identification of permian palaeowind direction from wave dominated lacustrine sediments lodeve basin france lacustrine environments are an excellent indicator of continental palaeoclimate in particular the sedimentary record of waves in lakes may be used to constrain atmospheric palaeocirculation wave ripples have been identified in a permian lacustrine basin the salagou formation 260 250 ma lodeve basin located in the southern french massif central part of the western european hercynian mountain chain wave ripple patterns are interpreted with regards to hydrodynamics and water palaeodepth it is shown that in the case of the salagou formation wave ripple orientations were controlled by the direction of the prevailing palaeowind the late permian wind blew from between north and 20 east of north possibly over several millions of years and certainly throughout the period of deposition of about 2000 m of strata in the lodeve basin permian lacustrine sedimentation is widespread and well preserved on the earth s surface and so wave ripple data may help constrain numerical modelling of the earth s past climates especially with regards to permian times outside of desert regions

basin morphology and seismic stratigraphy of lake kotokel baikal region russia the basin of lake kotokel located along the eastern shore of lake baikal russia has attracted several scientific projects to investigate the climate vegetation and lake history throughout the late pleistocene and holocene however little was known about its basin structure and sediment architecture echo sounding and 3 5 khz single frequency sub bottom profiling were used to decipher the basin morphology and seismic stratigraphy to a depth of approximately 50 m the bathymetric map shows a very shallow lake of 4 m mean water depth and an almost flat lake bottom a distinct elongated small sized depression of up to 12 m water depth between the north western coast and a small island developed along an nw se oriented fault line a total of 46 km of seismic profiles crossing the lake along 12 transects shows that the bottom sediments consist of three different facies which accords to previously analyzed core sequences several distortions of sediment layers at various sites indicate tectonically induced impact which resulted in up to 3 m vertical offsets of sediment packages at local sites the offsets indicate a probably still active fault along the western shoreline of the lake soft gyttja of the upper 6 m does not show distortions and may have obscured potential younger tectonic activity the sediments date to the late pleistocene small updoming features along the boundary between layers i and ii may be assigned to degassing processes or to seismic activity river channel fills along the north eastern coast are indicative of a lower lake level prior to 15 ka bp the sediment stratigraphy indicates that suitable coring sites for paleoclimate studies are only located in the southern part of the basin where almost undisturbed sediments can be expected

geochemical study of a crater lake pavin lake france identification location and quantification of the chemical reactions in the lake abstract a study of the main geochemical characteristics of the pavin crater lake was performed in september 1992 associated with previous results on the hydrochemical budget of the lake the present study points out that 1 1 in the mixolimnion the major reactions are photosynthesis removal of silica by diatoms iron oxidation and alkali and alkaline earth incorporation in a solid phase 2 2 the major reduction reactions occur within the sediment and the products of the reaction are brought to the lake by diffusion 3 3 some reactions silica dissolution manganese oxide reduction sulfate sulfide transformations iron and phosphate precipitation occur within the monimolimnion 4 a complete budget of transfers and chemical reactions is presented for some components such as silica

uplift of quaternary shorelines in eastern patagonia darwin revisited during his journey on the beagle darwin observed the uniformity in the elevation of coastal eastern patagonia along more than 2000 km more than one century later the sequences of quaternary shorelines of eastern patagonia have been described and their deposits dated but not yet interpreted in terms of geodynamics consequently we i mapped the repartition of the quaternary coastal sequences in argentinean patagonia ii secured accurate altitudes of shoreline angles associated with erosional morphologies i e marine terraces and notches iii took into account previous chrono stratigraphical interpretations in order to calculate mean uplift rates since 440 ka mis 11 and proposed age ranges for the higher and older features up to 180 m and iv focused on the last interglacial maximum terrace mis 5e as the best constrained marine terrace in terms of age and altitude in order to use it as a tectonic benchmark to quantify uplift rates along the entire passive margin of eastern south america our results show that the eastern patagonia uplift is constant through time and twice the uplift of the rest of the south american margin we suggest that the enhanced uplift along the eastern patagonian coast that interested darwin during his journey around south america on the beagle could originate from the subduction of the chile ridge and the associated dynamic uplift

geochemistry and anthropogenic inputs of metals in a tropical lake in venezuela lake valencia is a tropical lowland lake in north central venezuela lake bottom sediments were collected from 25 locations in april 1988 at 2 locations water ph conductivity dissolved o2 and temperature were measured at successive depths after drying 5 sediment samples were sieved into 5 mechanical fractions each was extracted with 1 m hno3 and analysed for ai ca cd co cr cu fe k mg mn na ni pb and zn the 63 m fraction of all samples was similarly analysed water temperatures declined with depth 1 c 25 m from approximately 26 c conductivity varied little with depth but dissolved o2 contents indicated anoxic conditions 25 m water ph 8 8 9 4 was consistent with high dissolved carbonates there was little consistent relationship between grain size and sediment metal contents approximate baseline metal contents were calculated from 21 of 25 samples the average composition of the sediments corresponded to an ideal mixture of shales carbonate rocks as 0 5 0 7 0 5 0 3 five samples from alluvial fans near the mouths of rivers traversing urban industrial zones had compositions different from the other sediments generally ph zn ni cd and cu were anthropogenically enriched by factors of 2 16 the major sources of pollutants were identified as domestic and industrial activities affecting the rivers that traverse the lakeside cities of maracay and valencia sodium mg ca mn and co3 showed natural enrichment arising from carbonate precipitation following a physical mixing of 2 sedimentary components biogenic carbonate and terrigenous material low geochemical mobility of metallic elements in neutral basic and reducing waters a processes of bury and mixture of sediments and precipitation of carbonate result in only 10 of the lake area being affected by contamination isoline plots of elements in the bottom sediments supported a hypothesis that material mixing physical transport and carbonate precipitation are the main controls of spatial distribution patterns

early diagenesis and isotopic composition of lead in lake laisan northern sweden water column dissolved suspended phase sediment traps and sediment data pore water solid phase sediment were combined with stable pb and pb 210 isotope data to trace the early diagenetic behaviour and geochemical cycling of pb in lake laisan a lake which has received large quantities of anthropogenic pb since the early 1940s early diagenetic remobilisation of pb is indicated by a subsurface pore water pb maximum 120 mug 1 1 in the oxic surface layer of the sediment where the solid phase pb concentration is 3400 4600 mug g 1 the remobilisation of pb appears to be caused by a ph controlled desorption of pb from solid phase sediment which is consistent with a model describing surface complexation of pb ii on hydrous goethite surfaces the diffusive pb flux from the subsurface pore water maximum towards the sediment surface 36 mug cm 2 year 1 exceeds the depositional pb flux 8 6 mug cm 2 year 1 by approximately a factor of four indicating that pb is highly mobile in the sediment stable pb isotope data and a mass balance calculation suggest that pb diffusing upwards is to a large extent trapped in the surface sediment lead that may diffuse into the slightly alkaline lake water appears to be efficiently sorbed to suspended particulate matter resulting in low dissolved pb concentrations in the water column 0 040 0 046 mug 1 1 sorption of pb to suspended particulate matter is consistent with the elevated suspended particulate pb concentrations in the hypolimnion 3800 4000 mug g 1 and the fact that the stable pb isotopic compositions of suspended matter and pore water are similar less

vortex lines within low level mesocyclones obtained from pseudo dual doppler radar observations abstract vortex lines passing through the low level mesocyclone regions of six supercell thunderstorms three nontornadic three tornadic are computed from pseudo dual doppler airborne radar observations obtained during the verification of the origins of rotation in tornadoes experiment vortex in every case at least some of the vortex lines emanating from the low level mesocyclones form arches that is they extend vertically from the cyclonic vorticity maximum then turn horizontally usually toward the south or southwest and descend into a broad region of anticyclonic vertical vorticity this region of anticyclonic vorticity is the same one that has been observed almost invariably to accompany the cyclonic vorticity maximum associated with the low level mesocyclone the vorticity couplet straddles the hook echo of the supercell thunderstorm the arching of the vortex lines and the orientation of the vorticity vector along the vortex line arches compared to the orientation of the ambient barotrop

role of sediment composition in trace metal distribution in lake sediments sediment cores were collected from 20 lakes from the muskoka region of ontario canada to study vertical changes in trace metal concentrations with depth and the distribution of metals amongst humic material amorphous and crystalline fe and mn oxides insoluble organics sulphides and silicates based on their total concentrations trace elements displayed different degrees of affinity for the organic fraction represented by organic c and the mineral fraction represented by al certain elements hg as sb pb cd and zn displayed a positive correlation with organic c a negative correlation with al and enrichment in surface sediments with enrichment factors ranging from 2 to 24 detailed speciation studies revealed that these elements were associated mainly with humic material and to a lesser extent with oxides in surface sediments other elements al cr co fe and mn displayed a negative correlation with organic c a positive correlation with al and no consistent enrichment in their total concentration at the surface the speciation study revealed that metals of the latter group were mainly associated with the silicate fraction in both surface and deep sediments this study shows that relative affinities for organic and mineral fractions play an important role in the distribution of trace metals during burial and diagenesis and hence in the shape of their vertical profiles

cosmogenic 10be and 26al dating of paleolake shorelines in tibet abstract we have used in situ produced cosmogenic nuclides 10be and 26al to date lacustrine shorelines around eight lakes in tibet two lakes located south of the yarlung tsangpo river discharged at high lake levels one of them drolung co co is a local term meaning lake became closed its water level fell below its outlet channel at 3 8 ka and lowered over 120 m vertically since then this implies a significant change in intensity of precipitation driven by the indian monsoon over southern tibet in the middle late holocene nam co and dajia co located to the north of the yarlung tsangpo river also drained at high lake levels and became closed 53 36 ka and 48 ka respectively of four other lakes developed closely in the qiangtang basin north of the yarlung tsangpo river tangra yum co and siling co located at 31 32 n show exposure ages for high lake shorelines of over 220 ka the oldest lake shorelines reported for tibet while towards the north and west the high lake of zhari nam co appeared after the last glacial maximum lgm the different pattern of lake development to the north of yarlung tsangpo river may reflect regional climate effects

late holocene isotope hydrology of lake qinghai ne tibetan plateau effective moisture variability and atmospheric circulation changes a sub centennial resolution record of lacustrine carbonate oxygen isotopes 18oc from the closed basin lake qinghai on the ne tibetan plateau shows pronounced variability over the past 1500 years changes in 18oc in hydrologically closed lakes are often interpreted in terms of changing effective moisture under this interpretation our record would imply increasing effective moisture during the little ice age lia compared to the medieval warm period mwp however independent evidence from other archives strongly suggests the asian summer monsoon was stronger during the mwp and weakened during the lia controls other than effective moisture the balance of water inputs over evaporative loss must therefore have contributed to the 18oc values we propose the lia signal in lake qinghai resulted from a reduction in evaporation caused by colder air temperatures coupled with a decrease in oxygen isotope composition of input waters as a result of an increase in the relative importance of westerly derived precipitation our results caution against simplistic interpretations of carbonate oxygen isotope records from hydrologically closed lakes and suggest all possible controlling factors must be taken into account in order to avoid misleading palaeoclimatic reconstructions

differences between east asian and indian monsoon climate records during mis3 attributed to differences in their driving mechanisms evidence from the loess record in the sichuan basin southwestern china and other continental and marine climate records abstract asian monsoons vary with global climatic change as is well recorded by chinese loess paleosol sequences a radiocarbon and osl dated grain size and magnetic susceptibility record of the loess paleosol sequence from the chengdu basin southwestern china contains a greatly amplified mis 3 indian monsoon climate record comparison of this record with other continental and marine climate records in the temporal and frequency domains indicates that the high amplitude mis3 feature dominates the indian monsoon region and weakens northward but is not observed in east asian monsoon climate records these observed differences in the amplitude of mis 3 climate variations between the two monsoonal regions may be caused by the different effects of the precession insolation forcing on the very different monsoonal driving mechanisms the indian monsoon which originates from the subtropical mascarene high in the southern hemisphere carries large precession signals from the equatorial and tropic zones leading to the overall intensification of mis 3 climate signals the northward decrease of the indian monsoon strength reduces precessional climate signals carried by the monsoon on the other hand the east asian monsoon is largely generated from the western pacific subtropical high in the northern subtropical zone where the impact of precessional insolation forcing and heat vapor transport are much weaker thus exerting a more limited spatial and temporal influence on climate records

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

seismic stratigraphy buried beach ridges and contourite drifts the late quaternary history of the closed lago cardiel basin argentina 49 s the results of a seismic stratigraphic analysis of a closed lake basin lago cardiel in southernmost south america are reported very few high resolution continental records spanning the late quaternary have been obtained from this region seismic sequence stratigraphic analysis allows a reconstruction of lake level variations two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period following the development of a relatively shallow lake during the late pleistocene and a short desiccation pulse around 11 220 14c yr bp a transgression of over 135 m occurred at the beginning of the holocene the transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern lago cardiel at four different elevations the preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level there is no seismic evidence of a major lowering of the lake below modern level during the entire holocene deposition since the mid holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution seismic reflection geometries as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80 100 km2 as lago cardiel is under the influence of westerly winds these most likely drove lake circulation the identification of drowned beach ridges and of contourite drifts illustrates that high resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins but it can also provide information about the rate of lake level changes and the presence and strength of lake currents

chronostratigraphy and lake level changes of laguna cari laufquen rio negro argentina abstract evidence from shoreline and deep lake sediments show laguna cari laufquen located at 41 s in central argentina rose and fell repeatedly during the late quaternary our results show that a deep 38 m above modern lake level lake persisted from no later than 28 ka to 19 ka with the deepest lake phase from 27 to 22 ka no evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake before regressing to present levels laguna cari laufquen broadly matches other regional records in showing last glacial maximum lgm highstands but contrasts with sub tropical lake records in south america where the hydrologic maximum occurred during deglaciation 17 10 ka our lake record from cari laufquen mimics that of high latitude records from the northern hemisphere this points to a common cause for lake expansions likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the lgm

an investigation of the goshen county wyoming tornadic supercell of 5 june 2009 using enkf assimilation of mobile mesonet and radar observations collected during vortex2 part i experiment design and verification of the enkf analyses abstracthigh resolution doppler radar velocities and in situ surface observations collected in a tornadic supercell on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 are assimilated into a simulated convective storm using an ensemble kalman filter enkf a series of enkf experiments using a 1 km horizontal model grid spacing demonstrates the sensitivity of the cold pool and kinematic structure of the storm to the assimilation of these observations and to different model microphysics parameterizations an experiment is performed using a finer grid spacing 500 m and the most optimal data assimilation and model configurations from the sensitivity tests to produce a realistically evolving storm analyses from this experiment are verified against dual doppler and in situ observations and are evaluated for their potential to confidently evaluate mesocyclone scale processes in the storm using trajectory analysis and calculations of lagrangian vorticity

wind and temperature retrievals in the 17 may 1981 arcadia oklahoma supercell ensemble kalman filter experiments abstract the feasibility of using an ensemble kalman filter enkf to retrieve the wind and temperature fields in an isolated convective storm has been tested by applying the technique to observations of the 17 may 1981 arcadia oklahoma tornadic supercell radial velocity and reflectivity observations from a single radar were assimilated into a nonhydrostatic anelastic numerical model initialized with an idealized horizontally homogeneous base state the assimilation results were compared to observations from another doppler radar the results of dual doppler wind syntheses and in situ measurements from an instrumented tower observation errors make it more difficult to assess enkf performance than in previous storm scale enkf experiments that employed synthetic observations and a perfect model nevertheless the comparisons in this case indicate that the locations of the main updraft and mesocyclone in the arcadia storm were determined rather accurately especially at midlevels the magnitudes of v

the influence of the shear induced pressure gradient on thunderstorm motion abstract in the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation the explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank to asses the validity of linear theory for large amplitude updrafts the three dimensional shallow anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed these results suggest that although the nonlinear effects strongly promote splitting of the updraft the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank we believe this differential forcing is a major contributor to the observed predominance o

the mar chiquita lake an indicator of intraplate deformation in the central plain of argentina abstract the mar chiquita saline lake is located in the lowest part of one of the largest endorreic saline basins of south america with a surface area of 6000 6500 km2 the lake is located in a tectonic depression with an asymmetric cross section the sierras pampeanas foothills with altitudes near 1500 m are to the west and a 100 m topographic high san guillermo high is to the east whose western border is bounded by a buried middle pleistocene fault the tostado selva fault the main tributary of the lake is the dulce river which flows from north to south the southward flow of the river was impeded by an obstacle that closed the dulce valley generating the mar chiquita lake the megafans of the primero segundo and tercero rivers deposited a large amount of sediment against the faulted border of the san guillermo high generating an obstacle that impeded the normal flow of the rivers and diverted the dulce and the salado rivers to their present positions precise data concerning the age of the impounding of mar chiquita does not exist but lacustrine conditions are undoubtedly younger than the uplift of the san guillermo high which occurred in the middle pleistocene the well preserved dry valley of the dulce river located southward of mar chiquita is still visible in satellite images and confirms the youth of the impounding the observations introduced in this paper allow us to understand the origin of a significant feature of the central plains of south america the generation of mar chiquita lake and upstream wetlands produced a pronounced environmental change in the arid chaco pampeana plain which favored human life by introducing changes in vegetation and fauna

the biogeochemical cycle of iron and associated elements in lake kinneret abstract iron biogeochemical cycling and distribution between particulate reactive colloidal dissolved oxine labile fe ii fractions were studied in the seasonally stratified mesotrophic lake kinneret this article presents various aspects of the fe budget in the lake and relates them to the chemical reactivity of various physicochemical forms of fe the budget of fe in lake kinneret is dominated by fluvial fe load rather than by internal recycling of fe from the sediment as shown by the fact that 75 to 94 of the variance in fe concentrations in the lake can be explained by the fluctuation in the water discharge of the jordan river iron associated with phytoplankton accounts for 9 16 of the bulk particulate fe in the lake however within patches of the dominate algae the dinoflagellate peridinium gatunense algal fe accounts for more than 70 of the lake s particulate fe the algal fe is predominantly intracellular and the fe chlorophyll a ratios were within the range of published values for dinoflagellates and cyanobacteria iron associated with particles larger than 0 025 m 20 300 nm accounts for 80 95 of total fe in the epilimnion of lake kinneret throughout the year in contrast this fraction of fe is dominant in the hypolimnion only during the period of lake mixing iron concentration of different size fractions 0 025 m in the surface water covaried throughout the research period these covariations suggest dynamic transformations of fe between different size fractions either due to partial dissolution precipitation or desorption adsorption oxine labile fe concentrations the fe fraction considered chemically labile and available for phytoplankton ranged from 15 to 75 nm in wintertime the oxine labile fe accounts for only 10 20 of the total fe while in other seasons most of the fe is oxine labile oxine labile fe concentrations always exceed the 0 025 m filtered fe implying that some of the larger particles contain oxine labile fe and therefore are reactive the fraction of reactive particles in lake kinneret 10 80 is high relative to that of the marine environments and can most likely be attributed to its fluvial source which contains a significant proportion of reactive fe oxide and hydrous oxide particles the annual variability in the epilimnetic concentrations of other trace elements and nutrients such as al mn cd zn pb and p were studied and grouped according to their resemblance with river water discharge redox processes or biological uptake and scavenging distribution patterns of al pb and cd resembled that of fe suggesting that similar processes control the concentrations of these metals namely significant contribution from the watershed high affinity to particulate matter and little control of biota on their fate in the lake other elements such as zn and p are more affected by biological uptake while mn is more affected by redox cycling within the lake

geostatistic recognition of genetically distinct shale facies in upper triassic chang 7 section the ordos basin north china abstract the ordos basin in north china may be one of the nonmarine basins with highest hydrocarbon generation per volume of sedimentary fill it has great potential for unconventional oil and gas exploration especially shale oil when evaluating and predicting shale oil resources the difference between different regions and different layers of shale is very obvious so it cannot be calculated simply by average a geostatistic decision tree was constructed based on a training set of 22 parameters geochemistry petrology and sedimentology for 110 shale samples from the basin which can be used to implement genetic classification of subsequently collected shale samples three shale facies are identified by the decision tree the properties of each facies are different such as toc kerogen type and sulfur content genetic properties indicate formation conditions and provide base for the geostatistic assignments the differential distribution of shale facies in the basin reflects their origins from different formation mechanism elements ratios isotopes and biomarkers can be used to infer the sedimentary environment for each shale facies facies 1 mainly occurs in the upper chang 7 section and shows evidence of quartz rich source rock deposited under suboxic anoxic condition facies 3 occurs at the lower chang 7 section and shows evidence of clay rich and pyrite rich shale deposited under reducing dysoxic conditions with numerous higher plants input facies 1 and 2 constitutes the upper chang 7 with interactive thick layers facies 2 and 3 constitute the lower chang 7 with interactive thin layers petrology geochemistry and sedimentology of the shale facies suggest facies 1 represents the suboxic anoxic upper chang 7 proximal quartz rich shale which has lower toc and sulfur content than other facies the organic lamina is straight but rare kerogen is type i and dominated by sapropel the content of saturated hydrocarbon in chloroform asphalt a extract is the highest facies 2 has higher toc value sulfur content and soluble hydrocarbon content than facies 1 it was formed in unstable hydrodynamic environment under weak anoxic condition it is characterized by abundant laminas with various deformation structures and more alginite and vitrinite in kerogen anoxic lower chang 7 distal sulfur rich shale source rock make up organic rich facies 3 7 0 17 0 wt toc this facies received more higher plant input than the other facies well preserved algae shells are common in numerous and flat laminas the content of chloroform asphalt of facies 3 is higher than that of other facies but among which the saturated hydrocarbon content is the lowest the aromatic non hydrocarbon and asphalt are the highest suggesting the fluidity of hydrocarbon is the worst compared to others this facies was formed in the environment where temperature is relative lower water is relative deeper productivity and salinity are relative higher and the reducibility is relative stronger a deeper understanding of shale classification and distribution is important for the accurate resource evaluation and optimal exploration planning of shale oil

geological and geochemical constraints on the genesis of the huachanggou gold deposit western qinling region central china the huachanggou gold deposit is located in lueyang county shaanxi province central china it is situated in the mian lue sutural zone in the western qinling orogen and controlled by a wnw striking ductile shear zone the ore deposit is developed in spilite limestone and phyllite in the middle lower devonian sanhekou group and the wall rocks show evidence of deformation pyrite is the main gold bearing mineral and the native gold is either visible or microscopic the huachanggou gold deposit is considered to be an orogenic gold deposit controlled by a ductile shear zone related to the indosinian qinling orogenic event the ores show a strong enrichment in au ag and as but exhibit a simple assemblage of au and ag that are strongly correlated together gold was deposited from a moderate to low salinity salt solution co2 hydrothermal fluid at medium temperature variations in s pb c and o isotopic composition indicate that the sulfur was derived from the reduction of seawater sulfate in the wall rocks the lead was derived mainly from the wall rocks the carbon was derived from the dissolution of marine carbonate the variations in h and o isotopic composition indicate that the ore forming fluids were derived originally from metamorphic fluid with meteoric water mixing in later stages au migrated mainly in the form of au hs 2 to form the deposit boiling of the fluid triggered the precipitation of the metal sulfides that contain the gold

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

linking mid scale distributive fluvial systems to drainage basin area geomorphological and sedimentological evidence from the endorheic gastre basin argentina

lake sediments record cycles of sediment flux driven by large earthquakes on the alpine fault new zealand large earthquakes in mountain regions commonly trigger extensive landsliding and are important drivers of erosion but the contribution of this landsliding to long term erosion rates and seismic hazard remains poorly understood here we show that lake sediments record postseismic landscape response as a sequence of turbidites that can be used to quantify erosion related to large moment magnitude m w 7 6 earthquakes on the alpine fault new zealand alpine fault earthquakes caused a threefold increase in sediment flux over the 50 yr duration of each postseismic landscape response this represents considerable delayed hazard following earthquake induced strong ground motion earthquakes were responsible for 27 of the sediment flux from the lake catchment over the past 1100 yr leading us to conclude that alpine fault earthquakes are one of the most important drivers of erosion in the range front of the southern alps

quaternary base level drops and trigger mechanisms in a closed basin geomorphic and sedimentological studies of the gastre basin argentina abstract evaluating the role of tectonics and climate as possible triggering mechanisms of landscape reconfigurations is essential for paleoenvironmental and paleoclimatic reconstructions in this study an exceptional receptive closed quaternary system of patagonia the gastre basin is described and examined in order to analyze factors triggering base level drops based on a geomorphological approach which includes new tectonic geomorphology investigations combined with sedimentological and stratigraphic analysis three large scale geomorphological systems were identified described and linked to two major lake level highstands preserved in the basin the results indicate magnitudes of base level drops that are several orders of magnitude greater than present day water level fluctuations suggesting a triggering mechanism not observed in recent times direct observations indicating the occurrence of quaternary faults were not recorded in the region in addition morphometric analyses that included mountain front sinuosity valley width height ratio and fan apex position dismiss tectonic fault activity in the gastre basin during the middle pleistocene holocene therefore we suggest here that upper pleistocene climate changes may have been the main triggering mechanism of base level falls in the gastre basin as it is observed in other closed basins of central patagonia i e carri laufquen basin

regional variations in tectonic geomorphology along a segmented convergent plate boundary pacific coast of costa rica abstract pacific coastal mountain piedmont landforms of costa rica extend across the tectonic boundary between the forearc and magnetic arc region of an active convergent margin this plate boundary became segmented circa 1 million years ago when the aseismic cocos ridge impinged upon the middle america trench offshore from the southernmost coastal area of costa rica morphometric analyses of 100 mountain fronts and numerous river long profiles radiometric dating and field studies were conducted in two study areas located arcward from the plate boundary where oceanic lithosphere of the cocos plate is being subducted beneath the caribbean plate region i and the partially subducted aseismic ridge is uplifting the plate margin by isostatic and collisional processes region ii values of tectonic geomorphic parameters mountain front sinuosity s percent dissected facets ffd river concavity k are not only different statistically in regions i and ii but are also different in the areas experiencing isostatic and collisional responses to the subducting aseismic ridge in the area experiencing collisional responses mountain fronts developed along ne dipping imbricate thrust and high angle reverse faults step upward and inland from the coast morphometric data along with the divergence of river terrace profiles from the coast piedmont inland toward the mountains indicates higher uplift rates along interior range mountain fronts isostatic uplift in the outer forearc area in region ii produces a distinctly different morphologic and neotectonic style characterized by regional uplift distributed across a number of blocks bounded by normal faults geomorphic analyses indicate a general southward trend of increasing tectonic uplift from region i into region ii where the highest frequency of mountain fronts with low values of s and ffd as well as rivers with the highest values of k occur over the crest of the subducted ridge field and historical seismic data for these regional trends include 1 fault scarps displacing late quaternary fluvial terraces and colluvial soils in areas of collisional responses 2 holocene latest pleistocene marine sediments uplifted tens of meters along normal faults in areas of isostatic response of region ii and 3 more frequent shallow high magnitude earthquakes in region ii this study indicates that spatial variations in the plate tectonic framework can be detected by regional morphometric analyses using techniques applied in extensional and compressional terranes of arid and semiarid regions but not previously applied to forearc systems along convergent plate boundaries in tropical areas

high resolution geochemical record for the last 1100 yr from lake toson northeastern tibetan plateau and its climatic implications abstract knowledge of the origin of past climatic variations on annual to decadal timescales is important for assessing the likelihood of the occurrence of similar variations in the future here we present a high resolution 82 m element record obtained using synchrotron radiation x ray fluorescence from the sediments of toson lake in the northeastern tibetan plateau the record which spans the last 1100 yr exhibits variability on an annual to decadal scale the results of principal component analysis of the element dataset indicates that the first three principal components reflect variations in detrital inputs via runoff and possibly eolian activity drought conditions and temperature variations respectively spectral analysis of samples scores on these components reveals strong el nino southern oscillation enso like variability at periods of 3 8 years which indicates that the regional climatic variability was effected by enso events over the last 1100 yr on the centennial time scale the element data and toc record suggest a warm and dry climate during the medieval warm period mwp and a cold and wet little ice age lia the early 20th century was a warm interval and drier than the lia but wetter than the mwp

origin and dynamics of fe and mn sedimentary layers in lake baikal remobilization and accumulation of iron and manganese were measured by porewater and sediment core analyses at six contrasting sedimentary environments of lake baikal with bulk sedimentation rates varying between 0 8 and 0 02 mm year 1 the results allow for the distinction between two types of fe and mn diagenesis in areas of relatively high sedimentation and in regions of low sedimentation rates in the first case only small fe mn enrichments near the sediment water interface were observed in the central and southern basins at the high sediment flux area near the selenga delta and in maloe more strait massive sedimentary layers enriched in fe and mn were found within the upper 15 25 cm of the sediments exclusively in northern baikal and in the underwater academician ridge which are characterized by low sedimentation rates and deep sulfate penetration depths in the porewaters the mn content in the enriched layers ranged from 10 5 mol cm 2 at the sites near the selenga delta up to 10 2 mol cm 2 at academician ridge the accumulation times for the enriched fe mn layers calculated from the size of the fe and mn oxide pools and the diffusive fluxes into the enriched zones also varied by a factor of 1000 they ranged from a few years near the selenga delta to several thousand years for the sites at academician ridge and northern baikal these values were generally congruent with the sediment age of the accumulation zones calculated from sedimentation rates these findings have significant implications for paleolimnological studies iron and manganese dynamics at sites with high sedimentation rates is dominated by allochthonous input which is only partially dissolved close to the sediment surface in contrast the massive fe mn sedimentary layers at sites of slow sedimentation are of autochthonous origin slow dissolution and reprecipitation maintain their constant position with respect to the sediment surface and prevent burial as long as the sedimentation regime remains constant buried fe mn sedimentary layers widespread in lake baikal may therefore serve as general indicators for low sedimentation rates and as specific proxies for sudden changes in the sediment regime d 2004 elsevier b v all rights reserved

model shows that rivers transmit high frequency climate cycles to the sedimentary record rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink although it is widely accepted that rivers are perturbed by millennial scale climatic variability the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated here we employ a physically based numerical model to address this outstanding issue our model shows that river transport strongly amplifies high frequency sediment flux variations arising from changing water discharge due to positive feedback between discharge and the channel gradient this behavior is distinctly different from short period sediment flux signals with constant water discharge where the output sediment flux is strongly dampened within the river due to negative feedback between the channel gradient and sediment concentration we conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge and ultimately climate variability whereas they may be relatively insensitive to pure sediment flux perturbations such as for example those induced by tectonics

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

geomorphic and chronometric evidence for high lake level history in gahai lake and toson lake of north eastern qaidam basin north eastern qinghai tibetan plateau palaeoshorelines highstand lacustrine sediments and lakeshore terraces are preserved around saline lakes in the arid qaidam basin previous research indicates that the chronology of a mega paleolake in the qaidam basin during the late pleisotocene is controversial here we report quartz optically stimulated luminescence osl age estimates of highstand lacustrine sediments shoreline features and geomorphic exposures that contribute to a revision of the lake level history of gahai and toson lakes in the north eastern qaidam basin on the northeastern qinghai tibetan plateau qtp margin the results imply that i high lake levels at gahai and toson lakes based on quartz osl dating occurred at 85 72 63 55 31 5 4 and 0 9 0 7 ka probably corresponding to periods of warm and wet climate ii periods of high lake levels are almost synchronous with other lakes on the qtp e g qinghai and namco lakes with the highest late pleistocene levels occurring during marine oxygen isotope stage 5 and iii highstand phases on the qtp are out of phase with those of low latitude lakes in the southern hemisphere possibly driven by solar insolation variability in the low latitude region copyright 2011 john wiley sons ltd

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

neogene uplift of central eastern patagonia dynamic response to active spreading ridge subduction the chile triple junction ctj episodically migrated northward during the past 14 ma from 54 s to its present day position at 46 30 s as different almost trench parallel spreading segments entered in subduction this migration resulted in the opening of an asthenospheric window below patagonia inducing a disturbance in the regional mantle convection on the overriding plate the middle miocene time corresponds to a major change in the central patagonian basin dynamics with a transition from subsidence to generalized uplift the detailed mapping and the morphological study of post middle miocene terraces evidence regional scale trench parallel tilt histories that differ depending on latitude south of 46 30 s the slopes of the fluvial terraces indicate a change from northward to southward tilt during late miocene terraces younger than the early pliocene do not show any trench parallel tilt north of 46 30 s in contrast only northward tilt active until the pleistocene is recorded we use a semianalytical model of dynamic topography which suggests that the northward migration of the chile triple junction should be accompanied by a dynamic uplift of the central patagonian basin uplift would cause both north directed and south directed tilt north and south of the triple junction respectively with values of 0 1 0 2 500 km east of the trench tilt measured in the southeastern part of the central patagonian basin 0 1 is comparable to values predicted using the semianalytical model the dynamic topography associated to the chile ridge subduction may have exerted a major control on the neogene dynamics of patagonia

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

saharan aeolian input and effective humidity variations over western europe during the holocene from a high altitude record saharan dust inputs affect present day ecosystems and biogeochemical cycles at a global scale previous saharan dust input reconstructions have been mainly based on marine records from the african margin nevertheless dust reaching western central europe is mainly transported by high altitude atmospheric currents and requires high altitude records for its reconstruction the organic and inorganic geochemical study of sediments from a southern iberia alpine lacustrine record has provided an exceptional reconstruction of saharan dust impact and regional climatic variations during the holocene after the last deglaciation results indicate that saharan dust reached western europe in a stepwise fashion from 7 0 to 6 0 cal kyr bp and increased since then until present promoting major geochemical changes in the lacustrine system effective humidity reconstruction indicates wetter conditions during the early holocene and progressive aridification during middle late holocene time boosting abrupt changes in the lacustrine system cyclostratigraphic analyses and transport mechanisms both point to solar irradiance and aridity as major triggering factors for dust supply over western europe during the holocene

sedimentary geochemical record of human induced environmental changes in the lake brunnsviken watershed sweden environmental changes in lake brunnsviken its watershed and the greater stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments these humaninduced perturbations within the lake s watershed included agriculture urbanization sewage and industrial disposal and water column aeration smaller d 15 ntotal values high organic carbon mass accumulation rates low c n ratios and larger d 13 corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake c s ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity accumulations of redox sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake a recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy

accelerated lake expansion on the tibetan plateau in the 2000s induced by glacial melting or other processes ccelerated lake expansion in the 2000s has been confirmed by both dramatic lake area increases for 312 lakes larger than 10 km2 derived from optical images and rapid water level rises for 117 lakes with water level data measured by satellite altimetry however the underlying climate causes remain unclear this paper analyzes the relationship between the water level changes of lakes on the plateau and the potential driving factors such as the glacier meltwater supply and a dependency on precipitation and runoff over the whole plateau and in each zone the results show that the rates of change of non glacier fed lakes in the 2000s were as high as those of glacier fed lakes across the whole plateau and the lake level changes were closely associated with the lake supply coefficients the basin lake area ratio the lake variations agreed well with the spatial pattern of precipitation changes however in different zones especially at around 33 n north of the plateau glacier fed lakes did exhibit faster lake level increases than no glacier fed lakes indicating that the presence of a glacier meltwater supply augmented the precipitation driven lake expansions in these areas despite the absence of quantitative modeling due to limited data availability this study provides qualitative support that the lake expansions on the tibetan plateau in the 2000s have been driven primarily by changes in precipitation and evapotranspiration and not solely by the effect of glacier wastage

the influence of horizontal environmental variability on numerically simulated convective storms part i variations in vertical shear abstract severe convective storms are typically simulated using either an idealized horizontally homogeneous environment i e single sounding or an inhomogeneous environment constructed using numerous types of observations representing opposite ends of the spectrum the former allows for the study of storm dynamics without the complicating effects of either land surface or atmospheric variability though arguably at the expense of physical realism while the latter is especially useful for prediction and data sensitivity studies though because of its physical completeness determination of cause can be extremely difficult in this study the gap between these two extremes is bridged by specifying horizontal variations in environmental vertical shear in an idealized controlled manner so that their influence on storm morphology can be readily diagnosed simulations are performed using the advanced regional prediction system arps though with significant modification to accommodate the analytically

impact of the dual polarization doppler radar data on two convective storms with a warm rain radar forward operator abstractthe dual polarization dual pol doppler radar can transmit receive both horizontally and vertically polarized power returns the dual pol radar measurements have been shown to provide a more accurate precipitation estimate compared to traditional radars in this study the horizontal reflectivity zh differential reflectivity zdr specific differential phase kdp and radial velocity vr collected by the c band advanced radar for meteorological and operational research armor are assimilated for two convective storms a warm rain scheme is constructed to assimilate zh zdr and kdp data using the three dimensional variational data assimilation 3dvar system with the advanced research weather research and forecasting model arw wrf the main goals of this study are first to demonstrate and compare the impact of various dual pol variables in initialization of real case convective storms and second to test how the dual pol fields may be better used with a 3dvar system the results show that the zh

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

spatial characteristics of sediment trace metals in an eastern boundary upwelling retention area st helena bay south africa a hydrodynamic biological pump hypothesis st helena bay a retention zone located in the southern benguela upwelling system is an important fish nursery however it suffers from seasonal bottom water hypoxia causing major economic losses anoxic conditions are linked to sulfide fluxes from bottom sediments defined by a high sedimentation rate of organic matter it is proposed that trace metals may play an important role in alleviating part of the ecological stress by forming sulfide complexes in such systems a spatially intensive data set of sediment biogeochemical characteristics showed that poc and trace metals cr cu zn ni etc accumulated in the central zone of the bay furthermore trace metal concentrations were strongly correlated with both poc and al to explain the observed biogeochemical relationships in st helena bay we propose a hypothesis that links the upwelling retention hydrodynamics primary productivity and sediment trace metal distribution trace metals are incorporated into phytoplankton cells in the euphotic zone but rapidly sediment along with particulate organics on their senescence both the biological pump and the dispersion of particulates are primarily controlled by the hydrodynamics prevalent within st helena bay which also govern the retention zone in the shadow of one of the major upwelling cells the dynamics of entrainmentestratification drives the productivity while a residual cyclonic gyre concentrates the surface productivity within the bay bed shear stresses spatially constrain the accumulation of biogenic organic matter which governs the trace metal biogeochemistry of the sediments along a narrow terrigenous mud belt 2005 elsevier ltd all rights reserved

the geomorphometry of endorheic drainage basins implications for interpreting and modelling their evolution endorheic basins are catchments with no hydrological connection with marine environments they cover 20 of the earth s surface and are mostly located in arid regions their drainage networks converge to lakes salt flats or alluvial plains whose dynamics are strongly driven by precipitation evapotranspiration and groundwater discharge among other factors integrated surface drainage and the creation of whole drainage systems typical of open basins are commonly restricted in these regions interestingly the fluvial basin morphology of endorheic basins has not been extensively studied and a variety of quantitative morphological descriptors used in open basins have not been utilized in the geomorphic analysis of endorheic basins the objective of this study is to better understand the basin morphology of endorheic river basins by using well known geomorphological properties and their variations across scales for three basins in northern chile we computed the following descriptors and the corresponding relevant scales the cumulative distribution of contributing area the horizontal shape of the basins i e hack s law normalized euclidean length and sinuosity of the streams slope area relationship horton s ratios and drainage density we detected several properties typically found in open basins but certain features which seem to be unique to closed basins were also identified in particular we found that horizontal and vertical geomorphic features seem to be linked which suggests that an independent treatment of these features may not be appropriate for closed basins similar results were found regardless of the basin area which illustrates the relevant effects of features that are specific to these particular regions it is expected that our findings will improve both the geomorphic assessment of these basins and hydrological modelling of surface water and groundwater copyright c 2013 john wiley sons ltd

tests of an ensemble kalman filter for mesoscale and regional scale data assimilation part i perfect model experiments abstract through observing system simulation experiments this two part study exploits the potential of using the ensemble kalman filter enkf for mesoscale and regional scale data assimilation part i focuses on the performance of the enkf under the perfect model assumption in which the truth simulation is produced with the same model and same initial uncertainties as those of the ensemble while part ii explores the impacts of model error and ensemble initiation on the filter performance in this first part the enkf is implemented in a nonhydrostatic mesoscale model the fifth generation pennsylvania state university ncar mesoscale model mm5 to assimilate simulated sounding and surface observations derived from simulations of the surprise snowstorm of january 2000 this is an explosive east coast cyclogenesis event with strong error growth at all scales as a result of interactions between convective meso and subsynoptic scale dynamics it is found that the enkf is very effective in keeping th

a tibetan lake sediment record of holocene indian summer monsoon variability article history sedimentological data and hydrogen isotopic measurements of leaf wax long chain n alkanes dwax from an alpine lake sediment archive on the southeastern tibetan plateau paru co provide a holocene perspective of indian summer monsoon ism activity the sedimentological data reflect variations in lake level and erosion related to local ism rainfall over the paru co catchment whereas dwax reflects integrated synoptic scale ism dynamics our results indicate that maximum ism rainfall occurred between 10 1 and 5 2 ka during which time there were five century scale high and low lake stands after 5 2 ka the ism trended toward drier conditions to the present with the exception of a pluvial event centered at 0 9 ka the paru co results share similarities with paleoclimate records from across the tibetan plateau suggesting millennial scale ism dynamics were expressed coherently these millennial variations largely track gradual decreases in orbital insolation the southward migration of the intertropical convergence zone itcz decreasing zonal pacific sea surface temperature sst gradients and cooling surface air temperatures on the tibetan plateau centennial ism and lake level variability at paru co closely track reconstructed surface air temperatures on the tibetan plateau but may also reflect indian ocean dipole events particularly during the early holocene when enso variability was attenuated variations in the latitude of the itcz during the early and late holocene also appear to have exerted an influence on centennial ism rainfall 2014 elsevier b v all rights reserved

constraining holocene lake level highstands on the tibetan plateau by 10be exposure dating a case study at tangra yumco southern tibet abstract many lakes on the tibetan plateau are surrounded by palaeo shorelines that document former lake level highstands and hence past changes in climate establishing accurate chronologies for these shorelines is crucial to correlate lake level fluctuations with palaeo environmental histories that are commonly inferred from lake sedimentary records here we apply surface exposure dating to constrain the age of two lake level highstands at one of the largest tibetan lakes tangra yumco which has well developed palaeo shorelines located up to 185 m above the current lake for sampling we focussed on wave cut bedrock terraces that vary considerably in width because they were carved into rocks of different erodibility samples from the highest strath terrace 180 185 m above the lake at three different sites yield tightly clustered 10 be ages between 7 39 0 19 ka and 7 87 0 27 ka internal errors which constrain the end of an early holocene lake level highstand at 7 6 0 6 ka external error the consistency of the 10 be ages indicates that bedrock erosion by wave attack reduced the inherited 10 be component to negligible amounts because otherwise samples would show considerable age scatter two bedrock samples from a lower terrace 140 145 m above the lake and one amalgamated clast sample from a beach ridge on the same terrace yield 10 be ages between 4 04 0 14 ka and 4 50 0 15 ka these ages document that the lake level dropped by 40 m between 7 6 ka and 4 3 ka granite boulders from the two investigated terraces yield apparent 10 be ages that are 6 ka and 27 ka older than the ages of the respective terraces indicating that this sample type is not reliable in this setting overall our results demonstrate that exposure dating of bedrock terraces provides a valuable tool to reconstruct lake level histories on the tibetan plateau

decoupling of foreland basin subsidence from topography linked to faulting and erosion many mountain ranges in regions of plate convergence are flanked by foreland sedimentary basins that are usually thought to result from flexing of the elastic lithosphere under the passive weight of sediments and thrust sheets emplaced in the mountain belt however in some places the depth of the foreland basin bears little relation to the weight of basin sediments and neighboring mountains implying that this model is too simple and or that additional forces must affect subsidence here i investigate this problem using a numerical model that incorporates coupling between an upthrusting mountain range and a subsiding basin i show that only part of the subsidence reflected in the shape of a foreland basin is a flexural isostatic response to crustal thickening and sediment loading the remaining subsidence results from dragging of the basin margin downward by slip on a range front fault and related flexural deformation of the surrounding lithosphere the maximum basin depth is shown to increase with increasing fault displacement and can become decoupled from the elevation of the mountain range especially as erosion becomes increasingly important deeply eroded model mountain belts may have foreland basins several times deeper than flexural models predict on the basis of surface loads these results challenge the prevailing view that fault bounded foreland basins result solely from the passive weight of mountains and sediments acting on the lithosphere and they highlight that slip on major range front reverse faults when repeated over many earthquake cycles may be recorded in their geometry and stratigraphic records

an evaluation of trace metal distribution and environmental risk in sediments from the lake kalimanci fyr macedonia pollution from mining activities is a significant problem in several parts of the republic of macedonia a geochemical study of the surficial sediments of lake kalimanci in the eastern part of the republic of macedonia was carried out to determine their elemental compositions and to evaluate the pollution status of lake sediments by employing an enrichment factor ef the major and trace element contamination in surficial lake sediments was studied to assess the effects of metalliferous mining activities the mean concentrations of major elements wt si 23 5 al 7 9 fe 6 6 mg 1 3 ca 3 8 na 1 1 k 2 3 ti 0 4 p 0 2 mn 0 6 and trace elements ranged within mo 1 0 4 6 mg kg 1 cu 144 4 1 162 mg kg 1 pb 1 874 16 300 mg kg 1 zn 2 944 20 900 mg kg 1 ni 21 7 79 3 mg kg 1 cd 16 5 136 mg kg 1 sb 0 6 3 6 mg kg 1 bi 3 0 24 3 mg kg 1 and ag 1 4 17 3 mg kg 1 the ef ranged within 0 12 590 3 among which cd pb zn and as have extremely severe enrichment the data indicate that trace elements had extremely high concentrations in lake kalimanci surficial sediments owing to the anthropogenic addition of contaminants

geochemistry of a tropical lake lake leopoldo on pseudo karst topography within the roraima group guayana shield venezuela abstract a geochemical assessment was performed on lake leopoldo a tropical lake located on the guayana shield venezuela the lake water was characterized ca2 mg2 na k cl no 3 no 2 so 4 2 nh 4 fe and p lacustrine setting the origin transport and fate of sedimentary material in this highly unusual lacustrine setting lake sediments were analyzed for textural mineralogical and chemical composition including the rare earth element ree contents in addition to toc 13c 15n and elemental c n ratios the molecular distributions of several biomarker compounds were determined and used to assess organic matter source and transport to the lake lake leopoldo developed on a sequence of quartz arenites of the precambrian roraima group the area conforms to the definition of pseudo karst morphology the results show that the lake is oligotrophic where primary production seems to be limited by nutrients in the sediments organic matter shows an overwhelming higher plant derived origin certain elements k v cu th ba hg and lree displayed enrichments with organic matter while others zr hf si sn pb and ta displayed an association with the mineral fraction the results obtained in this study suggest that the lake water characteristics and the affinities of trace elements for sediment organic fractions are controlled by biogeochemical processes within the surrounding forest soil environment prior to the transport of the terrestrially derived organic matter to the lake the most significant geochemical finding is that organic matter can play an important role in the distribution of trace metals in such highly oligotrophic terrains of humid tropical environments

late quaternary hydrological changes inferred from lake level fluctuations of nam co tibetan plateau china abstract this paper discusses the range of lake level changes using hydro acoustic techniques and sediment core data for lake nam co in central tibet china this second largest tibetan lake is situated at an elevation of 4718 m a s l lake level changes with different high stands documented by beach remnants are widespread on the tibetan plateau and also in lake nam co they indicate significant changes in the hydrological system triggered by the monsoonal circulation using hydro acoustic techniques submerged beach remains at approximately 10 15 m 30 m 45 m 70 m and 95 m below present day lake level were detected indicating a more negative water balance than today the 10 15 m lake level is dated to an age equal to the little ice age all deeper lake levels are assumed to have been formed prior to 10000 cal bp folded older sediments detected in the hydro acoustic profiles indicate a possible larger extent of the glaciers during or prior to the last glacial maximum lgm this is followed by a low stand or even by possible desiccation of the entire lake basin during or after the lgm

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

the tornadic supercell on the kanto plain on 6 may 2012 polarimetric radar and surface data assimilation with enkf and ensemble based sensitivity analysis abstracta tornadic supercell and associated low level mesocyclone lmc observed on the kanto plain japan on 6 may 2012 were predicted with a nonhydrostatic mesoscale model with a horizontal resolution of 350 m through assimilation of surface meteorological data horizontal wind temperature and relative humidity of high spatial density and c band doppler radar data radial velocity and rainwater estimated from reflectivity and specific differential phase with a local ensemble transform kalman filter with assimilation of both surface and radar data a strong lmc was successfully predicted near the path of the actual tornado when either surface or radar data were not assimilated however the lmc was not predicted therefore both surface and radar data were essential for successful lmc forecasts the factors controlling the strength of the predicted lmc defined as a low level maximum vertical vorticity were clarified by an ensemble based sensitivity analysis esa which is a new approach for ana

changes of climate glaciers and runoff in china s monsoonal temperate glacier region during the last several decades changes of climate glaciers and runoff during the last several decades in china s monsoonal temperate glacier region have been studied temperature has increased in a fluctuating manner during the last several decades and temperature rise has accelerated since the 1980s net accumulation of dasuopu ice core has consistently declined and the precipitation decrease was also obvious from the end of 1970s through the middle 1980s and particularly after the 1990s in china s monsoonal temperate glacier region as a response to climate change eight monsoonal temperate glaciers were stationary or advancing between the 1900s 1930s and the 1960s 1980s and were in retreat from the 1930s to the 1960s and from the 1980s to the present ablation is heavy in the glacier tongue areas and the mean ablation water equivalent in hailuogou glacier during 1990 91 1997 98 was 876 mm more than that in 1982 83 ablation depth on the exposed ice area increased by 1 4 m a 1 over the period 1983 84 1990 91 mass balance records also show that glaciers suffered a constant mass loss of snow and ice and the accumulated mass balance in hailuogou basin and baishui glacier no 1 was 10 83 m water equivalent in the past 45 years and 11 38 m in the past 52 years as glaciers become shorter narrower and thinner under the background of climate warming changes of internal and upper surface morphology also occurred providing evidence of the response to climatic warming in recent years local hydrological and climatic data demonstrated that in yanggong basin during 1979 2003 and hailuogou basin during 1988 2004 runoff from the glacier areas has been increasing both seasonally and annually overall it is clear that china s monsoonal temperate glaciers are losing mass and are retreating under the background of climate warming c 2009 elsevier ltd and inqua all rights reserved

regional geochemistry of trace elements in chesapeake bay sediments the concentrations of cr mn fe co ni cu zn cd and pb in 177 surface sediment samples from throughout chesapeake bay are reported analyses were made of both unfractionated samples and the 63 m fractions analytical uncertainty always less than 10 controlled reproducibility in analyses of the 63 m fractions but sampling variance controlled reproducibility in the unfractionated samples especially when coarse grained sediments were being analyzed sediments in the northernmost part of the bay are enriched relative to average continental crust in all elements except cr this reflects the composition of dissolved and suspended material being delivered to that region by the susquehanna river the enriched sediments appear not to be transported south of baltimore in significant quantily zinc cadmium and lead are enriched relative to average crust throughout the bay and in most other estuaries in the eastern united states

morphodynamics and lake level variations at paiku co southern tibetan plateau china abstract proxy records from lakes on the tibetan plateau are commonly used to infer monsoon related climatic changes during the late quaternary specific influences of catchment processes and their interaction with the lake basin are seldom utilized based on morphological field investigations supported by remote sensing analyses in combination with radiocarbon dated sediment data from lacustrine sequences along paleoshorelines and terraces we can demonstrate that close relationships exist between glacier dynamics fluvial alluvial fan terrace formation and lake level and lake area changes of paiku co southern tibet our results show that the formation of large scale fluvial alluvial fans f1 predates the maximum advance of the xixiabangma glaciers the latter formed a distinct terminal moraine complex north of the present glaciers during the local lgm llgm at 42 21 cal ky bp a younger fan generation f2 developed from the llgm to the late holocene which was accompanied by lake level fluctuations with a generally decreasing trend the highest morphologically traceable lake level at 4665 m asl existed prior to 25 cal ky bp and induced a potential overflow to the neighboring langqiang co and pengqu river a high level also existed during the llgm followed by a minor decline until ca 15 cal ky bp owing to reduced meltwater discharge under cold and dry climatic conditions a return to the previous level during the late glacial early holocene period between 11 9 and 9 5 cal ky bp is likely caused by climate warming increased meltwater discharge and enhanced indian summer monsoon ism moisture supply afterwards paiku co shrank gradually toward its present level while the youngest fan f3 generation evolved as individual small sized bodies under ephemeral discharge conditions from the mid holocene to the present the formation of four terrace levels t4 1 is likely the result of sequential incision into the fan generations with a mean erosion rate of 50 cm ky caused by lake level lowering tectonic impact cannot be completely ruled out since 1976 the glaciers lost ca 15 in area accompanied by lake area loss of 3 7 between 1972 and june 2014 seasonal lake level variations of about 1 2 m in height occur in response to summer monsoon rainfall our data show a close interaction between glacial dynamics fluvial processes terrace formation and water budget changes throughout the last 25 cal ky bp in response to the well known insolation driven ism effective moisture supply during the late glacial and holocene period temperature driven meltwater dynamics were the controlling factors for variations in water balance of paiku co

assessment of relative active tectonics southwest border of the sierra nevada southern spain abstract we present a new method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography indices used include stream length gradient index sl drainage basin asymmetry af hypsometric integral hi ratio of valley floor width to valley height vf index of drainage basin shape bs and index of mountain front sinuosity smf results from the analysis are accumulated and expressed as an index of relative active tectonics iat which we divide into four classes from relatively low to highest tectonic activity the study area along the southwest border of the sierra nevada in southern spain is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front the study area has variable rates of active tectonics resulting from the collision of africa with europe that has produced linear east west anticlinal forms as well as extension with variable vertical rates of normal faulting to about 0 5 m ky we test the hypothesis that areas of known relatively high rates of active tectonics are associated with indicatives values of iat

a high resolution monsoon record of millennial scale oscillations during late mis 3 from wulu cave south west china a speleothem record from south western china characterizes in detail the millennial scale changes in asian monsoon am intensity from 39 3 to 28 7 ka the calcite 18o profile with an average resolution of 8 years shows several strong monsoon events concurrent with greenland interstadials gis 8 4 to gain a systematic perspective of am millennial scale variability the new and previously reported data from the same cave are combined showing that am variation exhibits a broad similarity with greenland ice 18o records and with antarctica but in an opposite sense for the interval that encompasses gis 5 and gis 4 1 however our stalagmite 18o record depicts a sustained strong monsoon with no distinctive oscillation between these interstadials another prominent characteristic in our record is a gradual transition into chinese interstadial cis 8 which is well constrained by an annually laminated sequence we find that an initial rise in monsoon intensity lasting a few centuries significantly precedes the abrupt onset of cis 8 in the am realm this suggests that atmospheric moisture and heat transport are probably capable of inducing abrupt climate change when a rapid reorganization of ocean atmosphere circulations passes a tipping point

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

major and trace element geochemistry in zeekoevlei south africa a lacustrine record of present and past processes this study reports a multi parameter geochemcial investigation in water and sediments of a shallow hyper eutrophic urban freshwater coastal lake zeekoevlei in south africa zeekoevlei receives it

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

simulation and analysis of tornado development and decay within a three dimensional supercell thunderstorm abstract a three dimensional numerical simulation using a two way interactive nested grid is to study tornado genesis within a supercell during a 40 minute period two tornadoes grow and decay within the storm s mesocyclone the tornadoes have life spans of approximately 10 minutes maximum ground relative surface wind speeds exceed 60 m s 1 during both tornadoes and horizontal pressure gradients reach 18 hpa km 1 during the second tornado comparison of the simulated storm evolution with doppler and field observations of supercells and tornadoes shows many similar features vertical vorticity in the mesocyclone and the tornado vortex at low levels is initially created by the tilting of the environmental vorticity and baroclinically generated vorticity along the forward gland gust front of the storm tornadogenesis is initiated when mesocyclone rotation increase above cloud base the increased rotation generates lower pressure in the mesocyclone increasing the upward pressure gradient forces the upwar

quaternary glaciations of the southern andes abstract the southern andes comprise the southernmost portion of the andean cordillera beginning at the edge of the puna altiplano lat 27 s and ending at isla de los estados lat 55 s the late cainozoic glacial record of these mountains spans the interval from the late miocene to the present and is one of the most complete to be found anywhere in the world this has arisen for several reasons i the conterminous mountain ice cap extended to the piedmont zone on both flanks of the range where the sedimentary and morphological record has been well preserved ii periodic volcanism mainly from monogenetic fissure eruptions of basalt east of the range and from central tephra producing cones along the mountain crest has provided opportunity for the preservation and radiometric dating of interbedded glacial deposits iii a tectonically induced interval of stream incision in the mid pleistocene and simultaneous uplift has preserved glacial sediments on interfluves iv in the chilean lakes region west of the mountains late quaternary glaciers terminated in a well vegetated landscape thus creating scope for radiocarbon dating of interbedded and incorporated organic materials consequently the last glaciation in the llanquihue area of chile is one of the best dated sequences in south america thus the llanquihue glaciation is proposed as the south american equivalent of the wisconsin and weichsel glaciations of north america and north west europe respectively

assimilation of simulated polarimetric radar data for a convective storm using the ensemble kalman filter part i observation operators for reflectivity and polarimetric variables abstract a radar simulator for polarimetric radar variables including reflectivities at horizontal and vertical polarizations the differential reflectivity and the specific differential phase has been developed this simulator serves as a test bed for developing and testing forward observation operators of polarimetric radar variables that are needed when directly assimilating these variables into storm scale numerical weather prediction nwp models using either variational or ensemble based assimilation methods the simulator takes as input the results of high resolution nwp model simulations with ice microphysics and produces simulated polarimetric radar data that may also contain simulated errors it is developed based on calculations of electromagnetic wave propagation and scattering at the s band of wavelength 10 7 cm in a hydrometeor containing atmosphere the t matrix method is used for the scattering calculation of raindrops and the rayleigh scattering approximation is applied to snow and ha

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

a numerical study of the 6 may 2012 tsukuba city supercell tornado part i vorticity sources of low level and midlevel mesocyclones abstracton 6 may 2012 an f3 supercell tornado one of the most destructive tornadoes ever recorded in japan hit tsukuba city in eastern japan and caused severe damage to clarify the generation mechanisms of the tornadic storm and tornado high resolution numerical simulations were conducted under realistic environmental conditions using triply nested grids the innermost simulation with a 50 m mesh successfully reproduced the tsukuba city tornadic supercell storm in this study the first of a two part study the vorticity sources responsible for mesocyclogenesis prior to tornadogenesis were investigated by analyzing vortex lines and the evolution of circulation of the mesocyclones vortex lines that passed through the midlevel mesocyclone 4 km height originated from the environmental streamwise vorticity whereas the low level mesocyclone and low level mesoanticyclone were connected by several arching vortex lines over the rear flank downdraft associated with the hook shaped distribution of hydromet

petrography geochemistry and tectonics of a rifted fragment of mainland asia evidence from the lasala formation mindoro island philippines petrological and geochemical investigations of the sedimentary lasala formation in northwest mindoro philippines offer new insights into the origin of this geologically contentious region mindoro island s position at the boundary between sundaland and the philippine mobile belt has led to variable suggestions as to how much of it is continent derived or not the eocene lasala formation overlies the jurassic halcon metamorphics a regionally metamorphosed suite generally thought to have formed as a result of arc continent collision processes the sedimentary formation consists mainly of sandstones and shales interbedded with mudstones basalt flows and subordinate limestones and conglomerates petrographic information on the lasala clastic rocks demonstrates a uniform framework composition that is predominantly quartzose major oxide trace element abundances and various elemental ratios similarly impart a strongly felsic signature these characteristics are taken to indicate a chiefly continental passive margin derivation and deposition of the lasala sediments during the eocene the weak indication of active margin influence is suggested to be an inherited signature supported by paleogeographic models of the southeastern asian margin area during the pre cenozoic

geochemistry of trace metals from chinese river estuary systems an overview abstract based on the data from extensive estuarine studies over 10 years 1983 93 the present work provides an overview of the geochemical features of large chinese river estuary systems elevated concentrations of major elements are observed in chinese rivers from north to south which is attributed to intense weathering and erosion over the drainage basins trace metal levels in chinese rivers are relatively low and similar to those from large and less disturbed world aquatic systems e g amazon and orinoco in the estuaries particulate elements show stable distributions in the mixing zone especially when absolute concentrations are normalized to aluminium and or scandium dissolved trace metals may have either conservative and or active non conservative distributions or both in chinese estuaries wherever non conservative distributions are observed trace elements may be remobilized and or scavenged from solution depending upon river discharge sedimentary dynamics and element biological uptake and regeneration of trace metals becomes more important in high salinity areas further offshore the riverine effluent plumes than inside correlation of heavy metals with grain size and operational chemical forms reveals a high proportion of elements associated with the fine size fraction compared to total sediments and elevated labile fractions in bottom sediments in anthropogenically disturbed systems finally an estimate is made towards the chemical flux of trace metals to the ocean through chinese estuaries

hydrological variations on the central tibetan plateau since the last glacial maximum and their teleconnection to inter regional and hemispheric climate variations decadal to sub decadal variability of inflow evaporation and biological productivity derived from lake nam co was used to reconstruct hydrological changes for the past ca 24 k cal a bp the timing of these variations corresponds to known climatic shifts on the northern hemisphere after a dry and cold last glacial maximum the lake level of nam co initially rose at ca 20 k cal a bp moist but further cold conditions between ca 16 2 and 14 k cal a bp correspond to heinrich event 1 a warm and moist phase between ca 14 and 13 k cal a bp is expressed as a massive enhancement in inflow and biological productivity and might be associated with a first intensification of the indian ocean summer monsoon coinciding with the bolling allerod complex a two step decrease in inflow and a contemporaneous decline in biological productivity until ca 11 8 k cal a bp points to cool and dry conditions during the younger dryas lake levels peak at ca 9 4 k cal a bp although hydrological conditions remain relatively stable during the holocene with only low amplitude variations observed

evaluating branched tetraether lipid based palaeotemperature proxies in an urban hyper eutrophic polluted lake in south africa we evaluate the application of the branched glycerol dialkyl glycerol tetraether br gdgt based palaeotemperature and palaeoenvironmental proxy to a hyper eutrophic polluted and shallow oxic lake lake zeekoevlei is the largest freshwater lake in south africa located close to cape town we use published lake based and soil based calibration equations and compare the reconstructed mean annual air temperature mat with regional south african and local cape town instrumental temperature records the distribution of br gdgts in the lake sediments is influenced by air temperature the lake based calibration equation which uses the methylation index of branched tetraethers cyclisation ratio of branched tetraethers mbt cbt formulated for african lakes tierney et al 2010 fits well with the instrumental temperature records moreover the cbt derived ph likely reflects historic socioeconomic changes in catchment our results suggest that a polluted hyper eutrophic status and shallow water urban setting do not preclude application of the mbt cbt mat proxy however further research is necessary to understand the behaviour of br gdgt producing bacteria in polluted and highly productive lakes

sensitivity of real data simulations of the 3 may 1999 oklahoma city tornadic supercell and associated tornadoes to multimoment microphysics part i storm and tornado scale numerical forecasts abstractnumerical predictions of the 3 may 1999 oklahoma city oklahoma tornadic supercell are performed within a real data framework utilizing telescoping nested grids of 3 km 1 km and 250 m horizontal spacing radar reflectivity and radial velocity from the oklahoma city wsr 88d are assimilated using a cloud analysis procedure coupled with a cycled 3dvar system to analyze storms on the 1 km grid for subsequent forecast periods single double and triple moment configurations of a multimoment bulk microphysics scheme are used in several experiments on the 1 km and 250 m grids to assess the impact of varying the complexity of the microphysics scheme on the storm structure behavior and tornadic activity on the 250 m grid this appears to be the first study of its type to investigate single versus multimoment microphysics within a real data context it is found that the triple moment scheme overall performs the best producing the smallest track errors for the mesocyclone on the 1 km grid and str

origin and evolution of major salts in the darling pans western cape south africa abstract sediment and water samples from 12 saline pans on the semi arid west coast of south africa were analysed to determine the origin of salts and geochemical evolution of water in the pans pans in the area can be subdivided into large gypsiferous coastal pans with 79 150 g kg total dissolved salt tds small inland brackish to saline 2 64 g kg tds pans and small inland brine 168 531 g kg tds pans that have a layer of black sulphidic mud below a halite crust the salinity of coastal pan waters varies with the seasonal influx of dilute runoff and dissolution of relict pleistocene marine evaporite deposits in contrast inland pans are local topographic depressions bordered on the north by downslope lunette dunes where solutes are concentrated by evaporation of runoff throughflow and groundwater seepage the composition of runoff and seepage inflow waters is determined by modification of coastal rainfall by weathering calcite precipitation and ion exchange reactions in the predominantly granitic catchment soils evaporation of pan waters leads to precipitation of calcite mg calcite dolomite gypsum and halite in a distinct stratigraphic succession in pan sediments bicarbonate limits carbonate precipitation ca limits gypsum precipitation and na limits halite precipitation dolomitisation of calcite is enhanced by the high mg ca ratio of brine pan waters brine pan waters evolve seasonally from na cl dominated brines in the wet winter months to mg cl dominated brines in the dry summer months when 5 20 cm thick halite crusts cover pan surfaces pan formation was probably initiated during a drier climate period in the early holocene more recent replacement of natural vegetation by cultivated land may have accelerated salt accumulation in the pans

geochemistry of trace metals and pb isotopes of sediments from the lowermost xiangjiang river hunan province p r china implications on sources of trace metals this paper reports a geochemical study of trace metals and pb isotopes of sediments from the lowermost xiangjiang river hunan province p r china trace metals ba bi sc v cr mn co ni cu zn mo cd sn sb pb tl th u zr hf nb and ta were analyzed using icp ms and pb isotopes of the bulk sediments were measured by mc icp ms the results show that trace metals cd bi sn sc cr mn co ni cu zn sb pb and tl are enriched in the sediments among these metals cd bi and sn are extremely highly enriched ef values 40 metals zn sn sb and pb significantly highly 5 ef 20 and metals sc cr mn co ni cu and tl moderately highly 2 ef 5 enriched in the river sediments all these metals however are moderately enriched in the lake sediments geochemical results of trace metals th sc co cr zr hf and la and pb isotopes suggest that metals in the river sediments are of multi sources including both natural and anthropogenic sources metals of the natural sources might be contributed mostly from weathering of the indosinian granites gr and palaeozoic sandstones pl and metals of anthropogenic sources were contributed from pb zn ore deposits distributed in upper river areas metals in the lake sediments consist of the anthropogenic proportions which were contributed from automobile exhausts and coal dusts thus heavy metal contamination for the river sediments is attributed to the exploitation and utilization e g mining smelting and refining of pb zn ore mineral resources in the upper river areas and this for the lake sediments was caused by automobile exhausts and coal combustion metals bi cd pb sn and sb have anthropogenic proportion of higher than 90 with natural contribution less than 10 metals mn and zn consist of anthropogenic proportion of 60 85 with natural proportion higher than 15 metals sc cr co cu tl th u and ta have anthropogenic proportion of 30 70 with natural contribution higher than 30 metals ba v and mo might be contributed mostly from natural process

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

the influence of environmental low level shear and cold pools on tornadogenesis insights from idealized simulations abstractidealized dry simulations are used to investigate the roles of environmental vertical wind shear and baroclinic vorticity generation in the development of near surface vortices in supercell like pseudostorms a cyclonically rotating updraft is produced by a stationary cylindrical heat source imposed within a horizontally homogeneous environment containing streamwise vorticity once a nearly steady state is achieved a heat sink which emulates the effects of latent cooling associated with precipitation is activated on the northeastern flank of the updraft at low levels cool outflow emanating from the heat sink spreads beneath the updraft and leads to the development of near surface vertical vorticity via the baroclinic mechanism as has been diagnosed or inferred in actual supercells that have been simulated and observed an intense cyclonic vortex forms in the simulations in which the environmental low level wind shear is strong and the heat sink is of intermediate strength relative to the

miocene block uplift and basin formation in the patagonian foreland the gastre basin argentina abstract the intraplate fault block mountains and intermontane deposits of the gastre basin which are recorded more than 550 km east of the andean trench in central patagonia argentina are analyzed the gastre basin is one of the largest patagonian intermontane basins limited by uplifted blocks strongly oblique to the andean chain it was originated by reverse faulting and inversion of pre existing normal faults associated with a mesozoic rift basin and defined by older crustal heterogeneities the deformational event occurred during the middle miocene related to a short contractional episode 16 1 14 86 ma probably in response to an eastward migration of the andean fold and thrust belt during pliocene to quaternary times neither younger fault block uplifts nor reconfigurations of the basin occurred similarities between the study area and other parts of the patagonian foreland such as the presence of miocene reverse or inversion tectonics as well as the accommodation of the miocene sedimentary successions suggest that the gastre basin is part of a major late early to middle miocene broken foreland system i e the patagonian broken foreland that exhumed discrete fault block mountains and generated contemporary basins along more than 950 km parallel to the andean trench i e between 40 00 and 48 00 south latitude based on recent studies on the southern andean margin this continental scale contractional episode may be the result of a flat slab subduction segment nevertheless such a hypothesis is very difficult to support when analyzing such a large flat subduction segment along the entire patagonian trench this suggests the need to consider alternative flat slab trigger mechanisms or other factors in the generation of broken foreland systems