open co2 underground water system in the west carpathians south poland chemical and isotopic evidence in the open co2 water system 13c of the total dissolved carbonate i e 13c tdc is pco2 and 13c co2 g dependent as tdc is pco2 dependent the variation of 13c tdc in such a system is described by the following equilibrium equation 13c tdc 13c co2 g 1000 0 h2co03 0k1 hco 3 h 0k1k2 co2 3 h 21 h2co03 k1 hco 3 h k1k2 co2 3 h 2 1000 chemical and isotopic data of waters in the west carpathians south poland when subjected to the necessary computation reflect properties of a system open to co2 pco2 of the waters of interest at the earth s surface is close to 1 2 atm their initial chemical speciation has been assigned to this value using program phreeqe then 13c values of dissolved carbonate species in the waters were calculated according to the wigley plummer pearson procedure to obtain the value for 13cf tdc which corresponds to pco2 1 2 atm resulting 13cf tdc values when plotted as a function of tdcf and phf fall well between two curves independently derived for 13c co2 g 1 and 3 and pco2 1 2 atm t 10 c and i 0 1 this implies that waters from the west carpathians are under almost constant co2 pressure and constant 13c co2 g moreover it suggests that a single origin of co2 is quite possible

remote impact of north atlantic sea surface temperature on rainfall in southwestern china during boreal spring as an important oceanic signal the north atlantic sea surface temperature sst affects not only the climate variability over east china and northeast china but also can affect climate variability over southwestern china swc based on station rainfall data and reanalysis datasets the present study investigates the relationship of north atlantic sst with swc rainfall during boreal spring for the period 1979 2016 the results show that there is a significant positive correlation between north atlantic sst and swc rainfall during boreal spring the atmospheric circulation over southern asia associated with north atlantic sst is favorable for positive rainfall anomalies further analyses show that north atlantic sst can induce a north atlantic western russia western tibetan plateau swc nrtc teleconnection wave train from upper level to low level at low level two anomalous anticyclones are found over the mid high latitude of north atlantic and the western tibetan plateau and two anomalous cyclones are observed over the western russia and bay of bengal bob respectively the nrtc teleconnection wave train plays a bridging role between the north atlantic sst and swc rainfall during boreal spring both the observational analysis and two numerical experiments suggest that the north atlantic sst during boreal spring can induce an anomalous cyclone over bob by the nrtc teleconnection pattern the anomalous cyclone over bob favors moisture transport to swc accompanying with significant anomalous ascending motion and thus results in positive rainfall anomalies in swc during boreal spring

the british baikal corridor a teleconnection pattern along the summertime polar front jet over eurasia abstractthe british baikal corridor bbc pattern a new teleconnection along the summertime upper tropospheric polar front jet pfj is investigated based on observational and reanalysis datasets

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

influence of the north atlantic sst on the atmospheric circulation using the monthly coads dataset and nmc ncar archives we show that significant anomalies of the atmospheric circulation are related to previous sst anomalies in the north atlantic a signal over the northwest labrador sea in late spring is associated with the dominant mode of sst variability during the preceeding winter it is more clearly seen in the mid troposhere than at sea level and appears to be related to the anomalous surface heat exchanges that slowly damp the sst anomalies in addition a nao like signal in early winter is associated with sst anomalies east of newfoundland and in the eastern subtropical north atlantic during the preceeding summer

deeper groundwater chemistry and geochemical modeling of the arsenic affected western bengal basin west bengal india abstract a regional scale hydrogeochemical study of a 21 000 km2 area in the western bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers spatial trends of solutes and geochemical modeling indicate that carbonate dissolution silicate weathering and cation exchange control the major ion chemistry of groundwater and river water the main aquifer water has also evolved by mixing with seawater from the bay of bengal and connate water the isolated aquifers contain diagenetically altered water of probable marine origin the postoxic main aquifer water exhibits overlapping redox zones metal reducing sulfidic and methanogenic indicative of partial redox equilibrium with the possibility of oxidation in micro scale environments the redox processes are depth dependent and hydrostratigraphically variable elevated dissolved as in the groundwater is possibly related to fe iii reduction but is strongly influenced by coupled fe s c redox cycles arsenic does not show good correlations with most solutes suggesting involvement of multiple processes in as mobilization the main river in the area the bhagirathi hoogly is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry arsenic in water of smaller streams jalangi and ichamati is probably introduced by groundwater discharge during the dry season

dynamical processes related to the appearance of the okhotsk high during early midsummer abstract the authors identified an upper level pressure anomaly pattern corresponding to the interannual variability of the okhotsk high in midsummer late july and early august as a predominant anomaly pattern in the northern hemisphere by using objectively analyzed data according to the results of empirical orthogonal function eof analyses and composite analyses a positive pressure anomaly appeared near the tropopause over eastern siberia in years with strong okhotsk highs examination of the heat budget in the lower troposphere revealed that a negative surface temperature anomaly observed in northern japan was brought by the advection of the climatological temperature gradient from the anomalous wind associated with the upper level anticyclonic anomaly it was also demonstrated that the anomaly field over siberia does not accompany predominant vorticity forcing or rossby wave propagation from the west with a specific phase however positive kinetic energy conversion from the climatological basic

northeast china summer temperature and north atlantic sst a previous study revealed a close relationship between interannual variations ofnortheast china nec summer temperature and a tripole sea surface temperature sst anomaly pattern in the north atlantic in preceding spring the present study investigatesthe change in the above relationship and the plausible causes for the change a tripole sstindex is defined with its positive value corresponding to positive sst anomalies in thetropics and midlatitudes and negative sst anomalies in the subtropics the tripole sstanomaly pattern has a weak correlation with nec summer temperature during the 1950sthrough the mid 1970s in sharp contrast to the 1980s and 1990s this change is related tothe difference in the persistence of the tripole sst pattern before the late 1970s thetripole sst pattern weakened from spring to summer and thus the spring north atlantictripole sst pattern had a weak connection with nec summer temperature on thecontrary after the late 1970s the tripole sst pattern displayed a tendency of persistencefrom spring to summer contributing to circulation changes that affected nec summertemperature there are two factors for the persistence of the tripole sst pattern fromspring to summer one is the north atlantic air sea interaction and the other is thepersistence of sst anomalies in the eastern equatorial pacific during the decay ofel nino southern oscillation enso it is shown that the north atlantic sst anomaliescan have an impact on nec summer temperature independent of enso

dynamical processes related to the appearance of quasi stationary waves on the subtropical jet in the midsummer northern hemisphere statistical features of quasi stationary planetary waves were examined on the subtropical jet in the midsummer northern hemisphere by using objectively analyzed data and satellite data as a result a quasi stationary wave train that is highly correlated with the midsummer climate over japan was identified a clear phase dependency of the appearance of waves was also confirmed an analysis of temporal evolution and wave activity flux revealed that the eastward propagation of the wave packet starts in the middle east passes over east asia and reaches north america the anomaly pattern is strengthened through kinetic energy conversion near the entrance of the asian jet over the middle east the interaction between the anomaly pattern and the basic field contributes to the appearance of the anomalous wavelike pattern although the wave train is correlated with the anomaly of convective activity over the western north pacific and the indian ocean it is implied that internal dynamics are important in determining the statistical features of the appearance of anomalous quasi stationary waves on the subtropical jet

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

a strengthened impact of november arctic oscillation on subsequent tropical pacific sea surface temperature variation since the late 1970s the connection between november arctic oscillation ao and the following spring summer tropical pacific sea surface temperature sst experienced a pronounced enhancement around the late 1970s the connection was weak before but strong after the late 1970s the present study investigates the plausible reasons for the connection change after the late 1970s significant anomalous cyclone appears over subtropical north pacific and pronounced anomalous westerly winds occur over tropical western pacific in the positive phase of november ao as such november ao could exert a significant influence on the subsequent spring summer tropical pacific sst variation by contrast before the late 1970s anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward thereby the connection between november ao and tropical pacific sst is weak further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical north pacific may be related to the change in the november ao s pacific component and the strength of feedback of synoptic scale eddy to mean flow specifically after the late 1970s november ao s pacific component displays a zonally elongated structure which is favorable for the formation of easterly wind anomalies over the mid latitude north pacific and related wave mean flow interaction in addition feedback of synoptic eddy to mean flow is enhanced after the late 1970s which is partly related to the intensification of the north pacific storm track this may also contribute to enhancement of the anomalous cyclone over the subtropical pacific

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

dominant modes of interannual variability in eurasian surface air temperature during boreal spring abstractthis study investigates interannual variations of surface air temperature sat over mid and high latitudes of eurasia during boreal spring and their association with snow atmospheric circulation and sea surface temperature sst changes the leading mode of spring sat variations is featured by same sign anomalies over most regions the second mode features a tripole anomaly pattern with anomalies over the central part opposite to those over the eastern and western parts of eurasia a diagnosis of surface heat flux anomalies suggests that snow change contributes partly to sat anomalies in several regions mainly by modulating surface shortwave radiation but cannot explain sat changes in other regions atmospheric circulation anomalies play an important role in spring sat variability via wind induced heat advection and cloud induced surface radiation changes positive sat anomalies are associated with anomalous westerly winds from the north atlantic ocean or with anomalous anticyclone and souther

a graphical method to evaluate predominant geochemical processes occurring in groundwater systems for radiocarbon dating a graphical method is described for identifying geochemical reactions needed in the interpretation of radiocarbon age in groundwater systems graphs are constructed by plotting the measured 14c 13c and concentration of dissolved inorganic carbon and are interpreted according to specific criteria to recognize water samples that are consistent with a wide range of processes including geochemical reactions carbon isotopic exchange 14c decay and mixing of waters the graphs are used to provide a qualitative estimate of radiocarbon age to deduce the hydrochemical complexity of a groundwater system and to compare samples from different groundwater systems graphs of chemical and isotopic data from a series of previously published groundwater studies are used to demonstrate the utility of the approach ultimately the information derived from the graphs is used to improve geochemical models for adjustment of radiocarbon ages in groundwater systems

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

structure and dynamics of a wave train along the wintertime asian jet and its impact on east asian climate based on observational and reanalysis datasets this study investigates the structure and dynamics of a wave like atmospheric teleconnection pattern along the wintertime asian jet and its influence on east asian climate along the jet the leading empirical orthogonal function eof mode of monthly meridional winds at 250 hpa in winter december january and february is organized as a wave train with maximum anomalies at upper troposphere the wave train propagates northeastward from the north atlantic to europe turns southeastward to the middle east with amplifying amplitude propagates along the jet to south china and reaches japan which is partly induced by sea surface temperature sst anomalies in the equatorial eastern pacific and the north atlantic oscillation over the sector from europe to the middle east the anomalous vortices in the wave train tilt northwestward with height and tilt northeast southwest in horizontal at 250 hpa favoring for extracting available potential energy and kinetic energy from mean flows effectively in addition there exists a positive feedback between transient eddies and the wave train related anomalous circulation over the north atlantic and europe these processes help to maintain and amplify the wave train moreover the wave train can exert significant influences on the wintertime climate in east asia when it is in the phase with a cyclone anticyclone over south china japan rainfall tends to be above normal in south and east china and surface air temperature tends to be above normal around japan and the korea peninsula

effect of land use and urbanization on hydrochemistry and contamination of groundwater from taejon area korea abstract taejon metropolitan city located in the central part of south korea has grown and urbanized rapidly the city depends heavily on groundwater as a water resource because of ubiquitous pollution sources the quality and contamination have become important issues for the urban groundwater supply this study has investigated the chemical characteristics and the contamination of groundwater in relation to land use an attempt was made to distinguish anthrophogenic inputs from the influence of natural chemical weathering on the chemical composition of groundwater at taejon groundwater samples collected at 170 locations in the taejon area show very variable chemical composition of groundwater e g electrical conductance ranges from 65 to 1 290 s cm most groundwater is weakly acidic and the groundwater chemistry is more influenced by land use and urbanization than by aquifer rock type most groundwater from green areas and new town residential districts has low electrical conductance and is of ca hco 3 type whereas the chemical composition of groundwater from the old downtown and industrial district is shifted towards a ca cl no 3 so 4 type with high electrical conductance a number of groundwater samples in the urbanized area are contaminated by high nitrate and chlorine and exhibit high hardness the epco 2 that is the co 2 content of a water sample relative to pure water was computed to obtain more insight into the origin of co 2 and bicarbonate in the groundwater the co 2 concentration of groundwater in the urbanized area shows a rough positive relationship with the concentration of major inorganic components the sources of nitrate chlorine and excess co 2 in the groundwater are likely to be municipal wastes of unlined landfill sites leaky latrines and sewage lines chemical data of commercial mineral water from other jurassic granite areas were compared to the chemical composition of the groundwater in the taejon area factor analysis of the chemical data shows that the hco 3 and no 3 concentrations have the highest factor loadings on factor 1 and factor 2 respectively factors 1 and 2 represent major contributions from natural processes and human activities respectively the results of the factor analysis indicate that the levels of ca 2 mg 2 na cl and so 4 2 derive from both pollution sources and natural weathering reactions

a review of single sample based models and other approaches for radiocarbon dating of dissolved inorganic carbon in groundwater abstract numerous methods have been proposed to estimate the pre nuclear detonation 14c content of dissolved inorganic carbon dic recharged to groundwater that has been corrected adjusted for geochemical processes in the absence of radioactive decay 14c0 a quantity that is essential for estimation of radiocarbon age of dic in groundwater the models approaches most commonly used are grouped as follows 1 single sample based models 2 a statistical approach based on the observed curved relationship between 14c and 13c data for the aquifer and 3 the geochemical mass balance approach that constructs adjustment models accounting for all the geochemical reactions known to occur along a groundwater flow path this review discusses first the geochemical processes behind each of the single sample based models followed by discussions of the statistical approach and the geochemical mass balance approach finally the applications advantages and limitations of the three groups of models approaches are discussed the single sample based models constitute the prevailing use of 14c data in hydrogeology and hydrological studies this is in part because the models are applied to an individual water sample to estimate the 14c age therefore the measurement data are easily available these models have been shown to provide realistic radiocarbon ages in many studies however they usually are limited to simple carbonate aquifers and selection of model may have significant effects on 14c0 often resulting in a wide range of estimates of 14c ages of the single sample based models four are recommended for the estimation of 14c0 of dic in groundwater pearson s model ingerson and pearson 1964 pearson and white 1967 han plummer s model han and plummer 2013 the iaea model gonfiantini 1972 salem et al 1980 and oeschger s model geyh 2000 these four models include all processes considered in single sample based models and can be used in different ranges of 13c values in contrast to the single sample based models the extended gonfiantini zuppi model gonfiantini and zuppi 2003 han et al 2014 is a statistical approach this approach can be used to estimate 14c ages when a curved relationship between the 14c and 13c values of the dic data is observed in addition to estimation of groundwater ages the relationship between 14c and 13c data can be used to interpret hydrogeological characteristics of the aquifer e g estimating apparent rates of geochemical reactions and revealing the complexity of the geochemical environment and identify samples that are not affected by the same set of reactions processes as the rest of the dataset the investigated water samples may have a wide range of ages and for waters with very low values of 14c the model based on statistics may give more reliable age estimates than those obtained from single sample based models in the extended gonfiantini zuppi model a representative system wide value of the initial 14c content is derived from the 14c and 13c data of dic and can differ from that used in single sample based models therefore the extended gonfiantini zuppi model usually avoids the effect of modern water components which might retain bomb pulse signatures the geochemical mass balance approach constructs an adjustment model that accounts for all the geochemical reactions known to occur along an aquifer flow path plummer et al 1983 wigley et al 1978 plummer et al 1994 plummer and glynn 2013 and includes in addition to dic dissolved organic carbon doc and methane ch4 if sufficient chemical mineralogical and isotopic data are available the geochemical mass balance method can yield the most accurate estimates of the adjusted radiocarbon age the main limitation of this approach is that complete information is necessary on chemical mineralogical and isotopic data and these data are often limited failure to recognize the limitations and underlying assumptions on which the various models and approaches are based can result in a wide range of estimates of 14c0 and limit the usefulness of radiocarbon as a dating tool for groundwater in each of the three generalized approaches single sample based models statistical approach and geochemical mass balance approach successful application depends on scrutiny of the isotopic 14c and 13c and chemical data to conceptualize the reactions and processes that affect the 14c content of dic in aquifers the recently developed graphical analysis method is shown to aid in determining which approach is most appropriate for the isotopic and chemical data from a groundwater system

quantitative study of geochemical processes in the dogger aquifer paris basin france the quantification of geochemical reactions in hydrothermal aquifers requires an exhaustive approach because of their interdependence all chemical elements likely to have a quantitative influence on dissolution or precipitation reactions have to be taken into account geochemical constraints the number of which equals the number of the chemical elements were determined with the help of chemical analyses of the solution in the case study of the dogger aquifer paris basin france 12 elements are taken into account al c cl ca f h k mg na o s si three constraints apply to water activity neutrality and conservation of chloride in aqueous solutions the determination of the remaining constraints was based on saturation indices stability diagrams of minerals and partial pressure of carbon dioxide pco2 the present day solutions are at equilibrium with respect to nine minerals albite anhydrite chalcedony calcite dolomite fluorite kaolinite k feldspar and illite or chlorite thus it was demonstrated that the composition of these solutions including computed pco2 is only a function of temperature and chloride content moreover it was possible to test the validity of the geochemical system by computing its speciation and comparing these theoretical results with actual chemical analyses ph and concentrations finally geochemical simulations were used in predicting what quantities would be dissolved or precipitated as either the temperature or the chlorinity varied although the rock is predominantly calcareous these quantities could not be determined if the influence of the aluminosilicates were neglected this chemical component approach with which one can pose and solve rigorously the chemical equilibrium problem constitutes a prerequisite for the quantitative study of geochemical processes related to fluid flow

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

observed positive feedback between the nao and the north atlantic ssta tripole 1 ncep ncar reanalysis data from 1948 to 2001 are used to examine the relationship between the north atlantic oscillation nao and the north atlantic sea surface temperature anomaly ssta tripole it is demonstrated that the atmospheric anomalies associated with nao produce tripole like sea surface temperature sst anomalies in turn the ssta tripole produces nao like atmospheric anomalies therefore a positive feedback between the nao and the ssta tripole is suggested the results are statistically significant they clarify prior uncertainties associated with the relationship between the nao and the north atlantic ssta tripole

structure and dynamics of the summertime pacific japan teleconnection pattern convective activity over the tropical western pacific is known to influence the extratropical circulation over east asia in the boreal summer in the form of teleconnection called the pacific japan pj pattern but its structure and dynamics have not yet been studied in depth in this study a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the philippines the composited monthly mean vorticity anomalies associated with the pj pattern are elongated zonally with a distinct poleward tilt with height this structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes as has widely been accepted as a conceptual model of the pj pattern a wave activity flux points polewards only in the lower troposphere indicating that rossby wave teleconnection occurs primarily through a low level south westerly jet those tilted anomalies over the western pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy ape in the presence of the vertically sheared jets the enhanced convection can generate ape effectively and the associated low level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre warmed ocean surface it is thus hypothesized that the pj pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the asian summer monsoon with an efficient self sustaining mechanism through moist processes copyright 2006 royal meteorological society

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

modulation of the interannual variation of the india burma trough on the winter moisture supply over southwest china anomalous moisture circulation associated with the interannual variation of the india burma trough was investigated to examine how the trough affects the moisture supply to southwest china in winter when the india burma trough is strong abnormal moisture is transported to southwest china mainly via the southern boundary in the 750 650 hpa layer instead of via the western boundary in contrast to the climatological situation the abnormal moisture convergence is constrained in a thin layer along the windward side of the tibetan plateau the moisture circulation response to the variation of the india burma trough shows great baroclinicity over the bay of bengal bob northwesterly transport behind and southwesterly transport ahead of the trough appear only between 850 and 650 hpa with anticyclonic moisture circulation underneath and cyclonic moisture circulation on top beyond the bob the moisture circulation response can be traced upstream with abnormal anticyclonic cyclonic moisture circulations over the mediterranean sea and arabian sea red sea above 850 hpa and downstream with anticyclonic moisture circulation over the philippine sea near the surface the activity of the india burma trough is not a local phenomenon but a part of the south asian jet wave trains and is modulated by the enso via the philippine sea anticyclone further investigation of the separate role of wind and moisture disturbances shows that the abnormal moisture flux is dominated by the wind disturbance as is the abnormal moisture divergence in the lower level while that in the upper level is dominated by both the wind and moisture disturbances

a precipitation seesaw mode between northeast asia and siberia in summer caused by rossby waves over the eurasian continent abstract there is a dominant seesaw pattern in summertime precipitation between northeast asia and siberia examined here is a mechanism of the seesaw mode focusing on quasi stationary rossby waves propagating on two upper tropospheric waveguides along the asian jet and over northern eurasia empirical orthogonal function eof analysis to the low frequency 10 day low pass filtered variation during summer reveals wave propagation patterns on both of the waveguides the time evolution of the two composite fields constructed using the obtained eof modes for each phase of the seesaw mode was investigated by the wave activity flux in both composite fields eastward propagating rossby waves originating from the north atlantic european sector branch off around eastern europe onto the two waveguides which become out of phase toward the east because of the difference in longitudinal wavelengths along them this results in opposite phase anomalies of meridional winds over northeast asia and siberia budget

relationship between ural siberian blocking and the east asian winter monsoon in relation to the arctic oscillation and the el nino southern oscillation this study attempts to assess the possible linkage between ural siberian blocking and the east asian winter monsoon eawm during the boreal winter the dominance of blocking thermally enhances cold advection downstream the frequent occurrence of ural siberian blocking potentially promotes a cold eawm and vice versa the seasonal blocking activity can be regarded as the combined effect of the arctic oscillation ao and the el nino southern oscillation enso weakened strengthened meridional flow in the positive negative phase of the ao is unfavorable favorable for the formation of blocking highs because the ao shows a close relationship with the north atlantic oscillation nao its teleconnection with ural siberian blocking may exist in the form of an eastward propagating wave train be that as it may the wave train signal across east asia may be disturbed by the external effect of a strong enso event which probably enhances weakens the westerlies near siberia in its warm cold phase consequently the blocking eawm relationship is stronger weaker when the ao and enso are in phase out of phase if both ao and enso attain the positive negative phase the siberian high tends to be weaker stronger and the temperature tends to be higher lower in east asia with less more ural siberian blocking on the other hand if they are out of phase they are not strongly linked to the intensity of the siberian high and the blocking activity over ural siberia is unclear

arsenic enriched aquifers occurrences and mobilization of arsenic in groundwater of ganges delta plain barasat west bengal india hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for as enrichment in part of the gangetic plain barasat west bengal india analysis of water samples from shallow tubewells depth 24 3 48 5m and piezometer wells depth 12 2 79 2m demonstrate that the groundwater is mostly the ca hco3 type and anoxic in nature mean ehshe 34mv arsenic concentrations ranged from 10 538 g l with high concentrations only present in the shallow to medium depth 30 50m of the aquifer along with high fe 0 07 9 8mg l and relatively low mn 0 15 3 38mg l as also evidenced in core sediments most groundwater samples contained both as iii and as v species in which the concentration of as iii was generally higher than that of as v exhibiting the reducing condition results show lower concentrations of no3 so4 and no2 along with higher values of doc and hco3 indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of as from sediments into groundwater positive correlations of as with fe and doc were also observed the presence of doc may actively drive the redox processes this study revealed that reduction processes of feooh was the dominant mechanism for the release of as into the groundwater in this part of the ganges delta plain

the influence of wave trains in mid high latitudes on persistent heavy rain during the first rainy season over south china based on daily precipitation data from the chinese meteorological administration and reanalysis data from the national centers for environmental prediction department of energy the character of low frequency precipitation variability during the first rainy season april june over south china and its corresponding atmospheric circulations in the mid high latitudes are investigated the results show that the precipitation anomalies during this period exhibit obvious quasi biweekly oscillation qbwo features with a period of 8 24 days the influence of wave trains in the mid high latitudes to low frequency persistent heavy rain event phr lf event the 8 24 day filtered precipitation larger than one standard deviation of filtered time series and persisting at least three days over south china is further discussed during the first rainy season over south china there are two low frequency wave trains in the mid high latitudes associated with the phr lf event the wave train crossing the eurasian continent and the wave train along the subtropical westerly jet analysis of wave activity flux indicates that the wave energy disperses toward eastern china along these two low frequency wave trains from north to south and from west to east and then propagates downward over south china accordingly the disturbance of the relative vorticity of the cyclonic anomalies over eastern china is strengthened which enhances the meridional gradient of relative vorticity owing to the transport of low frequency relative vorticity and geostrophic vorticity by meridional wind the ascending motion over south china intensifies and lasts for a long time triggering a phr lf event in addition the tropical system is also a key factor to phr lf event the qbwo of the convection over the south china sea provide moisture for phr lf events maintaining persistent rainfall and vertical ascending motion over south china

on the association between spring arctic sea ice concentration and chinese summer rainfall 1 a statistical relationship between spring arctic sea ice concentration sic and chinese summer rainfall is identified using singular value decomposition svd results show that decreased increased spring sic in the arctic ocean and the greenland sea corresponds to increased decreased summer rainfall in northeast china and central china between the yangtze river and the yellow river 28 36 n and decreased increased rainfall in south china corresponding summer 500 hpa height anomalies show a eurasian wave train structure which originates in northern europe and extends southeastwards to northeast china and a south north dipole structure over east asia south to lake baikal such a spatial distribution of 500 hpa height anomalies and corresponding summer rainfall anomalies cannot be entirely attributed to the impact of east asian summer monsoon easm variability the spring arctic sic provides a complementary precursor for chinese summer rainfall variability the combined impacts of both spring arctic sic and eurasian snow cover on the eurasian wave train may explain their statistical linkage

diagenetic and other highly mineralized waters in the polish carpathians abstract highly mineralized waters of different chemical types and origin occur in the flysch formations and their bedrocks in the western part of the polish carpathians the marine sedimentation water of the flysch formations is not preserved as the most mineralized and the heaviest isotopic values of flysch waters are characterized by 18 o and 2 h values in the ranges of 5 7 and 20 30 respectively their origin is related to the dehydration of clay minerals during burial diagenesis with molecules of marine water completely removed by molecules of released bound water they are relatively enriched in na in respect to the marine water supposedly due to the release of na during the illitization of smectites and preferable incorporation of other cations from the primary brine into newly formed minerals in some parts of younger formations i e in the badenian sediments brines occur with isotopic composition close to smow and cl contents greatly exceeding the typical marine value of about 19 6 g l supposedly due to ultrafiltration most probably the marine water of the flysch formations was similarly enriched chemically in its initial burial stages final cl contents in diagenetic waters depend on different cl contents in the primary brines and on relationships between diagenetic and further ultrafiltration processes in some areas diagenetic waters migrate to the surface along fault zones and mix with young local meteoric waters becoming diluted with the isotope composition scattering along typical mixing lines in areas with independent co 2 flow from great depths they form chloride co 2 rich waters common co 2 rich waters are formed in areas without near surface occurrences of diagenetic waters they change from the hco 3 ca type for modern waters to hco 3 mg ca hco 3 na ca and other types with elevated tds mg 2 and or na contents for old waters reaching even those of glacial age bedrocks of the flysch are represented by mesozoic and paleozoic mudstones sandstones and carbonates and in some areas by badenian sediments brines of the mesozoic and paleozoic bedrocks are usually significantly enriched in ca 2 and mg 2 in comparison with the badenian brines by analogy to the deepest brines in the adjacent upper silesian coal basin they are supposed to originate from paleometeoric waters of a hot climate

structure and dynamics of a springtime atmospheric wave train over the north atlantic and eurasia the leading pattern of boreal spring 250 hpa meridional wind anomalies over the north atlantic and mid high latitude eurasia displays an obvious wave train the present study documents the structure energy source relation to the north atlantic sea surface temperature sst and impacts on eurasian climate of this wave train during 1948 2018 this atmospheric wave train has a barotropic vertical structure with five major centers of action lying over subtropics and mid latitudes of the north atlantic northern europe central eurasia and east asia respectively this spring wave train can efficiently extract available potential energy from the basic mean flow the baroclinic energy conversion process and positive interaction between synoptic scale eddies and the mean flow both play important roles in generating and maintaining this wave train the north atlantic horseshoe like nah sst anomaly contributes to the persistence of the wave train via a positive air sea interaction specifically the nah sst anomaly induces a rossby wave type atmospheric response which in turn maintains the nah sst anomaly pattern via modulating surface heat fluxes this spring atmospheric wave train has significant impacts on eurasian surface air temperature sat and rainfall during the positive phase of the wave train pronounced sat warming appears over central eurasia and cooling occurs over west europe and eastern eurasia in addition above normal rainfall appears over most parts of europe and around the lake baikal accompanied by below normal rainfall to east of the caspian sea and over central asia

geochemistry of aquifer sediments and arsenic rich groundwaters from kandal province cambodia abstract elevated as is well known to be present in aquifers utilised for drinking water and irrigation in west bengal and bangladesh this problem has also more recently been discovered in other parts of asia including vietnam cambodia inner mongolia and the middle ganges plain analysis of groundwaters in kandal province of cambodia found waters with comparable geochemistry to the as rich groundwaters of the west bengali delta similarities included high but heterogeneous as distributions predominantly in the form as iii high fe moderate to high hco 3 circumneutral ph low so 4 2 and geochemical components indicative of reducing conditions good positive correlations between as fe hco 3 and nh 4 and dissolved organic c is consistent with as release predominantly via microbially mediated reductive dissolution of as bearing fe iii oxides further evidence for such a process is found from correlations between as fe and organic matter from analysis of aquifer sediments by the presence of goethite in the finer fractions and from the association of as with amorphous poorly crystalline and well crystallised hydrous fe oxides the presence of several high as but low fe wells implies that microbes could have a more direct role in mediating as release via the direct utilisation of fe iii or as v as electron acceptors the presence of elevated as in waters with short aquifer residence times as indicated by their geochemical signature highlights the possible vulnerability of these aquifers to the influx of surface derived waters providing an additional source of labile organic c that could exacerbate as release by stimulating microbial activity

mobility of arsenic in west bengal aquifers conducting low and high groundwater arsenic part i comparative hydrochemical and hydrogeological characteristics abstract the present study demonstrates the importance of hydrogeochemical characteristics groundwater flow and recharge of an aquifer in the release of as to groundwater the study area 20 km 2 is located in chakdaha block nadia district west bengal which hosts groundwaters of variable as content the spatial distribution pattern of as is patchy with areas containing groundwater that is high in as 200 g l 1 found in close vicinity to low as 1 groundwaters within 100 m the concentration of groundwater as is found to decrease with depth in addition the data shows that there is no conspicuous relationship between high groundwater as concentration and high groundwater abstraction although the central cone of depression has enlarged over 2 a and is extending towards the se of the study area the river hooghly which forms the nw boundary of the study site shows dual behaviour effluent and influent during pre and post monsoon periods respectively complicating the site hydrogeology the observed groundwater flow lines tend to be deflected away from the high as portion of the aquifer indicating that groundwater movement is very sluggish in the as rich area this leads to a high residence time for this groundwater package prolonging sediment water interaction and hence facilitating groundwater as release

model simulation and projection of european heat waves in present day and future climates abstractthe synoptic behavior of present day heat waves hw over europe is studied using the gfdl high resolution atmospheric model hiram with 50 km grid spacing three regions of enhanced and coherent temperature variability are identified over western russia eastern europe and western europe the simulated hw characteristics are compared with those derived from climate forecast system reanalysis products composite charts for outstanding hw episodes resemble well known recurrent circulation types the hw region is overlain by a prominent upper level anticyclone which blocks the passage of synoptic scale transients the altered eddy vorticity transports in turn reinforce the anticyclone the anticyclone is part of a planetary scale wave train the successive downstream development of this wave train is indicative of rossby wave dispersion additional runs of hiram are conducted for the time slices of 2026 35 and 2086 95 in the climate scenario corresponding to representative concentration pathway

interannual variability of surface air temperature over mid high latitudes of eurasia during boreal autumn this study analyzes the dominant modes of interannual variability of surface air temperature sat during boreal autumn over the mid high latitudes of eurasia and investigates their associations with snow cover atmospheric circulation and sea surface temperature sst the first second and third empirical orthogonal function eof mode of autumn sat anomalies displays same sign distribution an east west dipole pattern and a south north dipole pattern respectively analysis of surface heat fluxes indicates that snow changes explain only small patches of sat anomalies related to the first two eofs via altering surface shortwave radiation atmospheric circulation anomalies have important contributions to the formation of sat anomalies southerly northerly wind anomalies generally favor positive negative sat anomalies via bringing warmer colder air from lower higher latitudes the atmospheric circulation anomalies related to the first eof mode are attributed to a combination of the arctic oscillation ao and the scandinavia pattern and those related to the second eof mode have a close relation with the east atlantic west russian eawr and circumglobal teleconnection cgt patterns formation of the atmospheric circulation anomalies related to the third eof mode is partly related to the arctic sea ice change around the barents kara seas sst anomalies have little contribution to the atmospheric circulation anomalies associated with the first three eof modes of eurasian autumn sat interannual variations hindcast skill of the sat anomalies related to the first second eof mode is improved when taking both the ao and scandinavia eawr and cgt patterns into account

the leading interannual variability modes of winter surface air temperature over southeast asia the present study analyzes the leading interannual variability modes of southeast asian surface air temperature sat during boreal winter the first empirical orthogonal function eof1 mode displays same sign sat anomalies over southeast asia with a center around the north indo china peninsula and south china the second eof eof2 shows a dipole sat anomaly pattern between the indo china peninsula and south china surface heat flux change may not be able to explain sat variation related to the eof1 but explain partly the sat change associated with the eof2 atmospheric anomalies play a crucial role in the sat variations via wind induced temperature advection specifically for the eof1 marked northerly anomalies appear over the southeast asia which bring colder air from higher latitude and contribute to negative sat anomalies change in the intensity of arctic oscillation siberian high and la nina like sea surface temperature sst anomalies over the tropical central eastern pacific play a key role in forming the northerly anomalies related to the eof1 for the eof2 at the lower troposphere a pair of anomalous cyclones appears over the tropical north and south indian ocean together with southwesterly wind anomalies extending from the indian ocean to the indo china peninsula which favor positive sat anomalies there formation of the twin cyclones is likely to be a gill type rossby wave response of the tropical indian ocean sst warming at the upper troposphere two wave trains one originated from the arctic region and another from the mediterranean sea contribute collectively to the atmospheric circulation anomalies over southeast asia related to the eof2

characterisation of organic matter in a shallow reducing arsenic rich aquifer west bengal abstract elevated arsenic in groundwaters extensively exploited for irrigation and drinking water in west bengal and bangladesh is causing serious impacts on human health a key mechanism for the genesis of arsenic as in these waters is microbially mediated reductive transformation of arsenic bearing fe iii hydrated oxides the role of organic c in this process whether from in situ organic matter om i e om from within the sediment or from other sources is widely recognised despite this there is a paucity of data about the characteristics of om in these as rich aquifers extraction and analysis of the polar and apolar fractions from seven different sediments from a known groundwater as hotspot in west bengal revealed om characteristic of the original terrestrial depositional environment however this was overprinted by abundant hydrocarbons with thermally mature e g petroleum distributions these hydrocarbons included abundant high molecular weight n alkanes and unresolved complex mixtures ucms as well as thermally mature distributions of hopanes and steranes additionally at certain depths surface sands 8 and 13 m deeper sands 25 m the om appeared to be biodegraded with the preferential removal of petroleum sourced n alkanes suggesting that indigenous microbes within the aquifer can utilise this carbon source the presence of this previously unreported source of bioavailable organic carbon is of importance as it has the potential to promote microbial activity and subsequent as release in the aquifers

possible mechanisms for the coupling between late spring sea surface temperature anomalies over tropical atlantic and east asian summer monsoon the relationship between the preceding late spring sea surface temperature sst over the tropical atlantic and the east asian summer monsoon easm is investigated based on the observational data and coupled model intercomparison project phase 5 cmip5 historical simulations the results show that warm cold tropical atlantic sst tasst during may tends to be followed by a strong weak easm with positive negative precipitation anomalies over the subtropical frontal area evidence is also provided that the atmospheric teleconnections propagating in both east and west directions are the key mechanisms linking the easm with the preceding may tasst that is the warm tasst anomaly during late spring can persist through the subsequent summer which in turn induces the gill type rossby wave response in the eastern pacific exciting the westward relay of the atlantic signal as well as the eastward propagation of the rossby wave along the jet stream furthermore the westward eastward propagating teleconnection signal may induce the anomalous anticyclone in the lower troposphere over the philippine sea anomalous tropospheric anticyclone with barotropic structure over the okhotsk sea the anomalous anticyclonic circulation over the philippine sea okhotsk sea brings warm and humid cold air to higher latitudes lower latitudes these two different types of air mass merge over the baiu meiyu changma region causing the enhanced subtropical frontal rainfall to support the observational findings cmip5 historical simulations are also utilized most state of the art cmip5 models can simulate this relationship between may tasst and the easm

transient eddy forcing of the time mean flow as identified by geopotential tendencies abstract the forcing of the time mean flow by transient eddies is examined within the framework of a quasi geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity the forcing functions of this equation are computed using observed circulation statistics for the wintertime northern hemisphere and solutions are sought for the three dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales in general the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere the geostrophic wind tendencies associated with synoptic scale eddies with periods between 2 5 and 6 days are strongest in the vicinity of the oceanic storm tracks the enhanced poleward heat transports by active disturbanc

impact of eurasian spring snow decrement on east asian summer precipitation abstractin this study the relationship between eurasian spring snow decrement ssd and east asian summer precipitation and related mechanisms were investigated using observational data and the community atmospheric model version 3 1 cam3 1 the results show that a west east dipole pattern in eurasian ssd anomalies with a negative center located in the region between eastern europe and the west siberia plain eewsp and a positive center located around baikal lake bl is significantly associated with east asian summer precipitation via triggering an anomalous midlatitude eurasian wave train reduced ssd over eewsp corresponds to anomalously dry local soil conditions from spring to the following summer thereby increasing surface heat flux and near surface temperatures similarly the increase in ssd over bl is accompanied by anomalously low near surface temperatures the near surface thermal anomalies cause an anomalous meridional temperature gradient which intensifies the lower level baroclinicit

stable isotope composition of spelean calcites and gaseous co2 from tylicz polish carpathians abstract spelean calcites discovered in fissures and caverns within flysch deposits at tylicz polish carpathians have been examined isotopically together with co 2 rich water from several springs occurring in this area 13 c values of tdc and spelean calcites indicate that caco 3 has precipitated under conditions close to carbon isotope equilibrium with participation of co 2 of deep origin analyses of 18 o suggest the existence of oxygen isotope disequilibrium between water and gaseous co 2 which can be explained by the short time of contact between the co 2 flux and the shallow groundwaters of meteoric origin

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

arsenic pollution in groundwater of west bengal india an insight into the problem by subsurface sediment analysis abstract arsenic values in groundwater above the maximum permissible limit of 0 05 mg l have been reported from several areas of the lower delta region of the ganga padma river system it is confined to areas east of hooghly river and to the shallow aquifer arsenic values in sub surface sediments from arsenious water zones are significantly higher than values from safe water zones the major part of the sediments consisting of non magnetic and some feebly magnetic minerals is arsenic free some iron rich clastic minerals like illite biotite chlorite fe coated grains and also the authigenic siderite concretions which together constitute only a small part of the sediments are carriers of arsenic and contribute the element to contaminate groundwater illite biotite and chlorite degenerate to produce iron oxide hydroxide coating on their surface and also on the surface of some other sand particles arsenic is adsorbed on the iron hydroxide coating creating one kind of sink for the element bacteria induced growth of siderite concretions grow initially on these clastic minerals and after attaining bigger size fall off as individual globules arsenic gets adsorbed on these concretions forming a second kind of sink for the element arsenic carrying river water inundates the lower delta at the time of seasonal flood arsenic percolates with the water downwards to the shallow aquifer it gets fixed in the aquifer sediments in the two ways described and is retained in the traps thus formed locally developed reducing condition causes dissolution of iron hydroxide coating on the surface of clastic arsenic traps and also of the siderite concretions this leads to increase in arsenic level in groundwater at these sites a currently active process of creation and periodic enrichment of the arsenic traps followed by their subsequent depletion through desorption and dissolution is suggested to be the reason for arsenic contamination of groundwater in this part of the delta