an experimental investigation of mechanisms involved in bed load sheet production and migration 1 field measurements indicate that in gravel bed rivers bed load may not be a one to one response to shear stress but may instead fluctuate a great deal over time for a given flow condition both in flume and field experiments these fluctuations were often associated with migration of low relief bed forms called bed load sheets whereas several studies have described bed load sheets as a consequence of grain sorting little is known about the mechanisms responsible for their production and migration these were investigated in flume experiments a set of 20 experiments was conducted under constant feeding rate conditions with mixtures of different uniform sediments and for slopes varying from 0 8 to 9 except for runs performed in high flow conditions we observed periodic bed load sheet production and migration associated with fluctuations of bed slope bed state bed fining and paving and bed load observations allowed us to conclude that bed load sheets resulted from very efficient vertical and longitudinal grain sorting that produced periodic local bed aggradation and erosion clearly observed in the upstream section of the flume fractional transport rates were measured in one run combined with the results of experiments previously conducted by authors with uniform sediments this experiment showed that the highest peak solid discharges were essentially caused by the much greater mobility of the coarser gravels when transported within bed load sheets a scenario is proposed for the mechanisms involved in bed load sheet production and migration

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

discussion of the relationship between dustfall grain size and the desert border taking the southern border of the tengger desert and the southern dust deposit area as an example abstract in northern china high spatial and temporal instability exists in the southern desert border since the region is very sensitive to the changes of global climate and the migration of the southern desert border threatens the survival of surrounding inhabitants it is very important to strengthen the research about the migration of the southern desert border of northern china the dust in the downwind of the desert contains relevant information of the desert evolutionary history in order to investigate the relationship between dustfall grain size and the southern border of northern china desert we collected 56 eolian surface soil samples from the south of the tengger desert selected two near north south transects from these samples and used the grain size class standard deviation method we finally obtained three sensitive grain size components ranking by degree of sensitivity from high to low 61 8 185 4 m 18 2 61 8 m and 2 3 18 2 m the values of the three sensitive grain size components from the 56 eolian surface soil samples and the three commonly used grain size indicators which are the median grain size 20 m and 63 m particle content have been converted to the grain size contour figures in the six grain size contour figures the contour of the 61 8 185 4 m particle content component has the highest degree of similarity with the southern border of the tengger desert followed by the 63 m particle content component and then the components of the median grain size 18 2 61 8 m particle content 20 m and 2 3 18 2 m particle content in turn relative to the 20 m and 63 m particle content indicators the indicator of 61 8 185 4 m particle content is not only the most sensitive one in theory but also has the highest degree of similarity between its contour and the southern desert border in practical terms moreover this indicator is further defined as the upper limit of coarse grain size since the coarse grains in the eolian deposits are mainly from the near source desert the component of 61 8 185 4 m particle content within the loess to the south of the tengger desert could be regarded as the indicator of the migration of the southern desert border which could be used to quantitatively reconstruct the desert palaeo border in the future

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

probabilistic exner sediment continuity equation for mixtures with no active layer the exner equation of sediment continuity is the foundation of river morphodynamics generalization of this equation to mixtures of grain sizes has required the introduction of an active layer i e a buffer layer between the sediment moving in the water column and the immobile substrate below the active layer is defined to be a well mixed layer with no vertical structure that encompasses those grains available to exchange directly with the moving sediment the sediment in the substrate below exchanges with the active layer only as the bed aggrades or degrades the active layer concept is a useful one that has served the research community well for 3 decades however the division of the erodible bed into a discrete active layer and substrate must represent only an approximation of a more general formulation that contains no active layer and in which parameters pertaining to the entrainment from and deposition to the bed vary continuously with depth below the sediment water interface here the probability density function of bed elevation is used to derive a general exner equation of sediment continuity with no discrete layers the formulation is applicable to both sediment mixtures and tracers in uniform sediment although the treatment requires more information than that of the active layer approach it offers the prospect of a better understanding of how streams create a stratigraphic record of their activities through deposition

reconstructing twentieth century sea surface temperature variability in the southwest pacific a replication study using multiple coral sr ca records from new caledonia 1 coral based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation analytical expense and time constraints coral sr ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of amedee island new caledonia different sampling resolutions were examined in coral sr ca fortnightly and monthly and 18o fortnightly monthly and seasonally as well as similar scale subsampling of the daily in situ sea surface temperature sst record the mean coral sr ca 18o and sst values do not change as a function of sampling resolution the coral sr ca signal is highly reproducible the average absolute offset between coeval monthly sr ca determinations between any two coral time series is 0 035 0 026 mmol mol 1 0 65 c which is less than twice the analytical precision of the coral sr ca measurements the stack average of the monthly coral sr ca variations and monthly anomalies are significantly correlated with monthly in situ sst 1967 1992 r 0 96 and 0 64 respectively p 0 05 and n 302 and 1 grid monthly sst data product 1900 1999 r 0 95 and 0 56 respectively p 0 05 and n 1198 the coral sr ca sst reconstruction exhibits interannual and decadal timescale fluctuations that exceed those observed in the gridded sst record which may reflect true differences between sst at a shallow reef site and those averaged over a 1 grid box or inadequacies in the methodology used to create the gridded sst product when few observations are available a warming trend of 0 6 c is observed in the twentieth century coral sr ca sst record

a reconstruction of sea surface temperature variability in the southeastern gulf of mexico from 1734 to 2008 c e using cross dated sr ca records from the coral siderastrea siderea this study uses skeletal variations in coral sr ca from three siderastrea siderea coral colonies within the dry tortugas national park in the southeastern gulf of mexico 24 42 n 82 48 w to reconstruct monthly sea surface temperature sst variations from 1734 to 2008 common era c e calibration and verification of the replicated coral sr ca sst reconstruction with local regional and historical temperature records reveals that this proxy temperature relationship is stable back to 1879 c e the coral sst reconstruction contains robust interannual 2 0 c and multidecadal variability 1 5 c for the past 274 years the latter of which does not covary with the atlantic multidecadal oscillation winter sst extremes are more variable than summer sst extremes 2 2 c versus 1 6 c 2 suggesting that loop current transport in the winter dominates variability on interannual and longer time scales summer sst maxima are increasing 1 0 c for 274 years mc 0 5 c 2 whereas winter sst minima contain no significant trend colder decades 1 5 c during the little ice age lia do not coincide with decades of sunspot minima the coral sst reconstruction contains similar variability to temperature reconstructions from the northern gulf of mexico planktic foraminifer mg ca and the caribbean sea coral sr ca suggesting areal reductions in the western hemisphere warm pool during the lia mean summer coral sst extremes post 1985 c e 29 9 c exceeds the long term summer average 29 2 c for 1734 2008 c e yet the warming trend after 1985 c e 0 04 c for 24 years mc 0 5 2 is not significant whereas caribbean coral sr ca studies contain a warming trend for this interval

surface ocean variability at galapagos from 1936 1982 calibration of geochemical tracers in corals a variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames the purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony over an extended period a 47 year growth interval 1936 1982 in a colony of pavona clavus taken from san cristobal island galapagos islands was sectioned into 187 quarterly intervals and analyzed for 18o 13o ba ca cd ca and mn ca the resulting time series are compared with eastern pacific sea surface temperatures one of few instrumental data bases available for calibration over this time period linear least squares regressions of four of the tracers 18o 13o ba ca cd ca against peruvian sst show highly significant correlations p 0 0001 over the annual biennial and enso 3 8 years frequency bands cross spectral comparisons show even stronger coherency with sst frequently accounting for 70 80 of the variance in these tracers these results as well as the phase relationships determined from the spectral analyses suggest that the coupling between sst and 18o and the nutrientlike tracers ba and cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by el nino and anti el nino phenomena an inverse relationship between sst and 13c has its primary origins in the co occurrence of the warm sst phase with high light levels during the first half of the calendar year the association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and caco3 skeleton the fifth tracer the transition metal mn exhibits poorer correlations against both sst and the other tracers slight shifts in phasing of the historical mn ca annual cycle suggest that the general water column distribution of this tracer which is the reverse of a nutrient may not be stable the erratic behavior of mn illustrates how complex hydrography near galapagos may influence tracers with diverse source signatures

velocity depth ambiguity of reflection traveltimes the conversion of time horizons to depth is fundamental to exploration geophysics the interval velocity used in the conversion is often estimated from the stacking velocity assuming that each layer s interval velocity is homogeneous however even for one laterally inhomogeneous layer above a flat reflector the stacking velocity can swing violently about its average and conventional methods of velocity estimation fail i show that violent swings in the stacking velocity are a symptom of a long wavelength ambiguity between the burial depth to an interface and interval velocity lateral variations in seismic velocity with a spatial wavelength of about 2 7 d where d is the depth to the reflecting horizon cannot be unambiguously resolved from traveltime measurements the spatial wavelength of this ambiguous component varies from 2 57 d for very small source receiver separations to 2 86 d for source receiver separations equal to d spectral components of the stacking velocity at wavelengths shorter than

megadroughts in the indian monsoon region and southwest north america and a mechanism for associated multidecadal pacific sea surface temperature anomalies abstract a 1360 yr control run from a global coupled climate model the parallel climate model is analyzed it simulates megadroughts in the southwestern united states and indian monsoon regions the megadroughts represent extreme events of naturally occurring multidecadal precipitation variations linked to the dominant pattern of multidecadal sst variability in the indian and pacific oceans gaining insight into the occurrence of megadroughts thus requires an understanding of the mechanism that is producing this multidecadal sst variability analysis of the model variability shows that the mechanism involves atmosphere ocean and tropical midlatitude interactions with a crucial element being wind forced ocean rossby waves near 20 n and 25 s in the pacific whose transit times set the decadal time scale at the western boundary the rossby waves reflect into the equatorial pacific to affect thermocline depth the resulting feedbacks involving surface temperature winds and the strength of the subtropi

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

the velocity depth ambiguity in seismic traveltime data an observed disturbance in seismic traveltimes to a reflector can be caused either by an anomalous velocity zone between the surface and the reflector or by a structural variation in the reflector itself this velocity depth ambiguity is formulated in terms of linear estimation theory such a formulation allows integration of various published results on velocity depth ambiguity and suggests improved methods of stabilizing the solution of a depth conversion problem by solving a relatively simple problem that is amenable to analysis a single reflector beneath an overburden with a variable velocity the following conclusions can be drawn 1 the velocity depth ambiguity is caused by traveltime errors and can be quantitatively related to those errors by closed form expressions if the velocities do not vary laterally or vary very slowly among other things those expressions show that for small spread lengths shorter than haft the depth the errors in velocity and depth are inversely proportional to the sq

interdecadal decadal climate variability from multicoral oxygen isotope records in the south pacific convergence zone region since 1650 a d 1 in the south pacific interdecadal decadal oceanic and atmospheric variability referred to as the interdecadal pacific oscillation ipo is most pronounced in the south pacific convergence zone spcz salinity front region here we have used annual average oxygen isotope 18o time series from five coral cores collected from fiji and tonga in this region to construct a fiji tonga interdecadal decadal pacific oscillation f t idpo index of low frequency 9 and 55 years climate variability back to 1650 a d we first demonstrate the consistency between this f t idpo index and a mean sea level msl pressure based spcz position index spi 1891 2000 thus verifying the ability of coral 18o to record past interdecadal decadal climatic variations in this region back to 1891 the f t idpo index is then shown to be synchronous with the ipo index 1856 2000 suggesting that this coral based index effectively represents the interdecadal decadal scale climate variance back to 1650 the regularity of the f t idpo index indicates that interdecadal decadal variability in the spcz region has been relatively constant over the past 350 years with a mean frequency of 20 years variance peaks near 11 and 35 years there is a consistent antiphase correlation of the f t idpo index and the interdecadal decadal components in equatorial pacific coral 18o series from maiana and palmyra this observation indicates that the eastward expansion westward contraction of the eastern salinity front of the western pacific warm pool wpwp occurs simultaneously 1 year with the westward eastward shift of the spcz salinity front during positive ipo negative ipo phases this is the same relationship observed during the phases of the el nino southern oscillation

is there a low frequency bias in multiproxy reconstructions of tropical pacific sst variability abstract decadal and longer term variability in the tropical pacific has the potential to impact climate worldwide yet paleoclimate observations and climate model simulations disagree on the nature of this variability in this study we investigate whether biases from paleoclimate reconstruction methodology and the currently available proxy network cause reconstructions of enso to overestimate the multidecadal century scale variability of the pacific we build new reconstructions using a variety of commonly employed methods and test the effects of four types of bias on analogous pseudoproxy reconstructions these biases include 1 the number of records used in the reconstruction 2 chronological uncertainty 3 noise in individual proxy records and 4 the geographical distribution of the proxy network we find that each of these biases cause enso reconstructions to overestimate the importance of low frequency variability these biases may partially explain why multiproxy reconstructions of pacific variability have stronger low frequency variability than predicted by historical observations or climate models and why these reconstructions do not have coherent signals over the multidecadal century scale

the effect of velocity uncertainty on migrated reflectors improvements from relative depth imaging we have studied the problem of uncertainty quantification for migrated images a traditional migrated image contains deterministic reconstructions of subsurface structures however input parameters used in migration such as reflection data and a velocity model are inherently uncertain this uncertainty is carried through to the migrated images we have used bayesian analysis to quantify the uncertainty of the migrated structures by constructing a joint statistical distribution of the location of these structures from this distribution we could deduce the uncertainty in any quantity derived from these structures we have developed the proposed framework using a simple model with velocity uncertainty in the overburden and we estimated the absolute positions of the horizons and the relative depth of one horizon with respect to another by quantifying the difference in the corresponding uncertainties we found that in this case the relative depths of the structures could be estimated much better than their absolute depths this analysis justifies redatuming below an uncertain overburden for the purposes of the uncertainty reduction

fragility of reconstructed temperature patterns over the common era implications for model evaluation climate field reconstructions cfrs enable spatially resolved estimates of past climates providing important insights about climate variability over the common era in particular a reconstructed la nina like pattern during the transition from the medieval climate anomaly mca to the little ice age has been widely tied to medieval droughts in southwest north america this pattern is now used as a key benchmark for global climate model simulations of the last millennium which have yet to reproduce it here we test the pattern s robustness by using four different cfr methods and two proxy networks with the older network we find the reconstructed patterns to be highly method dependent with the la nina like pattern not reproduced by two of the cfr methodologies with the updated proxy network a globally uniform mca emerges with all methods in agreement with simulations from the paleoclimate modelling intercomparison project phase 3 ensemble our results caution against drawing dynamical interpretations from a single cfr and affirm the importance of developing cfrs through improved statistical methodology and community driven proxy syntheses

monsoon tropical ocean interaction in a network of coral records spanning the 20th century abstract the 20th century evolution of basin wide gradients in surface ocean properties provides one essential test for recent models of the interaction between the asian monsoon and the tropical ocean because various feedback mechanisms should result in characteristic regional patterns of variability although the instrumental record of climate variability in the tropics is essentially limited to the last few decades the stable isotopic composition of living corals provides an effective means for extending the instrumental observations here we present two coral isotopic records from the indonesian maritime continent and we use these records with other previously published records to describe i the relationship between western pacific and central pacific climate variability over the past century with special emphasis on the biennial band and ii the strength of the west east indian ocean dipole we find that the amplitude of the biennial cycle in the pacific did not vary inversely with the strength of enso el nino southern oscillation as might be expected from some models of monsoonal feedback on the central pacific instead the biennial variability was modulated on decadal timescales throughout much of the pacific we also show that the zonal oxygen isotopic gradient in the indian ocean coral records was significantly correlated with central pacific sea surface temperature on a variety of timescales thus it is likely that this coral dipole was a product of strong enso like teleconnections over the indian ocean as opposed to being the result of unique indian ocean or monsoonal dynamics

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

reconstructing enso the influence of method proxy data climate forcing and teleconnections in this study we compare three newly developed independent nino3 4 sea surface temperature sst reconstructions using data from 1 the central pacific corals 2 the texmex region of the usa tree rings and 3 other regions in the tropics corals and an ice core which are teleconnected with central pacific ssts in the 20th century although these three reconstructions are strongly calibrated and well verified inter proxy comparison shows a significant weakening in inter proxycoherenceinthe 19thcentury thisbreakdownin commonsignalcouldberelatedtoinsufficient data dating errors in some of the proxy records or a breakdown in el nino southern oscillation s enso s influence on other regions however spectral analysis indicates that each reconstruction portraysenso likespectralproperties superposedepochanalysisalsoshowsthateachreconstruction shows a generally consistent el nino like response to major volcanic events in the following year while duringyearst 4tot 7 la nina like conditions prevail theseresults suggest thateachofthe series expresses enso like behaviour but this behaviour does not appear to be spatially or temporally consistent this result may reflect published observations that there appear to be distinct types of enso variability depending on location within the tropical pacific future work must address potential dating issues within some proxies i e sampling of multiple coral heads for one location as well as assessing the time stability of local climate relationships with central pacific ssts more emphasis is needed on sampling new and extending old coral proxy records from the crucial central and eastern tropical pacific region copyright 2009 john wiley sons ltd and crown copyright 2009

the changing relationship between enso variability and moisture balance in the continental united states the el nino southern oscillation enso system orchestrates a well documented suite of climate anomalies worldwide the details of enso s extratropical influence vary among events but this variability has not been described or diagnosed beyond the past few decades and previous descriptions have looked at inter event differences rather than decadal patterns we use a new tree ring based drought reconstruction for the continental u s and instrumental enso indices to document systematic decadal changes in the u s drought enso relationship since the late 19th century significant enso drought correlation occurs consistently in the southwest u s but the strength of penetration of moisture anomalies into the continent varies substantially the most striking change over the past 130 years is the initiation of a bipolar enso drought signature around 1920 producing opposite sign moisture anomalies in the southwest and mid atlantic states shifts in teleconnection patterns coincide with variations in the strength of enso and in a north pacific mode

response of bed surface patchiness to reductions in sediment supply 1 river beds are often arranged into patches of similar grain size and sorting patches can be distinguished into free patches which are zones of sorted material that move freely such as bed load sheets forced patches which are areas of sorting forced by topographic controls and fixed patches of bed material rendered immobile through localized coarsening that remain fairly persistent through time two sets of flume experiments one using bimodal sand rich sediment and the other using unimodal sand free sediment are used to explore how fixed and free patches respond to stepwise reductions in sediment supply at high sediment supply migrating bed load sheets formed even in unimodal sand free sediment yet grain interactions visibly played a central role in their formation in both sets of experiments reductions in supply led to the development of fixed coarse patches which expanded at the expense of finer more mobile patches narrowing the zone of active bed load transport and leading to the eventual disappearance of migrating bed load sheets reductions in sediment supply decreased the migration rate of bed load sheets and increased the spacing between successive sheets one dimensional morphodynamic models of river channel beds generally are not designed to capture the observed variability but should be capable of capturing the time averaged character of the channel when applied to our experiments a 1 d morphodynamic model rte bookagdegnormgravmixpw xls predicted the bed load flux well but overpredicted slope changes and was unable to predict the substantial variability in bed load flux and load grain size because of the migration of mobile patches our results suggest that 1 the distribution of free and fixed patches is primarily a function of sediment supply 2 the dynamics of bed load sheets are primarily scaled by sediment supply 3 channels with reduced sediment supply may inherently be unable to transport sediment uniformly across their width and 4 cross stream variability in shear stress and grain size can produce potentially large errors in width averaged sediment flux calculations

regional calibration of coral based climate reconstructions from palau west pacific warm pool wpwp article ocrl a parameter subject to multiple regional and local environmental influences location specific calibration of 18 ocrl is a necessary first step for developing long term paleoceanographic reconstructions here we present four new coral 18 o stratigraphies from the republic of palau 7 5 n 134 5 e and compare our records with instrumental measurements for the period 1950 2008 we also compare our results with a previously pub lished coral record from palau we employ a new sea surface salinity sss product and validate its utility for coral based paleoclimate calibrations we not only examine differences among the records but also identify strong and regionally coherent environmental signals we find that sss variability is the dominant influence on 18 ocrl in palau while sea surface temperature sst is of secondary importance our results show that time averaging multiple 18 ocrl records into a single composite series produce greater correlations with instru mental data and indices than individual stratigraphies alone our results are consistent with observations of a strengthening of the hydrological cycle in the wpwp region over the past 50 years though the magnitudes of long term linear trends differ among the different palau 18 ocrl records interannual and interdecadal

reply to comment on near surface location geometry and velocities of the santa monica fault zone los angeles california by r d catchings g gandhok m r goldman d okaya m j rymer and g w bawden by t l pratt and j f dolan in a comment on our 2008 paper catchings gandhok et al 2008 on the santa monica fault in los angeles california pratt and dolan 2010 herein referred to as p d cite numerous objections to our work inferring that our study is flawed however as shown in our reply their objections contradict their own published works published works of others and proven seismic methodologies rather than responding to each repeated invalid objection we address their objections by topic in the subsequent sections in catchings gandhok et al 2008 we presented high resolution seismic reflection images that showed two near surface faults in the upper 50 m beneath the grounds of the wadsworth veterans administration hospital wvah although p d suggest we effectively duplicated their seismic acquisition our survey was not a duplication of their efforts rather we conducted a seismic imaging survey over a similar profile as pratt et al 1998 but used a different data acquisition system and different data processing methods to evaluate methods of seismically imaging blind faults in the wake of the 17 january 1994 m 6 7 northridge earthquake we used an acquisition method that provides both tomographic seismic velocities and reflection images our combined data approach allowed for shallower imaging 2 5 m minimum than the 20 m minimum of pratt et al 1998 clearer images of the fault zone and more accurate depth determinations rather than time images in processing the reflection images we used prestack depth migration which is generally accepted as the only proper imaging method for imaging subsurface structures with strong lateral velocity variations versteeg 1993 a condition shown to exist at the wvah site we correlated our reflection images with refraction tomography images borehole lithology and velocity data interferometric synthetic aperture radar images and changes in groundwater depths except for some minor differences our seismic reflection images coincide with previously published seismic reflection

reliability of coral isotope records from the western pacific warm pool a comparison using age optimized records stable isotope analysis of two separate corals from nauru island in the warm pool of the western tropical pacific confirm that coral oxygen isotopes are a robust recorder of environmental variables coral delta 18 o faithfully records interannual variability even when strongly influenced by kinetic effects interannual to decadal variability of coral delta 13 c remains enigmatic only one of the two corals exhibits the expected light delta 13 c response in the interannual band coral delta 18 o from this region has a great similarity to global instrumental temperature records reflecting the impact of the pacific warm pool and variations of the indonesian low in concert with el nino southern oscillation on global climate since 1896 coral delta 18 o has exhibited a cumulative decrease of 0 7 parts per thousand which reflects a combination of warming and more frequent el nino events precipitation affecting the surface waters of this region

estimating central equatorial pacific sst variability over the past millennium part ii reconstructions and implications abstractreducing the uncertainties surrounding the impacts of anthropogenic climate change requires vetting general circulation models gcms against long records of past natural climate variability this is particularly challenging in the tropical pacific ocean where short sparse instrumental data preclude gcm validation on multidecadal to centennial time scales this two part paper demonstrates the application of two statistical methodologies to a network of accurately dated tropical climate records to reconstruct sea surface temperature sst variability in the nino 3 4 region over the past millennium while part i described the methods and established their validity and limitations this paper presents several reconstructions of nino 3 4 analyzes their sensitivity to procedural choices and input data and compares them to climate forcing time series and previously published tropical pacific sst reconstructions the reconstructions herein show remarkably similar behavior at decadal to multidecadal s

el nino southern oscillation enso and decadal scale climate variability at 10 n in the eastern pacific from 1893 to 1994 a coral based reconstruction from clipperton atoll we have developed a 101 year 1893 1994 subseasonal oxygen 18o and carbon 13c isotopic time series from clipperton atoll in the eastern pacific using the coral porites lobata in agreement with linsley et al 1999 we find that seasonal and interannual coral 18o variability at clipperton results from variability in both water temperature and salinity three new coral time series demonstrate the reproducibility of a secular coral 18o trend of 0 35 since 1910 but show varying 13c trends strong decadal scale variability in the 18o record appears related to the pacific decadal oscillation pdo through postulated changes in the strengths of the equatorial counter current and north equatorial current interannual variability in this coral 18o record is directly related to the el nino southern oscillation enso and isolation of this frequency band indicates reduced enso variability in the eastern equatorial pacific in the period 1925 to 1940 in agreement with instrumental and other pacific coral records

quantifying errors in coral based enso estimates toward improved forward modeling of δ18o 1 the oxygen isotopic ratio 18o in tropical pacific coral skeletons reflects past el nino southern oscillation enso variability but the 18o enso relationship is poorly quantified uncertainties arise when constructing 18o data sets combining records from different sites and converting between 18o and sea surface temperature sst and salinity sss here we use seasonally resolved 18o from 1958 to 1985 at 15 tropical pacific sites to estimate these errors and evaluate possible improvements observational uncertainties from kiritimati new caledonia and rarotonga are 0 12 0 14 leading to errors of 8 25 on the typical 18o variance multicoral syntheses using five to seven sites capture the principal components pcs well but site selection dramatically influences enso spatial structure using sites in the eastern pacific western pacific warm pool and south pacific convergence zone spcz captures eastern pacific type variability while central pacific type events are best observed by combining sites in the warm pool and spcz the major obstacle to quantitative enso estimation is the 18o climate conversion demonstrated by the large errors on both 18o variance and the amplitude of the first principal component resulting from the use of commonly employed bivariate formulae to relate sst and sss to 18o errors likely arise from either the instrumental data used for pseudoproxy calibration or influences from other processes 18o advection atmospheric fractionation etc at some sites modeling seasonal changes to these influences reduces conversion errors by up to 20 this indicates that understanding of past enso dynamics using coral 18o could be greatly advanced by improving 18o forward models

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

great barrier reef coral luminescence reveals rainfall variability over northeastern australia since the 17th century 1 northeast tropical queensland rainfall is concentrated in the summer half year and characterized by high interannual variability partly related to el nino southern oscillation enso events this results in highly variable river flows affecting nearshore coral reefs of the great barrier reef australia freshwater flood events are recorded in long lived annually banded massive coral skeletons as luminescent lines quantitative measurements of luminescence intensity were made for 20 porites coral cores from nearshore reef sites between 11 s and 23 s seventeen of the coral luminescence series were significantly correlated with an instrumental record of northeast queensland summer rainfall and were used to develop seven significantly calibrated and verified rainfall reconstructions based on between 17 starting 1891 and 1 starting 1639 coral series the longest reconstruction based on more than one coral provides insights into northeast queensland rainfall variability from the late 17th century comparisons with various independent climate proxies are equivocal the magnitude and significance of relationships with for example a proxy enso index vary through time an extended drier period reconstructed from approximately the 1760s to the 1850s is associated with lower interannual rainfall variability since the late 19th century average rainfall and its variability have significantly increased with wet and dry extremes becoming more frequent than in earlier centuries this suggests that a warming global climate maybe associated with more variable tropical queensland rainfall

may september precipitation in the bhutan himalaya since 1743 as reconstructed from tree ring cellulose δ18o 1 we developed a 50 year tree ring 18o chronology for each of three tree species juniperus indica larix griffithii and picea spinulosa using a total of 12 trees four trees per species from the bhutan himalaya despite originating from different species sampled at two different altitudes the 18o chronologies are highly correlated with one another r 0 76 0 89 response analyses reveal that tree ring 18o values are controlled mainly by summer precipitation irrespective of species based on these results a robust 269 year 18o chronology was established to reconstruct the amount of may september precipitation based on data from four larch trees our tree ring 18o data show significant correlations with those from other regions of the himalaya and the tibetan plateau indicating that common signals related to monsoon activity are recorded in the data however at centennial timescales our data from bhutan show normal conditions during the 20th century whereas records from sites in western nepal and the southern eastern tibetan plateau show weakening trends in monsoon intensity during the last 100 200 years the weakening trends may be the result of a reduction in the meridional sea surface temperature gradient in the indian ocean during this time at continental scales the tree ring records show that areas more from ocean basins are particularly sensitive to reduced monsoon circulation correlation analyses suggest that the el nino southern oscillation enso plays an important role in modulating summer precipitation however the teleconnected relationship disappears during the period 1951 1970 coinciding with a negative phase of the pacific decadal oscillation pdo implying interdecadal modulation of the pdo on the influence of the enso on precipitation in bhutan

resolving seasonality in tropical trees multi decade high resolution oxygen and carbon isotope records from indonesia and thailand abstract dendrochronological techniques have found limited applications in the tropics because of invisible or indistinct banding in wood the seasonal cycles of rainfall and relative humidity in these regions while not sufficient to produce distinct visible rings may still generate seasonal signals in the oxygen isotopic composition of tree cellulose which can be used for climate reconstruction and chronology we explore this approach using trees from indonesia and thailand from three different families multi decade 18o records from javanese cross dated teak rings and bomb radiocarbon dated suar wood lacking visible rings demonstrate the reproducibility of the signal between trees grown at the same locality as well as from wider geographical regions these results confirm predictions that the trees oxygen isotopic signatures reflect an external climatic forcing high resolution 18o records reveal large seasonal cycles up to 4 for javanese suar samples and up to 18 for a thai podocarpus sample we show that the six 18o and 13c cycles measured on a podocarpus match the number of growth years for the period spanning the time of wounding and cutting of the wedge section this result demonstrates that the isotopic cycles found in this tree with indistinct annual rings are indeed seasonal and could be used for chronology we present evidence that stable isotope chronologies of tropical trees also contain insights in tropical tree physiology and growth dynamics

early marine diagenesis in corals and geochemical consequences for paleoceanographic reconstructions detecting the potential geochemical consequences of early marine diagenesis is essential for establishing the validity of past climate reconstructions from coral we present coral skeletal 18o and sr ca data for two long coral cores spanning 1839 1994 ad at ningaloo reef western australia one of which includes significant secondary precipitation of marine inorganic aragonite long term trends in reconstructed sea surface temperatures ssts for the well preserved coral correlate strongly with instrumental sst records spanning the 20th century in contrast the 18o and sr ca for the diagenetically altered coral give identical cool sst anomalies of 4 5 c as a consequence of the addition of secondary aragonite enriched in 18o and sr our results indicate that cross checking of paleoclimate reconstructions with two supposedly independent paleothermometers may not be valid and that coral records showing cooler ssts in the past need to be interpreted with caution furthermore modern coral records with long term trends in 18o indicating recent warming and freshening of the ocean can be potentially explained by early marine diagenesis

the stable oxygen and carbon isotopic record from a coral growing in florida bay a 160 year record of climatic and anthropogenic influence abstract a 160 year record of skeletal 13 c and 18 o was examined in a specimen of the coral solenastrea bournoni growing in florida bay variations in the 18 o of the skeleton can be correlated to changes in salinity while changes in the 13 c reflect cycling of organic material within the bay based on the correlation between salinity and skeletal 18 o we have concluded that there has been no long term increase in salinity in this area of florida bay over the past 160 years using salinity correlations between the various basins obtained from instrumental data we have been able to extend our interpretations to other parts of florida bay reaching similar conclusions in contrast to current ideas which have focused on changes in florida bay water quality over the past 20 yr history of the bay as causative in its decline we have determined that changes in water quality in this basin were already set in motion between 1905 and 1912 by the construction of the florida east coast railway from miami to key west the construction of the railway resulted in the restriction of the exchange of water between the florida reef tract and the gulf of mexico causing florida bay to become more eutrophic evidence of this process is observed in the sudden shift to relatively lower 13 c values coincident with railway construction natural events also appear to have influenced the water in the bay between 1912 and 1948 frequent hurricanes had the effect of increasing exchange of water between the bay and reef tract and removing large quantities of organic rich sediments however since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions

intercomparison of coral oxygen isotope data and historical sea surface temperature sst potential for coral based sst field reconstructions we examine the extent to which the large scale features of the sea surface temperature sst anomaly field are represented by a sparse observational network of coral oxygen isotope 18o time series regression of annually averaged 18o data against gridded estimates of local sst anomaly within the period 1856 1990 confirm the literature regression of 18o anomaly on sst anomaly for indo pacific corals however while interannual sst variability is generally well represented by individual coral time series observed decadal and secular variability does not always display a linear relationship to local sst anomaly instead many records appear to better recover nonlocal large scale phenomena which in turn are related to either the coral local sst or sst covariant changes in seawater 18o we employ empirical orthogonal function eof analysis to identify common patterns of variability in the coral data we find two significant patterns which are interpretable as the oceanographic signature of the el nino southern oscillation enso and as a near global warming in which the eastern equatorial pacific cools a third pattern weakly resembles the pacific decadal oscillation these modes are seen more clearly in a singular vector decomposition svd of the covariance between the coral data and the dominant patterns of large scale historical sst variability the results are consistent with those found in eof and svd analyses of sst data from the coral locations as additional coral based proxy estimates become available they will improve the resolution of the patterns recovered these results suggest that a sparse network of coral data may be used to reconstruct interannual secular and decadal sst variability for preinstrumental periods albeit with large uncertainty

vertical sorting and the morphodynamics of bed form dominated rivers a modeling framework uncertainties and errors in predictions by morphodynamic models of rivers with nonuniform sediment are usually attributed to shortcomings pertaining to the submodel of sediment transport this mistakenly neglects shortcomings in the submodel of sediment continuity which describes the vertical sorting and the bed surface composition whereas the latter is one of the main input parameters for calculating sediment transport and thus morphological changes hirano 1971 1972 was the first to develop a sediment continuity model for nonuniform sediment since this commonly used hirano active layer model and its variants suffer from a number of shortcomings the authors have developed a new type of sediment continuity model that describes the bed composition and vertical sorting fluxes without distinguishing discrete bed layers this continuum sorting model is aimed at conditions dominated by bed forms and bed load transport it is based on 1 the parker paola leclair framework for sediment continuity 2 the einstein step length formulation 3 a newly developed lee sorting function and 4 a newly developed method to account for the variability in bed form trough elevations the resulting model is deterministic in the computation of the vertical sorting profile and is probabilistic in terms of the riverbed surface due to the presence of dunes

improving coral base paleoclimate reconstructions by replicating 350years of coral sr ca variations abstract coral based climate reconstructions are typically based on a single record and this lack of replication leads to questions in regards to chronology accuracy and reliability of the inclusive geochemical variations to record climate viability here we present two multi century coral sr ca records recovered from a porites lutea colony offshore of amedee island new caledonia 22 28 8 s 166 27 9 e the chronology was developed by cross dating the coral sr ca time series and verifying the chronology with high precision absolute 230th dating we identify chronological discrepancies of 2 3 and 3 7 years century 1 for reconstructions based on a single core with uncertainty increasing after 250 years we assess the impact of porites skeletal architecture on coral geochemistry by characterizing centimeter scale architectural structures with respect to sampling optimal sampling paths are those on the slab surface parallel to the growth direction of individual corallites along the central axis of an actively extending corallite fan coral sr ca time series extracted from optimal skeletal structures are highly reproducible with a mean absolute difference of 0 021 mmol mol 1 or 0 39 c for monthly determinations suboptimal skeletal architecture is characterized by corallites extending through the slab surface and the coral sr ca determinations derived from suboptimal paths tend to produce a warm bias that varies between 0 04 and 2 30 c disorganized skeletal architecture is characterized by small terminating or unclear corallite fans that produce a cold bias of 0 11 to 2 45 c in coral sr ca determinations these problematic architecture types also produce biases in coral 18o determinations but to a lesser extent we assess the impact of sampling a coral colony along paths that vary from vertical to horizontal in large and small porites colonies with extension rates 6 mm year 1 and we determine there is no significant difference in the coral sr ca records

seismic imaging and velocity analysis for an alberta foothills seismic survey seismic imaging of complex structures from the western canadian foothills can be achieved by applying the closely coupled processes of velocity analysis and depth migration for the purposes of defining these structures in the shaw basing area of western alberta we performed a series of tests on both synthetic and real data to find optimum imaging procedures for handling large topographic relief near surface velocity variations and the complex structural geology of steeply dipping formations to better understand the seismic processing problems we constructed a typical foothills geological model that included thrust faults and duplex structures computed the model responses and then compared the performance of different migration algorithms including the explicit finite difference f x and kirchhoff integral methods when the correct velocity was used in the migration tests the f x method was the most effective in migration from topography in cases where the velocity model was not assumed known

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

decadal sea surface temperature variability in the subtropical south pacific from 1726 to 1997 a d we present a 271 year record of sr ca variability in a coral from rarotonga in the south pacific gyre calibration with monthly sea surface temperature sst from satellite and ship measurements made in a grid measuring 1 degrees by 1 degrees over the period from 1981 to 1997 indicates that this sr ca record is an excellent proxy for sst comparison with sst from ship measurements made since 1950 in a grid measuring 5 degrees by 5 degrees also shows that the sr ca data accurately record decadal changes in sst the entire sr ca record back to 1726 shows a distinct pattern of decadal variability with repeated decadal and interdecadal sst regime shifts greater than 0 75 degrees c comparison with decadal climate variability in the north pacific as represented by the pacific decadal oscillation index 1900 1997 indicates that several of the largest decadal scale sst variations at rarotonga are coherent with sst regime shifts in the north pacific this hemispheric symmetry suggests that tropical forcing may be an important factor in at least some of the decadal variability observed in the pacific ocean

toward forward modeling for paleoclimatic proxy signal calibration a case study with oxygen isotopic composition of tropical woods a forward model of the oxygen isotopic composition 18o of wood cellulose is parameterized for time series prediction in tropical environments and driven with meteorological data observed at la selva biological research station costa rica for 1985 2001 monthly resolution model results correlate modestly r 0 34 p 0 05 with observed isotopic data with higher correlation r 0 45 p 0 01 over the earliest 10 years of comparison and nonsignificant correlation over the most recent 6 years of record analysis of model output for la selva suggests that isotopic variations are strongly controlled by rainfall amount the model simulates an analogous but stronger than observed negative isotopic anomaly associated with positive july september rainfall anomalies during el nino southern oscillation enso warm phase event years simulated tree isotope data for the global tropics suggest that a network of well replicated data series from selected locations may resolve the large scale precipitation anomaly pattern associated with enso

a 400 year record of hydroclimate variability and local enso history in northern southeast asia inferred from tree ring δ18o abstract we present here a chronology of tree ring cellulose 18 o for the period 1588 2002 based on individual measurements of seven fokienia hodginsii trees growing in northern laos response function analysis of meteorological data revealed that this oxygen isotope chronology has a significant negative correlation with monsoon season precipitation the water level of the mekong river and the palmer drought severity index pdsi our reconstructed monsoon season pdsi which accounts for 41 5 of pdsi variance showed that wetter phases occurred during the periods ad 1660 1695 and ad 1705 1790 that the main drier periods were ad 1630 1660 ad 1900 1940 and ad 1954 2002 and that there has been a trend of decreasing moisture during the monsoon season over the last 200 years a reduction in monsoon activity can also be seen in various tree ring oxygen isotope records from the himalaya tibet plateau and southeast asia rising sea surface temperatures over the tropical pacific and indian ocean could be responsible for this reduction in the asian summer monsoon by combining proxies sensitive to the el nino southern oscillation enso in northern laos and vietnam we were able to reconstruct the annual multivariate enso index mei and local enso event history and so improve our understanding of long term variations in enso and its influences on southeast asia

a coral based reconstruction of sea surface salinity at sabine bank vanuatu from 1842 to 2007 ce climate variability associated with the el nino southern oscillation enso results in large sea surface temperature sst and sea surface salinity sss anomalies in many regions of the tropical pacific ocean we investigate interannual changes in sss driven by enso in the southwestern pacific at sabine bank vanuatu sbv 166 04 e 15 94 s using monthly variations in coral 18o from 1842 to 2007 ce we develop and apply a coral 18o sss transfer function which is assessed using a calibration verification exercise 1970 2007 ce the 165 year reconstructed sss record contains a prominent trend toward freshening from 1842 to 2007 ce mean sss for 1842 1872 ce is 35 46 0 28 psu which contrasts with a mean value of 34 85 0 31 psu for 1977 2007 ce with a freshening trend during the latter part of the 20th century that is not unprecedented with respect to the overall record variance in the record is concentrated in the interannual 42 and interdecadal 29 bands the sbv sss record matches well with a similarly reconstructed sss time series at malo channel vanuatu which is located 120 km to the east of sbv this regional signal is likely driven by enso related changes in the spcz and interdecadal changes in surface water advection the pattern of interdecadal variability at sbv agrees reasonably well with coral records of interdecadal variability from fiji and tonga especially in the pre 1940 portions of the records further evidence for the regional extent of the salinity signal at sabine bank vanuatu

unprecedented pressure increase in deep magma reservoir triggered by lava dome collapse 1 the collapse of the soufriere hills volcano lava dome on montserrat in july 2003 is the largest such event worldwide in the historical record here we report on borehole dilatometer data recording a remarkable and unprecedented rapid 600s pressurisation of a magma chamber triggered by this surface collapse the chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site by analyzing the strain data and using added constraints from experimental petrology and long term edifice deformation from gps geodesy we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 mpa and average radius 1 km pressurisation is attributed to growth of 1 3 of gas bubbles in supersaturated magma triggered by the dynamics of surface unloading recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude

a multiproxy index of the el nino southern oscillation a d 1525 1982 1 an understanding of past variability in the el nino southern oscillation enso on interannual interdecadal and longer time scales would be useful in assessing recent observed changes to enso and in determining the realism of climate model simulations using tree ring coral and ice core data we reconstruct a proxy based enso index between a d 1525 and 1982 unlike most previous studies which have drawn climate proxies from limited geographic regions our network is pacific basin wide using enso sensitive proxies from the western equatorial pacific new zealand the central pacific and subtropical north america by considering multiple teleconnection regions this network provides a more robust proxy enso signal the common signal recorded in the multiproxy network has a high correlation with the southern oscillation index soi nino 3 4 sea surface temperature nino3 4 sst and a combined ocean atmosphere enso index cei the proportion of instrumental variance explained is 47 for the soi 48 for nino3 4 sst and 52 for the cei the proxy enso index also displays skill in reproducing warm and cold extremes of the soi the proxy enso index over the last 450 years shows considerable amplitude and frequency modulation in the 3 10 year band on multidecadal time scales there is a relative reduction in the amplitude of high frequency variability during the sixteenth early seventeenth and mid eighteenth centuries in contrast high frequency enso variability has increased over the last 200 years variability during the first half of the twentieth century is similar to that evident in the nineteenth century

a model to predict the evolution of a gravel bed river under an imposed cyclic hydrograph and its application to the trinity river 1 major changes in the morphology of the trinity river in california such as narrowing of the cross section and sedimentation of fine sediment in pools occurred after the closure of a system of dams these changes caused a dramatic reduction in the salmonid population and a resulting decline of the fishery gravel augmentation regulated flood releases and mechanical channel rehabilitation are currently being implemented to help restore the aquatic habitat of the river the present paper describes a tool named the spawning gravel refresher for designing and predicting the effects of gravel augmentation in gravel bed rivers the tool assumes an imposed cycled hydrograph the model is calibrated and applied to the regulated reach of the trinity river in four steps 1 zeroing runs to reproduce conditions of mobile bed equilibrium as best can be estimated for the predam trinity river 2 runs to compare the predictions with the results of previous studies 3 runs at an engineering time scale to reproduce the effects of the dams and 4 runs to design gravel augmentation schemes in the fourth group of runs the combined effects of engineered flood flow releases and gravel augmentation are predicted at an engineering time scale the model indicates that the fraction of fine sediment in the surface layer and in the topmost part of the substrate should decrease when subjected to these two restoration measures with a consequent improvement of the quality of the spawning gravel

enhanced multidecadal climate variability in the seventeenth century from coral isotope records in the western indian ocean 1 the slowly growing coral diploastreaheliopora affords a novel opportunity to obtain multicentury records of paleoclimate including details of the interannual rhythms associated with the el nino southern oscillation enso system we examine climate variability in an enso teleconnected region using new oxygen isotope records from d heliopora spanning most of the twentieth 1896 1998 and seventeenth 1622 1722 centuries from the mafia archipelago tanzania the modern record demonstrates coherency with relevant instrumental and proxy time series documents twentieth century warming and displays significant power at enso periodicities the seventeenth century record lacks any trend exhibits interannual variance comparable to the modern record and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records we find no clear evidence of solar irradiance influence on interannual variability in the western indian ocean during these intervals although the mean sea surface temperature appears to vary inversely with insolation

prestack kirchhoff time migration of 3d coal seismic data from mining zones conventional seismic data processing methods based on post stack time migration have been playing an important role in coal exploration for decades however poststack time migration processing often results in low quality images in complex geological environments in order to obtain high quality images we present a strategy that applies the kirchhoff prestack time migration pstm method to coal seismic data in this paper we describe the implementation of kirchhoff pstm to a 3d coal seam meanwhile we derive the workflow of 3d kirchhoff pstm processing based on coal seismic data the processing sequence of 3d kirchhoff pstm includes two major steps 1 the estimation of the 3d root mean square rms velocity field 2 kirchhoff prestack time migration processing during the construction of a 3d velocity model dip moveout velocity is served as an initial migration velocity field we combine 3d kirchhoff pstm with the continuous adjustment of a 3d rms velocity field by the criteria of flattened common reflection point gathers in comparison with post stack time migration the application of 3d kirchhoff pstm to coal seismic data produces better images of the coal seam reflections

comparison of kirchhoff and reverse time migration methods with applications to prestack depth imaging of complex structures the performance of two popular migration methods the kirchhoff integral and reverse time migrations is evaluated through applications to imaging complex structures using prestack shot records the migration results from the marmousi model data demonstrate that reverse time migration is more accurate than kirchhoff migration in imaging the steeply dipping faults however the improved accuracy of reverse time migration requires higher computational costs in the application to the alberta foothills data where a good estimate of the velocity model is available however both the kirchhoff and the reverse time migration methods produce almost identical results this implies that in the real world of exploration seismology it will be relatively difficult to identify which method performs better because we never know the exact answer of the subsurface

a fiji multi coral δ18o composite approach to obtaining a more accurate reconstruction of the last two centuries of the ocean climate variability in the south pacific convergence zone region the limited availability of oceanographic data in the tropical pacific ocean prior to the satellite era makes coral based climate reconstructions a key tool for extending the instrumental record back in time thereby providing a much needed test for climate models and projections we have generated a unique regional network consisting of five porites coral 18o time series from different locations in the fijian archipelago our results indicate that using a minimum of three porites coral 18o records from fiji is statistically sufficient to obtain a reliable signal for climate reconstruction and that application of an approach used in tree ring studies is a suitable tool to determine this number the coral 18o composite indicates that while sea surface temperature sst variability is the primary driver of seasonal 18o variability in these fiji corals annual average coral 18o is more closely correlated to sea surface salinity sss as previously reported our results highlight the importance of water mass advection in controlling fiji coral 18o and salinity variability at interannual and decadal time scales despite being located in the heavy rainfall region of the south pacific convergence zone spcz the fiji 18o composite presents a secular freshening and warming trend since the 1850s coupled with changes in both interannual ia and decadal interdecadal d i variance the changes in ia and d i variance suggest a re organization of climatic variability in the spcz region beginning in the late 1800s to period of a more dominant interannual variability which could correspond to a southeast expansion of the spcz

diagenesis in live corals from the gulf of aqaba i the effect on paleo oceanography tracers abstract the effect of early diagenesis on trace element abundance in coral skeleton was studied in live coral heads porites from the nature reserve reef nrr elat gulf of aqaba northern red sea petrography of the corals shows diagenetic features of dissolution recrystallization and secondary aragonite precipitation pore filling which are most extensive in the oldest part of the coral coral porewaters were extracted with a special setup and were analyzed for chemical composition the total alkalinity and sr deficit in pore water as compared to reef water is consistent with both precipitation of secondary aragonite and recrystallization of primary skeleton the present rate constant of pore filling by secondary aragonite was estimated by a water replacement experiment to be 0 0015 y 1 which equals to pore filling rate of 1 5 0 3 kg aragonite per year the corals show clear seasonal fluctuations in sr ca ratios that are interpreted as reflecting changes in sea surface temperature sst yet the secondary aragonite is characterized by a significantly higher sr ca ratio than the average ratio in primary aragonite thus measuring a mixed sample of pristine and secondary aragonite may produce erroneous about 2 c lower sst estimates by the sr ca thermometers it appears that the sr ca ratio a major proxy for paleo environmental marine studies is sensitive to subtle pore filling and replacement of the original coral matrix by secondary aragonite in the marine environment

tracking the extent of the south pacific convergence zone since the early 1600s 1 the south pacific convergence zone spcz is the largest and most persistent spur of the intertropical convergence zone at the southeastern edge of the spcz near 170 w and 15 20 s a surface ocean salinity frontal zone exists that separates fresher western pacific warm pool water from saltier and cooler waters in the east this salinity front is known to shift east and west with the phase of the el nino southern oscillation we have generated subannually resolved and replicated coral oxygen isotopic time series from fiji 17 s 179 e and rarotonga 21 5 s 160 w that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front and eastern extent of the spcz has shifted east west through 10 to 20 of longitude three times during this interval the most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the spcz since the mid 1800s the expansion of the spcz implies a gradual change in the south pacific to more la nina like long term mean conditions this observation is consistent with the ocean thermostat mechanism for the pacific coupled ocean atmosphere system whereby exogenous heating of the atmosphere would result in greater warming in the western pacific and a greater east west surface temperature gradient components 8034 words 7 figures 2 tables

a strategy to improve the contribution of coral data to high resolution paleoclimatology abstract various geochemical tracers measured in massive coral skeletons have the potential to compliment other sources of high resolution proxy climate information e g tree rings ice cores by providing paleoclimatic data from shallow water tropical ocean regions twenty previously published coral records 19 18o and one sr ca series between 54 and 346 years in length were examined for their local and larger scale relationships el nino southern oscillation with climate series were examined in a consistent manner over the same time periods and relationships were tested for stability through time the results demonstrate a spectrum of climatic interpretation ranging from 1 no significant relationship of the coral record with either local or larger scale climate variables 2 significant relationship of the coral record with climate but the relationship is not stable through time and 3 the coral record shows a significant and temporally stable relationship with climate which explains a significant and useful proportion of climate variance it is concluded that reliance to date on analyzing only one long coral core from a site has prevented identification of coral records or parts of coral records where non climatic factors are dominating the geochemical signal various factors may cause these non climatic signals to dominate more process studies into how corals of particular species with various growth rates and from various environmental settings incorporate geochemical tracers into their skeleton are required to understand exactly what is being measured in addition it is recommended that some level of replication ideally three separate corals of geochemical tracers will ensure accurate dating of the record identification of periods when non climatic factors dominate and thus enhance the reliability of the paleoclimatic record such an approach will allow the rich archive of environmental information contained in massive coral skeletons to make a significant contribution to high resolution paleoclimatology and improve our understanding of the nature and causes of past climate variability

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

ambiguity in analysis of velocity and depth velocity analysis methods generally involve an analysis of the traveltime moveout of seismic events to investigate ambiguities for such methods we can start with a simple single layer model and investigate the uncertainty in the estimation of velocity and reflector depths this analysis will show that the velocity depth ambiguity is dependent on the offset depth ratio and on the accuracy of traveltime picks

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

interpretation validation on vertically exaggerated reflection seismic sections abstract reflection seismic data is usually displayed with a vertical exaggeration factor in the range 2 6 irrespective of whether it is time or depth domain data this vertical exaggeration gives certain advantages to stratigraphic and structural interpretation and is sometimes a prerequisite to view long wavelength structures however vertical exaggeration distorts geological structures affecting dip curvature line length cross sectional area volume and angular relationships reflection seismic can be assigned a vertical exaggeration heterogeneity factor based on the extremes of seismic velocities in the absence of appreciable poorly compacted units and bathymetry and generally on depth domain data vertical exaggeration is relatively homogeneous analytical solutions are derived to quantify the distortion of angular relationships curvature and bed thickness under homogeneous vertical exaggeration modelled extensional and compressional geometries give acceptable area balance restorations using vertical shear under homogeneous vertical exaggeration these vertically exaggerated restorations are neither admissible nor viable because the deformed and restored state sections are unrealistic given low heterogeneity of vertical exaggeration and relatively simple structure that typifies many extensional geometries and some thrust geometries aspect ratios of 1 1 are not definitively required for section validation by restoration

estimating and interpreting velocity uncertainty in migrated images and avo attributes estimating a suitable velocity field for use in prestack depth migration is inherently uncertain because of limitations on the available data and estimation techniques this uncertainty affects both the migrated depth of structures and their amplitudes in the inverted images these effects can be estimated by performing multiple migrations with a set of velocity fields and colocating features in the migrated images this lets us examine the imaging procedure s sensitivity to changes in the velocity field so we can assess both structural and amplitude uncertainties in migrated images these two types of uncertainties affect interpretation in different ways for instance with structural uncertainty interpretation we consider the change in migrated location of structures when deciding on drilling locations optimizing well trajectories or computing uncertainty in volumetric calculations with amplitude uncertainty or amplitude versus offset avo uncertainty interpretation we consider 1 uncertainty in c

subtropical coral reveals abrupt early twentieth century freshening in the western north pacific ocean instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century unlike for temperature continuous salinity observations in the surface ocean are scarce prior to 1970 and the magnitude of salinity changes during the twentieth century is largely unknown surface ocean salinity is a major component in climate dynamics as it influences ocean circulation and water mass formation here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical north pacific ocean since 1873 based on bimonthly records of 18o sr ca and u ca in a coral from the ogasawara islands the reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910 observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the kuroshio current system and the associated subtropical gyre circulation we note that the abrupt early twentieth century freshening in the western subtropical north pacific precedes abrupt climate change in the northern north atlantic by a few years the potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades

investigation of sea surface temperature changes from replicated coral sr ca variations in the eastern equatorial pacific clipperton atoll since 1874 abstract sub seasonally resolved and replicated coral sr ca time series at clipperton atoll 10 18 n 109 13 w in the eastern pacific are assessed as a sea surface temperature sst proxy in this region with small seasonal sst variability the composite coral sr ca time series is a partially replicated record of three live and one sub modern colony of porites lobata extending back to 1874 large inter colony coral sr ca offsets equate to relative sst differences of 0 6 to 4 3 c and limit the ability to reconstruct absolute sst changes moreover the replication method revealed a 12 year section of growth in one colony where mean sr ca was anomalously low 1 c higher sst relative to the other colonies without evidence of diagenesis or other significant skeletal alterations the presence of this anomalous interval supports the need for multi coral sr ca replication in specific sites or regions the clipperton composite sr ca anomaly record is significantly coherent r 0 71 0 76 p

a mechanism for the recurrence of wintertime midlatitude sst anomalies abstract in the early 1970s namias and born speculated that ocean temperature anomalies created over the deep mixed layer in winter could be preserved in the summer thermocline and reappear at the surface in the following fall or winter this hypothesis is examined using upper ocean temperature observations and simulations with a mixed layer model the data were collected at six ocean weather stations in the north atlantic and north pacific concurrent and lead lag correlations are used to investigate temperature variations associated with the seasonal cycle in both the observations and the model simulations concurrent correlations between the surface and subsurface temperature anomalies in both the data and the model indicate that the penetration of temperature anomalies into the ocean is closely tied to the seasonal cycle in mixed layer depth high correlations extend to relatively deep shallow depths in winter summer lead lag correlations in both the data and the model at some of the stations

effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals abstract the integrity of coral based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post depositional alteration on coral skeletal geochemistry here we combine millimeter scale and micro scale coral sr ca data scanning electron microscopy sem images and x ray diffraction with previously published 18o records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub fossil corals from the central tropical pacific in a 40 year old modern coral we find secondary aragonite is associated with relatively high coral 18o and sr ca equivalent to sea surface temperature sst artifacts as large as 3 and 5 c respectively secondary aragonite observed in a 350 year old fossil coral is associated with relatively high 18o and sr ca resulting in apparent paleo sst offsets of up to 2 and 4 c respectively secondary ion mass spectrometry sims analyses of secondary aragonite yield sr ca ratios ranging from 10 78 to 12 39 mmol mol significantly higher compared to 9 15 0 37 mmol mol measured in more pristine sections of the same fossil coral widespread dissolution and secondary calcite observed in a 750 year old fossil coral is associated with relatively low 18o and sr ca sims sr ca measurements of the secondary calcite 1 96 9 74 mmol mol are significantly lower and more variable than sr ca values from more pristine portions of the same fossil coral 8 22 0 13 mmol mol our results indicate that while diagenesis has a much larger impact on sr ca based paleoclimate reconstructions than 18o based reconstructions at our site sims analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of sr ca which can be used to derive paleo ssts

el nino variability in simple ocean data assimilation soda 1871 2008 1 a new ocean reanalysis that covers the period from 1871 to 2008 is used to explore the time evolving characteristics of el nino the new reanalysis assimilates all available hydrographic and sea surface temperature data into a model of the global ocean forced with surface boundary conditions from an atmospheric reanalysis that also covers the period from 1871 through 2008 using traditional measures of el nino our reanalysis shows that the timing of el nino events is in agreement with sea surface temperature reconstructions but el nino in the reanalysis is stronger particularly from 1871 to 1920 a new index based on the first moment of the temperature anomaly is introduced the new index is used to characterize the strength and location of el nino events and has the advantage that it is independent of the location of el nino using the new index el nino in the reanalysis shows prominent decadal variability of strength but relatively little long term trend el nino events were strong in the last part of the 19th century and first part of the 20th century and again in the latter part of the 20th century with weak el nino events in the middle of the 20th century the location of el nino also varies considerably ranging from the western to the eastern pacific near the coast of south america however the null hypothesis that the location of el nino can be represented as a random distribution about a central longitude of about 140 w cannot be rejected

environmental control of the oxygen isotope composition of porites coral microatolls abstract understanding the influence of climatic and non climatic factors on geochemical signals in corals is critical for assessing coral derived records of tropical climate variability porites microatolls form large disk shaped colonies constrained in their upward growth by exposure at or close to mean spring low water level and occur on indo pacific reefs microatolls appear suitable for paleoclimate reconstruction however the systematics of the microatoll chemistry climate relationship are yet to be characterized in this study the 18o signal in porites microatolls from well flushed reef flats on kiritimati christmas island central pacific was investigated for intra coral growth aspect and extension rate effects and between coral effects and to explore the climate signal contained within their skeletons samples for 18o analysis were taken from six individual transects from different positions within porites microatoll xm22 the results show that 1 the average standard deviation for the mean 18o values of transects that represent the same time periods is 0 03 and is within measurement error for a single analysis 0 04 2 the average standard deviation for time equivalent near monthly samples along the transects within the same microatoll is 0 07 and 3 comparison of the average 18o values of records for different microatolls from across kiritimati island show only a small between coral differences of 0 04 and 0 11 for different time periods these differences in mean 18o are within the range for intra and inter colony differences in seasonal and interannual 18o reported for dome shaped porites based on these results a stacked microatoll 18o record was constructed for the period 1978 2007 for comparison with published coral 18o records for nearby dome shaped porites there is a systematic offset between the two types of records which is probably due to variations in 18o seawater across kiritimati island despite the offset all records show similar amplitudes for the seasonal cycle of 18o and there is a strong correlation r 0 71 between microatoll 18o and local sea surface temperature sst the 18o sst slope relationship for microatolls is 0 15 c very similar to that reported for fast growing domed corals 0 18 to 0 22 c statistical analysis of the stacked microatoll 18o record shows that it is correlated with both local and large scale climate variables primarily sst at semiannual annual and interannual timescales our results show that the signal reproducibility and fidelity of skeletal 18o in coral microatolls is comparable to that observed for more conventional coral growth forms longer lived and fossil porites microatolls where they have grown in suitably flushed environments are likely to contain 18o signals that can significantly extend instrumental records of tropical climate variability

variation of initial 230th 232th and limits of high precision u th dating of shallow water corals one hundred eighty u th data including 23 isochrons on 24 pristine modern and holocene corals and 33 seawater samples were analyzed using sector field mass spectrometry to understand the variability of initial 230th 232th 230th 232th0 this dataset allows us to further assess the accuracy and precision of coral 230th dating method by applying quality control including careful sampling and subsampling protocols and the use of contamination free storage and workbench spaces the resulting low procedural blanks give an equivalent uncertainty in age of only 0 2 0 3 yr for 1 2 g of coral sample using site specific 230th 232th0 values or isochron techniques our study demonstrates that corals with an age less than 100 yrs can be 230th dated with precisions of 1 yr six living subtidal coral samples were collected from two continental shelf sites nanwan off southern taiwan in the western pacific and son tra off central vietnam in the south china sea one coral core was drilled from an open ocean site santo island vanuatu in the western tropical pacific and modern and fossil intertidal coral slabs 17 in total were cut from six sites around the islands of simeulue lago north pagai and south pagai of sumatra in the eastern indian ocean the results indicate that the main source of thorium is the dissolved phase of seawater with variation of 230th 232th0 depending on local hydrology with intense input of terrestrial material low 230th 232th0 atomic ratios of 4 9 10 6 and 3 2 10 6 with a 10 variation are observed in nanwan and son tra respectively at the santo site we find a value of 5 6 10 6 at 4 horizons and one high value of 24 10 6 in a sample from ad 1974 6 0 5 likely due to the upwelling of cold water during a la nina event between ad 1973 and 1976 the natural dynamics of 230th 232th0 recorded in the intertidal corals at sites in the sumatran islands are complicated so that this value varies significantly from 3 0 to 9 4 10 6 three of the 141 modern coral 230th ages differ from their true ages by 23 to 4 indicating the presence of detrital material with anomalous 230th 232th values duplicate measurement of coeval subsamples is therefore recommended to verify the age accuracy this improved high precision coral 230th dating method raises the prospects of refining the age models for band counted and tracer tuned chronologies and of advancing coral paleoclimate research

evidence for stronger el nino southern oscillation enso events in a mid holocene massive coral we present a 47 year long record of sea surface temperature sst derived from sr ca and u ca analysis of a massive porites coral which grew at 4150 calendar years before present b p in vanuatu southwest tropical pacific ocean mean sst is similar in both the modern instrumental record and paleorecord and both exhibit el nino southern oscillation enso frequency sst oscillations however several strong decadal frequency cooling events and a marked modulation of the seasonal sst cycle with power at both enso and decadal frequencies are observed in the paleorecord which are unprecedented in the modern record

sensitivity analysis of seismic depth migrations depth migration is the processing step that can position seismic reflectors in their proper spatial locations beneath the earth9s surface accurate seismic imaging assists in structural interpretation and determination of optimum drilling locations there are many migration algorithms to perform this depth imaging step many of these algorithms and their applications to foothills data have been summarized by lines et al 1999 as mentioned by parkes and hatton 1987 most depth migration algorithms and seismic time measurements are quite accurate but to improve the migrated image greater emphasis needs to be placed on improving the accuracy of the input velocity field in addition a greater awareness of depth imaging errors due to velocity inaccuracy is crucial parkes and hatton 1987 state that depth migration uncertainty is primarily a result of the velocity field uncertainty used to map seismic data from time to space

velocity depth ambiguity in the dipping reflector case seismic or acoustic wave velocity is a vital parameter for processing and interpretation of seismic data various velocity analysis methods using traveltime moveout of seismic events have been described in literature in certain cases these methods provide ambiguous results hence there is a need to investigate velocity depth ambiguity in such cases

smiles and frowns in migration velocity analysis reliable seismic depth migrations require an accurate input velocity model inaccurate velocity estimates will distort point diffractors into smiles or frowns on a depth section for both poststack and prestack migrated sections high velocities cause deep smiles while low velocities cause shallow frowns on migrated gathers however for prestack images in the offset domain high velocities cause deep frowns while low velocities cause shallow smiles if the velocity is correct there will be no variation in the depth migration as a function of offset and no smiles or frowns in the offset domain we explain migration responses both mathematically and graphically and thereby provide the basis for depth migration velocity analysis

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia

interpretation of velocity estimates from coherency inversion velocity estimation by coherency inversion provides a velocity depth macro model of the subsurface the accuracy of this model is critical for imaging techniques such as depth migration and inversion therefore the reliability of seismic interpretation is strongly dependent on the accuracy of the derived model uncertainties in the velocity and depth estimates for the model can be calculated using a combination of the response surface technique and the dix equation in the layer stripping strategy the method takes into account the local errors connected mainly to the current layer and the global errors connected to the derived overburden examples using synthetic and real data show that the coherency inversion produces accurate macro models

mathematical analysis of the saint venant hirano model for mixed sediment morphodynamics sediment of different size are transported in rivers under the action of flow the first and still most popular sediment continuity model able to deal with mixed sediment is the so called active layer model proposed by hirano 1971 1972 in this paper we consider the one dimensional hydromorphodynamic model given by the saint venant equations for free surface flow coupled with the active layer model we perform a mathematical analysis of this model extending the previous analysis by ribberink 1987 including full unsteadiness and grainsize selectivity of the transported load by explicitly considering multiple sediment fractions the presence of multiple fractions gives rise to distinct waves traveling in the downstream direction for which we provide an analytical approximation of propagation velocity under any froude regime we finally investigate the role of different waves in advecting morphodynamic changes through the domain to this aim we implement an analytical linearized solver to analyze the propagation of small amplitude perturbations of the bed elevation and grainsize distribution of the active layer as described by the system of governing equations we find that initial gradients in the grainsize distribution of the active layer are able to trigger significant bed variations which propagate in the downstream direction at faster pace than the bed wave arising from the unisize sediment saint venant exner model we also verify that multiple sorting waves carry multiple associated bed perturbations traveling at different speeds

characterizing decadal to centennial variability in the equatorial pacific during the last millennium 1 the magnitude of sea surface temperature variability in the nino3 4 region of the equatorial pacific on decadal and longer timescales is assessed in observational data state of the art coupled model intercomparison project 5 climate model simulations and a new ensemble of paleoclimate reconstructions on decadal to multidecadal timescales variability in these records is consistent with the null hypothesis that it arises from multivariate red noise a multivariate ornstein uhlenbeck process generated from a linear inverse model of tropical ocean atmosphere dynamics on centennial and longer timescales both a last millennium simulation performed using the community climate system model 4 ccsm4 and the paleoclimate reconstructions have variability that is significantly stronger than the null hypothesis however the time series of the model and the reconstruction do not agree with each other in the model variability primarily reflects a thermodynamic response to reconstructed solar and volcanic activity whereas in the reconstruction variability arises from either internal climate processes forced responses that differ from those in ccsm4 or nonclimatic proxy processes that are not yet understood these findings imply that the response of the tropical pacific to future forcings may be even more uncertain than portrayed by state of the art models because there are potentially important sources of century scale variability that these models do not simulate