controls on the 87sr 86sr composition of seawater from the middle eocene to oligocene hole 689b maud rise antarctica a 87sr 86sr isotope curve of the middle eocene to oligocene was produced from analysis of foraminifera in ocean drilling program hole 689b maud rise near the coast of antarctica sediments from the hole are well preserved with no evidence of diagenetic alteration the sequence is nearly complete from 46 3 to 24 8 ma with an average sampling interval of 166 kyr excellent magnetostratigraphy in hole 689b allows calibration to the geomagnetic polarity time scale of cande and kent 1992 marine strontium isotopic ratios were nearly stable from 46 3 to 35 5 ma averaging near 0 70773 after which they began to increase a slow increase began after 40 4 ma rising at a rate of only about 8 10 6 m y from base values of 0 707707 from 35 5 ma to 24 8 ma the average slope increased to 40 10 6 m y the slope remained constant at least until 24 8 ma when the record becomes discontinuous owing to unconformities we evaluate several possible controls on the marine strontium isotope curve that could have led to the observed growth in 87sr 86sr ratios near the eocene oligocene boundary three mechanisms are considered including the onset of antarctic glaciation increased mountain building in the himalayan tibetan region and decreased hydrothermal activity none of the mechanisms alone seems to adequately explain the increased 87sr 86sr ratios during the oligocene glaciation as a weathering agent was too episodic and probably began too late to explain the upturn in marine 87sr 86sr ratios there is evidence that uplift in the himalayan tibetan region began in the miocene much too late to control oligocene strontium isotope ratios lastly hydrothermal flux changes since the eocene were apparently not great enough alone to account for the rise in marine 87sr 86sr ratios we suggest that a combination of causes such as decreased hydrothermal activity perhaps followed by increased glaciation and mountain building might best explain the growth of the marine 87sr 86sr curve during the oligocene

a young multilayered terrane of the northern mare imbrium revealed by chang e 3 mission china s chang e 3 ce 3 spacecraft touched down on the northern mare imbrium of the lunar nearside 340 49 e 44 12 n a region not directly sampled before we report preliminary results with data from the ce 3 lander descent camera and from the yutu rover s camera and penetrating radar after the landing at a young 450 meter crater rim the yutu rover drove 114 meters on the ejecta blanket and photographed the rough surface and the excavated boulders the boulder contains a substantial amount of crystals which are most likely plagioclase and or other mafic silicate mineral aggregates similar to terrestrial dolerite the lunar penetrating radar detection and integrated geological interpretation have identified more than nine subsurface layers suggesting that this region has experienced complex geological processes since the imbrian and is compositionally distinct from the apollo and luna landing sites

pitfalls in gpr data interpretation differentiating stratigraphy and buried objects from periodic antenna and target effects periodic events in ground penetrating radar gpr data may result from antenna and target effects rather than reflections from geologic features one of the most common pitfalls in gpr data interpretation is to identify each event on a radar cross section as scattering from a discrete horizon without considering other possible sources of these events soil electrical properties and surface roughness affect ground penetrating radar antenna radiation and waveform characteristics an impedance mismatch occurs over soils with electrical properties different than those for which the antennas were designed to perform optimally over and results in periodic ring down which can be misinterpreted as stratigraphy or multiple reflections in addition target resonance can introduce additional periodic features that can lead to misinterpretation in regards to the number of targets present co pole and cross pole antenna configurations can be combined with polarization dependent scattering characteristics of subsurface objects to recognize and reduce antenna ring down for improved imaging and interpretation

sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

the subsurface structure on the ce 3 landing site lpr ch 1 data processing by shearlet transform the lunar penetrating radar lpr carried by chang e 3 ce 3 mission is an important application of radar in lunar exploration an opportunity of significance to detect the information of regolith and the subsurface structure on the landing site is offered by lpr aboard the yutu rover on the basis of a data processing flow a low frequency radar image has been available for mapping subsurface structure the noise interfered data give a huge challenge for geological stratification and interpretation to solve the limitation imposed by noise we adopt the shearlet transform as a promising tool for data analysis and noise attenuation the different distributions of the noise and signal in the shearlet domain decrease the difficulty of noise attenuation to optimize the denosing strategy we replace a local adaptive thresholding function with the conventional hard threshold the quality of the processed data is improved which is helpful for geological stratification and interpretation finally by combining these data with the regional geology and previous research especially the lpr data we can provide an interpretation of the lpr ch 1

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

on the cenozoic oceans evidence of the calcium carbonate content δ13c and δ18o abstract the present pattern of the vertical circulation of the oceans was established c 6 2 ma ma million years ago the vertical circulation in the north atlantic was intensified at the onset of the northern glaciation c 2 4 ma as well as during each of the following glaciations particularly during the last three elsterian saalian and weichselian the last two interglacials eemian and holocene were probably cooler than those prior to the saalian it is suggested that the northern glaciations resulted from the opening of the bering strait which started the fresh water cycle atlantic n pacific arctic ocean n atlantic this inflow together with river water created the salinity stratification in the arctic ocean the prerequisite for a sea ice cover there the albedo change produced the temperature drop necessary to initiate glaciations the fixture of the greenland ice sheet probably during the saalian has resulted in an intensified vertical circulation of the oceans prior to 6 2 ma the southern ocean was the only source of deep water at the eocene oligocene transition there was a drastic change in the ocean circulation caused by the cooling from the ice sheet which then formed over eastern antarctica the 13 c is useful for tracing the source and the paths of deep water the 18o in pre quaternary sequences is greatly influenced by a non constant 18 o of the sea water caused by the water circulation through the oceanic crust

a revision of blight s model of field vane testing vane shear test data obtained by a number of researchers show that the excess pore pressures generated within the soil surrounding the vane by vane insertion and rotation and their effects on the m

variations in the strontium isotope composition of seawater during the paleocene and early eocene from odp leg 208 walvis ridge we refined the strontium isotope seawater curve for the paleocene and early eocene by analysis of samples recovered from the walvis ridge during ocean drilling project odp leg 208 the highest sr 87 sr 86 values occurred in the earliest paleocene at similar to 65 ma and generally decreased throughout the paleocene reaching minimum values between 53 and 51 ma in the early eocene before beginning to increase again at similar to 50 ma a plausible explanation for the sr 87 sr 86 decrease between 65 and 51 ma is increased rates of hydrothermal activity and or the eruption and weathering of large igneous provinces e g deccan traps and north atlantic strontium isotope variations closely parallel sea level and benthic delta o 18 changes during the late paleocene and early eocene supporting previous studies linking tectonic reorganization and increased volcanism to high sea level high co2 and warm global temperatures

volcanic eruptions on mid ocean ridges new evidence from the superfast spreading east pacific rise 17 19 s uniform sediment cover were recovered from lava that buries older faulted terrain the boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector consistent with magmas from two separate reservoirs being erupted in the same event chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments a comparison of our results to global data on submarine mid ocean ridge eruptions suggests consistent dependencies of erupted volume activated fissure lengths and chemical heterogeneity with spreading rate consistent with expected eruptive characteristics from ridges with contrasting thermal properties and magma reservoir depths index terms 3035 marine geology and geophysics midocean ridge processes 8414 volcanology eruption mechanisms 8439 volcanology physics and chemistry of magma bodies 3655 mineralogy and petrology major element composition keywords lava flow chemical heterogeneity erupted volume lava morphology side scan sonar

a 6 year time series of hydrothermal plumes over the cleft segment of the juan de fuca ridge the causal links between magmatic tectonic processes and hydrothermal venting along the mid ocean ridge axis will be difficult to discern without broadband observations of the temporal variability of hydrothermal activity i report here on temporal variability in the intensity and distribution of chronic and event plumes generated by continuous and episodic hydrothermal discharge at two vent fields on the cleft segment of the juan de fuca ridge hydrothermal temperature and light attenuation c anomalies were comprehensively mapped between 1 and 4 times per year during nine cruises from 1986 to 1991 intensity of and c in the chronic plume overlying the north cleft vent field showed more variability between years than within a given year both and c were exceptionally high in 1986 fell to moderate levels during 1988 to 1990 and declined to minimum values in 1991 the chronic plume over the south cleft vent field varied similarly superimposed on the chronic plumes were brief and intense releases of hydrothermal fluid that created event plumes distinguishable by their symmetry and exceptional rise height event plumes at the north cleft field ranged from the 1986 megaplume with a rise height exceeding 1000 m to smaller events in 1987 and 1989 with rise heights of 400 m chronic hydrothermal heat 660 277 1 mw and mass 204 86 1 g s 1 fluxes from the north cleft field were determined by assuming these fluxes were equivalent to the long term net advection of a mean cross section of the vertically integrated and c in the plume this 6 year history of hydrothermal plumes indicates that episodic discharge has been an important component of the recent hydrothermal flux and that the aggregate heat and mass fluxes declined significantly though not consistently between 1986 and 1991

pitfalls in gpr data interpretation false reflectors detected in lunar radar cross sections by chang e 3 chang e 3 ce 3 has been the first spacecraft to soft land on the moon since the soviet union s luna 24 in 1976 the spacecraft arrived at mare imbrium on december 14 2013 and the same day yutu lunar rover separated from lander to start its exploration of the surface and the subsurface around the landing site the rover was equipped among other instruments with two lunar penetrating radar systems having a working frequency of 60 and 500 mhz the radars acquired data for about two weeks while the rover was slowly moving along a path of about 114 m at navigation point n0209 the rover got stacked into the lunar soil and after that only data at a fixed position could be collected the low frequency radar data have been analyzed by different authors and published in two different papers which reported totally controversial interpretations of the radar cross sections this paper is devoted to resolve such controversy by carefully analyzing and comparing the data collected on the moon by yutu rover and on earth by a prototype of lpr mounted onboard a model of the ce 3 lunar rover such analysis demonstrates that the deep radar features previously ascribed to the lunar shallow stratigraphy are not real reflectors rather they are signal artifacts probably generated by the system and its electromagnetic interaction with the metallic rover

evidence of an effect of heat flux from the east pacific rise upon the characteristics of the mid depth waters on an isopycnal surface that lies at mid depth in the south pacific ocean there is a zone of high temperature near 10 s 20 s heat flux into the water from the crest of the east pacific rise and westward flow of the heated water may account for this temperature pattern

volcanic mound fields on the east pacific rise 16 19 s low effusion rate eruptions at overlapping spreading centers for the past 1 myr 1 volcanic mound fields identified on seamarc ii and hmr1 12 khz side scan data from the southern east pacific rise sepr occur near overlapping spreading centers oscs and migration traces of oscs the volcanic mound fields appear as a distinctive hummocky seafloor fabric due to side scan backscatter reflections from clusters of mound shaped reflectors the lack of growth of the mound fields away from the ridge axis and their occurrence in association with osc traces suggests that mound fields form along the ridge crest near oscs volcanic mound fields are found where 120 khz side scan and visual observations find fields of pillow mounds since pillow mounds are constructed by low effusion rate eruptions the volcanic mound fields found near the oscs and in their migration traces indicate that volcanic effusion rates tend to be lower near ridge discontinuities than midsegment regions this tendency for low effusion rate eruptions at oscs is documented for the past 1 myr three independent measurements of ridge segmentation 1 volcanic segment boundaries marked by the low effusion rate eruptions 2 tectonic segments defined by oscs and 3 magmatic segment boundaries based on continuity of parental magma composition all coincide in the study area high backscatter off axis lava fields not associated with seamounts are found on seafloor younger than 0 2 ma the 0 2 ma corridor corroborates previous results from the distribution of small isolated volcanoes that indicates randomly distributed off axis eruptions mainly occur on crust younger than 0 2 ma

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

piston core record of late paleogene 31 ma to recent seafloor hydrothermal activity in the southwest pacific basin a large diameter piston core containing 8 35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote southwest pacific basin 31 42 194 s 143 30 331 w 5082 m water depth providing unique insight into hydrothermal activity and eolian sedimentation there since the early oligocene a combination of fish teeth sr isotope stratigraphy and inaa geochemical data reveals an exponentially decreasing hydrothermal flux 31 ma to the present although hydrothermal sedimentation related to seafloor spreading explains this trend a complex history of late eocene early oligocene ridge jumps propagating rifts and plate tectonic reorganization of south pacific seafloor could have also played a role a possible hiatus in deposition as recorded by changes in core composition just below 2 m depth is beyond the resolution of the fish teeth sr isotope dating method employed here however the timing of this interval may be coincident with extinction of the pacific farallon ridge at 20 ma a low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth consistent with dust generating continental sources far to the west australia new zealand this is the first long term paleoceanographic record obtained from within the south pacific bare zone rea et al 2006 an anomalous region where pacific seafloor has largely escaped sediment accumulation since the late cretaceous

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

the mid cretaceous super plume carbon dioxide and global warming carbon dioxide releases associated with a mid cretaceous super plume and the emplacement of the ontong java plateau have been suggested as a principal cause of the mid cretaceous global warming the authors developed a carbonate silicate cycle model to quantify the possible climatic effects of these co sub 2 releases utilizing four different formulations for the rate of silicate rock weathering as a function of atmospheric co sub 2 they find that co sub 2 emissions resulting from super plume tectonics could have produced atmospheric co sub 2 levels from 3 7 to 14 7 times the modern pre industrial value of 285 ppm based on the temperature sensitivity to co sub 2 increases used in the weathering rate formulations this would cause a global warming of from 2 8 to 7 7c over today s global mean temperature altered continental positions and higher sea level may have been contributed about 4 8c to mid cretaceous warming thus the combined effects of paleogeographic changes and super plume related co sub 2 emissions could be in the range of 7 6 to 12 5c within the 6 to 14c range previously estimated for mid cretaceous warming co sub 2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20 of the mid cretaceous increase in atmospheric co sub 2

hafnium isotope stratigraphy of ferromanganese crusts a cenozoic record of hafnium isotopic compositions of central pacific deep water has been obtained from two ferromanganese crusts the crusts are separated by more than 3000 kilometers but display similar secular variations significant fluctuations in hafnium isotopic composition occurred in the eocene and oligocene possibly related to direct advection from the indian and atlantic oceans hafnium isotopic compositions have remained approximately uniform for the past 20 million years probably reflecting increased isolation of the central pacific the mechanisms responsible for the increase in87sr 86sr in seawater through the cenozoic apparently had no effect on central pacific deep water hafnium

late tertiary history of hydrothermal deposition at the east pacific rise 19 s correlation to volcano tectonic events commonly it is assumed that the intensity of mid ocean ridge hydrothermal activity should correlate with spreading rate since high spreading rates are an indication of large subcrustal heat sources needed for intense hydrothermal activity we have tested this hypothesis by modeling the deposition of hydrothermal precipitates from cores from deep sea drilling project leg 92 taken on the west flank of the east pacific rise at 19 s although spreading rates at the east pacific rise and its predecessor the mendoza rise have varied by only 50 in the last 30 million years we found certain episodes at about 25 18 14 and 9 million years ago of hydrothermal manganese deposition as much as a factor of 20 higher than equivalent holocene accumulation these eposides do not correlate with spreading rate changes and instead seem to occur at times of major tectonic reorganizations we propose that ridge jumps and changes of ridge orientation may substantially increase hydrothermal activity by fracturing the ocean crust and providing seawater access to deep seated heat sources

lunar radar sounder observations of subsurface layers under the nearside maria of the moon observations of the subsurface geology of the moon help advance our understanding of lunar origin and evolution radar sounding from the kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria comparison with the surface geology in the serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts the stratification indicates a tectonic quiescence between 3 55 and 2 84 billion years ago mare ridges were formed subsequently the basalts that accumulated during this quiet period have a total thickness of only a few hundred meters these observations suggest that mascon loading did not produce the tectonics in serenitatis after 3 55 billion years ago global cooling probably dominated the tectonics after 2 84 billion years ago

parameters and structure of lunar regolith in chang e 3 landing area from lunar penetrating radar lpr data abstract chang e 3 ce 3 landed in the northwest mare imbrium a region that has not been explored before yutu rover that released by ce 3 lander carried the first lunar surface penetrating radar lpr for exploring lunar regolith thickness and subsurface shallow geological structures in this paper based on the lpr data and the panoramic camera pc data we first calculate the lunar surface regolith parameters in ce 3 landing area including its permittivity density conductivity and feo tio2 content lpr data provides a higher spatial resolution and more accuracy for the lunar regolith parameters comparing to other remote sensing techniques such as orbit radar sounder and microwave sensing or earth based powerful radar we also derived the regolith thickness and its weathered rate with much better accuracy in the landing area the results indicate that the regolith growth rate is much faster than previous estimation the regolith parameters are not uniform even in such a small study area and the thickness and growth rate of lunar regolith here are different from other areas in mare imbrium we infer that the main reason should be geological deformation that caused by multiple impacts of meteorites in different sizes

frequency dependent attenuation analysis of ground penetrating radar data in the early 1990s it was established empirically that in many materials ground penetrating radar gpr attenuation is approximately linear with frequency over the bandwidth of a typical pulse further a frequency independent q parameter characterizes the slope of the band limited attenuation versus frequency curve here i derive the band limited q function from a first order taylor expansion of the attenuation coefficient this approach provides a basis for computing q from any arbitrary dielectric permittivity model for cole cole relaxation i find good correlation between the first order q approximation and q computed from linear fits to the attenuation coefficient curve over two octave bands the correlation holds over the primary relaxation frequency for some materials this relaxation occurs between 10 and 200 mhz a typical frequency range for many gpr applications frequency dependent losses caused by scattering and by the commonly overlooked problem of frequency dependent reflection

late miocene early pliocene manganese redirection in the central indian ocean expansion of the intermediate water oxygen minimum zone decomposition of organic matter combined with density stratification generate a pronounced intermediate water oxygen minimum zone omz in the northwest indian ocean this zone currently lies between water depths of 200 and 2000 m and extends approximately 5000 km southeast from the arabian coast based upon benthic foraminiferal assemblage changes it has been suggested that this omz was even more extensive during the late miocene early pliocene 6 5 3 0 ma with a maximum volume and or intensity at approximately 5 0 ma while this inference may contribute to an understanding of the history of northwest indian ocean upwelling corroborating geochemical evidence for this interpretation has heretofore been lacking ocean drilling program odp sites 752 754 and 757 on broken and ninetyeast ridges are located within central indian ocean intermediate water depths 1086 1650 m but outside the present lateral dimensions of the indian ocean omz high resolution chemical analyses of sediment from these sites indicate significant reductions in the flux of mn and normalized mn concentrations between 6 5 and 3 0 ma that are most pronounced at approximately 5 0 ma because late miocene pliocene paleodepths for these sites were essentially the same as at present and because extremely low sedimentation rates 0 3 1 3 cm ky most likely precluded sedimentary metal oxide diagenesis we suggest that the observed mn depletions reflect diminished deposition of reducible mn oxyhydroxide phases within o2 deficient intermediate waters and that this effect was most intense at approximately 5 0 ma this interpretation implies that waters with less than 2 0 ml l o2 extended at least 1500 km beyond their present limits and is consistent with changes in benthic foraminifera assemblages we further suggest this expanded indian ocean omz is related to regionally and or globally increased biological productivity

distribution of isolated volcanoes on the flanks of the east pacific rise 15 3 s 20 s volcanic constructions not associated with seamount or volcano chains are abundant on the flanks of the east pacific rise epr but are rare along the axial high the distribution of isolated volcanoes based on multibeam bathymetric maps is approximately symmetric about the epr axis this symmetry contrasts with the asymmetries in the distribution of volcano chains more abundant on the west flank the seafloor subsidence rates slower on the west flank and the distribution of plate motion parallel gravity lineaments more prominent on the west flank most of the isolated volcanoes complete their growth within 14 km of the axis on crust younger than 0 2 ma while seamount chain volcanoes continue to be active on older crust volcanic edifices within 6 km of the ridge axis are primarily found adjacent to axial discontinuities suggesting a more sporadic magma supply and stronger lithosphere able to support volcanic constructions near axial discontinuities the volume of isolated near axis volcanoes correlates with ridge axis cross sectional area suggesting a link between the magma budget of the ridge and the eruption of near axis volcanoes within the study area off axis volcanic edifices cover at least 6 of the seafloor and contribute more than 0 2 to the volume of the crust the inferred width of the zone where isolated volcanoes initially form increases with spreading rate for the mid atlantic ridge 4 km northern epr 20 km and southern epr 28 km so that isolated volcanoes form primarily on lithosphere younger than 0 2 ma 4 6 km brittle thickness independent of spreading rate this suggests some form of lithospheric control on the eruption of isolated off axis volcanoes due to brittle thickness increased normal stresses across cracks impeding dike injection or thermal stresses within the newly forming lithosphere

is the south pacific helium 3 plume dynamically active it is suggested that the hydrothermal vents of the south pacific rise produce a beta governed circulation at mid depth and that perhaps the associated plume of excess3he lupton and craig 1 points westward because of the dynamics of this circulation rather than as a passive tracer

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise

dielectric properties estimation of the lunar regolith at ce 3 landing site using lunar penetrating radar data abstract the second channel ch2 of the lunar penetrating radar lpr carried on the chang e 3 ce 3 yutu rover was used to determine the thickness and structure of the lunar regolith accurately revealing the true structure beneath the surface requires knowledge of the dielectric permittivity of the regolith which allows one to properly apply migration to the radar image in contrast to simple assumptions in previous studies this paper takes account of heterogeneity of the regolith and derives regolith s permittivity distribution laterally and vertically by a method widely used in data processing of terrestrial ground penetrating radar gpr we find that regolith permittivity at the landing site increases with depth more quickly than previously recognized at a depth of 2 5 3 m the dielectric constant reaches the value of solid basalt the radar image was migrated on the basis of the permittivity profile we do not find any continuous distinct layers or an apparent regolith rock interface in the migrated radargram which implies that this area is covered by relatively young poorly layered deposits

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick