litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

ikaite precipitation in a lacustrine environment implications for palaeoclimatic studies using carbonates from laguna potrok aike patagonia argentina abstract the monoclinic mineral ikaite caco 3 6h 2 o and its pseudomorphs are potentially important archives for palaeoenvironmental reconstructions natural ikaite occurs in a small temperature range near freezing point and is reported mainly from marine and only rarely from continental aquatic environments ikaite transforms to more stable anhydrous forms of caco 3 after an increase in temperature or when exposed to atmospheric conditions the knowledge about conditions for natural ikaite formation its stable isotope fractionation factors and isotopic changes during transformation to calcite is very restricted here for the first time primary precipitation of idiomorphic ikaite and its calcite pseudomorphs are reported from a subsaline lake laguna potrok aike in southern argentina the calculated stable oxygen isotope fractionation factor between lake water and ikaite derived calcite pai 1 0324 at a temperature of 4 1 c is close to but differs from that of primarily inorganically precipitated calcite pseudomorphs after ikaite rapidly disintegrate into calcite powder that is indistinguishable from m sized calcite crystals in the sediment record of laguna potrok aike suggesting an ikaite origin of sedimentary calcites therefore the holocene carbonates of laguna potrok aike have the potential to serve as a recorder of past hydrological variation

glendonites and methane derived mg calcites in the sea of okhotsk eastern siberia implications of a venting related ikaite glendonite formation mg calcite cemented bioturbation traces glendonite aggregates of idiomorphic bi pyramidal crystals and porous amber colored carbonate concretions were recovered from a methane dominated cold vent area in 380 m water depth at the northern sakhalin slope sea of okhotsk bioturbation traces consist of mg calcite cemented sediment with 13c values between 37 and 46 peedee belemnite pdb which implicate methane as the carbon source glendonite a calcite pseudomorphosis after ikaite caco3 6h2o and amber colored concretions are both composed of varying amounts of calcite and mg calcite with 13c values between 19 and 34 pdb isotope analyses of an ikaite crystal recovered in the vicinity reveals 13c values between 20 and 22 pdb indicating organic matter as the carbon source microscopic investigations of glendonites and amber colored concretions show a porous fabric of a primary calcite phase that is overgrown by a secondary mg calcite cement as ikaite pseudomorphs to porous calcite and as carbon isotope values are the same for the ikaite and the high end member values of glendonite samples the primary calcite phase is suggested to be a former ikaite phase because they share the equal color fabric mineral and isotopic composition with glendonites the amber colored concretions are also suggested to represent calcite that transformed from ikaite a mixture of pseudomorph calcite 13c 20 pdb which originally formed as ikaite from degraded organic matter and mg calcite 13c 43 pdb which crystallized due to the anaerobic oxidation of methane can explain the varying carbon isotope data of the glendonites and the amber colored concretions the growth of ikaite the transformation of ikaite to calcite and the crystallization of mg calcite indicate changing geochemical conditions within a cold vent environment at different times ideal conditions for the ikaite formation are given during the establishment of a cold vent site when upward migrating methane rich fluids enhance the anaerobe decomposition of organic matter which again increases the phosphate and alkalinity concentrations near the sediment surface lower rates of organic matter decomposition during on going venting decrease these high phosphate but also sulphate concentrations and allows other carbonate phases as mg calcite to form this additional carbonate precipitation and the ikaite formation itself lower the high alkalinity and destabilize ikaite which pseudomorphs to porous calcite triggered by the further upward shifting so4 h2s boundary and increasing methane oxidation rates the typical cold vent methane derived carbonate genesis takes place which cements the sediment pore space and induces the secondary mg calcite crystallization within the glendonite fabric taking this scenario into account ikaite formation should be a common process in the beginning of methane dominated vent activity at cold bottom water temperatures glendonite pseudomorphs can be assumed to represent a typical manifestation at fossil and recent cold vents at high latitudes

the fate of the submarine ikaite tufa columns in southwest greenland under changing climate conditions abstract ikaite is considered a metastable mineral forming and stable only at low temperatures and therefore an indicator of low temperature carbonate precipitation often associated with cold marine seeps it is found world wide but most spectacularly in ikka fjord in southwest greenland as submarine carbonate tufa columns here ikaite is formed as a result of submarine spring water mixing with cold seawater as ikaite disintegrates at temperatures above 6 7 c it has been speculated that global warming could endanger this unique habitat as well as other sites in ikka fjord in situ water chemistry in and around an ikaite column measured continuously over two years showed that the column water is alkaline ph 9 10 throughout the year with temperatures of 1 3 6 0 c and conductivities of 5 7 7 9 ms cm 1 favoring year round growth of columns at 4 5 cm per month short term in situ measurements with needle micro sensors from both older dehydrated and calcified parts and more recently formed solid parts of an ikaite tufa column showed similar ph and temperature values including a temperature variation over the tidal cycle in the uppermost recently deposited ikaite matrix spring water escaping at the top causes passive drag of seawater into the porous ikaite matrix leading to a mixing layer several centimeters thick that has ph values intermediate to the spring water in the column and the surrounding seawater we conclude that the main part of the columns consisting of fossilized ikaite inverted to calcite partly sealed by calcifying coralline algae and with year round flow of alkaline freshwater through distinct channels are resistant to warming in the more diffuse top part of the columns the formation of ikaite and thus column growth will be limited in the future due to increased fjord water temperature during the

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

lateglacial and holocene climatic changes in south eastern patagonia inferred from carbonate isotope records of laguna potrok aike argentina abstract first results of strontium calcium carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of laguna potrok aike located in southern patagonia are presented morphological and isotopic investigations of m sized carbonate crystals in the sediment reveal an endogenic origin for the entire holocene during this time period the calcium carbonate record of laguna potrok aike turned out to be most likely ikaite derived as ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 c the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures we suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the southern hemisphere westerlies and discuss the role of this wind belt as a driver for climate change in southern south america in combination with other proxy records the evolution of westerly wind intensities is reconstructed our data suggest that weak shw prevailed during the lateglacial and the early holocene interrupted by an interval with strengthened westerlies between 13 4 and 11 3 ka cal bp wind strength increased at 9 2 ka cal bp and significantly intensified until 7 0 ka cal bp subsequently the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the little ice age strontium isotopes 87 sr 86 sr ratio were identified as a potential lake level indicator and point to a lowering from overflow conditions during the glacial 17 ka cal bp to lowest lake levels around 8 ka cal bp thereafter the strontium isotope curve resembles the lake level curve which is stepwise rising until the little ice age the variability of the ca isotope composition of the sediment reflects changes in the ca budget of the lake indicating higher degrees of ca utilisation during the period with lowest lake level

secondary alteration of the gronnedal ika igneous complex and the genesis of ikaite caco3 6h2o sw greenland abstract the mineral ikaite caco3 6h2o precipitates from a mixture of spring water and seawater as tufa columns which grow at a rate of up to 50 cm per year reaching heights of up to 18 m in ikka fjord sw greenland in the fjord column formation occurs only at the base of a nepheline syenite carbonatite complex that flanks the fjord and an association has therefore been proposed the spring water that seeps up at the bottom of the fjord is oversaturated in na and hco3 in this study we show that these ions were acquired by alteration reactions in the syenite carbonatite complex na is released during replacement of nepheline by illite and analcime in nepheline syenite rocks and hco3 is released by oxidation of siderite to goethite in carbonatite rocks the chemically charged groundwater mixes with seawater and gives rise to the formation of the tufa columns we performed a mass balance to show that the mass of the carbonatite in the complex is more than sufficient to provide the co2 needed to produce the observed mass of tufa columns we estimated a time frame of 600 years to produce the necessary co2 to form the 700 ikaite columns in the fjord

surface mass redistribution inversion from global gps deformation and gravity recovery and climate experiment grace gravity data monitoring hydrological redistributions through their integrated gravitational effect is the primary aim of the gravity recovery and climate experiment grace mission time variable gravity data from grace can be uniquely inverted to hydrology since mass transfers located at or near the earth s surface are much larger on shorter timescales than those taking place within the deeper earth and because one can remove the contribution of atmospheric masses from air pressure data yet it has been proposed that at larger scales this may be achieved independently by measuring and inverting the elastic loading associated with redistributing masses e g with the global network of the international gps service igs this is particularly interesting as long as grace monthly gravity solutions do not yet match the targeted baseline accuracies at the lower spherical harmonic degrees in this contribution 1 we describe and investigate an inversion technique which can deal jointly with gps data and monthly grace solutions 2 previous studies with gps data have used least squares estimators and impose solution constraints through low degree spherical harmonic series truncation here we introduce a physically motivated regularization method that guarantees a stable inversion up to higher degrees while seeking to avoid spatial aliasing 3 we apply this technique to gps data provided by the igs service covering recent years we can show that after removing the contribution ascribed to atmospheric pressure loading estimated annual variations of continental scale mass redistribution exhibit pattern similar to those observed with grace and predicted by a global hydrology model although systematic differences appear to be present 4 we compute what the relative contribution of grace and gps would be in a joint inversion using current error estimates gps could contribute with up to 60 to degree 2 till 4 spherical harmonic coefficients and up to 30 for higher degree coefficients

geochemistry of ikaite formation at mono lake california implications for the origin of tufa mounds the mineral ikaite caco 3 6h 2 o not previously observed in lake environments precipitates seasonally along the shore of mono lake california where ca hco 3 spring water mixes with cold na co 3 lake water during the winter cold water temperatures and high concentrations of po 4 3 and organic carbon inhibit calcite precipitation allowing the metastable ikaite to form during the spring warming however ikaite decomposes to form calcium carbonate and water occasionally leaving pseudomorphs of the primary precipitate the identification of modern ikaite suggests that both pleistocene and holocene tufas in the mono basin originally precipitated as ikaite this mineral may also form in other lake environments but rapid recrystallization after warming destroys the physical chemical and isotopic evidence of formation and alters the geochemical record

direct observations of the current structure east of the bahamas quasisynoptic absolute velocity sections were obtained in the western north atlantic to the east of the bahamas on five cruises from 1992 to 1994 showing complex spatial and temporal variability of the currents throughout the water column lowered acoustic doppler current profilers were used on all cruises for comparison an acoustically tracked free fall profiler was used on the august 1992 and june 1993 cruises where simultaneous profiles from both methods are available depth averaged differences are less than 0 01 m s 1 in the ensemble mean and standard deviation though small the mean difference appears to be statistically non zero for one of the two doppler profilers used no cause has been found the individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth averaged components extending over the full sampling domain two sections show a picture of the southward flowing deep western boundary current dwbc differing from previous observations during august 1992 and june 1993 the mean dwbc core was located more than 100 km offshore in observations prior to 1990 it was usually near 50 km offshore net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 sv with a mean of about 40 sv 1 sv 1 106 m s 1 our mean is consistent with previous estimates our sections add new evidence that the transport is highly variable to at least 400 km offshore

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

structure of the atlantic ocean equatorial deep jets the equatorial deep jets in the atlantic ocean are described using vertical strain jz estimated from all available deep ctd stations in the region wavelet analysis reveals a distinct energy peak around 661 sdbar vertical wavelength 1232 dbar pressure and 61 58 latitude from the equator this high vertical wavenumber and off equatorial maximum coupled with previously published velocity data that show nodes in zonal velocity near 61 58 is grossly consistent with the structure of first meridional mode equatorial rossby waves however the meridional scale obtained from the observations exceeds by about 1 5 the theoretical meridional scale for these waves the jets are strong with zonal velocities similar in magnitude to the kelvin wave phase speed for their vertical wavelength harmonics of jz at vertical wavelengths of 1 2 1 4 and perhaps 1 8 that of the primary peak provide evidence of a large amplitude structure although sparse available phase data at the 661 sdbar vertical wavelength suggest downward and westward phase propagation assuming sinusoidal character in time and longitude gives estimates of a 5 61 yr period and a 708 6608 zonal wavelength these vertical temporal and zonal scales are roughly consistent with first meridional mode equatorial rossby wave dynamics however although vertical and zonal phase propagation are discernible there is no obvious signature of upward energy propagation in the variance vertical maxima which is problematic for a simple linear rossby wave interpretation

tectonic contraction across los angeles after removal of groundwater pumping effects after the 1987 whittier narrows and 1994 northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan los angeles a network of 250 continuously recording global positioning system gps stations was deployed to monitor displacements associated with deep slip on both blind and surface faults here we augment this gps data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike slip faulting after removing these non tectonic signals we are left with 4 4 mm yr 1 of uniaxial contraction across the los angeles basin oriented n 36 degrees e perpendicular to the major strike slip faults in the area this indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast trending strike slip faults we have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults in the 40 km long santa ana basin groundwater withdrawal and re injection produces 12 mm yr 1 of long term subsidence accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally

monohydrocalcite in the arctic ikka fjord sw greenland first reported marine occurrence abstract monohydrocalcite mhc has previously been known only from fresh water and terrestrial environments however as documented in the present paper mhc is a common mineral up to 55 in debris fragments from submarine ikaite caco3 6h2o tufa columns in the cold marine ikka fjord sw greenland the columns form where alkaline fresh water from submarine springs mixes with cold seawater and precipitates ikaite petrographical and geochemical data indicate that mhc represents a transitional diagenetic phase in the recrystallization process of metastable ikaite to final calcite the stable isotope data 13c and 18o document a closer relationship of mhc with the precursor ikaite than with calcite replacement of ikaite by mhc is suggested to take place by dissolution and precipitation in a semi closed pore water system dominated by alkaline spring water and with only limited access of seawater in this environment nucleation of calcite is inhibited by phosphate ions apart from calcite aragonite and hydrous mg carbonates were also observed in the tufa debris the mg carbonates represent late diagenetic phases probably formed from recrystallization of mch in normal seawater environments

calcium carbonate hexahydrate from organic rich sediments of the antarctic shelf precursors of glendonites large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the bransfield strait antarctic peninsula at a water depth of 1950 meters and sub zero bottom water temperatures the chemistry mineralogy and stable isotope composition of this hydrated calcium carbonate phase its environment of formation and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation

impact of the equatorial deep jets on estimates of zonal transports in the atlantic the structure and variability of the zonal equatorial flow in the atlantic is studied on the basis of velocity profiles obtained with lowered acoustic doppler current profilers during multiple surveys the vertical extent of the zonal currents is found to vary considerably it can be as small as 100 m or as large as 1000 m in the atlantic vertical scales of 400 600 m have been associated with the equatorial deep jets they are also frequently called deep jets or stacked jets typical amplitudes of the zonal velocity are about 20 cm s 1 an analysis of quasi synoptic surveys indicates that the zonal extent of most jets is likely to be at least 27d they can rise or deepen from west to east although the deepening was observed more often and is often more pronounced the west to east deepening can be as large as 320 m 10d basin wide mean depth changes of the jets are mostly on the order of 50 m 10d and the largest depth changes are typically observed between 35d and 23d w the existence of these changes indicates that vertically propagating equatorially trapped waves might be one cause for the jet structure however the dependence of the slope on the longitude indicates that other processes must be involved as well the typical vertical extent of the jets is small enough to result in several direction changes of the zonal flow in the antarctic intermediate water aaiw and the north atlantic deep water nadw layer from transport estimates for 14 meridional sections it is found that the transport for the westward component of the flow within the aaiw layer 500 1000 m can be as large as 24 sv 1 sv 10 6 m s 1 within 1d of the equator for the eastward component of the flow in the aaiw layer the transport can be as large as 8 sv adding the transport components for each section results in a range of total aaiw transports from 24 to 7 sv this suggest that the annual mean transport of aaiw is westward the only months with eastward total transports are june and july this is consistent with earlier lagrangian and some other observations that indicated that the aaiw flow along the equator is governed by an annual cycle in the nadw layer 1200 3900 m the transport for the westward eastward flow can be as large as 25 sv 23 sv within 1d of the equator this results in a range of total nadw transports from 10 to 18 sv the variations of the total transports of aaiw and nadw are anti correlated with a correlation coefficient of 0 86 since only eight sections reached deep enough to allow transport estimates in the nadw layer it is more difficult to come to a conclusion about the mean transport in this layer than for the transport in the aaiw layer for the latter layer 14 sections were available nevertheless the obtained estimates suggest that the total nadw transport may be eastward

source parameter inversion for recent great earthquakes from a decade long observation of global gravity fields we quantify gravity changes after great earthquakes present within the 10 year long time series of monthly gravity recovery and climate experiment grace gravity fields using spherical harmonic normal mode formulation the respective source parameters of moment tensor and double couple were estimated for the 2004 sumatra andaman earthquake the gravity data indicate a composite moment of 1 2 1023 n m with a dip of 10 in agreement with the estimate obtained at ultralong seismic periods for the 2010 maule earthquake the grace solutions range from 2 0 to 2 7 1022 n m for dips of 12 24 and centroid depths within the lower crust for the 2011 tohoku oki earthquake the estimated scalar moments range from 4 1 to 6 1 1022 n m with dips of 9 19 and centroid depths within the lower crust for the 2012 indian ocean strike slip earthquakes the gravity data delineate a composite moment of 1 9 1022 n m regardless of the centroid depth comparing favorably with the total moment of the main ruptures and aftershocks the smallest event we successfully analyzed with grace was the 2007 bengkulu earthquake with m0 5 0 1021 n m we found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events deeper sources i e in the upper mantle could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume thus reducing the negative gravity component focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum

forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide the products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers although forsterite is not a common mineral in deep saline aquifers the experiments offer insights into the effects of relevant temperatures and pco2 levels on silicate mineral dissolution and subsequent carbonate precipitation mineral suspensions and aqueous solutions were reacted at 30 c and 95 c in batch reactors and at each temperature experiments were conducted with headspaces containing fixed pco2 values of 1 and 100 bar reaction products and progress were determined by elemental analysis of the dissolved phase geochemical modeling and analysis of the solid phase using scanning electron microscopy infrared spectroscopy and x ray diffraction the extent of forsterite dissolution increased with both increasing temperature and pco2 the release of mg and si from forsterite was stoichiometric but the si concentration was ultimately controlled by the solubility of amorphous silica during forsterite dissolution initiated in deionized water the aqueous solution reached supersaturated conditions with respect to magnesite however magnesite precipitation was not observed for reaction times of nearly four weeks magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution the precipitation of magnesite appears to be limited by the process of nucleation and nucleation requires a critical saturation index between 0 25 and 1 14 at 95 c and 100 bar pco2 magnesite precipitation is fastest in the presence of an initial magnesite seed although magnesite precipitates do form on the surfaces of forsterite particles the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid free systems

first estimates of the contribution of caco3 precipitation to the release of co2 to the atmosphere during young sea ice growth 1 we report measurements of ph total alkalinity air ice co2 fluxes chamber method and caco3 content of frost flowers ff and thin landfast sea ice as the temperature decreases concentration of solutes in the brine skim increases along this gradual concentration process some salts reach their solubility threshold and start precipitating the precipitation of ikaite caco3 6h2o was confirmed in the ff and throughout the ice by raman spectroscopy and x ray analysis the amount of ikaite precipitated was estimated to be 25 mol kg 1 melted ff in the ff and is shown to decrease from 19 to 15 mol kg 1 melted ice in the upper part and at the bottom of the ice respectively co2 release due to precipitation of caco3 is estimated to be 50 mol kg 1 melted samples the dissolved inorganic carbon dic normalized to a salinity of 10 exhibits significant depletion in the upper layer of the ice and in the ff this dic loss is estimated to be 2069 mol kg 1 melted sample and corresponds to a co2 release from the ice to the atmosphere ranging from 20 to 40 mmol m 2 d 1 this estimate is consistent with flux measurements of air ice co2 exchange our measurements confirm previous laboratory findings that growing young sea ice acts as a source of co2 to the atmosphere caco3 precipitation during early ice growth appears to promote the release of co2 to the atmosphere however its contribution to the overall release by newly formed ice is most likely minor

control of a calcite inhibitor phosphate and temperature on ikaite precipitation in ikka fjord southwest greenland abstract ikaite caco3 6h2o forms submarine tufa columns in ikka fjord sw greenland this unique occurrence is thought to relate to aqueous phosphate concentration and low water temperatures

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

variability of the horizontal velocity structure in the upper 1600 m of the water column on the equator at 10 w this paper presents initial results from new velocity observations in the eastern part of the equatorial atlantic ocean from a moored current meter array during the equalant program 1999 2000 a mooring array was deployed around the equator near 10 w that recorded one year of measurements at various depths horizontal velocities were obtained in the upper 60 m from an upward looking acoustic doppler current profiler adcp and at 13 deeper levels from current meters between 745 and 1525 m to analyze the quasiperiodic variability observed in these records a wavelet based technique was used quasiperiodic oscillations having periods between 5 and 100 days were separated into four bands 5 10 10 20 20 40 and 40 100 days the variability shows i a strong seasonality the first half of the series is dominated by larger periods than the second one and ii a strong dependence with depth some oscillations are present in the entire water column while others are only present at certain depths for the oscillations that are present in the entire water column the origin of the forcing can be traced to the surface while for the others the question of their origin remains open phase shifts at different depths generate vertical shears in the horizontal velocity component with relatively short vertical scales this is especially visible in long duration events 100 days of the zonal velocity component comparison with a simultaneous lowered acoustic doppler current profiler ladcp section suggests that some of these flows may be identified with equatorial deep jets a striking feature is a strong vertical shear lasting about 7 months between 745 and 1000 m these deep current meter observations would then imply a few months of duration for the jets in this region

a joint analysis of gps displacement and grace geopotential data for simultaneous estimation of geocenter motion and gravitational field this work is funded by the university of newcastle to support nasa s grace and grace follow on projects as an international science team member to the missions and by australian research council dp170100224 as well as nasa support to j sauber as a science team member

ongoing drought induced uplift in the western united states the western united states has been experiencing severe drought since 2013 the solid earth response to the accompanying loss of surface and near surface water mass should be a broad region of uplift we use seasonally adjusted time series from continuously operating gps stations to measure this uplift which we invert to estimate mass loss the median uplift is 4 mm with values up to 15 mm in california s mountains the associated pattern of mass loss which ranges up to 50 cm of water equivalent is consistent with observed decreases in precipitation and streamflow we estimate the total deficit to be about 240 gt equivalent to a 10 cm layer of water over the entire region or the annual mass loss from the greenland ice sheet

inversion of earth s changing shape to weigh sea level in static equilibrium with surface mass redistribution 1 we develop a spectral inversion method for mass redistribution on the earth s surface given geodetic measurements of the solid earth s geometrical shape using the elastic load love numbers first spectral coefficients are geodetically estimated to some degree spatial inversion then finds the continental surface mass distribution that would force geographic variations in relative sea level such that it is self consistent with an equipotential top surface and the deformed ocean bottom surface and such that the total ocean plus continental mass load has the same estimated spectral coefficients applying this theory we calculate the contribution of seasonal interhemispheric degree 1 mass transfer to variation in global mean sea level and nonsteric static ocean topography using published gps results for seasonal degree 1 surface loading from the global igs network our inversion yields ocean continent mass exchange with annual amplitude 2 92 0 14 1015 kg and maximum ocean mass on 25 august 3 days after correction for the annual variation in global mean vertical deformation of the ocean floor 0 4 mm amplitude we find geocentric sea level has an amplitude of 7 6 0 4 mm consistent with topex poseidon results minus steric effects the seasonal variation in sea level at a point strongly depends on location ranging from 3 to 19 mm the largest being around antarctica in mid august seasonal gradients in static topography have amplitudes of up to 10 mm over 5000 km which may be misinterpreted as dynamic topography peak continental loads occur at high latitudes in late winter at the water equivalent level of 100 200 mm

ikaite precipitation by mixing of shoreline springs and lake water mono lake california usa abstract metastable ikaite caco3 6h2o forms abundantly during winter months along the south shoreline of mono lake where shoreline springs mix with lake water ikaite precipitates because of its decreased solubility at low temperature and because of orthophosphate ion inhibition of calcite and aragonite during the spring some of the ikaite is transformed to anhydrous caco3 and is incorporated into tufa but most is dispersed by wave action into the lake where it reacts to form gaylussite na2ca co3 2 5h2o spring waters have low ph values are dominantly ca na hco3 have low radiocarbon activities and are mixtures of deep seated geothermal and cold groundwaters chemical modeling reveals that precipitation of caco3 can occur over a broad range of mixtures of spring and lake water with a maximum production occurring at 96 spring water and 4 lake water under these conditions all the ca and a significant fraction of the co3 of the precipitate is spring supplied a radiocarbon age of 19 580 years obtained on a natural ikaite sample supports this conclusion with the springs supplying a large and probably variable portion of the carbonate and with apparent 14c age of the carbonate varying from spring to spring tufa of similar actual antiquity may yield significantly different 14c dates making tufa at this location unsuitable for absolute age dating by the radiocarbon method

laboratory study on coprecipitation of phosphate with ikaite in sea ice ikaite caco3 6h2o has recently been discovered in sea ice providing first direct evidence of caco3 precipitation in sea ice however the impact of ikaite precipitation on phosphate po4 concentration has not been considered so far experiments were set up at ph from 8 5 to 10 0 salinities from 0 to 105 temperatures from 24 c to 0 c and po4 concentrations from 5 to 50 mmol kg 1 in artificial sea ice brine so as to understand how ikaite precipitation affects the po4 concentration in sea ice under different conditions our results show that po4 is coprecipitated with ikaite under all experimental conditions the amount of po4 removed by ikaite precipitation increases with increasing ph changes in salinity s 35 as well as temperature have little impact on po4 removal by ikaite precipitation the initial po4 concentration affects the po4 coprecipitation these findings may shed some light on the observed variability of po4 concentration in sea ice

equatorial currents at 1000 m in the atlantic ocean twenty seven profiling alace palace floats were deployed in the equatorial atlantic during july august 1997 the floats were ballasted to drift at 1000 m for 10 to 14 days return to the surface while obtaining a temperature profile transmit data via satellite and then after one day return to 1000 m one year float paths are now available floats deployed on the equator were launched into a deep westward jet the jet extends some 1 o 2 o north of the equator with eastward motion observed in floats to the north of 2 on the equatorial current reverses in the central basin to the east in mid october and then back to the west in mid february flow to the north also reverses the short space and time scales contrast with earlier work based on fewer floats that inferred space scales of some 5 o 10 o in latitude and time scales greater than one year the new results are consistent with models that indicate that equatorial rossby waves are the cause of the reversing currents

deep currents and their interpretation as equatorial waves in the western pacific ocean abstract vertical profiles of current and density made within 5 latitude of the equator along longitudes 168 and 179 e the vicinity of the gilbert islands reveal multiple deep current reversals which are confined to the equator these current jets have amplitudes of roughly 5 20 cm s 1 vertical scales of order hundreds of meters and time scales longer than the one month of measurements during the cruise spectral analysis of profiles indicates that 1 meridional trapping varies roughly as the square root of the vertical scale 2 both east and north currents are coherent over meridional separations of 0 45 within roughly 1 30 of the equator and 3 zonal current lags vertical displacement by 4 in depth within 0 45 of the equator zonal coherence scales are smaller than the smallest separation of 3 30 along the equator kinetic energy decreases near the island chain current meter records taken over nearly two years near the islands suggest strong quasi annual variability in deep currents near t

wide but not ubiquitous distribution of glendonite in the doushantuo formation south china implications for ediacaran climate abstract glendonites are pseudomorphs of syndepositional or early authigenic ikaite caco3 6h2o that often forms at near freezing temperatures silicified glendonite has been reported from inner shelf deposits of the lower ediacaran doushantuo formation at a single stratigraphic section in south china where they are stratigraphically associated with the positive 13c excursion ep1 but predate the negative 13c excursion en3 shuram excursion indicating a period of cool climate somewhere between 609 ma and 551 ma this interpretation predicts a wider geographic distribution of ediacaran glendonites in equivalent strata in the yangtze block of south china to test this prediction we conducted a regional survey of doushantuo formation and found that although glendonites are not universally present they occur in expected stratigraphic intervals and in association with ep1 at two new sections representing inner shelf and intrashelf basin facies the wide but not ubiquitous distribution of doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica the calcite spar is characterized by highly variable and mostly negative 13c values as low as 37 indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment the new data suggest an early ediacaran cold period prior to en3 or the shuram excursion and facilitation of glendonite ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations

the effect of orthophosphate on carbonate mineral dissolution rates in seawater the dissolution kinetics of a variety of synthetic and biogenic carbonates low mg calcite mg calcite and aragonite were investigated in gulf stream seawater salinity s 35 spiked with orthophosphate to a concentration of 50 m phosphate is known to inhibit calcite dissolution and has been reported to catalyze the dissolution of aragonite the main goal of the study was to assess whether the degree of inhibition depends on the mineralogy of the dissolving carbonate phase dissolution experiments were conducted at 25 c and a pco2 of 10 2 5 atm using the ph stat technique dissolution rates were measured at saturation states ranging from 0 1 to 0 8 times saturation with respect to the dissolving carbonate mineral and were compared to rates measured in low phosphate seawater the degree of inhibition caused by phosphate addition increased as saturation state with respect to the dissolving carbonate mineral increased at a saturation state of 0 2 addition of phosphate reduced dissolution rates by about a factor of 2 closer to equilibrium at a saturation state of 0 8 dissolution rates were reduced by about a factor of 4 more importantly all carbonate samples whether of synthetic or biogenic origin were inhibited to similar degrees at equivalent saturation states the catalysis reported by previous workers for synthetic aragonite appears to be an artifact of its anomalous non linear dissolution rate over time because phosphate inhibits the dissolution of different carbonate minerals to similar degrees selective dissolution of aragonite from metastable carbonate sediments cannot be promoted by the presence of orthophosphate

ikaite tufa towers in ikka fjord southwest greenland their formation by mixing of seawater and alkaline spring water abstract ikka fjord in southwest greenland is the type locality for ikaite a metastable hexahydrate of calcium carbonate here ikaite forms submarine tufa columns rising up to 18 m above the fjord bottom the columns are spectacular examples of abiogenic carbonate precipitation in a cold seawater environment and so far represent the only known formation of ikaite in seawater we have analyzed the 2h 13c 14c 18o and 87sr contents and major element and minor element compositions of ikaite and of the different water types in and around ikka fjord in order to understand the formation of the ikka columns water from inside the columns is fresh but alkaline rich in ions of sodium bicarbonate and carbonate and has a stable isotope composition identical to precipitation falling on the nearby gronnedal ika igneous complex and we conclude that the tufa columns form over submarine springs issuing from the bottom of ikka fjord dissolution of unidentified sodium carbonate minerals in carbonatites in the igneous complex probably accounts for the peculiar chemistry of the springs ikaite supersaturation and precipitation is controlled by mixing of spring water and seawater at the cold 6 c fjord bottom and precipitation is accelerated by the formation of hydrated caco3o aq ion pairs while phosphate ions in the spring water act as inhibitor for precipitation of anhydrous carbonates we propose that the spring water seeps in ikka fjord literally create their own conduits in the form of the vertical chimney like columns with ikaite forming continuously at the tops of the columns the only limits to upward growth are winter ice and the fresh water layer capping the fjord during summer

the solubility and stabilization of ikaite caco3 6h2o from 0 to 25 c environmental and paleoclimatic implications for thinolite tufa we determined the solubility of ikaite from 0 to 25 c to model its saturation state in natural waters and test the hypothesis that it is the precursor of the calcite pseudomorphs in thinolite tufa of quaternary lake lahontan reversible solubility at buffered p co 2 yields the following expression for the dissolution constant of ikaite log k ikaite 0 15981 2011 1 t where t circ k and 0 circ c leq t leq 25 circ c derived standard state properties are delta g ikaite circ 2541 9 kjmol 1 pm 0 66 delta h ikaite circ 2973 4 kjmol 1 pm 1 02 s ikaite circ 306 6 jt 1 mol 1 pm 1 2 modeling shows that ikaite is undersaturated at all temperatures in seawater and in alkaline lakes but that it rapidly approaches saturation near 0 c its precipitation in near freezing marine sediments requires large additions of hco 3 to pore fluids from the diagenetic decomposition of organic matter its crystallization in tufas of alkaline lakes howeve

deep circulation in the equatorial atlantic ocean in the atlantic ocean the northward export of warm surface water is compensated by a southward flow of cold north atlantic deep water nadw the nadvv is transported southward along the american continental margin within the deep western boundary current dwbc some tracer and float observations have shown that part of the dwbc water flows eastward along the equator here we present three meridional velocity sections which give an instantaneous image of the lop to bottom zonal circulation along the equatorial atlantic they reveal the presence of equatorial deep jets edjs between 1 30 n and 1 30 s alternating eastward westward currents with short vertical scale surrounded by columns of eastward currents the extra equatorial jets or eejs at 2 n and 2 s in addition to direct velocity measurements tracer distributions give indications of water mass feeding of the edjs and eejs by the dwbc

submarine columns of ikaite tufa in the small ikka fjord in southwestern greenland we have studied remarkable submarine tufa columns forming over alkaline springs by abiotic precipitationof the metastable cold water mineral ikaite caco3 6h2o 1 3 the columns which support a rich marine life are up to 20 m high with annual growth of more than 50 cm we wish to nominate the locality which seems to be unique for classification as a geological world heritage site

ikaite pseudomorphs in the zaire deep sea fan an intermediate between calcite and porous calcite translucent brown aggregates of calcium carbonate crystals have been found in cores from the zaire deep sea fan west equatorial africa the aggregates are well preserved but very friable upon storage they become yellowish white and cloudy and release water chemical mineralogical xrd petrographical crystal morphological and stable isotope data demonstrate that the crystals have passed through three phases 1 an authigenic carbonate phase probably calcium carbonate which is represented by the external habit of the present crystals 2 a translucent brown ikaite phase caco 3 6h 2 o unstable at temperatures above 5 c and 3 a phase consisting of calcite microcrystals that are poorly cemented and form a porous mass within the crystal form of the morphologically unchanged first phase the transformation from the first phase into ikaite was probably a kinetic replacement the transformation from ikaite into the third phase occurred because of storage at room temperature the presence of ikaite is indicative of a low temperature anaerobic organic carbon rich marine environment ikaite is probably the precursor of a great number of porous calcite pseudomorphs and possibly also of many marine authigenic microcrystalline carbonate nodules

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures