ut variation of internal sq currents and the oceanic effect during 1980 march 1 18 summary ut variation of the internal part of sq currents is examined using the geomagnetic data during 1980 march 1 18 and the effect of the ocean is found the ratio of the internal currents to the external increases when the external current vortex comes above the atlantic and pacific oceans and the internal current vortex shifts to the oceans when the external vortex approaches the edge of the oceans the existence of the ocean increases the total induced current by about 30 per cent and this amount is consistent with model calculations for sq by previous workers

electric currents in the ocean induced by the geomagnetic sq field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the geomagnetic sq field are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the simulation results show that the induced currents have maximum intensity in the northern pacific ocean at 22 hr ut and enhance the total induced fields by about 60 per cent even when the external current vortex is located above the eurasian continent the internal current vortex is enhanced by about 10 per cent by the existence of the ocean next we have checked the effects of the electric currents in the ocean on the estimation of the mantle conductivity and found that ignoring the currents induced in the shell gives a less conductive and shallower estimation of the mantle conductor furthermore an apparent dependence of the conductivity on the depth appears because of the effects of the currents induced in the shell even if the mantle is a uniform conductor the conductivity and depth are estimated to be 0 1 sm 1 and 500km respectively from the data analysis for the 1 day period variation field of the p12 mode if the effects of the currents in the shell are ignored but it should be 1s m 1 and 780 km if the effects are considered

fluid venting activity within the eastern nankai trough accretionary wedge a summary of the 1989 kaiko nankai results fluid flow manifestations within the outer 20 km of the eastern nankai accretionary wedge between the water depths of 4000 and 2000 m are concentrated near the outcrop of a shallow detachment fault immediately behind the frontal thrust near a depth of 3800 m and along a probable strike slip fault on the top of a 2000 m deep pop up structure 20 km inside the wedge using subbottom temperature measurements we estimate darcy upward flow velocities below clams colonies at the 3800 m site and show that one can associate a narrow range of velocities with the different types of colonies then combining a statistical survey of the distribution of colonies with the velocity estimates we compute a yearly outflow budget of 200 m 3 per metre of width of the wedge in the toe area this is forty times larger than the amount expected from steady state compactive dewatering we propose however that 80 90 of this flow is produced by shallow seawater convection because variations in sea bottom temperatures were too large we could not estimate fluid outflow budgets in the 2000 m venting area however 20 000 and 130 000 year old shells fossilized within widespread carbonate concretions indicate that fluid flow has been active in the 2000 m venting area since at least 130 000 years ago probably in a sporadic fashion chemical evidence indicates that a significant part of the fluid is coming from a depth of at least several hundred metres subbottom temperature measurements over a period of two months in the 3800 m venting site show fluctuations of 20 30 in the venting velocity below an active colony that have an apparent period of two weeks although the fluid circulation appears to be controlled by active faults at least in the shallow part of the wedge not every active fault corresponds to an aquifer in the absence of good high resolution seismic data and drill holes we cannot describe this plumbing system in any detail and are not able to show why some active faults correspond to fluid outlets and some do not

geomagnetic quiet day selection based on published literature and the response to a questionnaire sent to geomagnetic field ionospheric and magnetospheric researchers several methods of choosing periods of quiet conditions based on geomagnetic records as well as other observed parameters have been identified caveats with respect to using geomagnetic indices to select quiet periods include the following 1 geomagnetic disturbances are strongly local even if the data from all available observatories indicate quiet behavior there is the distinct possibility that some other location not sampled may be disturbed 2 geomagnetic indices are convenient but imperfect indicators of geomagnetic activity indices based on a quiet day reference level have uncertainties comparable to the threshold value for quiet conditions indices representing average conditions during a 24 hr ut day may not be appropriate 3 geomagnetic activity does not fully reflect the range of possible factors that influence the ionosphere or magnetosphere

the planetary scale distribution of telluric currents and the effect of the equatorial electrojet an investigation by canonical gds the planetary scale distribution of electrical currents in the earth is still largely unknown the role of the oceans for long period hours to days inducing electromagnetic fieldsbe of external origin has been investigated by several authors while the role of telluric current channelling from the planetary viewpoint is still far from a satisfactory understanding canonical geomagnetic depth sounding gds analysis can yield locally a direction parallel to the strike of a telluric current density flowing in a region around the recording site and which also has the property of being the most relevant source for the internal origin fieldbi observed at the given site at the given frequency the use of such local information from 64 geomagnetic observatories is discussed here in a study to infer evidences of a the role of the polarization properties ofbe and b the role of the telluric current channelling within conductivity anomalies relevant to the planetary scale circuitry the results show clear evidence of the influence of the equatorial electrojet on the polarization ofbe in a latitudinal band between 15 20 latitude there is also evidence that thebe associated with the equatorial electrojet produces telluric currents which flow at a much shallower depth than the skin depth to be expected in the case of a plane earth this implies that the parkinson planes in these regions reflect the conductivity structure underground more than the polarization ofbe due to the equatorial electrojet further it clearly appears that some regular planetary scale pattern of telluric currents plays a more significant role than current channelling within some conductivity anomalies of fixed strike close to some geomagnetic observatories finally the number of observatories used in this study appears to be insufficient to deduce any information concerning a seasonal evolution of the telluric current pattern on a planetary scale

fluid flow and mass flux determinations at vent sites on the cascadia margin accretionary prism fluid venting from the toe of the accretionary prism off oregon was measured in situ during a series of dives with dsrv alvin in 1987 and 1988 a benthic chamber was placed over active vent sites to sequentially collect samples of venting fluids and to make direct measurements of discharge rates calibrated flow meter measurements and flow rates determined from dissolved methane transfer indicate that discharge from two vent sites alvin 1428 and alvin 1900 ranges roughly between 100 and 500 l m 2 d 1 with the most reliable estimates falling in the range of 125 150 l m 2d 1 these rates imply subsurface advective flow on the order of 100 m yr 1 comparison of observed discharge rates with rates calculated for steady state expulsion supported by accretion related compaction indicates that the observed flow is greater than predicted flow by several orders of magnitude the disparity dictates that fluids are not derived locally but are transported laterally within the prism or that flow is not steady state and that individual vents are short lived features in the ongoing accretion process

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

pore fluid chemistry of the north anatolian fault zone in the sea of marmara a diversity of sources and processes as part of the 2007 marnaut cruise in the sea of marmara an investigation of the pore fluid chemistry of sites along the main marmara fault zone was conducted the goal was to define the spatial relationship between active faults and fluid outlets and to determine the sources and evolution of the fluids sites included basin bounding transtensional faults and strike slip faults cutting through the topographic highs the basin pore fluids are dominated by simple mixing of bottom water with a brackish low density pleistocene lake marmara end member that is advecting buoyantly and or diffusing from a relatively shallow depth this mix is overprinted by shallow redox reactions and carbonate precipitation the ridge sites are more complex with evidence for deep sourced fluids including thermogenic gas and evidence for both silicate and carbonate diagenetic processes one site on the western high displayed two mound structures that appear to be chemoherms atop a deep seated fluid conduit the fluids being expelled are brines of up to twice seawater salinity with an exotic fluid chemistry extremely high in li sr and ba oil globules were observed both at the surface and in cores and type ii gas hydrates of thermogenic origin were recovered hydrate formation near the seafloor contributes to increase brine concentration but cannot explain their chemical composition which appears to be influenced by diagenetic reactions at temperatures of 75 c 150 c hence a potential source for fluids at this site is the water associated with the reservoir from which the gas and oil is seeping which has been shown to be related to the thrace basin hydrocarbon system our work shows that submerged continental transform plate boundaries can be hydrologically active and exhibit a diversity of sources and processes

nankai trough and zenisu ridge a deep sea submersible survey abstract eight submersible dives between 3000 and 4200 m water depth were made off southern japan in the eastern nankai subduction zone benthic communities associated with chemosynthetic processes were discovered along the 800 m wide active tectonic zone at the toe of the accretionary prism a benthic community was also discovered along a zone of active compression at the foot of zenisu ridge 30 km south of nankai trough temperature measurements within the sediments below the benthic communities confirm that upward motion of interstitial water occurs there studies of water samples indicate advection of methane and light hydrocarbons specimens of the benthic community have been shown to have included in their shells carbonate resulting from methane consumption thus the benthic communities are related to overpressure driven fluid advection along tectonic zones with active surface deformation a 300 m high active scarp at the toe of the accretionary prism is related to relative motion in a 280 direction which is close to the 305 average direction of subduction in this area the dives establish further that compressive deformation is presently occurring at the foot of zenisu ridge the previous interpretation of the zenisu ridge as a zone of recent north south intraplate shortening 40 km south of the nankai trench is confirmed we conclude that tectonic evolution might well lead to future detachment of the zenisu ridge and overthrusting of this large piece of oceanic crust over the continental margin such a process might be an efficient one to emplace ophiolites over continents

induction in arbitrarily shaped oceans vi oceans of variable depth we present calculations of t he electric currents induced in a model ocean by the 24 hr sq variation the model has realistic bathymetry and represents a further step of a consistent approach to oceanic induction in which we have introduced various complexities in order of priority the solution obtained is compared with our previously published results for the case of an ocean of realistic shape and uniform depth it is found that the major shelf seas considerably modify the pattern of elect ric current circu lation in the oceans of the southern hemisphere the consistent nature of the method of matched outer and inner expansions which we have used is also discussed it seems probable that other methods not limited to finding an outer solution and consequently more complicated will at best only produce an outer solution since in practice the relatively coarse mesh necessarily used in the computation of realistic global problems precludes a fine resolution of the coastal bathymetry finally the meaning of the internal and external legendre coefficients and their relationship to sq over the oceans is briefly discussed

detection of fluid flow variations at the nankai trough by electric and magnetic measurements in boreholes or at the seafloor detection of changes in the flow rate of expelled fluids in accretionary prisms by monitoring of electric and magnetic fields is discussed a numerical model of the electric and magnetic fields associated with fluid flow variations at the nankai trough is presented which gives a numerical solution of the coupled system of electric convection currents and conduction currents that directly determines the magnetic anomaly itself measurements in a borehole located between two vents are shown to be well adapted to detection of fluid flow variations using the vertical gradient of the electric potential and the horizontal magnetic field the vertical electric field is about 10 mv km up to 500 m depth where there is a lithologic reflector and about 50 mv km below this reflector the horizontal gradient of the magnetic field is 2 nt km at the seafloor modelization with a lower fault conductivity and a larger decollement thickness has also been modeled the vertical gradient of the horizontal magnetic field is 5 to 15 nt km a variation of 3 mv and 1 5 to 3 nt at 600 m depth in a borehole could reveal a fluid flow rate variation of 20 which is a reasonable fluid flow change based on some observations at short scale time since a 1 5 to 3 nt anomaly seems easier to detect than a 3 mv anomaly it is likely that the variation of the magnetic field would more sensitively reveal fluid flow variations when monitoring the magnetic field at the seafloor a change of 0 4 nt km in the horizontal gradient could reveal a fluid flow rate variation of 20

variscan sourcing of westphalian pennsylvanian sandstones in the canonbie coalfield uk the zircon age spectrum in a sample from the canonbie bridge sandstone formation asturian of southern scotland contains two main peaks one is early carboniferous in age 348 318 ma and corresponds to the age of igneous activity during the variscan orogeny the other is of late neoproterozoic to early cambrian age 693 523 ma corresponding to the cadomian together these two groups comprise 70 of the zircon population the presence of these two peaks shows unequivocally that a significant proportion of the sediment was derived from the variscides of western or central europe the zircon population also contains a range of older proterozoic zircons and a small devonian component these could have been derived from the variscides but it is possible that some were locally derived through recycling of northerly derived sandstones of devonian carboniferous age the zircon age data confirm previous suggestions of variscide sourcing to the canonbie area made on the basis of petrographical heavy mineral and palaeocurrent evidence and extend the known northward distribution of variscan derived westphalian sediment in the uk

the secular variation of the geomagnetic field and the shape of the earth abstract we generalize on the planetary scale some results by mundt aubert and kas yanenko for the european area we prove that the secular variation sv shows a scatter with respect to some smooth trend which correlates with a suitable surface specifically with its radial distance from the earth s centre at each geomagnetic observatory obtained by interpolating the ocean floors and by extrapolating them inside the continental areas such a surface has been selected from 30 different ones including the geoid by a statistical analysis of 20 160 possible plots a very tentative interpretation can be proposed in terms of a possible role of long period telluric currents flowing in the asthenosphere mostly zonally and in an equatorial belt this conclusion however could find additional confirmation by means of some suitable further investigations and harder thinking for which a few suggestions are proposed here furthermore an interesting by product is the evidence of an apparent and clear periodicity of 11 3 years in the geomagnetic yearly values which also needs to be discussed further

surface expression of fluid venting at the toe of the nankai wedge and implications for flow paths abstract cold seeps have been observed with manned submersibles at many sites on the tokai margin most sites are found on the hanging wall of major thrust faults within 1 2 km of their outcrop few sites relate to purely erosional features this relationship between thrusting and venting may be explained either by fluid flow along fault zones by fluid flow along permeable layers outcropping at the fault scarp or by diffuse upward flow of fluids released during footwall compaction we use deep towed side scan sonar and sediment sounder profiles acquired at the toe of the nankai accretionary wedge to identify the context of seepage at a smaller scale modes of fluid expulsion inferred from observations in this zone include flow channelling along strata along thrusts along gravity faults and along joint fractures as well as diffuse flow we then combine visual observation and monitoring of electrochemical potential eh to assess the relative importance of seepage sites we show that bacterial mats are better visual indicators of active seepage than bivalve beds and that the most active seepage sites correlate with outcrops of coarse turbidites cemented by authigenic carbonates these were sampled and have permeability high enough to channel fluid flow 1 4 10 14 m2 we suggest they are the main conduits near the seafloor however seepage sites are also observed directly on the outcrop of major thrusts indicating that they do play a role as fluid conduits we observe negative polarity seismic reflections on these faults below 1 km depth and wonder about their significance

strong lg attenuation in the tibetan plateau the widespread existence of strong lg attenuation in the tibetan plateau is further demonstrated by analysis of lg spectra on many paths within the plateau and quantitative estimates of the lg attenuation from low frequency lg signals for new localized path geometries strong path length dependent shifts of the lg spectra to lower corner frequencies with increasing distance are observed across the plateau consistent with a low regional average 1 hz lg attenuation value q 0 of about 125 there are clearly lateral variations within the plateau found in this and other recent studies with localized areas having q 0 values of 60 90 low enough to eliminate high frequency lg energy over path lengths of just several hundred kilometers while some localized areas may have higher q 0 values of up to 147 or higher a q 0 value of 103 is found in south central tibet compatible with recent work by others for higher frequencies on very localized scales and values from 83 to 147 are found in eastern tibet the lowest q 0 estimates found in tibet tend to be in areas for which there is evidence of volcanism and or partial melting within the crust however the strong regional attenuation may have a contribution from scattering by small scale crustal heterogeneity the strong lg attenuation in tibet gives a new constraint for understanding the tectonic development of the plateau and presents challenges to seismic monitoring of the region for possible clandestine nuclear tests

geological imprint of methane seepage on the seabed and biota of the convergent hikurangi margin new zealand box core and grab carbonate results abstract short box cores to 30 cm bsf and seafloor carbonate grab samples were acquired at mapped hydrocarbon seep sites 600 1200 m water depths during the 2007 rv sonne so191 cruise on the hikurangi margin offshore eastern north island new zealand to evaluate the influence of methane seepage on sedimentologic biotic mineralogic and stable isotopic attributes of seabed sediments sedimentary horizons in the box cores consist of siliciclastic silts and sands shell beds and nodular microcrystalline aragonite bands up to 15 cm thick the megafauna is dominated by infaunal to semi infaunal chemosymbiotic bivalves calyptogena lucinoma and acharax as well as associated worms and carnivorous and grazing gastropods burrows in silts some occupied by worms or juvenile acharax mainly have simple morphologies more typical of high energy nearshore settings than deep sea environments while a few are large and sparsely branched with wall scratch marks inferred to be of decapod crustacean origin the box core silts and nodular carbonate samples vary in toc content from 0 2 to 0 9 wt carbonate content from 4 to 78 and 13 c and 18 o values from 50 3 to 0 6 pdb and 0 77 to 3 2 pdb respectively low carbonate content silt samples have the most enriched 13 c values implying a seawater source for their pore water bicarbonate negative 13 c and positive 18 o values typify the nodular microcrystalline aragonite bands indicating formation during microbially mediated sulphate dependent anaerobic oxidation of methane aom in a cold near seafloor environment as is also supported by lipid biomarker data a clear isotopic mixing trend of decreasing 13 c and increasing 18 o and carbonate content in the fine seafloor grab carbonate samples show greater textural variability and are divided into two types fresh appearing grey to white blocks yield similar mineralogic isotopic and biomarker signatures to the nodular carbonate bands in the cores a largely seep related epifauna affiliated with these grab samples include chemosymbiotic bathymodiolin mussels siboglinid tube worms methanotrophic suberitid sponges and grazing limpets which in places are entombed within the carbonate by contrast some dark reddish to brown iron stained microcrystalline dolomitic slabs and tubular concretions support abundant non seep epifaunal encrusters from the surrounding deep sea indicative of long exposure on the seafloor distinct stable isotopic signatures of these exhumed dolostones 13 c c 20 pdb 18 o up to 7 pdb suggest derivation from an oxidised methane pool and pore fluid freshening by gas hydrate dissociation or from mobilized burial fluids that have undergone clay mineral dehydration

day to day variability of geomagnetic hourly amplitudes at low latitudes summary a study of the variability of the amplitude of sq at a fixed hour from one day to the next at nine stations from the dip equator to about 22 north of it has produced interesting results the amplitude and sign of the variability change virtually randomly making the mean practically zero the variability occurs at all hours of the day its magnitudes in the components d h and z have the same diurnal variation which peaks in the noon period like sq h in low latitudes and a weak seasonal variation that peaks at the june solstice local summer it is demonstrated that changes in the current intensities of the equatorial electrojet eej and the worldwide part of the sq w sq current layers have contrasting phases and can sometimes be in antiphase indeed the changes are mostly independent inclusion of the magnetic element d revealed that the eej current system has not only an east west but also a north south component the study shows that the meridional component of the eej current intensity evidenced at the kodaikanal and annamalainagar stations is an integral part of the zonal component at trivandrum this confirms the results of rastogi 1996 and validates those of onwumechili 1997 the results suggest that ionospheric conductivity mainly controls the magnitude while the electric field and ultimately winds mainly control the phase and randomness of the day to day variability of the hourly amplitudes of sq the random component is attributed to local and or regional atmospheric winds probably of gravity wave origin

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

accretion and erosion in subduction zones the role of fluids convergence occurs today along about 60 000 km of plate boundaries parsons 1981 in this paper we consider frontal subduction which occurs along about 40 000 km of convergent plate boundaries using the kine matic solution of de mets et al 1990 and including 0 5 km 2 yr1 of marginal basin openings otsuki 1989 we find that 2 95 km 2 per year disappear in frontal subduction at an average rate of 7 3 cm yr the upper overriding plate is significantly modified not only through the addition of a large amount of magmatic material markhinin 1968 but also through tectonic processes which result either in outgrowth of the margin through addit ion of sediments silver 1969 or in recession through frontal and subcrustal erosion which appears to be linked to sediment subduction coats 1962 gilluly 1963 the various phenomena observed must in some way be related to variations in mechanical coupling between the two plates uyeda kanamori 1979 had proposed that the transition from erosion to accretion results from increasing mechanical coupling the marianas trench was presented as typical of an crosional margin and the chile trench of an accreting margin ruff kanamori 1980 and kana mori 1986 showed that the magnitude of the subduction earthquakes increases with the convergence velocity and the inverse of the age of the subducted lithosphere this correlation was qualitatively explained by the control of age on the d ip of the platc and of convergence velocity on the

mud volcano field seaward of the barbados accretionary complex a submersible survey we describe a 0 55 km2 semicircular mud pie and three adjacent diapiric mounds explored using the submersible nautile near 13 50 n 12 km seaward of the barbados accretionary complex deformation front this diapiric field had been previously explored with an acoustically navigated deep towed side scan sonar thus providing an accurate base map the mud pie is situated at a depth of 4938 m in addition to visual observations water rock sediment and biological sampling we measured temperature gradients and made geochemical analyses of the samples fluid venting associated with chemosynthetic animal communities is widespread on all four structures but is maximal in the central third of the mud pie the chemosynthetic life distribution on the mud pie displays a concentric zonation which we relate to an increase in venting activity toward the center as evidenced by thermal gradients recent mud flows are present in the centralmost part of the mud pie the simplest interpretation of the structure is that it is a mud lake covered by a mechanically resistant carbonate crust we determine that approximately 106 m3 of fluid are advected upward through the crust of the mud lake every year this large amount of fluid implies large scale lateral transport

pore water geochemistry of eastern mediterranean mud volcanoes implications for fluid transport and fluid origin abstract the pore water chemistry of mud volcanoes from the olimpi mud volcano field and the anaximander mountains in the eastern mediterranean sea have been studied for three major purposes 1 modes and velocities of fluid transport were derived to assess the role of upward advection and bioirrigation for benthic fluxes 2 differences in the fluid chemistry at sites of milano mud volcano olimpi area were compiled in a map to illustrate the spatial heterogeneity reflecting differences in fluid origin and transport in discrete conduits in near proximity 3 formation water temperatures of seeping fluids were calculated from theoretical geothermometers to predict the depth of fluid origin and geochemical reactions in the deeper subsurface no indications for downward advection as required for convection cells have been found instead measured pore water profiles have been simulated successfully by accounting for upward advection and bioirrigation advective flow velocities are found to be generally moderate 3 50 cm y 1 compared to other cold seep areas depth integrated rates of bioirrigation are 1 2 orders of magnitude higher than advective flow velocities documenting the importance of bioirrigation for flux considerations in surface sediments calculated formation water temperatures from the anaximander mountains are in the range of 80 to 145 c suggesting a fluid origin from a depth zone associated with the seismic decollement it is proposed that at that depth clay mineral dehydration leads to the formation and advection of fluids reduced in salinity relative to sea water this explains the ubiquitous pore water freshening observed in surface sediments of the anaximander mountain area multiple fluid sources and formation water temperatures of 55 to 80 c were derived for expelled fluids of the olimpi area

time variations of fluid expulsion velocities at the toe of the eastern nankai accretionary complex abstract the temperatures in the bottom seawater and down to a depth of 60 cm in the sediment were measured over two active fluid seeps at the toe of the eastern nankai accretionary complex for periods of 12 and 32 days successively at the first station the fluid advection velocity is low less than 10 m a and the sediment temperature fluctuations closely reflect those of seawater at the second location the fluid advection velocity is greater with a darcy velocity of the order of 100 m a and sediment temperature fluctutations mainly reflect variations in the fluid velocity the temperature data suggest amplitude fluctuations of the fluid velocity of the order of 15 over characteristic periods of about 14 days they also suggest a 30 increase in the velocity over the one month period of the observation

daily geomagnetic variations on the iberian peninsula summary mean hourly values of the horizontal and vertical components of the geomagnetic field at six observatories on the iberian peninsula were analysed to study seasonal and spatial behaviour of the solar and lunar ionospheric and oceanic daily geomagnetic variations the results are tabulated and their characteristics are discussed the influence of local oceanic effects on the lunar oceanic contribution at the peninsular observatories is noted in particular the spatial behaviour of the lunar oceanic contribution is considered whereas the mean value for the peninsula is consistent with that expected according to an existing model for electric currents in the eastern atlantic ocean individual values are not the influence of tide in the mediterranean sea of water currents in the strait of gibraltar and of local effects in the atlantic ocean is proposed as the reason for this behaviour

an introduction to quiet daily geomagnetic fields on days that are quiet with respect to solar terrestrial activity phenomena the geomagnetic field has variations tens of gamma in size with major spectral components at about 24 12 8 and 6 hr in period these quiet daily field variations are primarily due to the dynamo currents flowing in the e region of the earth s ionosphere are driven by the global thermotidal wind systems and are dependent upon the local tensor conductivity and main geomagnetic field vector the highlights of the behavior and interpretation of these quiet field changes from their discovery in 1634 until the present are discussed as an introduction to the special journal issue on quiet daily geomagnetic fields

electrokinetic signature of the nankai trough accretionary complex preliminary modelling for the kaiko tokai program abstract fluid flow in the nankai trough accretionary complex has been observed during the previous phases of the kaiko project to be of order 100 m year 1 in small scale high permeability conduits and 10 m year 1 where shallow detachment faults intersect the seafloor the rate of flow was also variable increasing up to 30 over a month monitoring the fluid flow will be one of the principal objectives of the next phase of the kaiko program known as kaiko tokai one method is to measure the electric and magnetic fields generated by the electrokinetic phenomena or streaming potential resulting from fluid flow in the porous sediments this paper describes modelling of fluid flow in the accretionary prism and the resulting electrokinetic signals which may be observed from sensors on the seafloor or in shallow boreholes a two dimensional finite difference model is used to study the hydrogeology of a realistic section of the nankai trough with constraints from seismic reflection data and ocean drilling program boreholes fluid sources owing to porosity reduction in the prism and of distant external origin are modelled we find that porosity reduction alone is insufficient to reproduced the observational estimates of excess pore pressure and fluid flux additional fluid source terms are therefore required along a low angle decollement or detachment fault which separates the deformed prism sediments from the undeformed underthrust sediments beneath the decollement must be significantly more permeable than the adjacent sediments our models suggest by approximately four orders of magnitude and is probably anisotropic parallel to the main structural trends from the hydrogeological model the electric potential and electric and magnetic fields within the ocean and sediments were calculated from the electrokinetic phenomena seafloor electric potentials are found to be of the order of a few millivolts with seafloor horizontal and vertical electric fields of the order of 0 5 vm 1 close to the deformation front as the electric potential rises significantly with depth through the sediments boreole measurements may be particularly useful we conclude with some comments about noise sources and experimental logistics for the kaiko tokai program

fluid circulation in the depths of accretionary prisms an example of the shimanto belt kyushu japan accretionary prisms constitute ideal targets to study fluid circulation and fluid rock interactions at depths beyond the reach of active margin deep drilling the highest grade rocks from the shimanto belt on kyushu were buried under 3 5 kbars at 300 c toriumi and teruya 1988 they contain abundant quartz veins formed throughout burial and exhumation and variably affected by brittle and ductile deformation cathodoluminescence cl reveals the existence of two distinct types of quartz characterized by a blue and brown color respectively cl blue quartz fills macro veins width 10 m while cl brown quartz is present in micro veins width 1 10 m and ductilely recrystallized domains on the basis of microstructures the fluids associated with the cl blue and cl brown quartz are interpreted as external and local respectively quartz growth rims of alternating cl colors as well as mutually cross cutting veins show that the two fluids cyclically wetted the host rock from fluid inclusions analysis the fluid associated with cl blue quartz has a salinity similar to seawater while the fluid associated with cl brown quartz is less saline in addition cl blue quartz is richer in aluminum than the cl brown one in contrast to the salinity aluminum signature the 18o isotopic signature of both quartz types is similar and buffered by host rock the difference between the preservation of the salinity signature of the fluid and the loss of its 18o signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration the local fluid associated with cl brown quartz reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals the external fluid associated with cl blue quartz is interpreted as seawater or pore water from shallow depth 1 2 km below seafloor sediments we propose that downward percolation of shallow water to depths 10km is a transient process associated with mega earthquakes

interpretation of temperature measurements from the kaiko nankai cruise modeling of fluid flow in clam colonies during the kaiko nankai detailed submersible survey numerous measurements of the temperature gradient inside the sediment were performed on the deepest active zone of fluid venting which is situated on the anticline related to the frontal thrust using the ifremer t naut temperature probe operated from the submersiblenautile we thus obtained the temperature structure below different types of clam colonies associated with fluid venting we used the finite element method to model the thermal structure and fluid flow pattern of these vents and to determine the velocity of upward fluid flow through the colonies on a biological basis four types of clam colonies are defined each biological type has distinctive thermal characteristics and corresponds to a particular fluid flow pattern darcian flow velocity in the most active type of colony type a is of the order of 100 m a the total amount of fluid flowing through colonies in the studied area is estimated to be 200 m3 a 1 per metre width of subduction zone most of the flow is vented through type a colonies this value is more than one order of magnitude too high to be compatible with the amount of water available from steady state compaction of sediments in the whole wedge thermal arguments suggest that downwelling of seawater occurs around type a colonies and that seawater is then mixed with upcoming fluids at a depth of 1 or 2 metres furthermore finite element modeling shows that a salinity difference of a few parts per mil between the upcoming fluids and seawater is sufficient to drive convection around the colonies as water samples from a few vents indicate that the fluid source should actually be significantly less saline than seawater we propose that the very high fluid flows measured are a consequence of the dilution of the fluid of deep origin with seawater by a factor of 5 to 10

tectonic significance of the cold seepage zones in the eastern nankai accretionary wedge an outcome of the 15 years kaiko projects abstract the tectonic significance of the cold fluid venting in the eastern nankai accretionary wedge has been elucidated based upon results of precise mapping and submersible observation executed since 1984 under the french japanese cooperative projects kaiko i ii kaiko nankai and kaiko tokai in conjunction with studies of the japan trench sagami bay and other regions the very sharp boundary of benthic communities associated with temperature anomalies indicates the occurrence of focused upflow of nutrient rich fluids through cracks in the carbonate crust existing on a near surface horizon of permeable sediment the linear alignment of venting zones is a surface expression of the shallow detachment faults methane rich fluids expelled from the conduit along a fault migrate in the overlying permeable sediment and react with circulating sea water containing sulfate to produce hydrogen sulfide and carbonate precipitate en echelon or zigzag patterns of the cracks are developed in the carbonate crust under the influence of tectonic shear stress it has been concluded that bivalve communities grow on a thin veneer of sediment above the cracks of carbonate through which fluid containing hydrogen sulfide diluted with sea water flows out on the other hand bacterial mats seem to flourish either on thin sediment overlying the fault conduit or over a thick cover of sediment without carbonate crust in the former case bivalves cannot grow because venting fluids are too dense with methane and hydrogen sulfide to maintain the oxygen rich condition of the bottom water in the western nankai trough fine grained less permeable sediment cover seems to prevent circulation of fluids whereas methane appears to be widespread in the deeper sedimentary layer there major distinctions in modes of seepage among sites are presumed to be caused by 1 the tectonic regime causing channels of upward fluid venting 2 rates and composition of venting fluids affected by mixing rates of sea water and 3 the permeability and thickness of the near bottom sediment

influence of seep emission on the non symbiont bearing fauna and vagrant species at an active giant pockmark in the gulf of guinea congo angola margin detailed surveying with an rov found that a dense and diverse cold seep community colonises a giant pockmark located at 3200 m depth 8 km north from the deep congo channel several types of assemblages either dominated by mytilidae and vesicomyidae bivalves or siboglinidae polychaetes are distributed on the 800 m diameter active area the site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high density clusters of mussels and siboglinids dominate in contrast the peripheral zones display large fields of dead and live vesicomyids on soft sediment with a lower mean density and lower methane concentration in seawater the associated megafauna includes alvinocarididae shrimps echinoids holothurians of the family synaptidae several species of gastropods two species of galatheids and zoarcidae and ophidiidae fishes multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission occurrence of hydrates substratum variability and by the presence of large symbiont bearing species several assemblages dominated either by mytilids vesicomyids or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements 13c and 15n of dominant species and food sources the highest estimates of megafauna densities have been obtained in mytilid beds according to their stable isotopes values non symbiont bearing species mainly rely on chemosynthesis originated carbon either as primary consumers of chemoautotrophic microorganisms or at higher trophic level recycling organic matter or relying on bivalve and tubeworm production most of them likely feed on different sources like shrimps but differences according to habitat have been evidenced carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis originated carbon in their diet from 15 to 38 according to the species captured as far as 4 km to the site

chemical biological and hydrological controls on the 14c content of cold seep carbonate crusts numerical modeling and implications for convection at cold seeps understanding the hydrology of cold seep environments is crucial to perform accurate estimates of fluid and chemical fluxes at sedimentary wedges shallow convection processes may affect fluid flux estimates and could favor the destabilization of gas hydrate accumulations increasing the sediment ocean methane flux evidence for the occurrence of convection at cold seeps however is still limited we use the concentration of 14c d14c in carbonate crusts formed at cold seeps of the eastern mediterranean sea as a tracer for convective recirculation of seawater derived fluids a numerical model is applied to investigate the controls on 14c incorporation in cold seep carbonates our simulations show that increased amounts of ch4 in the expelled fluids result in elevated crust d14c while high ca2 and hco3 concentrations produce the opposite effect convection is the only transport process that can significantly increase crust d14c advection bioirrigation eddy diffusion and bioturbation instead have little effect on or produce a decrease of crust d14c in addition the presence of old or modern carbon mc in host sediments prior to cementation and the 14c decay associated to the time needed to form the crust contribute in defining the d14c of carbonate crusts we then use the model to reproduce the 14c content of the eastern mediterranean sea crusts to constrain the chemical and hydrological conditions that led to their formation some crusts contain relatively low amounts of 14c 945 0 d14c 930 2 which assuming no ageing after crust formation can be reproduced without considering convection other crusts from two sites the amsterdam and napoli mud volcanoes instead have a very high 14c content 899 0 d14c 838 4 which can only be reproduced by the model if convection mixes deep fluids with seawater order of magnitude calculations using the rayleigh criterion for convection suggest that the slow seepage about 10 cm year 1 of low salinity 20 fluids at the amsterdam sites could trigger haline convection there on the napoli mud volcano where high density brines are expelled density driven convection cannot take place and other processes possibly involving the rapid movement of free gas in the sediment could be important

major and trace element and sr isotope constraints on fluid circulation in the barbados accretionary complex part ii circulation rates and fluxes abstract 87 sr 86 sr ratios of pore fluids recovered from diapiric structures east of the deformation front of the barbados accretionary prism remain quasi constant from the surface to depths of 8 m the sr isotopic ratios are non radiogenic compared with seawater which implies that non local fluid was expelled at such a high rate that its sr isotopic composition was dominated by the source fluid and not by pore fluid or seawater chloride depletion recorded in the fluids corresponds to a five fold dilution in the deepest sample from the atalante diatreme this also strongly suggests upward flow the comparison of measured chloride contents and sr isotope depth profiles with theoretical values obtained using a steady state advection diffusive model gives some constraints on the fluid circulation rate in the two diatremes atalante and cyclope and in one mud diapir c the velocities are variable but the diatremes which have the largest thermal and chemical anomalies yield the highest estimated advection rates the fluid circulation rate in the centre part of the largest diatreme atalante 0 47 km 2 total surface is estimated at about 1 m yr the fluid flux from the deepest to shallowest levels of the atalante diatreme was estimated on the basis of the fluid circulation rate calculations fluid release is clearly favoured if active conduits are present as they are in the diatremes but not in the mud diapirs however even though this steady state advection diffusion model provides a rough estimation of flow rates modification of the fluid pressure and therefore fluid volume during earthquakes may superimpose large but transient fluid expulsions

fluid venting along japanese trenches tectonic context and thermal modeling abstract large benthic chemosynthetic communities have been observed at four main locations during the kaiko submersible dives in the japanese trenches they appear to be associated with venting along fractures the first site for our observation was along the japan and kuril trenches where the continental margin is eroded by the subducting plate and collapses into the trench the benthic communities there seem to be related to tension gashes parallel to the subduction vector the other communities were found on the toe of the nankai accretionary prism along the frontal thrust and tension gashes the temperature anomaly associated with one of the communities is modeled to constrain the upward flow of interstitial water as the anomaly has a small spatial extent and as the peak thermal gradient is high the best fitting model is to be found in a vertical upward flow at a velocity of 100 m yr in a cylindrical conduit leading out of an underlying shallow thrust

quantification of methane emission from bacterial mat sites at quepos slide offshore costa rica seafloor methane emission from the quepos slide on the submarine segment of the costa rica fore arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats this approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes model results suggest that the majority of the studied seeps transport rather limited amount of methane on average 177 mol cm 2 a 1 into the water column due to moderate upward advection allowing for intense anaerobic oxidation of methane aom on average 53 of the methane flux is consumed depth integrated aom rates 56 1 538 mol ch4 cm 2 a 1 are comparable with values reported from other active seep sites the overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the quepos slide is estimated to be about 0 28 106 mol a 1 this conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage however at present the global extent of methane seepage from submarine slides is largely unknown