microbially induced cementation to control sand response to undrained shear current methods to improve the engineering properties of sands are diverse with respect to methodology treatment uniformity cost environmental impact site accessibility requirements etc all of these methods have benefits and drawbacks and there continues to be a need to explore new possibilities of soil improvement particularly as suitable land for development becomes more scarce this paper presents the results of a study in which natural microbial biological processes were used to engineer a cemented soil matrix within initially loose collapsible sand microbially induced calcite precipitation micp was achieved using the microorganism bacillus pasteurii an aerobic bacterium pervasive in natural soil deposits the microbes were introduced to the sand specimens in a liquid growth medium amended with urea and a dissolved calcium source subsequent cementation treatments were passed through the specimen to increase the cementation level of the sand particle matrix the results of both micp and

dynamics of potential vorticity fronts and eddy detachment abstract the formation and detachment of quasi geostrophic eddies in a 1 layer jet is studied using a piecewise uniform potential vorticity model a vorticity front separates the two pieces and thus the jet has cusplike character the evolution of large amplitude initial disturbance whose origin may be attributed to barotropic baroclinic instability mechanisms not explicit in our model is computed by the method of contour dynamics certain numerical results such as the steepening of the front prior to eddy detachment can be physically explained in terms of differential mean field advection and vortex induction computations are made for a variety of initial conditions and we indicate the amplitude scale conditions necessary for the detachment of an eddy the discussion is directed to the problem of the formation of warm cold rings in the gulf stream the effect of a coast on large perturbations of a jet is also briefly discussed

miocene gypcretes from the calama basin northern chile gypcretes of miocene age are preserved beneath a 9 53 0 36 ma ignimbrite along the eastern margin of the oligo pleistocene calama basin northern chile they are restricted to a single stratigraphic horizon developed within laterally extensive 35 km coalesced alluvial fan deposits developed along the margin of an endorheic basin two types of gypcrete are recognized type 1 comprises almost completely gypsum cemented sandstones containing alabastrine nodules and columns sub vertical and horizontal veins of fibrous gypsum and v shaped cracks infilled by clastic material and are interpreted as surface weathered gypsic crusts type 2 gypcretes are composed of massive reddened poikilitic and mesocrystalline gypsum up to 80 of the rock with isolated bedding parallel clast rich lenses 200 30 cm and sub vertical veins of fibrous gypsum the massive texture resembles that of well developed b horizons in quaternary alluvial desert soils the crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic poikilitic and illuvial mesocrystalline processes with the fibrous gypsum veins suggestive of periodic surface exposure gypcrete horizons are up to 25 m thick and composed of both gypcrete types they represent superimposed phases of surface and subsurface gypcrete development quaternary gypcretes are developed in arid climatic regimes but are not considered to develop under hyper arid climates an arid climate is considered to have prevailed in the study area up to 9 5 ma after which a change to hyper aridity favoured gypcrete preservation

stress strain behavior of sands cemented by microbially induced calcite precipitation abstractmicrobial induced calcite precipitation micp is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil the evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests micp treated sands with cementation levels ranging from young uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear a transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed moderately cemented specimens are subjected to various stress paths which result in a change to the shear strength and volumetric behavior shear wave velocity is used to nondestructively monitor the change in small strain stiffness during shearing which provides an indication of cementation degradation as a function of strain level because shear wave velocity is influenced by

extensive carbonate algal bioherms in upper pleistocene saline lakes of the central altiplano of bolivia during the upper pleistocene the central altiplano of bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands discontinuously covering the 300 km long and 100 km wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of uyuni distribution size and shape of the bioherms are diverse due to various factors e g the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth on larger palaeoterraces the build ups coalesced to form platform like carbonate accumulations although the morphologies closely resemble those induced by cyanobacteria they were predominantly constructed by other plant communities probably dominated by filamentous green algae cyanobacterial communities flourished in association with these plants but they did not contribute significantly to the architecture of the bioherms they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build ups a prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects the build ups located between 3660 and 3680 m elevation display up to three major parts 1 a massive inner core formed during an early minchin highstand before 40 ka 2 a large peripheral envelope deposited at about 40 ka late minchin and 3 a thinner outermost crust formed during a late glacial event lake level dropped during interlacustrine stages sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system i e the present day salar of uyuni

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

the structure and transport of the gulf stream at 73 w abstract between september 1980 and may 1983 16 sections of temperature and velocity were obtained with the pegasus instrument along a transect crossing the gulf stream at 73 w the mean temperature and velocity fields of the upper 2000 meters were calculated the transport above 2000 meters calculated from the sections had a mean of 87 8 17 3 106 m3 s 1 a comparison with mass flux measurements obtained by previous investigators at cape fear indicated that the addition to the transport of the stream in the region was uniform with depth above 800 meters the mean inflow measured at the pegasus line was found to be uniform above 800 meters and to decrese substantially below this depth the increase in transport at the line estimated from the mean cross stream velocity field was 15 4 5 8 106 m3 s 1 per 100 km downstream distance the temporal fluctuation of the pegasus transport measurements was consistent with an annual cycle with a maximum in april the mean eddy kinetic energy at the surface

climate and lake level history of the northern altiplano bolivia as recorded in holocene sediments of the rio desaguadero abstract strata exposed in terraces and modern cutbanks along the rio desaguadero contain a variety of lithofacies that were deposited in four distinct facies associations these facies associations document a history of aggradation and downcutting that is linked to holocene climate change on the altiplano braided stream meandering stream deltaic and shoreline and lacustrine sediments preserved in multi level terraces in the northern rio desaguadero valley record two high water intervals one between 4500 and 3900 yr bp and another between 2000 and 2200 yr bp these wet periods were interrupted by three periods of fluvial downcutting centered at approximately 4000 yr bp 3600 yr bp and after 2000 yr bp braided river sediments preserved in a single terrace level in the southern rio desaguadero valley record a history of nearly continuous fluvial sedimentation from at least 7000 yr bp until approximately 3200 yr bp that was followed by a single episode post 3210 yr bp of downcutting and lateral migration the deposition and subsequent fluvial downcutting of the northern strata was controlled by changes in effective moisture that can be correlated to holocene water level fluctuations of lake titicaca the deposition and dissection of braided stream sediments to the south are more likely controlled by a combination of base level change and sediment input from the rio mauri

cemented sands under static loading cemented sands are found in many areas of the world one of their distinguishing characteristics is their ability to stand in steep natural slopes large deposits are located along the california coast and in a number of areas intense urban development has occurred near the crest of high steep slopes because of the hazards posed by slope failures in the cemented sands a test program was undertaken to define the nature of the cementation and its effect on behavior of the soils a total of 137 laboratory compression and tension load tests were performed on undisturbed samples of naturally cemented sands and artificially prepared cemented sands the materials exhibited friction angles similar to uncemented sands but had a cementation strength intercept and a tensile strength the primary cementing agents of the sands tested were silicates and iron oxides the strength of the cemented sands were found to be a function of density amount of cementing agent grain shape and grain arrangement

strength stiffness and microstructure characteristics of biocemented calcareous sand calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects microbially induced calcite precipitation micp is an innovative soil imp

meander evolution on piecewise uniform quasi geostrophic jets abstract a variety of simple two layer representations of a quasi geostrophic jet along a vorticity front are initialized with a simple meander the subsequent evolution of the jet is followed and related to the observed behavior of the gulf stream front east of the new england sea mounts by varying the horizontal and vertical structure of the jet a range of behavior is obtained that includes shingle formation and eddy detachment these effects can be related to the linear stability properties of the jet the structure that exhibits the most realistic meander evolution is that of a jet associated with a simple baroclinic vorticity front separating two pools of vorticity in the upper layer and two weaker pools in the lower layer this picture is consistent with what one can inter from the known density structure of the gulf stream in this region

warm outbreaks of the gulf stream into the sargasso sea a warm outbreak is a large body of gulf stream water with apparent anticyclonic circulation that detaches from the gulf stream and exists as a well defined entity in the sargasso sea because warm outbreaks are warmer at the surface than sargasso sea water they are often clearly visible in satellite thermal infrared imagery from a survey of over 750 satellite images covering the sargasso sea immediately to the south of the gulf stream between 64 and 74 w and spanning a 5 year period 18 possible outbreaks have been observed all formed west of 65 w with the majority forming between 67 and 72 w five of the 18 were observed to detach completely from the gulf stream and have the following properties in common 1 they all formed in several days at or near the point of maximum cyclonic curvature of a large gulf stream meander 2 the surface expression was relatively short lived of the order of 10 to 20 days and 3 their dimensions and those of the other 13 were of the order of 100 by 200 km given the similarity between the characteristics of warm outbreaks and those of opposite vortices predicted by ikeda and apel 1981 from a two layer quasi geostrophic model of an eastward flowing jet it is suggested that the two phenomena are related further support of this hypothesis is the fact that the rate of formation of warm outbreaks between two and six per year is similar to that of anticyclonic eddies observed in expendable bathythermograph surveys of this area

high ground water levels and dune development in central australia tl dates from gypsum and quartz dunes around lake lewis napperby northern territory abstract an episode of high lake levels prior to the last maximum glaciation has been identified at many localities in wastern australia similar events have been recognized at playa lakes in central australia where gypsum dunes along playa margins formed during one or more episodes of high groundwater discharge with a large influx of calcium sulphate at lake lewis exposures at two islands show similar sediment sequences three pedogenic gypcrete layers interbedded with aeolian quartz and gypsum sand horizons form three units within gypsum dunes up to 7 m high the lowest unit has cliffed edges buried by the upper units indicating a significant time break four tl dates coarse grained quartz show that this lowest unit was deposited at or before 70 80 ka the middle unit of mixed gypsum and quartz sand capped by gypcrete represents the major phase of gypsum dune formation and 6 tl dates range from 33 to 46 ka with overlapping error bars these are slightly younger but statistically similar to tl dates from 39 to 59 ka of the shoreline gypsum dune at lake amadeus in the same region the top unit of the two islands up to 1 m thick has not yet been well dated one date is inconsistent with the well dated middle layer below possibly because of incomplete bleaching and has been rejected the other date 17 5 ka is much younger which possibly indicates a minor and local reactivation of old gypsum sediments at the lake margin there are quartz dunes overlying the gypsum dunes and a buried aeolian quartz sand layer occurs in a lake margin terrace these represent reactivation of the regional quartz dune field after the major gypsum dune formation two consistent tl dates 21 4 ka and 23 6 ka indicate that regional dunes were active at about the time of the last glacial maximum

biogeochemical processes and geotechnical applications progress opportunities and challenges consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems this is a new paradigm for many in geotechnical engineering realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification this paper assesses the progress opportunities and challenges in this emerging field biomediated geochemical processes which consist of a geochemical reaction regulated by subsurface microbiology currently being explored include mineral precipitation gas generation biofilm formation and biopolymer generation for each of these processes subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals organic matter pore fluids and gases that constitute soil geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance sequestration of carbon soil erosion control groundwater flow control and remediation of soil and groundwater impacted by metals and radionuclides challenges in biomediated ground modification include upscaling processes from the laboratory to the field in situ monitoring of reactions reaction products and properties developing integrated biogeochemical and geotechnical models management of treatment by products establishing the durability and longevity reversibility of the process and education of engineers and researchers

equilibration of baroclinic meanders and deep eddies in a gulf stream type jet over a sloping bottom abstract spatiotemporal evolution of a small localized meander on a gulf stream type baroclinically unstable jet over a topographic slope is investigated numerically using a three dimensional primitive equation model an unperturbed jet is prescribed by a potential vorticity front in the upper thermocline overlaying intermediate layers with weak isentropic potential vorticity gradients and a quiscent bottom layer over a positive same sense as isopycnal tilt cross stream continental slope a series of numerical experiments with the same initial conditions over a slope and flat bottom on the plane and on the f plane has been carried out an initially localized meander evolves into a wave packet and generates deep eddies that provide a positive feedback for the meander growth meanders found growing over a flat bottom are able to pinch off resembling warm and cold core rings while in the presence of a weak bottom slope such as 0 002 the maximum amplitudes of meanders and associated deep eddies saturat

regional primitive equation studies of the gulf stream meander and ring formation region abstract primitive equation and quasi geostrophic eddy resolving open ocean models are used for hindcast studies in the gulf stream meander and ring formation region a feature model approach is used to initialize the models based on one month of observations during november to december 1984 flat bottom and topographic calculations are carried out using an initial gulf stream velocity profile based on the pegasus dataset all of the major events observed in the upper thermocline are reproduced by both numerical models the addition of bottom topography is shown to significantly alter the character of the deep velocity fields large basin scale circulations found near the bottom in both flat bottom calculations were replaced by energetic jets and eddies associated with the dominant spatial scales of the bottom topography use of the quasi geostrophic model to dynamically adjust the initial conditions for the primitive equation model is shown to reduce the growth of large scale meanders on time scales o

the structure and nonlinear evolution of synoptic scale cyclones life cycle simulations with a cloud scale model abstract high resolution simulations of idealized baroclinic wave life cycles on both the f plane and the plane are performed the anelastic nonhydrostatic equations are employed in these analyses and motions are assumed dry adiabatic and inviscid apart from a weak horizontal diffusion cyclogenesis is documented in considerable detail and features the formation of an occlusion with spiraling temperature contours that cuts off completely from the main warm air mass late in the life cycle in all cases thereafter the occlusion develops independently of the remaining warm cold frontal cusp and decays by becoming zonally elongated later redevelopment involving reorganization of the occlusion into the more nearly circular shape that obtains at the time of cut off can reoccur on the f plane leading to an oscillatory life cycle features of the simulated synoptic scale vortices that are in common with observed cyclones are the comma shaped vertical velocity pattern the spiraling temperature and vorticity

calcium carbonate cementation of sand a method for producing artificially cemented samples for geotechnical testing and a comparison with natural cementation processes abstract the experience of dutch dredging companies is that cemented layers in holocene calcareous sands are much more frequent than expected in an effort to alleviate this problem a method for producing slightly calcium carbonate cemented sand is presented these samples being used to better constrain the geotechnical parameters of slightly cemented carbonate sands when assessing dredging conditions the most important environments where early marine cementation mainly by high magnesian calcite and aragonite occur are intertidal beaches and tidal flats subtidal sandflats and reefs each environment has its typical occurrence and dimension of cemented layers and a characteristic form and distribution of cementing materials within the sandstone it is therefore expected that sandstones from each environment will have a distinct set of geotechnical properties important factors controlling calcium carbonate cementation are the chemistry of the seawater the source of the cementing material the physical conditions in terms of hydraulic energy sedimentary parameters such as permeability texture and composition of the sand and an initially stabilizer of the loose sediment all these factors and the way in which they relate to each other explain large variability in marine cement forms and the variability of the geotechnical properties of the cemented calcareous sediments the factors controlling early cementation in the shallow marine environment are discussed in order to evaluate the boundary conditions for a laboratory model used to produce artificially cemented and by simulating natural subtidal cementation processes the resulting cemented sands are shown to be comparable with natural sandstones and to exhibit similar behaviour during strain tests for the purposes of assessing dredging conditions these artificial samples have advantages over natural samples

gulf stream meander propagation past cape hatteras the propagation and growth characteristics of gulf stream meanders past the stream s separation point at cape hatteras are analyzed using yearlong time series from a mooring program sponsored by the minerals management service which included moorings imbedded in the gulf stream cyclonic flank both upstream south and downstream north of cape hatteras in the upstream region energetic meanders of 3 8 day period 180 380 km wavelength propagate downstream along the gulf stream at speeds of 40 55 km day 21 this variability decays almost completely across the gulf stream separation with growth in lower frequency variability 30 120 day in the downstream direction wavelength and phase speed in the 3 8 day band are strong functions of frequency with increasing phase speed for increasing wavenumber phase speeds upstream from cape hatteras and across the gulf stream separation point are faster for a given wavenumber than downstream from cape hatteras in keeping with prior published estimates at the upstream end of the study site both baroclinic and barotropic mechanisms contribute to the decay of 3 8 day meanders and growth of lower frequency 30 120day variability in the downstream direction at the downstream end of the study region the reverse holds with both baroclinic and barotropic mechanisms contributing to growth of 3 8 day meanders and decay of lowerfrequency 30 120 day variability

baroclinic and barotropic instabilities of coastal currents the two layer baroclinic instability model of the california undercurrent from mysak 1977 is modified to investigate the effects of the lateral boundary conditions on the stability properties of the system as is common in baroclinic instability calculations mysak 1977 assumes the mean flow along the continental rise to be bounded laterally by vertical rigid walls thus allowing the cross stream structure of the perturbation flow to be decomposed into simple normal modes instability then occurs when waves of the same cross stream structure interact the dominant instability is that associated with the gravest mode in the first model presented here we consider the effect of replacing the rigid outer boundary with a quiescent constant depth ocean waves of short longshore wavelength are not greatly affected by the open seaward boundary however as consideration is turned to waves of longer longshore wavelength the cross stream wavenumber departs further from the integral values of the channel flow problem and another class of baroclinic instabilities occurs due to interaction between waves of differing cross stream structure nevertheless the dominant baroclinic instability remains that associated with the gravest mode a new barotropic instability is also present drawing energy from the horizontal shear between the coastal current and the quiescent ocean in the second model the rigid outer boundary is retained but the inner boundary is replaced by a shallow sloping region modeling the effects of a sloping shelf adjoining the coastal current which flows along the continental rise topographic waves are present above the sloping inshore region these waves are coupled with the channel waves once again the cross stream wavenumber departs from the integral values of the channel problem and instabilities are present due to interaction between waves of differing cross stream structure as in the previous model the dominant baroclinic instability is that of the gravest mode and a new barotropic instability is present due to the lateral shear in the mean flow at the shelf break for both models a parameter study is presented in which we determine the effects of varying the shear stratification and bottom slope

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

the average distribution of volume transport and potential vorticity with temperature at three sections across the gulf stream abstract average cross sections of downstream velocity and temperature obtained using pegasus current profiles at three locations along the gulf stream have been partitioned into 2 5 c temperature intervals to examine the distribution of transport increase versus temperature between the two southern sections 27 and 29 n and off cape hatters 73 w between 27 and 29 n the total transport of the florida current over the sections increased only by about 3 106 m3 s 1 3 sv but the current broadens by about 50 by cape hatteras the transport has increased nearly three fold to 93 7 sv of which two thirds of the increase is contained in the 19 5 17 0 c 18 layer and in water colder than the 7 c still temperature found at 27 n cross stream distributions of layer transport potential vorticity and thickness are estimated at each section the 10 10 7 m 1 s 1 contour tends to be a boundary independent of temperature between the region of relatively uniform layer potential vorticity on the a

aeolian landscapes in central australia gypsiferous and quartz dune environments from lake amadeus there are two different dune systems in central australia regional quartz dunefields and transverse gypsiferous dunes associated with playa lakes these two systems especially gypsiferous dunes at lake amadeus the largest playa in central australia provide a sedimentary geomorphological and environmental history of the region during the late quaternary the gypsifierous dunes consist of a surficial gypcrete overlying an aeolian sediment sequence below a mixture of gypsum sand and quartz sand no clay pellets have been found in the dune sequence in significant contrast to the gypsiferous clay dunes in other parts of australia three possible models of the environmental controls of gypsiferous dune formation are discussed the most plausible one suggests simultaneous gypsum precipitation and deflation sandsized gypsum was precipitated in a groundwater seepage zone around the playa margin during seasonally high water tables and these crystals were deflated onto land during dry intervals forming the marginal gypsiferous dunes these processes require conditions of high regional water table strong climatic seasonality and probably a windier and overall wetter climate at least two separate gypsiferous duneforming episodes can be recognized the age of formation of the younger one has been dated by thermoluminescence at 44 54 ka the gypcrete crust capping the dunes is characterized by intergrown microcrystalline gypsum crystals showing evidence of leaching dissolution and recrystallization it is interpreted as a pedogenic product formed during a stable period after accumulation of the gypsiferous dune after the construction of the younger gypsiferous dune there was a major episode of activation of regional quartz dunefields which formed thick quartz sand mantles overlying gypsiferous dunes on both playa margins and the dune islands within the playa an equivalent aeolian sand layer was deposited within the playa soil structures in this unit indicate that the sand sheet over the playa was later colonized by vegetation activation of the regional dunefields suggests a major period of dry climate which although not dated may correlate with the last glacial maximum identified as a period of maximum aridity from 25 to 18 ka at other sites in australia

the applicability of microbially induced calcite precipitation micp for internal erosion control in gravel sand mixtures seepage induced internal erosion in earth filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades microbially induced carbonate prec

quaternary geochemical evolution of the salars of uyuni and coipasa central altiplano bolivia risacher f and fritz b i99 i quaternary geochemical evolution ofthe salars of uyuni and coipasa central altiplano bolivia chem geol 90 21 1 231 the central trough of the bolivian altiplano is occupied by two wide salt crusts the salar of uyuni which is probably the largest salt pan in the world 10 000 km and the salar of coipasa 2 500 km both crusts are essentially made of porous halite filled with an interstitial brine very rich in li k mg b up to 4 7 g l li 4 3 g l b 30 g l k and 75 g l mg lithium reserves are the highest known in the world around 9x io6 tons potassium magnesium and boron reserves in brines are also important around 194x io6 tons k 8x 10 tons b and 21 1 x io6 tons mg the cnists are the remnant of saline lake tauca 13 000 10 000 yr bp its salinity was estimated approximately at 80 g l its paleochemistry was derived in two ways 1 by dissolving the present amounts of all chemical components in the former lake volume and 2 by simulating the evaporation of the major inflows to the basin the resulting chemical compositions are quite different the dissolution derived one is 5 to 50 times less concentrated in li k mg b than the evaporation simulated ones however all compositions present the same na and ci contents this suggests either a removal of bittern salts or an enrichment of the former lake water in na and ci the most probable interpretation is that lake tauca redissolved a salt crust akin to that existing today several older lakes have been detected on the altiplano nevertheless such an explanation only pushes the problem back it is likely that the anomaly was transferred from one lake to an other three hypotheses may be put forward 1 bittern seepage through bottom sediments 2 uptake of the missing components by minerals and 3 leaching of ancient evaporites from the catchment area at the beginning of the lacustrine history of the basin the excess halite could have been recycled from lake to lake this latter process seems to be the most effective to explain the large excess of na and ci over the bittern solutes li k mg and b the occurrence of almost pure na ci saline springs flowing out from a gypsum diapir in the northern altiplano gives substantial support to this hypothesis

steep shelf stabilization of the coastal bransfield current linear stability analysis abstractin situ measurements obtained during the 2010 coupling cruise were analyzed in order to fully characterize the velocity structure of the coastal bransfield current an idealized two layer shallow water model was used to investigate the various instability processes of the realistic current along the coastal shelf particularly studied is how the topographic parameter to ratio between the shelf slope and the isopycnal slope of the surface current impacts the growth and the wavelength of the unstable perturbations for small bottom slopes when the evolution of the coastal current is controlled by the baroclinic instability the increase of the topographic parameter to yields a selection of smaller unstable wavelengths the growth rates increase with small values of to for larger values of to to 10 which is relevant for the coastal bransfield current the baroclinic instability is strongly dampened and the horizontal shear instability becomes the dominant one in this steep shelf regime the

evolution of a dune from crescentic to parabolic form in response to short term climatic changes rabjerg mile skagen odde denmark abstract rabjerg mile a complex parabolic dune reaches a height of 20 m above the deflation plain the width of the dune is 900 m and the length of the whole dune is 1500 m the dune is covered by 0 5 1 5 m high transverse dune ridges the dune has migrated approximately 1 km since 1887 a d accompanied by a change in the migration direction from ese 100 to ene 68 the morphology of rabjerg mile through the last 100 years is illustrated by a geographical information system arc info applied to a series of high quality topographical maps based on the digitized contour lines the evolution of rabjerg mile can be followed from an initial crescentic form in 1887 a d to a complex parabolic dune in this century dune dynamics and sites of erosion and deposition are evaluated from the digital terrain models changes in vegetation cover documented from the maps and air photos indicate that vegetation in the study area steadily increased with time calculations of resultant drift directions and gross bedform normal transport are based on climatic data from the skagen changed from an almost perfect transverse bedform 1887 1924 to an oblique imperfectly transverse bedform 1966 to present the bedform alignment followed the gross bedform normal transport rule in most years the evolution of a parabolic dune after 1924 is related to a period of reduced wind energy and increased vegetation cover this parabolic dune was maintained after 1960 when wind energy increased and the wind regime was more complex at the same time the dune became markedly asymmetric because of the frequent occurrence of strong southerly and easterly winds

propagation and growth of gulf stream meanders between 75 and 45 w abstract analysis of the gulf stream path between 75 and 60 w indicates that the spectral signature of propagating and standing meanders is qualitatively similar to that observed for the upstream region 74 70 w progressive retrogressive and standing meanders coexist at periods of several months and longer the amplitude dependent dispersion relation obtained for the region 75 45 w demonstrates the decrease of phase speed as the amplitude increases the dependence of phase speed on amplitude is found to be stronger than that on wavelength the average phase speed decreases with downstream distance primarily due to the downstream increase of meander amplitude consequently a relation between phase speed and wavelength for the region west of 70 w averaged over all amplitudes is not uniformly valid for a larger domain furthermore downstream propagating meander troughs are steeper and travel more slowly than meander crests the average stationary wavelength 700 800 km for 75 60 w is much shorter t

parabolic halite dunes on the salar de uyuni bolivia abstract palaeoenvironmental interpretation in desert and evaporitic sediments is often ambiguous consequently the recognition of primary sedimentary structures that indicate subaerial exposure or shallow marine conditions are therefore of crucial importance when interpreting marginal sedimentary evaporite facies parabolic halite dunes described here for the first time are observed on the salt crust of the largest salt flat in the world the salar de uyuni in bolivia the halite dunes are relatively small 0 7 1 3 m in width and length well defined lobate to hemicyclic parabolic dunes and are formed directly on the salt crust a model describing the formation and migration of the dunes in relation to brine level and climatic conditions is presented

rock physics diagnostic of north sea sands link between microstructure and seismic properties velocity in high porosity sands strongly depends on the position and amount of intergranular material velocity is high if the original grains are cemented at their contacts it is low if the pore filling material is placed away from the contacts the amount and type of intergranular material can be theoretically determined from velocity and porosity data by adjusting an effective medium theoretical model curve to a trend in the data and then assuming that the microstructure of the sediment is such as used in the model we apply this diagnostic method to clean sands in the heimdal formation the north sea the results show that the reservoir zone sand in one well under examination has slight contact cementation while it is completely uncemented and friable in another well this conclusion is supported by microscopic grain images the rock physics diagnostic is important for establishing a velocity porosity trend consistent with local geology such trends can improve the accuracy of porosity prediction from seismic data

late pleistocene climate and water budget of the south american altiplano abstract geomorphic evidence from the peruvian bolivian altiplano indicates that during episodes prior to 28 000 and around 12 500 11 000 yr b p lakes covered an area about six and four times as large as at present respectively within the constraints of the heat and water budget model calculations are used to estimate the precipitation rate that would allow hydrologic equilibrium on this basis it is suggested that rainfall on the altiplano during the episodes of enlarged lakes was respectively some 300 and 200 mm annum 1 larger than at present representing increases of about 75 and 50 respectively field evidence suggests that the episodes of enlarged lakes on the altiplano may have preceded or coincided with periods of maximum glaciation in the neigh boring andes in this region with high elevation of the ice equilibrium line increased precipitation is particularly conducive to glaciation

lake level chronology on the southern bolivian altiplano 18 23 s during late glacial time and the early holocene stratigraphic analyses of outcrops shorelines and diatoms from the southern bolivian altiplano uyuni coipasa basin reveal two major lacustrine phases during the late glacial period and the early holocene based on a chronology established by radiocarbon and u th control a comparison of14c and230th 234u ages shows that during times of high lake level radiocarbon ages are valid however during low water periods 14c ages must be corrected for a reservoir effect the lacustrine tauca phase started a little before 16 00014c yr b p and the lake level reached its maximum between 13 000 and 12 00014c yr b p a dry event ticana occurred after ca 12 000 and before 950014c yr b p a moderate lacustrine oscillation coipasa event occurred between ca 9500 and 850014c yr b p using a reservoir corrected conventional14c chronology comparisons between the lake level chronology in the uyuni coipasa basin and data from other southern tropical areas of south america suggest that the lacustrine evolution may reflect large scale climatic changes

experimental optimization of microbial induced carbonate precipitation for soil improvement abstractimplementation of laboratory tested biomediated soil improvement techniques in the field depends on upscaling the primary processes and controlling their rates microbial induced carbonate precipitation micp holds the potential for increasing the shear stiffness and reducing the hydraulic conductivity by harnessing a natural microbiological process that precipitates calcium carbonate the study presented herein focuses on controlling micp treatment of one dimensional flow half meter scale column experiments treatment was optimized by varying procedural parameters in five pairs of experiments including flow rates flow direction and formulations of biological and chemical amendments monitoring of column experiments included spatial and temporal measurements of the physical chemical and biological properties essential to the performance of micp including shear wave velocity permeability calcium carbonate content aqueous calcium aqueous ammonium aqueous urea and bacterial density rela

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

giant polygons in the triassic salt of cheshire england a thermal contraction model for their origin abstract the triassic salt in cheshire england has large polygonal patterns on bedding surfaces the polygons are bounded by deep v shaped fissures the fissures have a banded internal structure made up of individual units of pure secondary salt and clastic rich halite the salt was deposited from shallow brines in an arid environment a thermal contraction model is proposed here for the formation of the polygons calculations of the depth of penetration of thermal waves and the net contraction of salt beds indicate that annual temperature fluctuations would produce fissures of the observed depth and width it is suggested that thermal contraction is the most important factor in the initiation of all polygonal patterns on salt surfaces and that the polygon form that eventually develops is de endent on the thickness of the salt bed and the availability of brines to the salt surface

asymmetry of an equilibrated gulf stream type jet over topographic slope abstract the symmetry properties of the gulf stream type jet equilibrated over topographic slope are investigated in a series of idealized numerical experiments a baroclinically unstable zonal jet equilibrates over a sloping bottom through the process of potential vorticity pv homogenization underneath the main thermocline by the bottom intensified eddy activity associated with the stream meandering potential vorticity homogenization underneath the main thermocline leads to formation of recirculation gyres on both sides of the jet the magnitude of the northern recirculation gyre as measured by its westward transport is larger than the magnitude of the southern recirculation gyre this asymmetry in recirculations is shown to be the result of an asymmetric pv mixing underneath the thermocline produced by an asymmetric jet in particular the lateral shift of the velocity maximum near the surface relative to the velocity maximum at depth is shown to be responsible for the asymmetry the results are re

the mediterranean messinian salinity crisis an apennine foredeep perspective abstract owing to its expanded stratigraphic sections the apennine thrust belt offers the opportunity to better understand the evaporitic and post evaporitic messinian events a physical stratigraphic framework of messinian deposits based on facies analysis and basin wide correlation of key surfaces and sedimentary cycles is presented it is shown that the messinian apennine foredeep had marginal basins with shallow water primary evaporites and deeper basins where resedimented evaporites accumulated under relatively deep water conditions like many other mediterranean examples primary shallow water evaporites of apenninic marginal basins show evidence for subaerial exposure and erosion however the development of such an erosional surface does not correspond to the deposition of primary evaporites in the deepest part of the basin s here the unconformity can be traced towards the base of resedimented evaporites or to a level within them implying that the deeper basins of the apennine foredeep never underwent desiccation during the messinian salinity crisis but rather received the eroded marginal evaporites this fact usually overlooked raises important questions about the deep desiccation model of the mediterranean

the formation of oceanic eddies in symmetric and asymmetric jets part ii late time evolution and coherent vortex formation abstract the dynamical processes involved in eddy genesis evolution and demise as revealed in a series of high resolution numerical simulations of perturbed oceanic jets are investigated comparisons are provided between the simulated eddy life cycles and observations of gulf stream warm and cold core rings the dynamics of the meandering process in particular are analyzed in terms of the quasigeostrophic qg geopotential tendency equation the vertical motions that develop during eddy genesis are analyzed in terms of the contribution to the qg omega equation by the advection of temperature and differential vertical vorticity an examination of the cross stream flux of isentropic potential vorticity during warm core and cold core events emphasizes the role of the near field circulations associated with the baroclinic meanderings of the jet in the detachment and evolution of the simulated eddies comments are offered concerning the total heat transport by a ring alone as opposed to that effected by

a model to estimate the depositional brine depths of ancient halite rocks implications for ancient subaqueous evaporite depositional environments a model is derived which allows a more general approach to the interpretation of bromine profiles in halite rocks than is possible with the models of kuhn or holser allowing for an open system with influx and reflux reduces the depth of brine necessary to generate a given salt deposit even very small and regular bromine gradients which historically have been interpreted as the result of deposition from deep brine bodies can be generated in an open system from brine no more than a few tens of metres deep the bromine gradient produced from a given depth of brine is strongly dependent on the composition and amount of influx but less so on the composition of brine already in the basin a zechstein profile is analysed which in a closed basin would require brine 2665 m deep it can equally be modelled by influx of normal seawater which fully replenishes a basin no more than 140 m deep a somewhat irregular profile from the paradox basin instead of requiring a basin 100 400 m deep can be modelled as being produced by deposition from brines only 10 m deep reflux in both cases can only be a few per cent of influx at a maximum

late quaternary spatio temporal limnological variations in the altiplano of bolivia and peru abstract between the western and eastern andean cordilleras in peru and bolivia there are three main lacustrine basins lake titicaca lake poopo and the group of coipasa uyuni for the past few millennia highly variable environmental conditions have been recorded in their sediments today a latitudinal meteorological gradient influences the lakes status leading to specific deposits and ostracod communities lake titicaca in the north is oligohaline whereas lake poopo further south is polyhaline in the south the coipasa uyuni depression is characterized by a 12 000 km2 surficial salt crust during the late pleistocene ca 40 000 to 25 000 yr b p the water depth and salinity in paleolake poopo fluctuated widely and paleolake titicaca was slightly larger than at present sedimentation was mostly biocarbonate in the shallower areas and it was detrital organic in the deepest zones during the holocene a dry period transformed lake poopo into a salar with evaporite precipitation lake titicaca registered a large decline in water level 8100 3600 yr b p initially inducing gypsum precipitation followed by short influxes of water with an ostracod faunal composition similar to that of the modern brines of lake poopo lake titicacas present condition only appeared between 2200 and 1500 yr b p

enhancing the axial compression response of pervious concrete ground improvement piles using biogrouting abstractthis paper presents an innovative grouted ground improvement pile alternative biogrouted pervious concrete pile biogrouting is a potential ground improvement technique that utilizes soil bacteria to induce calcium carbonate caco3 precipitation to cement soil particles the most commonly investigated biogrouting method is microbial induced carbonate precipitation micp previous large scale applications of micp have encountered practical difficulties including bioclogging which results in a limited zone of cemented soil around injection points and heterogeneous distribution of caco3 the research presented in this paper focuses on evaluating the feasibility of micp biogrouting of a limited soil zone surrounding permeable piles to improve their responses when subjected to axial compression loading to investigate this two instrumented pervious concrete piles with diameters of 76 mm and lengths of 1 07 m with and without micp biogrouting were subjected to compression loading at the soil struc

influence of confinement and cementation level on the behavior of microbial induced calcite precipitated sands under monotonic drained loading abstractmicrobial induced calcite precipitation micp is a novel ground improvement method to increase strength and stiffness of sand using natural biogeochemical processes cementation level and confining pressure are two important factors that control the behavior of micp sand the monotonic mechanical response of micp cemented sand is systematically investigated using four cementation levels untreated lightly treated moderately treated and heavily treated and three levels of effective confining pressure 100 200 and 400 kpa the results indicate that the stiffness peak shear strength and dilation increases with an increase in calcite content at a given effective confining pressure and the dilation is suppressed with an increase in effective confining pressure this behavior is consistent with soil like behavior therefore all the micp soils presented herein are evaluated using critical state soil mechanics and not an analogous fracture mechanics framework the experimental results also indi

salinities and sediment transport in the bolivian highlands guyot j l roche m a noriega l calle h and quintanilla j 1990 salinities and sediment transport in the bolivian highlands j hydrol 113 147 162 salinities and sediment loads of the rivers of the entire interior drainage basin of the lake titicaca rio desaguadero lake poopo and salars as well as their evolution from upstream to downstream have been characterized on the basis of the results of four samplings during runoff periods on the other hand the regimes of dissolved and suspended matter transport are characterized with perioclic measurements and samplings at hydrometrical stations over several years the junction of lake poopo and the salar of coipasa since 1985 is noted which recalls that an unique terminal lake of large area existed during some parts of the quaternary mechanical and chemical erosion rates have been calculated for the basins that drain the western rio mauri and eastern rio suches cordilleras of the bolivian andes most of the sediment comes from the western cordillera with a mechanical erosion rate of 640 t kmz yr i for the basin of the rio mauri on the other hand lake titicaca is the main source of dissolvea matter to lake poopo via the rio desaguadero

the formation of oceanic eddies in symmetric and asymmetric jets part i early time evolution and bulk eddy transports abstract a numerical study of the life cycles of eddies formed in perturbed baroclinic jets emphasizing the influence of spanwise asymmetry in the initial structure of the jet on the downstream evolution of the flow is presented in particular attention is focused on the early time evolution of two such currents that are fully determined by their lateral vertical cross sections of streamwise velocity and balanced temperature fields the first jet profile is constructed so as to be representative of a typical observational cross section of the gulf stream off cape hatteras it therefore has laterally asymmetric baroclinicity and barotropy the second cross section consists of a jet with laterally symmetric velocity shear primitive equation nonseparable linear stability analyses of these two mean states are performed to determine the wavelengths phase speeds and growth rates of the fastest growing normal modes of temporal instability the life cycles of the eddies that develop on these jets are invest

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north

bedforms in salt deposits of the dead sea brines abstract study of salt deposits emphasizes the mineralogical and geochemical aspects of origin with but little attention to processes and features of physical sedimentation deposition from saturated brines along one of the main conveyance canals of the dead sea works near sedom southern israel indicates however that in open channel flow the halite sediment develops bedforms identical to those reported in alluvial channel deposits the conveyance canal is trapezoidal with side slopes of 1 2 bottom width of 17 m bankfull depth of 1 5 m and a gradient of 0 00022 design manning s n is 0 0223 decreasing to about 0 020 after deposition of the fine halite lining under normal operating conditions flow velocity is about 30 cm s and depth is about 1 m the conveyed brine with a densi y of 1 29 and viscosity of 5 cp is supersaturated with respect to halite and deposition of halite occurs aided by temperature fluctuations mixing and natural and pump induced turbulence the sediment consists of halite with minor amounts of carnallite and it is very poorly sorted a conventional interpretation of the grain size distribution is not applicable however since the finer fractions up to about 100 microns consist of single cube block or prism shaped crystals whereas the coarser material includes mainly porous and irregular clusters of crystals and larger ball like aggregates up to about 3 mm in diameter bedforms encountered along the canal include current crescents and shadows due to deformation of flow around obstacles such as bottom irregularities and salt l mps transverse linguoidal and catenary ripples and megaripples some of which may easily be mistaken for karrenlike products of solution mass transfer and for features of syneresis and longitudinal ridge patterns due to three dimensional systems of streamwise vortices the comparison of results of stokesian settling hindered settling and pipe flow of brines and of suspensions with different concentrations of solids indicates similar hydraulic behavior of salt brine and quartz water systems after adjustment for particle and fluid properties the observed bedforms fall into the same hydraulic factor fields as determined for bedforms in alluvial channels salt deposits therefore clearly belong to the wide group of chemical precipitates ranging from igneous rocks to industri l slurry deposits which record the process of mechanical transport and deposition

alternate interpretation of the messinian salinity crisis controversy resolved a high resolution chronology of the mediterranean messinian salinity crisis is proposed two types of evaporite deposition may be distinguished those in marginal areas vs those in basinal ones their diachroneity is deduced from the stratigraphic relationships linking these evaporites to a major messinian erosional surface a two step model is proposed for the evolution of the salinity crisis through time during the first phase from 5 75 to 5 60 ma the deposition of marginal evaporites took place in response to a modest sea level fall in the second interval from 5 60 to 5 32 ma the mediterranean basin became isolated during this later period the deposition of basinal evaporites and the cutting of the mediterranean canyons took place

saturn s northern hemisphere ribbon simulations and comparison with the meandering gulf stream voyager observations of saturn in 1980 81 discovered a wavy feature engirdling the planet at 47 n planetographic latitude its latitude coincides with that of an eastward jet stream which is the second fastest on saturn after the equatorial jet the 47 n jet s wavy morphology is unique among the known atmospheric jets on the gas giant planets since the voyagers it has been seen in every high resolution image of this latitude for over 25 years and has been termed the ribbon the ribbon has been interpreted as a dynamic instability in the jet stream this study tests this interpretation and uses forward modeling to explore the observed zonal wind profile s stability properties unforced initial value numerical experiments are performed to examine the nonlinear evolution of the jet stream parameter variations show that an instability occurs when the 47 n jet causes reversals in the potential vorticity pv gradient which constitutes a violation of the charney stern stability criterion after the initial instability development the simulations demonstrate that the instability s amplitude nonlinearly saturates to a constant when the eddy generation by the instability is balanced by the destruction of the eddies when the instability saturates the zonal wind profile approaches neutral stability according to arnol d s second criterion and the jet s path meanders in a ribbon like manner it is demonstrated that the meandering of the 47 n jet occurs over a range of tropospheric static stability and background wind speed the results here show that a nonlinearly saturated shear instability in the 47 n jet is a viable mechanism to produce the ribbon morphology observations do not yet have the temporal coverage to confirm the creation and destruction of eddies but these simulations predict that this is actively occurring in the ribbon region similarities exist between the behaviors found in this model and the dynamics of pv fronts studied in the context of meandering western boundary currents in earth s oceans in addition the simulations capture the nonlinear aspects of a new feature discovered by the cassini visual and infrared mapping spectrometer vims the string of pearls which resides in the equatorward tip of the 47 n jet the explicit planetary isentropic coordinate epic model is used herein

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

meanders and detached eddies of a strong eastward flowing jet using a two layer quasi geostrophic model abstract the process of meander growth on and eddy detachment from an eastward flowing oceanic jet which is modeled after the gulf stream east of cape hatteras is studied using numerical solutions of nonlinear equations the equations express potential vorticity conservation in a two layer quasi geostrophic model with a weak planetary effect solutions are restricted to a spatially periodic temporally growing case initially small amplitude meanders are given being superimposed on the jet the solutions describe a process in which the meanders grow increasingly larger the larger meanders are cut off and cyclonic and anticyclonic eddies are detached southward and northward respectively concurrent with the eddy detachment an eastward flow is restored in the upper layer and the lower layer develops an eastward flow under the restored jet and two westward flows north and south of it a baroclinic instability is very effective in meander growth while a weak effect is necessary for eddy detachme

halite depositional facies in a solar salt pond a key to interpreting physical energy and water depth in ancient deposits subaqueous deposits of aragonite gypsum and halite are accumulating in shallow solar salt ponds constructed in the pekelmeer a sea level salina on bonaire netherlands antilles several halite facies are deposited in the crystallizer ponds in response to difference in water depth and wave energy cumulate halite which originates as floating rafts is present only along the protected upwind margins of ponds where low energy conditions foster their formation and preservation cornet crystals with peculiar mushroom and mortarboard shaped caps precipitate in centimetre deep brine sheets within a couple of metres of the upwind or low energy margins downwind from these margins cornet and chevron halite precipitate on the pond floors in water depths ranging from a few centimetres to approximately 60 cm halite pisoids with radial concentric structure are precipitated in the swash zone along downwind high energy shorelines where they form pebbly beaches this study suggests that primary halite facies are energy and or depth dependent and that some primary features if preserved in ancient halite deposits can be used to infer physical energy conditions subenvironments such as low to high energy shorelines and extremely shallow water depths in ancient evaporite basins

potential vorticity structure across the gulf stream observations and a pv gradient model abstract potential vorticity pv structure across a baroclinic front is a property that determines the stability characteristics of that front cross frontal exchange and the behavior of the vortical waves that this front enables hence there has been much interest in estimating pv across the gulf stream gs however pv estimations have typically encountered two problems the horizontal resolution of sampling has been inadequate and noise in measurements gets amplified by differentiation when estimating pv this paper s approach addresses both of these problems the authors have used a unique set of highly resolved simultaneous density and direct velocity measurements across the gulf stream first to calculate the pv structure and then to obtain its idealization within density layers using a pv gradient pvg model the pvg model inverts an input pv in layers to determine the isopycnal depths and velocities in isopycnal layers by comparing the observed and pvg modeled velocities and isopycnal posi

downstream development of the gulf stream from 68 to 55 w abstract two ctd sections across the gulf stream at 68 and 55 w were acquired in late march of 1988 within 11 days of one another as part of an effort to look at downstream changes in the current using complementary current meter measurements sections of total barotropic and geostrophic baroclinic velocity are constructed and used to calculate transport in potential density classes potential vorticity sections are presented for both locations including the effects of planetary stretching and relative vorticity the data are also used to examine the core properties of recently formed 18 water at the two sections it is found that 1 water parcels in the exposed surface layers experience downstream density and potential vorticity changes consistent with surface forcing 2 thermocline gulf stream transport is conserved downstream and below the exposed layers is conserved within individual density classes 3 subthermocline gulf stream transport increases modestly at levels above the sill depth of th

a geological numerical model for paleozoic global evaporite deposition a geologically driven model for evaporative deposition of marine sulfate and other sulfur fluxes roughly reproduces the observed stratigraphic record of paleozoic global evaporite depositional rates and the observed delta 34 s age curve erosional and depositional fluxes in this model are controlled by areas available for erosion and deposition which are in turn controlled by sea level global hypsography and plate tectonic movement of the continents through low latitude evaporite belts sea level also provides the record of seafloor spreading rates needed to determine fluxes at mid ocean ridges the success of this geologically driven model as opposed to geochemical models dependent on isotopic compositions or reservoir contents to determine fluxes suggests the possibility of modeling fluxes of elements that have no useful isotopic record it also suggests that variability of the stratigraphic record of evaporite deposition is not entirely the result of accidents of erosion and preservation bu

feature modeling approach to simulating loop current frontal eddies abstract loop current frontal eddies lcfe in the gulf of mexico are simulated with a regional configuration of the princeton ocean model using a feature oriented initialization technique the initialization procedure is based on a prior investigation of stability characteristics of the loop current lc zonal channel experiments conducted with a multi layer intermediate equations model allowed to identify conditions necessary for formation and growth of frontal eddies the simulations were able to reproduce key features of lcfe topography interaction in the desoto canyon region observed during the eddy intrusion study

quantifying level of microbial induced cementation for cyclically loaded sand abstractmicrobial induced calcite precipitation micp is a novel soil improvement technique that improves the behavior of sands subjected to dynamic loading the level of cementation of micp treat

mechanical behavior of sands treated by microbially induced carbonate precipitation abstractthe mechanical behavior of sands treated using microbially induced carbonate precipitation micp has been investigated at the macroscale and the microscale triaxial and confined compression tests with embedded shear and compression wave s wave and p wave sensors were conducted on two micp treated sands ottawa 50 70 and 20 30 silica sands triaxial compression tests were conducted at three different confining pressures 25 50 and 100 kpa tests were also performed at calcium chloride cacl2 concentrations of 0 1 and 0 3 m resulting in specimens with average calcium carbonate caco3 content ranging from 1 5 to 2 5 for the 50 70 sand and from 1 to 1 6 for the 20 30 sand in contrast to previous research the results of triaxial tests presented in this paper show an increase of the soil strength even at 1 calcium carbonate content after the tests samples taken from the specimens were utilized to measure the caco3 content and to perform analysis using scanning electron microscopy sem

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

cross shelf and out of bay transport driven by an open ocean current abstractthis paper studies the interaction of an antarctic circumpolar current acc like wind driven channel flow with a continental slope and a flat bottomed bay shaped shelf near the channel s southern boundary interaction between the model acc and the topography in the second layer induces local changes of the potential vorticity pv flux which further causes the formation of a first layer pv front near the base of the topography located between the acc and the first layer slope the newly formed pv front is constantly perturbed by the acc and in turn forces the first layer slope with its own variability in an intermittent but persistent way the volume transport of the slope water across the first layer slope edge is mostly directly driven by eddies and meanders of the new front and its magnitude is similar to the maximum ekman transport in the channel near the bay s opening the effect of the topographic waves excited by offshore variability dominates the cross isobath exchange and induces a

instability of baroclinic flows with horizontal shear along topography abstract the stability of baroclinic flows with horizontal shear over sloping topography is analyzed with special emphasis on the structure and energetics of the unstable perturbatiorts the study is conducted by using a linearized two layer quasi geostrophic channel model for different topography profiles and distributions of the basic velocity field interactions between the two fluid layers and the energy conversions by the unstable porturbations are described it is found that topography sloping as opposed to the fluid interface contributes to enhance the perturbation amplitude in the upper lower layer relative to the lower upper layer the results for bottom topography with dithering characteristics across the flow indicate pronounced localized effects on the energy conversions over the slopes and the meridional scale of the perturbations in the lower layer

bromine geochemistry of salar de uyuni and deeper salt crusts central altiplano bolivia abstract the salar of uyuni in the central bolivian altiplano is probably the largest salt pan in the world 10 000 km 2 a 121 m deep well drilled in the central salar disclosed a complex evaporitic sequence of 12 salt crusts separated by 11 mud layers in the lower half of the profile thick halite beds alternate with thin mud layers the mud layers thicken upwards and show clear lacustrine features the thickness of the salt beds decreases markedly from the base upward the bromine content of the halite ranges from 1 3 to 10 4 mg kg the halite does not originate from the evaporation of the dilute inflow waters of the altiplano which would lead to br content of tens of mg kg the presence of halite of very low br content 2 mg kg in a gypsum diapir strongly suggests that most of the halite deposited at uyuni originated from the leaching of ancient salt formations associated with the numerous gypsum diapirs of the altiplano the deep and thick halite beds were probably deposited in a playa lake as suggested by their very low and fairly constant br content 1 6 2 3 mg kg and by the abundance of detrital minerals thereafter perennial salt lakes of increasing duration flooded the central altiplano increasing amounts of dilute inflow waters of low cl br ratio and the exhaustion of diapiric halite lead to an increase of both the thickness of the lacustrine layers and of the bromine content of the salt crusts 5 10 mg kg deposited as the lakes dried up paleolake levels in the central altiplano rose as those in the northern altiplano the titicaca basin were simultaneously falling the progressive fluvial erosion of the threshold between the northern and the central altiplano lowered the levels of the northern lakes and allowed more dilute waters of low cl br ratio to flood the central altiplano therefore both the thickness of lacustrine sediments and the bromine content of the salt crust increased to the present the three upper crusts show a decrease in bromine content which may reflect a recent modification of the inflow regime to the last lakes the salt crust deposited by the last salt lake 10 000 years ago shows a bromine distribution that unexpectedly increases with depth as the lake dried the salt crust was probably initialy distributed over a wider area than the present flat crust covering the topographic surface up to the level of the lake where halite reached saturation the dissolution of the initial salt of low br content from the margins of the lake to the center is probably responsible for the observed br distribution in the surface salt as in a playa during the holocene a severe drought hit the altiplano and drastically lowered the intracrustal brine table within the salt crust leaving a thin layer of high concentrated residual brine at the bottom of the crust bromine rich halite replaced primary halite by a temperature activated mechanism in the lower crust further increasing the br gradient with depth

sedimentology and development of parabolic dunes grande prairie dune field alberta the grande prairie dune field in northwest central alberta is composed of parabolic and dome dunes presently inactive but which had developed under westerly winds two parabolic dune types are rec