a 2100 year trace element and stable isotope record at decadal resolution from rice lake in the northern great plains usa a 2100 year multiple proxy record at decadal resolution from a topographically closed but hydrolog ically open lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated northern great plains ngp at rice lake north dakota the ostracode mg ca ratios show good correlation with other ostracode diatom and aeolian proxy records from other sites in the ngp all of these records show significant century scale periodicities which have been related to solar variability as inferred from atmospheric radiocarbon records this coherent and consistent pattern suggests that these sites record climatic variability at regional scales the interval of the mediaeval climatic anomaly from 900 to 550 cal yr bp contains two pronounced dry periods during the following little ice age a single period of frequent drought that peaked at 300 cal yr bp was bracketed by wet periods before and af

a regional approach for modeling cliff retreat rate the makhteshim country israel abstract cliff retreat rate significantly affect the evolution of landforms and cliff stability cliff retreat studies also provide intriguing clues regarding past geomorphic conditions and environmental changes we hereby present a model to calculate cliff retreat rate based on spatial data of cliff structure and morphology the model is applied to numerous cliffs in the arid makhteshim country israel and results are calibrated using published rates of two local cliffs the calculated retreat rates confirm previous assertions that the crater cliffs are receding very slowly but reveal that the rates vary significantly along the cliffs 1 18 cm ky 1 results also provide first estimates of retreat rates of other major cliffs in the region including fast retreat rates at the sede zin cliff 300 600 cm ky 1 the proposed model provides a robust analysis to account for local cliff talus morphology and yields rate estimates representative of current conditions rather than a long term geologic average rate results presented constitute important new insights into regional geomorphic processes and on the stability of specific cliff sections within the study area

stability of composite river banks the stability of a river bank depends on the balance of forces motive and resistive associated with the most critical mechanism of failure many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size geometry and structure of the bank the engineering properties of the bank material the hydraulics of flow in the adjacent channel and climatic conditions rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt clay bank erosion occurs by fluvial entrainment of material from the lower cohesionless bank at a much higher rate than material from the upper cohesive bank this leads to undermining that produces cantilevers of cohesive material upper bank retreat takes place predominantly by the failure of these cantilevers three mechanisms of failure have been identified shear beam and tensile failure the stability of a cantilever may be analysed using static equilibrium and beam theory and dimensionless charts for cantilever stability constructed application of the charts requires only a few simple measurements of cantilever geometry and soil properties in this analysis the effects of cracks and fissures in the soil must be taken into account these cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface following mechanical failure blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue hence the rate of bank retreat is fluvially controlled even though the mechanism of failure of the upper bank is not directly fluvial in nature this cycle of bank erosion undermining cantilever failure and fluvial scour of the toe operates over several flood events and has important implications for river engineering channel changes and the movement of sediment through fluvial systems

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

seismic evidence of shallow gas from lake van eastern turkey analysis of multi channel seismic reflection and chirp data from lake van eastern turkey reveals various shallow gas indicators including seismic chimneys enhanced reflections bright spots mud volcanoes pockmarks and acoustic blanking the enhanced reflections suggesting the presence of free gas are most dominant and observed at more than 200 locations they are characterized by very high amplitude reflections and occur in both deep and shallow sedimentary sections some enhanced reflections are accompanied by very subtle seafloor expressions such as mounds which may suggest active venting activity seismic chimneys or columnar zones of amplitude blanking have been observed in much of the surveyed area seismic chimneys in the study area cannot be associated with any known faults that would act as migration pathways for deep fluids this suggests that the observed structures in lake van sediments allow the preferential emission of gases which might be for a large share of biogenic origin the acoustic blanking characterized by transparent or chaotic seismic facies is seen in the eastern part of the lake the lakeward edge of the acoustic blanking largely coincides with the 100 m water depth contour indicating that past changes of the hydrostatic pressure may be responsible for the distribution of these anomalies mound like features interpreted as mud volcanoes occur in a few locations the presence of these features may suggest active gas emission very strong amplitude anomalies or bright spots with negative polarity indicating gas charged zones are also seen in a number of locations pockmarks are observed only in the northeastern part of the study area the scarce occurrence of pockmarks in the study area might be ascribed to a higher permeability of the lake sediments or to the absence of the substrate reservoir providing the critical mass of gases necessary to produce such features turbidites tephra layers and deltaic deposits have the potential to provide ideal conditions to allow the sediments to act as a gas reservoir

effect of the development of notches and tension cracks on instability of limestone coastal cliffs in the ryukyus japan abstract notches cut by waves are currently developing at the base of vertical coastal limestone cliffs in okinawa japan the cliff height varies from 3 0 22 1 m and the maximum notch depth is 8 8 m many rectangular or cubic blocks which appear to have originated from cliff failures are found on platforms in front of the cliffs on the flat top surface of the cliff tension cracks often run parallel to the cliff face the vertical face of the cliffs displays small undulations but no sliding striation suggesting that cliff failures have been caused by toppling rather than by shearing or sliding we use slope stability analysis to determine the critical condition for toppling failure physical and mechanical properties of the cliff material were first obtained from laboratory tests the results indicate that the strength of limestone shows a scale effect such that the strength decreases with increasing size of the test specimens based on this result we estimated the strength of a rock mass corresponding to the size of the coastal cliff cliff stability was then analyzed using a cantilever beam model comparison of the stability analysis and the dimension of fallen blocks indicates that toppling failure is strongly associated with the development of notches and tension cracks

geochemistry of ostracode calcite part 2 the effects of water chemistry and seasonal temperature variation on candona rawsoni abstract reconstruction of lake paleochemistry from the isotope and trace element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonality of shell formation monthly field collections of live candona rawsoni from two hyposaline lakes in the eastern dakotas reveal large variations in 18 o values 2 5 o and mg ca and sr ca ratios up to 35 among individual adults within the same assemblage because the measured variations in water chemistry were small the amplitude of ostracode 18 o and mg ca variations must result from seasonal temperature variation ostracode sr ca ratios which should be temperature independent shows strong positive covariance with shell mg ca these results imply that sr uptake in ostracode calcite increases with the mg content of the shell the partitioning coefficient for mg on the other hand appears to decreases at high values of mg ca in the host water the geochemical variability in the field collections indicates that c rawsoni populations are composed of multiple overlapping generations that attain maturity at different times many juveniles apparently undergo several molts in mid summer and persist as penultimate instars a 1 into the following spring geochemical analysis of late instar juvenile c rawsoni from lacustrine sedimentary records is likely to provide information on mid summer conditions large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate region lakes

geological controls on shallow gas distribution and seafloor seepage in an arctic fjord of spitsbergen norway abstract this study integrates high resolution shallow and deep geophysical datasets to study the seabed seepage systems linked to subsurface shallow gas and geological features influencing the fluid flow in nordfjorden central spitsbergen arctic norway this is one of the tributary fjords of the isfjorden fjord system in spitsbergen which has the highest density of pockmarks ranging up to 20 km2 the 535 pockmarks identified manually in the 300 km2 large study area have diameters ranging from 10 m to 212 m and depth varying between 1 m and 8 m sub surface seep related acoustic features such as enhanced reflections acoustic blanking and turbidity zones recorded on 55 km of new high resolution sub bottom acoustic data suggest shallow gas free and or dissolved occurrences in the marine sediments beneath the pockmarks structural features thrust faults and associated folds belonging to the palaeogene west spitsbergen fold and thrust belt and early cretaceous igneous sills have been interpreted on 2d multichannel seismic data in the triassic and permian successions some of these faults and igneous sills form seafloor ridges where pockmark density is high and they are typically aligned acoustic flares attributed to active gas seepage from the seafloor were imaged in the water column in the southern part of nordfjorden above the sub surface shallow gas occurrences and thrust faults the integrated analysis of these geophysical datasets suggests that the near seafloor tectonically deformed stratum plays an important role in the up dip propagation of fluids liquids and or gas distribution of shallow gas in marine sediments and seepage at the seafloor

palaeoenvironmental reconstruction of a pleistocene lacustrine sequence from faunal assemblages and ostracode shell geochemistry baza basin se spain abstract we have reconstructed the early pleistocene palaeoenvironmental record for a shallow lacustrine sequence from the baza basin southern spain using faunal assemblages and the shell chemistry of two ostracode species candona sp and cyprideis torosa in the ne basin sector orce area a lower pleistocene lacustrine sequence up to 10 m thick contains alternating phases of two fossil assemblages which differ in their salinity requirements the faunal assemblages record phases of 1 slightly saline ca bicarbonate rich water when freshwater organisms predominated and 2 saline nacl dominant water in which marine like organisms lived the ostracode shells from intervals with a saline fauna have higher 18o values than those from intervals with a freshwater fauna this feature corresponds to a parallel alternation of positive and negative hydrologic balances 18o and 13c values from ostracode calcite display a covariant trend which indicates that the ostracodes lived in a closed lacustrine system the isotopic data show a better agreement with the inferences from faunal assemblages than with trace element trends the trace element data although locally fitting well with the isotope and faunal interpretations suggest overall that trace element contents in ostracodes are not consistent indicators of salinity and or temperature variations but depend on a set of complex factors which may not be easily deciphered the alternation of concentration dilution phases recorded in the studied section can be correlated with climatic cycles described from synchronous ocean basin records from the late matuyama chron

surface lowering rates of uplifted limestone terraces estimated from the height of pedestals on a subtropical island of japan in kikai jima south western japan many pedestal rocks have developed on the surface of holocene raised coral reef terraces with known dates of emergence pedestals are formed just under boulders which are considered to have been transported by tsunami and settled on a reef flat before emergence on the assumption that boulders protect the underlying limestone terrace from rainfall solution the rate of surface lowering of these limestone terraces was evaluated from the height of pedestals and the period of their formation the result showed that the mean lowering rate over 6000 years is 205 mm ky copyright 2007 john wiley sons ltd

a new process response coastal recession model of soft rock cliffs abstract the development of cliff erosion predictive models is limited by the complex interactions between environmental processes and material properties over a range of temporal and spatial scales current models incorporate a stochastic representation of cliff behavior based on assumptions regarding the magnitude and frequency of events in a probabilistic framework the new model presented here has been developed to incorporate the behavioral and mechanical characteristics of coastal cliffs which are dominated geologically by overconsolidated clays tills and an associated protective colluvial wedge this model is capable of providing precise and stable responses to some of the inherent uncertainties in cliff recession processes including those caused by different failure mechanisms e g colluvium generation groundwater and erosive tidal cycles material strength is incorporated using the unconfined compressive strength of the material that composes the cliff unlike previous models a calibration parameter is restricted to account for uncertainties linked to marine processes the mechanisms of cliffline retreat have been identified as slump and topple landslides once cliff material has fallen colluvium formation at the cliff foot is incorporated into the model using three different procedures according to the geomechanical characteristics of the debris the model is validated through profile evolution assessment at various locations of coastline retreat on the holderness coast uk higher groundwater content also produces an increase in the number and size of the slope failures the results represent an important step forward in linking material properties to the processes of cliff recession

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

characteristics of sea cliff erosion induced by a strong winter storm in the eastern mediterranean abstract changes in sea cliff morphologies along the 30 km long sharon escarpment segment of israel s weakly cemented mediterranean eolianite cliff line were analyzed to gain quantitative insights into erosion characteristics associated with a high energy winter storm 10 20 year return interval ground based repeat lidar measurements at five sites along the cliff line captured perturbations of cliff stability by basal wave scouring during the storm subsequent post storm gravity driven slope failures in the cliff face above and return of the system to transient stability within several months post storm erosion which amounted to 70 of the total volume of cliff erosion documented resulted in dramatic local effects of up to 8 m of cliff top retreat and yet at the larger scale of the 30 km cliff line examined erosion during the storm and the year that followed affected less than 4 of the cliff length and does not appear to be above the average cliff length annual erosion implied by previously published decadal scale retreat rates along this sea cliff our results do not support a direct association between strong storm events and elevated erosion and retreat at the cliff line scale

towards an improved understanding of erosion rates and tidal notch development on limestone coasts in the tropics 10 years of micro erosion meter measurements phang nga bay thailand knowledge and understanding of shore platform erosion and tidal notch development in the tropics and subtropics relies mainly on short term studies conducted on recently deposited carbonate rocks predominantly holocene and quaternary reef limestones and aeolianites this paper presents erosion rates measured over a 10 year period on notches and platforms developed on the permian ratburi limestone at phang nga bay thailand in so doing it contributes to informing a particular knowledge gap in our understanding of the erosion dynamics of shore platform and tidal notch development in the tropics and subtropics notch erosion rates on relatively hard ancient limestones measured directly on the rock surface using a micro erosion meter mem over time periods of a decade or more the average intertidal erosion rate of 0 231 mm yr is lower than erosion rates measured over 2 3 years on recent weaker carbonate rocks average erosion rates at phang nga vary according to location and site and are in rank order from highest to lowest mid platform 0 324 mm yr notch floor 0 289 mm yr rear notch wall 0 228 mm yr lower platform 0 140 mm yr notch roof 0 107 mm yr and supratidal 0 095 mm yr the micro relief of the eroding rock surfaces in each of these positions exhibits marked differences that are seemingly associated with differences in dominant physical and bio erosion processes the results begin to help inform knowledge of longer term shore platform erosion dynamics models of marine notch development and have implications for the use of marine notches as indicators of changes in sea level and the duration of past sea levels copyright 2014 john wiley sons ltd

mg ca and sr ca of ostracod valves from living species of lake geneva abstract the mg ca and sr ca ratios of living ostracods belonging to 15 different species and sampled monthly over a one year cycle at five sites 2 5 13 33 and 70 m water depths in western lake geneva switzerland are compared to the oxygen and carbon isotope compositions measured on the same samples as well as to the temperature and chemical composition of the water 18 o h2o 13 c dic mg ca h2o and sr ca h2o at the time of ostracod calcification the results indicate that trace element incorporation varied at the species level mainly because of the ecological and biological differences between the different species life cycle micro habitat preference biomineralisation processes and the control thereof on trace element incorporation of the ostracods in littoral zones the mg ca and sr ca of ostracod valves increase as temperature and mg ca and sr ca of water increase during spring and summer hence reflecting mainly seasonal variations however given that for lake geneva the mg ca and sr ca of water also vary with temperature it is not possible to distinguish the effects of temperature from those of changes in chemical composition of water on the trace element content in ostracod valves results support that both water temperature and water mg ca and sr ca ratios control the final trace element content of cyprididae valves in contrast the trace element content of species living in deeper zones of the basin is influenced by variations in the chemical composition of the pore water for the infaunal species trace element content measured for these specimens cannot therefore be used to reconstruct the compositions of the water lake bottom in addition incorporation of mg and sr into the shell differs from one family sub family or even species to the other this suggests that the distinctive mg and sr partition coefficients for the analysed taxa result from different valve calcification strategies that may be phylogenetic

geo and hydro acoustic manifestations of shallow gas and gas seeps in the dnepr paleodelta northwestern black sea shallow gas occurs between 0 and 1000 m below the sea floor it consists mainly of microbial formed or thermogenic methane or a combination of both sometimes with a limited admixture of higher hydrocarbons propane butane etc

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

modeling cyclic recession of cohesive clay coasts effects of wave erosion and bluff stability abstract a mathematical model combining the effects of wave erosion beach sediment and bluff slope stability has been developed to study the episodic cyclical recession of cohesive clay coasts the model was applied to the southern great lakes in north america which although non tidal experience seasonal fluctuations in lake level of about 0 5 m and long term fluctuations of up to 2 m model runs were designed to explore the interaction between various components of the system including profile shape bluff recession rates lake level variations beach morphodynamics the geomechanical characteristics of the material and the type slump topple and size of the slope failures model runs were made for the equivalent of 100 years quasi equilibrium conditions developed in the runs which had similar erosion rates to the field with parallel slope retreat in the upper portion of the profiles and slope decline in the lower portion temporal variations in the rate of recession of the crest of the bluff closely matched changes in lake level the model confirmed previous work that suggested that rates of bluff recession are strongly controlled by the rate of erosion below the water surface but it also provided support for a more recent proposal that rates of bluff recession also influence rates of erosion in shallow water it was found that positive and negative changes in the size of the beach can either promote or hinder bluff and profile erosion depending on local circumstances the model demonstrated that bluff height debris mobility wave undercutting and groundwater levels are key factors in determining the stability of coastal bluffs the model represents a promising new tool to forecast and thereby mitigate the effects of climate change on marine and lacustrine coasts

identification of shallow gas by seismic data and avo processing example from the southwestern continental shelf of the ulleung basin east sea korea abstract this study investigates the evidence of shallow gas from a newly collected dataset comprising 2d multi channel seismic mcs single channel seismic scs chirp sub bottom profiler sbp and multi beam echo sounder mbes data from the southwestern continental shelf of the ulleung basin east sea korea various indicators of shallow gas were identified in this part the shelf including seismic chimneys acoustic flares in the water column pockmarks enhanced reflections and acoustic blanking seismic chimneys which are related to fluid leakage within the subsurface are characterized weak to high amplitude upturned or concave upward internal reflection with polarity reversal in mcs section whereas they are faint or transparent on scs section with 700 hz and chirp sbp sections with 3 5 khz frequency acoustic flares which are diagnostics of active gas venting were detected only on the chirp sbp sections there is also evidence of small scale depressions immediately below the acoustic flares these are interpreted as formed by the sudden explosion of gas enhanced reflections 3 km long concordant with stratification are observed at different levels acoustic blanking anomalies caused by absorption of acoustic energy due to the presence of gas are seen in the range 50 200 ms twt below seabed amplitude versus offset avo analysis indicates the presence of free gas ca 350 ms twt below sea surface using the mcs dataset recorded by a 600 m long streamer cable the avo cross section shows that the lower repetitive signals in the mcs data are due to the gas plume not lithological contrast our study highlights that avo analysis is an extremely useful tool for identifying free gas helping to discriminate water gas contacts and bright events among the chaotic signals on the mcs data

variability in ostracod partition coefficients d sr and d mg implications for lacustrine palaeoenvironmental reconstructions living and sub recent ostracods were collected from four lakes and foul springs located in belgium france and spain characterized by low water mg ca ratios from 0 08 to 0 65 valves of ostracods belonging to cyprideis torosa candona neglecta c marchica and c candida have been extensively analysed for their magnesium and strontium contents with respect to calcium comparisons of these results are made using the same elements from the waters in which the ostracod valves calcified our results offer new and somewhat different interpretations with respect to the uptake of mg and sr in the calcitic ostracod valves these findings include the following 1 the partition coefficient l sr for ostracods belonging to the same genus candona is not a constant the observed variability in d sr values could be due to the rare of biological calcification although more investigations are necessary to assess the influence of this factor it is possible that some taxa grouped under the genus candona belong to a different genus 2 even at the species level cyprideis torosa the ostracod d sr cannot be considered to be constant at low water mg ca ratio 0 65 our d sr value for c torosa is higher than those determined by others for c torosa calcified in evolved marine water 3 the mg ca ratio of the water appears as a major factor influencing d mg for ostracods for low water mg ca values similar to 2 d mg drastically increases this phenomenon is also effective for inorganic calcite implying a non biologic effect that could be linked to mg2 adsorption consequently large variations in me content of fossil ostracod valves from selected lacustrine sequences with expected low water mg ca similar to 2 can be due to small variations in water mg ca c 1998 elsevier science b v all rights reserved

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

mg ca ratios in the shells of cultured specimens and natural populations of the marine ostracode xestoleberis hanaii crustacea abstract we studied mg ca ratios in the shells of the shallow water ostracode xestoleberis hanaii ishizaki 1968 ishizaki k 1968 ostracodes from uranouchi bay kochi prefecture japan tohoku university science report second series geology 40 1 1 45 in laboratory cultured and field collected samples x hanaii was cultured in our laboratory from a 7 to adult stage under controlled temperatures 15 28 c results of the culture experiments show that the mg ca ratio of x hanaii is strongly correlated with water temperature within the temperature range of 15 28 c in the field collected samples seasonally fluctuating mg ca ratios of their shells parallel the variation in the seasonal seawater temperature and the water temperature estimated from the mean value of the adult stage samples collected on any given date agreed quite well with the average water temperature for the period of 8 days prior to the collection date based on the changes in mg ca ratios and shell morphology in the course of ontogeny we suggest that mg is contained in the organic matter which is one of the shell components that form the network or the framework within which the calcite crystals are formed

ostracode geochemical record of holocene climatic change and implications for vegetational response in the northwestern alaska range abstract trace element analysis of the calcareous shells of ostracodes in a sediment core from farewell lake provides the first limno geochemical record for climatic reconstructions in alaska when compared with pollen data from the same site this record offers new insights into climatic controls over vegetation dynamics during the holocene the low mg ca ratios and high sr ca ratios suggest that a relatively cold dry climate prevailed in this region between 11 000 and 9000 yr b p uncalibrated14c ages are used throughout the paper this result contrasts with previous interpretations of a thermal maximum at this time corresponding to the widespread establishment ofpopuluswoodland forest the trace element record suggests instead that the warmest period of the early holocene at farewell lake was between 8500 and 8000 yr b p during the decline ofpopulus marked decreases in sr ca and mg ca suggest a major increase in effective moisture around 6500 yr b p which coincided with the establishment ofpiceaboreal forests in the farewell lake region this climatic change was probably widespread throughout much of alaska and adjacent canada and might have induced the rapid spread ofalnusand the shift frompicea glaucatop marianadominance across that region our geochemical record also suggests that the late holocene climate history was more complex than previously thought on the basis of palynological studies according to this record growing season temperatures increased 6000 4500 yr b p decreased 4500 1500 yr b p and increased with fluctuations afterward after 6000 yr b p stratigraphic changes in pollen percentages ofpiceaappear to be positively related with those of mg ca this relationship implies that once the threshold of effective moisture was crossed for the establishment ofpiceaforests temperature was the primary control ofpiceapopulation density

genesis of channel bank overhangs in the niger delta and analysis of mechanisms of failure abstract the instability of channel banks carries a significant economic implication because of its effect on navigation and channel commercial development the impact of bank instability in the niger delta is accentuated by the dense network of rivers and creeks the occurrence of overhangs in channel banks is not restricted to stratified banks in which clay overlies sand field observation and analysis indicate that factors such as stratigraphy local climate bio technical and fluvio tidal processes act singly or in combination to generate overhangs in channel banks the failure of channel banks with overhangs involves one of four mechanism namely rotation beam shear and tension failure a mathematical basis for the discrimination of these failure mechanisms is described the significance of identifying the critical location of tension cracks for the failure of the overhang is discussed although the study is based on experience in the niger delta the principles applied and the conclusions reached undoubtedly apply to areas of similar geological and environmental conditions

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

a global evaluation of temperature and carbonate ion control on mg ca ratios of ostracoda genus krithe 1 improving estimates of past ocean temperatures is paramount to our understanding of ocean circulation and its role in climate change magnesium calcium mg ca ratios of carapaces of the benthic ostracod genus krithe were determined from new globally distributed core top samples from the norwegian sea cape hatteras shelf gulf of mexico sulawesi margin indonesia new zealand shelf ceara rise and the north atlantic a linear regression of the krithe mg ca ratios and bottom water temperature bwt reveals a significant correlation for locations where temperature during carapace calcification was above 3 c which can be described by the equation mg ca 0 972 0 152 bwt 7 948 1 103 consistent with previous north atlantic calibrations deviations from the global calibration line below 3 c follow the same pattern observed for benthic foraminifera suggesting that the incorporation of magnesium into ostracodal calcite may be secondarily controlled by changes in carbonate ion concentration therefore we propose a linear regression that describes the relationship between magnesium incorporation temperature and carbonate saturation for low temperatures 3 c mg ca 0 972 0 152 bwt 0 100 0 030 d co3 4 440 1 103 1 se 0 3 c while the standard error of the calibration is small it requires an accurate knowledge of past d co3 concentration which necessitates additional proxy data applying the calibration to glacial samples from the deep north atlantic ocean we show that estimates of bottom water temperatures generated from the new d co3 corrected equations are more consistent with results from oxygen isotopes and pore water studies

the spatial pattern and drainage cell characteristics of a pockmark field nile deep sea fan over 25 300 seabed pockmarks were mapped from the rosetta channel region of the western niledeepseafan ndsf using concurrent high resolution 2d chirp profiler and multibeam bathymetry data which spans the holocene pleistocene period within the region apockmarkfield containing 13 800 pockmarks was analysed using spatial statistics to determine the distribution of pockmarks within the field pockmarks within the field are small 16 m diameter shallow 0 5 m deep circular depressions which formed within the last 6500 years the fluid source for the field is identified as an accumulation generation of gas beneath a hemipelagic seal c 20 40 ms beneath the seabed the position of the pockmarks is shown to be unrelated to the depth to the fluid source and an irregular high amplitude acoustic anomaly which is tentatively interpreted as a possible carbonate precipitate of biogenic microbial activity statistical spatial analysis of the field confirms the distribution of pockmarks is not random an exclusion zone surrounding each individual pockmark is identified the exclusion zone is a unique minimum radius around each pockmark which is not penetrated by any other pockmark the exclusion zone works in unison with self organised criticality soc in determining the spatial distribution of pockmarks within the field the exclusion zone is interpreted as apockmark drainagecell a conceptual model for apockmarkdrainagecell is proposed whereby pockmark formation dissipates a radius area of fluid and overpressure thereby preventing the formation of another pockmark within that cell consequently pockmarks are observed to separate or produce anti clustering tendencies within the field

independent impacts of calcium and carbonate ion concentration on mg and sr incorporation in cultured benthic foraminifera abstract laboratory culture experiments were conducted to determine effects of seawater carbonate ion concentration co32 and thereby calcite saturation state on mg and sr incorporation into calcite of two species of shallow water benthic foraminifera ammonia tepida and heterostegina depressa impact on mg and sr incorporation by increased seawater co32 and thereby higher is absent in either species comparison to results from a similar culturing experiment in which was varied as a function of ca2 reveals that saturation state affects incorporation of mg and sr through calcium rather than carbonate availability the similarity in response by both species is surprising since the average mg ca ratio is 70 times higher in h depressa than in a tepida furthermore these results suggest that the ions involved in biomineralization i e ca2 and dic are processed by separate cellular transport mechanisms the similar response of mg and sr incorporation in this study suggests that only differences in the ca2 transport mechanism affect divalent cation partitioning

palaeoenvironment and palaeoclimate of the middle miocene lake in the steinheim basin sw germany a reconstruction from c o and sr isotopes of fossil remains a differentiated reconstruction of palaeolimnologic environmental and climatic conditions is presented for the middle miocene long term freshwater lake 14 3 to 13 5 ma of the steinheim basin on the basis of a combined c o and sr isotope study of sympatric skeletal fossils of aquatic and terrestrial organisms from the lake sediments the oxygen isotope composition for lake water of the steinheim basin 18oh2o 2 0 0 4 vsmow n 6 was reconstructed from measurements of 18opo4 of aquatic turtle bones the drinking water calculated from the enamel of large mammals proboscideans rhinocerotids equids cervids suids has 18oh2o values 18oh2o 5 9 1 7 vsmow n 31 typical for middle miocene meteoric water of the area this 18oh2o value corresponds to a mean annual air temperature mat of 18 8 3 8 c calculated using a modern day 18oh2o mat relation hence large mammals did not use the lake water as principal drinking water in contrast small mammals especially the then abundant pika prolagus oeningensis drank from 18o enriched water sources 18oh2o 2 7 2 3 vsmow n 7 such as the lake water differences in sr and o isotopic compositions between large and small mammal teeth indicate different home ranges and drinking behaviour and support migration of some large mammals between the swabian alb plateau and the nearby molasse basin while small mammals ingested their food and water locally changes in the lake level water chemistry and temperature were inferred using isotopic compositions of ostracod and gastropod shells from a composite lake sediment profile calcitic ostracod valves ilyocypris binocularis 18o 1 7 1 2 vpdb 13c 0 5 0 9 vpdb n 68 and aragonitic gastropod shells gyraulus spp 18o 2 0 1 3 vpdb 13c 1 1 1 3 vpdb n 89 have 18o and 13c values similar to or even higher than those of marine carbonates 13c values of the biogenic carbonates parallel lake level fluctuations while 18o values scatter around 2 2 and reflect the short term variability of meteoric water inflow vs longer term evaporation 87sr 86sr ratios of aragonitic gyraulus spp gastropod shells parallel the lake level fluctuations reflecting variable inputs of groundwater and surface waters using a water 18oh2o value of 2 0 vsmow water temperatures calculated from skeletal tissue 18o values of ostracods are 16 7 5 0 c gastropods 20 6 5 6 c otoliths 21 8 1 4 c and fish teeth 17 0 2 7 c the calculated mat 19 c lake water temperatures 17 to 22 c and the 18o enriched water compositions are indicative of warm temperate climatic conditions possibly with a high humidity during this period vegetation in the area surrounding the basin was largely of the c3 type as indicated by carbon isotopic compositions of tooth enamel from large mammals 13c 11 1 1 1 vpdb n 40

coastal notches their morphology formation and function deep coastal notches develop through undercutting of steep coastal slopes consisting of rocks that are strong enough to support the weight of the overburden notches are found from the tropics to the poles and in a wide range of rock types virtually tideless to megatidal seas and high to low wave energy environments the emphasis in the literature has been on notches in calcareous rocks in warm microtidal seas and with the general assumption that they have been produced by bioerosion or chemical dissolution few scientifically rigorous attempts have been made to determine the processes responsible for notch formation in different environments and rock types however or to determine whether different processes produce distinct notch morphologies within the same tidal and wave environments the use of notches as palaeo sea level markers and to determine rates of tectonic uplift has been particularly important in the mediterranean notches are more difficult to employ for this purpose in the middle latitudes where higher waves and tides amplify the range of elevations over which the erosional mechanisms are effective as well as increasing the exposure and effect of rocks of variable resistance to erosion to maximize the utility of notches as sea level markers and to better understand and model their development in a wide range of environments we need to understand and be able to quantify the relationship between notch shape and size and the elevational efficacy of the various erosional processes

boulder coastal deposits at favignana island rocky coast sicily italy litho structural and hydrodynamic control abstract boulders are frequently dislodged from rock platforms transported and deposited along coastal zones by high magnitude storm waves or tsunamis their size and shape are often controlled by the thickness of bedding planes as well as by high angle to bedding fracture network we investigate these processes along two coastal areas of favignana island by integrating geological data for 81 boulders 49 rupture surfaces called sockets and fracture orientation and spacing with four radiocarbon dates numerical hydrodynamic analysis and hindcast numerical simulation data boulders are scattered along the carbonate platform as isolated blocks or in small groups which form as a whole a discontinuous berm underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform boulders are composed of ruditic to arenitic size clastic carbonates their size ranges from 0 6 to 3 7 m 0 55 to 2 4 m and 0 2 to 1 m on the major a medium b and minor c axes respectively the highest value of mass estimation is 12 5 t almost all of boulders and sockets are characterized by a tabular or bladed shape the comparisons between a the fractures spacing and the length of a and b axes and b the frequency peaks of c axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho structural control in the size and shape of joint bounded boulders these comparisons together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets suggest that blocks originate by detachment from the platform edge thus the most common pre transport setting is the joint bounded scenario hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from 2 m to 8 m for joint bounded boulders and from few tens of centimeters up to 11 m for submerged boulders the comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders our data suggest that boulders have been transported by several storm events even in very recent times

how does wave impact generate large boulders modelling hydraulic fracture of cliffs and shore platforms abstract boulder quarrying by large waves along steep high energy coastlines contributes to erosion both by causing inland migration of cliff faces and by vertical lowering of coastal platform surfaces it also leads to the formation of coastal boulder deposits cbd above and inland of the high water mark we describe mechanisms by which hydraulic fracture creates boulders from cliffs and bedrock platforms intense fluid pressures are induced by wave impact on the base of overhanging ledges and also along interior surfaces as cracks fill with water during wave runup and overtopping these processes impose large loads on the overlying rock and bending stresses thus induced can create or propagate microcracks in the rock repeated loading leads to complete fracture and detachment of bedrock slabs which are liberated as boulders we consider these processes using the aran islands ireland as a type locality both because cbd there are well documented and because flat lying strata and orthogonal joint patterns yield tabular bedrock geometry which lends itself to modelling the loaded rock is modelled as a beam with a microcrack that is fractured by a bending stress from an applied hydrodynamic load this simple approach allows us to examine general scalings and dependencies we determine a condition for fracture relating the fluid pressure loaded area fracture stress microcrack position and geometry in some situations the fluid pressure need only be a fraction of the fracture stress fracture is most likely to occur during extreme wave conditions and when the exposed rock has a large eroded area for loading the balance of forces suggests that larger beams break more easily facilitating the creation of large boulders

ostracod shell chemistry as proxy for paleoenvironmental change abstract the application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades most studies have investigated mg and sr in ostracod shells as proxies for temperature and salinity and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems only a few preliminary studies have used trace metals in paleolimnological studies such as cd ba and zn as paleonutrient indicators or mn fe and u as redox and oxygenation indicators this paper reviews the state of the art of geochemical analyses in microfossils such as ostracods foraminifera and corals and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies in paleoceanography foraminifera and corals are most prominently used to reconstruct past climate conditions well established proxies such as 18o mg ca and sr ca provide information about changes in sea surface temperatures in addition a great number of new proxies have been developed recently such as radiogenic isotopes and redox sensitive trace elements in paleolimnology ostracod shell chemistry is widely used to assess paleohydrological changes reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as mg ca and sr ca ratios but depending on the hydrological and geological settings of the lake system local calibrations are needed to assess which proxy is suited to reflect which processes new proxies need to be tested by novel techniques that recently have become available compared to conventional instrumentation used in ostracod shell chemistry methods such as laser ablation icp ms and nanosims allow single shell analysis and provide high resolution data the potential of ostracods in paleolimnology is not yet fully assessed but can be developed by learning from paleoceanographic studies

critical notch depths for failure of coastal limestone cliffs case study at kuro shima island okinawa japan development of a notch at the base of a cliff reduces cliff stability and often induces a collapse pleistocene limestone coastal cliffs of elevation 5 m in kuro shima ryukyu islands have a prominent notch with a depth of 3 4 m at their bases around these coastal cliffs collapses different from previous studies of cliff collapses in the ryukyu islands were found collapses in kuro shima have a horizontal failure surface the horizontal failure surface situated at the height of the failure surface corresponding to the retreat point of the notch is bounded by vertical joints cutting the whole cliff and the reef flat in front of the cliff two types of horizontal failure surface were found triangular and quadrangular the distinction appears to depend on the angle between the vertical joints and the front face of the cliff prior to collapse these cliffs appear to have been separated from the adjacent cliffs by the development of vertical joints consequently a cliff that will collapse can be identified in advance cliff instability is strongly dependent on the development of a notch to study the effect of notch development on cliff collapse the notch depth at which collapse occurs was calculated using stability analysis instability of a cliff increases with notch depth collapse occurs at the horizontal failure surface when the ratio of the notch depth to the seaward length of the cliff is approximately 0 5 0 7 for a triangular failure surface and 0 7 0 9 for a quadrangular failure surface copyright 2010 john wiley sons ltd

effect of salinity and seawater calcite saturation state on mg and sr incorporation in cultured planktonic foraminifera abstract trace elements incorporated in planktonic foraminiferal test carbonate are commonly used as paleoproxies for instance mg ca ratios are frequently used for reconstructing sea surface temperature and together with the foraminiferal stable oxygen isotope ratios are also used as paleosalinity proxy foraminiferal sr ca ratios constitute another example of the application of trace elements in paleostudies since they may reflect the sr ca values of seawater however over the past few decades it has been proven that the incorporation of trace elements in foraminiferal calcite is controlled by more than one environmental parameter to quantify the effect of salinity on mg and sr incorporation planktonic foraminifera globigerinoides sacculifer sensu stricto were grown in the laboratory under different environmental conditions laboratory experiments allowed us to separate a direct salinity effect from a possible independent impact through differences in the calcite saturation state of the seawater although the temperature effect is more important than the salinity effect a change of 4 salinity units is equivalent to a 1 c bias on mg ca based temperatures this effect of salinity on mg incorporation is minor however when using mg ca based temperatures in combination with foraminiferal 18o to calculate salinity it cannot be neglected the present study shows salinity as the overriding control on mg incorporation within the range of studied between 5 25 and 6 50 co32 between 218 and 270 mol kg at a constant temperature of 26 c in contrast appears to be the main control on foraminiferal sr incorporation 0 10 mmol mol per 100 mol kg rise in co32 whereas salinity has a non significant influence on sr ca

threshold height of coastal cliffs for collapse due to tsunami theoretical analysis of the coral limestone cliffs of the ryukyu islands japan abstract stability analyses were made for both gravity and wave induced collapses of coastal cliffs with a vertical failure surface to determine the threshold cliff height for tsunami induced collapses the models proposed in this study have two distinct parameters characterizing the cliff height calculations of the critical notch depth from these models show that gravity induced collapses occur on cliffs of any height whereas the threshold cliff heights for tsunami induced collapses are controlled by the height of the tsunamis the relation between the threshold cliff height and the tsunami height is represented by a power law function

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

shore platform development on an uplifting limestone island over multiple sea level cycles niue south pacific abstract niue is an uplifted limestone island which preserves an atoll morphology with a sequence of terraces around its outer margin a modern terrace fringes much of the island and this paper examines the extent to which this terrace can be considered accretionary and constructed by coral and coralline algae or erosional and truncated by those processes that form shore platforms the occurrence of pleistocene limestone outcropping across this terrace and the continuation of caves and other karst features dissecting the sub aerial limestones onto the forereef indicate the overall significance of erosion at present live coral cover is restricted to isolated colonies growing in grooves potholes and karstic channels eroded into the modern terrace surface coralline algae coat the outer margin of this terrace and also veneer prominent surf benches that occur on the windward shore 1 2 m above the terrace surface terrace evolution on niue therefore appears to be primarily erosional in origin there is little accommodation space for reef growth and as a result accretional fringing reefs are absent around most of the island erosional processes have also dominated landscape evolution for at least the past few eustatic cycles fringing reef growth is absent or severely restricted during the last interglacial and occurs as sporadic small reefs on the seaward margin of an erosional terrace during the penultimate interglacial the development of terrace features in uplifting reef settings does not necessarily originate through accretional reef processes and may in fact be entirely erosional although reef terraces are frequently depositional in other settings those present on niue indicate a predominance of erosion indicating the need to discriminate emergent terraces in terms of the extent to which they are erosional or accretionary when using such features to reconstruct island palaeoenvironments

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

paleoenvironmental changes in northern mongolia during the last deglaciation revealed by trace element records in ostracods from lake hovsgol ostracods possess bivalve carapaces composed of low mg calcite which can be preserved in a variety of sedimentary environments they are a useful paleoenvironmental indicator in particular for non marine environments although previous studies of lake baikal and lake hovsgol have provided some evidence of large scale paleoenvironmental changes in central asia during the late pleistocene trace element records in ostracods from these two lakes which may reveal the detailed limnological processes have not yet been reported in this study we analyzed stable isotopes and trace elements in ostracods in three gravity core sediments recovered from lake hovsgol northern mongolia to reconstruct the long term limnological histories of the lake radiocarbon dating results indicated that ostracod bearing core sediments were deposited from 14 5 to 21 5 ka which corresponds to the early stage of the last deglaciation including the last glacial maximum lgm the mg ca and sr ca ratios from two species of ostracods c lacustris and l inopinata ranged from 4 to 25 and 3 5 mmol mol respectively with distinct and consistent decreasing trends the changes in the mg ca and sr ca ratios indicate that the salinity of the lake water decreased substantially at the initial transition from the last glacial to the current interglacial period which was mainly due to the ice melting and introducing fresh water into the lake changes in the fe ca and u ca ratios were interpreted as water circulation changes in the bottom of the lake after the lgm the fe ca and u ca ratios gradually increased indicating that inflowing cold water induced stronger water circulation and subsequently a higher dissolved oxygen content in the bottom water of the lake the mn ca ratio had the opposite trend to the u ca and fe ca ratios which suggests that it was affected by the weathering intensity in the area around lake hovsgol the stable isotopic results for c lacustris support our paleoenvironmental interpretations in the region on the basis of trace elements as a result ostracod geochemical records from lake hovsgol northern mongolia provide new insights into paleoenvironmental changes in central asia during the onset of the last deglaciation

bioerosion of intertidal limestone co clare eire 1 paracentrotus lividus abstract the boring sea urchin paracentrotus lividus is widely distributed in the mid and lower intertidal zones on carboniferous limestone in co clare eire erosion rates have been estimated from the measurement of excavation depth and the counting of growth rings on the test shell the rates ranged from 0 25 1 5 cm a 1 on an exposed shore to 0 1 0 cm a 1 on a sheltered site larger older individuals were commoner on the exposed site the distribution activities and geomorphological significance of the organisms are discussed together with the validity of the procedures adopted to estimate erosion rates it is clear that paracentrotus is a major factor in pool deepening in the mid intertidal zone and in weakening the rock mass in the lower intertidal especially when paracentrotus erosion rates are compared with general surface lowering rates of 0 2 mm a 1

controls on ostracod valve geochemistry part 1 variations of environmental parameters in ostracod micro habitats abstract the variations of environmental conditions t ph 13 c dic dic 18 o mg ca and sr ca of ostracod habitats were examined to determine the controls of environmental parameters on the chemical and isotopic composition of ostracod valves results of a one year monitoring of environmental parameters at five sites with depths of between 2 and 70 m in lake geneva indicate that in littoral to sub littoral zones 2 5 and 13 m the chemical composition of bottom water varies seasonally in concert with changes in temperature and photosynthetic activity an increase of temperature and photosynthetic activity leads to an increase in 13 c values of dic and to precipitation of authigenic calcite which results in a concomitant increase of mg ca and sr ca ratios of water in deeper sites 33 and 70 m the composition of bottom water remains constant throughout the year and isotopic values and trace element contents are similar to those of deep water within the lake the chemical composition of interstitial pore water also does not reflect seasonal variations but is controlled by calcite dissolution aerobic respiration anaerobic respiration with reduction of sulphate and or nitrate and methanogenesis that may occur in the sediment pores relative influence of each of these factors on the pore water geochemistry depends on sediment thickness and texture oxygen content in bottom as well as pore water variations of chemical compositions of the ostracod valves of this study vary according to the specific ecology of the ostracod species analysed that is its life cycle and its micro habitat littoral species have compositions that are related to the seasonal variations of temperature 13 c values of dic and of mg ca and sr ca ratios of water in contrast the compositions of profundal species are largely controlled by variations of pore fluids along sediment depth profiles according to the specific depth preference of the species the control on the geochemistry of sub littoral species is a combination of controls for the littoral and profundal species as well as the specific ecology of the species

stability analysis of waterfall cliff face at niagara falls an implication to erosional mechanism of waterfall although recession of waterfalls or knickpoints in bedrock rivers is a common geomorphological process detailed mechanics of waterfall recession has only been examined in a few cases caprock recession model at niagara falls in which gravitational collapse of caprock induced by undercutting notch plays a significant role has been one of the well known models describing the waterfall erosion but the validity of the model has hardly been examined in a quantitative context here we assess the stability of the cliff of waterfall face of niagara falls in terms of the strength of bedrock and the length of undercutting notch the result of a cantilever model analysis shows that the caprock remains stable until the undercut reaches tens to over a hundred meters however the actual length of undercutting notch of waterfall face is up to 10 m and such a long notch to cause gravitational collapse of the caprock can hardly be formed the recession of the waterfall could therefore be caused by gradual detachment of the rock of the waterfall face induced by fluvial erosion of surface water flow rather than by elongation of undercutting notch and episodic gravitational collapses of the caprock

quantification of paleotemperature changes during isotopic stage 2 in the la draga continental sequence ne spain based on the mg ca ratio of freshwater ostracods past summer temperature changes are quantified from the la draga sequence banyoles ne spain during stage 2 24 10 ka bp using trace element content in lacustrine ostracod valves the high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the north atlantic area providing a discussion about the magnitudes of some temperature changes in ne spain and offshore portugal the coldest part of stage 2 is not documented at the classical date of similar to 18 c 14 ka bp similar to 21 5 calendar ka bp but rather occurred later date of ca 17 15 ka cal bp in the north atlantic area the onset of the bolling allerod interstadials was relatively synchroneous at similar to 14 6 ka cal bp although the magnitude of the bolling allerod improvement was more important in the southern area than in the northern area the duration of the younger dryas is discussed even if different durations are reported from calendar ages it seems that the summer temperature cooling of the younger dryas was similar around the north atlantic area c 1996 elsevier science ltd

alkalinity control on the partition coefficients in lacustrine ostracodes from australia the partition coeffi cients k d guiding the uptake of mg and sr in the low mg calcite valves of ostracodes in australian saline lakes have been reviewed in line with new information on the bicarbonate content and the mg ca of the ambient waters strongly alkaline and very high mg ca 20 waters cause the partition coeffi cients of ostracodes to differ signifi cantly from those found in other lakes with lower mg ca values water salinity does not affect the uptake of mg or sr in ostracode valves whereas the hco 3 of the water strongly correlates to k d sr with high hco 3 resulting in a signifi

palynomorphs in surface sediments of the north western black sea as indicators of environmental conditions abstract most previous black sea palynology studies have used pollen spore assemblages as proxies for climate and landscape changes and dinocyst assemblages as proxies for surface water salinity however there are few data on within region variations in these assemblages using large sets of surface samples and a full suite of palynomorphs including terrigenous pollen spores freshwater algal spores and organic remains of marine microplankton micro and meiobenthos here we fill this knowledge gap using results from a palynological study of 43 surface samples from water depths of 71 905 mbsl on the ukrainian shelf and adjoining continental slope nw black sea the palynology samples were collected in conjunction with water and sediment chemistry data grain size micropaleontological and meiobenthos data from the eu fp6 project hermes hotspot ecosystems research on the margins of european seas this dataset uniquely covers shelf and upper slope areas east and west of the odessa sinop fault zone osfz that delimits areas of lower and higher hydrocarbon gas contents respectively the new data show that on the wide shelf with a shallow ca 80 m oxycline pollen assemblages differ from classical models for marine pollen transport on the ukrainian shelf pollen concentrations are extraordinarily high far offshore and the grains are often pyrite infilled these features apparently reflect high pollen preservation potential in low oxygen sediments probably enhanced by cross shelf transport of land derived particulate organic matter the new data have important consequences for accurate modelling of carbon burial and storage in epicontinental seas and they provide a baseline for evaluating marine pollen concentrations expected to reflect the early neolithic farming on the ukrainian shelf furthermore although large concentrations of dinocysts comprise more than half of the total non pollen palynomorphs npp the high pollen concentrations skew the p d index pollen dinocyst ratio commonly used to evaluate changes in paleo shoreline proxy sea level positions despite the discharge of several large rivers to the ukrainian shelf there are negligible traces of freshwater algae in the hermes samples except at sta 15 where pediastrum is abundant overall palynomorphs of terrestrial origin make up about half 52 of the acid resistant organic walled particles on the outer nw black sea shelf and adjacent slope the abundances of the major micro and meiobenthic palynomorph groups show the same trends east and west of the osfz as the micropaleontological data reported for the hermes samples taken at the same sites the combined microzooplankton and zoobenthos surface assemblage data provide an important new baseline for evaluating historical and past changes in biodiversity and aquatic foodweb structure in the now polluted nw black sea comparison can also be made with foodweb reconstructions for permian black shales

widespread active seepage activity on the nile deep sea fan offshore egypt revealed by high definition geophysical imagery fluid escape structures on the nile deep sea fan were investigated during the mediflux mimes expedition in 2004 mud volcanoes pockmarks and authigenic carbonate structures were surveyed for the first time with a high resolution deep towed 75 khz sidescan sonar and a 2 8 khz chirp sediment echosounder in combination with existing multibeam bathymetry and detailed seafloor in situ geological observations these new data allowed detailed seep analyses about 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data atwater depths from 770 to 1700 m these gas flares coincide at the seabed with 1 the centres of the mud volcanoes where mud is also extruded 2 the borders of the mud volcanoes where the emitted gases contribute to the precipitation of authigenic carbonates and 3 to the edges of broad sheets of authigenic carbonates subsurface sediments are commonly disturbed by ascending fluids throughout the delta with an abundance of seep related carbonate structures on the seafloor the feeder channels below mud volcanoes similar to the gas conduits below the widespread carbonate crust structures and pockmarks are relatively narrow and for the vast majority of them do not exceed a few metres in diameter the seeps on the nile deep sea fan clearly follow lineations on the seafloor that ee can relate to faults

preliminary assessments on the modes of instability of the antalya sw turkey coastal cliffs cliff erosion and the consequent instabilities present a significant risk to antalya city sw turkey erosional processes include the chemical action of mixing zone water the mechanical action of waves salt erosion and biological degradation the rock properties lithology stratification strength etc are the controlling factors to this erosion the coastal cliffs of antalya are composed of tufa type carbonate rocks which occur in a wide range from collapsible soil to hard rock the instability problems of the cliffs of antalya tufa commonly involve rock fall cave collapse raveling washout of weakly lithified tufa shear failure and secondary toppling secondary toppling type instabilities culmann type failures and complex failures a combination of these two are widespread on the cliffs the occurrence of large failures are usually associated with heavy rainfall as heavy rainfall causes the saturation of pores increases pore water pressures and reduces the strength of the rock comparison between aerial photographs and topographic maps of different dates do not provide evidence of considerable retreat according to the historical data there has been little or no cliff retreat for 2 000 years therefore the erosion rate of the antalya tufa cliffs is said to be so very slow that retreat is valid only in a geological timescale however in an engineering timescale these cliffs are subjected to instabilities and to local failures causing local retreats

geological controls on boulder production in a rock coast setting insights from south wales uk abstract we investigate some of the geological controls on boulder size using a heterogeneous outcrop of blue lias limestone discontinuity and predicted boulder size data were collected on different layers of blue lias limestone on a shore platform in wales united kingdom significant differences in joint spacing were found between the four layers examined and significant differences in the predicted boulder size were found between many of the ten stratigraphic layers examined predicted boulder size ranged from 0 18 to 4 00 m measured on the longest axis these data demonstrate that the shape and size of boulders liberated from the platform is dependent on which layer of limestone is at the surface since the size of boulders varies between layers depending on the thickness of beds and joint spacing the magnitude of wave energies required to detach entrain and transport boulders must vary boulder erosion is therefore geologically contingent and highly variable through time and space this variability requires us to develop methods to predict where boulder scale erosion is likely to occur and what wave conditions are required to add these materials to the sediment supply we therefore considered the reliability of predictions of boulder size for two layers examined layers 19 and 24 predicted boulder sizes were compared with boulders recently detached by storm waves i e within 2 5 months of detachment from the same layer results show that boulder volume was statistically similar between predicted and actual boulders and either the long or intermediate axis measurements were statistically similar variations between predicted and actual boulder axis lengths are attributed to the sampling design for measuring predicted boulders variable detachment processes and the rapid breakdown of rock masses post detachment our results demonstrate that in locations where repeated entrainment transport and boulder breakdown are observed loose boulder size may not be a reliable means of reconstructing wave energies required to detach entrain and transport boulders

autogenic entrenchment patterns and terraces due to coupling with lateral erosion in incising alluvial channels the abandonment of terraces in incising alluvial rivers can be used to infer tectonic and climatic histories a river incising into alluvium erodes both vertically and laterally as it abandons fill cut terraces we argue that the input of sediment from the valley walls during entrenchment can alter the incision dynamics of a stream by promoting vertical incision over lateral erosion using a numerical model we investigate how valley wall feedbacks may affect incision rates and terrace abandonment as the channel becomes progressively more entrenched in its valley we postulate that erosion of taller valley walls delivers large pulses of sediment to the incising channel potentially overwhelming the local sediment transport capacity based on field observations we propose that these pulses of sediment can form talus piles that shield the valley wall from subsequent erosion and potentially force progressive channel narrowing our model shows that this positive feedback mechanism can enhance vertical incision relative to 1 d predictions that ignore lateral erosion we find that incision is most significantly enhanced when sediment transport rates are low relative to the typical volume of material collapsed from the valley walls the model also shows a systematic erosion of the youngest terraces when river incision slows down the autogenic entrenchment due to lateral feedbacks with valley walls should be taken into account in the interpretation of complex response terraces