tide model accuracy in the amundsen sea antarctica from radar interferometry observations of ice shelf motion 1 this study assesses the accuracy of tide model predictions in the amundsen sea sector of west antarctica tide model accuracy in this region is poorly constrained yet tide models contribute to simulations of ocean heat transfer and to the removal of tidal signals from satellite observations of ice shelves we use two satellite based interferometric synthetic aperture radar insar methods to measure the tidal motion of the dotson ice shelf at multiple epochs a single difference technique that measures tidal displacement and a double difference technique that measures changes in tidal displacement we use these observations to evaluate predictions from three tide models tpxo7 1 cats2008a opt and fes2004 all three models perform comparably well exhibiting root mean square deviations from the observations of 9 cm single difference technique and 10 cm double difference technique care should be taken in generalizing these error statistics because 1 the dotson ice shelf experiences relatively small semidiurnal tides and 2 our observations are not sensitive to all tidal constituents an error analysis of our insar based methods indicates measurement errors of 7 and 4 cm for the single and double difference techniques respectively a model based correction for the effect of fluctuations in atmospheric pressure yields an 6 improvement in the agreement between tide model predictions and observations this study suggests that tide model accuracy in the amundsen sea is comparable to other antarctic regions where tide models are better constrained these methods can be used to evaluate tide models in other remote antarctic waters

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

variations in thickness of layer 3 dominate oceanic crustal structure abstract seismic refraction studies have determined that while much of the crust underlying the world s oceans is about 7 km thick it also occurs in lesser and considerably greater thicknesses here we show that vastly different thicknesses of oceanic crust formed at ridges by seafloor spreading are generally characterized by the two gradient velocity structure recognized as typical of 6 7 km thick oceanic crust adopting a standard we study ninety published seismic velocity structures of oceanic crust ranging in thickness from 2 to 37 km several structures formed in midplate settings ocean islands and seamounts are also considered for comparison regardless of origin ridge or midplate we find that the percentage of the whole crust formed by layer 2 systematically decreases with increasing total crustal thickness while the average velocity of layer 2 varies widely for all crust the average velocity of layer 3 increases systematically with increases in the average whole crustal thickness and velocity crust formed in midplate settings differs in that the thickness of layer 2 velocity crust is generally two to three times that of crust formed at ridges residual depths were calculated for oceanic crust by removing the effects of sediment loading and subsidence due to lithospheric cooling most of the data fall close to a model whereby different crustal thicknesses result from different extents of partial melting of oceanic upper mantle the crustal sections were restored to zero age assuming the average depth of emplacement for 7 km thick oceanic crust is 2 5 km below sea level from this restoration it appears that the depth to the top of layer 3 at the time it was formed is 4 25 1 25 km below sea level regardless of whole crustal thickness or spreading rate these results suggest that the mechanism of construction of oceanic crust is in many ways remarkably uniform despite very large changes in the total thickness of the crust produced very basic questions remain it is for instance not at all clear why layer 2 and layer 3 exist in the proportions they do while neutral buoyancy or melt trapping at the base of a brittle lid may account for local properties of the layer 2 3 boundary they do not seem adequate to account for the global phenomenon

residual ocean tide signals from satellite altimetry grace gravity fields and hydrodynamic modelling summary improvements of a global state of the art ocean tide model are identified and quantified by applying three independent approaches namely i empirical ocean tide analysis of multimission altimeter data ii evaluation of grace data and gravity field models and iii high resolution hydrodynamic modelling although these approaches have different capabilities to sense ocean tides they obtain results which are basically consistent one with each other the analysis of altimeter data clearly identifies significant residual amplitudes over shallow water for all major diurnal and semidiurnal constituents and the non linear tide m4 grace data and the time series of monthly gravity field models exhibit on a larger scale residual ocean tide signals over much the same areas the analysis of dynamic residuals of hydrodynamic modelling with data assimilation proves the validity of linear dynamics in the deep ocean and shows correlation of dynamic residuals with energy dissipation in these areas

the influence of porosity and crack morphology on seismic velocity and permeability in the upper oceanic crust 1 the purpose of this study is to explore the relationships between porosity crack morphology seismic velocity and permeability in the upper oceanic crust in a theoretical model velocity is a quadratic function of porosity and the coefficients are functions of the fractional area of asperity contact af across the cracks a measure of crack morphology thus v v af fits to data sets from the lava and dike sections in holes 504b and 1256d yield af 0 096 8 and 0 045 3 with rms errors of 1 7 and 0 3 respectively lower values of af account for the high porosities and low velocities observed in layer 2a after 0 2 ma the porosities of both layer 2a and the deeper part of the lava pile remain in the range 8 4 the observed increase of layer 2a velocities after 0 2 ma is caused largely by changing crack morphology as opposed to decreasing porosity at 8 porosity an increase of af from 0 003 to 0 1 accounts for an increase of velocity from 3 to 5 km s an empirical log linear relationship between permeability and v suggests a relationship between and af as well this relationship between and v can be explained if the permeability coefficient o is a closely constrained quadratic function of the area of asperity contact af af is thus the primary variable affecting both seismic velocities and the permeability of the uppermost oceanic crust

effects of early diagenesis on molecular distributions and carbon isotopic compositions of leaf wax long chain biomarker n alkanes comparison of two one year long burial experiments two burial experiments were performed to compare and contrast the effects of degradation and early diagenesis on the molecular distributions and compound specific carbon isotope compositions of leaf wax n alkanes under different conditions leaves of the bamboo neosinocalamus affinis and the shrub osmanthus fragrans were packaged in perforated aluminum packets and buried in soil at two different subtropical locations in china the packets were recovered after successive intervals totaling 1 year and the n alkane properties of their leaves compared to those of the fresh leaves and the surrounding soil concentrations of total leaf n alkanes decreased in both experiments the waxes of n affinis exhibited a fairly rapid decrease in their proportions of c23 c27n alkanes and increases of less than 1 in n alkane 13c values during the burial time in contrast the leaves of o fragrans showed little change in either their molecular distributions or isotopic compositions during burial the results of the two experiments indicate that early diagenesis can lead to losses of leaf wax biomarker n alkanes during burial in soil but has little to no effect on their stable carbon isotopic signatures validating the reliability of compound specific n alkane 13c values as proxies for paleoecological and paleoenvironmental reconstructions

evolution of seismic layer 2b across the juan de fuca ridge from hydrophone streamer 2 d traveltime tomography how oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the earth s interior and the oceans although considerable work has been done characterizing the evolution of seismic layer 2a there has been little analysis of the processes that affect layer 2b after formation here we present high resolution 2 d tomographic models of seismic layer 2b along 300 km long multichannel seismic transects crossing the endeavour northern symmetric and cleft segments of the juan de fuca ridge these models show that seismic layer 2b evolves rapidly following a different course than layer 2a the upper layer 2b velocities increase on average by 0 8 km s and reach a generally constant velocity of 5 2 0 3 km s within the first 0 5 myr after crustal formation this suggests that the strongest impact on layer 2b evolution may be that of mineral precipitation due to active hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber variations in upper layer 2b velocity with age at time scales 0 5 ma show correlation about the ridge axis indicating that in the long term crustal accretion processes affect both sides of the ridge axis in a similar way below the 0 5 ma threshold differences in 2b velocity are likely imprinted during crustal formation or early crustal evolution layer 2b velocities at propagator wakes 5 0 0 2 km s where enhanced faulting and cracking are expected and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2b analysis of the layer 2b velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2b velocities respectively additionally the distance between present up flow and down flow zones is related to the amount of sediment cover because as sediment cover increases and basement outcrops become covered direct pathways from the igneous basement through the seafloor are cut off forcing convective cells to find alternate paths

ice shelf elevation changes due to atmospheric pressure variations the inverse barometer effect ibe is the isostatic response of ocean surface height to changes in atmospheric pressure p air at a rate of about 1 cm hpa 1 the ibe is a significant contributor to variability of ice shelf surface elevation ice as we demonstrate with simultaneous global positioning system measurements of ice and local measurements of p air from the amery brunt and ross ice shelves antarctica we find that an ibe correction is justified for frequencies covering the weather band 0 03 0 5 cpd cycles per day the ibe correction reduces the standard deviation of the weather band signal of ice from 9 cm to 3 cm with this correction the largest remaining high frequency error signal in ice is the inaccuracy of the present generation of antarctic tide models estimated to be of order 10 cm for most of antarctica

river discharge influences on particulate organic carbon age structure in the mississippi atchafalaya river system 1 applying ramped pyrolysis radiocarbon analysis to suspended river sediments we generate radiocarbon 14c age spectra for particulate organic carbon poc from the lower mississippi atchafalaya river system mars to better understand a major river system s role in carbon transport ramped pyrolysis 14c analysis generates age distributions of bulk carbon based on thermochemical stability of different organic components our results indicate higher proportions of older material in the poc during higher discharge ages increase throughout the high discharge age spectra indicating that no single component of the poc is responsible for the overall age increases observed instead older material is contributed across the poc age spectrum and unrelated to increased bedload suspension in this comparison of 2 spring discharges less than half of the poc transported during higher discharge is less than 1000 14c years in age constraining of the role of the mars as a flux of atmospheric co2 toward longer term sedimentary sinks in the mississippi delta and the gulf of mexico the results suggest that delta building processes benefit disproportionately from high discharge events carrying larger amounts of sediment because these events involve both a higher proportion of millennially aged carbon from floodplain exchange of poc and a potentially higher proportion of petrogenic carbon 30 530 increase overall an internally consistent picture of po14c age distributions from a major river system emerges as differences in space and time are small compared to the range of ages of poc sources in such a large basin

runoff driven export of particulate organic carbon from soil in temperate forested uplands we characterise the sources pathways and export fluxes of particulate organic carbon poc in a headwater catchment in the swiss alps where suspended sediment has a mean organic carbon concentration of 1 45 0 06 by chemically fingerprinting this carbon and its potential sources using carbon and nitrogen elemental and isotopic compositions we show that it derives from binary mixing between bedrock and modern biomass with a soil like composition the hillslope and channel are strongly coupled allowing runoff to deliver recent organic carbon directly to the stream beyond a moderate discharge threshold at higher flows more biomass is mobilised and the fraction of modern carbon in the suspended load reaches 0 70 increased from 0 30 during background conditions significant amounts of non fossil organic carbon are thus transferred from the hillslope without the need for extreme events such as landsliding precipitation is key as soon as the rain stops biomass supply ceases and fossil carbon again dominates we use rating curves modelled using samples from five storm events integrated over 29 year discharge records to calculate long term export fluxes of total poc and non fossil poc from the catchment of 23 3 5 8 and 14 0 4 4 t km 2 yr 1 respectively these yields are comparable to those from active mountain belts yet the processes responsible are much more widely applicable such settings have the potential to play a significant role in the global drawdown of carbon dioxide via riverine biomass erosion and their contribution to the global flux of poc to the ocean may be more important than previously thought

the roof of an axial magma chamber a hornfelsic heat exchanger the heat flux from an axial magma chamber into the convecting hydrothermal system at mid ocean ridges is governed by the conductive boundary layer separating them the nature of this critical interface has been modeled and seismically imaged but its characteristics have hitherto rarely been documented in ocean crust here hornfelsic rocks from the sheeted dike gabbro transitions at two tectonic exposures of fast spreading east pacific rise crust at the pito and hess deeps and in the oman and troodos ophiolites are described these rocks record thermal metamorphism to hornblende and pyroxene hornfels at 700 1000 c these temperatures in conjunction with their geological relationships imply that the hornfels are preserved fragments of conductive boundary layers their distribution at the base of sheeted dike complexes in narrow contact aureoles and dikes intruding the uppermost gabbros tracks the vertical migration of axial magma chambers over minimum depth ranges of 200 400 m the heat flux across the hornfelsic aureoles 11 44 mw km is comparable to hydrothermal fluxes released along fast spreading ridges confirming that the heat driving hydrothermal convection is transferred across conductive boundary layers

tides on the ross ice shelf observed with icesat 1 the ice cloud and land elevation satellite icesat provides the first opportunity for measurement of surface elevation hi over the portions of the antarctic ice shelves that are south of the european remote sensing ers satellite maximum latitude 81 5 s the dominant source of short period variability in hi is ocean tides we use crossover elevation difference hi data from the ross ice shelf ris to demonstrate icesat s ability to detect the tidal signal and to compare the accuracy of several tide models the root mean square rms value of all ris measurements of hi is 0 74 m after removing the tide using the most accurate model the rms of the residual signal in regions of optimal model performance is 0 16 0 03 m this value corresponds to an uncertainty in hi of 0 11 0 02 m we postulate that the primary sources of the residual signal are tide model errors and the inverse barometer effect

tidally induced variations in vertical and horizontal motion on rutford ice stream west antarctica inferred from remotely sensed observations to better understand the influence of stress changes over floating ice shelves on grounded ice streams we develop a bayesian method for inferring time dependent 3 d surface velocity fields from synthetic aperture radar sar and optical remote sensing data our specific goal is to observe ocean tide induced variability in vertical ice shelf position and horizontal ice stream flow thus we consider the special case where observed surface displacement at a given location can be defined by a 3 d secular velocity vector a family of 3 d sinusoidal functions and a correction to the digital elevation model used to process the sar data using nearly 9 months of sar data collected from multiple satellite viewing geometries with the cosmo skymed 4 satellite constellation we infer the spatiotemporal response of rutford ice stream west antarctica to ocean tidal forcing consistent with expected tidal uplift inferred vertical motion over the ice shelf is dominated by semidiurnal and diurnal tidal constituents horizontal ice flow variability on the other hand occurs primarily at the fortnightly spring neap tidal period m sf we propose that periodic grounding of the ice shelf is the primary mechanism for translating vertical tidal motion into horizontal flow variability causing ice flow to accelerate first and most strongly over the ice shelf flow variations then propagate through the grounded ice stream at a mean rate of 29 km d and decay quasi linearly with distance over 85 km upstream of the grounding zone

how crack porosity and shape control seismic velocities in the upper oceanic crust modeling downhole logs from holes 504b and 1256d mounting evidence from holes 504b and 1256d suggests that porosity is the principal factor affecting velocities in the upper oceanic crust spheroidal inclusion and asperity compression models based on reprocessed sonic velocity logs and apparent fractional porosities estimated from deep resistivity logs reveal how both porosity and the geometry of the pore space affect seismic velocities in layer 2 models that best match the data indicate the following first there are three populations of cracks in hole 504b most of the transition zone and the dike section are populated by low concentrations of weak cracks while the upper part of the transition zone and the extrusive pile contain a higher concentration of stiffer cracks similarly the deepest part of the dike section in hole 1256d can be modeled by a dilute concentration of thin or weak cracks while the overlying dikes the transition zone and the extrusive pile contain a higher concentration of stiffer cracks second in a striking confirmation that porosity controls velocities throughout layer 2 90 or more of the variance of sonic velocities logged at both sites is explained by porosity in these models while third the effect of pressure on the variation of sonic velocity is essentially negligible fourth while there is no direct correlation between crack populations and igneous lithostratigraphy some changes of crack population do correspond to metamorphic transitions and fifth velocities typical of layer 3 are reached when the porosity falls to low values 0 2 in hole 1256d and 0 6 in hole 504b

modeling antarctic tides in response to ice shelf thinning and retreat tides play an important role in ice sheet dynamics by modulating ice stream velocity fracturing and moving ice shelves and mixing water beneath them any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability here we show that removal or reduction in extent and or thickness of the ross and ronne filchner ice shelves would have a significant impact on the tides around antarctica the ronne filchner appears particularly vulnerable with an increase in m2 amplitude of over 0 5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf sheet dynamics these results highlight the importance of understanding tidal feedbacks on ice shelves streams due to their influence on ice sheet dynamics

loading and fate of particulate organic carbon from the himalaya to the ganga brahmaputra delta abstract we use the evolution of river sediment characteristics and sedimentary corg from the himalayan range to the delta to study the transport of corg in the ganga brahmaputra system and especially its fate during floodplain transit a detailed characterisation of both mineral and organic particles for a sampling set of river sediments allows taking into account the sediment heterogeneity characteristic of such large rivers we study the relationships between sediment characteristics mineralogy grain size specific area and corg content in order to evaluate the controls on corg loading contributions of c3 and c4 plants are estimated from corg stable isotopic composition 13corg we use the evolution of 13corg values from the himalayan range to the delta in order to study the fate of corg during floodplain transit ganga and brahmaputra sediments define two distinct linear relations with specific area in spite of 4 5 times higher specific area ganga sediments have similar corg content grain size and mineralogy as brahmaputra sediments indicating that specific area does not exert a primary control on corg loading the general correlation between the total corg content and al si ratio indicates that corg loading is mainly related to 1 segregation of organic particles under hydrodynamic forces in the river and 2 the ability of mineral particles to form organo mineral aggregates bed and suspended sediments have distinct 13corg values in bed sediments 13corg values are compatible with a dominant proportion of fossil corg derived from himalayan rocks erosion suspended sediments from himalayan tributaries at the outflow of the range have low 13corg values 24 8 average indicating a dominant proportion of c3 plant inputs in the brahmaputra basin 13corg values of suspended sediments are constant along the river course in the plain on the contrary suspended sediments of the ganga in bangladesh have higher 13corg values 22 4 to 20 0 consistent with a significant contribution of c4 plant derived from the floodplain our data indicate that during the plain transit more than 50 of the recent biogenic corg coming from the himalaya is oxidised and replaced by floodplain corg this renewal process likely occurs during successive deposition erosion cycles and river course avulsions in the plain

velocity and attenuation in young oceanic crust new downhole log results from dsdp odp iodp holes 504b and 1256d 1 to characterize the acoustic properties of oceanic crust and investigate the nature of the oceanic layer 2 3 seismic boundary we analyze sonic logging waveforms recorded in the two deepest holes ever drilled in intact oceanic crust ocean drilling program odp integrated ocean drilling program iodp hole 1256d and deep sea drilling program dsdp odp hole 504b hole 1256d penetrated 15 ma old crust on a superfast spreading segment of the cocos plate while hole 504b was drilled in a 6 ma old section of an intermediate spreading segment of the nazca plate careful reprocessing of different sets of waveforms allows us to draw depth profiles of the primary parameters controlling wave propagation in the crust compressional and shear velocities vp and vs and attenuation the results underline the importance of proper filtering and processing parameters for the acquisition of acoustic logs in hard rocks while the reprocessed vp logs improve previous data particularly at the bottom of hole 1256d the vs logs represent significant enhancements in quality and in extent of previous profiles in the two holes attenuation results provide the first measure of intrinsic attenuation in these holes the velocity and attenuation logs confirm that hole 504b had reached oceanic layer 3 without recovering gabbros conversely while gabbros were recovered in hole 1256d no layer 3 velocity values were recorded in the interval logged however the reprocessed data suggest that the transition to layer 3 might occur within the deepest 87 m of the hole that were not logged or immediately below accordingly the layer 2 3 seismic boundary does not appear to be related to the top of the plutonic crust despite different ages spreading rates and mineralogy however the two sites display remarkably similar velocity and attenuation profiles through the entire crustal sections logged suggesting that they can be reliably considered representative of the acoustic properties of the nazca cocos spreading system and more generally of undisturbed oceanic crust

a rouse based method to integrate the chemical composition of river sediments application to the ganga basin 1 the ganga river is one of the main conveyors of sediments produced by himalayan erosion determining the flux of elements transported through the system is essential to understand the dynamics of the basin this is hampered by the chemical heterogeneity of sediments observed both in the water column and under variable hydrodynamic conditions using acoustic doppler current profiler adcp acquisitions with sediment depth profile sampling of the ganga in bangladesh we build a simple model to derive the annual flux and grain size distributions of the sediments the model shows that ca 390 30 mt of sediments are transported on average each year through the ganga at haring bridge bangladesh modeled average sediment grain size parameters d 50 and d 84 are 27 4 and 123 9 mm respectively grain size parameters are used to infer average chemical compositions of the sediments owing to a strong grain size chemical composition relation the integrated sediment flux is characterized by low al si and fe si ratios that are close to those inferred for the himalayan crust this implies that only limited sequestration occurs in the gangetic floodplain the stored sediment flux is estimated to c a 10 of the initial himalayan sediment flux by geochemical mass balance the associated globally averaged sedimentation rates in the floodplain are found to be ca 0 08 mm yr and yield average himalayan erosion rate of ca 0 9 mm yr this study stresses the need to carefully address the average composition of river sediments before solving large scale geochemical budgets citation lupker m c france lanord j lave j bouchez v galy f metivier j gaillardet b lartiges and j l mugnier 2011 a rouse based method to integrate the chemical composition of river sediments application to the ganga basin

assimilation of grace tide solutions into a numerical hydrodynamic inverse model 1 we assimilate localized mass anomalies inferred from grace ranging measurements into a hydrodynamic model to improve tidal solutions around antarctica for the m2 s2 and o1 constituents the variational approach used accounts for the spatial averaging of tidal elevations implicit in the mass anomaly parametrization used for the grace tidal analysis as well as spatial correlation of errors in the resulting estimates the inverse solution shows better agreement with independent station tide measurements around antarctica and it reduces cross over residuals for icesat laser altimeter data over the filchner ronne and ross ice shelves demonstrating that grace data can provide useful constraints for improving hydrodynamic tidal models at high latitudes

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

branched gdgt signals in fluvial sediments of the danube river basin method comparison and longitudinal evolution abundances and distributional changes of branched glycerol dialkyl glycerol tetraethers brgdgts in fluvially influenced sediments are used in various paleoclimate studies to reconstruct variations in soil export continental air temperature and soil ph in corresponding river basins for accurate interpretation of these records it is important to understand the provenance and the evolution of biomarker signals as they move through the river system here we investigate the brgdgt composition of modern river sediments of the danube river the second largest river in europe brgdgt based mean annual air temperature and soil ph parallel the actual values of air temperature and soil ph from the upper to the lower basin showing that signals predominantly reflect local as opposed to basin wide environmental conditions furthermore data generated using the recently developed method with improved chromatography separating the 6 methyl isomers from the 5 methyl isomers was compared with that resulting from the conventional method we show that the temperatures and ph values reconstructed using the data obtained by improved chromatography best resemble the local environmental conditions throughout the danube river basin our results highlight the importance of in depth studies within river systems to better understand the provenance of biomarker signals in fluvially derived sedimentary archives

the geochemical filter of large river confluences abstract this study reports the behaviour and fate of major and trace elements in solid and solution in the encontro das aguas mixing zone in the amazonian basin this area results from the confluence of acidic organic rich rio negro and andean sediment rich rio solimoes the differences existing between these two water masses are likely to modify the partitioning of elements between solid and solution or to induce losses by physical or chemical removal to account for lateral and vertical heterogeneities in the river sections the fluxes of elements in dissolved and solid loads were estimated as accurately as possible using an interpolation technique a general loss of suspended particulate matter spm of 23 is measured 80 km after the confluence but the various elements and their associated hosted minerals are not affected in a similar way sispm caspm naspm or srspm mostly associated with coarse phases quartz and ca na feldspars are preferentially lost refractory elements cospm crspm tispm alspm nispm other alkali a and alkali earth ae elements kspm mgspm baspm fespm or organic carbon oc are lost to a lesser extent due to their occurrence in finer fractions such as clays smectite illite or kaolinite oxides and particulate organic matter pom in solution a ae and cudiss mostly originating from the rio solimoes behave conservatively by contrast refractory elements coming mostly from the rio negro exhibit important losses from 10 for doc to 60 for codiss changes in ph and ionic strength during the mixing may induce a sorption of these elements to particles supplied by the rio solimoes a clustering and or a settling of nanokaolinites phases or a sorption of aldiss fediss codiss mndiss or zndiss by dissolved organic matter dom the differential elemental settling at a river confluence could thus induce a phase shift between element supply and export out of a watershed the physical and chemical processes reported here for a river confluence could be applied in other mixing zones such as estuaries or mining exhausts

controls on the age of vascular plant biomarkers in black sea sediments abstract transfer of organic carbon oc from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport before transport however terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils using compound specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated here we show compound specific radiocarbon 14c ages of terrigenous biomarkers and bulk 14c ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the black sea 14c ages of long chain n alkanes long chain n fatty acids and total organic carbon toc are highest in front of the river mouths correlating well with bit branched and isoprenoid tetraether indices which indicates contribution of pre aged soil derived terrigenous organic matter the radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter average terrestrial residence times of vascular plant biomarkers deduced from n c29 31 alkanes and n c28 30 fatty acids ages from stations directly in front of the river mouths range from 900 70 years to 4400 170 years these average residence times correlate with size and topography in climatically similar catchments whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the black sea catchment along transect data imply petrogenic contribution of n c29 31 alkanes and input via different terrigenous biomarker transport modes i e riverine and aeolian resulting in aged biomarkers at offshore core locations because n c29 31 alkanes show contributions from petrogenic sources n c28 30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers moreover sedimentary n c28 and n c30 fatty acids appear clearly much less influenced by autochthonous sources than n c24 and n c26 fatty acids as indicated by increasing radiocarbon ages with increasing chain length and are thus more representative as vascular plant biomarkers

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

ice shelf tidal motion derived from ers altimetry 1 ocean tides beneath floating ice shelves can affect heat and water circulations within the subshelf cavity which may influence patterns of basal melting accurate tidal predictions are essential to eliminate vertical tide motions when mapping the flow speeds and thickness changes of floating ice global ocean tide solutions are typically accurate to 2 3 cm in amplitude however their coarse resolution limits their utility in coastal regions moreover the absence of satellite and extensive gauge station data in the polar regions has resulted in significant differences between recent tide model solutions around the antarctic continent we use 9 years of high resolution european remote sensing ers satellite radar altimeter range measurements and a modified form of the orthotide method to generate tidal solutions for a series of ice shelves around the antarctic peninsula we compare our tidal solution at george vi ice shelf on the western coast of the antarctic peninsula to direct measurements from british antarctic survey tide gauge records and contrast the results with solutions from the fes99 and kantha2 0 global and the cats01 02 antarctic ocean tide models the average root mean square vector difference between the tide gauge and tide model predictions of amplitude and phase was 10 9 17 1 4 2 and 15 4 cm for the ers ice shelf kantha2 0 cats01 02 and fes99 models respectively tidal predictions derived from the ers ice shelf model are closer to the tide gauge recordings than those of the global models and the inclusion of ers altimeter data may lead to improved global model performance

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

in situ produced branched glycerol dialkyl glycerol tetraethers in suspended particulate matter from the yenisei river eastern siberia abstract soil derived branched glycerol dialkyl glycerol tetraethers brgdgts in marine river fan sediments have a potential use for determining changes in the mean annual temperature mat and ph of the river watershed soils prior to their incorporation in marine sediments the compounds are transported to the marine system by rivers however emerging evidence suggests that the brgdgts in freshwater systems can be derived from both soil run off and in situ production the production of brgdgts in the river system can complicate the interpretation of the brgdgt signal delivered to the marine system therefore we studied the distribution of brgdgt lipids in suspended particulate matter spm of the yenisei river chromatographic improvements allowed quantification of the recently described hexamethylated brgdgt isomer characterized by having two methyl groups at the 6 6 instead of the 5 5 positions in an environmental dataset for the first time this novel compound was the most abundant brgdgt in spm from the yenisei its fractional abundance correlated well with that of the 6 methyl isomer of the hexamethylated brgdgt that contains one cyclopentane moiety the yenisei river watershed is characterized by large differences in mat 11 c as it spans a large latitudinal range 46 73 n which would be expected to be reflected in brgdgt distributions of its soils however the brgdgt distributions in its spm show little variation furthermore the reconstructed ph values are high compared to the watershed soil ph we therefore hypothesize that the brgdgts in the yenisei river spm are predominantly produced in situ and not primarily derived from erosion of soil this accounts for the absence of a change in the temperature signal as the river water temperature is more stable using a lake calibration the reconstructed temperature values agree with the mean summer temperatures mst recorded the brgdgts delivered to the sea by the yenisei river during this season are thus not soil derived possibly complicating the use of brgdgts in marine sediments for palaeoclimate reconstructions

tides on filchner ronne ice shelf from ers radar altimetry 1 we use harmonic analysis of 8 years of ers satellite radar altimeter ra data at orbital crossovers to retrieve complex amplitude amplitude and phase coefficients for several major tidal harmonics over the filchner ronne ice shelf fris antarctica we describe a method for estimating the accuracy of this method which ranges from 2 to 8 cm per harmonic a comparison between m2 complex amplitude from a recent ocean model and from our ers ra analyses identifies two regions of the fris where the ra data are inconsistent with the model in both regions the differences can be attributed to incorrect specification of the grounding line location in the model our study demonstrates the value of ers ra data in antarctic ice shelf tide modeling and the potential for future altimeter satellites with high polar orbits to contribute to the definition of global tide height variations

temporal variability in composition and fluxes of yellow river particulate organic matter this study examines temporal variations of the abundance and carbon isotopic characteristics of particulate organic carbon poc and specific source compounds in the context of hydrological variability in the yellow river the content and bulk carbon isotopic characteristics 13c and 14c of poc were relatively uniform over the hydrologic seasonal cycle we attribute these temporally invariant geochemical characteristics to the dominant contribution of loess material to the suspended particulate matter spm in contrast molecular level signals revealed that hydrologic conditions exert a significant influence on the proportional contributions of petrogenic and especially fresh plant derived oc while pre aged soil oc is mobilized via deeper erosion processes e g gully erosion mudslides and is independent of hydrodynamics and surface runoff a coupled biomarker isotope mixing model was applied to estimate the time varying supply of contemporary modern biomass pre aged soil and fossil oc components to chinese marginal seas from the yellow river we found that natural e g precipitation and human induced e g water and sediment regulation variations in hydrological regime strongly influence the flux with the magnitude of the corresponding annual fluxes of poc ranging between 0 343 0 122 mt yr 1 and 0 581 0 213 mt yr 1 but less strongly infleunce proportions of the different oc constituents inter annual differences in pre aged soil and fossil oc fluxes imply that extreme climate events e g floods modulate the exhumation and export of old carbon to the ocean but the oc homogeneity in the pre aged mineral soil dominated watersheds facilitates robust predictions in terms of oc transport dynamics in the past sediment cores and in the future

four dimensional upper crustal construction at fast spreading mid ocean ridges a perspective from an upper crustal cross section at the hess deep rift abstract the faulted walls of the hess deep rift in the equatorial pacific provide one of the few significant tectonic windows into the oceanic crust created at a fast spreading mid ocean ridge the 5000 m deep rift graben exposes a slightly dismembered section of oceanic crust created at the east pacific rise 1 ma the upper portion of the north wall of the rift features a laterally extensive exposure of upper crustal rock units similar to those found in many ophiolite complexes for tens of kilometers along the rift wall basaltic lavas with sparse dikes grade down into a spectacular sheeted dike complex that is underlain locally by a heterogeneous assemblage of gabbroic rocks the geometry of lava flows dikes and fault zones that developed during magmatic accretion provide constraints on the cross axis temporal evolution of the upper crust in this area outcrop scale digital imagery from submersible vehicles provides a well constrained geological framework for samples collected from these upper crustal rock units and the geochemistry of lava and dike samples provides additional temporal constraints on crustal accretion and the role of along axis magma transport during accretion integrated results of geological and geochemical investigations suggest a four dimensional model for upper crustal construction whereby tectonic and magmatic processes act in concert to construct the upper oceanic crust within a few kilometers few tens of thousands of years of a fast spreading ridge axis in this model a sub axial melt lens where it exists is recharged from below with distinct parental melts and limited along axis mixing preserves geochemical segmentation of the melt lens dikes emanate from distinct portions of the melt lens and transport magmas vertically as well as significant distances laterally along axis erupting lavas in the special case where magmas ascend through dikes to higher levels in the crust and intersect the seafloor differences in the phenocryst contents and compositions of lavas and dikes suggests that density filtering of buoyant magmas among other factors including magma overpressure and orientations of local stresses plays a role in the eruption of magma on the surface during spreading and magmatic construction subaxial subsidence accommodates thickening of the basaltic lava unit sub axial subsidence faulting and block rotation result in an upper crust with inward dipping toward the axis lava flows and outward dipping away from the axis dikes substantial differences in upper crustal geology may result from segment scale variations in which vertical magma delivery dominates in areas of robust magma supply likely over sites of recently recharged melt lenses at segment centers but lateral magma transport dominates in areas of relatively lower magma supply possibly toward segment ends

surface elevation changes at the front of the ross ice shelf implications for basal melting 1 rapid melting beneath the ross ice shelf ris occurs near the ice front likely in response to a secondary buoyant plume with tidal mixing and is sensitive to seasonal water temperatures in front of the ice shelf the front of the ris is examined using glas icesat laser altimetry data spatial and temporal changes in surface elevations are attributed to enhanced basal melting of the ice shelf near the ice front melt rates b increase exponentially as the front is approached from approximately zero at 40 km from the front to an average of 2 8 1 0 m a 1 within the front kilometer melt estimates within the front 60 km are best fit by the relationship b 2 0 exp x 11900 m a 1 where x denotes distance from the front frontal melt totals approximately 16 km3 a 1 in the front 40 km which accounts for between 10 and 40 of current published estimates of total melt beneath the ris spatial averaging along the front reveals a different pattern of melt in regions that have recently calved as compared to regions that have not calved frontal melt is modeled as a one dimensional buoyant plume with tidal currents included these model results imply that modest increases in sea surface temperatures will lead to considerable increases in melting beneath the ice shelf front

identification and carbon isotope composition of a novel branched gdgt isomer in lake sediments evidence for lacustrine branched gdgt production branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids that occur ubiquitously in soils and lacustrine sediments and have great potential as proxy indicators for paleotemperature and ph reconstructions initially brgdgts in lakes were thought to originate from soils of the watershed the composition of the lacustrine brgdgt pool however often differs substantially from that in catchment soils complicating the application of the brgdgt paleothermometer to lake sediments this suggests that terrigenous brgdgt signals in lacustrine sedimentary archives may be affected by aquatic in situ production in sediments of a swiss mountain lake we detected a novel hexamethylated brgdgt which elutes between the known 5 and 6 methyl brgdgt isomers during hplc ms analysis this novel isomer accounted for 8 5 of the total brgdgts most remarkably this brgdgt was not detected in soils collected from the catchment of the lake providing circumstantial evidence for an in situ brgdgt source in the lake s water column or sediments isolation of the compound by preparative hplc and subsequent gc ms analysis of the alkyl chains revealed that the novel brgdgt comprises two structural isomers one possesses a 5 13 16 and a 6 13 16 trimethyloctacosanyl moiety and constitutes 84 of the new brgdgt the second contains a 13 16 dimethyloctacosanyl and a 5 13 16 23 tetramethyloctacosanyl moiety the 13c values of both the alkyl chains derived from the novel brgdgt 46 and all other major brgdgts 43 to 44 were significantly lower than those of brgdgt derived alkanes in catchment soils 27 to 28 further attesting to in situ production of brgdgts in the studied lake

improving antarctic tide models by assimilation of icesat laser altimetry over ice shelves 1 assimilation of laser altimeter data from the ice cloud and land elevation satellite icesat significantly improves the accuracy of ocean tide models for the ross ice shelf ris for the most energetic tidal harmonic k1 assimilation reduces the root mean square error rmse between the model and a set of 16 independent tide records on and near the ris from 6 0 to 2 8 cm and the combined rmse for the six most energetic tidal harmonics from 7 7 to 5 4 cm when only the six most recent and highest quality tide records are considered the combined rmse is 4 8 cm this value is close to the uncertainty expected from tidal analyses of the short 1 2 month validation records indicating that assessing further improvements in tide model accuracy will require development of a higher quality validation data set

tide deflection of campbell glacier tongue antarctica analyzed by double differential sar interferometry and finite element method abstract a glacier tongue the terminus of a glacier projecting out from the coastline and floating over the ocean experiences vertical deflection due to the fluctuation of ocean tide accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice we extracted the tidal deflection of campbell glacier tongue cgt one of the fast flowing glacier tongues in east antarctica by using 120 double differential interferometric sar ddinsar images from the 16 cosmo skymed one day tandem interferometric sar image pairs obtained during 2010 and 2011 a map of tide deflection ratio map defined as the ratio of the tidal deflection over tide height was generated by pixel based linear regression between the ddinsar derived tidal deflection and the tidal variation predicted by various tide models such as tpxo7 1 fes2004 cats2008a and ross inv after the inverse barometer effect correction we also generated the maps of r 2 root mean square error rmse and intercept of the linear regression model we confirmed that the horizontal flow of the campbell glacier is steady over the whole data acquisition period due to the fact that values were close to zero over the grounded part of the glacier ross inv provided the most reliable map with the highest r 2 0 97 and the smallest rmse 0 3 cm beyond the hinge zone than other tide models the spatial variation of the tidal response of the whole cgt was clearly defined from the map the grounding line retreated by 0 3 1 5 km in comparison with that in 1996 defined by rignot et al 2011a the ice thickness of cgt was estimated to be 397 71 m from icesat surface elevation data the young s modulus of cgt was found to be 0 5 1 3 gpa 0 8 gpa at an ice thickness of 397 m by simulating the in the hinge zone using a 2 dimensional finite element method

soil carbon storage controlled by interactions between geochemistry and climate rising temperature can increase soil organic matter decomposition and co2 emissions in a 4 000 km north south transect in chile and antarctica soil geochemistry which can be modified by climate is the dominant direct control of carbon storage soils are an important site of carbon storage1 climate is generally regarded as one of the primary controls over soil organic carbon1 2 but there is still uncertainty about the direction and magnitude of carbon responses to climate change here we show that geochemistry too is an important controlling factor for soil carbon storage we measured a range of soil and climate variables at 24 sites along a 4 000 km long north south transect of natural grassland and shrubland in chile and the antarctic peninsula which spans a broad range of climatic and geochemical conditions we find that soils with high carbon content are characterized by substantial adsorption of carbon compounds onto mineral soil and low rates of respiration per unit of soil carbon and vice versa for soils with low carbon content precipitation and temperature were only secondary predictors for carbon storage respiration residence time and stabilization mechanisms correlations between climatic variables and carbon variables decreased significantly after removing relationships with geochemical predictors we conclude that the interactions of climatic and geochemical factors control soil organic carbon storage and turnover and must be considered for robust prediction of current and future soil carbon storage

hydrologic controls on seasonal and inter annual variability of congo river particulate organic matter source and reservoir age we present dissolved organic carbon doc concentrations particulate organic matter pom composition 13c 15n 14c n c and particulate glycerol dialkyl glycerol tetraether gdgt distributions from a 34 month time series near the mouth of the congo river an end member mixing model using 13c and n c indicates that exported pom is consistently dominated by c3 rainforest soil sources with increasing contribution from c3 vegetation and decreasing contribution from phytoplankton at high discharge large c4 inputs are never observed despite covering 13 of the catchment low and variable 14c values during 2011 annual mean 148 82 when discharge from left bank tributaries located in the southern hemisphere reached record lows likely reflect a bias toward pre aged pom derived from the cuvette congolaise swamp forest in contrast 14c values were stable near 50 between january and june 2013 when left bank discharge was highest we suggest that headwater pom is replaced and or diluted by c3 vegetation and pre aged soils during transit through the cuvette congolaise whereas left bank tributaries export significantly less pre aged material gdgt distributions provide further evidence for seasonal and inter annual variability in soil provenance the cyclization of branched tetraethers and the gdgt 0 to crenarchaeol ratio are positively correlated with discharge r 0 70 p value 4 3 10 5 due to the incorporation of swamp forest soils when discharge from right bank tributaries located in the northern hemisphere is high both metrics reach record lows during 2013 supporting our interpretation of increased left bank contribution at this time we conclude that hydrologic variability is a major control of pom provenance in the congo river basin and that tropical wetlands can be a significant pom source despite their small geographic coverage

pre aged soil organic carbon as a major component of the yellow river suspended load regional significance and global relevance abstract large rivers connect the continents and the oceans and corresponding material fluxes have a global impact on marine biogeochemistry the yellow river transports vast quantities of suspended sediments to the ocean yet the nature of the particulate organic carbon poc carried by this system is not well known the focus of this study is to characterize the sources composition and age of suspended poc collected near the terminus of this river system focusing on the abundance and carbon isotopic composition 13c and 14c of specific biomarkers the concentrations of vascular plant wax lipids long chain c24 n alkanes n fatty acids and poc co varied with total suspended solid tss concentrations indicating that both were controlled by the overall terrestrial sediment flux poc exhibited relatively uniform 13c values 23 8 to 24 2 and old radiocarbon ages 4000 4640 yr however different biomarkers exhibited a wide range of 14c ages short chain c16 c18 fatty acid 14c ages were variable but generally the youngest organic components from 502 yr to modern suggesting they reflect recently biosynthesized material lignin phenol 14c ages were also variable and relatively young 1070 yr to modern suggesting rapid export of carbon from terrestrial primary production in contrast long chain plant wax lipids display relatively uniform and significantly older 14c ages 1500 1800 yr likely reflecting inputs of pre aged mineral associated soil oc from the yellow river drainage basin even carbon numbered n alkanes yielded the oldest 14c ages up to 26 000 yr revealing the presence of fossil petrogenic oc two isotopic mass balance approaches were explored to quantitively apportion different oc sources in yellow river suspended sediments results indicate that the dominant component of poc 53 57 is substantially pre aged 1510 1770 yr and likely sourced from the extensive loess paleosol deposits outcropping within the drainage basin of the remaining poc between 10 and 31 is fossil in origin 26 000 yr resulting from the physical erosion of ancient sedimentary rock and input of fossil fuel residues from anthropogenic activity and 16 33 is modern carbon derived from terrestrial and aquatic productivity these findings have implications both regarding the provenance and vintage of organic matter signatures emanating from the yellow river basin and similar catchments containing extensive paleosol sequences as well as for the reactivity and fate of this poc upon supply to adjacent marginal seas

mapping of seismic layer 2a 2b boundary above the sheeted dike unit at intermediate spreading crust exposed near the blanco transform 1 we present results from a study mapping the seismic layer 2a 2b boundary in young ocean crust located adjacent to the north wall of the blanco transform fault btf we review seafloor features geochemical and petrologic data seismic imaging and seismic structure and conclude that the btf seismic study region is representative of crust formed at the intermediate spreading juan de fuca ridge the mean layer 2a two way travel time beneath the seafloor is 0 37 0 10 s for the 42 12 km seismic survey area several regions are observed where layer 2a is consistently thin or thick over lateral distances of 5 10 km both in a ridge parallel and ridge perpendicular direction layer 2a thicknesses appear more variable in the ridge parallel isochron direction than the ridge perpendicular flow line direction there is no systematic pattern of layer 2a thickness variability with distance from the btf nor is there a correlation between seafloor topography and layer 2a thickness calculated mean layer 2a thickness for the seismic study region is 485 135 m assuming an interval velocity of 2 65 km s the imaged layer 2a 2b boundary projects on average 600 650 m above the top of the sheeted dike complex mapped on the adjacent btf north wall we argue that the geologic context of the layer 2a 2b boundary will vary as competing processes of magmatic construction and fracturing increasing porosity and crustal thickening compaction dike intrusion and hydrothermal sealing decreasing porosity vary as the crust spreads laterally from the ridge axis to ridge flanks

the fate of river organic carbon in coastal areas a study in the rhone river delta using multiple isotopic delta c 13 delta c 14 and organic tracers a significant fraction of the global carbon flux to the ocean occurs in river dominated ocean margins riomar although large uncertainties remain in the cycle of organic matter om in these syste

source to sink evolution of lignin composition in the madre de dios river system with connection to the amazon basin and offshore while lignin geochemistry has been extensively investigated in the amazon river little is known about lignin distribution and dynamics within deep stratified river channels or its transformations within soils prior to delivery to rivers we characterized lignin phenols in soils river particulate organic matter pom and dissolved organic matter dom across a 4 km elevation gradient in the madre de dios river system peru as well as in marine sediments to investigate the source to sink evolution of lignin in soils we found more oxidized lignin in organic horizons relative to mineral horizons the oxidized lignin signature was maintained during transfer into rivers and lignin was a relatively constant fraction of bulk organic carbon in soils and riverine pom lignin in dom became increasingly oxidized downstream indicating active transformation of dissolved lignin during transport especially in the dry season in contrast pom accumulated undegraded lignin downstream during the wet season suggesting that terrestrial input exceeded in river degradation we discovered high concentrations of relatively undegraded lignin in pom at depth in the lower madre de dios river in both seasons revealing a woody undercurrent for its transfer within these deep rivers our study of lignin evolution in the soil river ocean continuum highlights important seasonal and depth variations of river carbon components and their connection to soil carbon pools providing new insights into fluvial carbon dynamics associated with the transfer of lignin biomarkers from source to sink

how important is it to integrate riverine suspended sediment chemical composition with depth clues from amazon river depth profiles abstract the vertical variability in mineralogical chemical and isotopic compositions observed in large river suspended sediments calls for a depth integration of this variability to accurately determine riverine geochemical fluxes in this paper we present a method to determine depth integrated chemical particulate fluxes of large rivers based on river sampling along depth profiles and applied to the amazon basin lowland tributaries the suspended particulate matter spm concentration data from depth profiles is modeled for a number of individual grain size fractions using the rouse model which allows to predict the grain size distribution of suspended sediment throughout the whole river cross section then using 1 the relationship between grain size distribution and the al si ratio 2 relationships between the al si ratio and the chemical concentrations the chemical composition of river sediment is predicted throughout the river cross section and integrated to yield the depth integrated chemical particulate flux for a number of chemical elements e g si al fe na rees for elements such as al fe rees th the depth integrated flux is around twice as high as the one calculated from river surface sample characteristics for na and si the depth integrated flux is three times higher than the surface estimate due to the enrichment of albite and quartz at the bottom of the river depth integrated 87sr 86sr composition of suspended sediment also predictable using this method differs by more than 10 3 from the surface sample composition finally potential implications of depth integrated estimates of amazon sediment chemistry are explored depth integration of particulate 87sr 86sr isotopic ratios is necessary for a reliable use of sr isotopes as a provenance tracer the concept of steady state weathering of a large river basin is revisited using depth integrated sediment composition this analysis shows that in the amazon basin river the previously observed discrepancy between 1 weathering intensities of channel surface sediment and 2 silicate derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities this observation confirms that most large rivers basins are not eroding at steady state

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

upper crustal evolution across the juan de fuca ridge flanks 1 recent p wave velocity compilations of the oceanic crust indicate that the velocity of the uppermost layer 2a doubles or reaches 4 3 km s found in mature crust in 10 ma after crustal formation this velocity change is commonly attributed to precipitation of low temperature alteration minerals within the extrusive rocks associated with ridge flank hydrothermal circulation sediment blanketing acting as a thermal insulator has been proposed to further accelerate layer 2a evolution by enhancing mineral precipitation we carried out 1 d traveltime modeling on common midpoint supergathers from our 2002 juan de fuca ridge multichannel seismic data to determine upper crustal structure at 3 km intervals along 300 km long transects crossing the endeavor northern symmetric and cleft ridge segments our results show a regional correlation between upper crustal velocity and crustal age the measured velocity increase with crustal age is not uniform across the investigated ridge flanks for the ridge flanks blanketed with a sealing sedimentary cover the velocity increase is double that observed on the sparsely and discontinuously sedimented flanks 60 increase versus 28 over the same crustal age range of 5 9 ma extrapolation of velocity age gradients indicates that layer 2a velocity reaches 4 3 km s by 8 ma on the sediment blanketed flanks compared to 16 ma on the flanks with thin and discontinuous sediment cover the computed thickness gradients show that layer 2a does not thin and disappear in the juan de fuca region with increasing crustal age or sediment blanketing but persists as a relatively low seismic velocity layer capping the deeper oceanic crust however layer 2a on the fully sedimented ridge flank sections is on average thinner than on the sparsely and discontinuously sedimented flanks 330 80 versus 430 80 m the change in thickness occurs over a 10 20 km distance coincident with the onset of sediment burial our results also suggest that propagator wakes can have atypical layer 2a thickness and velocity impact of propagator wakes is evident in the chemical signature of the fluids sampled by odp drill holes along the east endeavor transect providing further indication that these crustal discontinuities may be sites of localized fluid flow and alteration

a preliminary tidal analysis of icesat laser altimetry southern ross ice shelf 1 satellite laser altimetry could soon play a key role in mapping poorly known ocean tides underneath antarctic ice shelves the amount of icesat data now collected over the southernmost part of the ross ice shelf is sufficient to warrant direct tidal analysis tides are estimated here from ten operational icesat periods totaling 363 days a response analysis helps overcome unfavorable tidal sampling especially an s2 correlation with the annual cycle comparisons of tidal estimates against independent station data show rms constituent differences around 3 cm still somewhat large but an encouraging result for such a challenging region

accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line

structure of young oceanic crust at 13 n on the east pacific rise from expanding spread profiles we present the results of the analysis of expanding spread profiles esps collected on and near the axis of the east pacific rise at 13 n these profiles were collected at 0 1 1 2 1 3 6 and 9 5 km from the rise axis and all but the most distant profile show a distinct low velocity zone lvz located within layer 3 of the oceanic crust at the ridge crest the top of the magma chamber is at the base of layer 2 while 3 6 km off axis the roof of the lvz is 1 1 km below the top of layer 3 the profile farthest from the ridge could possibly have a residual lvz confined to the lower 1 5 km of the crust the total width of the lvz as determined from the esp data is at least 6 km and possibly much greater this wide lvz apparently contradicts multichannel seismic data which show cross axis reflections from the magma chamber with a width of 5 km we suggest that a resolution of this apparent contradiction lies in a model of the rise axis with a small and transient central magma chamber of high partial melt fraction surrounded by a much larger and permanent region of hot rock with only isolated pockets of partial melt the esp data are sensitive to this larger region while the reflection data accurately map the presence or absence of the central magma chamber with its high impedance contrast we identify the presence of a layer at the top of the oceanic crust with initial p wave velocities between 2 35 and 2 6 km s while the s wave velocity is estimated as being 0 8 km s the layer thickness lies between 100 and 200 m these velocities are consistent with previous estimates for the pacific and recent results for the atlantic the thickness of this layer is consistent with that of layer 2a determined from geophysical measurements at deep sea drilling project hole 504b

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms