rock coast inheritance an example from galicia northwestern spain a shore platform on the western coast of galicia in northwestern spain has been inherited from interglacial stages when sea level was similar to today the wide gently sloping intertidal platform is backed in places by supratidal rock ledges and in other places by a steeper and narrower supratidal ramp the gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range but the slope of the ramp is much too high the abandoned and degraded sea cliff is grass covered along most of this coast and the ledges and the ramp which extend up to several metres above the highest tides are covered by lichen and in places by salt tolerant plants radiocarbon dated sediments in the cliff which range up to 36 000 years in age lie on top of an ancient beach deposit the former beach remnants of which are found in situ on the ramp and rock ledges as well as two caves that are filled with the dated sediments are probably last interglacial in age the morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage whereas the wider intertidal platform is probably the product of several older interglacials when sea level was generally similar to today a general model is proposed for the inheritance of shore platforms in macro and microtidal environments copyright 1999 john wiley sons ltd

predicting the crest height of a gravel beach the beach crest is a common morphological feature formed by the deposition of sediment carried up slope by wave swash the elevation to which waves can pile gravel is a function of the size and density of the material relative to the hydraulic components of swash velocity wave frequency and runup height two equations 17 and 21 that predict the height of the beach crest to the wave forces and the beach material are derived the first derivation compares the wave force acting to move a stone up the beach face with a weight force acting to hold the stone in place the second derivation relates the potential energy per unit area of the beach crest to the total wave energy that lifted and deposited the material above a given sea level datum as a test of the derived equations the actual crest height of one natural gravel beach was accurately estimated by both equations derived further research and testing on other natural beaches are needed to fully verify eqs 17 and 21 a comparison of other equations eqs 2 3 and 4 that predict crest height is also made the poor fit of the other equations are a result of using values for the coefficients that were established in wave tank experiments another shortcoming of eqs 3 and 4 is that they do not include variables related to the beach material hence they predict that all particle sizes from sand to boulders would be piled to the same elevation by the same wave forcing eq 2 includes a particle size variable but predicts increasingly higher beach crests for larger particles more realistic results for all three equations eqs 2 3 and 4 would be expected with field tested values for the coefficients but a range in values for each different beach would be necessary the advantage of eqs 17 and 21 is that equations are not dependent on coefficients whose values come from correlation with other data sets

climate control on late holocene high energy sedimentation along coasts of the northeastern atlantic ocean abundant sedimentological and geochronological data gathered on european sandy coasts highlight major phases of increased high energy sedimentation in the north atlantic ocean during the late holocene owing to an inconsistent use of the terminology it is often difficult to determine whether studies have described storm built or wave built deposits both deposits can be identified by overall similar coarse grained sedimentary facies but may provide contradictory paleoenvironmental interpretations the aim of this study is to address this issue by analysing a set of published 14c ages recovered from wave built sediment bodies of the pertuis charentais france integration of 14c data highlights seven coarse grained sedimentation pulses csps that reflect a synchronous increase in wave induced sediment supply occurring around 2650 2420 1240 970 800 650 and 450 cal yr b p csps can be matched with geochronological data published on other exposed sandy coasts of the western europe in first order csps were preserved during phases of decreased storm activity and thus limited coastal erosion in the north atlantic ocean from 2700 to 2000 and from 1200 to 600 cal yr b p in second order csps occurred during positive nao and or negative ea wr peaks which are known from previous studies to induce higher waves and to enhance wave induced sediment transport in the pertuis charentais chronological boundaries of csps could be used as a diagnostic tool to differentiate storm deposits indicative of sudden episodic very high energy sedimentation from wave deposits resulting from the sustained action of above average westerly winds blowing across the north atlantic ocean

a new contribution to the late quaternary tephrostratigraphy of the mediterranean aegean sea core lc21 tephra layers preserved in marine sediments can contribute to the reconstruction of volcanic histories and potentially act as stratigraphic isochrons to link together environmental records recent de velopments in the detection of volcanic ash tephra at levels where none is macroscopically visible so called crypto tephra have greatly enhanced the potential of tephrostratigraphy for synchronising environmental and archaeological records by expanding the areas over which tephras are found in this paper crypto tephra extraction techniques allow the recovery of 8 non visible tephra layers to add to the 9 visible layers in a marine sediment core lc21 from the se aegean sea to form the longest single core record of volcanic activity in the aegean sea using a novel shard specific methodology sources of the tephra shards are identified on the basis of their major and trace element single shard geochemistry by comparison with geochemical data from proximal mediterranean volcanic stratigraphies the results indicate that the tephra layers are derived from 14 or 15 separate eruptions in the last ca 161 ka bp 9 from santorini 2 or 3 from kos yali or nisyros 2 from the campanian province and one from pan telleria the attributions of these tephra layers indicate that 1 inter plinian eruptions from santorini may have produced regionally significant tephra deposits 2 marine tephrostratigraphies can provide unique and invaluable data to eruptive histories for island volcanoes and 3 tephra from both pantelleria and campania may be used to correlate marine records from the aegean sea to those from the tyrrhenian adriatic and ionian seas

boulders of mis 5 age deposited by a tsunami on the coast of otago new zealand abstract a series of elevated imbricated boulders were investigated on the otago coastline southeast new zealand through field surveying and optical luminescence dating by using established hydrodynamic relationships of sediment transport the energy required to move the clasts was calculated and compared to the historic record of marine inundations of that coast the boulders are platy in shape and are over 2 m long in some cases and are sourced from a locally outcropping conglomerate unit which appears to be the only lithology on this section of coast that erodes to produce clasts of this size it is estimated that the boulders were deposited by a tsunami between 2 and 3 m high during the latter part of marine isotope stage 5 they therefore represent the first pre holocene tsunami deposit and one composed of large boulders described on the new zealand coastline

a field based classification scheme for gravel beaches a tripartite classification of gravel beaches based upon morphodynamic properties is proposed and demonstrated for 42 new zealand beaches the main advantage of this scheme is that it is based on simple visual classification that can be applied globally in the field and is underpinned by morphodynamic differences between the beach types the three types identified from the results are 1 pure gravel beach 2 mixed sand and gravel beach 3 composite gravel beach pure gravel beaches have steep slopes tan 0 08 0 24 and gravels extending from the storm berm to below mean low water spring tide level mixed sand and gravel beaches have moderate slopes tan 0 04 0 13 with sand and gravel entirely mixed both cross shore and at depth composite gravel beaches have a steep gravel berm fronted by a low angle intertidal terrace with overall beach slopes of tan 0 05 0 14 on composite beaches there is distinct hydrodynamic cross shore sorting of the sand and gravel component these broad types are tested using discriminant analysis and the three classes are shown to be highly significant f 16 24 df 8 p 0 00005 the key discriminating variables are iribarren number beach width average grain size and storm berm height

quartz grains reveal sedimentary palaeoenvironment and past storm events a case study from eastern baltic abstract sediment record collected from the coastal lake serves as a powerful tool for reconstructing changes in palaeoenvironment and understanding the potential signals of past storminess in this study we use several proxies from sediment of the holocene thermal maximum at coastal lake lilaste latvia we focus on surface texture of quartz grains from the mineral inorganic fraction as indicators of depositional environments we then use this as a proxy for potential storm transport and combine with information on granulometry diatom stratigraphy and chronology to answer the question whether flux of quartz grains in the lake originated from the sea or from the land analyses in a binocular and scanning electron microscope reveal that most of the investigated quartz grains originate from dwelling in the seawater and wave action in the nearshore zone grains representing very energetic subaqueous environment similar to storm events are also present terrestrial record is of minor significance and visible through occurrence of aeolian quartz grains during drier and colder conditions an influx of sand with aeolian imprint was delivered to the lake between 8500 and 7800 cal yr bp marine and terrestrial conditions alternated between 7800 and 6000 cal yr bp storm induced grains were likely deposited three times at 7300 cal yr bp 6600 6400 cal yr bp and 6200 6000 cal yr bp overall stable marine environmental conditions prevailed between 6000 and 4000 cal yr bp except of the last portion of terrestrial induced sediment at 4100 cal yr bp

boulders as a signature of storms on rock coasts this paper is the first review of coastal boulder studies it serves as a peer reviewed introduction to a special issue on the topic of boulders as a signature of storms on rock coasts since 2004 and the indian ocean tsunami most coastal boulder research has been focused on using boulders as sedimentary signatures of palaeo tsunami events and the most commonly used transport equations typically suggest that large boulder deposits are products of tsunami rather than storms there is growing empirical evidence demonstrating on inter annual to century timescales that storm waves are capable of transporting and depositing boulders of significant size at elevations well above sea level current process studies of how boulders are eroded transported and deposited have not received wide attention by rock coast geomorphologists or palaeoenvironmental reconstruction scientists this special issue is framed around the goal of highlighting our current understanding of the role of storm waves as a driving mechanism for boulder erosion transport and deposition here we review the current state of knowledge about boulder dynamics boulder responses to storms and boulders as sedimentary signatures of storm events we identify gaps in our conceptual and quantitative understanding lastly we propose means of addressing research gaps improving consistency between researchers and collecting multi purpose data this review and the papers contained within the special issue provide an improved understanding of coastal dynamics particularly the role storms can play in influencing erosion rates and depositional patterns of coarse material i e boulders or larger which has hitherto been under represented in the literature

sand invasion along the portuguese coast forced by westerly shifts during cold climate events phases of higher aeolian activity are responsible for the formation and movement of large transgressive dunefields well reported phases of aeolian activity in northwest europe are coincident with global cooling events and were related to enhanced westerly winds and storminess however the extent to which these climatic episodes influenced dunefield dynamics in southwest europe remains an open question ground penetrating radar gpr was used to image the stratigraphy of a cliff top coastal transgressive dunefield in portugal and reconstruct former windfield regimes using optically stimulated luminescence osl five major phases of aeolian activity were dated at 12 6 5 6 1 2 0 4 and 0 3 ka and related to coastal instability and enhanced westerlies these phases were later reconciled to favorable patterns of atmospheric circulation simulated by global and regional climate models at both synoptic and local scales respectively the results prove that major phases of aeolian activity in southwest europe are associated with the onset of cold climate events of global distribution coinciding with aeolian accumulation in northwest europe this implies the dominance of zonal westerlies along the western coast of europe from denmark to portugal during the onset of cold climate events model simulations suggest that the pattern of atmospheric circulation during periods of enhanced aeolian activity is compatible with prolonged negative phases of the north atlantic oscillation nao

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

optically stimulated luminescence dating of large storm events in northern scotland climate changes over the holocene have directly impacted on both coastal processes and human use of coastal areas this paper presents results from the dating of wind blown sand deposits collected from coastal and archaeological sites in northern scotland archaeological remains are frequently found interspersed with sand deposits and represent distinct periods of occupation of settlement sites within the local landscapes in some cases storm events sufficiently inundate the sites with sand to result in periodic abandonment storm events can also have dramatic results on adjacent rock coastlines with storm boulder ridges emplaced by large waves burying sand deposits on cliff top sites work has been undertaken using a quartz sar protocol to date sand deposition at two archaeological sites in orkney and a cliff top site in shetland these dates provide chronological information which help to construct regional chronologies of climatic instability and environmental change and allow the sar osl method to be assessed as an accurate sediment dating tool in this context

redox control of arsenic mobilization in bangladesh groundwater abstract detailed hydrochemical measurements 34sso4 and 3h analyses were performed on 37 groundwater samples collected during february 1999 january and march 2000 from 6 locations in eastern and southeastern bangladesh to examine redox processes that lead to as mobilization in groundwater the study sites were chosen based on available nation wide as surveys to span the entire spectrum of as concentrations in bangladesh groundwater and to represent 3 of 5 major geological units of the ganges brahmaputra delta uplifted pleistocene terrace fluvial flood plain and delta plain arsenic was found to be mobilized under fe reducing conditions in shallow aquifers 50 g l or 0 7 m were always accompanied by high dissolved hco3 4 mm and were close to saturation with respect to calcite groundwater enriched in as 200 800 g l or 2 7 10 7 m and phosphate 30 100 m but relatively low in dissolved fe 5 40 m probably resulted from re oxidation of reducing as and fe enriched water this history was deduced from isotopic signatures of 34sso4 and 3h2o 3h to delineate the nature of redox changes for some of the reducing groundwaters in contrast as is not mobilized in presumed pleistocene aquifers both shallow 30 60 m and deep 150 270 m because conditions were not reducing enough due to lack of sufficient o2 demand

patterns and rates of erosion produced by high energy wave processes on hard rock headlands the grind of the navir shetland scotland abstract the grind of the navir is an ignimbrite headland on the exposed atlantic coast of the shetland islands scotland during storms offshore wave heights exceed 20 m and deep water close inshore allows high energy waves to impact on these cliffs the cliff top at 15 m above sea level is awash with wave water when wave heights exceed 8 m a condition met in storms in most years detailed mapping ground photography and patterns of lichen colonisation and growth allow the processes patterns and rates of erosion to be assessed on different parts of the headland over the past 100 years recent fractures in the rock of the cliff face and top indicate that wave impact forces exceed the 1 5 kpa tensile strength of the rock and fresh sockets low on the cliff face record the removal of fracture bounded blocks that are lost to seaward on the upper part of the cliff face upward moving water flow is capable of removing blocks from both vertical faces and stepped overhangs clefts in the cliff face are extended inwards and upwards by crack propagation and block removal leading to the development of slot caves the movement of waves across the cliff top in fast moving bores quarries blocks from the cliff face close to the edge and from rock steps on the cliff top promoting further rock fracturing socket sizes and block characteristics indicate that blocks of 1 m 3 are rotated from sockets on the cliff top platform and carried landwards for up to 60 m to be deposited in a series of boulder ridges on the cliff top multiple boulder movements during a storm in january 2005 generated impact marks and orientated striations that allow the pattern of water movement to be reconstructed across considerable areas of cliff top the average rate of erosion at the grind is estimated at 1 3 6 0 mm yr on the cliff face and 5 mm yr on the cliff top although erosion rates vary in both time and space although block movement on the cliff top occurs in most years erosion of rock by block removal is most active during major storms nevertheless some parts of the cliff top and face remain blackened by lichen and so have experienced little recent erosion over the last 70 years or so although erosion occurs at the base of the cliffs in recent decades it has been concentrated on upper part of the cliff face and top cliff top erosion is most intense where stepped geos act as channels for waves to access the cliff top the most active features on the cliff top are the boulder ridges where substantial changes can be traced to storms over the past century unlike conventional models of cliff erosion where erosion is concentrated by wave attack at the waterline wave impacts on this headland may occur on any part of cliff face and top and appear particularly effective on the upper cliff and cliff top platform

8000 years of environmental evolution of barrier lagoon systems emplaced in coastal embayments nw iberia the rocky and indented coast of nw iberia is characterized by the presence of highly valuable and vulnerable small and shallow barrier lagoon systems structurally controlled the case study was se

the role of relative sea level rise and changing sediment supply on holocene gravel barrier development the example of porlock somerset uk the holocene development of the coastal system at porlock has been driven by variations in the rate of relative sea level rise providing a long term control on longshore sediment supply which in t

identification of aniakchak alaska tephra in greenland ice core challenges the 1645 bc date for minoan eruption of santorini pearce nicholas westgate j a eastwood w j preece s j 2006 identification of aniakchak alaska tephra in greenland ice core challenges the 1645 bc date for minoan eruption of santorini geochemistry geophysics and geosystems 5 pp q03005 rae2008

cliff top megaclast deposits of ireland a record of extreme waves in the north atlantic storms or tsunamis past occurrences of major tsunami in the global record have often been inferred from the presence of megaclast accumulations at significant heights above sea level which sometimes exhibit a pronounced seaward directed imbricate fabric the aran islands off the west coast of ireland exist in a marine environment which is totally unprotected from the most extreme sea states encountered in the north atlantic spectacular megaclast accumulations are found along the tops of vertical cliffs on these islands the elevation of these deposits varies from 0 m to 50 m above mean sea level and they include clasts weighing 250 tonnes at sea level over 117 tonnes at 12 m and 2 9 tonnes at 50 m above sea level imbrication measurements on these megaclasts indicate a well defined and consistent mean direction from the southwest for the emplacing waves one that is consistent with the prevalent storm wind direction for the area the megaclast accumulations are subject to episodic and on going erosion by cliff retreat but the existing accumulations are estimated to record events since at least 1839 recent emplacement and reworking is evidenced by trapped plastic detritus within the deposits and eyewitness accounts of large storms during which clasts have been emplaced similar deposits are found on the exposed coasts of the shetland and orkney islands off scotland there is at present no evidence of any tsunami in recorded history affecting the western irish and scottish coasts other than those generated by the lisbon earthquake of 1755 where the wave effects were slight thus the presence of megaclast accumulations at significant heights above sea level on exposed coasts and exhibiting imbrication should not be used as a definitive criterion for the past occurrence of tsunami these deposits attest to extreme wave conditions occasionally encountered in the north atlantic and act as a record of such events extending back at least 160 years such data on extreme wave conditions are essential for the prediction of the effects of deepwater waves on structures such as offshore drilling platforms

extremely high energy wave deposits inside the great barrier reef australia determining the cause tsunami or tropical cyclone abstract a hydrodynamic approach is used to determine whether tsunami or cyclone generated waves were responsible for the deposition of fields of well imbricated rock boulders up to 290 tonnes along the coast of cairns inside the great barrier reef australia calculations of the overturning moments show that only tsunami are capable of moving such large boulders in this environment it is hypothesised that large tsunami 11 m have been able to penetrate the great barrier reef through wide 5 10 km 50 70 m deep passages between individual reefs three such passages each approximately 35 km apart and oriented in the same direction exist in the cairns region it is possible that these passages have funnelled and amplified palaeotsunamis the preferential location of eroded coral boulders up to 3 m in length on reef flats alongside these passages and their absence on other reefs throughout the region provide further evidence that extremely high energy waves have been able to penetrate the great barrier reef into the inner channel adjacent to the mainland carbon 14 ages of the coral boulders on these reef flats matches closely the ages of coral fragments pinned below the very large rock boulders along the coast these ages suggest that the cairns region has experienced large tsunami twice over the last millennium

observations of morphological change and sediment transport on a steep gravel beach abstract observations of morphological change and swash sediment loads concurrent with measurements of water level waves and currents were obtained during a spring to spring tidal cycle on a steep macrotidal gravel beach in southwest england the wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0 4 m and 6 s respectively incident frequency water motions dominated the hydrodynamics and the phasing between water surface elevation and cross shore and alongshore currents was inconsistent with standing edge wave motion morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified regression and rollover in response to falling and rising water levels respectively and removal and reformation during and after storms respectively swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1 kg per swash onshore per unit metre beach width steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches

late holocene north atlantic climate seesaws storminess changes and greenland ice sheet gisp2 palaeoclimates the oxygen isotope record of palaeotemperature from greenland ice cores has for many years been the kingpin of climate reconstructions for the north atlantic region and northern europe an air temperature seesaw between greenland and northern europe first described in ad 1765 is also well known and is related to the north atlantic oscillation nao whereas the nao index series is based on instrumental records of air pressure the north atlantic climate seesaw has conventionally been based on air temperature records here we describe relationships between this seesaw mechanism and the greenland gisp2 oxygen isotope chronology of air temperature variations as well as relationships between gisp2 na sea salt variations and instrumental records of north atlantic storminess the gisp2 proxy air temperature record is calibrated for the last 130 years with instrumental weather records for west greenland while the na series is compared with instrumental records of north atlantic storminess change reconstruction of an annual series of these climate parameters for the last 1000 years shows that during the mediaeval warm period there were no years characterized by high na extremes high north atlantic storminess but there were many years when there were extremes of temperature remarkably there were no years of exceptionally low air temperature and high na precipitation at gisp2 between ad 1650 and 1710 a period of time that in northern europe incorporates the period of maximum little ice age cooling it would appear also that for the last thousand years the most extreme seesaw winters when gisp2 temperatures were very low and na concentrations were high occurred in discrete clusters and pairs of years

mobility of arsenic in west bengal aquifers conducting low and high groundwater arsenic part ii comparative geochemical profile and leaching study aquifer sediments from areas of low and high as groundwater were characterized mineralogically and geochemically at a field site in the nadia district of west bengal india leaching experiments and selective extraction of the sediments were also carried out to understand the release mechanism of as in the sub surface the correlation between measured elements major minor and trace from low and high as groundwater areas are only significant for as fe and mn the borehole lithology and percentage of silt and clay fraction demonstrates the dominance of finer sediments in the high as aquifer multivariate analysis of the geochemical parameters showed the presence of four different mineral phases heavy mineral fraction phyllosilicates biotite fe oxyhydroxides carbonates and sulphides in the sediments selective extraction of sediment reveals that amorphous fe oxyhydroxide acts as a potential sink for as in the sub surface the result is consistent with microbially mediated redox reactions which are controlled in part by the presence of natural organic matter within the aquifer sediments the occurrences of as bearing redox traps primarily formed of fe and mn oxides hydroxides are also important factors that control the release of as into groundwater at the study site

an analysis of the gravity field and tectonic evaluation of the northwestern part of bangladesh abstract the total bouguer anomaly values of the northwestern part of bangladesh have been analysed on the basis of the trend shape and magnitude of the anomaly values residual gravity and the second vertical derivatives of gravity show only two near surface features viz the nilphamari and rangpur highs geological models of the two highs have been constructed on the basis of gravity modelling gravity data in conjunction with aeromagnetic and bore hole data enable us to propose four tectonic elements of the northwestern part of bangladesh the northern slope of the platform the stable platform the nawabganj gaibandha intracratonic high and the southern part of the platform

trace element composition of single glass shards in distal minoan tephra from sw turkey volcanic glass from the seventeenth century bc c 3600 bp minoan eruption of santorini thera has been recovered from a 4 cm thick tephra deposit at golhisar golu a small lake in sw turkey analysis of single grains of this glass by laser ablation inductively coupled plasma mass spectrometry la icp ms provides for the first time an accurate determination of the trace element composition of the juvenile glass component of this eruption free from contaminants such as phenocrysts or detrital material individual glass shards 150 m show a large degree of variation in their trace element composition indicative of substantial small scale compositional heterogeneity in the magma this is a result of the proximity of crystallizing phases and provides insights into the chemical evolution of the minoan magma the range of elemental compositions displayed by individual glass shards combined with the consistency of many trace element ratios are characteristics of the minoan glass these features provide a trace element signature for the minoan tephra which will be of value in stratigraphic correlation across the eastern mediterranean

modeling the accumulation and dynamics of beaches on shore platforms a mathematical model was used to study the development and dynamics of beaches on shore platforms the model was based on assumptions that the gradient of the beachface at its seaward edge must be greater than platform gradient beach sediment tends to move landwards and beach occurrence and extent depends upon the amount of sediment available equilibrium beachface gradient was related to breaker height wave period and sediment grain size three grain sizes were used representing fine and coarse sand and pebble two deep water wave sets representing storm wave and west coast swell wave environments and two tidal ranges of 9 1 and 3 3 m runs were made using linear concave and convex platform profiles with gradients ranging between about 0 6 and 8 because platform and beachface gradients are normally quite similar shore platforms are unable to store much sediment for a linear platform with a lower gradient than the beachface sediment first accumulates at the cliff base and then depending on the sediment available extends increasingly seawards beach development first occurs on the gently sloping seaward portions of concave platforms and on the more landward portions of convex profiles the amount of available material partly determines the landward and seaward extent of these beaches respectively although it is also controlled by beachface and platform gradients beaches on shore platforms become thinner and more gently sloping during storms and they may disappear completely depending on such factors as sediment grain size platform gradient the amount of sediment that can be stored during calm conditions wave characteristics and the duration of the storm the response of beaches on rocky coasts to rising sea level will be different from those on sedimentary coasts and will depend in part on the morphology of the rocky foundation

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

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

storminess and vulnerability along the atlantic coastlines of europe analysis of storm records and of a greenhouse gases induced climate scenario abstract identification of the distinctive circulation patterns of storminess on the atlantic margin of europe forms the main objective of this study dealing with storm frequency intensity and tracking the climatology of the extratropical cyclones that affect this region has been examined for the period 1940 1998 coastal meteorological data from ireland to spain have been linked to the cyclone history for the north atlantic in the analysis of storm records for european coasts the study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the north atlantic oscillation nao results indicate a seasonal shift in the wind climate with regionally more severe winters and calmer summers established this pattern appears to be linked to a northward displacement in the main north atlantic cyclone track an experiment with the echam4 a gcm at high resolution t106 has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region the experiment consists of 1 a 30 year control time slice representing present day equivalent co 2 concentrations and 2 a 30 year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent co 2 concentrations the boundary conditions have been obtained from an atmosphere ocean coupled oa gcm simulation at low horizontal resolution an algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones for most of the northern part of the study region covering ireland and scotland results describe the establishment by ca 2060 of a tendency for fewer but more intense storms the impacts of these changes in storminess for the vulnerability of european atlantic coasts are considered for low lying exposed and soft sedimentary coasts as in ireland these changes in storminess are likely to result in significant localised increases in coastal erosion

magnitude and frequency of extra tropical north atlantic cyclones a chronology from cliff top storm deposits cliff top storm deposits ctsds are known to occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles eye witness accounts and time series field mapping of ctsds demonstrate their formation over the historical period and their continued modification during major storms with ctsds burying a range of modern human derived debris older deposits show surface lichen growth and weathering effects that relate to the relative age of ctsds over longer time spans buried sand and peat deposits provide dates on phases of ctsd emplacement and mobilisation and so provide an indication of the frequency and timing of the most severe storms two adjacent sites in shetland provide a combination of 14c dates on peat buried beneath storm deposited boulders 14c dates on marine shells buried inside ctsd boulder ridges and optically stimulated luminescence osl ages on sands intercalated with storm derived boulders although the precision is low this evidence identifies phases of exceptional storm activity spanning approximately 400 550 700 1050 1300 1900 and since 1950 ad by the very nature of cliff top erosion and deposition these records are fragmentary yet the timeline of major storms recorded in the shetland cliffs matches fairly well with the more general record of storminess in the north atlantic derived from the sea salt record in the gisp2 ice core as such ctsds represent an overlooked archive of storm sedimentation with the potential to elucidate local storm chronologies as well as informing debate surrounding the palaeo tempestology and impact of major cyclones and hurricanes

geomorphological control on boulder transport and coastal erosion before during and after an extreme extra tropical cyclone extreme wave events in coastal zones are principal drivers of geomorphic change evidence of boulder entrainment and erosional impact during storms is increasing however there is currently poor time coupling between pre and post storm measurements of coastal boulder deposits importantly there are no data reporting shore platform erosion boulder entrainment and or boulder transport during storm events rock coast dynamics during storm events are currently unexplored here we use high resolution daily field data to measure and characterize coastal boulder transport before during and after the extreme northeast atlantic extra tropical cyclone johanna in march 2008 forty eight limestone fine medium boulders n 46 and coarse cobbles n 2 were tracked daily over a 0 1 km2 intertidal area during this multi day storm boulders were repeatedly entrained transported and deposited and in some cases broken down n 1 or quarried n 3 during the most intense days of the storm eighty one percent n 39 of boulders were located at both the start and end of the storm of these 92 were entrained where entrainment patterns were closely aligned to wave parameters these data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions no statistically significant relationship was found between boulder size mass and net transport distance graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold other factors influence transport distance paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance where net transport distances were up to 39 times less where geomorphological control was greatest these results have important implications for understanding and for accurately measuring and modelling boulder entrainment and transport coastal managers require these data for assessing erosion risk 2016 the authors earth surface processes and landforms published by john wiley sons ltd

shore platform abrasion in a para periglacial environment galicia northwestern spain abstract the schmidt rock test hammer was used to study the effect of abrasion on shore platforms in galicia northwestern spain on platforms where tidally induced weathering salt wetting and drying etc is dominant rock strength is significantly lower than in areas where abrasion is or has been active in the recent past this suggests that abrasion removes weathered surface material exposing the stronger less weathered rock below abrasion downwearing measured with a transverse micro erosion meter ranged between 0 13 and 1 8 mm yr 1 over the last year most active abrasion occurs in the upper part of the intertidal zone but weathering is slowly destroying formerly abraded surfaces at lower elevations these abandoned surfaces were abraded by materials supplied by erosion of fluvio nival and periglacial slope deposits that covered or partially covered parts of the galician coast during the middle and late weichselian during the holocene rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level the spatial and temporal role of abrasion on this coast is therefore closely associated with the exhumation and inheritance of ancient platform surfaces from beneath weichselian deposits

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

bacteria in deep coastal plain sediments of maryland a possible source of co2 to groundwater nineteen cores of unconsolidated coastal plain sediments obtained from depths of 14 to 182 m below land surface near waldorf maryland were collected and examined for metabolically active bacteria the age of the sediments cored range from miocene to early cretaceous acridine orange direct counts of total viable and nonviable bacteria in core subsamples ranged from 108 to 104 bacteria g of dry sediment direct counts of viable bacteria ranged from 106 to 103 bacteria g of dry sediment three cores contained viable methanogenic bacteria and seven cores contained viable sulfate reducing bacteria the observed presence of bacteria in these sediments suggest that heterotrophic bacterial metabolism with lignitic organic material as the primary substrate is a plausible source of co2 to groundwater however the possibility that abiotic processes also produce co2 cannot be ruled out estimated rates of co2 production in the noncalcareous magothy upper patapsco and lower patapsco aquifers based on mass balance of dissolved inorganic carbon groundwater flow rates and flow path segment lengths are in the range 10 3 to 10 5 mmol l 1 yr 1 isotope balance calculations suggest that aquifer generated co2 is much heavier isotopically 10 to 5 per mil than lignite 24 per mil present in these sediments this may reflect isotopic fractionation during methanogenesis and possibly other bacterially mediated processes

arsenic enrichment and mobilization in the holocene alluvial aquifers of the chapai nawabganj district bangladesh a geochemical and statistical study abstract core sediments from three boreholes to a depth of 50 m and groundwater from 20 as enriched water wells were collected in the chapai nawabganj area of northwestern bangladesh for geochemical analyses multivariate statistical analyses including factor analysis cluster analysis and multidimensional scaling were applied to the hydrogeochemical data the results show that a few factors adequately represent the traits that define water chemistry sodium cl so4 total dissolved solids tds and electrical conductivity ec are grouped under the first factor representing the salinity sources of waters the second factor represented by as and mn is related to as mobilization processes the third factor of fe and alkalinity is strongly influenced by bacterial fe iii reduction which would raise both fe and hco 3 concentrations in water the fourth factor of ca and mg reflects the hardness of the ca hco3 type of groundwater which is confirmed by the hydrochemical facies analysis cluster analysis leads to the formulation of four water types including highly moderately and slightly as enriched groundwater as well as groundwater with elevated so 4 2 from anthropogenic sources multivariate analyses of the geochemical parameters suggest that fe and mn oxyhydroxides and mineral phases of phyllosilicates e g biotite are the main hosts of as in the sediments statistical analysis also shows that as is closely associated with fe and mn in sediments while as is positively correlated with mn in groundwater these correlations along with results of sequential leaching experiments suggest that reductive dissolution of mnooh and feooh mediated by anaerobic bacteria represents an important mechanism for releasing as into the groundwater

distinguishing tsunami and storm deposits an example from martinhal sw portugal abstract geological identification of past tsunamis is important for risk assessment studies especially in areas where the historical record is limited or absent the main problem when using the geological evidence is to distinguish between tsunami and storm deposits both are high energy events that may leave marine traces in coastal stratigraphic sequences at martinhal sw portugal both storm surge and tsunami deposits are present at the same site within a single stratigraphic sequence which makes it suitable to study the differences between them excluding variations caused by local factors the tsunami associated with the lisbon earthquake of november 1st 1755 ad had a major impact on the geomorphology and sedimentology of martinhal it breached the barrier and laid down an extensive sheet of sand as described in eyewitness reports besides the tsunami deposit the stratigraphy of martinhal also displays evidence for storm surges that have breached and overtopped the barrier flooding the lowland and leaving sand layers both marine derived flood deposits show similar grain size characteristics and distinctive marine foraminifera the most important differences are the rip up clasts and boulders exclusively found in the tsunami deposit and the landward extent of the tsunami deposit that everywhere exceeds that of the storm deposits identification of both depositional units was only possible using a collection of different data and extensive stratigraphical information from cores as well as trenches

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

competing mechanisms for boulder deposition on the southeast australian coast this study investigates the role of late holocene sea level change large storms and possible pre historic tsunami in the deposition of boulder features on an exposed headland and sheltered rock ramp large accumulations of boulders are found on coastal rock platforms cliff tops and ramps in the jervis bay region of southeastern australia these deposits are elevated above sea level and in places exhibit obvious signs of imbrication as a response to flow in a landward direction the event history of these features is controversial and holocene sea level change storms and tsunami can be considered as possible non mutually exclusive mechanisms of deposition it is apparent that even if the detachment site transport distance elevation and final orientation of a boulder can be identified deciphering the event history remains a difficult task

late holocene storm imprint in a coastal sedimentary sequence northwest iberian coast a combination of sedimentological geomorphological and pedological methods has been used to study a late holocene sedimentary sequence in a rock coast sector from nw spain with the aim of relating it to storm events and their morphodynamic effects the sequence contains two coarse beach layers at an elevation of 2 8 3 5 m above the present highest astronomical tide hat radiocarbon dating revealed that their deposition had begun during 1735 1590 cal yr bp and has continued until the present the entire beach system experienced considerable morphological change after 1320 1230 cal yr bp with a westward displacement of the beach and a retreat of the sedimentary cliff in the eastern section the two beach layers seem to have been formed by vertical aggradation of clasts and sand during high energy storm events highlighting the role of these events in the formation of sedimentary sequences on the rocky coasts of mid atlantic europe the effects of a recent storm event recorded in march 2008 and the

the tsunami hypothesis comparisons of the field evidence against the effects on the western australian coast of some of the most powerful storms on earth the tsunami hypothesis proposes that prehistoric tsunamis may have been larger than historic ones along coasts normally historically not associated with major tsunamis the evidence for the hypothesis rests with the types of unusual sedimentary deposits and erosional forms along coasts where the largest historic and prehistoric storm waves do not appear capable of forming the features this is especially the case at locations where boundary conditions i e offshore water depth coastal geomorphology and meteorological limitations are not conducive to the propagation of sufficiently large storm waves at the shore the tsunami hypothesis has been barely debated in the literature this is despite the view of some who suggest that storms have been overlooked or underestimated as a cause few comparisons have been made of the supposed tsunami generated features and the impacts on coasts of extreme intensity storms four of the most powerful tropical cyclones anywhere in the world in recent times struck the western australian coast between 1999 and 2002 the results of post event surveys of these storms showed that none of them produced the enigmatic forms attributed elsewhere to tsunamis

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

sedimentology of rocky shorelines 1 a review of the problem with analytical methods and insights gained from the hulopoe gravel and the modern rocky shoreline of lanai hawaii abstract hypotheses advanced concerning the origin of the pleistocene hulopoe gravel on lanai include mega tsunami abandoned beach multiple event rocky shoreline and for parts of the deposit native hawaiian constructions and degraded lava flow fronts uplift of lanai shorelines has been suggested for deposits occurring up to at least 190 m these conflicting hypotheses highlight problems with the interpretation of coarse gravel deposits containing marine biotic remains the geological records of the processes implied by these hypotheses should look very different discrimination among these or any other hypotheses for the origins of the hulopoe gravel will require careful study of vertical and lateral variations in litho and biofacies facies architecture contact relationships and stratal geometries of this deposit observations of modern rocky shorelines particularly on lanai adjacent to hulopoe gravel outcrops have shown that distinctive coarse gravel facies are present several of which occur in specific geomorphic settings tectonic isostatic and eustatic changes which cause rapid shoreline translations on steep slopes favour preservation of former rocky shorelines and associated sedimentary deposits both above and below sea level the sedimentary record of those shorelines is likely to be complex the modern rocky shoreline sedimentary environment is a hostile one largely neglected by sedimentologists a range of high energy processes characterize these shorelines long period swell tsunami and storm waves can erode hard bedrock and generate coarse gravel they also erode older deposits depositing fresh ones containing mixtures of materials of different ages additional gravelly material may be contributed by rivers draining steep hinterlands to fully evaluate rocky shoreline deposition in the broadest sense for both the hulopoe gravel and other deposits sedimentary facies models are needed for rocky shorelines occurring in a range of settings recognition and description of rocky shoreline deposits are crucial for correctly interpreting the geological history of oceanic and volcanic arc islands for distinguishing between ancient tsunami and storm deposits and for interpreting coarse grained deposits preserved on high energy coasts of continents problems include not only the absence of appropriate sedimentary facies models linking rocky shoreline deposits and environments but also until recently lack of a systematic descriptive scheme applicable to coarse gravel deposits generally two complementary methods serve to integrate the wide range of bed and clast attributes and parameters which characterize complex coarse gravel deposits the composition and fabric caf method has a materials focus providing detailed description of attributes of the constituent clasts petrology the proportions of gravel sand and mud and the ways in which these materials are organized the sedimentary facies model building fmb method emphasizes the organization of a deposit on a bed by bed basis to identify facies and infer depositional processes the systematic use of a comprehensive gravel fabric and petrography log gfpl in conjunction with detailed vertical profiles provides visual representations of a range of deposit characteristics criteria useful for distinguishing sedimentary facies in the hulopoe gravel are grain size modes amount of matrix bed geometry sedimentary structures bed fabric and clast roundness

arsenic incorporation into authigenic pyrite bengal basin sediment bangladesh abstract sediment from two deep boreholes 400 m approximately 90 km apart in southern bangladesh was analyzed by x ray absorption spectroscopy xas total chemical analyses chemical extractions and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the bengal basin authigenic framboidal and massive pyrite median values 1500 and 3200 ppm as respectively is the principal arsenic residence in sediment from both boreholes although pyrite is dominant ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment bound arsenic between approximately 20 and 100 m which is the depth range of wells containing the greatest amount of dissolved arsenic the lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources the ability of deeper aquifers 150 m to produce ground water with low dissolved arsenic in southern bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis

the last 3000 years in the ria de vigo nw iberian margin climatic and hydrographic signals the hydrographic evolution of the r o a de vigo nw spain during the last 3000 years has been reconstructed using benthic foraminiferal assemblages stable oxygen isotopes molecular biomarkers and sea surface temperatures sst reconstructed from the u k9 37 index benthic oxygen isotopes and sst records provide evidence of episodic salinity contrasts between surface and bottom waters the comparison of ssts with other climate records for the northern hemisphere has allowed the inference of oceanographic and climatic signals which describe the changes in hydrographic conditions of the r oa in general two different periods can be recognized from 975 cal bc to cal ad 1000 the organic carbon is mainly of continental origin benthic foraminiferal assemblages are typical of environments that are poorly oxygenated rich in organic matter and dominated by eurihaline taxa percentages of planktonic foraminifera are low and ssts are warmer than today these data suggest a restricted environment where the exchange with open ocean waters was diminished at cal ad 1000 an important hydrographic change in the r oa circulation involved an intensie cation of coastal upwelling processes as ree ected in colder ssts and increases in the contribution of marine organic carbon and planktonic and opportunistic benthic foraminifera in these conditions the sediments of the r oa recorded not only local factors but also several well known northern hemisphere climate signals

climate change and coastal hydrographic response along the atlantic iberian margin tagus prodelta and muros ria during the last two millennia the tagus prodelta w portugal and the muros ro a nw spain are areas of high deposition rates registering high resolution palaeoclimatic records for western iberia we compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature sea surface temperatures and oxygen isotopes continental input grain size iron and magnetic susceptibility and productivity inorganic and organic carbon carbon isotopes benthic foraminifera and diatoms biogeochemical changes in the tagus prodelta reflect widely recognized north atlantic climatic periods encompassing the roman period ad 0 350 the dark ages ad 400 700 the mediaeval warm period mwp ad 800 1200 and the little ice age lia ad 1300 1750 the atmospheric north atlantic oscillation nao drives the tagus prodelta multidecadal long term variability in precipitation river input during cold periods negative nao and marine upwelling during warmer periods positive nao a scheme that is reversed in the galician region the muros ro a shows only local hydrodynamics until ad 1150 including a suboxic event in the inner ro a around ad 500 700 since ad 1150 atlantic warm upwelled waters have ventilated the outer ro a but only reach the inner ro a at ad 1750 the twentieth century records are also interpreted as a reflex of the inverse nao mode in both areas resulting in amplification of the lia biogeochemical water conditions centennial scale solar activity appears to be another important forcing mechanism or the only one if solar activity drives the nao and bond cycles behind changes in the hydrography of the tagus prodelta and primary production bottom ventilation and organic carbon degradation in the muros ro a

a wave competence approach to distinguish between boulder and megaclast deposits due to storm waves versus tsunamis abstract size and mass of boulders and megaclast deposited from intense wave events of the past coupled with measures of depositional elevation and transport distance are useful metrics to distinguish between tsunami or storm wave period this outcome provides for a wave competence scaling approach to better help distinguish between large storms and tsunamis because wave period for tsunamis and wind driven storm waves differ by an order of magnitude however wave competence equations are simple linear approximations of a complex non linear processes hence interpretations of the results need to be taken carefully at best they may help approximate wave forcing based on size of material transported coupled with other pieces of information gained from stratigraphy imbrications and morphology of boulder and megaclast deposits as well as aging techniques for temporal correlation with known storms and or tsunamis the focus here is to present a conceptual example of how to apply a wave competence approach to a beach exposed to both tsunamis and major storm waves and how variance in backshore topography hills and valleys and source material sea cliff erosion and scree slope development may play into interpreting the mathematical results

evolution and inheritance of a rock coast western galicia northwestern spain there is increasing evidence that shore platforms and other elements of rock coasts may be inherited at least in part from interglacial stages when sea level was similar to today s most of this evidence which includes ancient beaches and datable terrestrial deposits has been obtained from areas of resistant slowly eroding rock where the platforms often appear to be much too wide to have developed since the sea reached its present level it is much more dif cult to demonstrate that inheritance has occurred in areas of weaker rock which generally lack any datable material the coast of western galicia in northwestern spain has shore platforms in igneous and metamorphic rocks that were deeply weathered during the tertiary these platforms are closely associated with ancient beaches from the last interglacial stage and associated periglacial and uvio nival deposits that covered and fossilized most of the eemian platforms and cliffs during the late middle and late weichselian glacial stage the sedimentary processes and the thickness and facies of the sediments were determined by the height aspect and gradient of the coastal mountains and their distance from the coast radiocarbon dating sedimentary analysis and platform morphology indicate that the shore platforms of galicia have been inherited from at least the last interglacial stage they were fossilized in places beneath thick weichselian deposits and then exhumed during the holocene transgression the abundant evidence for inheritance in galicia has important implications for other coasts in fairly weak rocks where such evidence is generally lacking copyright 2003 john wiley sons ltd

chemical differences between the island and submarine pumice layers of thera abstract investigations on tephra layers of deep sea cores from near the island of santorini showed that only the pumice clasts from the west of the island can be attributed to the minoan eruption the tephra layers within the caldera are of uncertain origin

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions

reactive transport of trace elements and isotopes in the eutaw coastal plain aquifer alabama 1 we integrate groundwater geochemistry mineralogy and numerical modeling techniques to study the reactive transport of heavy metals and isotopes in the eutaw coastal plain aquifer alabama geochemical data show that the elevated concentrations of fe mn and sr can be correlated with high ph and alkalinity these geochemical correlations suggest that that elevated metal concentrations may be derived from bacterial iron and manganese reduction geochemical modeling of bacterial fe iii and mn iv reduction shows that the biotransformation of iron and manganese minerals could control mobility and concentrations of fe and mn in coastal plain aquifers petrographic sem and edax studies of sediments show the formation of biogenic siderite rhodochrosite and pyrite in sediments associated with fe and mn rich groundwater rhodochrosite and siderite occur together as spheroids 1 0 mm in which rhodochrosite forms the center and siderite forms an outer rind which is consistent with the redox sequence of mineral precipitation predicted by the geochemical modeling the low 13c ratios of siderite and rhodochrosite 14 4 to 15 4 pdb and groundwater dic 20 6 to 14 1 pdb imply carbon of biogenic origin higher dic 13c levels are found to be correlated with elevated fe and mn concentrations and high ph values of groundwater this unexpected result implies novel carbon isotopic fractionation processes associated with bacterial fe iii reduction we used 36cl cl ratios of groundwater and isotope transport modeling to calculate the residence time of regional groundwater in the eutaw aquifer the calculation considering the natural decay only would yield 36cl levels that are significantly higher than field data suggesting that a significant mixing with cl rich older groundwater at depth is an important reason for substantial 36cl depletion along flow path

millennial surface water dynamics in the ria de vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers a combined study of coccolith assemblages and biomarkers in a gravity core collected from the ria de vigo nw spain allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years the quantitative distribution of coccolithophore species points to three different intervals within the core dated by ams radiocarbon measurements the first interval ca 975 bc 252 ad characterized by high abundances of calcidiscus leptoporus and gephyrocapsa muellerae i s thought to represent moderate water temperatures suggesting a transition from a warmer to a cooler period the second interval ca 252 1368 ad characterized by the dominance of coccolithus pelagicus helicosphaera carteri and syracosphaera spp and a high concentration of hexacosanol linked to terrestrial input is interpreted as having been a humid period with fluvial input the third interval ca 1368 ad 1950 is characterized by a high abundance of gephyrocapsa oceanica high alkenone values and low values of hexacosanol and is thought to represent a period dominated by oceanic conditions within the ria taking into account the ocean atmospheric system affecting the region studied here we propose an alternation in the mean state of north atlantic oscillation nao at millennial time scales awell developed upwelling system and an active ria ocean connection during the warmer interval i suggest a nao phase influenced by a hypsithermal period the occurrence of the humid and relatively warm interval ii is consistent with a negative phase in the nao as well as a relative restriction in ocean ria exchange interval iii which was drier and more productive again suggests the dominance of a positive phase in the nao with a more intense oceanic connection and more energized upwelling d 2004 elsevier b v all rights reserved

distribution geomorphology and lithofacies of cliff top storm deposits examples from the high energy coasts of scotland and ireland abstract cliff top storm deposits ctsds occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles this study examines the distribution geomorphology and lithofacies of ctsds at sites from shetland orkney caithness and the outer hebrides in scotland and from the aran islands in galway bay in ireland ctsds are generated largely by the quarrying of blocks from the cliff top and transported by green water bores across cliff top platforms and ramps to be deposited in backing ridges or as debris spreads maximum boulder sizes reach 48 m 3 but it is likely that much larger blocks can be quarried prior to disintegration during transport eye witness accounts and field mapping demonstrate that formation and modification of ctsds has continued during major storms over recent decades recent ctsds bury a range of man made debris but older deposits lack this and instead show weathering effects that indicate a longer residence time in shetland osl dates on intercalated sands suggest that the oldest ctsds date from 800 ad radiocarbon dates on shell buried inside ctsd ridges relate to major storms between 1700 and 1900 ctsds represent an overlooked archive of storm sedimentation that has great potential for the elucidation of local storm chronologies ctsds also provide evidence of wave impacts on any part of the cliff face or top in fundamental contrast to the concentration of wave action at the cliff foot implicit in traditional models of the erosion of rock coasts

factors responsible for high arsenic concentrations in two groundwater catchments in taiwan abstract high as contents in groundwater were found in two neighboring catchments the chianan plain and the southern choushui river alluvial fan in taiwan the groundwater quality the redox potential and the as distribution of the chianan plain were characterized using factor analysis redox zoning and a geochemical program the results were compared with those of the southern choushui river alluvial fan possible as release mechanisms are also elucidated factors 1 and 2 of the groundwater in the chianan plain the salinization factor and the as enrichment factor are similar to those in the southern choushui river alluvial fan however the spatial distribution of reductive tendency in the chianan plain is different to that in the choushui river alluvial fan and yields spatially distinct hydrogeochemical environments in these two neighboring areas the reduction potential in the chianan plain is stronger than that in the choushui river alluvial fan the difference between the reduction potentials in these two vicinal areas influences the concentrations of as in groundwater the reductive dissolution of as rich fe oxyhydroxide is suggested to be the major mechanism for release of as to the groundwater in the chianan plain and the choushui river alluvial fan of taiwan

historical storminess and climate see saws in the north atlantic region the existence of a well defined climate see saw across the north atlantic region and surrounding areas has been known for over 200 years the occurrence of severe winters in western greenland frequently coincides with mild winters in northern europe conversely mild winters in western greenland are frequently associated with cold winters across northern europe whereas this see saw is normally discussed in terms of air temperature and pressure differences here we explore how the climate see saw is reflected in records of historic storminess from scotland nw ireland and iceland it is concluded that the stormiest winters in these regions during the last ca 150 years have occurred when western greenland temperatures have been significantly below average in contrast winters of reduced storminess have coincided with winters when air temperatures have been significantly above average in western greenland this reconstruction of winter storminess implies a relationship between chronologies of coastal erosion and the history of north atlantic climate see saw dynamics with sustained winter storminess and hence increased coastal erosion taking place when the icelandic low pressure cell is strongly anchored within the circulation of the northern hemisphere considered over the last ca 2000 years it would appear that winter storminess and climate driven coastal erosion was at a minimum during the medieval warm period by contrast the time interval from ca ad 1420 until present has been associated with sustained winter storminess across the north atlantic that has resulted in accelerated coastal erosion and sand drift d 2004 elsevier b v all rights reserved

evaluating the impacts of huge waves on rocky shorelines an essay review of the book tsunami the underrated hazard abstract tsunami the underrated hazard draws together and summarizes a wealth of information about the nature impacts and causes of tsunamis written from a natural hazards perspective the book stresses that large tsunamis can affect even protected coasts that have not experienced large tsunamis historically many deposits and erosional features described and discussed as tsunami signatures have yet to be linked specifically with tsunamis cited references in the book do not necessarily support a tsunami origin for these features because accepted scientific citation practices have not been followed although rocky shorelines in southeastern australia the hawaiian islands and elsewhere generate and preserve a variety of boulder and block deposits and erosional features their sediment dynamics and geomorphology are poorly studied and unequivocal criteria for distinguishing between deposits of storms and tsunamis have yet to be developed despite its shortcomings this book should be on the library shelves of all marine geoscientists who study modern and ancient shorelines however it should be used with great circumspection because the process product relationships it assumes are equivocal

overwash threshold for gravel barriers abstract this paper uses results obtained from the large scale bardex experiments undertaken in the delta flume to investigate the morphological response of a prototype gravel barrier to wave and tidal forcing during overwash conditions gravel barrier behaviour depends upon a number of factors such as sediment properties porosity permeability grainsize geological setting and wave climate since overwash processes are known to control short term gravel barrier dynamics and long term barrier migration the development of a robust quantitative method to define the critical conditions leading to gravel barrier overwashing is important both for scientific and practical management purposes it is known that when wave runup exceeds the barrier crest elevation three outcomes are possible 1 insignificant morphological change when wave runup just overtops the barrier crest and flow velocities are very weak 2 overtopping resulting in accretion on the barrier crest region and barrier stabilisation and 3 overwashing resulting in erosion lowering of the crest region and ultimately to barrier inundation this study provides an insight into the critical conditions that distinguish these two possible outcomes and to the different mechanisms that provide the required positive and negative feedbacks to the sediment dynamics in order to define the overwash threshold condition and to predict the morphological outcome of particular overwash events use is made here of the overwash potential op defined as the difference between the wave runup and the barrier crest elevation to make effective use of op it is necessary to identify a reliable runup predictor following tests using 12 runup equations the stockdon et al stockdon h f holman r a howd p a sallenger a h 2006 empirical parameterization of setup swash and runup coast eng 53 573 588 approach has been identified as the best predictor of runup conditions necessary to generate positive values of op with overtopping and overwashing predicted to occur for average op values of 0 2 m and 0 5 m respectively the use of op values provides a practical means by which to identify potential coastal hazards associated with gravel barrier overwash processes and is considered to have a range of practical coastal management applications

tsunami and palaeotsunami depositional signatures and their potential value in understanding the late holocene tsunami record in recent years much research on modern and palaeotsunami deposits has been published from these studies a range of signature types has been identified identifying and dating such deposits is an important element in understanding late holocene tsunami hazard and risk however important questions such as do modern and palaeotsunami leave similar or dissimilar traces do tsunami leave the same signatures all around the world or are there significant variations and what is the actual record of tsunami in different parts of the world still remain answering these questions is not an easy task but examining megatsunami flood deposits should shed some light on these questions because such high magnitude events should leave very clear and detailed traces within the coastal landscape the coast of se australia is reported to have been affected by numerous palaeomegatsunami in the late holocene as such the coast of new south wales offers an important natural laboratory to examine in detail deposits associated with such events here we summarize the published characteristics of modern and palaeotsunami deposits globally and within australia we briefly outline the tsunami risk to australia before examining a site called minnamurra point on the coastline of se australia south of sydney that has previously been described as containing evidence for a palaeomegatsunami of an unknown age we describe the results of a detailed coastal survey field stratigraphic investigation and various standard laboratory analyses surprisingly we are unable to replicate the previously reported findings of tsunami deposits whilst we prefer the interpretation that the sequence is an in situ soil the sediment sequence examined contains none of the usually reported lines of evidence to demonstrate tsunami provenance we recognize and discuss the significance and difficulty of identifying tsunami deposits in the field and consider the implications of our findings to the wider debate about the preservation of tsunami deposited sediments

sedimentology of rocky shorelines 4 coarse gravel lithofacies molluscan biofacies and the stratigraphic and eustatic records in the type area of the pleistocene hulopoe gravel lanai hawaii abstract during the pleistocene the south flank of lanai was the site of repeated erosion and deposition as a consequence of glacio eustasy superimposed on tectono isostasy throughout this time terrigenous and bioclastic gravel was generated along mainly rocky shorelines gravelly sediment was deposited in topographically low areas of the shoreface and inner shelf that later were uplifted isostatically the sedimentary lithofacies and biofacies in these deposits are distinctive but they represent a deposystem and suite of environments that hitherto have not been studied systematically these unrecognised circumstances have fuelled controversies about the nature and significance of the hulopoe gravel most notably the claim that it represents a mega tsunami deposit the hulopoe gravel in its type area displays a lithofacies succession that encompasses a complete disconformity bounded transgressive regressive cycle on a sand poor rocky shoreline this succession incorporates not only a distinctive vertical assemblage of rocky shoreline litho and biofacies but also internal disconformities that record episodes of erosion and non deposition during shoreline migration repetition of the lithofacies succession imparts overall stratigraphic order to the hulopoe gravel four unconformity bounded transgressive regressive cycles correspond to eustatic highstands of oxygen isotope stages 5 and 7 superimposed on continuing tectono isostatic uplift driven by growth of the island of hawaii this study of the hulopoe gravel demonstrates that the sedimentary record of mixed volcaniclastic carbonate depositional systems developed on rocky shorelines of tropical and subtropical oceanic island coasts can be preserved this record may include depositional products of both transgressive and regressive shorelines although tsunami and giant submarine landslides are known to occur in the hawaiian islands deposits and features that result from tsunami inundation above the shoreline such as might be expected from landslide related mega tsunami have not been recognised in the type area of the hulopoe gravel rocky palaeoshoreline records on oceanic volcanic islands may yield oceanographic and climatic clues that complement data obtained from other palaeoshoreline types

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

mobility of arsenic in a bangladesh aquifer inferences from geochemical profiles leaching data and mineralogical characterization aquifer geochemistry was characterized at a field site in the munshiganj district of bangladesh where the groundwater is severely contaminated by as vertical profiles of aqueous and solid phase parameters were measured in a sandy deep aquifer depth 150 m below a thick confining clay 119 to 150 m a sandy upper aquifer 3 5 to 119 m above this confining layer and a surficial clay layer 3 5 m in the deep aquifer and near the top of the upper aquifer aqueous as levels are low 10 g l but aqueous as approaches a maximum of 640 g l at a depth of 30 to 40 m and falls to 58 g l near the base 107 m of the upper aquifer in contrast solid phase as concentrations are uniformly low rarely exceeding 2 g g in the two sandy aquifers and never exceeding 10 g g in the clay layers solid phase as is also similarly distributed among a variety of reservoirs in the deep and upper aquifer including adsorbed as as coprecipitated in solids leachable by mild acids and reductants and as incorporated in silicates and other more recalcitrant phases one notable difference among depths is that sorbed as loads considered with respect to solid phase fe extractable with 1 n hcl 0 2 m oxalic acid and a 0 5 m ti iii citrate edta solution appear to be at capacity at depths where aqueous as is highest this suggests that sorption limitations may in part explain the aqueous as depth profile at this site competition for sorption sites by silicate phosphate and carbonate oxyanions appear to sustain elevated aqueous as levels in the upper aquifer furthermore geochemical profiles are consistent with the hypothesis that past or ongoing reductive dissolution of fe iii oxyhydroxides acts synergistically with competitive sorption to maintain elevated dissolved as levels in the upper aquifer microprobe data indicate substantial spatial comapping between as and fe in both the upper and deep aquifer sediments and microscopic observations reveal ubiquitous fe coatings on most solid phases including quartz feldspars and aluminosilicates extraction results and xrd analysis of density magnetic separates suggest that these coatings may comprise predominantly fe ii and mixed valence fe solids although the presence of fe iii oxyhydroxides can not be ruled out these data suggest as release may continue to be linked to dissolution processes targeting fe or fe rich phases in these aquifers copyright 2004 elsevier ltd

geomorphologic equifinality a comparison between shore platforms in hoga kusten and faro sweden and the vale of glamorgan south wales uk this paper presents a case study comparing shore platforms of the same lithology and different rock structures limestone with those of different lithologies but similar rock structures limestone dolerite in wales and sweden results of this study illustrate that different erosion mechanisms i e wave action and ice scour produce similar erosion products and meso scale cm m landforms i e stepped shore platforms in structurally similar lithologies in contrast lithologically similar rocks i e limestones generate different meso scale landforms and shore platform morphologies thus structural controls appear to be more critical than lithological controls in generating meso scale erosion products such as rock blocks in this comparative study the similarities in the meso scale geomorphology appear to be caused by uniform rock structure i e rock hardness joint density spacing of bedding horizontal jointing and the slope and direction of bedding horizontal jointing in relation to the sea blocks produced by the jointing have been eroded by high energy waves in the case of wales and drifting sea ice in the case of one of the swedish sites meanwhile different rock structures in a similar lithology i e limestone resulted in very different landforms under the same environmental conditions as the previous example as such this research also provides observational evidence supporting the concept of equifinality

natural arsenic contamination of holocene alluvial aquifers by linked tectonic weathering and microbial processes 1 linked tectonic geochemical and biologic processes lead to natural arsenic contamination of groundwater in holocene alluvial aquifers which are the main threat to human health around the world these groundwaters are commonly found a long distance from their ultimate source of arsenic where chemical weathering of as bearing minerals occurs we propose a gbh as model that ties together all of the important tectonic biologic and hydrologic processes that cause natural as release in groundwater in holocene terrestrial deposits processes highlighted by the gbh as model can explain the movement of arsenic from lithosphere to hydrosphere however we propose a factor that has increased dissolved as concentrations in holocene aquifers to levels where human health is threatened mechanical weathering associated with pleistocene glaciation our model invokes erosion of mountain belts aided by glaciers transport of arsenic by surface waters adsorption of as by stream sediments and deposition of stream sediments and organic matter in alluvial deposits subsequently fe iii reducing bacteria present in alluvial aquifers cause the release of sorbed as to groundwater under moderately reducing conditions

organisational controls typologies and time scales of paraglacial gravel dominated coastal systems abstract the fundamental controls on the initiation and development of gravel dominated deposits beaches and barriers on paraglacial coasts are particle size and shape sediment supply storm wave activity primarily runup relative sea level rsl change and terrestrial basement structure primarily as it affects accommodation space this paper examines the stochastic basis for barrier organisation as shown by variation in gravel barrier architecture we recognise punctuated self organisation of barrier development that is disrupted by short phases of barrier instability the latter results from positive feedback causing barrier breakdown when sediment supply is exhausted we examine published typologies for gravel barriers and advocate a consolidated perspective using rate of rsl change and sediment supply we also consider the temporal variation in controls on barrier development these are examined in terms of a simple behavioural model barch for prograding gravel barrier architecture and its sensitivity to such controls the nature of macroscale 10 2 10 3 years gravel barrier development including inherited characteristics that influence barrier genesis as well as forcing from changing rsl sediment supply headland control and barrier inertia is examined in the context of long surviving barriers along the southern england coastline

relative sea level change and evidence for the holocene storegga slide tsunami from a high energy coastal environment cocklemill burn fife scotland uk a site in the cocklemill burn valley on the north shore of the firth of forth scotland provides evidence of relative sea level changes during the holocene from ca 7970 to ca 5090 radiocarbon years bp and of the holocene storegga slide tsunami dated here as having taken place after ca 7215 radiocarbon years bp marine sediments associated with two shorelines widely present in mainland scotland the main postglacial shoreline and the blairdrummond shoreline are recorded the holocene storegga slide tsunami deposits are unique here in the record of such sediments in eastern scotland in that they occur within marine sands of which the upper horizons are intertidal sandflat deposits the tsunami deposits probably accumulated shortly after a period of accelerated relative sea level rise the pattern and timing of which could have played a role in triggering the holocene storegga slide

on the role of discontinuities in mediating shore platform erosion in this paper we quantitatively demonstrate that dominant erosion processes on different shore platforms can be explained in part by geological properties we selected sites with a considerable history of rock coast geomorphology study to evaluate whether geological data can improve our understanding of spatial variations in erosion between sites schmidt hammer tests and discontinuity data were collected on blue lias limestone shore platforms in wales uk and sandstone platforms in victoria australia significant differences in joint spacing persistence of discontinuities and block size were found between the australian and welsh study sites these data were related to evidence of meso scale erosion to examine how geological contingency influences the nature and scale of erosion processes and thresholds this study quantitatively demonstrates that discontinuities play a fundamental role in altering rock resistance the findings of this research have important implications for the design of rock coast erosion studies concerned with measuring rates of change and determining the relative contributions of different processes to platform development

boulder accumulations related to storms on the south coast of the reykjanes peninsula iceland coastal boulder accumulations are often mentioned in the literature even though their interpretation remains difficult especially along rock coasts affected both by storms and tsunamis studies on the geomorphic impact of such high energy events are actually of great interest since their intensity and frequency are key issues for the future evolution of coasts in the framework of the global change the southwest coast of iceland faces the powerful storms of the north atlantic ocean with wave heights of more than 15 m the probability for past and present tsunamis to hit this coast is very low in this paper we describe boulder accumulations along the volcanic rock coast of reykjanes southwest iceland they consist of cliff top boulders clusters and ridges beaches and boulder fields large boulders up to 70 t in weight have been transported and deposited up to 65 m inland 6 masl the maximum limit of boulder deposition and driftwood was found respectively 210 m and 550 m inland storms appear to be a predominant factor in the geomorphic evolution of reykjanes coasts our observations also give new insight for the interpretation of coastal boulder accumulations processes of erosion and deposition by tsunamis are a rising topic in the literature and the effects of recurrent and powerful storms are neglected

reconnaissance of historic post ad 1000 high energy deposits along the atlantic coasts of southwest britain ireland and brittany france abstract sand and gravel deposits from the atlantic coasts of southwest britain brittany and western ireland are identified as potential indicators of historic post ad 1000 ocean sourced high energy events such as storm surges and tsunami this is an important historic period as it includes the climatic perturbations of the medieval warm period and the little ice age and also seismogenic events such as the lisbon tsunami of 1755 ten new sites are identified from various coastal settings and dated using eight new radiocarbon dates alongside previously published data generally sites do not appear to record multiple high energy events suggesting that either only the most extreme and or recent events are registered a number of radiocarbon dates from marine shell yield modern ages when corrected for the marine reservoir effect rather than necessarily indicating recent deposition this may reflect a poor understanding of terrestrial carbon input into coastal and estuarine waters and the practice of applying broad regional r values at the local scale two groupings of radiocarbon dates are recognised a medieval group and a post medieval group which might reflect events within known climatic perturbations and or tsunami occurrences these events may include the lucia flood of 1287 the all saint s day flood of 1570 the 1607 flood the great storm of 1703 and the lisbon tsunami some older pre ad 1000 deposits indicate the potential to construct frequency magnitude records of high energy events throughout the holocene data presented here support the view that salt marshes within the bristol channel and severn estuary were completely eroded away early in the 17th century

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

formation of freshwater fe mn coatings on gravel and the behavior of 60co 90sr and 137cs in a small watershed iron and manganese oxide coatings are actively forming on stream substrates in the white oak creek watershed in east tennessee although oxidizing conditions are required for fe mn oxide precipitation coatings accumulate only if dissolved iron and manganese exceed 50 g l below this coatings are lost by abrasion as fast as or faster than they form annual rates of formation of 3 mg g on substrate gravel were observed manganese is dissolved from coatings between eh values of 100 to 300 mv and below 1 mg l dissolved o2 at ph 6 5 to 7 5 iron oxides can be precipitated under these conditions uncontaminated gravels with oxide coatings composed of illite quartz and feldspar adsorbed radionuclides rapidly from waters below mpc maximum permissible concentration levels contaminated gravels placed in uncontaminated waters lost 60co by abrasion in oxidizing conditions and by dissolution of manganese coatings in reducing conditions exchangeable 90sr was completely lost after one month whereas nonexchangeable 90sr was lost more slowly 137cs was totally retained by the gravels gravels such as these can be used to monitor the radionuclide content of waters in the environment