land ice elevation changes from photon counting swath altimetry first applications over the antarctic ice sheet satellite altimetric time series allow high precision monitoring of ice sheet mass balance understanding elevation changes in these regions is important because outlet glaciers along ice sheet margins are critical in controlling flow of inland ice here we discuss a new airborne altimetry dataset collected as part of the icecap international collaborative exploration of the cryosphere by airborne profiling project over east antarctica using the alamo airborne laser altimeter with mapping optics system of a scanning photon counting lidar combined with a laser altimeter we extend the 2003 09 surface elevation record of nasa s icesat satellite by determining cross track slope and thus independently correcting for icesat s cross track pointing errors in areas of high slope cross track errors result in measured elevation change that combines surface slope and the actual z t signal slope corrections are particularly important in coastal ice streams which often exhibit both rapidly changing elevations and high surface slopes as a test case assuming that surface slopes do not change significantly we observe a lack of ice dynamic change at cook ice shelf while significant thinning occurred at totten and denman glaciers during 2003 09

a decade of progress in observing and modelling antarctic subglacial water systems in the decade since the discovery of active antarctic subglacial water systems by detection of subtle surface displacements much progress has been made in our understanding of these dynamic systems here we present some of the key results of observations derived from icesat laser altimetry cryosat 2 radar altimetry operation icebridge airborne laser altimetry satellite image differencing and ground based continuous global positioning system gps experiments deployed in hydrologically active regions these observations provide us with an increased understanding of various lake systems in antarctica whillans mercer ice streams crane glacier recovery ice stream byrd glacier and eastern wilkes land in several cases subglacial water systems are shown to control ice flux through the glacier system for some lake systems we have been able to construct more than a decade of continuous lake activity revealing internal variability on time scales ranging from days to years this variability indicates that continuous accurate time series of altimetry data are critical to understanding these systems on whillans ice stream our results from a 5 year continuous gps record demonstrate that subglacial lake flood events significantly change the regional ice dynamics we also show how models for subglacial water flow have evolved since the availability of observations of lake volume change from regional scale models of water routeing to process models of channels carved into the subglacial sediment instead of the overlying ice we show that progress in understanding the processes governing lake drainage now allows us to create simulated lake volume time series that reproduce time series from satellite observations this transformational decade in antarctic subglacial water research has moved us significantly closer to understanding the processes of water transfer sufficiently for inclusion in continental scale ice sheet models

potential for travertine formation fossil creek arizona abstract chemical analyses of water emanating from fossil springs in central arizona were conducted to predict changes in travertine deposition related to changes in stream discharge caused by diversion for hydroelectric power generation during spring of 1996 water was sampled at 15 locations during normal seepage flow in a 6 7 km reach below fossil springs and at full baseflow during turbine maintenance analyses resulted in a rate of 11 923 kg d 1 of caco3 precipitated from 1218 l s 1 of water emanating from the springs while flows of 5 6 l s 1 that seep past a diversion dam produced 46 kg d 1 of caco3 precipitation active travertine dams currently occur predominantly below the irving hydroelectric powerplant with partial return of diverted flow back into the natural channel the lower reach resulted in 519 kg d 1 of caco3 precipitated from the return of 56 6 l s 1 with a reduced rate of precipitation during surface runoff conditions due to a dilution effect artificial substrates were located at sites in the lower reach for comparison with mass transfer rates derived from changes in water chemistry comparison between actual precipitation rates and overall mass transfer rates suggested preferential deposition was occurring at dam locations rates of mass transfer for high flow were greater than lower flow overall mass transfer rates for the upper reach were proportional to the flow velocities with total mass transfers for both flows being approximately equal

upscale impact of mesoscale disturbances of tropical convection on 2 day waves abstractwestward propagating 2 day waves with embedded mesoscale disturbances contribute a large portion of synoptic variability of tropical convection over the western pacific it is of crucial im

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

stratigraphy and geologic history of pennsylvanian and permian rocks mogollon rim region central arizona and vicinity stratigraphic paleontologic sedimentologic and petrographic data are used to construct a revised system of correlation and stratigraphic nomenclature for pennsylvanian and permian rocks of central and northern arizona and adjacent regions the resulting scheme emphasizes major tectonic and depositional events but also provides for recognition of local to regional minor events by recognizing stratigraphic spikes in the rock record and combining these with available biostratigraphic data regional correlation is established in spite of a sparsity of fossils complex cyclic lithologic units abrupt facies changes sporadic subsurface data and drastic differences in quality and extent of outcrops highlights of the proposed correlation and nomenclature include the following 1 differentiation of supai and naco formations and restriction of use of the term supai 2 correlation of the supai group and the hermit formation into the western part of central arizona as far east as sedona 3 formal definition of a new stratigraphic unit the schnebly hill formation and several formal members 4 correlation of pennsylvanian and permian strata of the grand canyon and defiance plateau with rocks in central arizona mogollon rim and adjacent areas with a clearer concept of stratigraphy and nomenclature the resulting sedimentologic and tectonic history of the region can be deciphered the resulting interpretation of geologic history provides a foundation for relating tectonic and sedimentologic events of the colorado plateau to the evolution of southwestern north america

orographic influence on the synoptic scale circulations associated with the genesis of hurricane guillermo 1991 abstract the early stages of tropical cyclogenesis in the eastern pacific ocean are investigated in this case study which is focused on the development of the initial circulation that eventually intensified into hurricane guillermo 1991 the authors document the synoptic and mesoscale winds from upper air soundings satellite imagery and a gridded analysis in addition flight level observations taken during the tropical experiment in mexico are used these winds reveal that prior to the formation of the tropical cyclone an easterly wave moved over the caribbean sea and that the initial circulation developed while the easterly wave was located over the central caribbean east of the mountains in central america numerical simulations with the pennsylvania state university national center for atmospheric research mesoscale model are used to examine the details of the structure of the flow that resulted in the formation of the eastern pacific circulation in these simulations the model is initialized

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

intrinsic and extrinsic controls of spatial and temporal variations in modern fluvial tufa sedimentation a thirteen year record from a semi arid environment sedimentological and hydrochemical parameters of the river piedra north east spain were monitored every six months from 1999 to 2012 at 24 sites at which tablets were installed all along the river the river water is of hco3 so4 ca type and is notably influenced by inputs from upstream karstic springs tufa deposition was first detected 8 km downstream of these springs and greatly increased from there primarily along the steeper stretch i e within the monasterio de piedra natural park then deposition decreased through the most downstream stretch with smaller ground water inputs the spatial evolution of the tufa thickness with parallel variations of pwp plummer wigley parkhurst rates was thus determined by the river water pco2 which was controlled by ground water inputs and by the river bed slope five fluvial subenvironments and seven sedimentary facies were characterized the water flow conditions are the primary factor responsible for the distinct deposition rates of facies mainly through co2 outgassing stromatolites and moss tufa and alga tufa had the highest rates whereas loose tufa formed in slow flowing water and tufa of spray areas had thinner deposition a six month pattern in the deposition rate was detected through thickness measurements that pattern was parallel to the seasonal pwp rates the increased deposition during warm periods spring and summer mean 5 08 mm compared with cool periods autumn and winter mean 2 77 mm is linked chiefly to temperature which controlled the seasonal changes in the physico chemical and biological processes this finding is supported by a principal components analysis seasonal variations of insolation and day duration also contributed to such a deposition pattern large discharge events which provoked erosion of tufa deposits and dilution of water caused the reversal of the seasonal deposition rate pattern stromatolites are likely to preserve the most complete sedimentary record although tufas are a potentially sensitive record of climate related parameters erosion is an intrinsic process that may overwhelm the effects of such parameters this issue should be considered in palaeoclimatic studies based on the tufa record particularly in semi arid conditions

investigating the stability of subglacial lakes with a full stokes ice sheet model despite the large amount of subglacial lakes present underneath the east antarctic ice sheet and the melt processes involved the hydrology beneath the ice sheet is poorly understood changes in subglacial potential gradients may lead to subglacial lake outbursts discharging excess water through a subglacial drainage system underneath the ice sheet such processes can eventually lead to an increase in ice flow in this paper a full stokes numerical ice sheet model was employed which takes into account the ice flow over subglacial water bodies in hydrostatic equilibrium with the overlying ice sensitivity experiments were carried out for small perturbations in ice flow and basal melt rate as a function of ice thickness general surface slope ice viscosity and lake size in order to investigate their influence on the subglacial potential gradient and the impact on subglacial lake drainage experiments clearly demonstrate that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events lake drainage can therefore be regarded as a common feature of the subglacial hydrological system and may influence to a large extent the present and future behavior of large ice sheets

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

a decade of west antarctic subglacial lake interactions from combined icesat and cryosat 2 altimetry we use cryosat 2 interferometric satellite radar altimetry over the mercer and whillans ice streams west antarctica to derive surface elevation changes due to subglacial lake activity at monthly resolution for the period 2010 to 2013 we validate cryosat 2 elevation measurements trends and spatial patterns of change using satellite image differencing and in situ vertical movement from global positioning system gps data two subglacial lake discharge events occur in the same subglacial hydrological catchment within a 9 month period using gps measurements that are spanning the gap between the ice cloud and land elevation satellite and cryosat 2 missions we cross calibrate the two missions to establish the efficacy of cryosat 2 altimetry to measure dynamic changes on the ice sheets

increased flow speed on a large east antarctic outlet glacier caused by subglacial floods large ice streams and outlet glaciers drain greenland and antarctica an observed acceleration of ice velocity in one of these outlet glaciers byrd glacier east antarctica coincides with a large water discharge from two subglacial lakes allowing direct attribution of the change in glacier dynamics to the water drainage network beneath the ice

oscillations of the intertropical convergence zone and the genesis of easterly waves part ii numerical verification a companion paper part i toma and webster 2008 argued that the characteristics of the mean intertropical convergence zone itcz arise from instabilities associated with the strong cross equatorial pressure gradient cepg that exists in the eastern pacific ocean as a result of the latitudinal sea surface temperature sst gradient furthermore it was argued that instabilities of the mean itcz resulted in the in situ development of easterly waves thus in part i it was hypothesized that the mean and transient state of eastern pacific convection was due to local processes and less so to the advection of waves from the north atlantic ocean to test this hypothesis and at the same time consider others such as a possible role of the equatorial and subtropical orography in generating local instabilities a series of controlled numerical experiments are designed using the wrf regional model the domain of the model was configured to include the western atlantic ocean the isthmus of panama and the eastern pacific ocean to 155 w lateral boundaries were set at 40 n and 40 s thus containing the mountains of central america the andes and the sierra madre of mexico in a series of experiments analysis products were used as boundary conditions that were successively updated four times per day set as 10 day running average fields or as running mean monthly fields finally the model was run with topography essentially eliminated over the land areas although there are differences between the details of the resultant fields the location of mean convection and the form of the transients remain the same it is concluded in support of the theoretical and diagnostic studies of part i that orographic forcing or waves generated in the north atlantic ocean are not the major causes of the mean and transient nature of disturbances in the eastern pacific

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

the interaction of easterly waves orography and the intertropical convergence zone in the genesis of eastern pacific tropical cyclones the interaction of an idealized easterly wave with an orographic feature representing the sierra madre of mexico and a large scale meridionally sheared zonal flow representing the itcz in the eastern north pacific is examined through numerical integration of the shallow water equations on an equatorial beta plane channel the model simulations show that as a wave approaches the orography from the east the relative vorticity in the lee increases due to the wave being modified by the orography this relative vorticity maximum increases the northward advection of the itcz in the lee of the mountain that occurs due to the influence of the mountain anticyclone the result of this interaction is the development of a localized region of enhanced cyclonic vorticity that moves parallel to the contours of the model orography there is a minimal increase in the amplitude of the vorticity occuring during interactions between the wave and orography itcz and orography and wave and itcz the position of the incident wave upstream of the orography at the time that the disturbance in the lee begins to develop and the subsequent motion of the leeside vorticity maximum are in agreement with an observed case of eastern pacific tropical cyclogenesis which is also presented

drainage networks lakes and water fluxes beneath the antarctic ice sheet antarctica bedmap2 datasets are used to calculate subglacial hydraulic potential and the area depth and volume of hydraulic potential sinks there are over 32 000 contiguous sinks which can be thought of as predicted lakes patterns of subglacial melt are modelled with a balanced ice flux flow model and water fluxes are cumulated along predicted flow pathways to quantify steady state fluxes from the main basin outlets and from known subglacial lakes the total flux from the continent is 21 km3 a 1 byrd glacier has the greatest basin flux of 2 7 km3 a 1 fluxes from subglacial lakes range from 1 10 4 to 1 5 km3 a 1 lake turnover times are calculated from their volumes and fluxes and have median values of 100 a for known active lakes and 500 a for other lakes recurrence intervals of a 0 25 km3 flood range from 2 months to 2000 a median 130 a for known active lakes and from 2 to 2400 a median 360 a for other lakes thus several lakes that have recently been observed to fill and drain may not do so again for many centuries and several lakes that have not so far been observed to fill and drain have the potential to do so even at annual to decadal timescales

itcz breakdown and its upscale impact on the planetary scale circulation over the eastern pacific abstractthe eastern pacific ep intertropical convergence zone itcz is sometimes observed to break down into several vortices on the synoptic time scale it is still a challenge for present day numerical models to simulate the itcz breakdown in the baroclinic modes also the upscale impact of the associated mesoscale fluctuations on the planetary scale circulation is not well understood here a simplified multiscale model for the modulation of the itcz is used to study these issues a prescribed two scale heating drives the planetary scale circulation through both planetary scale mean heating and eddy flux divergence of zonal momentum where the latter represents the upscale impact of mesoscale disturbances in an idealized scenario where the heating only varies on the mesoscale key features of the itcz breakdown in the baroclinic modes are captured the eddy flux divergence of zonal momentum is characterized by midlevel low level eastward westward momentum forcing at subtropical latitudes of th

the age and origin of the labyrinth western dry valleys antarctica evidence for extensive middle miocene subglacial floods and freshwater discharge to the southern ocean a 50 km long network of bedrock channels and scoured terrain occupies the ice free portion of a major trough that crosses the transantarctic mountains in southern victoria land the channels collectively termed the labyrinth emerge from beneath the margin of the east antarctic ice sheet wright upper glacier and are incised into a 300 m thick sill of ferrar dolerite at the head of wright valley upper and intermediate elevation erosion surfaces of the labyrinth exhibit striations and molding characteristic of glacial erosion channels and canyons on the lower surface are as much as 600 m wide and 250 m deep have longitudinal profiles with many reverse gradients and contain potholes 35 m deep at tributary junctions these characteristics are most consistent with incision from fast flowing subglacial meltwater estimated discharge is on the order of 1 6 2 2 10 6 m 3 s 1 our 40 ar 39 ar analyses of volcanic tephra from the labyrinth show that the chan nels are relict that major channel incision predates 12 4 ma and that the last major subglacial flood occurred sometime between 14 4 ma and 12 4 ma the most plausible origin for the labyrinth is erosion associated with episodic drainage of subglacial lakes in east antarctica one compelling possibility is that discharge of large volumes of sub glacial meltwater to the southern ocean and to the ross sea in particular may have coincided with and contributed to oscillations in regional and or global climate during the middle miocene

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

ice sheet elevations from across track processing of airborne interferometric radar altimetry 1 interferometric radar altimeters ira s use dual receive antennas to overcome one of the spatial limitations of pulse limited altimeters in a conventional ira measurement the range and across track direction of a scatterer are determined using the phase difference between the antennas we demonstrate a method of determining multiple elevation points across a swath orthogonal to the instrument ground track in regions of steep terrain such as ice sheet margins we use data from an airborne ira a prototype of the cryosat 2 instrument and compare the results to simultaneous airborne laser scanner als observations this application results in a 75 fold increase in measurement density compared to conventional radar altimetry along a 2 5 km ground track the rms departure between the ira and als derived measurements was 1 67 m based on our result although our approach is limited to areas of relatively steep slope a 25 to 75 fold increase in elevation measurements could be achieved in coastal regions of antarctica and greenland with similar processing of cryosat 2 data

influence of the madden julian oscillation and caribbean low level jet on east pacific easterly wave dynamics abstractthe east pacific warm pool exhibits basic state variability associated with the madden julian oscillation mjo and caribbean low level jet cllj which affects the development of easterly waves ews this study compares and contrasts composite changes in the background environment eddy kinetic energy eke budgets and ew tracks during mjo and cllj events while previous studies have shown that the mjo influences jet activity in the east pacific the influence of the mjo and cllj on the east pacific and ews is not synonymous the cllj is a stronger modulator of the itcz than the mjo while the mjo has a more expansive influence on the northeastern portion of the basin anomalous low level westerly mjo and cllj periods are associated with favorable conditions for ew development paralleling the central american coast contrary to previous findings about the relationship of the cllj to ews easterly mjo and cllj periods support enhanced itcz ew development although the cllj is a greater modulato

four years of tropical era 40 vorticity maxima tracks part i climatology and vertical vorticity structure abstract using the 40 yr european centre for medium range weather forecasts re analysis era 40 vorticity maxima vm have been manually tracked and classified as developing and nondeveloping the vm are identified on hovmoller plots for june october 1998 2001 within 0 35 n 140 10 w over 600 low level and midlevel vm are tracked the era 40 vm track climatology compares favorably with previous knowledge about easterly waves some new results have also been found the vm are not equivalent to easterly waves so it is important to distinguish between the large scale wave and the embedded vm unlike waves individual vm leaving africa generally do not survive to cross the entire atlantic unlike waves which can cross central america most individual east pacific vm originate in the east pacific genesis productivity is defined as the fraction of nontropical cyclone vm that eventually develop it reaches 50 in the eastern north pacific epac and 30 in the atlantic where there is geographical separ

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

an improved real time global sea surface temperature analysis abstract the monthly global sea surface temperature sst analysis of reynolds using real time in situ and satellite sst data has now been improved by using sea ice data to simulate ssts in ice covered regions the simulated ssts now become the external boundary condition for the analysis solution this technique eliminates any high latitude satellite biases and extends the analysis to the ice edge the analysis with the ice data has been computed for the period january 1982 to present

oscillations of the intertropical convergence zone and the genesis of easterly waves part i diagnostics and theory we examine the mean and transient state of the intertropical convergence zone itcz by analyzing data and using simple theory we concentrate on the tropical eastern pacific ocean noting that there exists in this region a well developed mean itcz furthermore it is a region where there has been considerable discussion in the literature of whether easterly waves develop in situ or propagate westwards from the atlantic ocean the region is typical of tropical regions where there is a strong cross equatorial pressure gradient cepg mean convection well removed from the equator but located equatorward of the maximum sea surface temperature sst and minimum sea level pressure mslp further to the west near the dateline where the cepg is much smaller convection is weaker and collocated with sst and mslp extrema it is argued that in regions of significant cepg that the near equatorial tropical system is inertially unstable and that the rectification of the instability for a given cepg determines the location and intensity of the climatological itcz using simple theoretical arguments we develop an expression for the mean latitude of the itcz as a function of the cepg we note on a day by day basis that the itcz is highly transient state with variability occurring on 3 8 day time scales transients with amplitudes about half of the mean itcz propagate northwards from the near equatorial southern hemisphere as anomalous meridional oscillations eventually amplifying convection in the vicinity of the mean itcz it is argued that in these longitudes of strong cepg the mean itcz is continually inertially unstable with advections of anticylonic vorticity across the equator resulting in the creation of an oscillating divergence convergence doublet the low level convergence produces convection and the resultant vortex tube stretching generates cyclonic vorticity which counteracts the northward advection of anticylonic vorticity during a cycle the mid troposphere heating near 10on oscillates between 6 and 12 k day at the inertial frequency of the latitude of the mean convection as a result there exists an anomalous and shallower oscillating meridional circulation with a magnitude about 50 of the mean itcz associated with the stable state following the generation of anticylonic vorticity further it is argued that the instabilities of the itcz are directly associated with in situ development of easterly waves which occur with the inertial period of the latitude of the mean itcz the dynamical sequences and the genesis of easterly waves are absent in the regions further to the east where the cepg is much weaker or absent altogether in a companion study part ii numerical experiments are conducted to test the hypothesis raised in the present study

active lakes of recovery ice stream east antarctica a bedrock controlled subglacial hydrological system a connected system of active subglacial lakes was revealed beneath recovery ice stream east antarctica by icesat laser altimetry here we combine repeat track analysis of icesat 2003 09 operation icebridge laser altimetry and radio echo sounding 2011 and 2012 and modis image differencing 2009 2011 to learn more about the lake activity history the surface and bedrock topographic setting of the lakes and the constraints on water flow through the system we extend the lake activity time series to 2012 for the three lower lakes and capture twomajor lake drainages one lake underwent a large deflation between 2009 and 2011 while another lake which had been continuously filling between 2003 and 2010 started to drain after 2011 most of the active lakes are located in a 1000 km long bedrock trough under the main trunk of recovery ice stream whose base is 1500 2000 m below present day sea level the hydrologic system beneath recovery ice stream is controlled by this unusually pronounced bedrock topography in contrast to most antarctic systems studied to date which are controlled by the ice surface topography hydrologic connections among the lakes appear to be direct and responsive and we reproduce the lake activity using a simple subglacial water model we discuss potential causes of non steady hydrologic behavior in major antarctic catchments

calibration of the cryosat 2 interferometer and measurement of across track ocean slope this paper describes the calibration of the cryosat 2 interferometer whose principal purpose is to accurately measure the height of the antarctic and greenland ice sheets a sequence of cryosat 2 data acquisitions over the tropical and midlatitude oceans were obtained between june and september 2010 from the siral a and redundant siral b radars operating in their sarin mode during a sequence of satellite rolls between 0 6 and 0 4 using the arrival angle of the echo relative to the interferometer baseline the attitude of the satellite determined by the star trackers and estimates of the ocean surface across track slope from the egm08 geoid we determined the errors in the interferometer estimate of surface slope as functions of the roll angle and ocean surface waveheight these were found to be in close agreement with the theoretical description the scale factor of the interferometric measurement of angle was determined to be 0 973 0 002 we estimate the accuracy of the across track slope measurement of the interferometer by applying this scale factor to the measured phase in applying this scale factor to the measurements the across track slope of the marine geoid was obtained with an accuracy of 26 rad at 10 km and 10 rad at 1000 km we conclude that the instrument performance considerably exceeds that needed for the accurate determination of height over the sloping surfaces of the continental ice sheets the results also demonstrate that cryosat 2 provides the first observations of the instantaneous vector gradient of the ocean surface and that the normal incidence interferometric configuration has a greater potential for the measurement of the ocean across track slope than has been previously recognized

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

shallow meridional circulation in the tropical eastern pacific abstract based on four independent datasets this study presents observational evidence of a shallow meridional circulation cell in the eastern tropical pacific in this shallow meridional circulation cell the northerly cross equatorial return flow from the itcz into the southern hemisphere is found immediately above the atmospheric boundary layer in contrast to the classic concept of the hadley type deep meridional circulation whose northerly return flow resides in the upper troposphere the strength and depth of this shallow meridional circulation undergo a distinct annual cycle possible causes and climatic implications of this shallow meridional circulation are discussed

calcite supersaturation and precipitation kinetics in the lower colorado river all american canal and east highline canal in situ ph determinations and analysis of major ions in solution indicated that the lower colorado river is supersaturated with respect to calcite throughout the entire daily cycle in both winter and summer although the ion activity product was 4 to 6 times greater than the calcite solubility product there was no detectable precipitation chemical analyses of water samples taken along 350 km of the river and canals from parker dam to the salton sea also revealed no evidence of calcium carbonate precipitation despite the inflow of saline and highly supersaturated irrigation return flows laboratory kinetic studies indicated that calcite crystal growth rates with colorado river water are about 30 of the rate for pure ca hco3 waters and about 70 of that for synthetic colorado river water calcite precipitation by crystal growth in the river is limited by the combination of short residence times and unavailability of reactive calcite critical supersaturation levels necessary for heterogeneous nucleation do not occur a high suspended load limits algal photosynthesis and thus prevents large decreases in daytime h2co3 levels

ecogeomorphic feedbacks in regrowth of travertine step pool morphology after dam decommissioning fossil creek arizona abstract the linkages between fluvial geomorphology and aquatic ecosystems are commonly conceptualized as a one way causal chain in which geomorphic processes create the physical template for ecological dynamics in streams with a travertine step pool morphology however biotic processes strongly influence the formation and growth of travertine dams creating the potential for numerous feedbacks here we take advantage of the decommissioning of a hydroelectric project on fossil creek arizona where restoration of caco 3 rich baseflow has triggered rapid regrowth of travertine dams to explore the interactions between biotic and abiotic factors in travertine morphodynamics we consider three conceptual frameworks where biotic factors independently modulate the rate of physical and chemical processes that produce travertine dams combine with abiotic factors in a set of feedback loops and work in opposition to abiotic processes such that the travertine step pool morphology reflects a dynamic balance between dominantly biotic constructive processes and dominantly abiotic destructive processes we consider separately three phases of an idealized life cycle of travertine dams dam formation growth and destruction by erosive floods dam formation is catalyzed by abiotic factors e g channel constrictions and bedrock steps and biotic factors e g woody debris and emergent vegetation from measurements of changes over time in travertine thickness on a bedrock step we find evidence for a positive feedback between flow hydraulics and travertine accrual measurements of organic content in travertine samples from this step show that algal growth contributes substantially to travertine accumulation and suggest that growth is most rapid during seasonal algal blooms to document vertical growth of travertine dams we embedded 252 magnets into nascent travertine dams along a 10 km stretch of river growth rates are calculated from changes over time in the magnetic field intensity at the dam surface at each magnet we record a range of hydraulic and travertine composition variables to characterize the dominant mechanism of growth abiotic precipitation algal growth trapping of organic material or in situ plant growth we find 1 rapid growth of travertine dams following flow restoration averaging more than 2 cm year 2 growth rates decline downstream consistent with loss of dissolved constituents because of upstream travertine deposition but also parallel to a decline in organic content in dam surface material and a downstream shift in dominant biotic mechanism 3 biotic mechanisms are associated with faster growth rates and 4 correlations between hydraulic attributes and growth rates are more consistent with biotic than abiotic controls we conclude that the strong influence of living organisms on rates of travertine growth coupled with the beneficial effects of travertine on ecosystem dynamics demonstrate a positive feedback between biology and geomorphology during our two year study period erosive flood flows occurred causing widespread removal of travertine the temporal distribution of travertine growth and erosion over the study period is consistent with a bimodal magnitude frequency relation in which growth dominates except when large infrequent storms occur this model may be useful in other systems where biology exerts strong controls on geomorphic processes

asiras airborne radar resolves internal annual layers in the dry snow zone of greenland 1 we present data from the european space agency s airborne sar interferometric radar altimeter system asiras flown during the cryovex 2004 field calibration validation campaign and new high resolution depth profiles of snow density measured in the field by neutron scattering we combine these data to calculate the depth of internal reflecting horizons in the asiras data the high resolution density data allow us to identify annual layers in the snow density profile and correlate their peaks with the reflecting horizons we use the thickness of the annual layers combined with the density profile to determine the spatial and temporal pattern of snow accumulation along the radar track for a period of 6 years from 1995 2002 our mean annual accumulation rate is 0 47 0 09 ma 1 water equivalent in agreement with the value determined from a core taken in this location in 1992 similarly our inter annual variability shows the same trends as recent model estimates over the entire ice sheet because asiras was designed to mimic as closely as possible the characteristics of the sar interferometric radar altimeter siral the principal payload of cryosat the detection of internal layering with asiras illuminates the possibility of detecting internal layers with a space borne radar and thus the possible application of this technique to the dry snow zones of antarctica greenland and smaller ice bodies

geochemistry of carbon dioxide in six travertine depositing waters of italy abstract the chemical compositions of six travertine depositing hot spring waters in italy are described with emphasis on the carbon dioxide system all springs contained high concentrations of co 2 20 mm l 1 with equilibrium partial pressures well above those which could have been formed in contact with a soil atmosphere after surfacing the co 2 is rapidly lost to the atmosphere with evasion rates close to the springs ranging from 0 45 4 41 mm m 2 s 1 partial pressures of c02 showed an exponential decline with distance which is consistent with the static film model where temperature and turbulence are constant downstream co 2 transfer coefficients which ranged from 66 to 360 cm h 1 were consistent with moderately turbulent flow however there was no correlation between turbulence measured as the mean shear stress and co 2 evasion rate the channels investigated had all been modified by man and most possessed even widths and gradients all waters became increasingly supersaturated with aragonite and calcite downstream and both of these minerals were present in fresh travertine deposits the supersaturation was driven almost exclusively by gas evasion comparison of daytime and nighttime evasion rates demonstrated that photosynthetic activity was an insignificant source of co 2 flux in the reaches investigated carbon dioxide evasion is therefore primarily responsible for the supersaturation and probably also the deposition of travertine at these sites the caco 3 content of the travertines ranged from 91 3 to 96 0 wt with 1 7 4 1 caso 4 traces of organic matter and acid insoluble minerals

antarctic subglacial conditions inferred from a hybrid ice sheet ice stream model abstract subglacial conditions of large polar ice sheets remain poorly understood despite recent advances in satellite observation major uncertainties related to basal conditions such as the temperature field are due to an insufficient knowledge of geothermal heat flow here a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots as well as the distribution of subglacial lakes in this way geothermal heat flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available results of the sensitivity experiments show that 55 of the grounded part of the antarctic ice sheet is at pressure melting point calculated basal melt rates are approximately 65 gt year 1 which is 3 of the total surface accumulation although these sensitivity experiments exhibit small variations in basal melt rates the impact on the ice age of basal layers is quite important in areas that are characterized by relatively low melt rates this may lead to standard deviations up to 50 in a model run over a period of 10 6 years subglacial water flow is concentrated underneath the large outlet glaciers of antarctica the larger subglacial lakes are perched at the head of these subglacial water systems an exception however is the lake system of the recovery ice stream catchment that receives a substantial amount of subglacial melt water from the upstream catchment

the role of the mean state in meridional mode structure and growth abstractthis study uses a simple linear coupled model to investigate the role of the wes feedback and itcz mean states in meridional mode variability optimal structures that maximize transient growth are calculated for mean states characteristic of boreal spring and boreal fall in the tropical atlantic during boreal spring the leading optimal structure is a zonal mode that propagates westward and does not resemble the observed meridional mode in contrast the leading optimal structure during fall is a sea surface temperature sst monopole over the northern hemisphere nh that propagates equatorward and westward and that closely matches meridional mode variability during this season it is found that the boreal fall optimal growth greatly exceeds growth of the corresponding optimal during boreal spring despite the observed boreal spring peak in atlantic meridional mode variance sensitivity studies are used to explore the role of northern or southern hemisphere initial conditions itcz width and itcz

connected subglacial lake activity on lower mercer and whillans ice streams west antarctica 2003 2008 we examine patterns of localized surface elevation change in lower mercer and whillans ice streams west antarctica which we interpret as subglacial water movement through a system of lakes and channels we detect and measure the lake activity using repeat track laser altimetry from icesat and image differencing from modis image pairs a hydrostatic potential map for the region shows that the lakes are distributed across three distinct hydrologic regimes our analysis shows that within these regimes some of the subglacial lakes appear to be linked with drainage events in one reservoir causing filling and follow on drainage in adjacent lakes we also observe changes near ice raft a in lower whillans ice stream and interpret them as evidence of subglacial water and other changes at the bed the study provides quantitative information about the properties of this complex subglacial hydrologic system and a relatively unstudied component of ice sheet mass balance subglacial drainage across the grounding line

the record 2013 southern hemisphere sea ice extent maximum observations of southern hemisphere sea ice from passive microwave satellite measurements show that a new record maximum extent of 19 58 10 6 km 2 was reached on 30 september 2013 the extent is just over two standard deviations above the 1979 2012 mean and follows a similar record 19 48 10 6 km 2 in 2012 on the record day in 2013 sea ice extent was greater than the 30 year average 1981 2010 in nearly all southern ocean regions for the year as a whole southern hemisphere sea ice area and extent were well above average and numerous monthly and daily records were broken analysis of anomaly patterns and the atmospheric and oceanic events suggests that a sequence of regional wind and cold freshened surface waters is likely responsible for the record maximum and the generally high 2013 extent in particular the ross sea sector experienced a combination of cold southerly winds associated with the position and depth of the amundsen sea low and lower than normal sea surface temperatures up to 2 c below normal the resulting very high anomaly in ice extent in this region was a major component of the overall record maximum

accurate coastal dem generation by merging aster gdem and icesat glas data over mertz glacier antarctica abstract mertz glacier mg calved in february 2010 and a 70 years calving cycle of mg was reported recently because of the shallow mertz bank to better investigate the calving process a high accurate surface digital elevation model dem with accurate date marker over mg is urgently required for numerical modeling especially over the ice tongue however it is quite challenging to generate an accurate dem over high relief and steep slope regions to solve this problem a new method for accurate coastal dem production by merging aster gdem and icesat glas data is designed which can effectively discriminate accurate elevation data from aster gdem then a dem corresponding to the end of 2002 over mg is generated which has an accuracy of 0 99 17 50 m this dem is several times better in accuracy than the original aster gdem accuracy 8 17 54 31 m and two new characteristics of aster gdem have been found through analysis first aster gdem has elevation bias varying from 23 m to 28 m spatially correlated to aster ground tracks which was most probably caused by uncertainty of attitude measurements of aster second aster gdem grids with stacking number 4 can be effectively adjusted by ground control points so as to improve elevation accuracy additionally this dem has the best accuracy by comparing with other dems ramp dem 47 71 91 61 m icesat glas dem 1 01 30 33 bamber dem 1 07 33 04 m bedmap 2 dem 9 19 48 34 m and cryosat 2 dem 5 42 32 02 m the high performance of our dem in accuracy indicates that our method is effective and has a potential to be widely used to improve existing aster gdem along antarctic coast

factors controlling present day tufa dynamics in the monasterio de piedra natural park iberian range spain depositional environmental settings sedimentation rates and hydrochemistry the tufa record and hydrochemical characteristics of the river piedra in the monasterio de piedra natural park ne spain were studied for 6 years the mean discharge of this river was 1 22 m3 s the water was supersaturated with calcium carbonate the hco3 ca2 and tdic concentrations decreased along the 0 5 km long studied stretch whereas the calcite si showed no systematic downstream or seasonal variation over the same stretch several sedimentary subenvironments exist in which four broad types of tufa facies form 1 dense laminated tufa stromatolites 2 dense to porous massive tufa 3 porous coarsely laminated tufa with bryophytes and algae and 4 dense hard laminated deposits in caves the half yearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls and lower in slow flowing or standing river areas and in spray and splash areas mechanical co2 outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls but this process does not explain the seasonal changes in depositional rates the deposition rates showed a half yearly period pattern recorded in all fluvial subenvironments persistent over time 5 26 mm 0 86 g cm2 in warm periods 2 26 mm 0 13 g cm2 in cool periods mass balance calculations showed higher calcite mass values in warm 21 58 mg l than in cool 13 68 mg l periods this biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity tufa sedimentation was therefore controlled by both physicochemical and biological processes the results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi arid conditions in particular in the quaternary

oxygen isotope composition of annually banded modern and mid holocene travertine and evidence of paleomonsoon floods grand canyon arizona usa abstract holocene and modern travertine formed in spring fed havasu creek of the grand canyon arizona was studied to determine the factors governing its oxygen isotope composition analysis of substrate grown travertine indicates that calculated calcite formation temperatures compare favorably with measured water temperatures and include silt rich laminae deposited by monsoon driven floods ancient spring pool travertine is dated by u series at 7380 110 yr and consists of 14 travertine silt couplets of probable annual deposition one hundred eighty high resolution 18o analyses of this mid holocene sample average 11 0 pdb the average value for modern travertine is 0 5 lower perhaps because mid holocene temperature was higher or there was proportionally greater summer recharge 18o cyclicity in the mid holocene travertine has average amplitude of 1 9 0 5 pdb slightly less than the inferred modern day annual temperature range of havasu creek the annual temperature range might have been reduced during the 14 yr interval compared to present although other non temperature factors could account for the muted annual variation silt rich laminae within isotopically lower calcite in the modern and mid holocene travertine verifies the seasonal resolution of both samples and suggests that similar temperature precipitation conditions as well as monsoon generated summer floods prevailed in the mid holocene as they do throughout the grand canyon region today

high resolution ground based gps measurements show intercampaign bias in icesat elevation data near summit greenland the geoscience laser altimeter system glas aboard the national aeronautics and space administration s ice cloud and land elevation satellite icesat collected data from early 2003 to late 2009 with the specific goal of measuring ice surface elevation changes while the precision of glas instrumentation has been studied over its intended target ice its accuracy has only been robustly estimated using independent terrestrial nonlaser methods over salt flats here we perform repeat high precision global positioning system gps surveys under four passes of icesat track 0412 campaigns l3i l3j l2d and l2e to compare directly glas elevation data footprints to a coincident gps ground truth near summit greenland analysis and comparison of glas data with gps data show a campaign dependent elevation bias ranging from 0 112 0 030 m l3j to 0 121 0 071 m l2e although uncorrected reflectance values and field observations both indicate that forward scattering of the laser signal through the atmosphere accounts for the anomalously negative l3j bias the biases of all campaigns studied are within the instrument s goal accuracy of 0 15 m however our analysis shows a campaign dependence in the bias which may propagate through estimates of mass balance the error introduced from intercampaign biases illustrates the importance of long term independent validation experiments of satellite altimetry data over ice sheets

recent advances in understanding antarctic subglacial lakes and hydrology it is now well documented that over 400 subglacial lakes exist across the bed of the antarctic ice sheet they comprise a variety of sizes and volumes from the approx 250 km long lake vostok to bodies of water less than 1 km in length relate to a number of discrete topographic settings from those contained within valleys to lakes that reside in broad flat terrain and exhibit a range of dynamic behaviours from active lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years here we critique recent advances in our understanding of subglacial lakes in particular since the last inventory in 2012 we show that within 3 years our knowledge of the hydrological processes at the ice sheet base has advanced considerably we describe evidence for further active subglacial lakes based on satellite observation of ice surface changes and discuss why detection of many active lakes is not resolved in traditional radio echo sounding methods we go on to review evidence for large scale subglacial water flow in antarctica including the discovery of ancient channels developed by former hydrological processes we end by predicting areas where future discoveries may be possible including the detection measurement and significance of groundwater i e water held beneath the ice bed interface

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

controlling processes in a caco3 precipitating stream in huanglong natural scenic district sichuan china abstract huanglong scenic district is well known for its unusual and diversified landforms such as travertine pools travertine falls and travertine flows these landforms resulting from high altitude surface cold water caco 3 precipitation were chosen by unesco in 1994 as an entry in the world s nature heritage huanglong is a pristine region where there are limited human activities water analyses and thin section glass slide precipitation experiments were conducted to determine the aqueous processes controlling caco 3 precipitation and travertine landform formation results from the travertine flow indicate that the concentrations of hco 3 ca 2 and h decrease regularly along the flow paths chemical equilibrium modeling results demonstrate the importance of co 2 out gassing and caco 3 precipitation processes co 2 out gassing and caco 3 precipitation increase with increasing flow velocities in the pool area varying hydrodynamics are the primary factors which determine the extent of processes such as advection and diffusion and hence also control caco 3 precipitation and co 2 out gassing when the pool water circulation is very slow the ph of water flowing over the travertine dams increases significantly approximately 0 15 ph units downstream when the circulation is relatively fast the ph of stream water initially decreases followed by an increase of approximately 0 21 ph units as it flows past the travertine pool dams in both cases the ph rise is caused by sudden changes in the hydrodynamics of the pools despite the different initial flow conditions pool development is a consequence of spatial variations in ph which provide different conditions for caco 3 precipitation inside the travertine dam where less precipitation or even dissolution occurs compared to conditions at the top and downstream side of the dams precipitation experiments demonstrate that the top and downstream side of travertine dams are the locations of the most active precipitation particularly for pools having faster circulation precipitation experiments also reveal that vaterite a rare polymorph of caco 3 co precipitates with calcite in milky opalescent water near the upstream input portion of the pool groups thin sections covered by algae at the bottom of pools have 40 less caco 3 precipitation than those not covered by algae sem photographs of the surface of natural travertine deposits show that biofilms with diatom minimize caco 3 precipitation and that diatom adhered calcite surfaces show signs of etching suggesting that calcite dissolution may be aided by diatoms

hydrochemical evolution and reaction simulation of travertine deposition of the lianchangping hot springs in yunnan china located in western yunnan of china the lianchangping hot springs are of so 4 hco 3 ca na type with total dissolved solids tds ranging from 3560 to 4240 mg l large amounts of travertine are deposited near the hot springs with a variety of travertine morphology including travertine terrace slope and ridge travertine is precipitating along the slope near one of the spring s thresholds chemical compositions of the hot water samples collected along travertine slope show that p co 2 p co 2 tds and contents of hco 3 and ca decrease downstream along the travertine slope due to travertine deposition the initial milliequivalent ratio of ca 2 hco 3 is greater than 1 5 before travertine precipitation and there is an increasing trend in the ratio downstream along the travertine slope high levels of sulphate are probably the result of gypsum dissolution in the sediments widespread in the lianchangping area the spring waters issuing from the land surface are slightly supersaturated with respect to calcite dolomite fluorite kaolinite halite plagioclase and carbon dioxide hydrochemical evolution of the lianchangping spring water along the slope is calculated with the phreeqc interactive 2 12 5 sets of minerals and gases reacted in appropriate amounts are recognized through reaction simulation quantitatively accounting for the variations in chemical compositions especially depositing minerals along the flow path on the travertine slope

in situ initiation of east pacific easterly waves in a regional model abstractthe in situ generation of easterly waves ews in the east pacific epac is investigated using the weather research and forecasting wrf model the sensitivity of the model to the suppression of ew forcing by locally generated convective disturbances is examined specifically local forcing of ews is removed by reducing the terrain height in portions of central and south america to suppress robust sources of diurnal convective variability most notably in the panama bight high terrain contributes to the initiation of mesoscale convective systems in the early morning that propagate westward into the epac warm pool when such mesoscale convective systems are suppressed in the model ew variance is significantly reduced this result suggests that epac ews can be generated locally in association with higher frequency convective disturbances and these disturbances are determined to be an important source of epac ew variability however epac ew variability is not completely eliminated in such sensi

three dimensional mapping by cryosat 2 of subglacial lake volume changes we analyze data acquired by the cryosat 2 interferometric radar altimeter and demonstrate its novel capability to track topographic features on the antarctic ice sheet we map the perimeter and depth of a 260 km2 surface depression above an antarctic subglacial lake sgl and in combination with ice cloud and land elevation satellite laser altimetry chart decadal changes in sgl volume during 2007 2008 between 4 9 and 6 4 km3 of water drained from the sgl and peak discharge exceeded 160 m3 s 1 the flood was twice as large as any previously recorded and equivalent to 10 of the meltwater generated annually beneath the ice sheet the ice surface has since uplifted at a rate of 5 6 2 8 m yr 1 our study demonstrates the ability of cryosat 2 to provide detailed maps of ice sheet topography its potential to accurately measure sgl drainage events and the contribution it can make to understanding water flow beneath antarctica key points assessment of novel cryosat 2 interferometric altimetry over land ice demonstration of interferometric capability to track off nadir topography mapping of largest antarctic subglacial lake drainage event observed to date

short term variability in greenland ice sheet motion forced by time varying meltwater drainage implications for the relationship between subglacial drainage system behavior and ice velocity 1 high resolution measurements of ice motion along a 120 km transect in a land terminating section of the gris reveal short term velocity variations 1 day which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface the seasonal changes in ice velocity at low elevations 1000 m are dominated by events lasting from 1 day to 1 week although daily cycles are largely absent at higher elevations reflecting different patterns of meltwater input using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time varying water input to a channelized subglacial drainage system our investigation substantiates arguments that variability in theduration and rate rather than absolute volume of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure and therefore ice velocity we suggest that interpretations of hydro dynamic behavior in land terminating sections of the gris margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion

modeling 5 years of subglacial lake activity in the macayeal ice stream antarctica catchment through assimilation of icesat laser altimetry subglacial lakes beneath antarctica s fast moving ice streams are known to undergo 1 km 3 volume changes on annual timescales focusing on the macayeal ice stream macis lake system we create a simple model for the response of subglacial water distribution to lake discharge events through assimilation of lake volume changes estimated from ice cloud and land elevation satellite icesat laser altimetry we construct a steady state water transport model in which known subglacial lakes are treated as either sinks or sources depending on the icesat derived filling or draining rates the modeled volume change rates of five large subglacial lakes in the downstream portion of macis are shown to be consistent with observed filling rates if the dynamics of all upstream lakes are considered however the variable filling rate of the northernmost lake suggests the presence of an undetected lake of similar size upstream overall we show that for this fast flowing ice stream most subglacial lakes receive 90 of their water from distant distributed sources throughout the catchment and we confirm that water is transported from regions of net basal melt to regions of net basal freezing our study provides a geophysically based means of validating subglacial water models in antarctica and is a potential way to parameterize subglacial lake discharge events in large scale ice sheet models where adequate data are available

upscale impact of mesoscale disturbances of tropical convection on convectively coupled kelvin waves abstracttropical convection associated with convectively coupled kelvin waves cckws is typically organized by an eastward moving synoptic scale convective envelope with numerous embedded westward moving mesoscale disturbances such a multiscale structure of tropical convection is a challenge for present day cloud resolving simulations and its representation in global climate models it is of central importance to assess the upscale impact of mesoscale disturbances on cckws as mesoscale disturbances propagate at various tilt angles and speeds besides it is still poorly understood whether the front to rear tilted vertical structure of cckws can be induced by the upscale impact of mesoscale disturbances in the presence of upright mean heating here a simple multiscale model is used to capture this multiscale structure where mesoscale fluctuations are directly driven by mesoscale heating and synoptic scale circulation is forced by mean heating and eddy transfer of momentum and temperature the results s

synthesizing multiple remote sensing techniques for subglacial hydrologic mapping application to a lake system beneath macayeal ice stream west antarctica we present an analysis of the active hydrologic system of macayeal ice stream macis west antarctica from a synthesis of multiple remote sensing techniques satellite laser altimetry satellite image differencing and hydrologic potential mapping using a satellite derived dem and a bedrock dem from airborne radio echo sounding combining these techniques augments the information provided by each one individually and allows us to develop a protocol for studying subglacial hydrologic systems in a holistic manner our study reveals five large active subglacial lakes under macis the largest of which undergoes volume changes of at least 1 0 km 3 we discuss the hydrologic properties of this system and present evidence for links between the lakes at least three of the lakes are co located with sticky spots i e regions of high local basal shear stress we also find evidence for surface elevation changes due to ice dynamic effects not just water movement caused by changes in basal resistance lastly we show that satellite radar altimetry is of limited use for monitoring lake activity on fast flowing ice streams with surfaces that undulate on 10 km length scales

dynamics of the intertropical convergence zone of the east pacific abstract the dynamical factors controlling the mean state and variability of the east pacific intertropical convergence zone itcz and the associated cross equatorial boundary layer flow are investigated using observations from the east pacific investigation of climate epic2001 project the tropical east pacific exhibits a southerly boundary layer flow that terminates in the itcz this flow is induced by the strong meridional sea surface temperature sst gradient in the region away from the equator and from deep convection it is reasonably well described on a day to day basis by an extended ekman balance model variability in the strength and northward extent of this flow is caused by variations in free tropospheric pressure gradients that either reinforce or oppose the pressure gradient associated with the sst gradient these free tropospheric gradients are caused by easterly waves tropical cyclones and the madden julian oscillation convergence in the boundary layer flow is often assumed to be r

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

calcite precipitation rates in the field measurement and prediction for a travertine depositing stream abstract rates of calcite precipitation from a travertine depositing stream were determined from changes in stream composition between consecutive sampling points and were compared with rates predicted from a laboratory derived rate law plummer et al 1978 the agreement in rates was generally within an order of magnitude and routinely within a factor of 3 least agreement between measured and predicted rates was obtained for sections of flowpath where relatively little change in bulk chemical composition occurred which were the sections with the greatest mass transfer calculation error and for the stream segment including a waterfall which was the section with the greatest error in estimated surface area reaction rate obtained from the mass of calcite precipitated onto seed crystals placed in the stream significantly underestimated the mass transfer rate for the travertine depositing stream of warm river cave and falling spring creek virginia the coupling of equilibrium speciation models with mass balance calculations and simple field measurements allowed successful field based quantification of reaction rates

the supply of subglacial meltwater to the grounding line of the siple coast west antarctica recent satellite studies have shown that active subglacial lakes exist under the antarctic ice streams and persist almost to their grounding lines when the lowest lying lakes flood the water crosses the grounding line and enters the sub ice shelf cavity modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice shelf base we examine the spatial and temporal variability in subglacial water supply to the grounding lines of the siple coast ice streams by combining estimates for lake volume change derived from ice cloud and land elevation satellite icesat data with a model for subglacial water transport our results suggest that subglacial outflow tends to concentrate towards six embayments in the siple coast grounding line although mean grounding line outflow is 60m3 s 1 for the entire siple coast maximum local grounding line outflow may temporarily exceed 300 m3 s 1 during the synchronized flooding of multiple lakes in a hydrologic basin variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the ross ice shelf cavity the temporal variability in grounding line outflow results in a net reduction in long term average melt rate but temporary peak melting rates may exceed the long term average by a factor of three

hydrogeochemical characterisation and modelling of groundwaters in a potential geological repository for spent nuclear fuel in crystalline rocks laxemar sweden two sites in the eastern coast of sweden have been investigated by the swedish nuclear fuel and waste management company skb within the framework of the site characterisation programme as possible candidates for hosting the proposed repository for the long term storage of spent nuclear fuel forsmark and laxemar this study presents the main results concerning the hydrogeochemical characterisation of the groundwaters in the second site laxemar the distribution of the main chemical variables in groundwaters are shown and interpreted in combination with the results from speciation solubility and reaction path simulations together with the available mineralogical information the results indicate that the main processes determining the overall geochemical evolution of the laxemar groundwaters are advective diffusive mixing and water rock interactions driven by past and present climatic changes inducing the input of different recharge waters over time glacial meltwater old marine water and modern meteoric water and affecting the preexisting very old saline groundwaters in the bedrock the superimposed effects of these mixing events deduced from the behaviour of the conservative elements cl and 18o have generated a rather steep salinity gradient in the groundwater system with diluted waters in the upper part brackish waters in the middle and saline waters in the lower part of the bedrock the resultant successive disequilibrium states imposed by mixing have conditioned the water rock interaction processes that have affected the non conservative elements to different degrees the main chemical reactions found to be important in controlling some of the variability of these elements and some important parameters like ph and alkalinity are aluminosilicate and carbonate dissolution precipitation quartz and fluorite equilibrium cation exchange and gypsum dissolution these reactions and their importance in the system are presented in this paper once the main hydrogeochemical features of the laxemar groundwaters and the potentially controlling water rock interactions in the system have been identified and justified with the help of thermodynamic simulations a general geochemical conceptual model has been proposed this model will be used as the basis for predicting the future evolution of the groundwater chemistry as an essential part of the safety assessment of the future repository

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

thirteen years of subglacial lake activity in antarctica from multi mission satellite altimetry the ability to detect the surface expression of moving water beneath the antarctic ice sheet by satellite has revealed a dynamic basal environment with implications for regional ice dynamics grounding line stability and fluxes of freshwater and nutrients to the southern ocean knowledge of subglacial activity on timescales important for near term prediction of ice sheet fluctuations decadal to century is limited by the short observational record of nasa s ice cloud and land elevation satellite icesat laser altimetry mission used to generate the last continent wide survey 2003 08 here we use synthetic aperture radar interferometric mode data from esa s cryosat 2 radar altimetry mission 2010 present which samples 45 of the icesat derived subglacial lakes to extend their time series to the end of 2016 the extended time series show that there have been surface height changes at 20 of the 45 lakes since 2008 indicating that some of these features are persistent and potentially cyclic while other features show negligible changes suggesting these may be transient or nonhydrological features continued monitoring of active lakes for both height and velocity changes as well as developing methods for identifying additional lakes is critical to quantifying the full distribution of active subglacial lakes in antarctica