sedimentary record of recent climate impacts on an insular coastal lagoon in the gulf of california abstract sedimentary records are useful to evaluate environmental changes either from natural or anthropogenic causes such as global and climate change the recent changes in accumulation rates and geochemical characteristics grain size distribution elemental composition organic carbon and carbonate concentrations recorded in a sediment core from san jose island lagoon sjil gulf of california were evaluated to determine its relationship with anthropogenic impacts and climatic variability the 210 pb derived chronology was corroborated with 239 240 pu and 137 cs stratigraphic markers the mass accumulation rate increased up to 3 times during the past 100 years 0 16 0 03 to 0 51 0 06 g cm 2 yr 1 the contents of terrigenous and marine salinity indicator elements as well as fine grained sediments also increased considerably although no anthropization evidences were observed indeed the enrichment factor of trace elements indicated that the ecosystem is still a pristine environment by using multivariate statistical techniques we inferred that the larger input of fine grained terrigenous sediments could be related to the enhancement of soil erosion from the catchment under the influence of higher rainfall rates especially during the last 20 years in addition the higher concentrations of salinity indicator elements most likely resulted from higher evaporation rates in the lagoon caused by higher minimum atmospheric temperatures we concluded that recent climate variability has become the main driver for sedimentary geochemical changes in san jose island lagoon these observations confirmed the usefulness of 210 pb dated geochemical sediment records to study the impacts of recent climate variability where long term environmental data is scarce or non existent

stratigraphic responses to a major tectonic event in a foreland basin the ecuadorian oriente basin from eocene to oligocene times the eocene to oligocene sediments of the ecuadorian oriente basin record two kinds of second order stratigraphic response to the tectonic evolution lower eocene shows evidences of local scale syntectonic deposits this tectonic activity can be related to right lateral convergent movements inverting pre cretaceous extensional structures upper eocene and oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition this response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations these data have allowed us to propose a new geodynamic model for the paleogene evolution of the oriente basin

low temperature thermochronology of the northern cordillera real ecuador tectonic insights from zircon and apatite fission track analysis the post early cretaceous tectonic development of the northern andean segment north of 5 s is loosely constrained by a series of partially and fully reset k ar ages new apatite and zircon fission track data from three traverses across the cordillera real of ecuador reveal distinct periods of accelerated crustal cooling during the cenozoic fission track ages range from 65 to 14 ma zircon and 44 to 8 ma apatite with apatite mean track lengths ranging from 14 6 to 12 1 m these results record rapid cooling rates during 43 30 ma 23 15 ma and 10 0 ma occurring at temperatures below 275 c the events reflect up to 9 km of crustal exhumation in various regions of the cordillera in response to relative changes in the kinematics of the farallon nazca and south american plates the exhumation history of the cordillera real was not continuous but rather evolved during separate phases these phases persisted for 10 myr and are partly coincident with tectonic phases of the central andes although extend for longer time periods possibly as a result of isostatically driven crustal exhumation large spatial variations in the zircon and apatite fission track data within the cordillera real indicate that local fault bounded massifs have experienced different thermal histories since 43 ma major variations are not restricted to the regional scale and exist within individual terranes faulted slivers within terranes demonstrate highly variable exhumation histories suggesting that deformation was not dominated by terrane bounding faults additionally n s variations in exhumation depths suggest that ne sw trending faults have been active since 10 9ma

the hydrological and environmental evolution of shallow lake melincue central argentinean pampas during the last millennium summary lake melincue located in the central pampean plains of argentina is a shallow 4 m subsaline lake tds 2000 ppm highly sensitive to hydrological changes the modern shallow lake system is composed of a a supralittoral area which includes a narrow mudflat a vegetated mudflat and wetlands subenvironments and b the main water body comprising lacustrine marginal and inner areas the development and extension of these subenvironments are strongly conditioned upon lake surface fluctuations past environmental changes were reconstructed through sedimentological physical and geochemical proxy analyses of two short sedimentary cores 127 cm well constrained 210 pb ages profiles were modeled and radiocarbon chronologies were determined covering a period from ad 800 to the present the analyzed sedimentary cores from lake melincue allowed for the reconstruction of past hydrological scenarios and associated environmental variability ranging from extremely low lake levels during dry phases to pronounced highstands at wet periods the paleohydrological reconstruction revealed very shallow conditions in the period between ad 806 and ad 1880 which was registered by massive deposits with low organic matter relatively wetter phases disrupting this dry period were represented by organic matter increases a major wet phase was registered by ad 1454 after the end of the medieval climate anomaly a subsequent abrupt shift from this wet phase to drier conditions could be matching the transition between the end of the medieval climatic anomaly and the beginning of the little ice age the occurrence of sedimentary hiatuses between ad 1492 and ad 1880 in melincue sequence could correspond to intensive droughts during the little ice age after ad 1880 banded and laminated autochthonous organic matter rich sediments registered an important lacustrine transgression and the onset of a permanent shallow lake corresponding to the beginning of the current warm period the uppermost recent fine grained low salinity organic sediments represent a lake transgression occurred in the 1970s coeval with a general increase in precipitation across southeastern south america this transgression is registered regionally in other pampean lakes and in the 20th century instrumental records of lake melincue this paleoenvironmental reconstruction provides a new high resolution record that registers striking hydroclimatic changes occurred at a regional scale across the pampean plains during the last millennium and it contributes to understand the past climatic history in southeastern south america

the 210pb chronology of late holocene deposition in an eastern australian lake basin we report here the results of detailed 210pb analysis of a sequence of lake sediments from little llangothlin lagoon on the new england tablelands of new south wales australia 210pb dating has been rarely employed in australia and prior to this work no attempt had been made to evaluate the method using independent dating techniques the chronology of deposition in the lake has been modelled using the constant initial concentration cic and constant rate of supply crs methods changes in the palynology and geochemistry of the sediments can be closely matched with well documented historic events in the lake catchment the dates of these events have been used to assess the modelled chronologies within the limits of resolution of the sampling interval there is good agreement between the chronology modelled using the crs approach and the dates inferred for geochemical and palynological events in the sequence the cic method provides a less successful match with the historical record although the differences between the dates derived by the two models are small

changes in biological productivity and ocean climatic fluctuations during the last 1 5 kyr in the humboldt ecosystem off northern chile 27 s a multiproxy approach abstract a sedimentary box core biac072014 collected in a coastal environment in the humboldt current ecosystem hce inglesa bay 27 s northern chile was used to reconstruct the changes in biological productivity and ocean climate fluctuations during the last 1 5 kyr via geochemical mineralogical and micropaleontological analyses from 510 ce to 930 ce el nino like conditions prevailed while during the medieval climate anomaly mca 950 ce to 1450 ce la nina like conditions predominated this pattern might have resulted from weakening strengthening of the walker cell contraction expansion of the south pacific sub tropical high spsh and a predominance of warm cold phases of the pacific decadal oscillation pdo between 1820 ce and the present inglesa bay experienced a reduction in the oxygen minimum zone omz intensity and biological productivity an increase in the detritic input and a decrease in sea surface temperature sst despite the regional intensification and secular cooling 14 s and 27 s of coastal upwelling the similarity between the reduction in biological productivity and omz intensity in this region and that in the central zone of chile 36 s suggests that inglesa bay acts a transition zone in relation to the oceanographic behaviour of the hce the reduction in the omz intensity and biological productivity during the last 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the eastern south pacific intermediate water espiw near 30 s in response to the strengthening of the circulation of the subtropical gyre the coastal cooling observed in the northern section of hce during the current warm period suggests that it is not possible to demonstrate that el nino like conditions promoted the reduction in biological productivity and omz intensity in inglesa bay

integrating u th 14c and 210pb methods to produce a chronologically reliable isotope record for the belize river valley maya from a low uranium stalagmite social and environmental changes had great spatiotemporal variability in the maya lowlands during the classic and postclassic periods and stalagmites promise high resolution paleoclimate data that

comment on substorm triggering by new plasma intrusion themis all sky imager observations by y nishimura et al 1 in their recent paper substorm triggering by new plasma intrusion themis all sky imager observations nishimura et al 2010 hereafter n2010 describe a sequence of events leading to substorm auroral onset they describe a distinct and repeatable sequence of substorm onset precursor events and discuss their finding in the light of different substorm onset models they present three cases of ground based auroral observations in detail showing the development of a poleward boundary intensification pbi followed by a north south aligned auroral arc moving equatorward toward the latitude of the subsequent substorm onset this development of a pbi and north south aurora is linked to fast plasma flows in the magnetotail resulting from enhanced reconnection near the open closed field line boundary the conclusion is drawn that the earthward transport of new plasma leads to the development of a near earth instability and auroral breakup about 5 5 min after the pbi formation 2 the event studies are accompanied by a statistical analysis of more than 200 substorm onsets that were observed by all sky imagers asi of the large themis ground based observatories gbo array harris et al 2008 mende et al 2008 using the results of their statistical study the authors determine the occurrence probability of precursor auroral forms before substorm onset they report a very impressive 84 1 occurrence frequency for the development of n s or e w auroral forms prior to substorm onset however here we will show that several aspects of their event selection and statistical analysis are flawed leading to grossly exaggerated results

climate changes reconstructed from a glacial lake in high central asia over the past two millennia abstract climatic changes in arid central asia aca over the past two millennia have been widely concerned however less attention has been paid to those in the high central asia hca where the asian water tower nurtures the numerous oases by glacier and or snow melt here we present a new reconstruction of the temperature and precipitation change over the past two millennia based on grain size of a well dated glacial lake sediment core in the central of southern tianshan mountains the results show that the glacial lake catchment has experienced cold wet climate conditions during the dark age cold period 300 600 ad dacp and the little ice age 1300 1870 ad lia whereas warm dry conditions during the medieval warm period 700 1270 ad mwp integration of our results with those of previously published lake sediment records stalagmite 18o records ice core net accumulation rates tree ring based temperature reconstructions and mountain glacier activities suggest that there has a broadly similar hydroclimatic pattern over the hca areas on centennial time scale during the past two millennia comparison between hydroclimatic pattern of the hca and that of the aca areas suggests a prevailing warm dry and cold wet hydroclimatic pattern over the whole westerlies dominated central asia areas during the past two millennia we argue that the position and intensity of the westerlies which are closely related to the phase of the north atlantic oscillation nao and the strength of the siberian high pressure sh could have jointly modulated the late holocene central asia hydroclimatic changes

variation in sedimentary 210pb over the last 60 years in the yangtze river estuary new insight to the sedimentary processes abstract anthropogenic activities have decreased the sediment transport from catchment to the river dominated continental margin mainly through river damming that controlled the estuarine and associated shelf modern sedimentation in this study radioisotopes 210pb 210pbex and 226ra and 137cs grain size and x radiograph were combined to evaluate the modern sedimentary processes in the yangtze river estuary yre we found that seabed cores collected on the estuary and associated shelf show a direct temporal correlation between decreases in initial activity and burial flux of 210pbex and suspended sediment load in relation to river damming and soil conservation from 1950 to 2016 most of sediment cores are characterized by low uniform and reverse 210pb patterns at surface and negligible sediment accumulation rates sars indicating that due to the limited sediment supply following the construction of the three gorges dam in 2003 erosion and remobilization of fine grained sediments by energetic tidal currents and biological mixing tends to have become determinant forces in controlling the fate of modern sediment burial in the yre moreover these results indicated that decline in sediment load and additional input of eroded materials will largely violate the basic assumption of constant 210pb flux raising a substantial challenge for 210pb chronology in the river dominated continental margins however we suggest that radiotracer 210pb could provide critical information for understanding the complex the sedimentary processes e g terrestrial sediment supply and redistribution by tidal currents and assessing past environmental status on the river and or tidal dominated estuaries subject to human modification

some considerations of the 210pb constant rate of supply crs dating model one of the most widely used radionuclides in the study of recent sedimentation processes is 210pb its depth profile in sediments is used as input for various dating models which provide chronologies mass fluxes and sedimentation rates in this work we revisited the crs constant rate of supply model widely used for dating sediments through 210pb a more general hypothesis periodic flux pf was proposed and although it confirmed the validity of crs chronology a detailed analysis of the mass sedimentation formula pointed out an inconsistency of the cited model a new mass sedimentation formula was proposed and validated with a lake sediment core and four marine sediment cores

a new technique for determining substorm onsets and phases from indices of the electrojet sophie we present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices by being able to prescribe different percentile values we can determine the onset and duration of substorm phases for smaller or larger variations of the auroral index or indeed any auroral zone ground based magnetometer data we apply this technique to the supermag al sml index and compare our expansion phase onset times with previous lists of substorm onsets we find that more than 50 of events in previous lists occur within 20 min of our identified onsets we also present a comparison of superposed epoch analyses of sml based on our onsets identified by our technique and existing onset lists and find that the general characteristics of the substorm bay are comparable by prescribing user defined thresholds this automated quantitative technique represents an improvement over any visual identification of substorm onsets or indeed any fixed threshold method

identifying instrumental and historical earthquake records in the sw iberian margin using 210pb turbidite chronology 1 textural mineralogical and geochemical analyses of near surface sediments from six different stations offshore sw iberian peninsula revealed the presence of thin detrital intervals corresponding to very fine grained turbidites precise dating of the two most recent sedimentary layers based on 210pb and 137cs geochronology provides ages of 1971 3 ad and 1908 8 ad these ages correspond to high magnitude historical and instrumental earthquakes that occurred in the region the 1969 horseshoe earthquake mw 8 0 and the 1909 benavente earthquake mw 6 0 such a good correlation between turbidites and high magnitude mw 6 historical and instrumental seismic events suggests that the record of mass transport deposits can also be used as a paleoseismic indicator in low convergence margins

accretion rates in coastal wetlands of the southeastern gulf of california and their relationship with sea level rise sea level rise slr is one of the most conspicuous examples of the environmental impact of recent climate change since slr rates are not uniform around the planet local and regional data are needed for proper adaptation plans 210pb dated sediment cores were analyzed to determine the trends of sediment accretion rates sars at three tropical saltmarshes in the estero de urias lagoon gulf of california mexico in order to estimate the slr trends during the past 100 years under the assumption that these ecosystems accrete at a similar rate to slr a chemometric approach including multivariate statistical analysis factor analysis of geochemical data including 13c 15n c n ratios and br na and cl as proxies for marine transgression was used to identify the marine transgression in the sediment records based on core geochemistry only one of the three cores provided a long term record attributable to marine transgression slr trends estimated from sars showed increasing values from a min

substorm evolution of auroral structures auroral arcs are often associated with magnetically quiet time and substorm growth phases we have studied the evolution of auroral structures during global and local magnetic activity to investigate the occurrence rate of auroral arcs during different levels of magnetic activity the ground magnetic and auroral conditions are described by the magnetometer and auroral camera data from five magnetometers ionospheric radars all sky cameras large experiment stations in finnish and swedish lapland we identified substorm growth expansion and recovery phases from the local electrojet index il in 1996 2007 and analyzed the auroral structures during the different phases auroral structures were also analyzed during different global magnetic activity levels as described by the planetary kp index the distribution of auroral structures for all substorm phases and kp levels is of similar shape about one third of all detected structures are auroral arcs this suggests that auroral arcs occur in all conditions as the main element of the aurora the most arc dominated substorm phases occur in the premidnight sector while the least arc dominated substorm phases take place in the dawn sector arc event lifetimes and expectation times calculated for different substorm phases show that the longest arc dominated periods are found during growth phases while the longest arc waiting times occur during expansion phases most of the arc events end when arcs evolve to more complex structures this is true for all substorm phases based on the number of images of auroral arcs and the durations of substorm phases we conclude that a randomly selected auroral arc most likely belongs to a substorm expansion phase a small time delay of the order of a minute is observed between the magnetic signature of the substorm onset i e the beginning of the negative bay and the auroral breakup i e the growth phase arc changing into a dynamic display the magnetic onset was observed to precede the structural change in the auroral display a longer delay of a few minutes was found between the beginning of the growth phase and the first detected auroral structure

residence times of surface water and particle reactive 210pb and 210po in the east china and yellow seas 228ra 226ra 210pb and 210po were measured in the surface waters of the east china and yellow seas using mass balance equations for the ra isotopes we estimated the total flux of diffusion from sediments and desorption from suspended particles to be 0 1 dpm 226ra cm 2 a 1 and 1 dpm 228ra cm 2 a 1 and residence times to be 2 3 years for the waters on the east china sea shelf and 5 6 years for yellow sea waters box model calculations yielded generally congruent scavenging residence times for 210pb and 210po in the waters of 2 months on the shelf and 7 months in the kuroshio current these suggest that reactive heavy metals and pollutants discharged through rivers from the continent to the east asian continental shelf are largely deposited on the bottom sediments prior to transport to the pelagic ocean by lateral mixing

substorm triggering by new plasma intrusion themis all sky imager observations 1 a critical long standing problem in substorm research is identification of the sequence of events leading to substorm auroral onset based on event and statistical analysis of themis all sky imager data we show that there is a distinct and repeatable sequence of events leading to onset the sequence having similarities to and important differences from previous ideas the sequence is initiated by a poleward boundary intensification pbi and followed by a north south n s arc moving equatorward toward the onset latitude because of the linkage of fast magnetotail flows to pbis and to n s auroras the results indicate that onset is preceded by enhanced earthward plasma flows associated with enhanced reconnection near the pre existing open closed field line boundary the flows carry new plasma from the open field line region to the plasma sheet the auroral observations indicate that earthward transport of the new plasma leads to a near earth instability and auroral breakup 5 5 min after pbi formation our observations also indicate the importance of region 2 magnetosphere ionosphere electrodynamic coupling which may play an important role in the motion of pre onset auroral forms and determining the local times of onsets furthermore we find motion of the pre onset auroral forms around the harang reversal and along the growth phase arc reflecting a well developed region 2 current system within the duskside convection cell and also a high probability of diffuse appearing aurora occurrence near the onset latitude indicating high plasma pressure along these inner plasma sheet field lines which would drive large region 2 currents

in situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge the substorm current wedge scw is a fundamental component of geomagnetic substorms models tend to describe the scw as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk linked by a westward electrojet we use multispacecraft observations from perigee passes of the cluster 1 and 4 spacecraft during a substorm on 15 january 2010 in conjunction with ground based observations to examine the spatial structuring and temporal variability of the scw at this time the spacecraft traveled east west azimuthally above the auroral region we show that the scw has significant azimuthal substructure on scales of 100 km at altitudes of 4000 7000 km we identify 26 individual current sheets in the cluster 4 data and 34 individual current sheets in the cluster 1 data with cluster 1 passing through the scw 120 240 s after cluster 4 at 1300 2000 km higher altitude both spacecraft observed large scale regions of net upward and downward field aligned current consistent with the large scale characteristics of the scw although sheets of oppositely directed currents were observed within both regions we show that the majority of these current sheets were closely aligned to a north south direction in contrast to the expected east west orientation of the preonset aurora comparing our results with observations of the field aligned current associated with bursty bulk flows bbfs we conclude that significant questions remain for the explanation of scw structuring by bbf driven wedgelets our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the scw

fallout 210pb as a soil and sediment tracer in catchment sediment budget investigations a review increasing anthropogenic pressures coupled with climate change impacts on natural resources have promoted a quest for innovative tracing techniques for understanding soil redistribution processes and assessing the environmental status of soil resources among the different existing tracers the fallout component of the radioisotope lead 210 also termed unsupported or excess lead 210 pb 210 ex when referring to its presence in soil or sediment arguably offers the broadest potential for environmental applications due to its origin and relatively long half life for more than five decades pb 210 ex has been widely used for dating sediments to investigate sedimentation processes and since the 1990s to provide information on the magnitude of soil and sediment redistribution the aim of this review is to provide a comprehensive evaluation and discussion of the various applications of pb 210 ex as a tracer in terrestrial and aquatic environments with particular emphasis on catchment sediment budget investigations this paper summarizes the state of the art related to the use of this tracer the main assumptions the requirements including the need for accurate analytical measurements and for parallel validation and the limitations which must be recognised when using this fallout radionuclide as a soil and sediment tracer lessons learned and current and future research needs in the environmental and radiochronological application of pb 210 ex are also presented and discussed c 2014 elsevier b v all rights reserved

sedimentary evolution of an active margin during middle and upper cretaceous times the north peruvian margin from late aptian up to senonian the sedimentary evolution of the north peruvian margin during upper cretaceous can be summarized as follows

the use of bomb spike calibration and high precision ams 14c analyses to date salt marsh sediments deposited during the past three centuries abstract a combination of bomb spike calibration and conventional calibration of ams 14c dating has been used to determine a detailed age depth model for a 1 m sediment section collected from a salt marsh in poole harbour southern england these data were compared with the chronology obtained from 210pb analysis and 137cs age markers we report post bomb values of over 1 46 f14c 146 modern 14c and both the rising and falling limbs of the atmospheric bomb spike are identified five pre bomb samples were analysed using multi target high precision 2 ams analysis and after the replicates were combined the one sigma uncertainty was as low as 9 14c yr on some ages these data and an additional three normal precision pre bomb 14c samples were calibrated using calib 5 0 and the chronology constrained using the prior knowledge of independent age markers obtained from the analysis of pollen and spheroidal carbonaceous particle scps no agreement was found between the 14c bomb spike dates and the crs 210pb chronology modelled for this sequence in addition poor agreement was found between the signal of the 1960s weapons test fallout indicated by the 14c bomb spike dates and the timing suggested by the 137cs data this disagreement is attributed to the influence of the local discharge of 137cs from the former ukaea site at winfrith we use our new chronology to confirm the existence of an acceleration in sedimentation rates in poole harbour during the last 100 yr previously reported for this site by long et al long a j scaife r g edwards r j 1999 pine pollen in intertidal sediments from poole harbour uk implications for late holocene sediment accretion rates and sea level rise quaternary international 55 3 16 and conclude that bomb spike 14c calibration dating may offer a more robust alternative to the use of 210pb chronologies for dating sediment deposition in salt marsh environments in addition we demonstrate how the use of high precision ams analysis has the potential for reducing some of the uncertainties involved in the high resolution dating of recent salt marsh sediments

earthward plasma sheet flows during substorm phases 1 magnetic reconnection in the earth s magnetotail converts open magnetic flux to closed producing fast flows in the plasma sheet earthward fast flows can thus be used as a proxy for energy and momentum transfer into the closed magnetosphere during the course of a substorm characteristics of flows observed before substorm onset can provide information on the role of the flows in substorm onset triggering as well as the sequence of substorm related processes we use 15 years of data obtained by geotail cluster and themis to study statistically the distribution of earthward plasma sheet flows during substorms substorm phases are determined from time series of the al index and the z component of the interplanetary magnetic field we find that the occurrence frequency of medium speed 100 km s 500 km s flows on the other hand does not clearly increase during the substorm growth phase the increase at substorm onset is more gradual than for the medium speed flows the occurrence frequency of high speed flows peaks at the beginning of substorm recovery these results indicate that any effect of the flows on substorm onset triggering would be caused by medium rather than very high speed flows

determination of recent deposition rates in lake constance with radioisotopic methods sedimentation rates were determined with the 210pb method in eight sediment cores from lake constance the rate of deposition in the main basin obersee varies from about 0 06 g cm 2 y 1 in the central part to 0 13 g cm 2 y 1 in the eastern part of the lake and then increases rapidly towards the rhine delta in the central lake area the rate of deposition has been approximately constant since 1900 and dating with the 210pb method is in good agreement with sedimentological observations in the konstanzer trichter area the deposition rate has been increasing since about 1955 as a result of eutrophication and subsequent high carbonate production dating with 137cs is fairly accurate for sediments deposited at a high rate but is questionable for slowly accumulating ones a positive correlation of 210pb fluxes and sedimentation rates indicates that 210pb flux into sediments follows the distribution pattern of solids 210pb profiles in four sediment cores interpreted in terms of a constant flux model display synchronous fluctuations of the sedimentation rate however their relation to long range particulate input variations remains to be proved sedimentation rates determined with the 210pb method were used to calculate recent nutrient and heavy metal fluxes anthropogenic fluxes of zn and pb are in the same range of magnitude as in other polluted areas in europe and america

anthropogenic and climate driven environmental change in the songnen plain of northeastern china over the past 200 years abstract multi proxy records pollen particle size loss on ignition c n ratios and radioisotopes 210pb and 137cs of natural and anthropogenic environmental change are reported for sediment cores from three lakes in the songnen plain of northeastern china these data provide high resolution records of vegetation history and catchment dynamics for the region over the past 200 years records show that vegetation initially responded to a cooler and drier climate during the little ice age with high values of pinus ephedra and amaranthaceae and low values of cyperaceae as anthropogenic activity increased in northeastern china pinus gradually declined while broad leaved deciduous vegetation increased in the region from 1900 ce aquatic taxa also increased from 1900 ce as the wetlands responded to changing lake water levels and agricultural activities land policy implementation had a profound impact on the vegetation with arboreal pollen in keqin and hongyan lakes declining from 1900 ce as marginal land was reclaimed and agricultural activities increased vegetation diversity increased as agricultural activities caused environmental disturbance with pollen taxa indicating human disturbance including humulus polygonum and xanthium silt and organic content increased and c n ratios declined after 1940 ce as erosion in the catchment and productivity in the lakes increased re vegetation strategies introduced in the late 1990s caused an increase in arboreal taxa in the pollen record this multi proxy palaeoenvironmental study improves understanding of the long term relationship between natural and anthropogenic environmental change in northeastern china

magnetic characterization of distinct soil layers and its implications for environmental changes in the coastal soils from the yellow river delta abstract the soils in the yellow river delta yrd were formed through the deposition of the yellow river sediments under complicated hydrodynamic conditions resulting in large variability in soil properties in this study environmental magnetic analyses were conducted on four typical soil profiles and one high resolution soil profile with distinct soil layers to examine the soil formation process and to track the environmental changes the results showed that the red clay layer rcl in the yrd soil profiles had unique magnetic properties which could be clearly separated from the yellow silt layer ysl at frequency dependent susceptibility fd 6 susceptibility of anhysteretic remanent magnetization arm 250 10 8 m3 kg 1 arm magnetic susceptibility lf 5 arm saturated isothermal remanent magnetization sirm 45 10 5 m a 1 and sirm lf

lacustrine sediment chronology defined by 137cs 210pb and 14c and the hydrological evolution of lake ailike during 1901 2013 northern xinjiang china abstract dating lake sediments in arid and semi arid zones by using 137cs and excessive 210pb 210pbex methods is challenging because of the irregular climatic variations and anthropogenic effects here we try to establish the reliable geochronology of the lacustrine core drilled from lake ailike northern xinjiang of china by using 137cs and 210pbex dating methods and improve our understanding of the principal factors that affect the dating results the results indicate that it is important to normalize the 137cs activities by particle size and organic matter in order to diminish their enrichment effects on 137cs activities and thus help us to obtain the accurate 137cs ages the performance of the sediment isotope tomography sit model is better than the other 210pbex derived models the erosion process results in the failure of the commonly used constant rate of supply crs model as well as the low values of the sedimentation rate the 137cs inventory and the post 1963 mean annual flux of 210pbex in ailike core furthermore based on the sit model chronology we further clarify the lake evolution history of the past century and assess the anthropogenic impacts on lake ailike the hydrology of lake ailike was mainly controlled by natural climate before 1960 ce whereas it was completely controlled by intensive human activities after 1960 ce this study supports that the 210pbex based sit model appears to be an adequate method for deriving ages in the lacustrine systems with strong hydrological variability

variations in carbon burial and sediment accretion along a tidal creek in a florida salt marsh salt marshes store large quantities of carbon in the form of buried organic matter om and consequently play a major role in the global carbon cycle yet vertical accretion and carbon burial rates cbrs can vary by orders of magnitude on small spatial scales the goal of this study was to provide insight into carbon burial variability of a single tidal salt marsh six marsh sediment cores were collected along a tidal creek in the big bend of florida from the mouth to the coastal forest within the marsh levee and plain each was analyzed for porosity om total organic carbon toc total nitrogen tn 13c 15n and excess 210pb to determine vertical accretion and cbrs porosity om and toc and tn were found to be highest in the low marsh and within the marsh levee stable isotopes of om indicate the source is dominated by c3 plant species in both the levee and plain average vertical accretion ranges from 0 9 mm yr 1 to 2 2 mm yr 1 with the slowest rates in the low marsh average carbon burial ranges from 49 5 g oc m 2 yr 1 to 109 5 g oc m 2 yr 1 high carbon burial associated with low sediment accumulation in the low marsh and low carbon burial associated with high sediment accumulation rates in the high marsh are typical in this marsh these variations imply that the highest carbon burial occurs in the zone most vulnerable to loss via inundation and erosion

cross stratigraphies from a seismically active mud lens off peru indicate horizontal extensions of laminae missing sequences and a need for multiple cores for high resolution records abstract marine laminated sediments in dysoxic areas of the ocean floor are an excellent archive for high resolution climate reconstructions while the existence of discontinuities produced by natural events such as underwater landslides slumps strong bottom currents and or bioturbation is usually acknowledged for long records the extent of their influence on high resolution sequences is usually not considered in the present work we show strong evidence for multiple stratigraphic discontinuities in different gravity and box cores retrieved off pisco peru covering the last 600 years chronostratigraphies are largely based on cross correlation of distinct sedimentary structures determined by x ray image analysis and validated using 210 pb 241 am and 14 c profiles as well as proxy records the cross correlation of distinct stratigraphic layers allows for chronostratigraphic tie points and clearly shows that some sedimentary sequences are continuous across scales of tens of kilometers indicating that regional processes often determine laminae formation some differences in laminae thickness were found among cores which could be explained by different sedimentation rates spatially variable deposition of diatom blooms changes in silica dissolution and partial deposition erosion caused by bottom currents using multiple stratigraphic tie points provides clear evidence for laminated sequences present in some cores to be missing in other cores moreover instantaneous depositions from upslope were identified in all the cores disrupting the continuity of the sediment records these discontinuities instantaneous deposits and missing sequences may be due to slumps possibly triggered by earthquakes and or erosion by strong bottom currents in spite of the missing sequences in some cores a continuous composite record of the last six centuries was reconstructed from spliced sequences of the different cores which provides a well constrained temporal framework to develop further high resolution proxies in this region the present work shows that paleoreconstructions developed from single cores particularly in areas with strong seismic activity and or strong bottom currents are subject to both temporal gaps and instantaneous depositions from upslope both of which could be misinterpreted as abrupt climate changes or anomalous climate events we stress the need for multiple cores to determine the stratigraphic continuity and chronologies for high resolution records

carbon burial in bosten lake over the past century impacts of climate change and human activity abstract lake sediment is an important carbon reservoir and thus may play an important role in the terrestrial carbon cycle bosten lake is the largest inland freshwater lake in china which has been influenced by both climate change and human activity especially since 1950 in this study two short sediment cores were collected from bosten lake grain size and total organic carbon toc and inorganic carbon tic were determined we also analyzed isotopic compositions of toc 13 c org and carbonate 13 c carb and 18 o carb and 137 cs and 210 pb we found that the tic burial rate 38 7 51 8 g c m 2 year 1 was much greater than for toc 17 7 20 1 g c m 2 year 1 over the past century the toc burial rate increased from 1 6 4 2 g c m 2 year 1 in the 1900s to 9 7 10 1 g c m 2 year 1 in the 1950s and then to 43 7 44 7 g c m 2 year 1 during the 2000s the tic burial rate increased from 5 3 9 2 g c m 2 year 1 in the 1900s to 22 5 36 2 g c m 2 year 1 in the 1950s to 69 4 111 8 g c m 2 year 1 in the 1990s and then decreased to 76 1 87 6 g c m 2 year 1 in the 2000s the pronounced increasing trend in the burial rate of toc tic during 1950 2012 1950 2002 was attributable to warming and or increased human activities the sharp decrease in tic during 2002 2012 was caused by reduced biological activity less evaporation and a rapid decline in lake level our study points out that climate change and human disturbance have significantly altered carbon burial in bosten lake over the last century

determination of geochronology and sedimentation rates of shallow lakes in the middle yangtze reaches using 210pb 137cs and spheroidal carbonaceous particles abstract accurate chronologies for recent sediments of shallow lakes in the yangtze floodplain are critical to calibrate proxy records for reconstructing environmental changes during the past century this study presents the results of detailed 210pb analysis from eight lake sediment cores collected from the middle yangtze reaches southeast china unsupported 210pb activities generally declined exponentially with mass depth in the eight cores the chronologies and sedimentation rates for the sediment cores were calculated using different 210pb based mathematical models the 137cs chronomarker i e the 1963 fallout peak and the spheroidal carbonaceous particle scp chronomarker i e the start of the rapid increase in 1970 ce were selected to validate the 210pb dating sedimentation rates derived from different models were validated using historical data including lake area arable land area sediment discharge and reservoir volume in the yangtze basin the scp corrected crs constant rate of supply model performs better than other models based on validation using historical documents in the yangtze basin the 137cs chronomarker might be erroneous due to catchment driven 137cs inputs from soil erosion and post depositional diffusion both scps and 137cs are susceptible to inputs from catchment soil erosion but scps show no apparent degradation and post depositional changes in lake sediments the scp profile provides a relatively reliable chronomarker which can be used for validating 210pb chronologies in these floodplain lakes generally sedimentation rates in the eight lakes were

the 1999 2000 seismic experiment of macas swarm ecuador in relation with rift inversion in subandean foothills we propose to explain the origin of the double trend in seismicity of the macas swarm in the subandean cordillera of cutucu ecuador and characterize the corresponding active deformation of that region for that purpose seismological and geological data have been used with the deployment of a temporary seismological array with geological field observations and image processing we found that some earthquakes are aligned on a well known nne ssw trend corresponding to the orientation of the nodal planes of the reverse focal mechanism of the mw 7 0 1995 macas earthquake as for its aftershocks

agricultural fingerprints in salt marsh sediments and adaptation to sea level rise in the eastern cantabrian coast n spain abstract a multi proxy approach based on benthic foraminifera sand content short lived radioisotope activities heavy metal concentrations and aerial photography was developed to characterise the process of human disturbance on the intensely impacted eastern cantabrian coast n spain over the last two centuries analysis of two 50 cm long sediment cores from different saltmarshes in the santona estuary and their comparison with previous results in nearby coastal areas defines criteria to identify records of agricultural activities in salt marsh sediments agricultural occupation of saltmarshes and the later regeneration was recognised based on foraminifera and sand content saltmarshes in the eastern cantabrian coast are expected to adapt to ongoing sea level rise based on the high sedimentation rates 14 18 mm yr 1 observed during the regeneration process of previously reclaimed areas these findings can potentially be useful in other temperate saltmarshes with abundant sediment input as a cost effective adaptation measure to counteract the effects of sea level rise

geodynamic evolution of the northern and central andes during early to middle mesozoic times a tethyan model the early to middle mesozoic sedimentary and magmatic history of the northern and central andes i e the nne trending colombian ecuadorian segment and the nw trending peruvian segment exhibits a spatially contrasted evolution involving several successive tectonic and geodynamic settings the late triassic to late liassic period began with a widespread marine transgression from the latest triassic the colombian marine shelf was progressively destroyed by southward propagating extensional tectonic activity but marine sedimentation continued in peru during this time no significant magmatic activity is recorded except in the emerging colombian area this period is interpreted as the result of rifting of a tethyan oceanic arm which separated the colombian and palaeo mexican margins from latest liassic an important calc alkaline magmatic arc developed along the emergent colombian segment further south the north peruvian shelf probably emerged but marine sedimentation continued in southern peru during middle and early late jurassic times the colombian segment was characterized by important magmatic activity and by coarse clastic continental sedimentation along the peruvian segment a turbiditic trough emergent areas and continental basins were created and the scarcity of calc alkaline magmatism suggests that only very local subduction took place this period is regarded as one of the southeastward subduction beneath the colombian segment and of tethyan oceanic crust originating in the newly formed colombian oceanic arm this pattern would have induced a chiefly left lateral transform motion along the peruvian segment by kimmeridgian tithonian times the palaeogeographic framework had drastically changed along the colombian segment magmatic activity ceased and continental accretions occurred along dextral strike slip sutures in peru tectonic activity was recorded by the creation of a new turbiditic trough and by the resumption of detrital sedimentation in the coastal area arc related volcanism indicated that subduction took place beneath this segment this geodynamic change is interpreted as the result of a sharp decrease in the spreading activity of the tethyan ridges and replacement by pacific spreading centres inducing a roughly northeastward convergence direction

holocene oceanographic and glacial changes recorded in maxwell bay west antarctica abstract three holocene core sections from maxwell bay south shetland islands west antarctica are investigated using ms grain size toc foraminifera 18o and 13c 14c and 210pb in order to examine holocene oceanographic glacial and climatic changes in the region they come from 190 221 and 333 m water depths and the bay margin proximal locations complementing earlier studies from the deep central part the three records vary between locations and reflect combined marine and terrigenous influence from the open ocean and surrounding islands respectively the longest and best dated composite section comes from the inner part of the bay core jtc jpc 17 and extends back to 6 3 cal kyr bp close to the termination of the holocene climatic optimum a combination of dating problems and mixed foraminiferal assemblages prevented reliable interpretation of core jpc 15 from the outer part of the bay core jpc 16 collected from the inner bay near the inlet between king george and nelson islands revealed repeated highs in planktonic neogloboquadrina pachyderma occurrence during last 3000 yr these highs are interpreted as indicating periods of decreased meltwater flow into the bay and thus greater influence of open marine surface waters core jtc jpc 17 located closest to king george island and the collins ice cap records increased glacial conditions at 2000 cal yr bp this event is recorded by turbidite deposition at core site jpc 16 major components of the benthic foraminiferal assemblage indicate decreasing tolerance to near glacier or near shore conditions however local climate variability appears to have overall little impact on benthic foraminiferal biota thus it is unlikely that in similar settings recent warming would be strongly manifest as changes in benthic foraminiferal communities stable isotopic analysis is based on cassidulinoides parkerianus and globocassidulina biora subtle decrease in 18o at 3500 cal yr bp followed by episodic increases at 1000 cal yr bp and in the youngest part of the record appear to correlate with the period prior to the beginning of the neoglacial with medieval warm period and with post little ice age warming respectively the latest event is also marked by a significant increase in sediment accumulation rate in the second half of the 20th century

sacha oil field of ecuadorian oriente the sacha oil field in the ecuadorian oriente was discovered in early 1969 production began in july 1972 and at the end of 1980 had exceeded 190 million bbl drilling through 1980 had resulted in 91 oil wells and 2 dry holes estimated original primary recoverable reserves surpass 632 million bbl the field is on a very low relief anticline about 17 5 mi 28 km long and averaging 4 mi 6 5 km wide vertical closure amounts to 200 ft 60 m and there are 41 000 acres 16 600 ha of areal closure on top of the principal reservoir the cretaceous sandstones at drilled depths between 9 300 and 10 100 ft 2 835 and 3 080 m provide excellent reservoirs the hollin formation the basal cretaceous sandstone is the principal reservoir having produced 80 of the oil through 1980 and containing about 68 of the original reserves

benthic foraminifera from capbreton canyon revisited faunal evolution after repetitive sediment disturbance abstract at a 650 m deep site in the axis of capbreton canyon an 18 cm thick turbidite was deposited in december 1999 during subsequent campaigns an almost monospecific fauna of the benthic foraminifer technitella melo considered as a pioneer species was found in may 2000 in 2001 this fauna had disappeared and was replaced by an exceptionally rich fauna strongly dominated by the opportunistic species bolivina subaenariensis we present sedimentological radionuclide and foraminiferal data of new cores sampled in 2005 and 2011 taken with the aim to study the further evolution of the benthic ecosystem cores sampled in 2005 show that in the canyon axis a new ca 5 cm thick turbidite has been deposited the live benthic foraminiferal faunas were much poorer than in 2001 but still had a high dominance and low diversity although less extreme than in 2001 we conclude that in the canyon axis benthic foraminiferal faunas remain in an early stage of ecosystem colonization it appears that the very thick 1999 turbidite marks an exceptional event the uncommonly rich faunas observed in 2001 could be a response to the concentration of organic rich material in the fine grained top of this deposit in 2011 cores were sampled at a slightly different site on the lower canyon flank the sedimentary sequence here is marked by the absence of coarse turbidite layers although some levels show slightly increased grain size and lower 210 pb xs activities indicative of an admixture with advected older sediments live foraminiferal faunas are much more equilibrated as shown by their higher diversity lower dominance and deeper penetration into the sediment all these characteristics are indicative of a much more stable ecosystem dead faunas are present throughout the core indicating that the levels with slightly elevated grain size are not typical turbidites resulting from hyperpycnal currents which are characterized by levels barren of foraminifera but denote other more long term sedimentary processes leading to the advection of older material such as bottom nepheloid layers or repetitive fine grained turbidite deposits due to small scale slumping the comparison of live and dead fauna shows that at both sites the foraminiferal turnover rates are fairly low at the lower canyon flank site sampled in 2011 the foraminiferal faunas are renewed every 1 5 2 years such a fairly long foraminiferal lifespan corresponds to earlier estimates but is surprisingly high for the opportunistic taxa that dominate the faunal assemblages in these unstable and food enriched submarine canyon settings

upper mississippi pb as a mid 1800s chronostratigraphic marker in sediments from seasonally anoxic lakes in eastern canada abstract sediment cores from eight headwater lakes located in southern quebec eastern canada were analyzed for pb stable pb isotopes and the radioelements 210 pb 137 cs 241 am and 226 ra the depth profiles of stable pb isotope ratios show for the post 19th century period the influence of several isotopically distinct anthropogenic lead sources mainly including emissions from two canadian smelters and from leaded gasoline combustion in canada and in the united states a most interesting feature of the profiles however is the presence of sharp stable pb isotope ratio peaks near the depth horizon where excess 210 pb becomes undetectable using a binary mixing model and assuming that natural pb concentrations and isotopic compositions from the catchment are given by the pre industrial sediments at the bottom of the cores we find that a significant part of the anthropogenic pb supplied to the sediments at this horizon originated from smelting activities in the upper mississippi valley we assess that the pb isotope ratio peaks also observed in the laminated sediments of the pettaquamscutt estuary rhode island usa are an accurate chronostratigraphic marker for the validation of mid 19th century 210 pb derived dates given that the study lakes are located up to 2000 km from the mississippi valley we conclude that this isotopic pb signal provides a widely distributed time marker that is key to validate 210 pb chronologies in environmental archives from eastern north america

pollen pb 210 and opaque spherules an integrated approach to dating and sedimentation in the intertidal environment abstract a combination of techniques was applied to the problem of dating recent intertidal deposits from eastern long island careful separation of important indicator pollen types allowed identification of regional changes in vegetation comparison of pollen profiles and historic documents supplied three dated horizons 1 a 1640 1680 rise in agricultural indicator at the time of settlement 2 an 1800 decline in oak pollen with the initiation of the cordwood industry and 3 a 1920 decline in chestnut pollen following the chestnut blight pb 210 provided chronologies for the last 100 150 year sections of cores chronologies from each were compared and used to date a 1900 rise in industrially derived opaque spherules independently results showed that a combination of techniques could be sed to obtain detailed chronologies from intertidal sediments deposited within the last 300 350 years and to interpret salt marsh and barrier island dynamics although pb 210 may be restricted in its application due to erratic sedimentation pollen analysis can be used to date strata from high energy marshes where sediment accumulation rates fluctuate

dinoflagellate cysts and enso pdo climate forcing in the southern gulf of california abstract this paper presents a high resolution analysis of dinoflagellate cyst groups 1959 to 2009 in the southern gulf of california goc we analyzed 100 samples of laminated sediments with an effective sampling resolution of 7 months our primary goal is to clarify the relation between changes in these groups and the climate forcing defined by the el nino southern oscillation enso and pacific decadal oscillation pdo indices principal component analysis indicates three groups a1 a2 and a3 a1 and a3 are mostly constituted by dinoflagellate cysts of heterotrophic taxa while a2 is composed mainly of autotrophic taxa strong el nino events decrease the contribution of all dinoflagellate cyst groups while extreme la nina events increase the contribution of the a2 and a3 groups also the pdo modulates the marine productivity in the southern goc with cold phases increasing productivity while the warm stages decrease productivity as with climatic events in the southern goc autotrophic and heterotrophic taxa of dinoflagellate cysts respond clearly when pdo and enso are in phase finally dinoflagellate cyst concentrations in laminated sediments can be used regionally as a chronostratigraphic tool in the last 50 years

substorm onset observations by image fuv 1 over the first 2 5 years of operation the fuv instrument on the image spacecraft observed more than 2400 substorm onsets in the northern hemisphere the observations confirm earlier results of statistical studies in terms of a median substorm onset location at 2300 hours mlt and 66 4 degrees magnetic latitude the purpose of this report is to publish the list to allow for further investigation the list can easily be searched for onsets close to certain ground stations or at specific magnetic latitudes or local times as one example of such use we demonstrate how the probability of onset observation was determined for the ground based automatic observatories of the themis time history of events and macroscale interactions during substorms project

independent time markers validate pb 210 chronologies for two shallow argentine lakes in southern pampas abstract we report here the results of detailed 210pb analysis from two lake sediment cores collected from lagunas encadenadas del oeste leo located in the southern argentinean pampas 37 s 62 w non exponential and non monotonic 210pbuns depth profiles in the sedimentary record of these shallow lacustrine systems indicate the interaction of complex processes behind radionuclide fluxes and lake sedimentation the chronologies and sediment accumulation rates sar for the lake sediment sequences were modeled using different 210pb based mathematical models since modeled 210pb ages must be validated against independent stratigraphic markers of known age two chrono stratigraphic markers were selected to control the upper and lowermost parts of the 210pb dated sediments the younger stratigraphic marker of ad 1980 2 corresponds to an uppermost organic carbon rich mud accumulated by 1977 78 matching the most noticeable lake highstand occurred during the 20th century registered on instrumental and paleolimnological records across the pampean plains the oldest stratigraphic marker corresponds to ad 1878 10 matching with a high lake productivity and wet phase related to anomalously intense rainfall and flooding events in southeastern south america for ad 1877 1878 when comparing the resulting ages to the stratigraphic markers our results show that crs model constant rate of supply performs better than the other models thus these independent chronostratigraphic markers used along the sedimentary records were critical to validate 210pb derived ages and therefore to select the most appropriate model to establish the chronological framework of the recent sediments of the leo system the crs model appears to be an adequate technique for deriving ages and sar in the leo sedimentary record and other pampean lacustrine systems under strong hydrological variability

earthquake impact on active margins tracing surficial remobilization and seismic strengthening in a slope sedimentary sequence strong earthquakes at active ocean margins can remobilize vast amounts of surficial slope sediments and dynamically strengthen the margin sequences current process understanding is obtained from resulting event deposits and low resolution shear strength data respectively here we directly target a site offshore japan where both processes are expected to initiate that is at the uppermost part 15 cm of a sedimentary slope sequence based on a novel application of short lived radionuclide data we identified dated and quantified centimeter scale gaps related to surficial remobilization temporal correlation to the three largest regional earthquakes attest triggering by strong earthquakes mw 8 also extremely elevated shear strength values suggest a strong influence of seismic strengthening on shallow sediments we show that despite enhanced slope stability by seismic strengthening earthquake induced sediment transport can occur through surficial remobilization which has large implications for the assessment of turbidite paleoseismology and carbon cycling at active margins

solar wind control of ionospheric equivalent currents and their time derivatives a solid understanding of the solar wind control of ground magnetic field disturbances is essential for utilizing the existing long time series of ground data to obtain information on solar wind magnetosphere ionosphere coupling we have used 20 years of international monitor for auroral geomagnetic effects magnetometer data 54 76 magnetic latitude to study the solar wind control of the ionospheric equivalent current density and its time derivative we found that peaks at the premidnight and prenoon ends of the westward electrojet the prenoon peak was most intense during fast solar wind and radial interplanetary magnetic field imf the location of the peak was not affected by the imf orientation but persisted at 8 10 magnetic local time and 70 75 latitude near the boundary between the westward and eastward electrojets sensitivity of this boundary to disturbances was suggested as a possible explanation for the persistent prenoon location of the peak the premidnight peak was most intense during southward imf orientation while faster solar wind mainly resulted in more intense in the premidnight sector stronger imf caused the region of intense to spread to the postmidnight dawn and dusk sectors a good correspondence was found between development of the nightside intensification and average substorm bulge and oval aurora as determined by gjerloev et al 2007 the bulge aurora covered the western end of the westward electrojet where the equivalent current also had a significant poleward component the substorm oval aurora on the other hand extended eastward along the westward electrojet

disequilibrium between 226ra and supported 210pb in a sediment core from a shallow florida lake sup 210 pb dating can be used to assign ages in lake sediment cores calculate rates of sediment accumulation and determine the timing of recent changes in lake watershed ecosystems we used low background gamma counting to measure sup 226 ra and total sup 210 pb activity in a core from lake rowell florida sup 226 ra activity was high and strongly variable throughout the core even exceeding total sup 210 pb activity in recently deposited sediments we traced one source of ra rich sediments to the only inflow alligator creek where stream bottom deposits display disequilibrium between sup 226 ra and supported sup 210 pb high and variable sup 226 ra activity in the lake rowell profile argues for direct estimates of in situ ra in lake sediment cores from disturbed watersheds that have ra bearing bedrock isotopic disequilibrium between sup 226 ra and supported sup 210 pb makes it difficult to distinguish between supported and unsupported sup 210 pb activity throughout the lake rowell core and would require special assumptions and nonconventional dating models to establish age depth relationships 78 refs 3 figs 1 tab

a combined radiometric and mineral magnetic approach to recent geochronology in lakes affected by catchment disturbance and sediment redistribution abstract as a result of empirical testing of 210 pb dating models in a wide variety of lakes we conclude that there are many situations where despite major changes in sedimentation rates as a result of lake or catchment disturbance the crs constant flux model provides a sound basis for establishing recent chronology factors which may complicate or vitiate the assumptions of the model include short water residence time bioturbation for which we propose a modified dating model discontinuous or disturbed sedimentation sediment resuspension and shifts in sediment source in the case of the last three processes we illustrate ways in which the problems can be identified and evaluated using mineral magnetic measurements we propose an evaluative approach to 210 pb dating projects with emphasis on independent dating evidence on tests of internal consistency and on the use of data from several correlatable cores

the utility of estuarine settling basins for constructing multi decadal high resolution records of sedimentation abstract obtaining long term records of sediment flux and sources to estuaries is a major challenge in coastal and estuarine research due to the dynamic processes that actively work to remove the high resolution long term sediment record examining cores from sediment settling basins directly adjacent to or within estuarine systems provides a potential alternative means of establishing a history of estuarine sedimentation as a recently established settling basin with high rates of sedimentation cape lookout bight nc presents an ideal coastal environment to capture a long term record of sedimentation in 2010 a 4 6 m long core was extracted from the deepest portion of the basin through lithologic description grain size water content and radioisotope analysis excess 210 pb a high resolution geochronology of sedimentation has been established for the basin the record begins with spit accretion that captured part of the marine shelf and formed the basin a transition in sediment type from dominantly marine through storm induced overwash to dominantly estuarine was identified in the basin this transition reflects the increased trapping efficiency of fine estuarine mud due to the changing geomorphology of the settling basin an abrupt increase in the rate of estuarine sedimentation occurred 1983 1985 after careful reconstruction of basin geomorphology this increased rate of sedimentation is not attributed to internal dynamics within the basin but instead is interpreted to be the result of increased estuarine sediment flux through barden s inlet from the upper estuary this work underscores the importance of considering changing basin physiography and sediment dynamics before interpreting the paleo record as those mechanisms can hide or eliminate allogenic signatures from the sediment profile

a decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the holocene sedimentary record of the gulf of trieste carbonate sediments in non vegetated habitats on the north east adriatic shelf are dominated by shells of molluscs however the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because i monitoring of ecosystems prior to the 20th century was scarce and ii ecosystem history inferred from cores is masked by condensation and mixing here based on geochronological dating of four bivalve species carbonate production during the holocene is assessed in the gulf of trieste where algal and seagrass habitats underwent a major decline during the 20th century assemblages of sand dwelling gouldia minima and opportunistic corbula gibba are time averaged to 1000 years and corbula gibba shells are older by 2000 years than shells of co occurring gouldia minima this age difference is driven by temporally disjunct production of two species coupled with decimetre scale mixing stratigraphic unmixing shows that corbula gibba declined in abundance during the highstand phase and increased again during the 20th century in contrast one of the major contributors to carbonate sands gouldia minima increased in abundance during the highstand phase but declined to almost zero abundance over the past two centuries gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top core increments but are rarely alive although gouldia minima is not limited to vegetated habitats it is abundant in such habitats elsewhere in the mediterranean sea this live dead mismatch reflects the difference between highstand baseline communities with soft bottom vegetated zones and hard bottom arca beds and present day oligophotic communities with organic loving species therefore the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century more than 50 of the shells on the sea floor in the gulf of trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats

three decades of dating recent sediments by fallout radionuclides a review this paper reviews the 210pb dating programme carried out at the university of liverpool over a period of three decades since its inception by frank oldfield in the mid 1970s the work at liverpool

climate change evidences from the end of the little ice age to the current warm period registered by melincue lake northern pampas argentina abstract geochemical sedimentological historical and instrumental information from melincue lake 33 43 s 61 28 w was analyzed in order to reconstruct main hydro climatic changes along the pampean region considering the end of the little ice age lia and the current warm period cwp climatic phases elemental x ray fluorescence determinations were performed on a dated short core extracted from the deepest part of the lake chemical ca sr al k si ti and fe variation was analyzed along with physical magnetic susceptibility dry bulk density and medium particle size and mineralogical proxies as well as carbon and nitrogen contents organic and inorganic carbon and organic nitrogen multicomponent statistical analyses allowed the identification of the main environmental processes ruling sedimentation which included carbonate precipitation detrital input and primary productivity homogeneous carbonate rich detrital rich and organic matter poor deposits reflect very shallow and ephemeral lake conditions during the last years of the lia period very low sedimentation rates and the presence of discontinuities in the sedimentary record pointed to episodes of extensive lake shrinkages and probable lake floor subaerial exposures bedded and laminated organic rich muds accumulated in perennial lake conditions after ca ad 1880 reveal an important environmental change concurrent with the onset of the current warm period the contrast of sediment composition and lithological characteristics with the instrumental record of the cwp allowed us to consider the development of a shallow saline lake system enhanced detrital input and carbonate precipitation during dry periods in turn higher lake levels and thus more diluted lake waters during wetter periods resulted in enhanced organic lake productivity and lower carbonate precipitation the comparison of the paleolimnological reconstruction from melincue lake to different hydrological and paleoclimatic records i e limnimetric measurements and ocean temperature changes suggests that the moisture variation registered between the lia and the cwp was consistent with and likely forced by large scale climatic oscillations the present study provides new evidences to evaluate the climate and environmental changes in central argentina related to the dynamics of the south american monsoon system during the last five centuries

natural and anthropocene fluxes of trace elements in estuarine sediments of galician rias the anthropocene has been proposed as a new geo stratigraphic epoch where humans have become a global factor affecting the ecosystems estuarine sediments constitute a biogeochemical reservoir where trace elements tes from natural sources mix with a fraction generated by human activities this study assessed the natural lithogenic imprint of tes from uncontaminated sedimentary records to study anthropogenic changes sediment cores were sampled in the estuarine part of the low populated and low industrialized rias of ares a betanzos b and cedeira c which are located in the nw of the iberian peninsula cores were dated by the 210pb method covering up to the last century period sedimentation rates in mm yr 1 were 3 4 0 6 older than 1961 and 8 2 3 2 younger than 1961 for core a 0 9 0 2 1940 and 4 2 2 3 for core b and 13 4 1 4 for core c the background fluxes of tes were in the ranges of in g m 2 yr 1 50 560 for al and fe 20 320 for poc and 8 100 for ps and in mg m 2 yr 1 20 120 for as 0 2 2 0 for cd 7 110 for co 40 870 for cr 20 230 for cu 0 1 0 6 for hg 290 2800 for mn 4 24 for mo 20 410 for ni 20 150 for pb 60 800 for v and 70 700 for zn the three cores showed an anthropogenic influence since the mid 20th century the detected human impact during the anthropocene was due to the eume river damming and as pontes lignite mining the largest mine open pit in the iberian peninsula in core a by bridge road constructions vehicles emissions and river mouth urbanization in core b and changes in land use in core c sediment accumulation rates increased 2 4 core a and 4 7 times core b while tes fluxes increased 2 4 times in core a and between 3 6 and 5 1 times in core b pre industrial sedimentary records showed the lithogenic differences of the drainage basins mainly granitic watersheds for cores a and b and the prevalence of basic rocks of the ortegal geological complex for core c this explains the high concentrations and fluxes of cr ni and v of core c the different lithogenic imprints highlight the value of using local background references in contamination studies such as those on the anthropocene influence in estuaries which occurred after the spanish civil war in the studied rias

shallow marine tsunami deposits in teluk banten nw java indonesia generated by the 1883 krakatau eruption teluk banten tb is a tropical shallow marine embayment with coral reef islands close to the krakatau volcanic complex the 1883 krakatau eruption generated a tsunami which had a devastating effect on the neighboring coastal areas the effects of the 1883 krakatau eruption and the associated tsunami on the bottom sediments in tb are assessed using textural compositional and 210 pb geochronological data an important diagnostic criterion consists of the occurrence of tephra conform descriptions of the 1883 eruption tephra the tsunamite consists of a sandy layer with abundant reworked shell and other carbonate fragments coarse components in the tsunamite consist of locally derived material eroded from the seabed land derived components are incorporated in the tsunamite only in close proximity to the coast the tsunamite is thickest in localized areas of the central part of the bay along the northern open sea facing slope of tb the tsunamite is relatively thin 6 7 cm thick but well preserved as little postdepositional modifications have occurred in the eastern bay area recent erosion since the redirection of the ciujung river in the 1920s has removed the krakatau tsunamite along the west coast of tb the only signature of the 1883 krakatau eruption consists of tephra and evidence for a high energy event is lacking presumably the western area was sheltered from the tsunami wave coming from the northwest at the shallower stations with low accumulation rates the tephra has been thoroughly mixed by bioturbation 2003 elsevier science b v all rights reserved

trace element fluxes during the last 100 years in sediment near a nuclear power plant abstract the salada coastal lagoon is located in veracruz mexico near the laguna verde nuclear power plant lvnpp currently the lagoon receives the cooling waters used in the lvnpp to evaluate the fluxes and mobilization of trace elements due to human activities in the area two sediment cores from the coastal flood plains of salada lagoon were analysed cores were collected using pvc tubes sediments cores were analysed every centimetre for dating 210 pb by alpha detector and trace metal analysis using icp mass spectrometry the dating of both sediment cores covers the period from 1900 to 2013 which includes the construction of the lvnpp 1970 s the normalized enrichment factor shows enrichment of ag as and cr in both sediment cores these enrichments correspond to the extent of mining activity which reached a maximum in the 1900 s and to the geological setting of the coastal zone the profiles of the element fluxes in both sediment cores reflected the construction and operation of the lvnpp however the elements content did not show evidence of pollution coming from the lvnpp

determination of the substorm initiation region from a major conjunction interval of themis satellites 1 we investigate in detail the time history of substorm disturbances in the magnetotail observed during a major tail conjunction of time history of events and macroscale interactions during substorms themis satellites on 29 january 2008 0700 0900 ut during this interval all themis satellites were closely aligned along the tail axis near midnight and were bracketed in local time by goes 11 and 12 the radial distance covered ranges from the geosynchronous altitude to 30 r e in the tail this interval consists of three activations detected by the themis satellites with good ground all sky camera observations of auroral activity the first activation is a small substorm with spatially limited disturbance in the tail the onset arc was equatorward of an undisturbed arc the second activation is a moderate size substorm with the onset arc also being equatorward of an undisturbed arc the third activation is an intensification of the substorm with its onset indicated by the second activation the active auroral arc for this intensification was near the poleward boundary of the auroral oval analysis of these observations indicates that the first activation is a small substorm initiated in the near earth plasma sheet and does not involve magnetic reconnection of open magnetic field lines magnetic reconnection on closed field lines can be ruled out for this substorm because it cannot generate the observed high speed plasma flow the second and third activations are part of a moderate size substorm initiated also in the near earth plasma sheet with a subsequent substorm intensification involving activity initiated tailward of 30 r e overall the time history of substorm activity for these two substorms is consistent with the near earth initiation model

sea level rise sedimentary record and organic carbon fluxes in a low lying tropical coastal ecosystem abstract sea level rise one of the most evident effects of recent climate change is already impacting coastal ecosystems because of its low relief population increase and economic development during the last century the celestun lagoon is highly vulnerable to global change including sea level rise here we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes some geochemical indicators in a 210pb dated sediment core showed clear signals of marine influence this was reflected on increased accretion rates from 0 3 0 1 mm yr 1 in 1941 to 2 9 1 2 mm yr 1 in 2012 these accretion rates were similar to eustatic sea level rise and mean acceleration ranged from 0 037 0 22 mm yr 2 implying a slr by 2100 ranging from 14 to 86 cm the one century 1917 2013 organic carbon stock in sediments was calculated to be 10 1 0 2 mg c ha 1 during the same period the organic carbon flux corrected for organic carbon degradation increased from 7 3 g c m 2 yr 1 to 73 26 g c m 2 yr 1 attributed to the impact of sea level rise in this ecosystem this work shows that tropical saltmarshes may provide useful information on sea level rise and the presented methodology may be used where instrumental records do not exist or they are too short

increasing hypoxia in the changjiang estuary during the last three decades deciphered from sedimentary redox sensitive elements abstract ranked as one of the world s largest seasonal hypoxic water bodies dissolved oxygen do 2 mg l 1 the changjiang hypoxia has been reported to grow rapidly worse in recent decades according to cruise observations but it has been seldom studied by sedimentary records in this paper four gravity cores e1 e4 retrieved from the changjiang estuary were dated by excess 210pb and analyzed with grain size compositions total organic carbon toc contents and rses redox sensitive elements compositions we aim to decipher rses enrichment characteristics and controlling mechanisms in the changjiang estuary the results show that mo and v enrichment is highly promoted by particle absorption and fe mn redox cycling at the shallow estuarine environment e1 and e2 with occasional hypoxic disturbances scavenging of mo and v by organic complexation becomes significant at the hypoxic center e3 together with great influence by fe mn redox cycling but they do not work effectively for u enrichment because of its easy remobilization and abundant riverine input moreover upcore increasing trends of mo v and u in e3 match well with a general lowering trend of bottom water do minima since the mid 1980s there are two progressive hypoxic development stages intercalated with a less do depleted period 1991 1997 as shown by both cruise observations and rses al records these findings are vital to better understanding coastal hypoxic development and rses enrichment mechanisms in the seasonal hypoxic settings because hypoxia is predicted to increase in the near future due to intensifying human disturbances

centennial scale lake level lowstand at lake uddelermeer the netherlands indicates changes in moisture source region prior to the 2 8 kyr event the uddelermeer is a unique lake for the netherlands containing a sediment record that continuously registered environmental and climatic change from the late pleistocene on to the present a 15 6 m long sediment record was retrieved from the deepest part of the sedimentary basin and an age depth model was developed using radiocarbon dating 210pb dating and bayesian modeling lake level change was reconstructed using a novel combination of high resolution palaeoecological proxies e g pollen non pollen palynomorphs chironomids quantitative determinations of lake level change ground penetrating radar and estimates of changes in precipitation lipid biomarker stable isotopes we conclude that lake levels were at least as high as present day water levels from the late glacial to 3150 cal yr bp with the exception of at least one lake level lowstand during the preboreal period lake levels were ca 2 5 m lower than at present between 3150 and 2800 cal yr bp which might have been the result of a change in moisture source region prior to the so called 2 8 kyr event increasing precipitation amounts around 2800 cal yr bp resulted in a lake level rise of about 3 5 4 m to levels that were 1 1 5 m higher than at present in line with increased precipitation levels as inferred for the 2 8 kyr event from nearby raised bog areas as well as with reconstructions of higher lake levels in the french alps all of which have been previously attributed to a phase of decreased solar activity lake levels decreased to their present level only during recent times although the exact timing of the drop in lake levels is unclear the author s 2016

rates of particle scavenging sediment reworking and longitudinal ripple formation at the hebble site based on measurements of 234th and 210pb between 1982 and 1986 seabed and water column samples were collected on five cruises to the hebble site two particle reactive radionuclides 234th and 210pb have been used to examine rates of particle scavenging in bottom waters sediment reworking in the surface seabed and formation of longitudinal ripples settling particles at the hebble site which have been resuspended by strong bottom currents and benthic storm activity scavenge approximately 60 of the 234th half life of 24 days produced in the bottom 100 m of the water column corresponding to removal of 15 dpm cm2 234th inventories from cores collected during a single cruise show substantial variability e g 1 18 dpm cm2 over the 8 km2 study area indicating that resuspended particles are not deposited uniformly across the seabed after storm events the activity of benthic fauna and non uniform deposition over a topographically variable seabed are important processes affecting boundary layer sedimentation and the development of radionuclide inventories in surface sediments the mean 234th seabed inventory from individual cruises to the hebble area varies to a greater extent 2 to 38 dpm cm2 than the mean 210pb inventory 47 to 82 dpm cm2 because 234th inventories are dominated by sedimentary processes associated with an individual storm event whereas 210pb inventories integrate these processes over several cycles of deposition and erosion sediments at the hebble site are biologically reworked very rapidly on a 100 day time scale with 234th mixing coefficients db 1 to 33 cm2 yr comparable to values observed in nearshore environments on time scales of months to years 210pb data indicate that strong currents and benthic storm activity have eroded and redeposited the upper 5 10 cm in 17 of the 20 cores examined reoccupying field sites during the 4 year field program provided the unique opportunity to evaluate steady state models commonly used to determine rates of sediment reworking 210pb profiles and inventories showed significant temporal variations at hebble sites occupied between 1982 and 1986 steady state models should not be used to evaluate profiles of 210pb or other tracers with comparable half life in a dynamic environment like the hebble area because steady state assumptions are not justified and rates of sediment reworking can be underestimated by nearly an order of magnitude 234th and 210pb analyses of core samples from two longitudinal ripples suggest that these sedimentary features form on a time scale of months and consist of a mixture of recently deposited material from the water column and older sediment from depth the absence of 234th activity in one of the ripples indicates that these bedforms may be stable for periods of months without significant growth

influence of suspended kelp culture on seabed sediment composition in heini bay china abstract kelp aquaculture activities occupy large nearshore areas with significant effects on sediment properties primarily caused by the influence of the suspended kelp on local hydrodynamics changes in sediment composition and grain size distributions were investigated prior to and following the commencement of kelp aquaculture activities in heini bay in eastern china seabed sediment types and the particulate matter in suspension during the kelp seeding and harvesting periods and in sediment cores were analyzed while suspended sediment in the kelp aquaculture area was up to 20 organic material sediment organic content on the seabed remained at similar levels as areas lacking aquaculture the composition of the seabed sediment in the kelp aquaculture area became finer grained by the capture of fine particles within the kelp aquaculture area the sediments are poorly sorted and positively skewed whereas at the shoreward and seaward of the aquaculture area the sediments are relatively coarse grained well sorted and nearly symmetrically distributed therefore the kelp aquaculture activities not only increase the fine particulate fraction in the sediments within the aquaculture area but also result in similar deposits seaward of it indicating that seabed erosion and accretion is also controlled by the sediment source and the hydrodynamic conditions the analysis of sediment cores showed that kelp culturing refines the sediment by preferentially capturing particles in the 38 40 m size class while having no effect on the

auroral substorm timescales imf and seasonal variations 1 the timescales and phases of auroral substorm activity are quantified in this study using the hemispheric power computed from polar ultraviolet imager uvi observations with this approach we are able to determine substorm phase self consistently from the uvi optical measurements without needing any ancillary metrics for auroral activity this technique also allows us to combine a quantitative measurement of substorm timescales with the qualitative description of auroral morphology during each event we show how the characteristics of substorms vary with imf bz orientation and season for several hundred substorm events substorm intensity as measured by the rate of energy deposition by electron precipitation exhibits greater variation with imf bz orientation than with season the timescale of substorm expansion shows comparable variation with both imf bz orientation and season on the other hand substorm recovery times vary more strongly with season than with imf bz direction the recovery time for substorm activity is well ordered by whether or not the nightside auroral region is sunlit substorms occurring in the winter and equinox periods have similar recovery timescales which are both roughly a factor of two longer than that for summer when the auroral oval is sunlit however imf bz orientation is shown to have a strong modulating effect on both substorm expansion and recovery timescales during the summer the winter summer asymmetries in the aurora described by previous studies are more completely explained by the seasonal variations of substorm recovery timescales characterized in this work our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

electron precipitation from emic waves a case study from 31 may 2013 on 31 may 2013 several rising tone electromagnetic ion cyclotron emic waves with intervals of pulsations of diminishing periods ipdp were observed in the magnetic local time afternoon and evening sectors during the onset of a moderate large geomagnetic storm the waves were sequentially observed in finland antarctica and western canada co incident electron precipitation by a network of ground based antarctic arctic radiation belt dynamic deposition vlf atmospheric research konsortia aarddvark and riometer instruments as well as the polar orbiting operational environmental satellite poes electron telescopes was also observed at the same time poes detected 30 80 kev proton precipitation drifting westwards at locations that were consistent with the ground based observations indicating substorm injection through detailed modelling of the combination of ground and satellite observations the characteristics of the emic induced electron precipitation were identified as latitudinal width of 2 3 or l 1 re longitudinal width 50 or 3 hours mlt lower cut off energy 280 kev typical flux 1 104 el cm 2 sr 1 s 1 300 kev the lower cutoff energy of the most clearly defined emic rising tone in this study confirms the identification of a class of emic induced precipitation events with unexpectedly low energy cutoffs of 400 kev

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

the 129iodine bomb pulse recorded in mississippi river delta sediments results from isotopes of i pu cs pb and c 129i t1 2 1 56 107 yr has both natural as well as anthropogenic sources anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years however the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of 129i and to a lack of knowledge regarding the forms of iodine from a vertical profile of 129i 127i ratios in sediments located in the mississippi delta region in approximately 60 meters water depth the 129i input function to this region was reconstructed dates in the core were assigned based on the plutonium peak at 20 cm depth assumed to have been deposited in 1963 and the excess 210pb profile in the same depth interval and below that based on the steadily decreasing 240pu 239pu ratios from a ratio of 0 18 at 22 cm to 0 05 at 57 cm depth the 1953 horizon these low 240pu 239pu values are attributed to low yield close in tropospherically transported bomb fallout produced from the nevada test site in the early 1950s which had a value of about 0 035 and strongly suggest a terrestrial source for pu isotopes 129i 127i ratios increased from 2 10 10 at 3 cm to 4 10 10 at 20 cm and from there decreased monotonously to pre anthropogenic values at 53 cm and below 129i concentrations ranged from 8 13 106 atoms g in the top 20 cm and decreased to values of less than 1 106 atoms g below 50 cm atom ratios of 129i 137cs decay corrected to 1962 the year of maximum radionuclide production are about 0 3 very close to the production ratios of about 0 2 during atomic bomb tests this evidence combined with other observations strongly suggests that 129i in mississippi river delta sediments originates from atomic bomb fallout eroded from soils of the mississippi river drainage basin with little alteration of the isotopic ratios during transport from watershed to coastal deposits this is further corroborated by a close correspondence between 129i 127i ratios and other bomb fallout nuclides in this core based on these observations and on laboratory evidence we propose a conceptual model which explains this correspondence and the low 129i 127i ratios found in our sediment core as caused by geochemical i isotope fractionation processes during organic carbon leaching from erodible soils in the mississippi river watershed differences in mobilities of the different chemical forms of 129i and 127i as well as the variances in chemical forms of 129i from nuclear bomb fallout versus nuclear fuel reprocessing are proposed to have created such a correspondence between i isotope ratios and bomb fallout nuclides without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the usa and europe