long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

chemical composition of rainfall and groundwater in recharge areas of the bet shean harod multiple aquifer system israel the bet shean and harod valleys are regional recipients and mixing zones for groundwaters draining from a regional multiple aquifer system comprising two different carbonate and two basalt aquifers as well as deep seated reservoirs of confined brines this paper the first of two describes the hydrochemistry of the groundwater bodies related to this multiple aquifer system the paper deals with the chemical composition of rain falling on natural recharge areas the chemical contribution of the aquifer rocks and the chemical evolution of groundwaters in the upper flow courses of all aquifers of this regional system the methodology applied is based on the determination of major dissolved ions and on the examination of their ratios and changes along the upper flow paths rain water falling on natural recharge areas has an average chlorinity of 12mgl 1cl and a calcium bicarbonate composition caused by dust borne terrigenous material this rain water salinity decreases with distance from the sea shore fresh groundwaters flowing through the different aquifers may be identified and differentiated by their characteristic salinity levels and ionic ratios groundwaters flowing through carbonate aquifers are identified by different salinity levels and by distinct rmg rca ratios reflecting dolomite calcite ratios in aquiferr rocks the groundwaters of the two basalt aquifers have typical cation assemblages and high na and mg2 concentrations far in excess of those typical of the recharging rainfall groundwater in the upper flow courses of all aquifers investigated is deficient in so2 4 and k relative to recharging rain water

nitrate perchlorate and iodate co occur in coastal and inland deserts on earth abstract deserts accumulate soluble salts from atmospheric deposition that impact human health are a source of nutrients for organisms and provide insight into how landscapes evolved on earth and mars we quantified perchlorate nitrate and iodate abundances and co occurrence in terrestrial deserts to identify fundamental controls on soluble salt deposition and post depositional cycling soils and nitrate deposits were examined in death valley usa atacama desert chile kumtag desert china and along an environmental gradient in the transantarctic mountains antarctica concentrations of soluble salts were highest in the transantarctic mountains and atacama desert where stable hyper arid landscapes accumulate atmospheric salts over million year time scales average nitrate concentrations of 61 3 g kg 1 in the transantarctic mountains and 53 0 g kg 1 in the atacama desert were significantly greater than respective averages of 8 60 g kg 1 and 5 14 g kg 1 in kumtag desert and death valley perchlorate and iodate concentrations in the atacama desert averaged 206 mg kg 1 and 344 mg kg 1 respectively which were two to three orders of magnitude greater than in antarctica and other sites our findings suggest that local processes in the atacama desert result either in higher rates of perchlorate and iodate deposition or a greater preservation of these salts relative to nitrate when compared to antarctic landscapes lower salt concentrations in the death valley and kumtag desert deposits likely result from relatively wet present day and paleoclimatic conditions a more active geologic history and a greater likelihood that biocycling disrupted long term salt accumulation associations of perchlorate and nitrate were significantly higher than iodate nitrate and iodate perchlorate correlations in the four deserts perchlorate nitrate relationships ranged from insignificant to highly significant with stronger correlations in the atacama desert and kumtag desert compared to the transantarctic mountains and death valley weaker geochemical associations with iodate were attributed to differences in local deposition rates or post depositional cycling interestingly relationships among perchlorate nitrate and iodate were generally stronger when examined by site within each desert compared to analyzing the soils for each desert as a whole suggesting more localized controls on soluble salt preservation we conclude that soluble salts vary in concentration and type across earth s deserts as a result of present day environment paleoclimate conditions biocycling and geologic age

massive atmospheric nitrate accumulation in a continental interior desert northwestern china large scale nitrate deposits are rare on earth s surface due to the high solubility of nitrate minerals exceptions are found in extremely old to 14 m y and hyperarid deserts such as the atacama desert in northern chile or the mcmurdo dry valleys in antarctica the nitrate in both of these regions has been determined to originate from atmospheric oxidation of nox here we report a new type of massive atmospheric nitrate deposit with resources equivalent to the atacama deposits in the turpan hami area northwestern china this deposit is characterized by 1 a location in the center of a large continent 2 young age pleistocene 3 general enrichment near the surface rather than at depth and 4 high spatial variability in the nitrogen and triple oxygen isotope composition within this arid region the 15n ranging from 0 7 to 27 6 18o from 30 2 to 46 7 and 17o from 5 9 to 20 7 the turpan hami nitrate deposit nitrogen and triple oxygen isotope composition is closely between those of the mojave desert southwestern united states and the atacama desert suggesting that 1 earth s low middle latitudes i e non polar sites have been receiving atmospheric nitrate deposition of similar nitrogen and triple oxygen isotope composition and 2 local or regional isotope differences in nitrate deposits can be attributed to postdepositional processes namely the difference in aridity and associated microbial activities

geochemical isotopic and mineralogical constraints on atmospheric deposition in the hyper arid atacama desert chile abstract modern atmospheric deposition across the atacama was collected by an array of dust traps that stretched from the pacific coast to the andean altiplano and the material was analyzed for its geochemical mass and isotopic composition the coastal trap had the second highest insoluble mineral particle and highest soluble salt deposition rates due to significant inputs from the morro mejillones range and the pacific ocean respectively the andean trap had the highest insoluble mineral particle deposition owing to transport of weathered material but the lowest deposition rate of soluble salts due to its distance from the ocean and anthropogenic sources the removal of oceanic material was effective by the coastal mountains while the westward transport of the andean material was determined to be minimal the atmospheric deposition in the inland traps was mainly from the local entrainment of surface material inland anthropogenic emissions and transport of marine aerosols the nitrate isotopes 15 n and 17 o suggested that no x sources and no 3 chemistry shifted along the west east transect and were greatly impacted by anthropogenic emissions with soil no 3 being a minor source of deposited nitrogen

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

andean uplift and climate evolution in the southern atacama desert deduced from geomorphology and supergene alunite group minerals abstract supergene alunite group minerals from the late eocene el salvador porphyry cu district the el hueso epithermal gold deposit and the coya porphyry au prospect located in the precordillera of northern chile 26 to 26 30 lat s have been dated by the 40 ar 39 ar method and analyzed for stable isotopes these data support published geomorphologic and sedimentologic evidence suggesting that the precordillera in the southern atacama desert had been uplifted as early as the late eocene and thus significantly prior to the altiplano which attained its high elevation only in the late miocene the oldest supergene alunite from the damiana exotic deposit at el salvador was dated at 35 8 1 ma and yielded a d vsmow value of 74 which indicates elevations of the precordillera near el salvador of at least 3000 m in the late eocene in contrast miocene supergene alunite from el salvador el hueso and coya have less negative d signatures reaching values as high as 23 to 25 at el hueso and el salvador between about 8 2 and 14 ma late miocene to holocene supergene alunite jarosite and natroalunite ages are restricted to el hueso and coya located near 4000 m above sea level in the precordillera roughly 1000 m higher than the present elevation of el salvador the d values of samples younger than 5 ma vary between 57 and 97 the complex evolution of the d signatures suggests that meteoric waters recorded in supergene alunite group minerals were variably affected by evaporation and provides evidence for climate desiccation and onset of hyper arid conditions in the central depression of the southern atacama desert after 15 ma which agrees well with published constraints from the atacama desert at 23 24 lat s our data also suggest that wetter climatic conditions than at present prevailed in the latest miocene and early pliocene in the precordillera the new and previously published age constraints for el salvador indicate that supergene mineralization at the damiana exotic cu deposit occurred periodically over 23 ma in a locally exceptionally stable paleohydrologic and geomorphologic configuration

seasonal fluctuation in δ15n of groundwater nitrate in a mantled karst aquifer due to macropore transport of fertilizer derived nitrate twenty wells were sampled and analyzed for nitrate content and nitrogen isotopes during late september 1986 the groundwater nitrate 15n values ranged from 6 8 to 17 6 with a mean of 10 3 eleven samples had 15n values greater than 9 5 indicating an animal waste origin septic tanks are probably the predominant source of waste derived nitrate macropores draining septic tank filter fields may provide a nearly continuous flow of effluent to the aquifer the 15n values of the other nine samples ranged from 6 8 to 8 4 suggesting a possible mixing of waste derived nitrate and that derived from isotopically lighter cultivation sources i e inorganic fertilizer and or mineralized soil organic nitrogen the twenty wells were resampled during late may 1987 shortly after inorganic fertilizers had been applied to the corpland throughout the study area the groundwater nitrate 15n values ranged from 3 6 to 14 7 with a mean of 8 3 nineteen of the wells showed a shift towards the lighter 15n values expected from the fertilizer derived nitrate the 15n decreases ranged from 0 6 to 4 8 with a mean of 2 2 despite the apparent influx of fertilizer derived nitrate eleven samples with 15n 8 0 to 14 7 still were composed of predominantly waste derived nitrate only nine samples with 15n 3 0 to 5 8 may have had fertilizer derived component approaching in magnitude that of waste derived nitrate regional groundwater nitrate concentration did not substantially increase macropore cracks root channels etc flow appears to contribute significantly to the recharge of the aquifer rapid response of the groundwater nitrate 15n values to fertilization demonstrates the ability of macropore flow to transport fertilizer derived nitrate which has been flushed from the tilled soil layer other agriculture chemicals pesticides and herbicides may also be transported to the aquifer in this manner

neoarchean subduction a case study of arc volcanic rocks in qinglong zhuzhangzi area of the eastern hebei province north china craton abstract we report on volcanic rocks of the qinglong zhuzhangzi area in northeastern eastern hebei province north china craton the supracrustal rock associations in the study area consist of amphibole biotite plagioclase gneiss mica plagioclase gneiss schist biotite k feldspar gneiss pyroxene plagioclase amphibolite and amphibolite twenty five new mafic intermediate to felsic samples can be geochemically classified into four groups group 1 is similar to fore arc low ti tholeiite and is characterized by low sio 2 49 7 wt and tio 2 0 43 wt slightly depleted lree and mree pattern with la yb n ratio of 0 74 gd yb n ratio of 0 82 it most likely derived from depleted mantle in a subduction initiation environment group 2 is akin to primitive arc tholeiites with low sio 2 49 7 51 8 wt slight enrichments of lree la sm n 1 06 1 53 and negative nb anomalies nb la pm 0 50 0 76 group 3 resembles evolved arc tholeiites and displays pronounced enrichments of lree la yb n of 2 38 11 3 la sm n of 1 70 2 86 and negative nb ta anomalies nb la pm 0 14 0 34 except sample 11jd28 4 with that ratio of 1 00 group 2 and 3 formed by partial melting of sub arc depleted mantle wedge modified by differing quantities of slab flux addition group 4 comprises k rich andesite dacites which are distinguished by the highest sio 2 54 0 71 8 wt k contents up to 5 03 wt strong enrichments of lree la yb n ratios of 4 83 19 and negative nb ta anomalies analogous to shoshonitic rocks marking late stage of subduction la icpms zircon u pb and lu hf analyses of evolved arc basalts and k rich andesite dacites display crystallization ages of 2511 2604 ma and single stage hf model ages of 2534 2927 ma most focus on 2650 2800 ma in contrast to 2510 2560 ma arc associations 2604 ma shoshonitic dacites most plausibly represent an older orogenic event collectively supracrustal rocks in the qinglong zhuzhangzi area constitute a series of volcanic arc associations that correspond to an entire subduction cycle ranging from orogen to primitive arc evolved arc and back to an orogenic setting which further demonstrate that by the late archean plate tectonic and subduction processes already closely resembled modern counterparts

neogene climate change and uplift in the atacama desert chile the relationship between andean uplift and extreme desiccation of the west coast of south america is important for understanding the interplay between climate and tectonics in the central andes yet it is poorly understood here we use soil morphological char acteristics salt chemistry and mass independent fractionation anomalies 17 o values in dated paleosols to reconstruct a middle miocene climatic transition from semiaridity to extreme hyperaridity in the atacama desert paleosols along the southeastern margin of the calama basin change from calcic vertisols with root traces slickensides and gleyed horizons to an extremely mature salic gypsisol with pedogenic nitrate we interpret this transition which occurred between 19 and 13 ma to represent a change in precipitation from 200 mm yr to 20 mm yr this drastic reduction in precipitation likely resulted from uplift of the central andes to elevations 2 km the uplift blocked moisture from the south american summer monsoon from entering the atacama the mid miocene gyp sisol with pedogenic nitrate is located at elevations between 2900 and 3400 m in the cal ama basin significantly higher than modern nitrate soils which occur below 2500 m modern and quaternary soils in this elevation zone contain soil carbonate and lack ped ogenic gypsum and nitrate we infer that 900 m of local surface uplift over the past 10 m y displaced these nitrate paleosols relative to modern nitrate soils and caused a return to wetter conditions in the calama basin by decreasing local air temperatures and creating an orographic barrier to pacific air masses

neoarchean magmatic arc in the western liaoning province northern north china craton geochemical and isotopic constraints from sanukitoids and associated granitoids abstract the neoarchean western liaoning basement terranes in the northern part of north china craton chiefly consist of tholeiitic basalts in the north ttg gneisses and metavolcanic rocks in the northwest and k rich granitoids in the southeast in the southeastern zone porphyritic monzodioritic quartz monzodioritic granodioritic monzogranitic mqgm gneisses are the major lithological assemblage and locally contain minor xenoliths of ttg gneisses based on the major mafic mineral phases the porphyritic mqgm gneisses can be divided into amphibole dominated and biotite dominated groups zircon u pb isotopic dating indicates that the amphibole dominated mqgm gneisses biotite dominated mqgm gneisses and tonalitic gneiss xenolith were emplaced during 2546 2529 ma 2546 2531 ma and at 2563 ma respectively the 2563 ma tonalitic gneiss xenolith displays geochemical affinities to high sio 2 adakites and may be formed by the partial melting of descending oceanic slabs with the melt contaminated by mantle peridotite the amphibole dominated mqgm gneisses are geochemically analogous to sanukitoids and their magmatic precursors were formed by partial melting of lithospheric mantle which was metasomatized by dehydration fluids and melts derived from subducted oceanic sediments and slabs the magmatic precursors of the biotite dominated mqgm gneisses were generated by the partial melting of medium k to high k mafic rocks at medium pressures integrated with previous studies on supracrustal sequences and granitoids in western liaoning province the neoarchean lithological assemblages in the southeastern zone were most likely formed in an active continental margin setting

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

150 million years of climatic stability evidence from the atacama desert northern chile the sedimentary succession in the atacama desert records deposition under an arid to semiarid climate from the late jurassic 150 ma to the present day palaeomagnetic data indicate no significant latitudinal movement of this area since the late jurassic the present day location of the atacama within the dry subtropical climate belt is the principal cause of aridity this situation is likely to have prevailed since the late jurassic supplemented by 1 the continentality effect enhanced by the gondwanan landmass and 2 the presence offshore of a cold upwelling current from at least the early cenozoic onwards and possibly earlier resulting in conditions promoting climatic stability and desert development rapid and extreme climatic fluctuations during the plio pleistocene were not sufficient to destabilize the climate within the atacama comparison with other long lived deserts e g sw usa namib sahara and australia suggests that the atacama is the oldest extant desert on earth

the geochemical associations of nitrate and naturally formed perchlorate in the mojave desert california usa abstract perchlorate is a widely studied environmental contaminant that may adversely affect human health and whose natural occurrence has emerged as a subject of great interest naturally formed perchlorate has been found to co occur with nitrate in arid environments worldwide but the relationship is not fully understood in the desert soils of the southwestern united states the main objective of this research was to explore the origin pedogenic distribution and possible preservation of perchlorate and nitrate in the mojave desert mud hill deposits of california and to determine if the co occurrence of putatively natural perchlorate was significantly correlated with nitrate in these soils we identified 39 soil horizons in the mojave desert california that contained reportable levels of perchlorate mrl 165 g kg 1 with a maximum concentration of 23 mg kg 1 a weak yet significant correlation was observed between perchlorate and nitrate r 2 0 321 which could be indicative of similar mechanisms of accumulation when compared to published data for the atacama desert the mojave desert perchlorate concentrations were remarkably lower for a given nitrate concentration oxygen isotopes in the nitrate were examined to identify variation within the mojave desert field sites and to compare with the available literature for the atacama desert the mojave desert 17 o values ranged from 7 to 13 indicating a mixture of biologically and atmospherically derived nitrate an investigation of the distribution of perchlorate among soil horizons revealed that over sixty percent of the samples containing perchlorate were from c horizons while only twenty percent of the samples were from b horizons and even fewer in the overlying a horizons soil chemical morphologic and geologic characteristics of the soils suggest that the perchlorate nitrate and or other soluble salts have moved in a bottom up manner wherein the salts were deposited in strata through geological time and have since been redistributed and evapo concentrated into the upper soil horizons by capillary rise

laboratory and field characterization of visible to near infrared spectral reflectance of nitrate minerals from the atacama desert chile and implications for mars

the composite archaean grey gneisses petrological significance and evidence for a non unique tectonic setting for archaean crustal growth abstract the geodynamic context of formation of the archaean continental crust is a matter of debate the crust is largely made of grey gneiss complexes a composite rock assemblage dominated by granitoids that are generally regarded as belonging to the ttg tonalite trondhjemite granodiorite series using a large database of published ttg and grey gneiss compositions it is possible to show that the granitoids forming grey gneiss complexes actually belong to at least four main geochemical groups i a potassic component made of granodiorites and formed by melting of existing crustal lithologies and ii three sodic groups ttg proper that comprise low medium and high pressure groups the geochemistry of the low pressure group is consistent with derivation from a plagioclase and garnet amphibolite the medium pressure group was formed in equilibrium with a garnet rich plagioclase poor amphibolite whereas the high pressure group derived from a rutile bearing eclogite as the temperature of melting of metamafic rocks is largely independent from pressure this corresponds to melting along a range of contrasting geothermal gradients in turn reflecting a range of tectonic sites for the formation of the archaean continental crust

large near surface nitrate pools in soils capped by desert pavement in the mojave desert california we found exceptionally high nitrate levels up to 12 750 kg ha 1 at shallow depths 1 m in soils mantled by desert pavement a common land surface feature in arid regions nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower the soil conditions coincident with desert pavement i e stability antiquity and virtually no leaching favor the retention and accumulation of nitrate delivered by atmospheric deposition or in situ fixation the nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen that has the potential to increase the global nitrogen inventory for near surface desert soils to five times previous estimates its near surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance risking contamination of surface and groundwaters

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

supergene enrichment of copper deposits since the onset of modern hyperaridity in the atacama desert chile supergene enrichment of cu deposits in the atacama desert has played a critical role in making this the prime cu producing province of the world previously this has been believed to have occurred exclusively over a long period from the middle eocene to the late miocene which ended when climatic conditions changed from arid to hyperarid here we report u series disequilibrium ages in atacamite bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the atacama desert 230th 234u ages of gypsum intergrown with atacamite in supergene veins from cu deposits cluster at 240 ka chuquicamata 130 ka mantos blancos spence and 80 ka mantos de la luna michilla when coupled with previous data these results indicate that supergene enrichment of cu deposits did not cease after the onset of hyperaridity we propose that supergene enrichment in the atacama region developed in two main stages the main phase caused by downward circulation of meteoric waters in a semi arid setting was active from 45 until 9 ma with a last pulse ca 5 ma in the southern atacama desert during this phase atacamite bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water this was followed by a second stage starting at 2 1 5 ma and continuing until at least the late pleistocene when deep formation waters derived from the basement passed up through and modified the pre existing supergene cu oxide minerals atacamite has then been preserved in the prevailing hyperarid climate

role of biological soil crusts in affecting soil evolution and salt geochemistry in hyper arid atacama desert chile abstract eight soil profiles either barren or covered with biological soil crusts bscs were sampled at multiple depths in a remote valley in the atacama desert chile to explore the impact of bscs on soil evolution and salt geochemistry bsc sites had thicker soil profiles compared to non bsc sites which could be a result of past geological processes and also partially accounted for by the establishment of bscs that can help limit erosion and promote significant soil accumulation the greater abundances of fine particles below bscs could essentially be attributed to the ability of bscs to trap more fine grains the generally higher salt ion inventories but smaller salt ion concentrations in soil profiles beneath bscs were probably due to that bscs can promote the retention of salt ions and insoluble dust simultaneously but the latter to a greater extent nitrate oxygen isotopes indicated the predominant existence of atmospheric nitrate in the soils suggesting biological processes of bscs may not significantly impact the ion accumulation or distribution in the underlying soils a mechanism of consistent soil accumulation via the retention of atmospheric deposition and occasional interruption of subsurface collapsing due to erosion processes was proposed to explain the development of soil profiles and different landscape features as well as the role of bscs in soil evolution in this study area the soil ages were estimated to be around 440 ky based on the proposed soil accumulation mechanism

discharge of nitrate containing groundwater into a coastal marine environment the discharge of nitrate containing fresh groundwater from a sandy coastal aquifer and into the adjacent shallow marine environment was investigated near esbjerg at the northern end of the wadden sea in denmark the geological structure of the coastal site was determined from drilling data and geoelectrical methods such as multi electrode profiling mep the distribution of shoreface sediment containing freshwater was mapped using mep underwater multi electrode profiling umep and the electrical conductivity measured on pore waters freshwater discharge fluxes were measured using seepage meters and estimated from observed head gradients and measured hydraulic conductivities in the aquifer sediments the nitrate distribution in the coastal sediments was obtained from water samples a groundwater flow model was established to quantify the groundwater flow and travel times and the distribution of freshwater discharge along the coastline results show that on the watershed scale the fresh groundwater discharge is controlled by sand filled buried channels that connect the aquifer with the shoreface sediments the freshwater discharge along the coastline is at this scale probably best estimated by the groundwater flow model however at a more detailed scale the distribution of freshwater discharge in the intertidal zone is controlled by small scale geological heterogeneity and models are unable to predict what happens at a small scale on the beach and offshore for that purpose umep seepage meters pore water sampling and local hydraulic gradients are more useful these measurements indicate that the freshwater discharge occurs in distinct zones and that the highest discharge is near the high tide line decreasing rapidly in a seaward direction nitrate is abundant in the shallow groundwater of the coastal aquifer and is also present in the discharging fresh groundwater at certain patches along the coast however on average very little nitrate is observed in the freshwater discharging at the coast the maximum travel time of groundwater through the aquifer until it discharges at the coast is 100 years and since nitrate leaching from soils has only taken place during the last 40 50 years part of the fresh groundwater discharging at the coast must be free of nitrate

nitrogen isotope analysis of groundwater nitrate in carbonate aquifers natural sources versus human pollution abstract results of nitrogen isotope analyses of nitrate in the waters of the cretaceous edwards aquifer in texas u s a indicate that the source of the nitrate is naturally occurring nitrogen compounds in the recharge streams in contrast nitrogen isotopes of nitrate in the fresh waters of the pleistocene ironshore formation on grand cayman island west indies indicate that human wastes are the source of the nitrate the cretaceous edwards limestone is a prolific aquifer that produces principally from fracture porosity along the balcones fault zone recharge is primarily by streams crossing the fault zone rainfall is 70 cm yr 1 and the water table is generally deeper than 30 m below land surface the 15 n of 73 samples of nitrate from edwards waters ranged from 1 9 to 10 with an average of 6 2 this 15 n range is within the range of nitrate in surface water in the recharge streams 15 n range 1 to 8 3 and within the range of nitrate in surface water from the colorado river texas 15 n range 1 to 11 no sample was found to be enriched in 15n which would suggest the presence of nitrate from animal waste 15 n range 10 to 22 the ironshore formation contains a small freshwater lens that is recharged entirely by percolation through the soil average rainfall is 165 cm yr 1 and the water table is within 3 m of land surface the 15 n of four nitrate samples from water samples of the ironshore formation ranged from 18 to 23 9 which indicates a cesspool septictank source of the nitrate limestone aquifers in humid environments that are recharged by percolation through the soil appear to be more susceptible to contamination by septic tanks than are aquifers in subhumid environments that feature thick unsaturated sections and are recharged by streams

oxygen 17 anomaly in soil nitrate a new precipitation proxy for desert landscapes abstract the nitrogen cycle in desert soil ecosystems is particularly sensitive to changes in precipitation even of relatively small magnitude and short duration because it is already under water stress this suggests that desert soils may have preserved past evidence of small variations in continental precipitation we have measured nitrate no 3 concentrations in soils from the atacama chile kumtag china mojave us and thar india deserts and stable nitrogen and oxygen isotope 15 n 17 o and 18 o abundances of the soil no 3 17 o anomalies 17 o the deviations from the mass independent isotopic fractionation were detected in soil no 3 from almost all sites of these four deserts there was a strong negative correlation between the mean annual precipitation map and soil no 3 17 o values o no 3 soil 17 this map o no 3 soil 17 correlation advocated o no 3 soil 17 as a new precipitation proxy and was then used to assess precipitation changes in southwestern us at the pliocene pleistocene boundary in south america during the miocene and the sahara desert in the past 10 kyr using no 3 17 o in paleosols or ancient aquifers global and the us maps of surface o no 3 soil 17 were also projected with available map datasets based on the map o no 3 soil 17 model

nutrient flux through soils and aquifers to the coastal zone of guam mariana islands nitrification enriches terrestrial soil waters with nitrate and other solutes also leach rapidly within hours to days after saturating rain through guam s northern karst plateau into a largely unconfined carbonate aquifer system nutrient chemistry and discharge of these enriched aquifer waters into the inter and subtidal zone was measured to evaluate the importance of this flux to the coastal nutrient regime of the island aquifer waters mix with seawater in the coastal transition zone produce about a 10 seawater mixture and leak year round through cracks and fissures and from seeps in beaches around the entire perimeter 57 km at rates of 2 2 l 10 m3 m of shoreline d l avg 5 1 m3 m l d l the theoretical maximum rate can average 14 m3 m l d l which is equal to net annual aquifer recharge at the shoreline the discharged aquifer waters average 3 14 salinity 96 2 1 pm n03 2826 8 im si 0 85ko 26 pm p and 0 18 0 19 pm fe n 238 deep seawater under the aquifer averages 33 87 salinity 8 5k2 1 pm no 7 2 1 8 pm si and 0 0510 04 pm fe n 47 the aquifer system can potentially discharge 1 340 390 12 and 2 5 pmol m 2 d l of n03 si p and fe out to a distance of 1 km from shore which enriches surface seawater by about 20 times the ambient concentration per day in general natural flux of nutrients in aquifer waters from tropical carbonate islands will increase as a function of island diameter aquifer recharge head the thickness of the soil layers in which remineralization occurs and as the acquisition of solutes from subterranean volcanics above sea level increases