marine transgression and dune initiation on western cape york northern australia abstract the chronostratigraphy of the coastal dunes on the western side of northern cape york differs from the general pattern of dune emplacement identified on easterly facing coasts across northern australia two episodes of dune emplacement are suggested by morphology prior to the establishment of the modern foredune tl dating and comparative soil profile development indicate the possibility of three episodes based on a small number of tl dates it is possible to associate dune emplacements at about 11 200 yrs b p 8300 yrs b p and 5200 yrs b p with shoreline disturbance and the destruction of shoreline vegetation by rising sea level stabilisation of the 11 200 yrs b p unit may be due to a short marine regression roughly around the time of the younger dryas the 8300 yrs b p unit probably stabilised due to changed environmental conditions and the 5200 yrs b p unit represents the cessation of post glacial sea level rise in northern australia

environmental context for late holocene human occupation of the south wellesley archipelago gulf of carpentaria northern australia a 2400 year record of environmental change is reported from a wetland on bentinck island in the southern gulf of carpentaria northern australia three phases of wetland development are identified with a protected coastal setting from ca 2400 to 500 years ago transitioning into an estuarine mangrove forest from ca 500 years ago to the 1940s and finally to a freshwater swamp over the past 60 years this sequence reflects the influence of falling sea levels development of a coastal dune barrier system prograding shorelines and an extreme storm cyclone event in addition there is clear evidence of the impacts that human abandonment and resettlement have on the island s fire regimes and vegetation a dramatic increase in burning and vegetation thickening was observed after the cessation of traditional indigenous kaiadilt fire management practices in the 1940s and was then reversed when people returned to the island in the 1980s in terms of the longer context for human occupation of the south wellesley archipelago it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years

equatorial waves in high resolution dynamics limb sounder hirdls data 1 we examine equatorial wave structure in temperature measurements from the high resolution dynamics limb sounder hirdls on the aura satellite waves with periods longer than 1 day and zonal wave numbers up to 8 depending on frequency are derived from an asynoptic fourier transform analysis hirdls measurement sampling and resolution afford unprecedented views of the latitude height structure of equatorial rossby wave mixed rossby gravity wave and kelvin wave modes at altitudes above cloud tops in the tropical upper troposphere and stratosphere wave modes with vertical wavelength as short as 4 km can be clearly seen in the data kelvin waves comprise a dominant signal throughout the 3 years of hirdls measurements and we further examine time height and longitude variations observed in the kelvin waves an annual cycle of kelvin wave temperature amplitudes near the tropopause is observed that may have implications for annual variations in wave cirrus formation in the tropics this annual variation can be largely explained by effects of the background wind and stability on kelvin wave propagation and potential energy in the tropical tropopause layer at altitudes 20 km and above the annual cycle gives way to an interannual cycle in kelvin wave amplitudes that is related to the quasi biennial oscillation in stratospheric winds this interannual variation is a signature of kelvin wave forcing of the descent of westerly winds in the oscillation and we compute the kelvin wave fractional contribution to the forcing

origin of atoll dolomites distinguished by geochemistry and crystal chemistry kita daito jima northern philippine sea abstract kita daito jima is a carbonate island located at the northwestern region of the philippine sea 25 55 6 57 6 n 131 16 9 19 8 e dolomites extend from the island surface to a depth of 100 m below the ground surface mbgs strontium isotope stratigraphy indicates that subsurface units c1 0 49 7 mbgs and c2 49 7 103 4 mbgs were dolomitized at 5 5 ma and 2 0 ma respectively and that island surface dolomites are products of dolomitization at 1 6 2 0 ma x ray diffraction analysis indicates that the island surface and borehole dolomites comprise variable mixtures of four and three dolomite crystal phases respectively each of these phases is distinguished by a different ca and mg content three textural types can be recognized in the kita daito jima dolomites fabric preserving crystalline nonmimetic cnm crystalline mimetic cm and fabric preserving microsucrosic ms cnm dolomites contain more calcian phases whereas ms dolomites commonly are richer in more stoichiometric phases backscattered electron images indicate that calcian dolomite phases were precipitated earlier than the more stoichiometric dolomite phases and that there is no significant hiatus between the phases although they are diachronous both the island surface and borehole cores dolomites show linear relationships between whole rock 18o composition and mg contents and between whole rock trace element concentrations sr and na and mg contents these covariances result from phase mixing not stoichiometric effects deconvolution of whole rock isotopic and elemental compositions based on the relative abundance of phases reveals that each phase has a distinct chemical and isotopic composition oxygen isotopic compositions of the island surface and borehole dolomites suggest that all dolomite phases formed in seawater and that dolomitization primarily occurred during glacio eustatic sea level lowstands and cooler ocean temperatures

dating the cooloola coastal dunes of south eastern queensland australia abstract the cooloola sand dunes are part of a series of aeolian parabolic dunes that stretch along the east coast of australia they form a chronosequence showing increasing weathering soil formation and water erosion across six geomorphically recognized soil landscapes these landscapes were recognized from air photographs and further refined on the basis of some 150 auger holes across the dunes data about the structure and floristics of the vegetation were collected at the same time there is a significant body of literature about the cooloola dunes but there are two areas that have not been satisfactorily considered first the previous dating which gave inconsistent results has been superseded by single grain osl dates and second cooloola has not been considered in a regional context here we report the results of single grain optically stimulated luminescence osl analyses for 31 samples for 21 sites across the geomorphic landscapes the sites were selected near the apex of each dune as this represents the last depositional date and the least disturbed by sand movement we recognized 10 units across the dunes on the basis of the dates available the dune ages ranged from recent to 725 ka the largest dunes at some 320 m high were dated at around 140 ka and these dunes carry the maximum vegetation biomass of this dunefield beyond this vegetation maximum the dunes had lost their parabolic shape due to prolonged weathering and erosion and the vegetation is greatly reduced in height and biomass the depth to the soil b horizon gradually deepens with age to form giant podzols in the older dunes the depth to the b horizon was remarkably consistent within the geomorphic landscapes across the length and breadth of the dunes these studies place the cooloola dunes in a unique position as the chronosequence is intact the possible processes that lead to the formation of the dunes and the regional implications are discussed secondly it shows the buildup and decline of the dune ecosystems and acts as a model for all ecosystems forest succession models which place less emphasis on soil development miss this important process

holocene development of an episodic transgressive dune barrier ramsay bay north queensland australia abstract an investigation of the stratigraphy and sedimentological properties of a tombolo barrier at ramsay bay north queensland has indicated that the barrier consists largely of aeolian sands which in places extend more than 30 m below present sea level two major episodes of dune activity are recognized on morphological and pedogenic criteria radiocarbon dating of organic muds associated with the barrier sands suggests the older dunes were partly drowned during the early holocene marine transgression 9500 6000 c 14 yrs b p the later generation of dunes formed in the late holocene probably within the last 900 c 14 yrs the ultimate causes of the aeolian episodes are not certain but appear to be related to periods of rapid shoreface erosion

growth demise and dolomitization of miocene carbonate platforms on the marion plateau offshore ne australia abstract strontium isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two miocene carbonate platforms cored by ocean drilling program odp leg 194 just seaward of the great barrier reef the results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform top sites oyster bearing beds at the base of both platform successions yield early oligocene ages 29 31 ma thus dating initial transgression of the marion plateau s volcanic basement there followed a period of slow accumulation of shallow water grainstones rich in quartz and phosphate grains in late oligocene time 29 23 ma seismic megasequence a the main growth of the carbonate platforms took place in early to late miocene time 23 7 ma comprising five depositional sequences the first four of these seismic megasequence b are common to both platforms and terminated with a possible karst surface at 10 7 ma different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied the final growth stage seismic megasequence c occurred only in the southern platform and terminated at 6 9 ma both platform demise events 10 7 and 6 9 ma approximately coincide with falls in global sea level combined with longer term trends of decreasing water temperature sr isotope ages of dolostones increase with depositional age and older dolostones in the southern platform have more coarsely crystalline and fabric destructive textures than overlying younger dolostones these relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

sensitivity of gravity wave fluxes to interannual variations in tropical convection and zonal wind using an idealized model framework with high frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds the authors examine the properties and effects of gravity waves in the lower stratosphere contrasting conditions in an el nino year and a la nina year the model generates a broad spectrum of tropical waves including planetary scale waves through mesoscale gravity waves the authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite and balloon based estimates of gravity wave momentum flux some interesting changes in the gravity spectrum of momentum flux are found in the model which are discussed in terms of the interannual variations in clouds precipitation and large scale winds while regional variations in clouds precipitation and winds are dramatic the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11 the modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations and the largest amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere this strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency these results suggest a way forward to improve model representations of the lowermost stratospheric quasi biennial oscillation winds and teleconnections

holocene sea level change and coastal landscape evolution in the southern gulf of carpentaria australia a revised holocene sea level history for the southern gulf of carpentaria is presented based on new data from the south wellesley archipelago and age recalibration of previous research results confirm that rising sea levels during the most recent post glacial marine transgression breached the arafura sill ca 11 700 cal yr bp sea levels continued to rise to ca 30 m by 10 000 cal yr bp leading to full marine conditions by 7700 cal yr bp sea level reached present mean sea level pmsl and continued to rise to an elevation of between 1 5 m and 2 m above pmsl sea level remained ca 1 5 between 7000 and 4000 cal yr bp followed by rapid regression to within 0 5 m of pmsl by ca 3500 cal yr bp when placed into a wider regional context results from this study show that coastal landscape evolution in the tropical north of australia was not only dependent on sea level change but also show a direct correlation with holocene climate variability specifically the formation and preservation of beach rock deposits intertidal successions beach and chenier ridge systems hold valuable sea level and holocene climate proxies that can contribute to the growing research into lower latitude holocene sea level and climate histories

chevrons origin and relevance for the reconstruction of past wind regimes abstract since its first use in the late 80 s the term chevron has been employed in numerous studies to describe large u and v shaped ridges found in or near shorelines worldwide most studies have so far focused on bahamian chevrons that are exclusively of late pleistocene age and on the supposed holocene chevrons found in s madagascar and australia in the bahamas these deposits have been interpreted as the product of extreme storms at the end of the last interglacial lig warm period in contrast the extensive chevrons complex exposed in s madagascar and on the western coast of australia have been associated with a tsunami induced by a meteorite impact finally several authors have also proposed a non catastrophic i e eolian origin based on the recognized importance of wind related processes in these coastal areas and term such deposits parabolic dunes in this paper we collect and synthesize existing data on the morphology sedimentology and age of these chevrons and review the different interpretations proposed in the literature with the aim to lay out a consistent database to assist further investigations on these important coastal morphologies in addition we generated a synthesis of wind data at the three study areas which highlights the relationship between present wind regimes and chevrons morphologies the ubiquity of chevrons likely actually parabolic dunes in coastal areas around the globe and their relationship with coastal processes makes them crucial archives for reconstructing past wind regimes

structure of the annual mean equatorial planetary waves in the era 40 reanalyses abstract the three dimensional structure of the annual mean equatorial planetary waves in the 40 yr ecmwf re analysis era 40 is documented the features in the free atmosphere are predominantly equatorially symmetric driven by east west heating gradients the geopotential height and wind perturbations are strongest at or just below the 150 hpa level below the level of maximum amplitude the circulations in the waves are thermally direct with latent heat release in deep convective clouds and radiative cooling in the intervening cloud free regions within the overlying capping layer the wave related circulations are thermally indirect with rising of the coldest air and sinking of air that is less cold at the cold point just above the 100 hpa 17 km level the era 40 annual mean vertical velocity in the equatorial belt ranges up to 3 mm s 1 over the equatorial western pacific during the boreal winter implying diabatic heating rates of up to 3 c day 1 an order of magnitude larger than typical clear

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

thermoluminescence dating of dune podzols at cape arnhem northern australia abstract quaternary lithostratigraphic units in coastal dunes have been dated at two locations in the dune fields near cape arnhem northern australia using coarse fraction thermoluminescence tl dating fifteen tl dates were measured five main chronostratigraphic units were identified which include a late pleistocene unit ca 19 000 yr an early holocene unit ca 9000 6500 yr a mid holocene unit ca 4000 yr and two late holocene units ca 2100 yr and ca 1000 yr these respectively have been associated with the deflation of exposed shelf sediments during the last glacial the disturbance of this material by rising sea level and climatic variations in the late holocene

equatorial waves in the upper troposphere and lower stratosphere forced by latent heating estimated from trmm rain rates abstractequatorial atmospheric waves in the upper troposphere and lower stratosphere utls excited by latent heating are investigated by using a global spectral model the latent heating profiles are derived from the 3 hourly tropical rainfall measuring mission trmm rain rates which include both convective and stratiform type profiles the type of heating profile is determined based on an intensity of the surface rain rate latent heating profiles over stratiform rain regions estimated from the trmm precipitation radar pr product are applied to derive the stratiform type latent heating profiles from the gridded rain rate data monthly zonal mean latent heating profiles derived from the rain rates appear to be reasonably comparable with the trmm convective stratiform heating product a broad spectrum of kelvin mixed rossby gravity mrg equatorial rossby er and inertia gravity waves are generated in the model particularly equatorial waves kelvin er and mrg waves of zonal wavenumbers 1

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

comparison of lower stratospheric tropical mean vertical velocities 1 we have analyzed 13 years 1993 2005 of tropical stratospheric water vapor data from the halogen occultation experiment and over 3 years of data october 2004 through november 2007 from the aura microwave limb sounder by correlating the phase lag of the water vapor tape recorder signal between levels we estimate the time mean vertical velocity our estimated vertical velocity compares well with calculations from the goddard earth observing system geos chemistry climate model ccm and from the geos data assimilation system between 18 and 26 km both the geos ccm simulations and water vapor observations agree that the vertical velocity is below 0 04 cm s with a minimum near 20 km of 0 03 cm s vertical velocities deduced from water vapor observations are higher than those from the geos ccm in the region 16 18 km 0 04 cm s and above 26 30 km up to 0 07 cm s these estimates are close to earlier estimates from a shorter water vapor record and radiative transfer models no evidence is found for velocities as high as 0 15 cm s as was recently estimated from aircraft co2 measurements in the upper troposphere lower stratosphere further diagnosis of the aircraft co2 data and model simulations of co2 show that while the co2 data give an apparent upward transport velocity of 0 06 cm s about half of this is due to vertical and horizontal eddy transport accounting for the eddy terms gives a co2 based estimate of the vertical velocity of 0 03 cm s in much closer agreement with that estimated from water vapor

aspects of the emplacement evolution and 14c chronology of ridges on a coastal spit groote eylandt northern australia a coastal spit on groote eylandt in the western gulf of carpentaria northern australia began to form between 3000 and 2000 yr b p in response to the migration of a large parabolic dune across the coastline systematic discrepancies in the 14c chronology and the remarkable preservation of fragile shelly material indicated a complex origin for a series of concentric beach ridges one of the shell species deposited in the beach ridges clypeomorus bifasciata sowerby was being continuously incorporated through normal wave action while a second species fragum whitleyi iredale was introduced only under storm conditions the importance of selecting a single shell species for 14c dating and understanding the environmental tolerance of the species is highlighted a conceptual model for the emplacement of surficial ridge material under bedload flow during storm set up is proposed it is argued that these ridges act as offshore bars rather than storm beaches during storm events this would have significant implications for the environmental interpretation of some types of spits and beach ridges in particular sea level estimates based on the assumption that these types of ridges are formed as beaches are open to question

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

morphology and chronostratigraphy of a coastal dunefield groote eylandt northern australia a coastal dunefield on groote eylandt in the gulf of carpentaria northern australia is stratigraphically described and dated using the coarse fraction thermoluminescence dating technique four phases of dune activity have been identified 1 modern active transverse and parabolic dunes 2 a parabolic dunefield apparently stabilized less than 2000 yr bp 3 a parabolic dunefield stablized between 6000 and 4800 yr bp 4 a basal dunefield unit emplaced prior to 100 000 yr bp the current dune systems are an expression of dune activation and stabilization events in the holocene but were formed from the deflation of an extensive pre holocene dunefield the destruction of the pre holocene dunefield appears to have been caused by sea level rise at the end of the pleistocene and during the early holocene the ages derived from the dunefield accord well with chronostratigraphic investigations of coastal dune systems elsewhere in northern australia and support theories of regional environmental change during the holocene

atoll stratigraphy as a record of sea level change problems and prospects stratigraphic hiatuses and solution unconformities in the subsurface of enewetak atoll northern marshall islands record periods of atoll emergence during low stands of sea level changes in sea level are also recorded in the atoll subsurface by variations in the rate of sediment accumulation relative to the subsidence rate of the underlying volcanic edifice past sea levels can be derived from atoll stratigraphy by correcting the present depth of dated subsurface horizons for thermal subsidence and lithospheric flexure since the time of deposition a correction for depositional paleodepth may also be necessary as a result of erosion and nondeposition during periods of emergence the history of sea level derived in this manner is discontinuous past sea levels derived from atoll stratigraphy can only be estimated to within 50 m relative to present sea level owing to uncertainties in the corrections for subsidence and flexure however the minimum magnitude of sea level falls estimated from stratigraphic hiatuses can be estimated to within 10 m owing to limited fossil based age resolution only long term sea level trends can be deduced from sediments dated by means of biostratigraphy based on the biostratigraphic ages of subsurface horizons at enewetak we can discern very little long term change in sea level from late eocene through late oligocene a rise to 110 m above present sea level in the early miocene a long term fall of 170 m through middle and late miocene time and a long term rise of 60 m from the end of the miocene to present resolution of the sea level history recorded beneath mid ocean atolls may be improved by determining the age of shallow marine carbonates by means of strontium isotope stratigraphy our interpretation of past sea levels based on 87sr 86sr chronostratigraphy from enewetak confirms the long term sea level trends inferred from biostratigraphic subsurface ages in addition we interpret three oligocene sea level falls with minimum magnitudes of 30 50 m at 35 33 30 and 25 ma and four miocene sea level falls greater than 30 95 m at 16 14 12 10 and 5 ma these estimates of the timing and magnitude of oligocene and miocene sea level changes derived from enewetak atoll stratigraphy are compared with sea level histories derived from continental margin stratigraphy and from ice volume changes inferred from deep sea foraminifera 18o records

stratigraphy vs pedogenesis problems of their correlation within coastal sedimentary facies abstract stratigraphic differentiation of wuaternary coastal sedimentary sequences is frequently based upon the recognition of individual palaeosols a number of assumptions are commonly made in the compilation of such lithostratigraphies first that the development of soil profiles spodosols within coastal sedimentary sequences occur within stable sedimentary units and second that one soil profile equals one sedimentary unit after examining and thermoluminescence dating podzol spodosol profiles within 11 barrier and dune complexes along a 900 km stretch of coastline in south east australia we can now show that such assumptions are not tenable at eight of the ten locations examined the a and b horizons of these soils although having the appearance of being intact and genetically related revealed great discrepancies in age we suggest that coastal podzol profiles are particularly susceptible to reworking primarily because of the variability in induration and hence preservation potential of successive horizons recognition of this situation as probably being the norm rather than a local anomaly suggests that the practice of dividing sedimentary units into lithostratigraphic units on the basis of palaeosols and then using this criteria as a basis for sampling and determining chronostratigraphies may well lead to erroneous interpretations especially when reconstructing quaternary environmental and geological histories

application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium this wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid rock interaction careful consideration of the uncertainties associated with trace element partitioning sample heterogeneity and fluid rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis goundwater evolution ancient seawater chemistry and isotope stratigraphy a principal uncertainty involved in the application of sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of sr between mineral and solution this variation may be a function of precipitation rate mineral stoichiometry crystal growth mechanism fluid composition and temperature calcite and dolomite in ancient limestones commonly have significantly lower sr concentrations 20 70 p p m than would be expected from published trace element distribution coefficient values and sr ca ratios of most modern sedimentary pore waters this discrepancy probably reflects the uncertainties associated with determining distribution coefficient values as techniques improve for the analytical measurement and theoretical modelling of sr concentration and isotopic variations the petrological analysis of carbonate samples becomes increasingly important the presence of even small percentages of non carbonate phases with high rb concentrations and high 87 sr86 sr values such as clay minerals can have significant effects on the measured 87 sr 86 sr values of carbonate rocks due to the decay of 87rb to 87 sr for example a permian marine limestone with 50 p p m sr and 1 p p m rb will have a present day 87 sr 86 sr value that is 2 10 4 higher than its original value this difference is an order of magnitude greater than the analytical uncertainty and illustrates the importance of assessing the need for and accuracy of such corrections a quantitative evaluation of the effects of water rock interaction on sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water rock interaction including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals quantitative modelling may also be used to construct diagnostic fluid rock interaction trends that are independent of distribution coefficient values and to distinguish between mixing of mineral end members and fluid rock interaction

dynamically forced increase of tropical upwelling in the lower stratosphere drivers of upwelling in the tropical lower stratosphere are investigated using the e39c a chemistry climate model the climatological annual cycle in upwelling and its wave forcing are compared to the interim ecmwf re analysis era interim the strength in tropical upwelling and its annual cycle can be largely explainedby local resolvedwave forcing the climatological meanforcing is due to both stationaryplanetaryscale waves that originate in the tropics and extratropical transient synoptic scale waves that are refracted equatorward increases in atmospheric greenhouse gas ghg concentrations to 2050 force a year round positive trend in tropical upwelling which maximizes in the lowermost stratosphere tropical ascent is balanced by downwelling between 208 and 408 strengthening of tropical upwelling can be explained by stronger local forcing by resolved wave flux convergence which is driven in turn by processes initiated by increases in tropical sea surface temperatures ssts higher tropical ssts cause a strengthening of the subtropical jets and modification of deep convection affecting latent heat release while the former can modify wave propagation and dissipation the latter affects tropical wave generation the dominant mechanism leading to enhanced vertical wave propagation into the lower stratosphere is an upward shift of the easterly shear zone due to the strengthening and upward shift of the subtropical jets

on the signatures of equatorial and extratropical wave forcing in tropical tropopause layer temperatures abstracttemperatures in the tropical tropopause layer ttl play an important role in stratosphere troposphere exchange and in the formation and maintenance of thin cirrus clouds many previous studies have examined the contributions of extratropical and equatorial waves to the ttl using coarse vertical resolution satellite and reanalysis data in this study the authors provide new insight into the role of extratropical and equatorial waves in the ttl using high vertical resolution gps radio occultation data the results examine the influence of four different wave forcings on the ttl extratropical waves that propagate vertically into the stratosphere extratropical waves that propagate meridionally into the subtropical stratosphere extratropical waves that propagate meridionally into the subtropical troposphere and the equatorial planetary waves the vertically and meridionally propagating extratropical stratospheric waves are associated with deep zonally symmetric temperature anomalies that extend a

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

the effect of moist convection on the tropospheric response to tropical and subtropical zonally asymmetric torques tropospheric winds can be altered by vertical transfers of momentum due to orographic gravity waves and convection previous work showed that in dry models such zonally asymmetric torques produce a pattern of tropical ascent that is well described by linear dynamics together with meridional shifts of the midlatitude jet here a series of idealizedmodels is used to understand the effects of moisture on the tropospheric responseto tropical and subtropical zonally asymmetric upper tropospheric torques the vertical motion response to a torque is shown to be amplified by the reduction in effective static stability that occurs in moist convecting atmospheres this amplification occurs only in precipitating regions and the magnitude of subsidence in nonprecipitating regions saturates when clear sky radiative cooling balances induced adiabatic warming for basic statesinwhichprecipitationisconcentrated inan intertropicalconvergence zone itcz most of the vertical motion response is thus confined within the basic state itcz even when the torqueisremotefromtheitcz tropicalandsubtropicaltorquesperturbtheextratropicalbarocliniceddyfield and the convectively coupled equatorial wave field resulting changes in momentum flux convergence by transient eddies induce secondary meridional overturning circulations that modify the zonal mean response to a torque the net effect allows tropical torques to merge a double itcz into a single equatorial itcz the response of tropical transient eddies is highly sensitive to the representation of convection so the zonal mean response to a torque is similarly sensitive even when the torque is located in the subtropics

pedogenic uranium thorium and thermoluminescence chronologies and evolutionary history of a coastal dunefield groote eylandt northern australia abstract u th disequilibrium dating of pedogenic ferruginous pisoliths and additional coarse fraction quartz thermoluminescense dates are used to test a tl based chronology of the umbakumba dunefield groote eylandt northern australia these dates support the established history of the dunefield and indicate that the field is at least mid quaternary in age and may be much older sea level fluctuation is identified as the dominant control on dunefield accretion and destruction the following model of sea level control of dunefield evolution is proposed 1 at sea levels of less than 40 m the system is inactive 2 from 40 to 5 m the system is accretionary 3 at sea levels from 5 m to 5 m the system is deflationary 4 above 5 m the dunefield would be destroyed modified versions of the conceptual model may be applicable to other coastlines where sediment supply is significantly altered by sea level fluctuations

tropical wave driving of the annual cycle in tropical tropopause temperatures part ii model results abstract the atmospheric response to a localized distribution of tropical heating is examined in terms of the stationary waves excited and how these impact the mean flow near the tropical tropopause this is done by examining nonlinear simulations of the gill model with a primitive equation model that extends from the surface up into the stratosphere the model produces strong cooling of zonal mean temperatures near the tropical tropopause when the heating is on the equator but weaker cooling with the heating at 15 n the model shows that equatorial rossby waves that penetrate the lower stratosphere and changes in ep flux divergence that correspond to the observed changes between december and august it is suggested that ascent in the upper tropical troposphere is driven by vorticity advection or equivalently potential vorticity fluxes due to these equatorial rossby waves particularly when the heating is close to the equator the model results provide support to the hypothesis that the annual cycle in tr

applications and limitations of thermoluminescence to date quaternary sediments abstract the thermoluminescence tl method dates sediment by quantifying time dependent dosimetric properties of mineral grains sunlight exposure of the sediment during transportation and deposition or heating resets the tl clock to time zero after burial of the mineral grains ionizing radiation from the decay of radioisotopes imparts a tl signal this accumulated tl signal is proportional to the equivalent dose ed which is a measure of radiation exposure during the burial period a tl age estimate is determined from the ratio of the ed to the environmental radiation dose rate the calculation of an ed is influenced by the susceptibility of sediments to optical bleaching the emission spectra of minerals and possible long and short term fading there are three basic methods for determining an ed regeneration total and partial bleach the regeneration technique may yield under estimates because of sensitivity changes with laboratory bleaching the latter two techniques are most useful for well and partially light bleached sediments respectively a number of sediments can be dated by the tl method eolian and a variety of terrestrial sediments yield apparently accurate tl age estimates though there are possible complications associated with pedogenesis it appears that some fluvial sediment can be accurately dated by tl but little is known about the efficiency of optical bleaching for fluvial depositional systems till and glacier proximal deposits are inadequately light bleached to be dated by tl sediments deposited distal from the glacier margin which are at least partially bleached are preferred for dating future research is needed to understand better the relationship between sedimentary environments and the extent of light bleaching also studies should concentrate on dating feldspar extracts from well dated sequences to more fully ascertain the temporal limitations of the method only by understanding the interplay of sedimentology tl dosimetry and environmental radiation can the tl method be effectively applied to the myriad of depositional environments spanning the late to middle pleistocene

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

an observational study on the latitudes where wave forcing drives brewer dobson upwelling the 40 yr ecmwf re analysis era 40 data are analyzed to demonstrate that wave forcing at lower latitudes plays a crucial role in driving the tropical upwelling portion of the brewer dobson circulation it is shown that subtropical wave forcing is correlated with tropical upwelling on both intraseasonal and interannual time scales when transient waves are taken into account and that tropical wave forcing exerts its influence on tropical upwelling via its body force on the zonal mean flow

strontium isotope stratigraphy of kita daito jima atoll north philippine sea implications for neogene sea level change and tectonic history abstract a detailed chronology of a 432 m core from kita daito jima an atoll on the philippine sea plate has been obtained by strontium isotope stratigraphy the atoll carbonate extends to late oligocene age the top 100 m plio pleistocene section of the core has been dolomitized and dolomite also extends to middle miocene sediments sr isotopes identify two dolomitization events at 2 and 5 ma atoll growth appears to have been continuous between 18 8 and 24 3 ma and the fit of the growth history to a standard model provides a successful confirmation of darwin s subsidence theory the atoll growth appears to have commenced about 42 ma ago 6 ma after volcanism producing a 2 km column of atoll carbonate in agreement with bathymetry the subsidence model defines an apparent loss of 360 m of the sedimentary record since the early middle miocene boundary the amount in excess of the 100 m associated with sea level fall is attributed to plio pleistocene uplift at rates of 20 30 m ma associated with the forebulge of the philippine sea plate prior to its subduction uplift rates have also been estimated using a the heights of dated last interglacial coral reefs on kita daito jima and nearby minami daito jima 17 m ma and 29 m ma b sr isotope ages of calcites from surface samples on minami daito jima 21 m ma and c contrasts in elevation with okino daito jima 100 km away 22 m ma the locations of hiatuses and ages of dolomitization indicate sea level falls of 80 m at 17 16 ma 30 m at 16 15 ma 125 m at 11 ma and 90 m at 5 ma and at 2 ma the data have been combined with those from enewetak atoll to produce a curve of sea level change for the neogene

the residual mean circulation in the tropical tropopause layer driven by tropical waves abstractlatent heating estimates derived from rainfall observations are used to construct model experiments that isolate equatorial waves forced by tropical convection from midlatitude synoptic scale waves these experiments are used to demonstrate that quasi stationary equatorial rossby waves forced by latent heating drive most of the observed residual mean upwelling across the tropopause transition layer within 15 of the equator the seasonal variation of the equatorial waves and the mean meridional upwelling that they cause is examined for two full years from 2006 to 2007 changes in equatorial rossby wave propagation through seasonally varying mean winds are the primary mechanism for producing an annual variation in the residual mean upwelling in the tropical tropopause layer averaged within 15 of the equator and between 90 and 190 hpa the annual cycle varies between a maximum upwelling of 0 4 mm s 1 during boreal winter and spring and a minimum of 0 2 mm s 1 during boreal summer this variabilit

early holocene aridity in tropical northern australia thermoluminescence ages from a longitudinal dunefield in tropical northern australia suggest that complete dune activation occurred here either continuously or sporadically between approximately 8 2 ka and 5 9 ka this period in australia is normally ascribed to one of increasingly warm and wet conditions towards the holocene climatic optimum however elsewhere this time 8 ka coincides with a brief period of global climate change recognized in 18 o records from antarctica methane records of the greenland summit ice cores changes to deep sea benthic foraminferal composition and atmospheric 14 c variations in tropical africa two distinct phases of aridity have been dated at approximately 8 ka and 6 ka the coincidence of aeolian reacti vation episodes in this north australian dunefield with brief phases of early holocene climate change elsewhere suggests possible global climatic teleconnections at this time

a holocene pollen and diatom record from vanderlin island gulf of carpentaria lowland tropical australia sedimentary palynological and diatom data from a dunefield lake deposit in the interior of vanderlin island in the gulf of carpentaria are presented prior to the formation of present perennial lake conditions the intensified australian monsoon associated with the early holocene marine transgression allowed cyperaceae sedges to colonise the alluvial margins of an expansive salt flat surrounded by an open eucalyptus woodland as sea level stabilised between 7500 and 4500 cal yr b p coastal dunes ceased to develop allowing dense melaleuca forest to establish in a restionaceae swamp dune sand input into the swamp was diminished further as the increasingly dense vegetation prevented fluvial and aeolian transported sand arriving from coastal sources this same process impounded the drainage basin allowing a perennial lake to form between 5500 and 4000 cal yr b p myriophyllum and other aquatic taxa colonised the lake periphery under the most extensive woodland recorded for the holocene the palynological data support an effective precipitation model proposed for northern australia that suggests more variable conditions in the late holocene a more precise measure of effective precipitation change is provided by diatom based inferences that indicate few changes in lake hydrology such interpretations are explained in terms of palynological sensitivity to adjustments in local fire regimes where regional precipitation change may only be recorded indirectly through fire promoting mechanisms including intensified enso periodicity and human impact

equatorial superrotation and the factors controlling the zonal mean zonal winds in the tropical upper troposphere the response of the zonal mean zonal winds in the tropical upper troposphere to thermal forcing in the tropics is studied using an idealized general circulation model with 18 vertical levels and simplified atmospheric physics the model produces a conventional general circulation with deep easterly flow over the equator when integrated using zonally invariant and hemispherically symmetric boundary conditions but persistent equatorial superrotation westerly zonal mean flow over the equator is obtained when steady longitudinal variations in diabatic heating are imposed at low latitudes the superrotation is driven by horizontal eddy momentum fluxes associated with the stationary planetary wave response to the applied tropical heating the strength of the equatorial westerlies is ultimately limited by vertical steady eddy momentum fluxes which are downward in the tropical upper troposphere and by the zonally averaged circulation in the meridional plane which erodes the mean westerly shear via vertical advection the transition to superrotation can be prevented by specifying offsetting zonally invariant heating and cooling anomalies on either side of the equator to create a solstitial basic state with a single dominant hadley cell straddling the equator superrotation is restricted in the solstitial climate because the strength of the mean meridional overturning is enhanced which increases the efficiency of vertical advection and because the cross equatorial flow in the upper troposphere provides an easterly zonal acceleration that offsets some of the momentum flux convergence associated with tropical eddy heating the cross equatorial flow aloft also reduces the stationary planetary wave response in the summer hemisphere these results suggest that hemispheric asymmetry in the mean meridional circulation is responsible for maintaining the observed mean easterly flow in the tropical upper troposphere against the westerly torques associated with tropical wave sources

quasi stationary temperature structure in the upper troposphere over the tropical indian ocean inferred from radio occultation data 1 vertical fine structure of tropical temperature profiles in the upper troposphere was analyzed with data obtained by the global positioning system radio occultation limb sounding technique of the constellation observing system for meteorology ionosphere and climate cosmic which has very high vertical resolution and global coverage inversion layers in the upper troposphere were detected using a 1 year record taken during 2007 they are observed most frequently during the boreal summer over the indian ocean the region has the characteristics of a shallow quasi stationary stable layer that is inclined from a horizontal surface it is higher in the east and to the north of the equator we also conducted statistical analysis with objective reanalysis data made by the european center for medium range weather forecasts era 40 1979 2001 and confirmed the presence of a warm anomaly that has a structure consistent with the stable layer detected by cosmic analysis we analyzed the three dimensional structure and relationship among the temperature geopotential height and wind field to discuss possible mechanisms for producing these quasi stationary structures from the viewpoints of response to the stationary heating of the asian summer monsoon and equatorial trapped stationary kelvin waves

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

eocene to early miocene growth of enewetak atoll insight from strontium isotope data the margin of enewetak atoll contains 1 260 to 1 405 m of cenozoic carbonates above a volcanic basement previous biostratigraphic studies on two deep wells e1 and f1 yielded conflicting results on the ages of tertiary strata on enewetak and on the presence of oligocene strata strontium isotope ratios support relatively continuous carbonate sedimentation from late eocene to early miocene 23 ma carbonate deposition on the atoll margin started with rapid aggradation during much of the late eocene followed by gradual seaward progradation of depositional facies during the latest eocene oligocene and early miocene the only distinct break in sedimentation from late eocene to early miocene was observed at 850 m in the e1 well here an unconformity formed by subaerial exposure separates backreef upper eocene grainstones from lower oligocene carbonates no contemporaneous subaerial exposure surface and unconformity were observed in the f1 well because correlative rocks were deposited in a slope environment extensive diagenesis occurred in upper eocene oligocene and lower miocene strata at the atoll margin where sea water circulated through in response to thermal convection and tidal pumping the main diagenesc processes are 1 aragonite dissolution 2 radiaxial calcite cementation 3 compaction in slope deposits and 4 dolomitization aragonite dissolution is pervasive below 375 m in the f1 well radiaxial calcite cement is common at 375 825 m in the f1 well compaction related fracturing and pressure solution are common in poorly cemented packstones and grainstones deposited in a slope environment and now buried more than 1 100 m deep dolomite is common in slope carbonates at 1 320 m in the f1 well and in reefal carbonates at 1 245 m in the e1 well stable carbon and oxygen isotope data support formation of radiaxial calcite and dolomite in cool sea water radiaxial calcite cement and dolomite have distinctly higher 87sr 86sr ratios than does adjacent depositional carbonate strontium isotope ratios of radiaxial calcite cements indicate precipitation at burial depths of 100 350 m the absence of meteoric cements and association of radiaxial calcite cement with aragonite dissolution suggest that aragonite dissolution also occurred in moderately deep sea water strontium isotope ratios in dolomites indicate dolomitization by sea water at burial depths greater than 950 m marine diagenesis is dependent on the saturation state of sea water relative to aragonite calcite and dolomite shallow sea water supersaturated with respect to aragonite and high magnesium calcite hmc precipitates aragonite and hmc moderately deep sea water undersaturated with respect to aragonite and hmc super saturated with respect to low magnesium calcite lmc dissolves aragonite converts hmc to lmc and precipitates lmc including radiaxial calcite deep sea water under saturated with respect to calcite supersaturated with respect to dolomite dissolves calcite and precipitates dolomite the intensity of marine diagenesis depends on the amount of sea water circulating through the platform or atoll margin

late quaternary barrier and fringing reef development of bora bora society islands south pacific first subsurface data from the darwin type barrier reef system the universally known subsidence theory of darwin based on bora bora as a model was developed without information from the subsurface to evaluate the influence of environmental factors on reef development two traverses with three cores each on the barrier and the fringing reefs of bora bora were drilled and 34 uranium series dates obtained and subsequently analysed sea level rise and to a lesser degree subsidence were crucial for holocene reef development in that they have created accommodation space and controlled reef architecture antecedent topography played a role as well because the holocene barrier reef is located on a pleistocene barrier reef forming a topographic high the pedestal of the fringing reef was pleistocene soil and basalt barrier and fringing reefs developed contemporaneously during the holocene the occurrence of five coralgal assemblages indicates an upcore increase in wave energy age depth plots suggest that barrier and fringing reefs have prograded during the holocene the holocene fringing reef is up to 20 m thick and comprises coralgal and microbial reef sections and abundant unconsolidated sediment fringing reef growth started 8780 50 yr bp accretion rates average 5 65 m kyr 1 the barrier reef consists of 30 m thick holocene coralgal and microbial successions holocene barrier reef growth began 10 030 50 yr bp and accretion rates average 6 15 m kyr 1 the underlying pleistocene reef formed 116 900 1100 yr bp i e during marine isotope stage 5e based on pleistocene age depth and coralgal palaeobathymetry the subsidence rate of bora bora was estimated to be 0 05 to 0 14 m kyr 1 in addition to subsidence reef development on shorter timescales like in the late pleistocene and holocene has been driven by glacioeustatic sea level changes causing alternations of periods of flooding and subaerial exposure comparisons with other oceanic barrier reef systems in tahiti and mayotte exhibit more differences than similarities

the sedimentary record of palaeoenvironments and sea level change in the gulf of carpentaria australia through the last glacial cycle abstract environmental evolution of the gulf of carpentaria region the world s largest tropical epicontinental seaway through the last glacial cycle has been determined from a series of six sediment cores these cores form the focus of a multi disciplinary study to elucidate sea level climate and environmental change in the region the sedimentary record reveals a series of facies including open shallow marine marginal marine estuarine lacustrine and subaerial exposure throughout the extent of the basin during this period the partial or complete closure of the central basin from marine waters results from sea level falling below the height of one or both of the sills that border the gulf the arafura sill to the west 53 m below present sea level bpsl and torres strait to the east 12 m bpsl the extent and timing of these closures and restriction of the shallow waterbody within are intrinsic to local ocean circulation available latent heat transport and the movement of people and animals between australia and new guinea whilst the occurrence of the palaeo lake carpentaria has previously been identified this study expands on the hydrological conditions of the lacustrine phases and extends the record through the last interglacial detailing the previous sea level highstand mis 5 5 and subsequent retreat when sea levels were low during the mis 6 glacial period the gulf was largely subaerially exposed and traversed by meandering rivers the mis 5 transgression 130 ka bp led to marine then alternating marine estuarine conditions through to mis 4 70 ka bp when a protracted lacustrine phase of varying salinity and depth area and including periods of near desiccation persisted until about 12 2 cal ka bp the lake expanded to near maximum size 190 000 km 2 following the intensification restoration of the australian monsoon at 14 ka bp this lake full phase was short lived as by 12 2 cal ka bp marine waters were entering the basin coincident with the progressive sea level rise fully marine conditions were restored by about 10 5 cal ka bp by westward connection to the arafura sea indian ocean whereas connections to the pacific ocean coral sea did not occur until about 8 cal ka bp

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

holocene sea levels in oceanic islands implications for the rheological structure of the earth s mantle abstract relative sea levels in oceanic islands that are situated sufficiently far from glaciated regions were studied in relation to the rheological structure of the earth s mantle the local hydro isostatic adjustment associated with the mantle flow from the oceanic side to an inland side depends on the size of the island the effective upper mantle viscosity and the elastic plate thickness the relative sea level has a significant dependence on the upper mantle rheology for islands with a radius larger than 10 km but it is almost independent of the upper mantle rheology for islands with a radius less than 10 km in other words the observed sea level changes in such small islands follow the global isostatic adjustment which depends strongly on the lower mantle viscosity in fact the relative sea levels in small oceanic islands impose important constraints on the lower mantle viscosity on the other hand the effective upper mantle viscosity and the elastic plate thickness are determined by analyzing the relative sea levels for islands greater than 10 km the observed sea level curves in japan and new zealand are consistent with the effective viscosity of the upper mantle equal to 2 to 6 10 21 poises the effective elastic plate thickness for japan and new zealand is estimated to be less than 50 km and greater than 100 km respectively the thickness of the lithosphere obtained by sea level curves in japan and new zealand is compatible with the results obtained by seismological studies

effect of tropical waves on the tropical tropopause transition layer upwelling abstract an initial value problem is employed with a gcm to investigate the role of the convectively driven rossby and kelvin waves for tropopause transition layer ttl upwelling in the tropics the convective heating is mimicked with a prescribed heating field and the lagrangian upwelling is identified by examining the evolution of passive tracer fields whose initial distribution is identical to the initial heating field this study shows that an overturning circulation induced by the tropical rossby waves is capable of generating the ttl upwelling even when the heating is placed in the eastern pacific the ttl upwelling occurs only over the western tropical pacific indicating that the background flow plays a crucial role the results from a rossby wave source analysis suggest that a key feature of the background flow is the strong absolute vorticity gradient associated with the asian subtropical jet in addition static stability is relatively weak over the western pacific suggesting that this ma

equatorial planetary waves and their signature in atmospheric variability abstractequatorial planetary waves are a fundamental component of the tropical climate system previous studies have examined their structure in the climatological mean circulation their role in the climatological mean momentum balance of the tropics and their contribution to the climatological mean upwelling across the tropical tropopause in this study the authors focus on the contribution of the equatorial planetary waves to variability in the tropical circulation about its climatological mean state the equatorial planetary waves that dominate the climatological mean exhibit considerable variability on intraseasonal and interannual time scales variability in the amplitude of the equatorial planetary waves is associated with a distinct pattern of equatorially symmetric climate variability that also emerges from empirical orthogonal function analysis of various tropical dynamical fields variability in the equatorial planetary waves is characterized by variations in 1 convection in the deep tropics

reconnaissance thermoluminescence dating of northern australian coastal dune systems abstract quaternary lithostratigraphic units in coastal dunes have been dated at three locations in northern australia cobourg peninsula shelburne bay and cape flattery by both radiocarbon dating of shell and organic carbon and thermoluminescence tl sediment dating both coarse fraction and fine fraction tl methods were used seventeen tl dates were measured none of the tl dates contradict the ages given by radiocarbon where multiple tl dates were taken from a unit they overlap within 2 standard deviation giving added confidence in the results a phase of dune emplacement during the late holocene ca 2700 1800 yr b p was identified in two of the dune fields an early holocene phase of dune emplacement ca 8600 7500 yr b p in two of the dune fields and a late pleistocene episode ca 24 000 17 000 yr b p in both the cape york dunefields three older units gave dates of about 29 000 81 000 and 171 000 yr b p but these must be treated with caution

thermoluminescence dating of coarse grain quartz from the malan loess at zhaitang section china thermoluminescence tl ages were obtained for five loess samples taken from the zhaitang section near beijing china using the coarse grain quartz technique the paleodose values have been determined by the method of total sample bleaching and regeneration of the tl growth curve the method appears to be suitable for the age determination of loess samples up to about 150 000 yr where the annual dose rate values are of the order 3 4 mgy yr this limit is a function of the total accumulated dose the ages are in good agreement with those obtained by a fine grain tl technique and are consistent with geological and geomagnetostratigraphic evidence

a diagnostic equation for tendency of lapse rate tropopause heights and its application abstractthe tropopause is the boundary between the troposphere and stratosphere and is normally defined by the temperature lapse rate previous studies have noted that synoptic scale and planetary

geochemical investigation of the south wellesley island wetlands insight into wetland development during the holocene in tropical northern australia the south wellesley islands in the gulf of carpentaria northern australia were the recent focus of a palynological investigation which found vegetation change during the holocene was driven by coastal progradation and regional climate here we present new elemental data from x ray fluorescence core scanning which provides non destructive continuous and high resolution analysis from three wetlands across bentinck island the largest of the south wellesley islands elemental data and grain size analyses are combined with lead 210 210pb and accelerator mass spectrometry ams carbon 14 14c dates an open coastal environment was present 1250 cal a bp on the south east coast of bentinck island with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock prograding shorelines dune development and river diversion formed a series of swales parallel to the coast by 800 cal a bp forming the marralda wetlands wetlands developed at sites

sr isotopic variation in shallow water carbonate sequences stratigraphic chronostratigraphic and eustatic implications of the record at enewetak atoll sr isotope data from two boreholes within the lagoon at enewetak atoll have been used to evaluate the use of such data to correlate date and monitor sea level change in shallow water carbonate sequences correlative stratigraphic intervals of relatively invariant 87sr separated by abrupt transitions to lower 87sr with increasing depth are recognized in both boreholes conversion of 87sr values to age via calibration with the seawater 87sr trend with age indicates that correlative and synchronous deposition of atoll sediments occurred at 0 4 1 2 and 2 1 ma in contrast a 5 m y hiatus is recognized in one borehole but not the other sr isotope stratigraphy sis is a powerful stratigraphic and chronostratigraphic tool in shallow water carbonate sequences only when significant secular variation of 87sr occurs and retention of depositional 87sr values is demonstrated the latter is best demonstrated when 87sr data are integrated with 18o 13c sr content data and petrographic observations several diagenetically altered intervals have greater 87sr values low 13c values and low sr ca ratios relative to adjacent intervals a combination that is consistent with open system meteoric diagenesis calcite cements from these intervals have early pleistocene 1 2 ma 87sr values despite their occurrence well within the late pliocene 2 1 ma sequence thus local sedimentological and diagenetic processes have produced intralagoon variability in the sis of the two boreholes complicating subsurface stratigraphic correlations the occurrence of anomalously young calcite cement relative to adjacent limestone is a direct response of the interaction of sea level change and meteoric phreatic diagenesis whereby overlying metastable carbonates with greater 87sr values are dissolved during periods of atoll emergence and sea level lowstand liberating sr and soil gas co2 to the pore fluid which is then incorporated into downflow meteoric phreatic diagenetic calcite the stratigraphic relation between the sites of carbonate dissolution and diagenetic calcite precipitation suggest an early pleistocene 1 2 ma sea level fall of between 34 and 64 m moreover the stratigraphic position and inferred age of paleophreatic lens calcite when backtracked for subsidence suggest that early pleistocene 1 2 ma sea level was 72 81 m range of 60 100 m below present sea level the enewetak record of early pleistocene sea level lowstand elevation agrees reasonably well with proxy sea level records inferred from sequence stratigraphy and deep sea foraminiferal 18o data however the enewetak record of the amplitude of early pleistocene sea level change is more consistent with the deep sea foraminiferal 18o proxy than the sequence stratigraphy proxy

strontium isotope stratigraphy and paleomagnetic age constraints on the evolution history of coral reef islands northern south china sea understanding the history of the response of coral reefs to past climate changes can provide valuable information for predicting the future response of modern reefs however dating such ancient biotic carbonate is still challenging because of its sensitivity to diagenetic alteration processes scarcity of well preserved fossils and low magnetic mineral content there have been a long debates about the origin and evolutionary history of coral reefs in the northern south china sea mainly due to the lack of direct and reliable age constraints this provides us with a good opportunity to verify the practicability of different dating approaches especially the strontium sr isotope analysis of bulk carbonate here we retrieved a 972 55 m long core from the xisha islands to provide a credible chronologic constraint on the carbonate platform evolution the lithostratigraphy strontium isotope stratigraphy and magnetostratigraphy were analyzed throughout the whole reef sequence the lithostratigraphic results show that the 873 55 m reef sequence developed on an ancient volcaniclastic basement and experienced multiple evolutionary phases the sr 87 sr 86 results of all 100 bulk carbonate samples vary from 0 708506 to 0 709168 and show a monotonic increase with decreasing depth except for a few outliers trace element criteria and stable isotope delta o 18 and delta c 13 methods were applied to these bulk carbonate samples and results imply that the primary or near primary seawater sr 87 sr 86 values were likely preserved although different degrees of diagenetic alteration occurred in addition the paleomagnetic results indicate 10 normal polarity and eight reversed polarity magnetozones based on the sr 87 sr 86 ratios of the selected 58 samples and paleomagnetic reconstruction of polarity reversals the bottom of the reef sequence is dated to 19 6 ma and the observed polarity chronozones extend from chron c6 19 722 18 748 ma at 866 60 m to present at the top based on the new data we propose a new chronologic framework for the evolutionary history of the reef islands where 1 the reefs initiated in the early miocene 19 6 ma and were drowned until 16 26 ma 2 during 16 26 10 66 ma lagoon to lagoon slope environments prevailed 3 the lagoon environment progressively transformed into a reef crest environment from 10 66 to 4 36 ma and 4 36 to 1 59 ma and 4 the reef started to be drowned again during 1 59 0 ma our study provides a new and reliable chronologic constraint on the general evolutionary history of the reef islands in the northern south china sea furthermore the sr 87 sr 86 results from bulk carbonate indicate that strontium isotope stratigraphy is a powerful dating tool only when rigid sample selection sequential leaching procedures and strict trace element and isotopic criteria are applied

reef talus a popular misconception reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of the reef however evidence from wave transport indicates that on present day reefs the bulk of the debris generated in this way accumulates in the back reef area with only finer grained sediment carried off reef by retreating flows or by overwash nevertheless in contrast to this observation fore reef debris slopes are commonly considered characteristic of phanerozoic reefs this apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef and the corresponding long term accretion of the carbonate platform on which it rests present day reefs are commonly although not exclusively additions to long lived carbonate platforms growth of the latter is intermittent and has been moderated by changes in sea level that for recent reefs have been on time scales of less than 100 ka during low sea level stands growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion similar changes are applied on a larger scale to the aggrading growth of carbonate platforms but the bulk accretion of these includes quite different processes and reflects far longer timescales during low sea level stands the margins of platforms commonly become unstable with instability reflected in slope failure and in the shedding of blocks ranging from metres to kilometres in diameter associated with the generation of debris flows and turbidites it is argued that these are the materials that are commonly described as reef talus in ancient structures although their formation is largely independent of any contemporary reef growth difficulties arise where the reef and the platform are treated as a single functional entity it is important to recognize the conceptual distinction between them reef talus is a misleading description of the debris predominantly generated by platform erosion and slope failure

geochronology and subsurface stratigraphy of pukapuka and rakahanga atolls cook islands late quaternary reef growth and sea level history eustatic sea level cycles superposed on thermal subsidence of an atoll produce layers of high sea level reefs separated by erosional unconformities coral samples from these reefs from cores drilled to 50 m beneath the lagoons of pukapuka and rakahanga atolls northern cook islands give electron spin resonance esr and u series ages ranging from the holocene to 600 000 yr b p subgroups of these ages and the stratigraphic position of their bounding unconformities define at least 5 periods of reef growth and high sea level 0 9000 yr b p 125 000 180 000 yr b p 180 000 230 000 yr b p 300 000 460 000 yr b p 460 000 650 000 yr b p only two ages fall within error of the last interglacial high sea level stand 125 000 135 000 yr b p this paucity of ages may result from extensive erosion of the last intergracial reef in addition post depositional isotope exchange may have altered the time ages of three coral samples to apparent ages that fall within glacial stage 6 for the record to be preserved vertical accretion during rising sea level must compensate for surface lowering from erosion during sea level lowstands and subsidence of the atoll erosion rates 6 63 cm 1000 yr can therefore be calculated from reef accretion rates 100 400 cm 1000 yr subsidence rates 2 6 cm 1000 yr and the duration of island submergence 8 15 of the last 600 000 yr the stratigraphy of coral ages indicates island subsidence rates of 4 5 2 8 cm 1000 yr for both islands a model of reef growth and erosion based on the stratigraphy of the cook islands atolls suggests average subsidence and erosion rates of between 3 6 and 15 20 cm 1000 yr respectively

the tropospheric response to tropical and subtropical zonally asymmetric torques analytical and idealized numerical model results abstractthe tropospheric response to prescribed tropical and subtropical zonally asymmetric torques which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection is investigated the linear analytical gill model response to westward upper tropospheric torques is compared to the response to a midtropospheric heating which is a familiar point of reference the response to an equatorial torque projects onto a kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels in contrast the torque and heating both produce rossby gyres of the same sign to the west of the forcing and the zonal mean streamfunction responses are identical when the forcings are shifted into the northern hemisphere the streamfunction responses have opposite signs there is upwelling in the southern northern hemisphere in response to the torque heating the nonlinear response to westward torques was explored in idealized