displacement pile behaviour in glacial clay the paper describes a programme of field experiments with heavily instrumented displacement piles installed in a stiff lodgement till measurements of the effective stresses recorded at various le

aeolian abrasion and modes of fine particle production from natural red dune sands an experimental study a series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles 125 m by 1 the release of resident fines 2 spalling chipping and breakage of particles and 3 the removal of grain surface coatings parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass test tube chamber for up to 120h the fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle size analyses using a coulter multisizer the abrasion of untreated parent samples produced fine particles in one of two main size classes 50 m but when the parent sample was sieved to exclude particles 250 m relatively more material in the range 10 50 m was produced for unsieved parent samples the size range associated with the dominant mode varied according to the length of the abrasion time the coarsest mode 63 m was dominant during the first 16 h of abrasion then became less significant and is thought to be associated with the release of resident fines into suspension the finest mode 10 m was absent or very weak during the first 16h of abrasion then became more significant and in some instances dominated the distribution as abrasion continued removal of grain surface coatings is the main source of fine material 10 m and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles by comparison with previous studies of aeolian particle abrasion these natural dune sands produced very low quantities of fine material by weight but their spatial extent makes them potentially a significant source of dust sized particles at the global scale

estimates of atmospheric processed soluble iron from observations and a global mineral aerosol model biogeochemical implications 1 desert dust deposition to the ocean may be a significant source of biogeochemically important elements specifically iron the bioavailability of iron in the oceans requires it to be in a soluble form and because atmospheric iron in desert dust is typically insoluble understanding the atmospheric processes that convert insoluble iron to more soluble forms is essential understanding these relationships is especially important in remote ocean regions where iron may be the limiting nutrient observations of soluble iron from 2001 cruise based aerosol measurements over the atlantic and pacific oceans ranged from 0 to 45 mean of 4 9 in the fine mode 2 5 m in diameter and 0 to 87 mean of 2 10 in the coarse mode we test two simple hypotheses of soluble iron enhancement in the atmosphere using a global model of mineral aerosols the first method assumes that iron solubility increases as iron is exposed to solar radiation approximating photoreduction reactions that are important pathways for enhancement of soluble iron in the presence of acidic solutions the second process imitates cloud processing of iron by increasing the amount of soluble iron when the mineral aerosol comes into contact with a cloud both methods resulted in similar average magnitudes of percent soluble iron compared to observations but did not capture specific events or have sufficient variability perhaps because the model does not include aerosol interactions between species other than mineral dust or other processes that may be important

magnesium isotope fractionation in biogenic and abiogenic carbonates implications for paleoenvironmental proxies abstract geochemical variations in marine biogenic carbonates that are preserved in the geological record serve as proxies of past environmental change however interpreting most proxies is complicated by biologically mediated vital effects highlighting the need to develop new tools for reconstructing paleoenvironmental change recently magnesium mg isotope variability in carbonates has been explored extensively to determine its utility as a paleoenvironmental proxy we review the results of these works which have yielded valuable information on the factors affecting mg isotope fractionation between carbonates and solution 26mgcarb sol in biogenic and abiogenic carbonate minerals strong evidence exists for a mineralogical control on 26mgcarb sol with the negative offset from 0 following the sequence aragonite 3 mol mol and saturation states 3 that are similar to seawater suggest that 26mgcarb sol has a temperature dependence of 0 01 c 1 and is insensitive to precipitation rate in contrast a significant precipitation rate dependence is observed in calcites precipitated from solutions with relatively low mg ca ratios

identifying regional dust transport pathways application of kinematic trajectory modelling to a trans tasman case pi kinematic trajectory model is used to investigate potential pathways of dust transport from australia to new zealand historically these have been assumed to follow rather direct west east trajectories spanning 2 to 3 days often resulting in red snow events in the southern alps of new zealand however results from the present study which examined the route taken by air parcels originating in southern australia during dust storms on 24 and 25 may 1994 indicate that trans tasman dust transport trajectories are more diverse than previously thought and display considerable variation during single events these mon divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the tasman sea and may account for the deposition of australian dust on sub antarctic islands located well south of the australian continent copyright 2000 john wiley sons ltd

factors affecting the nature and rate of dust production from natural dune sands this paper evaluates the influence of natural sand particle characteristics on the amount and particle size distributions of dust produced by aeolian abrasion it contrasts with previous studies of aeolian abrasion by conducting experiments using i whole sand samples as opposed to selected size fractions ii natural mature dune sands rather than artificial or freshly crushed material and iii weathered sands that have acquired a superficial clay coating instead of grains with clean surfaces whilst previous research has found clear positive relationships between particle size sorting roundness and the amount of dust produced by aeolian abrasion the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained the most important factor affecting the amount and particle size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process the dust produced by this mechanism had a modal size of 2 5 m and material 10 m comprised up to 90 of the particles produced

moho structure of central america based on three dimensional lithospheric density modelling of satellite derived gravity data the central american isthmus hosts a highly variable moho structure due to the diverse origin and composition of the crustal basement and the influence of large scale neotectonic processes gravity data from the combined geopotential model egm2008 were interpreted via forward modelling to outline the three dimensional lithospheric density structure along the middle american trench as well as the segmentation of the oceanic cocos and nazca plates and the overriding caribbean plate in this work results for the depth of the moho obtained from the density model are presented the quaternary volcanic arc correlates with a maximum moho depth of 44 km in western guatemala to the south east of the continental shelf the caribbean plate shows moho depths between 20 and 12 km whereas to the north values as shallow as 8 km are observed at the cayman trough for the oceanic cocos plate depths between 16 and 21 km are obtained for the moho along the cocos ridge contrasting with values between 15 and 12 km for the seamount segment and 8 and 11 km for the segments of the crust that are not affected by the galapagos hot spot track

response of surface nutrient inventories and nitrogen fixation to a tropical cyclone in the southwest pacific to examine the controls of new nitrogen supply in oligotrophic waters nitrogen fixation and nutrients were monitored during a quasi lagrangian study in surface waters of the north tasman sea during march april 2006 the study was initiated coincident with a tropical cyclone with high rainfall and winds that eroded surface layer density structure and increased surface phosphate and silicate concentrations by 50 however there was no corresponding increase in nitrate as the enhanced vertical mixing perturbed the phosphacline but not the deeper nitracline dissolved iron was highest in the upper 20 m and declined to a minimum at 100 150 m indicating wet deposition as the source as also inferred from the salinity decrease nitrogen fixation increased significantly by an order of magnitude over the following 9 d in deckboard perturbation experiments immediately after the cyclone phosphate and iron addition did not elicit a response in nitrogen fixation whereas 8 d later when in situ dissolved iron had declined the addition of iron stimulated nitrogen fixation by 1 5 fold conversely the addition of dust from australia and the gobi desert immediately after the cyclone increased nitrogen fixation by 2 and 4 5 fold respectively the observed 10 fold increase in nitrogen fixation in situ exceeded that reported in other nutrient perturbation experiments despite comparatively low in situ dissolved iron indicating that iron bioavailability may be a critical factor although stimulation by a cyclone was unexpected it promoted favorable conditions for diazotrophy by enhancing phosphate availability in the absence of nitrate and increased dissolved iron supply and availability via wet deposition this suggests that future increases in tropical cyclones combined with other climate driven trends may increase nitrogen fixation in the north tasman sea

on the southerly extent of the antarctic circumpolar current in the southeast pacific a front at 67 s in the bellingshausen sea at 85 w is shown to be part of the antarctic circumpolar current acc and the southernmost zone of concentrated eastward transport at that longitude the front lies 6 south of the polar front at 88 w and 3 north of the continental water boundary the front is continuous to the east through drake passage where it forms a southern branch of the polar front for which reason we have named it the southern polar front data from a towed profiling ctd were able to distinguish the polar front from the southern polar front even though they were only 0 5 apart thus the width of the acc south of the polar front varied considerably about a third of the transport of the acc also lay south of the polar front with 15 sv carried by the southern polar front alone at 85 w distinguishing features of the southern polar front were a water mass boundary associated with a zone of concentrated baroclinic flow and a surface salinity minimum these features also have been found at the greenwich meridian at 53 s so the southern polar front can be traced round at least a quarter of the globe to the west of the bellingshausen sea both eltanin data and the fine resolution antarctic model show that the aac is at its narrowest at 145 w where its southern boundaries lie as far north as 56 s at this longitude the acc meets the topographic barrier of the pacific antarctic ridge to conserve potential vorticity the current is forced to make a southward loop as it crosses the ridge and the current broadens dramatically the flow remains broad until forced to sharpen by the constriction of drake passage a similar broadening of the acc is seen where it crosses the southwest indian ridge south of africa at 30 e here it remains broad until it encounters the kerguelen plateau thus the eastern boundaries of both the weddell and ross gyres are determined by where the acc crosses midocean ridges

dissolved aluminium cycling in the northern equatorial and subtropical gyre region of the indian ocean abstract dissolved aluminium hereafter dal concentrations have been determined on 34 full vertical water column profiles sampled along the two separate geotraces india transects gi 01 and gi 06 to understand the biogeochemical controls on dal distribution in the northern the bay of bengal the andaman sea and the arabian sea equatorial and subtropical gyre region of the indian ocean al released due to the partial dissolution of and or al desorption from the suspended lithogenic sediments supplied in a huge amount to the bay of bengal bob waters by the ganga brahmaputra g b river system indian peninsular rivers and sediment resuspension from the continental shelf and slope predominantly controls the dal distribution in the bob and results in an overall increase in the dal concentrations throughout the water column towards the northern bob and the eastern coast of india considering the steady state balance between the dal input from the lithogenic sediment flux in the upper water column and first order scavenging removal of dal the fractional solubility of al from the lithogenic sediments in the bob surface waters is estimated to be in the range of 1 1 4 7 advection of indonesian sea surface waters through the strait of malacca and dal input from the partial dissolution of resuspended terrigenous sediments sourced from the insular shelf of the nicobar islands set major controls on the dal distribution in the surface and upper thermocline waters of the southern andaman sea and the southern bob region near the nicobar islands rapid renewal of and vertical mixing in the deeper waters 1000 m relative to scavenging removal of dal results in near uniform dal concentrations 3 7 nm in the deeper waters at the center of the southern andaman sea in the south eastern arabian sea the continental outflow of mineral dust and advection of dal enriched bay of bengal surface waters control the dal distribution in the surface water layer dal in the surface waters of the equatorial indian ocean during the late winter sampling period of the gi 06 cruise is predominantly determined by the mixing between dal rich surface waters of the southern bob and relatively dal depleted surface waters of the southern arabian sea under the influence of the northeast monsoon current the scavenging residence time of dal in the deep waters of the equatorial indian ocean is estimated using a 1 d scavenging advection diffusion model and found to be in the range of 92 141 years deposition of australian dust and advection of indonesian throughflow water translates to the dal enrichment in the upper water column 3500 m advects across the ninety east ridge from the western australian basin to bring the dal rich waters to the northern end of the central indian ocean basin

iron and other transition metals in patagonian riverborne and windborne materials geochemical control and transport to the southern south atlantic ocean abstract the bulk of particulate transition metals transported by patagonian rivers shows an upper crustal composition riverine particulate 0 5 n hcl leachable trace metal concentrations are mainly controlled by fe oxides complexation of fe by dissolved organic carbon doc appears to be an important determinant of the phases transporting trace metals in patagonian rivers in contrast aeolian trace elements have a combined crustal and anthropogenic origin aeolian materials have fe mn and al contents similar to that found in regional topsoils however seasonal concentrations of some metals e g co pb cu and zn are much higher than expected from normal crustal weathering and are likely pollutant derived we estimate that patagonian sediments are supplied to the south atlantic shelf in approximately equivalent amounts from the atmosphere 30 10 6 t yr 1 and coastal erosion 40 10 6 t yr 1 with much less coming from the rivers 2 0 10 6 t yr 1 low trace metal riverine fluxes are linked to the low suspended particulate load of patagonian rivers inasmuch most of it is retained in pro glacial lakes as well as in downstream reservoirs based on our estimation of aeolian dust fluxes at the patagonian coastline the high nutrient low chlorophyll sub antarctic south atlantic could receive 1 0 to 4 0 mg m 2 yr 1 of leachable 0 5 n hcl fe past and present volcanic activity in the southern andes through the ejection of tephra must be highlighted as another important source of fe to the south atlantic ocean based on the 1991 hudson volcano eruption it appears that volcanic events can contribute several thousand fold the mass of leachable fe to the ocean as is introduced by annual patagonian dust fallout

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

fecycle attempting an iron biogeochemical budget from a mesoscale sf6 tracer experiment in unperturbed low iron waters 1 an improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high nitrate low chlorophyll hnlc oceanic regions iron budgets for hnlc waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics in summer 2003 we conducted fecycle a 10 day mesoscale tracer release in hnlc waters se of new zealand and measured concurrently all sources with the exception of aerosol deposition to sinks of iron from and rates of iron recycling within the surface mixed layer a pelagic iron budget timescale of days indicated that oceanic supply terms lateral advection and vertical diffusion were relatively small compared to the main sink downward particulate export remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in australia prior to and during fecycle one of which may have deposited iron at the study location however iron deposition rates cannot be derived from such observations illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric supply despite the threefold uncertainties reported for rates of aerosol deposition duce et al 1991 published atmospheric iron supply for the new zealand region is 50 fold i e 7 to 150 fold greater than the oceanic iron supply measured in our budget and thus was comparable i e a third to threefold to our estimates of downward export of particulate iron during fecycle the fluxes due to short term hours biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron i e estimated atmospheric and measured oceanic supply giving an fe ratio uptake of new iron uptake of new regenerated iron of 0 17 i e a range of 0 06 to 0 51 due to uncertainties on aerosol iron supply and an fe ratio biogenic fe export uptake of new regenerated iron of 0 09 i e 0 03 to 0 24

the influence of temperature and vital effects on magnesium isotope variability in porites and astrangia corals abstract the magnesium isotope composition 26 mg of sub annually and bulk sampled porites corals is presented and suggests that the coral seawater fractionation factor 26 mg is temperature dependent with a sensitivity of 0 03 c 1 although the apparent temperature dependence of 26 mg in porites corals could be used empirically to reconstruct paleoclimate its temperature sensitivity is about three times that of abiogenic aragonites which indicates that kinetic and or biologically induced processes collectively known as vital effects are also important comparison with data from abiogenic aragonite precipitation experiments suggests that 26 mg vital effects vary seasonally in porites the 26 mg of skeleton deposited in winter is within the analytical error of abiogenic aragonite but that of skeletal aragonite grown during summer exhibits significantly smaller fractionations that may be associated with light enhanced calcification the observed vital effect is consistent with 26 mg but cannot be evaluated with current data however the observed vital effect is not consistent with the isotope fractionation expected from rayleigh processes ion attachment detachment kinetics or diffusion furthermore the 26 mg of symbiotic and asymbiotic astrangia corals is within analytical error and indicates that vital effects cannot be attributed to the presence of photosymbionts some data suggest that the offset between coral and abiogenic aragonite 26 mg may be proportional to that for oxygen isotope fractionations raising the possibility that vital effects in both isotope systems may be influenced by a common mechanism although the presence of vital effects and analytical limitations will complicate the development of a 26 mg based paleothermometer it may still be a valuable tool for reconstructing seawater 26 mg or investigating biomineralization processes especially when applied as part of a multi proxy approach

biogeochemistry of iron in australian dust from eolian uplift to marine uptake 1 dust is an important vector for iron supply to the ocean which subsequently impacts ocean productivity atmospheric co2 concentrations and hence global climate here we synthesize the processes influencing the biogeochemistry of australian dust and compare them with those from other southern hemisphere dust sources our observations range from soil and dust physical properties to abrasion and cloud chamber chemistry experiments to dust storms and their dispersion and deposition we then present satellite observations of the impact of episodic dust deposition events on the productivity of low iron oceanic waters north i e low nitrate low chlorophyll lnlc and south i e high nitrate low chlorophyll hnlc of australia dust deposition from the largest dust storm in over 40 years did not result in iron mediated algal blooms in either oceanic region a comparison of australia with other southern hemisphere source regions reveals that the relatively well sampled australian system is a poor generic model furthermore there are marked distinctions between southern and northern hemisphere iron dust biogeochemistry that must be recognized by modelers and included in future simulations better information is required on the relative role of the atmosphere and ocean on influencing iron biogeochemistry and how their relative influences might change in the future due to climate change

effects of spatial variations in source areas upon dust concentration profiles during three wind erosion events in australia dust storms are a major contributor to soil erosion in inland australia and the simpson desert channel country region is one of the most active wind erosion regions while information is available on wind erosion rates at the land type level little is known about the influence spatial variations in the erodibility within a land type has on the resulting dust concentration profile a gaussian plume model dsis is presented along with tower based dust data to describe the influence of different spatial combinations of dust sources areas during three dust events on the diamantina river flood plain in western queensland australia

processes governing the supply of iron to phytoplankton in stratified seas 1 the impact of iron speciation on phytoplankton dynamics in the marine environment is currently not well understood in this study we modified the existing ciao model of the ross sea to include major aspects of iron chemistry and examined the processes governing the supply of iron to phytoplankton we suggest that the melting of sea ice and ensuing stratification dictates the speciation and bioavailability of iron photoreduction is the key process governing the supply of bioavailable fe to the resident phytoplankton of the ross sea access to organically complexed iron is of greater significance in strongly stratified waters dominated by diatoms than in weakly stratified waters dominated by phaeocystis antarctica light may control phytoplankton taxonomic composition in the ross sea by impacting both photosynthetic performance and iron speciation the efficiency with which iron fuels phytoplankton carbon incorporation is greater in seasonal ice zones than in permanently ice free waters therefore changes in the physical structure of the southern ocean could impact iron bioavailability independent of any change in iron supply

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

new and revised palaeomagnetic secular variation records from post glacial volcanic materials in new zealand abstract global databases suffer from a paucity of palaeomagnetic secular variation psv data from the sw pacific region and are often affected by inconsistencies in data quality or available age control of the sampled units here we present new psv records obtained from post glacial 15 kyrs bp volcanic materials mainly lavas from new zealand the new dataset incorporates a compilation and critical assessment of all previous discrete psv data and their age controls and the results of new sampling in the taupo volcanic zone the overall dataset includes 23 directional and 10 absolute palaeointensity records primarily from lavas of rhyolitic or andesitic composition age constraints on the rhyolitic lavas are available from correlation with distal radiocarbon dated tephra deposits age controls on the andesites from field relationships or from 40 ar 39 ar dating directional swings ranging from 326 5 to 26 0 declination and 81 4 to 46 3 inclination and intensity variations from 37 0 to 71 6 t fall well into the range of psv expected for this time frame in new zealand and reproduce features of continuous sediment records

biogeochemical iron budgets of the southern ocean south of australia decoupling of iron and nutrient cycles in the subantarctic zone by the summertime supply 1 climate change is projected to significantly alter the delivery stratification boundary currents aridification of landmasses glacial melt of iron to the southern ocean we report the most comprehensive suite of biogeochemical iron budgets to date for three contrasting sites in subantarctic and polar frontal waters south of australia distinct regional environments were responsible for differences in the mode and strength of iron supply mechanisms with higher iron stocks and fluxes observed in surface northern subantarctic waters where atmospheric iron fluxes were greater subsurface waters southeast of tasmania were also enriched with particulate iron manganese and aluminum indicative of a strong advective source from shelf sediments subantarctic phytoplankton blooms are thus driven by both seasonal iron supply from southward advection of subtropical waters and by wind blown dust deposition resulting in a strong decoupling of iron and nutrient cycles we discuss the broader global significance our iron budgets for other ocean regions sensitive to climate driven changes in iron supply

in situ lateral stress coefficient k0 from shear wave velocity measurements in soils abstractthe at rest lateral stress coefficient k0 is an important soil parameter in geotechnical design problems and yet it is quite elusive in our ability to assess its value either by laboratory or in situ tests in this study an innovative geophysics approach toward the evaluation of the in situ k0 profile with depth is obtained by using small strain stiffness anisotropy ratio g0 hh g0 vh in soils the newly proposed k0 equation is derived from a database compiled from 12 test sites which have direct k0 measurements as procured from field tests either self boring pressuremeters sbp or total stress cells tsc and or laboratory triaxial tests instrumented consolidometers and or suction measurements the data show a strong relationship between the overconsolidation difference ocd p vo and stiffness anisotropy ratio thus enabling a k0 assessment in clays silts and sands

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

horizontal and vertical transport of air over southern africa tropospheric air trajectories that occurred during the southern african fire atmosphere research initiative safari in august october 1992 are described in terms of a circulation classification scheme and the vertical stability of the atmosphere three major and frequently occurring stable discontinuities are found to control vertical transport of aerosols in the subtropical atmosphere at the end of the dry season of these the main subsidence induced feature is a spatially ubiquitous and temporally persistent absolutely stable layer at an altitude of about 5 km 3 5 km above the interior plateau elevation this effective obstacle to vertical mixing is observed to persist without break for up to 40 days below this feature an absolutely stable layer at 3 km 1 5 km above the surface prevails on and off at the top of the surface mixing layer for up to 7 days at a time being broken by the passage of regularly occurring westerly wave disturbances above the middle level discontinuity a further absolutely stable layer is frequently discerned at an altitude of about 8 km it is shown that five basic modes can be used to describe horizontal aerosol transportation fields over southern africa dominating these is the anticyclone mode which results in frequent recirculation at spatial scales varying from hundreds to thousands of kilometers in exiting the anticyclonic circulation transport on the northern periphery of the system is to the west over the atlantic ocean via a semistationary easterly wave over the western part of the subcontinent on the southern periphery wave perturbations in the westerly enhance transports which exit the subcontinent to the east into the indian ocean independently derived data suggest that during safari only 4 of the total transport of air from three locations south of 18 degrees 8 was into the atlantic ocean over 90 of the transport was into the indian ocean across 35 degrees e this result reflects circulation fields typical of the extremely dry conditions prevailing in 1992 the integrated effect of the control exerted by atmospheric stability on vertical mixing on the one hand and the nature of the horizontal circulation fields on the other is to produce a distinctive suite of transport patterns that go a long way to explain the observed high concentrations of tropospheric aerosols and trace gases observed over the subcontinent in winter and spring as well as over the tropical south atlantic and southwestern indian oceans

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

dust source identification using modis a comparison of techniques applied to the lake eyre basin australia the impact of mineral aerosol dust in the earth s system depends on particle characteristics which are initially determined by the terrestrial sources from which the sediments are entrained remote sensing is an established method for the detection and mapping of dust events and has recently been used to identify dust source locations with varying degrees of success this paper compares and evaluates five principal methods using modis level 1b and modis level 2 aerosol data to a differentiate dust mineral aerosol from non dust and 2 determine the extent to which they enable the source of the dust to be discerned the five modis l1b methods used here are 1 un processed false colour composite fcc 2 brightness temperature difference 3 ackerman s 1997 j geophys res 102 17069 17080 procedure 4 miller s 2003 geophys res lett 30 20 art no 2071 dust enhancement algorithm and 5 roskovensky and liou s 2005 geophys res lett 32 l12809 dust differentiation algorithm the aerosol product is modis deep blue hsu et al 2004 ieee trans geosci rem sensing 42 557 569 which is optimised for use over bright surfaces i e deserts these are applied to four significant dust events from the lake eyre basin australia omi ai was also examined for each event to provide an independent assessment of dust presence and plume location all of the techniques were successful in detecting dust when compared to fccs but the most effective technique for source determination varied from event to event depending on factors such as cloud cover dust plume mineralogy and surface reflectance significantly to optimise dust detection using the modis l1b approaches the recommended dust non dust thresholds had to be considerably adjusted on an event by event basis modis l2 aerosol data retrievals were also found to vary in quality significantly between events being affected in particular by cloud masking difficulties in general we find that omi ai and modis aqua l1b and l2 data are complementary the former are ideal for initial dust detection the latter can be used to both identify plumes and sources at high spatial resolution overall approaches using brightness temperature difference bt10 11 are the most consistently reliable technique for dust source identification in the lake eyre basin one reason for this is that this enclosed basin contains multiple dust sources with contrasting geochemical signatures in this instance btd data are not affected significantly by perturbations in dust mineralogy however the other algorithms tested including modis deep blue were all influenced by ground surface reflectance or dust mineralogy making it impossible to use one single modis l1b or l2 data type for all events or even for a single multiple plume event there is however considerable potential to exploit this anomaly and to use dust detection algorithms to obtain information about dust mineralogy

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

the signature of river and wind borne materials exported from patagonia to the southern latitudes a view from rees and implications for paleoclimatic interpretations abstract riverine and wind borne materials transferred from patagonia to the sw atlantic exhibit a homogeneous rare earth element ree signature they match well with the ree composition of recent tephra from the hudson volcano and hence this implies a dominance of material supplied by this source and other similar andean volcanoes due to the trapping effect of proglacial and reservoir lakes the larger patagonian rivers deliver to the ocean a suspended load with a slightly modified andean signature that shows a ree composition depleted in heavy rees in this paper we redefine patagonia as a source of sediments which is in contrast with other sources located in southern south america quaternary sediments deposited in the northern and to a lesser extent in the southern scotia sea and most of the dust in ice cores of east antarctica have ree compositions very similar to the loess from buenos aires province and to patagonian eolian dust however we rule out buenos aires province as a holocene major source of sediments similarly to buenos aires loess a proximal facies it is likely that the ree compositions of most sediment cores of the scotia sea and antarctica reflect a distal transport of dust with an admixed composition from two main sources a major contribution from patagonia and a minor proportion from source areas containing sediments with a clear upper crustal signature e g western argentina or from bolivia s altiplano evidence indicates that only during the last glacial maximum patagonian materials were the predominant sediment source to the southern latitudes

variability in magnesium carbon and oxygen isotope compositions of brachiopod shells implications for paleoceanographic studies abstract this study presents the carbon oxygen and magnesium isotope compositions of two modern brachiopods terebratalia transversa and frieleia halli and one fossil specimen 2 3 ma terebratula scillae the aim of this study is to investigate the variability of these isotopic compositions and to evaluate the potential of brachiopods as a proxy of past seawater 26mg values the two investigated brachiopod shells present the same range of 26mg variation up to 2 this variation cannot be ascribed to changes in environmental parameters temperature or ph as has been previously observed the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater in contrast the 26mg value of the primary layer is comparable to that of the secondary calcite layer value in both t scillae and t transversa negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions these trends can be explained by kinetic effects linked to changes in growth rate during the brachiopod life the innermost calcite layer of t transversa is in isotopic equilibrium for both oxygen and magnesium and could therefore be the best target for reconstructing past 26mg values of seawater

chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the arabian sea labile fe ii and other trace metals atmospheric deposition of iron fe to certain regions of the oceans is an important nutrient source of fe to the biota and the ability of the biota to uptake fe is dependent on the speciation of the fe therefore understanding the speciation of fe in the atmosphere is critical to understanding the role of fe as a nutrient source in surface ocean waters labile ferrous iron fe ii concentrations as well as total concentrations for fe and other important trace metals cations and anions were determined over the arabian sea for two nonconsecutive months during 1995 ambient aerosol samples were collected during the indian ocean intermonsoon and southwest monsoon seasons over the arabian sea sampling took place aboard the german research vessel meteor in the months of may leg m32 3 intermonsoon and july august leg m32 5 southwest monsoon both cruise tracks followed the 65th east meridian traveling for 30 days each from north to south during leg m32 3 and from south to north during leg m32 5 a high volume dichotomous virtual impactor with an aerodynamic cutoff size of 3 m was used to collect the fine and coarse aerosol fractions for metal analysis a low volume collector was used to collect aerosol samples for anion and cation analysis the analysis for labile fe ii was done immediately after sample collection to minimize any possible fe redox reactions which might occur during sample storage the analytical procedure involved filter extraction in a formate formic acid buffered solution at ph 4 2 followed by colorimetric quantification of soluble fe ii metals anions and cations were analyzed after the cruise total atmospheric aqueous labile fe ii concentrations during the intermonsoon were between 4 75 and 80 was present in the fine fraction 3 0 m during the southwest monsoon atmospheric aqueous labile fe ii concentrations were consistently below the detection limit 0 34 to 0 089 ng m 3 depending on the volume of air sampled air mass back trajectories 5 day three dimensional showed that air masses sampled during the southwest monsoon had advected over the open indian ocean while air masses sampled during the intermonsoon had advected over northeast africa the saudi arabian peninsula and southern asia these calculations were consistent with the results of the statistical analysis performed on the data set which showed that the variance due to crustal species during the intermonsoon samples was greater than the variance due to crustal species during the southwest monsoon the factor scores for the crustal components were also greater when the back trajectories had advected over the nearby continental masses principal component analysis was also performed with the intermonsoon samples where aqueous labile fe ii was above the detection limit aqueous labile fe ii did not correlate well with other species indicating possible atmospheric processing of the iron during advection

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

color development of iron oxides during rhyolite weathering over 52 000 years abstract to evaluate the behavior of iron during weathering colors of four rhyolites with different degrees of weathering eruption ages 1 1 1 8 26 and 52 ka were studied because the initial chemical compositions of the four lavas were similar to one another it is considered that the four lavas had similar whitish color at the time of eruption however at present more weathered lavas have more yellow brownish color indicating the formation of iron hydr oxides or fe bearing clays in order to characterize those weathering products spectro colorimetry and differential dissolution method were combined the colors of 1 1 and 1 8 ka lavas are close to the color of ferrihydrite whereas those of 26 and 52 ka lavas approach to the color of goethite this indicates that the initial stage of weathering is dominated by the formation of ferrihydrite and with increasing weathering the transformation from ferrihydrite to goethite proceeds it is estimated from the change of rock color that the half life for the transformation reaction of ferrihydrite to goethite in the field is 1100 years which is at least 80 times longer than previously reported values based on laboratory experiments the presence of impurities such as si and al in ferrihydrite can be a possible origin for retarding the transformation rate in the field

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

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

simulation of chlorophyll and iron supplies in the sub antarctic zone south of australia the sub antarctic zone saz is part of the high nutrient low chlorophyll region of the southern ocean where low iron availability limits phytoplankton productivity in the tasman sea the saz displays a unique and large zonal gradient in the surface chlorophyll concentrations in situ measurements show higher dissolved iron in the east than in the west which could explain the zonal chlorophyll gradient to assess and quantify the major sources of iron in this region we use an eddy resolving model to simulate the dissolved fe distribution arising from both the shelf and the dust supply of iron the simulation showed that dissolved fe from the shelf is only transported eastward to about 155 e and the shelf source of dissolved iron is unable to supply iron to the entire tasman sea saz region even when we assume that there no iron losses the simulation with the atmospheric source of iron showed that through a combination of atmospheric transport and ocean transport enough dissolved fe can be supplied to the entire tasman sea saz region to relieve iron limitation from the model simulations we conclude that atmospheric iron supply is essential to generating the observed gradient of the chlorophyll in the saz region of the tasman sea

dust and pollution a recipe for enhanced ocean fertilization 1 for fe contained in aeolian dust to act as a micronutrient for oceanic phytoplankton some fraction of it must first be transformed mobilized into a form soluble in ocean water fe solubilization in deliquesced mineral dust aerosols emanating from east asia during the springtime outflow conditions is investigated here with a lagrangian box model of the gas and aqueous phase chemistry the model simulates the scavenging of soluble and reactive gaseous species by mineral dust aerosols chemical reactions of these species and mineral dust ions in deliquesced solution and dissolution of fe iii oxides that occurs as a result of the acid mobilization the calculations indicate that mineral calcite caco3 strongly buffers deliquesced dust aerosols with a ph that remains close to 8 until the amount of acid added to the aerosol solution exceeds caco3 alkalinity so2 pollutant emissions are a potential source of acidity to advecting dust from east asia the model is used to simulate the chemical evolution of dust plumes formed from two contrasting documented gobi desert storms that advected dust to fe limited regions of the north pacific ocean npo these calculations indicate that only plumes with relatively high initial so2 to dust ratios are capable of delivering significant amounts of bioavailable fe to the npo the estimated change in phytoplankton population inferred from the model calculated inputs of bioavailable fe for these two episodes is consistent with the satellite measured chlorophyll a concentrations in the npo model simulations indicate that 1 large dust advection episodes that can export vast amounts of mineral dust to the open ocean should have insignificant dissolved iron fraction dif as the amount of so2 required to acidify such dust plumes is about an order of magnitude higher than what can typically be entrained in the plume during its advection 2 smaller dust plumes will generally have higher difs because they require lower amounts of so2 and even if such small plumes may not cause algae blooms they could still be important sources of dissolved fe to the npo the calculations suggest that future changes in so2 pollutant emissions from east asia either up or down may affect the productivity of the npo

atmospheric iron fluxes over the last deglaciation climatic implications a decrease in the micronutrient iron supply to the southern ocean is widely believed to be involved in the atmospheric co2 increase during the last deglaciation here we report the first record of atmospheric iron fluxes as determined in 166 samples of the dome c ice core and covering the last glacial interglacial transition 22 9 kyr b p it reveals a decrease in fallout flux from 24 10 2 mg fe m 2 yr 1 during the last glacial maximum to 0 7 10 2 mg fe m 2 yr 1 at the onset of the holocene the acid leachable fraction of iron determined in our samples was the 60 of the total iron mass in glacial samples about twice the value found for holocene samples this emerging difference in iron solubility over different climatic stages provides a new insight for evaluating the iron hypothesis over glacial interglacial periods

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

dust size evidence for opposite regional atmospheric circulation changes over east antarctica during the last climatic transition three east antarctic ice cores dome b epica dome c and komsomolskaia give evidence for a uniform dust input to the polar plateau during the last glacial maximum lgm holocene transition 20 to 10 kyr bp and the 87sr 86sr versus 143nd 144nd isotopic signature of the mineral particles highlights a common provenance from southern south america at that time however the size distribution of dust from the three ice cores highlights important differences within the east antarctic during the lgm and shows clearly opposite regional trends during the climatic transition between dome b and dome c the timing of these changes is also different a geographical diversity also arises from the different phasing of the short term multi secular scale dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes we hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway either in terms of horizontal trajectory or in altitude of transport such mechanism is supported also by the dust size changes observed during a volcanic event recorded in vostok ice ice core dust size data suggest preferential upper air subsidence over the edc kms region and easier penetration of relatively lower air masses to the db area during the lgm at the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward the scenario proposed supported also by the lgm holocene regional changes of snow accumulation likely operates even at sub millennial time scale

soil abrasion and eolian dust production implications for iron partitioning and solubility 1 eolian dust is a source of iron for phytoplankton in many ocean areas and there are complex pathways of atmospheric processing from soil to ocean overlooked parts of the pathways are the impact of large 10 m grains including a role as proxies for the behavior of smaller grains and the effect of multiple cycles of uplift and abrasion in the dust source region partitioning readily released acid leachable and refractory and dissolution rates of iron were determined for an artificial dust produced by abrading an australian soil untreated soil abraded soil after production of the artificial dust and a natural australian eolian dust sample taken during a dust storm readily released iron is not created during abrasion and therefore the amount of readily released iron in a dust or dust derived soil depends on processing events since the dust or soil last experienced an abrasion event our study develops a method for the partitioning of iron within airborne dusts and appears to be the first to consider the effect of multiple uplift events on iron partitioning

micro investigation of epica dome c bottom ice evidence of long term in situ processes involving acid salt interactions mineral dust and organic matter abstract the epica dome c ice core edc reached a final depth of 3260 m at a maximum height of about 15 m above the ice bedrock interface in december 2004 we present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice this part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo records that were very likely modified by long term in situ processes our study combines high resolution ion chromatography high resolution synchrotron x ray micro fluorescence micro xrf scanning and transmission electron microscopy our aim was to identify the long term physico chemical processes at work close to the bedrock to determine how they have altered the initial registers and ultimately to extract information on the very ancient antarctic environment the ubiquitous presence of nanometer iron oxide crystals at the surface of wind borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and thus to the progressive reactivation of dormant bacterial activity in warming ice inclusions of size and number density increasing with depth observed in the 12 last meters 3248 3260 m contain liquid and solid species among them marine biogenic acids numerous wind borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum the refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures in addition to the very fine micrometer size minerals windborne from extra antarctic continental sources and often accreted in large aggregates single medium size particles a few to ca 20 m and among them organic debris are commonly encountered their size surface shape and mineralogy suggest that aerosol transport from antarctic ice free areas played a significant role at the time edc bottom ice was formed concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material very large well preserved mineral particles several tens of micrometers in diameter and biotope relics in deeper ice close to 3260 m likely come from the sub glacial environment

dust transport to dome c antarctica at the last glacial maximum and present day the antarctic polar ice core records show large changes in the concentration of dust over glacial interglacial timescales this paper explores how much of this variation is due to changes in the transport of dust from arid regions to the ice cores back trajectories initialised from the site of dome c ice core antarctica are calculated using an offline trajectory code forced by modelled winds output from the ukmo unified model running under present day and lgm boundary conditions as well as comparing the present day and lgm back trajectories their seasonal and interannual variability is also explored the results suggest that the patagonian provenance of the dome c dust can be understood in terms of the atmospheric transport whereas the total change in dust concentration requires changes to the sources or sinks

quaternary aeolian dust processes and sediments in the australian region abstract aeolian dust processes have played an important role in the evolution of the australian landscape yet little is known of the processes and their sediments two major dust transport pathways are described based upon paleo dune patterns and present day dust storms and related processes these dust pathways have been fed by alluvium deposited in internally draining river basins during the period leading up to and including the late pleistocene aridity rates of dust entrainment transport and deposition were significantly higher than at present the ocean sediments of the tasman sea the pacific and indian oceans received massive amounts of aeolian sediment dust contributions to some australian soils have also been considerable

assessment of the coefficient of the earth pressure at rest from shear wave velocity measurements the paper presents an attempt to evaluate the feasibility of predicting the value of the coefficient of the earth pressure at rest k of natural soil deposits on the basis of the measured velocities of the seismic shear waves the experimental data presented were obtained from seismic tests performed in a calibration chamber on laboratory prepared specimens of seven granular materials with grades ranging from fine sand to gravelly sand the relationship between k and the shear wave velocity established using the calibration chamber results was used successfully to predict k at two well documented sites for which both cross hole seismic and seismic piezocone penetration test results are available cet expose dicrit un essai destine a evaluer la faisabilite dune pr6vision de la valeur du coefficient de pression au sol au repos ko des depots de sol naturels en se basant sur les velocies mesurees des ondes sismiques transversales les donn6es experimentales qui sont presentees dans cet exposa viennen

episodic enhancement of phytoplankton stocks in new zealand subantarctic waters contribution of atmospheric and oceanic iron supply 1 around 30 of oceanic waters are high nitrate low chlorophyll hnlc where low iron levels limit algal growth hnlc waters have mainly been studied using shipboard and lab experiments since 1997 remote sensing of phytoplankton via seawifs ocean color has permitted monitoring of the constancy of this hnlc condition i e spatial homogeneity and low temporal variability of chlorophyll over annual cycles these trends can be exploited as episodic iron inputs should be conspicuous by subsequent expression as iron elevated algal stocks subantarctic sa waters near new zealand are hnlc and the proximity of the arid australian landmass and the iron rich subtropical front provide natural laboratories to detect episodic atmospheric and oceanic iron supply respectively two approaches were used oceanic supply was inferred from episodic increases in chlorophyll concentrations in sa waters detected using ocean color archives additional archives were used to confirm the oceanic provenance of iron supply and identify supply mechanism s atmospheric supply was assessed using data on source areas and loads for dust storms monitored in central australia dust transport and its fate was assessed using air mass forward trajectories and seawifs ocean color and aerosol optical depth maps during 1997 2001 episodic elevated chlorophyll events occurred in sa waters southeast of new zealand there was no evidence of these events being mediated by atmospheric iron supply however neither wind driven lateral advection or vertical mixing alone could account for these episodes dust storms over this period sent plumes either into high iron subtropical st waters or into sa waters in early spring when cells are probably light rather than iron limited

dust induced changes in phytoplankton composition in the tasman sea during the last four glacial cycles 1 an increase in iron supply associated with enhanced dust inputs could be responsible for higher marine phytoplankton production leading to the typically lower glacial atmospheric co2 concentrations as suggested by the iron hypothesis the enhanced dust supply may also have provided the oceans with significant amounts of silica which would have favored the growth of diatoms over coccolithophores as suggested by the silica hypothesis here we present new data on molecular biomarkers in a sediment core from the midlatitudes of the southern hemisphere which reveal dust induced changes in the relative contribution of the phytoplankton to total productivity our results illustrate a shift in the relative abundance of siliceous over calcareous organisms during glacial times when terrestrial aeolian input was enhanced although we did not detect a significant glacial decrease in coccolithophorid productivity the decrease in the caco3 corg rain ratio could have still contributed to some extent in lowering atmospheric co2 levels

warm pool hydrological and terrestrial variability near southern papua new guinea over the past 50k here we presenta 50k archiveof u37 seasurface temperature sst planktic foraminifera oxygen isotopes and terrestrial input indicators including branched and isoprenoid tetraether bit biomarkers 232 th activity and non biogenic sediment components recorded in core md052928 from the wpwp near southern papua new guinea png the planktic foraminifer oxygen isotopes in the core show millennial scale changes indicating fresher seawater during the nh cold periods i e heinrich events hes and suggesting hydrological changes that are most likely linked to the strength of the boreal winter asian australian monsoon aam our observations are corroborated by evidence from the same core that indicates increased terrestrial input caused by higher precipitation on land and more river runoff from southern png during the cold periods consistent with other nearby hydrological records from land our study indicates persistent millennial scale hydrological changes within the past 50k in the western tropical pacific and southeast asia the timing of the millennial scale changes appears to have been determined by the latitudinal displacement of the intertropical convergencezone itcz thatreflectsahistoryofheattrans

comparing the epica and vostok dust records during the last 220 000 years stratigraphical correlation and provenance in glacial periods a new aeolian dust record from the first 2200 m of the epica dome c ice core 75 06 s 123 21 e covering about 220 000 years of climatic history is compared to the vostok 78 28 s 106 48 e ice core nature 399 1999 429 the two dust profiles are very similar and several common dust events allow to establish stratigraphical links the late quaternary period is characterized at both sites and likely overall east antarctic plateau by high dust input during glacial periods in the epica dome c ice core the dust flux rises by a factor of 25 20 and 12 in glacial stages 2 4 and 6 with respect to interglacial periods holocene and stage 5 5 the magnitude and pattern of changes are comparable in the vostok ice core in this study the geographical origin of ice core dust icd in cold periods has been investigated at both sites through 87sr 86sr versus 143nd 144nd isotopic tracers following the previous studies of grousset et al earth planet sci lett 111 1992 175 and basile et al earth planet sci lett 146 1997 573 the new data and the existing ones allow to define the isotopic fields for dust at the two antarctic sites that are almost identical and restricted into the 0 708 87sr 86sr 0 711 and 5 end 0 5 ranges this suggests a common geographical provenance for dust at vostok and dome c and for all the glacial periods of the late pleistocene to decipher the icd provenance more than 50 samples of loess and aeolian deposits sands and fluvioglacial sediments from the potential source areas psas of the southern hemisphere have been collected however the methodology has been refined with respect to former studies first the isotopic fractionation that can occur in function of grain size has been taken into account and the psa s signature has been defined in the 5 m size range within which fine grained dust reaching antarctica is found moreover a possible contribution from carbonates on the samples from psas has also been also considered south africa and australia can be excluded as dominant sources but a partial overlap arises among southern south america new zealand and the antarctic dry valleys isotopic fields these latter two documented for the first time a possible contribution from all these three sources cannot be excluded but complementary arguments suggest the dominant contribution to east antarctic dust in glacial times deriving from the southern south american region of patagonia and the pampas this study shows a first order uniformity in the dust flux and geographical provenance to the east antarctica plateau during glacial periods

insolation and cross hemispheric controls on australian monsoon variability over the past 180 ka new evidence from offshore southeastern papua new guinea the australian summer monsoon asm is primarily a synoptic feature determined by the differential thermal response to solar insolation between the australian continent and the western pacific warm pool wpwp in austral summer little is known about the process involved in driving long term asm variability here we present a 180 ka record of terrestrial fluxes into offshore southeastern papua new guinea png a prevailing monsoon area in the wpwp terrestrial fluxes were estimated by a 230th normalized method indicating higher terrestrial inputs into the ocean during glacial stages we argue that the higher terrestrial fluxes are mainly fluvial which in turn are linked to stronger asm precipitation on land though the increased terrestrial flux could possibly also be due to the lowstand or glacial erosion of mountain glaciers cross spectral analysis indicates that the asm precipitation maxima are controlled by local summer insolation maxima wpwp sea surface temperature minima and east asian winter monsoon eawm maxima in precession frequency bands 21 ka 1 this result suggests that the 21 ka components of the asm in the past 180 ka are not only insolation driven but also a dynamic component strengthened by cross hemispheric pressure gradient resulted from the precession maxima forcing copyright 2012 john wiley sons ltd

iron mobilization in mineral dust can anthropogenic so2 emissions affect ocean productivity 1 for fe contained in long range transported aeolian dust to act as a micronutrient for oceanic phytoplankton it must be first dissolved or mobilized we propose that fe mobilization can occur in mineral dust from east asia by the incorporation of so2 into the advecting dust plumes and subsequent acidification of the dust through heterogeneous so2 oxidation to test this hypothesis we consider a dust plume that originated from the gobi deserts and advected over the pacific ocean data collected over the yellow sea confirm that this plume contained high concentrations of dust and so2 significant gaseous hno3 concentrations indicate that the dust particles were acidified i e ph 2 at these ph s 1 2 of the fe contained in a deliquescent mineral dust particle would be mobilized within 3 5 days these results suggest a possible link between the rate of c fixation in so called high nitrate low chlorophyll regions of the pacific ocean and so2 emissions from east asia

australian dust storms in 2002 2003 and their impact on southern ocean biogeochemistry during late 2002 and early 2003 southern australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent southern ocean we use meteorological records of dust activity satellite ocean colour and aerosol optical depth data and dust transport modeling to investigate the transport and deposition of mineral dust from australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll a concentration in five degree latitude bands from 40 60 s seasonal maxima in mean surface chlorophyll a of 0 5 mg m 3 were not achieved until late jan 2003 or during february in the more southerly bands which when compared with a 9 year satellite mean climatology suggests the phenology of the bloom in 2002 03 was atypical contemporaneous field data on co2 fugacity collected on transects between tasmania and antarctica show that significant atmospheric co2 drawdown occurred as far south as 60 s during february 2003 our results provide strong evidence for a large scale natural dust fertilization event in the australian sector of the southern ocean and highlight the importance of dust derived nutrients in the marine carbon cycle of the southern ocean

seismic site classification and empirical correlation between standard penetration test n value and shear wave velocity for guwahati based on thorough subsoil investigation data guwahati the gateway of india in the northeast is a large business and development center past seismic scenarios suggest moderate to significant effects of regional earthquakes eqs in guwahati in terms of liquefaction as well as building damages considering the role of local soil in amplifying eq generated ground motions and controlling surface damages present study attempts seismic site classification of subsoil of guwahati subsoil is explored based on 43 geophysical tests and 244 borelogs gathered from different resources based on the borehole data 4 numbers of 2d cross sections are developed from different parts of guwahati clearly indicating that a majority of the locations are composed of clay of intermediate to high plasticity while at specific locations only layers of sand are found at selective depths further seismic site classification based on 30 m average spt n suggests that a major part of guwahati falls under seismic site class ssc d such as balaji temple and airport however assam zoo pan bazaar iit campus dhol gobinda and maligaon show ssc e clearly indicating the presence of soft soil deposits at these locations similar site classification is also attempted from masw test based 30 m average shear wave velocity vs30 vs30 based site classification also categorizes most of guwahati under ssc d however there are locations in the southern part of guwahati which belong to ssc c as well mismatch in ssc based on two different test findings for indian soil found here are consistent with previous studies further three empirical correlations based on both spt n and vs profiles at 22 test locations are developed for 1 clayey 2 sandy and 3 all soil types proposed correlation for all soil types is validated graphically and is found closely matching with similar correlations for turkey and lucknow

evaluating the in situ lateral stress coefficient k0 of soils via paired shear wave velocity modes abstractthe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated specifically the lateral stress coefficient k0 field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well documented test sites involving a variety of geomaterials focus is particularly placed on shear wave velocities measured by downhole tests vsvh crosshole tests vshv and special rotary type crosshole tests vshh at these sites field k0 stress states have been quantified using one or more direct assessment techniques including self boring pressuremeter total stress cells and hydrofracture in field testing as well as suction measurements special consolidometers and or triaxial arrangements on undisturbed samples in the laboratory although the specific delineation of stress induced versus inherent or fabric anisotropy may be difficult it is shown that the ratio of horizontally polarized