hydrodynamics of the caribbean low level jet and its relationship to precipitation abstract the easterly caribbean low level jet cllj is a prominent climate feature over the intra america seas and it is associated with much of the water vapor transport from the tropical atlantic into the caribbean basin in this study the north american regional reanalysis narr is analyzed to improve the understanding of the dynamics of the cllj and its relationship to regional rainfall variations horizontal momentum balances are examined to understand how jet variations on both diurnal and seasonal time scales are controlled the jet is geostrophic to the first order its previously documented semidiurnal cycle with minima at about 0400 and 1600 lt is caused by semidiurnal cycling of the meridional geopotential height gradient in association with changes in the westward extension of the north atlantic subtropical high nash a diurnal cycle is superimposed associated with a meridional land sea breeze solenoidal circulation onto the north coast of south america so that the weakest jet velo

hydrological changes in western central asia kyrgyzstan during the holocene as inferred from a palaeolimnological study in lake son kul abstract the hydrology of western central asia is highly sensitive to climatic perturbations in order to understand its long term variability and to infer linkages between precipitation and atmospheric and oceanic systems we conducted a thorough sedimentary and geochemical study on a composite core retrieved in lake son kul central kyrgyzstan a multi proxy approach was conducted on lake sediments based on grain size analyses magnetic susceptibility total organic carbon toc total nitrogen tn and carbon and oxygen isotope analyses on bulk and biogenic materials ostracoda and molluscs shells at a resolution equivalent to ca 40 years aiming to characterise the sequence of palaeolimnological changes in son kul as indicated by 18 o record of bulk carbonates mainly consisting of aragonite the holocene hydrological balance was negative during most of time suggesting an excess of evaporation e over precipitation p limnological conditions fluctuated rapidly before 5000 cal yr bp indicating significant changes in regional hydrology and climate in particular the long term negative hydrological balance was impeded by several short stages with marked increase of precipitation lasting several decades to a few centuries e g 8300 8200 6900 6700 6300 6100 5500 5400 5300 5200 and 3100 3000 cal yr bp precipitation changes as inferred from 18 o data are also documented by increased minerogenic detritus and higher toc we propose that the seasonal pattern of precipitation varied transiently in western central asia during the holocene although evaporation changes may also account for the rapid changes observed in 18 o data when the annual water balance was less critical p e the excess of water might be ascribed to increased precipitation during cold seasons mainly because winter precipitation has more negative 18 o than its summer equivalent conversely when the annual water balance is negative p e the moisture was mainly delivered during the warm season as between 5000 and 2000 cal yr bp our results thus imply that moisture sources could have changed as well during the holocene moisture was delivered as today mainly during summer from the extended caspian aral basin and eastern mediterranean although arctic and even north atlantic seas might be important moisture sources when seasonal precipitation was dominated by winter precipitation we hypothesise that warming arctic and north atlantic seas were important for the north hemisphere circulation during the cold season

isotopic and geochemical evidence of palaeoclimate changes in salton basin california during the past 20 kyr 1 δ18o and δ13c records in lake tufa deposits abstract investigation of 18 o and salt content of surface waters in the salton basin california shows that there is a strongly positive correlation between 18 o values and salt contents and that the 18 o of salton sea is much heavier than that of its input waters due to strong evaporation using a steady state 18 o model we have discussed the 18 o of lake cahuilla an ancient lake in the basin under through flowed closed and overflowed situations an ams 14 c dated stable isotope record of a 60 cm lake tufa slice lc 1 from the ancient shoreline of lake cahuilla indicates that the lake experienced closed and or overflowed conditions between 1 300 and 20 500 yr bp the variations in 18 o and 13 c values of lc 1 ranging from 8 52 to 2 50 pdb and from 0 8 to 3 76 respectively reflect changes in the relative humidity in salton basin and variations in the colorado river inflow and hence climatic conditions in the colorado river drainage basin the tufa record exhibits palaeoclimates of salton basin as follows 1 relatively dry climate between 20 and 18 kyr bp was followed by a wet climate between 18 and 17 kyr bp 2 decreasing effective moisture precipitation evaporation from 17 to 16 kyr bp corresponded to heinrich 1 event whereas effective moisture increased at ca 15 5 kyr bp during the trans us wet period contrasting patterns between the lc 1 record and the greenland ice core and chinese speleothem records during the bolling allerod interstadial from 15 2 to 11 7 kyr bp may be caused by age uncertainty of the lc 1 record further study of this interval is needed 3 wet warm early holocene corresponding to the maximum effective moisture period perhaps brought about by the strengthening of north american monsoon 4 toward 2 kyr bp the climate became dryer apparently resulting from weakening of the monsoons especially around 6 2 and 2 5 kyr bp 5 a wet regime occurred in the basin during the medieval warm period

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

exceptionally fast growth rate of 100 yr old tufa big soda lake nevada implications for using tufa as a paleoclimate proxy large tufa mounds 3 m tall with a basal circumference of 5 m have been discovered on the margin of big soda lake nevada usa these tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage which can be seen emanating from the top of the tufa mounds big soda lake is a volcanic crater lake whose water level is maintained exclusively by groundwater the age of the tufa mounds is well constrained because prior to the development of the newlands irrigation project in 1907 the water level was 18 m lower than the current lake level the vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially thus the tufa mounds are 100 yr old and have grown at a rate 30 mm yr stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature the exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater

dynamics of the 1984 rock avalanche and associated distal debris flow on mount cayley british columbia canada implications for landslide hazard assessment on dissected volcanoes abstract in 1984 a mass of quaternary pyroclastic rock est vol 0 74 106m3 slid from the western flank of mount cayley volcano in southwest british columbia the disintegrating rock mass entrained a further 0 20 106 m3 and formed a rock avalanche that travelled a horizontal distance of 3 46 km from its source over a vertical elevation difference of 1 18 km equivalent to a fahrboschung of 19 from the superelevation of the debris trimline in the mid path it is estimated that velocities reached at least 42 m s in the upper part of its path velocities may have approached 70 m s the rock avalanche was partially transformed into a distal debris flow that travelled a further 2 6 km down turbid creek in a narrow channelised path to the squamish river temporarily blocking it the motion of the rock avalanche including the production of a distal debris flow was successfully simulated using a dynamic analytical model both the results of this analysis and field evidence indicate that the rock avalanche did not come to a halt in the upper part of its path as suggested by cruden and lu 1992 but travelled to its distal limit in one uninterrupted movement this finding has important implications for landslide hazard assessment at mount cayley and similar sites the landslide is typical of those which occur on the steep slopes of dissected volcanoes and is one of seven high velocity rock avalanches that have occurred in the garibaldi volcanic belt of southwest british columbia since 1855

the isotopic and hydrologic response of small closed basin lakes to climate forcing from predictive models application to paleoclimate studies in the upper columbia river basin simulations conducted using a coupled lake catchment hydrologic and isotope mass balance model indicate that small closed basin lakes in north central washington are isotopically sensitive to changes in precipitation relative humidity and temperature most notably model simulations predicted inconsistent lake responses to precipitation changes due to differences in lake outseepage rates and surface area to volume sa v ratios greater outseepage within model experiments resulted in increased sensitivity to changes in mean precipitation moreover simulations suggest that in lakes with appreciable outseepage sa v ratio changes resulting from lake level variations control the direction of changes in lake water oxygen isotope composition 18o specifically in lakes with a sa v ratio that increases at higher lake levels steady state 18o values will increase in response to greater long term average precipitation these results suggest that closed basin lakes with low outseepage rates will exhibit a transient isotopic response to stochastic variability in hydrologic forcing but will not strongly respond at steady state to variation in mean hydrologic conditions conversely closed basin lakes with appreciable outseepage will exhibit strong isotopic responses to both stochastic variability and variation in mean hydrologic conditions i e mean precipitation relative humidity and temperature control of catchment hydrologic inputs to the lake these relationships provide a mechanism for explaining inconsistencies in the isotopic responses of lakes within a given region to hydrologic forcing and demonstrate that semiquantitative models for describing the relationship between lake hydrologic and isotopic responses to climate variability are not appropriate for all closed basin lakes

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

upper ocean temperature structure inertial currents and richardson numbers observed during strong meteorological forcing abstract upper ocean currents and temperature in the northeastern pacific were measured during a 14 day period in november 1980 as part of strex velocities in the upper ocean are dominated by near inertial frequency oscillations thew oscillations are modified by wind stress variations associated with the passage of a strong cold front the change in the inertial currents both in the mixed layer and below is qualitatively consistent with linear internal wave dynamics if turbulent stresses during the storm are assumed to extend 10 20 m below the mixed layer the ratio of mean squared buoyancy frequency n2 and mean squared shear s2 computed over a 10 m interval defines an average richardson number r0 n2 s2 r0 is approximately 2 5 except in regions of high inertial shear in particular values as low as 0 7 are obtained in a 20 m thick region immediately below the base of the mixed layer the data are consistent with a model of the oecanic shear field consisting of a background shear corresponding to a va

internal swell generation the spatial distribution of energy flux from the wind to mixed layer near inertial motions the energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50 8 st o 508n for the years 1996 99 the wind stress t is computed from 6 h 2 58 resolution ncep ncar global reanalysis surface winds the inertial mixed layer response ui and the energy flux p5 t ui are computed using a slab model the validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and adcp velocity records from ndbc buoys at latitudes 508 the inertial response is too fast to be resolved by the reanalysis wind 6 h output interval midlatitude storms produce the greatest fluxes resulting in broad maxima near 40 8 latitude during each hemisphere s winter concentrated in the western portion of each basin northern hemisphere fluxes exceed those in the southern hemisphere by about 50 the global mean energy flux from 1996 to 1999 and 508 st o 508n is 0 98 6 0 08 3 1023 wm 22 for a total power of 0 29 tw 1 tw 5 1012 w this total is the same order of magnitude as recent estimates of the global power input to baroclinic m2 tidal motions suggesting that windgenerated near inertial waves may play an important role in the global energy balance

a lake sediment stable isotope record of late middle to late holocene hydroclimate variability in the western guatemala highlands abstract long term perspectives on past hydroclimate variability provide context for evaluating the potential future impacts of changes in northern hemisphere temperatures and oceanic atmospheric circulation on the timing and distribution of precipitation in central america here we use the isotopic composition of fine grained 18 ocalcite and 13 ccalcite from lake kail located in the western highlands of guatemala to infer multi decadal to multi centennial scale variability in the balance between precipitation and evaporation p e over the last 6000 years the sediment age model is based on 210pb and 41 14c ages with chronological uncertainty estimated using bayesian methods a model that couples lake hydrology and isotope mass balance is applied to characterize the isotopic responses of lake water and calcite to changes in drought controlling climate variables such as precipitation temperature and relative humidity the 18 ocalcite variations indicate intermediate to dry p e conditions during the late middle holocene from 6000 to 4100 cal yr bp there was then a shift to drier conditions at the start of the late holocene until 3050 cal yr bp followed by a trend to wetter conditions until 1500 cal yr bp the most recent 1500 years is characterized by high and relatively stable p e with particularly wet intervals from 1500 to 1170 cal yr bp and from 470 to 260 cal yr bp comparisons of the lake kail 18 ocalcite record with central american circum caribbean proxy datasets spanning the late middle and late holocene indicate northern tropical hydroclimate changes were highly variable across space and time and were likely driven by regional oceanic atmospheric responses with a secondary influence by insolation forcing

a review of holocene solar linked climatic variation on centennial to millennial timescales physical processes interpretative frameworks and a new multiple cross wavelet transform algorithm article i nfo wereportontheexistenceandnature of holocene solar andclimaticvariationson centennialto millennial time scales we introduce a new solar activity proxy based on nitrate no3 concentration from the talos dome ice core east antarctica we also use a new algorithm for computing multiple cross wavelet spectra in time fre quency space that is generalized for multiple time series beyond two our results provide a new interpretive framework for relating holocene solaractivity variations on centennial to millennial timescales to co varying cli mate proxies drawn from a widespread area around the globe climatic proxies used represent variation in the north atlantic ocean western pacific warm pool southern ocean and the east asian monsoon regions our wavelet analysis identifies fundamental solar modes at 2300 yr hallstattzeit 1000 yr eddy and 500 yr unnamed periodicities leaves open the possibility that the 1500 1800 yr cycle may either be fundamental or derived and identifies intermediary derived cycles at 700 yr and 300 yr that may mark rectified responses of the atlantic thermohaline circulation to external solar modulation and pacing dating uncertainties suggest that the 1500 yr and 1800 yr cycles described in the literature may represent either the same or two separate cycles but in either case and irrespective too of whether it is a fundamental or derived mode in the sense of dima and lohmann 2009 the 1500 1800 yr periodicity is widely represented in a large number of paleoclimate proxy records it is obviously premature to reject possible links between changing solar activity at these multiple scales and the variations that are commonly observed in paleoclimatic records

evaporation induced 18o and 13c enrichment in lake systems a global perspective on hydrologic balance effects growing pressure on sustainable water resource allocation in the context of global development and rapid environmental change demands rigorous knowledge of how regional water cycles change through time one of the most attractive and widely utilized approaches for gaining this knowledge is the analysis of lake carbonate stable isotopic compositions however endogenic carbonate archives are sensitive to a variety of natural processes and conditions leaving isotopic datasets largely underdetermined as a consequence isotopic researchers are often required to assume values for multiple parameters including temperature of carbonate formation or lake water delta o 18 in order to interpret changes in hydrologic conditions here we review and analyze a global compilation of 57 lacustrine dual carbon and oxygen stable isotope records with a topical focus on the effects of shifting hydrologic balance on endogenic carbonate isotopic compositions through integration of multiple large datasets we show that lake carbonate delta o 18 values and the lake waters from which they are derived are often shifted by 10 parts per thousand relative to source waters discharging into the lake the global pattern of delta o 18 and delta c 13 covariation observed in 70 of the records studied and in several evaporation experiments demonstrates that isotopic fractionations associated with lake water evaporation cause the heavy carbon and oxygen isotope enrichments observed in most lakes and lake carbonate records modeled endogenic calcite compositions in isotopic equilibrium with lake source waters further demonstrate that evaporation effects can be extreme even in lake records where delta o 18 and delta c 13 covariation is absent aridisol pedogenic carbonates show similar isotopic responses to evaporation and the relevance of evaporative modification to paleoclimatic and paleotopographic research using endogenic carbonate proxies are discussed recent advances in stable isotope research techniques present unprecedented opportunities to overcome the underdetermined nature of stable isotopic data through integration of multiple isotopic proxies including dual element c 13 excess values and clumped isotope temperature estimates we demonstrate the utility of applying these multi proxy approaches to the interpretation of paleohy droclimatic conditions in ancient lake systems understanding past present and future hydroclimatic systems is a global imperative significant progress should be expected as these modern research techniques become more widely applied and integrated with traditional stable isotopic proxies c 2015 elsevier ltd all rights reserved

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

the rockslide and debris flow from mount cayley b c in june 1984 a major rockslide and debris flow occurred on mount cayley british columbia in june 1984 approximately 3 2 million cubic metres of volcanics travelled 2 0 km down avalanche creek at velocities up to 35 m s to dam the confluence of avalanche and turbid creeks the breaking of the landslide dam caused an extremely fast debris flow the velocity of the debris flow and associated wind gusts up to 34 m s caused superelevations hurled rocks and wood through the air uprooted trees and spattered mud 16 m up trees the debris flow removed the logging road bridge and road approaches at the mouth of turbid creek blocked the squamish river during surges and introduced huge quantities of sediment to the squamish river the uniaxial compressive strength of wet tuff collected from the head scarp of the rock slide is 1 0 1 5 mpa about two thirds of the strength of dry specimens the friction angle on wet tuff bedding surfaces is 30 and the slake durability index is 26 weak tuffs form the rupture surface of

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

quantifying high frequency wind energy flux into near inertial motions in the southeast pacific abstractwind forced internal waves close to the inertial frequency are ubiquitous throughout the world s oceans but observational constraints on their global energetics and impact on subsurface mixing remain scarce this study reports on velocity measurements from three electromagnetic autonomous profiling explorers em apex deployed in february 2009 these floats observed downward propagating near inertial internal waves near the subantarctic and polar fronts of the antarctic circumpolar current these waves were episodic and enhanced at middepth between 500 and 1000 m depth integrated kinetic energy varied between 1 and 7 kj m 2 and averaged 1 6 kj m 2 with typical group velocities of 40 m day 1 implying an average energy flux of 3 mw m 2 at the mixed layer base decreasing to approximately 25 of that value at 1500 m modeled currents forced by reanalysis winds along each float track agree with observed surface currents from em apex provided that mixed layer depth is restricted to the layer of weak

the andean type gangdese mountains paleoelevation record from the paleocene eocene linzhou basin abstract paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the cenozoic uplift of the himalayas and the tibetan plateau this paper presents new oxygen and carbon isotopic compositions from well dated tertiary paleosols lacustrine calcareous carbonates and marls from the nianbo 60 54 ma and upper pana formations 51 48 ma of the linzizong group in the linzhou penbo basin the sediments of the nianbo formation which are 180 m thick were deposited in alluvial fans braided rivers fan deltas and on nearshore to offshore lacustrine settings whereas those of the upper pana formation are 100 m thick and are comprised predominantly of proximal alluvial fan and braided river deposits correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment it is confirmed that the 18 o c and 13 c c values from nianbo and pana formations have not yet been reset by late stage diagenesis based on petrographic examination oxygen isotope of the fossil ostracodes and tectonic deformation of strata the paleoelevations are reconstructed using the corrected most negative paleosurface water 18 o psw values these imply that the linzhou area had attained an elevation of 4500 400 m during the period of the indo asian collision i e achieved a near present elevation and may form an andean type mountain range stretching the gangdese arc before collision the gangdese mountains probably maintained high elevations since at least the paleocene and could play a crucial role in the climate change in the interior of the tibetan plateau during the early cenozoic the paleogeomorphic scenario of the eocene tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin

later pleistocene holocene climate conditions of qinghai xizhang plateau tibet based on carbon and oxygen stable isotopes of zabuye lake sediments abstract we present a time series of carbon and oxygen stable isotope records of the last 30 000 14c years throughout the last glacial postglacial cycle from western qinghai xizhang tibet plateau a 20 m core drilled in the south basin of zabuye salt lake was analyzed for inorganic and organic carbon and total sulfur contents 13c and 18o values of carbonates our results indicate that climatic changes have led to a drastic negative shift of stable isotope ratios at the transition between the last full glacial and the postglacial phase during later pleistocene times 16 2 kyr bp and a rapid positive shift at the transition from pleistocene to holocene 10 6 kyr bp the first shift is marked by the drop of 18ocarb values of about 10 from 2 to 8 and 13ccarb values of about 3 from 5 to 2 the second shift which occurred at the transition from pleistocene to holocene was of similar magnitude but in the opposite direction isotope data combined with total organic and inorganic carbon contents and the lithological composition of the core suggest this lake was an alluvial pre lake environment prior to ca 28 14c kyr bp during ca 28 16 2 14c kyr bp zabuye lake was likely a moderately deep lake with limited outflow the cool and arid glacial climate led the lake level to drop drastically extended residence time overwhelmed the lower temperature and caused a steady increase of 13ccarb and 18ocarb values and total inorganic carbon content in the sediments during ca 16 2 10 6 14c kyr bp this lake probably overflowed and received abundant recharge from melting glaciers when the deglaciation was in its full speed a spike of markedly enhanced 13ccarb and 18ocarb is seen at 11 5 kyr bp probably due to the isotopic effects left behind by the short but severe younger dryas yd event after ca 10 6 14c kyr bp zabuye lake probably closed its surface outflow due to strong desiccation and drastic climate warming the early and middle holocene were characterized by unstable climatic conditions with alternating warmer cooler episodes as indicated by the severe fluctuations of total organic carbon 13c and 18o values a hypersaline salt lake environment was finally formed at zabuye after 5 14c kyr bp when the mirabilite and halite concentrations steadily increased and became the dominant minerals in the sediments severe imbalance of inflow outflow resulted in the drastic increase of total sulfur 13ccarb and 18ocarb values and dominance of halite in the lake since ca 3 8 kyr bp to present

shoreline tufa and tufaglomerate from pleistocene lake bonneville utah usa stable isotopic and mineralogical records of lake conditions processes and climate shoreline carbonate deposits of pleistocene lake bonneville record the conditions and processes within the lake including the evaporative balance as well as vertical and lateral chemical and isotopic gradients tufas swash zone and tufaglomerates cemented subaqueous colluvium or beachrock on multiple well developed shorelines near the silver island range utah also present an opportunity to examine physicochemical lake processes through time three shorelines are represented by carbonate deposits including the 23 20 ka stansbury stage 15 14 5 ka bonneville stage and 14 5 14 ka provo stage mean 18ovsmow values of all three shorelines are statistically indistinguishable 27 1 when a few bonneville samples of unusual composition are neglected however differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water second in order to sustain a much smaller shallower lake during the colder stansbury stage the climate must have also been relatively dry third 18o values in tufa are higher than tufaglomerate by 0 5 consistent with greater evaporative enrichment of lake water in the swash zone fourth mean 13c values for the provo stansbury and bonneville shorelines 4 4 5 0 and 5 2 respectively show that carbon species were dominated by atmospheric exchange with the variations produced by differences in the oxidation of organic matter comparisons of shoreline carbonates with deep lake marls of the same approximate age indicate that shoreline carbonate was much higher in 13c and 18o values both 2 5 during bonneville time whereas isotopic differences were minor both 1 in stansbury time in particular the bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on 18o values in contrast the lake during the much shallower stansbury stage may have been well mixed differences in the primary mineralogy stansbury and bonneville aragonite calcite provo calcite aragonite reflect profound differences in lake chemistry in terms of open versus closed basin lakes the establishment of a continuous outlet during provo time probably reduced the mg2 ca2 ratio of lake water curiously regardless of primary mineralogy tufaglomerate cements are enriched in na and cl and depleted in mg2 relative to capping tufa of the same age this probably reflects vital or kinetic effects in the swash zone tufa we suspect that abiotic effects may have been important in the dark pore space of developing tufaglomerate where the absence of light suppressed photosynthesis copyright 2005 john wiley sons ltd

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

restratification of the surface mixed layer with submesoscale lateral density gradients diagnosing the importance of the horizontal dimension abstract a depth cycling towed conductivity temperature depth ctd and vessel mounted acoustic doppler current profiler adcp were used to obtain four dimensional measurements of the restratification of the surface mixed layer sml at a submesoscale lateral density gradient near the subtropical front with the objective of studying the role of horizontal processes in restratification the thermohaline and velocity fields were monitored for 33 h by 16 small scale 15 km2 surveys centered on a drogued float daytime warming by insolation caused a unidirectional displacement of the initially vertical isopycnals toward increasing density across the entire sml 50 m vertical scale solar insolation accounted for 60 of observed restratification but over 10 m scales the percentage decreased with depth from 80 at 25 35 m to 25 at 55 65 m below 35 m stratification was enhanced by the vertically sheared horizontal advection of the lateral density gradient due to a near inertial wave of 100 m vertica

palaeohydrological significance of late quaternary strontium isotope ratios in a tropical lake ostracods preserved in late quaternary sediments of wallywash great pond a fresh coastal lake in sw jamaica record temporal variations in the strontium isotope composition of lake water oxygen isotope and sr ca ratios in ostracods reveal temporal variations in the lake s hydrology related to effective precipitation and in its salinity related to varying marine saline groundwater input from changes in relative sea level evaluation of isotopic and trace element data indicates that the stratigraphic variations in 87sr 86sr ratios during the late quaternary are best explained by climatically controlled hydrological changes during wetter periods the lake s sr budget was dominated by springwater input with relatively low 87sr 86sr ratio whereas during drier times reduced springflow possibly coupled with input of more radiogenic sr from other sources such as sea spray aerosols and perhaps saharan dust led to an increase in the sr isotope ratio of the lake water despite proximity of the lake to the sea and evidence for slight intrusion of marine saline groundwater in the past however the extent of marine input appears to have had limited influence on the lake s sr isotope ratios whereas the 87sr 86sr ratios cannot be used as a palaeosalinity proxy in this particular lake they do provide valuable information about the mechanisms underlying hydrological change

large 13c enrichment in primary carbonates from andean altiplano lakes northwest argentina abstract we report here extreme 13 c enrichments up to 13 pdb in primary calcite and aragonite precipitates in saline well oxygenated waters from high altitude lakes in the southern andean altiplano northwestern argentina biological effects as well as variations in carbon source inputs and in the exchange rate with atmospheric co 2 are commonly considered the main controls on the carbon isotope values of authigenic lacustrine carbonate we present sedimentological and geochemical evidence that favors physical processes evaporation effects and co 2 degassing as major controls on 13 c enrichment we propose that large enrichments may result from the non equilibrium gas transfer isotope fractionation during co 2 degassing from thermal springs and evaporation effects in arid environments the dilution effect by large quantities of 14 c free co 2 hinders accurate 14 c chronology of these lake records based on lacustrine organic matter and aquatic plants our results indicate that geothermal and volcanic co 2 sources in lake basins located in volcanic settings and physical fractionation may have a greater significance than commonly accepted to explain lacustrine carbon isotope records

when mixed layers are not mixed storm driven mixing and bio optical vertical gradients in mixed layers of the southern ocean author s carranza mm gille st franks pjs johnson ks pinkel r girton jb abstract 2018 american geophysical union all rights reserved mixed layers are defined to have homogeneous density temperature and salinity however bio optical profiles may not always be fully homogenized within the mixed layer the relative timescales of mixing and biological processes determine whether bio optical gradients can form within a uniform density mixed layer vertical profiles of bio optical measurements from biogeochemical argo floats and elephant seal tags in the southern ocean are used to assess biological structure in the upper ocean within the hydrographically defined mixed layer the profiles show significant vertical variance in chlorophyll a chl a fluorescence and particle optical backscatter biological structure is assessed by fitting chl a fluorescence and particle backscatter profiles to functional forms i e gaussian sigmoid exponential and their combinations in the southern ocean which characteristically has deep mixed layers only 40 of nighttime bio optical profiles were characterized by a sigmoid indicating a well mixed surface layer of the remaining 60 that showed structure 40 had a deep fluorescence maximum below 20 m depth that correlated with particle backscatter furthermore a significant fraction of these deep fluorescence maxima were found within the mixed layer 20 80 depending on mixed layer depth definition and season results suggest that the timescale between mixing events that homogenize the surface layer is often longer than biological timescales of restratification we hypothesize that periods of quiescence between synoptic storms which we estimate to be 3 5 days depending on season allow bio optical gradients to develop within mixed layers that remain homogeneous in density

turbulent vertical kinetic energy in the ocean mixed layer abstract vertical velocities in the ocean boundary layer were measured for two weeks at an open ocean wintertime site using neutrally buoyant floats simultaneous measurements of the surface meteorology and surface waves showed a large variability in both wind and wave properties and only weak correlations between them buoyancy forcing was weak the mean square vertical velocity in the boundary layer 2w measured from the vertical motion of the floats was proportional to the squared friction velocity u2 estimated from shipboard meteorological measurements using bulk formulas thus 2w au2 the rate of momentum transport from the atmosphere to the ocean is u2 where is the density of the water the deviations from this relation can be attributed entirely to statistical variation and measurement error the measured values of 2w were corrected for measurement biases and the nonturbulent contributions of internal waves the value of the turbulent part of a is 1 75 2 times that measured in laborato

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

carbon oxygen isotopic covariation in hydrothermal calcite during degassing of co 2 the effect of the outgassing of co2 from a hydrothermal fluid on the c and o isotopic compositions of calcite which is precipitated from this fluid is quantitatively modelled in terms of batch and rayleigh distillation equations both co2 degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid combined degassing precipitation models are then developed by taking h2co3 and hco 3 respectively as the dominant dissolved carbon species a positive correlation array between 13c and 13o values of calcite can be yielded by the precipitation of calcite from a h2co 3 dominant fluid accompanied by a progressive decrease in temperature during co2 degassing whereas calcite precipitated from a hco 3 dominant fluid under the same conditions tends to display much smaller variation in 13c values than in 18o values the combined processes of co2 degassing and calcite precipitation result in lowering the 13c value of calcites with respect to those precipitated in a closed system simply due to temperature effect carbon and oxygen isotopic data for calcite from the kushikino gold mining area in japan illustrate the application of quantitative modelling and degassing of co2 is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

numerical simulation of debris flows a key requirement in the assessment of landslide risk in such densely populated urban areas as hong kong consists of the prediction of potential runout distance or the extent of the subsequent debris flow this paper presents a three dimensional dynamic model of unsteady gravity driven debris flow the lagrangian galerkin finite element method is used to determine the nodal velocity and depth of soil column elements within the sliding mass with the momentum and mass conservation mathematically closed within the soil column elements the numerical solution also features a lumped mass matrix and a volume weighted procedure the method of least squares approximation plays a smoothing role which enhances stability and efficiency of the numerical solution scheme the nodal elevation during sliding is obtained via a dynamic bilinear interpolation of the elevation function for the base of the sliding mass furthermore the accuracy robustness and generality of this method are validated by experimental results

oxygen isotope values of precipitation and surface waters in northern central america belize and guatemala are dominated by temperature and amount effects abstract an understanding of the climatic controls on precipitation 18 o is required to interpret isotopic records of paleoclimate and paleoaltimetry however variations in precipitation 18 o in time and space are only poorly known in northern central america to test the hypothesis that precipitation and surface water 18 o values are dominated by temporal and spatial amount effects we analyzed 18 o in surface waters collected from guatemala and belize and in precipitation from the global network for isotopes in precipitation database for veracruz mexico and san salvador el salvador herein we show that the dominant controls on 18 o values of precipitation and surface waters are fairly simple temporally the dominant control on precipitation 18 o values is the amount effect whereby there is an inverse correlation between rainfall amount and 18 o precipitation 18 o values decrease by 1 24 per 100 mm increase of monthly rainfall spatially only two variables distance from the coast and mean catchment altitude explain 84 of the surface water 18 o variability surface water 18 o values show an altitude effect of 1 9 to 2 4 km 1 and a continental effect of 0 69 per 100 km once corrected for altitude effects a decrease in surface water 18 o by 3 to 4 from the caribbean sea to the pacific ocean is evident as an isotopic rain shadow on the pacific slope our data also show that river waters in this humid tropical environment are good proxies for 18 o values of precipitation in northern central america the guatemala belize surface water line is defined as d 8 0 18 o 8 7 which is similar to the meteoric water line at san salvador of d 8 1 18 o 10 9 spatial variability in 18 o values is interpreted to reflect 1 progressive rainout of caribbean sourced air masses upon traverse of central america and 2 the temperature dependent equilibrium fractionation between vapor and condensate related to the altitude effect the data show that the northeast trade winds are the dominant moisture source to central america mixing with pacific derived moisture west of the cordilleran divide

abrupt climate oscillations during the last deglaciation in central north america evidence from stable isotopes and a variety of proxies from two ontario lakes demonstrate that many of the late glacial to early holocene events that are well known from the north atlantic seaboard such as the gerzensee killarney oscillation also known as the intra allerod cold period younger dryas and preboreal oscillation also occurred in central north america these results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

a 2200 yr record of hydrologic variability from foy lake montana usa inferred from diatom and geochemical data abstract a 2200 yr long high resolution 5 yr record of drought variability in northwest montana is inferred from diatoms and 18o values of bio induced carbonate preserved in a varved lacustrine core from foy lake a previously developed model of the diatom response to lake level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data high frequency decadal fluctuations in the de trended 18o record mirror variations in wet dry cycles inferred from banff tree rings demonstrating the sensitivity of the oxygen isotope values to changes in regional moisture balance low frequency multi centennial isotopic changes may be associated with shifts in the seasonal distribution of precipitation from 200 b c to a d 800 both diatom and isotope records indicate that climate was dry and lake level low with poor diatom preservation and high organic carbon nitrogen ratios subsequently lake level rose slightly although the climate was drier and more stable than modern conditions at a d 1200 lake level increased to approximately 6 m below present elevation after which the lake fluctuated between this elevation and full stage with particularly cool and or wetter conditions after 1700 the hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake s outlet spectral analysis of the 18o data indicates that severe droughts occurred with multi decadal 50 to 70 yr frequency

isotopic hydrology and paleohydrology of the madagi kenya natron tanzania basin during the late quaternary abstract three generations of stromatolites mark the recent extension of paleolakes in the magadi natron basin on the border between tanzania and kenya the last two generations are observed some 50 m above the modern lakes level they are respectively attributed to the beginning of the last interglacial and to the pleistocene holocene transition analysis of the morphology and texture of the stromatolites reveals an ecological zonation between 0 and 10 14 m below the shoreline their relatively high 18o and 13c values reflect a long residence time for the paleolake water which would have been favorable to the establishment of an isotopic equilibrium between atmospheric co2 and the dissolved inorganic carbon despite deep carbon inputs in relation to carbonititic volcanism a study of the 18o 2h and 13c contents in the hydrothermal springs perennial rivers and lacustrine brines indicates that during the last period of significant renewal of the deep saline groundwater precipitation was depleted in heavy isotopes when compared to modern precipitation this difference corresponds to a drop of about 600 1000 m in altitudinal hydroclimatic zones finally a comparison between the modern and paleohydrological data leads us to believe that the stabilization of the paleolake shorelines at the same altitude can be attributed to control by the water table level in the aquifer of the basaltic plateaus east of the basin

modelling tailings dams and mine waste dumps failures this paper presents a depth integrated model that can be used to simulate the flowslides mudflows and debris flows that are caused by the failure of tailing dams mining waste dumps and other similar structures the sliding mass is first determined using a coupled elastoplastic finite element code and a suitable constitutive equation once failure has been triggered propagation of the mobilised material is analysed considering flow properties averaged over depth a simple law of pore pressure dissipation is postulated for cases in which the consolidation and propagation times are of the same order of magnitude

holocene hydrologic balance of tropical south america from oxygen isotopes of lake sediment opal venezuelan andes precipitation in the south american andes is derived from atlantic ocean evaporation which is modified by passage over lowland south america the isotopic composition of andean precipitation reflects evaporation conditions over the atlantic ocean moisture recycling during advection across the south american lowlands and uplift to the andes records of the oxygen isotope composition of precipitation in the venezuelan andes derived from lake sediment diatom 18 o measurements show a 2 4 decrease during the past 10 000 yr a simple model of the evaporation advection and uplift processes is used to understand the cause of the isotope shift the data and model suggest that the decreasing 18 o reflects a decrease in the fraction of moisture entering south america that reaches the andes ice cores from peru and bolivia exhibit similar isotope trends indicating that the shift occurred in both hemispheres an isotopic record of amazon river discharge is consistent with the andean records indicating increasing continental runoff was associated with the decreasing export of water vapor orbital changes in solar insolation cannot explain the synchronous trends in both hemispheres changing climate in the tropical pacific is an attractive explanation for the trends because modern interannual variability in this region has similar effects in both hemispheres

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

mimoc a global monthly isopycnal upper ocean climatology with mixed layers a monthly isopycnal mixed layer ocean climatology mimoc global from 0 to 1950 dbar is compared with other monthly ocean climatologies all available quality controlled profiles of temperature t and salinity s versus pressure p collected by conductivity temperature depth ctd instruments from the argo program ice tethered profilers and archived in the world ocean database are used mimoc provides maps of mixed layer properties conservative temperature absolute salinity sa and maximum p as well as maps of interior ocean properties sa and p to 1950 dbar on isopycnal surfaces a third product merges the two onto a pressure grid spanning the upper 1950 dbar adding more familiar potential temperature and practical salinity s maps all maps are at monthly 0 5 0 5 resolution spanning from 80 s to 90 n objective mapping routines used and described here incorporate an isobath following component using a fast marching algorithm as well as front sharpening components in both the mixed layer and on interior isopycnals recent data are emphasized in the mapping the goal is to compute a climatology that looks as much as possible like synoptic surveys sampled circa 2007 2011 during all phases of the seasonal cycle minimizing transient eddy and wave signatures mimoc preserves a surface mixed layer minimizes both diapycnal and isopycnal smoothing of s as well as preserves density structure in the vertical pycnoclines and pycnostads and the horizontal fronts and their associated currents it is statically stable and resolves water mass features fronts and currents with a high level of detail and fidelity

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

discrete element simulations of bed force anomalies due to force chains in dense granular flows abstract surficial flows on volcanic edifices are often comprised of high concentrations of granular materials either derived from juvenile eruptive material or material sourced from an unstable edifice although much attention has been given to granular flow mobility the physics that govern flow internal behavior and substrate interaction are still poorly understood recent laboratory experiments have shown that force chains transmit extreme localized forces to the substrates of free surface granular flows in this work we combine computational and experimental approaches to investigate the forces at the bed of a simplified granular flow a photoelastic experimental approach is used to resolve discrete forces in the granular flows we also conduct discrete element model dem simulations using input parameters derived from measureable physical material properties of experimental and natural materials that successfully reproduce the experimental bed forces generated by filamentary force chain structures observed in free surface granular flows the dem results show particular sensitivity to values prescribed for contact stiffness which is in contrast with previous reports indicating that stiffness values have insignificant influence on flow behavior the transient forces at the bed generated by force chain structures can greatly exceed by several 100 the bed forces predicted from continuum approaches and our simulation results imply that natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses this work suggests that force chain activity may play an important role in the bed physics of dense volcanic flows by influencing substrate entrainment

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

stable isotopic record of hydrological changes in subtropical laguna mar chiquita argentina over the last 230 years laguna mar chiquita a highly variable closed saline lake located in the pampean plains of cetral argentina is presently the largest saline lake in south america 6000km2 the availability of hitorical instrumental lake level and salinity data for the past 100 years allows for the calibration of the isotopic archive recorded in the lake sediments prolonged intervals with either negative or positive hydrlogical balances have severely modified lakewater levels salinity and primary productivity and have also controlled the isotopic composition of both the authigenic carbonate 8ooarb and f133ccarb and sedimetary organic matter 6 c0 extensive evaporation during lowstand stages results in an enrichment of 180 and 13c in the lake waters and is recorded in the sediments as the most positive 8o8arb and 613c carb compositions 0 0 o and 1 9yoo respectively conversely more negative 6f 8ocarb and 813ccarb values 1 8 o and 3 8yoo respectively are the result of increasing freshwater input into

influence of the pacific decadal oscillation on the climate of thesierra nevada california and nevada mono lake sediments have recorded five major oscillations in the hydrologic balance between a d 1700 and 1941 these oscillations can be correlated with tree ring based oscillations in sierra nevada snowpack comparison of a tree ring based reconstruction of the pacific decadal oscillation pdo index d arrigo et al 2001 with a coral based reconstruction of subtropical south pacific sea surface temperature linsley et al 2000 indicates a high degree of correlation between the two records during the past 300 yr this suggests that the pdo has been a pan pacific phenomena for at least the past few hundred years major oscillations in the hydrologic balance of the sierra nevada correspond to changes in the sign of the pdo with extreme droughts occurring during pdo maxima four droughts centered on a d 1710 1770 1850 and 1930 indicate pdo related drought reoccurrence intervals ranging from 60 to 80 yr

the response of enso flavors to mid holocene climate implications for proxy interpretation the response of el nino southern oscillation enso to mid holocene boundary conditions remains an open question paleoclimate proxies and climate model simulations do not agree in the magnitude of the reduction of enso variability while recent proxy evidence from fossil corals from the central pacific show that the reduction in mid holocene enso variability compared to the end of the twentieth century is not different from the reduction during other holocene time intervals this is inconsistent with the interpretation of lake and ocean sediment records from the eastern pacific which show a significant reduction compared to all other holocene periods in order to reconcile the seemingly conflicting proxy evidence from the eastern and central pacific we hypothesize that enso remained active during the mid holocene however there was a change in the spatial pattern of the sea surface temperature anomalies also known as enso flavors using national center for atmospheric research s community climate system model version 4 forced with mid holocene orbital conditions we find that the frequency of occurrence of the strongest eastern pacific ep events decreases in the mid holocene and their variance is reduced by 30 while the frequency of central pacific cp events slightly increases and their variance does not change we also find a shift in the seasonality of ep events but not in that of cp events lastly mid holocene ep events develop more slowly and decay faster the differential response of enso flavors to mid holocene forcing is remotely forced by the west pacific where a weakening of the trade winds in early boreal spring in the mid holocene initiates an anomalous downwelling annual kelvin wave which reaches the eastern pacific during the enso development season weakens the upper ocean stratification and results in reduced enso upwelling feedback the simulated reduction in the ep flavor versus the cp flavor in the mid holocene is consistent with proxy evidence the teleconnection patterns of the two flavors with temperature precipitation and salinity are distinct and proxies from different regions of the pacific might be recording variability associated with only one of the flavors or some combination of their relative effects

lake carbonate δ18o records from the yukon territory canada little ice age moisture variability and patterns abstract a 1000 yr history of climate change in the central yukon territory canada is inferred from sediment composition and isotope geochemistry from small groundwater fed seven mile lake recent observations of lake water 18 o lake level river discharge and climate variations suggest that changes in regional effective moisture precipitation minus evaporation are reflected by the lake s hydrologic balance the observations indicate that the lake is currently 18 o enriched by summer evaporation and that during years of increased precipitation when groundwater inflow rates to the lake increase lake water 18 o values decrease past lake water 18 o values are inferred from oxygen isotope ratios of fine grained sedimentary endogenic carbonate variations in carbonate 18 o supplemented by those in carbonate and organic 13 c c n ratios and organic carbon carbonate and biogenic silica accumulation rates document changes in effective moisture at decadal time scales during the early little ice age period to present results indicate that between ad 1000 and 1600 effective moisture was higher than today a shift to more arid climate conditions occurred after ad 1650 the 19th and 20th centuries have been the driest of the past millennium temporal variations correspond with inferred shifts in summer evaporation from marcella lake 18 o a similarly small stratified alkaline lake located 250 km to the southwest suggesting that the combined reconstructions accurately document the regional paleoclimate of the east central interior comparison with regional glacial activity suggests differing regional moisture patterns during early and late little ice age advances

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

lacustrine stable isotope record of precipitation changes in nicaragua during the little ice age and medieval climate anomaly discerning the infl uences of the el nino southern oscillation enso and the north atlantic oscillation nao on drought variability in the tropics during the medieval climate anomaly mca and little ice age lia will help to improve our understanding of climate system responses to internal and external forcing sediments from lago el gancho nicaragua provide an 1400 yr record of water balance precipitation and evaporation changes from a region that is sensitive to teleconnected pacifi c and atlantic ocean atmosphere dynamics oxygen isotope values of ostracod carapaces 18 o ostracod are consistently low in el gancho sediments between ca a d 950 and 1250 indicating that wetter conditions prevailed during the mca a period of la nina like mean state conditions in the tropical pacifi c and a positive mean state of the nao the 150 yr period between the mca and lia was marked by an abrupt shift to persistently drier conditions at a time of highly variable pacifi c sea surface temperatures and a transition toward a more negative nao phase in sediment from ca a d 1450 to the present 18 o ostracod values increase suggesting that drier conditions persisted through most of the lia a time of a relatively negative nao phase and el nino like mean state conditions in the tropical pacifi c the long term precipitation trends inferred from the el gancho data are not entirely consistent with modern associations between precipitation in the circum caribbean region and the nao suggesting that present day hydroclimatic shifts resulting from variability in synoptic climate patterns are dissimilar to changes resulting from teleconnected ocean atmosphere dynamics that operated during the mca and lia

morphology and substrate control on the dynamics of flowlike landslides a numerical model set up to simulate rapid flowlike landslide motion across three dimensional terrain has been used to investigate the capability of various constitutive relationships to model the dynamics of complex events characterized by a changing type of substrate and morphology e g glacier bends the numerical procedure is based on a continuum mechanics approach and on depth averaged st venant equations for shallow flows the developed rash3d code includes the possibility of using several rheological laws whose parameter values can vary along the runout path two rock avalanche cases with some morphological peculiarities along the propagation path have been numerically back analyzed with both a frictional and a voellmy rheology of the two considered rheologies the voellmy model produces the most consistent results in terms of runout area as well as velocity values the main drawbacks of the frictional model are the tendency to predict excessive spreading of the mass and to overestimate the velocities the results show that when a complex problem of runout of rapid flowlike landslides has to be analyzed it is necessary to have detailed knowledge of the geological and morphological features and to resort to increasingly complex rheologies

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

the taravilla lake and tufa deposits central iberian range spain as palaeohydrological and palaeoclimatic indicators 21 pages 8 figures 3 tables available online oct 13 2007 issue title lake systems sedimentary archives of climate change and tectonics egu general assembly

ground water processes controlling a prairie lake s response to middle holocene drought lake response to climate forcing is commonly regarded as being controlled by within lake processes we present a case from the northern great plains in which holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water middle holocene ostracode assemblages were dominated by halophylic limnocythere staplini indicating increased lake water salinity yet the oxygen isotope values in this period decreased by 2 to 3 contrary to expectations of evaporative dominance we infer from these proxy records and ground water flow model results that the paleoclimatic record in the lake was mediated by changes in ground water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins

late glacial and holocene record of climatic change in the southern rocky mountains from sediments in san luis lake colorado usa abstract large rapid climate changes occurred over the last glacial cycle in the southwestern united states and elsewhere in many regions of the world some of these changes were attributed to alternations between stadial and interstadial conditions in the north atlantic but intense debate exists on how climate anomalies in the north atlantic transmit to the southwest here we report a sediment record from san luis lake in southern colorado through analyses of grain size magnetic susceptibility mg ca total inorganic carbon 18 o and 13 c to indicate climatic and environmental changes in the southern rocky mountains over the last 16 5 ka we found that san luis lake remained hydrologically closed most of the time but overflowed during the second half of the mystery interval the big wet 15 7 14 9 ka and the latter part of the mid holocene the neopluvial 4 3 ka over the course of the last deglaciation san luis lake underwent a series of large millennial scale hydroclimatic changes such as the big dry 16 5 15 7 ka the big wet the bolling allerod dry 14 9 12 7 ka and the younger dryas wet 12 8 11 6 ka corresponding to warm cold phases in the high latitude northern hemisphere the north american monsoon waxed during the pre boreal interval 11 6 10 5 ka and waned through the holocene in phase with northward and southward displacement of the intertropical convergence zone itcz the san luis lake basin was relatively dry in the early holocene 10 5 6 7 ka wet and fluctuating in the mid holocene 6 7 2 6 ka and dry and less variable in the late holocene 2 6 0 ka we found evidence that extreme pluvial episodes of the southern rocky mountains and elsewhere in the american southwest were coeval with cold phases of the north pacific our results highlight the role of the north pacific in modulating atmospheric circulations over the region on millennial timescales

reconstructing the paleotopography of mountain belts from the isotopic composition of authigenic minerals the paleorelief of mountain belts can be estimated from the 18 o value of authigenic minerals development of relief during mountain building often creates lee side rain shadows in which precipitation is depleted in 18 o and d the magnitude of this rain shadow effect is strongly correlated to relief a compilation of 18 o data from surface waters throughout the globe shows a linear relationship between net elevation change and 18 o r 2 0 79 through the use of this relationship we investigated the timing and magnitude of elevation change in the southern alps of new zealand and the sierra nevada of california the 18 o values of kaolinites from new zealand show an 6 decrease in the early pliocene that corresponds to an 2 km elevation change in the southern alps the 18 o of smectites from the sierra nevada show little change since 16 ma suggesting that these mountains have been a long standing topographic feature

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

southern ocean mixed layer depth from argo float profiles 1 argo float profiles of temperature salinity and pressure are used to derive the mixed layer depth mld in the southern ocean mld is determined from individual profiles using both potential density and potential temperature criteria and a monthly climatology is derived from individual mlds using an objective mapping method quantitative data are available in the auxiliary material the spatial structures of mlds are similar in each month with deep mixed layers within and just north of the antarctic circumpolar current acc in the pacific and indian oceans the deepest mixed layers are found from june to october and are located just north of the acc where antarctic intermediate water aaiw and subantarctic mode water samw are formed examination of individual mlds indicates that deep mixed layers mld 400 m from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of samw the surface salinity for these deep mixed layers associated with the samw formation are slightly fresher compared to historical estimates differences in air sea heat exchanges wind stress and wind stress curl in the pacific and indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes wind mixing and ekman transport of cold water from the south may assist the samw formation in the indian ocean in the eastern pacific the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling

age and paleoclimatic implications of the bet shean travertines abstract from 41 000 to over 22 000 yr b p a massive and areally extensive spring travertine was deposited in the bet shean valley israel this travertine is coeval with the ami az member of the lisan formation which represents a high lake stand the travertine deposition is contemporaneous with a more active hydrologic regime associated with wetter conditions in the arid zones of the southern levant adjacent to southern israel these wetter conditions facilitated formation of a widespread spring tufa and also enhanced the water levels of lake lisan

a 15 000 year stable isotope record from sediments of lake steisslingen southwest germany abstract stable isotope records for carbon and oxygen in bulk carbonates carbon in bulk organic matter and for total and chromium reducible sulfur in a lacustrine sediment core from lake steisslingen southwest germany show several distinct and abrupt shifts during the last 15 000 years variations in the isotopic composition of authigenic carbonates indicate two major phases in the lake history in the pre holocene the hydrological budget of the lake was apparently stable variations of 18 o values of authigenic carbonates were therefore dominantly controlled by temperature changes a decrease in the 18 o carb values of about 2 at the allerod younger dryas transition is interpreted as a drop in mean annual air temperatures of approximately 5 c an abrupt temperature increase of a similar magnitude is inferred at the younger dryas preboreal boundary throughout most of the holocene the isotopic composition of authigenic carbonates was influenced by marked changes in the hydrological budget of the lake a major positive excursion in the 13 c carb and 18 o carb values at the beginning of the atlantic and a smaller one in the preboreal were related to evaporation effects which indicate that dry climatic conditions must have prevailed at that time a simultaneous increase in 13 c values of bulk organic matter at the beginning of the atlantic suggests a high level of productivity in the lake as a consequence aqueous sulfate became limited as indicated by variations in the 34 s values of total and chromium reducible sedimentary sulfur therefore we conclude that the beginning of the atlantic was characterized not only by dry but also by warm climatic conditions which triggered a higher productivity in the lake in the subatlantic sediments large variations in carbon oxygen and sulfur isotope ratios were observed as a result of human activities causing considerable perturbations in the biogeochemical element cycling of lake steisslingen results obtained by the study of the continuous 15 ka record of lake steisslingen document clearly that isotopic proxy data from lacustrine sediments can provide useful information on environmental and climatic changes of local regional and in the case of the younger dryas event of even hemispherical significance

antarctic intermediate water and subantarctic mode water formation in the southeast pacific the role of turbulent mixing abstract during the 2005 austral winter late august early october and 2006 austral summer february mid march two intensive hydrographic surveys of the southeast pacific sector of the southern ocean were completed in this study the turbulent kinetic energy dissipation rate diapycnal diffusivity and buoyancy flux jb are estimated from the ctd o2 and xctd profiles for each survey enhanced of o 10 3 to 10 4 m2 s 1 is found near the subantarctic front saf during both surveys during the winter survey enhanced was also observed north of the subduction front the northern boundary of the winter deep mixed layer north of the saf in contrast the summer survey found enhanced across the entire region north of the saf below the shallow seasonal mixed layer the enhanced below the mixed layer decays rapidly with depth a number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity the observed buoyancy flux 4 0 10 8 m2 s 3 surr

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

insights from a synthesis of old and new climate proxy data from the pyramid and winnemucca lake basins for the period 48 to 11 5 cal ka abstract a synthesis of old and new paleoclimatic data from the pyramid and winnemucca lake basins indicates that between 48 0 and 11 5 103 calibrated years bp hereafter ka the climate of the western great basin was to a degree linked with the climate of the north atlantic paleomagnetic secular variation psv records from pyramid lake core plc08 1 were tied to the gisp2 ice core record via psv matches to north atlantic sediment cores whose isotopic and or carbonate records could be linked to the gisp2 18o record relatively dry intervals in the western great basin were associated with cold heinrich events and relatively wet intervals were associated with warm dansgaard oeschger do oscillations the association of western great basin dry events with north atlantic cold events and vice versa switched sometime after the laurentide ice sheet lis reached its maximum extent for example the lahontan highstand which culminated at 15 5 ka and a period of elevated lake level between 13 1 and 11 7 ka were associated with cold north atlantic conditions the latter period with the youngest dryas event relatively dry periods were associated with the bolling and allerod warm events a large percentage of the lis may have been lost to the north atlantic during heinrich events 1 and 2 and may have resulted in the repositioning of the polar jet stream over north america the trego hot springs wono carson sink and marble bluff tephras found in core plc08 1 have been assigned gisp2 calendar ages of respectively 29 9 33 7 34 1 and 43 2 ka given its unique trace element chemistry the carson sink bed is the same as wilson creek ash 15 in the mono lake basin this implies that the mono lake magnetic excursion occurred at approximately 34 ka and it is not the laschamp magnetic excursion the entrance of the first americans into the northern great basin is dated to approximately 14 4 ka a time when the climate was relatively dry evidence for human occupation of the great basin is lacking for the next 1100 years y i e the oldest western stemmed point site in the great basin dates to 13 3 ka two hypotheses are suggested for this cultural hiatus 1 the climate had deteriorated to the point that people vacated the great basin or 2 people moved to basin bottom wetlands that persisted during the dry period and then the subsequent younger dryas wet event erased the archaeological evidence deposited around the low elevation wetland sites

are two elements better than one dual isotope ratio detrending of evaporative effects on lake carbonate paleoelevation proxies 1 stable isotope based proxy methods enhance our ability to interpret geodynamical histories for tectonic provinces via paleoelevational reconstructions these methods require that the unmodified isotopic composition of meteoric water is recorded by authigenic minerals a critical assumption that has not been tested across wide ranging environmental and topographical contexts here we show that quaternary lake carbonate 18o values are not strongly nor significantly correlated with regional elevation due to the isotopic modification of in flow waters following entry into the lake environment these modifications are largely caused by surface water evaporation and can result in 3 km errors in paleoelevation estimates if not accounted for however our analysis suggests that positive shifts in surface water 18o are accompanied by similar magnitude shifts in 13c dic this positive co variation in 18o and 13c may be used to detrend lake carbonate compositions for the effects of surface water evaporation using a parameter we define here as the 13c excess when tibetan lakes are excluded from the data set 13c excess values are significantly correlated with mean up slope hypsometric altitude with an error of 500 m application of the13c excess approach to cenozoic lake carbonate records from the western u s cordillera both challenges and reinforces previous paleoelevational interpretations based on 18o alone

climatic hydrologic oscillations since 155 000 yr b p at owens lake california reflected in abundance and stable isotope composition of sediment carbonate abstract sediment grain size carbonate content and stable isotopes in 70 cm long 1500 yr channel samples from owens lake core ol 92 record many oscillations representing climate change in the eastern sierra nevada region since 155 000 yr b p to first order the records match well the marine 18o record at owens lake however the last interglaciation appears to span the entire period from 120 000 to 50 000 yr b p according to our chronology and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate sediment proxies reveal that the apparent timing of glacial interglacial transitions notably the penultimate one is proxy dependent in the grain size and carbonate content records this transition is abrupt and occurs at 120 000 yr b p in contrast in the isotopic records the transition is gradual and occurs between 145 000 and 120 000 yr b p differences in timing of the transition are attributed to variable responses by proxies to climate change

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

surface boundary layer evolution and near inertial wind power input deep weakly stratified surface layers in the southern ocean complicate the identification of the mixed layer base which is critical in estimating the wind power input through the ocean surface typically used mixed layer depth criteria often ignore weak stratification which traps momentum near the surface and significantly enhances the near inertial band wind power input the thickness of the active mixing layer the turbulent layer in contact with wind stress is needed to accurately estimate wind power input a fine density threshold criterion of 0 005 kg m 3 just above the noise floor of most autonomous instruments was applied to observed profiles of potential density to estimate the thickness of the actively mixing layer vertical shear langmuir cells and buoyant convection are investigated as possible mechanisms maintaining turbulence within the mixing layer over 90 of the observed variance of the mixing layer thickness is explained by either shear driven entrainment which is simulated using the price weller pinkel model or by a parameterization of downwelling plumes due to langmuir cell convergence in general surface buoyancy fluxes are too weak to drive mixed layer turbulence comparison of national oceanographic data center nodc climatological mixed layer thickness to those determined using the 0 005 kg m 3 density threshold suggests a multiplicative seasonally varying correction of 1 5 3 5 should be applied to wind work estimates made using the nodc climatological mixed layer thickness in the southern ocean

oxygen 18 and carbon 13 records for the last 14 000 years from lacustrine carbonates of siling co lake in the qinghai tibetan plateau to understand paleoenvironmental changes for the central qinghai tibetan plateau we analyzed stable isotopes of oxygen and carbon from calcium carbonates in a bottom sediment core collected from siling co lake five conventional and two tams 14c dates indicate that the core recovered sediments of the last 14 000 years calcium carbonates in the sediments seem to be primary carbonates precipitated chemically in the lake and not clastic particles from limestones distributed around the lake because of large variation of isotopic ratios isotopic covariance since 6 000 yr bp and similarity between dates from total calcium carbonates and organic carbon their isotopic composition therefore reflects that of the lake water we present the following paleoenvironmental history over the last 14 000 years in the central part of the plateau from secular variations of 18o 13c and caco3 content throughout the core 1 desiccation was dominant during the latter part of the last glacial stage 14 000 to 11 000 yr bp 2 the last glacial stage abruptly terminated at 11 000 yr bp 3 a temperate and stable climate was dominant from 11 000 to 5 000 yr bp 4 climatic conditions fluctuated from 5 000 to the present including two strong desiccation periods 5 000 to 4 000 yr bp and 3 000 to 2 000 yr bp and an intermediate period of heavy rainfall 4 000 to 3 000 yr bp this period is also characterized by a covariant o and c isotopic trend

an 8700 year paleoclimate reconstruction from the southern maya lowlands abstract analysis of a sediment core from lago puerto arturo a closed basin lake in northern peten guatemala has provided an 8700 cal year record of climate change and human activity in the southern maya lowlands stable isotope magnetic susceptibility and pollen analyses were used to reconstruct environmental change in the region results indicate a relatively wet early to middle holocene followed by a drier late holocene which we interpret as reflecting long term changes in insolation precession higher frequency variability is more likely attributable to changes in ocean atmosphere circulation in both the north atlantic and the pacific oceans pollen and isotope data show that most of the period of prehispanic agricultural settlement i e 5000 1000 cal yr bp was characterized by drier conditions than previous or subsequent periods the presence of zea corn pollen through peak aridity during the terminal classic period 1250 1130 cal yr bp suggests that drought may not have had as negative an impact as previously proposed a dramatic negative shift in isotope values indicates an increase in precipitation after 950 cal yr bp hereafter bp