late quaternary sedimentological and climate changes at lake bosumtwi ghana new constraints from laminae analysis and radiocarbon age modeling abstract the lake bosumtwi sediment record represents one of the longest and highest resolution terrestrial records of paleoclimate change available from sub saharan africa here we report a new sediment age model framework for the last 45 cal kyr of sedimentation using a combination of high resolution radiocarbon dating bayesian age depth modeling and lamination counting our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities radiocarbon uncertainties of at least a few hundred years are unavoidable age model uncertainties are smallest during the holocene 205 yr and the glacial 360 yr but are large at the base of the record 1660 yr due to a combination of decreasing sample density larger calibration uncertainties and increases in radiocarbon age scatter for portions of the chronology older than 35 cal kyr additional considerations such as the use of a low blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon a comparison of radiocarbon age model results and lamination counts over the time interval 15 30 cal kyr agree with an overall discrepancy of 10 and display similar changes in sedimentation rate supporting the annual nature of sediment laminations in the early part of the record changes in sedimentation rates reconstructed from the age depth model indicate that intervals of enhanced sediment delivery occurred at 16 19 24 and 29 31 cal kyr broadly synchronous with reconstructed drought episodes elsewhere in northern west africa and potentially with changes in atlantic meridional heat transport during north atlantic heinrich events these data suggest that millennial scale drought events in the west african monsoon region were latitudinally extensive reaching within several hundred kilometers of the guinea coast this is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt decreased convection or both

a different perspective on glauconite as a chronometer for geologic time scale studies there are advocates of the use of glauconite as a chronometer for geologic time scale studies who insist that if the geohistory of the sample in question is known in detail one can ascertain before hand that the sample will yield a radiometric result that is accurate in the geological sense examples are presented indicating that while some glauconite samples may yield the correct age within their assigned analytical uncertainties when compared to high temperature minerals others clearly do not and are too young by varying degrees the outright acceptance of published results on glauconite can result in erroneous age estimates of various biostratigraphic levels and stage or epoch boundaries

reconstructing mid late holocene cyclone variability in the central pacific using sedimentary records from tahaa french polynesia abstract we lack an understanding of the geographic and temporal controls on south pacific cyclone activity overwash records from backbarrier salt marshes and coastal ponds have been used to reconstruct tropical cyclone strikes in the north atlantic basin however these specific backbarrier environments are scarce in the south pacific with cyclone records limited primarily to the period of modern observation this instrumental record suggests a correlation with the el nino southern oscillation enso but longer records are necessary to test this relationship over geologic timescales and explore other potential climate drivers of tropical cyclone variability deep lagoons behind coral reefs are widespread in the pacific and provide an alternative setting for developing long term sedimentary reconstructions of tropical cyclone occurrence coarse grained event deposits within the sediments of a back reef lagoon surrounding tahaa reveal a 5000 year record of cyclone occurrences timing of recent high energy deposits matches well with observed tropical cyclone strikes and indicates coarse deposits are storm derived longer records show tropical cyclone activity was higher from 5000 to 3800 and 2900 to 500 yrs bp comparison to records from the north pacific out of phase and north atlantic in phase suggests a coordinated pattern of storm activity across tropical cyclone basins over the mid late holocene the changes in tropical cyclone activity we observe in the south pacific and across other basins may be related to enso as well as precession driven changes in ocean atmosphere thermal gradients

the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

effect of tsunamis generated in the manila trench on the gulf of thailand abstract tsunamis generated in the manila trench can be a threat to thailand besides runup of tsunamis along the eastern coast infrastructures in the gulf of thailand for example gas pipelines and platforms can be affected by tsunamis in this study the simulation of tsunamis in the gulf of thailand is conducted six cases of fault ruptures in the manila trench are considered for earthquakes with magnitudes of 8 0 8 5 and 9 0 the linear shallow water wave theory in spherical coordinate system is used for tsunami simulation in the large area covering southeast asia while the nonlinear shallow water wave theory in cartesian coordinate system is used for tsunami simulation in the gulf of thailand it is found that tsunamis reach the southern part of thailand in 13 h after an earthquake and reach bangkok in 19 h the tsunami amplitude is largest in the direction towards the philippines and vietnam the southern part of china is also severely affected the gulf of thailand is affected by the diffraction of tsunamis around the southern part of vietnam and cambodia the tsunami amplitude at the southernmost coastline is about 0 65 m for the mw 9 0 earthquake the current velocity in the gulf of thailand due to the mw 9 0 earthquake is generally less than 0 2 m s

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

holocene climate variability and change a data based review the holocene thermal maximum with peak temperatures prior to 7 ka bp is mostly accentuated in the northern hemisphere still visible in the southern hemisphere and possibly did not exist in the tropics between this period and the modern warming a remarkable negative temperature trend occurred in the northern hemisphere which was probably the effect of a decreasing orbital induced insolation during the boreal summer on average the northern hemisphere humidity precipitation records do not show any significant trend a mechanistic explanation for the multi decadal to century scale holocene cold relapses which mainly occurred in the atlantic european regions exists for only the early holocene cooling events which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the laurentide ice sheet possibly the late holocene cold events after c 4 ka bp are influenced by the covarying influence of major tropical volcanic eruptions and grand solar minima

sea level changes in the tectonically stable malay thai peninsula abstract the malay thai peninsula is part of sundaland a geological region of relative crustal stability therefore the positions of old shorelines of the past 20 000 years or so can be considered to indicate positions of actual past sea levels over 200 shoreline indicators at positions below as well as above present sea level have been radiocarbon dated these dated positions indicate that prior to 6 ka the sea rose from at least 90 m below present sea level at rates that initially amounted to 15 mm year and later became 6 mm year at ca 6 ka the rising sea surpassed its current position and at ca 5 ka it reached 5 m during this maximum marine inundation the peninsula was narrower since the low coastal plains did not yet exist in the period following this maximum transgression the available shoreline data indicate that regional sea level subsided through a series of fluctuations that were characterized by amplitudes of 2 m and periods of about 2000 years the peaks and troughs of the fluctuations became progressively lower the latest peak was at about 1 7 m or 0 7 m above present high tide a few hundred years ago the cause of these fluctuations is not yet known but the trend suggests that in the near future regional sea level may subside at annual rates between 1 5 mm and 2 mm this rate of descent is 25 to 30 of the estimated rate of sea level rise that may result from global warming in other words for the malay thai peninsula the effect of sea level rise on account of manmade greenhouse gases will be partly compensated by actual subsidence of regional sea level

assessing sedimentary records of paleohurricane activity using modeled hurricane climatology patterns of overwash deposition observed within back barrier sediment archives can indicate past changes in tropical cyclone activity however it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane overwash reconstruction to alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean atmosphere hurricane model set to simulate modern climatology thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes a prescribed threshold for overwash and a specified temporal resolution based on sedimentation rates observed at a particular site as a test case we apply this monte carlo technique to a hurricane induced overwash reconstruction developed from laguna playa grande lpg a coastal lagoon located on the island of vieques puerto rico in the northeastern caribbean apparent overwash rates in the lpg overwash record are observed to be four times lower between 2500 and 1000 years b p when compared to apparent overwash rates during the last 300 years however probability distributions based on monte carlo simulations indicate that as much as 65 of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates periods of no apparent overwash activity at lpg between 2500 and 3600 years b p and 500 1000 years b p are exceptionally long and are unlikely to occur above 99 confidence under the current climate conditions in addition breaks in activity are difficult to produce even when the hurricane model is forced to a constant el nino state results from this study continue to support the interpretation that the western north atlantic has exhibited significant changes in hurricane climatology over the last 5500 years

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

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

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

saturn s icy satellites thermal and structural models abstract thermal histories of the small icy saturnian satellites mimas tethys dione rhea and iapetus are constructed by assuming that they formed as homogeneous ice silicate mixtures the models include effects of radiogenic and accretional heating conductive and subsolidus convective heat transfer and lithospheric growth accretional heating is unlikely to have melted the water ice in the interiors of these bodies and solid state creep of the predominately ice material precludes melting by radiogenic heating mimas is so small that its thermal evolution is essentially purely conductive at present it is a cold nearly isothermal body any subsolidus convection or thermal activity in mimas would have been confined to a brief period in its early history and would have been due to a warm formation the four largest satellites are big enough and contain sufficient heat producing silicates that solid state convection beneath a rigid lithosphere is inevitable independent of initial conditions dione and rhea have convective interiors for most of their thermal histories while tethys and iapetus have mainly conductive thermal histories with early periods of convective 0activity the thermal histories of the five satellites for the last 4 by are independent of initial conditions at present they have cold conductive interiors the model thermal histories are qualitatively consistent with the appearances of these satellites mimas has an ancient heavily cratered surface tethys and probably iapetus have both heavily cratered and more lightly cratered areas and dione and rhea have extensively modified surfaces because of their similar sizes and densities mimas and enceladus are expected to have similar surfaces and thermal histories but instead enceladus has the most modified surface of all the small icy saturnian satellites our results suggest a heat source for enceladus in addition to radiogenic and accretional heating tidal dissipation is a possibility because the water ice in these bodies does not melt resurfacing must be accomplished by the melting of a low melting temperature minor component such as ammonia hydrate

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

fluid dynamics of local martian magma oceans the evolution of a melt region produced by a large impact during mars formation is addressed while some impact induced melt is redistributed during crater excavation sufficiently large impacts much larger than basin forming impacts generate an intact melt region which is retained beneath the excavation zone i e a local magma ocean local magma ocean evolution depends on the effective rheology controlling large scale deformation of the solid part of the planet mechanism of crystallization and melt region size within the uncertainties of various parameters two scenarios are possible for sufficiently weak rheology or large melt region size evolution is characterized by rapid extrusion and formation of a global magma ocean for sufficiently strong rheology or small melt region size in situ crystallization to a partially molten solid state occurs prior to isostatic adjustment subsequent to in situ crystallization local magma ocean evolution depends on melt region size and efficiency of lateral redistribution compared to bulk conductive cooling for large melt regions lateral spreading occurs via plastic deformation and results in an asymmetric global partial melt layer for small melt region size viscous spreading viscous can result in bulk cooling below the solidus prior to formation of a global layer a hypothesis for the origin of the hemispherical crustal dichotomy and tharsis rise is suggested the dichotomy is associated with a global partial melt layer produced by evolution of a large local magma ocean after dichotomy formation evolution of a second smaller local magma ocean is related to tharsis development

a backbarrier overwash record of intense storms from brigantine new jersey abstract analysis of aerial photographs and historic charts indicates that the barrier beach at brigantine nj has migrated landward 300 to 400 m since 1869 primarily as a result of overwash during hurricanes and winter storms a series of vibracores from the backbarrier salt marsh reveals a millennial scale stratigraphic record of overwash deposition carbon 14 c 14 and cesium 137 cs 137 radioisotopic methods were used to date overwash deposits washovers the ages of recent washovers are consistent with deposition during intense storms in 1938 1944 1950 and 1962 an additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788 two prehistoric overwash fans were likely deposited by intense storms striking the new jersey coast in the 7th to 14th centuries and 6th to 7th centuries a d the landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans the greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period the hurricane of 1821 the spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments

magnitude of hurricane ike storm surge sedimentation implications for coastal marsh aggradation there is a paucity of information on the regional distribution and magnitude of hurricane storm surge sedimentation this study assesses the spatial extent and magnitude of hurricane ike s 2008 storm surge sedimentation and discusses implications for the role of hurricanes in marsh aggradation the characteristics of the storm surge deposit including thickness inland penetration volume and mass were determined for 15 transects across marshes bordering the gulf of mexico in south eastern texas and south western louisiana the deposit is up to 0 85 m thick extends up to 3 6 km inland and has an estimated volume of about 13 7 million m3 and an estimated mass of about 16 2 million metric tons this level of sedimentation is one to two orders of magnitude larger than other potential sources of marsh sedimentation including annual riverine inputs and inputs from alongshore sediment transport the study findings add support to a growing body of evidence that hurricanes may be the predominant sediment source for long term aggradation of many coastal marshes bordering the gulf of mexico copyright 2012 john wiley sons ltd

ultimate strength of solids and formation of planetary cores some previous experiments and theory have suggested that the ultimate strengths of silicates are 1 2 gpa 10 20 kbar that the ultimate strength of ice is about 0 1 gpa 1 kbar and that the confining pressures of planetary interiors 100 gpa would not increase these strengths by more than a factor of two deviatoric stresses of these magnitudes are easily generated in planetary interiors by density heterogeneities of tens of kilometers radius this implies that once such heterogeneities had formed core segregation would not be further inhibited by the strength of a cold protoplanetary interior it is further suggested that core segregation may be initiated by heterogeneous impact heating well before extensive near surface melting occurs and that in the most favorable circumstance segregation could begin in a 700 km radius protoplanet or a 500 km radius icy satellite these considerations increase the likelihood that core segregation in larger planets and satellites was essentially contemporaneous with accretion

consequences of giant impacts in early mars core merging and martian dynamo evolution a giant impact is an increasingly popular explanation for the formation of the northern lowland on mars it is plausible that at the impact time both mars and the impactor were differentiated with solid silicate mantles and liquid iron cores such a large impact likely resulted in merging of the cores of both bodies a process which will have implications on the thermal state of the planet we model the evolution of the martian mantle following a giant impact and characterize the thermochemical consequences of the sinking of an impactor s core as a single diapir the impact heating and the viscous heating induced during the core merging may affect the early thermal state of mars during several tens of million years our results show that large viscosity contrasts between the impactor s core and the surrounding mantle silicates can reduce the duration of the merging down to 1 kyr but do not modify the merging temperature when the viscosity contrast between the diapir and the surrounding silicates is larger than a factor of 1000 the descent of the diapir can lead to some entrainment of the relatively shallow silicates to deepest regions close to the core mantle boundary finally the direct impact heating of martian core leads to thermal stratification of the core and kills the core dynamo it takes on the order of 150 200 myr to reinitiate a strong dynamo anew the merging of the impactor s core with the martian core only delays the reinitiation of the dynamo for a very short time

impact origin for the martian crustal dichotomy half emptied or half filled 1 one possible mechanism for martian hemispherical dichotomy formation is excavation of the northern lowland basin in the existing crust by a single giant impact here we explore a related scenario in which the impact melt volume is sufficient to fill the excavated cavity produce a thickened crust and generate a topographic basin centered on the opposite side of the planet we investigate this mechanism by formulating a model for viscous spreading of a partially molten layer over a spherical surface we derive numerical solutions and calculate the final area of the spreading layer as a function of impactor size and shape of the layer boundary due to an initially asymmetric melt region results are compared with observations including lowland basin size shape of the dichotomy boundary age difference between crustal provinces and crustal thickness

sedimentary evidence of hurricane strikes in western long island new york 1 evidence of historical landfalling hurricanes and prehistoric storms has been recovered from backbarrier environments in the new york city area overwash deposits correlate with landfalls of the most intense documented hurricanes in the area including the hurricanes of 1893 1821 1788 and 1693 a d there is little evidence of intense hurricane landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense hurricane landfalls around 300 years ago occurs during the latter half of the little ice age a time of lower tropical sea surface temperatures multiple washovers laid down between 2200 and 900 cal yr b p suggest an interval of frequent intense hurricane landfalls in the region our results provide preliminary evidence that fluctuations in intense hurricane landfall in the northeastern united states were roughly synchronous with hurricane landfall fluctuations observed for the caribbean and gulf coast suggesting north atlantic wide changes in hurricane activity

geologic records of holocene typhoon strikes on the gulf of thailand coast abstract washover sedimentation resulting from modern typhoon strikes on the gulf of thailand coast forms anomalous sand layers in low energy coastal environments including marshes ponds and swales the primary diagnostic for recognizing prehistoric typhoon deposited sand layers in the geologic record are sharp upper and lower contacts between coarser grained transported sand layers and finer grained in situ sediments in this first paleotempestology study in thailand cores from two low energy settings on the gulf of thailand coast a coastal marsh near cha am and beach ridge plain swales near kui buri reveal geologic evidence of up to 19 typhoon strikes within the last 8000 years the sand layers have sharp upper and lower contacts with enclosing finer sediments some sand layers also contain other evidence of a sudden powerful landward directed surge of ocean water including gravel sized clasts offshore foraminifera abundant shell fragments plant debris and mud rip up clasts sand layers record eleven typhoon strikes at cha am ranging in age from ad 1952 to 7575 cal yr bp and eight typhoon strikes at kui buri ranging in age from 4075 to 7740 cal yr bp bayesian age depth models derived from eight ams radiocarbon dates suggest that the frequency of typhoon strikes was 2 5 times greater from 3900 to 7800 cal yr bp compared to 0 3900 cal yr bp possible explanations for this variability in the typhoon record are that typhoons were more frequent and or more intense in southeast asia in the mid holocene because of climatic changes associated with the mid holocene warm period or that the record reflects site sensitivity changes resulting from a mid holocene sea level highstand the preliminary finding of a possible link between warmer conditions and a greater frequency of intense typhoon strikes could have important societal implications given possible consequences of ongoing global warming

paleogene calcareous nannofossil magnetobiochronology results from south atlantic dsdp site 516 abstract the detailed study of an expanded paleogene section with abundant moderate to well preserved calcareous nannofossils from south atlantic dsdp site 516 has resulted in a precise correlation of most calcareous nannofossil markers with the magnetostratigraphy many nontraditional datums have also been documented and correlated to the magnetostratigraphy comparison of the results from site 516 with those of previous studies from other areas enables a critical evaluation of the accuracy synchroneity or diachroneity of the species events over geographically long distances of special significance is the correlation for the first time of the stratigraphic ranges of chiasmolithus gigas and rhabdosphaera gladius with the magnetostratigraphy other important results include the following first occurrence fo of cruciplacolithus primus 66 3 ma fo chiasmolithus danicus 65 6 66 0 ma fo prinsius martinii 65 5 66 0 ma fo heliolithus kleinpellii 59 8 61 6 ma probably diachronous last occurrence lo of tribrachiatus orthostylus 51 0 54 8 ma unreliable fo chiasmolithus gigas 47 4 ma fo reticulofenestra umbilica 44 6 ma lo chiasmolithus gigas 44 4 46 8 ma diachronous lo nannotetrina fulgens 44 2 ma lo chiasmolithus grandis 40 0 41 6 ma probably diachronous fo chiasmolithus oamaruensis 39 8 40 4 ma unreliable fo isthmolithus recurvus 39 5 ma lo reticulofenestra reticulata 37 6 ma lo discoaster saipanensis 36 4 ma end acme of ericsonia subdisticha diachronous fo and lo sphenolithus distentus unreliable and lo reticulofenestra bisecta 24 0 ma

holocene sea levels and palaeoenvironments malay thai peninsula southeast asia sedimentological and palynological investigations of great songkhla lakes east coast of the malay thai peninsula southeast asia reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps compared with other regions in southeast asia the assemblages are of relatively low diversity geochronological data indicate that the great songkhla lakes record one of the earliest mangrove environments in southeast asia 8420 8190 cal yr bp which are subsequently replaced by a freshwater swamp at 7880 7680 cal yr bp owing to the decline of marine influence sea level observations from great songkhla lakes and other areas of the malay thai peninsula reveal an upward trend of holocene relative sea level from a minimum of 22 m at 9700 9250 cal yr bp to a mid holocene high stand of 4850 4450 cal yr bp which equates to a rise of c 5 5 mm yr the sea level fall from the high stand is steady at c 1 1 mm yr geophysical modelling shows that hydroisostasy

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

the importance of quaternary records in reducing risk from tropical cyclones numerous late holocene records of tropical cyclones have been collected from north east queensland australia they are in the form of multiple sedimentary ridges paralleling the shore the ridges are composed of coral fragments or shell and sand or pure sand a method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events the results suggest that extrapolations of long term cyclone magnitude and frequencies from the 30 to 40 year long instrumental record which is the method commonly used to assess risk from this hazard substantially underestimate the risk from this hazard this is confirmed for the cairns region by an 800 year long high resolution isotope record of tropical cyclones preserved in a limestone stalagmite together the sedimentary and isotope records suggest that tropical cyclone activity in north east queensland has been in a phase of quiescence since before european settlement of the region in approximately ad 1870 it is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence

coastal geomorphic conditions and styles of storm surge washover deposits from southern thailand abstract the characteristics of tropical storm washover deposits laid down during the years 2007 to 2011 along the southern peninsular coast of the gulf of thailand got were described in relation to their different geomorphic conditions including perched fan washover terrace and sheetwash lineations preserved behind the beach zone within 100 m of the shoreline as a result washover terrace and sheetwash lineations were found where the beach configuration was uniform and promoted an unconfined flow non uniform beach configurations that promoted a confined flow resulted in a perched fan deposit washover sediments were differentiated into two types based on sedimentary characteristics including i a thick bedded sand of multiple reverse grading layers and ii a medium bedded sand of multiple normal grading layers in the case of thick bedded washover deposits the internal sedimentary structures were characterized by the presence of sub horizontal bedding reverse grading lamination foreset bedding and wavy bedding whereas horizontal bedding normal grading and dunes were the dominant structures in the medium bedded washover sand rip up clasts were rare and recognized only in the washover deposits in the bottom unit which reflects the condition when a mud supply was available all washover successions were found in the landward inclined bedding with a basal sharp contact a high elevated beach ridge associated with a large swale at the backshore proved suitable for a thick bedded washover type whereas a small beach ridge with uniformly flat backshore topography promoted a medium bedded washover sediment

early transient superplumes and the origin of the martian crustal dichotomy 1 the large temperature difference between the core and mantle of mars at the end of planetary accretion creates a hot internally convecting thermal boundary layer at the base of the mantle whose viscosity is several orders of magnitude lower than the viscosity of the mantle above it theoretical analysis and numerical simulations of the instability of this thermal boundary layer show that it is likely that only one large plume forms this superplume may play a role in the formation of crustal dichotomy and generation of the magnetic field in the early history of mars

sedimentary evidence of intense hurricane strikes from new jersey nine vibracores from the backbarrier marsh at whale beach new jersey reveal three large scale overwash deposits associated with historic and prehistoric storms the uppermost and smallest overwash fan was deposited in the ash wednesday northeaster of march 5 8 1962 a second more substantial overwash fan between 100 and 35 cm depth dates to the late eighteenth or early nineteenth century this fan was most likely deposited during the 1821 hurricane the only intense hurricane to make landfall in new jersey in the past 350 yr a third larger overwash fan between 200 and 300 cm depth was deposited between a d 1278 and 1438 and is likely the result of a prehistoric intense hurricane strike the combination of historical and stratigraphic evidence indicates that two intense hurricanes winds 50 ms 21 have likely made landfall on the southern new jersey coast in the past 700 yr resulting in an annual landfall probability of 0 3

can a sinking metallic diapir generate a dynamo metallic diapirs may have strongly contributed to core formations during the first million years of planetary evolutions the aim of this study is to determine whether the dynamics induced by the diapir sinking can drive a dynamo and to characterize the required conditions on the size of the diapir the mantle viscosity and the planetary latitude at which the diapir sinks we impose a classical hadamard flow solution for the motion at the interface between a spherical sinking diapir and a viscous mantle on dynamical simulations that account for rotational and inertial effects in order to model the flow within the diapir the flows are confined to a velocity layer with a thickness that decreases with increasing rotation rate these 3d flows are is then used as input for kinematic dynamo simulations to determine the critical magnetic reynolds number for dynamo onset our results demonstrate that the flow pattern inside a diapir sinking into a rotating planet can generate a magnetic field large diapirs r 10 km sinking in a mantle with a viscosity ranging from 10 9 to 10 14 pa s provide plausible conditions for a dynamo equatorial sinking diapirs are confined to a thicker velocity layer and are thus possibly more favorable for dynamo generation than polar sinking diapirs in addition equatorial sinking diapirs produce stronger saturated magnetic fields however for the range of parameters studied here estimation of the intensity of diapir driven magnetic fields suggests that they could not have contributed to the lunar or martian crustal paleomagnetic fields

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

greater frequency variability of landfalling tropical cyclones at centennial compared to seasonal and decadal scales assessing risk from tropical cyclones and predicting the impact of this hazard under a human altered climate is based exclusively upon the behaviour of these events over the past 50 100 yr and often less critical to these determinations is an understanding of the full extent of the natural variability of this hazard the coarse resolution of millennial scale sedimentary records brevity of the instrumental register imprecision of longer historical accounts and lack of any long term high resolution records has led to the assumption that the total variability of tropical cyclone behaviour is encompassed within the seasonal to multi decadal oscillations observed to date we present a near 800 yr long annual resolution isotope record of tropical cyclones in northeast australia which displays marked centennial scale regimes our record demonstrates that the frequency variability of intense landfalling cyclones is greatest at centennial scale compared to seasonal and decadal oscillations switching between centennial scale regimes in this record occurred rapidly 10 20 yr highlighting the importance of accounting for this phenomenon in coastal planning and risk assessment our study highlights the importance of obtaining high resolution multi century records of tropical cyclone activity in order to more accurately assess future impacts of this hazard to human society

holocene sea levels along the andaman sea coast of thailand for the malay thai peninsula several sea level curves for the younger holocene based on field evidence as well as on hydro isostatic modelling of a far field site have been published the general assumption is a rapid rise to a mid holocene maximum up to 5 m above present sea level followed by a constant or oscillating regression however from the andaman sea coast of thailand which was affected by the 2004 tsunami only isolated observations are available regarding holocene sea levels thus the timing and magnitude of the holocene highstand as well as the course of the regression remain to be defined as several palaeotsunamis could be detected in the meantime it is important to know the related sea levels as exactly as possible to judge the energy inundation width and potential wave height of these events therefore fixed biological indicators from the rocky coasts of the phang nga bay and phuket as well as morphological indicators from beach ridge and swale sequences along the exposed west coast ko phra thong were studied to gain information about the holocene sea level development in this region while oyster and coral data from the phang nga bay and phuket document a holocene maximum of 2 6 m at 5700 cal bp the ridge crests and swale bases in the northwest of the study area point to maximum heights of 1 5 2 0 m above the present level around 5300 years ago during the last 3000 years to when the largest part of the holocene palaeotsunami deposits from thailand was dated relative sea levels rsl in both areas did not exceed 1 5 m

tropical cyclone activity in the northwest pacific in relation to the el nino southern oscillation phenomenon abstract the interannual variations in tropical cyclone activity in the northwest pacific nwpac and their relationships with the el nino southern oscillation enso phenomenon were studied using the method of spectral analyses time series of a southern oscillation index soi defined as the sea level pressure difference between easter island and darwin and tropical cyclone activity in the entire nwpac ocean basin as well as in different regions of the nwpac were analyzed two spectral peaks are apparent in all these time series one corresponds to the generally accepted southern oscillation with a period of 3 to 3 5 years and another at the quasi biennial oscillation qbo frequency cross spectral analyses between the soi and tropical cyclone activity show significant coherence in these two spectral peaks the dominant peak is at the southern oscillation frequency with the soi leading typhoon activity by almost a year at the qbo frequency the two series are almost in phase cyclone activity in t

700 yr sedimentary record of intense hurricane landfalls in southern new england five intense category 3 or greater hurricanes occurring in 1635 1638 1815 1869 and 1938 have made landfall on the new england coast since european settlement historical records indicate that four of these hurricanes 1635 1638 1815 and 1938 and hurricane carol a strong category 2 storm in 1954 produced significant storm surges 3 m in southern rhode island storm surges of this magnitude can overtop barrier islands removing sediments from the beach and nearshore environment and depositing overwash fans across back barrier marshes lakes and lagoons in a regime of rising sea level accumulation of marsh lake or lagoon sediments on top of overwash deposits will preserve a record of overwash deposition we examined the record of overwash deposition at succotash salt marsh in east matunuck rhode island and tested the correlation with historical records of intense storms aerial photographs taken after hurricanes in 1954 and 1938 show overwash fans deposited at the site analysis of 14 sediment cores from the back barrier marsh confirmed the presence of these fans and revealed that 4 additional large scale overwash fans were deposited within the marsh sediments the four overwash fans deposited since the early seventeenth century at succotash marsh matches the historical record of significant hurricane induced storm surge these fans were most likely deposited by hurricanes in 1954 1938 1815 and either 1638 or 1635 radiocarbon dating of two prehistoric overwash fans indicated that these were deposited between a d 1295 1407 and 1404 1446 and probably represent intense hurricane strikes in the past 700 yr at least 7 intense hurricanes struck the southern rhode island coast and produced a storm surge that overtopped the barrier at succotash marsh

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

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

holocene changes in flooding frequency in south korea and their linkage to centennial to millennial scale el nino southern oscillation activity to trace past changes in flooding frequency we investigated fluvial sediments in the middle reach of the nakdong river south korea sediments with larger grain size lower total organic carbon percentage and depleted 13 c values in the recovered sediment cores were interpreted as periods of more frequent flooding patterns of decreased long term flooding frequency and vegetation changes during the early to late holocene were similar to the decreasing regional summer monsoon intensity multicentennial frequent flooding periods in the study area 2900 3400 cal yr bp 3600 3900 cal yr bp 4600 5300 cal yr bp and 5800 6400 cal yr bp corresponded to stronger el nino southern oscillation enso activity periods based on previous studies showing that high frequency tropical typhoon driven coastal inundation along the western coast of japan during the middle to late holocene was coupled with stronger enso activity it is likely that the observed centennial to millennial scale flood frequency change in south korea was influenced mainly by changes in the genesis and tracks of tropical typhoons at centennial to millennial time scales this suggests that the centennial to millennial scale hydrologic changes in east asia were linked to the remote atmospheric oceanic circulation changes represented by an enso like pattern

high spatial resolution models of time dependent layered mantle convection summary the degree of geochemical mixing that occurred during the mantle s early evolution is dependent on the history of convective motions in the mantle we present time dependent tnodels of mantle convection that show for certain conditions in the newly formed earth s mantle a transient phase of layered convection results during which geochemical differences between the upper and lower mantle could have been preserved the basic model assumes that the initial temperature profile for subsolidus mantle convection is strongly superadiabatic the mantle is represented by a constant viscosity boussinesq fluid in a 2 d cartesian box heated from the bottom the models have considerably greater spatial resolution 90 x 90 uniformly spaced grid points than our previous work parameters that have been vaned include the rayleigh number ra lo5 lo8 the aspect ratio 1 4 9 the buoyancy of the initial temperature profde and the maximum temperatures allowed for subsolidus convection the models support our previous assertion that there is a critical value of ra above which superadiabatic initial conditions result in a burst of convection that inverts the temperature gradient in the bulk of the mantle sufficiently to temporarily prohibit a single layer of convection instead two layers result this critical value is about ra lo6 for a mantle with the maximum amount of buoyancy for less buoyant initial conditions this critical value is somewhat higher the layering lasts on the order of lo9 yr for ra lo6 10 considering that ra for the early mantle was certainly much larger than lo6 this suggests that a transient phase of multiple layering may have prevented vigorous convection from geochemically homogenizing the early mantle however if a less buoyant initial condition prevailed or one where supersolidus convection controls the maximum temperature of the upper mantle the transient layering could not have taken place

rb sr glauconite isochron of the eocene castle hayne limestone north carolina further discussion an examination of the calcareous nannoplankton and planktonic foraminifera of the lectostratotype castle hayne formation new hanover county north carolina has shown that it is of late middle eocene latest lutetian or earliest bartonian age upper zone np16 to lower np17 and p12 13 respectively rather than latest eocene zone np19 20 as has been reported recently dinoflagellate biostratigraphy supports this age assignment a rb sr glauconite isochron date of 34 8 1 ma reported from the lectostratotype in support of an age estimate of about 33 ma for the eocene oligocene boundary is shown to be irrelevant to the boundary age problem anomalously young and indeed about 8 to 10 rn y younger than the age estimated on the basis of magnetobiochronology

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

foraminiferal biodiversity and holocene evolution of the phetchaburi coastal area thailand gulf abstract twenty three surface sediments were collected in may 2002 in the phetchaburi coastal area thailand gulf starting from the outer margin of the vegetated zone to a depth of about 20 m covering an area of about 800 km 2 one core was taken in the north eastern area of the mae khlong delta plain to investigate the recent paleoenvironmental evolution of this zone thirteen core levels were collected for micropaleontological foraminifers investigation this highly populated area is characterized by the inflow of the mae khlong the second major river in thailand and the khlong ban labun river empty tests pertaining to the thanathocoenosis are dominant and as for the few living specimens are most frequently represented by ammonia spp the collected species are typically of brackish water settings foraminiferal diversity is rather low and increases from the northern part to the central southern part of the studied area where taxa typical of the indo pacific realm such as miliolids and schackoinella globosa are more abundant than the cosmopolitan species such as ammonia tepida and gaudryina exilis the geographic distribution of the four foraminiferal assemblages defined on the basis of the cluster analysis indicates that the northern sector is affected by severe environmental conditions since this area is affected by the mae khlong river input the salinity fluctuation is probably a controlling factor on the foraminifers distribution ammonia tepida a inflata murrayinella murrayi and miliolinella sp 1 are the most opportunistic species able to tolerate wide environmental variability as regards to the holocene data the study carried out on the core located on the mae khlong delta plain indicates that the tidal flat paleoenvironment has been subject to different fresh water influence with a general prograding trend