dietary reconstruction of an early to middle holocene human population from the central california coast insights from advanced stable isotope mixing models the inherent sampling and preservational biases of the archaeological record make it difficult to quantify prehistoric human diets especially in coastal settings where populations had access to a wide range of marine and terrestrial food sources in certain cases geochemical proxies such as stable isotope ratios may be utilized to provide robust estimates on the relative proportions of various food resources consumed by prehistoric populations the harkins slough archaeological site scr 60 130 is an early to middle holocene coastal assemblage located on monterey bay in central ca the carbon d 13 c and nitrogen d 15 n isotope composition of human burials and associated archaeofauna excavated from the site were measured for input into a concentration dependent isotope mixing model that is able to statistically discriminate among multiple o3 food sources the human burials segregate into two distinct groups an early w7000 bp and middle w4500 bp holocene population with significant dietary differences stable isotope analyses indicate a 70e84 marine food source contribution for the early holocene group ehg but only a 48e58 marine dietary contribution for the middle holocene group mhg results also suggest that pinnipeds were an important marine food source for both groups modeling results are in agreement with archaeological evidence from southern ca suggesting that early holocene coastal populations were highly dependent on marine resources with the ability to procure both littoral and pelagic species further the use of terrestrial plant sources likely increased over time with the feasible contribution range doubling from the ehg 4e30 mean 19 to mhg 10e52 mean 38 this trend is supported by regional archaeological evidence for the advent of technological innovations linked to intensive terrestrial plant processing beginning in the middle holocene methodologically this work demonstrated the utility of a concentration dependent stable isotope mixing model in an iterative framework to provide feasible ranges of dietary contribution when the number of food sources is too high to allow a unique solution 2004 published by elsevier ltd

tectonic history of the metamorphic basement rocks of the sierra del carmen coahuila mexico the ouachita interior zone arching through central texas into the big bend region of the rio grande has been defined chiefly on the basis of well samples and its associated gravity high the only known exposure of rocks of the interior zone lies at the base of the sierra del carmen normal fault escarpment under approximately 1100 m of lower cretaceous carbonates in northern coahuila mexico these lower greenschist facies metamorphic rocks are thinly interlayered graphitic muscovite schist graphitic marble and minor quartzite with abundant quartz veins the dominant structures shown by the metamorphic rocks are isoclinal folds f2 that have a well defined axial planar foliation s2 earlier f1 folds refolded by f2 are locally preserved at the microscopic scale s2 is a crenulation cleavage of the s1 foliation that has been enhanced by pressure solution feldspar porphyroblasts overgrow a folded graphitic s1 foliation throughout the area a second crenulation cleavage s3 is present on the s2 foliation surface as an intersection lineation l3 subsequent laramide regionalto outcrop scale folds and associated thrusts overprint these ductile structures lower cretaceous carbonates form a large east verging overturned to recumbent anticline syncline fold pair with a northwest trending fold axis the s2 metamorphic foliations define an antiform that is nearly coincident in trend to that of the fold in the overlying carbonates indicating that the metamorphic rocks were also folded by this regional structure a basin and range normal fault is interpreted to have reactivated the laramide thrust fault responsible for the contractional deformation one to two normal faults cut the carbonates and metamorphic rocks and truncate the anticline syncline fold pair the maximum offset along the normal fault is 1600 m rb sr data from the muscovite schist gives a six point mineral whole rock isochron age of 277 10 ma indicating that polyphase deformation and metamorphism occurred during the late paleozoic ouachita orogeny an initial sr ratio of 0 721 suggests an ancient source for these metasediments common pb ratios of the metamorphic whole rock and galena from the puerto rico mine are isotopically distinct from those of the north american craton suggesting that they were derived from a non north american source and thus may be equivalent to unmetamorphosed ouachita flysch sediments this indicates that the metamorphic rocks of the ouachita interior zone were derived from an ancient allochthonous source that was deformed and metamorphosed during the late paleozoic ouachita orogeny

stable isotope composition of late pleistocene holocene eobania vermiculata muller 1774 pulmonata stylommatophora shells from the central mediterranean basin data from grotta d oriente favignana sicily abstract this paper presents stable isotopic results oxygen and carbon from both modern and late pleistocene holocene shells of the land snail eobania vermiculata muller 1774 from favignana island sicily it aims to contribute to the understanding of climate and vegetation history of this region during formation of upper palaeolithic mesolithic and meso neolithic deposits of grotta d oriente ort results from both an evaporative model fbm and an empirical regional isotopic model i e linear relation between oxygen isotopic composition of shells 18 os and those of local precipitation 18 op indicate that the 18 os values of modern specimens are mainly controlled by local temperature relative humidity and 18 op at the time of snail activity data also suggest that the modern snails are nocturnally active almost all year round in the study area the carbon isotopic compositions of shells 13 cs of the same specimens indicate a diet prevalently or exclusively composed of c3 vegetation the 18 os values of late pleistocene specimens suggest that climate conditions at 14 2 ka cal bp were similar to the present day in agreement with additional 18 os records from southern italy by contrast early middle holocene shells are notably 18 o depleted and suggest wetter conditions possibly combined with a decrease in isotopic composition of precipitation source compared to the present day when compared with regional palaeoclimatic records a large scale isotopic response to millennial scale changes in atmospheric and hydrological conditions e g enhanced rainfall in the central eastern mediterranean is observed during the early middle holocene the 13 cs of late pleistocene and holocene specimens are consistently higher than those of modern ones for the late pleistocene this could be reasonably explained in terms of water stressed vegetation on the other hand this seems to be less valid for holocene counterparts when the climate was wetter probably 13 cs values result from the combination of distinct competing factors involving atmospheric co 2 concentration seasonal water budget vegetation type cover and other carbon sources results reveal coherent relationships between regional 18 os and 13 cs demonstrating that late pleistocene holocene land snail shell remains from archaeological sites may provide useful snapshots of past seasonal climate conditions

oxygen isotope signatures from land snail helix melanostoma shells and body fluid proxies for reconstructing mediterranean and north african rainfall abstract in this paper we show that oxygen isotope ratios from the shell carbonate of the land snail helix melanostoma reflect local rainfall parameters stable oxygen isotopes were measured in the body fluid 18 o body and shells 18 o shell of live collected h melanostoma along a north south transect across the gebel akhdar in northeast libya 18 o body ranged between 8 1 and 13 0 whilst 18 o shell ranged between 1 0 and 2 8 to investigate the relationship between snail oxygen isotope composition and climate these measurements were correlated with ambient air temperature relative humidity rainfall amount and the 18 o composition of rainwater 18 o rain strong and significant correlations were found between 18 o shell and 18 o rain and between 18 o shell and rainfall amount r 2 0 79 and 0 85 respectively suggesting that h melanostoma shells can be used as a proxy for past rainfall conditions when combined in multiple linear regressions 18 o rain and rainfall amount explained 90 of the variance in 18 o shell r 2 0 90 simple and multiple linear regressions were used to develop predictive models for these climate parameters as h melanostoma shells are commonly found in mediterranean and north african archaeological and geological deposits the predictive equations developed in this study hold great potential for reconstructing pleistocene to holocene rainfall and aridity patterns in the gebel akhdar and for assessing the relationship between environmental changes and human behavioural changes

the influence of diet on the δ13c of shell carbon in the pulmonate snail helix aspersa abstract the influence of diet and atmospheric co2 on the carbon isotope composition of shell aragonite and shell bound organic carbon in the pulmonate snail helix aspersa raised in the laboratory was investigated three separate groups of snails were raised on romaine lettuce c3 plant 13c 25 8 corn c4 plant 13c 10 5 and sour orange 12c enriched c3 plant 13c 39 1 the isotopic composition of body tissues closely tracked the isotopic composition of the snail diet as demonstrated previously however the isotopic composition of the acid insoluble organic matrix extracted from the aragonite shells does not track diet in all groups in snails that were fed corn the isotopic composition of the organic matrix was more negative than the body by as much as 5 whereas the matrix was approximately 1 heavier than the body tissues in snails fed a diet of c3 plant material these results indicate that isotopic composition of the organic matrix carbon cannot be used as an isotopic substrate for paleodietary reconstructions without first determining the source of the carbon and any associated fractionations the isotopic composition of the shell aragonite is offset from the body tissues by 12 3 in each of the culture groups this offset was not influenced by the consumption of carbonate and is not attributable to the diffusion of atmospheric co2 into the hemolymph the carbon isotopic composition of shell aragonite is best explained in terms of equilibrium fractionations associated with exchange between metabolic co2 and hco3 in the hemolymph and the fractionation associated with carbonate precipitation these results differ from previous studies based primarily on samples collected in the field that have suggested atmospheric carbon dioxide contributes significantly to the shell 13c the culture results indicate that the 13c of aragonite is a good recorder of the isotopic composition of the snail body tissue and therefore a better recorder of diet than is the insoluble shell organic carbon because the systematic fractionation of carbon isotopes within the snail is temperature dependent the 13c of the shell could provide an independent technique for estimating paleotemperature changes

holocene trends in 18o in land snail shells from the negev desert and their implications for changes in rainfall source areas abstract the 18o value of the carbonate of land snail shells is related to the 18o content of precipitation which in turn relates to the source region and trajectory of the rain bearing air masses analyses of 18o of the shell carbonate of 76 radiocarbon dated holocene samples of the land snail trochoidea seetzeni from the northern negev desert in southern israel were carried out and the results were compared to modern snails from the same region early holocene 18o values are similar to modern but during the period centered around 6500 6000 yr b p a depletion of some 2 below modern is observed a change in the atmospheric circulation pattern for this period is thus indicated most likely an increase in the frequency of storm systems reaching the region from north eastern africa by 3500 yr b p 18o values had reached modern levels and indicate a stable pattern of atmospheric circulation since that time

overview of the oxygen isotope systematics of land snails from north america continental paleoclimate proxies with near global coverage are rare land snail 18o is one of the few proxies abundant in quaternary sediments ranging from the tropics to the high arctic tundra however its application in paleoclimatology remains difficult attributable in part to limitations in published calibration studies here we present shell 18o of modern small 10 mm snails across north america from florida 30 n to manitoba 58 n to examine the main climatic controls on shell 18o at a coarse scale this transect is augmented by published 18o values which expand our coverage from jamaica 18 n to alaska 64 n results indicate that shell 18o primarily tracks the average annual precipitation 18o shell 18o increases 0 5 0 7 for every 1 increase in precipitation 18o and 0 3 0 7 for every 1 c increase in temperature these relationships hold true when all taxa are included regardless of body size ranging from 1 6 to 58 mm ecology herbivores omnivores and carnivores or behavior variable seasonal active periods and mobility habits future isotopic investigations should include calibration studies in tropical and high latitude settings arid environments and along altitudinal gradients to test if the near linear relationship between shell and meteoric precipitation 18o observed on a continental scale remains significant

surf zone currents over irregular bathymetry drifter observations and numerical simulations 1 surf zone currents over irregular bathymetry were observed with gps tracked drifters and modeled with the depth integrated nonlinear shallow water equations trajectories of drifters released in 1 2 m depth sometimes defined rip currents and surf zone eddies features that have been difficult to resolve with fixed instruments the drifter delineated surf zone circulation evolved as the tidal level changed during each 4 6 hour deployment in one case as the tide dropped a shore normal rip current present for the first 2 hours evolved to a more shore parallel flow in a second case on a rising tide a well developed bifurcated rip current was replaced by a weak amorphous circulation rip current velocities were strongest near the surf zone edge and decayed by an order of magnitude within 2 surf zone widths from the shoreline an eddy was observed to persist over a bathymetric depression within the surf zone for at least 1 hour observed and numerically simulated drifter trajectories define similar flow features but the observed and modeled velocities differed by roughly a factor of 2 and flow evolution observed during roughly 0 5 m changes in tidal level were reproduced only if the simulated water levels varied by about 1 m the alongshore momentum balance was spatially variable with wave forcing balanced by pressure gradient friction and advective terms the cross shore momentum balance was everywhere dominated by wave forcing and pressure gradient terms of about equal magnitude in the vicinity of a simulated rip current the residual of the cross shore wave forcing and pressure gradient increased and was balanced by advection terms

rb sr ages of diagenesis of mg rich clay in permian sediments palo duro basin texas panhandle u s a abstract mid to upper permian sedimentary rocks in the shallow 3 km intracratonic palo duro basin texas panhandle occur in multicyclic carbonate evaporite redbed sequences interpreted to be hypersaline shelf depositional assemblages certain marker horizons can be traced continuously over the entire basin clay minerals include distinctive varieties of mg rich smectite chlorite or mixed layer species resulting from diagenesis in an evaporitic environment discrete particle size fractions of clay were separated from core recovered from the tubb leonardian san andres unit 4 lower guadalupian upper seven rivers upper guadalupian and salado tansill guadalupian ochoan formations to determine the times of mineral genesis rb sr isotopic data for aliquots of a clay sample that has been leached by diverse ion exchange reagents plot as a linear array in a rb sr isochron diagram for ultra fine clay 0 05 m interpreted to be diagenetic the slope of the data array corresponds to the time of diagenesis ages of clay diagenesis in the four sampled stratigraphic units agree generally with ages of deposition according to the geologic time scale signifying that diagenesis was penecontemporaneous with deposition analyses of coarser clay fractions 0 2 0 5 m and 2 4 m indicate the presence of a detrital component in most instances initial 87sr 86sr in diagenetic clay is higher than the sr isotope ratio measured directly in associated anhydrite introduction of radiogenic sr from occasional stream influx or from concurrent diagenetic dissolution of silicate detritus could have elevated 87sr 86sr in the ambient brine that mediated clay diagenesis

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

a self similar scaling for cross shelf exchange driven by transient rip currents transient rip currents episodic offshore flows from the surf zone to the inner shelf present a recreational beach hazard and exchange material across the nearshore ocean the magnitude and offshore extent of transient rip current induced exchange and its relative importance to other inner shelf exchange processes are poorly understood here 120 model simulations with random normally incident directionally spread waves spanning a range of beach slopes and wave conditions show that the transient rip current exchange velocity is self similar the nondimensional exchange velocity surf zone flushing time and cross shore decay length scale are scaled by beach slope and wave properties depending strongly on wave directional spread transient rip current driven exchange can be compared to other cross shelf exchange processes for example transient rip current driven exchange is stronger than wave induced stokes drift driven exchange up to six surf zone widths from shore

stable carbon isotope record of middle to late holocene climate changes from land snail shells at hinds cave texas abstract stable carbon isotope ratios of shell carbonate and shell organic matter from land snails rabdotus alternatus from hinds cave texas are used to reconstruct the climate history of the drier western part of the southern great plains present mean annual rainfall of 400 mm over the last ca 5000 yr ams radiocarbon analyses of four individual shells from each of two strata indicate that there are no problems of reworking or age mixtures within strata however burning is evident in many shells amino acid composition and racemization were used to identify shells that had been significantly heated and these were rejected for isotopic analysis because of possible alteration of the isotopic signal fourteen samples of snails from hinds cave each consisting of 2 6 individual shells from the same provenience were radiocarbon dated by ams and analyzed for stable carbon isotopes in addition a sample collected alive ca ad 1890 from a nearby site was analyzed to represent modern conditions the shells show no decrease in organic content with age indicating good preservation of shell organic matter both the organic and carbonate isotope values show similar temporal trends the oldest samples 4100 4600 cal yr bp are relatively depleted in 13 c maximum 13 c values are reached at ca 3500 cal yr bp thereafter there is a regular depletion in 13 c with the recent sample showing the lowest 13 c value the change in the isotopic values over time is quite large range of 4 5 for organic matter and indicates substantial climatic changes the variations in isotopic values are interpreted as resulting primarily from changes in moisture conditions affecting the abundance of drought adapted cam crassulacean acid metabolism plant species enriched in 13 c thus relatively moist mid holocene conditions are indicated with increasingly dry conditions reaching a maximum at ca 3500 cal yr bp followed by progressively moister conditions through the late holocene

the effect of wave breaking on surf zone turbulence and alongshore currents a modeling study the effect of breaking wave generated turbulence on the mean circulation turbulence and bottom stress in the surf zone is poorly understood a one dimensional vertical coupled turbulence k and mean flow model is developed that incorporates the effect of wave breaking with a time dependent surface turbulence flux and uses existing published model closures no model parameters are tuned to optimize model data agreement the model qualitatively reproduces the mean dissipation and production during the most energetic breaking wave conditions in 4 5 m water depth off of a sandy beach and slightly underpredicts the mean alongshore current by modeling a cross shore transect case example from the duck94 field experiment the observed surf zone dissipation depth scaling and the observed mean alongshore current although slightly underpredicted are generally reproduced wave breaking significantly reduces the modeled vertical shear suggesting that surf zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations model inferred drag coefficients follow parameterizations manning strickler that depend on the bed roughness and inversely on the water depth although the inverse depth dependence is likely a proxy for some other effect such as wave breaking variations in the bed roughness and the percentage of breaking wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient however covarying the wave height forcing and dissipation and bed roughness separately results in an alongshore current drag coefficient only weakly strongly dependent on the bed roughness because of the competing effects of increased turbulence wave forcing and orbital wave velocities

the major ion composition of permian seawater abstract the major ion mg2 ca2 na k so42 and cl composition of permian seawater was determined from chemical analyses of fluid inclusions in marine halites new data from the upper permian san andres formation of texas 274 272 ma and salado formation of new mexico 251 ma analyzed by the environmental scanning electron microscopy esem x ray energy dispersive spectrometry eds method along with published chemical compositions of fluid inclusions in permian marine halites from north america two formations of different ages and the central and eastern european basins eight formations of four different ages show that permian seawater shares chemical characteristics with modern seawater including so42 ca2 at the point of gypsum precipitation evolution into mg2 na k so42 cl brines and mg2 k ratios 5 permian seawater however is slightly depleted in so42 and enriched in ca2 although modeling results do not rule out ca2 concentrations close to those in present day seawater na and mg2 in permian seawater are close to slightly below their concentrations in modern seawater permian and modern seawater are both classified as aragonite seas with mg2 ca2 ratios 2 conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements the chemistry of permian seawater was modeled using the chemical composition of brine inclusions for three periods lower permian asselian sakmarian 296 283 ma lower permian artinskian kungurian 283 274 ma and upper permian tatarian 258 251 ma parallel changes in the chemistry of brine inclusions from equivalent age evaporites in north america central europe and eastern europe show that seawater underwent secular variations in chemistry over the 50 million years of the permian modeled so42 concentrations are 20 mmol per kg h2o mmolal and 19 mmolal in the asselian sakmarian and artinskian kungurian with higher concentrations in the upper permian tatarian 23 mmolal modeled ca2 is at or above its concentration in modern seawater throughout the permian mg2 is close to slightly below its concentration in modern seawater 55 mmolal in the asselian sakmarian 52 mmolal and tatarian 52 mmolal but slightly higher than modern seawater in the artinskian kungurian 60 mmolal mg2 ca2 ratios are 3 5 total range 2 7 to 5 5 in the lower permian and rose slightly to 3 7 total range 3 1 to 5 8 in the upper permian primarily due to decreases in ca2 these results are consistent with models that predict oscillations in the major ion composition of phanerozoic seawater on the basis of changes in the midocean ridge river water flux ratio driven by changes in the rate of midocean ridge crust production the permian was characterized by low sea levels icehouse conditions and southern hemisphere glaciation such conditions analogous to the present ice age and the similarities between permian seawater and modern seawater all suggest that general phanerozoic supercycles driven by mantle convection and global volcanicity also control the major ion chemistry of seawater

late glacial to holocene transition in northern spain deduced from land snail shelly accumulations abstract shells of the helicid cepaea nemoralis were studied using taphonomic isotopic and morphometric measurements to estimate late glacial holocene 12 1 6 3 cal ka bp environmental conditions in northern spain higher taphonomic alteration among holocene shells suggests lower sedimentation rates or higher shell destruction rates than during glacial conditions shells preserved the aragonitic composition despite differing degree of skeleton damage shell 13 c values were 10 3 1 1 8 2 2 3 and 7 3 1 6 for modern holocene and late glacial individuals respectively higher 13 c values during the late glacial and some holocene periods imply higher water stress of c 3 plants and or higher limestone contribution than today intrashell 13 c values were higher during juvenile stages suggesting higher limestone ingestion to promote shell growth shell 18 o values were 1 1 0 7 0 9 0 8 and 0 1 0 7 for modern holocene and late glacial specimens respectively a snail flux balance model suggests that during 12 1 10 9 cal ka bp conditions were drier and became wetter at 8 4 6 3 cal ka bp and today intrashell 18 o profiles reveal that glacial individuals experienced more extreme seasonality than interglacial shells despite possible larger hibernation periods shell size correlated positively with 18 o values suggesting that growth rates and ultimate adult size of c nemoralis may respond to climate fluctuation in northern spain

stable isotope δ18o δ13c and δd signatures of recent terrestrial communities from a low latitude oceanic setting endemic land snails plants rain and carbonate sediments from the eastern canary islands abstract stable isotopes of oxygen and carbon extracted from fossil land snail shells have been used increasingly to interpret past environments to evaluate the utility of this approach for low latitude oceanic islands populations of the modern helicid land snail theba geminata a species also abundant in the quaternary fossil record of the region were sampled at ten low altitude d and 2 v smow for 18 o ranging from 11 to 2 v smow and from 2 6 to 0 7 v smow respectively the local vegetation is heterogeneous including c 3 c 4 and cam plants 13 c values vary from 13 0 to 29 0 v pdb across plant species of the 24 species five are c 4 15 are c 3 and four are cam plants the 18 o values for shells represent a narrow range of values from 0 3 to 2 5 v pdb which is consistent with the low climate seasonality typifying low latitude oceanic settings hypothetical model of the expected 18 o value for shell aragonite precipitated in equilibrium suggests that the most negative 18 o shell represent the closest estimate for 18 o rain water the 13 c values of shells range from 9 4 to 1 7 v pdb the most positive 13 c values are attributed to a diet based on c 4 plants the comparison of 13 c values of soft tissues and shells suggests that snails ingested notable amounts from 20 up to 40 of foreign carbonates consequently fossil shells with the most negative 13 c values should be selected for radiocarbon dating in future geochronological studies of the region the 13 c values of body tissues vary from 12 0 to 27 2 v pdb indicating that land snails consumed c 3 and c 4 plants indiscriminately the mean carbon isotopic composition averaged across multiple fossil specimens may thus provide a useful tool for reconstructing paleoclimates and paleoenvironments throughout the quaternary history of the canary islands and other comparable low latitude oceanic settings

study of the diet effect on δ13c of shell carbonate of the land snail helix aspersa in experimental conditions abstract this study aims to demonstrate the influence of the metabolic co2 derived from the diet and of the atmospheric co2 on the shell carbonate 13c of the pulmonate snail helix aspersa maxima raised under controlled conditions adult snails were analyzed and compared with three hatching and 1 day old young snails stemming from the same breeding one day after the 2 day old individuals were raised during 1 month three groups of gastropods were fed with fresh lettuce c3 plant 13c 27 49 three groups with corn c4 plant 13c 11 7 and three groups ate alternately both c3 c4 the difference between the average 13c values of the adult snails on the one hand and the hatched and 1 day old snails on the other hand indicates a depletion of 2 47 therefore the isotopic parents offspring signal is not preserved the depleted ingested albumen by the snail embryo in the egg during the building of the shell could explain this depletion the c3 diet experiment gave the expected isotopic composition difference between the diet lettuce and the shells average 13cshell lettuce 13 75 0 52 this result shows a clear diet effect on the isotopic composition of the snail shells for the c4 experiment the difference in carbon isotope composition between the corn and the shell 13cshell corn yielded an average value of 4 89 0 87 the main result is that 13c is not constant and appears to depend on the type of ingested food several hypotheses can arise from this study to explain the different fractionations a differences in the quality of the two diets b differences in turnover rate for c3 and c4 feeders the groups regularly fed with mixed diet yielded 13c values showing a preferential use of c3 food for most values the c3 c4 mixed dietary alternation probably led snails to use mainly the lettuce instead of the corn powder

paleoclimatic implications of the spatial patterns of modern and lgm european land snail shell δ18o abstract the oxygen isotopic composition of land snail shells may provide insight into the source region and trajectory of precipitation last glacial maximum lgm gastropod shells were sampled from loess from belgium to serbia and modern land snail shells both record 18 o values between 0 and 5 there are significant differences in mean fossil shell 18 o between sites but not among genera at a single location therefore we group 18 o values from different genera together to map the spatial distribution of 18 o in shell carbonate shell 18 o values reflect the spatial variation in the isotopic composition of precipitation and incorporate the snails preferential sampling of precipitation during the warm season modern shell 18 o decreases in europe along a n s gradient from the north sea inland toward the alps modern observed data of isotopes in precipitation gnip demonstrate a similar trend for low altitude sites lgm shell 18 o data show a different gradient with 18 o declining toward the ene implying a mid atlantic source due to increased sea ice and a possible southern displacement of the westerly jet stream balkan lgm samples show the influence of a mediterranean source with 18 o values decreasing northward

oxygen isotope composition of living land snail shells data from italy sixty seven shells of living land snails were selected from 31 different localities across italy to investigate the relationships between their oxygen isotopic composition 18os and the mean value of local rainfall 18op despite the difficulty for some localities to correctly estimate the oxygen isotopic composition of local rainfall a good relationship was found this indicates that the oxygen isotopic composition of environmental water used by the snails is in italy strictly related to that of the local meteoric precipitation however the relationship found is substantially different from that previous established for central europe indicating that regional climatic conditions are important in defining the final isotopic composition of land snail shells moreover these equations may not hold for different climatic conditions existing during for instance glacial and interglacial periods the data also show that isotopic differences among species are relatively narrow and that they may depend on ecological factors i e style of life rather than any clearly identifiable different vital offset

carbon isotope signatures from land snail shells implications for palaeovegetation reconstruction in the eastern mediterranean in this study we compare carbon isotope values in modern helix melanostoma shell carbonate 13cshell from the gebel al akhdar region of libya with carbon isotope values in h melanostoma body tissue 13cbody local vegetation 13cplant and soil 13csoil all vegetation in the study area followed the c3 photosynthetic pathway however the 13cplant values of different species formed two distinct isotopic groups this can be best explained by different water use efficiencies with arid adapted species having significantly more positive 13cplant values than less water efficient species the ranges and means of 13cbody and 13cplant were statistically indistinguishable from one another suggesting that 13cbody was primarily a function of local vegetation composition h melanostoma 13cshell reflected the 13cplant of local vegetation with a positive offset between body diet and shell of 14 5 1 4 therefore in the gebel al akhdar where only c3 plants are present higher mean 13cshell values likely reflect greater abundances of water efficient c3 plants in the snails diet and therefore in the landscape whilst lower mean 13cshell values likely reflect the consumption of less water efficient c3 plants the distribution of these plants is in turn affected by environmental factors such as rainfall these findings can be applied to archaeological and geological shell deposits to reconstruct late pleistocene to holocene vegetation change in the southeast mediterranean

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary abstract organic rich calcite laminated with gypsum in the evaporitic non fossiliferous castile formation of the delaware basin southwest usa yields a total pb u isochron age of 251 5 2 8 ma mswd 1 3 the castile formation is almost certainly late permian based on its 87 sr 86 sr value of 0 706923 identical to the distinct minimum in the late permian sr curve in this paper we explore the potential for using u pb calcite ages to date traditionally undatable sections and show how this southern midcontinent usa far west texas and southeast new mexico deposit can be correlated to the type section in china we accept that diagenetic alteration can bias u pb results but the data set we present shows no evidence for such alteration clearly with alteration the age we present would represent a minimum age for the castile formation if the age actually dates the castile formation then it requires the permian triassic boundary to be younger than 251 5 2 8 ma

rip current types circulation and hazard abstract rip currents are narrow and concentrated seaward directed flows that extend from close to the shoreline through the surf zone and varying distances beyond rip currents are ubiquitous on wave exposed coasts each year they cause hundreds of drowning deaths and tens of thousands of rescues on beaches worldwide and are therefore the leading deadly hazard to recreational beach users the broad definition above masks considerable natural variability in terms of rip current occurrence in time and space flow characteristics and behaviour in particular surf zone rip currents have long been perceived as narrow flows extending well beyond the breakers flushing out the surf zone at a high rate exit flow circulation regime while more recent studies have shown that rip flow patterns can consist of quasi steady semi enclosed vortices retaining most of the floating material within the surf zone circulatory flow circulation regime building upon a growing body of rip current literature involving numerical modelling and theory together with emergence of dense lagrangian field measurements we develop a robust rip current type classification that provides a relevant framework to understand the primary morphological and hydrodynamic parameters controlling surf zone rip current occurrence and dynamics three broad categories of rip current types are described based on the dominant controlling forcing mechanism each category is further divided into two types owing to different physical driving mechanisms for a total of six fundamentally different rip current types hydrodynamically controlled 1 shear instability rips and 2 flash rips which are transient in both time and space and occur on alongshore uniform beaches bathymetrically controlled 3 channel rips and 4 focused rips which occur at relatively fixed locations and are driven by hydrodynamic processes forced by natural alongshore variability of the morphology in both the surf zone and inner shelf zone and boundary controlled 5 deflection rips and 6 shadow rips which flow against rigid lateral boundaries such as natural headlands or anthropogenic structures for each rip current type flow response to changes in hydrodynamic and morphologic forcing magnitude is examined in regard to velocity modulation and changes in circulation regime providing key force response relationships of rip currents we also demonstrate that in the real world rip currents form through a mixture of driving mechanisms and the discrete rip types defined in fact form key elements in a wide and complex spectrum of rip currents on natural beaches it is anticipated that this rip current type classification will serve as a resource for coastal scientists and non specialists with an interest in the rip current hazard and as a platform for future rip current studies finally we suggest some important future research directions highlighting the need for coastal and beach safety communities to collaborate in order to improve rip current education and awareness

holocene paleoenvironment 7200 4000 cal bp of the los castillejos archaeological site se spain inferred from the stable isotopes of land snail shells abstract neolithic copper age and modern land snail shells from the los castillejos archeological site 37 20 n se iberian peninsula were analyzed for 13 c 12 c and 18 o 16 o ratios to estimate the paleoenvironmental conditions during shell deposition modern and ancient 13 c values ranged from 9 2 to 7 7 and from 13 6 to 5 7 respectively and they differed among taxa 13 c values were similar for neolithic 13 c 8 1 2 3 copper age 13 c 8 4 0 6 and modern 13 c 8 4 0 5 herbivorous cernuella specimens alternatively fossil shells of the herbivorous ferussacia folliculum 13 c 9 9 1 2 and the omnivorous rumina decollata 13 c 11 1 2 showed substantially lower 13 c values than modern specimens which may suggest lower water stress during the early to mid holocene than today the 18 o values from modern specimens ranged from 1 1 to 0 6 while the 18 o values from fossil specimens ranged from 6 7 to 0 and they differed among species cernuella exhibited shell 18 o values that increased from the neolithic 18 o 2 3 1 8 and copper age 18 o 1 7 0 6 to the present 18 o 0 3 0 5 the 18 o values of fossil shells of f folliculum 18 o 3 7 1 0 and r decollata 18 o 4 0 1 6 were also lower than modern shells calculations of a published snail flux balance mixing model for 18 o values indicate that early to mid holocene shells precipitated during times when relative humidity was greater than today the se iberian peninsula was noticeably wetter 7200 cal bp and experienced drier conditions thereafter the results are consistent with other regional paleoclimatic proxies and reinforce the potential use of land snail shells as paleoenvironmental archives

boussinesq modelling of transient rip currents the flow on a plane beach with a random directionally spread wave field was simulated with a boussinesq model the random wave spectra were directionally symmetric with their central direction perpendicular to the beach so no constant longshore current was generated variable wave averaged currents were generated because of the spatially variable wave field and sometimes formed offshore directed rip currents that appear in variable longshore locations the rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone three different beach slopes and four different wave spectra are simulated the frequency duration and intensity of the transient rips depend on both the beach slope and the incident wave spectra the results have important engineering implications for the transport of material in the nearshore zone in particular on longshore uniform beaches

stable isotope composition of late glacial land snail shells from grotta del romito southern italy palaeoclimatic implications abstract stable isotope composition of living and fossil land snail shells was determined at grotta del romito southern italy with the aim to reconstruct environmental and climatic variation in the area during late upper palaeolithic the investigated succession comprised 15 different excavated layers spanning between ca 13 000 and 14 500 yr cal bp the oxygen isotope composition of snail shells indicates a marked decrease at the layer d8 suggesting a climatic deterioration consistent with the gi 1d climatic event older dryas this climate deterioration may have been related to a substantial decrease of mean annual temperature with associated changes in the regional atmospheric circulation however the environmental conditions at the time of shell s growth in the other intervals sampled suggest condition comparable to the present day the carbon isotope composition of fossil snail shells is in agreement with other records which indicate a general increase of the 13 c values of organic matter during pleniglacial to late glacial caused by substantially lower atmospheric co 2 concentration at that time

effect of wave frequency and directional spread on shoreline runup 1 wave breaking across the surf zone elevates the mean water level at the shoreline setup and drives fluctuations about the mean runup runup often is divided into sea swell 0 04 0 3 hz and lower frequency infragravity 0 00 0 04 hz components with energetic incident waves runup is dominated by infragravity frequencies and total water levels combined setup and runup can exceed 3 m significantly contributing to coastal flooding and erosion setup and runup observations on sandy beaches are scattered about empirical parameterizations based on near shoreline beach slope and deep water wave height and wavelength accurate parameterizations are needed to determine flooding and erosion risk to coastal ecosystems and communities here numerical simulations with the boussinesq wave model funwavec are shown to statistically reproduce typical empirical setup and runup parameterizations furthermore the model infragravity runuprs ig strongly depends on the incident wave directional and frequency spread about the mean direction and peak frequency realistic directional spread variations change rs ig equivalent to a factor of two variation in incident wave height the modeled rs ig is shown to vary systematically with a new non dimensional spreading parameter that involves peak frequency frequency spread and directional spread this suggests a new parameterization forrs ig potentially useful to predict coastal flooding and erosion

paleoenvironment of the folsom archaeological site new mexico usa approximately 10 500 14c yr b p as inferred from the stable isotope composition of fossil land snail shells abstract well preserved aragonitic land snail shells vallonia from late pleistocene eolian sediment in the folsom archaeological site in new mexico exhibit an overall decrease of 18opdb from maximum values of 2 7 more positive than modern to younger samples with lower average values of about 3 6 within the modern range the age of the samples approximately 10 500 14c yr b p suggests that the decrease in 18o may manifest climatic changes associated with the younger dryas some combination of increased relative humidity and cooler temperatures with decreased 18o of precipitation during the times of snail activity can explain the decrease in shell 18o a well known paleoindian bison kill occurred at the folsom site during this inferred environmental transition average 13c values of the aragonite shells of the fossil vallonia range from 7 3 to 6 0 among different archaeological levels and are not as negative as modern values this suggests that the proportion of c4 vegetation at the folsom site approximately 10 500 14c yr b p was greater than at present a result which is consistent with other evidence for higher proportions of c4 plants in the region at that time

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

implications of the apparent 14c age of cultured achatina fulica and the spatial features of 14c ages among modern land snail shells in china abstract it has long been known that many terrestrial snail shells are subject to the so called limestone effect however the magnitude and impact of this effect on the 13c values of snail shells and soft body tissue 13cshell and 13cbody are still unknown in this study achatina fulica snails were hatched and cultured under controlled conditions and supplied with 14c free calcium carbonate and lettuce a c3 plant as a calcium source and food supply respectively the snail shells and soft body tissues were sampled monthly for 5 months and 13c and radiocarbon dating analyses were conducted to trace carbon source variations at different growth stages our results show that the apparent 14c age of the shells and the corresponding 13cshell values increased progressively from the 1st to 3rd months and subsequently decreased during the 4th and 5th months the results demonstrate for the first time that carbonate ingestion has a straightforward influence on the 14c ages and 13c values of shells and that the limestone effect changes over the lifetime of snails moreover the apparent 14c ages of snails sampled in the field are older than modern ages when taken from the northern carbonate region and relatively young or the same as modern ages when collected from ferralic soils this further supports our findings from cultured snails and suggests that snail shells are good archives for radiocarbon dating purposes in southern china although the 13c values of the soft body tissues of cultured snails vary synchronously with those of the shell this seemingly common phenomenon cannot be easily explained by carbonate ingestion as the snail bodies are of more recent origin than the shells atmospheric co2 may be another candidate explaining the synchronicity between 13cshell and 13cbody as well as the f 14c variations of snail bodies however it is still unclear how snails differentially incorporate carbon from different sources e g carbonate and atmospheric co2 at different growth stages since carbon from different sources is combined in the bicarbonate pool in the hemolymph before being used by snails

40ar 39ar dating of late permian evaporites southeastern new mexico usa 40ar 39ar dating of the potassium magnesium sulfate mineral langbeinite from permian evaporites of the salado formation near carlsbad new mexico provides quantitative evidence that some salts in these deposits have not recrystallized for 251 myr since deposition survival of permian salts supports the possibility that bacillus bacteria recovered from nearby halite was isolated in a closed system and represents a sample of uncontaminated permian life local recrystallization of langbeinite and other nearby minerals is also indicated by the dating suggesting both the need and the opportunity to document closed system behavior more rigorously the shoaling and desiccation event recorded by the salado formation began at least 1 myr before the permian triassic boundary temporal correlation of the salado with the zechstein evaporites of north central europe supports previously inferred regression models for the origin of these deposits significant paleoenvironmental change at the permian triassic boundary thus occurred on a time scale more protracted than that implied by geologically instantaneous events such as bolide impacts

modeling surf zone tracer plumes 2 transport and dispersion 1 five surf zone dye tracer releases from the hb06 experiment are simulated with a tracer advection diffusion model coupled to a boussinesq surf zone model funwavec model tracer is transported and stirred by currents and eddies and diffused with a breaking wave eddy diffusivity set equal to the breaking wave eddy viscosity and a small 0 01 m2 s 1 background diffusivity observed and modeled alongshore parallel tracer plumes transported by the wave driven alongshore current have qualitatively similar cross shore structures although the model skill for mean tracer concentration is variable from negative to 0 73 depending upon release cross shore integrated tracer moments normalized by the cross shore tracer integral have consistently high skills 0 9 modeled and observed bulk surf zone cross shore diffusivity estimates are also similar with 0 72 squared correlation and skill of 0 4 similar to the observations the model bulk absolute cross shore diffusivity is consistent with a mixing length parameterization based on low frequency 0 001 0 03 hz eddies the model absolute cross shore dispersion is dominated by stirring from surf zone eddies and does not depend upon the presence of the breaking wave eddy diffusivity given only the bathymetry and incident wave field the coupled boussinesq tracer model qualitatively reproduces the observed cross shore absolute tracer dispersion suggesting that the model can be used to study surf zone tracer dispersion mechanisms

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

stable isotope ecology of land snails from a high latitude site near fairbanks interior alaska usa abstract land snails have been investigated isotopically in tropical islands and mid latitude continental settings while high latitude locales where snails grow only during the summer have been overlooked this study presents the first isotopic baseline of live snails from fairbanks alaska 64 51 n a proxy calibration necessary prior to paleoenvironmental inferences using fossils 13c values of the shell 10 4 0 4 and the body 25 5 1 0 indicate that snails consumed fresh and decayed c3 plants and fungi a flux balance mixing model suggests that specimens differed in metabolic rates which may complicate paleovegetation inferences shell 18o values 10 8 0 4 were 4 higher than local summer rain 18o if calcification occurred during summer a flux balance mixing model suggests that snails grew at temperatures of 13 c rainwater 18o values of 15 and relative humidity of 93 results from fairbanks were compared to shells from san salvador bahamas at 24 51 n average annual 18o values of shells and rainwater samples from the bahamas were both 10 18o enriched with respect to seasonal summer alaskan samples at a coarse latitudinal scale shell 18o values overwhelmingly record the signature of the rainfall during snail active periods while tropical snails record annual average environmental information high latitude specimens only trace summer season climatic data

breaking wave induced cross shore tracer dispersion in the surf zone model results and scalings 1 the dispersion of surf zone tracers including pollutants and bacteria is determined by many processes acting over a range of timescales and space scales breaking waves bores are clearly important to cross shore tracer dispersion in the surf zone but little is known about the dispersal effects of bores here a simple model for bore induced cross shore dispersion are developed based upon the diffusion equation with an eddy diffusivity that propagates with the bores depth uniform tracer and bore induced mixing along with alongshore uniformity are assumed the bores are assumed well developed and the dispersion results are for a self similar constant wave height to water depth ratio surf zone four nondimensional parameters are identified and solution space is explored the tracer center of mass is approximately constant and tracer width grows with the square root of time tracer distribution becomes initially skewed after the passage of the first bore but becomes symmetric after multiple bores have passed the nondimensional tracer patch growth and dilution rates depend strongly upon the nondimensional phase speed and wave period the simple model results are consistent with the a boussinesq wave model where the breaking wave eddy viscosity is used for the bore eddy diffusivity the scaling of the dimensional parameters regarding the bore eddy diffusivity and the ranges of the nondimensional parameters are examined covariation of the nondimensional phase speed and wave period suggest that nondimensional tracer dispersion is largely cross shore independent

pleistocene holocene environmental change in the canary archipelago as inferred from the stable isotope composition of land snail shells abstract the isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern canary islands 28 29 n over the last 50 ka shell 13c values range from 8 9 to 3 8 at various times during the glacial interval 15 to 50 ka moving average shell 13c values were 3 higher than today suggesting a larger proportion of c4 plants at those periods shell 18o values range from 1 9 to 4 5 with moving average 18o values exhibiting a noisy but long term increase from 0 1 at 50 ka to 1 6 1 8 during the lgm 15 22 ka subsequently the moving average 18o values range from 0 0 at 12 ka to 0 9 at present calculations using a published snail flux balance model for 18o constrained by regional temperatures and ocean 18o values suggest that relative humidity at the times of snail activity fluctuated but exhibited a long term decline over the last 50 ka eventually resulting in the current semiarid conditions of the eastern canary islands consistent with the aridification process in the nearby sahara thus low latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical subtropical environmental change

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

early middle holocene land snail shell stable isotope record from grotta di latronico 3 southern italy this paper compares stable isotope d 18 o and d 13 c records of early middle holocene land snail shells from the archaeological deposits of grotta di latronico 3 ltr3 southern italy with modern shell isotopic data no substantial interspecific variability was observed in shell d 18 o d 18 os of modern specimens pomatias elegans cornu aspersum eobania vermiculata helix ligata and marmorana fuscolabiata in contrast interspecific shell d 13 c d 13 cs variability was significant probably due to different feeding behaviour among species the d 18 os values of living land snails suggest that species hibernate for a long period during colder months so that the signal of 18 o depleted winter rainfall in their d 18 os is lost this suggests that d 18 os and d 13 cs values of pomatias elegans from this archaeological succession provide valuable clues for seasonal spring autumn climatic con ditions during the early middle holocene the d 18 os values of fossil specimens are significantly lower than in modern shells and in agreement with other palaeoclimatic records suggesting a substantial increase of precipitation and or persistent changes in air mass source trajectories over this region between ca 8 8 cal ka bp and 6 2 6 7 ka ago the d 13 cs trend suggests a transition from a slightly 13 c enriched to a 13 c depleted diet between early and middle holocene compared to present conditions we postulate that this d 13 cs trend might reflect changes in the c3 vegetation community potentially combined with other environmental factors such as regional moisture increase and the progressive decrease of atmospheric co2 concentration copyright 2010 john wiley sons ltd

oxygen and carbon stable isotopes of modern land snail shells as environmental indicators from a low latitude oceanic island abstract land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells which are generally highly abundant and well preserved in the fossil record contain a temporal record of environmental change in the form of isotope codes to evaluate the utility of this approach for a low latitude oceanic setting 207 modern shells of 18 species of land snail were analyzed for their oxygen and carbon isotope composition along a north and south facing altitudinal gradient 10 2160 m a s l in tenerife island 28 n of the canary archipelago shells collected at each locality showed a relatively large range in isotope composition which was greater along the south facing transect drier and hotter suggesting that the variance in shell isotope values may be related to water stress although pooled isotope values did not generally show strong relationships with environmental variables i e altitude temperature and precipitation mean isotope values were strongly associated with some climatic factors when grouped by site the mean 18o value of the shell 18oshell by site displayed a negative correlation with elevation which is consistent with the positive relationship observed between temperature and the 18o value of rain 18orain calculated 18o values of the snail body water 18obody derived from observed temperatures and 18oshell values using the equation of grossman and ku grossman e l and ku t l 1986 oxygen and carbon isotope fractionation in biogenic aragonite chem geol isotope geosci sec 59 59 74 displayed a trend with respect to altitude that was similar to measured and hypothetical 18o values for local rain water the calculated 18obody values from the shell declined 0 17 vsmow per 100 m which is consistent with the altitude effect observed for tropical rains in western africa and it correlated negatively with rainfall amount accordingly lower 18oshell values indicate lower temperatures lower 18orain values and possibly higher rainfall totals a positive correlation between the mean 13c values of shells 13cshell and plants by site suggests that shells potentially record information about the surrounding vegetation the 13cshell values varied between 15 7 and 0 6 vpdb indicating that snails consumed c3 and c4 cam plants where more negative 13cshell values probably reflects the preferential consumption of c3 plants which are favored under wetter conditions individuals with more positive 13cshell values consumed a larger percentage of c4 plants other potential factors such as carbonate ingestion or atmospheric co2 contribution were unlikely that were more common at lower elevations of the hotter and drier south facing transect the relatively wide range of shell isotope values within a single site requires the analysis of numerous shells for meaningful paleoclimatic studies although small differences were observed in isotope composition among snail species collected at a single sampling site they were not significant suggesting that isotope signatures extracted from multi taxa snail data sets may be used to infer environmental conditions over a broad range of habitats

carbon and oxygen isotope composition of shell carbonate of desert land snails abstract variation in 13 c 12 c and 18 o 16 o ratios in the shell carbonate of several species of land snails was studied along a climatic gradient in semi arid to arid areas in the southern levant 13 c was found to be enriched in snails from communities having plants with a c 4 photosynthetic pathway depleted 13 c values were found in areas with high mean annual rainfall apparently due to higher input of metabolic co 2 as a result of greater snail activity shell carbonate 18 o values show a weak relation to the 18 o values of rainwater the shell 18 o values are enriched by 2 8 relative to isotopic equilibrium with environmental waters enrichment is suggested to result from metabolic effects on body water with lower activity producing greater enrichment but evaporation could also be a factor consistent differences in both 13 c and 18 o were found among species and may relate to the time when shell deposition occurs as with most paleoenvironmental indicators the application of shell isotopes is complicated by the multiplicity of controls of isotopic composition

stable isotope ecology δ18o δ13c δ15n of modern land snails along an altitudinal gradient in southern appalachian mountains usa abstract the first isotopic baseline is established for the snail neohelix from the big santeetlah creek watershed appalachian mountains shell 18o 3 6 to 0 4 declined with altitude 0 06 per 100 m and correlated with measured rain 18o a flux balance model suggests that relative humidity increased from 0 89 at 710 m to 0 91 at 1620 m in agreement with higher precipitation at higher altitudes coherent relationships between shell precipitation and humidity suggest that this taxon should be a valid paleoprecipitation archive in north america the respective 13c and 15n values of body 28 3 to 23 2 0 4 to 4 9 and shell organics 28 2 to 24 0 0 0 to 3 4 did not exhibit a trend with altitude and were uncorrelated with potential food resources a stable isotope mixing model suggests that neohelix primarily consume fungi 48 and lichen 17 with minimal ingestion of c3 plants the relative contributions of different food items however varied in an unpredictable fashion along the altitudinal gradient this study illustrates that even though snail foraging ecology from woodlands is complex and more variable than anticipated combining several isotope systems permits dietary inferences more easily than field observations alone

a late pleistocene refugium in mediterranean north africa palaeoenvironmental reconstruction from stable isotope analyses of land snail shells haua fteah libya abstract the late pleistocene to holocene archaeological record of north africa is key to understanding the emergence of anatomically modern humans into west asia and europe and the broadening of subsistence strategies in the shift from hunter gatherer to pastoral agricultural lifeways some contend that these developments were modulated by major shifts in climate and environment evaluation of this hypothesis requires the pairing of local and regional climate records with well dated archaeological sequences the haua fteah archaeological site in the gebel akhdar region of libya provides a key site to test this hypothesis as the cave contains one of the longest and most complete sequences of human occupation in north africa as well as abundant material for palaeoenvironmental reconstruction this study uses stable isotope analyses 18o and 13c of the terrestrial mollusc helix melanostoma to construct a palaeoenvironmental framework for interpreting north african human environment interactions from the upper palaeolithic to the neolithic 30 000 to 5000 years ago the land snail stable isotope records from haua fteah suggests that cool arid conditions in the cave peaked during marine isotope stage mis 2 this stage was however only marginally drier than previous and subsequent stages and coincided with an increase in occupation density in the cave this suggests that the gebel akhdar may have served as an environmental refugium from the more extreme aridity in the surrounding sahara and arid coastal plains for late stone age lsa populations in north africa conditions became progressively wetter towards the holocene however generally wetter conditions were interrupted by two arid episodes at c 8 0 ka and 7 3 ka that appear to coincide with regional changes reflected elsewhere in the mediterranean basin

cross shore surfzone tracer dispersion in an alongshore current 1 cross shore surfzone tracer dispersion in a wave driven alongshore current is examined over a range of wave and current conditions with 6 continuous dye releases each roughly 1 2 hours in duration at huntington beach california fluorescent dye tracer released near the shoreline formed shore parallel plumes that were sampled on repeated cross shore transects with a jet ski mounted fluorometer ensemble averaged cross shore tracer concentration profiles are generally shoreline attached maximum at or near the shoreline with increasing cross shore widths and decreasing peak values with downstream distance more than a few 100 m from the source tracer is often well mixed across the surfzone i e saturated with decreasing tracer concentrations farther seaward for each release cross shore surfzone absolute diffusivities are estimated using a simple fickian diffusion solution with a no flux boundary at the shoreline and range from 0 5 2 5 m2 s 1 surfzone diffusivity scalings based on cross shore bore dispersion surfzone eddy mixing length and undertow driven shear dispersion are examined the mixing length scaling has correlation r2 0 59 and the expected best fit slope 1 indicating that horizontal rotational motions are important for cross shore tracer dispersion in the surfzone

holocene 4 5 1 7 cal kyr bp paleoenvironmental conditions in central argentina inferred from entire shell and intra shell stable isotope composition of terrestrial gastropods the isotopic fingerprint of terrestrial gastropods has been increasingly used as a credible natural paleoenvironmental archive most published work has used this proxy at tropical and temperate latitudes of the northern hemisphere and focused on entire shell analysis the present study provides entire shell and intra shell isotopic profiles to infer average and seasonal late holocene environmental conditions in central argentina 30 s shells of plagiodontes daedaleus gastropoda odontostomidae were retrieved from the alero deodoro roca sector b site one of the few archaeological sites in central argentina rich in shells collected by pre hispanic hunter gatherer groups ancient entire shells exhibited values that were 2 5 higher in 13c and 1 8 higher in 18o than modern individuals pointing to higher abundance of c4 plants and overall drier conditions lower relative humidity and or higher rain 18o during 4 5 1 7 cal kyr bp than today in agreement with published regional proxies intra shel

stable carbon and oxygen isotopic variations in modern rabdotus land snail shells in the southern great plains usa and their relation to environment abstract variations of stable isotopic ratios of carbon 13c 12c and oxygen 18o 16o were investigated in modern shells of two species of rabdotus land snails r dealbatus and r alternatus in the southern great plains geographic variation in relation to climate and vegetation microgeographic variation variability among individuals and detailed records of seasonal variations within individual shells were studied stable carbon isotopic ratios in shell carbonate are primarily a function of the isotopic composition of the diet of the snails as represented by the isotopic composition of shell organic matter this in turn reflects the presence or absence of cam crassulacean acid metabolism or c4 plants vegetation density may have a small effect on the carbon isotope ratios microgeographic variation samples within 25 to 300 m is greater than that seen across different climatic regions and points to very local control of isotopic variations predominantly related to vegetation seasonal variations as assessed through serial analysis of individual shells up to 35 samples per shell may provide a means for distinguishing between isotopic influences of perennial cam vs annual c4 plants carbon isotopic variations in time series of shells from a site provide a means of reconstructing temporal changes in environment and climate oxygen isotopic values of shell carbonate are uniform across the region and also show no significant microgeographic variation the oxygen isotopic composition appears to be mainly a function of the rainwater isotopic composition with no direct influence of rainfall amount or evaporative effects the 18o values are only 2 enriched relative to estimated equilibrium with rainwater variability is low sd of 0 8 among sites so the isotopic composition of fossil rabdotus shells can provide a precise record of changes in the isotopic composition of rain over time

environmental significance of 13c 12c and 18o 16o ratios of modern land snail shells from the southern great plains of north america c 12 c and 18 o 16 o ratios of aragonite shells of modern land snails from the southern great plains of north america were measured for samples from twelve localities in a narrow east west corridor that extended from the flint hills in north central oklahoma to the foothills of the sangre de cristo mountains in northern new mexico usa across the study area shell y 18 o values pdb scale ranged from 4 1x to 1 2x while y 13 c values ranged from 13 2x to 0 0x y 18 o values of the shell aragonite were predicted with a published steady state evaporative flux balance model the predicted values differed with one exception by less than 1x from locality averages of measured y 18 o values this similarity suggests that relative humidity at the time of snail activity is an important control on the y 18 o values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells correlated y 13 c values of coexisting vallonia and gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern great plains plant ecology although there is considerable scatter multispecies transect average y 13 c values of the modern aragonite shells are related to variations in the type of photosynthesis i e c3 c 4 in the local plant communities the results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals species etc and thus better represent the bneighborhoodq scale temporal and or spatial environmental variations of interest in studies of modern and ancient systems d 2004 university of washington all rights reserved

stable isotope composition of middle to late holocene land snail shells from the marroquies archeological site jaen southern spain paleoenvironmental implications abstract the marroquies archeological site located in the metropolitan area of jaen 37 46 southern spain contains land snail shells which have been preserved jointly with other human and zooarcheological remains new radiocarbon analyses carried out on pristine domestic animal and human bones confirmed that these remains belong to the copper age interval 4470 3880 cal bp n 8 land snail entire shells of two species one herbivorous and one omnivorous were analyzed for 13 c 12 c and 18 o 16 o ratios to estimate the paleoenvironmental conditions prevailing during the middle to late holocene in the southernmost part of europe the 13 c values of fossil shells ranged from 13 8 to 8 1 n 15 whereas modern specimens ranged from 10 8 to 8 6 n 20 the fact that ancient and modern shells generally exhibited similar 13 c values suggests that the 13 c values of the vegetation have remained relatively stable during 4470 3880 cal bp and the present snail species did not differ in 13 c values despite their differing dietary habits the 18 o values of fossil shells ranged from 4 9 to 1 2 n 15 whereas modern specimens ranged from 2 8 to 0 9 n 20 fossil shells were on average 2 lower in 18 o values than modern shells calculations from a snail evaporative steady state flux balance model suggest that shells at 4470 3880 cal bp precipitated under appreciably higher relative humidity conditions than today whereas rain 18 o values and air temperatures at the soil air interface during snail active period were possibly similar although samples from this study represent a time period in which the well documented late holocene aridification trend in southern spain already started snails suggest conditions at 4470 3880 cal bp were yet noticeably wetter than at present this study shows that land snail shells preserved in holocene archeological sites offer valuable paleoenvironmental information in their isotope codes

the effect of stokes drift and transient rip currents on the inner shelf part i no stratification abstractthis is part ii of a two part study focused on stokes drift and transient rip current trc effects on the unstratified part i and stratified this paper inner shelf part i focuses on funwavec coupled ocean atmosphere wave sediment transport coawst coupling and trc effects on mixing and exchange on an unstratified inner shelf here two simulations r3 and r4 are performed on a stratified inner shelf and surfzone with typical bathymetry stratification and wave conditions r3 is a coawst only simulation no trcs while r4 has funwavec coawst coupling with trcs in r4 trcs lead to patchy near surface cooling vertical isotherm displacement and increased water column mixing for both r3 and r4 the mean lagrangian circulation has two nearly isolated surfzones and inner shelf overturning circulation cells with a stronger r4 inner shelf circulation cell the r4 inner shelf vertical velocity variability is 2 3 times stronger than a simulation with trcs and no stratification relative

younger dryas early holocene transition in the south eastern iberian peninsula insights from land snail shell middens the land snail sphincterochila candidissima from archeological records in villena se spain was studied isotopically to estimate the younger dryas yd early holocene transition in the western mediterranean live collected individuals exhibited body 21 8 1 6 and shell 5 8 1 4 d 13 c values typical of a c3 plant diet probably combined with carbonate ingestion calculations of a carbon flux balance mixing model suggest that living specimens experienced similar metabolic rates with comparable ratio of input and output fluxes of bicarbonate from the snail hemolymph all fossil shells showed comparable d 13 c values among each other but values were 2 higher than living specimens this may be explained by higher water stress at the yd holocene transition or by the suess effect shell d 18 o values averaged 1 3 0 8 for living individuals 0 5 0 8 for holocene 8 4 10 2 cal ka bp specimens and 0 4 0 6 for yd 12 0 12 4 cal ka bp snails an oxygen flux balance mixing model suggests that yd shells precipitated during relative humidity rh values of 79 82 after which rh increased gradually reaching maximum values of 87 88 at 8 4 8 6 cal ka bp and from there rh eventually declined to present values of 82 comparisons with other snail data suggest that the xerophilous sphincterochila records different environmental signatures fro other contemporaneous taxa copyright 2013 john wiley sons ltd

a lagrangian stochastic model of surf zone drifter dispersion 1 drifter derived cross shore and alongshore surf zone diffusivities were previously estimated on an alongshore uniform beach over 1000 s for five huntington beach california 2006 hb06 experiment release days the cross shore diffusivity kx had a nonmonotonic time dependence potentially due to the shoreline or to weaker diffusivity seaward of the surf zone the alongshore diffusivities ky were qualitatively consistent with shear dispersion but differed from the classic taylor laminar theory here modeled and analytic diffusivities for the five release days are derived from a lagrangian stochastic model lsm that uses the drifter derived bulk cross shore averaged velocity variance and cross shore dependent mean alongshore current the lsm modeled and analytic cross shore diffusivities are nonmonotonic due to the shoreline and strongly suggest that the observed cross shore diffusivity is shoreline affected the lsm typically reproduce well the observed kx with lagrangian time scale between 75 and 200 s consistent with surf zone eddy time scales hb06 drifter trajectories were too short to observe the analytic long time kx limit and weaker diffusivity seaward of the surf zone may be important at longer times 1000 s on all release days the lsm model and analytic alongshore diffusivity reproduce well the observed ky with alongshore lagrangian time scales between 95 and 155 s the isolated shear induced diffusivity is very well represented by an analytic theory which incorporates a nonzero lagrangian time scale many of the stochastic model parameters can be specified a priori with reasonable assumptions to predict surf zone dispersion of an initial value problem pollution spill

modeling surf zone tracer plumes 1 waves mean currents and low frequency eddies 1 a model that accurately simulates surf zone waves mean currents and low frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion in this paper a wave resolving time dependent boussinesq model is compared with waves and currents observed during five surf zone dye release experiments in a companion paper clark et al 2011 compare a coupled tracer model to the dye plume observations the boussinesq model uses observed bathymetry and incident random directionally spread waves for all five releases the model generally reproduces the observed cross shore evolution of significant wave height mean wave angle bulk directional spread mean alongshore current and the frequency dependent sea surface elevation spectra and directional moments the largest errors are near the shoreline where the bathymetry is most uncertain the model also reproduces the observed cross shore structure of rotational velocities in the infragravity 0 004 f 0 03 hz and very low frequency vlf 0 001 f 0 004 hz bands although the modeled vlf energy is 2 3 times too large similar to the observations the dominant contributions to the modeled eddy induced momentum flux are in the vlf band these eddies are elliptical near the shoreline and circular in the mid surf zone the model data agreement for sea swell waves low frequency eddies and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion