late holocene record of lagoon evolution climate change and hurricane activity from southeastern cuba a sediment core from a lagoon in southeastern cuba was the focus of a multi proxy paleoenvironmental study to investigate lagoon response to sea level change and climate change and also to infer changes in the frequency of past hurricane strikes the proxy data examined included benthic foraminifera fossil pollen particle size analysis and macrocharcoal influx values the core was dated using 137cs and accelerator mass spectrometry ams radiocarbon methods the results show that lagoon formation began approximately 4000 years ago and that the lagoon environment evolved through four phases 1 from 4000 to 2800 cal yr bp the lagoon was a shallow polyhaline to euryhaline system with limited mangrove coverage 2 from 2800 to 2000 cal yr bp there was a decrease in salinity which facilitated the expansion of red mangrove 3 from 2000 to 1000 cal yr bp sea level rise resulted in an increase in water depth and possibly salinity and 4 from 1000 cal yr bp to the present water level continue

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

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

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

glacial to holocene implications of the new 27000 year dust record from the epica dome c east antarctica ice core insoluble dust concentrations and volume size distributions have been measured for the new 581 m deep dome c epica ice core antarctica over the 27000 years spanned by the record microparticle measurements from 169 levels to date confirm evidence of the drastic decrease in bulk concentration from the last glacial maximum lgm to the holocene interglacial by a factor of more than 50 in absolute value and of about 26 in flux unique new features revealed by the epica profile include a higher dust concentration during the antarctic cold reversal phase acr by a factor of 2 with respect to the holocene average this event is followed by a well marked minimum that appears to be concomitant with the methane peak that marks the end of the younger dryas in the northern hemisphere particle volume size distributions show a mode close to 2 m in diameter with a slight increase from the lgm to the holocene the lgm holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 m it changes from 50 to 6 glacial samples are characterised by well sorted particles and very uniform distributions while the interglacial samples display a high degree of variability and dispersion this suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into antarctica in the holocene than during glacial times assuming that southern south america remained the main dust source for east antarctica over the time period studied the higher dust content recorded during the acr which preceded the younger dryas period represents evidence of a change in south america environmental conditions at this time a wet period and likely mild climate in south america is suggested at circa 11 5 11 7 kyr bp corresponding to the end of the younger dryas the holocene part of the profile also shows a slight general decrease in concentration but with increasingly large particles that may reflect gradual changes at the source

holocene sedimentary evolution of a mid ocean atoll lagoon maldives indian ocean based on detailed analyses of cores covering the lagoon of rasdhoo atoll maldives six carbonate facies one soil and one peat facies have been identified the abundance of carbonate and rare opaque grains was quantified with a point counter x ray diffractometry was used to measure mineralogical composition of samples the statistical delineation of facies using cluster analysis was based on point count mineralogical and textural analyses in decreasing abundance the six carbonate facies are classified as mollusk coral algal floatstone to rudstone 30 mollusk coral red algae rudstone 23 mollusk coral algal wackestone to floatstone 23 mollusk coral wackestone 13 mollusk coral mudstone to wackestone 9 and mollusk mudstone 2 the carbonate facies represent lagoonal background sedimentation mostly consisting of fine sediments and event sedimentation depositing transported coarse grained reefal components fifty seven carbonate samples and one peat sample were dated radiometrically covering the holocene transgression from 10 kyrs bp until today comparing the sediment accumulation data of the lagoon with two local sea level curves three systems tracts can be identified 1 a lowstand systems tract characterized by karst and soil deposition 10 kyrs bp 2 a transgressive systems tract with peat and carbonate separated by hiatus 10 6 5 kyrs bp and 3 a highstand systems tract dominated by carbonate sedimentation 6 5 0 kyrs bp and further divided into three stages 6 5 3 3 1 and 1 0 kyrs bp during the holocene transgression sedimentation rates increased continuously to a maximum of 1 4 m kyr during 3 1 kyrs bp modern 1 0 kyrs bp mean sedimentation rates average 0 6 m kyr a simple calculation suggests that two processes background sedimentation and sand apron progradation will probably fill up the accommodation space of the lagoon during the holocene highstand but these processes will not suffice to fill the larger atoll lagoons of the archipelago

beach ridge plain evidence of a variable late holocene tropical cyclone climate north queensland australia abstract to date most studies of long term tropical cyclone records from beach ridge plains coral shell and sand have suggested that there has been little variation in the intensity of these events over the late holocene this study of a sand beach ridge plain in northeast queensland australia using sedimentary analysis and luminescence chronology suggests there has been considerable variation in both the intensity and frequency of tropical cyclones here since the mid holocene most of the previous beach ridge studies have been of relatively uniform elevation coral shingle shell and sand beach ridges within the plain here at rockingham bay the sediments are composed of coarse grained sand and there is considerable variation in ridge height and the number of ridges emplaced over different time intervals it may be that pure sand ridges provide a more sensitive record of variations in long term tropical cyclone climatology which in turn may contribute to a considerably improved understanding of the behaviour of this natural hazard

quartz grains reveal sedimentary palaeoenvironment and past storm events a case study from eastern baltic abstract sediment record collected from the coastal lake serves as a powerful tool for reconstructing changes in palaeoenvironment and understanding the potential signals of past storminess in this study we use several proxies from sediment of the holocene thermal maximum at coastal lake lilaste latvia we focus on surface texture of quartz grains from the mineral inorganic fraction as indicators of depositional environments we then use this as a proxy for potential storm transport and combine with information on granulometry diatom stratigraphy and chronology to answer the question whether flux of quartz grains in the lake originated from the sea or from the land analyses in a binocular and scanning electron microscope reveal that most of the investigated quartz grains originate from dwelling in the seawater and wave action in the nearshore zone grains representing very energetic subaqueous environment similar to storm events are also present terrestrial record is of minor significance and visible through occurrence of aeolian quartz grains during drier and colder conditions an influx of sand with aeolian imprint was delivered to the lake between 8500 and 7800 cal yr bp marine and terrestrial conditions alternated between 7800 and 6000 cal yr bp storm induced grains were likely deposited three times at 7300 cal yr bp 6600 6400 cal yr bp and 6200 6000 cal yr bp overall stable marine environmental conditions prevailed between 6000 and 4000 cal yr bp except of the last portion of terrestrial induced sediment at 4100 cal yr bp

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

an ice core indicator of antarctic sea ice production 1 the sea ice surface not open water is the dominant source of sea salt to aerosol and ice cores in coastal antarctica here we show that it may also form the dominant source for central antarctica we can then explain higher concentrations in the winter and last glacial maximum lgm as being due to increased sea ice production this suggests that ice core sea salt can indicate at least the timing of changes in antarctic sea ice production the pattern of sea salt in ice cores is consistent with marine evidence about sea ice changes in the holocene and lgm sea salt shows no change at the initial co2 increase out of the last glacial making it unlikely this was primarily due to changing sea ice cover the sea salt record should not be treated as an indicator of meridional transport

the earthquake and tsunami of 1865 november 17 evidence for far field tsunami hazard from tonga summary historical reports of an earthquake in tonga in 1865 november identify it as the only event from that subduction zone which generated a far field tsunami observable without instruments run up heights reached 2 m in rarotonga and 80 cm in the marquesas islands hydrodynamic simulations require a moment of 4 1028 dyn cm a value significantly larger than previous estimates of the maximum size of earthquake to be expected at the tonga subduction zone this warrants an upwards re evaluation of the tsunami risk from tonga to the cook islands and the various polynesian chains which had hitherto been regarded as minor

the mode and timing of windward reef island accretion in relation with holocene sea level change a case study from takapoto atoll french polynesia abstract takapoto atoll northern tuamotu islands french polynesia central pacific was selected as a test area to clarify the conditions of atoll island accretion in relation to mid to late holocene sea level changes surveys were conducted along two distinct cross island profiles on the windward coast of the atoll in addition the stratigraphy of an ocean facing islet was described from an excavation in order to reconstruct the successive island accretionary stages at both sites the basement of the atoll rims consists of conglomerate pavements on which lie shingle ridges reaching 4 m in elevation stratigraphic analysis of the excavated ridge reveals alternation of gravelly sand supported to gravel dominated sediments the chronology of island accretion is based on dating of 41 u th surface and excavated coral specimens ridge initiation occurred from about 1000 yr bp when sea level was close to its present position shingle deposits progressively prograded from the lagoon margins oceanwards and were partially cemented at their bases cementation may have increased the resistance of the islets to erosion as a result some island lands accumulated and have persisted over the last millennium the modern gross island morphology was acquired during the last 500 years this model can be considered to be of regional value for the northern tuamotu islands adjusted for local thermal subsidence hydroisostasy and or lithospheric flexure compared to some other indo pacific reef islands island initiation at takapoto appears to be have been delayed by 2 to 4 millennia probably in response to retardation in the reef catching up with mid holocene sea level dating of individual coarse grained coral clasts allowed the major wave surge events that have hit takapoto to be identified for the last millennium the use of gravels results in the identification of a greater number of medium energy surge impacts when compared with megaclast based records the frequency of storm events identified is consistent with that derived from historical observations severe storms have a very low frequency of occurrence one to two events per century on average

sea ice switch mechanism and glacial interglacial co2 variations 1 a physical mechanism is proposed for the glacial interglacial variations in the rate of vertical mixing and in sea ice cover in the southern ocean such variations were postulated without an explanation by toggweiler 1999 and stephens and keeling 2000 who used them to explain the glacial interglacial co2 variations in the physical mechanism explored here initially given by gildor and tziperman 2001b changes in the stratification of the southern ocean due to the cooling of north atlantic deep water nadw during glacial maxima reduce the rate of vertical mixing of the surface water with the deep water the changed temperature of the nadw arriving to the southern ocean and the reduced vertical mixing there also increase the southern ocean sea ice cover during glacial maxima these vertical mixing and sea ice cover changes are shown to be a natural result of the sea ice switch mechanism of the glacial cycles a box model of the climate system is used to demonstrate the above physical mechanism and its effect on the atmospheric co2 because of the uncertainties in the exact dependence of the vertical mixing on vertical stratification it is impossible to quantify the exact separate contribution of reduced vertical mixing and larger sea ice cover to the glacial co2 variations the co2 variations are not essential to the existence of the glacial cycles in the sea ice switch mechanism yet they are shown to amplify the glacial interglacial variability consistent with the view of the role of co2 deduced from proxy observations

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

aerosol deposited in east antarctica over the last glacial cycle detailed apportionment of continental and sea salt contributions 1 the major ions sodium na calcium ca2 and chloride cl deposited in central antarctica and preserved in ice cores originate from both marine and continental sources they provide important proxy records helping to reconstruct past climatic processes however it is difficult to clearly separate the individual contributions from the two sources particularly the continental one during glacial periods on the basis of na and ca2 records at an unprecedented resolution from the european project for ice coring in antarctica epica dome c ice core back to the penultimate glacial period mean ion mass ratios were deduced for the continental and the sea salt aerosol body over east antarctica the sea salt ion mass ratios are in the range predicted for both wind induced bubble bursting of breaking waves on the open ocean and sea ice brine derived aerosols respectively thus allowing no clear decision on the contribution of sea ice to the central antarctic sea salt aerosol the continental ion mass ratios point to a substantial contribution by halide aerosols which is in agreement with the source properties in southern south america although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source while during cold glacial periods continental sources accounted for more than 90 of the total ca2 input this contribution was highly variable during the remaining glacial periods covarying with the antarctic warm events during the holocene it was less than 50 but it was significantly higher during the last interglacial period the sea salt aerosol contribution to the total na input which was mostly dominant and higher than 90 was reduced to only two thirds during the last two glacial maxima and the period around 60 ka thus the glacial continental na contribution appears to be more important than previously assumed implying that na records not corrected for continental na do not represent a pure marine signal at the east antarctic plateau during glacial times

holocene sea level changes in french polynesia abstract new data on holocene sea levels have been obtained in 28 atolls and 10 high islands in the society tuamotu gambier and austral islands in an area of the south pacific as wide as western europe sea level indicators are often very accurate 0 1 m and include exposed corals abandoned algal ridges and reef frameworks in growth position emerged tidal notches and skeletal reef conglomerates in which the position of the former low water level at the time of cementation has been determined by petrological analysis over 110 new samples have been dated by radiocarbon the overall pattern is that of a msl standstill at 0 8 1 0 m between 5000 and 1250 yr b p a set of radiocarbon dated samples covering the period 4500 1250 yr b p almost continuously is evidence that lasting msl drops could not ever have occurred below 0 7 m throughout this time the highest sea level peak about 1 0 m seems to have been reached between 2000 and 1500 yr b p since 1500 yr b p msl has been dropping gradually from about 1 0 m to the present position which has been reached only recently some islands show however a slightly different pattern the holocene emergence is smaller than average in moorea and tahiti and larger in rurutu makatea anaa and possibly hereheretue some data suggest also the possibility of a slight increase in the holocene emergence towards the south possible geodynamic isostatic oceanic and climatic causes of the sea level variations observed are discussed

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

tropical cyclones in the southwest pacific spatial patterns and relationships to southern oscillation and sea surface temperature abstract an analysis of a 20 yr dataset of tropical cyclones in the southwest pacific has been made to determine the spatial patterns of cyclone occurrence and how these depend on the southern oscillation so and sea surface temperature a local measure of cyclone incidence is defined as the number of cyclones that enter into a 2 lat long square during some period eg within one season and this quantity is mapped for four southern oscillation index soi categories the maps show that the geographical distribution of cyclone incidence shifts eastward and northward during negative soi phases and vice versa the mean annual incidence for the whole region is 28 higher than average for our strongly negative so category and 16 below average for our near zero category to explore the roles of the so and local sst correlation analysis was applied to mean values of cyclone incidence for four subregions of 20 longitude width between 10 and 22 s markedly different soi sst responses were found on either s

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

south pacific hydrologic and cyclone variability during the last 3000 years publisher s version pdf must be used in institutional repository 6 months after publication

sedimentary facies of bora bora darwin s type barrier reef society islands south pacific the unexpected occurrence of non skeletal grains abstract barrier reefs when encircling small islands have been comparatively little noticed by voyagers but they well deserve attention in their structure they are little less marvelous than atolls and they give a singular and most picturesque character to the scenery of the islands they surround darwin 1842 p 2 sediment sampling revealed six modern sedimentary facies in the barrier reef system around the volcanic island of bora bora including mixed skeletal packstone peloidal packstone halimeda rich packstone to grainstone coralgal grainstone wackestone and mudstone whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals mud rich sediments with mollusks and foraminifera occur in deep lagoons 15 40 m carbonate mud is composed largely of aragonite needles probably derived from codiaceans like halimeda and coccoliths in moderate abundances despite the proximity to a volcanic island the content of siliciclastics in the sediments is low 10 on average which is a consequence of the absence of permanent water courses in addition to skeletal grains non skeletal grains cemented fecal pellets aggregates occur in high abundance 30 50 in shallow lagoons 5 m on the eastern side of bora bora this observation opposes the widely held concept that non skeletal carbonate grains are abundant on platforms from the atlantic ocean but virtually missing in recent indo pacific reefs and carbonate platforms in bora bora non skeletal grains and aggregates apparently form in warm shallow 5 m moderately agitated areas with relatively low sedimentation rates in addition early cementation is probably favored by elevated alkalinity and ph in surface waters in this part of the south pacific in the same area some 900 km to the southwest of the study area ooids and peloids have recently been discovered in the shallow lagoon of aitutaki cook islands more occurrences of abundant non skeletal grains probably exist in the indo pacific region however too few locations have been systematically studied a comparison of the new bora bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk foram halimeda and non skeletal grains and fines still grain abundances may vary significantly among locations and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments

punctuated global tropical cyclone activity over the past 5 000 years 1 there are now a substantial number of millennial scale records of tropical cyclones from a variety of locations globally some of these such as those in the atlantic and gulf of mexico show patterns of long term generally intense tropical cyclone tc behaviour that have been suggested to be due to either variations in enso or shifts in the position of the atlantic high pressure system and the jet stream comparisons are made here of the sedimentary overwash records from the gulf of mexico and atlantic ocean basin with the overwash records from the north west pacific and beach ridge records from the south west pacific and south east indian ocean basins there is a substantial degree of synchroneity in global intense tc behaviour over the past 3 000 to 5 000 years one of the most striking aspects of these records is they all display extended alternating periods centuries to millennia of relative quiescence and heightened intense tc activity irrespective of both the resolution and type of long term tc record the cause s of this punctuated activity are at present difficult to identify but are likely exogenic in origin rather than due to an intrinsic aspect of the records or the methods used to derive them the identification of punctuated global long term tc behaviour is important for understanding future tc activity and for assessing risk to coastal communities

late holocene sea levels and coral reef development in vahitahi atoll eastern tuamotu islands pacific ocean abstract preliminary quantitative data are provided on the latest stage of development and morphological evolution of the closed atoll vahitahi in the eastern tuamotus from before 4300 to at least 2400 yrs b p sea level was at least 0 7 m higher than at present during this time the development of a flat reef pavement now slightly emerged gradually separated the lagoon from the ocean at about 1200 yrs b p the water level of the lagoon already closed was still slightly above the present level the response of the reef was a rapid upward accretion until about 3000 yrs b p then an oceanward development at rates averaging from 0 04 to 0 13 m yr 1

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

reappraisal of antarctic seasonal sea ice at the last glacial maximum we used modern analog technique applied to antarctic diatoms to quantitatively reconstruct seasonal sea ice extent at the last glacial maximum winter maximum sea ice limit occurred around 48 s in the atlantic and western indian sectors around 55 s in the eastern indian and western pacific sectors and around 58 60 s in the eastern pacific sector of the southern ocean summer maximum sea ice extents during the last ice age and today are similar which contradicts climap s findings this implies a reduced summer albedo feedback of the southern hemisphere and a greater transfer of heat and moisture from the ocean to the atmosphere than shown by previous qualitative studies

reconstructing 7000 years of north atlantic hurricane variability using deep sea sediment cores from the western great bahama bank q1 enso show abrupt changes around 6000 yrs b p but most coastal sedimentary records do not span this time period establishing longer records is essential for understanding mid holocene patterns of storminess and their climatic drivers which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep sea and bank edge sediments may offer an unexplored archive of long term hurricane activity here we develop this new approach reconstructing more than 7000 years of north atlantic hurricane variability using coarse grained deposits in sediment cores from the leeward margin of the great bahama bank high energy event layers within the resulting archive are 1 broadly correlated throughout an offbank transect of multi cores 2 closely matched with historic hurricane events and 3 synchronous with previous intervals of heightened north atlantic hurricane activity in overwash reconstructions from puerto rico and elsewhere in the bahamas lower storm frequency prior to 4400 yrs b p in our records suggests that precession and increased nh summer insolation may have greatly limited hurricane potential intensity outweighing weakened enso and a stronger west african monsoon factors thought to be favorable for hurricane development

tropical sand cays as natural paleocyclone archives sand cays are valuable paleo archives that can significantly increase our understanding of holocene tropical cyclone variability here we conducted detailed sedimentological and chronological analyses from a 195 cm depth pit excavated on guangjin island northern south china sea a cay influenced by frequent tropical cyclones radiometric dating of multiple deposits revealed that foraminifera soft coral spicules and gastropod shells yielded variable age distributions while u th ages of pristine acropora branches provided a clear record of deposition and cay formation based on this robust chronostratigraphy the proportions of 2 mm grain size fraction within the deposits corresponded with the frequency of paleotyphoons recorded by historical records in recent centuries u th ages ce 1687 12 ce 1735 6 and ce 1813 5 of acropora branches from the deposits matched with three known historical typhoon events our results highlight the potential of cyclone deposited sand cays as new archives for recording paleocyclones

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

late holocene sea level changes in the northwest tuamotu islands french polynesia abstract field surveys of several sea level indicators exposed in situ reef framework conglomerates coral colonies and tridacna shells in a growth position sea corrosion notches carried out on six atolls from the nw tuamotus mataiva rangiroa arutua kaukura apataki and takapoto and data from four subsurface boreholes drilled through mataiva show that during the late holocene mean sea level msl reached a maximum elevation at approximately 0 9 m it remained above the present msl from between 6000 and 5500 yr b p until at least 1200 yr b p human settlements on the atolls were extremely unlikely and probably impossible throughout this time the area investigated seems to have been tectonically quite stable during the late holocene a local curve of msl variations may be representative of the regional eustatic pattern

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

dust and sea salt variability in central east antarctica dome c over the last 45 kyrs and its implications for southern high latitude climate a detailed record of non sea salt calcium a proxy for dust and sea salt sodium a proxy for sea salt covering the last 45 kyr is presented it shows that in the first part of the transition from the last glacial period to the holocene 18 15 kyr bp the changes in dust flux mainly reflect changes at the dust source namely vegetation cover and local climate the changes in the later part of the transition 12 11 kyr bp are similar in extent to the changes seen in sea salt and most likely reflect a reorganization of the atmospheric circulation during the last glacial period considerable variation of dust but not of sea salt is observed pointing to climatic changes in patagonia the main dust source for dome c a comparison of the glacial records from dome c and taylor dome suggests that similar influences controlled aerosol input at both sites during this period

spatial and seasonal variations of the snow chemistry at the central filchner ronne ice shelf antarctica the chemical stratigraphy of the surface firn of the central filchner ronne ice shelf was determined in conjunction with stable isotopes from shallow firn cores and snow pit samples collected at 1 1 widely distributed sites and covering a time period of at least 20 years the chemical analysis included ecm profiling and the determination of chloride non sea salt nss sulphate methanesulphonate msa nitrate and partly sodium and bromide throughout the investigated area winter time nss sulphate levels are found to be substantially negative indicating that the sulphate to sodium ratio in airborne sea salt particles is depleted by a factor of 5 approximately in relation to the bulk sea water ratio while winter firn layers appear to be marked by episodic events of large sea salt inputs pronounced annual cycles with maxima in summer firn layers are commonly observed for the ecm signal and for nss sulphate nitrate and msa at all sites for msa however this phase relation is almost reversed for depths greater than 3 4m the mean impurity levels consistently are strongly depleted with increasing distance from the ice edge by about 30 100 km for sea salt 25 100 km for msa and only 10 100 km for nss sulphate however no substantial trend is observed for nitrate it is concluded therefore that the sea salt and the biogenic sulphur compounds deposited on the filchner ronne ice shelf mainly originate from the adjacent weddell sea further important implications of the continental effects are a an atmospheric residence time of nss sulphate apparently exceeding that of msa probably due to the supplementary sulphate production on the ice shelf from biogenic so 2 and b a substantial limitation of the potential of deep ice cores already drilled on the filchner ronne ice shelf in extracting reliable net temporal changes of sea salt and biogenic sulphur species

palaeohurricane reconstructions from sedimentary archives along the gulf of mexico caribbean sea and western north atlantic ocean margins hurricanes annually threaten the atlantic ocean margins historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity here we review palaeo trends in hurricane activity elucidated from sedimentary archives we discuss dating methods site selection and stat istics associated with previously published records these archives have been useful for under standing the long term evolution of coastal systems and the response of intense hurricane activity to climatic changes regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability including el nino southern oscillation and the north atlantic oscillation but could also reflect regional scale controls on hurricane activity

juxtaposed beach ridges and foredunes within a ridge plain wonga beach northeast australia abstract reports describing aeolian foredunes and wave derived beach ridges juxtaposed within a single coastal barrier complex are rare perhaps because morphological similarities make the two ridge types difficult to differentiate this study of an approximately 4500 year old sand ridge plain in northeast queensland australia using landform morphology sedimentology and luminescence chronology suggests that ridge plain development here has been interrupted along part of the sequence by localised alterations in coastal sedimentation a switch from coarse to fine grained sand supply along one part of the beach has caused the development of prograding foredunes in the northeastern sector of the sequence over the past 700 years contemporaneously coarser textured beach ridges have continued to form behind the remainder of the beach the result is a complex barrier where a single ridge plain contains both foredunes developed through high frequency low intensity events and beach ridges developed through high intensity low frequency events associated with intense tropical cyclones

reef sedimentary accretion model reefsam understanding coral reef evolution on holocene time scales using 3d stratigraphic forward modelling abstract a detailed understanding of the development of coral reefs and their internal structure has important applications for predicting future reef trajectories in light of climate changes petroleum exploration and reconstructing past environmental changes such as sea level numerical computer modelling provides a quantitative means of testing and understanding reef processes and better predicting past and future reef development however most existing carbonate stratigraphic forward models sfms focus on the platform scale and several limitations in their simulation of important reef processes and reef scale features e g patch reefs sand aprons have been previously identified we present the reef sedimentary accretion model reefsam a new carbonate sfm designed to test new approaches to modelling processes important at the reef scale with the goal of better simulating reef features and evolution at higher temporal and spatial resolutions specific developments include a sediment transport model which calculates deposition based on a range of grain sizes additional controls on coralgal growth including wave energy and surface substrate specificity and model outputs showing categorized paleo conditions composition paleo depth and paleo energy along with numerous quantitative measures for objective comparison of model results to real world observational data which is often more abundant for modern holocene reefs than buried ancient reefs simulations of the well studied holocene one tree reef otr in the southern great barrier reef gbr showed improvements upon previous modelling attempts in both quantitative measures e g lagoon size or reef sea level catch up time and the ability to produce more realistic reef scale morphological features e g lagoonal patch reefs mostly sand filled lagoon and reef development characteristics e g transition from mostly vertical aggradation during sea level catch up to horizontal progradation afterwards controls on reef maturity lagoonal filling identified in previous modelling experiments were corroborated sensitivity testing also revealed a very high sensitivity to reef drowning these results indicate the new modelling approaches are viable and provide a way forward for future holocene reef evolution model development

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

frost flowers implications for tropospheric chemistry and ice core interpretation 1 this paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation analysis of antarctic frost flowers shows that they are highly saline and fractionated in sea salt ions with sulfate being depleted strongly relative to sodium because frost flowers give a bright return on satellite scatterometer images the times and places of their formation can be identified when winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers the collected aerosol is also depleted in sulfate because the flowers have a large salinity bromide concentrations are elevated in frost flowers relative to seawater with their high surface area it is possible that bromine is released to the atmosphere from frost flowers with consequent implications for tropospheric ozone depletion the finding that quantities of fractionated sea salt are available at the sea ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records analysis of one near coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water hitherto strong sea salt signals in ice cores have been attributed to increased open water and more efficient transport inland perhaps due to stormier weather at least in coastal regions however these signals may be related instead to the increased formation of sea ice and frost flowers

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

a tentative chronology for the epica dome concordia ice core a tentative age scale edc1 for the last 45 kyr is established for the new 788 m epica dome c ice core using a simple ice flow model the age of volcanic eruptions the end of the younger dryas event and the estimated depth and age of elevated 10be about 41 kyr ago were used to calibrate the model parameters the uncertainty of edc1 is estimated to 10 yr for 0 to 700 yr bp up to 200 yr back to 10 kyr bp and up to 2 kyr back to 41 kyr bp the age of the air in the bubbles is calculated with a firn densification model in the holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

southern ocean sea ice control of the glacial north atlantic thermohaline circulation 1 a coupled model simulates a shallower and weaker north atlantic deep water circulation at the last glacial maximum compared to the modern with an enhanced intrusion of antarctic bottom water into the north atlantic these circulation changes are caused by the enhanced antarctic bottom water formation which is triggered by the enhanced equatorward sea ice transport ultimately by increased westerlies in the southern ocean at the last glacial maximum

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

variations in tropical cyclone genesis factors in simulations of the holocene epoch the thermodynamic factors related to tropical cyclone genesis are examined in several simulations of the middle part of the holocene epoch when the precession of earth s orbit altered the seasonal distribution of solar radiation and in one transient simulation of the millennium preceding the industrial era the thermodynamicpropertiesmostcrucialforgenesisdisplayabroadstabilityacrossbothperiods althoughbothorbital variations during the mid holocene mh 6000 years ago 6ka and volcanic eruptions in the transient simulation have detectable effects it is shown that the distribution of top of the atmosphere radiation 6ka altered the northern hemisphere seasonal cycle of the potential intensity of tropical cyclones in addition to slightly increasing the difference between middle tropospheric and boundary layer entropy a parameter that has been related to the incubation period required for genesis the southern hemisphere which receives more solar radiation during its storm season today than it did 6ka displays slightly more favorable thermodynamic properties during the mh than in the preindustrial era control surface temperatures over the ocean in both hemispheres respond to radiation anomalies more slowly than those in upper levels altering the thermal stability volcanism produces a sharp but transient temperature response in the last millennium simulation that stronglyreducespotentialintensityduringthe seasonsimmediatelyfollowingamajor eruption here too the differential vertical temperature response is key temperatures in the lower and middle troposphere cool while those near the tropopause rise aside from these deviations there is no substantial variation in thermodynamic properties over the 1000 yr simulation

the influence of indian ocean atmospheric circulation on warm pool hydroclimate during the holocene epoch existing paleoclimate data suggest a complex evolution of hydroclimate within theindo pacific warm pool ipwp during the holocene epoch here we introduce a new leafwax isotope record from sulawesi indonesia and compare proxy water isotope data withocean atmosphere general circulation model oagcm simulations to identifymechanisms influencing holocene ipwp hydroclimate modeling simulations suggestthat orbital forcing causes heterogenous changes in precipitation across the ipwpon a seasonal basis that may account for the differences in time evolution of the proxydata at respective sites both the proxies and simulations suggest that precipitationvariability during the september november son season is important for hydroclimatein borneo the preeminence of the son season suggests that a seasonally laggedrelationship between the indian monsoon and indian ocean walker circulation influencesipwp hydroclimatic variability during the holocene

dust transport to dome c antarctica at the last glacial maximum and present day the antarctic polar ice core records show large changes in the concentration of dust over glacial interglacial timescales this paper explores how much of this variation is due to changes in the transport of dust from arid regions to the ice cores back trajectories initialised from the site of dome c ice core antarctica are calculated using an offline trajectory code forced by modelled winds output from the ukmo unified model running under present day and lgm boundary conditions as well as comparing the present day and lgm back trajectories their seasonal and interannual variability is also explored the results suggest that the patagonian provenance of the dome c dust can be understood in terms of the atmospheric transport whereas the total change in dust concentration requires changes to the sources or sinks

seismic evidence of glacial age river incision into the tahaa barrier reef french polynesia rivers have long been recognized for their ability to shape reef bound volcanic islands on the time scale of glacial interglacial sea level cycles fluvial incision of exposed barrier reef lagoons may compete with constructional coral growth to shape the coastal geomorphology of ocean islands however overprinting of pleistocene landscapes by holocene erosion or sedimentation has largely obscured the role lowstand river incision may have played in developing the deep lagoons typical of modern barrier reefs here we use high resolution seismic imagery and core stratigraphy to examine how erosion and or deposition by upland drainage networks has shaped coastal morphology on tahaa a barrier reef bound island located along the society islands hotspot chain in french polynesia at tahaa we find that many channels incised into the lagoon floor during pleistocene sea level lowstands are located near the mouths of upstream terrestrial drainages steeper antecedent topography appears to have enhanced lowstand fluvial erosion along tahaa s southwestern coast and maintained a deep pass during highstands upland drainages appear to contribute little sediment to refilling accommodation space in the lagoon rather the flushing of fine carbonate sediment out of incised fluvial channels by storms and currents appears to have limited lagoonal infilling and further reinforced development of deep barrier reef lagoons during periods of highstand submersion

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

coastal vulnerability to typhoon inundation in the bay of bangkok thailand evidence from carbonate boulder deposits on ko larn island abstract at the head of the gulf of thailand the subsiding chao phraya delta and adjacent low lying coastlines surrounding the bay of bangkok are at risk of coastal flooding although a significant marine inundation event has not been experienced in historical times this work identifies coastal depositional evidence for high energy waves in the past on ko larn island in eastern bay of bangkok numerous coastal carbonate boulders ccbs were discovered at elevations up to 4 m above sea level the largest weighing over 1 3 tonnes for the majority of ccbs their karstified appearance bears testimony to long periods of immobility since original deposition whilst their geomorphic settings on coastal slopes of coarse blocky talus is helpful in recognising lifting saltation as the probable mode of wave transport in the absence of local tsunamigenic potential these ccbs are considered to be prehistoric typhoon deposits presumably sourced from fringing coral reefs by high energy wave action application of existing hydrodynamic flow transport equations reveals that 4 7 m s and 7 1 m s are the minimum flow velocities required to transport 50 and 100 of the measured ccbs respectively such values are consistent with cyclone impacted coastlines studied elsewhere in the tropical asia pacific region overall the evidence of elevated carbonate boulder deposits on ko larn implies that typhoons before the modern record may have entered the bay of bangkok the recurrence of a similar event in future would have the potential to cause damaging marine inundation on surrounding low lying coastlines

limited migration of soluble ionic species in a siple dome antarctica ice core high resolution 10 samples a i glaciochemical analyses covering the last 110 years from a siple dome antarctica ice core reveal limited migration of certain soluble ionic species methane sulfonic acid n03 and mg2 the observed chemical m igration m ay be due in part to seasonal alternation between less acidic winter from h igh sea salt concentrations and m ore acidic summer from high m arine biogenic acid concentrations layers common at coastal sites such as siple dome exact mechanisms to explain the migration are unclear although simple diffusion and gravitational movement are unlikely since new peaks are formed where none previously existed in each case initial migration of each species is both sh allower and earlier at siple dome than at other sites in antarctica where similar phenomena have been observed which may be related to the relatively low accumulation rate at siple dome 13 3 cm ice a i migration appears to be limited to either the preceding or fol lowing seasonal layer for each species suggest ing that paleoclimatic interpretations based on data with lower than annual resolution are not likely to be affected

facies variations in response to holocene sea level and climate change on bora bora french polynesia unravelling the role of synsedimentary siderite in a tropical marine mixed carbonate siliciclastic lagoon abstract five mixed carbonate siliciclastic sedimentary facies were identified in the barrier reef lagoon of bora bora using microfacies and statistical analyses of 70 sediment samples taken at high resolution from two vibrocores facies and facies successions were interpreted with respect to holocene sea level and climate changes the windward lagoon core is characterized by sideritic marly wackestones and foraminifera sideritic wackestones deposited around 7700 years bp years before present during the early mid holocene transgression at that time extensive weathering and erosion of iron bearing minerals from the volcanic island due to a wetter climate were expressed in the formation of synsedimentary siderite in lagoonal sediments the enrichment in 18o 0 32 to 0 54 in the siderite grains indicates marine to mixed marine meteoric conditions during precipitation siderite formation resulted from microbial degradation of organic material indicated by depleted 13c values 13 61 to 14 48 that led to reducing conditions in lagoonal sediments and resulted in iron reduction in the presence of dissolved bicarbonate the chemical compositions of the siderites changes upcore from relatively high fe 91 95 mol and low mn 5 6 mol at the core base to relatively low fe 83 88 mol and high mn 11 16 mol at the core top the substitutions of fe by mn ca and mg at grain margins illustrate changes in pore water chemistry towards more oxygenated conditions and reflect sea level rise and elevated rainfall during the early mid holocene a drier climate during the mid late holocene was accompanied by reduced iron input and the proportion of siderite decreased approaching zero in the upper section of the core in the leeward lagoon core siderite is again common in the lower section and decreases in abundance upcore mollusc foraminifera marly packstones and mollusc wackestones accumulated 5400 3500 years bp during the mid holocene in the windward core early in this period rotalid and miliolid foraminifera dominated these are tolerant of environmental stress such as changes in water quality nutrients or salinity from the mid holocene to the present textularid foraminifera are common in both cores and indicate normal marine lagoonal conditions since the mid late holocene sea level highstand and fall to modern level mudstones have dominated in both cores during the last 1000 years coral fragments have increased in abundance in the windward lagoon presumably as a result of lagoonward progradation of fringing reefs in the mid late holocene since the late holocene motus on the windward side of bora bora have hampered sediment transport and lagoonward progradation of sand aprons increasing numbers of peloids largely hardened faecal pellets in the windward core in the last 1000 years may reflect early submarine lithification within the lagoon our study shows that during the holocene sea level and climate change have influenced sediment import composition and distribution in the bora bora lagoon the sensitive response of the environment to external changes demonstrates the potential of tropical reef lagoons as archives of climate and sea level changes

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

microfossils from coastal environments as indicators of paleo earthquakes tsunamis and storms abstract coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest but least frequent events coastal sediments from low energy depositional environments archive geologic evidence of paleo earthquakes tsunamis and storms many of the best reconstructions of these events are derived from changes in microfossil diatoms foraminifera and pollen assemblages in this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines examples from the united states alaska and the pacific northwest japan and chile show that microfossil based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles we discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance e g beach nearshore or offshore sources and identify overwash deposits and how this information can be used to reconstruct the recurrence of tsunamis and storms analysis of overwash deposits from thailand and malaysia indicates the ability of microfossils to resolve individual waves within tsunami sediments and an example from the sendai coastal plain in japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 tohoku tsunami deposit finally we present recent examples from the gulf of mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

a new model evaluating holocene sediment dynamics insights from a mixed carbonate siliciclastic lagoon bora bora society islands french polynesia south pacific abstract mixed carbonate siliciclastic lagoons of barrier reefs provide great potential as sedimentary archives focusing on paleoenvironmental and paleoclimatic changes as well as on event deposition sediment sources include lagoonal carbonate production the marginal reef and the volcanic hinterland mixed carbonate siliciclastic continent attached coastal lagoons have been intensively studied however their isolated oceanic counterparts have been widely disregarded here we present a new model of holocene sediment dynamics in the barrier reef lagoon of bora bora based on sedimentological paleontological geochronological and geochemical data the lagoonal succession started with a pleistocene soil representing the lowstand systems tract as the rising holocene sea inundated the carbonate platform peat accumulated locally 10 650 9400 years bp mixed carbonate siliciclastic sedimentation started ca 8700 5500 years bp and represents the transgressive systems tract during that time sediments were characterized by relatively coarse grain size and contained high amounts of terrestrial material from the volcanic hinterland as well as carbonate sediments mainly produced within the lagoon siliciclastic content decreases throughout the holocene after the rising sea had reached its modern level sand aprons formed between reef crest and lagoon creating transport pathways for reef derived material leading to carbonate dominated sedimentation ca 6000 3000 years bp during the highstand systems tract however mainly fine material was transported and accumulated in the lagoon while coarser grains were retained on the prograding sand apron from ca 4500 500 years bp significant variations in grain size total organic carbon as indicator for primary productivity ca and cl element intensities as qualitative indicators for carbonate availability and lagoonal salinity are seen such patterns could indicate event re deposition and correlate with contemporaneous event deposits found in the lagoon of nearby tahaa which are supposed to be induced by elevated cyclone activity correspondingly enhanced erosion and run off from the volcanic hinterland as well as lower lagoonal salinity would be associated with intense rainfall during repeated cyclone landfall increased amounts of coarse grained sediment from marginal reef areas would be transported into the lagoon however ti ca and fe ca ratios as proxies for terrigenous sediment delivery have incessantly declined since the mid holocene also benthic foraminiferal faunas do not validate reef to lagoon transport of sediment alternatively the apparent onset of higher hydrodynamic energy conditions can be explained by more permanent southeast trade winds and higher than present sea level which are supposed for the mid late holocene in the south pacific sustained winds would have flushed higher amounts of open ocean water into the lagoon enhancing primary productivity and the amount of pelagic organisms within the lagoon while lowering lagoonal salinity we propose the shift towards coarser grained sedimentation patterns during the mid late holocene to reflect sediment load shedding of sand aprons due to oversteepening of slopes at sand apron lagoon edges during times of stronger trades and higher than present sea level of the highstand systems tract which led to redeposition of sediment even within the lagoon center modern conditions including a sea level fall to modern level were reached ca 1000 years bp and lagoonal infill has been determined to a large part by fine grained carbonate dominated sediments produced within the lagoon and derived from the marignal reef infill of lagoonal accommodation space via sand aprons is estimated to be up to six times higher than infill by lagoonal background sedimentation and emphasizes the importance of the progradation of sand aprons contrary to the commonly supposed assumption that coarse grained sediment layers within fine grained lagoonal successions represent overwash events induced by storms or periods of higher storm activity we postulate a new model of long term lagoonal sediment dynamics including sea level climatic change and geomorphological variation of the barrier reef lagoon

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

new insights into the holocene development history of a pacific low lying coral reef island takapoto atoll french polynesia abstract low lying atoll islands are known to be made up of unconsolidated coral rich detritus together with high amounts of foraminifera derived from both outer reef and lagoonal environments while regarded as highly vulnerable to ongoing global changes these islands are poorly constrained in term of development history herein is presented a detailed chronostratigraphic study of tuamotu atoll islands french polynesia south central pacific based on analyses of sedimentary sequences through seven excavations along two transects across both windward and leeward rim areas around takapoto atoll the island accretionary chronology is supported by radiometric dating of 62 coral and molluscan clasts the sequences range between 3 80 m and 1 20 m in thickness from the oceanic shoreline lagoonwards four lithofacies were identified from sediment composition and texture a coral pocilloporid rich gravel supported preferentially located in the outermost rim areas a coral rich gravelly sand supported locally interbedded with gravel supported units a foraminifera amphisteginid rich sand dominated mainly located at the central and innermost rim settings and an organic rich sand facies atop of some sequences a model of atoll islet formation is drawn up in relation to mid to late holocene sea level changes the foundations of islets motus namely conglomerate platforms started to form with deposition of patchy rubble spreads over the upper reef rim surfaces from ca 4 500 yr bp as sea level was about 0 80 m above its present mean level on these platforms islets started to accrete not before ca 2 300 yr bp from isolated depocentres located midway between outer reef and lagoon margins at that time sea level at about 0 60 m above present mean sea level was starting to slowly decrease to its present position the major growth phases occurred in a context of continued sea level fall islets continued to accrete through concentric ridges mainly until the last 300 years accretion was dominantly driven by low frequency high energy wave surge events from dating of coral clasts a number of one to two events by century were identified as having apparently contributed to island formation at takapoto regionally predicted increase in the rates of sea level rise may have negative impacts on such islands since these have evolved under conditions of falling sea level

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

ice core evidence for the extent of past atmospheric co2 change due to iron fertilisation 1 an extended high resolution ice core record of dust deposition over the past 60 ka from dome c antarctica is presented the data are in conflict with the idea that changes in aeolian iron input into the southern ocean were the major cause for the 80 ppm glacial interglacial co2 increase during the deglaciation the co2 increase shows a linear relationship with the fall of the logarithm of the nss ca2 flux a proxy for dust deposition however the very large variations in the nss ca2 flux related to the glacial antarctic warm events a1 to a4 were accompanied by small co2 variations only our data based analysis suggests that decreased southern ocean dust deposition caused at most a 20 ppm increase in co2 at the last glacial interglacial transition rapid decreases in dust deposition to the northern pacific could have been responsible for a maximum of 8 ppm in addition

imprints of archean to neoproterozoic crustal processes in the madurai block southern india madurai block the largest crustal block in the southern granulite terrane sgt of peninsular india preserves the imprints of multistage tectonic evolution here we present u pb and hf isotope data on zircons from a charnockite granite suite in the north western part of this block the oscillatory zoning and the lree to hree enriched patterns of the zircons with positive ce and negative eu anomalies suggest that the zircon cores are of magmatic origin with ages in the range of 2634 2435 ma implying neoarchean paleoproterozoic magmatism followed by subsequent metamorphism and protocontinent formation in the north western part of the madurai block a regional 550 500 ma metamorphic overprint is also preserved in the zircons coinciding with the final amalgamation of the gondwana supercontinent the hf isotopic data suggest that the granite and charnockite were derived from isotopically heterogeneous juvenile crustal domains and the charnockites show a significant contribution of mantle derived components therefore the hf isotopic data reflect mixing of crustal and mantle derived sources for the generation of neoarchean crust in the north western madurai block possibly in a suprasubduction zone setting during continent building processes c 2014 elsevier ltd all rights reserved

understanding the history of extreme wave events in the tuamotu archipelago of french polynesia from large carbonate boulders on makemo atoll with implications for future threats in the central south pacific abstract numerous large carbonate boulders up to 164 tonnes in mass were investigated on the reef flat and beaches of makemo atoll in the tuamotu archipelago of french polynesia to reveal the past occurrence and to anticipate the future potential threat of extreme wave events possibly generated by tropical cyclones and tsunamis the modern reef edge and emerged mid holocene coastal landforms were identified as sources of boulders mobilized during extreme wave events in the past the minimum flow velocities produced by extreme wave events were estimated to exceed 5 4 15 7 m s at the reef edge on different parts of the atoll comparison of uranium thorium ages of boulder coral fabric with written historical records indicates that two large boulders 77 and 68 tonnes were possibly emplaced on the reef flat by a powerful cyclone in february 1878 although most boulder dates are older than the earliest historical cyclone and tsunami records in french polynesia their ages concur with the following a periods of storminess i e increased cyclone activity compared to today in the central south pacific over the last millennium and b periods of high sea surface temperature sst at the great barrier reef possibly associated with higher than normal ssts pacific wide that facilitated the generation of cyclones affecting the central south pacific ocean none of the boulders on makemo were dated younger than ce1900 implying that the last century has not experienced extreme waves of similar magnitude in the past nevertheless the findings suggest that waves of comparable magnitudes to those that have transported large boulders on makemo may recur in the tuamotus and threaten island coasts across the central south pacific in the future