profiles of trace elements and stable isotopes derived from giant long lived tridacna gigas bivalves potential applications in paleoclimate studies this study investigates the environmental and biological controls on trace element partitioning and stable isotope composition of modern giant long lived bivalves tridacna gigas with the aim to use these archives for paleoclimatic reconstructions firstly the intra shell variability is studied by measuring time equivalent profiles in the different shell layers characterised by different growth rates secondly the inter site variability is studied by comparing profiles derived from three modern specimens collected in sites across the indo pacific region characterised by different ranges of temperature and productivity these results show that 18o profiles are highly reproducible across the shell regardless of significantly different growth rates shell 18o is primarily controlled by water 18o and temperature comparison of intra shell mg ca profiles shows a clear and systematic partitioning where inner layer mg ca values are a least 2 3 times higher than outer layer and hinge areas inner layer mg ca shows seasonal oscillations but superimposed on an ontogenetic trend with increasing values and increasing amplitude mg ca oscillations with age the sr ca profiles do not show clear reproducible seasonal trends in the different shell zones it is concluded that mg ca and sr ca profiles appear to reflect a combination of biological and environmental controls that will need to be disentangled before using these proxies in paleoclimatic studies finally intra shell ba ca profiles are reproducible in great detail for all modern specimens studied inter site comparison shows that the amplitude and the timing of the ba ca peaks appear to reflect the timing and the amplitude of the chlorophyll peaks associated with phytoplankton blooms at each locality making this tracer a potential paleoproductivity indicator

strong biological controls on sr ca ratios in aragonitic marine bivalve shells 1 it is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments sr ca ratios have been successfully used as a temperature proxy in corals and sclerosponges previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on sr ca ratios as many studies have used bivalve growth rates to determine temperature we tested if sr ca ratios could predict temperature through its relationship with growth rate shells from the two species of clams from the same family veneroidea studied here saxidomus giganteus and mercenaria mercenaria show vastly different seasonal sr ca profiles a strong relationship between average annual sr ca ratios and annual growth rate was found in s giganteus shells from both washington r2 0 87 and alaska r2 0 64 usa but not in m mercenaria shells from north carolina usa furthermore the sr ca growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in s giganteus r2 0 73 although there were significant positive correlations between sr ca ratios and temperature in s giganteus shells the correlations were weak 0 09 r2 0 27 and thus sr ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves it is clear from this study that sr ca ratios are not under thermodynamic control in either clam species since thermodynamics predict a negative correlation between sr ca ratios and temperature in aragonite this points toward dominance of biological processes in the regulation of sr2 this is also reflected by the largely differing sr ca partition coefficients dsr in these shells dsr 0 25 when compared to inorganic coral and sclerosponge studies dsr 1 all of which show a negative dependence of sr ca on temperature we suggest that caution be taken when using sr ca in any biogenic aragonite as a temperature proxy when the dsr greatly deviates from one as this indicates the dominance of biological controls on sr ca ratios

holocene thermal optimal and climate variability of east asian monsoon inferred from forest reconstruction of a subalpine pollen sequence taiwan the east asian monsoon holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation in this study we show holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central taiwan based on modern analogues of various altitudinal biomes in the region a warmer interval occurred between 8 and 4 ka bp calibrated 14 c years when the subtropical forests were more extensive the holocene thermal optimum is represented by an altitudinal tropical forest at 6 1 5 9 ka bp and 6 9 ka bp and only the latter was accompanied by wet conditions indicating decoupling of thermal and precipitation mechanism in the middle holocene abrupt and relative severe cold phases shown by biome changes occurred at about 11 2 11 0 ka bp 7 5 ka bp 7 2 ka bp 7 1 ka bp 5 2 ka bp 5 0 ka bp and 4 9 ka bp a spectral analysis of pollen of a relatively cold taxon salix reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of indian and western pacific oceans the cold warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of be 10

late holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western guangdong south china abstract the study of a 300 cm thick exposed lacustrine sediment section in the hedong village in zhaoqing area which is located in sub tropical west guangdong province in south china demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of asian monsoon climate multi proxy records including the humification intensity total organic carbon and grain size fractions reveal a general trend towards dry and cold conditions in the late holocene that this is because of a decrease in solar insolation on an orbital scale three intensified asian summer monsoon asm intervals 3300 3000 cal yr bp 2600 1600 cal yr bp and 900 600 cal yr bp and three weakened asm intervals 4000 3300 cal yr bp 3000 2600 cal yr bp and 1600 900 cal yr bp are identified our humification record hd cal shows a good correlation on multi centennial scale with the tree ring 14 c record a proxy of solar activity a spectral analysis of hd cal reveals four significant cycles i e 1250 yr 300 yr 110 yr and 70 yr and most of these cycles are related to the solar activity our findings indicate that solar output and oceanic atmospheric circulation probably have influenced the late holocene climate variability in the study region

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

a 60 year isotopic record from a mid holocene fossil giant clam tridacna gigas in the ryukyu islands physiological and paleoclimatic implications we have constructed a 60 year stable isotope record from a 14c dated fossil giant clam tridacna gigas 6216 years bp at its northernmost latitudinal limit in the geological past on kume island central ryukyu archipelago japan stable oxygen 18o and carbon 13c isotopic analyses are combined with observations of growth lines seen on the inner shell layer sixty pairs of summer winter growth lines which preserve daily growth increments were observed in the inner shell layer two growth phases characterized by a growth curve and isotopic profiles are clearly recognized throughout the growth history of this specimen no significant shifts in average values of the two isotopic ratios were detected during its growth history although the growth rate varied widely from 1 to 15 mm year over 60 years including after the onset of sexual maturity spectral analysis of the fossil tridacna 18o time series implies that decadal variability observed in the north pacific ocean during the past hundred years also existed 6000 years ago our study implies that fossil giant clams are one of the best means of inferring isotopic records of annual to decadal climate variations giant clams have the advantages of a dense shell high growth rate long lifespan and geographically and geologically broad distributions

numerical model predictions of autogenic fluvial terraces and comparison to climate change expectations terraces eroded into sediment alluvial and bedrock strath preserve an important history of river activity river terraces are thought to form when a river switches from a period of slow vertical incision and valley widening to fast vertical incision and terrace abandonment consequently terraces are often interpreted to reflect changing external drivers including tectonics sea level and climate in contrast the intrinsic unsteadiness of lateral migration in rivers may generate terraces even under constant rates of vertical incision without external forcing to explore this mechanism we simulate landscape evolution by a vertically incising meandering river and isolate the age and geometry of autogenic river terraces modeled autogenic terraces form for a wide range of lateral and vertical incision rates and are often paired and longitudinally extensive for intermediate ratios of vertical to lateral erosion rate autogenic terraces have a characteristic reoccurrence time that scales with the time for relief generation there is a preservation bias against older terraces due to reworking of previously visited parts of the valley evolving spatial differences in bank strength between bedrock and sediment reduce terrace formation frequency and length favor pairing and can explain sublinear terrace margins at valley boundaries age differences and geometries for modeled autogenic terraces are consistent in cases with natural terraces and overlap with metrics commonly attributed to terrace formation due to climate change we suggest a new phase space of terrace properties that may allow differentiation of autogenic terraces from terraces formed by external drivers

lithologic and tectonic controls on bedrock channel form at the northwest himalayan front 1 recognition that channel form reflects a river s ability to erode rock and transport material has spawned stream power models that estimate incision patterns by approximating energy dissipation within a channel these models frequently assume that channel width scales as a power law with drainage area partly because drainage area is easily extracted from digital elevation models dems however this assumption is often confounded by local variations in rock strength and rock uplift rate that can cause channel constriction downstream here we investigate the morphological response to spatial changes in rock strength and rock uplift rate of 10 bedrock channels traversing the mohand range along the northwest himalayan front we present a new method to continuously measure and compare channel width slope and other hydraulic parameters that integrate satellite imagery and dem analysis our method corrects for an 13 overestimation of average channel gradient from a 90 m resolution dem that arises from short circuits of fine scale meanders we find that channels 1 narrow 1 km upstream from knickpoints formed by an increase in rock strength 2 adjust laterally more than vertically in response to downstream decreases rock erodibility and uplift rate and 3 meander where shear stresses are high and channel widths are low we attribute these results to a high ratio of sediment supply to transport capacity which enhances lateral erosion relative to vertical incision our results suggest that substrate strength and sediment supply substantially influence channel form and that channel width should be explicitly measured when interpreting tectonic signals from bedrock channel morphology

landscapes depositional environments and human occupation at middle paleolithic open air sites in the southern levant with new insights from nesher ramla israel abstract middle paleolithic human occupation in the levant 250 50 ka ago has been recorded in roofed cave and rockshelter and open air sites research at these different types of sites yielded different perspectives on the middle paleolithic human behavior and evolution until recently open air middle paleolithic sites in the levant were found in three major sedimentary environments fluvial lake margin and spring here we describe a unique depositional environment and formation processes at the recently discovered open air site of nesher ramla israel and discuss their contribution to understanding site formation processes in open air sites in the levant the site is 8 m thick middle paleolithic sequence osl dated to 170 80 ka that is located in a karst sinkhole formed by gravitational deformation and sagging into underground voids the sedimentary sequence was shaped by gravitational collapse cyclic colluviation of soil and gravel into the depression waterlogging in situ pedogenesis and human occupation original bedding and combustion features are well preserved in the lower archaeological sequence a rare occurrence in comparison to other open air archaeological sites this phenomenon coincides with episodes of fast sedimentation burial which also allowed better preservation of microscopic remains such as ash the upper archaeological sequence does not exhibit bedding or preservation of ash despite presence of heat affected lithic artifacts which makes it similar to other open air sites in the levant we suggest that rate of burial is the major factor that caused the difference between the upper and lower sequences the differences in the burial rate may be connected to environmental and vegetation changes at the end of mis 6 we also identified an interplay between sediment in wash and density of human activity remains i e during episodes of low natural sediment input the density of artifacts is higher relative to episodes with high rate of sediment in wash the detailed analysis of natural and anthropogenic processes at nesher ramla suggests a much wider spectrum of processes than previously reported for southern levantine paleolithic sites nesher ramla shares certain depositional and post depositional characteristics with both cave and open air sites and provides a better insight into processes which control both types of sites

geochemical variation in microstructural shell layers of the southern quahog mercenaria campechiensis implications for reconstructing seasonality abstract shells of the northern and southern quahogs mercenaria mercenaria and mercenaria campechiensis respectively from paleontological and archaeological deposits have been used to reconstruct climate environmental conditions and ecological relationships seasonal fluctuations in temperature and salinity are recorded in shell carbonate as variations in 18 o and 13 c values and sr ca ratios however these environmental proxies have not yet been calibrated for m campechiensis previous geochemical studies of quahog shells focused on the outer prismatic layer as an ecological archive the outer layer is often not preserved in fossil and archaeological shells moreover recent innovations in microsampling techniques allow high resolution sampling of the middle cross lamellar layer this study tests whether outer prismatic and middle cross lamellar layers record similar variations in 18 o and 13 c values and sr ca ratios in modern shells of m campechiensis and whether profiles are similar among individuals the last 2 years of shell growth from three individuals 6 7 and 9 years old collected alive near bokeelia southwest florida were microsampled for geochemical analyses 18 o varies seasonally relative to translucent summer and opaque winter growth increments variation of 18 o from outer and middle layers are identical within and among shells however the oldest individual did not preserve the most positive values represented in the two younger shells 13 c from both layers are similar within shells although the outer layer is more variable and the range of values varies somewhat among individuals sr ca ratios from the outer and middle layers within shells do not track each other well and profiles among individuals are different to evaluate whether a seasonal signal was present sr ca ratios were compared to 18 o values there was no co variation within the outer layer in any of the shells therefore this layer should be avoided when using sr ca ratios as a temperature proxy the middle layer from the 6 year old shell showed no co variation the 7 year old shell exhibited a moderate negative co variation r 2 0 55 p r 2 0 72 p 18 o and environmental interpretations made using 13 c values should be treated with caution

numerical simulations of bedrock valley evolution by meandering rivers with variable bank material bedrock river valleys are fundamental components of many landscapes and their morphologies from slot canyons with incised meanders to wide valleys with strath terraces may record environmental history several formation mechanisms for particular valley types have been proposed that involve changes in climatic and tectonic forcing but the uniqueness of valley evolution pathways and the long term stability of valley morphology under constant forcing are unknown and are not predicted in existing numerical models for vertically incising rivers because rivers often migrate more rapidly through alluvium than through bedrock we explore the hypothesis that the distribution of bank materials strongly influences river meandering kinematics and can explain the diversity of bedrock river valley morphology simulations using a numerical model of river meandering with vector based bank material tracking indicate that channel lateral erosion rate in sediment and bedrock vertical erosion rate and initial alluvial belt width explain first order differences in bedrock valley type that bedrock bound channels can evolve under steady forcing from alluvial states and that weak bedrock and low vertical incision rates favor wide shallow valleys while resistant bedrock and high vertical incision rates favor narrow deep valleys during vertical incision sustained planation of the valley floor is favored when bedrock boundaries restrict channel migration to a zone of thin sediment fill the inherent unsteadiness of river meandering in space and time is enhanced by evolving spatial contrasts in bank strength between sediment and bedrock and can account for several valley features including strath terraces and underfit valleys commonly ascribed to external drivers

controlling factors in the distribution and development of incised meanders in the central colorado plateau a study of the distribution and geometry of incised meanders in 64 reaches encompassed approximately 600 km of the green colorado and san juan rivers in the central colorado plateau the sinuosity average planform size and average cross sectional symmetry of each reach were determined by map measurements and by spectral analysis of the curvature series for each reach as determined from interpolations of the digitized traces of the channels possible controlling variables examined including average channel gradient drainage area average bedrock erodibility and bedrock structure were compiled for each reach using available maps gradients in the studied reaches are significantly correlated with bedrock type sinuous incised channels are generally found in low gradient reaches in the san juan river the channel is sinuous where it flows against the bedrock dip and generally straight in reaches where flow is downdip this correlation is weak in the green and colorado rivers the average meander size of the sinuous reaches as described by the median curvature value for each reach is generally less in steeper reaches than in low gradient reaches although the relation of bend size to controlling variables is much less clear than for sinuosity or cross section shape most meander cross sections in the area are relatively symmetrical but highly ingrown forms are also present in general symmetric bends are associated with resistant bedrock units whereas ingrown forms develop in massive sandstone and in highly erodible bedrock gradient significantly influences the distribution of ingrown bends with asymmetric meanders concentrated in reaches of low average gradient this correlation is stronger than that between cross section shape and lithology itself incised meanders of the central colorado plateau are probably at least partly inherited from ancestral streams of unknown age that flowed across the area before the present canyons were cut correlation between meander distribution and regional structures suggests that the general location of low gradient sinuous reaches has probably not changed during the incision of the present canyons incised meanders however are clearly able to modify their geometry in response to changes in bedrock resistance as indicated by the strong correlation between bedrock type and cross section symmetry one mechanism of modification is abandonment of bends which is documented by 18 cutoff meanders in the study area

the climatic signature of incised river meanders climate controls landscape evolution but quantitative signatures of climatic drivers have yet to be found in topography on a broad scale here we describe how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the western north pacific spatially averaged river sinuosity generated from digital elevation data peaks in the typhoon dominated subtropics where extreme rainfall and flood events are common and decreases toward the equatorial tropics and mid latitudes where such extremes are rare once climatic trends are removed the primary control on sinuosity is rock weakness our results indicate that the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

environmental controls on the stable isotopic composition of mercenaria mercenaria potential application to paleoenvironmental studies 1 we have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of north america seasonal profiles of 18o and 13c obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity we show that m mercenaria 18o profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell 18o values growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10 c implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations although further measurements of water 18o and a better understanding of seasonal variations of the water 18o salinity relationships are necessary mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium whereas the amplitude of the seasonal profiles of 18o reflects variations in water temperature the annual average 18o decreases with latitude reflecting the trend of rainfall and riverwater 18o with latitude over the northern american continent

the cueva del angel lucena spain an acheulean hunters habitat in the south of the iberian peninsula the cueva del angel archaeological site is an open air sedimentary sequence remnant of a collapsed cave and part of a karst complex the faunal assemblage dominated by equus ferus large bovids and cervids has been subjected to intense anthropic actions reflecting selective predation the fauna may be correlated with european faunistic associations of the end of the middle pleistocene to the beginning of the upper pleistocene the cueva del angel lithic assemblage dominated by non modified flakes and abundant retouched tools with the presence of 46 handaxes appears to fit well within the regional diversity of a well developed non levallois final acheulean industry a preliminary 230th 234u age estimate the review of the lithic assemblage and faunal evidence would favour a chronological positioning of the site in a period stretching from the end of the middle pleistocene to the beginning of the upper pleistocene mis 11 mis 5 the acheulean lithic assemblage found at the cueva del angel fits very well with the hypothesis of a continuation of acheulean cultural traditions in the site distinct from the contemporaneous uniquely mousterian complexes witnessed in other parts of the iberian peninsula and western europe

reconstructing estuarine conditions oyster shells as recorders of environmental change southwest florida abstract live collected shells of the oyster crassostrea virginica contain geochemical records of modern temperature and salinity so records of prehistoric conditions may be obtained from subfossil shells restoration of channelized watersheds in florida is receiving much attention and plans for targeted watersheds require information about estuarine conditions before channelization lack of historical records necessitates alternative methods to understand pre disturbance conditions a 14c calibrated amino acid geochronology based on racemization of glutamic acid yielded ages ranging from 190 1220 ad and from 1270 1860 ad for subfossil oysters from blackwater river near natural watershed and for faka union bay channelized watershed respectively 18o and 13c values of subfossil shells from blackwater river indicate salinity and summer temperatures similar to present winter temperatures recorded in shells from 190 590 720 and 1050 ad appear 1 5 c colder than present winter temperatures whereas the shell from 1220 ad records winter temperatures similar to modern winter temperatures these temperature shifts may indicate change in climate or natural seasonal variation of winter temperature from year to year subfossils from faka union bay may reflect a complicated hydrology which cannot be evaluated by isotopic compositions alone and demonstrates the need for development of independent elemental proxies for temperature and salinity decreases in 13c from subfossil to modern shells may in part result from co2 added to the atmosphere from fossil fuel burning the suess effect subfossil 13c that is 1 more positive than modern shells suggest a change in the dominant carbon sources from terrestrial c4 or aquatic plants to c3 plants mangroves

rainfall and hydrological controls on speleothem geochemistry during climatic events droughts and typhoons an example from seopdong cave republic of korea abstract a five year old 20 cm long soda straw sd 1 was analyzed geochemically to delineate the relationship between the geochemical record and climatic behavior the growing tip of the soda straw was marked on july 18 1999 and the sample was collected on july 16 2004 thus the growth period of this speleothem is well constrained during the five years the soda straw grew about 20 cm a mean growth rate of about 4 cm year fast growth rate of this speleothem enabled not only to understand seasonal variations of geochemical data but also to compare these data directly with outside climatic variations near the cave 210 pb ex excess or unsupported 210 pb results suggest that the overall pattern of 210 pb ex changes as well as the frequency and relative intensity of their peaks show a strikingly similar pattern to that of the amounts of precipitation in the study area this suggests that 210 pb ex was transported into the cave with infiltrating rainwater mostly during rainy summers because 210 pb ex is a particle reactive element controlling detailed growth rates by the 210 pb ex fluctuations it can be noticed that 18 o compositions vary very little in spite of significant droughts and typhoon events whereas 13 c values clearly display impacts of a severe drought from 2000 to 2001 the sr ca ba ca u ca and mn ca ratios coincide with the 13 c trends and show anomalies during the drought period these coeval trends strongly indicate that hydraulic factors in vadose zone that were directly controlled by the amount of rainfall influenced on the geochemical imprints of the sd 1 this study illustrates the behavior of an atmospheric radionuclide 210 pb ex the o and c stable isotopes and trace elements in calcite speleothems and furthermore implies that they can be used to detect short term climatic behavior including climatic extreme events as well as the long term climatic fluctuations in the past

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

paleolithic caves and hillslope processes in south western samaria israel environmental and archaeological implications abstract south western samaria is emerging as a major province of paleolithic cave sites most recently discovered caves have been naturally filled with terra rossa type colluvial deposits when the hillslopes above the caves were stripped from vegetation during late quaternary times site formation processes differ significantly between caves with pit like openings such as qesem emanuel and rantis caves vs those with cliff side entrances such as shukbah tinshemet and deir kaddis caves the former favored accumulation of colluvial debris while the latter were relatively protected from these deposits caves discovered in the 20th century were mainly of the latter cliff face type while in the 21st century new discoveries commonly occur where construction works intersect previously unnoticed filled caves

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

the roles of flood magnitude and duration in controlling channel width and complexity on the green river in canyonlands utah usa abstract predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response however because these relations assume equilibrium sediment transport their applicability to cases where streamflow and sediment transport are decoupled may be limited these general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity which is often of ecological interest we integrate historical records of channel change observations of scour and fill during a snowmelt flood measurements of sediment transport and predictions from a two dimensional streamflow model to describe how annual peak flow magnitude and peak flow duration interact with the upstream sediment supply to control channel form for a 15 km study reach on the regulated green river in canyonlands national park utah two major decadal scale episodes of channel narrowing have occurred within the study area for each of these episodes the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude however channel narrowing occurred during periods of exceptionally low annual floods the most recent episode of channel narrowing occurred between 1988 and 2009 during low flow cycles when the 5 yr mean peak flow was less than 60 of the long term 1959 2016 mean peak flow these findings together with findings from previous studies demonstrate that decreases in peak flow magnitude caused by streamflow regulation climate change or a combination of those factors have driven episodes of channel narrowing on the green river observations of streamflow sediment transport and morphologic change coupled with predictions from a two dimensional streamflow model indicate that peak flow magnitudes of at least 75 of the long term mean peak flow are required to transport bed material sand in suspension in all regions of the multi thread channel and that the 2 month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance these results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration

streamflow regulation and multi level flood plain formation channel narrowing on the aggrading green river in the eastern uinta mountains colorado and utah abstract the style and degree of channel narrowing in aggrading reaches downstream from large dams is dependent upon the dominant geomorphic processes of the affected river the magnitude of streamflow regulation and the post dam sediment transport regime we measured different magnitudes of channel adjustment on the green river downstream from flaming gorge dam ut usa that are related to these three factors bankfull channel width decreased by an average of about 20 in the study area in reaches with abundant debris fans and eddy deposited sand bars the amount of channel narrowing was proportional to the decrease in specific stream power the fan eddy dominated reach with the greatest decrease in stream power narrowed by 22 while the reach with the least decrease in stream power narrowed by 11 in reaches with the same magnitude of peak flow reduction meandering reaches narrowed by 15 to 22 and fan eddy dominated reaches narrowed by 11 to 12 specific stream power was not significantly affected by flow regulation in the meandering reaches in the diverse array of reach characteristics and deposit types found in the study area all pre and post dam deposits are part of a suite of topographic surfaces that includes a terrace that was inundated by rare pre dam floods an intermediate bench that was inundated by rare post dam floods and a post dam floodplain that was inundated by the post dam mean annual flood analysis of historical photographs and tree ring dating of tamarix sp shows that the intermediate bench and post dam floodplain are post dam landforms in each reach type although these two surfaces occur at different levels they are forming simultaneously during flows of different magnitude and while the relative elevation and sedimentologic characteristics of the deposits differ between meandering reaches and reaches with abundant debris fans and eddies both reach types contain deposits at all of these topographic levels the process of channel narrowing varied between fan eddy dominated and meandering reaches in the meandering reaches where stream power has not changed narrowing was accomplished by essentially the same depositional processes that operated prior to regulation in fan eddy dominated reaches where significant reductions in stream power have occurred channel narrowing has been accompanied by a change in dominant depositional processes mid channel sand deposits are aggrading on deposits that in the pre dam era were active gravel bars these deposits are creating new islands and decreasing the presence of open framework gravel bars in eddies bare sand bars are replaced with vegetated bars that have a simpler topography than the pre dam deposits

shell gathering from mangroves and the seasonality of the southeast asian monsoon using high resolution stable isotopic analysis of the tropical estuarine bivalve geloina erosa from the great cave of niah sarawak methods and reconnaissance of molluscs of early holocene and modern times this paper describes a reconnaissance high resolution study of stable isotopes 18o and 13c from modern shells of the estuarine bivalve geloina erosa and those dated to the early holocene that were harvested by people from mangroves near the great cave of niah on the north coast of borneo this reconnaissance study provides high resolution palaeoclimatic palaeohydrological information concerning early human activity in the region and the past character of the southeast asian monsoon laser ablation continuous flow isotope ratio mass spectrometry la cf irms on modern shells of geloina erosa revealed saw tooth stable isotopic profiles that bear a close resemblance to peaks and troughs of trends in recent local rainfall including the 1998 el nino drought highlighting the potential of geloina erosa for reconstructing seasonality of the southeast asian palaeomonsoon la cf irms analysis of prehistoric shells of geloina erosa held in the harrisson archives of the sarawak museum revealed cyclical shifts in 18o with similar amplitudes of variation as found in modern shells of geloina erosa as at the present day this probably reflects the changing seasonality of the monsoon rains with shifts to negative 18o values during periods of high runoff lighter mean 18o values of the prehistoric shells however may indicate a greater annual surplus of rainfall and possibly consistent with the early holocene strengthening of the summer monsoon at that time the similarity of the last growth increment 18o of the prehistoric shells to their mean 18o profile values suggests that gathering took place during times of moderate runoff

middle paleolithic sidescrapers were resharped or recycled a view from nesher ramla israel abstract the resharpening of sidescrapers is a widely discussed issue in recent middle paleolithic studies however in the levantine record the evidence for sidescraper resharpening is meager the middle paleolithic site of nesher ramla israel represents a rare case in which sidescrapers were frequently modified by removal of longitudinal spalls from their edges both parent sidescrapers and spalls long sharpening flakes lsf are abundant throughout the site s stratigraphy providing a rare opportunity for a complementary study of both artifact groups the aim of the present study is to reconstruct the life history of sidescrapers retrieved from nesher ramla we ask how the lsf removal changed the morphology of the sidescraper edge at which stage of the sidescraper life history it occurred what was the purpose of lsf removal and was it a part of a recycling system aimed at producing a new edge tool type or the maintenance of the existing tool edge the studied artifacts 100 parent sidescrapers and 60 complete lsf were sampled randomly from the most intensively occupied and richest layers of the site our results suggest that sidescraper edge modification was a well mastered and skillful process that resulted in standardized and morphologically distinct products in most cases the sidescrapers were not further retouched after the lsf removal this leads us to propose that the major goal was to transform the sidescraper into a tool with a sharp straight and flat edge the lsf removal at nesher ramla provides an exceptional case in which a simple raw edge was deliberately manufactured at the expense of the previously retouched edge this reinforces the previous assumptions that simple raw edges were often preferred over retouched ones

mid latitude interhemispheric hydrologic seesaw over the past 550 000 years an interhemispheric hydrologic seesaw in which latitudinal migrations of the intertropical convergence zone itcz produce simultaneous wetting increased precipitation in one hemisphere and drying in the other has been discovered in some tropical and subtropical regions for instance chinese and brazilian subtropical speleothem cave formations such as stalactites and stalagmites records show opposite trends in time series of oxygen isotopes a proxy for precipitation variability at millennial to orbital timescales suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics this tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing the impacts of such an interhemispheric hydrologic seesaw on higher latitude regions and the global climate system however are unknown here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid latitude western pacific ocean our results are based on a new 550 000 year record of the growth frequency of speleothems from the korean peninsula which we compare to southern hemisphere equivalents the korean data are discontinuous and derived from 24 separate speleothems but still allow the identification of periods of peak speleothem growth and thus precipitation the clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550 000 years extended at least to the mid latitudes such as northeast asia and that orbital timescale itcz shifts can have serious effects on temperate climate systems furthermore our result implies that insolation driven itcz dynamics may provoke water vapour and vegetation feedbacks in northern mid latitude regions and could have regulated global climate conditions throughout the late quaternary ice age cycles

a new regional mid holocene palaeoprecipitation signal of the asian summer monsoon the dongge cave speleothem 18o record which lies in the pearl river basin china has been interpreted as recording a regional decline in asian summer monsoon precipitation over the last 6 5 ka the same overall trend is seen in the bulk sedimentary organic 13corg record from a core in the pearl river estuary however the two records differ in detail and the regional nature of the dongge palaeoprecipitation signal has therefore been questioned our study re evaluates both records by constructing for the same estuarine core biomarker and compound specific 13c records which have better constrained terrestrial and marine end members than 13corg providing additional insights into the evolution of the asian summer monsoon the branched isoprenoidal tetraether bit index reflects the ratio of soil versus marine organic matter the bit record from the estuarine core co varies with the dongge cave 18o record suggesting the two share a common control which is likely to be driven by regional climate by contrast the sterols n alcohols and n fatty acid ratios show the same overall trend as dongge but parallel the 13corg record s variability between 6 5 and 2 ka indicating a partial decoupling between soil and land plant organic matter fluxes in the pearl river basin there is clear divergence between the biomarker and 13corg records from 2 ka to present analysis of the leaf wax 13c suggests that this results from an abrupt change in vegetation probably resulting from local anthropogenic cultivation two thousand years ago the basin scale of these estuarine records equates to up to 15 grid cells in typical earth system models used for simulating global climate this permits comparison of palaeoclimate model intercomparison project simulations of the mid holocene with spatially equivalent data relating to the summer asian monsoon for the first time

a 2000 yr record of sacramento san joaquin river inflow to san francisco bay estuary california oxygen and carbon isotopic measurements of fossil bivalves macoma naarfa contained in estuarine sediment are used to reconstruct a late llolocene record of sitlinity and stream flow in san francisco bay discharge into the bay is a particularly good indicator of paleoclin ate in california because the bay s influent streams drain 40 of the state the isotopic record suggests that hetween al oul 1670 ant1 1900 calcnd r yc trs yr cal 1i i inflow to the bay was sul stantially greirler tlian the cstinli tecl precliversion inllow ol 1100 m3 s an unconforn ity representing a 900 yr hiatus is present in the core between 1670 ancl 750 yr cirl ii 13 possil ly r lusc cl by i n tjor 11ydrologic rl event over the p ist 750 yr strcitn ilow to s iii i ril cisco ikty ii is vitrirtl wit11 i pcriotl ol 200 yr i1lter11itte wet iltttl tlry i tlrougl t intc r rls typiritlly 11 rvc i lstecl 40 to 100 yr

measuring bluff erosion part 2 pairing aerial photographs and terrestrial laser scanning to create a watershed scale sediment budget effectively managing and reducing high suspended sediment loads in rivers requires an understanding of the magnitude of major sediment sources as well as erosion and transport processes that deliver excess fine sediments to the channel network the focus of this research is to determine the magnitude of erosion from tall bluffs a primary sediment source in the 2880 km2 le sueur watershed minnesota usa we coupled analyses of seven decades of aerial photographs with four years of repeat terrestrial laser scanning tls to determine erosion rates on bluffs together these datasets provide decadal scale retreat rates throughout the entire watershed and high resolution geomorphic change detection on a subset of bluffs to both constrain erosion rates and document how environmental conditions affect bluff retreat erosion rates from aerial photographs and tls were extrapolated from 243 and 15 measured bluffs respectively to all 480 bluffs in the le sueur watershed using multiple techniques to obtain estimates of sediment loading from these features at the watershed scale despite different spatial and temporal measurement scales the aerial photograph and tls estimates yielded similar results for bluff retreat rate and total mass of sediment derived from bluffs with bluffs in the le sueur watershed yielding 135 000 39 000 mg yr of fine sediment comparing this value to the average annual total suspended solids tss load determined from gauging from 2000 to 2010 we determined that bluffs comprise 57 16 of the total tss load making bluffs the single most abundant fine sediment source in the basin copyright 2012 john wiley sons ltd

handaxe manufacture and re sharpening throughout the lower paleolithic sequence of tabun cave abstract in this paper we assess the evidence for on site manufacture and re sharpening of handaxes in the lower paleolithic layers of tabun cave by examining the ratio of thinning flakes the typical waste of bifacial manufacture to handaxes our study of twenty nine assemblages ranging from the acheulean to the acheulo yabrudian complex combining results from jelinek s and ronen s excavations shows that thinning flakes are scarce throughout the entire sequence results indicate that handaxes were commonly not manufactured or re sharpened in the excavated area and that these activities were most likely conducted outside the site the late lower paleolithic in various parts of eurasia and africa is characterized by high variability in lithic technology which in the case of the levant is best reflected in the acheulo yabrudian complex this study aids our understanding of variability in the levantine late lower paleolithic by adding the concept of segmentation of reduction as an integral part of late lower paleolithic lithic technology significantly in tabun cave the segmentation of reduction that characterizes handaxe manufacture differs from the patterns observed in amudian blade production and yabrudian scraper manufacture which were both regularly conducted on site the extent of variability and flexibility is thus reflected not only in the technologies employed but also in how different reduction sequences were segmented and executed across the landscape suggesting a link between technical knowledge mobility patterns and landscape exploitation

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

the use of the lateral tranchet blow technique at nesher ramla israel a new cultural marker in the levantine middle paleolithic abstract the open air middle paleolithic site at nesher ramla israel dated to the end of marine isotope stage 6 and marine isotope stage 5 is characterized by extensive use of the lateral tranchet blow technique this technique consists of the removal of an elongated thin spall along the retouched edge of the blank in nesher ramla this technique is used for producing a specific tool kit component unifacially retouched tools with a lateral tranchet blow ltb the tools with ltb were systematically produced throughout the 8 m thick middle paleolithic sequence of nesher ramla representing the major typological category in some of the layers together with tools with ltb the assemblages contain large numbers of ltb spalls here we present a detailed techno morphological analysis of the tools and spalls from nesher ramla unit iii one of the richest archaeological layers of the site our results suggest that the goal of the ltb technique at nesher ramla was to manufacture a tool with an edge that is partially retouched and partially sharp i e shaped by ltb the ltb technique employs a long knapping routine including a series of compulsory and optional steps implying non opportunistic behavior although on site use of the ltb technique is attested the fact that these tools were also often introduced to the site as finished objects further emphasizes their importance and suggests that most of them were not produced on site in response to an immediate need for sharp edges this tool type represents a new previously unreported component in the levantine middle paleolithic toolkit a comparison with other archaeological units along the 8 m thick stratigraphy of nesher ramla suggests that the ltb technique was one of the major techniques for manufacturing tools at that site and that the tools with ltb represent a cultural marker for nesher ramla hominins and possibly a new cultural marker in the levantine middle paleolithic according to a comparison of tools shaped by ltb from other geographic and temporal contexts most notably the central european keilmesser the nesher ramla tools with ltb were likely designed and used by right handed hominins in a longitudinal cutting motion

annual growth banding in a cave stalagmite the presence of microscopic luminescence banding in cave calcite deposits speleothems has recently been reported1 3 the luminescence seems to be caused by excitation of humic and fulvic acids derived from the overlying soil and subsequently incorporated into the calcite3 4 we have tested whether such luminescence corresponds to annual growth layers using high precision thermal ionization mass spectrometric 238u 234u 230 th ages from banded sections of a holocene stalagmite we report here that the timespans yielded by counting bands on the assumption that they are annual agree within error limits with those obtained by our uranium thorium dating this demonstration that the banding is annual should make banded speleothems valuable resources for providing high resolution records of past climate in which precipitation can be estimated from growth rates5 6 and temperatures from stable isotope measurements7 and solar terrestrial correlations as the luminescence intensity can be related to the solar sunspot cycle1 3

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

a late pleistocene to holocene record of precipitation reflected in margaritifera falcata shell δ18o from three archaeological sites in the lower salmon river canyon idaho oxygen 18 18o concentrations in margaritifera falcata shells preserved in three archaeological sites in the lower salmon river canyon of idaho are compared with modern mussel shells shell 18o records show that late pleistocene and early holocene climates were drier with occasional periods of increased precipitation after c 4000 years bp precipitation is higher in the salmon river basin than at present and trends toward modern conditions after c 1800 years bp the climatic conditions reflected by fluctuations in shell 18o are matched by regional palaeoenvironmental records including pollen glacial and palaeohydraulic proxy sources and are compared with major changes in plateau prehistoric cultural patterns studies of late quaternary records of freshwater bivalve shell 18o are useful for reconstructing climatic conditions and complement geoarchaeological studies in riparian contexts

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

the rate and pattern of bed incision and bank adjustment on the colorado river in glen canyon downstream from glen canyon dam 1956 2000 closure of glen canyon dam in 1963 transformed the colorado river by reducing the magnitude and duration of spring floods increasing the magnitude of base flows and trapping fine sediment delivered from the upper watershed these changes caused the channel downstream in glen canyon to incise armor and narrow this study synthesizes over 45 yr of channel change measurements and demonstrates that the rate and style of channel adjustment are directly related to both natural processes associated with sediment deficit and human decisions about dam operations although bed lowering in lower glen canyon began when the first cofferdam was installed in 1959 most incision occurred in 1965 in conjunction with 14 pulsed high flows that scoured an average of 2 6 m of sediment from the center of the channel the average grain size of bed material has increased from 0 25 mm in 1956 to over 20 mm in 1999 the magnitude of incision at riffles decreases with distance downstream from the dam while the magnitude of sediment evacuation from pools is spatially variable and extends farther downstream analysis of bed material mobility indicates that the increase in bed material grain size and reduction in reach average gradient are consistent with the transformation of an adjustable bed alluvial river to a channel with a stable bed that is rarely mobilized decreased magnitude of peak discharges in the post dam regime coupled with channel incision and the associated downward shifts of stage discharge relations have caused sandbar and terrace erosion and the transformation of previously active sand bars and gravel bars to abandoned deposits that are no longer inundated erosion has been concentrated in a few pre dam terraces that eroded rapidly for brief periods and have since stabilized the abundance of abandoned deposits decreases downstream in conjunction with decreasing magnitude of shift in the stage discharge relations in the downstream part of the study area where riffles controlling channel elevation have not incised channel narrowing has resulted from decreased magnitude of peak discharges and minor post dam deposition these physical changes to the aquatic and riparian systems have supported the establishment and success of an artifact ecosystem dominated by non native species models for the channel response downstream from large dams typically consider factors such as the degree of sediment deficit the pre dam surface and subsurface grain size and the magnitude of post dam average flows these results suggest that it is also necessary to consider 1 the possibility of variable responses among different channel elements and 2 the potential importance of exceptional flows resulting from management decisions

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

multi channel patterns of bedrock rivers an example from the central narmada basin india abstract an anomalous multiple channel pattern in bedrock is observed on a predominantly downcutting reach of the narmada river the multi channel reach 800 2750 m in width and 8500 m in length is bounded by major faults and is underlain by granite and gneiss bedrock geomorphological investigations reveal differences among the upstream middle and downstream sub reaches of the multi channel study area whereas the upstream sub reach is dominated by deep flows and fine sediments the lower sub reach is characterized by a steep gradient and rapids the middle sub reach is the widest and is marked by thickly forested islands and boulder berms the characteristics of the three different sub reaches suggest control by the interactions of lithology flood processes and tectonics estimations of hack s 1973 stream gradient index values indicate considerable variations for the sl values along the length of narmada river the highest value of gradient index sl 797 is associated with the multi channel reach implying lithologic or tectonic control given the dimensions of the reach and its channels it appears that the present hydrological regime is inadequate to produce the feature we hypothesize that the multi channel pattern development in bedrock was initiated by block or domal uplift enhanced gradients and extreme floods permitted the system to exploit linear weaknesses in the bedrock leading to the development of anabranches and establishment of multiple channels in bedrock abrupt changes in the channel planform and morphology at the study site indicate that the river is adjusting its channel geometry width depth gradient and plan configuration to a new equilibrium channel morphology through the action of the extreme floods characteristic of this fluvial environment

a vector based method for bank material tracking in coupled models of meandering and landscape evolution sinuous channels commonly migrate laterally and interact with banks of different strengths an interplay that links geomorphology and life and shapes diverse landscapes from the seafloor to planetary surfaces to investigate feedbacks between meandering rivers and landscapes over geomorphic timescales numerical models typically represent bank properties using grids however this approach produces results inherently dependent on grid resolution herein we assess existing techniques for tracking landscape and bank strength evolution in numerical models of meandering channels and show that grid based models implicitly include unintended thresholds for bank migration that can control simulated landscape evolution building on stratigraphic modeling techniques we develop a vector based method for land surface and subsurface material tracking that overcomes the resolution dependence inherent in grid based techniques by allowing high fidelity representation of bank material properties for curvilinear banks and low channel lateral migration rates we illustrate four specific applications of the new technique 1 the effect of resistant mud rich deposits in abandoned meander cutoff loops on meander belt evolution 2 the stratigraphic architecture of aggrading alluvial meandering channels that interact with cohesive bank and floodplain material 3 the evolution of an incising meandering river with mixed bedrock and alluvial banks within a confined bedrock valley and 4 the effect of a bank height dependent lateral erosion rate for a meandering river in an aggrading floodplain in all cases the vector based approach overcomes numerical artifacts with the grid based model because of its geometric flexibility the vector based material tracking approach provides new opportunities for exploring the coevolution of meandering rivers and surrounding landscapes over geologic timescales

annually resolved δ13cshell chronologies of long lived bivalve mollusks arctica islandica reveal oceanic carbon dynamics in the temperate north atlantic during recent centuries abstract the ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change however relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long term high resolution dissolved inorganic carbon isotope 13 c dic data especially for the temperate north atlantic which is the major oceanic sink for anthropogenic co 2 here we report shell carbon isotope values 13 c shell a potential proxy for 13 c dic of old grown specimens of the long lived bivalve mollusk arctica islandica this paper presents the first absolutely dated annually resolved 13 c shell record from surface waters of the north atlantic iceland gulf of maine covering the time interval between 1753 and 2003 according to our results the 13 c shell data were unaffected by trends related to ontogenetic age however the shell carbonate was precipitated with a constant offset from expected equilibrium by 1 54 to 2 7 0 2 corresponding to a 6 2 to 10 8 0 8 contribution of respiratory co 2 25 the offset did not appear to vary through the lifetime of individual specimens and among specimens therefore the 13 c shell data of this species can very likely be used as a measure of 13 c dic furthermore shell stable carbon isotope chronologies exhibited habitat specific differences and a significant inter annual and decadal variability related to the natural carbon cycle in addition a distinct negative 13 c shell shift was found reflecting the oceanic suess effect i e the admixture of anthropogenic co 2 however this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic polar front in the nordic seas and a large scale reorganization of atmospheric and oceanic currents in the north atlantic this likely resulted in a reduced admixture of cold polar water onto the north icelandic shelf through the east iceland current and the gulf of maine through the labrador current with an increased volume of warmer isotopically well equilibrated atlantic waters our shell based 13 c dic proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the north atlantic

epeirogenic controls on canadian river incision and landscape evolution great plains of northeastern new mexico abstract the canadian river has carved a deep bedrock canyon into the great plains of northeastern new mexico in response to a complex interaction of post laramide epeirogenic rock uplift processes along the jemez lineament and downstream baselevel fall caused by late tertiary and quaternary evaporite dissolution broad slow bulging along the jemez lineament a lithospheric scale structure with prolific late cenozoic volcanism along its trend helps drive incision in the canyon canadian river canyon fluvial terraces mapped and correlated according to soils elevation and rock type criteria reveal longitudinal profiles that appear broadly warped across the jemez lineament and converge to the modern channel profile both upstream and downstream of the canyon similarly the modern channel long profile is distinctly and broadly convex through its great plains reach a unique feature among major rivers draining the eastern flank of the southern rocky mountain front radiocarbon dated charcoal from terrac

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

geomorphic and sedimentary responses of the bull creek valley southern high plains usa to pleistocene and holocene environmental change abstract fluvial geomorphology and stratigraphy often reflect past environmental and climate conditions this study examines the response of bull creek a small ephemeral creek in the oklahoma panhandle to environmental conditions through the late pleistocene and holocene fluvial terraces were mapped and their stratigraphy and sedimentology documented throughout the course of the main valley based on their elevations terraces were broadly grouped into a late pleistocene fill terrace t3 and two holocene fill cut terrace sets t2 and t1 terrace systems are marked by similar stratigraphies recording the general environmental conditions of the time sedimentary sequences preserved in terrace fills record the transition from a perennial fluvial system during the late glacial period and the younger dryas to a semiarid environment dominated by loess accumulation and punctuated by flood events during the middle to late holocene the highest rates of aeolian accumulation within the valley occurred during the early to middle holocene our data provide significant new information regarding the late pleistocene and holocene environmental history for this region located between the well studied southern and central high plains of north america

high resolution geochemical investigation of the bivalve shells glycymeris sp from shell mounds in jeju island korea late holocene paleoclimatic implications related to east asian monsoon climate abstract recent and shell mound bivalves glycymeris sp were collected from two sites sangmori and udo jeju island to investigate paleoceanographic conditions using high resolution stable isotope and trace element data the radiocarbon ages are about 3210 50 and 4210 60 bp for the sangmori and udo shell mounds respectively both oxygen and carbon isotopic compositions of the shell mound bivalve shells show clear seasonal cycles with depleted values during summer and the coeval trend which indicates that they were controlled by freshwater input similar ranges of both isotopes indicate that shallow seawater conditions near the sangmori and udo shell mounds are more or less similar however more negative oxygen and carbon isotope values of the shell mound bivalves than the recent counterpart suggest that surface seawater salinity near jeju island was lower due to the increase in changjiang river discharge mg contents of the recent bivalve reflect surface seawater temperature changes whereas sr and ba contents were controlled by nutrient concentrations directly influenced by changjiang river discharge geochemical data of the recent and shell mound bivalves may imply higher precipitation more intense east asian summer monsoon activity at 3 2 and 4 2 ka under the influence of the terminal stage of holocene climatic optimum in south china or may reflect smaller fluctuating peaks during its decline

landscape evolution valley excavation and terrace development following abrupt postglacial base level fall many high latitude fluvial systems are adjusting to base level changes since the last glaciation channels that experienced base level fall may still be incising often through glacial diamictons tills these tills can be quite competent behaving more like weak bedrock than unconsolidated sediment and erode at a fast pace thus providing a unique opportunity to test models of channel incision and knickpoint migration in transient systems here we integrate light detection and ranging lidar topography strath terrace chronology and numerical modeling to determine knickpoint migration and incision history of the le sueur river in central minnesota usa results indicate that the le sueur river is best modeled as a detachment limited channel with downstream coarsening related to lag clasts from tills playing a critical factor in longitudinal profile development the le sueur river meanders as it incises so we coupled the best fit incision model to a meander model to determine valley excavation history the excavation history was used to determine a natural background erosion rate prior to land use changes associated with settlement and agricultural expansion in the mid 1800s we compared background fine sediment silt and clay erosion rates with historic decadal average annual suspended loads results show that modern fine sediment contributions from sources associated with valley excavation are three times higher than modeled presettlement loads recent changes in hydrology associated with land use and climate change have increased flows in rivers leading to higher sediment loads not just from field erosion but from increased bank and bluff erosion in the deeply incised valleys

a holocene climatic record from arid northwestern china abstract the history of climatic changes during the interval 8500 3000 cal yr b p has been reconstructed from stratigraphical and chronological studies and the results of total organic carbon toc total inorganic carbon tic element composition pollen and stable isotope analyses of a section along the hongshui river in the southern tengger desert nw china the record suggests that from 8450 bottom of the studied section to 7500 yr b p the climate was characterized by instability from 7500 to 5070 yr b p the climatic conditions improved and can be divided into two parts a warm humid spell between 7290 and 6380 yr b p during which the average temperature was 3 4 c higher than that of today and a warm dry spell lasting from 5950 to 5720 yr b p the climate deteriorated between 6380 and 5950 yr b p from 5720 to 5070 yr b p the temperature decreased but humidity increased an abrupt temperature drop occurred between 5340 and 5290 yr b p that indicated the decline of the warmer and humid mid holocene climate from 5070 yr b p onward the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070 4670 yr b p 4300 3740 yr b p and 3410 3230 yr b p top of the section respectively the climatic fluctuations recorded in the southern tengger desert appear in phase with climatic changes recognized in the tibetan plateau suggesting that the period between 7290 and 6380 yr b p was the most warm humid spell one extremely dry event occurred at ca 3000 yr b p and subsequently the fluvial lacustrine depositional process terminated and wind action prevailed in the area both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation which are closely connected with global changes

geoarchaeology in action a sedimentological analysis of anthropogenic shell mounds from the cape york region of australia abstract large mounded deposits of shell are prominent archaeological features across much of the north australian tropical coast many of the shell mounds are composed almost entirely of the bivalve anadara granosa linnaeus 1758 a food source for aboriginal people in the past a relatively long history of inquiry into the nature and significance of the shell mounds has focussed primarily on analysing the shell component as clues to australian aboriginal coastal economies in the past this paper presents results of new analyses on the non shell sediments examining the physical and chemical signatures of depositional and post depositional processes within shell mounds near weipa in far north queensland australia with a view to obtaining insights into how they formed and for what purposes and how their morphology structure and content may have changed since they ceased accumulating we also consider how such changes might relate to past and present environmental conditions physical and chemical analyses indicate that the primary purpose of mound building was most likely to discard the large volumes of shell resulting from a granosa harvesting and consumption post depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under the seasonal high rainfall conditions as such the mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of or an opening to the past

formation processes and combustion features at the lower layers of the middle palaeolithic open air site of nesher ramla israel the lower stratigraphic sequence units iii vi of the middle palaeolithic site of nesher ramla was studied using geoarchaeological methods field observations indicate that the site formed within a karst depression that was infilled by colluvium and in which intermittent human activity occurred including two layers highly rich in anthropogenic remains units iii and v infrared analysis of bones determined that black bones are carbonized and that certain white bones are calcined quantitative analysis of wood ash pseudomorphs indicates specific areas of high concentrations of ash micromorphological analysis enabled identification of two distinct features associated with ash and burnt bones one is a thinly bedded complex of blacked soil overlain by ash and charcoal and the second is a 20 cm thick massive fine grained layer of mixed ash the first feature is interpreted as an in situ hearth macroscopically similar features have not yet been analyzed the second feature is interpreted as ash in secondary position i e an ash pile midden that formed following hearth rake out activities these findings are unique considering that most middle palaeolithic open air sites in the levant are single layered and that in most evidence for hominin use of fire is scarce or absent we discuss the factors that may affect the preservation of ash in open air sites and conclude that the setting of nesher ramla in a topographic low provided relative protection from wind which prevented ash deflation and at the same time hominin activity remains were buried relatively fast which detached the ashes and combustion features from direct rainfall and from decalcifying root activity

the indian ocean 13c suess effect the 13c of dissolved inorganic carbon dic decrease the 13c suess effect in the indian ocean was calculated using a multiparameter linear regression comparison of the 1978 geochemical ocean sections study and 1995 world ocean circulation experiment 13c of dic hydrographic and nutrient data the surface ocean 13c decrease rate along 80 and 115 e ranged from approximately 0 1 decade 1 at 55 s to a maximum of approximately 0 18 decade 1 at 35 s and decreased northward to around 0 13 decade 1 at the equator using a global extrapolation based on ocean model results bacastow et al 1996 and previous 13c changes calculated from 1970 to 1993 station reoccupations in the pacific ocean and based on preformed 13c versus chlorofluorocarbon age trends in the indian pacific and atlantic oceans sonnerup et al 1999 an ocean wide average surface ocean 13c rate of change of 0 15 to 0 17 decade 1 was estimated the average depth integrated 13c change rate between 1978 and 1995 along 80 and 115 e was 6 9 0 5 m yr 1 from 58 s to 5 n

a lithologic control on active meandering in bedrock channels topographic evidence requires that some rivers actively meander in bedrock yet the way in which rivers can erode laterally and meander within bedrock banks is not well understood lateral channel migration and especially lateral channel migration via active bedrock meandering is commonly responsible for the preservation of unpaired strath terraces a process level understanding of lateral channel migration and active meandering in bedrock rivers is key to interpreting the climatic and tectonic significance of unpaired strath terraces and the planform shape of bedrock rivers in this study we compare erosional processes in two adjacent bedrock channels in the santa cruz mountains california the main differences between these channels are that pescadero creek actively meanders within mudstone while butano creek is straight and incises sandstone laboratory rock strength and slake durability tests show that while the two lithologies have similar tensile strengths before drying the meander supporting mudstone loses strength dramatically when dried and rewet slakes while the sandstone does not the slaked mudstone bank rock was easily detached without the need for bed load tools during in situ erosion tests while mudstone that had not dried and sandstone were not detachable the depth of bank rock detached solely from rewetting of previously dried mudstone ranges between 1 and 8 mm which is well in excess of annual background erosion in the santa cruz mountains in addition hand samples of the mudstone rapidly disintegrated upon wetting and drying in the laboratory whereas sandstone hand samples remained intact in the meandering stream there is a consistent pattern of scoured bedrock exposed to drying and slaking along the outside cutbank of meander bends and forced bars that grade into soil and vegetation which protect the bedrock from slaking along the inside of bends additionally in the meandering stream subaerially exposed mudstone clasts are often found to be disintegrating on the surface of bars taken together these observations suggest that slaking allows for bedrock meandering in two fundamental ways first by rapidly disintegrating coarse hillslope derived sediment that is deposited in the channel slaking suppresses the negative feedback on lateral channel migration that would otherwise result from the buildup of talus along a retreating bedrock valley wall on the outside of a meander bend second at cutbanks where scour exposes bare bedrock to drying slaking weakens a layer of bank rock to the point where it can be eroded by clear water flows in these ways slaking enables erosion into bedrock banks in response to curvature driven fluid shear stress perturbations as in alluvial rivers

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

palaeosol development in the chinese loess plateau as an indicator of the strength of the east asian summer monsoon evidence for a mid holocene maximum the interpretation of the stalagmite delta o 18 record from southern china as an indicator of east asian summer monsoon easm rainfall amount or intensity is strongly debated soil development in the chinese loess plateau clp situated in the modern summer monsoon domain has long been treated as a direct and reliable easm proxy in this study we compiled 81 loess and 229 palaeosol dates from 77 profiles across the clp and synthesized the data statistically in order to investigate the easm history during the holocene the resulting history of holocene loess deposition and palaeosol development demonstrates that 1 loess deposition decreased and palaeosol formation increased across the clp after 11 5 ka 1 ka 1000 cal yr bp revealing a gradually intensified easm during the early holocene 2 numerous palaeosols developed in the clp between 8 8 ka and 3 4 ka indicating a generally strong easm during the mid holocene 3 the number of palaeosol dates decreased rapidly at around 3 ka suggesting a sudden retreat of the easm in the late holocene these trends of easm evolution are broadly consistent with variations in aeolian sand activity in the four main sandlands the mu us otindag horqin and hulun buir sandlands along the modern monsoon fringe in northern china and are supported by a wide range of independent evidence in addition we also found that high loess deposition and stronger aeolian activity occurred at similar to 5 ka representing a weak easm event within the context of an overall strong mid holocene easm the strong mid holocene easm revealed by palaeosol development in the clp and aeolian sand activity in the sandlands in northern china contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china our results are compatible with the proposal that the stalagmite delta o 18 variations in china do not result from changes in easm rainfall amount or intensity but instead reflect changes in moisture source driven by variations in atmospheric oceanic circulation c 2014 elsevier ltd and inqua all rights reserved

elemental and isotopic proxies of paleotemperature and paleosalinity climate reconstruction of the marginal northeast pacific ca 80 ka isotope 18 o and minor element mg ca sr ca analyses of a fossil shell of the marine mussel mytilus trossulus gould from the whisky run terrace at coquille point bandon oregon enable reconstruction of a paleoclimatic profile for the temperate northeastern pacific ca 80 85 ka the whisky run terrace is correlative with marine oxygen isotope 18 o substage 5a the final sea level highstand of the last interglacial complex herein we provide sea surface temperature estimates and report on a new technique that allows estimates to be made of 18 o of seawater and riverine discharge from the skeletal chemistry of a single mussel shell estimates of mean annual temperature from mg ca ratios are lower than those suggested by the accompanying fossil fauna and significantly lower than present day conditions the data also suggest a decrease in the range of seasonal temperature extremes at 80 ka compared to today estimates of the fresh water and seawater 18 o end members 4 5 and 0 5 respectively are slightly greater than modern values