microbially induced cementation to control sand response to undrained shear current methods to improve the engineering properties of sands are diverse with respect to methodology treatment uniformity cost environmental impact site accessibility requirements etc all of these methods have benefits and drawbacks and there continues to be a need to explore new possibilities of soil improvement particularly as suitable land for development becomes more scarce this paper presents the results of a study in which natural microbial biological processes were used to engineer a cemented soil matrix within initially loose collapsible sand microbially induced calcite precipitation micp was achieved using the microorganism bacillus pasteurii an aerobic bacterium pervasive in natural soil deposits the microbes were introduced to the sand specimens in a liquid growth medium amended with urea and a dissolved calcium source subsequent cementation treatments were passed through the specimen to increase the cementation level of the sand particle matrix the results of both micp and

liquefaction and post liquefaction assessment of lightly cemented sands post liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage in the current study the effect of degree of ce

atmospheric radiocarbon during the younger dryas production ventilation or both a new reconstruction of past atmospheric v 14 c v 14 catm based on polish lake varved sediments has suggested that previous v 14 catm values e g from the cariaco basin record for the beginning of the younger dryas cold event yd are overestimates and that the v 14 catm rise at the yd onset could only be due to changes in atmospheric 14 c production pc 14 this result would have profound climatic implications for the yd is a paradigm example of abrupt climate change which is usually thought to have been triggered by a reduction in the northward heat flux by the atlantic thermohaline circulation here we examine results from a large number of simulations 300 based on a zonally averaged ocean circulation model to constrain the effect on v 14 catm of pc 14 changes during the yd as reconstructed from a greenland ice core record of 10 be flux our results suggest that the scatter in the lake data set is too large to exclude the probable change in deep ocean ventilation at the onset of the yd by contrast the model fit to the higher v 14 catm levels throughout the yd detected in the marine record is generally better when a substantial decrease in deep ocean ventilation is simulated the early v 14 catm drawdown that initiated during the first half of the yd however could entirely be due to production changes if this was the case the drawdown would not reflect an increasing formation of north atlantic intermediate water or southern ocean water as previously suggested the rapid v 14 catm rise at the yd onset documented in the marine record however remains unexplained fl 2001 elsevier science b v all rights reserved

conceptual model for millennial climate variability a possible combined solar thermohaline circulation origin for the 1 500 year cycle dansgaard oeschger and heinrich events are the most pronounced climatic changes over the last 120 000 years although many of their properties were derived from climate reconstructions the associated physical mechanisms are not yet fully understood these events are paced by a 1 500 year periodicity whose origin remains unclear in a conceptual model approach we show that this millennial variability can originate from rectification of an external solar forcing and suggest that the thermohaline circulation through a threshold response could be the rectifier we argue that internal threshold response of the thermohaline circulation thc to solar forcing is more likely to produce the observed do cycles than amplification of weak direct 1 500 year forcing of unknown origin by thc one consequence of our concept is that the millennial variability is viewed as a derived mode without physical processes on its characteristic time scale rather the mode results from the linear representation in the fourier space of nonlinearly transformed fundamental modes

eight centuries of north atlantic ocean atmosphere variability climate in the tropical north atlantic is controlled largely by variations in the strength of the trade winds the position of the intertropical convergence zone and sea surface temperatures a high resolution study of caribbean sediments provides a subdecadally resolved record of tropical upwelling and trade wind variability spanning the past 825 years these results confirm the importance of a decadal 12 to 13 year mode of atlantic variability believed to be driven by coupled tropical ocean atmosphere dynamics although a well defined interdecadal mode of variability does not appear to be characteristic of the tropical atlantic there is evidence that century scale variability is substantial the tropical atlantic may also have been involved in a major shift in northern hemisphere climate variability that took place about 700 years ago

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

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

mantle plume noble gas component in glassy basalts from reykjanes ridge basalts from the reykjanes ridge contain noble gases delivered from the non degassed lower mantle by the iceland plume these lower mantle gases are thought to be a mixture of planetary and solar components as would be expected if the earth accreted from fine silicate particles

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

little ice age clearly recorded in northern greenland ice cores four ice cores drilled in the little investigated area of northern and northeastern greenland were evaluated for their isotopic 18o and chemical content from these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced which reveals distinct climate cooling during the 17th and the first half of the 19th century timing of the preindustrial temperature deviations agrees well with other northern hemisphere temperature reconstructions however their extent 1 c significantly exceeds both continental records as well as previous southern and central greenland ice core time series a 20 30 increase in the sea salt aerosol load during these periods supports accompanying circulation changes over the north atlantic comparison with records of potential natural climate driving forces points to an important role of the long term solar influence but to only episodically relevant cooling during years directly following major volcano eruptions

degradation of stiffness of cemented calcareous soil in cyclic triaxial tests the deformation characteristics of artificially cemented calcareous soil subjected to undrained cyclic triaxial loading are investigated at different confining pressure and cyclic stress levels the influence of cementation on the shear stiffness is investigated by comparing the behavior of cemented and uncemented soils with similar initial conditions it is observed that the deviator stress and the deviatoric strain at yield reduced with increasing number of cycles for cemented sand due to progressive degradation of bond which results in significant decrease in stiffness on the other hand a strain hardening effect is observed in uncemented sand and this results in increasing yield stress and strain with progressive number of cycles a linear relationship between degradation index and number of cycles is observed for cemented sand this relationship has been synthesized in the form of an empirical equation by modifying a previously proposed equation for cohesive soils this empirical equation was further used to evaluate the fatigue life of soils by adopting a failure criterion

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

timing and dynamics of the last deglaciation from european and north african δ13c stalagmite profiles comparison with chinese and south hemisphere stalagmites abstract the last deglaciation and its climatic events such as the bolling allerod ba and the younger dryas yd have been clearly recorded in the 13 c profiles of three stalagmites from caves from southern france to northern tunisia the three 13 c records dated by thermal ionization mass spectrometric uranium thorium method tims show great synchroneity and similarity in shape with the chinese cave 18 o records and with the marine tropical records leading to the hypothesis of an in phase between 15 5 and 16 ka 0 5 ka postglacial warming in the northern hemisphere up to at least 45 n the ba transition appears more gradual in the speleothem records than in the greenland records and the allerod seems warmer than the bolling showing here close similarities with other marine and continental archives a north south gradient is observed in the ba trend it cools in greenland and warms in our speleothem records several climatic events are clearly recognizable a cooler period at about 14 ka older dryas od the intra allerod cold period at about 13 3 ka the yd cooling onset between 12 7 and 12 9 0 3 ka similar to the ba the yd displays a gradual climate amelioration just after its onset at 12 75 0 25 ka up to the preboreal and is punctuated by a short climatic event at 12 15 ka even though the southern hemisphere stalagmite records seem to indicate that the postglacial warming started about 3 ka 1 8 ka earlier in new zealand 41 s and about 1 to 2 ka earlier in south africa 24 1 s large age uncertainties essentially due to slow growth rates make the comparison still perilous the overall 13 c speleothem record seems to follow a baseline temperature increase controlled by the increase in insolation and punctuated by cold events possibly due to the n america freshwater lake discharges

cementation of porous materials using calcite a technique of cementing porous materials artificially using calcite is presented the technique depends on flushing a mixture of chemical solutions through a porous medium leading to precipitation of calcite due to reaction of the solution ingredients the experimental procedures adopted to achieve the cementation are described the response of different soils to the cementation process is analysed the bond mechanism created by the calcite is illustrated using optical and electron micrographs the paper discusses the factors that appear to determine the response of geomaterials to calcite treatment it has been found that the strength of a calcite treated material increases with a intrinsic strength of the individual grains b density c decreasing particle size of the host grains d pre coating of grains with calcite and e roundness and non angularity of soil grains the cementation technique described in this paper has proved successful in reproducing the mechanical behaviour of natural

paleo environment and radiocarbon calibration as derived from lateglacial early holocene tree ring chronologies abstract we present an overview of the extended hohenheim oak chronology hoc and the dendrochronologically dated preboreal pine tree ring chronology ppc both provide an absolute annual time frame of the holocene extending into the younger dryas yd back to 11 919 bp two floating pine and larch chronologies are 14 c dated covering large parts of the lateglacial dendro ecological parameters such as ring width and stable isotope variation are used to infer past environmental conditions 14 c analyses on decadal sections provide a high precision high resolution data set for calibration of the radiocarbon time scale based on a marked change in ring width and growth pattern the yd termination is clearly identified in the german pine chronology its absolute age of 11 570 bp appears synchronous within the errors of the respective chronologies to related signals in the greenland ice cores grip gisp2 and in lacustrine varve sequences the 14 c age of the laacher see tephra lst is determined from a series of decadal tree ring samples to 11 063 12 14 c bp the calibrated range is 13 010 13 200 cal bp the climatic impact of the lst is reflected in the growth pattern of our tree ring chronologies

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

role for eurasian arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century a hypothesized low frequency climate signal propagating across the northern hemisphere through a network of synchronized climate indices was identified in previous analyses of instrumental and proxy data the tempo of signal propagation is rationalized in terms of the multidecadal component of atlantic ocean variability the atlantic multidecadal oscillation through multivariate statistical analysis of an expanded database we further investigate this hypothesized signal to elucidate propagation dynamics the eurasian arctic shelf sea region where sea ice is uniquely exposed to open ocean in the northern hemisphere emerges as a strong contender for generating and sustaining propagation of the hemispheric signal ocean ice atmosphere coupling spawns a sequence of positive and negative feedbacks that convey persistence and quasi oscillatory features to the signal further stabilizing the system are anomalies of co varying pacific centered atmospheric circulations indirectly related to dynamics in the eurasian arctic these anomalies appear to negatively feed back onto the atlantic s freshwater balance earth s rotational rate and other proxies encode traces of this signal as it makes its way across the northern hemisphere

noble gas isotopic systematics of fe ti v oxide ore related mafic ultramafic layered intrusions in the panxi area china the role of recycled oceanic crust in their petrogenesis olivine and clinopyroxene grains have been separated from four large fe ti v oxide ore bearing intrusions panzhihua hongge baima and taihe in the panxi area emeishan large igneous province southwest china for he and ar isotope studies the samples examined revealed extremely low 3 he 4 he ratios 0 078 4 34 ra with the mean value 0 78 ra for gases extracted by stepwise heating this feature combined with low 40 ar 36 ar ratios can be interpreted as due to addition of subduction related fluids and melts that had been stored in the lithospheric mantle for long periods considering the regional geologic history such addition can be attributed to the paleo subduction that occurred along the western margin of the yangtze block during the neoproterozoic the subducted oceanic crust beneath the panxi area underwent eclogite facies metamorphism and subsequent exhumation the infiltration of subduction related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the sr nd and pb isotopic data of the emeishan basalts and picrites in addition considerable amounts of eclogitic melts produced by partial melting of eclogite facies oceanic crust extensively contaminated the lithospheric mantle during the late permian partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental fe rich magma that supplied the ore bearing intrusions the combination of these factors may have been the crucial reason that many world class fe ti v oxides deposits are clustered in the panxi area

yielding and pre failure deformation of structured sands many natural sands have a structure that is imparted to them during their geological life and that significantly modifies their pre failure behaviour when compared with that of the reconstituted material unlike clays for which emphasis has been given to both the bonding and fabric components of structure for sands structure has generally been simply identified with bonding whereas the effects of fabric have often been overlooked an understanding of the way in which these components of structure influence the yielding and stiffness of these materials is required to formulate constitutive models that can adequately predict their response the paper examines the pre failure behaviour of two structured sands in triaxial compression performed over a wide range of pressures since yielding occurred at small strains laboratory techniques were developed to produce reliable and accurate determinations of stiffness ranging from 1 microstrain to failure the influence of structure on the shear stiffness was in

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

liquefaction of crushable soils crushable soils when sheared in a dense state have stress paths which are similar to those for loose hard grained sands however because of their angular nature they do not liquefy as easily under cyclic loading in the hyogo ken nambu 1995 earthquake there was widespread liquefaction of land areas reclaimed from the sea using a crushable highly angular decomposed granite soil masado which was previously regarded as a high quality fill material with little risk of liquefaction in earthquakes results are presented from monotonic and cyclic triaxial tests on three types of crushable soil namely masado shirasu volcanic sand and dogs bay carbonate sand together with standard silica toyoura sand to establish liquefaction criteria which can be applied not only to hard grained silica sands but also to more angular crushable sands in monotonic triaxial testing the stress paths passed through a point of phase transformation with each material exhibiting large strains after this point normalization

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

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

unstable early holocene climatic and environmental conditions in northwestern russia derived from a multidisciplinary study of a lake sediment sequence from pichozero southeastern russian karelia unstable early holocene climate and enviromental conditions in northwestern russia derived from a multidisciplinary study of a lake sediment sequence from pichozero southeastern russia karelia

an ocean model s response to north atlantic oscillation like wind forcing the response of the atlantic ocean to north atlantic oscillation nao like wind forcing was investigated using an ocean only general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the interannual to multi decadal frequency response of the ocean to a winter wind anomaly pattern overall the strength of the sst response increased slightly with longer forcing periods in the subpolar gyre however the model showed a broad response maximum in the decadal band 12 16 years

atmospheric and juvenile noble gases in the skaergaard layered igneous intrusion abstract gabbro and diorite from the skaergaard layered igneous intrusion contain noble gases which are mixtures of atmospheric and juvenile components atmospheric noble gases predominate in samples that have undergone extensive oxygen isotope exchange with meteoric hydrothermal water the source of the atmospheric noble gas component is inferred to be the hydrothermal circulation system a juvenile component with 40 ar 36 ar 6100 and containing fission xenon is also present this component predominates in samples showing unaltered magmatic oxygen isotope compositions neon of atmospheric isotopic composition is associated with the juvenile radiogenic 40 ar and fission xenon the source of this second noble gas component may be either the crustal country rock or the upper mantle if the neon is juvenile primordial neon from a mantle source region terrestrial primordial 20 ne 22 ne is the same as atmospheric to within 4 however subduction of atmospheric noble gases into the upper mantle may provide an alternate source of neon and other noble gases in the mantle

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

the influence of the de vries 200 year solar cycle on climate variations results from the central asian mountains and their global link long term climatic changes related to solar forcing were examined using millennium scale palaeoclimatic reconstructions from the central asian mountain region i e summer temperature records for the tien shan mountains and precipitation records for the tibetan plateau the reconstructions were based on juniper tree ring width records i e juniperus turkestanica for the tien shan and sabina przewalskii for the tibetan plateau the data were processed using spectral and wavelet analysis and filtered in the frequency range related to major solar activity periodicities the results obtained for various tree ring chronologies indicate palaeoclimatic oscillations in the range of the de vries similar to 210 year solar cycles through the last millennium the quasi 200 year variations revealed in the palaeoclimatic reconstructions correlate well r 2 0 58 0 94 with solar activity variations delta c 14 variations the quasi 200 year climatic variations have also been detected in climate linked processes in asia europe north and south america australia and the arctic and antarctica the results obtained point to a pronounced influence of solar activity on global climatic processes analysis has shown that climate response to the long term global solar forcing has a regional character an appreciable delay in the climate response to the solar signal can occur up to 150 years in addition the sign of the climate response can differ from the solar signal sign the climate response to long term solar activity variations from 10s to 1000s years manifests itself in different climatic parameters such as temperature precipitation and atmospheric and oceanic circulation the climate response to the de vries cycle has been found to occur not only during the last millennia but also in earlier epochs up to hundreds of millions years ago c 2007 elsevier b v all rights reserved

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

millennial scale climate cycles in permian carboniferous rhythmites permanent feature throughout geologic time two late paleozoic glacial rhythmite successions from the itarare group parana basin brazil were examined for paleoclimate variations paleomagnetic characteristic remanent magnetization chrm and magnetic susceptibility k z measurements taken from the rhythmites are interpreted as paleoclimatic proxies ratios of low frequency components in the k z variations suggest milankovitch periodicities this leads to recognition of other millennial scale variations reminiscent of abrupt climate changes during late quaternary time and are suggestive of bond cycles and the 2 4 k y solar cycle we infer from these patterns that millennial scale climate change is not restricted to the quaternary period and that millennial forcing mechanisms may have been prevalent throughout geologic time

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

late holocene sedimentary response to solar and cosmic ray activity influenced climate variability in the ne pacific marine laminated sediments along the ne pacific coast effingham inlet vancouver island provide an archive of climate variability at annual to millennial scales a 7 75 m portion of piston core tul99b 03 was deposited during a 3045 year interval 1440 4485 years before present ybp under primarily anoxic conditions darker clay laminae were deposited under higher precipitation conditions in winter and diatom dominated laminae were laid down when marine productivity was higher in the spring through autumn wavelet transform and other time series analysis methods were applied to sediment color i e gray scale values line scans obtained from x ray images and compared with global records of cosmogenic nuclides 14 c and 10 be as well as the ice drift index hematite stained grains record to detect cycles trends and nonstationarities in the climate and sedimentary pattern our results show that the marine sedimentary record in the ne pacific responded to abrupt changes and long term variability in climate that can be linked to external forcing e g solar and cosmic irradiance specifically a strong cooling in the ne pacific at 3550f160 ybp can be correlated to a weakening of high frequency 50 150 years pulses in sun activity at the gleissberg cycle band similar to what occurred at the onset of the dlittle ice aget at 1630 ad three intervals of unusually low sun activity at 2350 2750 and 3350 ybp are characterized by thick clay rich annual sedimentation that we interpret as representative of unusually wet conditions these intervals of higher precipitation conditions may have been related to a regional intensification of the aleutian low al caused by an eastward migration of the center of action coa of the al which occurs during intervals of solar minima dryer conditions in the region occur when the coa of al migrates westward and the coa of the north pacific high nph migrates northward during intervals of solar maxima a cyclicity of 50 85 33 36 and 22 29 years in the sediment color record lamination thickness and 14 c cosmogenic nuclide characterized the relatively warm interval from 3550 to 4485 ybp this record is similar to that of present day low and highfrequency variants of the pacific decadal oscillation and aleutian low d 2004 elsevier b v all rights reserved

evaluation of cyclic shear strength of two cemented calcareous soils the mechanism controlling the cyclic shear strength of cemented calcareous soils was investigated based on the results obtained from monotonic and cyclic triaxial tests on two different types of calcareous soil undrained cyclic triaxial tests performed on artificially cemented calcareous soils with different loading combinations showed that the effective stress path moved towards or away from the origin due to the generation or dissipation of pore pressure with progressive cycles previous investigations have shown that the peak strength envelope or the state boundary surface or the critical state line forms a boundary beyond which effective stress paths during cyclic loading cannot exist however in this study it was observed that the maximum stress ratio h max obtained from monotonic tests defined the boundary for the cyclic tests based on the information obtained from this study an approach for evaluating the cyclic shear strength is proposed it was observed that the modified normalized cyclic shear strength had a strong linear relationship with the logarithm of the number of cyclic to failure irrespective of confining pressure type of consolidation and stress reversal

holocene cyclic climatic variations and the role of the pacific ocean as recorded in varved sediments from northeastern china we present an n alkane and compound specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of lake xiaolongwan northeastern china the n alkane distribution suggests that lake xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent submerged macrophytes in the early holocene to a eutrophic state with high algal production and abundant emergent submerged macrophytes since the middle holocene the pattern of variation observed in the biomarker proxies acl the n alkane average chain length paq aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio and lptp lake productivity terrigenous organic production is throughout the record similar to that of the total organic carbon the variation of compound specific carbon isotopic values in the middle and short chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time in this forested region where the vegetation is dominated by c 3 plants the long chain n alkanes c27ec31 are predominantly derived from leaf wax lipids the compound specific d 13 c27e31 value is sensitive to effective precipitation and therefore represents a useful indicator of regional monsoonal precipitation spectral analysis on the d 13 c27e31 time series reveals significant periodicities of 87e89 205e212 1020e1050 and 1750e2041 years on the centennial timescale the quasi periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall the millennial monsoon cycle in northeastern china is associated with sea surface temperature sst variations in two active centers of the summer monsoon the western pacific subtropical high wpsh and the okhotsk high increasing sst in the subtropical sea may cause a northwards shift of the wpsh which extends the monsoon rain band meiyu to northeastern china and thus increasing rainfall in that region meanwhile decreasing sst in the okhotsk sea may strengthen the okhotsk high bringing more moisture into northeastern china we suggest that the pacific ocean is a main regulator for summer monsoon rainfall in northeastern china at present and at different time scales during the holocene

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

critical state soil constitutive model for methane hydrate soil 1 this paper presents a new constitutive model that simulates the mechanical behavior of methane hydrate bearing soil based on the concept of critical state soil mechanics referred to as the methane hydrate critical state mhcs model methane hydrate bearing soil is under certain geological conditions known to exhibit greater stiffness strength and dilatancy which are often observed in dense soils and also in bonded soils such as cemented soil and unsaturated soil those soils tend to show greater resistance to compressive deformation but the tendency disappears when the soil is excessively compressed or the bonds are destroyed due to shearing the proposed model represents these features by introducing five extra model parameters to the conventional critical state model it is found that for an accurate prediction of ground settlement volumetric yielding plays an important role when hydrate soil undergoes a significant change in effective stresses and hydrate saturation which are expected during depressurization for methane gas recovery

short term orbital forcing a quasi review and a reappraisal of realistic boundary conditions for climate modeling abstract the aim of this paper is to provide geoscientists with the most accurate set of the earth s astro climatic parameters and daily insolation quantities able to describe the short term orbital forcing stof as represented by the ever changing incoming solar radiation we provide an updated review and a pragmatic tool database using the latest astronomical models and orbital ephemeris for the entire holocene and 1 kyr into the future our results are compared with the most important database produced for studying long term orbital forcing showing no systematic discrepancies over the full thirteen thousand years period studied our detailed analysis of the periods present in stof as perturbed by solar system bodies yields a very rich dynamical modulation on annual to decadal timescales when compared to previous results in addition we addressed for the first time the error committed considering daily insolation as a continuous function of orbital longitudes with respect to the nominal values i e calculating the corresponding daily insolation with orbital longitudes tabulated at noon we found important relative differences up to 5 which correspond to errors of 2 5 w m 2 in the daily mean insolation for exactly the same calendar day and set of astro climatic parameters this previously unrecognized error could have a significant impact in both the initial and boundary conditions for any climate modeling experiment

holocene climate and vegetation dynamics on nightingale island south atlantic an apparent interglacial bipolar seesaw in action abstract high resolution analyses of a sediment sequence from an in filled lake on nightingale island at 37 s in the south atlantic have revealed hydrological variations during the last 10 700 cal yr bp which are linked to shifts in the southern hemisphere westerlies and the meridional overturning circulation moc in the atlantic the lowermost part of the sequence 10 700 8600 cal yr bp consists of peat the peat is overlaid by gyttja which continues up to the final overgrowing of the basin around 500 years ago the transition from peat to gyttja at 8600 cal yr bp implies a significant increase in effective humidity probably caused by a northward shift of the southern hemisphere westerlies after the end of the antarctic thermal optimum recurring phases of increased erosion with high deposition of minerogenic particles terrestrial organic matter high c n ratios and pollen grains from plant taxa growing in more distal parts of the catchment indicate periods with higher precipitation these high precipitation periods correspond to periods of southward shifted southern hemisphere westerlies inferred from south america and with periods of weaker moc in the north atlantic therefore we conclude that these periods also characterized by decreased influence from marine aerosols were not caused by the stronger westerlies but by weaker moc and less heat transport from the south to the north atlantic causing warmer sea surface temperatures ssts and increased precipitation in the south atlantic this is the expression of the bipolar seesaw mechanism and implies that it may have been operational also during interglacial conditions

a possible 20th century slowdown of southern ocean deep water formation chlorofluorocarbon 11 inventories for the deep southern ocean appear to confirm physical oceanographic and geochemical studies in the southern ocean which suggest that no more than 5 x 10 6 cubic meters per second of ventilated deep water is currently being produced this result conflicts with conclusions based on the distributions of the carbon 14 carbon ratio and a quasi conservative property po 4 in the deep sea which seem to require an average of about 15 x 10 6 cubic meters per second of southern ocean deep ventilation over about the past 800 years a major reduction in southern ocean deep water production during the 20th century from high rates during the little ice age may explain this apparent discordance if this is true a seesawing of deep water production between the northern atlantic and southern oceans may lie at the heart of the 1500 year ice rafting cycle

cyclic response of calcareous soil from the north west shelf of australia this paper reports the results from 23 cyclic ciu and cau triaxial tests on undisturbed samples of calcareous soil the samples which include both uncemented and cemented material have heen subjected to a range of mean and cyclic shear stresses results from the tests on the uncemented soil display many of the characteristics of the cyclic response of other cohesionless soils the more cemented soils sustained higher cyclic stresses and depending on the load level showed either elastic behaviour with no pore pressure build up eventual stabilization after some pore pressure build up or steady state pore pressure build up and eventual failure the effect of frequency on the response in the range 0 1 to 10 hz has heen studied since no dramatic differences in performance could he detected no firm conclusions could be drawn regarding the effect of testing rate l article preente les reultats obtenus a partir de 23 essais triaxiaux cycliques de type ciu et cau effectues sur des echantillons de sol calca

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

40ar39ar dating of the skaergaard intrusion we report the first 40ar 39ar data for the skaergaard intrusion based on analyses of hornblende and biotite from a transgressive granophyre from upper zone a uza of the layered series hornblende separates heated in a resistance furnace and laser heated single crystals of biotite from the granophyre give plateau ages that are consistent with isochron ages of 55 48 0 30 and 55 40 0 14 ma respectively 2 internal uncertainty with initial 40ar39ar ratios of 292 4 19 0 and 291 1 7 2 if uncertainties in the ages of 40ar 39ar standard fluence monitors are considered external uncertainties 2 errors are 0 76 and 0 72 ma respectively resistance heating analysis of biotite separated from a gabbro from lower zone a lza of the skaergaard layered series indicates that the sample has been extensively contaminated by ar inherited from old crust and does not constrain the intrusion age apart from indicating that it is less than approximately 57 ma old the ar cooling ages are consistent within uncertainty with both pluton cooling models presented by norton and taylor 1 but the data agree best with their model s2 which assumes a smaller permeability 10 13 cm2 combination of the new ages and the norton and taylor cooling models constrains the emplacement and final crystallization of the skaergaard magma chamber to be at 55 75 0 30 ma and 55 65 0 30 ma respectively evidence for late crystallizing quartz and tridymite near the sandwich horizon sh combined with phase equilibria constraints on the near solidus crystallization temperature of the sh 975 25 c require the pressure of sh solidification to be 60 15 mpa this means that the tertiary basalts and sediments overlying the kangerdlugssuaq region were 3 2 0 8 km thick at 55 65 0 30 ma assuming that the 6 7 km thick tertiary section exposed further east along the east greenland coast is representative of that which accumulated above the skaergaard we infer that the skaergaard emplacement occurred during the main stage of the east greenland flood basalt event after approximately half of the tertiary section had erupted the onset of coastal flexure in the kangerdlugssuaq region was after 55 48 0 76 ma

role of critical state framework in understanding geomechanical behavior of methane hydrate bearing sediments a proper understanding of geomechanical behavior of methane hydrate bearing sediments is crucial for sustainable future gas production there are a number of triaxial experiments conducted over synthetic and natural methane hydrate mh bearing sediments and several soil constitutive models have been proposed to describe their behavior however the generality of a sophisticated model is questioned if it is tested only for a limited number of cases furthermore it is difficult to experimentally determine the associated parameters if their physical meanings and significance are not elucidated the objective of this paper is to demonstrate that a simple extension of the critical state framework is sufficient to capture the geomechanical behavior of mh bearing soils from various sources around the world while the significance of each parameter is quantified through variance based global sensitivity analyses our results show that the influence of hydrates can be largely represented by one hydrate dependent parameter pcd which controls the expansion of the initial yield surface this is validated through comparisons with shearing and volumetric response of mh bearing soils tested at various institutes under different confining stresses and with varying degrees of hydrate saturation our study suggests that the behavior of mh bearing soils can be reasonably predicted based on pcd and the conventional critical state parameters of the host sediments that can be obtained through typical geotechnical testing procedures

uptake of excess co2 by an outcrop diffusion model of the ocean a carbon cycle model is presented in which direct ventilation of intermediate and deep ocean waters in high latitudes is taken into account the 1 dimensional ocean model is an extension of a box diffusion model including a deep sea outcrop at the surface if both are calibrated in a consistent way the outcrop diffusion ocean takes up more excess co2 than the box diffusion ocean because the outcropping deep water is essentially virgin as to fossil co2 two calibration methods are compared using the distribution either of natural or of bomb produced 14c the latter leads to a higher oceanic uptake of excess co2 than the former and to a better agreement with the observed atmospheric increase long term model responses are also discussed

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

biomarkers in coastal marshlands environmental characteristics of the mazarron basin during the middle pleistocene mis 7 and holocene mis 1 abstract we reconstructed the paleoenvironmental conditions of the mazarron basin during mis 7 and mis 1 based on their alkane and fatty acid contents their mineralogy and the fossil content of an amino acid dated sediment sequence the n alkane and fatty acid indices proved to be excellent paleoenvironmental proxies for studying the paleo hydrogeological and paleoclimatological evolution of this marshland three geochemical units gus were identified from the abundance of the c25 n alkane and the acl tarhc and paq values confirming the importance of phases with terrestrial plant input or aquatic macrophyte predominance these gus were used to define three paleoenvironmental episodes pes during mis 7 in pe7 1 the contribution of algal and aquatic macrophytes predominated in a temporarily flooded saline muddy plain in pe7 2 the major contribution was from aquatic macrophytes flooded marsh although it was marked by episodes of emersion with greater terrestrial contribution at the top of the mis 7 record pe7 3 there was a significant reduction in the water depth with the main input deriving from terrestrial plants in a muddy alluvial plain six pes were established during mis 1 holocene of which three predominately received organic matter derived from aquatic macrophytes while the major contribution in the other three came from terrestrial plants the two sets of pes were linked to episodes of increased and decreased water level respectively this interpretation is consistent with the characteristics of the sediment facies with pe1 1 1 3 and 1 5 corresponding to a marsh with deeper water and a greater input of detrital materials and pe1 2 1 4 and 1 6 to a shallow environment with carbonates and gypsum deposits direct marine influence was limited so the oscillations in the water level in the marsh were likely to be more related to climatic changes drier wetter phases and recent tectonics than to large changes in sea level emersion led to degradation of the organic matter and enrichment in short chain and branched saturated fatty acids

deformation characteristics of two cemented calcareous soils the effect of cementation on the deformation characteristics of two cemented calcareous soils was investigated through a series of undrained triaxial tests performed under both monotonic and cyclic

non linear soil stiffness in routine design soil stress strain behaviour is highly non linear and this has an important influence on the selection of design parameters for simple routine geotechnical calculations non linear behaviour can be characterized by rigidity and degree of non linearity and these can be determined from measurements of very small strain stiffness peak strength and failure strain very small strain stiffness can be found from measurements of shear wave velocity in situ or in laboratory tests peak strength and failure strain can be measured in routine laboratory tests but are strongly influenced by initiation of shear bands the important non linear stiffness parameters for soil are related to its composition and to its current state back analyses of the load settlement behaviour of full scale and model foundations demonstrate the influence of non linear soil behaviour variations of stiffness with settlement calculated from full scale and model foundations agree well with non linear soil stiffnesses based on rigidity and d

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

hydrologic variation during the last 170 000 years in the southern hemisphere tropics of south america despite the hypothesized importance of the tropics in the global climate system few tropical paleoclimatic records extend to periods earlier than the last glacial maximum lgm about 20 000 years before present we present a well dated 170 000 year time series of hydrologic variation from the southern hemisphere tropics of south america that extends from modern times through most of the penultimate glacial period alternating mud and salt units in a core from salar de uyuni bolivia reflect alternations between wet and dry periods the most striking feature of the sequence is that the duration of paleolakes increased in the late quaternary this change may reflect increased precipitation geomorphic or tectonic processes that affected basin hydrology or some combination of both the dominance of salt between 170 000 and 140 000 yr ago indicates that much of the penultimate glacial period was dry in contrast to wet conditions in the lgm our analyses also suggest that the relative influence of insolation forcing on regional moisture budgets may have been stronger during the past 50 000 years than in earlier times d 2003 university of washington all rights reserved

tracing the north atlantic decadal scale climate variability in a late holocene pollen record from southern siberia abstract this paper presents a new palynological record from a 146 cm long finely laminated sediment core obtained in 2009 from the deep water meromictic lake shira 54 30 38 n 90 12 09 e ca 353 m a s l situated in the khakassian steppe region of southern siberia between the rivers ob and yenisei the area is rich in lakes and represents an exceptionally well preserved sequence of bronze and iron age archeological cultures little is known about the changes in vegetation and climate of the region during the holocene the palynological analysis of the core allows us to partly fill up this gap in current knowledge the record of pollen and non pollen palynomorphs presented here covers the past 2450 year interval with an average resolution of 22 years the results obtained support the interpretation that the late holocene vegetation changes around lake shira are mainly associated with large scale atmospheric circulation processes controlling the regional water balance rather than with human activities an attempt to trace human impact in the pollen assemblages provides no clear evidence for anthropogenic activity except for the last few decades since ca 1955 though the region has a long history of mobile pastoralists for explanation of decadal scale changes in the regional vegetation cover the artemisia chenopodiaceae a c pollen ratio proved to be a reliable indicator of effective moisture availability using available fossil and published instrumental data our study suggests a link between the north atlantic warmer colder temperatures and higher lower atmospheric precipitation or moisture availability in southern siberia at multi decadal to centennial scales

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

information on past solar activity and geomagnetism from 10 be in the camp century ice core a nearly continuous record of the concentration of 10be from ice core data is compared with the tree ring derived record for 14c over the same period and it is found that short term trends in these data sets provide a record of solar activity no definitive relationship between the long term trends and the geomagnetic dipole moment is found

decadal to millennial scale periodicities in north iceland shelf sediments over the last 12 000 cal yr long term north atlantic oceanographic variability and solar forcing giant piston core md99 2269 recovered 25 m of sediment in hunafloaall a deep trough on the north iceland margin fronting the iceland sea and the site of a shelf sediment drift the rate of sediment accumulation is 2 m kyr 5 yr cm the core terminated in the vedde tephra v12 cal ka the sediment was sampled at between 5 and 50 yr sample including rock magnetic grain size and sediment properties data reduction was carried out using principal component analysis two pc axes for the 5 yr sample magnetic data are strongly correlated with measures of coercivity arm20 mt arm and magnetic concentrations karm in turn arm20 mt arm is highly correlated negatively with grain size and the mean size of the sortable silt fraction analyses of the two pc axes with mtm spectral methods indicate a series of significant s 99 periodicities at millennial to multidecadal scales including those at v200 125 and 88 yr which are associated with solar variability we also document a strong correlation between the sediment magnetic properties and the d 18 o on benthic foraminifera on the north iceland inner shelf we hypothesize that the links between variations in grain size magnetic concentrations and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of atlantic and polar waters along the north iceland margin today these changes are associated with variations in the deep convection in the greenland and iceland seas the precise linkages are however presently elusive although a combination of coarser sediments and low d 18 o values define a holocene thermal maximum between v8 and 6 cal ka 2003 elsevier science b v all rights reserved

evidence of higher order solar periodicities in china temperature record we examine here a 2000 year long record of surface air temperature from china using powerful spectral and statistical analysis techniques to assess the trend and harmonics if any our analyses reveal statistically significant periodicities of order 900 50 480 20 340 10 190 10 and 130 5 years which closely match with the known higher order solar cycles these periodicities are also similar to quasi periodicities reported in the climate records of sedimentary cores of subarctic and subpolar regions of north america and north pacific thus attesting to the global signature of solar signals in temperature variability a visual comparison of the temperature series shows that the nodes and antinodes of the underlying temperature variation also match with sunspot variations we also compare the china temperature ct with temperature of northern and southern hemispheres of the past 1000 years the study reveals strong correlation between the southern hemispheric temperatures and ct during the past 1000 years however the northern hemisphere temperature shows strong correlation with ct only during the past century interestingly the variations in the correlation coefficient also have shown periodicities that are nearly identical to the periods observed from ct and higher order solar cycles we suggest that the solar irradiance induces global periodic oscillations in temperature records by transporting heat and thermal energy possibly through the coupling of ocean atmospheric processes and thereby reinforcing the sun ocean climate link

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr