modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

on the spreading of the east pacific rise abstract we analyze through statistical methods the mechanics of the east pacific rise by considering the relative angular velocities of spreading of the pacific nazca pacifie cocos and pacific rivera margins we focus our attention on verifying the validity of some issues such as the constancy of the velocity of spreading the symmetry of the spreading and the rigid rotational behaviour of the plates our findings can be summarized in the following four points 1 a the relative velocities of all considered margins decreased in modulus around 1 5 m y ago 2 b the spreading is asymmetric and the pattern is in general agreement with the model of stein et al 1977 3 c the pacifie cocos and the pacific nazca margins are migrating respectively eastward and westward 4 d statistical evidence suggests that a rigid rotational behaviour is not always verified

northwest pacific tectonic evolution in the middle mesozoic abstract two magnetic bights implying pacific izanagi farallon p i f ridge ridge ridge rrr triple junctions occur in the northwest pacific basin one is formed in anomalies m26 m21 southeast of shatsky plateau while the second is formed in anomalies m10 cl1 the latter a new anomaly between m1 and m0 northeast of shatsky plateau the offset between these two bights is in a n40 e direction parallel to the p f relative motion during m20 to m10n time half spreading rates and directions and the assumption of symmetric orthogonal spreading permit the solution of the p i f velocity triangle and reveal an isosceles triangle with the i f rate equal to the p f rate this is a necessary condition for a stable fault fault ridge ffr triple junction which would migrate in the n40 e direction of the offset between magnetic bights the growth of the p f transform fault explains the increasing offset across the ends of anomalies m20 m10n projected onto the trace of shatsky plateau subsequent evolution led to the formation of a system of long transform faults offset by short spreading centers which we call the shatsky fracture zones and which extend eastward across the pacific from the plateau the original trace of the transform fault fracture zone that formed at the triple junction underlies the main mass of the shatsky plateau and would suggest that the formation of the plateau is at least coincidental with the existence of the ffr triple junction at 21 ma

the distribution of intraplate volcanism in the pacific ocean basin a spectral approach summary although the major linear island chains in the pacific ocean basin have been extensively studied relatively little attention has been given to the origin of the numerous seamounts and oceanic islands that are concentrated in the western pacific spectral analysis of shipboard gravity and bathymetry data provides a means for statistically estimating the distribution of this volcanism in space and time estimates of the power spectrum of the bathymetry fb and the average gravitational admittance z cross spectrum correlation of gravity and bathymetry were obtained as functions of age of the oceanic lithosphere by dividing the pacific plate into eight age regions a h the power spectrum of the bathymetry is indicative of the overall bathymetric roughness primarily volcanic in each region this roughness shows three gradations regions a d 140myr with many large volcanic features are very rough the average gravitational admittance is indicative of the degree of isostatic compensation of bathymetric features in each region and can be used to estimate the proportionh of total bathymetric power that was emplaced on relatively old lithosphere and the proportion that formed on young lithosphere at or near a mid ocean ridge crest the highest proportion of bathymetry that formed on old lithosphere occurs in region h fi 0 90 and the lowest proportion occurs in regions g and e fi 0 40 0 60 the power spectrum of the bathymetry and the gravitational admittance allow an estimate of the total bathymetric power pi ipb accounted for by intraplate volcanism intraplate power and the power pr 1 fi pb which is of on ridge origin ridge power at long wavelengths in regions e g the amount of on ridge volcanism exceeds the amount of intraplate volcanism pr pi indicating the presence of several large plateaus and rises which formed at ridge crests this suggests the

seamount topography by least squares inversion of altimetric geoid heights and shipborne profiles of bathymetry and or gravity anomalies summary altimetric measurements of sea surface heights have long been used to locate uncharted marine features newly available data sets geosat gm ers 1 and topex poseidon now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper this method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and or gravity anomalies when available furthermore uncertainties can be computed together with the topography which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases tests are performed using simulated data in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling these errors can be maintained under the 100 m level rms for altimetric data with a measurement noise of 5 cm rms or less which is achieved for geosat ers 1 and topex poseidon altimeters an example of inversion of seasat data is presented in the case of a seamount in french polynesia

three dimensional estimation of elastic thickness under the louisville ridge a three dimensional approach to estimating elastic thickness is presented which uses dense satellite altimetry and sparse ship bathymetry this technique is applied to the louisville ridge system to study the tectonic history of the region the inversion is performed as both a first order approximation and a nonlinear relationship between gravity and topography based on parker s 1973 equation while the higher order effect on the gravity anomaly is nearly zero for most of the region the magnitude is significant over the summits of the ridge nevertheless the inclusion of the nonlinear terms has only a minor influence on the elastic thickness estimate within each region lowering the value by 1 2 km compared with the linear result the incorrect assumption of two dimensionality for circular features exhibits a marked effect on the gravitational anomaly resulting in false sidelobe structure of nearly 20 mgal for large seamounts our elastic thickness estimates are compared with the contradictory values obtained in previous studies by cazenave and dominh 1984 and watts et al 1988 we find an increasing elastic thickness along the chain from southeast to northwest with a discontinuity along the wishbone scarp the jump in elastic thickness values northwest of the scarp appears to be an indication of an age discontinuity caused by an extinct spreading center north of the ridge

a stable isotope study of cave seepage waters an isotope study 18o 2 h of 62 samples of waters from both the interior of the nerja cave malaga southern spain and the exterior sinkholes and springs at the site was carried out rainfall water in the study area was also studied the mean value of seepage waters can be considered as the mean isotopic value of the precipitation waters of the area the origin and aquifers of these different types of waters has also been studied obtaining a clear meteoric origin both for the seepage waters and the waters from the wells and springs but the aquifer of the latter is different showing more negative isotopic values this suggests that they could have mixed with waters from other aquifers which are either deeper or originate at other altitudes

on geoid heights and flexure of the lithosphere at seamounts the sea surface height has now been mapped to an accuracy of better than 1 m by using radar altimeters on board orbiting satellites the major influence on the mean sea surface height is the marine geoid which is an equipotential surface we have carried out preliminary studies of how oceanic volcanoes which rise above the ocean floor as isolated seamounts and oceanic islands or linear ridges contribute to the marine geoid simple one and two dimensional models have been constructed in which it is assumed that the oceanic lithosphere responds to volcanic loads as a thin elastic plate overlying a weak fluid substratum previous studies based on gravity and bathymetry data and uplift subsidence patterns show that the effective flexural rigidity of oceanic lithosphere and the equivalent elastic thickness te increase with the age of the lithosphere at the time of loading the models predict that isolated seamounts emplaced on relatively young lithosphere on or near a mid ocean ridge crest will be associated with relatively low amplitude geoid anomalies about 0 4 0 5 m km of height while seamounts formed on relatively old lithosphere on ridge flanks will be associated with much higher amplitude anomalies 1 4 1 5 m km studies of the seasat altimetric geoid prepared by nasa s jet propulsion laboratory support these model predictions geoid amplitudes are relatively low over the mid pacific mountains and line islands which formed on or near a mid ocean ridge crest and relatively high over the magellan seamounts and wake guyots which formed off ridge direct modeling of the altimetric geoid over these features is complicated however by the wide spacing of the satellite tracks which can exceed 100 km and poor bathymetric control beneath individual satellite tracks in regions where multibeam bathymetric surveys are available models can be constructed that fit the altimetric geoid to better than 1 m studies of geoid anomalies over the emperor seamount chain for example suggest that these seamounts formed on 20 30 ma old oceanic lithosphere while anomalies over the louisville ridge and the hawaiian ridge suggest that these seamounts formed on lithosphere older than about 80 ma this indicates that geoid anomalies over bathymetrie features depend not only on the crustal structure prior to loading and the overall shape and density of the features but also on their tectonic setting we examine the implications of these results to studies which attempt 1 to separate temporal variations of the sea surface due to oceanographic effects 2 to predict seamounts directly from satellite derived gravity and geoid data and 3 to isolate the geoid effects of deep processes occurring beneath the lithosphere such as those due to mantle convection

a record of pleistocene climate from a stalactite nerja cave southern spain a study of stable isotopes n 18 o n 13 c of a uranium series dated aragonitic stalactite from nerja cave malaga southern spain was carried out in order to determine the conditions of deposition in isotopic equilibrium and non equilibrium we obtained a record of climate change from 190 000 to 160 000 years ago a series of carbon n 13 c and oxygen n 18 o isotopes analyses have been carried out in parallel to the stalactite growth axis sampling was done in each growth layer a curve of the secular n 18 o aragonite variations for the stalactite suggests cooler climate conditions

recharge processes on typical karst slopes implied by isotopic and hydrochemical indexes in xiaoyan cave guilin china summary measurements of the hydrogen and oxygen isotopic composition of precipitation and drip stream water at drip site xy5 in xiaoyan cave in guilin city were conducted to investigate the infiltration and vadose flow processes and to characterize precipitation discharge relationship in the overlying karst hillslope area a marked seasonal variability of oxygen and hydrogen isotopes was observed in precipitation ranging from 18 7 to 0 6 for 18 o and 139 to 5 for d respectively during the study period from november 2013 to october 2014 however the narrow range observed for cave drip stream water d of 43 to 22 18 o of 7 3 to 4 3 was attributed to homogenization via mixing of meteoric waters in the unsaturated zone above the cave although drip stream waters plot close to or slightly above the local meteoric water line the weighted average 18 o value of precipitation is depleted than in dripwater which is attributed to evaporation predominantly in the rainy season when cave air circulation is most active the relationship between surface infiltration or leakage and cave discharge is connected by the distinct models of flow through the epikarst zone vadose flow showed high peaking hydraulic responses but buffered rain isotope responses with an attenuate magnitude of 5 0 9 4 for 18 o the sudden hydrochemical proxy variability was related closely to increase of discharge and the flushing out of old water with higher dissolved calcite a threshold of flow generation expressed by precipitation amount must be exceeded to create a peak in discharge as a function of excessing the field capacity of soil and residual capacity of epikarst zone the sources of vadose seepage are soil and epikarst reservoir water with the attenuation of the isotopic fluctuations 4 28 to 5 92 for 18 o and slight hydrological response indicating mixed signals of infiltration water in epikarst storage reservoir the total discharge volume of percolating water is 2084 l derived from piston flow due to the increased hydraulic head in the dry season which provides a quantitative evidence of the potential adaptive capacity of the system to deal with the extreme droughts

seismic evidence for a mantle plume oceanwards of the kamchatka aleutian trench junction summary a non linear iterative p wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km rising across the 600 km discontinuity and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate data from the geophysical survey of russia 1955 1997 were inverted jointly with the catalogues of international seismological centre and usgs national earthquake information centre 1964 1998 the result shows a 300 500 kmwide cylindrical low velocity anomaly yx2 per cent that extends from a depth of greater than 900 km to shallower than 200 km the anomaly is almost vertical at depths up to y400 km and rises obliquely to the north up to y200 km under the ocean floor near the northern end of emperor seamounts above y300 km depth a subsidiary anomaly extends subhorizontally to the nw in fair agreement with the direction of movement of the pacific plate the overlying seafloor is characterized by anomalously high heat flow which may be attributed to the thermal effect of the mantle plume

the magnetic structure of axial seamount juan de fuca ridge axial seamount is a large volcanically active seamount located in the eastern pacific on the central juan de fuca jdf ridge at 46 n 130 w sea surface magnetic anomaly data show that axial lies completely within crust formed during the brunhes normal polarity epoch the edifice however does not produce a simple positive magnetic anomaly related to the excess mass above mean seafloor several pronounced negative magnetic anomalies are associated with the seamount including both a circular shaped low located west of the summit and an elongate low trending nw on the southeast flank of the volcano these two anomalies form part of a nw se magnetic trough which extends across the seamount edifice oblique to the general jdf ridge trend of n20 e a third negative anomaly is observed on the northern flank of the seamount associated with north helium basin a deep elongate basin which indents the northeast flank of the seamount both inversion of sea surface magnetics data and forward modelling of topography constrained by magnetization values of dredged samples show that bathymetric effects can explain the helium basin anomaly but topography alone cannot produce the low magnetization values which extend across the seamount summit magnetization of crustal rocks does not vary spatially over the seamount so that negative anomalies at the summit can be explained by variations in the effective thickness of the magnetic source layer a simple forward model of uniform magnetization shows that the anomaly source layer would have to thin by 50 to less than 700 m thick in order to generate the observed magnetic response a thinned source layer is consistent with the presence of either a substantial magma chamber at depth beneath the summit of axial or a zone of substantial crustal alteration the shape of the anomaly implies the trend of either of these sources must be oriented obliquely to the general ridge trend but parallel to the direction of the absolute plate motion

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

compensation of swells and plateaus in the north pacific no direct evidence for mantle convection at intermediate and long wavelengths the ratio of geoid height to topography is sensitive to the depth and mode of compensation a low geoid topography ratio 8 m km in conjunction with a poor correlation between geoid height and topography is evidence of mantle convection after subtracting a reference geoid from the observed geoid previous studies have found a regular pattern of geoid highs and lows with a characteristic wavelength of 3000 4000 km since these geoid highs and lows were poorly correlated with topography and resulted in very high geoid topography ratios 10 20 m km they were believed to reflect the planform of mantle convection we show that the regular pattern of geoid highs and lows is an artifact caused by truncating the reference geoid at spherical harmonic degree 10 since the geoid spectrum is red the residual geoid is dominated by degree 11 when the harmonics of the reference geoid are rolled off gradually the regular pattern of geoid highs and lows disappears in the northeast pacific the new residual geoid reflects the lithosphere age offsets across the major fracture zones in the northwest pacific the residual geoid corresponds to isostatically compensated swells and plateaus we have calculated the geoid topography ratio for 10 swells and plateaus and have found a range of compensation depths the highest geoidaopography ratio of 5 5 m km occurs on the flanks of the hawaiian swell intermediate ratios occur in four areas including the midway swell these intermediate ratios reflect a linear combination of the decaying thermal swell and the increasing volume of airy compensated seamounts low geoid topography ratios occur over the remaining five areas e g emperor seamounts reflecting the absence of a thermal swell our findings do not support the hypothesis that the planform of mantle convection is evident in the geoid we see only indirect evidence of thermal plumes reheating the lower lithosphere

rainfall and cave water isotopic relationships in two south france sites this article presents isotopic measurements 18o and d of precipitation and cave drip water from two sites in southern france in order to investigate the link between rainfall and seepage water and to characterize regional rainfall isotopic variability these data which are among the longest series in france come from two rainfall stations in south west france le mas 1996 2012 and villars 1998 2012 typically under atlantic influence and from one station in the south east orgnac 2000 2012 under both mediterranean and atlantic influence rainfall isotopic composition is compared to drip water collected under stalactites from the same sites villars cave four drip stations 1999 2012 in the south west and chauvet cave two drip stations 2000 2012 in the south east near orgnac the study of these isotopic data sets allows the following conclusions to be drawn about the rainfall drip water relationships and about rainfall variability 1 the cave drip water isotopic composition does not show any significant changes since the beginning of measurements in order to explain its isotopic signature it is necessary to integrate weighted rainfall 18o of all months during several years which demonstrates that even at shallow depths 10 50 m cave drip water is a mixture of rain water integrated over relatively long periods which give an apparent time residence from several months to up to several years these results have important consequences on the interpretation of proxies like speleothem fluid inclusions and tree ring cellulose isotopic composition which are used for paleoclimatic studies 2 in the villars cave where drip stations at two different depths were studied lower 18o values were observed in the lower galleries which might be due to winter season overflows during infiltration and or to older rain water with a different isotopic composition that reaches the lower galleries after years 3 local precipitation is characterized by local meteoric water lines lmwl with 18o d slopes close to 7 in both areas and correlations between air temperature and precipitation 18o are low at both monthly and annual scales even with temperature weighted by the amount of precipitation 4 the mesoscale climate model remoiso equipped with a water isotope module allows the direct comparison of modeled and observed long term water isotope records the model slightly overestimates rainfall 18o at the respective sampling stations however it simulates very well not only the seasonal rainfall isotopic signal but also some intra seasonal patterns such as a typical double peak 18o pattern in winter time

new global seamount census from altimetry derived gravity data summary recent revisions to the satellite derived vertical gravity gradient vgg data reveal more detail of the ocean bottom and have allowed us to develop a non linear inversion method to detect seamounts in vgg data we approximate vgg anomalies over seamounts as sums of individual partially overlapping elliptical polynomial functions which allows us to form a non linear inverse problem by fitting the polynomial model to the observations model parameters for a potential seamount include geographical location peak vgg amplitude major and minor axes of the elliptical base and the azimuth of the major axis the non linear inversion is very sensitive to the initial values for the location and amplitude hence they are constrained by the centre and amplitude of the uppermost contours obtained with a 1 eotvos contour interval with these initial conditions from contouring we execute a step wise and fully automated inversion and obtain optimal model estimates for potential seamounts these are statistically evaluated for significance using the akaike information criterion and f tests a logarithmic barrier technique is applied to ensure positivity of all seamount amplitudes after automatic and manual inspections of the model parameters we estimate actual heights and basal ellipses of the inspected potential seamounts directly from the predicted bathymetry grid in this study we find globally 24 643 potential seamounts h 0 1 km that are located away from continental margins 8458 potential seamounts are taller than 1 km although our global estimate is significantly lower than predictions from previous studies a first order reconciliation of the size frequency statistics obtained from those studies reveals that the previous counts are systematically overestimated because of the ambiguity of gravity signals due to small seamounts of h 1 km and the overlap with abyssal hills we estimate the global seamount census to lie in the 40 000 55 000 range the seamount data from this study are accessible from http www soest hawaii edu pt smts

seasat derived gravity over the musicians seamounts the two dimensional gravity field over the musicians seamount province in the pacific ocean has been derived from seasat altimetry geoid maps were produced by fitting a minimum curvature surface to the sea surface height measurements as a check on the quality of this interpolation method we also gridded the data using weighted grid point averages fourier transforms of both the geoid and geoid gradient were used to determine the gravity field we have compared gravity maps produced these different ways in order to identify the problems involved in pushing seasat data to the limits of its spatial resolution and accuracy our minimum curvature interpolation scheme was determined to be the more accurate and cost effective mapping method while gravity obtained by transforming the geoid produced more reliable gravity maps the bathymetry of this area was used to predict the gravity field by filtering the bathymetry under the assumption that it is regionally compensated by a thin elastic plate gravity fields predicted for a variety of effective elastic thicknesses were compared to the seasat derived gravity particularly in areas with good track coverage the derived gravity tends to favor a thin plate with an effective elastic thickness of 5 km though the east west ridges in the south display a smaller signal more consistent with airy compensation this variation may be indicative of early fracturing of the lithosphere in the south or it may be a manifestation of the age difference and early thermal structure across the murray fracture zone which separates the seamount province into northern and southern sections neighboring seamounts with different flexural signatures particularly in the south may indicate that volcanism occurred in the same location over an extended period of time

lithospheric response to volcanic loading in the southern cook islands abstract the response of the ocean lithosphere to volcanic island loading has been investigated for the southern cook islands of rarotonga mangaia and the aitutaki mauke group using 1 estimates of the change with distance from the load of uplift of islands located on the flexure created arch 2 geoid height perturbations as observed with the geos 3 and seasat radar altimeters and 3 bathymetric evidence for the moat and arch about the island loads the effective flexural rigidity for rarotonga is found to be higher than for the older and nearby islands of mangaia and aitutaki this together with an earlier result for tahiti 1 suggests that stress relaxation of the lithosphere has occurred and that this layer behaves as a viscoelastic material with an effective viscosity of about 5 10 10 25 poise the observations for the flexural rigidity do not indicate any dependence on the age of the lithosphere at the time the loading occurred this suggests that there are no significant differences in lithospheric properties for plates in the age range of 6 7 10 7 years altimeter passes to the east of mauke indicate that there may be an uncharted submarine extension of the aitutaki mauke chain

the transfer of seasonal isotopic variability between precipitation and drip water at eight caves in the monsoon regions of china abstract this study presents new stable isotope data for precipitation 18op and drip water 18od from eight cave sites in the monsoon regions of china mrc with monthly to bi monthly sampling intervals from may 2011 to april 2014 to investigate the regional scale climate forcing on 18op and how the isotopic signals are transmitted to various drip sites the monthly 18op values show negative correlation with surface air temperature at all the cave sites except shihua cave which is opposite to that expected from the temperature effect in addition although the monthly 18op values are negatively correlated with precipitation at all the cave sites only three sites are significant at the 95 level these indicate that due to the various vapor sources a large portion of variability in 18op in the mrc cannot be explained simply by either temperature or precipitation alone all the thirty four drip sites are classified into three types based on the 18od variability about 82 of them are static drips with little discernable variation in 18od through the whole study period but the drip rates of these drips are not necessary constant their discharge modes are site specific and the oxygen isotopic composition of the stalagmites growing from them may record the average of multi year climatic signals which are modulated by the seasonality of recharge and potential effects of evaporation and in some cases infiltration from large rainfall events about 12 of the thirty four drip sites are seasonal drips although the amplitude of 18od is narrower than that of 18op the monthly response of 18od to coeval precipitation is not completely damped and some of them follow the seasonal trend of 18op very well these drips may be mainly recharged by present day precipitation mixing with some stored water thus the stalagmites growing under them may record portions of the seasonal climatic signals embedded in 18op about 6 of the thirty four drip sites are medium variability drips with constant and relatively low 18od values in the wet season but with variable and relatively high 18od values in the dry season reflecting flow switching in the karst or evaporation inside the cave

thermal bending stresses and vertical motion on oceanic transform fault the conductive cooling of new oceanic lithosphere causes both horizontal and vertical contraction along transform faults and fracture zones the contraction of material on each side of the fault leads to differential subsidence since juxtaposed seafloor of different ages subside at different rates horizontal contraction causes accumulation of thermal bending stresses which are partly relieved by flexural bending along the transform the relative vertical motion implied by plate flexure at the transform is more important than that predicted by differential subsidence when combined this net vertical slip rate may exceed 5 of the full spreading rate for slow spreading ridges the high vertical to horizontal slip ratios implied may explain anomalously high subsidence rates for seafloor in the proximity of ridge transform intersections departure from horizontal strike slip inferred from transform fault focal mechanisms may possibly be used to put additional constraints on the isotherm controlling the transition from brittle to ductile failure in the oceanic lithosphere

crustal structure of the madeira tore rise eastern north atlantic results of a dobs wide angle and normal incidence seismic experiment in the josephine seamount region summary during november december 1988 an extensive geophysical data set was collected over the josephine seamount which is located at the northeasterly end of the madeira tore rise in the eastern north atlantic the josephine seamount lies at the intersection of the madeira tore rise and azores gibraltar fracture zone the latter representing the africa eurasia plate boundary in this part of the eastern north atlantic from this data set a 275 km long explosive refraction line has been modelled together with wide angle airgun profiles seismic reflection and gravity data the velocity depth model shows that the crust either side of the seamount is typically oceanic in character however beneath the seamount there exists a region of anomalously high velocity and crustal thickening to a depth of about 17 18 km gravity modelling also suggests that the josephine seamount is compensated by a crustal root and that the josephine seamount madeira tore rise system is in local isostatic equilibrium calculations of the flexural rigidity and effective elastic thickness of the lithosphere in this region suggest that the madeira tore rise formed contemporaneously with the lithosphere on which it lies this age of crustal loading is consistent with the proposal that the madeira tore rise is an aseismic ridge which formed at or near the mid atlantic ridge

the use of shallow dripwater as an isotopic marker of seepage in karst areas a comparison between western sicily italy and the harz mountains germany abstract the isotopic signature of slow flowing dripwater collected in caves located in western sicily italy was determined for evaluating its possible use as an isotopic tracer of the local groundwater recharge these spot measures were compared with a longer series of local rain and spring compositions and with other samples taken under different hydrogeological conditions in caves of the harz mountains northern germany the slow flowing dripwater from sicily showed 18 o d ratios similar to those of local rain and groundwater demonstrating that these three are all parent waters a parallel similarity was found in the vertical isotopic gradient 18 o of the three groups of water accounting for their common meteoric origin in the colder harz region dripwater spring water and rain have the same 18 o d ratio but fast flowing dripwater infiltrating through open cracks is significantly enriched in lighter isotopes and representative of short residence time percolation these results lead to the conclusion that dripwater even if collected as spot samples can be considered as a good isotopic marker of the average local groundwater recharge on the condition that only slow diffused drips due to seepages are sampled

seismic velocity structure and deformation due to the collision of the louisville ridge with the tonga kermadec trench new marine geophysical data recorded across the tonga kermadec subduction zone are used to image deformation and seismic velocity structures of the forearc and pacific plate where the louisville ridge seamount chain subducts due to the obliquity of the louisville ridge to the trench and the fast 128 mm yr 1 south southwest migration of the ridge trench collision zone post current and pre seamount subduction deformation can be investigated between 23 s and 28 s we combine our interpretations from the collision zone with previous results from the post and pre collision zones to define the along arc variation in deformation due to seamount subduction in the pre collision zone the lower trench slope is steep the mid trench slope has 3 km thick stratified sediments and gravitational collapse of the trench slope is associated with basal erosion by subducting horst and graben structures on the pacific plate this collapse indicates that tectonic erosion is a normal process affecting this generally sediment starved subduction system in the collision zone the trench slope decreases compared to the north and south and rotation of the forearc is manifest as a steep plate boundary fault and arcward dipping sediment in a 12 km wide 2 km deep mid slope basin a 3 km step increase in depth of the middle and lower crustal isovelocity contours below the basin indicates the extent of crustal deformation on the trench slope at the leading edge of the overriding plate upper crustal p wave velocities are 4 0 km s 1 and indicate the trench fill material is of seamount origin osbourn seamount on the outer rise has extensional faulting on its western slope and mass wasting of the seamount provides the low vp material to the trench in the post collision zone to the north the trench slope is smooth the trench is deep and the crystalline crust thins at the leading edge of the overriding plate where vp is low 5 5 km s 1 these characteristics are attributed to a greater degree of extensional collapse of the forearc in the wake of seamount subduction the northern end of a seismic gap lies at the transition from the smooth lower trench slope of the post collision zone to the block faulted and elevated lower trench slope in the collision zone suggesting a causative link between the collapse of the forearc and seismogenesis along the forearc the transient effects of a north to south progression of ridge subduction are preserved in the geomorphology whereas longer term effects may be recorded in the 80 km offset in trench strike at the collision zone itself

the determination of geoid undulations and gravity anomalies from seasat altimeter data the global seasat altimeter data set has been edited and adjusted using a crossing arc procedure fixing one long arc to provide control in doing this a set of 168 master arcs were formed from repeat and near repeat arcs the adjustment carried out by d rowlands was done in a global net and four regional areas the average crossover discrepancy before the adjustment was 1 5 m while after the adjustment solving for a bias and trend it was 28 cm the examination of the crossover discrepancies by area indicated larger than normal discrepancies in certain areas such as the hudson bay the mediterranean and the north and baltic seas some of these discrepancies are caused by invalid tide values applied to the altimeter data in these areas the adjusted seasat sea surface heights were used to predict point values at 1 1 intersections in 10 different geographic regions for comparison with corresponding geos 3 values a mean difference geos 3 minus seasat of 1 3 0 67 m was found the mean difference being caused by different ellipsoid parameters the adjusted data were also used to determine mean surface heights and gravity anomalies in 37 9051 1 and 1178 5 equal area blocks with some of these values being on land these estimations were done using least squares collocation using covariances functions scaled to each 5 region the average predicted standard deviation of the 1 1 anomalies was 5 1 mgal and 2 7 mgal for the 5 blocks seasat values were compared to the geos 3 values finding a difference of 7 8 mgal and 0 87 m for the 1 1 data and 2 2 mgal and 0 76 m for the 5 data comparisons with terrestrial data showed no significant difference between the geos 3 seasat implied anomalies although a number of significant discrepancies have been resolved with the seasat data

a paleoclimate record of the last 17 600 years in stalagmites from the b7 cave sauerland germany abstract petrographical and geochemical parameters of stalagmites from the b7 cave in iserlohn letmathe northern rhenish massif nw germany record late and postglacial climate changes temperature and or precipitation fabrics and microfacies of the stalagmite profiles lead to a differentiation of four hierarchies of rhythms clastic layers in the stalagmites are caused by flooding events and are time markers twenty four tims th u age dates provide a time calibration of stalagmite growth phases one stalagmite reveals an early growth period between 17 6 and 16 7 ka bp between 9 6 and 5 5 ka bp atlantic episode of the holocene the growth rate of the stalagmites was higher than before and after this time with dominant light porous microfacial laminae and high 18 o and 13 c values representing partly kinetic fractionation effects this part of the holocene is interpreted as a mainly warm episode with frequent interruptions of dripping within the past 4 ka the profiles with predominant dark compact facies reveal low isotopic values which may be interpreted as a temperature proxy record the stalagmite records resemble records from an irish stalagmite correlation with the 14 c record from european tree rings suggests that colder periods in the north atlantic were accompanied by drier winters in central europe

potential influence of temperature changes in the southern hemisphere on the evolution of the asian summer monsoon during the last glacial period abstract a precisely 230th dated 18o record of a stalagmite from yangkou cave chongqing southwest china is proposed to reconstruct the evolution of the east asian summer monsoon easm during the last glacial period lgp from 37 8 to 48 7 ka bp the 18o record reveals dansgaard oeschger d o 8 12 and heinrich h4 h5 climatic events the inferred d o events at easm territory do not exhibit the asymmetrical feature of rapid warming slow cooling recorded in greenland ice cores the yangkou record is consistent with other records of hulu and xiaobailong caves in the chinese monsoon realm changes in the period from d o 12 to d o 9 and h4 events in the stalagmites is similar to the temperature changes recorded in the european project for ice coring in antarctica epica dronning maud land ice core edml this similarity implies that southern hemisphere thermal condition could affect the easm the location of the intertropical convergence zone itcz and also the hadley circulation changes in d o 12 and the end of the h5 in chinese records are different from those in socotra island located in the indian summer monsoon ism region which are concurrent with ngrip records during the h5 period in the southern hemisphere temperature increased gradually to a maximum and the hadley circulation intensity in the southern hemisphere decreased simultaneously the southeast trade winds in the southern hemisphere gradually weakened resulting in the weakening of the ism and eventually the weakest ism at 47 2 ka bp our records support that the evolution of the summer monsoon in the low latitude asian zones was not only affected by summer insolation and climatic changes in the high latitudes of the northern hemisphere but also by temperature changes in the southern hemisphere

an isotopic calibration study of precipitation cave dripwater and climate in west central florida a calibration study of oxygen and hydrogen isotopic composition from precipitation and cave dripwater was conducted in west central florida at legend cave during 2007 2008 this study was performed to better understand how modern precipitation patterns can be discerned through examination of cave dripwater and speleothem calcite for paleoclimate reconstruction the amount effect was shown to be a dominant control on the oxygen isotopic composition of precipitation for the study area a meteoric water line with a slope of 6 7 suggests evaporative effects occur either during precipitation or subsequent hydrological processes however 18o values of cave dripwater averaged near the mean annual amount weighted average of precipitation suggesting that the isotopic composition of dripwater tracks the long term average of rainfall an observed weak seasonal influence occurred in the d excess values with summer precipitation being more enriched due to increased evaporative effects comparison of precipitation 18o values to synoptic weather data shows the dominant amount effect influence occurs due to strong convective storms producing highly 18o depleted rainfall at greater amounts during the year constant 18o values of the dripwater indicate that paleoclimate reconstructions using speleothems from this area would record changes in annual to interannual shifts in precipitation amount above the cave copyright 2011 john wiley sons ltd

non linear altimetric geoid inversion for lithospheric elastic thickness and crustal density summary the inversion of high resolution geoid anomaly maps derived from satellite altimetry should allow one to retrieve the lithospheric elastic thickness t e and crustal density r c indeed the bending of a lithospheric plate under the load of a seamount depends on both parameters and the associated geoid anomaly is correspondingly dependent on the two parameters the diverence between the observed and modelled geoid signatures is estimated by a cost function j of the two variables t e and r c we show that this cost function forms a valley structure along which many local minima appear the global minimum of j corresponding to the true values of the lithospheric parameters classical gradient methods fail to find this global minimum because they converge to the first local minimum of j encountered so that the final parameter estimate strongly depends on the starting pair of values t e r c we here implement a non linear optimization algorithm to recover these two parameters from altimetry data we demonstrate from the inversion of synthetic data that this approach ensures robust estimates of t e and r c by activating two search phases alternately a gradient phase to find a local minimum of j and a tunnelling phase through high values of the cost function the accuracy of the solution can be improved by a search in an iteratively restricted parameter subspace applying our non linear inversion to the great meteor seamount geoid data we further show that the inverse problem is intrinsically illposed as a consequence minute geoid or gravity data errors can induce large changes in any recovery of lithospheric elastic thickness and crustal density

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

topography and geoid undulations caused by small scale convection beneath continental lithosphere of variable elastic thickness summary the effect of subcontinental upper mantle convection on topography gravity and geoid undulation is studied with special regard to the effective elastic thickness of the continental lithosphere hel we designed a numerical model of the upper mantle lithosphere system consisting of a constant viscosity fluid overlayed by a partly elastic plate the boundary tractions stresses at the top of the convecting mantle model were applied to the lithosphere model for which we used the thin plate approximation the total thickness of the lithosphere was kept constant to 150 km while the elastic thickness was varied between 0 and 150 km the aspect ratio of the convecting mantle was varied between 0 7 and 3 and the rayleigh number between 104 and 106 our calculations demonstrate the effect of a thick elastic lithosphere on the surface observables peak to peak averaged amplitude of topography geoid undulation and gravity are strongly reduced and their spectra are low pass filtered for an aspect ratio less than 1 and a very thick elastic lithosphere topography tends to zero and while geoid undulation and gravity may even become negative above the up welling plume the spectral relation of geoid or gravity to topography admittance is nearly unaffected for hie 70km for aie 70km admittance values for all wavelengths generally decrease with increasing elastic thickness of the plate and may become negative geoid admittance for the basic mode increases with larger aspect ratio while gravity admittance for hie 100 km slightly decreases associating higher rayleigh numbers of the convecting fluid with lower viscosity an increase in rayleigh number leads to considerable decrease of the surface observables however admittance values are only slightly affected and decrease approximately linearly with increasing rayleigh number comparison of our results with observations of the topography spectrum and the free air gravity admittance for north america suggests that large aspect ratio cells beneath continents are unlikely however convection cells of aspect ratio 1 or less underlying an elastic lithosphere of at least 100 km thickness is in agreement with data the rayleigh number should be as high as 106

the seasat altimeter mean sea surface model gridding techniques are used to combine an 18 day set of seasat altimeter data and two precisely computed seasat ephemerides in order to arrive at global contour maps of the mean sea surface topography the altimeter data have an rms agreement of 111 cm with the ss3 mean sea surface computed by means of the pgs s3 ephemerides and of 70 cm with the ss4 mean surface derived from the pgs s4 ephemerides while comparisons with the gem 10b 1 x 1 deg gravimetric geoid have yielded rms differences of 2 8 m those with a global mean sea surface derived from geos 3 altimeter data show rms differences of 1 3 m and 1 1 m for the cases of the ss3 and ss4 surfaces respectively an ss4 mean sea surface topograph is featured among the study findings presented further improvements in the representation of mean sea surface topography are expected with the development of more accurate gravity models for orbit computation

use of total organic carbon toc as tracer of diffuse infiltration in a dolomitic karstic system the nerja cave andalusia southern spain 1 recent studies in several karstic systems in france have highlighted that total organic carbon toc was a relevant parameter in order to characterise the behaviour of aquifers to differentiate the water types that participate in karstic flow fast infiltration unsaturated zone saturated zone and to evaluate their vulnerability this study on toc dynamics at the experimental site of the nerja cave has been performed to test the potential of this tracer in a particular climatic mediterranean climate lithologic dolomitic marbles and hydrodynamic diffuse flow behaviour context toc evolution compared to those of classical tracers used in hydrogeology permits the understanding of the hydrodynamical behaviour of the unsaturated zone of this dolomitic aquifer whose response to precipitation is slower than that commonly obtained in karstic aquifers of calcareous nature

paleomagnetism of the joban seamount chain its origin and tectonic implications for the pacific plate the paleomagnetism of 10 seamounts from the joban seamount chain northwestern pacific were studied using a method that calculates mean magnetization parameters by an inversion of magnetic anomaly and edifice bathymetry of the 10 seamounts eight gave results consistent with other paleomagnetic studies of pacific seamounts joban seamounts appear to have formed at two different mean paleolatitudes contrary to what would be expected for a single hotspot origin furthermore six of the consistent poles plot along the 129 to 82 ma portion of the pacific plate apparent polar wander path apwp implying the seamounts formed mainly during the mid to late cretaceous two other poles from iwaki and hitachi seamounts are located northwest of the older end of the established pacific apwp possibly indicating early cretaceous ages because iwaki and hitachi seamounts are located in the middle of the chain age does not progress along the chain arguing against a single hotspot origin perhaps the chain formed by recurrent volcanism along a line of weakness or by another mechanism iwaki and hitachi seamounts display smaller northward drift compared to the others consistent with the pacific plate drifting southward from late jurassic or early cretaceous to mid cretaceous time

assessment of sidoarjo mud flow embankment stability using very low frequency electromagnetic method the earth on lusi embankment has a high failure potential due to several factors such as seepage leakage vertical and horizontal deformation cracking and fault discontinuity overtopping mud slide and swelling very low frequency electromagnetic method was carried out at lusi embankment in order to delineate fracture and potential pathway of seepage occurring through the subsurface structure the embankment body to reach these objectives several methods were carried out in the selected area such as direct current resistivity total station and rayleigh wave dispersion to provide information on the mechanical properties lusi embankment subsurface this study indicates that seepage and fracture through the lusi embankment is presented by a set of lines which are possibly caused by deformation in the lusi area furthermore based on the fracture and seepage positions and mud or fluid flow direction the unstable lusi embankment is determined as located around the northwest and northern parts of the area

fossil dripwater in stalagmites reveals holocene temperature and rainfall variation in amazonia abstract most proxy records used for reconstruction of holocene climate of amazonia are unable to quantitatively distinguish between the effect of temperature and rainfall amounts we present a new isotope technique applied to a 13 500 yr stalagmite archive from peruvian amazonia by analysing the coupled isotope composition of fossil dripwater trapped in stalagmite fluid inclusions and that of the calcite hosting the fluid inclusions we were able to calculate independent paleotemperatures and rainfall amounts this stalagmite record shows that holocene climate variation was controlled by orbitally forced southward migration of the inter tropical convergence zone while temperature remained constant isotope variation of rainwater reflected in fluid inclusion water 18o composition suggests a 15 30 increase in convective rainfall through the holocene a comparison of the low land peruvian fluid inclusion record with the high andean huascaran ice core record shows a constant 12 offset of 18o curves for the holocene suggesting that andean vertical temperature gradients lapse rates did not vary much over the last 9000 years during the younger dryas interval however the offset of 18o values was much higher than in the holocene this may be attributed to a relative drop in air temperatures in the highlands higher lapse rate caused by long distance teleconnections to climate perturbations in the north atlantic in a wider perspective fluid inclusion isotope analysis drastically improves paleotemperature reconstructions based on speleothem calcite 18o data because it provides the 18o value of drip water through time which is usually the most important unknown in paleotemperature equations

water isotopic variability in mallorca a path to understanding past changes in hydroclimate this paper reports the first results on 18o and 2h analysis of precipitations cave drip waters and groundwaters from sites in mallorca balearic islands western mediterranean a key region for paleoclimate studies understanding the isotopic variability and the sources of moisture in modern climate systems is required to develop speleothem isotope based climate reconstructions the stable isotopic composition of precipitation was analyzed in samples collected between march 2012 and march 2013 the values are in the range reported by gnip palma station based on these results the local meteoric water line 2h 7 9 0 3 18o 10 8 2 5 was derived with slightly lower slope than gmwl the results help tracking two main sources of air masses affecting the study sites rain events with the highest 18o values 5 originate over the mediterranean sea whereas the more depleted samples 50 m limestone cap arta exhibit more negative values a well homogenized aquifer supplied by rainwaters of both origins is clearly indicated by groundwater 18o values which show to be within 2 4 of the unweighted arithmetic mean of 7 4 although limited the isotopic data presented here constitute the baseline for future studies using speleothem 18o records for western mediterranean paleoclimate reconstructions

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

genetic algorithms for geophysical parameter inversion from altimeter data summary a new approach for inverting several geophysical parameters at the same time from altimeter and marine data by implementing genetic algorithms gas is presented these original techniques of optimization based on non deterministic rules simulate the evolution of a population of candidate solutions for a given objective function to minimize they offer a robust and efficient alternative to gradient techniques for non linear parameter inversion here genetic algorithms are used for solving a discrete gravity problem of data associated with an undersea relief to retrieve seven parameters at the same time the elastic thickness the mean ocean depth the seamount location longitude latitude its amplitude radius and density from its observed gravity geoid signature this approach was also successfully used to adjust lithosphere parameters in the real case of the rarotonga seamount 21 2us 159 8uw in the southern cook islands region where ga simulations provided robust estimates of these seven parameters the ga found very realistic values for the mean ocean depth and the seamount amplitude and the precise geographical location of rarotonga island moreover the values of elastic thickness y14 15 km and seamount density y2850 2870 kg m x3 estimated by the ga are consistent with the ones proposed in earlier studies

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

interpretations of geoid anomalies around the iceland hotspot summary geoid height anomalies around the iceland hotspot in an area extending between 50 w to 14 e and 45 n to 72 n have been investigated to search for evidence of an upper mantle thermal anomaly after removing wavelengths longer than 3800 km the effect of the cooling lithosphere was eliminated by low pass filtering of age data and applying the boundary model the effects of the various platforms and swells in the north atlantic were removed by an airy model since the geoid to topography ratio is lower than 1 5 m km for all areas of elevated topography independent of their origin the residual geoid shows a large positive anomaly with a steep constant slope towards a location north west of iceland beneath greenland the amplitude of the anomaly can be estimated to at least 8m the geoid to topography ratio reaches a value of 7mkm which is in good agreement with a plume related anomaly

geoid heights over the louisville ridge south pacific geoid heights over the louisville ridge seamount chain deduced from the seasat satellite altimeter data have been analyzed and interpreted two uncharted seamounts belonging to the chain have been detected the elastic thickness of the oceanic lithosphere has been determined along the chain this was done rigorously using the three dimensional geoid and bathymetry maps and was also computed approximately using spectral methods on geoid and bathymetry profiles a slightly increasing elastic thickness from the southeast to the northwest in the range 15 5 22 5 km has been estimated

tectonic evolution of the north pacific during the cretaceous quiet period the cretaceous quiet period ended with a significant reorganization of the plate tectonics of the north pacific the farallon plate broke into three primary pieces 1 the kula plate 2 a large fragment transferred to the pacific plate and 3 the continued farallon plate the time of the rearrangement is constrained to just before magnetic anomaly 34 by its presence contrasts in tectonic spreading fabric tsf the emperor trough and the chinook trough our model is based on 1 a complete reevaluation of primary bathymetric and magnetic data 2 the distribution of major troughs emperor chinook hokkaido and krusenstern 3 mapping and analysis of tsf orientation and amplitude on quiet zone crust and 4 available deep sea drilling project drill hole data east west trending magnetic reversal lineations and tsf south of the aleutian trench are bounded on the west by the buldir fracture zone at 175 e the major troughs mark the abandonment and initiation of spreading in the reorganization their absence elsewhere precludes other long distance boundary relocations emperor trough is the abandoned pacific farallon spreading center rift initiation and early slow spreading have created the high amplitude topography of the chinook trough we believe that the hokkaido trough is the initiation site of a failed oceanic rift the incorporation of large amounts of farallon plate into the pacific plate obviates the need for the very rapid pacific farallon spreading rates of previous models and significantly alters the interpretation of mid pacific geology

thermomechanical evolution of oceanic fracture zones a fracture zone fz model is constructed from existing models of the thermal and mechanical evolution of the oceanic lithosphere as the lithosphere cools by conduction thermal and mechanical boundary layers develop and increase in thickness as age 1 2 surface expressions of this development such as topography and deflection of the vertical i e gravity field are most apparent along major fz s because of the sharp age contrast a simple model including the effects of lateral heat transport but with no elastic layer predicts that variations in seafloor depth and deflection of the vertical will become increasingly smooth and ultimately disappear as the fz ages observations however show that both the fz topography and the deflection of the vertical remain sharp as the fz evolves these two observations as well as the observed asymmetry in deflection of the vertical profiles across the udintsev romanche and mendocino fz s are explained by including a continuous elastic layer in the model the asymmetry in deflection of the vertical is a consequence of elastic thickness variations across the fz modeling also shows that the evolution of the fz topography is extremely sensitive to the initial thermal structure near the ridge transform intersection model geoid steps and their development with age are used to access techniques for measuring geoid offsets across fz s reasonable step estimation techniques will underestimate the overall step amplitude by up to 50 this implies that abnormally thin thermal boundary layers derived from studies of geoid height versus age are not required by the data

jasper seamount structure seafloor seismic refraction tomography the velocity structure of jasper seamount was modeled using one and three dimensional inversions of p wave travel times the results represent the first detailed seismic images of a submerged intraplate volcano two seismic refraction experiments were completed on jasper seamount incorporating ocean bottom seismometers and navigated seafloor shots the p wave travel times were first used to compute a one dimensional velocity profile which served as a starting model for a three dimensional tomographic inversion the seamount p velocities are significantly slower than those observed in typical oceanic crust at equivalent subbasement depths this suggests that jasper seamount is constructed predominantly of extrusive lavas with high average porosity the velocity models confirm morphological predictions jasper seamount is a shield volcano with rift zone development high seismic velocities were detected beneath the large radial ridges while low velocities characterize the shallow summit and flanks comparisons between p velocity models of jasper seamount and the island of hawaii reveal that these two shield volcanoes are not structurally proportional jasper seamount is far smaller than hawaii yet both volcanoes exhibit an outer extrusive layer of similar thickness this suggests that seamount size influences the intrusive extrusive proportions density equilibrium between melt and country rock may explain this behavior

the effective elastic lithosphere under the cook austral and society islands abstract we have determined the elastic thicknesste of the oceanic lithosphere along two volcanic chains of the south central pacific cook austral and society islands we used a three dimensional spatial method to model the lithospheric flexure assuming a continuous elastic plate the model was constrained by geoid height data from the seasat satellite along the cook austral chain the elastic thickness increases westward from 2 4 km at mcdonald hot spot to 14 km at rarotonga at mcdonald seamount however the data are better explained by a local compensation model the observed trend shows an increase ofte with age of plate at loading time however the elastic layer under the cook austral appears systematically thinner by several kilometers than expected for normal seafloor suggesting that substantial thermal thinning has taken place in this region considering the apparent thermal age of the plate instead of crustal age improves noticeably the results along the society chainte varies from 20 km under tahiti to 13 km under maupiti which is located 500 km westward when plotting together the society and cook australte results versus age of load we notice that within the first five million years after loading te decreases significantly while tending rapidly to an equilibrium value this may be interpreted as the effect of initial stress relaxation which occurs just after loading inside the lower lithosphere and suggests that the presently measured elastic thickness under the very young tahiti load 0 8 ma is not yet the equilibrium thickness

precise location of unsurveyed seamounts in the austral archipelago area using seasat data summary seasat altimetric geoid data are used to detect uncharted seamounts in the austral archipelago area the various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location these parameters are the shape of the seamount its density the crustal model the effective elastic thickness of the lithosphere and the distance between the seamount and sub satellite tracks respectively the results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks it is possible to locate it with good confidence and to give an estimation of its height if the correct elastic thickness is assumed the precision on the location is order 15 km ten previously unsurveyed seamounts have been located in the austral archipelago it appears that they are emplaced along two well defined azimuths n 1 10 e and n 150 e and that two parallel distinct volcanic chains form the austral archipelago

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

flexural isostasy constraints from gravity and topography power spectra we have used spherical harmonic coefficients that describe earth s gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure power spectra reveal that the gravity effect of topography and its flexural compensation contributes significantly to the observed free air gravity anomaly spectra for spherical harmonic degree 33 400 and lower n 33 degrees but topography appears either uncompensated or fully compensated at these degrees irrespective of the actual te all isostatic models underpredict the spectra at 2 n 12 and so we interpret the low order earth s gravity field as caused at least in part by non isostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in earth s mantle

on the interpretation of frequency response functions for oceanic gravity and bathymetry summary oceanic bathymetry and gravity comprise a geophysical system which is often characterized by a linear frequency response function or admittance the actual behaviour of this system differs in important respects however from that of an ideal linear model three sources of such differences are considered in this study the presence of noise in the data non linearity due to finite amplitude and intrinsic two dimensionality of the data fields the high positive correlation between admittance amplitude and coherence estimates obtained in a number of studies indicates that the noise is not normally distributed with zero mean as generally assumed non linear modification of the admittance results from the finite amplitude of the bathymetry and the non linear elasticity of the lithosphere the former effect increases with bathymetric roughness and is most pronounced for shortwavelength uncompensated bathymetry the latter is significant only if the deflection of the lithosphere is comparable to its elastic thickness as for certain large seamounts in the pacific ocean which were emplaced on lithosphere near ridge crests the most severe problem arises for features which are markedly two dimensional features typical of observed oceanic seamounts are characterized by admittances along tracks which differ substantially from those appropriate to one dimensional bathymetry this difference occurs primarily in the long wavelength portion of the admittance rendering problematic the comparison of observed admittances or gravity anomalies with theoretical expressions

observations of flexure and the rheology of oceanic lithosphere the principal evidence for the long term i e 1 myr mechanical behaviour of the oceanic lithosphere has come from studies of how it deforms in response to large loads such as volcanoes and sediments a model widely used to explain the deformation is an elastic plate in which flexural rigidity depends on the thermal age of the lithosphere at the time of loading an elastic model however is time invariant and does not take into account temporal changes that may occur in the flexural rigidity as a consequence of loading there is evidence for example that the flexural rigidity of the oceanic lithosphere also depends on load age being large at short times and small at long times thus competing effects may exist between thermal cooling which strengthens the lithosphere and some form of load induced stress relaxation which weakens it in order to investigate the relative roles of these processes we have developed a multilayered viscoelastic model which is based on the results of experimental rock mechanics that creep in the lithosphere is a thermally activated process and on a thermal structure that is given by the plate cooling model by comparing the predictions of the model with a new compilation of flexural rigidity estimates we have found that if the upper mantle viscosity is 1020 pa s the activation energy that best describes the long term mechanical behaviour of the oceanic lithosphere is 120 kj mol 1 this parameter pair explains the dependence of flexural rigidity on both plate and load age it also helps account for the subsidence and uplift history of oceanic islands and the stratigraphic patterns that develop in the flexural moats that flank them at atolls a multilayered viscoelastic model explains the rapid subsidence that follows shield building and does not require that the age of the lithosphere that supports a volcano is thermally re set to a younger value our studies suggest that while the oceanic lithosphere has viscoelastic properties the viscosity of its upper layers is so much higher than that of its lower layers that in effect it behaves as a thin elastic plate on long timescales there will therefore be a certain permanence to the observations of oceanic flexure such that they may be used with some confidence to evaluate the tectonic setting of individual features of the seafloor and in some cases their age

a high resolution fluid inclusion δ18o record from a stalagmite in sw france modern calibration and comparison with multiple proxies abstract the 18 o of speleothem fluid inclusions can provide information about local climate and the atmospheric circulation if the fate of oxygen isotopes from precipitation to the stalagmite is well understood at villars cave sw france the present day relationship between the 18 o of precipitation and the 18 o of cave drip water has been determined by previous monitoring studies in this article we examine the link between drip water and fluid inclusions in speleothems from the same cave and investigate whether the fossil water in the stalagmites provides a record of the isotopic composition of precipitation replicated fluid inclusion isotope measurements d and 18 o from two modern calcite samples which had precipitated under the monitored stalactites are in agreement with the corresponding contemporaneous drip waters the drip water in turn represents average pluri annual precipitation this gives strong evidence that the isotopic composition of the infiltrating water is preserved in the pores of speleothem calcite thus providing a record of average precipitation 18 o at the site furthermore we measured isotope ratios in fluid inclusions in the stalagmite vil stm1 a 2300 year old sample with a high growth rate up to 0 6 mm yr 1 and a high water content which allows a high resolution reconstruction of the drip water isotopic composition covering the last two millennia the stalagmite is well dated by 13 u th ages and the counting of annual growth layers the fluid inclusion 18 o varies by 2 with high 18 o values in medieval times and low values during the little ice age indicating a temperature influence on precipitation 18 o however temperature change alone cannot account for the full range of variability observed other proxies measured in the same stalagmite indicate that the cave environment has undergone substantial changes during this period stable isotopes and trace element concentrations in calcite show large variations with amplitudes similar to those found in other villars speleothems during large climatic shifts such as dansgaard oeschger events or glacial interglacial transitions in the context of the last 2000 years the proxy variability cannot be attributed to climate alone but is likely influenced by anthropogenic deforestation and the associated changes in carbon dynamics and hydrology these changes might also have an influence on the isotope ratios in drip water relative to precipitation e g through an altered evaporation transpiration ratio nevertheless despite some common trends in all proxy records the marked shifts in the other proxies are not seen in the fluid inclusion stable isotopes which gives evidence that the relationship between precipitation and drip water 18 o in the past was similar to present day conditions and not much affected by the anthropogenic impact a replication of the fluid inclusion isotope record using stalagmites from the same region will be necessary to determine whether local cave processes or large scale temperature and atmospheric circulation dominate the fluid inclusion 18 o signal and in how far the fluid inclusions can provide a direct record of precipitation 18 o

estimation of seamount compensation using satellite altimetry the degree of seamount compensation can be estimated from satellite radar altimetry and bathymetry data seamount signatures in the sea surface topography are detected located and extracted from seasat radar altimetry data using a matched filtering algorithm we have developed an efficient method for determining the two dimensional undulation signature of any axi symmetric seamount with an arbitrary degree of compensation given the seamount dimensions as determined from bathymetry we vary its degree of compensation until the model signature matches the signature extracted from seasat data we use this technique to map the relative degrees of local seamount compensation within a region we have applied this technique to 14 of the musicians seamounts two of these seamounts have been analyzed using two crossing tracks each and confirm the repeatability of the technique the results suggest the existence of a chain of low compensation seamounts within the highly compensated musicians independent verification is needed from other geophysical and geochemical analyses to support this hypothesis

climate controls on rainfall isotopes and their effects on cave drip water and speleothem growth the case of molinos cave teruel ne spain the interpretation of stable isotopes in speleothems in terms of past temperature variability or precipitation rates requires a comprehensive understanding of the climatic factors and processes that influence the 18o signal in the way through the atmosphere to the cave where carbonate precipitates acquiring its final isotopic composition this study presents for the first time in the iberia peninsula an integrated analysis of the isotopic composition of rainfall 18op during 2010 2012 years and through a detailed monitoring survey the transference of the primary isotopic signal throughout the soil and epikarst into the molinos cave teruel ne spain both air temperature and amount of precipitation have an important effect on 18op values clearly imprinting a seasonal variability modulated by an amount effect when rainfall events are more frequent or intense air mass history and atmospheric circulation influences are considered through the study of weather types synoptic scale climate patterns and large scale atmospheric circulation indexes north atlantic oscillation and western mediterranean oscillation revealing a dominant source effect on 18op values in this region where tropical north atlantic and western mediterranean are the two moisture source regions a delay of 2 3 months occurs between the dripwater oxygen isotopic composition 18od respect to 18op values as a consequence of large residence time in the epikarst limited calcite precipitates are found from winter to spring when 18od values are less negative and dripwater rates are constant this study suggests that ne iberian 18ocalcite proxy records are best interpreted as reflecting a combination of parameters not just paleotemperature or paleorainfall and if extending present day situation towards the recent past a biased signal towards winter values should be expected in molinos speleothem records

early tertiary rupture of the pacific plate 1700 km of dextral offset along the emperor trough line islands lineament abstract between 67 and 40 ma ago a northwest southeast trending fracture system over 8000 km long split the pacific plate and accumulated at least 1700 km of dextral offset between the east and west portions this system here named the emperor fracture zone efz system consisted of several segments one along the present trace of the emperor trough and another along the line islands joined by short spreading ridges the efz terminated at its northern end against the kula pacific ridge and at its southern end in a ridge transform system called the emperor spreading system which extended to the west north of australia the finite angular velocity vector describing the relative motion between the east and west pacific plates is 0 6 ma about a pole at 36 n 70 w this vector added to the known early tertiary motion of the pacific plate with respect to the global hotspot reference frame accounts in large part for the nnw trend of the emperor seamount chain relative to the wnw hawaiian trend without violation of the integrity of the antarctic plate the meiji emperor and emperor hawaiian bends date respectively the initiation 67 ma ago and cessation 40 ma ago of seafloor spreading on the emperor spreading system the postulated early tertiary relative motion along the efz between the east and west pacific plates explains 1 the present misalignment of the two sets of magnetic bights of the pacific 2 the abrupt truncation of eastern pacific bathymetric lineaments against the emperor trough and line islands 3 the contrast in paleolatitude between the eastern and western pacific as indicated by paleomagnetic and sedimentologic studies and 4 the anomalous gravity signature of the central hawaiian ridge that indicates that the ridge loaded thin hot lithosphere

vailulu u seamount samoa life and death on an active submarine volcano submersible exploration of the samoan hotspot revealed a new 300 m tall volcanic cone named nafanua in the summit crater of vailulu u seamount nafanua grew from the 1 000 m deep crater floor in 4 years and could reach the sea surface within decades vents fill vailulu u crater with a thick suspension of particulates and apparently toxic fluids that mix with seawater entering from the crater breaches low temperature vents form fe oxide chimneys in many locations and up to 1 m thick layers of hydrothermal fe floc on nafanua high temperature 81 c hydrothermal vents in the northern moat 945 m water depth produce acidic fluids ph 2 7 with rising droplets of probably liquid co2 the nafanua summit vent area is inhabited by a thriving population of eels dysommina rugosa that feed on midwater shrimp probably concentrated by anticyclonic currents at the volcano summit and rim the moat and crater floor around the new volcano are littered with dead metazoans that apparently died from exposure to hydrothermal emissions acid tolerant polychaetes polynoidae live in this environment apparently feeding on bacteria from decaying fish carcasses vailulu u is an unpredictable and very active underwater volcano presenting a potential long term volcanic hazard although eels thrive in hydrothermal vents at the summit of nafanua venting elsewhere in the crater causes mass mortality paradoxically the same anticyclonic currents that deliver food to the eels may also concentrate a wide variety of nektonic animals in a death trap of toxic hydrothermal fluids

the marcus wake seamounts and guyots as paleofracture indicators and their relation to the dutton ridge abstract the dutton ridge is on the oldest extant oceanic crust the jurassic in the northwestern pacific and lies on the pacific plate because of internal alignments and different summit plateau break depths in line on a secondary axis the ridge was probably once more contiguous in the form of a plateau the direction of movement of the pacific plate is known to have been northwesterly for the past 43 m y and almost due north from then into the cretaceous however there is a southwesterly azimuth through the region from the hawaiian emperor elbow to the subduction zone where the dutton ridge presently resides this portion of the pacific plate is overprinted by the marcus wake seamounts which formed during the cretaceous evidence of the sw striking features including fracture zones flank rift zones ridge alignments and tectonic spreading fabric is shown the time frame of the change in spreading direction and consequent fracture zone formation is suggested to have been between the formation of the dutton plateau and the marcus wake group possibly from late jurassic to early cretaceous the breakup of the dutton plateau to form the dutton ridge is suggested to have been caused by fracturing

contrasting geophysical and geochemical signatures of a volcano at the axis of the wharton fossil ridge n e indian ocean the styx volcano is a prominent seamount 20 30 km diameter 2500 m high located at the axis of the wharton fossil spreading center n e indian ocean where seafloor spreading stopped 40 ma ago gravity modeling shows that it was emplaced on a weak lithosphere in agreement with an on axis origin when seafloor spreading was active the rocks dredged at the summit of the volcano are extreme typical alkaline basalts indicating a deep enriched mantle source we show here that most of this seamount was emplaced during the final stage of the seafloor spreading in the wharton basin we then discuss how alkaline magmatism can be emplaced at the summit of the styx

sizes and ages of seamounts using remote sensing implications for intraplate volcanism satellite altimetry was used to identify and characterize pacific intraplate seamounts the gravimetric amplitudes of seamounts appear to be related to the age difference between the sea floor and seamounts by inverting this relation pseudo ages can be obtained for undated seamounts these pseudo ages imply that excursions in seamount volcanism generally correlate with times of formation of large oceanic plateaus

isostatic response of the lithosphere beneath the mozambique ridge sw indian ocean and geodynamic implications summary the sw indian ocean is characterized by the presence of several aseismic features the mozambique ridge an elongated feature lying roughly parallel to the se coast of africa is by far the least known of those structures mainly due to the scarcity of marine data to date the crustal nature and the origin of the ridge are still controversial points since knowledge of the origin of the mozambique ridge is important for a better understanding of the evolution of the sw indian ocean the isostatic response of the lithosphere beneath the ridge is analysed in order to characterize its effective elastic thickness and the emplacement process of the feature two different approaches are applied the direct computation of the geoid anomaly over the ridge by means of a 2 5 dimensional method and the computation of the admittances between the bathymetry and both the geoid and gravity anomalies both approaches point to a local isostatic response of the lithosphere the crustal thickness beneath the mozambique ridge ranges from 17 to 30 km and the average density from 2 78 to 2 7 103 kg m 3 varying with locality in good agreement with the few existing refraction profiles based on our results on the geochemical similarity between the basalts cored at the dsdp site 249 and the mor basalts erlank reid 1974 thompson et al 1982 and on the present knowledge of the sw indian ocean kinematics martin hartnady 1986 we propose an on ridge origin for the mozambique ridge the ridge would have been formed by the anomalous activity of a spreading axis linking the northern mozambique and the transkei basins accretion centres between m10 and m2 times at the m2 epoch a ridge jump event would have caused the spreading to cease the astrid ridge a poorly known aseismic structure lying close to the coast of antarctica near 15 e may be the antarctic counterpart of the mozambique ridge formed by the same accretionary phenomenon the two ridges breaking apart at m2 time due to the ridge jump event however any admittance computation at such high latitudes is impossible at present due to the very poor quality of both bathymetry and altimetry and so this hypothesis cannot be verified

millennial scale asian monsoon variability during the late marine isotope stage 6 from hulu cave china a precisely 230 th dated stalagmite 13 c profile from hulu cave china is presented to characterize the frequency and pattern of millennial scale asian monsoon am variability from 160 6 to 132 5 ka evidence for an antiphased relationship of the 13 c and 18 o on the millennial scale suggests that the 13 c is indicative of the local hydrological cycle associated with changes in am strength owing to the 13 c responding to am changes more sensitively than the 18 o we could identify 15 strong am events that correlate to cold intervals recorded in antarctic ice cores within 230 th dating uncertainty this result supports a dynamic link of am strength and southern hemispheric climates via the cross equatorial airflows power spectrum analysis shows a predominant periodicity of 1 5 2 5 ka for the 13 c profile similar to the dansgaard oeschger frequency during the last glacial period moreover the am events are characterized by rapid transitions at the onset suggesting that the observed millennial scale am variability is likely forced by northern high latitude climates via north south shifts of the intertropical convergence zone associated with the bipolar seesaw mechanism as evidence for a common mechanism for ice age terminations a strong am event 134 ka surrounding termination ii is analogous to the bolling allerod warming interval

an estimation of the elastic thickness of the lithosphere in the canary archipelago using admittance function a recent compilation of shipborne gravity and bathymetry data has been used to determine the effective elastic thickness eet of the lithosphere beneath the canary islands volcanic complex by means of the admittance technique as a first approach we have computed the admittance which is interpreted in terms of isotropic elastic plate thickness with an eet of 23 km nevertheless the proximity of the west african continental margin wacm together with the lateral variability in lithosphere structure in part caused by the large volcanic history of the canaries require a slightly different approach to minimize the influence of the margin and to check whether or not any significant variation in eet occurs related to the known canary hotspot we have computed the admittance following the isochron lines the results show a higher eet 35 km than that obtained by the first approach but slightly smaller than that predicted by the cooling plate model

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

flexure of the ocean lithosphere from island uplift bathymetry and geoid height observations the society islands summary ln flexure models of the response of the ocean lithosphere to seamount loading three key unknowns must generally be considered the density distribution of the load the degree of fd in of the deflection created moat and the flexural rigidity the models are usually constrained by one of three types of observations gravity or geoicl height anomalies the moat and arch geometry and the amount of uplift of islands on this arch the determination of the model parameters from geoid anomalies is critically dependent on the interpretation of the broad and regional geoid rise that is seen over many of the younger seamount chains and likewise the flexure parameters deduced from the moat and arch geometry are a function of the interpretation of the associated bathymetric swell the uplift data require that the tectonic erosional and sea level history of the region be known although this requirement can be relaxed if rather than the uplift relative to sea level the change in uplift with distance from the load is used as the observed quantity all these types of observations have been used in this paper to constrain the flexure model for the society islands and while any one data type on its own does not lead to reliable flexure parameters a consistent solution is found when the three are taken together the results point to a relatively low load density of 2 5 g m apart from a high density core a moat that is partly fdled in with sediment or volcanic debris and a flexural rigidity of about 3 x dyne cm

elastic layer thickening with age of the oceanic lithosphere a tool for prediction of the age of volcanoes or oceanic crust summary to first order the estimated thickness te of the elastic part of the oceanic lithosphere increases linearly with the square root of the age of the lithosphere at the time of loading t in order to quantify this relationship in the particular case of volcanic loading a synthesis of te estimates reported both in this paper and in previous studies is conducted excluding the anomalously low estimates from the south central pacific the values are very consistent for the three main oceans and follow the empirical relationship te km 2 7 0 15 t ma the relationship is used to predict the age of volcanoes when the age of the crust is known for the trindade chain in the south atlantic ocean and to predict the age of the crust when the age of the volcanoes is known for the pacific plate east of the tonga trench the age estimates are in good agreement with the structural setting

guyots of the mid emperor chain mapped with multibeam sonar abstract bathymetry of seven of the middle emperor chain guyots from u s naval oceanographic office multibeam narrow beam swath mapping surveys is presented these data are contoured at a 100 fm interval using different theories on formation juxtaposed with the accurate bathymetry of this chain tectonic possibilities are shown for changes in plate direction and conduit activity fluctuations the range for one complete pulse of this activity is shown to be 280 nm 518 km for the emperor chain

role of subducted lithospheric slab in uplift and subsidence of the northwestern pacific margins abstract vertical movements of the ocean floor and its margins at present and in the geological past were reviewed with the focus on the regions surrounding the japanese islands it is emphasized that uplift and subsidence can essentially be explained by two mechanisms one is isostatic equilibrium and the other a non isostatic dynamic force a typical example of the former is thermal subsidence of the ocean floor with time an example of the latter is rapid uplift of fore arc margins associated with large positive gravity anomalies caused by collision and accreting subduction such as at kikai jima and the okushiri ridge repeated collision of the plates in the pacific ocean caused uplift and subsidence of the ogasawara islands and their fore arc zone the present day honshu island japan has an elevation of 1 000 m above sea level with large positive gravity anomalies which are maintained by a rigid inclined slab beneath the island very young and embryonic back arc basins are generally shallower than the ocean subsidence curves give and show positive gravity anomalies such a non isostatic uplift is also dynamically supported by a rigid slab subducted beneath the basins on the other hand the mariana trough has normal back arc ocean depths due to strong warping of the mariana subducted slab which can not support the overlying arc and back arc region immediately after the zones lost the support of the underlying slab they subsided very rapidly much faster than the normal subsidence of the ocean floor by cooling rapid subsidence of some rifted basins such as the initial stage of the shikoku basin and the sea of japan demonstrated by dsdp odp cores appears to have been caused by this mechanism inner and fore arc zones of the ne honshu arc have experienced a remarkable subsidence during the oligocene and miocene distribution patterns of the horizontal stress field are synchronous with the vertical displacement of the area it is obvious that uplift is generally associated with compression and high positive gravity whereas subsidence is associated with extension and zero gravity anomalies i propose that the succession of these two events can be explained by a simplified model of slab support

stable isotope study of cave percolation waters in subtropical brazil implications for paleoclimate inferences from speleothems we analyze the interannual monthly variability of oxygen isotope ratios in data from iaea stations along the atlantic coast of south america between 238 and 348 s to evaluate the influence of parameters such as temperature rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical brazil in addition a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the santana cave system 24831v s 48843v w is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water d 18 o interannual monthly variations in d 18 o of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer negative values of d 18 o to a more extratropical regime in winter positive values of d 18 o variations in groundwater d 18 o indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters regardless of location of collection in the cave in addition the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs significant perturbations in the groundwater composition characterized by more positive values of d 18 o are probably connected to an increased atlantic moisture contribution associated with extratropical precipitation this implies that the d 18 o of speleothems from caves in this region may be a suitable proxy for studying