seismic moulin tremor through glacial moulins meltwater is routed from the glacier surface to its base moulins are a main feature feeding subglacial drainage systems and thus influencing basal motion and ice dynamics but their geometry remains poorly known here we show that analysis of the seismic wavefield generated by water falling into a moulin can help constrain its geometry we present modeling results of hour long seimic tremors emitted from a vertical moulin shaft observed with a seismometer array installed at the surface of the greenland ice sheet the tremor was triggered when the moulin water level exceeded a certain height which we associate with the threshold for the waterfall to hit directly the surface of the moulin water column the amplitude of the tremor signal changed over each tremor episode in close relation to the amount of inflowing water the tremor spectrum features multiple prominent peaks whose characteristic frequencies are distributed like the resonant modes of a semiopen organ pipe and were found to depend on the moulin water level consistent with a source composed of resonant tube waves water pressure waves coupled to elastic deformation of the moulin walls along the water filled moulin pipe analysis of surface particle motions lends further support to this interpretation the seismic wavefield was modeled as a superposition of sustained wave radiation by pressure sources on the side walls and at the bottom of the moulin the former was found to dominate the wave field at close distance and the latter at large distance to the moulin

vibrational modes of hydraulic fractures inference of fracture geometry from resonant frequencies and attenuation oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems including volcanoes glaciers and ice sheets and hydrocarbon and geothermal reservoirs to better quantify the physical dimensions of fluid filled cracks and properties of the fluids within them we study wave motion along a thin hydraulic fracture waveguide we present a linearized analysis valid at wavelengths greater than the fracture aperture that accounts for quasi static elastic deformation of the fracture walls as well as fluid viscosity inertia and compressibility in the long wavelength limit anomalously dispersed guided waves known as crack or krauklis waves propagate with restoring force from fracture wall elasticity at shorter wavelengths the waves become sound waves within the fluid channel wave attenuation in our model is due to fluid viscosity rather than seismic radiation from crack tips or fracture wall roughness we characterize viscous damping at both low frequencies where the flow is always fully developed and at high frequencies where the flow has a nearly constant velocity profile away from viscous boundary layers near the fracture walls most observable seismic signals from resonating fractures likely arise in the boundary layer crack wave limit where fluid solid coupling is pronounced and attenuation is minimal we present a method to estimate the aperture and length of a resonating hydraulic fracture using both the seismically observed quality factor and characteristic frequency finally we develop scaling relations between seismic moment and characteristic frequency that might be useful when interpreting the statistics of hydraulic fracture events

basal dynamics of kronebreen a fast flowing tidewater glacier in svalbard non local spatio temporal response to water input we evaluate the variability in basal friction for kronebreen svalbard a fast flowing tidewater glacier we invert 3 years 2013 15 of surface velocities at high temporal resolution generally 11 days to estimate the changing basal properties of the glacier our results suggest that sliding behaviour of kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another at present models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect for such ice masses with strong seasonal variations of surface melt the spatio temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and or time at least in a timescale of a few years basal sliding may not only be governed by local processes such as basal topography or summer melt but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation ice thickness changes or calving front geometry

tide modulated ice flow variations drive seismicity near the calving front of bowdoin glacier greenland glacier microseismicity is a promising tool to study glacier dynamics however physical processes connecting seismic signals and ice dynamics are not clearly understood at present particularly the relationship between tide modulated seismicity and dynamics of calving glaciers remains elusive here we analyze records from an on ice seismometer placed 250 m from the calving front of bowdoin glacier greenland using high frequency glacier flow speed measurements we show that the microseismic activity is related to strain rate variations the seismic activity correlates with longitudinal stretching measured at the glacier surface both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching long term microseismic monitoring could therefore provide insights on how a calving glacier s force balance and flow regime react to changes at the ice ocean interface

nucleation and seismic tremor associated with the glacial earthquakes of whillans ice stream antarctica 1 the ability to monitor transient motion along faults is critical to improving our ability to understand many natural phenomena such as landslides and earthquakes here we usedata from a gps and seismometer network that were deployed to monitor the regularly repeating glacial earthquakes of whillans ice stream west antarctica to show that a unique pattern of precursory slip precedes complete rupture along the bed of the ice stream additionally we show that rupture can be independently tracked by increased levels of microseismic activity including harmonic tremor that are coincident with the onset of slip at any location thus providing a remote means of monitoring stress and rupture propagation during the glacial earthquakes

amplitude variation with offset and prestack waveform inversion a direct comparison using a real data example from the rock springs uplift wyoming usa abstractrecent advances in seismic data acquisition and processing allow routine extraction of offset angle dependent reflection amplitudes from prestack seismic data for quantifying subsurface lithologic and fluid properties amplitude variation with offset avo inversion is the most commonly used practice for such quantification although quite successful avo has a few shortcomings primarily due to the simplicity in its inherent assumptions and for any quantitative estimation of reservoir properties they are generally interpreted in combination with other information in recent years waveform based inversions have gained popularity in reservoir characterization and depth imaging going beyond the simple assumptions of avo and using wave equation solutions these methods have been effective in accurately predicting the subsurface properties developments of these waveform inversions have so far been along two lines 1 the methods that use a locally 1d model of the subsurface for each common midpo

iron solubility driven by speciation in dust sources to the ocean particulate aerosols are thought to be the primary source of iron to the oceans but the factors determining their solubility and thus bioavailability are unclear x ray absorption analysis reveals that speciation controls the solubility of iron in three large sources of aerosol iron

a previously unreported type of seismic source in the firn layer of the east antarctic ice sheet we identify a unique type of seismic source in the uppermost part of the east antarctic ice sheet recorded by temporary broadband seismic arrays in east antarctica these sources termed firnquakes are characterized by dispersed surface wave trains with frequencies of 1 10 hz detectable at distances up to 1000 km events show strong dispersed rayleigh wave trains and an absence of observable body wave arrivals most events also show weaker love waves initial events were discovered by standard detection schemes additional events were then detected with a correlation scanner using the initial arrivals as templates we locate sources by determining the l2 misfit for a grid of potential source locations using rayleigh wave arrival times and polarization directions we then perform a multiple filter analysis to calculate the rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure the resulting velocity structure is used as an input model to calculate synthetic seismograms inverting the dispersion curves yields ice velocity structures consistent with a low velocity firn layer 100 m thick and show that velocity structure is laterally variable the absence of observable body wave phases and the relative amplitudes of rayleigh waves and noise constrain the source depth to be less than 20 m the presence of love waves for most events suggests the source is not isotropic we propose the events are linked to the formation of small crevasses in the firn and several events correlate with shallow crevasse fields mapped in satellite imagery

pathways of high latitude dust in the north atlantic abstract the contribution of mineral dust from high latitude sources has remained an under examined feature of the global dust cycle dust events originating at high latitudes can provide inputs of aeolian sediment to regions lying well outside the subtropical dust belt constraining the seasonal variability and preferential pathways of dust from high latitude sources is important for understanding the potential impacts that the dust may have on wider environmental systems such as nearby marine or cryospheric domains this study quantifies dust pathways from two areas exhibiting different emission dynamics in the north and south of iceland which is a prominent northern hemisphere dust source the analysis uses air parcel trajectory modelling and for the first time for high latitude sources explicitly links all trajectory simulations to time specific meteorological observations of suspended dust this approach maximises the potential for trajectories to represent dust and illustrates that trajectory climatologies not limited to dust can grossly overestimate the potential for dust transport preferential pathways emerge that demonstrate the role of iceland in supplying dust to the northern atlantic and sub arctic oceans for dust emitted from northern sources a dominant route exists to the northeast into the norwegian greenland and barents seas although there is also potential for delivery to the north atlantic in summer months from the southern sources the primary pathway extends into the north atlantic with a high density of trajectories extending as far south as 50 n particularly in spring and summer common to both southern and northern sources is a pathway to the west southwest of iceland into the denmark strait and towards greenland for trajectories simulated at 500 m the vertical development of dust plumes from iceland is limited likely due to the stable air masses of the region suppressing the potential for vertical motion trajectories rarely ascend high enough to reach the central portions of the greenland ice sheet the overall distribution of trajectories suggests that contributions of icelandic dust are relatively more important for neighbouring marine environments than the cryosphere

controls on tungsten concentrations in groundwater flow systems the role of adsorption aquifer sediment fe iii oxide oxyhydroxide content and thiotungstate formation abstract groundwater samples were collected along flow paths within the carrizo sand aquifer southeastern texas and the aquia aquifer coastal maryland for analysis of dissolved tungsten w concentrations along with the major solutes ph and measures of in situ redox conditions e g dissolved fe ii fe iii and s ii concentrations in addition sediment samples were collected from both aquifers to evaluate the solid phase speciation of w tungsten concentrations in the carrizo sand aquifer range from 3 64 to 1297 pmol kg 1 mean sd 248 440 pmol kg 1 with the lowest concentrations reported from the recharge area tungsten concentrations progressively increase down gradient along the flow path within carrizo sand aquifer groundwaters reaching the highest levels in sulfidic groundwater roughly 50 60 km from the recharge zone tungsten is strongly correlated with ph and dissolved sulfide i e s ii concentrations in carrizo groundwaters r 0 78 and 0 95 respectively in aquia aquifer groundwaters w concentrations range between 14 3 and 184 4 pmol kg 1 mean sd 63 9 59 pmol kg 1 and exhibit no or at best weak relationships with other geochemical parameters measured along the flow path e g r 0 4 and 0 08 for w vs ph and s ii respectively the data suggest that the increase in w concentrations in carrizo groundwaters reflects in part ph related adsorption desorption which has been shown to be substantial for groundwaters and lake waters with ph 8 owing to the similar chemical properties of w and mo which form thiomolybdates in sulfidic waters the formation of thiotungstate complexes may also be important in the sulfidic waters of the carrizo aquifer the substantially lower w concentrations in aquia aquifer groundwaters reflect the fact that the maximum groundwater ph never exceeds 8 4 mean sd ph 7 97 0 23 dissolved low s ii concentrations remain low mean sd s ii 0 29 0 16 mol kg 1 and that aquia aquifer sediments have substantially higher fe iii oxide oxyhydroxide contents compared to the carrizo sand aquifer our data indicate that ph related adsorption desorption reactions and the fe iii oxide oxyhydroxide content of aquifer sediments are key controls affecting w concentrations in oxic suboxic and anoxic groundwaters and further that the formation of thiotungstate species may also be important in some anoxic i e sulfidic waters

distributed acoustic sensing of seismic properties in a borehole drilled on a fast flowing greenlandic outlet glacier distributed acoustic sensing das is a new technology in which seismic energy is recorded at high spatial and temporal resolution along a fibre optic cable we show analyses from the first glaciol

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

modelling the long term mass balance and firn evolution of glaciers around kongsfjorden svalbard we analyse the long term 1961 2012 distributed surface mass balance and firn evolution of the kongsvegen and holtedahlfonna glacier systems in northwestern svalbard we couple a surface energy balance model to a firn model with forcing provided from regional climate model output in situ observational data are used to calibrate model parameters and validate the output the simulated area averaged surface mass balance for 1961 2012 is slightly positive 0 08 m w e a 1 which only fractionally compensates for mass loss by calving refreezing of percolating water in spring summer 0 13 m w e a 1 and stored water in fall winter 0 18 m w e a 1 provides a buffer for runoff internal accumulation i e refreezing below the previous year s summer surface in the accumulation zone peaks up to 0 22 m w e a 1 and is unaccounted for by stake observations superimposed ice formation in the lower accumulation zone ranges as high as 0 25 m w e a 1 a comparison of the periods 1961 99 and 2000 12 reveals 21 higher annual melt rates since 2000 and a 31 increase in runoff which can only in part be ascribed to recent warmer and drier conditions in response to firn line retreat both albedo lowering snow ice albedo feedback and lower refreezing rates refreezing feedback further amplified runoff

unraveling the mineralogical complexity of sediment iron speciation using sequential extractions author s slotznick sp sperling ea tosca nj miller aj clayton ke van helmond nagm slomp cp swanson hysell nl abstract 2019 american geophysical union all rights reserved iron speciation is one of the most widely applied proxies used to reconstruct oxygen levels and redox conditions in past aqueous environments the iron speciation proxy estimates proportions of different reactive iron species in fine grained sedimentary rocks which are mapped to redox conditions based on empirical calibrations from modern sediments it is based on a standardized extraction technique of sequentially applying acetate hydroxlamine hcl dithionite and oxalate solutions to a powdered sample in order to dissolve iron phases and quantify the amount of iron carried by carbonates easily reducible oxyhydroxides ferric iron oxyhydr oxides and magnetite respectively although tested on pure minerals and mixtures assessments of whether this sequential extraction process accurately dissolves the targeted minerals in natural sediments and sedimentary rocks are lacking in our study residues from each sequential extraction step were analyzed using rock magnetic and x ray diffraction experiments to identify and quantify the iron bearing minerals that were dissolved the dithionite extraction robustly removes the targeted mineralogy as magnetic data show it to solubilize nearly all of the goethite however magnetic quantification of magnetite was orders of magnitude less than the iron measured in the oxalate extraction x ray diffraction data suggest that dissolution of iron bearing clays specifically berthierine chamosite could explain this disparity our data compilation shows higher values of iron from the oxalate extraction in precambrian sedimentary rock samples suggesting a significant temporal shift in iron cycling recognition of heterogeneity in chemical extraction efficiency and targeting is vital for holistic multiproxy interpretation of past oxygen levels and communication between disciplines

characterization of seasonal glacial seismicity from a single station on ice record at holtedahlfonna svalbard glacial seismicity provides important insights into glacier dynamic processes we study the temporal distribution of cryogenic seismic signals icequakes at holtedahlfonna svalbard between april

influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean empirical estimates for island sites in the north atlantic the results of several recent studies challenge the reigning paradigm that continental soil dust provides the only significant atmospheric source of dissolved iron to the surface ocean this evidence includes correlations between the operational solubility of aerosol iron and atmospheric loadings of black carbon and aluminum normalized vanadium and nickel each of which are associated with emissions from the combustion of fossil fuel oil these observations suggest that the relative solubility of aerosol iron hence the eolian flux of soluble iron to the surface ocean may be significantly impacted by anthropogenic oil combustion products using recent field data from the bermuda region we have developed an empirical method to estimate the solubility of aerosol iron using bulk aerosol concentrations of fe v and al we apply this method to a large body of published data from the aeroce program for north atlantic island sites on tenerife barbados bermuda and ireland where the relative proportions of anthropogenic aerosols range from minor to major respectively our aerosol iron solubility estimates suggest that anthropogenic emissions contribute approximately 70 and 85 of the annual dry deposition of soluble iron to the surface ocean near bermuda and ireland respectively implying that human activities have profoundly affected the iron budget of the north atlantic region the annual mean dry deposition of soluble iron at barbados and izana is dominated by soil dust the anthropogenic contribution at these two sites ranges from 12 to 30 and is highly dependent on the soil dust solubility of fe employed in the model the low end 12 estimate appears to be more representative of these high dust sites

evidence of decoupling between arsenic and phosphate in shallow groundwater of bangladesh and potential implications reductive dissolution of iron oxyhydroxides and reduction of arsenic are often invoked as leading causes of high dissolved as levels in shallow groundwater of bangladesh the second of these assumptions is questioned here by comparing the behavior as and phosphate p a structural analogue for as v which also adsorbs strongly to fe oxyhydroxides but is not subject to reduction the first line of evidence is provided by a detailed groundwater time series spanning two years for three wells in the 6 9 m depth range showing removal of as iii from shallow groundwater during the monsoon without of loss of p the data indicate a loss of 90 of the dissolved as from groundwater in the intermediate well relative to a level of 3 mol l as predicted by conservative mixing between groundwater sampled from the shallower and the deeper well in contrast p concentrations of 30 mol l in the intermediate well closely match the prediction from conservative mixing reduction therefore appears to inhibit the release of as to groundwater at this site relative to p instead of enhancing it a re analysis of existing groundwater as and p data from across the country provides a broader context for this finding and confirms that without reduction elevated concentrations of as would probably be even more widespread in shallow aquifers of bangladesh without providing definite proof x ray absorption spectroscopy of sediment from the time series site and elsewhere suggests that the loss of as from groundwater may be coupled to precipitation of as sulfide further study is needed to assess the implications of these observations for shallow aquifers that have been subjected to increased withdrawals for irrigation in recent decades

atmospheric transport of mineral dust from the indo gangetic plain temporal variability acid processing and iron solubility atmospheric transport of chemical constituents from the indo gangetic plain igp to the bay of bengal is a conspicuous seasonal feature that occurs during the late ne monsoon december march with this perspective aerosol composition and abundance of mineral dust have been studied during november 2009 to march 2010 from a sampling site kharagpur 22 3 n 87 3 e in the igp representing the atmospheric outflow to the bay of bengal the chemical composition of pm2 5 suggests the dominance of nss so42 6 9 24 3 g m 3 whereas the abundance of mineral dust varied from 3 to 18 g m 3 the concentration of aerosol iron fetot and its fractional solubility fews fews fetot 100 where fews is the water soluble fraction of fetot varied from 60 to 1144 ng m 3 and from 6 7 to 26 5 respectively a striking similarity in the temporal variability of total inorganic acidity tia no3 nss so42 and fews provides evidence for acid processing of mineral dust alluvium during atmospheric transport from the igp the contribution of tia to water soluble inorganic species nss so42 no3 wsis mass ratios of ca al and fe al and abundance of dust and fews in the igp outflow are similar to the aerosol composition over the bay of bengal with the rapid increase in anthropogenic activities over south and south east asia the enhanced fractional solubility of aerosol iron attributed to acid processing of mineral dust has implications to further increase in the air sea deposition of fe to the ocean surface

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

estimating the long term calving flux of kronebreen svalbard from geodetic elevation changes and mass balance modelling this study independently quantifies geodetic elevation change and models surface mass balance to solve the continuity equation the approach is tested on two dynamically different glaciers kongsvegen and kronebreen in northwest svalbard through two time epochs 1966 1990 95 i and 1990 95 2007 ii on kongsvegen a dynamically inactive glacier the residual term represents an error associated with determining elevation changes and surface mass balance it is apparent that centerline mass balance estimates are not representative of the entire glacier which we relate to center line accumulation being larger than the elevation bin average on kronebreen a fast flowing and actively calving glacier a significant part of the residual is identified with the long term calving flux for both glaciers the cumulative surface mass balance remained close to zero during the first epoch but became increasingly negative in the second epoch the long term calving flux of kronebreen is estimated to be 0 14 0 03 km3 w e a 1 during epoch i and 0 20 0 05 km3 w e a 1 in epoch ii

subglacial discharge at tidewater glaciers revealed by seismic tremor subglacial discharge influences glacier basal motion and erodes and redeposits sediment at tidewater glacier termini discharge drives submarine terminus melting affects fjord circulation and is a central component of proglacial marine ecosystems however our present inability to track subglacial discharge and its variability significantly hinders our understanding of these processes here we report observations of hourly to seasonal variations in 1 5 10 hz seismic tremor that strongly correlate with subglacial discharge but not with basal motion weather or discrete icequakes our data demonstrate that vigorous discharge occurs from tidewater glaciers during summer in spite of fast basal motion that could limit the formation of subglacial conduits and then abates during winter furthermore tremor observations and a melt model demonstrate that drainage efficiency of tidewater glaciers evolves seasonally glaciohydraulic tremor provides a means by which to quantify subglacial discharge variations and offers a promising window into otherwise obscured glacierized environments

a 15 year record of frontal glacier ablation rates estimated from seismic data we present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at kronebreen svalbard using linear statistical models we calibrate the seismic record with seven years of satellite derived frontal ablation measurements the two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise frontal ablation follows the seasonal glacier speed up peaking 1 2 months after the melt season maximum short lived peaks are associated with melt and rain events cumulative frontal ablation of kronebreen between 2001 and 2015 is about 4 0 km3 3 7 gt with the greatest annual loss 0 45 km3 between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation

atmospheric iron deposition in the northwestern pacific ocean and its adjacent marginal seas the importance of coal burning this study applied a regional air quality model incorporated with an emission module to quantitatively differentiate the atmospheric iron sources originating from lithogenic dusts or coal burning fly ashes deposited in the northwestern pacific ocean and its marginal seas particular attention was paid to the high iron content of fly ashes emitted from steel and iron plants burning coals using the year 2007 as an example the modeling results exhibit large seasonal variations in iron deposition with highest deposition fluxes occurred during spring and autumn which are comparable to the seasonal fluctuation of chlorophyll a concentrations estimated by satellite images in the oceanic regions fly ash from coal burning accounted for 7 2 of the total iron deposited over the northwestern pacific ocean and 15 of that over the northern south china sea after considering the difference of iron solubility in the aerosols anthropogenic aerosol associated with coal burning would be the major bioavailable iron source in the surface water of the oceanic regions

dissolution of aerosol iron in the surface waters of the north pacific and north atlantic oceans as determined by a semicontinuous flow through reactor method aerosol iron dissolution in oceanic waters is determined with a semicontinuous batch leaching method in this procedure aerosol samples that were collected from the marine boundary layer were leached in an all teflon flow through reaction chamber by multiple aliquots of similar to 40 ml 0 4 mu m filtered oceanic surface water collected using ultraclean techniques each aliquot of seawater is permitted to leach the aerosol sample in the reaction chamber for a predetermined time before the seawater solution is separated from the aerosol sample by a 0 4 mu m nucleopore filter membrane a new aliquot of seawater is then added to the leaching chamber to continue leaching the same aerosol particles retained on the filter the procedure is repeated with progressive increases in leaching time the method allows the fe released from the aerosol particles to be continuously removed from the system before saturating the complexation capacity of the seawater leaching solution or adsorbing onto the leaching chamber wall this method results in accurate measurements of seawater dissolvable labile aerosol fe that is independent of the total aerosol fe concentrations in the sample the aerosol fe solubility determined using this method ranges from 3 5 1 5 for the north atlantic during september 2005 to 5 7 2 0 for the north pacific during april 2005 and april 2006

surface complexation modeling of groundwater arsenic mobility results of a forced gradient experiment in a red river flood plain aquifer vietnam abstract three surface complexation models scms developed for respectively ferrihydrite goethite and sorption data for a pleistocene oxidized aquifer sediment from bangladesh were used to explore the effect of multicomponent adsorption processes on as mobility in a reduced holocene floodplain aquifer along the red river vietnam the scms for ferrihydrite and goethite yielded very different results the ferrihydrite scm favors as iii over as v and has carbonate and silica species as the main competitors for surface sites in contrast the goethite scm has a greater affinity for as v over as iii while po43 and fe ii form the predominant surface species the scm for pleistocene aquifer sediment resembles most the goethite scm but shows more si sorption compiled as iii adsorption data for holocene sediment was also well described by the scm determined for pleistocene aquifer sediment suggesting a comparable as iii affinity of holocene and pleistocene aquifer sediments a forced gradient field experiment was conducted in a bank aquifer adjacent to a tributary channel to the red river and the passage in the aquifer of mixed groundwater containing up to 74 channel water was observed the concentrations of as

geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of araihazar bangladesh implications for deeper aquifers as drinking water sources sediment and groundwater profiles were compared in two villages of bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved as concentrations in groundwater in both villages fine grained sediment layers separate shallow aquifers 28 m high in as from deeper aquifers 40 90 m containing 10 g l as in one village dari radiocarbon dating indicates deposition of the deeper aquifer sediments 50 ka ago and a residence time of groundwater of thousands of years in the other village bay the sediment is 20 ka old down to 90 m and the deeper aquifer groundwater is younger with a residence time of hundreds of years the shallow aquifers in both villages that are high in as contain bomb 3 h and bomb 14 c indicating recent recharge the major and minor ion compositions of the shallow and deeper aquifers also differ significantly deeper aquifer water is of the na hco3 type with relatively little dissolved nh4 76 192 mol l fe 27 43 mol l and mn 3 2 mol l in contrast shallow aquifer water is of the ca mg hco3 type with elevated concentrations of dissolved nh4 306 355 mol l fe 191 73 mol l and mn 27 43 mol l in both villages the quantity of as extractable from deeper aquifer sands with a 1 mol l phosphate solution 0 2 0 3 mg kg n 12 0 1 0 1 mg kg n 5 is 1 order of magnitude lower than p extractable as from shallow deposits 1 7 1 2 mg kg n 9 1 4 2 0 mg kg n 11 the differences suggest that the concentration of p extractable as in the sediment is a factor controlling the concentration of as in groundwater low p extractable as levels are observed in both deeper aquifers that are low in as even though there is a large difference in the time of deposition of these aquifers in the two villages the geochemical data and hydrographs presented in this study suggest that both holocene and pleistocene deeper aquifers that are low in as should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of 1 cm yr copyright 2005 elsevier ltd

mineralogy as a critical factor of dust iron solubility 1 to understand the impact of dust deposition on ocean primary productivity the evaluation of dust input is not sufficient and the soluble iron supply is also needed measurements of iron in aerosols suggest a much higher solubility than in soil implying substantial atmospheric processing of chemical or physical nature here we have investigated the effect of the mineralogy on iron solubility we have measured iron solubility from some minerals commonly found in dust clay feldspar and iron hydr oxides firstly we observe a greater solubility of iron resulting from clays 4 in comparison to iron hydr oxides 1 independently of specific surface of minerals secondly by considering amount of dissolved iron and the mineralogical composition of dust our results indicate that dissolved iron fraction mainly comes from clay dissolution in contrast to that assumed in some biogeochemical models in consequence it appears that iron solubility is closely linked to the mineralogical composition of aerosol

orbital and sea level changes regulate the iron associated sediment supplies from papua new guinea to the equatorial pacific abstract iron fe supplied to the equatorial pacific are thought to play a critical role in marine biogeochemical cycle and the related air sea co2 flux previous studies have shown that papua new guinea png is a major fe contributor for the western equatorial pacific however key issues of this fe supply including the exact sources transport processes and distribution range remain unclear especially its long term variability associated with hydroclimatic and paleoceanographic changes using a set of cores collected offshore the northern png and from the ontong java plateau ojp shown to situate along the pathway of fe delivery by undercurrents here we compile high resolution records to explore how the fe associated sediment supplies varied and distributed on orbital time scale during the past 400 ka the chronologic frameworks of these cores are established by using 14c datings and stratigraphic correlations of foraminiferal 18o records and carbonate contents the sedimentary fe and clay mineral smectite in the offshore png sites show a prominent precession cycle in phase with the march insolation change at 5 s such precessional predominance suggests the control of local precipitation and river runoff on the offshore deposition of the fe associated sediment for the ojp sites the proxies derived from terrigenous detrital component give a spectral pattern however prevailed by 100 ka cycle with secondary precessional highs the significant 100 ka cycle can best be attributed to glacial interglacial changes in oceanic transports likely caused by sea level regulated variability in the strength and or route of the coastal undercurrents off png this variability may have influenced the long distance transport of fe rich particulates from the png to the ojp and further eastwards via the equatorial undercurrent

the use of operationally defined sequential fe extraction methods for mineralogical applications a cautionary tale from mossbauer spectroscopy abstract reactive iron minerals are crucial components of global nutrient cycles directly controlling carbon transport and storage in marine sediments sequential selective extraction is frequently used for quantitatively characterising and chemically isolating individual fe mineral phases reagent specific mineral solubility is fundamental to the success of any sequential extraction but is strongly affected by the varying physical and chemical morphology intrinsic to natural mineral samples natural sediment rock and soil samples often contain a mineral mixture which further modifies solvent efficacy 57fe mossbauer spectroscopy only probes the hyperfine interactions between next nearest neighbouring atomic nuclei in the crystal lattice and is less affected by variation in mineral grain size and crystallinity than conventional x ray based methods in this study we used mossbauer spectroscopy in a novel context to cross calibrate and optimise a popular but frequently misused sequential fe extraction protocol our results showed that incomplete and premature removal of the target fe minerals could occur at nearly every stage of the extraction and in many cases the leachate fe content did not represent the target phase at all crystalline natural siderite and amorphous synthetic goethite were detected in the mossbauer spectrum of the ammonium oxalate extraction for magnetite after which all reactive fe minerals should have been removed consistent with previous studies and unlike many other clay minerals nontronite was extracted as part of the highly reactive fe pool and in fact our data indicate that this mineral was extracted by the initial na acetate extraction that targets carbonate bound fe matrix effects appeared to cause variable yield efficiencies synthetic goethite was successfully removed when present as an individual mineral yet persisted beyond its target extraction when present in an fe mineral mixture although suitable for the quantification of operationally defined fe pools we caution the unverified use of sequential fe extraction protocols for mineral specific applications the application of sequential fe extractions to define the reactive fe pools as a paleoredox proxy of depositional conditions appears relatively robust the premature removal of 2 line ferrihydrite observed in this study due to the use of the more aggressive na acetate extraction for crystalline siderite does not limit the quantitative use of the sequential fe extraction in ancient sediments where such easily reducible oxides are unlikely to persist in contrast attributing the outcomes of operationally defined fe pools to specific fe minerals is precarious and potentially entirely erroneous where fe mineral specificity or separation is required we recommend post extraction validation by another secondary technique mossbauer spectroscopy offers such a method that can independently verify extraction stages and assess mineral specificity

basal icequakes recorded beneath an alpine glacier glacier d argentiere mont blanc france evidence for stick slip motion while basal icequakes associated with glacier motion have been detected under antarctica for several decades there remains very little evidence of stick slip motion for alpine glaciers here we analyzed 2357 basal icequakes that were recorded at glacier d argenti ere mont blanc massif between february and november of 2012 and that are likely to be associated with basal sliding these events have been classified into 18 multiplets based on their waveforms the strong similarity of the waveforms within each multiplet suggests an isolated repeating source despite this similarity the peak amplitude within each multiplet varies gradually in time by up to a factor of 18 the distribution of these events in time is relatively complex for long time scales we observe progressive variations in the amplitudes of events within each multiplet for intermediate time scales hours the events occur regularly in time with typical return times of several minutes up to several hours for short time scales from 0 01 to 100 s the largest multiplet shows clus tering in time with a power law distribution of the interevent times the location of these events and their focal mechanisms are not well constrained because most of these events were detected by a single seismometer nevertheless the locations can be estimated with an accuracy of a few tens of meters using a polarization analysis the estimated average depth of the basal events is 179 m which is in good agreement with the estimated glacier thickness the relative changes in distance between the source and the sensor can be measured accurately by correlating separately the p wave and s wave parts of the seismograms of each event with the template waveforms which are obtained by averaging the signals within each multiplet we observed small variations in the times between the p wave and the s wave of up to 0 6 ms over 50 days these variations cannot be explained by displacement of the sensor with respect to the glacier but might be due to small changes in the seismic wave velocities with time finally we found using numerical simulations that the observed signals are better explained by a horizontal shear fault with slip parallel to the glacier flow than by a tensile fault these results suggest that the basal events are associated with stick slip motion of the glacier over rough bedrock the rupture length and the slip are difficult to estimate nonetheless the rupture length is likely to be of the order of meters and the total seismic slip accumulated over one day might be as large as the glacier motion during the most active bursts

germanium silicon ratios in the copper river basin alaska weathering and partitioning in periglacial versus glacial environments 1 glacial to interglacial variation in the germanium to silicon ratio ge si of biogenic opal in oceanic sediment cores has been proposed to record terrestrial silicate weathering intensity however data connecting ge si ratios to weathering are sparse especially for cold regions to characterize ge si of the dissolved loads of rivers draining modern glacial and periglacial regions we measured ge and major element chemistry of more than 30 streams in the copper river basin of south alaska we measured significantly higher ge si in rivers with greater than 15 glacial cover in their basins than in rivers draining areas with less glacial cover which we attribute to preferencial subglacial weathering of biotite we also ran laboratory experiments to investigate the role of differential sorption of ge and si on hydrous iron oxides in moderating the ge si ratio of rivers in recently deglaciated basins these experiments indicate that ge is preferentially adsorbed over si by hydrous iron oxides over a wide range of ph values and support differential sorption as a potentially significant fractionation process our measured high ge si in glaciated basins is in striking contrast to the low ge si in the oceanic record during glacial periods the glacial to interglacial changes in marine ge si cannot simply reflect changes in glacier cover on land as the mineralogy of silicates weathered and processes partitioning ge in soils must also strongly influence the fluvial ge and si inputs to the ocean

clay mineral assemblages in weathered basalt profiles from central and southern portugal climatic significance abstract mineralogical and chemical changes during weathering of basalts from central and southern portugal were studied both regions have a temperate mediterranean type climate the algarve being more arid the areas concerned are the lisbon 72 ma and the runa volcanic complexes 100 70 ma and rio maior 160 130 ma in central portugal and budens 170 180 ma in the south the basalts are generally rich in olivine phenocrysts clay minerals are in general well crystallised and comprise smectites associated with 1 1 minerals principally halloysite illite and palygorskite kaolin minerals prevail in topographic highs whilst smectites predominate in lower areas smectites were analysed from the

soluble iron inputs to the southern ocean through recent andesitic to rhyolitic volcanic ash eruptions from the patagonian andes patagonia due to its geographic position and the dominance of westerly winds is a key area that contributes to the supply of nutrients to the southern ocean both through mineral dust and through the periodic deposits of volcanic ash here we evaluate the characteristics of fe dissolved into soluble and colloidal species from volcanic ash for three recent southern andes volcanic eruptions having contrasting features and chemical compositions contact between cloud waters wet deposition and end members of andesitic hudson volcano and rhyolitic chaiten volcano materials was simulated results indicate higher fe release and faster liberation rates in the andesitic material fe release during particle seawater interaction dry deposition has higher rates in rhyolitic type ashes rhyolitic ashes under acidic conditions release fe in higher amounts and at a slower rate while in those samples containing mostly glass shards fe release was lower and faster the 2011 puyehue eruption was observed by a dust monitoring station puyehue type eruptions can contribute soluble fe to the ocean via dry or wet deposition nearly reaching the limit required for phytoplankton growth in contrast the input of fe after processing by an acidic eruption plume could raise the amount of dissolved fe in surface ocean waters several times above the threshold required to initiate phytoplankton blooms a single eruption like the puyehue one represents more than half of the yearly fe flux contributed by dust

seismic reservoir description using hybrid seismic inversion a 3d case study from the maria ines oeste field argentina maria ines oeste an oil and gas field in argentina s magallanes foreland basin also called austral basin produces from maria inees sandstones that are known to represent the base of a second order transgressive system tract tst deposited during late maastrichtian times in a coastal to open shelf environment figure 1 outlines the basic tectonic framework of the austral basin

motion of an antarctic glacier by repeated tidally modulated earthquakes subglacial seismicity reveals information about glacier behaviour analysis of repeated seismic events beneath an antarctic outlet glacier is consistent with sliding of debris laden ice over a bedrock asperity with an event frequency that is modulated by the ocean tides

iceberg calving as a primary source of regional scale glacier generated seismicity in the st elias mountains alaska 1 since the installation of the alaska regional seismic network in the 1970s data analysts have noted nontectonic seismic events thought to be related to glacier dynamics while loose associations with the glaciers of the st elias mountains have been made no detailed study of the source locations has been undertaken we performed a two step investigation surrounding these events beginning with manual locations that guided an automated detection and event sifting routine results from the manual investigation highlight characteristics of the seismic waveforms including single peaked narrowband spectra emergent onsets lack of distinct phase arrivals and a predominant cluster of locations near the calving termini of several neighboring tidewater glaciers through these locations comparison with previous work analyses of waveform characteristics frequency magnitude statistics and temporal patterns in seismicity we suggest calving as a source for the seismicity statistical properties and time series analysis of the event catalog suggest a scale invariant process that has no single or simple forcing these results support the idea that calving is often a response to short lived or localized stress perturbations our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of iceberg calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat especially when existing seismic infrastructure can be used

characterisation of fe bearing particles and colloids in the lena river basin ne russia abstract rivers are significant contributors of fe to the ocean however the characteristics of chemically reactive fe remain poorly constrained especially in large arctic rivers which drain landscapes highly susceptible to climate change and carbon cycle alteration the aim of this study was a detailed characterisation size mineralogy and speciation of riverine fe bearing particles 0 22 m and colloids 1 kda 0 22 m and their association with organic carbon oc in the lena river and tributaries which drain a catchment almost entirely underlain by permafrost samples from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in june 2013 and summer baseflow in july 2012 fe bearing particles were identified using transmission electron microscopy as large 200 nm 1 m aggregates of smaller 20 30 nm spherical colloids of chemically reactive ferrihydrite in contrast there were also large 500 nm 1 m aggregates of clay illite particles and smaller 100 200 nm iron oxide particles dominantly hematite that contain poorly reactive fe tem imaging and scanning transmission x ray microscopy stxm indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon poc and attached to the surface of primary produced organic matter and clay particles together these larger particles act as the main carriers of nanoscale ferrihydrite in the lena river basin the chemically reactive ferrihydrite accounts for on average 70 15 of the total suspended fe in the lena river and tributaries these observations place important constraints on fe and oc cycling in the lena river catchment area and fe bearing particle transport to the arctic ocean

simultaneously quantifying ferrihydrite and goethite in natural sediments using the method of standard additions with x ray absorption spectroscopy abstract the presence of ferrihydrite in sediments soils is critical to the cycling of iron fe and many other elements but difficult to quantify extended x ray absorption fine structure exafs spectroscopy has been used to speciate fe in the solid phase but this method is thought to have difficulties in distinguishing ferrihydrite from goethite and other minerals in this study both conventional exafs linear combination fitting lcf and the method of standard additions are applied to the same samples in attempt to quantify ferrihydrite and goethite more rigorously natural aquifer sediments from bangladesh and the united states were spiked with known quantities of ferrihydrite goethite and magnetite and analyzed by exafs known mineral mixtures were also analyzed evaluations of exafs spectra of mineral references and exafs lcf fits on various samples indicate that ferrihydrite and microcrystalline goethite can be distinguished and quantified by exafs lcf but that the choice of mineral references is critical to yield consistent results conventional exafs lcf and the method of standard additions both identified appreciable amount of ferrihydrite in bangladesh sediments that were obtained from a low arsenic pleistocene aquifer ferrihydrite was also independently detected by sequential extraction and 57fe m ssbauer spectroscopy these observations confirm the accuracy of conventional exafs lcf and demonstrate that combining exafs with additions of reference materials provides a more robust means of quantifying short range ordered minerals in complex samples

aerosol iron and aluminum solubility in the northwest pacific ocean results from the 2002 ioc cruise dust aerosol samples were collected across the western north pacific ocean during may june 2002 samples were analyzed for soluble aerosol fe ii fe ii fe iii and al as well as major cations and anions the aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the instantaneous soluble fraction a variety of analytical methods were employed including 57fe isotope dilution high resolution icp ms energy dispersive x ray fluorescence graphite furnace aas ion chromatography and the felume chemiluminescent technique fe was found to be more soluble in ultrapure deionized water leaches especially during periods of higher dust concentrations fe solubility averaged 9 8 in ultrapure water leaches and 6 5 in seawater leaches significant correlations were found between both soluble aerosol fet and soluble fe ii concentrations and aerosol acidity however the percentages of soluble aerosol fet and fe ii did not correlate with aerosol acidity we also did not observe significant correlations between total and soluble aerosol fe concentrations and the concentrations of either particulate fe or dissolved fe in surface waters

dynamic perennial firn aquifer on an arctic glacier ice penetrating radar and gps observations reveal a perennial firn aquifer pfa on a svalbard ice field similar to those recently discovered in southeastern greenland a bright widespread radar reflector separates relatively dry and water saturated firn this surface the phreatic firn water table is deeper beneath local surface elevation maxima shallower in surface lows and steeper where the surface is steep the reflector crosscuts snow stratigraphy we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases our observations indicate that pfas respond rapidly subannually to surface forcing and are capable of providing significant input to the englacial hydrology system

impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron evidence from the sargasso sea we report empirical estimates of the fractional solubility of aerosol iron over the sargasso sea during periods characterized by high concentrations of saharan dust summer 2003 and by low concentrations of aerosols in north american maritime north atlantic air masses spring 2004 and early summer 2004 we observed a strong inverse relationship between the operational solubility of aerosol iron defined using a flow through deionized water leaching protocol and the total concentration of aerosol iron whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low this relationship is consistent with source dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model wherein bulk aerosols represent a conservative mixture of two air mass end members that carry different aerosol types saharan air which contains a relatively high loading of aerosol iron 27 8 nmol fe m 3 that has a low fractional solubility 0 44 and north american air which contains a relatively low concentration of aerosol iron 0 5 nmol fe m 3 that has a high fractional solubility 19 historical data for aerosols collected on bermuda indicate that the low iron loadings associated with north american air masses are typically accompanied by elevated v al fe al and v mn mass ratios in the bulk aerosol relative to saharan dust which are indicative of anthropogenic fuel combustion products the identification of similar compositional trends in our sargasso sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with north american air masses reflects the presence of anthropogenic combustion products which contain iron that is readily soluble relative to iron in saharan soil dust we thus propose that the source dependent composition of aerosol particles specifically the relative proportion of anthropogenic combustion products is a primary determinant for the fractional solubility of aerosol iron over the sargasso sea this hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

antarctic icequakes triggered by the 2010 maule earthquake in chile large earthquakes can trigger seismicity in remote regions analysis of seismic data from antarctica reveals ice quakes coincident with passing seismic waves from the 2010 chile earthquake suggesting that the ice sheet is sensitive to such triggers

the contribution of aeolian sand and dust to iron fertilization of phytoplankton blooms in southwestern ross sea antarctica iron is a limiting micronutrient for primary production in the ross sea antarctica recent observations reveal low dissolved fe dfe concentrations in the ross sea polynya following high initial rates of primary production in summer after the dfe winter reserve has been consumed significant new sources of dfe are therefore required to further sustain phytoplankton blooms iron from aeolian sand and dust asd released from melting sea ice is one potential source to constrain aeolian fe inputs we determined asd mass accumulation rates and the total and soluble fe content of asd on sea ice in mcmurdo sound southwestern sw ross sea the mean mass accumulation rate was 1 5 g m 2 yr 1 total fe content of this asd was 4 1 wt and the percentage of soluble fe was 11 1 our mean estimate of the bulk aeolian dfe flux of 122 1 mol m 2 yr 1 for the mcmurdo sound region suggests that aeolian fe can support between 9 0 109 and 4 1 1011 mol c yr 1 0 1 4 9 tg c yr 1 of new primary production this equates to only 15 of new primary production in the sw ross sea suggesting that aeolian dfe is a minor component of seasonal fe supply the very high asd accumulation on sea ice in mcmurdo sound compared to other regions of antarctica suggests that our results represent the upper limit of dfe supply to the ocean from this source in the ross sea

solid phases and desorption processes of arsenic within bangladesh sediments abstract arsenic is a contaminant in the groundwater of bangladesh and west bengal india where an estimated 57 million people may be drinking water with unsafe arsenic levels the source of arsenic appears to be natural solid phase arsenic in the sediments and various theories have been put forth regarding the modes of arsenic release ranging from the oxidative or reductive degradation of arsenic bearing solids to competitive ligand displacement by phosphate currently however reductive dissolution of fe iii hydr oxides and concomitant arsenic release is the most widely accepted explanation of high arsenic groundwater concentrations using micro x ray fluorescence elemental mapping and micro x ray absorption near edge structure spectroscopy we detect arsenic bearing sulfides in the aquifer sediments from our field site in munshiganj bangladesh reduction of fe and as in surface soil layers is apparent but fe iii hydr oxides are not detected in the holocene aquifer materials rapid abiotic desorption of arsenic from sediments is observed in batch experiments and positive controls with ferrihydrite dismiss the role of ferric hydr oxides in arsenic retention within the aquifer sediments based on our laboratory results we do not see evidence for ferric hydr oxide reductive dissolution at well depths in the holocene aquifer in contrast our data suggest that arsenic is only released via redox cycling in surface soils sediments and thus must then be transported to well depth through the sandy aquifer

aeolian input of bioavailable iron to the ocean 1 atmospheric deposition of mineral dust supplies much of the essential nutrient iron to the ocean presumably only the readily soluble fraction is available for biological uptake previous ocean models assumed this fraction was constant here the variable solubility of fe in aerosols and precipitation is parameterized with a two step mechanism the development of a sulfate coating followed by the dissolution of iron hydr oxide on the dust aerosols the predicted soluble fe fraction increases with transport time from the source region and with the corresponding decrease in dust concentration the soluble fraction is 1 percent near sources but often 10 40 percent farther away producing a significant increase in soluble fe deposition in remote ocean regions our results may require more rapid biological and physicochemical scavenging of fe than used in current ocean models we further suggest that increasing so2 emission alone could have caused significant fe fertilization in the modern northern hemisphere oceans

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

atmospheric deposition of glacial iron in the gulf of alaska impacted by the position of the aleutian low our understanding of glacial flour dust storm delivery of iron to the gulf of alaska goa is limited here we interpret concurrent time series satellite meteorological and aerosol geochemical data from the goa to examine how interannual variability in regional weather patterns impacts offshore aerosol glacial fe deposition in 2011 when a northerly aleutian low al was persistent during fall dust emission was suppressed and highly intermittent due to prevalent wet conditions low winds and a deep early season snowpack conversely in 2012 frequent and prolonged fall dust storms and high offshore glacial fe transport were driven by dry conditions and strong offshore winds generated by persistent strong high pressure over the alaskan interior and bering sea and a southerly al twenty five fold interannual variability in regional offshore glacial aerosol fe deposition indicates that glacial dust s impact on goa nutrient budgets is highly dynamic and particularly sensitive to regional climate forcing

evidence for deep icequakes in an alpine glacier to obtain more reliable information about the focal depth distribution of icequakes in april 1997 we operated an array of seven portable digital seismographs on unteraargletscher central swiss alps over 5000 events were detected by at least two instruments during the 9 day recording period p wave velocities 3770 m f were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole whereas s wave velocities 1860 ms 1 were derived from a simultaneous inversion for vp vs6 applied to 169 icequakes so far hypocentral locations have been calculated for over 300 icequakes besides confirming the occurrence of shallow events associated with the opening of crevasses our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed one event was found at an intermediate depth of about 120 m three dimensional particle motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the rayleigh wave on the other hand for events occurring at depths greater than about 40 m the rayleigh wave disappears almost entirely therefore a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival time inversions thus our results demonstrate that deep icequakes do occur and that simple rheological models according to which brittle deformation is restricted to the uppermost part of a glacier may need revision

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

deep icequakes what happens at the base of alpine glaciers 1 basal seismicity cannot be attributed exclusively to glacier stick slip motion as shown by previous studies on temperate alpine glaciers there also exist basal seismic sources which are not due to pure shear mechanisms their moment tensors have substantial if not dominant isotropic components based on first motion data of high quality seismic records from gornergletscher and triftgletscher switzerland we argue that the observed isotropic components can be explained by tensile faulting the implied coseismic volumetric change can be both positive fracture opening and negative fracture collapse we attribute these observations to hydraulic processes near water filled cavities whose connectivity to the subglacial drainage system changes over time thus our proposed icequake source mechanisms cannot be reconciled with pure shear sources at the glacier bed which would be expected for basal stick slip motion this sliding mode has recently been proposed as a realitively common mechanism which can substantially enhance subglacial erosion the existence of several seismic source mechanisms tensile shear or some combination of the two of basal icequakes implies that a solid understanding about the nature of these events is indispensible if conclusions about glacier sliding subglacial erosion and other basal processes are to be drawn from observed seismicity

composition and sources of atmospheric dusts in snow at 3200 meters in the st elias range southeastern alaska usa abstract dusts in snow from the accumulation zone in the st elias range appear from their chemical compositions to have come from terranes of rocks of ferromagnesian composition these dusts with respect to their composition and to the moderate degree of variation that occurs through a depositional year are similar those deposited in greenland the high portion of the st elias range is isolated from dominance by any local dust source terranes because of altitude and the extent of the surrounding glacierized and snow covered region in greenland the altitude is typically lower but local sources are even less likely to dominate the character of the dusts deposited into the ice record there the similar compositions and moderate compositional variations of dusts from these two places bear on the question of whether the dusts that are transported over long distances by the atmosphere under modern and glacial period conditions are uniform and representative of a broad regional or even hemispheric background dust the dusts in the snow were measured by means of a suite of major minor and trace rock forming metals chosen to give information about rock types their constituent minerals degree of degradation weathering and energies of atmospheric uptake from source the variations in amounts of rock dust through the year in the st elias range snowpack have no time stratigraphic correspondence to the also large variations in concentrations of other species that are not constituents of rock derived dusts such the anions chloride sulfate and nitrate the highs and lows of the two types of materials are apparently completely independent the structure revealed by the moderately fine scale sampling of the present study 10 increments y serves as a background for the interpretation of analysis of ice core samples in which annual layers may be too compressed to permit analysis of sub annual samples

nanogoethite is the dominant reactive oxyhydroxide phase in lake and marine sediments iron oxides affect many elemental cycles in aquatic sediments via numerous redox reactions and their large sorption capacities for phosphate and trace elements the reactive ferric oxides and oxyhydroxides are usually quantified by operationally defined selective chemical extractions that are not mineral specific we have used cryogenic 57fe mossbauer spectroscopy to show that the reactive iron oxyhydroxide phase in a large variety of lacustrine and marine environments is nanophase goethite feooh rather than the assumed surface complex stabilized two line ferrihydrite and accompanying mixture of clay and oxyhydroxide fe bearing phases this result implies that the kinetic and stability parameters of the type of nanogoethite that we observe to be present in sediments should be first determined and then used in models of early diagenesis the identity and characteristics of the reactive phase will also set constraints on the mechanisms of its authigenesis

intermediate depth icequakes and harmonic tremor in an alpine glacier glacier d argentiere france evidence for hydraulic fracturing we detected several thousand deep englacial icequakes on glacier d argentiere mont blanc massif between 30 march and 3 may 2012 these events have been classified in eight clusters inside each cluster the waveforms are similar for p waves and s waves although the time delay between the p waves and s waves vary by up to 0 03 s indicating an extended source area although these events were recorded by a single accelerometer they were roughly located using a polarization analysis the deepest events were located at a depth of 130 m 60 m above the ice bed interface the clusters are separated in space the largest cluster extends over about 100 m for this cluster the strike of the rupture plane is nearly parallel to the direction of the open crevasses and the dip angle is 56 deep icequakes occur in bursts of activity that last for a few hours and are separated by quiet periods many events occurred on 28 29 april 2012 during the warmest days when snow melting was likely important the distribution of events in time and space obeys a power law as also observed for earthquakes but with larger exponents the polarity of the p waves for all of the events is consistent with tensile faulting finally between 25 april and 3 may we observed a gliding harmonic tremor with a fun damental resonance frequency that varied between 30 hz and 38 hz with additional higher frequency harmonics during this time we also observed shallow hybrid events with high frequency onsets and a monochromatic coda these events might be produced by the propagation of fractures and the subsequent flow of water into the fracture the strongest resonance was observed just after a strong burst of deep icequakes and during an un usually warm period when the snow height decreased by 60 cm in one week the res onance frequency shows a succession of several sharp decreases and phases of progressive increases one of the strongest negative steps of the resonance frequency on 28 april coincides with a burst of deep icequakes these events appear to be associated with the propagation of fractures which can explain the decrease in the resonance frequency finally we observed an acceleration of glacier flow on 29 april and suggested that melt water had reached the ice bed interface these observations suggest that deep icequakes are due to hydraulic fracturing and that they can be used to track fluid flow inside glaciers

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

mobilization of arsenic and iron from red river floodplain sediments vietnam abstract sediments from the red river and from an adjacent floodplain aquifer were investigated with respect to the speciation of fe and as in the solid phase to trace the diagenetic changes in the river sediment upon burial into young aquifers and the related mechanisms of arsenic release to the groundwater goethite with subordinate amounts of hematite were using mossbauer spectroscopy identified as the iron oxide minerals present in both types of sediment the release kinetics of fe as mn and po 4 from the sediment were investigated in leaching experiments with hcl and 10 mm ascorbic acid both at ph 3 from the river sediments most of the fe and as was mobilized by reductive dissolution with ascorbic acid while hcl released very little fe and as this suggests as to be associated with an fe oxide phase for oxidized aquifer sediment most fe was mobilized by ascorbic acid but here not much as was released however the reduced aquifer sediments contained a large pool of fe ii and as that is readily leached by hcl probably derived from an unidentified authigenic fe ii containing mineral which incorporates as as well extraction with ascorbic acid indicates that the river sediments contain both as v and as iii while the reduced aquifer sediment almost exclusively releases as iii the difference in the amount of fe ii leached from river and oxidized aquifer sediments by ascorbic acid and hcl was attributed to reductive dissolution of fe iii the reactivity of this pool of fe iii was quantified by a rate law and compared to that of synthetic iron oxides in the river mud fe iii had a reactivity close to that of ferrihydrite while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic fe oxides as a reference sediments were incubated both unamended and with acetate added and monitored for up to 2 months the river mud showed the fastest release of both fe and as while the effect of acetate addition was minor this suggests that the presence of reactive organic carbon is not rate limiting in the case of the river and aquifer sediments the release of fe and as was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor the reduced aquifer sediment apparently can sustain slower but prolonged microbially driven release of as the highly reactive pools of fe iii and as in the river mud could be due to reoxidation of as and fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of as onto the floodplain and into the underlying aquifers

composition age and provenance of organic matter in nw african dust over the atlantic ocean 1 eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992 1993 in the northeast atlantic off northwest africa 18 n 22 w afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance the sample was subjected to microscopic examination and bulk elemental isotopic black carbon and molecular lignin lipid analyses the bulk elemental composition and organic carbon oc content 1 02 dry weight establishes the dust s origin as continental upper crust and is typical of dusts that emanate from west africa these data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the sahara and sahel regions e g nasa toms aerosol index microscopic examination reveals that charcoal like particles from vegetation fires black carbon bc are the most abundant morphologically distinct organic components accelerator mass spectrometry ams 14c analysis yields conventional 14c ages for bulk oc of 1260 40 years and bc of 2070 35 years taken together with corresponding stable carbon isotopic compositions 13c 18 9 and 15 1 respectively these results suggest the presence of biomass and burning residues derived from predominantly c4 vegetation that accumulated in soils over the late holocene molecular level measurements are also consistent with this scenario for example lignin derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass type tissue the altered nature of the lignin suggests storage as residues in soils solvent extractable lipid constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region the hydrocarbon fraction contained some diesel type contamination but the n alkanes c23 c33 retained a prominent odd even distribution with 13c ranging from 26 7 to 28 5 the suite of even carbon numbered n alkanols c22 c32 is 14c dated at 647 150 years with 13c values ranging from 23 9 to 30 4 the long chain n alkanoic acids c22 c32 exhibited 13c values ranging from 22 6 to 27 4 these waxes are evidently a mixed signal derived from contemporary c3 and c4 vegetation and from ablated soils and desiccated lake sediments of middle to late holocene age this molecular approach shows promise as a tool for continental paleoenvironmental assessment particularly with respect to past vegetation cover regional aridity and wind systems

large flux of iron from the amery ice shelf marine ice to prydz bay east antarctica the antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide co2 sink through the photosynthetic fixation of co2 via the biological pump sustaining such high productivity requires a large supply of the essential micronutrient iron fe however the pathways for fe delivery to these zones vary spatially and temporally our study is the first to report a previously unquantified source of concentrated bioavailable fe to antarctic surface waters we hypothesize that fe derived from subglacial processes is delivered to euphotic waters through the accretion fe storage and subsequent melting fe release of a marine accreted layer of ice at the base of the amery ice shelf ais using satellite derived chlorophyll a data we show that the soluble fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required fe necessary to sustain the large annual phytoplankton bloom in prydz bay our finding of high concentrations of fe in ais marine ice and recent data on increasing rates of ice shelf basal melt in many of antarctica s ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt currently the distribution volume and fe concentration of antarctic marine ice is poorly constrained this uncertainty combined with variable forecasts of increased rates of ice shelf basal melt limits our ability to predict future fe supply to antarctic coastal waters

azimuthal anisotropy analysis of p wave seismic data and estimation of the orientation of the in situ stress fields an example from the rock springs uplift wyoming usa abstractestimating the orientation and magnitude of maximum and minimum horizontal in situ stress is important for characterizing naturally fractured unconventional and carbon sequestered reservoirs for naturally fractured reservoirs they are needed to guide directional drilling for unconventional reservoirs they are used for optimal placements of hydraulic fractures and for carbon sequestered reservoirs they are used to avoid fracturing of overlying seal rocks in addition a knowledge of stress fields can be used to induce fractures within the target reservoirs and enhance additional storage for carbon sequestration experiments the orientation and magnitude of in situ stress can be calculated at the well locations for locations away from the wells analysis of the azimuthal dependence of the amplitude variation with angle gradient or azimuthal angle stacks are used to quantify anisotropy which are then related with well data and other geologic information for stress estimation such azimutha

sustained seismic tremors and icequakes detected in the ablation zone of the greenland ice sheet during summer 2011 seismic activity in the ablation zone of the western greenland ice sheet gris was monitored using a network of three component seismometers the seismic record includes a large variety of icequakes and seismic tremors that demonstrate a clear correlation with subglacial water flow we verified the existence of well known shallow icequakes related to surface crevasse formation deep icequakes located at 100 160 m depth and narrow banded short term seismic tremors tens of seconds in duration in addition we present previously unreported long term tremors lasting several hours using attenuation of the measured tremor amplitude we locate the epicentre of this long term tremor to a large moulin within our study area between 3 and 11 hz our continuous seismic record is dominated by this moulin tremor and shows strong correlation with the water level of the generating moulin we argue that monitoring of icequake and glacial tremor sources bears high potential for investigating glacier hydraulics and dynamics and is thus an ideal supplement to traditional glaciological measurements

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

a zonal picture of the water column distribution of dissolved iron ii during the u s geotraces north atlantic transect cruise geotraces ga03 we report measurements of the transient species iron ii in filtered water column samples collected during the u s geotraces north atlantic transect cruise geotraces ga03 which was comprised of legs from lisbon to cape verde in october november 2010 and from woods hole to cape verde in november december 2011 dissolved iron ii dfe ii was determined at sea in 0 2 m filtered samples as soon as possible after collection and filtration using flow injection analysis with mean detection limits of 0 06 nm and 0 01 nm during the 2010 and 2011 cruise legs respectively water column concentrations along the cruise transects were generally low 0 2 nm with the exception of deep water samples collected over the trans atlantic geotraverse hydrothermal field in which dfe ii was as high as 70 nm and accounted for more than 80 of the dissolved iron pool in the near field hydrothermal plume smaller local concentration maxima were observed near 1000 m depth in the low oxygen iron rich waters to the east of cape verde where dfe ii is correlated with apparent oxygen utilization and in the upper water column at several stations in the subtropical gyre where dfe ii can account for greater than 50 of the dissolved iron pool in the lower euphotic zone elevated dfe ii concentrations were also observed over much of the water column on the bermuda platform although the source of this enrichment remains uncertain in the absence of data between woods hole and bermuda

tracking eolian dust with helium and thorium impacts of grain size and provenance reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples more recently dust fluxes have been estimated from measurements of helium and thorium as rare isotopes of these elements he 3 and th 230 allow estimates of sediment flux and the dominant isotopes he 4 and th 232 are uniquely associated with the lithogenic fraction of marine sediments in order to improve the fidelity of dust flux reconstructions based on he and th we present a survey of he and th concentrations in sediments from dust source areas in east asia australia and south america our data show systematic relationships between he and th concentrations and grain size with he concentrations decreasing and th concentrations increasing with decreasing grain size we find consistent he and th concentrations in the fine fraction 5 m of samples from east asia australia and central south america puna central west argentina with th concentrations averaging 14 g g and he concentrations averaging 2 cc stp g we recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine grained and suggest that previous studies may have systematically overestimated th based dust fluxes by 30 source areas in patagonia appear to have lower he and th contents than other regions as fine fraction concentrations average 0 8 cc stp g and 9 g g for 4he and 232th respectively the impact of grain size on lithogenic he and th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably our data also have important implications for the hosts of he in long traveled dust and for the 3he 4he ratio used for terrigenous he in studies of extraterrestrial he in sediments and ice we also investigate the use of he th ratios as a provenance tracer our results suggest differences in fine fraction he th ratios between east asia australia central south america and patagonia with ratios showing a positive relationship with the geological age of source rocks he th ratios may thus provide useful provenance information for example allowing separation of patagonian sources from puna central west argentina or australian dust sources he th ratios in open ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas he th ratios in mid latitude south atlantic sediments suggest that dust in this region primarily derives from the puna central west argentina region 23 32 s rather than patagonia 38 s in the equatorial pacific he th ratios are much lower than in extratropical pacific sediments or potential source areas measured as a part of this study east asia south america australia for reasons that are at present unclear complicating their use as provenance tracers in this region