climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

textures in layered silicates progressive changes through diagenesis and low temperature metamorphism abstract phyllosilicates in samples from gulf coast cores and the martinsburg formation near lehigh gap pennsylvania which together represent a continuous sequence from mudstone to slate are shown by tem studies to possess imperfections on a massive scale and to exhibit a progressive increase in perfection through diagenesis and low grade metamorphism in shallow portions 1 750 and 2 450 m of the gulf coast core smectites have irregular and curved layers with high dislocation densities and many small angle grainlike boundaries in both the deeper portion 5 500 m of the gulf coast sediments and in the martinsburg mudstone samples gram perfection increases in illites but a complex mosaic structure with small angle grain boundaries and edge dislocations still prevails in the martinsbu g slate phyllosilicates exhibit layers which are continuous and straight and have few imperfections original clays which form at low temperatures have highly imperfect and metastable structures changes with increasing diagenesis are akin to annealing processes with increasing perfection of grains being an approach to a more stable strain free structure temperature pore water time and other variables affecting these changes act only to promote reaction rates to the defect free stable structures

high frequency of super cyclones along the great barrier reef over the past 5 000 years understanding long term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances1 2 3 4 5 for predicting present and future community vulnerability and economic loss6 and for assessing whether changes in the variability of such cyclones are induced by climate change7 our ability to accurately make these assessments has been limited by the short less than 100 years instrumented record of cyclone intensity here we determine the intensity of prehistoric tropical cyclones over the past 5 000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse grained alluvial fan deposits these features occur along 1 500 km of the great barrier reef and also the gulf of carpentaria australia we infer that the deposits were formed by storms with recurrence intervals of two to three centuries8 9 10 11 and we show that the cyclones responsible must have been of extreme intensity central pressures less than 920 hpa our estimate of the frequency of such super cyclones is an order of magnitude higher than that previously estimated which was once every several millennia12 13 14 and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events

3500 year western pacific storm record warns of additional storm activity in a warming warm pool abstract frequent storm surges often cause catastrophic impacts on human lives and the global economy however these phenomena are not well understood in this study a regional storm reconstruction is performed based on a grain size analysis and stratigraphic modelling of the accelerator mass spectrometry radiocarbon dates of benthic foraminifera from two neighbouring lagoon cores from lingyang reef in the xisha islands located in the northern south china sea of the western pacific the dating results from the lagoon cores reveal a 3500 year depositional history three different depositional units are recognized based on a time series of distinct grain size variations that correspond to the following three stages of storm activity intense and frequent storms from 3500 to 3100 cal yr bp and 1800 cal yr bp to present and weak and infrequent storms from 3100 to 1800 cal yr bp a high sedimentation rate remarked by reverse and chaos age is observed from 2800 to 2600 cal yr bp in both cores and it was likely associated with a tsunami event in addition grain size variability may be associated with changes over time caused by the synchronous asian monsoon and may also be correlated with climate records retrieved from the ice cores from greenland thus this variability could indicate pervasive global climatic teleconnections the overall temporal patterns of the isolated coral branches and shells from the sediment sequences are well correlated with the high sea surface temperatures in the western tropical pacific we suggest that increasing sea surface temperatures in the future may lead to more intense storm activity in the western pacific warm pool as the planet warms

investigating enso and wpwp modulated typhoon variability in the south china sea during the mid late holocene using sedimentological evidence from southeastern hainan island china abstract the link between tropical cyclone tc activity in the south china sea scs and global climate change is commonly debated and there is a clear need for long term geological records of tc activity if we are to clarify this connection multi millennial high resolution paleo storm records from the scs are rare in the region and this causes difficulties for those exploring potential climate drivers of tc variability over centennial to millennial timescales and reduces our ability to fully assess the risks associated with future tc activity this paper presents an age constrained mud dominated sedimentary sequence from a coastal lagoon on hainan island china multiproxy analyses incorporating chronological lithological sedimentological and geochemical evidence were used to infer storm deposits preserved within the sequence and to reconstruct a time series of storm activity in the scs during the mid to late holocene this long sedimentary record shows that tcs were highly active over the periods 5500 to 3500 and 1700 to 0 cal yrs bp and these periods contrast with a relatively quiet period 3500 1700 cal yrs bp an apparent inverse correlation between tc reconstructions from the scs and those from the korean peninsula and japan implies an oscillating pattern across the scs and western north pacific wnp over centennial to millennial timescales a comparison between the sedimentary and paleoclimatic records implies that the el nino southern oscillation was not the only mechanism responsible for typhoon variability over the past 7500 cal yrs bp suggesting that other factors such as the thermal state of the western pacific warm pool likely also had a strong influence on both scs and wnp tc variability

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

high precision u series dating of very young cyclone transported coral reef blocks from heron and wistari reefs southern great barrier reef australia numerous high energy transported coral reef blocks occur on the outer reef flats of heron and wistari reefs at the southern end of the great barrier reef in a pilot study five samples from heron and one from wistari were collected for high precision u series dating by thermal ionization mass spectrometry five of the six dated corals yield u series dates that suggest these corals were killed and transported during the last century without precise knowledge of cyclone impacts in the area it is not possible to unequivocally link these reef blocks to specific cyclones nevertheless this pilot study demonstrates that cyclone transported coral reef blocks over the past 300 years can be precisely dated to an age uncertainty of 1 4 years this opens up the opportunity for high age resolution reconstruction of cyclone history and high precision assessment of the trend and frequency of cyclone occurrences over the past millennium as well as for a better understanding of anthropogenic impact on cyclone activity c 2008 elsevier ltd and inqua all rights reserved

petrographic examination of sedimentary rocks in the sem using backscattered electron detectors abstract most of the geological work in scanning electron microscopy has been undertaken using the secondary electron se mode and to a lesser extent the cathodoluminescence cl mode but in the last few years attention has been drawn to the advantages of imaging with backscattered electrons bse the coefficient of electron backscattering from polished specimens is strongly dependent on average atomic number allowing different mineral phases to be distinguished on the basis of differences in gray level a great deal of useful information about the size distribution shape orientation and textural relationships of minerals in situ can be gained from bse images these data can be processed by various image analysis systems which are now commercially available this paper reviews the na ure and formation of bse electrons discusses some of the problems which limit the quality of bse images of sedimentary rocks and illustrates some applications of the technique

the structure and driving mechanisms of the baltic intrusions abstract data from closely spaced ctd profiling performed in the eastern gotland basin after the 1993 inflow event are used to study thermohaline intrusions in the baltic sea two ctd cross sections display abundant intrusive layers in the permanent halocline despite the overwhelming dominance of the salinity stratification diffusive convection is shown to work in the baltic halocline enhancing diapycnical mixing to understand the driving mechanisms of observed intrusions these are divided into different types depending on their structural features only two types of observed intrusions are suggested to be strongly influenced by diffusive convection 1 relatively thin 3 5 m and long up to 8 km intrusions inherent to high baroclinicity regions and 2 relatively thick 10 m and short 2 5 km intrusions inherent to low baroclinicity regions to verify this hypothesis the linear stability models of 3d and 2d double diffusive interleaving in approximation of a finite width front were used it is sh

depositional evidence for the kamikaze typhoons and links to changes in typhoon climatology in the late 13 th century kublai khan ruler of the mongol empire launched one of the world s largest armadas of its time in an attempt to conquer japan early narratives described the decimation and dispersal of these fleets by the kamikaze of 1274 ce and 1281 ce a pair of intense typhoons divinely sent to protect japan from invasion these historical accounts are prone to exaggeration and significant questions remain regarding the occurrence and true intensity of these legendary typhoons to provide independent insight we present a new 2000 yr sedimentary reconstruction of extreme coastal flooding from a coastal lake near the location of the mongol invasions two marine sourced flood deposits date to the kamikaze typhoons and are the events of record in the reconstruction the complete reconstruction indicates periods of greater flood activity relative to modern beginning ca 250 ce and extending past the timing of the kamikaze events to 1600 ce comparisons with additional reconstructions are consistent with greater regional typhoon activity during the mongol invasions due to the preferential steering of storms toward japan and driven by greater el nino activity relative to modern results are consistent with the paired kamikaze typhoons being of significant intensity and support accounts of them playing an important role in preventing the conquering of japan by mongol fleets the kamikaze typhoons may therefore serve as a prominent example for how past increases in severe weather associated with changing climate have had significant geopolitical impacts

an experimental study on the formation and survival of stratified subsurface eddies we report the results of laboratory experiments on the formation and survival of internally stratified subsurface eddies in a rotating fluid the eddies were created by injecting a dense turbulent plume at the surface of a linearly stratified environment the relative vorticity of the lenses was always negative but larger than that of homogeneous lenses created by laminar injection during the first 100 revolutions the eddies shed fluid in two symmetric arms the shedding which is believed to result from shear instabilities always resulted in a stationary axisymmetric eddy after the eddy had spun down the remnant fluid persisted for thousands of rotations as a circular feature with internal stratification identical to that of the environment we created eddies with and without double diffusive convective instabilities and compared the volume of dyed fluid and the evolution of their aspect ratios sugar and salt were used as laboratory analogues of salt and heat respectively the burger number of the lenses decreased rapidly within the first 200 revolutions and then much more slowly to reach a value between 0 2 and 0 4 these latter values are larger than those predicted by gill 1981 for a homogeneous lens due to the internal stratification of the lenses radial spreading of the lens due to double diffusive intrusions was found to be larger but of the same order of magnitude as that induced by the vertical exchange of momentum in the absence of double diffusive convection we formed eddies internally stratified in the diffusive sense stable sugar gradient and unstable salt gradient or doubly stable stable sugar and salt gradients by changing the ratio of the volume flux at the source to the volume flux at the spreading level as described by bormans and turner 1990 when the stratification in the eddies was doubly stable three distinctive regions were observed a region of convective layers and diffusive density interfaces at the top a central region with no apparent structure and a bottom region dominated by fingers sheared by rotation this type of eddy is compared to the particular case of a meddy

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

phytolith assemblages as indicators of coastal environmental changes and hurricane overwash deposition we demonstrate that phytolith assemblages are a useful proxy for reconstructing coastal environmental changes and for validating the overwash origin of sand layers in palaeotempestology studies phytolith analysis was conducted on 50 topsoil or surface sediment samples collected from a variety of coastal plant communities or depositional environments in the southeastern usa the data suggest that different coastal subenvironments can be distinguished by their modern phytolith assemblages for example coastal marsh samples contain a diverse phytolith assemblage dominated by smooth elongate and square morpho types and maritime forest samples are dominated by phytoliths from palms and broadleaf dicotyledonous plants remarkably the phytolith assemblages from sand dunes are characterized by high percentages of two horned tower flat tower spool horned tower and short saddle types phytolith analysis of three prehistoric sand layers in a sediment core from western lake northwestern florida shows that they contain a phytolith assemblage similar to those characteristic of sand dunes and interdune meadows these observations are confirmed by the results of principal components analysis and discriminant analysis on the modern and fossil phytolith data sets our study results support the interpretation that the sand layers in western lake were indeed formed by the erosion of sand dunes during overwash processes caused by landfalling catastrophic hurricanes

grain size of lake qinghai sediments implications for riverine input and holocene monsoon variability abstract grain size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment various grain size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake here we present the grain size results of a 5 m core retrieved from lake qinghai northeastern tibetan plateau in order to address the links between holocene depositional process and climatic change our results indicate that two parameters skewness and grain size ratio of 8 50 2 8 m are sensitive to hydrodynamic changes in lake qinghai which are further linked to the strength of the asian summer monsoon variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late holocene superimposed by persistent centennial variability with dominant periods at 0 35 0 23 and 0 12 kyr comparison of grain size variations with solar activities and north atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

phyllosilicates in hydrothermally altered basalts from dsdp hole 504b leg 83 a tem and aem study phyllosilicates occurring as replacements of olivine clinopyroxene and interstitial materials and as veins or fracture fillings in hydrothermally altered basalts from dsdp hole 504b leg 83 have been studied using transmission and analytical electron microscopy the parageneses of phyllosilicates generally change systematically with depth and with the degree of alteration which in turn is related to permeability of basalts saponite and some mixed layer chlorite smectite are the dominant phyllosilicates at the top of the transition zone chlorite corrensite and mixed layer chlorite corrensite occur mainly in the lower transition zone and upper levels of the sheeted dike zone chlorite talc and mixed layer talc chlorite are the major phyllosilicates in the sheeted dike zone although replacement of talc or ohvine by saponite is observed the phyllosilicates consist of parallel or subparallel discrete packets of coherent layers with packet thicknesses generally ranging from 100 a to a few hundred a the packets of saponite layers are much smaller or less well defined than those of chlorite corrensite and talc indicating poorer crystal linity of saponite by contrast chlorite and talc from the lower transition zone and the sheeted dike zone occur in packets up to thousands of a thick the si si al ratio of these trioctahedral phyllosilicates increases and fe fe mg decreases in the order chlorite corrensite saponite and talc these relations reflect optimal solid solution consistent with minimum misfit of articulated octahedral and tetrahedral sheets variations in composition of hydrothermal fluids and precursor minerals especially in si si al and fe fe mg ratios are thus important factors in controlling the parageneses of phyllosilicates the phyllosilicates are generally well crystallized discrete phases rather than mixed layered phases where they have been affected by relatively high fluid rock ratios as in high permeability basalts in veins or areas adjacent to veins intense alteration in basalts with high permeability indicating high fluid rock ratios is characterized by pervasive albitization and zeolitization minimal alteration in the basalts without significant albitization and zeolitization is characterized by the occurrence of saponite mixed layer chlorite smectite in the low temperature alteration zone and mixed layer chlorite corrensite or mixed layer talc chlorite in the high temperature alteration zone textural non equilibrium for phyllosilicates is represented by mixed layering and poorly defined packets of partially incoherent layers the approach to textural equilibrium was controlled largely by the availability of fluid or permeability

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

holocene sea level history of the northern coast of south china sea abstract this study has collected and analyzed seven sediment cores from the pearl river delta from which 16 new and high quality sea level index points are generated using a new approach this study has also re checked and re calibrated the previously published sea level data from china s southeast coast with corrections made for tectonic subsidence and sediment compaction factors these sea level data indicate a rise of relative sea level from 49 3 0 8 m to the present height between 10 500 and 7000 cal a bp this sea level history is similar to those recorded from other far field locations and ice volume equivalent sea level models the early to early middle holocene sea level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16 4 6 1 mm a at 10 500 cal a bp to 33 0 7 1 mm a at 9500 cal a bp this phase was followed by a period of rapid decrease in the rate of sea level rise to 8 8 1 9 mm a at 8500 cal a bp and 1 7 1 3 mm a at 7500 cal a bp during the past 7000 years the relative sea level in the study area changed very little this new and complete history of holocene sea level change supports the following findings 1 no obvious higher than present sea level highstand in the holocene is found from the northern south china sea 2 certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area 3 meltwater pulse 1b likely exists spanning into the early holocene 4 there are significant misfit between sea level data and glacial isostatic adjustment models and a revision to the existing ice melting history for the early holocene is possibly needed

storm cycles in the last millennium recorded in yongshu reef southern south china sea large storm relocated porites coral blocks are widespread on the reef flats of nansha area southern south china sea detailed investigations of coral reef ecology geomorphology and sedimentation on yongshu reef indicate that such storm relocated blocks originated from large porites lutea corals growing on the spurs within the reef front living coral zone because the coral reef has experienced sustained subsidence and reef development during the holocene dead corals were continuously covered by newly growing coral colonies for this reason the coral blocks must have been relocated by storms from the living sites and therefore the ages of these storm relocated corals should approximate the times when the storms occurred rapid emplacement of these blocks is also evidenced by the lack of coral overgrowth encrustation or subtidal alteration u series dating of the storm relocated blocks as well as of in situ reef flat corals suggests that during the last 1000 years at least six strong storms occurred in 1064 30 1210 5 1201 4 1336 9 1443 9 1685 8 1680 6 1872 15 ad respectively with an average 160 year cycle 110 240 years the last storm which occurred in 1872 15 ad also led to mortality of the reef flat corals dated at similar to 130 years ago thus the storm had significant impacts on coral reef ecology and morphology c 2004 elsevier b v all rights reserved

extracting historic cyclone data from coastal dune deposits in eastern hainan island china abstract understanding long term large cyclone activity is critical for coastal management and disaster prevention and mitigation particularly with projected rising sea level and increasing cyclone frequency and the intensity here we present sedimentary evidence cyclone overwash deposits beachrock boulders and cyclone induced clastic deposits of historic large cyclone events from coastal dune deposits on eastern hainan island china based on luminescence dating and sedimentological analysis eight historic tropical cyclone events at 1095 90 bce 900 1000 bce 975 50 ce 1720 20 ce 1740 35 ce 1790 25 ce 1850 15 ce and 1895 10 ce have been identified in this region the elevation of the termination point of cyclone overwash deposit layers that represent the paleo cyclone minimum wave run up stage in combination with knowledge of present day cyclone events was applied to assess the intensity of these extreme events the intensity of these cyclone events was likely greater than that of cyclones in the local instrumental records furthermore these large cyclone events correspond to historic records of devastating cyclones through comparison with regional and global climate records we infer that the variability of large cyclones in the south china sea was probably modulated by the el nino southern oscillation western pacific warm pool and local sea surface temperatures over the past 3400 yr these results provide an improved understanding of long term extreme cyclone events and their response to climate change thereby contributing to regional planning and coastal defense strategies

double diffusive interleaving part i linear stability analysis abstract quasi horizontal interleaving between water masses is frequently observed in the frontal regions between different water masses where there are significant compensating isopycnal gradients of temperature and salinity it is believed that these intrusions are driven by double diffusive convection which transports salt heat and density across sharp quasi horizontal interfaces i e across regions of large vertical property gradients stern and other investigators have parameterized the vertical flux of salt in these intrusions by an eddy diffusivity multiplied by the vertical gradient of salinity whereas laboratory experiments show that sharp interfaces tend to occur by double diffusive convection and that the vertical fluxes of properties depend on the property contrasts across the interfaces in this paper it is assumed that the vertical fluxes of double diffusive convection are proportional to the salinity contrast across the sharp interfaces that occur between the quasi horizontal intrusio

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

chlorite illite muscovite interlayered and interstratified crystals a tem stem study phyllosilicates in rocks which are transitional from mudstone to slate from lehigh gap pa have been studied by a variety of techniques including high resolution transmission electron microscopy and analytical electron microscopy the principal minerals are white mica which is transitional from illite in mudstone to ordered twolayer mica in slate and chlorite 7a berthierine occurs more rarely dioctahedral and trioctahedral layers are shown to be interleaved in individual crystals at all scales between the following two end members 1 both random and regular 1 1 interlayering at the scale of individual layers as shown in part by lattice fringe images 2 packets of trioctahedral and dioctahedral layers up to a few thousand angstroms or microns in thickness detectable with ordinary optical techniques the complete range of intermediate structures is represented in samples which are in transition to slate bulk analytical empa x ray diffraction or other measurements are shown to result in averages over both kinds of layers when tem techniques are not used

the behavior of double diffusive intrusion in a rotating system the effects of earth s rotation on the stability of a thermohaline front of finite width are studied by means of a linear theory it is found that when the rotation is present two different types of unstable modes are possible when the front is narrow and a rossby radius of deformation based on ruddick and turner s 1979 vertical scale is large in comparison with the width of the front the fastest growing intrusion is nearly two dimensional nonrotational mode and its vertical scale is given by ruddick and turner s scale when the rossby radius becomes small in addition to the nonrotational mode there appears another unstable mode the rotational mode which has a smaller vertical wave number than the nonrotational mode with the introduction of rotation the fastest growing mode has nonzero along frontal wave number that is the intrusion becomes tilted in the along frontal direction when the rossby radius of deformation is sufficiently small in comparison with the width of the front transition from the nonrotational mode to the rotational one occurs the transition from nonrotational to rotational mode becomes less pronounced when the width of the front is increased for fixed horizontal density compensating gradients of temperature and salinity for a wide front the growth rate and vertical wave number for both modes becomes similar which agrees with the results of previous studies for infinite fronts that rotation does not modify the behavior of the intrusion except for the occurrence of along frontal tilt

chronostratigraphy and geomorphology of washover fans in the exmouth gulf nw australia a record of tropical cyclone activity during the late holocene abstract washover fans typically form due to barrier overwash or breaching and coastal inundation and generally represent geomorphological and depositional evidence of intense storms few studies have investigated the chronostratigraphy of washover fans in order to infer magnitude frequency patterns of extreme wave events over longer time scales here we present new data on the chronostratigraphy of late holocene washover fans in the exmouth gulf western australia by using ground penetrating radar and unmanned aerial vehicle uav survey techniques as well as geomorphological sedimentological and chronological investigations this study aims to i provide a detailed characterization of the washover fans geomorphology and stratigraphical architecture ii document depositional processes involved in their formation iii establish a chronostratigraphy based on optically stimulated luminescence osl and iv understand the significance of the washover fans for recording past tropical cyclone tc activity the fans consist of multiple sequences of sand shell debris and coral rubble comprising depositional units related to tc induced inundation the units are separated by palaeosurfaces with incipient soil formation formed during periods of reduced depositional activity in combination with the interpretation of a uav based high resolution digital surface model multiple phases of reactivation are inferred osl results allow the establishment of a local long term tc record and suggest storm induced deposition at 170 360 850 and 1300 years ago further units were dated to 1950 2300 and 2850 years ago the chronology of tc events is consistent with other work relating tc activity with el nino southern oscillation enso and sea surface temperature sst patterns corroborating the regional palaeotempestological relevance of this unique geomorphological record

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

genesis and solvus relations of submicroscopically intergrown paragonite and phengite in a blueschist from northern california electron microbeam techniques have been used to examine submicroscopically intergrown paragonite phengite and chlorite from the south fork mountain schist of the franciscan terrane of northern california which was subjected to blueschist facies metamorphism the sample also contains quartz albite lawsonite and rutile the subassemblage albite lawsonite rutile requires metamorphic conditions on the low temperature side of the equilibrium albite lawsonite rutile paragonite sphene quartz h2o t 200 c and p 7 4 kbars based on thermodynamic data of holland and powell 1990 the white micas appear to be optically homogeneous but back scattered electron images can distinguish two different micas by their slight difference in contrast electron microprobe analyses empa of micas show na na k ranging from 0 2 to 0 8 the two micas are resolved by transmission electron microscopy tem as packets of phengite and paragonite that range from 20 to several hundred nm in thickness the compositions determined by analytical electron microscopy aem constrain the limbs of the phengite paragonite solvus to values of na na k 0 02 and 0 97 representing less mutual solid solution than ever reported by empa the textural relations imply that the sheet silicates were derived from reactions between fluids and detrital clays and that they are in an intermediate stage of textural development we caution that microprobe analyses of apparently homogeneous sheet silicates may yield erroneous data and lead to faulty conclusions using phengite barometry and paragonite muscovite thermometry especially in fine grained rocks that formed at relatively low temperatures

partial interlayers in phyllosilicates studied by transmission electron microscopy interstratification of complete layers has long been recognized in phyllosilicates interlayering on a fine scale with a host containing partial layers of a second phase has only recently been recognized by using tem considering similarities in structural units of phyllosilicates this type of interlayering should be expected alteration samples from butte montana show extensive development of partial interlayers in kaolinite sericite and pyrophyllite kaolinite found in plagioclase sites always grows from smectite and in the growth process incorporates unit cell thick lenses of the smectite the interlayers show up as increased spacing in 001 fringes and cause considerable strain in the surrounding kaolinite structure pyrophyllite studied was found to have abundant interlayers and inclusions of muscovite this muscovite was identified from diffuse 10 a reflections and microanalysis the muscovite inclusions are usually less than 5 layers thick and extend from 50 a to 1 000 a in the ab plane in sericite fine interlayering is subtle for the interlayers vary only slightly in unit cell size and composition from the host however structural changes are significant enough to cause imagable strain contrast in the host zones of fine interlayers are thought to mark healed subgrain boundaries which originally were zones of compositional heterogeneity

thermohaline intrusions in the frontal zones of a warm core ring observed by batfish hydrographic data collected with a towed depth cycling instrument batfish in the frontal regions of warm core ring 82h during and immediately after its formation were analyzed to study small scale structure and processes the frontal and slope water regions are characterized by a complex water mass structure resulting from mixing of the shelf the slope and the sargasso sea waters thermohaline intrusions along constant density surfaces are frequently observed two forms of thermohaline intrusions are studied in detail subsurface tonguelike intrusions and cold filaments a subsurface tongue of shelf water origin was found in the slope water region outside the frontal zone at 70 m depth it had a width of 4 km a thickness of 20 m and a length of at least 40 km and moved in a southeast direction toward the front alongside the subsurface tongue a cold filament 10 km wide extending from the surface to 120 m depth was observed as the subsurface tongue and the filament moved toward the frontal zone their orientation became more and more aligned with the front when they reached the front the strong frontal current carried them downstream and hence prevented further intrusion into the ring mixing in the form of interleaving then became the most important process for cross front mixing interleaving occurs along the side walls of the subsurface tongue and filament with more intense interleaving associated with stronger intrusions this suggests a double diffusive generation mechanism of the interleaving

holocene vegetation environment and anthropogenic influence in the fuzhou basin southeast china a 40 m sediment core fz4 was collected from the fuzhou basin near the lower reaches of the min river in fujian province on the southeast coast of china the sediment and pollen record contributes to our understanding of holocene paleogeography including local changes in vegetation and climate in the context of neolithic cultural developments the sediment record reveals a fluvial environment in the fuzhou basin during the late pleistocene and it demonstrates that a change from fluvial to estuarine conditions at 9000 cal yr bp resulted from postglacial sea level rise evidence of abundant marine diatoms and tidal flat laminations observed in the fz4 sediments implies that the fuzhou basin was under marine influence between 9000 and 2000 cal yr bp after 2000 cal yr bp a rapid retreat in coastline associated with fluvial aggradation and coastal progradation produced more shallow water for wetlands and initiated formation of the floodplain landscape the pollen record reveals the presence of a dense subtropical forest between ca 9000 and 7000 cal yr bp representing the holocene thermal maximum which is linked with rising sea level and marine transgression in the fuzhou basin between ca 5500 and 2000 cal yr bp the thermophilous forest dominated by castanopsis retreated and coniferous forest expanded reflecting moderate climatic cooling during this period timing of the high frequencies for pinus and ferns correspond with the mid late holocene cooling trend recorded in local mountain peatland and coastal regions of the lower yangtze and hanjiang deltas anthropogenically induced land cover change was negligible prior to the tanshishan cultural period which marks the beginning of neolithic era sedentary village life on the fujian coast around 5500 bp the pollen transition at ca 3000 1500 cal yr bp distinguished by rising frequencies of poaceae and taxa including cyperaceae and artemisia closely associated with agricultural land cover indicates exploitation of newly formed lowlands in the emerging min river floodplain the historic era intensification of rice agriculture is reflected in this trend of rising frequencies of poaceae after ca 2000 cal yr bp we observe the onset of a marine regression followed by evidence for an intensely human impacted environment characterized by sharp rises in pioneer plants such as poaceae and dicranopteris this transition coincides with a rapid retreat of coastline and emergence of the fuzhou basin floodplain

relationship of concretions and chlorite muscovite porphyroblasts to the development of domainal cleavage in low grade metamorphic deformed rocks from north central wales great britain abstract spaced or domainal cleavage is widespread in deformed rocks of low metamorphic grade this study presents evidence on the origin of spaced cleavage in deformed pelites from silurian turbidite sequences in north central wales the variable development of cleavage folia is related to the presence of concretions which served to concentrate strain effects of well developed cleavage folia in the matrix in some zones and to produce strain shadows few or no cleavage folia in others compositional differences between matrix narrow transition zones and concretions also influenced the development of cleavage folia chlorite muscovite porphyroblast growth was initiated before cleavage formation but its further growth and development took place during cleavage formation the relationship of cleavage to the concretions and to the chlorite muscovite porphyroblasts indicates that cleavage developed in a matrix that must have been in an advanced state of lithification anchimetamorphic to lowermost greenschist facies of metamorphism and not during soft sediment deformation

high resolution record of paleoclimate since the little ice age from the tibetan ice cores climate changes during the little ice age were studied based on oxygen isotope values 18o measured from ice cores recovered on and nearby the qinghai tibetan plateau three cold periods have been identified and are supported by three widely existing moraine ridges formed during the little ice age importantly the amplitude of the three cold periods differ in the cores studied in the dunde ice core the coldest period occurred in the 17th century while it occurred in the 19th century in the guliya ice core all the ice cores recovered from the tibetan plateau and nearby regions show strong climatic warming in the 20th century

600 year sedimentary archive of hurricane strikes in a prograding beach ridge plain southwestern louisiana abstract this study tests a novel approach to paleotempestology substituting the lateral time depth of a prograding beach ridge plain for the vertical time depth of an aggrading coastal lake pond lagoon swamp or marsh trenching and coring of a beach ridge plain in southwestern louisiana revealed six sand beds and one shell bed interpreted as hurricane washover deposits the sand beds are readily distinguished from enclosing marsh sediments by their higher sand content lower organic content and contrasting microfossil assemblages based on the modern analogs of hurricanes audrey 1957 rita 2005 and ike 2008 and consideration of nearby landfalling hurricanes in the historical record it was determined that the storm intensity threshold of the study site is equivalent to a category 3 hurricane there is a wide variation in hurricane strike frequency between this site and other sites bordering the gulf of mexico this variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records the approach demonstrated by this study could have applicability at other sites around the world where beach ridge plains are subject to tropical cyclone strikes

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

numerical experiments on double diffusive intrusions in the ocean and their relation to laboratory experiments abstract numerical experiments on double diffusive intrusions are reviewed briefly though the number of studies is very limited at present they have undoubtedly an advantage that a heat salt system can be studied without undesired heat loss from the boundaries several possibilities for future numerical experiments are summarized

dehydration related deformation during regional metamorphism nw sardinia italy the relationship between deformation and dehydration has been investigated in hercynian regionally metamorphosed rocks exposed on nw sardinia two episodes of prograde mineral growth m1 m2 involving dehydration are recognized growth of chlorite phengite porphyroblasts at anchizone metamorphic conditions contemporaneous with the first phase of deformation d1 and growth of biotite from chlorite and phengite coincident with the second phase of deformation d2 deformation during both episodes of dehydration is characterized by penetrative axial planar foliations defined by well developed phyllosilicate preferred orientations quantified by xrd textural goniometry tight to isoclinal similar folds interlimb angles 40 low strain similar folds and minor brittle deformation systematic variations in macrofold interlimb angles with respect to the timing of mineral growth indicate that enhanced shortening c 80 occurred during dehydration microfabrics show that the onset of dehydration is associated with the transition from a crenulation cleavage to a penetrative foliation the presence of axial planar hydrofractures that formed coevally with dehydration and fabric development requires that supralithostatic fluid pressures and low differential stresses c 20 mpa accompanied dehydration these features demonstrate a connection between the timing of dehydration and the style of deformation

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

high precision tims u series and ams c 14 dating of a coral reef lagoon sediment core from southern south china sea accurate dating of lagoon sediments has been a difficult problem although lagoon profiles usually with high deposition rates have a great potential for high resolution climate reconstruction we report 26 high precision tims u series dates on 25 coral branches and five ams c 14 dates on foraminifera for a 15 4 m long lagoon core from yongshu reef nansha area southern south china sea all the dates are in the correct stratigraphical sequence providing the best chronology so far reported for lagoon deposits the results reveal a similar to 4000 a continuous depositional history with sedimentation rates varying from 0 8 to 24 6 mm a 1 with an average of 3 85 mm a 1 which corresponds to an average net carbonate accumulation rate of similar to 2700 g caco3 m 2 a 1 significantly higher than the mean value 800 400 g caco3 m 2 a 1 used for lagoons in general in previous studies of global carbonate budget episodes of accelerated depositions within the last 1000 years correlate well with strong storm events identified by u series dates of storm transported coral blocks in the area however in the longer term the sedimentation rates during the past 1000 years were much higher than earlier on probably due to more vigorous wave reef interaction as a result of relative sea level fall since 500 ad and expansion of reef flat area supplying more sediments the coral tims u series ages and foraminifera ams 14c dates reveal intriguing apparent radiocarbon reservoir ages r from 572 to 1052 years which are much higher than global mean values of similar to 400 years c 2006 elsevier ltd all rights reserved

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

cyclone frequency during the last 5000 years at curacoa island north queensland australia abstract a series of storm deposits at curacoa island a steep bedrock island in the palm group north queensland record the passage of cyclonic events storm ridge accretion occurs when cyclonic waves and surge combine to transport coarse sediment mostly broken coral onto the shore and deposit it above normal tidal levels narrow fringing reefs at curacoa act as a rapidly replenished sediment source augmented by lithic gravel transported longshore beachface stormberm ridge platform and washover deposits can accrete during a single event a series of storm ridges were examined via stratigraphic pits and trenches on two traverses deposits from 22 events were identified and their ages were determined using 68 radiocarbon dates from coral clasts most dates from each storm deposit formed statistically accordant groups only 15 of the dates were older than the group ages and were interpreted as reworked specimens accordant ages within each group were combined and converted to calibrated radiocarbon ages ridge ages decrease uniformly with distance from the oldest ridge indicating uniform depositional processes over the last 5000 years a time series of storm deposit ages indicates that cyclone frequency was statistically constant over the last 5000 years this suggests that cyclone frequency may not have been affected by sea surface temperatures in the region which appear to have been about 1 c warmer about 5000 years ago gagan m k ayliffe l hopley d cali j mortimer g chappell j mcculloch m head m j 1998 temperature and surface water balance of the mid holocene tropical western pacific science 279 1014 1018

a linear stability theory of double diffusive horizontal intrusions in a temperature salinity front on suppose que les doigts de sel sont responsables des transports verticaux de salinite et de chaleur le front est toujours instable meme en presence de viscosite les intrusions horizontales sont engendrees par l instabilite et l eau douce et froide descend tandis que l eau salee et chaude monte

sudoite a rock forming mineral in verrucano of the northern apennines italy and the sudoite chloritoid pyrophyllite assemblage in prograde metamorphism sudoite the di trioctahedral chlorite with ideal composition mg2al al2 si3al o10 oh 8 is a widespread rock forming mineral in meta siltstones and psammites of the verrucano sequence of the northern apennines sub ellipsoidal aggregates probably derived from muscovite clasts consisting of sudoite pyrophyllite and muscovite are common sudoite may also occur as thin blades in the rock matrix the co existence of sudoite ferich chloritoid and pyrophyllite reported here for the first time has been observed in specimens from the m argentario and monticiano roccastrada areas this three phase assemblage diagnostic of a specific metamorphic facies may be a tool for detailed zonation of low grade terranes

estimation of temperature change and of gas age ice age difference 108 kyr b p at vostok antarctica air trapped in ice core bubbles provides our primary source of information about past atmospheres air isotopic composition 15n 14n and 40ar 36ar permits an estimate of the temperature shifts associated with abrupt climate changes because of isotope fractionation occurring in response to temperature gradients in the snow layer on top of polar ice sheets a rapid surface temperature change modifies temporarily the firn temperature gradient which causes a detectable anomaly in the isotopic composition of nitrogen and argon the location of this anomaly in depth characterizes the gas age ice age difference age during an abrupt event by correlation with the d or 18o anomaly in the ice we focus this study on the marine isotope stage 5d 5c transition 108 kyr b p a climate warming which was one of the most abrupt events in the vostok antarctica ice isotopic record petit et al 1999 a steplike decrease in 15n and 40ar 4 from 0 49 to 0 47 possibly a gravitational signal due to a change in firn thickness is preceded by a small but detectable 15n peak possibly a thermal diffusion signal we obtain an estimate of 5350 300 yr for age close to the model estimate of 5000 years obtained using the vostok glaciological timescale our results also suggest that the use of the present day spatial isotope temperature relationship slightly underestimates but by no more than 20 15 the vostok temperature change from present day at that time which is in contrast to the temperature estimate based on borehole temperature measurements in vostok which suggests that antarctic temperature changes are underestimated by up to 50 salamatin et al 1998

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

nonlinear equilibration of thermohaline intrusions abstract the nonlinear behavior of thermohaline intrusions on a wide front is investigated using a one dimensional numerical model the model is used to follow the evolution of a field of intrusions from infinitesimal amplitude to a large amplitude state characterized by inversions in temperature and salinity it is thus possible to extend the analytical studies of toole and georgi and others to large amplitude allowing for the effects of amplitude dependent diffusivities and for the appearance of stably stratified diffusively stratified and statically unstable regions in the water column as the intrusions grow the model runs are initialized with infinitesimal disturbances that grow exponentially in time until inversions in temperature and salinity occur after inversions appear the intrusions evolve toward an equilibrium state in which friction balances buoyancy forces for both finger and diffusive sense basic state stratifications these equilibrium states are characterized by statically unstabl

re equilibration of detrital muscovite and the formation of interleaved phyllosilicate grains in low temperature metamorphism northern apennines italy low temperature metamorphosed clastic rocks of northern apennines verrucano contain detrital and metamorphic muscovite along with aggregates of interleaved phyllosilicate grains the extent of celadonite substitution in the metamorphic muscovite progressively increases from al rich pyrophyllite bearing samples to al poor k feldspar bearing samples and appears to be compatible with the phase relation in the akf and akna diagrams some detrital muscovite grains not equilibrated with the present metamorphic mineral assemblages seem to be unreacted grains retaining their premetamorphic composition the chemistry of the re equilibrated detrital muscovite is mainly controlled by the activity of al2o3 that is implied by mineral assemblages in the host rocks and is independent of the original composition of detrital mica four types of phyllosilicate associations in the interleaved phyllosilicate grains were recognized 1 muscovite pyrophyllite sudoite 2 muscovite pyrophyllite chlorite 3 muscovite paragonite chlorite 4 muscovite chlorite a microstructural and petrological model is proposed for the origin of interleaved phyllosilicate grains in the verrucano rocks the model supports the idea that the interleaved phyllosilicate grains are the result of the trend towards equilibrium between detrital muscovite metamorphic mineral assemblages and the fluid phase

how lime sand islands in the south china sea have responded to global warming over the last 30 years evidence from satellite remote sensing images abstract as global warming threatens their existence there are widespread concerns regarding the persistence of lime sand islands and the future of mid ocean atoll nations to investigate how climate change has affected lime sand islands changes in vegetation and other characteristics of such islands in the south china sea scs were investigated from 1989 to 2019 using 67 satellite images first boundaries of the lime sand islands and their vegetation were extracted using an active contour extraction procedure called the gradient vector flow snake model afterwards the spatial extents were estimated by enclosing the extracted boundaries and the digital shoreline analysis system was used to calculate beach widths finally area growth rates and speeds were used to evaluate areal changes in the lime sand islands and their respective vegetation based on the estimated area growth rates area growth speeds and beach widths the lime sand islands in scs eroded over the past three decades whereas their vegetation expanded further analysis suggested that direct inundation caused by sea level rise might not be clearly identified from the satellite images however other climate change related factors were most likely responsible for the observed island erosions these factors included higher wave energy stronger typhoon intensity and destructiveness and accelerated coral reef degradation in addition the observed expansion of vegetation on the lime sand islands was likely due to the increase in precipitation in a warming world the results show that 1 the lime sand islands will continue to erode whereas vegetation will continue to expand 2 as vegetation growth is significantly inhibited by salt water when it is adjacent to the ocean vegetation areas on lime sand islands may start to continuously decline overall this study is the first to quantitatively examine changes in scs lime sand islands due to global warming

a decadally resolved paleohurricane record archived in the late holocene sediments of a florida sinkhole article i nfo a 4500 year record of hurricane induced storm surges is developed from sediment cores collected from a coastal sinkhole near apalachee bay florida recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant historic storm surges at the site modeled using slosh and the best track post 1851 a d dataset using the historic portion of the record for calibration paleohurricane deposits were identified by sand content and dated using radiocarbon based age models marine indicative foraminifera some originating at least 5 km offshore were present in several modern and ancient storm deposits the presence and long term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil based paleohurricane reconstructions in the future due to the sub decadal 7 years resolution of the record and the site s high susceptibility to hurricane generated storm surges the average local frequency of recorded events approximately 3 9 storms per century is greater than that of previously published paleohurricane records from the region the high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone with intervals of both anomalously high and low storm frequency identified however the rate at which smaller layers were deposited was relatively constant over the last five millennia this may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events the frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago high magnitude events were relatively rare with about 0 3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago a marked decline in the number of large storm deposits which began around 600 years ago has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia

fine scale chlorite muscovite association in low grade metapelites from nurra nw sardinia and the possible misidentification of metamorphic vermiculite chlorite muscovite porphyroblasts occur in the low grade metapelites from nurra nw sardinia although actually heterogeneous and built up by two different intermixed minerals the porphyroblasts strongly simulate optical homogeneity and produce microprobe analyses that are typical for metamorphic vermiculite transmission and scanning electron microscopy combined with analytical facilities leads to a deeper characterization of the porphyroblasts that actually consist of a random association of chlorite and muscovite

microstructures and mixed layering in intergrown wonesite chlorite talc biotite and kaolinite post pond volcanics vermont transmission electron microscopy and diffraction the chlorite occurs in intergrown 1 layer and disordered polytypes the wonesite occurs in 1 layer 2 layer 3 layer and disordered forms and the biotite occurs as 1 layer and 2 layer polytypes with minor stacking disorder modified journal abstract

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

strengthening of paleo typhoon and autumn rainfall in taiwan corresponding to the southern oscillation at late holocene the purpose of this study is to improve prehistoric knowledge of paleo typhoon and winter monsoon activity in the western north pacific after 8 cal ka bp we examine two sediment cores derived from lakes located to the south and north of the ilan plain in northeastern taiwan seasonal and typhoon rainfall data over the past several decades are collected for this study region we also use mineral indicators k rb ratios and grain size to estimate sediment sources intensity of chemical weathering and rainfall intensity the results show that the chemical weathering index k rb ratio of meihua lake indicates the continuing effects of autumn rainfall while coarse grain sizes of dahu lake sediments suggest increased intensity in typhoon rainfall grain size results reveal that increasing el nino southern oscillation intensity in the tropical pacific has intensified the activity of super typhoons in the western north pacific finally we find that frequent activity of super paleo typhoons occurred in taiwan during the la nina like state and the strengthening winter monsoon activity and higher sea surface temperature enhanced plentiful autumn rainfall in el nino like state after comparing our results with the paleo typhoon data in japan and south china we suggest that the tracks of super typhoon are mainly affected by variations in the warm pool and subtropical northwestern pacific high in the western pacific copyright 2012 john wiley sons ltd

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

high precision u series ages of transported coral blocks on heron reef southern great barrier reef and storm activity during the past century transported coral blocks scattered on reef flats have previously been identified as useful proxies for past storm occurrences high precision tims u series dating and detailed field observations of 110 coral samples collected from 102 individual transported coral colonies coral blocks and 4 transported sections of reef matrix reef blocks from the northern side of heron reef southern great barrier reef indicate that 1 the youngest age of corals attached to reef blocks may represent the age of possible past storm occurrence providing a proxy for historical storm reconstruction 2 most ages of dated storm transported coral and reef blocks match well relatively with known cyclone and storm events further supporting that they are good indicators of past storm events and 3 age distribution and relative probability frequency analysis of the dated coral and reef blocks suggest that there have been eight broad periods of storm occurrence since 1900 ad 1904 1909 1914 1916 1935 1941 1945 1960 1965 1967 1976 1977 1983 1988 and 2001 2007 roughly showing decadal variations the coral based storm reconstruction therefore extended the database of past storm occurrences around heron reef area these findings suggest that coral reefs in the southern great barrier reef are frequently influenced by periods of high storm activity and show strong resilience to natural disturbances over the past century additionally our results show for the first time that the blue skeletal coral heliopora coerulea order helioporacae has u concentrations of only 0 12 to 0 30 ppm similar to 5 10 that of common reef building corals with white skeletons order scleractinia which may be a unique chemical signature of the only living species of the helioporidae family c 2012 elsevier b v all rights reserved

millennial scale storminess variability in the northeastern united states during the holocene epoch for the purpose of detecting the effects of human activities on climate change it is important to document natural change in past climate1 in this context it has proved particularly difficult to study the variability in the occurrence of extreme climate events such as storms with exceptional rainfall1 previous investigations have established storm chronologies using sediment cores from single lakes2 3 4 5 6 7 8 but such studies can be susceptible to local environmental bias here we date terrigenous inwash layers in cores from 13 lakes which show that the frequency of storm related floods in the northeastern united states has varied in regular cycles during the past 13 000 years 13 kyr with a characteristic period of about 3 kyr our data show four peaks in storminess during the past 14 kyr approximately 2 6 5 8 9 1 and 11 9 kyr ago this pattern is consistent with long term changes in the average sign of the arctic oscillation9 suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of holocene climate variability in north america and europe

metamorphic evolution of the palaeozoic series of the betic cordilleras nevado filabride complex se spain and its relationship with the alpine orogeny the palaeozoic rocks of the veleta nappe nevado filabride complex betic cordilleras southern spain consist of graphite mica schists with oxychlorite chloritoid albite garnet porphyroblasts crystal chemistry of the minerals their phase relations and microfabrics are consistent with a normal prograde metamorphic evolution and a slight retrograde overprint the basis of the overlying mulhacen nappe consists also of palaeozoic graphite mica schists but with clear signs of polymetamorphic development an early low pressure metamorphism with andalusite and chloritoid is overprinted by high pressure metamorphism with kyanite and mg rich chloritoid this later development is of alpine age which is demonstrated by the metamorphic conditions of permo triassic rocks in the upper part of the mulhacen nappe included formation of eclogites followed by an amphibolite facies overprint the metamorphism of the veleta nappe is regarded as pre alpine a possible alpine overprint did not cause an increase in temperatures no inverse metamorphic gradient exists between veleta and mulhacen nappes because of the different ages of metamorphism

peregrinations of the greenland ice sheet divide in the last glacial cycle implications for central greenland ice cores abstract the superb quality of the climate chronology archived in the summit greenland ice cores grip gisp2 testifies that the greenland ice sheet divide has been generally stable through the last glacial cycle the ice sheet has experienced a broad range of paleoclimate conditions ice sheet margin configurations and internal dynamical adjustments in glacial interglacial transitions however it is unlikely that the summit region escaped shifts in ice divide position geometry elevation and flow characteristics details of this dynamical history are important to several aspects of ice core studies the magnitudes of pure and simple shearing reconstruction of vertical ice velocity the explicit location of the ice divide and the divide residence time at different locations are all of interest in interpretation of climatic variables and physical properties of ice in the ice cores we apply a three dimensional thermomechanical ice sheet model to examine the evolution of these dynamical variables over the last 160 kyr in central greenland while a high elevation ice dome is present in the summit region throughout the simulation ice divide migrations of up to 150 km are predicted all points in the vicinity of the summit ice cores including the modern divide have been subject to flowline shifts and variable non zero shear deformation during the adjustment from glacial to holocene conditions from ca 10 ka to the present modelled divide peregrinations and strain rate history are consistent with the observed disturbance of deep ice in the grip and gisp2 ice cores which has muddled paleoclimate reconstructions for the last interglacial eemian period in greenland dynamical excursions are also evident north of the modern summit where the ngrip ice core is currently being drilled dahl jensen et al j glaciol 43 1997 300 306 however the prevailing flow direction and deformation regime at the ngrip site are much more stable than those at grip and gisp2 in the simulations combined with the greater depth of ice at this site this lends cautious optimism to the hope that eemian ice at ngrip may contain an intact record of eemian climate

sediment accumulation and budget in the bohai sea yellow sea and east china sea abstract sediment accumulation and budget in the continental margins provides abundant information of source sink processes from the land to the sea including weathering human activities and sedimentary environment here we show the distribution of mud areas modern sedimentation rates and sediment budget in the bohai sea yellow sea and east china sea using grain size data of 18 000 surface sediment samples and 210 pb data from 413 sites we identify five areas with sediments mainly composed of fine grained fractions mean grain size 6 and find a relatively high sedimentation rates of 1 5 mm yr in the mud areas near the yellow and yangtze river deltas sedimentation reaches 95 0 mm yr approximately 1185 4 10 6 tons of fine grained sediment accumulate annually in the mud areas of the east china seas atmospheric deposition contributes 6 tons yr while the riverine sediment inputs account for 75 917 10 6 tons yr the remainder comes from all other sources including coastal erosion and resuspension of bottom sediments in addition 45 of the fluvial sediment supply deposits on the subaerial delta 40 50 is trapped on the subaqueous delta and shelf and the remainder

holocene marine 14c reservoir age variability evidence from 230th dated corals in the south china sea the south china sea scs is well connected with the western pacific and influenced by the east asian monsoon we have examined temporal variations in radiocarbon marine reservoir ages r and regional marine reservoir corrections delta r of the scs during the holocene using paired measurements of ams c 14 and tims th 230 on 20 pristine corals the results show large fluctuations in both r and delta r values over the past 7500 years yrs with two distinct plateaus during 7 5 5 6 and 3 5 2 5 thousand calendar years before present cal ka bp the respective weighted mean delta r values of these plateaus are 151 85 and 89 59 yrs which are significantly higher than its modern value of 23 52 yrs this suggests that using a constant modern delta r value to calibrate c 14 dates of the scs marine samples will introduce additional errors to the calibrated ages our results provide the first database for the holocene r and delta r values of the scs for improved radiocarbon calibration of marine samples we interpret the two delta r plateaus as being related to two intervals with weakened el nino southern oscillation enso and intensified east asian summer monsoon easm this is because the c 14 content of the scs surface water is controlled by both the c 14 concentration of the pacific north equatorial current nec which is in turn influenced by enso induced upwelling along the pacific equator and vertical upwelling within the scs as a result of moisture transportation to midlatitude region to supply the easm rainfall

interlayering and interlayer slip in biotite as seen by hrtem partial interlayers of brucite like sheets which form with the adjacent talc like layers of the mica single chlorite layers interstratified in the mica structure brucite interlayering is interpreted as a brucitization of an interlayer level of the mica where partial slip or cleavage has previously occurred example of a chemical process at the atomic scale favored by deformation microstructures modified journal abstract

ammonium vermiculite in schists from the betic cordillera spain nh 4 bearing phases from pre permian schists of the internal zones of the betic cordillera spain have been characterized by x ray diffraction differential thermal analysis and thermogravimetry infrared spectroscopy and transmission analytical electron microscopy the content and distribution of nh 4 in these phases have been estimated by combining elemental analysis of n with mineral quantification based on x ray diffraction whole rock composition and electron microprobe data the obtained results indicate that the nh 4 content in vermiculite ranges between 0 5 and 1 0 wt leading to terms with nh 4 k in the interlayer the nh 4 content is 4 contents 0 04 wt through the complete sequence we interpret that initially contained in low grade dioctahedral mica nh 4 was incorporated in the structure of the trioctahedral phases formed at increasing metamorphic conditions the entry of nh 4 in the interlayer was favored in chlorite vermiculite mixed layered structures and transitional phases with vacancies in the a site vermiculite and weak cohesion between layers nh 4 appears to favor the formation of intermediate phases instead the direct transformation of chlorite to biotite

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

reconstruction of storm tsunami records over the last 4000 years using transported coral blocks and lagoon sediments in the southern south china sea large transported coral blocks on reef flats and elevated sedimentation rates in atoll lagoons were demonstrated to be excellent proxies for past strong storms tsunamis in the southern south china sea here we introduce another important proxy coarse fraction contents of lagoon sediments this proxy is based on the principle that coarse fractions of enclosed lagoon sediments are usually controlled by strong sedimentary dynamics on the surrounding reef flat and thus increases in the weight percentages of coarse grained fractions of the lagoon sediments should also reflect strong storm tsunami events or increases in storminess with the size of the content peak as the proxy for the degree of storminess bearing this in mind we measured the contents of the 1 mm grain size fractions referred to as coarse fraction content in an undisturbed lagoon core precisely dated to cover the last 4000 years the decadal resolution data show a systematic variation with some peaks strongly correlated with in timing with strong storm tsunami events dated at ad 1872 15 1685 8 similar to 1680 6 1443 9 1336 9 1210 5 similar to 1201 4 and 1064 30 using wave transported coral blocks using the mean coarsefraction content 9 2 for the entire core as a reference line a total of 77 peaks were identified for the past 4000 years twenty of these peaks are higher than 23 the mean value for peaks that are correlated in age with the six strong storm events identified using independently dated coral blocks among these 23 peaks 13 occurred within the last 1000 years the concentration of contentpeaks in the last millennium could be partially due to higher deposition rates and sampling resolution over the last similar to 4000 years there appears to be a weakly increasing trend in coarse fraction contents towards present time but this trend is not obvious within the last millennium this long term variation may be related to changes in both storminess and reef lagoon morphology however the data do suggest three extremely stormy periods centring around ad similar to 1200 similar to 400 bc and similar to 1200 bc respectively overall this study demonstrates that combined use of transported coral blocks and coarse fraction contents of lagoon sediments provides an excellent means for comprehensive reconstruction of past storm tsunami activity c 2008 elsevier ltd and inqua all rights reserved

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong