joint sun glitter and radar imagery of surface slicks a method is proposed to retrieve and interpret fine spatial variations of the sea surface roughness in sun glitter imagery observed sun glitter brightness anomalies are converted using a transfer function determined from the smoothed shape of sun glitter brightness the method is applied to modis and meris sun glitter imagery of natural oil seeps and the catastrophic deepwater horizon oil spill in the gulf of mexico the short scale roughness variations in the presence of mineral oils slicks are consistently extracted and compared to variations associated with the biogenic slicks in doing so the wind speed dependency on the roughness anomalies is also considered a comparison to normalized radar cross section nrcs anomalies taken from the corresponding high resolution asar images is performed and similarities as well as differences are investigated the results document significant benefit from the synergetic use of sun glitter and radar imagery for detection and monitoring of surface slicks

paleoclimate and location of the border between mediterranean climate region and the saharo arabian desert as revealed by speleothems from the northern negev desert israel speleothem bearing karstic caves of the northern negev desert southern israel provides an ideal site for reconstructing the paleoclimate and paleo location of the border between mediterranean climate region and the saharo arabian desert major periods of speleothem deposition representing humid periods were determined by high resolution 230 th u dating and corresponding studies of stableisotopecompositionwereusedtoidentifythesourceofrainfallduringhumidperiodsandthevegetationtype majorhumidintervals

evaluation of aquifer thickness by analysing recession hydrographs application to the oman ophiolite hard rock aquifer for more than a century hydrologists and hydrogeologists have been investigating the processes of stream and spring baseflow recession for obtaining data on aquifer characteristics the maillet formula librairie sci a hermann paris 1905 218 an exponential equation widely used for recession curve analysis is an approximate analytical solution for the diffusion equation in porous media whereas the equation proposed by boussinesq c r acad sci 137 1903 5 j math pure appl 10 1904 5 that depicts baseflow recession as a quadratic form is an exact analytical solution other formulas currently used involve mathematical functions with no basis on groundwater theory only the exact analytical solutions can provide quantitative data on aquifer characteristics the efficiency of the two methods was compared on the basis of recession curves obtained with a 2d cross sectional finite differences model that simulates natural aquifers simulations of shallow aquifers with an impermeable floor at the level of the outlet show that their recession curves have a quadratic form thus the approximate maillet solution largely overestimates the duration of the influenced stage and underestimates the dynamic volume of the aquifer moreover only the boussinesq equations enable correct estimates of the aquifer parameters numerical simulations of more realistic aquifers with an impermeable floor much deeper than the outlet proves the robustness of the boussinesq formula even under conditions far from the simplifying assumptions that were used to integrate the diffusion equation the quadratic form of recession is valid regardless of the thickness of the aquifer under the outlet and provides good estimates of the aquifer s hydrodynamic parameters nevertheless the same numerical simulations show that aquifers with a very deep floor provide an exponential recession thus in that configuration the maillet formula also provides a good fit of recession curves even if parameter estimation remains poor in fact the recession curve appears to be closer to exponential when flow has a very important vertical component and closer to quadratic when horizontal flow is dominant as a consequence aquifer permeability anisotropy also changes the recession form the combined use of the two fitting methods allows one to quantify the thickness of the aquifer under the outlet

integrated multi site u th chronology of the last glacial lake lisan abstract we present a new integrated multi site chronology for lake lisan which occupied the dead sea basin and jordan valley during the last glacial period 70 14 kka marine isotope stages 4 3 2 the dead sea basin lacustrine deposits are unique among closed basin sediments in that they formed in a deep hypersaline water body that precipitated primary aragonite which is amenable to radiometric dating by u series providing a solid basis for studies of the relationship of middle east climate to other changes in the high latitudes or the tropics the application of u th dating for lacustrine carbonates requires corrections for detrital u and th and hydrogenous initial 230th here we followed an iterative approach in which we evaluate the composition of the detrital contamination independently for every set of coeval samples to determine the corrected ages these were further filtered and combined with lithological limnological considerations which were used to construct age height models for all studied stratigraphic sections finally the ages of stratigraphic tie points were used to integrate the individual age height models into a unified chronology the resulting chronological framework indicates that the ages of several primary gypsum units associated with catastrophic lake level drops correspond with the timing of heinrich events in the north atlantic thus a final iterative step involves refining the ages of lisan gypsum events based on the ages of heinrich events 6 5 5a 4 and 1 this approach yields an unprecedented basin wide unified event anchored chronology for the lisan formation with typical age uncertainties ca 1000 2000 years 95 confidence limit across the entire last glacial well below those typically related to individual u th and radiocarbon dating of dirty carbonates from similar time intervals the results can be further extrapolated to new sites and serve as a geochronometric reference for the reconstruction of the limnological history of lake lisan

tims u series dating and stable isotopes of the last interglacial event in papua new guinea the extensive flight of uplifted reef terraces which occurs along the vitiaz strait on the northern flank of the huon peninsula in png papua new guinea contains a particularly good record of sea level changes in the last 250 ky the huon terraces were the target of an international expedition which took place in july august 1988 in particular we searched for suitable samples for u series dating in a reef complex designated as vii which is correlated with the last interglacial episode and high sea level stand this complex is composed of a barrier reef viib a lagoon and a fringing reef viia twelve corals from these terraces and two corals from the older reef complex viii were selected for analysis the petrography oxygen and carbon isotope compositions and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium 230 th 234 u ages of the corals with 99 aragonite having primary textures and which show u sr ratios around 0 4 10 3 and initial 234 u values close to that of present seawater appear to be reliable the most reliable ages from complex vii corals fall in two tight groups centered at 118 ky and 134 ky corals with 234 u t values higher than 160 and u sr ratios substantially lower than seawater are assumed to have undergone diagenetic alteration which appears to be common in this area the simplest model for sea level height for terrace vii is a continuous rise between 134 and 118 ky alternatively there may have been two periods of rapid sea level rise in contrast in the bahamas there is evidence that sea level remained rather constant over the time interval 132 to 120 ky the absence of ages between 132 and 120 ky in png could be the result of changes in the local tectonic uplift rates during that time or erosion that disrupted the continuous record in any event we find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation or as a test of climatic models the older ages reported here precede the milankovitch solar insolation peak at 128 ky and the younger ages are 10 ky after this peak if the present high precision data are correct then it will be necessary to reassess the validity of the milankovitch theory of climatic changes the fundamental issue which must now be resolved is a means of identifying coral samples that have not been disturbed by diagenetic processes

seismic velocities anisotropy and shear wave splitting of antigorite serpentinites and tectonic implications for subduction zones 1 antigorite the high temperature ht form of serpentinite is believed to play a critical role in various geological processes of subduction zones we have measured p and s wave velocities vp and vs anisotropy and shear wave splitting of 17 serpentinite samples containing 90 antigorite at pressures up to 650 mpa the new results combined with data for low temperature lt lizardite and or chrysolite reveal distinct effects of lt and ht serpentinization on the seismic properties of mantle rocks at 600 mpa vp 5 10 and 6 68 km s vs 2 32 and 3 67 km s and vp vs 2 15 and 1 81 for pure lt and ht serpentinites respectively above the crack closure pressure 150 mpa the velocity ratio of antigorite serpentinites displays little dependence on pressure or temperature serpentine contents within subduction zones and forearc mantle wedges where temperature is 300 c should be at least twice that of previous estimates based on lt serpentinization the presence of seismic anisotropy high pressure fluids or partial melt is also needed to interpret ht serpentinized mantle with vp 1 81 the intrinsic anisotropy of the serpentinites 3 8 16 9 with an average value of 10 5 for vp and 3 6 18 3 with an average value of 10 4 for vs is caused by dislocation creep induced lattice preferred orientation of antigorite three distinct patterns of seismic anisotropy correspond to three types of antigorite fabrics s l and ls tectonites formed by three categories of strain geometry i e coaxial flattening coaxial constriction and simple shear respectively our results are thought to provide a new explanation for various anisotropic patterns of subduction systems observed worldwide

synoptic conditions of fine particle transport to the last interglacial red sea dead sea from nd sr compositions of sediment cores abstract the sediments deposited at the depocenter of the dead sea comprise high resolution archive of hydrological changes in the lake s watershed and record the desert dust transport to the region this paper reconstructs the dust transport to the region during the termination of glacial marine isotope stage 6 mis 6 135 129 ka and the last interglacial peak period mis5e 129 116 ka we use chemical and nd and sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the dead sea the data is integrated with data achieved from cores drilled at the floor of the red sea thus forming a red sea dead sea transect extending from the desert belt to the mediterranean climate zone the dead sea accumulated flood sediments derived from three regional surface cover types settled desert dust mountain loess soils and loess soils filling valleys in the dead sea watershed termed here valley loess the valley loess shows a distinct 87sr 86sr ratio of 0 7081 1 inherited from dissolved detrital calcites that originate from dried waterbodies in the sahara and are transported with the dust to the entire transect our hydro climate and synoptic conditions reconstruction illustrates the following history during glacial period mis6 mediterranean cyclones governed the transport of saharan dust and rains to the dead sea watershed driving the development of both mountain soils and valley loess then at heinrich event 11 dry western winds blew saharan dust over the entire red sea dead sea transect marking latitudinal expansion of the desert belt later when global sea level rose the dead sea watershed went through extreme aridity the lake retreated depositing salt and accumulating fine detritus of the valley loess during peak interglacial mis 5e enhanced flooding activity flushed the mountain soils and fine detritus from all around the dead sea and red sea marking a significant contraction of the desert belt at the end of mis 5e the effect of the regional precipitation diminished and the dead sea and red sea areas re entered sever arid conditions with extensive salt deposition at the dead sea

u series ages of solitary corals from the california coast by mass spectrometry the purpose of this study is to evaluate the feasibility of dating fossil solitary corals from pleistocene marine strandlines outside tropical latitudes using the recently developed high sensitivity high precision u series technique based on thermal ionization mass spectrometry tims the tims technique is much more efficient than conventional a spectrometry and as a result multiple samples of an individual coral skeleton or different specimens from the same bed can be analyzed detached and well rounded fossil specimens of the solitary coral balanophyllia elegans were collected from relict littoral deposits on emergent marine terraces along the california coast at cayucos terrace elevation 8 m previously dated at 124 and 117 ky by counting shell beach terrace elevation about 25 m previously undated nestor terrace san diego elevation 23 m previously dated at 131 to 109 ky bird rock terrace san diego elevation 8 m previously dated at 81 ky attached living specimens were collected from the intertidal zone on the modern terrace at moss beach concentrations of 232 th in both living and fossil specimens are much higher than in reef building corals 12 to 624 pmol g vs 0 1 to 1 6 pmol g respectively however because 230 th 232 th in balanophyllia elegans are very low 2 22 10 3 to 4 33 10 4 the high 232 th concentrations have negligible effect on the 230 th 234 u dates the high 232 th concentration in the living specimen 33 1 pmol g indicates that a significant amount of 232 th is incorporated in the aragonitic skeleton during growth or attached to clay sized silicates trapped in the skeletal material the calculated initial 234 u activities in the fossil specimens of balanophyllia elegans are higher than the 234 u activity in modern seawater or in the modern specimen the higher initial activities could possibly reflect the influx of 234 u enriched continental water into pleistocene coastal waters or it could reflect minor diagenetic alteration a persistent and fundamental problem in dating all corals samples from a compound specimen from the cayucos terrace were subjected to different preparation procedures samples prepared by a standard acid washing procedure yielded 230 th 234 u ages of 125 123 and 122 ky whereas samples prepared by an abbreviated procedure without acid washing yield significantly lower ages of 113 and 112 ky two other specimens from the same bed yielded 230 th 234 u ages of 118 and 115 ky also two specimens from a stratigraphically higher bed yielded ages of 120 and 117 ky and three specimens from a lower bed yield ages of 115 113 and 101 ky nine of the twelve ages of the treated samples from the cayucos terrace range from 125 to 113 ky however the ages do not follow the stratigraphie order two possible interpretations are 1 the age of the terrace deposit is 125 ky and all younger ages reflect variable diagenetic alteration or 2 the age of the terrace is 125 to 113 ky and the ages reflect sediment reworking over a period of 12 ky three specimens from a single bed on the shell beach terrace yield ages of 126 122 and 121 ky similar to the older ages from cayucos the ages of solitary corals from the cayucos and shell beach terraces are similar to ages of reef building corals from terraces at numerous tropical localities these are correlated with the last interglacial sea level highstand which probably stood 2 to 10 m above present sea level the youngest ages and present elevations of the cayucos and shell beach terraces yield tectonic uplift rates of 0 01 and 0 15 m ky respectively assuming the original elevation of each terrace was 7 m four specimens from the basal gravel on the nestor terrace yielded ages of 145 143 137 and 133 ky the three oldest ages however are older than that associated with the last interglacial the possible explanations for these older ages are 1 diagenic alteration or 2 the nestor terrace deposits reflect in some way a poorly documented early phase of the last interglacial sea level high stand

ocean wave spectra derived from shuttle imaging radar b imagery and surface measurements during the shuttle imaging radar b sir b mission in october 1984 synthetic aperture radar sar images were taken off the coast of japan wave spectra derived from sir b imagery were compared with simultaneous wave buoy observations waves at the time of flight were nearly perpendicular to the sar flight direction and were composed of two major systems a swell of about 200 m wavelength and wind waves with 70 m wavelength both the swell and wind wave peaks were identifiable in the sar image spectrum after stationary response correction peak frequencies derived from sir b images and from the wave gauge agreed satisfactorily however the relative magnitudes of the peaks are not in accordance with the surface measurements possible reasons for the disagreement are discussed

abrupt changes in early holocene tropical sea surface temperature derived from coral records for many high latitude regions of the globe it is now clear that the transition to modern climate following the last glacial maximum was punctuated by a number of rapid and substantial climate oscillations1 2 in contrast relatively little is known about how the tropics responded to the deglaciation because few high resolution records are available from lower latitudes corals have recently been shown to provide an important source of tropical climate records because they can be easily and accurately dated using either 14c or 230th and because past sea surface temperatures can be recovered from the sr ca ratios in coral skeletons here we use this technique to derive several early holocene sea surface temperature records from a coral drill core recovered from espiritu santo vanuatu in the tropical southwest pacific ocean these records indicate that sea surface temperatures in this region were depressed by as much as 6 5 c below modern values at 10 350 calendar years bp but rose very abruptly during the following 1 500 years this temperature increase lags the post younger dryas increase observed in a coral record from the tropical atlantic ocean3by about 3 000 years an unexpected phase shift that may ultimately shed light on the mechanisms of deglacial climate change

u series dating of diagenetically altered fossil reef corals initial 234u 238u activity ratios higher than those expected from closed system evolution of seawater are an outstanding problem in u series dating of fossil reef corals the increased activity ratios are ascribed to post depositional diagenesis we analysed six last interglacial and one holocene coral of the genus porites collected near the northern end of the gulf of aqaba northern red sea together with three recent corals from this location as a modern reference while the values measured on the recent samples show no deviation from expected values the holocene and last interglacial corals display highly elevated 234u 238u activity ratios as well as increased 238u and 232th concentrations 234u 238u activity ratios are strongly correlated with 230th 238u and total uranium content a model assuming different degrees of uranium addition and subsequent loss in different sub samples of one coral produces straight lines isochrons on a 234u 238u 230th 238u plot and predicts that the true age of the coral can be calculated by intersecting this isochron with the seawater evolution curve we used the strong correlation detected in the aqaba corals to calculate isochron ages the isochron age of the holocene coral 3116 167 156 yr is concordant with its calibrated 14c age 2963 92 103 yr the ages of the last interglacial corals are between 121 6 7 5 3 and 121 9 7 0 6 3 kyr for a higher terrace 7 10 m asl and 106 4 8 9 8 1 and 117 1 19 7 15 3 kyr for a lower terrace 4 5 m asl one last interglacial coral with an aragonite content of 85 could not be dated the elevation and ages of the fossil terraces are consistent with existing sea level reconstructions from the red sea

precise chronology of the last interglacial period 234u 230th data from fossil coral reefs in the bahamas a detailed study of 238 u 234 u 230 th ages was made for different coral species from two bahamian reefs to determine the time scale of the sea level high during the last interglacial period using recently developed mass spectrometric techniques for the measurement of u and th isotopes thirty seven coral samples were analyzed in replicate typical errors at 125 ky are 1 5 ky 2 and 3 ky time intervals appear to be well resolved this high precision permits detailed chronologic study with time resolution adequate to define stages of the reef s history these data demonstrate that the time between transgression and regression of the ocean in the last interglacial was about 12 ky after which sea level fell rapidly at more than 2 m ky the high sea level stand began possibly by 132 ky and certainly by 129 ky ago when sea level reached 6 m above present mean low sea level high sea level was sustained until 120 ky and then fell rapidly this time period covers the milankovitch insolation peak at 65 n but is not sharply defined and the sea level high lasted from about 4 ky before the insolation peak to 8 ky after it we find no evidence for a double peak of sea level rise in the last interglacial episode that is high stands at both 125 and 142 ky there appears to be some discrepancy between this precise chronology for a coral reef on a tectonically stable platform and the chronology assigned to deep sea sediments the present results show that the duration of the last interglacial led to a 12 ky period of high sea level stand which is much longer than the insolation peak the study area consists of two sizeable bank barrier coral reefs of sangamon age that crop out along the coast northwest of cockburn town on san salvador island and at devil s point on great inagua island the initial stage of reef development is not revealed at either site but the main parts of both reefs are well preserved at cockburn town the beginning of the reef was marked by colonization of acropora palmata on hardground areas and possibly other corals at 132 ky ago patch reefs at the southeastern flank of the developing reef were growing by 129 to 126 ky ago by 126 to 123 ky ago the crest of the reef was formed by the frame building coral a palmata and associated patch reefs flourished along its flanks a palmata coral heads grew upward to a mean low sea level 6 m above the present one the reef began to decline as sea level dropped at about 123 to 120 ky ago near two measured profiles at devil s point the top of a rubblestone dominated by a cervicornis and patch reef corals preserved in growth position have been beveled off and represent an ancient wave cut surface 230 th ages on corals below and above this surface indicate that it was cut at about 125 1 ky ago

the magnetic anisotropy of mantle peridotites example from the twin sisters dunite washington abstract the twin sisters dunite massif washington state provides unweathered peridotites for magnetic analysis these rocks have been chosen to test a new magnetic fabric based on measuring the anisotropy of magnetic susceptibility ams in high field with a vibrating sample magnetometer although the dunites are fresh they host small quantities of secondary magnetite formed along cracks under low field conditions magnetite masks the magnetic fabric of olivine and thus the magnetic fabric does not reflect mantle flow deformation above the magnetic saturation at a field of 1 t the ferrimagnetic component is removed and the high field slope represents the paramagnetic ams only this high field ams originates from the magnetocrystalline anisotropy of olivine the high field ams are compared with lattice preferred orientation lpo fabric data obtained by electron backscatter diffraction lpo point distributions are formed by high temperature plastic flow and match the high field measurements in contrast girdle lpos present notable departures from the high field ams axes

dead sea drawdown and monsoonal impacts in the levant during the last interglacial sediment cores recovered by the dead sea deep drilling project dsddp from the deepest basin of the hypersaline terminal dead sea lake floor at 725 m below mean sea level reveal the detailed climate history of the lake s watershed during the last interglacial period marine isotope stage 5 mis5 the results document both a more intense aridity during mis5 than during the holocene and the moderating impacts derived from the intense mis5e african monsoon early mis5e 133 128 ka was dominated by hyperarid conditions in the eastern mediterranean levant indicated by thick halite deposition triggered by a lake level drop halite deposition was interrupted however during the mis5e peak 128 122 ka by sequences of flood deposits which are coeval with the timing of the intense precession forced african monsoon that generated mediterranean sapropel s5 a subsequent weakening of this humidity source triggered extreme aridity in the dead sea watershed and resulting in the biggest known lake level drawdown in its history reflected by the deposition of thick salt layers and a capping pebble layer corresponding to a hiatus at 116 110 ka the dsddp core provides the first evidence for a direct association of the african monsoon with mid subtropical latitude climate systems effecting the dead sea watershed combined with coeval deposition of arabia and southern negev speleothems arava travertines and calcification of red sea corals the evidence points to a climatically wet corridor that could have facilitated homo sapiens migration out of africa during the mis5e peak the hyperaridity documented during mis5e may provide an important analogue for future warming of arid regions of the eastern mediterranean levant

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

mantle flow in subduction systems the mantle wedge flow field and implications for wedge processes 1 the mantle wedge above subducting slabs is associated with many important processes including the transport of melt and volatiles our understanding of mantle wedge dynamics is incomplete as the mantle flow field above subducting slabs remains poorly understood because seismic anisotropy is a consequence of deformation measurements of shear wave splitting can constrain the geometry of mantle flow in order to identify processes that make first order contributions to the pattern of wedge flow we have compiled a data set of local s splitting measurements from mantle wedges worldwide there is a large amount of variability in splitting parameters with average delay times ranging from 0 1 to 0 3 s up to 1 0 1 5 s and large variations in fast directions we tested for relationships between splitting parameters and a variety of parameters related to subduction processes we also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge we find that no simple model can explain all of the trends observed in the global data set mantle wedge flow is likely controlled by a combination of downdip motion of the slab trench migration ambient mantle flow small scale convection proximity to slab edges and slab morphology with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology there is also a likely contribution from b type olivine and or serpentinite fabric in many subduction zones governed by the local thermal structure and volatile distribution

open system u series ages of corals from a subsiding reef in new caledonia implications for sea level changes and subsidence rate abstract on the amedee islet 4 drill cores were recovered from the barrier reef of western new caledonia the coral reef is slowly subsiding and is thus percolated by sea water during sea level highstands the cores sample a 10 m thick holocene reef overlying a 24 m thick reef of marine isotope stage mis 5 5 which in turn overlies older reef material from mis 7 5 and beyond 234 u 238 u and 230 th 238 u ratios and 232 th were determined by thermal ionization mass spectrometry on aragonitic coral samples that were carefully investigated using x ray diffraction and scanning electron microscopy the petrographic study shows an increasing coral weathering with growing coral age that causes different degree of u series open system behavior and 232 th accumulation holocene corals exhibit a small degree of early diagenesis and yield 230 th 238 u ages according to the holocene sea level rise from 8200 years to 5000 years bp corals from the last interglacial section have experienced more frequent replacement of aragonite fibers and minor dissolution and u series open system behavior is evident to estimate the impact of recoil processes and alteration on the u series system two models by villemant and feuillet b villemant n feuillet dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces earth and planetary science letters 210 2003 105 118 and thompson et al w g thompson m w spiegelman s l goldstein r c speed an open system model for u series age determinations of fossil corals earth and planetary science letters 210 2003 365 381 have been tested these models yield identical ages within uncertainty which are in agreement to the sea level history of the past 250 000 years as long as physico chemical alteration and re crystallization is small consequently we were able to estimate the subsidence rate from the subsidence observed between the end of mis 5 5 and the early holocene which is 0 16 0 04 m per 1000 years in addition by using this subsidence rate and the sea level highstand of 6 3 m during mis 5 5 we can estimate the sea level highstand at 244 000 mis 7 5 to be between 2 m to 2 m respectively corals from underneath the marine isotope stage 7 5 sequence show more significant dissolution increasing re crystallization elevated 232 th and excess 234 u and 230 th here the villemant and feuillet b villemant n feuillet dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces earth and planetary science letters 210 2003 105 118 model fails to predict ages but the thompson et al w g thompson m w spiegelman s l goldstein r c speed an open system model for u series age determinations of fossil corals earth and planetary science letters 210 2003 365 381 model was applicable predicting ages between 355 000 to 430 000 years i e coral growth potentially during mis 9 or 11

sun glitter radiance and radar cross section modulations of the sea bed aircraft and satellite borne multispectral sensors such as ocean color scanners spectrometers and scanning lidar s have proved to be effective in detecting submarine shallow water bottom topography in clear coastal waters for such studies the blue green band of the visible electromagnetic spectrum wavelength between 400 and 580 nm is used because natural light in this range has the deepest penetration into the water column however if the water becomes turbid the reflection from the submarine sea bed disappears in this case the only possible mechanism available in the optical range of the electromagnetic spectrum for detecting surface signatures of shallow water bottom topography is through the observation of direct sunlight specularly reflected from a roughened sea surface known as sun glitter radiance as the tidal flow over irregularities on the submarine sea bed creates surface roughness variations sun glitter imagery can be used to detect such features in this paper a first order theory of the sun glitter imaging mechanism of submerged sand waves is presented the results of sun glitter radiance modulations are compared with simulations of p band radar cross section modulations and with experimental data calculations of both the constant background sun glitter radiance and the sun glitter radiance modulation show that these parameters are very sensitive to wind speed to view angle with respect to acquisition time and to observation geometry as a whole

quaternary isotope stratigraphy and paleoclimate of coral reef terraces gulf of aqaba south sinai egypt five quaternary coral reef terraces have been recognized along sharm elsheikh ras mohammed coast of which terraces v to ii form a well developed staircase at um seed while recognized separately at ras mohammed terrace i was only observed as a reef pathches at sharm elsheikh ras mohammed road terraces v to i exist at elevations of 1 b s 1 to 0 m 3 6 m 10 12 m 15 20 m and 25 35 m a s 1 respectively uranium series dates of samples representing terraces v iv iii ii and i show ages grouped as ka 118 125ka 200ka 280 300ka and older 300ka which are related to isotope stages 1 5e 7 9 and 11 respectively the variation of 18o for samples from these terraces show evidence of at least four major warm wet climatic periods in relationship to high sea level and contemporaneous with the formation of the reef terraces faulting affects only the older terraces i and ii and along with the occurrence of terrace iv of last interglacial age at elevation of 3 6 m suggest that the coastal area has not been subjected to major tectonic activities at least with the last 125 ka

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

emplacement of serpentinites in the chohar gonbad gugher baft ophiolitic melange southeast iran examination of the mineral chemical petrologic and structural features the chohar gonbad gugher baft ophiolite melange located along the major baft and shahr e babak fault zones southeast iran represents remnants of neo tethyan oceanic lithosphere this melange contains blocks of harzburgite dunite lherzolite basalt and other ophiolite related lithologies tectonically mixed with and embedded in a serpentinite matrix field petrographic and geochemical data show that peridotites in this melange belong to the upper mantle they seem to have undergone up to 20 partial melting in a supra subduction zone setting based on their spinel cr values 0 21 0 53 chemical compositions and textures in the serpentinites indicate that they were partially hydrated during emplacement and further mobilized diapirically to the surface the different deformation stages occurred in an accretionary wedge environment petrographic evidence shows that the first serpentinization event produced mesh textured serpentinites formed under static conditions in an ocean floor environment nain baft ocean crust where the initial lizardite bastite and chrysotile veins formed plastic deformation occurred due to the subduction of nain baft oceanic lithospheric beneath the central iranian microcontinent with antigorite bearing flare textured serpentinites produced during progressive exhumation of the nain baft ophiolite melange the serpentinites were affected by ductile ductile brittle and brittle deformation respectively accretion and resultant diapirism are the most important processes in the emplacement of serpentinite which is a consequence of hydration of the ocean crust in this example late stage emplacement via thrusting occurred along the northern extent of the southern sanandaj sirjan zone s sz

surface current measurements using airborne visible image time series abstract measurements of nearshore water currents are important for a number of reasons including understanding sediment transport and beach erosion planning and evaluation of littoral construction projects and military operations in very shallow water because direct measurements are difficult and expensive to make remote sensing techniques are of great interest a digital camera system has been used to remotely measure ocean surface currents from an aircraft by estimating the doppler shift of gravity waves navigational data are used to map each of a sequence of images to a geodetic reference frame at the level of the mean ocean surface the 3 d frequency wave number spectrum of the luminance modulations in subsets of these mapped data exhibits the dispersion relation for surface gravity waves and the 2 d velocity vector is retrieved by estimating the doppler shift of the higher frequency waves in this spectrum wavelengths in the band of about 5 30 m the relationship of this technique to that of tracking visible surface features between image pairs is examined with examples current retrievals in shallow water outside the surf on a quasi linear beach and in an exposed tidal inlet channel are favorably compared with simultaneous in situ current measurements with errors of 10 in magnitude and 5 in direction

seismic and magnetic anisotropy of serpentinized ophiolite implications for oceanic spreading rate dependent anisotropy compressional and shear wave anisotropy shear wave birefringence and the anisotropy of magnetic susceptibility were measured on a series of dunites sampled from the dinardic hellenic ophiolites the densities of these materials ranged from 3330 kg m 3 to 2620 kg m 3 and indicate degrees of serpentinization from 2 3 to 87 9 respectively magnetic susceptibility increases and the compressional and shear wave velocities decrease in proportion to the degree of serpentinization as has been observed by other workers in all cases the magnetic susceptibility tensor is described by an oblate spheroid whose minor axis is closely aligned to the pole of the foliation but the magnetic anisotropy is not related to the degree of serpentinization the compressional wave anisotropy e monotonically decays from 12 for nearly pure olivine dunite to less than 2 for the most serpentinized sample this observation strongly suggests that serpentinization progressively destroys the original anisotropy by consuming the preferentially aligned olivines and replacing them with randomly oriented serpentines typical serpentine mesh textures seen in microscopic thin section examinations support this suggestion this loss of anisotropy with serpentinization may partly explain the apparent relationship between seismic compressional wave anisotropy of the oceanic lithosphere the more complex geological structure of slow spreading ridges may admit more sea water via faults for deep circulation which increases serpentinization and consequence of which is decreased seismic anisotropy 2007 elsevier b v all rights reserved

open system coral ages reveal persistent suborbital sea level cycles sea level is a sensitive index of global climate that has been linked to earth s orbital variations with a minimum periodicity of about 21 000 years although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbital frequency sea level change has been difficult to resolve primarily because of problems with uranium thorium coral dating here we use a new approach that corrects coral ages for the frequently observed open system behavior of uranium series nuclides substantially improving the resolution of sea level reconstruction this curve reveals persistent sea level oscillations that are too frequent to be explained exclusively by orbital forcing

ocean wave dispersion surface measured with airborne ir imaging system image sequences of the ocean have been collected at long range and low grazing angle with an airborne infrared system the images are geographically registered and 3d frequency wavenumber spectra are calculated and shown to have a strong 2d dispersion surface that is characteristic of wind waves and swell wave directions compare well with in situ measurements and their speeds are consistent with the water depth the authors conclude that temporal sequences of ir images acquired from long distance can provide information for extracting surface wave parameters

pressure and temperature dependence of p and s wave velocities seismic anisotropy and density of sheared rocks from the sierra alpujata massif ronda peridotites southern spain seismic wave velocities and densities and their pressure and temperature dependence of rock samples recovered from surface exposures at the sierra alpujata were determined in order to better understand the petrological controls on velocity and density the rock samples studied are representative of the major lithologies of the ronda ultramafic body and its metamorphic aureole the suite of ultramafic rocks includes dunite harzburgite and lherzolite exhibiting different degrees of deformation and serpentinization the rocks representing the metamorphic aureole comprise coarse grained migmatites to ultramylonitic migmatites gneisses and eclogites the experimental data include measurements of elastic wave velocities vp vs and densities at confining pressures up to 600 mpa and temperatures up 600 c at 600 mpa the determination of the pressure and temperature derivatives of velocities and densities and the determination of velocity anisotropy average p and s wave velocities at 600 mpa for rocks of the ultramafic body vary from 6 47 to 8 22 km s 1 and 3 27 to 4 75 km s 1 respectively mainly due to different degrees of serpentinization maximum vp and vs anisotropy is about 8 0 and 9 5 respectively and is primarily related to the preferred orientation of olivine in rocks of the metamorphic aureole average p velocities are in the range 5 61 7 23 km s 1 and s velocities vary from 3 48 to 4 04 km s 1 p and s velocity anisotropy is highest about 6 4 and 4 6 in sheared rocks mylonites and is mainly due to the preferred orientation of biotite and sillimanite the geophysical significance of the experimental data is briefly discussed

modelling the anisotropic seismic properties of partially molten rocks found at mid ocean ridges abstract the problem of modelling the seismic properties of mid ocean ridge rocks of the axial magma chamber amc and the low velocity triangle lvt immediately below it has been addressed using two samples from oman ophiolite as examples the specimens are a layered gabbro from the lower oceanic crustal sequence and a harzburgite from the upper most mantle section at the palaeo ridge axis the seismic properties have been simulated at a temperature of 1200 c and pressure of 200 mpa so that the basalt melt is above its solidus various effective medium methods are discussed in the perspective of modelling rocks that have a strong background elastic anisotropy due to crystal preferred orientation cpo and an introduced anisotropy due to oriented melt filled inclusions calculations using various methods show a wide range of predicted melt fractions for a given seismic velocity the self consistent scheme scs and differential effective medium dem are compared in some detail a tensorial model was developed using a poro elastic method of gassman at low seismic frequency and a standard dem with isolated basalt inclusions at high frequency at low frequency the basalt pore fluid is considered to be everywhere connected and the pressure uniform whereas at high frequency basalt inclusions are isolated assuming the medium to be a standard linear solid the low and high frequency velocities were used to calculate the anisotropy of attenuation calculations with spherical basalt inclusions show that the seismic velocities decrease and attenuation increase with increasing melt fraction the symmetry of the background anisotropy due to cpo is preserved but gradually reduced with increasing melt fraction for the seismic velocities observed for the axial magma chamber amc with v p of 3 5 to 4 7 km s the model predicts 50 70 melt for the low velocity triangle lvt below the amc with v p of 4 8 5 6 km s the model predicts 35 50 melt predictions from the observed attenuations q 1 at the amc of 0 05 0 02 and in the lvt of 0 02 0 01 are around 60 and 45 melt respectively seismic anisotropy has been modelled with ellipsoidal basalt pancake shaped inclusions with their circular sections in the xy foliation plane only a 2 3 of ellipsoidal basalt inclusions are required to over print the anisotropy of the background medium there is a rapid decrease in v p and increase of q 1 for propagation normal to the foliation z with increasing axial ratio of the inclusions with increasing axial ratio the model predicts decreasing amounts of melt for given velocity v p in the z direction for the lvt only 15 25 melt is predicted for a 10 1 inclusion instead of the 35 50 of the spherical inclusion

234u 238u ratios and230th ages for hateruma atoll corals implications for coral diagenesis and seawater234u 238u ratios published results for corals that are more than ca 50 ka old from for example barbados and vanuata often yield initial 234u 238u activity ratios that are significantly greater than 1 144 0 004 the value for modern seawater this study reports results for corals from hateruma atoll japan and investigates the effects of diagenesis on the initial 234u 238u ratios of the corals hateruma consists of over 95 reef material of less than 500 ka in age because groundwaters associated with recent carbonates tend not to have elevated 234u 238u ratios the scope for increasing the 234u 238u ratios of hateruma corals through groundwater interaction should be minimal the corals examined range from those which show no petrographic or x ray evidence for diagenetic alteration and are pristine to those containing secondary cements of either aragonite or high or low mg calcite these various phases have been mechanically separated and analysed in agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples it is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial 234u 238u ratios of the six pristine corals three have anomalous 230th 238u ratios requiring u loss and or230th addition the remaining fifteen of the eighteen total analyses reported here yield ages from 1 6 ka to 260 ka no evidence for an increase in 234u 238u ratios in past seawater from this period has been found the best estimates for 234u 238u ratios are close to the current seawater value

fabric changes and their influence on p wave velocity patterns examples from a polyphase deformed orthogneiss abstract the complete p wave velocity distribution preferred orientation of rock forming minerals and microcracks of two differently deformed orthogneisses from the kutna hora crystalline unit were investigated the complete symmetry of p wave velocities were determined as a function of confining pressure on the basis of 132 independent propagation directions up to 400 mpa the two samples are of almost identical mineralogical composition but exhibit different fabrics which can be related to different positions within a large scale fold structure the symmetry of the vp diagrams change from nearly transversely isotropic for the sample from the limb area to orthorhombic for the sample from the hinge zone which shows an additional crenulation cleavage this change of symmetry is observed at all pressure levels reorientation of the main velocity directions vpmin vpmax kpint between hinge and limb is controlled by the microcrack fabric and the texture of the rock forming minerals this can cause significant differences in reflectivity related to fabric changes within large scale folds

an open system model for u series age determinations of fossil corals the source of excess 234u in fossil corals and its relationship to u series age determinations has been an outstanding problem in geochronology for more than 20 years with increasing numbers of u series isotope measurements in corals and significant improvements in analytical precision through mass spectrometry it is increasingly apparent that a substantial fraction of observed isotope ratios cannot be reasonably explained by closed system decay moreover observations of a positive correlation between 234u 238u and 230th 238u ratios in corals from the same terrace are difficult to explain however the decay of dissolved uranium and recoil mobilization of uranium daughters produce particle reactive 234th and 230th and the coupled addition of these th isotopes could simultaneously increase coral 234u 238u and 230th 238u here we present a quantitative model based on decay dependent redistribution of 234th and 230th permitting calculation of open system coral ages these equations provide a general solution to the recoil redistribution problem applicable to any alpha decay series while measured isotope ratios of corals from the three youngest stratigraphically defined barbados terraces are inconsistent with closed system decay they fall in broadly linear arrays agreeing with model predictions isotopic arrays of older barbados corals and corals from terraces around the world are also consistent with model predictions suggesting the open system model is generally applicable corals with extreme isotopic compositions that are impossible to produce by closed system decay are consistent with the limited range of isotopic compositions predicted by the model at ages older than 600 ka for corals from a single terrace 234th and 230th redistribution appears to be a source of systematic conventional age error even for corals with slightly elevated 234u however open system ages are consistent even for corals with extremely elevated 234u for the youngest three barbados terraces mean open system terrace ages are consistent with mean conventional terrace ages calculated from pristine samples if the most accurate conventional ages are from corals with an initial 234u 238u identical to modern seawater then the open system model will improve the accuracy of coral u series age determinations and dramatically increase the number of reliable ages

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

freshwater on the route of hominids out of africa revealed by u th in red sea corals a fundamental issue in the evolution of human culture concerns the route and conditions of anatomically modern hominids during the migration out of africa a particular question is how could anatomically modern hominids cross the hyperarid arabian deserts here we outline the evidence for significant presence of freshwater along the red sea shores during the last interglacial period freshwater caused an extensive recrystallization of coral reefs from aragonite to calcite indicating uplift of the reefs through well developed phreatic freshwater coastal aquifers applying novel open system u th dating methodology to the calcitic corals we dated the freshwater recrystallization to ca 140 ka consistent with other geological lines of evidence placing the migration of anatomically modern hominids out of africa at the onset of the last interglacial

seismic waves velocities and anisotropy in serpentinized peridotites from xigaze ophiolite abundance of serpentine in slow spreading ridge the effect of serpentinization on seismic wave velocity and anisotropy has been analysed in 6 peridotite samples of the xigaze ophiolite having harzburgitic composition and a degree of serpentinization ranging from 3 to 70 we found i p and s wave velocities are linearly correlated with serpentine content ii anisotropy of p and s waves decreases with increasing serpentinization while in fresh peridotites anisotropy is of the order of 6 for 70 of serpentinization it drops to 1 for p waves and to 2 for s waves comparison of published laboratory velocity data in oceanic lithologies like gabbros and dolerites with serpentinized peridotite data shows the difficulty of distinguishing between gabbros and peridotites having a percentage of serpentine between 10 and 40 by seismic waves velocities only this comparison suggests that seismic velocity data are consistent with the existence of partialy serpentinized peridotites up to 40 of serpentinization in the oceanic crust formed at slow spreading ridges in accordance with geological observation

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

pore fluid effects on elastic wave velocities of serpentinite and implications for estimates of serpentinization in oceanic lithosphere abstract recent seismic refraction surveys at various outer rise regions have identified low seismic velocities in the uppermost mantle which is indicative of mantle hydration serpentinization related to water infiltration along bending related faults prior to subduction serpentinization could lead to the development of pore spaces during hydration reaction which influences seismic velocity here we measured the elastic wave velocity of low temperature serpentinites with various porosities and reevaluated the degree of serpentinization of the oceanic mantle in outer rise regions accounting for pore fluid effects experimental results show that the elastic wave velocity of serpentinite decreases with increasing porosity this relationship indicates that the estimated degree of serpentinization decreases with increasing serpentinite porosity we then applied these experimental data to the geophysical observations of the outer rise regions to reevaluate the amount and the type of water carried into earth s interior at subduction systems

silicified serpentinite in the semail nappe of oman abstract the nature and origin of silicified serpentinite in the semail nappe of oman is described and discussed its formation was caused by fracturing of the basal serpentinite by late tectonic events followed by dissolution of serpentine and precipitation of silica under slightly acidic high pco 2 groundwater conditions the source of co 2 was transient and atypical of present day groundwater in the oman environment silicification was restricted to groundwater pathways in wholly serpentinised ultramafic rock elsewhere the process was inhibited by restricted groundwater flow inadequate co 2 concentration and strongly alkaline conditions caused by continuing low temperature serpentinisation a hitherto unexamined paragenesis of associated niccolite mineralisation results from low temperature aqueous precipitation the ni being released by serpentine dissolution whilst the as is leached from the fe oxide hydroxide products of initial serpentinisation

diagenetic effects on the distribution of uranium in live and holocene corals from the gulf of aqaba abstract we investigated the effects of diagenetic alteration dissolution secondary aragonite precipitation and pore filling on the distribution of u in live and holocene coral skeletons for this we drilled into large porites lutea coral heads growing in the nature reserve reef nrr northern gulf of aqaba a site close to the marine biology laboratory elat israel and sampled the core material and porewater from the drill hole in addition we sampled holocene corals and beachrock aragonite cements from a pit opened in a reef buried under the laboratory grounds we measured the concentration and isotopic composition of u in the coral skeletal aragonite aragonite cements coral porewater and open nrr and gulf of aqaba waters uranium concentration in secondary aragonite filling the skeletal pores is significantly higher than in primary biogenic aragonite 17 3 0 6 compared to 11 9 0 3 nmol g 1 respectively this concentration difference reflects the closed system incorporation of uranyl tri carbonate into biogenic aragonite with a u ca bulk distribution coefficient kd of unity versus the open system incorporation into secondary aragonite with kd of 2 4 the implication of this result is that continuous precipitation of secondary aragonite over 1000 yr of reef submergence would reduce the coral porosity by 5 and can produce an apparent lowering of the calculated u ca sst by 1 c and apparent age rejuvenation effect of 7 with no measurable effect on the calculated initial u isotopic composition all modern and some holocene corals with and without aragonite cement from elat yielded uniform 234u 144 5 similar to the gulf of aqaba and modern ocean values elevated 234u values of 180 were measured only in mid holocene corals 5000 yr from the buried reef the values can reflect the interaction of the coral skeleton with 234u enriched ground seawater that washes the adjacent granitic basement rocks we conclude that pore filling by secondary aragonite during reef submergence can produce small but measurable effects on the u ca thermometry and the u th ages this emphasizes the critical importance of using pristine corals where the original mineralogy and porosity are preserved in paleooceanographic tracing and dating

precise determination of the open ocean 234u 238u composition uranium has a long residence time in the open oceans and therefore its salinity normalized u concentration and 234u 238u activity ratio expressed herein as 234u the deviation from secular equilibrium are assumed to be uniform the marine 234u 238u activity ratio is currently in radioactive disequilibrium and shows a 15 excess of 234u with respect to the secular equilibrium value due to continuous input from riverine sources knowledge of the marine 234u and how it has evolved through the quaternary is important for validating age accuracy in the u series dating of marine carbonates which is increasingly relied upon for providing a chronological basis in paleoclimate research however accurate and precise measurements of 234u are technically difficult thus existing compilations of the open ocean 234u value vary by up to 10 and the assumed uniformity in the oceanic 234u remains to be confirmed using mc icpms techniques and a suite of multiple faraday cups instead of the typical configurations based on a combined faraday cup multiplier array a long term reproducibility of better than 0 3 2 is achieved for 234u measurements applying these very high precision techniques to open ocean seawater samples an average 234u of 146 8 0 1 2 m n 19 is obtained these high precision seawater measurements yield an external reproducibility of better than 0 4 2 and show that the open oceans have a uniform 234u on the sub level these new data constrain the vertical mixing time of the open oceans to less than 1000 years

improved constraints on open system processes in fossil reef corals by combined th u pa u and ra th dating a case study from aqaba jordan abstract here we present 230th u 231pa u as well as 226ra 230th isotope ratios from five fossil reef corals of last interglacial origin from the gulf of aqaba northern red sea the results show clear evidence for open system behaviour with strongly elevated 234u values and u concentrations indicating post depositional u addition the combined application of all isotope systems enables us to better constrain the nature and timing of the open system processes than only based on the 230th u data quantitative modelling of the diagenetic processes allowed us to reproduce the trends in the isotope ratios two of the five corals were probably affected by two separate phases of u addition with different 234u values the trends observed for two other corals can be explained by u addition followed by u loss the fifth coral shows signs of both u gain and loss at the same time in the more recent past the timing of the diagenetic processes is remarkably similar for the five corals and can be constrained to approx 1 and 6 thousand years ka and 100 and 102 ka after coral growth respectively based on the modelling results we suggest that conventional 231pa 230th ages provide the best estimate for the true age of four of the five corals which range from 109 1 to 114 1 ka this implies a late last interglacial time of deposition for the fifth coral the most reliable age estimate is the conventional 230th u age of one of the subsamples 117 3 ka based on a concordia diagram for all subsamples the timing of the modelled open system processes suggests that the early event of u addition was associated with interaction of the corals with 234u enriched seawater or saline groundwater the later open system event can be described as u redistribution within the coral reef since some corals apparently lost u while others gained u the timing of the second event is broadly consistent with the bolling allerod interstadial which was probably characterised by enhanced wetness in this typically hyper arid region

structural framework of the gulf of elat aqaba northern red sea the gulf of elat aqaba occupies the southern part of the dead sea rift the rift is considered to be a plate boundary of the transform type partially leaky which connects seafloor spreading in the red sea with the sagros taurus zone of continental collision the deep water in the gulf of elat up to 1850 m provides a rare opportunity to examine the process of continental rifting by marine geophysical techniques the bathymetry alone provides much information about fault patterns in this area the fragmentation of the once continuous arabian african platform is a complicated process it shapes the structure of the gulf which has developed through continuing tectonism primarily consisting of faulting recent geophysical and geological studies of the gulf of elat including bathymetry bottom photographs continuous seismic profiles seismic refraction gravity magnetics heat flow and coring provide new information about the shallow and deep crustal structure of this important segment of the world rift system the shallow structure of the gulf is dominated by three elongated en echelon basins which strike n20 25 e undulations in the floors of the basins produce several distinct deeps these basins are interpreted as pullaparts the new data from the gulf suggest that classical models for the formation of these structures should be modified only one of the longitudinal faults of each depression is a strike slip fault while the other is predominantly a normal fault the situation with the other two sides of the basin which are supposed to be composed of normal faults may also be more complex than previously thought at least in one case one such boundary is composed of a strike slip fault while the other has no significant fault crustal models of the gulf of elat based on gravity data indicate that the basins are rather shallow and do not extend into the lower crust the fill of the basins extends to about 5 km below the seafloor in the northern and southern basins and less in the central basin most significant magnetic anomalies in the gulf of elat extend from land into the sea none of them however extends from one coast to another across the gulf this supports the geological evidence for a shear between the arabia and sinai plates the magnetic field over the southern third of the gulf is rather smooth and markedly different from that of the other parts the nature of the magnetics the crustal structure of the western margin and the heat flow values indicate a thinner crust and different tectonic processes in the southern part of the gulf overall it seems that within the southern gulf of elat a transition occurs between crustal spreading that takes place in the red sea to a rifting without spreading that takes place along the dead sea transform spreading activity propagates from south to north the most active place is the central basin which is being propagated northward into the shallow northern basin

measuring sea surface mean square slope with a 36 ghz scanning radar altimeter values of sea surface mean square slope mss computed from the backscattered power falloff with incidence angle measured by an airborne 36 ghz scanning radar altimeter are presented when the mss values are plotted against the 10 m wind speed extrapolated from the 46 to 110 m aircraft height for wind speeds up to 7 m s 1 the values scatter about a curve which is scaled from that obtained by wu 1990 by a factor of 0 85 wu s result was a reanalysis of the optical measurements of cox and munk 1954 the offset between the microwave and optical curves is reasonable because one would expect the surface to appear smoother to the microwave wavelength than to the optical this is unlike the mss values inferred from absolute power measurements at nadir by 14 ghz satellite altimeters which indicate a higher mss under light wind conditions than the optical measurements indicate for wind speeds below 7 m s 1 the peak of the backscattered power distribution is observed at nadir but for higher speeds the peak shifts off nadir in the downwind direction

daylight imagery of ocean surface waves for wave spectra abstract both surface reflected daylight and upwelling light are modeled to second order to help provide a quantitative and physically interpretable description of daylight imagery of ocean surface waves for wave spectra an image recording of the slope modulated reflected and upwelled radiance can be optically analyzed to provide the surface slope spectrum as a function of wavenumber for a particular patch on the ocean surface sources of error involved in obtaining ocean spectral information from daylight imagery are outlined and methods of alleviating them discussed errors resulting from the nonlinear nature of the transfer function relating wave slope to radiance at the sensor are shown to be minimized using the second order theory in evaluating potential sensor geometries the directional sensitivity of daylight imagery to waves traveling in various directions is also evaluated a modified pierson wave spectrum was used to generate numerically a one dimensional wave slope profile this slope profi

uranium series dating of fossil coral reefs extending the sea level record beyond the last glacial cycle abstract absolutely dated records of past sea level change are extremely important for understanding the advance and retreat of the large ice sheets when combined with other complementary climate archives and climate models such records offer the potential to gain an improved understanding of earth s natural climate cycles providing a firmer basis for assessing the role of anthropogenic effects such as greenhouse gas emissions in modifying climate the u series dating of fossil coral reefs has been widely utilized to provide absolutely dated records of past sea level change and numerous observations now exist for the past 130 000 years spanning the last glacial cycle despite this controversies still exist regarding the exact timing and character of sea level events within this time interval and extending the sea level history further back in time on the basis of robust and independent age constraints for older fossil reefs remains very elusive this is primarily due to a progressive loss in the resolution of the u series chronometer as one goes further back in time coupled to a lack of well preserved dateable coral in older fossil reefs to overcome these limitations the primary challenges are three fold first new analytical protocols are required to improve the resolution of the u series chronometer enhanced analytical precision must be coupled to accuracy through continued refinement of the u series decay constant determinations and via the implementation of rigorous inter laboratory calibration exercises second efforts should continue to be focussed on gaining an improved understanding of the mechanisms controlling open system exchange of the u series isotopes in fossil reef systems this will allow the number of reliable u series observations to be extended third alternative dateable archives of past sea level change must continue to be emphasized to further complement the coral reef database these limitations are discussed in the context of current developments that further advance the application of u series chronology to older fossil reef systems formed prior to the last glacial cycle

ams ultrasonic p wave velocity and rock strength analysis in quartzites devoid of mesoscopic foliations implications for rock mechanics studies abstract in this study anisotropy of magnetic susceptibility ams measurements are made on quartzites that do not contain visible foliations using ams data the magnetic foliation is recognized in the quartzites ultrasonic p wave velocity and point load strength which is a proxy for uniaxial compressive strength are determined in cores drilled parallel as well as perpendicular to the magnetic foliation ultrasonic p wave velocity is greater in the direction parallel to the foliation and lower perpendicular to the same conversely point load strength is lower in the direction parallel to the magnetic foliation and greater perpendicular to it ams data are compared with the anisotropy of p wave velocity as well as rock strength anisotropy it is noted that quartzites with a strong magnetic fabric also have a high p wave velocity anisotropy as well as rock strength anisotropy based on the results usefulness of ams in identification of principal testing directions for rock mechanics investigations in rocks devoid of mesoscopic foliations is discussed

northward intrusions of low and mid latitude storms across the saharo arabian belt during past interglacials the rain regime of the levant during the late quaternary was controlled primarily by mediterranean cyclonic systems associated with north atlantic climate shifts lake levels in the dead sea basin have been robust recorders of the regional hydrology and generally indicate highstand wet conditions throughout glacial intervals and lowstands dry during interglacials however sporadic deposition of travertines and speleothems occurred in the negev desert and arava valley during past interglacials suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid latitude red sea synoptic troughs and or low latitude tropical plumes the southerly incursions of wetness were superimposed on the long term interglacial levantine arid conditions as refl ected by the current prevailing hyperaridity and could have had an important impact on human migration through the red sea dead sea corridor

high precision u series dating of corals from western australia and implications for the timing and duration of the last interglacial abstract u series ages using methods of thermal ionisation mass spectrometry tims are reported for last interglacial fossil reefs along the stable coastal margin of western australia thorium isotope ratios were measured with superior precision using methods of charge collection high levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors excluding the uncertainty in the decay constants by a factor of four over the precisions reported by many earlier tims workers uncertainties in 234u t determined from both 230th 238u and 234u 238u are also significantly smaller than previously reported allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified strict criteria were adopted to screen the new western australian data reliable ages range from 127 to 122 ka published tims observations from other localities have been assessed using the same strict criteria when these are combined with glacio hydro isostatic sea level models they indicate that the last interglacial period occurred from at least 130 to 117 ka however these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the last interglacial globally the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka in direct agreement with the narrow range in ages obtained from the western australian sites this may indicate that the last interglacial was of short duration extending from 127 to 122 ka only alternatively this interval may reflect a major reef building event in the middle of a longer duration 130 117 ka interglacial interval

uranium series dating of marine and lacustrine carbonates of the possible uranium series dating schemes the most important and most widely applied to marine carbonates is 230th dating with 231pa dating playing an increasingly important role for this reason this review will focus on these two methods 230th dating also referred to as u th dating or 238u 234u 230th dating involves calculating ages from radioactive decay and ingrowth relationships among 238u 234u and 230th 232th is also typically measured as a long lived essentially stable index isotope over the time scales relevant to 230th dating at present 230th dating can in principle be used to date materials as young as 3 years and in excess of 600 000 years edwards et al 1987a 1993 edwards 1988 see stirling et al 2001 for an example of dating corals in excess of 600 000 years old 231pa dating also referred to as u pa dating involves calculating ages from the ingrowth of 231pa from its grandparent 235u at present 231pa dating can be used to date materials as young as 10 years and as old 250 000 years edwards et al 1997 230th dating covers all of the 231pa time range and more with somewhat higher precision and is therefore the method of choice if a single method is applied however the combination of 231pa and 230th dating is of great importance in assessing possible diagenetic mobilization of the pertinent nuclides and thereby the accuracy of the ages allegre 1964 ku 1968 even if the primary age exceeds the 250 000 year limit of 231pa dating the combined methods can be used to assess the degree to which the samples have remained closed over the past 250 000 years e g edwards et al 1997 thus

the effect of oriented microcracks on seismic velocities in an ultramylonite the influence of oriented microcracks on the directional dependence of p and s wave velocities has been investigated in an epidote muscovite ultramylonite optical and sem studies revealed that the fabric of the mylonite is characterized by oriented intragranular and grain boundary cracks comparison of orientation patterns of cracks with calculated elastic properties voigt average of a model rock isotropic matrix ultramylonite crack geometry and laboratory seismic data indicates that wave propagation is particularly affected by oriented grain boundary cracks microcracks are most effective at low pressure and largely closed above about 200 300 mpa the residual part of velocity anisotropy observed above this crack closing pressure is mainly due to preferred mineral orientation in particular of mica maximum concentration of poles to 001 mica planes corresponds to the maximum of poles to oriented grain boundary cracks so that the effects of texture and oriented cracks on wave velocities line up giving rise to extreme values of velocity anisotropy and shear wave splitting at low pressure conditions

seismic structural and petrological models of the subcrustal lithosphere in southern germany a quantitative revaluation anisotropy in the subcontinental lithosphere becomes increasingly important because it is observed in many seismic studies especially for p n waves typical rocks of the uppermost mantle are peridotites which predominantly exhibit a pronounced elastic anisotropy this anisotropy is mainly caused by the anisotropic elastic properties and the lattice preferred orientation here referred to as texture of olivine to evaluate the elastic anisotropy of peridotites from the subcontinental lithosphere specimens of the northern hessian depression germany and the balmuccia ultramafic massif northern italy have been used they comprise four olivine texture types which are characteristic for olivine textures observed worldwide the bulk rock elastic properties have been calculated using olivine and orthopyroxene textures their single crystal elastic constants at ambient pressure temperature conditions and their volume fraction clinopyroxene and spinel are assumed to be randomly distributed the effect of four different orientations of the foliation within the uppermost mantle has been evaluated since this orientation is usually unknown two of the olivine textures have a pronounced azimuthal dependence of compressional waves when a horizontal foliation within the uppermost mantle is presumed these variations cause significant azimuthal variations of the p wave reflections coefficients at the moho primarily we predict a significant azimuthal dependence of the critical points where the reflected amplitude increases from approximately 15 to 95 possibly these azimuthal variations can be detected by seismic reflection measurements carried out at earth surface the remaining two texture types only manifest a small directional dependence when anisotropy of compressional waves is observed in seismic studies these latter types can only be of subordinate importance however all of the peridotites investigated are able to explain the seismically observed azimuthal variations of compressional waves when a vertical foliation is proposed this ambiguity can be substantially reduced when shear waves s waves are considered the directional distribution of s wave velocities and of the s wave splitting exhibits characteristic patterns for the different olivine texture types this could be used to discriminate between different texture types and orientations of the foliation within the uppermost mantle a fundamental requirement for a more comprehensive interpretation is the availability of detailed s wave observations the maximum s wave splitting in the peridotites investigated coincides with the maximum of the faster leading s wave this may be of importance to detect s wave splitting in future seismic studies

holocene sea level determination relative to the australian continent u th tims and 14c ams dating of coral cores from the abrolhos islands u th tims and 14 c ams measurements are presented from two coral cores from the easter group of the houtman abrolhos islands between 28 s and 29 s on the western continental margin of australia the u th measurements on the morley core from morley island cover a depth interval from 0 2 m above present sea level to 24 4 m below present sea level and comprise eleven samples the ages vary between 6320 50 a at 0 2 m above sea level and 9809 95 a at 24 4 m below sea level all errors are 2 the mean growth rate is 7 1 0 9 m ka the 14 c dates of selected morley core corals show that the 14 c ages are 1000 a younger than their corresponding u th ages which agrees with previous results the main purpose of our 14 c measurements is to be able to compare them precisely with other coral cores where no u th measurements are available the u th measurements of the suomi core from suomi island cover a depth interval from 0 05 m to 14 2 m below present sea level and consist of four samples the ages vary between 4671 40 a at 0 05 m below sea level and 7102 82 a at 14 2 m below sea level with a mean growth rate of 5 8 0 2 m ka the growth history of both cores is explained by a simple model in which the growth rates of the morley core can be interpreted as reflecting local rates of sea level rise whereas the suomi core is interpreted as reflecting lateral growth during the past 6000 a our results indicate that sea level relative to the western margins of the australian continent was about 24 m lower than present at about 9800 a b p 14 c gives a date of 8500 a b p sea level then rose and reached a highstand slightly higher than the present position at about 6300 a b p 14c date 5500 a this highstand declined but was still higher than present at 4600 a b p this is in agreement with previous observations along the australian coastal margins and with observations from the huon peninsula papua new guinea our results are very similar to theoretical numerical models which take into consideration water loading and isostatic compensation and viscous mantle flow in contrast coral cores from barbados show that corals with a 14 c age of 5500 a b p are some 10 m b p s l we interpret the difference between the barbados core and the morley core as resulting from additional flooding of barbados by water redistribution due to changes in the earth s geoid but not reflecting global sea level rise or major addition of melt waters over the past 6000 a the difference in the geoid at barbados between 6000 a b p and the present will require a refinement in the geophysical models precise 230 th tims measurements on continental coasts will be required to provide an adequate data base for modelling deformation flow of mantle material and sea level height

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

determination of bathymetric and current maps by the method disc based on the analysis of nautical x band radar image sequences of the sea surface november 2007 morphodynamic processes in coastal areas are affected by tidal currents and sea state the continuous observation of near coastal areas is important in order to monitor dangerous current regime and bathymetry changes therefore there is an urgent need for remote sensing techniques delivering the important hydrographic parameters with a high spatial resolution dispersive surface classificator disc is a newly developed method based on the analysis of nautical x band radar image sequences of sea surface waves to determine spatial maps of hydrographic parameters e g spatial maps of the bathymetry and the ocean current field the method disc is described and is illustrated by the presentation of results based on a dataset acquired with a ground based x band radar installation mounted on the island of sylt in the german bight the calculated bathymetric maps are verified by multibeam echo sounder observations

diagenesis in live corals from the gulf of aqaba i the effect on paleo oceanography tracers abstract the effect of early diagenesis on trace element abundance in coral skeleton was studied in live coral heads porites from the nature reserve reef nrr elat gulf of aqaba northern red sea petrography of the corals shows diagenetic features of dissolution recrystallization and secondary aragonite precipitation pore filling which are most extensive in the oldest part of the coral coral porewaters were extracted with a special setup and were analyzed for chemical composition the total alkalinity and sr deficit in pore water as compared to reef water is consistent with both precipitation of secondary aragonite and recrystallization of primary skeleton the present rate constant of pore filling by secondary aragonite was estimated by a water replacement experiment to be 0 0015 y 1 which equals to pore filling rate of 1 5 0 3 kg aragonite per year the corals show clear seasonal fluctuations in sr ca ratios that are interpreted as reflecting changes in sea surface temperature sst yet the secondary aragonite is characterized by a significantly higher sr ca ratio than the average ratio in primary aragonite thus measuring a mixed sample of pristine and secondary aragonite may produce erroneous about 2 c lower sst estimates by the sr ca thermometers it appears that the sr ca ratio a major proxy for paleo environmental marine studies is sensitive to subtle pore filling and replacement of the original coral matrix by secondary aragonite in the marine environment

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

u th dating of calcite corals from the gulf of aqaba abstract most of the fossil corals in the elevated reef terraces along the gulf of aqaba goa were extensively altered to calcite this observation indicates extensive interaction with freshwater possibly when the terraces passed through a coastal aquifer that existed along the shores of the goa implying a wetter climate during the time of recrystallization from aragonite to calcite thus dating of the recrystallization events should yield the timing of past wetter conditions in the current hyper arid area of the goa in the present study 18 aragonite and calcite corals were collected from several elevated coral reef terraces off the coast south of the city of aqaba while aragonite corals were dated with the conventional closed system age equation assuming zero initial th the dating of the calcite corals required the development of adequate equations to allow the calculation of both the initial formation age of the aragonite corals and the time of recrystallization to calcite the two age calculations were based on the assumptions that each reef terrace went through a single and rapid recrystallization event and that the pristine aragonite corals were characterized by a rather uniform initial u concentration typical for pristine modern corals two recrystallization events were identified at 104 6 ka and 124 8 ka the ages coincide with the timing of sapropel events s4 and s5 respectively when the african monsoon induced enhanced wetness in the desert area considering the age uncertainties the times of formation of the two major reef terraces are estimated to be 124 ka reef terrace r2 and 130 ka reef terrace r3 matching the peaks in the global sea level during the last interglacial mis 5e stage apparently sea level of the goa did not fluctuate a lot during the period between 130 ka and 104 ka and remained close to the marine isotopic stage mis 5e highstand the availability of freshwater during the sapropel periods and limited sea level fluctuations facilitated the recrystallization of the goa reef corals to calcite

comparison of airborne synthetic aperture radar imagery with in situ surface slope measurements across gulf stream slicks and a convergent front synthetic aperture radar sar imagery showing two types of features near the inshore edge of the gulf stream are compared with nearly simultaneous estimates of the sea surface slope field derived from optical shipboard measurements one class of feature consists of a set of narrow dark lines having radar signal modulations of about 10 db at l band these modulations are comparable to those observed in the in situ wave slope data over wavenumbers corresponding to the radar resonant bragg waves these modulations are also predicted by a simplified equilibrium wave spectrum model using a surface elasticity of about 25 mn m as determined from in situ measurements of surface tension and a wind friction velocity of about 10 cm s from buoy and shipboard measurements these results support lyzenga and marmorino s 1998 inference that the gulf stream dark lines represent relatively passive biogenically derived surfactant slicks that are advected and strained by the large scale surface flow field the second class of feature consists of a pair of bright dark signatures over the shallow continental shelf region near cape hatteras north carolina these features are characterized by signal modulations of about 4 and 4 db in both the l band sar and in situ data these modulations appear to be due to the interaction of surface waves with the current convergence and divergence regions associated with a rotary circulation in a shallow convergent front model calculations of this interaction by lyzenga 1998 indicate that the positive perturbations associated with current convergence should be relatively independent of the wavenumber which is in approximate agreement with the in situ measurements of the present paper the model also indicates that the negative perturbations associated with the region of current divergence should decrease for wavenumbers higher than l band that trend is observed in the sar data but not in the in situ data which show significant perturbations at higher wavenumbers it is conjectured that this is due to the effects of surfactants and either along front or time variability in the frontal dynamics which are not included in the model additional comparisons of this kind should be useful to further test and improve physical models of near surface phenomena

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

calibration of shear wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska abstract despite the abundance of measurements of shear wave splitting around the world some fundamental questions about its geological interpretation have not yet been answered in order to constrain 1 i the orientation and magnitude of s wave anisotropy 2 ii the thickness of the anisotropic layer and 3 iii the possible variation of the anisotropy with depth in the subcontinental upper mantle beneath active orogenic belts we have carried out a systematic investigation on shear wave properties of mantle xenoliths from recent alkaline basalts of the canadian cordillera and alaska it is found that the polarization direction of the fast s wave as well as the time delay t between the two arrivals are strongly dependent on the propagation direction with respect to the structural frame at a single station the variations of measured and t values for sks phases from different events can result from this dependence because the average grain size of olivine in upper mantle samples is commonly larger than 0 5 mm dislocation creep prevails over a thickness of at least 250 km and results in olivine lpo and hence anisotropy and shear wave splitting a single thick anisotropic layer in mountain parallel subvertical shear zones may cause high values of tgd while multiple subhorizontal layers will produce multiple splitting making the measurement and interpretation of s wave splitting difficult our results also suggest that the s wave splitting observed in cold old stable cratons such as the canadian shield is likely dominated by fossil anisotropy whereas that observed in hot active orogenic regions such as the northwest american cordillera and the tibetan plateau may be dominated by modern tectonic deformation in the lithosphere and flow in the asthenosphere

an examination of fetch limited wave growth off the west coast of new zealand by a comparison with the jonswap results abstract a long term wave recording program based on the west coast of new zealand has allowed a number of fundamental properties of the ocean wave field to be studied this paper deals with wave generation processes and in particular compares the spectral properties of fetch limited seas with those found in the jonswap and other northern hemisphere studies

seismic wave velocity and anisotropy of serpentinized peridotite in the oman ophiolite shallow seismic measurements in harzburgite from the oman ophiolite performed in a zone where the maximum horizontal anisotropy is expected vertical foliation and horizontal lineation point to a dominant dependence of seismic properties on fracturing optical microscopy studies show that microcracks are guided by the serpentine lizardite penetrative network oriented subparallel to the harzburgite foliation and subperpendicular to the mineral lineation and that serpentine lizardite vein filling has a maximum concentration of 001 planes parallel to the veins walls the calculated elastic properties of the oriented alteration veins filled with serpentine in an anisotropic matrix formed by oriented crystals of olivine and orthopyroxene are compared with seismic velocities measured on hand specimens laboratory ultrasonic data indicate that open microcracks are closed at 100 mpa pressure e g j geophys res 65 1960 1083 and proc odp sci results leg 118 1990 227 above this pressure laboratory measurements and modeling show that p compressional and s shear wave velocities are mainly controlled by the mineral preferred orientation veins scaled with serpentine are effective in slightly lowering p and s velocities and increasing anisotropy the penetrative lizardite network does not affect directly the geometry of seismic anisotropy but contributes indirectly in the fact that this network controls the microcrack orientations comparison between seismic measurements of peridotite and gabbro in the same conditions suggest that p and s waves anisotropies are a possible discriminating factor between the two lithologies in the suboceanic lithosphere c 2003 published by elsevier b v

wave spectrum retrieval from airborne sunglitter images abstract reconstruction and evolution of two dimensional spectra of surface waves in the gulf of mexico are derived from airborne sun glitter imagery as the proposed method is based on a linear transfer function deduced from the shape of the sunglitter brightness the absolute wavenumber elevation spectrum does not require any additional assumption or information about sky brightness wind or wave energy the detailed description of the airborne image processing method is given as demonstrated retrieved spectra agree well with nearby ndbc buoy data both for spectrum shape level and energy angular distribution the 180 degree wave direction ambiguity inherent to image derived spectra is eliminated by using cross correlation analysis between two consecutive images a case study corresponding to the spectral evolution with increasing distance from shore in slanting fetch conditions is then considered energy level and peak position transformation are consistent with established approximations and laws of wind sea development the technical requirements flight altitude image resolution view angles etc and applicability of the suggested methodology are also discussed these results demonstrate the potential efficiency of high resolution sea state monitoring from drones or light aircrafts using sunglitter imagery

aragonite to calcite transformation during fresh water diagenesis of carbonates insights from pore water chemistry dissolved strontium and calcium concentrations in fresh water lenses fwl and associated mixing zones mz on two small holocene ooid sand islands in the schooner cays bahamas were monitored during a 1 yr period to quantitatively analyze the transformation of aragonite to calcite the observed characteristics of this mass transfer are functions of climate and hydrology aragonite to calcite transformation in all hydrologic zones is primarily associated with meteoric recharge the transformation occurs throughout the fwl and in the mz to relative salinities of 19 and 36 sea water on the two islands rates of transformation are rapid in all zones and are greatest in the fwl a limestone composed of 100 calcite should form from an aragonite precursor within 4 700 to 15 600 yr in the fwl and within 8 700 to 60 000 yr in the upper mz efficiencies of transformation can vary between hydrologic zones due to pco2 effects yet the efficiency of the entire system fwl mz is high 87 this indicates that most caco3 derived from aragonite dissolution is reprecipitated as calcite somewhere in the fresh water system or upper mixing zone co2 effects fresh water sea water mixing and the differing solubilities between aragonite and calcite all drive the mass transfer the latter is the most significant accounting for up to nine times more mass transfer than co2 effects and at least ten times more mass transfer than fresh water sea water mixing differing solubilities should also cause mass transfer to occur throughout the hydrologic cycle but it apparently becomes ineffective after the rainy season possibly due to the inhibition of calcite precipitation

hydro climate research of the late quaternary of the eastern mediterranean levant region based on speleothems research a review abstract the eastern mediterranean em levant region is the eastern borderland of the eastern mediterranean sea ems the ems brings mediterranean climate zones to the immediate coastal region and hinterland but away from the influence of the ems the region rapidly becomes a desert paleoclimate evidence derived from a large number of studies on speleothems from caves located along sharp climatic gradients enables deep insight into the climate in the em levant region growth periods and isotopic composition of speleothems from the various climate regimes capture the regional signals of temperature rainfall amount and vegetation speleothems from northern and central israel grew continuously in areas where present day annual rainfall is 400 500 mm and show that water was always available during glacials and interglacials these speleothems display a well defined 18o orbital modulation of glacial and interglacial marine isotope stages mis and show good correlations with the ems marine records pointing to strong direct sea land links the climatic record indicates relatively drier and cooler glacials but extreme wet peaks during interglacials mainly mis 5e between 128 120 ka bp pluvial conditions penetrated to the northern central and southern negev desert the present day climatic gradient between the different climatic regions existed through interglacials however growth periods of speleothems from the northern negev desert from the rain shadow desert and the dead sea basin suggest that during last glacial the desert boundary moved from its interglacial and present day position 30 km farther south and 60 km farther east due to positive water balance

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

last interglacial sea levels and regional tectonics from fossil coral reefs in the northeast gulf of aqaba abstract elevated reef terraces in the northeast gulf of aqaba goa constrain the history of tectonic uplift and local relative sea level changes during the last interglacial period these relative sea level changes were inferred from measured elevations coupled with u th ages of aragonite precipitation and recrystallization to calcite all studied reef terraces were formed and the corals comprising them were recrystallized from aragonite to calcite when sea level was at or close to its stable mis5e elevation a few meters above the modern goa level the terraces comprise fringing reefs some with clear reef structure consisting of a reef flat and a shallow back lagoon accurately marking sea levels at low tide terrace r3 probably formed at the earlier stage of mis5e at 130 132 ka and recrystallized to calcite at 124 8 ka terrace r2 comprising a wide and developed reef flat formed during the stable sea level of peak mis5e at 129 121 ka and was recrystallized to calcite at 104 6 ka terrace r1 formed during a short still stand at 117 3 ka the recrystallization age of terrace r2 implies that at around 104 6 ka mis5c sea level was close to its mis5e elevation the elevation and ages of the reef flats indicate a slow average uplift 0 13 0 05 m kyr similar to rates inferred for other last interglacial reef terraces along goa and the red sea this suggests an overall long term slow uplift of the arabian lithosphere at the flanks of the dead sea transform during the late quaternary

230th u dating of last interglacial brain corals from bonaire southern caribbean using bulk and theca wall material abstract we compared the suitability of two skeletal materials of the atlantic brain coral diploria strigosa for 230th u dating the commonly used bulk material comprising all skeletal elements and the denser theca wall material eight fossil corals of presumably last interglacial age from bonaire southern caribbean sea were investigated and several sub samples were dated from each coral for four corals both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232th content and 230th 238u ratios the bulk material samples of another coral show younger ages and lower 230th 238u ratios than the corresponding theca wall samples this coral also contains a considerable amount of 232th the application of the available open system models developed to account for post depositional diagenetic effects in corals shows that none of the models can successfully be applied to the bonaire corals the most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set comparison of the theca wall and bulk material data enables us to obtain information about the open system processes that affected the corals the corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary detrital phase the most likely source of the detrital material is carbonate sand the higher 230th 232th ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk earth 230th 232th ratio and that the threshold for the commonly applied 232th reliability criterion would be much lower than the generally used value of 1 ng g 1 the coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process a potential scenario is a combination of detrital contamination and u addition by secondary pore infillings our results show that the dense theca wall material of d strigosa is generally less affected by post depositional open system behaviour and better suited for 230th u dating than the bulk material this is also obvious from the fact that all ages of theca wall material reflect a last interglacial origin 125 ka whereas the bulk material samples are either substantially older or younger however for some corals the 230th u ages and activity ratios of the bulk material and the theca wall samples are similar this shows that strictly reliable 230th u ages can also be obtained from bulk material samples of exceptionally well preserved corals however the bulk material samples more frequently show elevated activity ratios and ages than the corresponding theca wall samples our findings should be generally applicable to brain corals mussidae that are found in tropical oceans worldwide and may enable reliable 230th u dating of fossil corals with similar skeletal architecture even if their bulk skeleton is altered by diagenesis the 230th u ages we consider reliable 120 130 ka along with a recently published age of 118 ka provide the first comprehensive dating of the elevated lower reef terrace at bonaire 118 130 ka which is in agreement in timing and duration with other last interglacial records

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

low wave velocity and high electrical conductivity layer of serpentine a compilation serpentine is formed by hydrothermal metasomatism and may penetrate into the deep crust or mantle of the earth it is considered to be the water resource of the mantle owing to its high water content and high temperature decomposition 600 900 c in some geological settings it has low wave velocity lower than that of the surrounding rocks and high electrical conductivity higher than that of the surrounding rocks which are the universal physical and geological properties of serpentine found across continents on earth studying the properties of this layer in particular the wave velocity and electrical conductivity contributes to a more in depth understanding of the mid lower crust or mantle of the earth it is also helpful for exploring the mechanism of seismicity owing to the relationship of this layer with the earthquake center location in subduction zones the stability of serpentine is a factor affecting seismicity in this study the wave velocity and electrical conductivity data for serpentine together with temperature and pressure have been collated from previous studies some of these studies provide more comprehensive results and others provide new conclusions overall the findings showed that a low wave velocity and high electrical conductivity layer can be found in serpentine under suitable geological settings details of the driving mechanism behind seismicity in subduction zones are also shown

relationships between lake level changes and water and salt budgets in the dead sea during extreme aridities in the eastern mediterranean abstract thick halite intervals recovered by the dead sea deep drilling project cores show evidence for severely arid climatic conditions in the eastern mediterranean during the last three interglacials in particular the core interval corresponding to the peak of the last interglacial marine isotope stage 5e or mis 5e contains 30 m of salt over 85 m of core length making this the driest known period in that region during the late quaternary this study reconstructs dead sea lake levels during the salt deposition intervals based on water and salt budgets derived from the dead sea brine composition and the amount of salt in the core modern water and salt budgets indicate that halite precipitates only during declining lake levels while the amount of dissolved na and cl accumulates during wetter intervals based on the compositions of dead sea brines from pore waters and halite fluid inclusions we estimate that 12 16 cm of halite precipitated per meter of lake level drop during periods of halite precipitation the mg2 concentration increases and the na cl ratio decreases in the lake our calculations indicate major lake level drops of 170 m from lake levels of 320 and 310 m below sea level mbsl down to lake levels of 490 and 480 mbsl during mis 5e and the holocene respectively these lake levels are much lower than typical interglacial lake levels of around 400 mbsl these lake level drops occurred as a result of major decreases in average fresh water runoff to 40 of the modern value pre 1964 before major fresh water diversions reflecting severe droughts during which annual precipitation in jerusalem was lower than 350 mm y compared to 600 mm y today nevertheless even during salt intervals the changes in halite facies and the occurrence of alternating periods of halite and detritus in the dead sea core stratigraphy reflect fluctuations between drier and wetter conditions around our estimated average the halite intervals include periods that are richer and poorer in halite indicating based on the sedimentation rate that severe dry conditions with water availability as low as 20 of the present day continued for periods of decades to centuries and fluctuated with wetter conditions that spanned centuries to millennia when water availability was 50 100 of the present day these conclusions have potential implications for the coming decades as climate models predict greater aridity in the region

serpentinization of mantle derived peridotites at mid ocean ridges mesh texture development in the context of tectonic exhumation at slow spreading ridges axial detachment faults exhume mantle derived peridotites and hydrothermal alteration causes serpentinization in a domain extending more than 1 km next to the fault at the microscopic scale serpentinization progresses from a microfracture network toward the center of olivine relicts and forms a mesh texture we present a petrographic study sem ebsd and raman of the serpentine mesh texture in a set of 278 abyssal serpentinized peridotites from the mid atlantic and southwest indian ridges we show that serpentinization initiated along two intersecting sets of microfractures that have consistent orientations at the sample scale and in at least one studied location at the 100 m scale we propose that these microfractures formed in fresh peridotites due to combined thermal and tectonic stresses and subsequently served as channels for serpentinizing fluids additional reaction induced cracks developed for serpentinization extents 20 the resulting microfracture network has a typical spacing of 60 m but most serpentinization occurs next to a subset of these microfractures that define mesh cells 100 400 m in size apparent mesh rim thickness is on average 33 19 m corresponding to serpentinization extents of 70 80 published laboratory experiments suggest that mesh rims formation could be completed in a few years i e quasi instantaneous at the plate tectonic timescale the depth and extent of the serpentinization domain in the detachment fault s footwall are probably variable in time and space and as a result we expect that the serpentine mesh texture at slow spreading ridges forms at variable rates with a spatially heterogeneous distribution

penultimate deglacial sea level timing from uranium thorium dating of tahitian corals the timing of sea level change provides important constraints on the mechanisms driving earth s climate between glacial and interglacial states fossil corals constrain the timing of past sea level by their suitability for dating and their growth position close to sea level the coral derived age for the last deglaciation is consistent with climate change forced by northern hemisphere summer insolation nhi but the timing of the penultimate deglaciation is more controversial we found by means of uranium thorium dating of fossil corals that sea level during the penultimate deglaciation had risen to 85 meters below the present sea level by 137 000 years ago and that it fluctuated on a millennial time scale during deglaciation this indicates that the penultimate deglaciation occurred earlier with respect to nhi than the last deglacial beginning when nhi was at a minimum

serpentine mineral replacements of natural olivine and their seismic implications oceanic lizardite versus subduction related antigorite we report on microstructural data obtained by optical microscopy and transmission electron microscopy concerning the crystallographic relationships of serpentine minerals with their host olivine in two contrasting situations in the first case mesh textured lizardite liz is developed in a standard 60 serpentinized oceanic harzburgite from the oman ophiolite where olivine converts to columnar lizardite the joined columns are perpendicular to the basal plane 001 liz corresponding to the pseudofibres observed optically the plane 001 liz is locally parallel to the narrow boundary ol liz thus column orientations register the interface of serpentinization the ol liz relationships are not strictly topotactic but reflect preferred cracking orientations in olivine parallel to 010 ol in the second case antigorite atg develops in a rare sample of antigorite schist in a kimberlite from moses rock colorado plateau representative of a suprasubduction zone mantle wedge high resolution transmission electron microscopy hrtem images along 010 atg show domains of very regular modulation with a 43 center dot 5 a wavelength m 17 where m is the number of silicate tetrahedra along the wave with few defects indicative of hp ht antigorite and also heavily kinked regions as fingerprints of strong tectonic shear tem imaging and electron diffraction patterns reveal two topotactic relationships between antigorite and olivine 100 atg 010 ol and atg ol the planes in contact are 001 atg 100 ol and 001 atg 010 ol respectively the 010 atg 001 ol and antigorite lamellae are parallel to the forsterite b axis in both cases the topography of olivine serpentine interfaces is controlled by open fluid pathways along microcracks oriented according to the anisotropy of the olivine aggregate in the cases studied the serpentine aggregate exhibits a preferred orientation inherited from that of the peridotite these results have some relevance to the seismic anisotropy of serpentinized mantle anisotropy of propagation of seismic waves as a result of the olivine fabric is maintained and reinforced with the development of lizardite conversely the development of antigorite produces a trench parallel fast s wave polarization and an anisotropy that is lowered at low degrees of serpentinization and then increased with increasing serpentinization

structural features of the subducting slab beneath the kii peninsula central japan seismic evidence of slab segmentation dehydration and anisotropy 1 seismic evidence of lithospheric slab segmentation dehydration and anisotropic rocks beneath the kii peninsula central japan is detected with receiver function rf analyses by stacking radial and transverse rfs with moveout perturbations we estimate the downdip azimuth dip angle and depth of the slab moho beneath each seismic station comparing the downdip azimuth to the slab convergence azimuth we can classify the slab into three segments the segments correspond to both the fault zones of past megathrust earthquakes and to the spatial distribution of intraslab seismicity the slab moho lies just above the intraslab seismicity in the southwestern kii peninsula slab moho lies deeper at the eastern part of the peninsula at the bottom of seismicity this suggests that earthquakes occur only within the slab mantle under the southern kii peninsula the dip angle of slab moho becomes steeper at 40 to 50 km depth perhaps caused by dehydration transformation of basalt to eclogite at some stations located in the western part of the kii peninsula rf estimated dip angle of the interface is much steeper than that estimated by spatial trends in seismicity since the local seismicity distribution reflects well the larger scale geometry of the slab the rf estimated dip angle may imply anisotropic wave speeds within strongly sheared and or hydrated media around the slab moho these detailed features of the slab may be one key in distinguishing the source regions of megathrust earthquakes in the nankai region

coral reefs and sea level change abstract coral reefs provide significant evidence for former sea level positions because of their geological preservation and suitability for dating interpretation of this evidence presumes an understanding of reef geomorphology modern reef organism distributions and environmental factors influencing them fossil reef terraces formed during the last interglacial marine oxygen isotope mis substage 5e 128 116 ka are prevalent on many tropical shorelines and there has been ongoing debate as to the height reached by sea level during that highstand observations from numerous last interglacial sites suggest that sea level was at least 3 m above present sea level implying less extensive icesheets than at present an elevation of 6 m has commonly been adopted when correcting tectonically active sites for uplift recent compilations suggest elevations up to 8 9 m but incorporate few observations from reefs where the last interglacial is found below sea level oscillation of sea level during mis 5e has been interpreted from several sites with recent studies inferring rapid rise of several metres at the end of the interglacial these interpretations are at the limits to the precision with which corals can currently be dated and their palaeo water depths inferred it is not surprising that constraining last interglacial sea level changes within uncertainties of less than 1 2 m remains controversial considering sea level variations recognised between reef sites in the holocene and observed geographical variation in isostatic or flexural adjustments fossil coral reefs on uplifting margins also provide clear evidence for mis substages 5c and 5a and those on huon peninsula indicate fluctuations related to heinrich events mis 3 interpretations show considerable variability between sites with still greater uncertainties about sea level timing and elevation during previous interglacials future study of extensive sequences of fossil reefs preserved on rapidly subsiding margins could address these uncertainties submerged reefs have already yielded important information about sea level rise during the last deglaciation coring around barbados and tahiti as well as on the huon peninsula has produced a broadly consistent picture of ice melt reflecting eustatic change since the last glacial maximum these studies have shown the sensitivity of reefs to rapid sea level rise associated with meltwater pulses with some reefs drowning while others back stepped integrated ocean drilling program iodp expeditions to tahiti and recently the great barrier reef extended these records but details of timing nature and impact of deglacial meltwater pulses remain elusive studies of holocene reefs have indicated different growth strategies some kept up with sea level while others caught up when sea level decelerated holocene sea level appears to have experienced a gradual rise up to present across the caribbean providing accommodation space for reefs to accrete vertically whereas in the indo pacific sea level has been near its present level since 7 ka with many reef flats emergent following a slight fall of sea level caused by ocean siphoning microatolls on reef flats provide perhaps the clearest evidence of past sea level position but in their absence novel biological or other sea level indicators are required to better constrain palaeo water depths there is an urgent need for further research from additional key reef locations not only to decipher processes driving past sea level change and its geographical variability but also to better understand how coral reefs will respond in the context of future sea level rise

imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data a synergetic approach for quantitative analysis of high resolution ocean synthetic aperture radar sar and imaging spectrometer data including the infrared ir channels is suggested this approach first clearly demonstrates that sea surface roughness anomalies derived from sun glitter imagery compare very well to sar roughness anomalies as further revealed using these fine resolution similar to 1 km observations the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature sst field to quantitatively interpret sar and optical in visible and ir ranges images equations are derived to relate the surface roughness signatures to the upper ocean flow characteristics as developed a direct link between surface observations and divergence of the sea surface current field is anticipated from these satellite observations intense cross frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the sst field as a plausible mechanism it is suggested that interactions of the wind driven upper layer with the quasi geostrophic current field via ekman advective and mixing mechanisms result in the generation of secondary ageostrophic circulation producing convergence and divergence of the surface currents the proposed synergetic approach combining sst sun glitter brightness and radar backscatter anomalies possibly augmented by other satellite data e g altimetry scatterometry ocean color can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence divergence upwelling downwelling this in turn establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two dimensional satellite surface expressions