use of doppler radar to assess ice cloud particle fall velocity size relations for remote sensing and climate studies knowledge of ice crystal terminal velocities both for individual crystals and for size distributions is important for an adequate representation of ice particle sedimentation in climate models while the terminal velocities t of individual crystals of simple shapes have been measured theoretical relations of the form t adb where d is the maximum particle dimension obtained using expressions for the aerodynamic drag force are often more useful because they can be applied to a wide range of particle sizes and heights and temperatures in the atmosphere for high tropospheric ice clouds the coefficient a has been found to vary over 1 order of magnitude the exponent b is generally within the range 0 7 1 4 aerodynamic drag force calculations show that a and b are related a and b can also be used to characterize terminal velocity particle characteristic size relations for size distributions in this study we use collocated vertically pointing measurements of ice cloud radar reflectivity doppler velocity and ir brightness temperatures to estimate the vertical profiles of cloud particle characteristic size cloud ice water content and vertically averaged value of the coefficient a emphasizing cirrus clouds we analyze variations in terminal velocity size relations for individual particles and corresponding variations for ensembles of particles for example in relations between the reflectivity weighted terminal velocity and the median volume size and between the mass weighted terminal velocity and the median volume size the retrievals indicate that a ranges from 250 to almost 4000 cgs units similar to the range found from the theoretical calculations the coefficient a tends to decrease as a characteristic particle size e g median size increases as a simplification for climate modeling efforts we present an empirical relation between median size and a although there is a fair amount of variability about this relation using the doppler measurements and retrieval data we also derive relations between the mass weighted terminal velocity and cloud ice water content such relations are useful for representing fallout of ice particles in climate and cloud resolving models

atoll reef island formation and response to sea level change west island cocos keeling islands abstract reef islands around the margin of coral atolls generally comprise unconsolidated holocene sands and gravels overlying a reef flat or cemented conglomerate platform such islands have accreted within the last 3000 4000 years since sea level has reached a level close to present and the reef flat and conglomerate platform have formed island morphology consists of an oceanward ridge a less distinct lagoonward ridge and low lying central depression several alternative models of how such reef islands might have developed are examined in relation to chronology and sediment provenance particularly in the context of the cocos keeling islands where this issue has been debated since darwin visited the atoll which of these models appears most appropriate for an elongate reef island on the atoll margin is assessed using conventional radiocarbon dating of coral shingle and accelerator mass spectrometry ams radiocarbon dating of individual sand grains from pits across west island the dating results suggest that both coral clasts and individual grains of various components are generally reliable and replicable indicators of the chronology of island accumulation implying rapid transport of skeletal material after death of the contributing organisms across the reef flat zone and relatively little reworking the central part of west island appears to have formed first with oceanward accretion up until about 2000 years bp gradual oceanward accretion with lesser lagoonward extension has continued beyond 2000 years bp at the northern and southern ends of the island and a sequence of lagoonward recurving spits has formed adjacent to the inter island passage at the southern end of the island radiocarbon dating of fossil microatolls indicates a gradual fall of sea level over this period which appears to have had little effect on the pattern of island accretion

how many paleointensity determinations are required from a single lava flow to constitute a reliable average 1 statistical analysis has been undertaken to investigate the minimum number of paleointensity estimates required to allow certainty at the 95 confidence limit that the mean is within 10 of the implied true mean for an entire lava flow the data used for the analysis was provided by previous paleointensity studies which used three different methods thellier coe shaw and microwave thellier on 19 or more samples from three different basalt lava flows the results strongly suggest that future paleointensity studies need to produce many more estimates per lava flow than is currently the norm in order to ensure that the calculated mean paleointensity does not differ significantly from the true flow mean furthermore they indicate that a low measured dispersion for a small number of estimates is not a safeguard against misrepresentation of the flow mean paleointensity finally we provide quantitative evidence that paleointensity studies should always attempt to maximise vertical coverage of lava flows to avoid biasing of the mean

spatiotemporal variability of typhoon impacts and relaxation intervals on jaluit atoll marshall islands storms are important drivers of geomorphic change within atoll settings causing rapid island erosion while also initiating island building through the generation of vast quantities of reef derived sediment due to the combined effects of storms and sea level rise reef islands are thought to be on an erosional trajectory jaluit atoll in the marshall islands was struck by typhoon ophelia in a d 1958 causing significant geomorphic change to reef islands using aerial photographs as well as recent satellite imagery we track the impacts of the typhoon and the multidecadal recovery of islands ophelia caused a significant reduction in total land area of jaluit atoll from 9 95 km 2 to 9 45 km 2 5 1 with islands on the northeast rim collectively reducing in size from 4 72 km 2 to 4 14 km 2 12 2 between 1976 and 2006 73 of 87 islands increased in size with the total landmass exceeding the pre typhoon area 10 25 km 2 however we observe considerable spatiotemporal variability of impacts and relaxation following the typhoon results indicate that despite significant typhoon driven erosion and a relaxation period coincident with local sea level rise islands have persisted and grown

new model of reef island evolution maldives indian ocean a new model of reef island evolution based on detailed morphostratigraphic analysis and radiometric dating of three islands in south maalhosmadulu atoll maldives is presented islands initially formed on a foundation of lagoonal sediments between 5500 and 4500 yr b p when the reef surface was as much as 2 5 m below modern sea level islands accumulated rapidly during the following 1500 yr effectively reaching their current dimensions by 4000 yr b p since then the high circum island peripheral ridge has been subject to seasonal and longer term shoreline changes while the outer reef has grown upward reducing the energy window and confining the islands this new model has far reaching implications for island stability during a period of global warming and raised sea level which will partially reactivate the energy window although it is not expected to inhibit upward reef growth or compromise island stability

coral islands defy sea level rise over the past century records from a central pacific atoll the geological stability and existence of low lying atoll nations is threatened by sea level rise and climate change funafuti atoll in the tropical pacific ocean has experienced some of the highest rates of sea level rise 5 1 0 7 mm yr totaling 0 30 0 04 m over the past 60 yr we analyzed six time slices of shoreline position over the past 118 yr at 29 islands of funafuti atoll to determine their physical response to recent sea level rise despite the magnitude of this rise no islands have been lost the majority have enlarged and there has been a 7 3 increase in net island area over the past century a d 1897 2013 there is no evidence of heightened erosion over the past half century as sea level rise accelerated reef islands in funafuti continually adjust their size shape and position in response to variations in boundary conditions including storms sediment supply as well as sea level results suggest a more optimistic prognosis for the habitability of atoll nations and demonstrate the importance of resolving recent rates and styles of island change to inform adaptation strategies

further evidence for low intensity of the geomagnetic field during the early cretaceous time using the modified shaw method and microwave technique summary we report new absolute palaeointensity estimates using basalts from northeastern china k ar age 125 120 ma using the modified shaw method in conjunction with the microwave technique samples for the palaeointensity experiments were selected mainly based on their good reversibility of thermomagnetic curves and single primary magnetization characteristics using the modified shaw method 28 out of 45 measured samples from 10 cooling units give a virtual dipole moment of 3 1 1 0 10 22 am 2 and the microwave technique using 14 acceptable determinations out of 20 measured give an average value of 2 9 0 9 10 22 am 2 results using both the modified shaw method and the microwave technique demonstrate that the geomagnetic field strength recorded by these lavas was low this is in agreement with previous results of the same time interval obtained by the thellier method with partial thermal remanence p trm checks the fact that different techniques give qualitatively compatible low palaeointensity results provides greater confidence that the weak field features seen just prior to the cretaceous normal superchron cns are the result of the actual field recorded by the basalts as opposed to artefacts of the method analysis this study also demonstrates that the microwave technique can be used for very old basalts

the importance of large benthic foraminifera to reef island sediment budget and dynamics at raine island northern great barrier reef low lying reef islands are among the most vulnerable environments on earth to anthropogenic induced climate change and sea level rise over the next century because they are low composed of unconsolidated sediment that is able to be mobilised by waves and currents and depend on sediments supplied by reef organisms that are particularly sensitive to environmental changes e g ocean temperatures and chemistry therefore the spatial and temporal links between active carbonate production and island formation and dynamics are fundamental to predicting future island resilience yet remain poorly quantified in this paper we present results of a detailed geomorphological and sedimentological study of a reef and sand cay on the northern great barrier reef we provide an empirical investigation of the temporal linkages between sediment production and reef island development using a large collection of single grain ams 14c dates large benthic foraminifera lbf are the single most important contributor to contemporary island sand mass 47 ranging from 36 to 63 at raine island reflecting rapid rates of sediment production and delivery standing stock data reveal extremely high production rates on the reef 1 8 kg m 2 yr 1 while ams 14c dates of single lbf tests indicate rapid rates of sediment transferral across the reef we also demonstrate that age is statistically related to preservation and taphonomic grade severely abraded tests moderately abraded tests pristine tests we construct a contemporary reef and island sediment budget model for raine island that shows that lbf baculogypsina marginopora and amphistegina contribute 55 of the sediment produced on the reef annually of which a large proportion 54 contribute to the net annual accretion of the island the tight temporal coupling between lbf growth and island sediment supply combined with the sensitivity of lbf to bleaching and ocean acidification suggests that islands dominated by lbf are likely to be very sensitive to short and long term climate change projections potential outcomes of this work relate to improving the understanding of the future change dynamics of reef islands in response to climate change

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

a reliable absolute palaeointensity determination obtained from a non ideal recorder reliable measurements of the intensity of the palaeomagnetic field are notoriously difficult to obtain the approach generally taken is to produce multiple estimates per rock unit and assume that those which meet certain minimum standards of technical quality will combine to produce an accurate mean however here using results produced from a package of 20th century basaltic lava flows from mount etna in sicily we demonstrate that this approach can fail in this case the application of typical sets of selection criteria actually introduces bias into the mean determination that we measure we demonstrate that this is caused by two types of non ideal behaviour acting in combination the first is a result of the multidomain grains that the samples contain and the second is caused by differences in the natural and laboratory cooling rates we discuss means of avoiding these sources of error in future palaeointensity studies performed on ancient rocks we also develop a new more general reliability criterion which is effective here and which we argue should be applied wherever possible in future palaeointensity studies in conjunction with standard criteria it requires two distinct types of materials which both produce some good quality palaeointensity measurements and uses their range of overlap to constrain the true palaeointensity both the application of this criterion and general reliability considerations require that future palaeointensity studies should measure many samples per cooling unit and that these should be as diverse in terms of their rock magnetic properties and cooling histories as possible

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

evidence for coral island formation during rising sea level in the central pacific ocean the timing and evolution of jabat island marshall islands was investigated using morphostratigraphic analysis and radiometric dating results show the first evidence of island building in the pacific during latter stages of holocene sea level rise a three phase model of development of jabat is presented initially rapid accumulation of coarse sediments on jabat occurred 4800 4000 years b p across a reef flat higher than present level as sea level continued to rise during the highstand island margins and particularly the western margin accreted vertically to 2 5 3 0 m above contemporary ridge elevations this accumulation phase was dominated by sand size sediments phase three involved deposition of gravel ridges on the northern reef as sea level fell to present position jabat has remained geomorphically stable for the past 2000 years findings suggest reef platforms may accommodate the oldest reef islands in atoll systems which may have profound implications for questions of prehistoric migration through pacific archipelagos

incremental accretion of a sandy reef island over the past 3000 years indicated by component specific radiocarbon dating 1 low lying reef islands appear particularly threatened by anticipated sea level rise and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management depositional chronology of warraber island a small sand cay in torres strait australia is re examined based on ams radiocarbon dating of specific skeletal components whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid late holocene deposition component specific ams radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation in contrast to bulk ages and other components produced at greater distances growth of sand cays depends on the rate and pattern of sediment supply which are functions of the local ecology of the surrounding reef and reef flat and hydrodynamic constraints

climatology of high cloud dynamics using profiling arm doppler radar observations abstractice cloud properties are influenced by cloud scale vertical air motion dynamical properties of ice clouds can be determined via doppler measurements from ground based profiling cloud radars here the decomposition of the doppler velocities into reflectivity weighted particle velocity vt and vertical air motion w is described the methodology is applied to high clouds observations from 35 ghz profiling millimeter wavelength radars at the atmospheric radiation measurement program arm southern great plains sgp climate research facility in oklahoma january 1997 december 2010 and the arm tropical western pacific twp site in manus july 1999 december 2010 the doppler velocity measurements are used to detect gravity waves gw whose correlation with high cloud macrophysical properties is investigated cloud turbulence is studied in the absence and presence of gw high clouds are less turbulent when gw are observed probability density functions of vt w and high cloud macrophysical propert

influence of cooling rate on thermoremanence of magnetite grains identifying the role of different magnetic domain states it is widely accepted that cooling rate can strongly influence the intensity of the thermal remanent magnetization trm acquired by rocks during cooling to ambient temperatures if ignored this effect might lead to underestimates or overestimates of the ancient magnetic field intensity to date however the cooling rate dependence of trm acquired by particles with different domain states has never been systematically analyzed from the theoretical or experimental point of view in this study we present measurements of the trm of synthetic magnetites with well defined grain sizes that were quenched with constant cooling rates of 0 05 0 1 1 3 10 and 15 k min while single domain sd and small pseudo single domain psd samples are found to show larger trms after slow cooling the trms of larger psd and multidomain md magnetites are not affected by an increase or decrease of the cooling rate overall our results suggest that only smallest magnetite grains acquire a cooling rate dependent trm therefore cooling rate corrections of paleointensity determinations are only necessary for samples dominated by sd remanence carriers while rocks dominated by psd and md carriers such as basalts which are most commonly used for paleointensity studies do not require such corrections

coral reef island initiation and development under higher than present sea levels coral reef islands are considered to be among the most vulnerable environments to future sea level rise however emerging data suggest that different island types in contrasting locations have formed under different conditions in relation to past sea level uniform assumptions about reef island futures under sea level rise may thus be inappropriate using chronostratigraphic analysis from atoll rim islands sand and gravel based in the southern maldives we show that while island building initiated at different times around the atoll 2 800 and 4 200 calibrated years before present at windward and leeward rim sites respectively higher than present sea levels and associated high energy wave events were actually critical to island initiation findings thus suggest that projected sea level rise and increases in the magnitude of distal high energy wave events could reactivate this process regime which if there is an appropriate sediment supply may facilitate further vertical reef island building

solving the mystery of the 1960 hawaiian lava flow implications for estimating earth s magnetic field studying historic lava flows provides a rare comparison between direct measurements of the earth s magnetic field and the field information recorded in the rock record connecting direct and indirect measurements provides a way to bridge the gap between historic data in the last 50 100 yr to geologic data over kyr to gyr the field strength in hawaii in 1960 was directly measured at the honolulu observatory to be 36 47 t so our palaeointensity analysis of the 1960 flow is expected to give the same value two vertical sections of the 1960 flow section 1 and section 2 were the focus of a previous microwave palaeointensity study the microwave experiments were run using the non standard perpendicular modified thellier type protocol and produced either apparently good quality data that were biased to low values section 1 or more scattered results averaging close to the expected value section 2 the cause of the non ideal behaviour observed in the data from the 1960 flow is a long standing mystery that it is important to resolve to confirm the reliability of palaeointensity measurements in general and the microwave demagnetization mechanism in particular here we test the hypothesis that higher quality unbiased only random noise measurements are possible using an improved thellier type protocol coupled to an updated microwave system new palaeointensity experiments were performed primarily using the izzi protocol which allows alteration checks during the experiment adapted for the microwave system the specimens from section 1 produced more linear arai plots and gave an estimate of 36 8 3 4 t whereas those from section 2 gave an estimate of 39 1 4 6 t our new experiments demonstrate the microwave system s ability to produce accurate results and efficiently run any thellier style experiment we investigate correcting perpendicular data for undetected alteration and find that using too strict selection criteria can be counterproductive to obtaining accurate and precise microwave palaeointensity results

an investigation of the magnetic variation within two recent lava flows summary samples collected in vertical sections from two recent 1169 ad and 1971 ad lava flows show significant variations in both the palaeomagnetic vector and the rock magnetic characteristics the age and the short cooling time of the flows both are less than 3 m thick are such that the observed range of palaeomagnetic variation is more than can reasonably be explained by secular variation the variations in palaeomagnetic and rock magnetic characteristics appear in part to be a response to the relative proportions of two coexisting ferrimagnetic phases one that displays a primary coarsegrained and ti rich composition and a second that has finer grained ti poor characteristics the use of af demagnetization in this study means that the latter phase will have a disproportionate influence on the palaeomagnetic results it has been suggested elsewhere that in such a magnetic system the ti poor phase may represent a crm formed at some temperature below its final curie temperature if so the results of this study imply that not only does it affect the palaeointensity estimate which requires a pure trm but it appears also to influence the palaeomagnetic direction to an extent that far exceeds the normal secular change that might be expected to occur during delayed acquisition such a result has important implications for palaeomagnetic studies that use lavas both in the selection of a suitable sampling strategy and in the geomagnetic interpretation of palaeomagnetic variation within single flow units

microwave palaeointensities from a recent mexican lava flow baked sediments and reheated pottery microwave palaeointensity pi estimates have been produced from samples from the 1670 yr old xitle lava flow mexico seventeen out of 19 experiments were successful producing high quality estimates and a mean pi of 58 3 7 9 5 wt within errors of that expected from global data for the time period the dispersion is high but could be reduced to 5 5 wt by using stricter selection criteria previous data obtained by the thellier coe method using samples from the same lava flow were less successful and of much lower quality producing a higher mean of 67 9 7 9 8 wt 25 out of 65 samples this difference is most probably caused by the presence of multi domain particles producing concave up arai plots combined with alteration processes affecting the thellier coe experiments at higher temperatures pi calculations restricted to the initial part of an arai plot therefore tend to overestimate the correct values in addition to lava samples microwave pis were also determined from pottery fragments recovered from the contact zone between the lava flow and the underlying baked sediments which were also studied these materials also provided good quality results with a higher mean pi of 66 8 7 7 1 wt which is still statistically indistinct from that produced by the microwave analysis of the lava samples nevertheless these samples seem to be less suitable for pi determinations because they are characterised by larger magnetic grains and apparently more prone to thermally induced alteration than the lava samples we conclude that in the case of the xitle lava the microwave pi method is superior to the conventional thellier coe method in many respects and that the results produced by the latter method even when satisfying strict acceptance criteria may be unreliable however we also draw attention to the fact that microwave produced pi determinations though of high technical quality may still be prone to inaccuracy when rock magnetic parameters indicate that the material is likely to be a poor pi recorder as for the pottery sediment and some of the lava samples described here 2003 elsevier b v all rights reserved

cloud radar doppler spectra in drizzling stratiform clouds 2 observations and microphysical modeling of drizzle evolution sites is presented the evolution of the doppler spectra moments is consistent with the onset and growth of drizzle particles and can be used to assist modeling studies of drizzle onset and growth time height radar observations are used to exhibit the coherency of the doppler spectra shape parameters and demonstrate their potential to improve the interpretation and use of radar observations in addition a simplified microphysical approach to modeling the vertical evolution of the drizzle particle size distribution in warm stratiform clouds is described and used to analyze the observations the formation rate of embryonic drizzle droplets due to the autoconversion process is not calculated explicitly however accretion and evaporation processes are explicitly modeled the microphysical model is used as input to a radar doppler spectrum forward model and synthetic radar doppler spectra moments are generated three areas of interest are studied in detail early drizzle growth near the cloud top growth by accretion of the well developed drizzle and drizzle depletion below the cloud base due to evaporation the modeling results are in good agreement with the continental and maritime observations this demonstrates that steady state one dimensional explicit microphysical models coupled with a forward model and comprehensive radar doppler spectra observations offer a powerful method to explore the vertical evolution of the drizzle particle size distribution

impacts of eustasy and hydro isostasy on the evolution and landforms of pacific atolls consideration of eustatic and hydro isostatic effects on late quaternary sea levels in the tropical pacific ocean indicates that the configuration of modern atolls with emergent annular reef flats is a transient morphology not developed until post mid holocene time annular atoll reefs perched atop carbonate platforms which cap buried volcanic edifices are underlain by 8 28 m of holocene limestone disconformably overlying a substratum of last interglacial or older limestone comparable thicknesses 9 23 m of holocene sediment are present beneath atoll lagoons that are uniformly 85 m deep during glacio eustatic drawdowns in global sea level by 120 125 m carbonate platforms of modern atoll provinces rose abruptly from the sea as clusters of subaerial limestone plateaus flanked by steep cliffs modern analogues are provided by emergent atolls uplifted on the flexural arches of trench forebulges slow subsidence coupled with karstic erosion of emergent atolls during the last glaciation lowered the surfaces of last interglacial reef edifices by the amounts needed to provide accommodation space for holocene reef growth during the postglacial eustatic rise in sea level modern atoll reef caps began to grow after 9 ka when rising holocene sea level overtopped degraded remnants of interglacial reefs but remained submerged until carbonate buildups approached sea level in mid holocene time 6 4 ka classic atoll morphology with circlets of multiple islets dotting annular reefs formed in combination with late holocene hydro isostatic drawdown in tropical pacific sea level in response to equatorial ocean siphoning a facet of global isostatic adjustment gia to deglaciation early holocene eustatic rise in sea level and late holocene hydro isostatic decline in sea level combined to produce a regionally variable mid holocene highstand in tropical pacific sea level that stood 1 0 2 6 m above modern sea level cemented mid holocene paleoreef flats now stranded well above sea level serve as resistant foundations for non migratory pinned islets that were not present along atoll rims until after the local crossover date when ambient high tide level first fell below mid holocene low tide level existing atoll landforms have a time depth generally 1 2 ka

formation and adjustment of typhoon impacted reef islands interpreted from remote imagery nadikdik atoll marshall islands abstract in 1905 a devastating typhoon hit nadikdik atoll 5 54 n and 172 09 e in the southern marshall islands evidence suggests that large sections of reef islands on nadikdik were overwashed and destroyed comparison of aerial photographs taken in 1945 and modern satellite imagery provides a unique record of the geomorphic adjustment of islands after the typhoon between 1945 and 2010 the vegetated area of islands on nadikdik grew from 0 74 to 0 90 km2 observed changes to nadikdik reef islands manifested through a range of styles and were largely accretionary of note the formation of a new island was tracked from an embryonic deposit to a fully vegetated and stable island over a 61 year period similarly a number of previously discrete islands have agglomerated and formed a single larger island these changes were rapid and indicate that reef island formation can occur quickly evidence suggests that despite the typhoon occurring over a century ago the geomorphic adjustment of islands is still on going

absolute palaeointensity variation during a precursor to the matuyama brunhes transition recorded in chilean lavas abstract following a detailed radioisotropic dating and palaeomagnetic investigation of transitional polarity lava flows of the tatara san pedro volcanic complex 36 s 71 w in the quebrada turbia valley central chile brown et al 2004 palaeointensity analysis has been carried out to complete a characterisation of the full geomagnetic field vector during a period of transitional geomagnetic field behaviour at 791 7 3 0 ka 16 ky before the full matuyama brunhes transition mbt seventy one samples from 30 lava flows were analysed in total with 34 found suitable for palaeointensity experiments after conducting microwave palaeointensity experiments 16 lava flows from two sections 2 km apart yielded 31 successful individual palaeointensity determinations which record consistently weak field intensity values during the transitional directions mean value of 5 1 1 t from 11 flows excluding a flow immediately above a reversed polarity flow palaeointensity values are nearly an order of magnitude lower than the overlying normal polarity lavas ranging from 30 to 47 t and half the values recorded in the underlying reversed polarity lavas 7 and 13 t these post transitional field high palaeointensity values and comparisons with relative palaeointensity records from sedimentary rocks suggest that the quebrada turbia lavas may document a partial record of the mbt precursor and the latter stages of the mbt itself

terminal fall velocity and the fastex cyclones knowledge of water drop and ice crystal terminal velocities is particularly important for an adequate representation of particle sedimentation in cloud resolving and large scale models in this paper a new method is proposed to retrieve terminal fall velocity from airborne doppler radar observations to extract the terminal fall velocity from the doppler information which mixes the three wind components and the terminal fall velocity statistical considerations are introduced stating that for a long sampling time span a whole aircraft mission for instance and for moderate storms such as stratiform precipitation the mean vertical air motions should vanish with respect to the mean terminal fall velocity statistical power law relationships between terminal fall speed and radar reflectivity are then developed as well as profiles of mean terminal fall velocity this underlying hypothesis of the method is validated with in situ measurements of the vertical wind component averages of convective scale retrievals of the vertical wind component and terminal fall speed radar reflectivity vt z relationships derived from in situ measurements of the drop size distribution these comparisons all indicate that the vertical air motion can indeed be neglected with respect to the terminal fall speed a detailed analysis of the statistical relationships obtained in liquid and ice phases for six frontal cyclones at different stages of development shows that a universal vt z rain relationship can be proposed for north atlantic frontal cyclones at mature stage this result and further arguments developed in the paper suggest that the drop size distributions are equilibrium distributions in the ice phase such a universal relationship is not found it is nevertheless suggested in this study that such a general relationship might be derived if the frontal cyclones are split into categories depending on their stage of development these vt z universal relationships can be introduced in large scale model parametrization schemes in order to better describe the sedimentation of ice and water and dynamical microphysical interactions occurring within north atlantic frontal cyclones finally a procedure is proposed to estimate the most representative type of ice particle from 2d p in situ sensor and airborne doppler radar measurements it consists of calculating the mean flight level z and the vt z relationships in the ice phase for several theoretical ice habits and to identify the ice habit that reasonably reproduces both the radar derived mean flight level z and vt z ice relationship copyright 2003 royal meteorological society

comment on recent eruptive history of stromboli aeolian islands italy determined from high accuracy archeomagnetic dating by s arrighi et al 1 arrighi et al 2004 hereinafter referred to as ar2004 recently reported paleomagnetic directions gathered from stromboli volcano by using the unconventional large sample method lsm these directions are partly different and have smaller confidence cones than those previously reported by speranza et al 2004 hereinafter referred to as sp2004 for the same spatter lavas by using the traditional core drilling and systematic stepwise demagnetization paleomagnetic technique hence ar2004 conclude that traditional paleomagnetic sampling cannot yield sufficient precision and is therefore unsuitable to study the paleosecular variation of the geomagnetic field recorded in volcanics and to use it as a dating tool here we contend that the laboratory procedures and analysis methods employed by ar2004 yield a fictitious improvement in statistical uncertainty we conclude that the traditional paleomagnetic techniques provide a more realistic estimate of archeomagnetic dating and related uncertainties

a preisach method for estimating absolute paleofield intensity under the constraint of using only isothermal measurements 2 experimental testing 1 this paper reports an empirical test of a new nonheating preisach based protocol for determining the absolute ancient magnetic field intensity paleointensity using a selection of synthetic samples and a large suite of modern lavas and pyroclastic lithic samples generally the preisach paleointensity estimates compare favorably with the expected field intensities 1 for the synthetic samples displaying single domain like behavior the method returned the correct result for the known field while multidomain samples yielded an underestimate and 2 averaging 168 post 1850 a d lavas yielded a value 6 within the expected field value these preisach paleointensity estimates are also compared with paleointensity determinations made on the same suite of samples using standard thellier type heating protocols and the nonheating remanence rem method the preisach paleointensity estimates compare favorably for samples that yielded correct thellier type determinations including the synthetic single domain like samples in addition the preisach method produced estimates for cases where the thellier type estimates failed a possible selection criterion was identified median destructive field which was found to improve the paleointensity estimates in some sample suites for the investigated sample set the preisach method was found to be much more accurate than the rem method the importance of cooling rate on the preisach paleointensity estimate is also examined

the geomagnetic field intensity in new zealand palaeointensities from holocene lava flows of the tongariro volcanic centre very few absolute palaeointensity data exist from holocene aged rocks in new zealand here we present a new suite of high quality palaeointensities supported by detailed rock magnetic investigations samples from 23 sites representing 10 distinct eruptive units of the tongariro volcanic centre taupo volcanic zone new zealand were studied both traditional double heating and microwave palaeointensity methods were employed the reliability of the palaeointensity data varies with rock magnetic properties of the samples corresponding in particular to their positions within the lava flows the highest success rates are from samples obtained from near the flow tops where a significant proportion of the remanence unblocked at intermediate temperatures 200 350 c by contrast samples from flow centres particularly the parts showing platey fracturing have the lowest success rates reliable high quality palaeointensity results ranging from 32 4 5 1 t to 72 1 4 7 t were obtained from six flows with ages between c 12 800 yr bp and the present these correspond to virtual dipole moments that increase from 52 10 zam2 in the early holocene and peak at 112 14 zam2 about 300 yr ago the data agree well with calibrated relative palaeointensities from new zealand lake sediments the volcanic and sedimentary data together yield a holocene virtual axial dipole moment curve that fits the global average variation well in the early holocene but which differs significantly in recent millennia this difference is associated with recent migration of the southern high latitude core mantle boundary flux lobe towards new zealand as is seen in global field models less

variability of surface ocean radiocarbon and stable isotopes in the southwestern pacific we present high precision radiocarbon 14c results and stable isotope 18o and 13c records for a coral from heron island 23 s 152 e and new stable isotope 18o and 13c records for annual coral bands from abraham reef 22 s 153 e in the southern great barrier reef studied earlier druffel and griffin 1993 these tracers provide unique information on the regional water mass history and together these data allow us to constrain the variability of circulation in the upper pacific over the past four centuries first we observe decreases in 18o of coral from abraham reef and heron island indicating an increase in sea surface temperature and or a decrease in surface salinity since 1850 second the small suess effect value 14c decrease from 1880 to 1955 due mostly to fossil fuel co2 observed previously at abraham reef druffel and griffin 1993 is confirmed in the measurements reported here from the heron island coral this value is low compared to those observed in other areas of the ocean druffel 1997 druffel and linick 1978 nozaki et al 1978 between 1880 and 1955 third we report alterations in the correlation between el nino events and the occurrence of low 14c which is indicative of long term change s in circulation in the sw pacific the 14c shifts reported here are not large but even small temporal changes in prebomb 14c suggest that important changes in the large scale state of the ocean have occurred such as a temporal change in circulation

large variations of surface ocean radiocarbon evidence of circulation changes in the southwestern pacific radiocarbon 14c and stable isotope 18o and 13c records are presented for biannual samples from a 323 year banded coral series collected from the southern great barrier reef australia the high precision 14c record contains variations on an interannual timescale that are particularly large between a d 1680 and 1730 by comparison with tree ring 14c records stuiver and quay 1980 m stuiver personal communication 1992 it is clear that these shifts were not caused by changes in the 14c of atmospheric co2 changes in vertical mixing and large scale advective changes involving source waters to the western coral sea region are likely processes that could account for these large 14c variations most low 14c values for the period a d 1635 1875 coincide with el nino southern oscillation enso events as reported by quinn et al 1987 for the eastern tropical pacific however enso does not explain all of the variations especially during 1875 1920 when 14c values remained high cross spectral analysis of the early half of the 14c and 18o records a d 1635 1795 reveals that the 6 year period is coherent this coherency is not present in the latter half a d 1797 1957 of the isotope records these data support the concept of century timescale changes in the nature of enso as it is manifest in the southwestern pacific our coral record shows no evidence of a suess effect the lowering of 14c from late 1800s through 1955 due mainly to co2 input from fossil fuel burning this is coincident with the change we observe in the nature of enso and is further evidence that a long term change in mixing of upper waters occurred in this region

the durability of bioclastic sediments and implications for coral reef deposit formation the generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of caco3 in conjunction with physical biological and chemical processes which act to break down and disperse skeletal remains using the results of detailed tumbling barrel experiments this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits the durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels results indicate that constituent durability varies considerably amongst common reef sediment constituents calcareous algae halimeda was the least durable constituent tested followed by larger benthic foraminifera baculogypsina sphaerulata and marginopora vertebralis and the pelecypod fragum fragum two species of branching coral acropora sarmentosa and acropora nasuta were found to be the most resistant to physical destruction these findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems

late holocene sea level change and reef island evolution in new caledonia abstract in new caledonia numerous cays are distributed on platform reefs in the southwest lagoon behind the barrier reef at mba island a vegetated sand cay in this area we examined holocene sea level change and reef development and evolution the late holocene sea level curve for the area was updated using newly found fossil microatolls component specific dating of foraminifera tests in the island sediment provided reliable ages of island formation mba island initially formed around 4500 cal yr b p when sea level was 1 1 m higher than at present the island formed on the leeward side of the platform reef where the base had been constructed of lagoon and reef derived sediment of the platform reef sea level fall since 2800 cal yr b p has likely caused reef flat emergence at low tide and created a suitable habitat for foraminifera such a transition in ecology due to sea level fall has been observed in other pacific reefs suggesting that the interaction between reef flat formation sediment production and sea level fall is one of the critical factors determining island development

testing determinations of absolute paleointensity from the 1955 and 1960 hawaiian flows abstract a new exhaustive study of the flows erupted in 1955 and 1960 from the kilauea volcano big island of hawaii has been conducted in order to constrain the dispersion inherent to the data of absolute paleointensity reported so far and ultimately to determine what are the most critical parameters to obtain suitable determinations the mean directions derived from both flows agree with the expected field within less than 2 paleointensity experiments have been performed using a double heating thellier procedure completed by systematic ptrm checks almost all samples display a linear nrm trm straight line but only 20 of the samples have provided suitable results less than 10 away from the expected field in the other cases the deviation from the expected paleointensity is related to the quality of the ptrm checks which thus provides a threshold value for acceptance of ptrm checks all successful determinations less than 10 away from the expected value have a maximum drat selkin and tauxe 2000 that never exceeds 5 while the mean value of all deviations is lower than 3 5 another interesting feature is the existence of a link between the unblocking temperature spectra and the accuracy of the paleofield which points out the origin of difficulties in the presence of a wide distribution of grain sizes and or the existence of several magnetic phases the results also indicate that magnetite with a narrow range of high unblocking temperatures and little variability in grain size is a favorable situation to obtain suitable determinations with a high success rate these observations may well explain the dispersion inherent to the previous studies of the hawaiian flows

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

reef island accretion and soil development on makin kiribati central pacific the late holocene accretionary history of reef islands on makin the northernmost table reef of the gilbert atoll chain western kiribati has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples and ams radiocarbon dating of individual grains makin is geomorphologically and sedimentologically simple comprising one main island with only a minor residual lagoon and composed of sand dominated by the reef flat foraminifera calcarina spengleri amphistegina lobifera and baculogypsina sphaerulata deposition commenced in mid platform around 2500 years ago in situ fossil coral heliopora dated at 2400 80 years bp indicates that sea level was 0 4 0 5 m above present at that time progradation occurred progressively to westward at a relatively constant rate of 200 300 m ka 1 however progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago the soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts and do not reflect reef island depositional history remnant stands of pisonia forest with an associated phosphatic soil are not related to any particular geomorphological feature or period of deposition the reef islands are continuing to accrete as a result of production of foraminifera on the reef flat

rapid reef island formation and stability over an emerging reef flat bewick cay northern great barrier reef australia a model that resolves reef island formation in relation to both reef platform substrate development and mid holocene sea level change is presented for bewick island northern great barrier reef based on morphostratigraphic analysis and radiometrically dated island sediments and reef corals on bewick island microatolls record reef flat development at higher sea level 1 5 m by 6500 yr b p island building began on a partially emergent reef flat 5000 4000 yr b p when sea level was 0 5 m above present as sea level fell to its present level the reef platform process window closed and the island core stabilized results present the first unequivocal evidence of island building directly over a reef flat comprising microatolls and the first detailed model of island formation from the great barrier reef the model demonstrates that the interplay of sea level and reef surface elevation can vary between sites but their convergence is critical for island initiation future trajectories of island change will vary dependent on the unique relative sea level and substrate depth conditions that govern island formation

revisiting a domain state independent method of palaeointensity determination abstract the use of a domain state independent method the wilson method of acquiring absolute palaeointensities is tested using three sets of historical lavas from mexico italy and iceland the wilson method works by plotting continuous thermal demagnetisation curve data for the original natural remanent magnetisation against those for a laboratory induced thermoremanence by comparing the predicted intensities with the known fields a new empirically derived rejection criterion is proposed that accounts for chemical alteration and improves the accuracy of the palaeointensity estimates the wilson palaeointensity estimates are compared with palaeointensity determinations made on sister samples using standard thellier type heating generally the wilson palaeointensity estimates compare favourably for samples that yielded technically correct thellier type determinations however at one locality the wilson method did not yield any estimates due to severe chemical alteration in contrast it was still possible to determine palaeointensity estimates from the lower temperature thellier data to assess the wilson palaeointensity protocol s ability to return a correct estimate for a true multidomain system a synthetic multidomain magnetite sample was imparted with a thermoremanent magnetisation the wilson protocol returned the correct palaeointensity within error in contrast the thellier type protocol failed as the wilson method is significantly faster than thellier type methods it is suggested that the wilson method should be tried as a first approach in palaeointensity studies or for samples dominated by multidomain material

on using the relationship between doppler velocity and radar reflectivity to identify microphysical processes in midlatitudinal ice clouds 1 ground based 35 ghz profiling doppler cloud radar observations of ice clouds were used to derive the power law relation between doppler velocity vd and radar reflectivity z vd azb by removing the vertical air motion from vd the power law can be rewritten as vt azb with vt being the reflectivity weighted particle terminal fall velocity profiles of this relation are variable with height an attempt was made to relate this variability to the dominant microphysical processes in different layers of the cloud based on that the possibility of using profiles of the parameters a and b to distinguish different microphysical regimes was explored the methodology was applied to long term measurements january 1997 to december 2010 at the atmospheric radiation measurement site in the southern great plains principal component analysis was used to determine the modes of the profiles that explain most of the observed variance in the observations profile averaged means and standard deviations of parameters a and b amounted to 0 65 0 42 and 0 03 0 19 respectively furthermore three commonly used microphysical relations related to bulk quantities were used to determine values of a and b these results were found to compare reasonably well with the values obtained from the radar observations finally microphysical considerations showed that radar derived values of parameter b can be explained in terms of particle size distribution moment changes

reliability of geomagnetic paleointensity data the effects of the nrm fraction and concave up behavior on paleointensity determinations by the thellier method abstract to test the reliability of the thellier method for paleointensity determinations we studied six historic lavas from hawaii and two gauss age lava flows from raiatea island french polynesia our aim is to investigate the effects of the nrm fraction and concave up behavior of nrm thermal remanent magnetization trm diagrams on paleointensity determinations for the hawaiian samples the paleointensity results were investigated at both sample and site levels for consistency and confidence in the paleointensity results it is important to measure multiple samples from each cooling unit the results from the raiatea island samples confirm that reliable paleointensities can be obtained from nrm trm diagrams with concave up curvature provided the data are accompanied by successful partial trm ptrm checks and no significant chemical remanent magnetization crm production we conclude that reliable determinations of the paleofield strength require analyses of linear segments representing at least 40 50 of the total nrm this new criterion has to be considered for future studies and for evaluating published paleointensities for calculating average geomagnetic field models using this condition together with other commonly employed selection criteria the observed mean site paleointensities are typically within 10 of the definitive geomagnetic reference field dgrf our new results for the hawaii 1960 lava flow are in excellent agreement with the expected value in contrast to significant discrepancies observed in some earlier studies overestimates of paleointensity determinations can arise from cooling rate dependence of trm acquisition viscous remanent magnetization vrm at elevated temperatures and trm properties of multidomain md particles these outcomes are exaggerated at lower temperature ranges therefore we suggest that provided the ptrm checks are successful and there is no significant crm production it is better to increase the nrm fraction used in paleointensity analyses rather than to maximize correlation coefficients of line segments on the nrm trm diagrams we introduce the factor q n q to assess the quality of the weighted mean paleointensity hw for each cooling unit

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

sand cay evolution on reef platforms mamanuca islands fiji abstract the sedimentary link between reef islands and their surrounding platforms is critical to understand if the morphological response of these systems to future boundary condition changes such as associated with human induced climate change is to be understood the sand cays of the mamanuca islands in fiji are an ideal system to investigate this link between reef and the islands that have developed on them the mamanuca s are a relatively simple sedimentary system being characterised by oval shaped platform reefs with a relatively uniform and horizontal reef crest and flat nine islands were investigated within the group through gps and auto level surveying with associated surface and subsurface sediment sampling the islands are composed of a typical chlorozoan sediment assemblage which is well mixed across each reef and island this mixing is related to the high transport capacity across the reef platforms with waves able to move sediment for at least 50 of the tidal cycle radiocarbon dating indicates the islands are young with modern ages returned on sand from the reef flat and ages of 500 600 years calbp from the island beaches dating from the centre of the islands at 2 m depth indicate island formation was occurring from at least 2260 2110 years calbp the young age of the sediments combined with the high transport potential suggests each cay is linked to the contemporary reefs that the islands are developed on it is inferred that the islands in the mamanuca group initially started as a subtidal gravel accumulation once wave energy is dissipated enough intertidal sands start to accumulate and eventually the islands reach a critical size where vegetation may colonise the contemporary development of the reef islands in the mamanuca s and their links to sediment production on the reef flat suggests that they may be able to adjust their morphology to future environmental conditions

evaluation of the multispecimen parallel differential ptrm method a test on historical lavas from iceland and mexico summary obtaining reliable geomagnetic palaeointensity pi estimates is still a difficult objective most common techniques in pi studies are based on various modifications of the thellier method but high failure rates and large uncertainties are common furthermore only rocks which obey stringent criteria are assumed to yield faithful pi estimates in general magnetic particles must be of single domain size the magnetization must be a thermoremanent magnetization and chemical alteration of magnetic carriers must be avoided during the laboratory experiment recently a new method for obtaining pis was proposed which on the grounds of results from two historic lavas and three simulated experiments is assumed to be independent of magnetic domain state this method uses multiple samples subjected to only one heating step at moderate temperatures here we present a test of the multispecimen parallel differential ptrm method on 11 historical lavas from iceland and mexico from which the actual field intensity is known either from magnetic observatory data or from magnetic field models our results show that the majority of pi estimates after the multispecimen parallel differential ptrm method yielded results that are very close or indistinguishable within the range of error from the expected intensity and thus largely confirm the findings from the initial study however there is in general a small overestimate which we show is associated with multidomain material when compared to a thellier type pi experiment carried out on sister samples from five icelandic lava flows the average multispecimen pi is closer to the actual field intensity samples from one lava characterized by low curie temperatures failed the thellier approach due to laboratory induced alteration but here the multispecimen method returned a reasonable pi even though there is evidence that the method is not entirely independent of magnetic domain state as previously proposed we regard this method as a valuable alternative in future pi studies

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

determining palaeointensity from the gilbert gauss reversal recorded in the pu u heleakala lava section wai anae volcano oahu hawaii abstract the ability of the earth s magnetic field to reverse is one of its most intriguing characteristics a full vector directions and intensity description during reversals is necessary to fully understand the magnetic field generation process in the earth s liquid outer core the reverse to normal gilbert gauss reversal 3 58 ma is recorded in a 470 m high sequence of lava flows at pu u heleakala waianae volcano oahu hawaii 133 samples from 34 flows sister samples from the directional study of herrero bervera and coe j geophys res 104 1999 29157 29173 were subjected to microwave demagnetisation experiments unfortunately many samples have been overprinted with a lightning induced remanence so that only 65 samples 49 were deemed suitable for microwave palaeointensity analysis both the 8 2 and 14 ghz systems were used with the perpendicular applied field and coe analogue methods individually acceptable results were obtained for 63 of the studied samples however not all flows gave internally consistent results in total 10 flows yielded microwave palaeointensity results from 2 or more samples that met the 25 self consistency criteria with flow mean palaeointensities ranging from 16 to 39 t it is pertinent to ascertain if there is any systematic behaviour seen between different reversals from the sparse data set obtained in this study the behaviour of the field appears to be different to that of the nearby pu u paheehee section that records the lower mammoth 3 33 ma transition however the two sections have different temporal resolution and the uncertainties in the palaeointensity estimates found in this study may account for some of the discrepancies

multi level consistency tests in paleointensity determinations from the welded tuffs of the aso pyroclastic flow deposits abstract we have performed multi level consistency tests in an ltd dht shaw paleointensity study on the welded tuffs of the aso pyroclastic flow deposits aso 1 aso 2 aso 3 and aso 4 in order to obtain reliable mean paleointensities from each unit for a unit level consistency test we collected samples at three or more sites in each unit to enhance a site level consistency test we conducted paleointensity experiments on both whole rock and glass samples from the same sites thermal demagnetization curves of the samples indicate that the main magnetic carrier is titanium poor titanomagnetite to pure magnetite hysteresis parameters are different among the sites of the same units also differences in unblocking spectra and hysteresis parameters are recognized between the whole rock and glass samples from the same sites therefore these samples of various properties are expected to work effectively for multi level consistency test twenty nine out of 65 whole rock samples and 10 out of 31 glass samples gave accepted paleointensity results at the site level consistency of paleointensity estimates is observed with the exception of one site two paleointensity estimates from glass samples of a site of aso 4 are inconsistent and are excluded from further analysis at the unit level consistency or inconsistency among the sites is observed for individual units for aso 1 inconsistency in paleointensity estimates among the sites is observed and we can recognize more reliable results from two sites for aso 2 consistency in paleointensity estimates from glass and whole rock samples supports the acceptance of a site for aso 3 all paleointensity estimates from two sites are thought to be reliable because consistency between the site means of the two sites as well as site level consistency between the glass and whole rock samples for each site is recognized for aso 4 some difference among the sites is observed but there is no obvious reason to exclude the results of particular sites overall both the site level and unit level consistency checks work effectively in these samples which confirm the reliability of the paleointensity estimates or highlights the erroneous ones on the basis of the reliable paleointensity estimates unit mean values are obtained as 24 9 2 2 1 t n 9 for aso 1 22 9 1 6 t n 5 for aso 2 28 3 3 4 t n 10 for aso 3 and 40 1 6 2 t n 7 for aso 4

thermoremanent magnetization of nonuniformly magnetized grains a simple and elegant interpretation of thermoremanent magnetization trm in uniformly magnetized single domain sd grains was given by neel 50 years ago but the trm acquisition processes in larger nonuniformly magnetized grains are more varied and difficult to describe theoretically sd trm is a frozen high temperature partition between two microstates spins parallel or antiparallel to an applied magnetic field nonuniformly magnetized grains have a much greater choice of microstates local energy minimum or lem states and partitioning among various lem states continues to change during cooling these changes may involve barkhausen jumps of domain walls between positions of minimum local energy or nucleation of new domains and walls because of the lower remanence capacity of nonuniform microstates compared to the uniform sd state trm intensity decreases as grain size increases although certain microstates e g single vortex states seem to contribute little to trm thermal demagnetization of trm begins just above room temperature and continues to the curie point quite unlike the sharp unblocking of sd trm this continuous demagnetization resulting from changes in microstates driven by the changing internal demagnetizing field during heating profoundly affects the separation of different components of natural remanent magnetization and the determination of paleomagnetic field intensity

the geomorphology development and temporal dynamics of tepuka island funafuti atoll tuvalu abstract the evolution sedimentary structure and morphodynamics of tepuka island a leeward vegetated sand cay on funafuti atoll tuvalu was examined based on morphostratigraphic analysis and radiometrically dated island sediments tepuka island formed rapidly on the leeward reef platform between 1100 and 500 cal years bp and presents the first evidence of island formation at current sea level postdating the holocene highstand the island is predominantly composed of foraminifera coralline algae and coral sands derived from the surrounding reef flat morphostratigraphic analysis suggests that the island formed as a central core and prograded rapidly through incremental accumulation results indicate that the vegetated core of tepuka has been stable since formation but the island margins have been morphologically dynamic over the past century the island has reduced in net area by approximately 23 substantial planform changes have been documented which have occurred through differential erosion of the shoreline in two phases lagoon shoreline erosion from 1897 to 1984 and ocean shoreline coupled with extension of the terminal ends of islands from 1984 to 2011 collectively these changes have caused a lengthening and clockwise rotation of the island on the reef platform the investigation highlights significant differences in the geomorphology sediment composition timeframe of formation and post formation island dynamics compared with the storm deposited and comparatively stable motu on the exposed eastern atoll rim