil creek arizona we found that travertine supports higher primary productivity faster rates of leaf litter decomposition and higher species richness of the native invertebrate assemblage observations from snorkeling in the stream indicate that fish density is also higher in the travertine reach we postulate that restoring travertine to fossil creek will increase stream productivity rates of litter processing and energy flow up the food web higher aquatic productivity could fundamentally shift the nature of the stream from a sink to a source of energy for the surrounding terrestrial landscape

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

the role of photosynthesis and co2 evasion in travertine formation a quantitative investigation at an important travertine depositing hot spring le zitelle lazio italy le zitelle hot springs contain high concentrations of dissolved ca and co 2 and precipitate copious quantities of aragonite and calcite as travertine a study of precipitation rates in the upper section of the stream was undertaken using marble tablets this showed that 1 precipitation rate increased with distance from the spring over the section studied 2 the rate was positively correlated with flow agreeing with previous experimental and theoretical studies 3 precipitation rates during the day and night did not differ statistically the last finding demonstrated a negligible effect of photosynthesis on travertine formation and was supported by further precipitation rate studies undertaken in clear and blackened tubes this conflicts with previous work that suggested an important role for microbial photosynthesis in travertine deposition at le zitelle the microbial flora consisted mainly of cyanobacteria spirulina and photosynthetic bacteria with smaller quantities of diatoms the biomass in most of the travertine was extremely low and often endolithic carbon fixation rates were also low a mass balance calculation of carbon flow showed that of 100 units of dissolved carbon entering the stream section investigated 51 units were lost to the atmosphere as co 2 0 9 units were deposited as travertine 0 09 units were fixed by photosynthesis and 48 units remained in the stream water we conclude that most of the zitelle travertine is formed abiotically casting doubt on the supposed biotic origin of travertine at this and other italian sites

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

two stable equilibria of the atlantic subpolar gyre the cyclonic circulation of the atlantic subpolar gyre is a key mechanism for north atlantic climate variability on a wide range of time scales it is generally accepted that it is driven by both cyclonic winds and buoyancy forcing yet the individual importance and dynamical interactions of the two contributions remain unclear the authors propose a simplified four box model representing the convective basin of the labrador sea and its shallow and deep boundary current system the western subpolar gyre convective heat loss drives a baroclinicflow of relatively light water around the dense center eddy salt flux from the boundary current to the center increases with a stronger circulation favors the formation of dense waters and thereby sustains a strong baroclinic flow approximately 10 25 of the total in contrast when the baroclinic flow is not active surface waters may be too fresh to convect and a buoyancy driven circulation cannot develop this situation corresponds to a second stable circulation mode a hysteresis is found for variations in surface freshwater flux and the salinity of the near surface boundary current an analytical solution is presented and analyzed

review of aragonite and calcite crystal morphogenesis in thermal spring systems abstract aragonite and calcite crystals are the fundamental building blocks of calcareous thermal spring deposits the diverse array of crystal morphologies found in these deposits which includes monocrystals mesocrystals skeletal crystals dendrites and spherulites are commonly precipitated under far from equilibrium conditions such crystals form through both abiotic and biotic processes many crystals develop through non classical crystal growth models that involve the arrangement of nanocrystals in a precisely controlled crystallographic register calcite crystal morphogenesis has commonly been linked to a driving force which is a conceptual measure of the distance of the growth conditions from equilibrium conditions essentially this scheme indicates that increasing levels of supersaturation and various other parameters that produce a progressive change from monocrystals and mesocrystals to skeletal crystals to crystallographic and non crystallographic dendrites to dumbbells to spherulites despite the vast amount of information available from laboratory experiments and natural spring systems the precise factors that control the driving force are open to debate the fact that calcite crystal morphogenesis is still poorly understood is largely a reflection of the complexity of the factors that influence aragonite and calcite precipitation available information indicates that variations in calcite crystal morphogenesis can be attributed to physical and chemical parameters of the parent water the presence of impurities the addition of organic or inorganic additives to the water the rate of crystal growth and or the presence of microbes and their associated biofilms the problems in trying to relate crystal morphogenesis to specific environmental parameters arise because it is generally impossible to disentangle the controlling factor s from the vast array of potential parameters that may act alone or in unison with each other

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

on the hydrographic and ice conditions in the northern north atlantic during different phases of a glaciation cycle abstract a theoretical investigation of the hydrographic conditions in the northern north atlantic n of the greenland scotland ridge for different forcing conditions is undertaken first a simple dynamical model for the mediterranean circulation in the greenland and norwegian seas the subpolar sea is developed the calculated contemporary rate of deepwater formation about 2 5 10 6 m 3 s seems to be quite realistic it is concluded that the mediterranean circulation is possible as long as the cyclonal atmospheric circulation in the subpolar sea is strong enough to prevent the fresher water in the coastal currents along the eastern and western boundaries from spreading over the interior utilizing the arctic ocean model in stigebrandt 1981 the hydrographic and ice conditions in the subpolar sea and the arctic ocean during different phases of a glaciation are finally investigated as so many parameters are involved the derivations are by necessity rather uncertain however it seems possible that the hydrographic state in the subpolar sea changes between mediterranean and estuarine circulation several times during a glacial cycle

the arctic atlantic thermohaline circulation abstractthe atlantic ocean s thermohaline circulation is an important modulator of global climate its northern branch extends through the nordic seas to the cold arctic a region that appears to be particularly influenced by climate change a thermohaline circulation is fundamentally concerned with two degrees of freedom this is in particular the case for the inflow of warm and saline atlantic water through the nordic seas toward the arctic that is balanced by two branches of outflow the authors present an analytical model rooted in observations that constrains the strength and structure of this arctic atlantic thermohaline circulation it is found maybe surprisingly that the strength of atlantic inflow is relatively insensitive to anomalous freshwater input it mainly reflects changes in northern heat loss freshwater anomalies are predominantly balanced by the inflow s partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth res

experimental modelling of beachrock cementation under microbial influence a laboratory model has been developed which reproduces natural conditions of beachrock formation these conditions include the porosity of beach sand tidal movements alternation of phreatic and vadose conditions temperature evaporation illumination and water composition seawater with a control of the following parameters salinity ca mg co2 ph caco3 saturation the conditions of two beachrocks from the red sea egypt and shark bay australia have been simulated and the influence of the micro organism population undetermined sampled in these beachrocks was observed for 3 4 months in the experiments inoculated with micro organisms biomineralization produced characteristic crystals of various forms from 1 to 20 m in size the precipitates resemble the micritic cements of natural beachrocks on the contrary precipitation was much less developed in the control experiments under nearly sterile conditions these results confirm the importance of microbial activity during beachrock formation the first micritic cement which seems to control cementation and produce the initial consolidation is formed under a strong microbial influence in or near a biofilm covering the grain surface the presence of this micritic cement is necessary for the development of the subsequent prismatic cement which probably results from an abiotic precipitation during higher fluid circulation

an urban model for dolomite precipitation authigenic dolomite on weathered building stones abstract formation of authigenic dolomite within alteration crusts developing on limestone surfaces of a historical building is confirmed by xrd polarising microscopy and sem with edx data two different types of authigenic dolomite occur limpid stoichiometric dolomite and ca rich protodolomite the presence of gypsum calcite pollution derived particles clay minerals and organic material within the crusts confirms their recent formation together with that of dolomite in a micro environment of high evaporation and ionic concentrations such environments are typically found in many urban centres on the basis of these findings an urban model for dolomite precipitation is proposed there are two sources of mg 1 dissolution of nearby dolostones overlying the limestones as a result of leaching by atmospheric so2 oxidised and hydrolysed as h2so4 and 2 mg rich metallic atmospheric particles elevated mg ca values are achieved by precipitation of gypsum which removes ca from the solution protodolomite then precipitates and later recrystallises as limpid dolomite due to changes in the pore fluids related with the environmental conditions co32 and co3h are provided by leaching of both the limestone support and the nearby dolostones additional sources of co2 are provided both by the polluted urban atmosphere rain water and the degradation of organic material within the crust organic matter fungi and bacteria pollution derived particulate matter and clays seem to play a key role in promoting dolomite precipitation in this micro environment by altering kinetic barriers and providing active sites for dolomite nucleation finally the formation of urban dolomite is compared with recent dolomites forming in natural environments with alternating evaporative fresh water conditions

nannobacteria and the precipitation of carbonate in unusual environments abstract nannobacteria are abundant not only in normal marine limestones but also in other environments such as continental caliches fresh water streams springs water pipes caves etc cells are typically 50 to 200 nm in diameter