Bedrock Elevation Research Articles

A New Bathymetry for the Southeastern Filchner‐Ronne Ice Shelf: Implications for Modern Oceanographic Processes and Glacial History

AbstractThe Filchner‐Ronne Ice Shelf, the ocean cavity beneath it, and the Weddell Sea that bounds it, form an important part of the global climate system by modulating ice discharge from the Antarctic Ice Sheet and producing cold dense water masses that feed the global thermohaline circulation. A prerequisite for modeling the ice sheet and oceanographic processes within the cavity is an accurate knowledge of the sub‐ice sheet bedrock elevation, but beneath the ice shelf where airborne radar cannot penetrate, bathymetric data are sparse. This paper presents new seismic point measurements of cavity geometry from a particularly poorly sampled region south of Berkner Island that connects the Filchner and Ronne ice shelves. An updated bathymetric grid formed by combining the new data with existing data sets reveals several new features. In particular, a sill running between Berkner Island and the mainland could alter ocean circulation within the cavity and change our understanding of paleo‐ice stream flow in the region. Also revealed are deep troughs near the grounding lines of Foundation and Support Force ice streams, which provide access for seawater with melting potential. Running an ocean tidal model with the new bathymetry reveals large differences in tidal current velocities, both within the new gridded region and further afield, potentially affecting sub‐ice shelf melt rates.

Brief communication: Candidate sites of 1.5 Myr old ice 37 km southwest of the Dome C summit, East Antarctica

Abstract. The search for ice as old as 1.5 Myr requires the identification of places that maximize our chances to retrieve old, well-resolved, undisturbed and datable ice. One of these locations is very likely southwest of the Dome C summit, where elevated bedrock makes the ice thin enough to limit basal melting. A 3-D ice flow simulation is used to calculate five selection criteria, which together delineate the areas with the most appropriate glaciological properties. These selected areas (a few square kilometers) lie on the flanks of a bedrock high, where a balance is found between risks of basal melting, stratigraphic disturbances and sufficient age resolution. Within these areas, several sites of potential 1.5 Myr old ice are proposed, situated on local bedrock summits or ridges. The trajectories of the ice particles towards these locations are short, and the ice flows over a smoothly undulating bedrock. These sites will help to choose where new high-resolution ground radar surveys should be conducted in upcoming field seasons.

New Mass‐Conserving Bedrock Topography for Pine Island Glacier Impacts Simulated Decadal Rates of Mass Loss

AbstractHigh‐resolution ice flow modeling requires bedrock elevation and ice thickness data, consistent with one another and with modeled physics. Previous studies have shown that gridded ice thickness products that rely on standard interpolation techniques (such as Bedmap2) can be inconsistent with the conservation of mass, given observed velocity, surface elevation change, and surface mass balance, for example, near the grounding line of Pine Island Glacier, West Antarctica. Using the BISICLES ice flow model, we compare results of simulations using both Bedmap2 bedrock and thickness data, and a new interpolation method that respects mass conservation. We find that simulations using the new geometry result in higher sea level contribution than Bedmap2 and reveal decadal‐scale trends in the ice stream dynamics. We test the impact of several sliding laws and find that it is at least as important to accurately represent the bedrock and initial ice thickness as the choice of sliding law.

Origin and location of new Arctic islands and straits due to glacial recession

A total of 34 new islands (each 0.5 km2 or above) have appeared due to recession of Arctic glaciers under climate warming since the 1960s. Analysis of maps and satellite images of the Arctic coasts has been a basic method of recognizing these islands. Their origin is the final stage of a process which began in the twentieth century. They appear only on the coasts where bedrock elevations above sea level are surrounded by depressions below this level, filled (at least from the landside) with glaciers. Their recession leads to flooding of the depressions by sea water, thus creating straits which separate the new islands from the mainland. Hence, such new islands appear only in Greenland and the European Arctic. Their ecosystems accommodate to new environmental conditions. In the near future, this process will be intensified in a situation of further warming.

Development of two components acceleration time histories for Semarang, Indonesia, due to Semarang fault earthquake scenarios using 30 meters soil deposit model

Development of surface acceleration time histories is important for dynamic analysis of structure design and evaluation. Acceleration time histories usually developed from seismograph records due to specific earthquake event. Following the research conducted by Team for Revision of Seismic Hazard Maps of Indonesia 2010 and 2016, Lasem fault and Semarang fault are two closest and dangerous shallow crustal fault earthquake sources which must be taken into account for seismic mitigation of Semarang. This paper presents the development two components surface acceleration time histories for Semarang caused by Semarang fault earthquake scenarios, with magnitude from 6 Mw to 7 Mw and maximum epicentre distance 15 Km. This research was performed by conducting deterministic hazard analysis, response spectral matching and site response analysis to obtain a pair of modified acceleration time histories. Site response analysis was performed by conducting 30 meters soil deposit model by taking the assumption that the position of bedrock elevation is 30 meters below the surface layer. Modified acceleration time histories were developed from a pair time histories (North-South/NS and East-West/EW direction) collected from worldwide historical earthquakes. Modified time histories were developed due to limited time histories data caused by Semarang fault earthquake source.

A simplified geographical information systems (GIS)-based methodology for modeling the topography of bedrock: illustration using the Canadian Shield

Many geology, mining, and geotechnical applications require or depend upon some form of modeling of bedrock topography. Optimizing the manner with which bedrock topography is modeled poses a significant challenge because of the unpredictable or erratic presentation of the surface shape of bedrock. Unlike surface topography, bedrock topography is more difficult to determine because direct observation points are often not readily or directly accessible, unless the bedrock outcrops at the surface and is exposed, a relatively rare occurrence. When bedrock is covered by granular deposits, the only methods that allow practitioners to objectively establish the location of the top of the bedrock are to drill boreholes or conduct geophysical surveys. This makes the determination of bedrock topography not only difficult but also expensive. This study proposes a new approach for optimizing the modeling of complex bedrock topography, whose originality is based on the addition of “virtual” data points derived from cross-sections located between known boreholes. The proposed methodology is thus composed of four steps: gathering the maximum amount of relevant surface and subsurface data (from observation points), selecting the most appropriate technique for interpolating the observed bedrock elevations that will be entered into the dataset to be modeled, enriching the quantity of modeling data by adding “virtual” data elements based on geological interpretations of cross-sections (inserted into the model alongside the original objective data), and finally the modeling itself. The proposed approach is illustrated using data from a study area located in the Canadian Shield. Thousands of borehole records and surficial geological data as well as geological cross-section records were integrated to construct a three-dimensional bedrock topography model. The new proposed methodology can be applied to other regions worldwide.

Development of site class and site coefficient maps of Semarang, Indonesia using field shear wave velocity data

The new Indonesian National Code for seismic resistance design (SNI-03-1726-2012) issued recently utilizes seismic response spectra for the whole area of the country. Site class and site coefficient are two parameters needed for designing response spectra. Site class can be estimated using average standard penetration test (N-SPT), average shear wave velocity (Vs) and average un-drained shear strength (Su) of top 30 meter soil deposit. Site coefficients can be predicted using probabilistic seismic hazard analysis (PSHA) by implementing total probability theorem. To perform PSHA, Vs30 is a parameter needed for calculating ground motion at bedrock elevation. This paper presents the results of PSHA and site class analysis using Vs30 values estimated based on N-SPT results collected from 265 boring locations in Semarang. Seismic data in a radius of 500 km from Semarang were collected for PSHA. Site class and site coefficient maps are then developed for the whole study area.

VÝVOJ LEDOVCOVÝCH SEDIMENTŮ NA KONTAKTU S ŽULOVSKÝM MASIVEM VE ŠTACHLOVICÍCH U VIDNAVY

The Žulová Upland is composed of granitoids of the Žulová batholith with relicts of Pleistocene (Elsterian) continental glaciation sediments. The investigated outcrop represents development of glacigenic sediments on rugged topography of the Žulová Upland. Investigated locality is situated on a hill located on the northern margin of the Žulová Upland. It is located near Štachlovice, local part of the Vidnava town. The exposed part of the hilltop reveals a preglacial basement covered by glacigenic sediments. The facies analysis and gravel petrology analysis of clasts with fraction 16–64 mm in b-axis were undertaken on the walls of the outcrop. The Georadar (GPR, Ground penetrating radar) was used to investigate the sedimentary landform and its relation to the basement. The granitoid basement is in places formed by elevations covered by glacigenic sediments. The height of elevation reaches 350 cmin outcrop, or ca ~400 cm according to the GPR survey. The glacitectonite, formed on the gentle side of elevation, is composed of angular blocks of granitoids of the Žulová batholith, diamicton, sand, gravel and deformed glacifluvial sand. The glacitectonite was deposited during the advancement of the continental glacier. The original subglacial cavity is enclosed by a steep side of the elevation. This cavity is filled by foreset body composed of stratified sand and gravel and nonstratified gravelly sand, gravel and diamicton. The cavity was filled by high-density turbidity currents and debris flow in subaqueous-subaerial environment. The infill of the cavity reaches ~400 cm in thickness according to the GPR survey. The cavity was filled during deglaciation in subglacial environment. The glacitectonite underlies the diamicton (supraglacial till) that was deposited as a debris flow during the retreat of the continental glacier. Unsorted gravel overlaps with erosional base the infill of the cavity, this gravel has a huge extent according to the GPR survey. This sediment represents the environment of terminoglacial stream. Gravel material of all types of glacigenic sediments is mainly composed of rocks from the Rychleby Mts. (amphibolites, Gierałtow orthogneiss, other diverse gneisses, quartzites, mica schist),quartz, and Nordic and Polish rocks. Subglacial sediments contain clasts of amphibolites (~40 %), on the other hand supraglacial and terminoglacial sediments are more polymict. Dominant subrounded shape (~60–70 %) of clasts and composition of this material indicates its origin in preglacial fluvial sediments. These fluvial sediments were deposited by river flowing from the Rychleby Mts. towards their northern foreland. The locality represents preglacial elevation of bedrock, which was glacitectonically deformed during the glaciation. Lots of different types of sediments (sub-, supra-, and terminoglacial) were deposited around the elevation during deglaciation period. The elevation was completely buried by these sediments. Deposition of these sediments was related with morphology of the elevation of bedrock. Formation of these sediments took place in environment analogous to environment of part bedrock/part till drumlin (Stokes et al. 2011).

A computationally efficient depression-filling algorithm for digital elevation models, applied to proglacial lake drainage

Abstract. Many processes govern the deglaciation of ice sheets. One of the processes that is usually ignored is the calving of ice in lakes that temporarily surround the ice sheet. In order to capture this process a “flood-fill algorithm” is needed. Here we present and evaluate several optimizations to a standard flood-fill algorithm in terms of computational efficiency. As an example, we determine the land–ocean mask for a 1 km resolution digital elevation model (DEM) of North America and Greenland, a geographical area of roughly 7000 by 5000 km (roughly 35 million elements), about half of which is covered by ocean. Determining the land–ocean mask with our improved flood-fill algorithm reduces computation time by 90 % relative to using a standard stack-based flood-fill algorithm. This implies that it is now feasible to include the calving of ice in lakes as a dynamical process inside an ice-sheet model. We demonstrate this by using bedrock elevation, ice thickness and geoid perturbation fields from the output of a coupled ice-sheet–sea-level equation model at 30 000 years before present and determine the extent of Lake Agassiz, using both the standard and improved versions of the flood-fill algorithm. We show that several optimizations to the flood-fill algorithm used for filling a depression up to a water level, which is not defined beforehand, decrease the computation time by up to 99 %. The resulting reduction in computation time allows determination of the extent and volume of depressions in a DEM over large geographical grids or repeatedly over long periods of time, where computation time might otherwise be a limiting factor. The algorithm can be used for all glaciological and hydrological models, which need to trace the evolution over time of lakes or drainage basins in general.

Groundwater seepage controls salinity in a hydrologically terminal basin of semi-arid northwest Australia

Very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments. However, this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds. In this study, we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the Fortescue Marsh (FM), one of the largest wetlands of semi-arid northwest Australia (∼1100km2). The groundwater outflow from aquifers underlying the FM to the Lower Fortescue catchment is constrained by an extremely low hydraulic gradient of <0.0001anda small ‘alluvial outlet’ of 0.35km2 because of relatively high bedrock elevation. However, FM groundwater salinity is far below saturation with respect to halite (TDS<160g/L), episodic flood water is fresh to brackish, and salt efflorescences are very sparse and evident only when the FM is dry. We show that if the FM was 100% “leakage free” i.e., a true terminal basin, groundwater would have achieved halite saturation (>300g/L) after ∼45ka. We calculated that only a very small seepage of ∼2GL/yr (∼0.03% of the FM water volume) is sufficient to maintain current salinity conditions. The minimum time required to develop the current hydrochemical groundwater composition under the FM ranges from ∼60 to ∼165ka. We conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins.

SEISMIC MICROZONATION OF SEMARANG, INDONESIA BASED ON SITE RESPONSE ANALYSIS USING 30 M SOIL DEPOSIT MODEL

Seismic microzonation study of Semarang is still on-going following the recommendations from the Team for Revision of Seismic Hazard Maps of Indonesia 2010 (TRSHMI-2010). The study was performed by carrying one-dimensional site response analysis at 190 locations and implementing Lasem fault as a closest seimic source that significantly influence the hazard of the city. The analysis was performed using two soil deposit models, 30 m and real soil deposit models, to get ground surface peak acceleration (PGA) and amplification factor of PGA. The results obtained using the first model are then compared with the results obtained using the second model. To perform the analysis bedrock elevation and acceleration time histories data are needed. The bedrock elevation was estimated based on 218 single station seismometer measurements. Five different time histories representing different earthquakes with magnitude 6.5 MW and maximum distance 20 km are collected from worldwide historical earthquake records. The results of this study includes the distribution of surface PGA and amplification factor of PGA. The PGA and amplification factor calculated using 30 meter soil deposit model are greater than the same values calculated using real soil deposit model.

Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions

Abstract. Ice flow models are now routinely used to forecast the ice sheets' contribution to 21st century sea-level rise. For such short term simulations, the model response is greatly affected by the initial conditions. Data assimilation algorithms have been developed to invert for the friction of the ice on its bedrock using observed surface velocities. A drawback of these methods is that remaining uncertainties, especially in the bedrock elevation, lead to non-physical ice flux divergence anomalies resulting in undesirable transient effects. In this study, we compare two different assimilation algorithms based on adjoints and nudging to constrain both bedrock friction and elevation. Using synthetic twin experiments with realistic observation errors, we show that the two algorithms lead to similar performances in reconstructing both variables and allow the flux divergence anomalies to be significantly reduced.

Stable finite volume element schemes for the shallow-ice approximation

ABSTRACTThe isothermal, non-sliding shallow-ice approximation, combined with mass conservation, is a fundamental model for ice-sheet and glacier flow. It determines the ice extent, geometry and velocity by the solution of a free-boundary problem. In this paper, the steady-state form of this problem is solved directly, without time-stepping, thereby demonstrating a fully implicit scheme with no stability restrictions. The classical Mahaffy (1976) finite difference method is first reinterpreted as a ‘finite volume element’ scheme that has both an everywhere-defined approximate thickness function and an approximation of the conservation equation in flux integral form. From this reinterpretation an improved scheme is built by using better quadrature in the integral and upwinding on that part of the flux which is proportional to the bed gradient. The discrete equations are then solved by a parallel Newton scheme which respects the constraint that ice thickness is non-negative. The results show good accuracy on both flat-bed and bedrock-step exact solutions. The method is then applied at high resolution to model the steady-state geometry of the Greenland ice sheet, using only bedrock elevation and present-day surface mass balance as input data.

Distribution of ice thickness and subglacial topography of the “Chinese Wall” around Kunlun Station, East Antarctica

As fundamental parameters of the Antarctic Ice Sheet, ice thickness and subglacial topography are critical factors for studying the basal conditions and mass balance in Antarctica. During CHINARE 24 (the 24th Chinese National Antarctic Research Expedition, 2007/08), the research team used a deep ice-penetrating radar system to measure the ice thickness and subglacial topography of the “Chinese Wall” around Kunlun Station, East Antarctica. Preliminary results show that the ice thickness varies mostly from 1600 m to 2800 m along the “Chinese Wall”, with the thickest ice being 3444 m, and the thinnest ice 1255 m. The average bedrock elevation is 1722 m, while the minimum is just 604 m. Compared with the northern side of the ice divide, the ice thickness is a little greater and the subglacial topography lower on the southern side, which is also characterized by four deep valleys. We found no basal freeze-on ice in the Gamburtsev Subglacial Mountains area, subglacial lakes, or water bodies along the “Chinese Wall”. Ice thickness and subglacial topography data extracted from the Bedmap 2 database along the “Chinese Wall” are consistent with our results, but their resolution and accuracy are very limited in areas where the bedrock fluctuates intensely. The distribution of ice thickness and subglacial topography detected by ice-penetrating radar clarifies the features of the ice sheet in this “inaccessible” region. These results will help to advance the study of ice sheet dynamics and the determination of future locations of the GSM’s geological and deep ice core drilling sites in the Dome A region.

Direct Reconstruction of Three-dimensional Glacier Bedrock and Surface Elevation from Free Surface Velocity

This study presents a new algorithm to reconstruct both the ice-surface elevation and the altitude of the bedrock of a glacier from the knowledge of the ice-surface velocity which could potentially be obtained from satellite data. It requires the prior knowledge of the surface mass balance and basal conditions. The algorithm is realized in two steps: the first one involves the solution of a partial differential equation obtained from a rearrangement of the shallow-ice approximation and the second one involves the mere downslope integration of a non-linear function of the ice velocity and ice thickness. It is therefore an efficient algorithm which is in principle easy to implement. The algorithm is tested on synthetic data and is shown to be very successful with an ideal dataset and robust even when significant noise is added to the input data. Importantly, the inversion algorithm does not appear to amplify the input error in the data

Direct Reconstruction of Three-dimensional Glacier Bedrock and Surface Elevation from Free Surface Velocity

This study presents a new algorithm to reconstruct both the ice-surface elevation and the altitude of the bedrock of a glacier from the knowledge of the ice-surface velocity which could potentially be obtained from satellite data. It requires the prior knowledge of the surface mass balance and basal conditions. The algorithm is realized in two steps: the first one involves the solution of a partial differential equation obtained from a rearrangement of the shallow-ice approximation and the second one involves the mere downslope integration of a non-linear function of the ice velocity and ice thickness. It is therefore an efficient algorithm which is in principle easy to implement. The algorithm is tested on synthetic data and is shown to be very successful with an ideal dataset and robust even when significant noise is added to the input data. Importantly, the inversion algorithm does not appear to amplify the input error in the data

The impact of dynamic topography change on Antarctic ice sheet stability during the mid-Pliocene warm period

The evolution of the Antarctic ice sheet during the mid-Pliocene warm period (MPWP) remains uncertain and has important implications for our understanding of ice sheet response to modern global warming. The extent to which marine-based sectors of the East Antarctic Ice Sheet (EAIS) retreated during the MPWP is particularly contentious, with geological observations and geochemical analyses being cited to argue for either a relatively minor or a significant ice sheet retreat in response to mid-Pliocene warming. The stability of marine-based ice sheets is intimately linked to bedrock elevation at their grounding lines, and previous ice sheet modeling assumed that Antarctic bedrock elevation during the MPWP was the same as today with the exception of a correction for the crustal response to ice loading. However, various processes may have perturbed bedrock elevation over the past 3 m.y., most notably vertical deflections of the crust driven by mantle convective flow, or dynamic topography. Here we present simulations of mantle convective flow that are consistent with a wide range of present-day observables and use them to predict changes in dynamic topography and reconstruct bedrock elevations during the MPWP. We incorporate these elevations into a simulation of the Antarctic ice sheet during the MPWP and find that the correction for dynamic topography change has a significant effect on the stability of the EAIS within the marine-based Wilkes Basin, with the ice margin in that sector retreating considerably further inland (200–560 km) relative to simulations that do not include this correction for bedrock elevation.

Antarctic bedrock topography uncertainty and ice sheet stability

AbstractAntarctic bedrock elevation estimates have uncertainties exceeding 1 km in certain regions. Bedrock elevation, particularly where the bedrock is below sea level and bordering the ocean, can have a large impact on ice sheet stability. We investigate how present‐day bedrock elevation uncertainty affects ice sheet model simulations for a generic past warm period based on the mid‐Pliocene, although these uncertainties are also relevant to present‐day and future ice sheet stability. We perform an ensemble of simulations with random topographic noise added with various length scales and with amplitudes tuned to the uncertainty of the Bedmap2 data set. Total Antarctic ice sheet retreat in these simulations varies between 12.6 and 17.9 m equivalent sea level rise after 3 kyrs of warm climate forcing. This study highlights the sensitivity of ice sheet models to existing uncertainties in bedrock elevation and the ongoing need for new data acquisition.

Evaluation of controls on silicate weathering in tropical mountainous rivers: Insights from the Isthmus of Panama

Research Article| July 01, 2015 Evaluation of controls on silicate weathering in tropical mountainous rivers: Insights from the Isthmus of Panama Steven T. Goldsmith; Steven T. Goldsmith 1Department of Geography and the Environment, Villanova University, Villanova, Pennsylvania 19085, USA Search for other works by this author on: GSW Google Scholar Russell S. Harmon; Russell S. Harmon 2Department of Marine, Earth Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695, USA Search for other works by this author on: GSW Google Scholar W. Berry Lyons; W. Berry Lyons 3School of Earth Sciences, Ohio State University, Columbus, Ohio 43210, USA4Byrd Polar and Climate Research Center, Ohio State University, Columbus, Ohio 43210, USA Search for other works by this author on: GSW Google Scholar Brendan A. Harmon; Brendan A. Harmon 2Department of Marine, Earth Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695, USA Search for other works by this author on: GSW Google Scholar Fred L. Ogden; Fred L. Ogden 5Department of Civil and Architectural Engineering, University of Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar Christopher B. Gardner Christopher B. Gardner 3School of Earth Sciences, Ohio State University, Columbus, Ohio 43210, USA Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (7): 563–566. https://doi.org/10.1130/G36082.1 Article history received: 15 Jul 2014 rev-recd: 02 Apr 2015 accepted: 05 Apr 2015 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Steven T. Goldsmith, Russell S. Harmon, W. Berry Lyons, Brendan A. Harmon, Fred L. Ogden, Christopher B. Gardner; Evaluation of controls on silicate weathering in tropical mountainous rivers: Insights from the Isthmus of Panama. Geology 2015;; 43 (7): 563–566. doi: https://doi.org/10.1130/G36082.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Isthmus of Panama comprises a lithologically diverse andesitic oceanic arc of Late Cretaceous to Holocene age; it has large spatial variation in rainfall, displays a large range of physical erosion rates, and, therefore, is an ideal location to examine silicate weathering in the tropics. We use a multiyear data set of river chemistry for a 450 km transect across the Cordillera Central of west-central Panama to investigate controls on chemical weathering in tropical small mountainous rivers. Sea-salt corrected cation weathering yields (Casil + Mgsil + Na + K) range over more than an order in magnitude from 3.1 to 31.7 t/km2/yr, while silicate weathering yields (Casil + Mgsil + Na + K + Si) range from 6.9 to 69.5 t/km2/yr. Watershed lithology is the primary control on riverine chemistry, but landscape topographic character and land cover and/or land use also influence solute delivery potential. Strong statistical links of small mountainous river chemical weathering fluxes with rainfall and physical weathering rates attest to the importance of runoff and erosion in maintaining elevated bedrock weathering rates. CO2 consumption ranges from 155 × 103 mol/km2/yr to 1566 × 103 mol/km2/yr, in the upper range of global rates, leading us to suggest that andesite terrains should be considered separately when calculating removal of CO2 from the atmosphere via silicate weathering. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Isotopic studies of the Upper and Middle Rio Grande. Part 1 — Importance of sulfide weathering in the riverine sulfate budget

In order to characterize the sulfide-derived SO4 fluxes in the Rio Grande, we collected seasonally (from 2009 to 2011) riverine, agricultural drain and groundwater samples and analyzed them for their major element chemistries and the δ34S and δ18O of dissolved SO4. The observed variation of δ34S (−4 to +8‰) and δ18O (−2 to +7‰) in the Rio Grande mainly resulted from mixing between sulfide- and sulfate-derived SO4 of volcanic and sedimentary origin. Our S isotope mass balance suggests that the average sulfide-derived SO4 flux usually accounted for 83–94% (±10–20%) of the sulfate source in the upstream Rio Grande and decreased downstream to 45–51% because of increasing contributions of sulfate-derived SO4. The sulfide-derived SO4 was related to snow melt in the high elevation watersheds and recycling of surficial sulfate-rich salts by episodic water activity in dry areas at lower elevations. Additionally, elevated bedrock sulfide contents in volcanic and some sedimentary terrains of the studied area have been recognized as important factors contributing to sulfide-derived SO4 in the Rio Grande.