late quaternary arroyo formation and climate change in the american southwest arroyos entrenched ephemeral streams that form in desert environments first appeared in the arid and semiarid american southwest after 8000 14 c yr b p for at least 7 k y prior to that time climate vegetation and groundwater conditions were not conducive for arroyo formation along the floors of desert valleys after a hiatus in arroyo formation the frequency of arroyo cutting and filling increased dramatically after 4000 14 c yr b p the early holocene arroyos and increased frequency of arroyo incision after 4000 14 c yr b p are related to the establishment and changes in postglacial vegetation climate and groundwater conditions as a result arroyo sequences preserve a record of large scale climate change and small scale climatic perturbations that occurred during the holocene human modification of valley flood plains is an additional factor that contributed to mid nineteenth and early twentieth century arroyo cutting

hydraulic stability of rock armors in breaking wave conditions abstract armor layers of mound breakwaters are usually designed with empirical formulas based on small scale tests in non breaking wave conditions however most rubble mound breakwaters are constructed in the depth induced breaking zone where they must withstand design storms having some percentage of large waves breaking before reaching the structure in these cases the design formulas for non breaking wave conditions are not fully valid to characterize double layer rock armor damage in breaking wave conditions 2d physical model tests were carried out with a bottom slope m 1 50 in order to develop a simple method to determine the wave parameters in the depth induced breaking zone experimental wave measurements were compared to the numerical estimations given by the swanone model an analysis was conducted to select the best characteristic wave height to estimate rock armor damage when dealing with depth induced breaking waves the spectral significant wave height h m0 estimated at a distance of 3h s seaward from the structure toe was found to be the most adequate a new hydraulic stability formula is proposed for double layer rock armors in breaking wave conditions considering the observed potential 6 power relationship between the equivalent dimensionless armor damage and the h m0 at 3h s seaward distance from the structure toe

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

late quaternary alluvial stratigraphy of a low order tributary in central texas usa and its response to climate and sediment supply abstract this paper presents the first comprehensive late quaternary alluvial stratigraphic study of a low order tributary in central texas using cowhouse creek as a case study the late pleistocene jackson ja alluvium forms the elevated t2 terrace the entrenched holocene valley is filled with the buried georgetown gt alluvium approximately 11 000 to 8000 14 c yr b p and associated royalty paleosol and the surficially exposed fort hood fh alluvium approximately 7000 to 5000 14 c yr b p and west range wr alluvium approximately 4200 to 600 14 c yr b p forming the broad t1 terrace the ford fo alluvium 14 c yr b p forms the modern t0 floodplain entrenched into t1 conditioned by cooler and wetter climates cowhouse creek was characterized by relatively high base flow and low sediment supply during deposition of the ja and gt alluvium appreciable upland soil erosion ensued during the middle holocene in response to warmer climate conditions resulting in widespread valley filling by the fh alluvium deposition of the late holocene wr and f0 alluvium was characterized by diminished sediment storage during relatively stable climate conditions the temporal alluvial stratigraphic framework of the bedrock confined cowhouse creek valley is out of phase with the alluvial sequence in the larger brazos river valley

spatial variability of late pleistocene early holocene soil formation and its relation to early human paleoecology in northwest mexico abstract in sonora northwest mexico we have recognized the existence of paleosol units of late pleistocene early and middle holocene age 13 000 to 4 250 cal years bp at several archaeological sites with paleo indian occupations e g la playa fin del mundo el bajio el aigame and el arenoso the few paleoenviromental reconstructions from the region indicate that the end of the pleistocene was dominated by temperate climate that promoted the establishment of the first people in coexistence and interaction with the pleistocene megafauna the study of the spatial distribution of various soil units developed during late pleistocene in the region provides information about local environmental settings of the initial peopling of sonora several pedosedimentary sequences were analyzed in the different parts of sonora the age control in which was provided by archaeological and paleontological findings and or by the radiocarbon dating of carbonates and paleosol humus two trends of the late pleistocene pedogenesis have been identified the profiles located in the south center and north of the state are dominated by red soils earlier referred as big red in the archaeological literature whose characteristics are represented by the red san rafael paleosol srp the properties of srp in the lower part of the profile rubification clay accumulation hig magnetic susceptibility illuvial carbonates and redoximorphic features are indicative of a more humid environment above them is a late holocene polycyclic sequence of soils with morphological characteristics displaying a more incipient development in contrast with the sequence described above el arenoso north of caborca show a sequence of gray soils two paleosols were formed in alluvial sediments at the cantera profile ctp and el arenoso profile arp paleosols are represented by bgk horizons and evidence of weathering and clay neoformation redoximorphic processes and illuvial accumulation of carbonates we explain the differences of north western profiles by specific geomorphic conditions which imply limited soil drainage and the possibility of over wetting these processes indicate alternating a humid environment weathering rubification clay formation and redoximorphic processes and dry periods carbonates accumulation despite regional differences of the late pleistocene paleosols the comparison with the holocene soils demonstrates clear trends towards desertification in the region the first people that inhabited sonora during the late pleistocene found a more temperate and wetter climate than they encountered further to the north but subsequent generations witnessed a rapid desiccation of the region with the formation of the sonoran desert in the early holocene

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

soil geomorphology and wet cycles in the holocene record of north central mexico abstract the distinction between the impact of climatic periodicities or land use practices on soil erosion is an important issue for pre hispanic and colonial mexico that question can best be addressed by first documenting the dynamics of changing wet cycles during the holocene in the central mexican region between the northern limits of pre hispanic agriculture and its southern margins in northwestern chihuahua consequently the laguna project targeted a 125 000 km 2 sector of north central mexico 250 km from north to south and 500 km from east to west from saltillo to durango some 40 sedimentary profiles with multiple cumulic soils were studied in the field and laboratory supported by 163 conventional 14 c and ams dates on charcoal and soil humates we distinguish 1 wet floodplains with humic paleosols redox phenomena reflecting high water tables channel ponding sequences and interbedded tufas that imply aquifer recharge sustained base flow and mainly low energy conditions and 2 high energy pulses of discharge that mobilized cobble gravels or forced channel entrenchment gullying and were tied to episodic excessive rains that promoted valley and slope instability in between such wet cycles and recurrent disequilibrium events climate was similar to today probably less humid with limited geomorphologic change or slow soil formation wet cycles were rare at the end of the pleistocene but prominent during the holocene disequilibrium proxies became common and dramatic after 2500 bp the drainages from the eastern and western sierra madres responded in phase but varied in detail around ad 1050 1200 natural erosion led to loss of soil organic carbon as alternating severe droughts and heavy rains destroyed the ground cover and led to ecological aridification well before arrival of spanish miners and settlers the evidence that human activity triggered pre hispanic or colonial erosion in central mexico should therefore be re evaluated global comparisons and interpretations are discussed but with caution since no single theory can explain the whole of the record the soil geomorphology geoarchive of north central mexico primarily is an environmental history of alternating wet cycles rather than of sustained wet or dry climates the critical differences between soaking and excessive rains with their respective impacts may be due to switching between winter and summer storm categories

january and july simulations with a spectral general circulation model abstract we describe the results of january and july simulations carded out with a nine level spectral model employing a rhomboidal truncation at wavenumber 15 sea surface temperature sea ice distribution and solar zenith angle are held constant in each simulation the model includes interactive clouds and radiative processes after ramanathan et al 1983 selected fields are shown which highlight the model s strengths and weaknesses the latitude height distribution of the zonal wind is successfully simulated the model captures the separation between the wintertime westerly jets in the troposphere and stratosphere and thus simulates the sign reversal in the vertical wind shear across the jet axis in the upper troposphere in addition to the zonal wind we show also the zonally averaged temperature meridional wind and vertical velocity regional distributions of sea level pressure surface air temperature precipitation and a number of other fields defined at various pressure levels are compared in

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

paleoclimatic changes during the late pleistocene holocene in laguna babicora near the chihuahuan desert mexico the paleoclimatic variability of northern mexico since the late wisconsinan is determined from sedimentological geochemical and stratigraphic studies of the lacustrine sequence of laguna babicora 29 4 n 107 7 w elevation 2100 m asl chronological control is based on 13 radiocarbon dates 6 from this study and 7 previously reported from four stratigraphic profiles that cover a range from 16 342 to 2800 bp two major periods of increased humidity are recognized by lake level variation during the late wisconsinan and early holocene the late wisconsinan humid period may be related to jet stream migration to southerly latitudes and the influence of the mobile polar high this period has been identified in the sedimentary record of el diablo profile with a radiocarbon date of 16 342 201 bp the early holocene humid period is recorded in el diablo 10 976 115 bp and cano profiles 9614 130 bp it is interpreted as a result of the younger dryas climatic anomaly characterized by a temperature decrease and cold paleoclimatic conditions similar to those for the late wisconsinan the early holocene was followed by an overall gradual drying that reached a maximum around 6000 bp during the middle holocene for the late holocene evidence of widespread erosion sedimentation changes flooded surfaces and paleosoils indicates that laguna babicora was subjected to short term climatic changes

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

holocene aridification vegetation change sedimentation regime and limits of carbon isotope data as indicated by the alluvial pollen sites of arroyo grande and el molino in north central mexico abstract a multi proxy record of palynological sedimentological archaeological and carbon isotopic data of alluvial sites in the upper nazas basin arroyo grande durango 1855 m amsl and the parras basin el molino coahuila 1245 m amsl is introduced describing environmental changes across a short grassland desert ecotone from the eastern margins of the sierra madre occidental smo these sites reconstruct holocene vegetation history in semi arid north central mexico and integrate fluvial geomorphology and palynology data in particular pollen data links a rise of xeric flora with higher energy deposition and increased erosion in upland basins of the eastern smo according to archaeological finds at examined sites human occupation is linked to mesic or afforested conditions however limitations of carbon isotope data for environmental historical reconstruction are indicated by somewhat stable values at arroyo grande durango especially while pollen sites show a replacement of short grasses and park woodlands by a more xeric flora at higher elevations with a development of chihuahuan desert flora at low elevations el molino coahuila vegetation reconstructions are supported by pollen analog data collected from the cuatro cienegas region in coahuila mexico

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

pleistocene water cycle and eastern boundary current processes along the california continental margin 1 coastal marine sediments contain mixtures of terrestrial and marine paleoclimate proxies that record how the coastal water cycle has behaved over long time frames we explore a 600 kyr marine record from odp site 1018 located due west of santa cruz california to identify coastal wet and dry periods and to associate them with oceanographic processes wet periods in central california identified by increased tree pollen relative to pollen from grasslands and scrublands are found on every major deglaciation in the last 600 kyr sea surface temperature sst data were collected for the last two deglaciations wet periods are associated with a rapid rise in sst off central california sst gradients along the california margin and changes in biogenic deposition show that wet periods in central california are associated with a weakening of the california current and weakened coastal upwelling high carbonate production suggests that there was significant curl of wind stress upwelling offshore we propose that wet periods in central california are associated with a meteorological connection to the tropical pacific and weakened southward flow in the california current that shunted temperate pacific water northward into the alaska gyre we do not observe evidence for a south shifted westerly storm track at the last glacial maximum but find that wet periods are diachronous along the california margin the wettest period around the santa barbara basin peaked at 16 ka preceding the wet peak in central and northern california by 4 kyr

stratigraphy and geochronology of la playa archaeological site sonora mexico abstract la playa archaeological site in northern sonora mexico contains a long record of human activity that includes the paleoindian period terminal pleistocene and much of the holocene the size and complexity of la playa has discouraged a systematic characterization of its stratigraphy and geochronology a deficiency we redress in the study we distinguished seven stratigraphic units ranging in age from 44 570 to 400 cal yr b p using 14 c dates from charcoal and terrestrial gastropods found mostly in archaeological features all of the buried in situ cultural remains are contained in units b 4690 1580 cal yr b p and c 1010 400 cal yr b p and represent overbank deposition from the nearby rio boquillas occupation at the site peaks in units b 4 and b 5 corresponding to the cienega phase 2800 1800 cal yr b p of the early agricultural period this period coincides with the growth of early agricultural villages in the region and is marked at la playa by thousands of archaeological features including roasting pits human burials and extensive canal irrigation systems the presence of semi aquatic and aquatic snails demonstrates that water was present year round in the canal systems constructed during this period stable and radiometric isotopic evidence suggests that early agriculturalists diverted ground water over several kilometers from the nearby rio boquillas the extensive cienega phase occupation ended after about 1700 cal yr b p with deep erosion of the site an event also visible in alluvial records in southern arizona that marked the end of the early agricultural period and significant changes in settlement organization in the region

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

paleoenvironmental and geomorphic significance of bluff top dunes along the au sable river in northeastern lower michigan usa abstract we report on the age and evolution of five well developed parabolic dunes that are perched on high 40 m bluffs along the southern lip of the au sable river valley in northeastern lower michigan u s a these dunes are located on west northwest facing exposures and mantle the jackpines delta which formed when the glacial au sable river system deposited sands and gravels into glacial lake warren in the huron basin sometime between 15 1 and 14 7 ka lake level subsequently fell 35 m as the ice margin retreated northward during the twocreekan interstadial this regression resulted in abandonment of the jackpines delta and incision of the associated surface by the ancestral au sable river lake level subsequently rose 50 m during the algonquin transgression which likely promoted valley widening through channel migration eight samples were collected for osl age determination of the dunes and yielded ages that suggest dune formation occurred mostly between 13 5 ka and 13 ka this result coupled with the landscape position of the dunes i e south side of river west northwest facing bluffs suggests that the dunes largely formed 1 during the algonquin transgression when bluffs were eroded by stream channel migration and 2 by west northwesterly winds that transported eolian sands from exposed bluff faces to the adjacent valley edge this study contributes to the understanding of perched dune formation in the great lakes region and further supports models indicating that westerly winds prevailed within 150 km of the ice margin during the late pleistocene it also demonstrates that interior dunes in this region formed in similar environmental settings to interior dunes in northern europe and suggests that local factors rather than specific climate intervals should also be considered as they relate to dune evolution

a probability distribution for depth limited extreme wave heights in a sea state a model for the depth limited distribution of the highest wave in a sea state is presented the distribution for the extreme wave height is based on a probability density function pdf for depth limited wave height distribution for individual waves mendez f j losada i j medina r 2004 transformation model of wave height distribution coastal eng vol 50 97 115 and considers the correlation between consecutive waves the model is validated using field data showing a good representation of the extreme wave heights in the surf zone some important statistical wave heights are parameterized obtaining useful expressions that can be used in further calculations

timing and extent of late quaternary paleolakes in the trans pecos closed basin west texas and south central new mexico abstract the trans pecos closed basin is a hydrographically closed region covering 20 000 km 2 centered on salt basin 160 km east of el paso texas geomorphic and limnetic evidence have been used to identify four major highstands for lake king during the last glacial maximum lgm additional geomorphic features from a second recently identified paleolake lake sacramento have been found in the beargrass subbasin a nested subbasin approximately 75 km northwest of salt basin radiocarbon ages of the organic material in lake king sediments date four abrupt climate changes and rapid lacustrine transgressions during the lgm with a quasi periodicity of 2000 yr geomorphic evidence in the beargrass subbasin identifies lake cycles contemporaneous with those in lake king the dates for these transgressions correlate with the dates of freshening events identified by researchers in paleolake basins elsewhere in new mexico the quasi periodicity of the events approximates that of dansgaard oeschger events identified from greenland ice cores the contemporaneity of the trans pecos transgressions with transgressive events in other basins in the region suggests that paleolakes in the region were in phase with respect to abrupt climate changes during the latter stages of the lgm

high precision ultra distal holocene tephrochronology in north america far travelled volcanic ashes tephras from holocene eruptions in alaska and the pacific northwest have been traced to the easternmost extent of north america providing the basis for a new high precision geochronological framework throughout the continent through tephrochronology the dating and correlation of tephra isochrons in sedimentary records the reported isochrons are geochemically distinct with seven correlated to documented sources in alaska and the cascades including the mazama ash from oregon w7600 years old and the eastern lobe of the white river ash from alaska w1150 years old these findings mark the beginning of a tephrochronological framework of enhanced precision across north america with applications in palaeoclimate surface process and archaeological studies the particle travel distances involved up to w7000 km also demonstrate the potential for continent wide or trans atlantic socio economic disruption from similar future eruptions

performance of rubble mound breakwaters under tsunami attack a case study haydarpasa port istanbul turkey abstract ports are one of the most vulnerable coastal utilities in case of marine natural hazards such as tsunamis and need to be protected against their devastating effects thus studying the effects of tsunamis on protective structures such as breakwaters is critical the sea of marmara is a part of an active earthquake zone that has generated tsunamis in the history in terms of population density coastal utilization and economic potential marmara coastline seems most vulnerable to marine hazards the availability of natural stones allows for wide use of rubble mound breakwaters as coastal protective structures in turkey the stability of these types of structures under the attack of storm waves has already been studied however their stability and performance under the effect of long waves and tsunami attacks have not yet been studied experimentally the present study is a case study focusing on haydarpasa port located at the southern entrance of istanbul bosphorus strait north coast of the sea of marmara it aims to investigate the performance level of the port in case of tsunami attack physical model experiments were conducted in the 105 m long wave flume in the port and airport research institute pari japan with a froude type length scale of 1 30 the experiments conducted to test the stability of rubble mound breakwater were twofold i solitary wave experiments and ii tsunami overflow experiments the heights of incoming tsunami waves were selected from results of simulations were conducted in the same region oyo int co 2007 ayca 2012 yalciner et al 2014 guler et al 2014 aytore 2015 first the incoming solitary wave heights were selected as 5 7 5 and 10 cm using the overflow heights obtained from solitary wave experiments i e wave height at the top of crown wall when the solitary waves are overtopping the crown wall tsunami overflow experiments were conducted ranging from an overflow height of 1 1 cm to 4 6 cm results of these experiments showed that haydarpasa breakwater especially the crown wall of the breakwater is not stable under a moderate tsunami attack therefore an improved cross section was also tested under the same conditions and the improvement proved successful

estimates of holocene precipitation for rajasthan india based on pollen and lake level data abstract a pollen profile obtained from lake sediments at lunkaransar rajasthan in northwest india was used along with a pollen climate calibration function to estimate past precipitation between 10 500 and 3500 yr b p the estimated precipitation was about 500 mm yr or about 200 mm yr above the modern value a model was used for the energy and hydrologic budget of a lake basin and lake at sambhar located 240 km se of lunkaransar to calculate that a 200 mm yr increase in rainfall above the modern amount would have raised the lake level about 20 m above the modern level topographic charts and satellite imagery provided some evidence in support of an enlarged paleolake of that elevation but field exploration would be required to confirm the size and date of a former lake after about 3500 yr b p the lunkaransar profile indicated a desiccated lake bed because no pollen was preserved the pollen climate calibration function was of no use for estimating the amount of the precipitation decline a reduction of precipitation of about 200 mm yr below the modern amount was estimated from the energy and hydrologic budget for paleolake sambhar by assuming that the lake was one tenth of its present size during the dry interval

paleoenvironmental and geoarchaeologic implications of late quaternary sediments and paleosols north central to southwestern san juan basin new mexico abstract soil sediment relationships from the west fork of gallegos canyon near farmington nm to the manuelito plateau northwest of gallup nm provide insight into the late pleistocene and holocene history of the north central to southwestern san juan basin soil formation suggests six widespread episodes of land surface stability the oldest and strongest paleosol is in eolian alluvial and playa sediments that were buried between 9560 and 7800 14 c yrs b p the second oldest paleosol developed within eolian and alluvial sediments and was buried at ca 4500 14 c yrs b p subsequent eolian alluvial and playa deposits contain a third paleosol that was buried ca 3100 14 c yrs b p in turn these sediments are mantled by eolian alluvial and playa sediments that exhibit remnants of a fourth paleosol that was buried by ca 2100 14 c yrs b p a fifth paleosol within eolian and alluvial sediments is associated with basketmaker iii pueblo iii cultural materials dating from 1300 to 660 14 c yrs b p the sixth soil sediment unit consists of eolian and alluvial deposits that date from 660 14 c yrs b p to the present and exhibits the modern soil in addition a very weak paleosol that was buried at ca 300 14 c yrs b p was encountered at a few locales because of discontinuous burial and preservation not all of these units are present at every locale within the study area several locales across the basin however exhibit five to six of these units in stratigraphic succession the widespread occurrence of these paleosols suggests that six episodes of regional stability and soil formation occurred in the western san juan basin during the holocene

evidence for younger dryas global climate oscillation and human response in the american southwest whether or not abrupt younger dryas climate change affected regional paleoenvironments and late pleistocene hunter gatherer populations is an important topic in the archaeology of the american southwest this paper reviews multiple age resolved proxy evidence to gauge the magnitude and direction of younger dryas chronozone ydc environmental changes in different settings and systems there is no record of ydc pluvial lake highstands in arizona or new mexico but there are impressive records of vegetation faunal stable isotope and geomorphological change coincident with the ydc these correlate with important adaptive changes in human hunting and land use as revealed in the analysis of the spatiotemporal distribution of late pleistocene hunting technologies clovis and folsom projectile point distributions do not support extant models of paleoenvironmental conditions in these interpretations significant cultural changes that coincide with the ydc include the clovis to folsom transition the demise of mammoth hunting and the development of a highly successful emphasis on bison increased regionalization and the abandonment of the northwestern chihuahuan and the sonoran deserts by mobile big game hunters

storm evolution characterization for analysing stone armour damage progression abstract storm evolution is fundamental for analysing the damage progression of the different failure modes and establishing suitable protocols for maintaining and optimally sizing structures however this aspect has hardly been studied and practically the whole of the studies dealing with the subject adopt the equivalent triangle storm as against this approach two new ones are proposed the first is the equivalent triangle magnitude storm model etms whose base the triangular storm duration d is established such that its magnitude area describing the storm history above the reference threshold level which sets the storm condition ht equals the real storm magnitude the other is the equivalent triangle number of waves storm etnws where the base is referred in terms of the real storm s number of waves nz three approaches are used for estimating the mean period tm associated to each of the sea states defining the storm evolution which is necessary to determine the full energy flux withstood by the structure in the course of the extreme event two are based on the jonswap spectrum representativity and the other uses the bivariate gumbel copula hs tm resulting from adjusting the storm peaks the representativity of the approaches proposed and those defined in specialised literature are analysed by comparing the main armour layer s progressive loss of hydraulic stability caused by real storms and that relating to theoretical ones an empirical maximum energy flux model is used for this purpose the agreement between the empirical and theoretical results demonstrates that the representativity of the different approaches depends on the storm characteristics and point towards a need to investigate other geometrical shapes to characterise the storm evolution associated with sea states heavily influenced by swell wave components

paleosol organic matter and pedogenic carbonates and paleontological δ13c records applied to the paleoecology of late pleistocene holocene in mexico abstract stable isotopes of carbon 13 c in terrestrial geological materials paleosol humus and carbonates as well as fossil bones collagen and tooth enamel are established as highly specific records on paleoenvironmental characteristics it was assumed that comparing the results of different types of materials on regional or local scales provides more accurate and reliable reconstructions and even opens new aspects of interpretation this was tested by the comparison of the data obtained from the late pleistocene paleosols and or remains of pleistocene megafauna in various locations in northwestern mexico sonora paleosols formed in mis3 mis2 and mis1 central northern mexico san luis potosi teeth corresponding to mis2 and mis1 and central southern mexico puebla paleosols corresponding to mis3 and mis2 and teeth associated with these paleosols and state of mexico teeth corresponding to mis2 the results of isotopic studies are complemented with other paleoenvironmental proxies the 13 c values of paleosols of sonora is 19 8 to 16 95 in organic matter and shows little difference between paleosols and holocene soils 13 c values of pedogenic carbonates are 6 4 to 4 52 in san luis potosi the 13 c values of paleosol are 12 16 in organic matter in puebla they vary from 24 6 in paleosols to 15 16 in the modern surface soil pointing to contrasting vegetation change the 13 c values in fossils range from 10 7 to 1 2 in slp of 2 73 and 2 93 in puebla and 6 5 to 1 3 in state of mexico the 13 c values of paleosols and analysis of megafauna in northwest and central northern mexico matched each other indicating mixed c3 c4 vegetation while for central southern mexico paleosols indicated predominance of c3 plants and megafauna indicated mixed c3 c4 composition in general the results indicate that in northern mexico environmental conditions were slightly wetter than at present while for the central area there was a large change in the environmental conditions of high humidity in mis3 and mis2 with a trend to drier climates in mis1

loading and gravitational effects of the 2004 indian ocean tsunami at syowa station antarctica the 2004 indian ocean tsunami reached syowa station antarctica approximately 12 5 hr after the december sumatra andaman earthquake we have analyzed the tsunami signals recorded on ocean bottom pressure gauges broadband seismometers sts 1 and a superconducting gravimeter sg we calculated the sea level variation tilt and gravity changes induced by the tsunami and compared these results to observations from this comparison we confirmed the loading and gravity effects of the tsunamis on the sts 1 horizontal components and the sg records at syowa station the magnitudes of these effects given as root mean square amplitudes are as follows for the tilt effects obtained from 20 hr long sts 1 records at frequencies in the range 0 3 0 6 mhz 5 and 8 gal 10 8 m sec 2 in the east west and north south directions respectively and for the gravity effect obtained from the sg records for the same time period of 20 hr at frequencies in the range 0 1 0 2 mhz 0 2 gal by using detailed bathymetry around syowa station the synthetic amplitudes similar to the observed were obtained although the waveforms of synthetic and observation are not always consistent

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

late quaternary fluvial landscape evolution in desert grasslands of northern chihuahua mexico presented here is the first comprehensive late quaternary alluvial stratigraphic record from desert grasslands in northern mexico the stratigraphic history was temporally constrained by radiocarbon dating whereas the ecology of c4 plants was inferred by stable carbon isotopes from buried soils environmental relationships within the casas grandes and san pedro river basins of the juanaquena study area provide a picture of evolving landscapes where fluvial behavior is driven by climate change and ecosystem instability seven periods of flood plain construction and six episodes of paleosol formation and channel erosion occurred during the last 14 000 1 4 c yr b p in the latest pleistocene channel erosion ensued in response to a general warming trend and landscape instability although c3 plants still dominated in the alluvial valleys in the holocene when c4 plants began to dominate channel erosion was typically initiated by a shift from relatively warmer and drier to cooler and wetter climates the timing of erosion events exhibits a remarkable correlation to arroyo formation and paleosol formation of ephemeral streams in the north american southwest in contrast to arroyos the casas grandes and san pedro rivers created flood plains having mixed to bedload mean derbelts that persisted throughout the late quaternary however bedrock valley constrictions accelerated flood plain building leading to periodic channel avulsion although intervals of landscape instability occurred numerous times in the late quaternary fluvial style was largely governed by the dominance of c4 grasslands which appears to have maintained sufficient upland vegetative cover to mitigate flash flooding typical of arid environments

geoarchaeological and paleohydrological evidence for a clovis age drought in north america and its bearing on extinction abstract at the murray springs clovis site in southeastern arizona stratigraphic and geomorphic evidence indicates that an abnormally low water table 10 900 yr b p was followed soon thereafter by a water table rise accompanied by the deposition of an algal mat the black mat that buried mammoth tracks clovis artifacts and a well this water table fluctuation correlates with pluvial lake fluctuations in the great basin during and immediately following clovis occupation of that region many elements of pleistocene megafauna in north america became extinct during the dry period oxygen isotope records show a marked decrease in 18o correlated with the younger dryas cold dry event of northern europe which ended 10 750 yr b p essentially the same time as the water table began to rise in southeastern arizona clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress if so both climate and human predation contributed to pleistocene extinction in america

on the stability of rock armored rubble mound structures abstract estimation of the required armor size is a major task in the design of coastal structures under wave loading such as breakwaters and revetments several semi empirical formulas have been developed for this purpose however these formulas are often either limited to certain water depth conditions or do not incorporate the permeability of the structure in an appropriate way the main objectives of this study are to a develop a unified physically sound formula for the estimation of the required rock size in all relevant water depth conditions and b to relate the effects of the permeability of the structure directly to physical parameters to achieve these first a comprehensive data base of deep and shallow water experiments within the design conditions was built then physical reasoning along with a robust data mining approach i e m5 model tree were used to develop formulas for armor stability in the stability formula wave characteristics such as the significant wave height and spectral energy mean period tm 1 0 are invoked while the permeability is incorporated using the ratio between the size of the core material and the armor stones accuracy metrics such as discrepancy ratio and scatter index indicated high performance of the model in different conditions finally a probabilistic formula and some guidelines are provided for practicing engineers

stable carbon isotopes c3 c4 vegetation and 12 800years of climate change in central new mexico usa abstract a thick sequence of fine textured alluvium in central new mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the great plains grassland the analysis of thirty eight ams radiocarbon ages 13 c values and modern weather data has produced a 12 800 cal yr record of changing c 3 c 4 vegetation temperature and precipitation the record begins with the younger dryas that was characterized by c 3 plants and was about 2 4 c cooler with over 100 mm rainfall than today after 11 000 cal yrs bp the climate became less cool and less wet reaching present day conditions by 9000 yrs the middle holocene was c 4 warm and dry although the 13 c record is incomplete for this interval from 3300 to 1400 cal yrs bp the climate was cool and wet with c 3 plants averaging 0 5 c cooler and 22 mm greater rainfall than today matching other records in the region for a wetter climate after 1400 cal yrs bp the local climate became warm and dry shifting to c 4 vegetation the severe second century drought first observed in tree rings in southern colorado is supported by the 13 c data and occurred during the interval a d 40 to a d 180 hiatuses in the local alluvial and 13 c record extend from 9000 to 6000 cal yrs bp and from 1000 cal yrs bp to present

paleosols bones phytoliths and δ13c signatures of humus and teeth in the alluvial sequence of axamilpa puebla inferences for landscape evolution and megafauna paleoecology during mis 3 2 in southern mexico abstract alluvial paleosol sedimentary sequences containing animal fossils and paleobotanical and paleopedological archives have a potential for reconstructing quaternary paleoenvironments in southern mexico and for understanding the paleoecology of pleistocene megafauna in the section of axamilpa river four pedostratigraphic units were recognized the lower gleyic and vertic pedological units are at the end of marine isotopic stage mis 3 while the upper humic and most probably calcic units correspond to mis 2 according to the radiocarbon dates of humus the micromorphological analysis indicates an incipient development and syn sedimentary character of paleopedogenesis in the periodically water saturated environment indicated by redoximorphic features hydrogenic carbonates and low values of magnetic susceptibility in most strata the 13 c values of the paleosol humus range from 22 6 to 24 7 indicating a c3 vegetation whereas in the modern soil it is higher 15 2 pointing to an abundance of the c4 and cam plants the 13 c signature of the vegetation inferred from the teeth enamel of the fossil fauna appeared to be less negative than that of humus from corresponding paleosols the alimentary preferences of the paleofauna which fed on grasses with high proportion of c4 plants explain this difference the phytolith analysis shows dominance in conifer forms followed by c4 and c3 grasses the content of conifer phytoliths is progressively reduced towards the top of the sequence we interpret the late pleistocene landscape of this area as a heterogeneous forest grassland landscape with the forest shrinking through time and the grass areas increasing swampy floodplain meadows inferred from paleopedological results could provide a habitat for grassy vegetation both isotope and phytolith records demonstrate a contrasting difference between pleistocene and recent vegetation dominated by xerophytic shrubs and succulents this vegetation change could play important role in the extinction of pleistocene megafauna

millennial scale dynamics of valley fills over the past 12 000 14c yr in northeastern new mexico usa we studied the alluvial histories of eight small 2 watersheds in the uplands of northeastern new mexico the data come from radiocarbon dated sections exposed in the banks of arroyos and permanent channel streams results show that nine periods of valley aggradation separated by incision episodes occurred over the past 12 000 14 c yr these millennial scale cycles occurred in rough synchrony within different drainages parts of some cycles coincided with well known climatic fluctuations for example aggradation occurred during the younger dryas chronozone 11 000 10 000 14 c yr b p and valley fills persisted in incised states during the early holocene peak in milanko vitch summer insolation incision occurred early in the medieval warm period ca a d 1000 1300 aggradation during the little ice age a d 1300 1880 and incision during the last century changes in precipitation tied to the strength of the north american monsoon system probably drive these cycles of aggradation and incision when the system is strong more frequent summer thunderstorms cause increased flooding in these small watersheds wetter summers over periods of decades to centuries allow forest vegetation to spread which reduces sediment input from hillslopes at the same time floods are eroding valley fills aggradation of valley fills probably occurs when summer thunderstorms are less frequent and large floods are correspondingly rare prolonged summer drought reduces forest cover which increases erosion from slopes and causes sediment to accumulate in valleys in turn the strength of the north american monsoon system is probably controlled by fluctuating sea surface temperatures the geomorphic cycles we describe may reflect a previously unrecognized millennial scale climate oscillation that is important in shaping the landscapes of the southern great plains

lake evolution during the past 30 000 years in china and its implications for environmental change abstract taking china as a whole lake expansion occurred 500 b c 0 a d 650 950 a d and 1250 1650 a d over the past 3000 yr the expansions were mainly due to climatic fluctuations and correspond to frequent flood reports three regional characteristics of lake development have been recognized 1 fluctuations of near coastal lakes and those in other regions as well were out of phase during 500 b c 500 a d which possibly resulted from out of phase fluctuations of climate and sea level on 10 to 100 yr time scale 2 as the lower yellow river channel migrated southward the lakes in the south of the north china plain formed and reached their largest sizes much later than those in the north 3 for the lakes in the middle and lower yangtze river valley the higher a lake basin lies above a neighboring river and the further the lake is from the river s mouth in general the younger the lake is through land reclamation the ancient chinese have changed most of the lakes greatly however human activities were also constrained in certain ways by the natural changes of the lakes reclamation usually was banned and farmland was abandoned to repair reservoirs while lakes were expanding

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

sea level variation in seismic normal mode band observed with on ice gps and on land sg at syowa station antarctica 1 we analyze sea level variation data acquired by a differential gps and gravity data acquired by a superconducting gravimeter sg at syowa station antarctica in an eight month period of 1998 at frequencies between 0 2 and 2 5 mhz in the seismic normal mode band we observe similar spectral peaks in both of the data sets we also observe high coherence and zero phase between the two data sets at the frequencies of these peaks the results of response analysis and simple mode calculation suggest that the observed peaks in the sg data are due to the effects of ocean water attraction and loading associated with sea level variation a possible cause of which is the seiche in lutzow holm bay around the station applying a transfer function method to both of the data sets we can reduce the background noise due to the oceanic effects in the sg data

the effects of the atmospheric pressure changes on seismic signals or how to improve the quality of a station seismic investigations are mainly limited by seismic noise two microbarometers have been installed in the seismic vault of two different geoscope stations one at ssb and the other at tam all vertical components and most of the horizontal components show a significant correlation with pressure in order to correct the seismic signals from the atmospheric pressure noise a transfer function between the pressure data and the seismic data is inverted results show that after correction the noise levels reached on the horizontal components are similar between the two stations and the vertical components display noise levels below the low noise model as defined by peterson 1993 this technique reduces part of the noise and allows detection of small earthquakes and a better extraction of normal modes the analysis of the lowest normal modes of the earth excited by the m s 8 2 macquarie island earthquake is given to illustrate the perspectives of the method

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

wave height distributions on shallow foreshores wave height distributions on shallow foreshores deviate from those in deep water due to the effects of the restricted depth to height ratio and of wave breaking laboratory data of wave heights on shallow foreshores of different slopes have been analysed to determine these effects and to derive generalised empirical parameterisations a model distribution is proposed consisting of a rayleigh distribution or a weibull distribution with exponent equal to 2 for the lower heights and a weibull with a higher exponent for the higher wave heights the parameters of this distribution have been estimated from the data and expressed in terms of local wave energy depth and bottom slope yielding a predictive model that is found to be significantly more accurate than existing expressions

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

late quaternary geology of the middle gila river gila river indian reservation arizona abstract stratigraphy and dating provide an 18 000 yr record of erosion and deposition by the middle gila river prior to 18 000 cal yr b p the gila river cut into its floodplain and created a deep wide channel sand and gravel accumulated within this channel until 4250 4400 cal yr b p by this time the channel of the gila river was narrow and deep around 5000 cal yr b p fine grained sediments began to accumulate on the floodplain at 800 950 cal yr b p there was a major period of channel widening after this erosional episode the channel again narrowed as it filled with sand and gravel until around 200 cal yr b p on the floodplain deposition continued from about 5000 cal yr b p to 500 cal yr b p a period of stability and soil formation occurred on the floodplain between 500 and 200 cal yr b p after which overbank deposition resumed and buried the soil channel widening again occurred in the late 19th century the changes observed in the sedimentologic history of the gila river show that during the late pleistocene the gila river was a competent stream capable of carrying and depositing coarse sediment loads later deposition of sand and gravel during the first half of the holocene implies an increase in sediment yield from upstream watersheds changes during the last 4000 years reflect the response of the river to climatic perturbations the timing of large floods internal landscape thresholds and human impacts

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

gps observation of the sea level variation in lutzow holm bay antarctica differential gps observations were conducted on the fast ice in lutzow holm bay antarctica the observations were carried out intermittently from april to december in 1998 the vertical displacement which is a combination of oceanic tidal variation and high frequency variations of 3 6 minutes period was clearly detected eight hours comparison of the height variation derived from gps with that from a video monitoring system showed good agreement with a standard deviation of 2 2 cm the high frequency fluctuations of about 1 cm were obvious in both observations and had significant correlation with each other the low pass filtered variations agreed well with a standard deviation of 1 7 cm tidal constituents derived from the gps observations for the entire period showed good agreement with those from the seven years of pressure gauge observations thus gps has demonstrated the ability to observe 2 cm accuracy sea level variations

long period tides observed with a superconducting gravimeter at syowa station antarctica and their implication to global ocean tide modeling abstract the long period tides mf and mm waves were analyzed with the 2 years data obtained with a superconducting gravimeter sg installed at syowa station 69 0 s 39 6 e antarctica the observed amplitudes phase lags and amplitude factors factors were 11 642 0 035 gal 0 12 0 17 and 1 1218 0 0034 for the mf wave and 6 143 0 058 gal 0 33 0 54 and 1 1205 0 0106 for the mm wave respectively 1 gal 10 8 m s 2 the ocean tide effects effects of the attraction and loading due to the ocean mass at the observation site were estimated using the five global ocean tide models equilibrium ocean tide model schwiderski model schwiderski e w 1980 on charting global ocean tides rev geophys space phys 18 243 268 dickman model dickman s r 1989 a complete spherical harmonic approach to luni solar tides geophys j int 99 457 468 csr model eanes r j 1995 private communication and desai and wahr model desai s h wahr j m 1995 empirical ocean tide models estimated from topex poseidon altimetry j geophys res 100 25205 25228 the averages of the five estimates are 0 433 gal and 0 244 gal in amplitude and 192 9 and 179 5 in phase for the mf and mm waves respectively the five estimates differ by a maximum of 0 104 gal in amplitude and 18 8 in phase for the mf wave and by 0 033 gal and 6 4 for the mm wave the estimated mm phases are nearly 180 for the five models and the variation of their values among the models is relatively small compared with that of the mf phases these indicate that the mm wave is much closer to an equilibrium tide than the mf wave due to the variation of the ocean tide corrections the corrected factors were scattered within the ranges of 1 158 to 1 169 for the mf wave and of 1 163 to 1 169 for the mm wave however it is noted that the mean factors of the five ocean models i e 1 162 0 023 for the mf wave and 1 165 0 014 for the mm wave prefer slightly larger value rather than those estimated from the theory of the elastic tide

stability of rubble mound breakwaters under tsunami first impact and overflow based on laboratory experiments abstract recent tragic tsunami events like those that occurred in the indian ocean in 2004 and in japan in 2011 have revealed the need of further work to reduce tsunami risk in coastal areas an important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami s energy dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences within this scope laboratory experiments on scaled models of two typical mediterranean rubble mound breakwater typologies under tsunami waves were conducted for the first time the tsunami s action was split into 2 parts 1 the first impact of solitons was tested by means of large solitary waves and 2 the subsequent overflow was approached by applying a pump driven wave maker the damage on the breakwaters due to these actions was measured and assessed the result is an in deep analysis of the relationships among stability number damage level and number of tsunami waves the outcome of this analysis includes the development of a set of formulae that provide in the range of the conducted tests the value of the damage parameter so that tsunami actions can be taken into account in the design of rubble mound structures finally based on the results of these experiments the threshold values of the damage parameter used to characterize damage in armors initiation of damage initiation of destruction destruction was particularized for tsunami actions

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

low holocene level 7700 to 3650 years ago of lake titicaca bolivia abstract preliminary results of sedimentological and paleontological analysis of two cores taken in lake titicaca bolivia indicate that between 7700 and 3650 yr b p the lake level was up to 50 m lower than at present evaporitic deposits occurred at the maximum low lake level

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

wave height parameter for damage description of rubble mound breakwaters abstract in this paper it will be shown that the wave height parameter h 50 defined as the average wave height of the 50 highest waves reaching a rubble mound breakwater in its useful life can describe the effect of the wave height on the history of the armor damage caused by the wave climate during the structure s usable life using thompson and shuttler thompson d m shuttler r m 1975 riprap design for wind wave attack a laboratory study on random waves hrs wallingford report 61 uk data it will be shown that h 50 is the wave parameter that best represents the damage evolution with the number of waves in a sea state using this h 50 parameter formulae as van der meer van der meer j w 1988 rock slopes and gravel beaches under wave attack phd thesis technical university of delft and losada and gimenez curto losada m a gimenez curto l a 1979 the joint effect of the wave height and period on the stability of rubble mound breakwaters using iribarren s number coastal engineering 3 77 96 are transformed into sea state damage evolution formulae using these h 50 transformed formulae for regular and irregular sea states it will be shown how damage predictions are independent of the sea state wave height distribution to check the capability of these h 50 formulae to predict damage evolution of succession of sea states with different wave height distributions some stability tests with regular and irregular waves have been carried out after analysing the experimental results it will be shown how h 50 formulae can predict the observed damage independently of the sea state wave height distribution or the succession of sea states

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

random breaking waves field verification of a wave by wave algorithm for engineering application abstract a simple numerical algorithm is utilized to test the wave by wave approach to modeling random wave transformation caused by shoaling breaking and reforming across nearshore profiles of arbitrary shape histograms of wave height and associated statistics predicted by the model show favorable comparison to measurements from the nine tests of the duck 85 field experiment with a root mean square error less than 10 for most wave statistics although suitable for use in many engineering applications the model does overpredict the number of waves that reform as they pass over a trough formation which is one facet that warrants improvement using the model predictions as a point of reference the qualitative effects of 1 an offshore wind 2 wave reflection and 3 surf beat are identified and discussed

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

effects of submerged berms on the stability of conventional rubble mound breakwaters abstract berms deployed at the toe of conventional breakwaters may be needed to reduce bottom settlements and to limit scour in front of the structure due to coastal currents in the mean time they may be effective in increasing the stability of the armor layer and also in minimizing the wave overtopping discharge compared to straight sloped conventional breakwaters without a berm this research aims to provide a new design criterion for the armor layer of conventional breakwaters with submerged berms marked by small thickness compared to water depth indeed past researches focused on the influence of relatively high berms on the stability of the armor layer the design of the berm itself is not tackled herein the effects of submerged berms on the incident waves transformation have been evaluated by means of a numerical model validated by using experimental data then a parametric correction factor of the incident significant wave height at the toe of the structure is provided and included in well established design criteria the experimental comparison confirms the reliability of the proposed method by highlighting the importance to use design criteria within their validity ranges in order to avoid an unsafe dimensioning of the armor elements

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

rupture of the pitaycachi fault in the 1887 mw 7 5 sonora mexico earthquake southern basin and range province rupture kinematics and epicenter inferred from rupture branching patterns during the 3 may 1887 mw 7 5 sonora earthquake surface rupture end to end length 101 8 km an array of three north south striking basin and range province faults from north to south pitaycachi teras and otates slipped sequentially along the western margin of the sierra madre occidental plateau this detailed field survey of the 1887 earthquake rupture zone along the pitaycachi fault includes mapping the rupture scarp and measurements of surface deformation the surface rupture has an endpoint to endpoint length of 41 0 km dips 70 w and is characterized by normal left lateral extension the maximum surface offset is 487 cm and the mean offset 260 cm the rupture trace shows a complex pattern of second order segmentation however this segmentation is not expressed in the 1887 along rupture surface offset profile which indicates that the secondary segments are linked at depth into a single coherent fault surface the pitaycachi surface rupture shows a well developed bipolar branching pattern suggesting that the rupture originated in its central part where the polarity of the rupture bifurcations changes most likely the rupture first propagated bilaterally along the pitaycachi fault the southern rupture front likely jumped across a step over to the teras fault and from there across a major relay zone to the otates fault branching probably resulted from the lateral propagation of the rupture after breaching the seismogenic part of the crust given that the much shorter ruptures of the otates and teras segments did not develop branches

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid

on noise reduction in vertical seismic records below 2 mhz using local barometric pressure we propose a simple method for the reduction of noise in vertical seismic recordings at frequencies below 2 mhz the method consists in subtracting the locally recorded scaled atmospheric pressure signal from the gravity record the scale factor is frequency independent and can be linearly estimated from the data while such a pressure correction was previously only used in the analysis of tidal records it is equally efficient at the low frequency end of the normal mode band and we use gravity recordings of the big 1994 shikotan and bolivian quakes to demonstrate this point our examples also show that this correction permits to achieve noise levels well below the new low noise model nlnm peterson 1993 the success of the correction also sheds some light on the physical processes responsible for the generation of low frequency seismic noise at quiet observatories