sheath fold like structures in pseudotachylytes abstract sheath fold like structures in pseudotachylyte samples from a gold mine in the witwatersrand basin south africa are explained by injections of frictionally produced silicate melt within the shear zone due to the formation of high and low pressure zones if the shear zone geometry is known the orientation of the fold closures can be used to determine the direction and the movement sense however if it is not possible to establish the shear zone geometry only the azimuth of movement can be estimated from the orientation of the sheath fold like folds the flow banding in these fault rocks is indicative of laminar flow which suggests a low reynold s number

the southern westerlies during the last glacial maximum in pmip2 simulations the southern hemisphere westerly winds are an important component of the climate system at hemispheric and global scales variations in their intensity and latitudinal position through an ice age cycle have been proposed as important drivers of global climate change due to their influence on deep ocean circulation and changes in atmospheric co2 the position intensity and associated climatology of the southern westerlies during the last glacial maximum lgm however is still poorly understood from empirical and modelling standpoints here we analyse the behaviour of the southern westerlies during the lgm using four coupled ocean atmosphere simulations carried out by the palaeoclimate modelling intercomparison project phase 2 pmip2 we analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks the models suggest that changes were most significant during winter and over the pacific ocean for this season and region three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere although the lgm atmosphere is colder and the equator to pole surface temperature gradient generally increases the tropospheric temperature gradients actually decrease explaining the weaker circulation we evaluated the atmospheric influence on the southern ocean by examining the effect of wind stress on the ekman pumping again three of the models indicate decreased upwelling in a latitudinal band over the southern ocean all models indicate a drier lgm than at present with a clear decrease in precipitation south of 40 s over the oceans we identify important differences in precipitation anomalies over the land masses at regional scale including a drier climate over new zealand and wetter over nw patagonia

a vegetation and fire history of lake titicaca since the last glacial maximum fine resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding lake titicaca 3810 m peru bolivia since ca 27 500 cal yr bp hereafter bp time control was based on 26 accelerator mass spectrometer ams radiocarbon dates seventeen ams dates and 155 pollen and charcoal samples between ca 17 500 bp and ca 3100 bp allow a centennial scale reconstruction of deglacial and early to mid holocene events local and regional fire signals were based on the separation of two charcoal size fractions 180 m and 179 65 m charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra little or no pollen was detected in the sedimentary record prior to ca 21 000 bp very cold climatic conditions prevailed with temperatures suggested to be at least 5 8 c cooler than present increases in pollen concentration suggest initial warming at ca 21 000 bp with a more significant transition toward deglaciation ca 17 700 bp between 17 700 bp and 13 700 bp puna brava is progressively replaced by puna and sub puna elements the most significant changes between the pleistocene and the holocene floras were largely complete by 13 700 bp providing an effective onset of near modern conditions markedly earlier than in other andean records fire first occurs in the catchment at ca 17 700 bp and becomes progressively more important as fuel loads increase no evidence is found of a rapid cooling and warming coincident with the younger dryas chron a dry event between ca 9000 bp and 3100 bp with a peak between 6000 and 4000 bp is inferred from changes in the composition of aquatics and the marsh community as pollen of cyperaceae is replaced by poaceae apiaceae plantago and the shrub polylepis human disturbance of the landscape is evident in the pollen spectra after ca 3100 bp with the appearance of weed species

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

for how long are pseudotachylytes strong rapid alteration of basalt hosted pseudotachylytes from a shallow subduction complex abstract basalt is one of the main components of megathrust faults in subduction zones where the world s largest earthquakes are generated paradoxically pseudotachylytes have never been reported from basaltic rocks deformed at conditions compatible with the thermally defined seismogenic zone we report the first discovery of pseudotachylyte from oceanic crustal basalt identified by microstructural criteria the fault is located within a late cretaceous subduction complex the mugi melange and either formed along the plate interface during subduction or within the upper plate during underplating after solidifying the pseudotachylytes were fragmented by cataclasis and subsequently partially hydrated to produce phyllosilicates previous experiments using dry felsic lithologies as starting material have shown that pseudotachylytes can be as strong as their host rock deterring re activation and favoring their preservation over geologic time however we show that where fluid is present pseudotachylyte can be replaced by phyllosilicate rich layers with a low frictional strength the rate of dissolution is dependent on the bulk composition of the pseudotachylyte with dissolution of mafic glasses occurring at least three orders of magnitude faster than felsic glasses under hydrothermal conditions the replacement of pseudotachylytes by layers of frictionally weak phyllosilicates is predicted to occur over time intervals shorter than the megathrust earthquake cycle this process likely reduces fault strength and promotes reactivation

seismic and aseismic weakening effects in transtension field and microstructural observations on the mechanics and architecture of a large fault zone in se tibet

relative levels of natural and anthropogenic lead in recent antarctic snow concentrations of lead have been measured by ultraclean isotope dilution mass spectrometry in large blocks of surface snow collected along a 433 km coast interior axis in east antarctica and near the geographic south pole slight contamination existed on the outside of the blocks but concentration profiles from their exteriors to their interiors indicate that lead concentrations in the innermost parts of the blocks do represent the original concentrations in present day antarctic snow geographical variations of lead concentrations appear to be mainly due to local emissions from dumont d urville and amundsen scott stations the globally significant lead concentration in present day antarctic snow is found to be about 2 pg pb g the corresponding value in antarctic air is estimated to be about 7 pg pb m 3 stp which is approximately fivefold larger than total natural lead contributed by soil dusts volcanoes and sea salts a tentative temporal curve of globally significant lead concentrations in antarctic ice and snow for the last 13 000 years is given it shows concentrations of about 0 4 pg pb g throughout most of the holocene with recent fivefold increases to about 2 pg pb g today the general picture is then that four fifths of total lead in the antarctic troposphere today is anthropogenic

234th 238u disequilibria within the california current1 profiles of dissolved and particulate sup 234 th were determined at several stations within the california current modeling of the disequilibria between the sup 234 th and sup 238 u within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging the particle residence time and the particulate sup 234 th flux exiting the surface layer the model derived first order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present model derived particulate sup 234 th fluxes are in good agreement with direct measurements by sediment traps

sudbury breccia canada a product of the 1850 ma sudbury event and host to footwall cu ni pge deposits abstract the sudbury structure formed by meteorite impact at 1850 ma consists of three major components 1 the sudbury basin 2 the sudbury igneous complex which surrounds the basin as an elliptical collar and 3 breccia bodies in the footwall known as sudbury breccia in general the breccia consists of subrounded fragments set in a dark fine grained to aphanitic matrix a comparison of the chemical composition of host rocks clasts and matrices indicates that brecciation was essentially an in situ process sudbury breccia forms irregular shaped bodies or dikes that range in size from mm to km scale contacts with the host rocks are commonly sharp the aspect ratio of most clasts is approximately 2 with the long axes parallel to dike walls the fractal dimension dr 1 55 although there appears to be some concentration of brecciation within concentric zones small sudbury breccia bodies within and outside these zones have more or less random strikes and steep dips sudbury breccia bodies near an embayment structure tend to be subparallel to the base of the sudbury igneous complex sudbury breccia occurs as much as 80 km from the outer margin of the sudbury igneous complex in an inner zone 5 to 15 km wide breccia comprises 5 of exposed bedrock with an increase in brecciation intensity in embayment structures sudbury breccia may be classified into three types based on the nature of the matrix clastic pseudotachylite and microcrystalline clastic sudbury breccia the dominant type in the southern province is characterized by flow surface structures possibly a sudden rise in pore pressure caused explosive dilation and fragmentation followed by fluidization and flowage into extension fractures pseudotachylite sudbury breccia mainly confined to archean rocks apparently formed by comminution and frictional melting microcrystalline sudbury breccia formed as a result of the thermal metamorphism of the north range footwall by the sudbury igneous complex this produced a zone approximately 1 2 km wide wherein the matrix of the breccia either recrystallized or locally melted an overprint of regional metamorphism obliterated contact effects in the south range footwall the ni cu pge magmatic sulphide deposits may be classified into four types based on structural setting sudbury igneous complex footwall contact footwall offset and sheared deposits sudbury breccia is the main host for footwall deposits e g mccreedy east victor lindsley sudbury breccia locally hosts mineralization in radial e g parkin and copper cliff and concentric e g frood stobie offset dikes

atmospheric circulation changes and neoglacial conditions in the southern hemisphere mid latitudes insights from pmip2 simulations at 6 kyr glacial geologic studies in the southern hemisphere sh mid latitudes 40 54 s indicate renewed glacial activity in southern south america patagonia and new zealand s nz south island starting at 7 kyr the so called neoglaciation available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric co2 and ch4 concentrations lower than present but increasing summer insolation and seasonality contrasts in this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete paleoclimate modelling inter comparison project pmip2 database of simulations at 6 kyr for the sh we observe that the amplitude of the annual insolation cycle in the sh did not change significantly at 6 kyr compared to the pre industrial values the largest difference occurring in autumn mam negative anomalies and spring son positive anomalies the simulated changes in temperatures over the sh respond to the insolation changes with a 1 2 month delay over the oceans this results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions except over patagonia and nz that show a slight increase in contrast large scale circulation features such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle as a direct response to the increased decreased insolation during the transitional seasons son mam in the annual mean there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1 3 over the entire sh which results in a small increase of wind speed over the south pacific and atlantic oceans north of 50 s and a widespread decline south of 50 s pmip2 simulations for 6 kyr indicate that in the annual mean the sh mid latitudes were colder wetter and with stronger winds north of about 50 s these conditions are consistent with the observed neoglacial advances in the region as well as with terrestrial paleoclimate records from patagonia that indicate cooling and a multi millennial rising trend in southern westerly wind intensity starting at 7 8 kyr

qualitative assessment of pmip3 rainfall simulations across the eastern african monsoon domains during the mid holocene and the last glacial maximum abstract in this paper we compare a compilation of multiproxy records spanning the eastern african margin with general circulation model simulations of seasonal precipitation fields for the mid holocene and the last glacial maximum lgm carried out as part of the third phase of the paleoclimate modelling intercomparison project pmip3 results show good agreement during the mid holocene the 6k experiment with palaeodata and model outputs correlating well and indicating that changes in insolation drove a stronger northern african monsoon north of 0 5 s during the terminal african humid period and a weaker southeast african monsoon for the lgm the 21k experiment however significant discrepancies exist both between model simulations and between existing palaeodata and simulated conditions both in terms of direction and amplitude of change none of the pmip3 simulations reflect the pattern inferred from the palaeodata two major discrepancies have been identified to explain this 1 the limited sensitivity of the southern monsoon domain to the colder temperatures of the indian ocean 2 c and 2 the absence of changes in the dynamic of the indian ocean walker circulation over the entire basin despite the exposure of the sahul and sunda shelves that weakened convection over the indo pacific warm pool during the lgm these results indicate that some major features of the atmospheric and oceanic teleconnections between the different monsoon regions require further consideration as models evolve

a new perspective on southern hemisphere storm tracks abstract a detailed view of southern hemisphere storm tracks is obtained based on the application of filtered variance and modern feature tracking techniques to a wide range of 45 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data it has been checked that the conclusions drawn in this study are valid even if data from only the satellite era are used the emphasis of the paper is on the winter season but results for the four seasons are also discussed both upper and lower tropospheric fields are used the tracking analysis focuses on systems that last longer than 2 days and are mobile move more than 1000 km many of the results support previous ideas about the storm tracks but some new insights are also obtained in the summer there is a rather circular strong deep high latitude storm track in winter the high latitude storm track is more asymmetric with a spiral from the atlantic and indian oceans in toward antarctica and a subtropical jet related lower latitu

dating of fault zone activity by apatite fission track and apatite u th he thermochronometry a case study from the lavanttal fault system eastern alps introductionfaulting in the upper crust may leadto thermal anomalies caused by fric tional heating e g maddock 1983 dalessio et al 2003 and or in ltra tion of hydrothermal uids yamadaet al 2007 heating e ects are ex pected to be localised along faultzones and restricted to zones a fewcentimetres adjacent to the main faultsurface dalessio et al 2003 in this study we attempted to datethermal anomalies within fault zonesby comparison of cooling ages at thetransition from fault related rocks tothe undeformed host rocks for thispurpose we chose the lavanttal faultsystem due to underground excava tion and cored drillings related togeological site investigations for amajor railway project in austria it isone of the best exposed fault zones inthe eastern alps we used a combi nation of ssion track aft and u th he analysis on apatites thesensitivity intervals of these thermo chronometers are often referred to aspartial annealing and retention zones apaz heprz and range from 120to 60 c and 80 to 40 c respectively green et al 1986 wolf et al 1996 assuming holding times over geo logical time scales wagner 1979 ketcham et al 1999 the low temperature sensitivity of these ther mochronometers allows thermalanomalies along surfaces of fault slipor uid pathways to be detected forsuch applications however annealingand retention depend not only onheating temperature but also on heat ing duration laslett et al 1987 murakami et al 2006 a combina tion of forward and inverse modellingon apatite age track length and hedata allows quantitative analysis ofthe cooling behaviour of the hostrocks our new results underline theimportance of using multiple low temperature thermochronometersin elucidating details of the thermalhistory of a fault zone geological outlinethe nnw trending lavanttal faultsystem one of the major strike slipfaults in the eastern alps fig 1 separates the basement complexes ofthe kor and saualm by dextral o setof approximately 10 km reinecker 2000 it is assumed to have beenactive since early miocene times withpeaks in activity between 18 16 and14 12 ma reinecker 2000 as indi cated by the evolution of adjacentsedimentary basins and the regionalstructural framework e g pischingeret al 2008 near its southern termi nation the lavanttal fault o sets theperiadriatic fault by about 20 km despite some models at the scale ofthe eastern alps describing the gen eral evolution of con ning fault zonesduring miocene times e g peressonand decker 1997 frisch et al 1998 2000 neubauer et al 2000 littleremains known about the evolutionof the lavanttal fault system how ever these models include a relation ship between the lavanttal faultsystem and the uplift of the koralmcomplex neubauer and genser 1990 previous thermochronologicalstudies documented that the koralmcomplex was already near the surfaceduring the whole cenozoic period hejl 1997 the timing of its naluplift however is less constrained sample descriptionparts of the lavanttal fault system arecharacterised by cataclasites and faultgouges up to several tens of metresthick thermochronological analyseswere carried out on drill core samples diameter 10 cm taken during thegeological investigations for thekoralm railway tunnel drillingabstract

concentrations provenance and flux of aerosol trace elements during us geotraces western arctic cruise gn01 abstract the arctic region is undergoing significant changes in climate with a notable decrease in summertime sea ice coverage over the past three decades this trend means an increasing proportion of arctic ocean surface waters can receive direct deposition of material from the atmosphere potentially influencing marine biogeochemical cycles and delivery of pollutants to the arctic ecosystem here we present aerosol concentrations of selected trace elements al ti v mn fe co ni cu zn cd and pb measured during the us geotraces western arctic cruise gn01 also known as hly1502 in august october 2015 concentrations of lithogenic elements al ti v mn fe and co were similar to those measured in remote and predominantly marine influenced air masses in previous studies reflecting the remoteness of the arctic ocean from major dust sources concentrations of ni cu zn pb and cd showed significant enrichments over crustal values and were often of similar magnitude to concentrations measured over the north atlantic in air masses of north american or european provenance we use 7be inventory and flux data from gn01 to estimate a bulk atmospheric deposition velocity during the study period and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the arctic region during late summer the resulting estimates for mineral dust and fe deposition fall at the low end of global estimates and confirm the arctic ocean as a low dust environment during the summer months this article is part of a special issue entitled conway geotraces edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

isotopic evidence of contaminant lead in the south atlantic troposphere and surface waters abstract the third intergovernmental oceanographic commission ioc baseline contaminant cruise may june 1996 has established the first lead isotopic compositions in the surface water and the atmosphere of the equatorial and south atlantic ocean these ratios have evidenced both anthropogenic and natural origins of lead along the cruise transect from 33 s to 10 n the isotopic gradients tentatively have been attributed to aeolian as well as surface water advective inputs from a suite of rather local and remote sources to the southern hemisphere relatively low 206pb 207pb ratios x sd were encountered within the south equatorial current between 17 s and 5 s 1 156 0 003 those were bracketed by more radiogenic ratios at higher latitudes in the southern hemisphere 33 s to 23 s within the brazil current and the subtropical gyre 1 163 0 003 and in the northern hemisphere 0 to 10 n 1 165 0 005 the latter were comparable to ratios of surface water in the north atlantic equatorial ocean 1 169 0 006 under a combined contaminant influence of both north american westerlies 1 19 1 20 and european easterlies 1 155 1 165 that predominance of contaminant lead contrasts with the measurable presence of natural lead in surface waters of the equatorial ocean which are attributed to aeolian inputs of saharan dust the ratios of lead in surface waters at higher latitudes in the south atlantic are characteristic of anthropogenic lead aerosols also detected in antarctic ice and could substantiate as well the hypothesized aerosol recycling of lead by sea spray emission in the far southern hemisphere the atmospheric lead isotopic compositions 206pb 207pb in bulk depositions 1 171 0 006 precipitation 1 171 0 006 and aerosols 1 168 0 011 were generally more radiogenic than the surface waters 1 162 0 005 beside a poor representation of a short term atmospheric sampling this difference could reflect a recent evolution in atmospheric lead emissions which have not yet been reflected in oceanic surface waters it may also be due in part to advective lead inputs from surface oceanic circulation of the south equatorial current

vesicles amygdales and similar structures in fault generated pseudotachylytes amygdales in fault generated pseudotachylytes from the outer hebrides thrust scotland and the ikertoq shear belt west greenland contain mineral assemblages dominated by k spar sphene epidote quartz and carbonates respectively these contrasting assemblages indicate that vesicle infilling took place under differing environmental conditions other filled cavities resembling amygdales in form and mineralogy are recognized as replacement pseudomorphs after porphyroclasts using published data relating vesicle abundance and solubility functions for h2o and co2 to pressure a palaeoseismic depth estimate equivalent to the depth of vesiculation of about 1 6 km is inferred for the greenland pseudotachylytes described in this paper

mid holocene and last glacial maximum climate simulations with the ipsl model part ii model data comparisons the climates of the mid holocene mh 6 000 years ago and the last glacial maximum lgm 21 000 years ago have been extensively documented and as such have become targets for the evaluation of climate models for climate contexts very different from the present in part 1 of the present work we have studied the mh and lgm simulations performed with the last two versions of the ipsl model ipsl cm4 run for the pmip2 cmip3 coupled model intercomparion project projects and ipsl cm5a run for the most recent pmip3 cmip5 projets we have shown that not only are these models different in their simulations of the pi climate but also in their simulations of the climatic anomalies for the mh and lgm in the part 2 of this paper we first examine whether palaeo data can help discriminate between the model performances this is indeed the case for the african monsoon for the mh or for north america south of the laurentide ice sheet the south atlantic or the southern indian ocean for the lgm for the lgm off line vegetation modelling appears to offer good opportunities to distinguish climate model results because glacial vegetation proves to be very sensitive to even small differences in lgm climate for other cases such as the lgm north atlantic or the lgm equatorial pacific the large uncertainty on the sst reconstructions prevents model discrimination we have examined the use of other proxy data for model evaluation which has become possible with the inclusion of the biogeochemistry morel pisces in the ipsl cm5a model we show a broad agreement of the lgm pi export production changes with reconstructions these changes are related to the mixed layer depth in most regions and to sea ice variations in the high latitudes we have also modelled foraminifer abundances with the foramclim model and shown that the changes in foraminifer abundance in the equatorial pacific are mainly forced by changes in ssts hence confirming the sst foraminifer abundance relationship yet this is not the case in all regions in the north atlantic where food availability can have a strong impact of foraminifer abundances further work will be needed to exhaustively examine the role of factors other than climate in piloting changes in palaeo indicators

cadmium copper cobalt nickel lead and zinc in the water column of the weddell sea antarctica abstract this paper presents results from the first complete investigation of the dissolved and suspended trace metals cadmium copper cobalt nickel lead and zinc in the water column of the weddell sea antarctica a total of 35 stations was covered in the central weddell sea and the shelf areas around the filchner depression and dronning mauds land snow samples were collected from the sea ice and from the antarctic continent to evaluate the importance of the fresh water influence on the weddell sea oceanographic data i e salinity temperature and nutrients are used to link the trace metal results to the different water masses the general range found is for cadmium 0 5 0 8 nm copper 2 0 2 9 nm cobalt 20 40 nm nickel 6 7 nm lead 10 pm zinc 3 7 nm the suspended trace metals are a small fraction but considerably higher than in other oceans the lowest concentrations of cadmium copper and zinc are found in the surface layer and in the whole water column at the filchner depression cobalt shows an increase in the surface water compared to the deep water this is suggested to be generated by the terrogent material from the antarctic continent from the melting of the ice no evidence of anthropogenic lead can be seen in the lead profile nutrient trace metal relations found show poor statistical correlation in contrast to what is found in other oceans this assumes that cadmium copper and zinc are not directly linked to the bioproduction cycle however the nutrient trace metal ratios found support the theory that the weddell sea is the ultimate source for generation of the nutrient trace metal ratios in the pacific ocean

constraining oceanic dust deposition using surface ocean dissolved al we use measurements of ocean surface dissolved al a global biogeochemical elemental cycling bec ocean model and the global dust entrainment and deposition dead model to constrain dust deposition to the oceans our al database contains all available measurements with best coverage in the atlantic vertical profiles and seasonal data exist in limited regions observations show that surface dissolved al is distributed similarly to the dust deposition predicted by dead and other models there is an equatorial atlantic al maximum that decreases toward higher latitudes there are high al concentrations in the mediterranean sea and the arabian sea and low concentrations in the pacific and the southern ocean the ocean basins maintain more distinct al profiles than fe profiles in the upper ocean consistent with a weaker biological influence on al than fe the bec predicted surface dissolved al compares relatively well with observations the al distribution reflects the combined effects of al input from dust and al removal by particle scavenging and biological uptake by diatoms model observed biases suggest a southward shift of maximum dust deposition compared to current dust model predictions dead appears to overestimate deposition north of 30 n in the pacific and to underestimate deposition south of 30 n observed al concentrations and the ocean model predicted surface al lifetime provide a semi independent method to estimate oceanic dust deposition this technique indicates that dead may overestimate dust deposition to the north equatorial atlantic but underestimate in other atlantic regions the southern ocean and the arabian sea however spatial variations in aerosol al solubility may also contribute to the model observation mismatch our results have implications for all dust borne ocean nutrients including fe and demonstrate the potential of marine geochemical data to constrain atmospheric aerosol deposition fields

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

injection veins of crushing originated pseudotachylyte and fault gouge formed during seismic faulting this paper describes the injection veins of crushing originated pseudotachylyte and fault gouge formed along the iida matsukawa fault in granitic cataclasite southern nagano prefecture central japan the pseudotachylyte which shows a dense and aphanitic appearances and fault gouge occur as simple veins fault vein along the main fault plane and as complex network veins injection vein in the neighboring cataclasite locally the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins powder x ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine grained angular clasts and that the pseudotachylytes and fault gouges have a similar x ray diffraction patterns with that of the host granite the similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine grained materials generated in the shear zone in a gas solid fluid system

isotopic evidence of pollutant lead transport from north america to the subtropical north atlantic gyre abstract lead isotope ratios have been measured in aerosols seawater and marine particles collected in 1990 1992 in the subtropical northeastern atlantic ocean as part of the jgofs eumeli program while the atmospheric input has unradiogenic 206 pb 207 pb ratios 1 158 0 006 typical of the tradewinds bringing lead from european countries all the samples collected in the water column have more radiogenic 206 pb 207 pb from 1 170 to 1 196 this demonstrates that lead at the eumeli sites contains a dominant input from american emissions that has been circulated across the north atlantic by the subtropical north atlantic gyre using measurements in sargasso sea surface waters as an estimate of the isotopic composition of this input 206 pb 207 pb 1 195 0 004 we calculate a contribution of 42 57 from america in these waters this demonstrates that american emissions still dominated lead contamination over the north atlantic in the early 1990s in spite of the early reduction of leaded gasoline in the usa these results also give new evidence of the equilibrium between dissolved and particulate phases during scavenging processes

isotopic equilibration between dissolved and suspended particulate lead in the atlantic ocean evidence from 210pb and stable pb isotopes decreased consumption of leaded gasoline in the united states over the past two decades has drastically altered the flux and isotopic composition of pb entering the western north atlantic from the atmosphere here we exploit the resulting temporal changes in the distribution and isotopic composition of oceanic pb to investigate interactions between dissolved and particulate pb in the oceanic water column measurements of dissolved pb isotopic composition on samples collected in 1987 in the upper water column near bermuda demonstrate that surface water 206pb 207pb decreased from 1 203 to 1 192 since 1983 and that a measurable change propagated to 300 500 m since the 1984 profile of shen and boyle 1988 the first accurate measurements of suspended particulate pb in an open ocean profile show concentrations of 1 3 pmol l equal to 2 4 of total pb vertical profiles of 1 the stable lead isotopic composition and 2 the ratio of total pb to 210pb in suspended particles closely track contemporaneous depth variations in these ratios for dissolved pb throughout the upper 2000 m of the sargasso sea near bermuda thus suspended particles reach isotopic equilibrium with ambient sea water pb on a time scale which is shorter than their residence time with respect to vertical removal in agreement with equilibrium scavenging hypotheses based on interpretations of th isotope distributions a simple flux model suggests that the effect of deep ocean scavenging processes on the flux and isotopic composition of pb sinking on large particles was minor throughout the preanthropogenic and most of the anthropogenic era but has become important as surface inputs decrease to pre leaded gasoline levels and may exceed the contribution of surface derived pb flux in the next decade

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

the destiny of a clast within a molten pseudotachylyte vein pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window on the other hand survivor fragmented clasts embedded in the quenched material are also very impor tant in that they provide information about the energy spent to create new fracture surfaces in this paper i study the temperature evolution of clasts subjected to the heat dissipated by a just formed molten pseudotachylyte pt vein in particular i find the analytical solutions for the temperature evolution within the pt vein the surrounding undamaged host rock and inside a clast according to the proposed model the numerical results show that the clasts tend to preferentially melt in the inner part of the pt vein i e they are completely assimilated by the pt in contrast some clasts can survive far from the pt vein center my solutions although based upon a simplified model can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the pt center the distribution of these survivor clasts follows a power law relation in terms of their radius and its features generally agree with field and laboratory observations

distribution of aluminium in waters of the north east atlantic 25 n to 35 n abstract dissolved al concentrations from the ne atlantic between 25 n and 35 n off the coast of nw africa range from 16 nm to 32 nm in a well mixed surface layer extending to 150 m depth increasing towards the maximum of the saharan dust plume mediterranean outflow water is detected as a high al anomaly corresponding to the salinity signal of the mediterranean water other than in surface and mediterranean waters al concentrations are invariant with depth but increase from 6 nm to 11 nm towards the continental margin the magnitude of the dissolved al signal in the surface layer is compatible with dissolution of al from the highest of present estimates of dust input to this area comparison with data from other areas indicates that al cannot be cycled through the oceans in parallel to silica as has been previously suggested

high resolution al and fe data from the atlantic ocean clivar co2 repeat hydrography a16n transect extensive linkages between atmospheric dust and upper ocean geochemistry 1 trace element sampling and shipboard flow injection analysis during the june august 2003 climate variability and predictability clivar co2 repeat hydrography a16n transect has produced a high resolution section of dissolved fe and al in the upper 1000 m of the atlantic ocean between 62 n and 5 s using the surface water dissolved al and the model of aluminum for dust calculation in oceanic waters madcow model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved fe concentrations the lowest mean mineral dust depositions of 0 2 g m 2 a 1 are found to the north of 51 n a region which also exhibits characteristics of biological fe limitation through its low dissolved surface water fe 0 1 nm and residual macronutrients e g nitrate 2 m to the south of this region mean dust deposition increases by an order of magnitude reaching 3 g m 2 a 1 at 10 n underneath the saharan dust outflow surface water fe values also increase along this section to 1 nm distinct minima in fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4 n illuminate the role that active biological uptake plays in fe cycling an extensive subsurface zone of enhanced dissolved fe concentrations 1 5 nm underlying this region is a result of the biological vertical transport and remineralization of the surface water fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region elevated concentrations of dissolved al in subsurface waters seen between 30 and 20 n coincide with the domain of the subtropical mode waters stmw which result from the sinking of surface waters in late winter in regions imprinted by dust deposition the magnitude of the al enrichment observed in this water mass implies that the predominant source to the stmw is from the more dust impacted western atlantic with only limited contributions from the stmw formation region near madeira a deeper subsurface al enrichment 30 45 n is associated with the outflow from the mediterranean another heavily dust impacted basin these two regions of al enrichment show the widespread geochemical connection between atmospheric transport processes and the north atlantic and underscore its susceptibility to imprinting by atmospherically borne materials natural as well as anthropogenic

coupled al si geochemistry in an ocean general circulation model a tool for the validation of oceanic dust deposition fields 1 we introduced the marine cycle of al into a geochemical ocean general circulation model in order to assess the potential of modeled surface ocean dissolved al as a tracer for dust input to the world ocean the geochemical cycles of si and al have been coupled through the dynamics of diatoms aluminum is added to the ocean by deposition of continental aerosols followed by partial dissolution of the aluminosilicate fraction dissolved al interacts with suspended siliceous particles according to a reversible first order scavenging reaction dust fields are provided by atmospheric general circulation models a database of marine dissolved al measurements was collated the ocean model results for two different dust deposition fields andersen et al 1998 mahowald et al 1999 are compared with these data the model confirms a solubility of the aluminosilicate fraction between 1 5 and 3 0 modeled levels of dissolved al in surface waters mirror the delivery of dust to the surface ocean comparing dissolved al distributions resulting from the two different dust fields yields significant differences in ocean dissolved al distributions which reflect a differential contribution of individual source regions model results suggest a significant overestimation of the north african arabian desert source region for the dust field after mahowald et al 1999 dust input to the central pacific ocean appears to be of the correct order of magnitude this approach allows for a direct comparison of dust fields and proposes an independent check of the underlying parameterization of uplift transport and deposition of dust

environment and climate of the last 51 000 years new insights from the potrok aike maar lake sediment archive drilling project pasado in this introductory paper we summarize the history and achievements of the potrok aike maar lake sediment archive drilling project pasado an interdisciplinary project embedded in the international continental scientific drilling program icdp the stringent multiproxy approach adopted in this research combined with radiocarbon and luminescence dating provided the opportunity to synthesize a large body of hydrologically relevant data from laguna potrok aike southern patagonia argentina at this site lake level was high from 51 ka until the early holocene when the southern hemisphere westerlies shw were located further to the north at 9 3 ka cal bp the shw moved southward and over the latitude of the study area 52 degrees s causing a pronounced negative water balance with a lake level decrease of more than 50 m two millennia later the shw diminished in intensity and lake level rose to a subsequent maximum during the little ice age since the 20th century a strengthening of the shw increased the evaporative stress resulting in a more negative water balance a comparison of our data with other hydrological fluctuations at a regional scale in south eastern patagonia provides new insights and also calls for better chronologies and high resolution records of climate variability

eastern patagonia seasonal precipitation influence of southern hemisphere circulation and links with subtropical south american precipitation abstractsome aspects of the seasonal precipitation over eastern patagonia the southernmost area of south america east of the andes cordillera are examined in this paper results indicate that the central north areas the southern continental region and the southernmost islands are three independent regions of seasonal precipitation and that each of them is associated with specific patterns of atmospheric circulation precipitation over the central north region is significantly related to the precipitation over a wide area of southern south america east of the andes during the four seasons enhanced reduced precipitation over this area is associated with weakened intensified westerly flow in the region precipitation over the southern continental area has a close connection with the dipolar pattern of precipitation over subtropical south america during spring summer and autumn the anomalies of atmospheric circulation at low and upper levels associated with the subtropical dipole are also able to

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

high resolution climate simulation of the last glacial maximum the climate of the last glacial maximum lgm is simulated with a high resolution atmospheric general circulation model the ncar ccm3 at spectral truncation of t170 corresponding to a grid cell size of roughly 75 km the purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography the lgm simulations were forced with modified climap sea ice distribution and sea surface temperatures sst reduced by 1 c ice sheet topography reduced co2 and 21 000 bp orbital parameters the high resolution model captures modern climate reasonably well in particular the distribution of heavy precipitation in the tropical pacific for the ice age case surface temperature simulated by the high resolution model agrees better with those of proxy estimates than does the low resolution model despite the fact that tropical ssts were only 2 1 c less than the control run there are many lowland tropical land areas 4 6 c colder than present comparison of t170 model results with the best constrained proxy temperature estimates noble gas concentrations in groundwater now yield no significant differences between model and observations there are also significant upland temperature changes in the best resolved tropical mountain belt the andes we provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells a longstanding model data discrepancy therefore appears to be resolved without invoking any unusual model physics the response of the asian summer monsoon can also be more clearly linked to local geography in the high resolution model than in the low resolution model this distinction should enable more confident validation of climate proxy data with the high resolution model elsewhere an inferred salinity increase in the subtropical north atlantic may have significant implications for ocean circulation changes during the lgm a large part of the amazon and congo basins are simulated to be substantially drier in the ice age consistent with many but not all paleo data these results suggest that there are considerable benefits derived from high resolution model regarding regional climate responses and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent

wet deposition of trace elements and radon daughter systematics in the south and equatorial atlantic atmosphere 1 atmospheric samples were collected aboard ship in the south and equatorial atlantic 35 s 10 n between 19 may and 20 june 1996 we measured 222rn in air 210pb in aerosol and trace elements fe mn zn pb cu cd ni and cr 210pb and 210po in precipitation samples the large variation of 222rn in air suggests a significant change in the incursion of continental air with time and latitude in the remote atlantic in the equatorial and subtropical atlantic 20 s 10 n 222rn activity was lower but 210pb 222rn ratios were higher than those at higher latitudes the higher 210pb 222rn ratios in the equatorial atlantic appear to be due to prevailing trade easterly winds which transport a supported source of 210pb in saharan dust from the african sahel the enrichment of noncrustal trace elements in precipitation samples from the remote equatorial atlantic was small on account of the remoteness from the continental emission regions and as a result of dilution with saharan dust the wet depositional fluxes of major crustal elements fe and mn were two to three fold higher while those of cd and zn were two to ten fold lower in the south and equatorial atlantic relative to the western north atlantic bermuda or north atlantic coast lewes delaware thus dominant wet precipitation of saharan dust in the intertropical convergence zone itcz areas of the equatorial atlantic appears to be a large potential source of micronutrients i e fe to surface seawater

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

the south atlantic convergence zone intensity form persistence and relationships with intraseasonal to interannual activity and extreme rainfall abstract the characteristics of intensity geographical location and persistence of the south atlantic convergence zone sacz during the austral summer are investigated intensity and spatial features of the sacz are identified by performing a factor analysis of structural properties of outgoing longwave radiation olr data the first two leading factors explain 65 of the total variance of structural properties and characterize the sacz according to intensity and location oceanic versus continental an index is constructed based on the magnitude of the factor scores to identify intense weak and oceanic continental sacz the intense sacz category is associated with negative olr anomalies over a large area of tropical south america extending from the western amazon to the atlantic ocean the weak sacz category is observed with positive olr anomalies over tropical south america and negative olr anomalies over southeastern south america oceanic and continental aspects of the sacz are related to a

nd isotopic constraints on the origin of suspended particles in the atlantic sector of the southern ocean 1 in the nutrient rich southern ocean fe is a vital constituent controlling the growth of phytoplankton despite much effort the origin and transport of fe to the oceans are not well understood in this study we address the issue with geochemical data and nd isotopic compositions of suspended particle samples collected from 1997 to 1999 in the south atlantic sector of the southern ocean al th and rare earth element ree concentrations as well as 143nd 144nd isotopic ratios in acetic acid leached particle samples representing the lithogenic fraction delineate three major sources 1 patagonia and the antarctic peninsula provide material with nd 4 that is transported toward the east with the polar and subpolar front jets 2 the south african shelf although its influence is limited by the circumpolar circulation and wind direction can account for material with nd of 12 to 14 adjacent to south africa and 3 east antarctica provides material with nd of 10 to 15 to the eastern weddell sea and adjacent antarctic circumpolar current for this region we interpret the nd isotopic evidence in combination with oceanographic atmospheric constraints as evidence for supply of significant amounts of terrigenous detritus by icebergs

depositional and post depositional processes in human modified cave contexts of west central patagonia southernmost south america abstract this contribution aims to analyse depositional and post depositional processes from two volcanic caves bano nuevo 1 and cueva de la vieja from west central patagonia in order to evaluate if natural and anthropogenic processes recorded therein are representative of basin scale processes for this purpose geomorphological sedimentological micromorphological petrographic magnetic paleontological and archaeological data are integrated results allow correlating the bano nuevo 1 and cueva de la vieja sequences comprising a record of ca 19 000 years in the first place the distinction between endogenous and exogenous detritus input mainly recorded by the mineralogy and lithotypes provided environmental data related to landscape stability i e vegetation cover the latter in turn could be interpreted as part of a complex feedback associated with major climatic changes on the other hand cave weathering rates observed through vertical variations of the gravel fraction along with bioactivity recorded by percentages of total organic carbon and micromorphological analysis provided constraints on temperature and or humidity being in agreement with available regional information main regional palaeoenvironmental changes observed in the sequences were the deglaciation processes the pleistocene holocene transition the holocene amelioration and the anthropocene although no distinctive variations were observed within holocene deposits biological processes mainly resultant of the human occupations could have obliterated such finer scale distinctions

dust deposition to the surface waters of the western and central north pacific inferred from surface water dissolved aluminum concentrations 1 dissolved al was determined on similar to 3500 surface water samples collected in the nw pacific during the 2002 intergovernmental oceanographic commission ioc contaminant baseline survey in addition dissolved al was determined on samples collected at 9 vertical stations occupied along the cruise track surface water al distributions when converted to annual mineral dust deposition measures and brown 1996 imply extremely low depositions mean values 0 3 g m 2 yr 1 to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of china the calculated deposition values are also much lower than the 1 10 g m 2 yr 1 predicted for this region by the gesamp model duce et al 1991 the lowest mineral dust depositions correspond to the high nutrient low chlorophyll hnlc region of the nw pacific which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input similar to other hnlc regions in the subtropical gyre the al derived dust deposition mean values 0 1 0 6 g m 2 yr 1 agrees well with the 1 g m 2 yr 1 predictions of the gesamp model enriched concentrations of dissolved al in the coastal waters near kauai from fluvial sources indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters in the vertical profiles elevated dissolved al concentrations 4 8 nm were found to correspond to the potential density of the western pacific subtropical mode waters which form in the recirculation zone of the kuroshio

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

temporal variability of lead in the western north atlantic consumption of alkyl leaded gasoline has decreased considerably in the united states over the last 15 years in order to evaluate the chemical response of the ocean to decreased atmospheric deposition of anthropogenic lead new 210pb and stable pb data have been obtained near bermuda june 1983 to december 1984 concentrations of these tracers in the mixed layer are highly variable during the period of observations 25 from june through september soluble eolian deposits accumulate in the shallow mixed layer because mixing and productivity are inhibited by the seasonal thermocline in the fall these enriched surface waters mix with upper thermocline waters and surface pb concentrations decrease in the winter storms from the east coast of north america cause local episodes of high pb and 210pb input into the ocean surface the resulting areally limited high pb concentrations are dispersed within less than 2 weeks by vertical and horizontal mixing pb 210pb ratios in surface waters are almost invariant over this period averaging 669 pmol dpm ranging from 564 to 718 pmol dpm surface pb 210pb appears to have declined by a factor of 2 since 1979 similar to the 2 6 fold decrease in u s leaded gasoline consumption during this period a substantial fraction on the order of 10 of gasoline pb is transported into the ocean pb concentrations in the upper thermocline may have declined by about 15 from 1979 to 1984 the helium tritium thermocline ventilation model of jenkins 1980 coupled with boundary conditions appropriate for pb and 210pb shows that the supply of pb and 210pb to the thermocline is dominated by lateral isopycnal ventilation the shape of the vertical profile is dominated by this physical ventilation near surface biological removal processes in situ scavenging and for stable lead time dependent input vertical transport by particles is responsible for minimal transport of dissolved lead into the upper ocean similar processes are likely to account for the plutonium maximum in the thermocline of the north pacific observations of pb and other reactive species in winter surface outcrops of thermocline isopycnals would provide valuable constraints on chemical processes within the thermocline

distribution of be al se and bi in the surface waters of the western north atlantic and caribbean abstract the mixed layer distributions of several trace elements have been determined along a detailed transect from rhode island to the panama canal when taken together with a new and existing profile data from the north atlantic and north pacific some general inferences emerge as to the processes controlling their concentrations in the surface waters the large enrichments in be observed in the upper waters of the north atlantic relative to the north pacific appear to be sustained mainly by fluvial inputs those of se are derived from atmospheric transport aluminium and bi also appear to have an aeolian source in the sargasso sea however in the tropical eastern pacific the al input may be fluvial on this cruise be al and the se species were analyzed on board ship within a few hours of collection the demonstration that this is feasible opens up the prospect of the application of large scale chemical hydrography to the study of the processes controlling the distribution and water column variability of trace elements in the oceans

a 45 kyr palaeoclimate record from the lowland interior of tropical south america we present a well dated high resolution 45 kyr lake sediment record reflecting regional temperature and precipitation change in the continental interior of the southern hemisphere sh tropics of south america the study site is laguna la gaiba llg a large lake 95 km2 hydrologically linked to the pantanal an immense seasonally flooded basin and the world s largest tropical wetland 135 000 km2 lake level changes at llg are therefore reflective of regional precipitation we infer past fluctuations in precipitation at this site through changes in i pollen inferred extent of flood tolerant forest ii relative abundance of terra firme humid tropical forest versus seasonally dry tropical forest pollen types and iii proportions of deep versus shallow water diatoms a probabilistic model based on plant family and genus climatic optima was used to generate quantitative estimates of past temperature from the fossil pollen data our temperature reconstruction demonstrates rising temperature by 4 c at 19 5 kyr bp synchronous with the onset of deglacial warming in the central andes strengthening the evidence that climatic warming in the sh tropics preceded deglacial warming in the northern hemisphere nh by at least 5 kyr we provide unequivocal evidence that the climate at llg was markedly drier during the last glacial period 45 0 12 2 kyr bp than during the holocene contrasting with sh tropical andean and atlantic records that demonstrate a strengthening of the south american summer monsoon during the global last glacial maximum 21 kyr bp in tune with the 20 kyr precession orbital cycle holocene climate conditions occurred as early as 12 8 12 2 kyr bp when increased precipitation in the pantanal catchment caused heightened flooding and rising lake levels in llg in contrast to this strong geographic variation in lgm precipitation across the continent expansion of tropical dry forest between 10 and 3 kyr bp at llg strengthens the body of evidence for widespread early mid holocene drought across tropical south america

lead concentrations and isotopes in corals and water near bermuda 1780 2000 abstract the history of the oceanic anthropogenic lead pb transient in the north atlantic ocean for the past 220 yr is documented here from measurements of pb concentration and isotope ratios from annually banded corals that grew in coastal seawaters near bermuda and from seawater samples collected during the last 20 yr of the 20th century anthropogenic pb emissions in this area have been dominated by the industrialization of north america beginning in the 1840s the introduction of leaded gasoline beginning in the 1920s and its phase out that began in the mid 1970s the phase out of leaded gasoline was largely completed by the late 1990s coral pb concentrations occur at a constant low level of about 5 nmol pb mol ca 15 pmol kg in seawater from the late 1700s to 1850 from 1850 to 1900 there is a small increase rising to a plateau at 25 nmol pb mol ca 80 pmol kg in seawater in the 1930s until the late 1940s at which point pb concentrations rapidly increase to 60 nmol pb mol ca 200 pmol kg in seawater in the mid 1970s pb began to decline to 25 nmol pb ca 40 pmol kg in seawater by the end of the 20th century comparable to levels occurring in the early 20th century pb isotope ratios pb i r show maximum 206pb 207pb 1 21 and 208pb 207pb 2 49 in the middle of the 19th century we conclude that this signal is a reflection of the early dominance of upper mississippi valley pb ore in the united states as previously seen in the estuarine sediments of rhode island after 1900 pb i r decrease only slightly until the 1960s when there is a significant local maximum in the 1970s to 206pb 207pb 1 19 and 208pb 207pb 2 45 as low pb i r sources were phased out in the united states then as us leaded gasoline utilization decreased more rapidly than european pb gas utilization which has lower pb i r western north atlantic pb i r decreased to 206pb 207pb 1 17 and 208pb 207pb 2 44 their lowest values in the past two centuries

aluminium in the south atlantic steady state distribution of a short residence time element the aluminium concentrations of water samples from 18 hydrographic profiles and 35 surface samples in the south atlantic were determined on board ship during leg iii of the south atlantic ventilation experiment save the observed surface water distributions range 0 5 to 57 nm are though to arise from the partial dissolution of eolian transported continental dusts coupled with limited lateral transport by prevailing surface currents in the deep water the greatest enrichments are observed coincident with the depth of the lower north atlantic deep water the similarity between the al si ratios in this water mass in both the south and north atlantic is taken as evidence that no significant al additions are being made to this water during its transit the lower al concentrations observed in the water masses of antarctic origin approximately 3 nm are consistent with their formation in areas of limited dust input the somewhat higher values observed in the antarctic bottom water suggest that the shelf component of this water mass may have elevated al concentrations

spatial and temporal evolution of lead isotope ratios in the north atlantic ocean between 1981 and 1989 29 68 w in the early 1980s 206 pb 207 pb ratios in the north african basin averaged 1 193 0 005 1 s similar radiogenic ratios within the level of analytical precision average 0 29 were found in the labrador and iceland basins 1 198 0 006 and in the norwegian sea 1 196 0 008 these radiogenic mixed layer signatures along with atmospheric global lead emission patterns suggest that most north atlantic lead in the early 1980s was derived from north american leaded gasoline samples in the east iberian basin near portugal and france showed lower 206 pb 207 pb ratios between 1 167 and 1 182 indicating a significant influence of less radiogenic atmospheric lead transported from europe and possibly the influence of the rio tinto acid mine drainage very close to shore in the gulf of cadiz pb across the entire north atlantic basin ranged between 54 and 145 pmol kg with the lowest values 54 74 pmol kg found at high latitudes 65 n in the late 1980s surface waters in the western subtropical north atlantic north american basin sargasso sea 47 w and in the eastern subtropical north atlantic north african basin central iberian basin 53 these elemental and isotopic results demonstrate the strongly variable isotopic and elemental signatures of north american and european lead throughout the north atlantic ocean frequently dominated by high 206 pb 207 pb and pb north

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

surface water dissolved aluminum and titanium tracers for specific time scales of dust deposition to the atlantic surface water distributions of dissolved al dal and dissolved ti dti were investigated along a meridional atlantic transect and related to dust deposition estimates in the zone of saharan dust deposition highest dal concentrations occurred in the tropical salinity minimum and suggest increasing al dissolution from saharan aerosols with wet deposition by contrast the dti distribution is not related to precipitation but agrees with the pattern of annual dust deposition in the zone of patagonian dust deposition elevated dti concentrations contrasted with decreased dal concentrations indicating excess dal scavenging onto biogenic particles in surface waters estimated residence times range from months to years for dal and are 10 times higher for dti this suggests that dal reflects seasonal changes in dust deposition while dti is related to longer temporal scales however spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

a 60 000 year record of hydrologic variability in the central andes from the hydrogen isotopic composition of leaf waxes in lake titicaca sediments abstract a record of the hydrogen isotopic composition of terrestrial leaf waxes d wax in sediment cores from lake titicaca provides new insight into the precipitation history of the central andes and controls of south american summer monsoon sasm variability since the last glacial period comparison of the d wax record with a 19 kyr d record from the nearby illimani ice core supports the interpretation that precipitation d is the primary control on d wax with a lesser but significant role for local evapotranspiration and other secondary influences on d wax the titicaca d wax record confirms overall wetter conditions in the central andes during the last glacial period relative to a drier holocene during the last deglaciation abrupt d wax shifts correspond to millennial scale events observed in the high latitude north atlantic with dry conditions corresponding to the bolling allerod and early holocene periods and wetter conditions during late glacial and younger dryas intervals we observe a trend of increasing monsoonal precipitation from the early to the late holocene consistent with summer insolation forcing of the sasm but similar hydrologic variability on precessional timescales is not apparent during the last glacial period overall this study demonstrates the relative importance of high latitude versus tropical forcing as a dominant control on glacial sasm precipitation variability

transient water adsorption on newly formed fault gouge and its relation to frictional heating determination of the amount of frictional heating on faults during slips provides insight into the mechanics of faulting fault slips cause frictional heating as well as production of gouge materials newly formed gouge is mechanochemically stimulated to gain a transient water adsorption ability we showed that the synthetic gouge from friction tests on rocks at a 1 mm s slip rate without frictional heating adsorbed a large amount of water comparable to that adsorbed by clay minerals the amount of adsorbed water decreased significantly with increasing slip rate to 100 mm s where the fault temperature increased above 400 c we confirmed there was no additional adsorption on the heated gouges after termination of the slip we conclude that the adsorption state can be considered a new indicator of a temperature rise of 400 c by frictional heating associated with recent near surface faulting

40ar 39ar geochronometry of pseudotachylytes by vacuum encapsulation north cascade mountains washington usa to determine a reliable means of dating pseudotachylytes we obtained total gas ages plateau ages and argon retention ages on samples from the north cascade mountains washington quartz ampoule vacuum encapsulation analysis of small grains a few milligrams from six samples allowed evaluation of 39 ar loss through recoil during irradiation and laser ablation on four samples allowed textural control in microlitic samples recoil loss 39 ar ranges from 0 2 to 8 4 the total gas ages incorporating this 39 ar are inconsistent but retention ages are much more internally consistent and within analytical error they match or nearly match plateau ages from most of the microlitic samples at 54 55 ma samples analyzed by laser ablation suggest one episode of faulting and pseudotachylyte formation at 55 59 ma and an earlier episode at ca 80 ma the partly glassy pseudotachylyte yielded laser ablation total gas and retention ages of ca 65 ma the microlitic pseudotachylytes indicate formation close to 55 ma with possible older faulting and pseudotachylyte formation at ca 81 84 ma the good consistency among the retention ages the laser ages with highest precision and especially the plateau dates combined with the ages falling within the anticipated time span provides confidence in the geologic reality of the ages nevertheless it is clear that large clasts and crystal fragments within these particular veins did not completely degas or may have an anomalous inherited radiogenic 40 ar component

continuous transects of cadmium copper and aluminium in surface waters of the atlantic ocean 50 n to 50 s correspondence and contrast with nutrient like behaviour on three north south transects across the atlantic ocean continuous profiles of cd cu and al were measured in surface waters with ultra clean sampling and analytical procedures salinity nutrients and al served as tracers to identify the characteristic oceanographic regimes sampled under the different circumstances encountered during three different seasons the behaviour of the biodepleted element cd and of the biointermediate element cu was then investigated in relation to hydrography and nutrient cycling trace metals and nutrients are generally uncoupled in surface waters a cd po4 relationship only exists at high concentration levels which were reached in winter under continental influence and in the immediate proximity to intense upwelling the preferential removal of cd over phosphate downstream of upwelling regions was confirmed the reverse situation was observed in the northeastern atlantic where cd depletion occurred after that for phosphate the difference is tentatively attributed to continental sources of zn for which cd substitutes the continent and the shelves are the major source for cu except in proximity to these sources the latitudinal cu distribution is very smooth with open ocean values around 0 65 to 1 nmol kg as a result of slow scavenging probably related to organic complexation the tropical atlantic ocean shows very distinct signatures of dissolved al and silicate in low salinity waters these signatures can be used to trace the origin of freshwater to atmospheric or river shelf inputs which have very different ai si ratios the amazon river was identified as the probable source of a low salinity zone sampled in october 1990 at 5 9 n 28 w with elevated nutrients particulate organic c cu and cd values

heavy metals in the near surface aerosol over the atlantic ocean from 60 south to 54 north the participate heavy metal concentrations of cr fe ni cu zn cd tl and pb were determined in the atmosphere over the atlantic ocean from 60 s to 54 n with the definitive method of isotope dilution mass spectrometry the samples were collected during an expedition with the german polar research ship polarstern the sampling and the sample treatment were carried out under strict contamination control fe was used as a reference element for the influence of crustal material calculating the corresponding enrichment factors ef fe for the other metal traces the heavy metal concentrations varied up to more than 3 orders of magnitude which represents the different natural and anthropogenic sources and influences on the composition of the marine aerosol tl showed the lowest abundance of all heavy metals with concentrations of less than 20 pg m 3 for all samples except those from the area around the english channel the concentration ranges for the other elements were cr 0 08 9 ng m 3 fe 2 6 7500 ng m 3 ni 0 05 10 ng m 3 cu 0 02 20 ng m 3 zn 0 09 450 ng m 3 cd 0 003 3 5 ng m 3 and pb 0 05 200 ng m 3 the lowest element concentrations were usually measured in the remote areas of the south atlantic whereas the highest ones were detected around the english channel however at some sampling sites over the north atlantic very low cd and pb values in the range of 6 20 pg m 3 and 0 5 ng m 3 respectively were determined which could be attributed to arctic air masses by their corresponding backward trajectories due to high fe concentrations a substantial influence of crustal material was observed in the atmosphere southeast of the south american continent in the south atlantic area of the southeast trades and over the north atlantic west of north africa ef fe values for the most part less than 10 for cr and ni and less than 50 for cu indicate that the influence of crustal material for these metals is much higher than for zn cd and pb where ef fe values between 500 and 5000 had often been determined this is due to anthropogenic and biological influences the anthropogenic influence was clearly identified e g over the south atlantic near the la plata area in the english channel and over the north sea whereas a substantial biological influence could be observed over the south atlantic in the area of the southeast trades

ductile reactivation of proterozoic brittle fault rocks an example from the vestfold hills east antarctica abstract brittle fault rocks usually in the form of minor pseudotachylyte veins have been reported from most high grade metamorphic archaean and proterozoic terrains in analyses of local crustal evolution such brittle structures are often ignored brittle faults commonly reflect the very last phases of local deformation during final uplift of the basement to shallow crustal levels and as such they are thought to be of minor or no importance in large scale archaean and proterozoic tectonics new data from archaean and proterozoic high grade terrains in australia and antarctica indicate that minor fault veins may in some cases represent significant early low grade brittle events which have been overprinted and largely erased by subsequent phases of ductile deformation this paper describes such a brittle event in the vestfold hills east antarctica which may represent an important phase of mid proterozoic uplift and crustal extension

palaeohydrology of laguna de tagua tagua 34 30 s and moisture fluctuations in central chile for the last 46 000 yr central chile 32 35 s lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient a new core from laguna de tagua tagua 34 30 0 s provides a sedimentologic geochemical and palynological record of regional hydrologic balance for the last 46 000 cal yr bp according to our age model relatively humid conditions occurred during glacial times before 43 500 cal yr bp and from 40 000 to 21 500 cal yr bp reduced moisture conditions and likely lower temperatures occurred from 42 400 40 100 cal yr bp higher lake levels and pollen assemblages with valdivian rainforest taxa imply much higher precipitation during glacial times 40 100 21 000 cal yr bp compared to today and therefore enhanced westerly activity in northern central chile afterwards the general decrease in moisture was punctuated by two abrupt arid periods at 21 000 19 500 cal yr bp and 17 000 15 000 cal yr bp and two more humid intervals 19 500 17 000 almost coincident with the global last glacial maximum lgm and 13 500 11 500 cal yr bp the early and mid holocene were the most arid periods in central chile for the studied time interval millennial scale palaeohydrological reconstructions from tagua tagua are consistent with regional climatic records copyright 2005 john wiley sons ltd

trace metals in bermuda rainwater the concentrations of cd cu fe mn ni pb and zn have been measured in bermuda rainwater factor analysis indicates that fe mn and pb have similar origins to acidic components derived from north america the other metals all behave similarly but differently to the acids sea salt even after allowances for fractionation apparently contributes minor amounts of cu pb and zn and uncertain amounts of fe mn and cd to atlantic ocean precipitation wash out ratios calculated from this data along with earlier measurements of atmospheric trace metal concentrations on bermuda are of the same order as those reported from other remote ocean areas the wet depositional fluxes of cu ni pb and zn to the western atlantic ocean are significant compared to measured oceanic flux rates however the wet depositional fluxes of fe and mn to this area are relatively small suggesting additional inputs while an excess wet depositional flux of cd suggests large scale atmospheric recycling of this element

quaternary marine terraces sea level changes and uplift history of patagonia argentina comparisons with predictions of the ice 4g vm2 model of the global process of glacial isostatic adjustment abstract quaternary marine terraces have been investigated along a 1000 km stretch of the coast of argentinian patagonia fossil mollusc shells most in living position and collected from raised beaches were dated using the u series esr and 14 c methods our analyses show that holocene sea level in this region culminated 7000 to 8000 bp at 6 7 m amsl this beach slightly increases in altitude southward the last interglacial stage 5e was identified at 16 17 m amsl whereas the highest and morphologically most distinctive radiometrically dated terrace at 250 000 to 330 000 bp exists at an elevation of 33 35 m amsl we estimate a constant rate of tectonic uplift of 0 09 m 1000 yr since the middle pleistocene using this estimate of the local rate of tectonic uplift we correct relative sea level r s l observations for the holocene epoch in turn the inferred holocene sea level histories are compared with those predicted using the ice 4g vm2 model of the global process of glacial isostatic adjustment this model accurately predicts r s l history from all sites along the northern part of the east coast of the south american continent venezuela brazil however along the southern part of the coast of argentinian patagonia there is evidence of an influence that is not accurately represented in this version of the model of the global process of glacial isostatic adjustment we suggest that this influence could be connected to the presence of the broad continental shelf that is located offshore of this region but the influence of significant neotectonic uplift cannot be dismissed

on the differences between last glacial maximum and mid holocene climates in southern south america simulated by pmip3 models abstract differences between climate conditions during the last glacial maximum lgm and the mid holocene mh in southern south america inferred from the state of the art pmip3 paleoclimatic simulations are described for the first time in this paper the aim is to expose characteristics of past climate changes occurred without human influence in this context numerical simulations are an indispensable tool for inferring changes in near surface air temperature and precipitation in regions where proxy information is scarce or absent the analyzed pmip3 models describe mh temperatures significantly warmer than those of lgm with magnitudes of change depending on the season and the specific geographic region in addition models indicate that seasonal mean precipitation during mh increased with respect to lgm values in wide southern continental areas to the east of the andes cordillera whereas seasonal precipitation developed in areas to the west of patagonian andes reduced from lgm to mh

mid holocene pmip3 cmip5 model results intercomparison for the south american monsoon system the mean precipitation fields for eastern south america from eight mid holocene 6 ka simulations part of the third phase of palaeoclimate modeling intercomparison project pmip3 and the fifth p

vertical concentration profiles of lead in the central pacific at 15 n and 20 s concentrations of lead were measured in a surface transect and at two vertical profile stations 15 n and 20 s in the central pacific these measurements complement similar measurements made earlier in the north pacific at 33 n and in the northwest atlantic at 34 n as well as recent measurements of eolian lead input fluxes near each of these locations the new transect of surface water concentrations of lead corroborates previous measurements which decrease from 13 ng kg at 30 n to 4 ng kg at 17 s in the central pacific this transect gradient is shown to overlie a similar geographic gradient of subsurface maximum concentrations of lead in the three pacific vertical profile stations decreasing from 14 ng kg at 33 n to 11 ng kg at 14 n to 2 5 ng kg at 20 s lead concentrations at each of those locations exhibit maxima at 400 m decreasing concentrations to 2500 m and approximately concentrations of 0 8 1 1 ng kg below that depth the subsurface maximum at the northwest atlantic profile station 36 ng kg at 34 n is also congruent with surface water lead concentrations which decrease from 806 ng kg to 32 ng kg in an offshore transect from rhode island to 34 n 66 w and the shape of the atlantic profile is congruent with those in the pacific there is a positive correlation between the magnitudes of eolian lead input fluxes and the magnitudes of the upper water maxima in lead concentration profiles at corresponding locations as follows south pacific easterlies 3 ng cm 2 yr vs 2 5 ng kg north pacific easterlies 6 ng cm 2 yr vs 11 ng kg north pacific westerlies 50 ng cm 2 yr vs 14 ng kg and north atlantic westerlies 170 ng cm 2 yr vs 36 ng kg this relationship enables one to view the anthropogenic perturbations of the marine lead cycle on a global scale since the industrial origin of eolian and seawater lead has been established by correlations between geographic patterns of industrial lead emissions to the atmosphere and isotopic ratios of industrial leads and by geographic patterns of pb silicate dust ratios and lead isotopic ratios in ocean surface waters these new data coupled with earlier biogeochemical data indicate that surface water concentrations of lead in the north pacific and north atlantic are now conservatively estimated to be 8 to 20 fold greater and those in the south pacific are 2 fold greater than natural concentrations because of industrial emissions of lead to the atmosphere

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

role of oceanic circulation on contaminant lead distribution in the south atlantic abstract both the relatively high lead concentrations and their characteristic anthropogenic isotopic compositions attest to the widespread contamination of industrial lead in the western equatorial and south atlantic ocean spatial gradients in those isotopic signatures evidence the conservative lateral transport of lead in oceanic water masses while the discrete isotopic signatures in deep oceanic waters substantiate the complementary hypothesis that the release of lead from settling particles is relatively small on a decadal time scale specifically the relatively low radiogenic lead e g 206pb 207pb 1 148 0 009 in the lower north atlantic deep water l nadw south of 10 north is primarily attributed to us industrial lead emitted in the northern hemisphere prior to 1965 and the more radiogenic lead e g 206pb 207pb 1 180 0 006 in the upper north atlantic deep water u nadw is primarily attributed to subsequent industrial lead emissions in that hemisphere in contrast the relatively radiogenic lead e g 206pb 207pb 1 186 0 007 in the antarctic bottom water aabw seemingly reflects a mixture of natural and anthropogenic lead sources within the southern hemisphere and its isotopic dissimilarity with that e g 206pb 207pb 1 159 0 002 of antarctic intermediate water aaiw and the aabw may be due to differences in either their aeolian or water mass inputs

geologic evidence for multiple slip weakening mechanisms during seismic slip in crystalline rock we examine exhumed seismogenic faults to investigate the mechanisms that may have achieved dynamic fault weakening during ancient ruptures field and microscope observations imply more than one weakening mechanism must have been active during slip events on the faults pseudotachylytes that are continuous over the scale of field exposures are indicative of melt lubrication a fault breccia crosscutting earlier formed cataclasites was mobilized during faulting and possibly represents a pressurized fault rock that resulted from thermal pressurization or elastohydrodynamic lubrication in some faults pseudotachylytes are developed in patches several meters long cataclasites in which there is no evidence for melting are present immediately along strike from the pseudotachylyte patches by considering the energy required for melting we show that the pseudotachylytes must have formed during ruptures larger than the patches implying that the cataclasites also accommodated seismic slip the distribution of fault rock types shows that the frictional response to slip during a single event was spatially variable reworked pseudotachylytes also indicate that coseismic processes change over time at a point on a fault these observations emphasize that macroscopic dynamic fault weakening is a function of multiple coeval processes at microscales to mesoscales detailed observations of the discontinuous pseudotachylytes show that slip zone thickness is the critical parameter that controls active coseismic processes the frictional response of a fault to slip is therefore dependent on the internal structure of faults given the along strike heterogeneity of most mapped fault zones the coexistence of multiple slip weakening mechanisms in a single earthquake will be common

dynamic variability of dissolved pb and pb isotope composition from the u s north atlantic geotraces transect abstract this study presents dissolved pb concentration and isotopic composition distributions from geotraces ga03 the u s north atlantic transect pb in the ocean is primarily derived from anthropogenic sources and pb fluxes into the north atlantic ocean have been steadily decreasing following the phase out of alkyl leaded gasoline usage in north america and europe between 1975 and 1995 a compilation of dissolved pb profiles from three stations occupied repeatedly during the last three decades reveals a dramatic decrease in concentrations within the surface layers and the thermocline maxima although elevated concentrations greater than 60 pmol kg are still observed in the center of the north atlantic gyre where ventilation timescales are longer than at the western boundary the evolution of stable pb isotopes at these stations shows a shift from dominantly north american like composition in surface waters in the early 1980s towards a more european like composition in later years the most recent shallow signatures at the bermuda atlantic time series station bats show an even more recent trend returning to higher 206pb 207pb ratios after the completed phase out of leaded gasoline in europe presumably because recently deposited pb is more strongly influenced by industrial and incineration pb than by residual alkyl leaded gasoline utilization in surface waters trends toward a more prominent european influence are also found in the middle of the basin and toward the european coast coincident with higher concentrations of surface dissolved pb scavenging of anthropogenic pb is observed within the tag hydrothermal plume and it is unclear if there is any significant contribution to deep water by basaltic pb leached by hydrothermal fluids in the upper water column many stations along the transect show pb concentration maxima at 100 m depth coincident with a low 206pb 207pb isotopic signature that is typical of european emission sources although pb ores from the united states historically tend to carry 206pb 207pb signatures 1 17 hurst 2002 subsurface signatures as low as 1 1563 in 206pb 207pb were observed in this feature this signature appears to be carried westward within saline subtropical underwater stuw that ventilates from the central eastern part of the north atlantic subtropical gyre where the lowest surface isotope 206pb 207pb ratios are observed along the western boundary deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation finally a low 206pb 207pb signature in bottom water along the eastern margin suggests that there may be some mobilization of european derived anthropogenic pb from recent surface deposits on the ocean floor

lead and aluminum in atlantic surface waters 50 n to 50 s reflecting anthropogenic and natural sources in the eolian transport lead and aluminum were measured with a 40 100 km resolution in surface water on two transects across the atlantic ocean one in may 1990 from cape town to the north sea the other in november 1990 from the north sea to the strait of magellan samples were drawn 14 m below surface at normal speed from a 2 m long snorkel system mounted on the bottom of the ship directly into a clean room area in the tropics both pb and al show maximum concentrations in the intertropical convergence zone itcz correlated with each other and with minimum salinities indicating wet deposition as their common source even in this area characterized by large inputs of mineral aerosols the pb al ratio shows that the major source of soluble lead 95 is anthropogenic at higher latitudes al is low throughout 10 20 nmol kg whereas enhanced pb values show the anthropogenic inputs off south africa northern argentina and especially western europe very low pb and especially al concentrations in the upwelling areas associated with the canary and benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition and of the adhering reactive trace metals

the role of dust deposition in determining surface water distributions of al and fe in the south west atlantic abstract underway dissolved al and fe determinations were made on surface water samples collected between 34 s and 8 n in the southern and tropical atlantic ocean using a towed surface water sampler the general distribution of dissolved al which ranged from 8 nm in the sub tropical gyre to 61 nm under the intertropical convergence zone itcz north of the equator corresponds clearly with atmospheric dust deposition patterns a striking correlation between al and surface water salinities between 28 s and 8 n further indicates that wet deposition is the predominant mechanism of delivery of this atmospheric source iron concentrations in contrast were more uniform varying between 0 6 and 0 8 nm south of the equator highest fe values up to 1 4 nm also were found associated with the maximum dust inputs at the itcz indicating an atmospheric source for this element whose input appears to be limited by the solubility of fe in sea water the lowest fe values 0 4 nm also were observed in the equatorial region and are assumed to result from the biological removal of fe from nutrient rich water masses originating in the nearby equatorial and coastal upwelling regions the high frequency data acquisition of the towed sampler revealed significant variations up to 50 in both al and fe concentrations over short distances most notably along the interface between the south equatorial and canary currents the high variability of a biologically important trace element such as fe in these dynamic regions is indicative of the interplay between chemical and biological patchiness in surface waters

tracing the agulhas leakage with lead isotopes the transport of warm and salty waters from the indian ocean to the south atlantic by the agulhas current constitutes a key return route of the meridional overturning circulation despite the importance of the agulhas leakage on interoceanic exchange its role on biogeochemical cycles is poorly documented here we present the first lead pb concentration and isotope data for surface seawater collected during the geotraces cruise d357 in the agulhas current system lead in surface waters of the cape basin is described by three distinct end members the south african coast open south atlantic seawater and indian ocean seawater the latter stands out in its pb isotopic composition and can be tracked within two distinct agulhas rings high pb concentrations in the agulhas rings further corroborate an indian ocean provenance of waters and suggest that the agulhas leakage represents a major conduit not only for heat but also for trace metals

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

large scale control on the patagonian climate abstractpatagonia located in southern south america is a vast and remote region holding a rich variety of past environmental records but a small number of meteorological stations precipitation over this region is mostly produced by disturbances embedded in the westerly flow and is strongly modified by the austral andes uplift on the windward side leads to hyperhumid conditions along the pacific coast and the western slope of the andes in contrast downslope subsidence dries the eastern plains leading to arid highly evaporative conditions the authors investigate the dependence of patagonia s local climate precipitation and near surface air temperature year to year variability on large scale circulation anomalies using results from a 30 yr long high resolution numerical simulation variations of the low level zonal wind account for a large fraction of the rainfall variability at synoptic and interannual time scales zonal wind also controls the amplitude of the air temperature annual cycle by changi

last glacial maximum in south america paleoclimate proxies and model results 1 observations in south america based on paleoenvironmental data for the last glacial maximum lgm that shows a generally lower temperatures and reduced precipitation of the region are compared to simulation results from the paleoclimate version of the national center for atmospheric research coupled climate system model analyses of the lgm wind simulation for the tropical atlantic show that the convergence zone does not extend all the way into south american continent during the austral summer this would have prevented moisture inflow into the adjacent continental area of equatorial northeastern brazil interpretations of paleoclimate proxy records from this region are consistent with this scenario in the subtropics lgm westerlies were weaker and data show characteristics of more humid conditions at higher latitudes model simulations suggest intensification of the westerlies which in combination with colder sea surface temperatures would imply less moisture influx into the south american continent from the atlantic sector low lake levels in high southern latitudes and general aridity would support the model findings